The reactions of N-heterocyclic carbene CuI and AgI halides with potassium thio- or seleno­cyanate gave unexpected products. The attempted substitution reaction of bromido­(1,3-dibenzyl-4,5-di­phenyl­imidazol-2-yl­idene)silver (NHC*—Ag—Br) with KSCN yielded bis­[bis­(1,3-dibenzyl-4,5-di­phenyl­imidazol-2-yl­idene)silver(I)] tris­(thio­cyanato)­argentate(I) diethyl ether disolvate, [Ag(C29H24N2)2][Ag(NCS)3]·2C4H10O or [NHC*2Ag]2[Ag(SCN)3]·2Et2O, (1), while reaction with KSeCN led to bis­(μ-1,3-dibenzyl-4,5-diphenyl-2-seleno­imidazole-κ2Se:Se)bis­[bromido­(1,3-dibenzyl-4,5-diphenyl-2-seleno­imid­azole-κSe)silver(I)] di­chloro­methane hexa­solvate, [Ag2Br2(C29H24N2Se)4]·6CH2Cl2 or (NHC*Se)4Ag2Br2·6CH2Cl2, (2), via oxidation of the NHC* fragment to 2-seleno­imidazole. This oxidation was observed again in the reaction of NHC*—Cu—Br with KSeCN, yielding catena-poly[[[(1,3-dibenzyl-4,5-diphenyl-2-seleno­imidazole-κSe)copper(I)]-μ-cyanido-κ2C:N] aceto­nitrile monosolvate], {[Cu(CN)(C29H24N2Se)]·C2H3N}n or NHC*Se—CuCN·CH3CN, (3). Compound (1) represents an organic/inorganic salt with AgI in a linear coordination in each of the two cations and in a trigonal coordination in the anion, accompanied by diethyl ether solvent mol­ecules. The tri-blade boomerang-shaped complex anion [Ag(SCN)3]2− present in (1) is characterized by X-ray diffraction for the first time. Compound (2) comprises an isolated centrosymmetric mol­ecule with AgI in a distorted tetra­hedral BrSe3 coordination, together with di­chloro­methane solvent mol­ecules. Compound (3) exhibits a linear polymeric 1∞[Cu—C≡N—Cu—] chain structure with a seleno­imidazole moiety additionally coordinating to each CuI atom, and completed by aceto­nitrile solvent mol­ecules. Electron densities associated with an additional ether solvent mol­ecule in (1) and two additional di­chloro­methane solvent mol­ecules in (2) were removed with the SQUEEZE procedure [Spek (2015). Acta Cryst. C71, 9–18] in PLATON.

The asymmetric unit of the title com­pound, catena-poly[[[(perchlorato-κO)copper(II)]-μ-3-(3-carb­oxy­prop­yl)-1,5,8,12-tetra­aza-3-azonia­cyclo­tetra­decane-κ4N1,N5,N8,N12] bis­(per­chlorate)], {[Cu(C13H30N5O2)(ClO4)](ClO4)2}n, (I), consists of a macrocyclic cation, one coordinated per­chlorate anion and two per­chlorate ions as counter-anions. The metal ion is coordinated in a tetra­gonally distorted octa­hedral geometry by the four secondary N atoms of the macrocyclic ligand, the mutually trans O atoms of the per­chlorate anion and the carbonyl O atom of the protonated carb­oxy­lic acid group of a neighbouring cation. The average equatorial Cu—N bond lengths [2.01 (6) Å] are significantly shorter than the axial Cu—O bond lengths [2.379 (8) Å for carboxyl­ate and average 2.62 (7) Å for disordered per­chlorate]. The coordinated macrocyclic ligand in (I) adopts the most energetically favourable trans-III conformation with an equatorial orientation of the substituent at the protonated distal 3-position N atom in a six-membered chelate ring. The coordination of the carb­oxy­lic acid group of the cation to a neighbouring com­plex unit results in the formation of infinite chains running along the b-axis direction, which are cross­linked by N—H⋯O hydrogen bonds between the secondary amine groups of the macrocycle and O atoms of the per­chlorate counter-anions to form sheets lying parallel to the (001) plane. Additionally, the extended structure of (I) is consolidated by numerous intra- and interchain C—H⋯O contacts.

The synthesis and crystal structures of 2-(4-fluoro­phen­yl)-3-phenyl-2,3-di­hydro-4H-pyrido[3,2-e][1,3]thia­zin-4-one toluene hemisolvate (1), C19H13FN2OS·0.5C7H8, and 2-(4-nitro­phen­yl)-3-phenyl-2,3-di­hydro-4H-pyrido[3,2-e][1,3]thia­zin-4-one iso­propanol 0.25-solvate 0.0625-hydrate (2), C19H13N3O3S·0.25C3H7O·0.0625H2O, are reported. Both are racemic mixtures (centrosymmetric crystal structures) of the individual com­pounds and incorporate solvent mol­ecules in their structures. Compound 2 has four thia­zine mol­ecules in the asymmetric unit. All the thia­zine rings in this study show an envelope pucker, with the C atom bearing the substituted phenyl ring displaced from the other atoms. The phenyl and aryl rings in each of the mol­ecules are roughly orthogonal to each other, with dihedral angles of about 75°. The extended structures of 1 and 2 are consolidated by C—H⋯O and C—H⋯N(π), as well as T-type (C—H⋯π) inter­actions. Parallel aromatic ring inter­actions (π–π stacking) are observed only in 2.

Charge-assisted hydrogen bonding plays a significant role in the crystal structures of solvates of ionic com­pounds, especially when the cation or cations are primary ammonium salts. We report the crystal structures of four ammonium salts of molybdenum halide cluster solvates where we observe significant hydrogen bonding between the solvent molecules and cations. The crystal structures of bis­(anilinium) octa-μ3-chlorido-hexa­chlorido-octa­hedro-hexa­molybdate N,N-di­­methyl­formamide tetra­solvate, (C6H8N)2[Mo6Cl8Cl6]·4C3H7NO, (I), p-phenyl­enedi­ammonium octa-μ3-chlorido-hexa­chlorido-octa­hedro-hexa­mol­yb­date N,N-di­methyl­formamide hexa­solvate, (C6H10N2)[Mo6Cl8Cl6]·6C3H7NO, (II), N,N'-(1,4-phenyl­ene)bis­(propan-2-iminium) octa-μ3-chlorido-hexa­chlo­rido-octa­hedro-hexa­molybdate acetone tris­olvate, (C12H18N2)[Mo6Cl8Cl6]·3C3H6O, (III), and 1,1'-dimethyl-4,4'-bipyridinium octa-μ3-chlo­rido-hexa­chlorido-octa­hedro-hexa­molybdate N,N-di­methyl­formamide tetra­solvate, (C12H14N2)[Mo6Cl8Cl6]·4C3H7NO, (IV), are reported and described. In (I), the anilinium cations and N,N-di­methyl­formamide (DMF) solvent mol­ecules form a cyclic R42(8) hydrogen-bonded motif centered on a crystallographic inversion center with an additional DMF mol­ecule forming a D(2) inter­action. The p-phenyl­enedi­ammonium cation in (II) forms three D(2) inter­actions between the three N—H bonds and three independent N,N-di­methyl­formamide mol­ecules. The dication in (III) is a protonated Schiff base solvated by acetone mol­ecules. Compound (IV) contains a methyl viologen dication with N,N-di­methyl­formamide mol­ecules forming close contacts with both aromatic and methyl H atoms.

The syntheses and crystal structures of five 2-benzyl­idene-1-benzosuberone [1-benzosuberone is 6,7,8,9-tetra­hydro-5H-benzo[7]annulen-5-one] derivatives, viz. 2-(4-meth­oxy­benzyl­idene)-1-benzosuberone, C19H18O2, (I), 2-(4-eth­oxy­benzyl­idene)-1-benzosuberone, C20H20O2, (II), 2-(4-benzyl­benzyl­idene)-1-benzosuberone, C25H22O2, (III), 2-(4-chloro­benzyl­idene)-1-benzosuberone, C18H15ClO, (IV) and 2-(4-cyano­benzyl­idene)-1-benzosuberone, C19H15NO, (V), are described. The conformations of the benzosuberone fused six- plus seven-membered ring fragments are very similar in each case, but the dihedral angles between the fused benzene ring and the pendant benzene ring differ somewhat, with values of 23.79 (3) for (I), 24.60 (4) for (II), 33.72 (4) for (III), 29.93 (8) for (IV) and 21.81 (7)° for (V). Key features of the packing include pairwise C—H⋯O hydrogen bonds for (II) and (IV), and pairwise C—H⋯N hydrogen bonds for (V), which generate inversion dimers in each case. The packing for (I) and (III) feature C—H⋯O hydrogen bonds, which lead to [010] and [100] chains, respectively. Weak C—H⋯π inter­actions consolidate the structures and weak aromatic π–π stacking is seen in (II) [centroid–centroid separation = 3.8414 (7) Å] and (III) [3.9475 (7) Å]. A polymorph of (I) crystallized from a different solvent has been reported previously [Dimmock et al. (1999) J. Med. Chem. 42, 1358–1366] in the same space group but with a packing motif based on inversion dimers resembling that seen in (IV) in the present study. The Hirshfeld surfaces and fingerprint plots for (I) and its polymorph are com­pared and structural features of the 2-benzyl­idene-1-benzosuberone family of phases are surveyed.

The title compound, [IrZnI2(C10H15)(C3H9P)2]·0.5C6H6 or [Cp*(PMe3)2Ir]-[ZnI2] (Cp* = cyclo-C5Me5) was obtained and characterized as its benzene solvate [Cp*(PMe3)2Ir]-[ZnI2]·0.5C6H6. The bimetallic complex in this structure contains the Lewis-acidic fragment ZnI2 bonded to the Lewis-basic fragment Cp*(PMe3)2Ir, with an Ir—Zn bond distance of 2.452 (1) Å. The compound was obtained by reacting [Cp*(PMe3)IrI2] with 2-Ad2Zn (2-Ad = 2-adamant­yl), resulting in the reduction of the IrIII complex and formation of the IrI–ZnII adduct. The crystal studied was a twin by non-merohedry with a refined BASF parameter of 0.223 (1).

In the title compound, di­aqua­bis­(ethyl­enedi­amine-κ2N,N')copper(II) bis­(2-nitro­benzoate), [Cu(C2H8N2)2(H2O)2](C7H4NO4)2, two di­aqua­bis­(ethyl­enedi­amine)­copper(II) cations and four nitro­benzoate anions are present in the asymmetric unit. All four anions are `whole-mol­ecule' disordered over two sets of sites. The major components have refined occupancies of 0.572 (13), 0.591 (9), 0.601 (9) and 0.794 (10). The CuII ions exhibit slightly distorted octa­hedral geometries. In the crystal, cations and anions are connected to each other via N—H⋯O and O—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (200). The inter­molecular contacts in the crystal were further analysed using Hirshfeld surface analysis, which indicates that the most significant contacts are O⋯H/H⋯O (42.9%), followed by H⋯H (35.7%), C⋯H/H⋯C (14.2%), C⋯C (2.9%), C⋯O/O⋯C (2.2%), N⋯H/H⋯N (0.9%) and N⋯O/O⋯N (0.3%).

Deuterated potassium orthophosphate hepta­hydrate, K3PO4·7D2O, crystallizes in the Sohnke space group P21, and its absolute structure was determined from 2017 Friedel pairs [Flack parameter 0.004 (16)]. Each of the three crystallographically unique K+ cations is surrounded by six water mol­ecules and one oxygen atom from the orthophosphate group, using a threshold for K—O bonds of 3.10 Å. The highly irregular coordination polyhedra are linked by corner- and edge-sharing into a three-dimensional network that is consolidated by an intricate network of O—D⋯O hydrogen bonds of medium strength.

A copper(II) dimer with the deprotonated anion of 2-bromo­nicotinic acid (2-BrnicH), namely, tetrakis(μ-2-bromonicotinato-κ2O:O')bis[aquacopper(­II)](Cu—Cu), [Cu2(H2O)2(C6H3BrNO2)4] or [Cu2(H2O)2(2-Brnic)4], (1), was prepared by the reaction of copper(II) chloride dihydrate and 2-bromo­nicotinic acid in water. The copper(II) ion in 1 has a distorted square-pyramidal coordination environment, achieved by four carboxyl­ate O atoms in the basal plane and the water mol­ecule in the apical position. The pair of symmetry-related copper(II) ions are connected into a centrosymmetric paddle-wheel dinuclear cluster [Cu⋯Cu = 2.6470 (11) Å] via four O,O'-bridging 2-bromo­nicotinate ligands in the syn-syn coordination mode. In the extended structure of 1, the cluster mol­ecules are assembled into an infinite two-dimensional hydrogen-bonded network lying parallel to the (001) plane via strong O—H⋯O and O—H⋯N hydrogen bonds, leading to the formation of various hydrogen-bond ring motifs: dimeric R22(8) and R22(16) loops and a tetra­meric R44(16) loop. The Hirshfeld surface analysis was also performed in order to better illustrate the nature and abundance of the inter­molecular contacts in the structure of 1.

A new pseudopolymorph of dodeca­chloro­penta­silane, namely a benzene monosolvate, Si5Cl12·C6H6, is described. There are two half mol­ecules of each kind in the asymmetric unit. Both Si5Cl12 mol­ecules are completed by crystallographic twofold symmetry. One of the benzene mol­ecules is located on a twofold rotation axis with two C—H groups located on this rotation axis. The second benzene mol­ecule has all atoms on a general position: it is disordered over two equally occupied orientations. No directional inter­actions beyond normal van der Waals contacts occur in the crystal.

The crystal structures of 5-bromo-1,3-di-tert-butyl-2-[(tri­methyl­sil­yl)­oxy]benzene, C17H29BrOSi, (I), 1,3-di-tert-butyl-2-[(tri­methyl­sil­yl)­oxy]benzene, C17H30OSi, (II), and N-(2,6-diiso­propyl­phen­yl)-1,1,1-trimethyl-N-(tri­methyl­sil­yl)silanamine, C18H35NSi2, (III), are reported. Compound (I) crystallizes in space group P21/c with Z' = 1, (II) in Pnma with Z' = 0.5 and (III) in Cmcm with Z' = 0.25. Consequently, the mol­ecules of (II) are constrained by m and those of (III) by m2m site symmetries. Despite this, both (I) and (II) are distorted towards mild boat conformations, as is typical of 2,6-di-tert-butyl-substituted phenyl compounds, reflecting the high local steric pressure of the flanking alkyl groups. Compound (III) by contrast is planar and symmetric, and this lack of distortion is compatible with the lower steric pressure of the flanking 2,6-diisopropyl substituents.

The whole mol­ecule of the cadmium(II) complex, di­iodido­{N,N',N'',N'''-[pyrazine-2,3,5,6-tetra­yltetra­kis­(methyl­ene)]tetra­kis­(N-methyl­aniline)-κ3N2,N1,N6}cadmium(II), [CdI2(C36H40N6)], (I), of the ligand N,N',N'',N'''-[pyrazine-2,3,5,6-tetra­yltetra­kis­(methyl­ene)]tetra­kis­(N-methyl­aniline) (L), is generated by a twofold rotation symmetry; the twofold axis bis­ects the cadmium atom and the nitro­gen atoms of the pyrazine ring. The ligand coordinates in a mono-tridentate manner and the cadmium atom has a fivefold CdN3I2 coordination environment with a distorted shape. In the zinc(II) complex, dichlorido{N,N',N'',N'''-[pyrazine-2,3,5,6-tetra­yltetra­kis­(methyl­ene)]tetra­kis­(N-methyl­aniline)-κ3N2,N1,N6}zinc(II) di­chloro­methane 0.6-solvate, [ZnCl2(C36H40N6)]·0.6CH2Cl2, (II), ligand L also coordinates in a mono-tridentate manner and the zinc atom has a fivefold ZnN3Cl2 coordination environment with a distorted shape. It crystallized as a partial di­chloro­methane solvate. In the crystal of I, the complex mol­ecules are linked by weak C—H⋯I contacts, forming ribbons propagating along [100]. In the crystal of II, the complex mol­ecules are linked by a series of C—H⋯π inter­actions, forming layers lying parallel to the (1overline{1}1) plane. In the crystals of both compounds there are metal–halide⋯π(pyrazine) contacts present. The Hirshfeld analyses confirm the importance of the C—H⋯halide contacts in the crystal packing of both compounds.

The crystal structures of tris­[9,9-dihexyl-2-(5-meth­oxy­pyridin-2-yl-κN)-9H-fluoren-3-yl-κC3]iridium pentane monosolvate, [Ir(C31H38NO)3]·C5H12, (I), di-μ2-chlorido-bis­{bis­[2-(5-fluoro­pyridin-2-yl)-9,9-dihexyl-9H-fluoren-3-yl]iridium} pentane 0.3-solvate, [Ir2(C30H35FN)4Cl2]·0.3C5H12, (II), di-μ2-cyanato-bis­{bis­[9,9-dihexyl-2-(5-meth­oxy­pyridin-2-yl)-9H-fluoren-1-yl]iridium} pentane monosolvate, [Ir2(C31H38NO)4(NCO)2(NCO)2]·C5H12, (III), and {μ-N,N'-bis­[3,5-bis­(tri­fluoro­meth­yl)phen­yl]oxamidato}bis(bis{2-[4-(2,4,6-trimethylphenyl)pyridin-2-yl]phenyl-κ2C1,N'}iridium)–chloro­benzene–pentane (1/2.3/0.4), [Ir2(C20H19N)4(C18H6F12N2O2)]·2.3C6H5Cl·0.4C5H12, (IV), synthesized in the quest for organic light-emitting devices, were determined. The bis-μ2-chloro and bis-μ2-cyanato complexes have ΔΔ and ΛΛ configurations of the distorted octa­hedral Ir centres in racemic crystals, whereas the oxamido complex has a centrosymmetric (meso) structure with the ΔΛ configuration. The bridging oxamido moiety has a nearly planar anti geometry. All structures show substantial disorder of both host mol­ecules and solvents of crystallization.

A new conjugated carbazole chalcone compound, (E)-3-[4-(9,9a-di­hydro-8aH-carbazol-9-yl)phen­yl]-1-(4-nitro­phen­yl)prop-2-en-1-one (CPNC), C27H18N2O3, was synthesized using a Claisen–Schmidt condensation reaction. CPNC crystallizes in the monoclinic non-centrosymmetric space group Cc and adopts an s-cis conformation with respect to the ethyl­enic double bonds (C=O and C=C). The crystal packing features C—H⋯O and C—H⋯π inter­actions whose percentage contribution was qu­anti­fied by Hirshfeld surface analysis. Quantum chemistry calculations including geometrical optimization and mol­ecular electrostatic potential (MEP) were analysed by density functional theory (DFT) with a B3LYP/6–311 G++(d,p) basis set.

The two new tetra­kis-substituted pyrazines, 1,1',1'',1'''-(pyrazine-2,3,5,6-tetra­yl) tetra­kis­(N,N-di­methyl­methanamine), C16H32N6, (I) and N,N',N'',N'''-[pyrazine-2,3,5,6-tetra­yltetra­kis­(methyl­ene)]tetra­kis­(N-methyl­aniline), C36H40N6, (II), both crystallize with half a mol­ecule in the asymmetric unit; the whole mol­ecules are generated by inversion symmetry. There are weak intra­molecular C—H⋯N hydrogen bonds present in both mol­ecules and in (II) the pendant N-methyl­aniline rings are linked by a C—H⋯π inter­action. The degredation product, N,N'-[(6-phenyl-6,7-di­hydro-5H-pyrrolo­[3,4-b]pyrazine-2,3-di­yl)bis(methyl­ene)]bis­(N-methyl­aniline), C28H29N5, (III), was obtained several times by reacting (II) with different metal salts. Here, the 6-phenyl ring is almost coplanar with the planar pyrrolo­[3,4-b]pyrazine unit (r.m.s. deviation = 0.029 Å), with a dihedral angle of 4.41 (10)° between them. The two N-meth­yl­aniline rings are inclined to the planar pyrrolo­[3,4-b]pyrazine unit by 88.26 (10) and 89.71 (10)°, and to each other by 72.56 (13)°. There are also weak intra­molecular C—H⋯N hydrogen bonds present involving the pyrazine ring and the two N-methyl­aniline groups. In the crystal of (I), there are no significant inter­molecular contacts present, while in (II) mol­ecules are linked by a pair of C—H⋯π inter­actions, forming chains along the c-axis direction. In the crystal of (III), mol­ecules are linked by two pairs of C—H⋯π inter­actions, forming inversion dimers, which in turn are linked by offset π–π inter­actions [inter­centroid distance = 3.8492 (19) Å], forming ribbons along the b-axis direction.

The title crystal structure is assembled from the superposition of two mol­ecular structures, (E)-1-(5-chloro­thio­phen-2-yl)-3-(3-methyl­thio­phen-2-yl)prop-2-en-1-one, C12H9ClOS2 (93%), and (Z)-1-(5-chloro­thio­phen-2-yl)-3-(3-methyl­thio­phen-2-yl)prop-1-en-1-ol, C12H11ClOS2 (7%), 0.93C12H9ClOS2·0.07C12H11ClOS2. Both were obtained from the reaction of 3-methyl­thio­phene-2-carbaldehyde and 1-(5-chloro­thio­phen-2-yl)ethanone. In the extended structure of the major chalcone component, mol­ecules are linked by a combination of C—H⋯O/S, Cl⋯Cl, Cl⋯π and π–π inter­actions, leading to a compact three-dimensional supra­molecular assembly.

The structures are described of two bis-chelated metal complexes of nickel(II) and copper(II) with S-n-hexyl 3-(1-phenyl­ethyl­idene)di­thio­carbazate Schiff bases in a cis configuration, namely, bis­[S-n-hexyl 3-(1-phenyl­ethyl­idene)di­thio­carbazato-κ2N3,S]nickel(II), [Ni(C15H21N2S2)2], and bis­[S-n-hexyl 3-(1-phenyl­ethyl­idene)di­thio­carbazato-κ2N3,S]copper(II), [Cu(C15H21N2S2)2]. In both complexes, the metals have distorted square-planar geometries. A search in the Cambridge Structural Database [Groom et al. (2016). Acta Cryst. B72, 171–179] for bis-chelated nickel(II) and copper(II) complexes with similar Schiff bases retrieved 55 and 36 hits for the two metals, respectively. An analysis of the geometrical parameters of complexes showing cis and trans configurations is reported and the values compared with those for the complexes described in this work.

Five examples each of 3-(5-ar­yloxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)-1-[4-(prop-2-yn-1-yl­oxy)phen­yl]prop-2-en-1-ones and the corresponding 1-(4-azido­phen­yl)-3-(5-ar­yloxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)prop-2-en-1-ones have been synthesized in a highly efficient manner, starting from a common source precursor, and structures have been determined for three examples of each type. In each of 3-[5-(2-chloro­phen­oxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl]-1-[4-(prop-2-yn-1-yl­oxy)phen­yl]prop-2-en-1-one, C28H21ClN2O3, (Ib), the isomeric 3-[5-(2-chloro­phen­oxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl]-1-[4-(prop-2-yn-1-yl­oxy)phen­yl]prop-2-en-1-one, (Ic), and 3-[3-methyl-5-(naphthalen-2-yl­oxy)-1-phenyl-1H-pyrazol-4-yl]-1-[4-(prop-2-yn­yloxy)phen­yl]prop-2-en-1-one, C32H24N2O3, (Ie), the mol­ecules are linked into chains of rings, formed by two independent C—H⋯O hydrogen bonds in (Ib) and by a combination of C—H⋯O and C—H⋯π(arene) hydrogen bonds in each of (Ic) and (Ie). There are no direction-specific inter­molecular inter­actions in the structure of 1-(4-azido­phen­yl)-3-[3-methyl-5-(2-methyl­phen­oxy)-1-phenyl-1H-pyrazol-4-yl]prop-2-en-1-one, C26H21N5O2, (IIa). In 1-(4-azido­phen­yl)-3-[5-(2,4-di­chloro­phen­oxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl]prop-2-en-1-one, C25H17Cl2N5O2, (IId), the di­chloro­phenyl group is disordered over two sets of atomic sites having occupancies 0.55 (4) and 0.45 (4), and the mol­ecules are linked by a single C—H⋯O hydrogen bond to form cyclic, centrosymmetric R22(20) dimers. Similar dimers are formed in 1-(4-azido­phen­yl)-3-[3-methyl-5-(naphthalen-2-yl­oxy)-1-phenyl-1H-pyrazol-4-yl]prop-2-en-1-one, C29H21N5O2, (IIe), but here the dimers are linked into a chain of rings by two independent C—H..π(arene) hydrogen bonds. Comparisons are made between the mol­ecular conformations within both series of compounds.

The in meso in situ serial X-ray crystallography method was developed to ease the handling of small fragile crystals of membrane proteins and for rapid data collection on hundreds of microcrystals directly in the growth medium without the need for crystal harvesting. To facilitate mounting of these in situ samples on a goniometer at cryogenic or at room temperatures, two new 3D-printed holders have been developed. They provide for cubic and sponge phase sample stability in the X-ray beam and are compatible with sample-changing robots. The holders can accommodate a variety of window material types, as well as bespoke samples for diffraction screening and data collection at conventional macromolecular crystallography beamlines. They can be used for convenient post-crystallization treatments such as ligand and heavy-atom soaking. The design, assembly and application of the holders for in situ serial crystallography are described. Files for making the holders using a 3D printer are included as supporting information.

Exact and approximate mathematical formulas of equatorial aberration for powder diffraction data collected with an Si strip X-ray detector in continuous-scan integration mode are presented. An approximate formula is applied to treat the experimental data measured with a commercial powder diffractometer.

Owing to their combined open-framework structures and semiconducting properties, two-dimensional thio­stannates show great potential for catalytic and sensing applications. One such class of crystalline materials consists of porous polymeric [Sn3S72−]n sheets with molecular cations embedded in-between. The compounds are denoted R-SnS-1, where R is the cation. Dependent on the cation, some R-SnS-1 thio­stannates transition into amorphous phases upon dispersion in water. Knowledge about the fundamental chemical properties of the thio­stannates, including their water stability and the nature of the amorphous products, has not yet been established. This paper presents a time-resolved study of the transition from the crystalline to the amorphous phase of two violet-light absorbing thio­stannates, i.e. AEPz-SnS-1 [AEPz = 1-(2-amino­ethyl)­piperazine] and trenH-SnS-1 [tren = tris­(2-amino­ethyl)­amine]. X-ray total scattering data and pair distribution function analysis reveal no change in the local intralayer coordination during the amorphization. However, a rapid decrease in the crystalline domain sizes upon suspension in water is demonstrated. Although scanning electron microscopy shows no significant decrease of the micrometre-sized particles, transmission electron microscopy reveals the formation of small particles (∼200–400 nm) in addition to the larger particles. The amorphization is associated with disorder of the thio­stannate nanosheet stacking. For example, an average decrease in the interlayer distance (from 19.0 to 15.6 Å) is connected to the substantial loss of the organic components as shown by elemental analysis and X-ray photoelectron spectroscopy. Despite the structural changes, the light absorption properties of the amorphisized R-SnS-1 compounds remain intact, which is encouraging for future water-based applications of such materials.

Ependymin was first discovered as a predominant protein in brain extracellular fluid in fish and was suggested to be involved in functions mostly related to learning and memory. Orthologous proteins to ependymin called ependymin-related proteins (EPDRs) have been found to exist in various tissues from sea urchins to humans, yet their functional role remains to be revealed. In this study, the structures of EPDR1 from frog, mouse and human were determined and analyzed. All of the EPDR1s fold into a dimer using a monomeric subunit that is mostly made up of two stacking antiparallel β-sheets with a curvature on one side, resulting in the formation of a deep hydrophobic pocket. All six of the cysteine residues in the monomeric subunit participate in the formation of three intramolecular disulfide bonds. Other interesting features of EPDR1 include two asparagine residues with glycosylation and a Ca2+-binding site. The EPDR1 fold is very similar to the folds of bacterial VioE and LolA/LolB, which also use a similar hydrophobic pocket for their respective functions as a hydrophobic substrate-binding enzyme and a lipoprotein carrier, respectively. A further fatty-acid binding assay using EPDR1 suggests that it indeed binds to fatty acids, presumably via this pocket. Additional interactome analysis of EPDR1 showed that EPDR1 interacts with insulin-like growth factor 2 receptor and flotillin proteins, which are known to be involved in protein and vesicle translocation.

Serial rotation electron diffraction (SerialRED) has been developed as a fully automated technique for three-dimensional electron diffraction data collection that can run autonomously without human intervention. It builds on the previously established serial electron diffraction technique, in which submicrometre-sized crystals are detected using image processing algorithms. Continuous rotation electron diffraction (cRED) data are collected on each crystal while dynamically tracking the movement of the crystal during rotation using defocused diffraction patterns and applying a set of deflector changes. A typical data collection screens up to 500 crystals per hour, and cRED data are collected from suitable crystals. A data processing pipeline is developed to process the SerialRED data sets. Hierarchical cluster analysis is implemented to group and identify the different phases present in the sample and to find the best matching data sets to be merged for subsequent structure analysis. This method has been successfully applied to a series of zeolites and a beam-sensitive metal–organic framework sample to study its capability for structure determination and refinement. Two multi-phase samples were tested to show that the individual crystal phases can be identified and their structures determined. The results show that refined structures obtained using automatically collected SerialRED data are indistinguishable from those collected manually using the cRED technique. At the same time, SerialRED has lower requirements of expertise in transmission electron microscopy and is less labor intensive, making it a promising high-throughput crystal screening and structure analysis tool.

This study explores the possibility of measuring the dynamics of proteins in solution using X-ray photon correlation spectroscopy (XPCS) at nearly diffraction-limited storage rings (DLSRs). We calculate the signal-to-noise ratio (SNR) of XPCS experiments from a concentrated lysozyme solution at the length scale of the hydrodynamic radius of the protein molecule. We take into account limitations given by the critical X-ray dose and find expressions for the SNR as a function of beam size, sample-to-detector distance and photon energy. Specifically, we show that the combined increase in coherent flux and coherence lengths at the DLSR PETRA IV yields an increase in SNR of more than one order of magnitude. The resulting SNR values indicate that XPCS experiments of biological macromolecules on nanometre length scales will become feasible with the advent of a new generation of synchrotron sources. Our findings provide valuable input for the design and construction of future XPCS beamlines at DLSRs.

The X-chromosome-linked inhibitor of apoptosis protein (XIAP) is a multidomain protein whose main function is to block apoptosis by caspase inhibition. XIAP is also involved in other signalling pathways, including NF-κB activation and copper homeostasis. XIAP is overexpressed in tumours, potentiating cell survival and resistance to chemotherapeutics, and has therefore become an important target for the treatment of malignancy. Despite the fact that the structure of each single domain is known, the conformation of the full-length protein has never been determined. Here, the first structural model of the full-length XIAP dimer, determined by an integrated approach using nuclear magnetic resonance, small-angle X-ray scattering and electron paramagnetic resonance data, is presented. It is shown that XIAP adopts a compact and relatively rigid conformation, implying that the spatial arrangement of its domains must be taken into account when studying the interactions with its physiological partners and in developing effective inhibitors.

As is well known, polymers commonly form lamellar crystals, and these assemble further into lamellar stacks and spherulites during quiescent crystallization. Fifty years ago, Vonk and Kortleve constructed the classical small-angle X-ray scattering theory (SAXS) for a lamellar system, in which it was assumed that the lamellar stack had an infinite lateral size [Vonk & Kortleve (1967), Kolloid Z. Z. Polym. 220, 19–24]. Under this assumption, only crystal planes satisfying the Bragg condition can form strong scattering, and the scattering from the lamellar stack arises from the difference between the scattering intensities in the amorphous and crystalline layers, induced by the incident X-ray beam. This assumption is now deemed unreasonable. In a real polymer spherulite, the lamellar crystal commonly has dimensions of only a few hundred nanometres. At such a limited lateral size, lamellar stacks in a broad orientation have similar scattering, so interference between these lamellar stacks must be considered. Scattering from lamellar stacks parallel to the incident X-ray beam also needs to be considered when total reflection occurs. In this study, various scattering contributions from lamellar stacks in a spherulite are determined. It is found that, for a limited lateral size, the scattering induced by the incident X-ray beam is not the main origin of SAXS. It forms double peaks, which are not observed in real scattering because of destructive interference between the lamellar stacks. The scattering induced by the evanescent wave is the main origin. It can form a similar interference pattern to that observed in a real SAXS measurement: a Guinier region in the small-q range, a signal region in the intermediate-q range and a Porod region in the high-q range. It is estimated that, to avoid destructive interference, the lateral size needs to be greater than 11 µm, which cannot be satisfied in a real lamellar system. Therefore, SAXS in a real polymer system arises largely from the scattering induced by the evanescent wave. Evidence for the existence of the evanescent wave was identified in the scattering of isotactic polypropyl­ene. This study corrects a long-term misunderstanding of SAXS in a polymer lamellar system.

The class B family of G-protein-coupled receptors (GPCRs) has long been a paradigm for peptide hormone recognition and signal transduction. One class B GPCR, the glucagon-like peptide-1 receptor (GLP-1R), has been considered as an anti-diabetes drug target and there are several peptidic drugs available for the treatment of this overwhelming disease. The previously determined structures of inactive GLP-1R in complex with two negative allosteric modulators include ten thermal-stabilizing mutations that were selected from a total of 98 designed mutations. Here we systematically summarize all 98 mutations we have tested and the results suggest that the mutagenesis strategy that strengthens inter-helical hydro­phobic interactions shows the highest success rate. We further investigate four back mutations by thermal-shift assay, crystallization and molecular dynamic simulations, and conclude that mutation I1962.66bF increases thermal stability intrinsically and that mutation S2714.47bA decreases crystal packing entropy extrinsically, while mutations S1932.63bC and M2333.36bC may be dispensable since these two cysteines are not di­sulfide-linked. Our results indicate intrinsic connections between different regions of GPCR transmembrane helices and the current data suggest a general mutagenesis principle for structural determination of GPCRs and other membrane proteins.

For serial femtosecond crystallography at X-ray free-electron lasers, which entails collection of single-pulse diffraction patterns from a constantly refreshed supply of microcrystalline sample, delivery of the sample into the X-ray beam path while maintaining low background remains a technical challenge for some experiments, especially where this methodology is applied to relatively low-ordered samples or those difficult to purify and crystallize in large quantities. This work demonstrates a scheme to encapsulate biological samples using polymer thin films and graphene to maintain sample hydration in vacuum conditions. The encapsulated sample is delivered into the X-ray beam on fixed targets for rapid scanning using the Roadrunner fixed-target system towards a long-term goal of low-background measurements on weakly diffracting samples. As a proof of principle, we used microcrystals of the 24 kDa rapid encystment protein (REP24) to provide a benchmark for polymer/graphene sandwich performance. The REP24 microcrystal unit cell obtained from our sandwiched in-vacuum sample was consistent with previously established unit-cell parameters and with those measured by us without encapsulation in humidified helium, indicating that the platform is robust against evaporative losses. While significant scattering from water was observed because of the sample-deposition method, the polymer/graphene sandwich itself was shown to contribute minimally to background scattering.

Serial crystallography has enabled the study of complex biological questions through the determination of biomolecular structures at room temperature using low X-ray doses. Furthermore, it has enabled the study of protein dynamics by the capture of atomically resolved and time-resolved molecular movies. However, the study of many biologically relevant targets is still severely hindered by high sample consumption and lengthy data-collection times. By combining serial synchrotron crystallography (SSX) with 3D printing, a new experimental platform has been created that tackles these challenges. An affordable 3D-printed, X-ray-compatible microfluidic device (3D-MiXD) is reported that allows data to be collected from protein microcrystals in a 3D flow with very high hit and indexing rates, while keeping the sample consumption low. The miniaturized 3D-MiXD can be rapidly installed into virtually any synchrotron beamline with only minimal adjustments. This efficient collection scheme in combination with its mixing geometry paves the way for recording molecular movies at synchrotrons by mixing-triggered millisecond time-resolved SSX.

Transforming growth factor β-1 (TGFβ-1) is a secreted signalling protein that directs many cellular processes and is an attractive target for the treatment of several diseases. The primary endogenous activity regulatory mechanism for TGFβ-1 is sequestration by its pro-peptide, latency-associated peptide (LAP), which sterically prohibits receptor binding by caging TGFβ-1. As such, recombinant LAP is promising as a protein-based therapeutic for modulating TGFβ-1 activity; however, the mechanism of binding is incompletely understood. Comparison of the crystal structure of unbound LAP (solved here to 3.5 Å resolution) with that of the bound complex shows that LAP is in a more open and extended conformation when unbound to TGFβ-1. Analysis suggests a mechanism of binding TGFβ-1 through a large-scale conformational change that includes contraction of the inter-monomer interface and caging by the `straight-jacket' domain that may occur in partnership through a loop-to-helix transition in the core jelly-roll fold. This conformational change does not appear to include a repositioning of the integrin-binding motif as previously proposed. X-ray scattering-based modelling supports this mechanism and reveals possible orientations and ensembles in solution. Although native LAP is heavily glycosylated, solution scattering experiments show that the overall folding and flexibility of unbound LAP are not influenced by glycan modification. The combination of crystallography, solution scattering and biochemical experiments reported here provide insight into the mechanism of LAP sequestration of TGFβ-1 that is of fundamental importance for therapeutic development.

Characterizing and controlling the uniformity of nanoparticles is crucial for their application in science and technology because crystalline defects in the nanoparticles strongly affect their unique properties. Recently, ultra-short and ultra-bright X-ray pulses provided by X-ray free-electron lasers (XFELs) opened up the possibility of structure determination of nanometre-scale matter with Å spatial resolution. However, it is often difficult to reconstruct the 3D structural information from single-shot X-ray diffraction patterns owing to the random orientation of the particles. This report proposes an analysis approach for characterizing defects in nanoparticles using wide-angle X-ray scattering (WAXS) data from free-flying single nanoparticles. The analysis method is based on the concept of correlated X-ray scattering, in which correlations of scattered X-ray are used to recover detailed structural information. WAXS experiments of xenon nanoparticles, or clusters, were conducted at an XFEL facility in Japan by using the SPring-8 Ångstrom compact free-electron laser (SACLA). Bragg spots in the recorded single-shot X-ray diffraction patterns showed clear angular correlations, which offered significant structural information on the nanoparticles. The experimental angular correlations were reproduced by numerical simulation in which kinematical theory of diffraction was combined with geometric calculations. We also explain the diffuse scattering intensity as being due to the stacking faults in the xenon clusters.

This study made use of a recently developed combination of advanced methods to reveal the atomic structure of a disordered nanocrystalline zeolite using exit wave reconstruction, automated diffraction tomography, disorder modelling and diffraction pattern simulation. By applying these methods, it was possible to determine the so far unknown structures of the hydrous layer silicate RUB-6 and the related zeolite-like material RUB-5. The structures of RUB-5 and RUB-6 contain the same dense layer-like building units (LLBUs). In the case of RUB-5, these building units are interconnected via additional SiO4/2 tetrahedra, giving rise to a framework structure with a 2D pore system consisting of intersecting 8-ring channels. In contrast, RUB-6 contains these LLBUs as separate silicate layers terminated by silanol/sil­oxy groups. Both RUB-6 and RUB-5 show stacking disorder with intergrowths of different polymorphs. The unique structure of RUB-6, together with the possibility for an interlayer expansion reaction to form RUB-5, make it a promising candidate for interlayer expansion with various metal sources to include catalytically active reaction centres.

The structure of a decagonal quasicrystal in the Zn58Mg40Y2 (at.%) alloy was studied using electron diffraction and atomic resolution Z-contrast imaging techniques. This stable Frank–Kasper Zn–Mg–Y decagonal quasicrystal has an atomic structure which can be modeled with a rhombic/hexagonal tiling decorated with icosahedral units at each vertex. No perfect decagonal clusters were observed in the Zn–Mg–Y decagonal quasicrystal, which differs from the Zn–Mg–Dy decagonal crystal with the same space group P10/mmm. Y atoms occupy the center of `dented decagon' motifs consisting of three fat rhombic and two flattened hexagonal tiles. About 75% of fat rhombic tiles are arranged in groups of five forming star motifs, while the others connect with each other in a `zigzag' configuration. This decagonal quasicrystal has a composition of Zn68.3Mg29.1Y2.6 (at.%) with a valence electron concentration (e/a) of about 2.03, which is in accord with the Hume–Rothery criterion for the formation of the Zn-based quasicrystal phase (e/a = 2.0–2.15).

Human carbonic anhydrase IX (CA IX) expression is upregulated in hypoxic solid tumours, promoting cell survival and metastasis. This observation has made CA IX a target for the development of CA isoform-selective inhibitors. To enable structural studies of CA IX–inhibitor complexes using X-ray and neutron crystallography, a CA IX surface variant (CA IXSV; the catalytic domain with six surface amino-acid substitutions) has been developed that can be routinely crystallized. Here, the preparation of protiated (H/H), H/D-exchanged (H/D) and deuterated (D/D) CA IXSV for crystallographic studies and their structural comparison are described. Four CA IXSV X-ray crystal structures are compared: two H/H crystal forms, an H/D crystal form and a D/D crystal form. The overall active-site organization in each version is essentially the same, with only minor positional changes in active-site solvent, which may be owing to deuteration and/or resolution differences. Analysis of the crystal unit-cell packing reveals different crystallographic and noncrystallographic dimers of CA IXSV compared with previous reports. To our knowledge, this is the first report comparing three different deuterium-labelled crystal structures of the same protein, marking an important step in validating the active-site structure of CA IXSV for neutron protein crystallography.

Olfactomedins are a family of modular proteins found in multicellular organisms that all contain five-bladed β-propeller olfactomedin (OLF) domains. In support of differential functions for the OLF propeller, the available crystal structures reveal that only some OLF domains harbor an internal calcium-binding site with ligands derived from a triad of residues. For the myocilin OLF domain (myoc-OLF), ablation of the ion-binding site (triad Asp, Asn, Asp) by altering the coordinating residues affects the stability and overall structure, in one case leading to misfolding and glaucoma. Bioinformatics analysis reveals a variety of triads with possible ion-binding characteristics lurking in OLF domains in invertebrate chordates such as Arthropoda (Asp–Glu–Ser), Nematoda (Asp–Asp–His) and Echinodermata (Asp–Glu–Lys). To test ion binding and to extend the observed connection between ion binding and distal structural rearrangements, consensus triads from these phyla were installed in the myoc-OLF. All three protein variants exhibit wild-type-like or better stability, but their calcium-binding properties differ, concomitant with new structural deviations from wild-type myoc-OLF. Taken together, the results indicate that calcium binding is not intrinsically destabilizing to myoc-OLF or required to observe a well ordered side helix, and that ion binding is a differential feature that may underlie the largely elusive biological function of OLF propellers.

In the structural biology of bacterial substrate-binding proteins (SBPs), a growing number of comparisons between substrate-bound and substrate-free forms of metal atom-binding (cluster A-I) SBPs have revealed minimal structural differences between forms. These observations contrast with SBPs that bind substrates such as amino acids or nucleic acids and may undergo >60° rigid-body rotations. Substrate transfer in these SBPs is described by a Venus flytrap model, although this model may not apply to all SBPs. In this report, structures are presented of substrate-free (apo) and reconstituted substrate-bound (holo) YfeA, a polyspecific cluster A-I SBP from Yersinia pestis. It is demonstrated that an apo cluster A-I SBP can be purified by fractionation when co-expressed with its cognate transporter, adding an alternative strategy to the mutagenesis or biochemical treatment used to generate other apo cluster A-I SBPs. The apo YfeA structure contains 111 disordered protein atoms in a mobile helix located in the flexible carboxy-terminal lobe. Metal binding triggers a 15-fold reduction in the solvent-accessible surface area of the metal-binding site and reordering of the 111 protein atoms in the mobile helix. The flexible lobe undergoes a 13.6° rigid-body rotation that is driven by a spring-hammer metal-binding mechanism. This asymmetric rigid-body rotation may be unique to metal atom-binding SBPs (i.e. clusters A-I, A-II and D-IV).

The analysis of large structural databases reveals general features and relationships among proteins, providing useful insight. A different approach is required to characterize ubiquitous secondary-structure elements, where flexibility is essential in order to capture small local differences. The ALEPH software is optimized for the analysis and the extraction of small protein folds by relying on their geometry rather than on their sequence. The annotation of the structural variability of a given fold provides valuable information for fragment-based molecular-replacement methods, in which testing alternative model hypotheses can succeed in solving difficult structures when no homology models are available or are successful. ARCIMBOLDO_BORGES combines the use of composite secondary-structure elements as a search model with density modification and tracing to reveal the rest of the structure when both steps are successful. This phasing method relies on general fold libraries describing variations around a given pattern of β-sheets and helices extracted using ALEPH. The program introduces characteristic vectors defined from the main-chain atoms as a way to describe the geometrical properties of the structure. ALEPH encodes structural properties in a graph network, the exploration of which allows secondary-structure annotation, decomposition of a structure into small compact folds, generation of libraries of models representing a variation of a given fold and finally superposition of these folds onto a target structure. These functions are available through a graphical interface designed to interactively show the results of structure manipulation, annotation, fold decomposition, clustering and library generation. ALEPH can produce pictures of the graphs, structures and folds for publication purposes.

Monoheme c-type cytochromes are important electron transporters in all domains of life. They possess a common fold hallmarked by three α-helices that surround a covalently attached heme. An intriguing feature of many monoheme c-type cytochromes is their capacity to form oligomers by exchanging at least one of their α-helices, which is often referred to as 3D domain swapping. Here, the crystal structure of NirC, a c-type cytochrome co-encoded with other proteins involved in nitrite reduction by the opportunistic pathogen Pseudomonas aeruginosa, has been determined. The crystals diffracted anisotropically to a maximum resolution of 2.12 Å (spherical resolution of 2.83 Å) and initial phases were obtained by Fe-SAD phasing, revealing the presence of 11 NirC chains in the asymmetric unit. Surprisingly, these protomers arrange into one monomer and two different types of 3D domain-swapped dimers, one of which shows pronounced asymmetry. While the simultaneous observation of monomers and dimers probably reflects the interplay between the high protein concentration required for crystallization and the structural plasticity of monoheme c-type cytochromes, the identification of conserved structural motifs in the monomer together with a comparison with similar proteins may offer new leads to unravel the unknown function of NirC.

Electron diffraction tomography (EDT) has gained increasing interest, starting with the development of automated electron diffraction tomography (ADT) which enables the collection of three-dimensional electron diffraction data from nano-sized crystals suitable for ab initio structure analysis. A basic description of the ADT method, nowadays recognized as a reliable and established method, as well as its special features and general applicability to different transmission electron microscopes is provided. In addition, the usability of ADT for crystal structure analysis of single nano-sized crystals with and without special crystallographic features, such as twinning, modulations and disorder is demonstrated.

The surface structure of fluoro­apatite (0001) (FAp0001) under quasi-dry and humid conditions has been probed with surface X-ray diffraction (SXRD). Lateral and perpendicular atomic relaxations corresponding to the FAp0001 termination before and after H2O exposure and the location of the adsorbed water molecules have been determined from experimental analysis of the crystal truncation rod (CTR) intensities. The surface under dry conditions exhibits a bulk termination with relaxations in the outermost atomic layers. The hydrated surface is formed by a disordered partially occupied H2O layer containing one water molecule (33% surface coverage) adsorbed at each of the three surface Ca atoms, and is coupled with one OH group randomly bonded to each of the three topmost P atoms with a 33% surface coverage.

In recent years, there have been numerous efforts worldwide to develop the synchrotron X-ray scanning tunneling microscopy (SX-STM) technique. Here, the inauguration of XTIP, the world's first beamline fully dedicated to SX-STM, is reported. The XTIP beamline is located at Sector 4 of the Advanced Photon Source at Argonne National Laboratory. It features an insertion device that can provide left- or right-circular as well as horizontal- and vertical-linear polarization. XTIP delivers monochromatic soft X-rays of between 400 and 1900 eV focused into an environmental enclosure that houses the endstation instrument. This article discusses the beamline system design and its performance.

This study relates to the INFN project SYRMA-3D for in vivo phase-contrast breast computed tomography using the SYRMEP synchrotron radiation beamline at the ELETTRA facility in Trieste, Italy. This peculiar imaging technique uses a novel dosimetric approach with respect to the standard clinical procedure. In this study, optimization of the acquisition procedure was evaluated in terms of dose delivered to the breast. An offline dose monitoring method was also investigated using radiochromic film dosimetry. Various irradiation geometries have been investigated for scanning the prone patient's pendant breast, simulated by a 14 cm-diameter polymethylmethacrylate cylindrical phantom containing pieces of calibrated radiochromic film type XR-QA2. Films were inserted mid-plane in the phantom, as well as wrapped around its external surface, and irradiated at 38 keV, with an air kerma value that would produce an estimated mean glandular dose of 5 mGy for a 14 cm-diameter 50% glandular breast. Axial scans were performed over a full rotation or over 180°. The results point out that a scheme adopting a stepped rotation irradiation represents the best geometry to optimize the dose distribution to the breast. The feasibility of using a piece of calibrated radiochromic film wrapped around a suitable holder around the breast to monitor the scan dose offline is demonstrated.

A Thomson scattering X-ray source can provide quasi-monochromatic, continuously energy-tunable, polarization-controllable and high-brightness X-rays, which makes it an excellent tool for X-ray fluorescence computed tomography (XFCT). In this paper, we examined the suppression of Compton scattering background in XFCT using the linearly polarized X-rays and the implementation feasibility of linearly polarized XFCT based on this type of light source, concerning the influence of phantom attenuation and the sampling strategy, its advantage over K-edge subtraction computed tomography (CT), the imaging time, and the potential pulse pile-up effect by Monte Carlo simulations. A fan beam and pinhole collimator geometry were adopted in the simulation and the phantom was a polymethyl methacrylate cylinder inside which were gadolinium (Gd)-loaded water solutions with Gd concentrations ranging from 0.2 to 4.0 wt%. Compared with the case of vertical polarization, Compton scattering was suppressed by about 1.6 times using horizontal polarization. An accurate image of the Gd-containing phantom was successfully reconstructed with both spatial and quantitative identification, and good linearity between the reconstructed value and the Gd concentration was verified. When the attenuation effect cannot be neglected, one full cycle (360°) sampling and the attenuation correction became necessary. Compared with the results of K-edge subtraction CT, the contrast-to-noise ratio values of XFCT were improved by 2.03 and 1.04 times at low Gd concentrations of 0.2 and 0.5 wt%, respectively. When the flux of a Thomson scattering light source reaches 1013 photons s−1, it is possible to finish the data acquisition of XFCT at the minute or second level without introducing pulse pile-up effects.

Enhancement of X-ray excited optical luminescence in a 100 µm-thick diamond plate by introduction of defect states via electron beam irradiation and subsequent high-temperature annealing is demonstrated. The resulting X-ray transmission-mode scintillator features a linear response to incident photon flux in the range 7.6 × 108 to 1.26 × 1012 photons s−1 mm−2 for hard X-rays (15.9 keV) using exposure times from 0.01 to 5 s. These characteristics enable a real-time transmission-mode imaging of X-ray photon flux density without disruption of X-ray instrument operation.

Time-resolved X-ray absorption spectroscopy (XAS) offers the possibility to monitor the state of materials during chemical reactions. While this technique has been established for transmission measurements for a number of years, XAS measurements in fluorescence mode are challenging because of limitations in signal collection as well as detectors. Nevertheless, measurements in fluorescence mode are often the only option to study complex materials containing heavy matrices or in samples where the element of interest is in low concentration. Here, it has been demonstrated that high-quality quick-scanning full extended X-ray absorption fine-structure data can be readily obtained with sub-second time resolution in fluorescence mode, even for highly diluted samples. It has also been demonstrated that in challenging samples, where transmission measurements are not feasible, quick fluorescence can yield significant insight in reaction kinetics. By studying the fast high-temperature oxidation of a reduced LaFe0.8Ni0.8O3 perovskite type, an example where the perovskite matrix elements prevent measurements in fluorescence, it is shown that it is now possible to follow the state of Ni in situ at a 3 s time resolution.

Quantum beats in fluorescence decay from Zeeman-split magnetic sublevels have been measured for helium Rydberg states excited by synchrotron radiation. The Zeeman quantum beats observed in this prototypical case were fitted with an equation from a theoretical formulation. It is proposed that Zeeman quantum beat measurement can be a useful way to simply evaluate the polarization characteristics of extreme ultraviolet light.

The Inorganic Crystal Structure Database (ICSD) is the world's largest database of fully evaluated and published crystal structure data, mostly obtained from experimental results. However, the purely experimental approach is no longer the only route to discover new compounds and structures. In the past few decades, numerous computational methods for simulating and predicting structures of inorganic solids have emerged, creating large numbers of theoretical crystal data. In order to take account of these new developments the scope of the ICSD was extended in 2017 to include theoretical structures which are published in peer-reviewed journals. Each theoretical structure has been carefully evaluated, and the resulting CIF has been extended and standardized. Furthermore, a first classification of theoretical data in the ICSD is presented, including additional categories used for comparison of experimental and theoretical information.

The microstructures of six stacking-faulted industrially produced cobalt- and aluminium-bearing nickel layered double hydroxide (LDH) samples that are used as precursors for Li(Ni1−x−yCoxAly)O2 battery materials were investigated. Shifts from the brucite-type (AγB)□(AγB)□ stacking pattern to the CdCl2-type (AγB)□(CβA)□(BαC)□ and the CrOOH-type (BγA)□(AβC)□(CαB)□ stacking order, as well as random intercalation of water molecules and carbonate ions, were found to be the main features of the microstructures. A recursive routine for generating and averaging supercells of stacking-faulted layered substances implemented in the TOPAS software was used to calculate diffraction patterns of the LDH phases as a function of the degree of faulting and to refine them against the measured diffraction data. The microstructures of the precursor materials were described by a model containing three parameters: transition probabilities for generating CdCl2-type and CrOOH-type faults and a transition probability for the random intercalation of water/carbonate layers. Automated series of simulations and refinements were performed, in which the transition probabilities were modified incrementally and thus the microstructures optimized by a grid search. All samples were found to exhibit the same fraction of CdCl2-type and CrOOH-type stacking faults, which indicates that they have identical Ni, Co and Al contents. Different degrees of interstratification faulting were determined, which could be correlated to different heights of intercalation-water-related mass-loss steps in the thermal analyses.