The title pyrazine dicarboxamide ligand, N2,N3-bis­(quinolin-8-yl)pyrazine-2,3-dicarboxamide (H2L1), C24H16N6O2, has a twisted conformation with the outer quinoline groups being inclined to the central pyrazine ring by 9.00 (6) and 78.67 (5)°, and by 79.94 (4)° to each other. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming layers parallel to the (10overline{1}) plane, which are in turn linked by offset π–π inter­actions [inter­centroid distances 3.4779 (9) and 3.6526 (8) Å], forming a supra­molecular three-dimensional structure. Reaction of the ligand H2L1 with Cu(ClO4)2 in aceto­nitrile leads to the formation of the binuclear complex, [μ-(3-{hy­droxy[(quinolin-8-yl)imino]­meth­yl}pyrazin-2-yl)[(quinolin-8-yl)imino]­methano­lato]bis­[diaceto­nitrile­copper(II)] tris­(per­chlor­ate) aceto­nitrile disolvate, [Cu2(C24H15N6O2)(CH3CN)4](ClO4)3·2CH3CN or [Cu2(HL1−)(CH3CN)4](ClO4)3·2CH3CN (I). In the cation of complex I, the ligand coordinates to the copper(II) atoms in a bis-tridentate fashion. A resonance-assisted O—H⋯O hydrogen bond is present in the ligand; the position of this H atom was located in a difference-Fourier map. Both copper(II) atoms are fivefold coordinate, being ligated by three N atoms of the ligand and by the N atoms of two aceto­nitrile mol­ecules. The first copper atom has a perfect square-pyramidal geometry while the second copper atom has a distorted shape. In the crystal, the cation and perchlorate anions are linked by a number of C—H⋯O hydrogen bonds, forming a supra­molecular three-dimensional structure.

In the title compound, [Cu(C16H8Br3N2O)2]·C2H6OS, the CuII atom is tetra­coordinated in a square-planar coordination, being surrounded by two N atoms and two O atoms from two N,O-bidentate (E)-1-[(2,4,6-tri­bromo­phen­yl)diazen­yl]naphthalen-2-olate ligands. The two N atoms and two O atoms around the metal center are trans to each other, with an O—Cu—O bond angle of 177.90 (16)° and a N—Cu—N bond angle of 177.8 (2)°. The average distances between the CuII atom and the coordinated O and N atoms are 1.892 (4) and 1.976 (4) Å, respectively. In the crystal, complexes are linked by C—H⋯O hydrogen bonds and by π–π inter­actions involving adjacent naphthalene ring systems [centroid–centroid distance = 3.679 (4) Å]. The disordered DMSO mol­ecules inter­act weakly with the complex mol­ecules, being positioned in the voids left by the packing arrangement of the square-planar complexes. The DMSO solvent mol­ecule is disordered over two positions with occupancies of 0.70 and 0.30.

The central thia­zolidine ring of the title salt, C16H16N3S+·Br−, adopts an envelope conformation, with the C atom bearing the phenyl ring as the flap atom. In the crystal, the cations and anions are linked by N—H⋯Br hydrogen bonds, forming chains parallel to the b-axis direction. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (46.4%), C⋯H/H⋯C (18.6%) and H⋯Br/Br⋯H (17.5%) inter­actions.

The crystal structure of the polymeric title compound, catena-poly[[[di­aqua­lithium]-μ-γ-cyclo­dextrin(1−)-[aqua­lithium]-μ-γ-cyclo­dextrin(1−)] pentadecahydrate], {[Li2(C48H79O40)2(H2O)3]·15H2O}n, consists of deprotonated γ-cyclo­dextrin (CD) mol­ecules assembled by lithium ions into metal–organic ribbons that are cross-linked by multiple O—H⋯O hydrogen bonds into sheets extending parallel to (0overline11). Within a ribbon, one Li+ ion is coordinated by one deprotonated hydroxyl group of the first γ-CD torus and by one hydroxyl group of the second γ-CD torus as well as by two water mol­ecules. The other Li+ ion is coordinated by one deprotonated hydroxyl and by one hydroxyl group of the second γ-CD torus, by one hydroxyl group of the first γ-CD torus as well as by one water mol­ecule. The coordination spheres of both Li+ cations are distorted tetra­hedral. The packing of the structure constitute channels along the a axis. Parts of the hy­droxy­methyl groups in cyclo­dextrin molecules as well as water mol­ecules show two-component disorder. Electron density associated with additional disordered solvent mol­ecules inside the cavities was removed with the SQUEEZE [Spek (2015). Acta Cryst. C71, 9–18] routine in PLATON. These solvent mol­ecules are not considered in the given chemical formula and other crystal data. Five out of the sixteen hy­droxy­methyl groups and one water mol­ecule are disordered over two sets of sites.

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 new heterometallic complex, aqua-1κO-bis­(μ2-2-imino­methyl-6-meth­oxy­phenolato-1κ2O1,O6:2κ2O1,N)bis­(thio­cyanato-1κN)calcium(II)copper(II), [CaCu(C8H8NO2)2(NCS)2(H2O)], has been synthesized using a one-pot reaction of copper powder, calcium oxide, o-vanillin and ammonium thio­cyanate in methanol under ambient conditions. The Schiff base ligand (C8H9NO2) is generated in situ from the condensation of o-vanillin and ammonia, which is released from the initial NH4SCN. The title compound consists of a discrete binuclear mol­ecule with a {Cu(μ-O)2Ca} core, in which the Cu⋯Ca distance is 3.4275 (6) Å. The coordination geometries of the four-coordinate copper atom in the [CuN2O2] chromophore and the seven-coordinate calcium atom in the [CaO5N2] chromophore can be described as distorted square planar and penta­gonal bipyramidal, respectively. In the crystal, O—H⋯S hydrogen bonds between the coordinating water mol­ecules and thio­cyanate groups form a supra­molecular chain with a zigzag-shaped calcium skeleton.

In the crystal of the title Schiff base compound, C13H9ClN2O2, [CNBA; systematic name: (E)-N-(4-chloro­phen­yl)-1-(4-nitro­phen­yl)methanimine], the CNBA mol­ecule shows whole-mol­ecule disorder (occupancy ratio 0.65:0.35), with the disorder components related by a twofold rotation about the shorter axis of the mol­ecule. The aromatic rings are inclined to each other by 39.3 (5)° in the major component and by 35.7 (9)° in the minor component. In the crystal, C—H⋯O hydrogen bonds predominate in linking the major components, while weak C—H⋯Cl inter­actions predominate in linking the minor components. The result is the formation of corrugated layers lying parallel to the ac plane. The crystal packing was analysed using Hirshfeld surface analysis and compared with related structures.

The asymmetric units of the title compounds, namely, catena-poly[[(1,4,8,11-tetra­aza­cyclo­tetra­decane-κ4N1,N4,N8,N11)nickel(II)]-μ-1,3-bis­(3-carboxyl­ato­prop­yl)tetra­methyl­disiloxane-κ2O:O'], [Ni(C10H24O5Si2)(C12H24N4)]n (I), and catena-poly[[[(1,4,8,11-tetra­aza­cyclo­tetra­decane-κ4N1,N4,N8,N11)nickel(II)]-μ-4-({[(3-carb­oxy­prop­yl)di­methyl­sil­yl]­oxy}di­methyl­sil­yl)butano­ato-κ2O:O'] per­chlorate], {[Ni(C10H25O5Si2)(C12H24N4)]ClO4}n (II), consist of one (in I) or two crystallographically non-equivalent (in II) centrosymmetric macrocyclic cations and one centrosymmetric dianion (in I) or two centrosymmetric monoanions (in II). In each compound, the metal ion is coordinated by the four secondary N atoms of the macrocyclic ligand, which adopts the most energetically stable trans-III conformation, and the mutually trans O atoms of the carboxyl­ate in a slightly tetra­gonally distorted trans-NiN4O2 octa­hedral coordination geometry. The crystals of both types of compounds are composed of parallel polymeric chains of the macrocyclic cations linked by the anions of the acid running along the [101] and [110] directions in I and II, respectively. In I, each polymeric chain is linked to four neighbouring ones by hydrogen bonding between the NH groups of the macrocycle and the carboxyl­ate O atoms, thus forming a three-dimensional supra­molecular network. In II, each polymeric chain contacts with only two neighbours, forming hydrogen bonds between the partially protonated carb­oxy­lic groups of the bridging ligand. As a result, a lamellar structure is formed with the layers oriented parallel to the (1overline{1}1) plane.

The title compound, [Mn(S4)(C8H20N4)], was accidentally obtained by the hydro­thermal reaction of Mn(ClO4)2·6H2O, cyclen (cyclen = 1,4,7,10-tetra­aza­cyclo­dodeca­ne) and Na3SbS4·9H2O in water at 413 K, indicating that polysulfide anions might represent inter­mediates in the synthesis of thio­metallate compounds using Na3SbS4·9H2O as a reactant. X-ray powder diffraction proves that the sample is slightly contaminated with NaSb(OH)6 and an unknown crystalline phase. The crystal investigated was twinned with a twofold rotation axis as the twin element, and therefore a twin refinement using data in HKLF-5 format was performed. The asymmetric unit of the title compound consists of one MnII cation, one [S4]2− anion and one cyclen ligand in general positions. The MnII cation is sixfold coordinated by two cis-S atoms of the [S4]2− anions, as well as four N atoms of the cyclen ligand within an irregular coordination. The complexes are linked via pairs of N—H⋯S hydrogen bonds into chains, which are further linked into layers by additional N—H⋯S hydrogen bonding. These layers are connected into a three-dimensional network by inter­molecular N—H⋯S and C—H⋯S hydrogen bonding. It is noted that only one similar complex with MnII is reported in the literature.

The crystal structures of praseodymium silicide (5/4), Pr5Si4, and neodymium silicide (5/4), Nd5Si4, were redetermined using high-quality single-crystal X-ray diffraction data. The previous structure reports of Pr5Si4 were only based on powder X-ray diffraction data [Smith et al. (1967). Acta Cryst. 22 940–943; Yang et al. (2002b). J. Alloys Compd. 339, 189–194; Yang et al., (2003). J. Alloys Compd. 263, 146–153]. On the other hand, the structure of Nd5Si4 has been determined from powder data [neutron; Cadogan et al., (2002). J. Phys. Condens. Matter, 14, 7191–7200] and X-ray [Smith et al. (1967). Acta Cryst. 22 940–943; Yang et al. (2002b). J. Alloys Compd. 339, 189–194; Yang et al., (2003). J. Alloys Compd. 263, 146–153] and single-crystal data with isotropic atomic displacement parameters [Roger et al., (2006). J. Alloys Compd. 415, 73–84]. In addition, the anisotropic atomic displacement parameters for all atomic sites have been determined for the first time. These compounds are confirmed to have the tetra­gonal Zr5Si4-type structure (space group: P41212), as reported previously (Smith et al., 1967). The structure is built up by distorted body-centered cubes consisting of Pr(Nd) atoms, which are linked to each other by edge-sharing to form a three-dimensional framework. This framework delimits zigzag channels in which the silicon dimers are situated.

In the title hydrated complex, [Co(C15H10ClN3)2]Cl2·4H2O, the complete dication is generated by overline{4} symmetry. The CoN6 moiety shows distortion from regular octa­hedral geometry with the trans bond angles of two N—Co—N units being 160.62 (9)°. In the crystal, O—H⋯Cl and C—H⋯O inter­actions link the components into (001) sheets. The title compound exhibits blue-light emission, as indicated by photoluminescence data, and a HOMO–LUMO energy separation of 2.23 eV was obtained from its diffuse reflectance spectrum.

The redetermined structure [for the previous study, see: Godfrey & Waters (1975). Cryst. Struct. Commun. 4, 5–8] of ammonium μ-oxido-μ-[1,5,6-tri­hydroxy­hexane-2,3,4-tris­(olato)]bis­[dioxidomolybdenum(V)] monohydrate, NH4[Mo2(C6H11O6)O5]·H2O, was obtained from an attempt to prepare a glutamic acid complex from the [Co2Mo10H4O38]6− anion. Subsequent study indicated the complex arose from a substantial impurity of mannitol in the glutamic acid sample used. All hydrogen atoms have been located in the present study and the packing displays N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds. A Hirshfeld surface analysis was also performed.

In the title compound, C9H10ClNOS, the amide functional group –C(=O)NH– adopts a trans conformation with the four atoms nearly coplanar. This conformation promotes the formation of a C(4) hydrogen-bonded chain propagating along the [010] direction. The central part of the mol­ecule, including the six-membered ring, the S and N atoms, is fairly planar (r.m.s. deviation of 0.014). The terminal methyl group and the C(=O)CH2 group are slightly deviating out-of-plane while the terminal Cl atom is almost in-plane. Hirshfeld surface analysis of the title compound suggests that the most significant contacts in the crystal are H⋯H, H⋯Cl/Cl⋯H, H⋯C/C⋯H, H⋯O/O⋯H and H⋯S/S⋯H. π–π inter­actions between inversion-related mol­ecules also contribute to the crystal packing. DFT calculations have been performed to optimize the structure of the title compound using the CAM-B3LYP functional and the 6–311 G(d,p) basis set. The theoretical absorption spectrum of the title compound was calculated using the TD–DFT method. The analysis of frontier orbitals revealed that the π–π* electronic transition was the major contributor to the absorption peak in the electronic spectrum.

The title compound, C11H9N3OS, (I), crystallizes in the monoclinic space group P21/n. The mol­ecular conformation is nearly planar and features an intra­molecular chalcogen bond between the thio­phene S and the imine N atoms. Within the crystal, the strongest inter­actions between mol­ecules are the N—H⋯O hydrogen bonds, which organize them into inversion dimers. The dimers are linked through short C—H⋯N contacts and are stacked into layers propagating in the (001) plane. The crystal structure features π–π stacking between the pyridine aromatic ring and the azomethine double bond. The calculated energies of pairwise inter­molecular inter­actions within the stacks are considerably larger than those found for the inter­actions between the layers.

The crystal structure of title compound, (C14H36N4)[CrO3Cl]2Cl2, has been determined by synchrotron radiation X-ray crystallography at 220 K. The macrocyclic cation lies across a crystallographic inversion center and hence the asymmetric unit contains one half of the organic cation, one chloro­chromate anion and one chloride anion. Both the Cl− anion and chloro­chromate Cl atom are involved in hydrogen bonding. In the crystal, hydrogen bonds involving the 1,4,8,11-tetra­methyl-1,4,8,11-tetra­azonia­cyclo­tetra­decane (TMC) N—H groups and C—H groups as donor groups and three O atoms of the chloro­chromate and the chloride anion as acceptor groups link the components, giving rise to a three-dimensional network.

The title compounds, [Mo(C5H5)(COCH3)(C6H12N3P)(CO)2], (1), and [Mo(C5H5)(COCH3)(C9H16N3O2P)(C6H5)2))(CO)2], (2), have been prepared by phosphine-induced migratory insertion from [Mo(C5H5)(CO)3(CH3)]. The mol­ecular structures of these complexes are quite similar, exhibiting a four-legged piano-stool geometry with trans-disposed carbonyl ligands. The extended structures of complexes (1) and (2) differ substanti­ally. For complex (1), the molybdenum acetyl unit plays a dominant role in the organization of the extended structure, joining the mol­ecules into centrosymmetrical dimers through C—H⋯O inter­actions with a cyclo­penta­dienyl ligand of a neighboring mol­ecule, and these dimers are linked into layers parallel to (100) by C—H⋯O inter­actions between the molybdenum acetyl and the cyclo­penta­dienyl ligand of another neighbor. The extended structure of (2) is dominated by C—H⋯O inter­actions involving the carbonyl groups of the acetamide groups of the DAPTA ligand, which join the mol­ecules into centrosymmetrical dimers and link them into chains along [010]. Additional C—H⋯O inter­actions between the molybdenum acetyl oxygen atom and an acetamide methyl group join the chains into layers parallel to (101).

The asymmetric unit of the title compound, C5H7N2O+·C4H4NO4S−, contains one cation and one anion. The 6-methyl-2,2,4-trioxo-2H,4H-1,2,3-oxa­thia­zin-3-ide anion adopts an envelope conformation with the S atom as the flap. In the crystal, the anions and cations are held together by N—H⋯O, N—H⋯N, O—H⋯O and C—H⋯O hydrogen bonds, thus forming a three-dimensional structure. The Hirshfeld surface analysis and fingerprint plots reveal that the crystal packing is dominated by O⋯H/H⋯O (43.1%) and H⋯H (24.2%) contacts.

4-[(Morpholin-4-yl)carbothioyl]benzoic acid, C12H13NO3S, a novel phen­yl(morpholino)methane­thione derivative, crystallizes in the monoclinic space group P21/n. The morpholine ring adopts a chair conformation and the carb­oxy­lic acid group is bent out slightly from the benzene ring mean plane. The mol­ecular geometry of the carb­oxy­lic group is characterized by similar C—O bond lengths [1.266 (2) and 1.268 (2) Å] as the carboxyl­ate H atom is disordered over two positions. This mol­ecular arrangement leads to the formation of dimers through strong and centrosymmetric low barrier O—H⋯O hydrogen bonds between the carb­oxy­lic groups. In addition to these inter­molecular inter­actions, the crystal packing consists of two different mol­ecular sheets with an angle between their mean planes of 64.4 (2)°. The cohesion between the different layers is ensured by C—H⋯S and C—H⋯O inter­actions.

The title compound, C19H16ClNO3S, consists of chloro­phenyl methyl­idene and di­hydro­benzo­thia­zine units linked to an acetate moiety, where the thia­zine ring adopts a screw-boat conformation. In the crystal, two sets of weak C—HPh⋯ODbt (Ph = phenyl and Dbt = di­hydro­benzo­thia­zine) hydrogen bonds form layers of mol­ecules parallel to the bc plane. The layers stack along the a-axis direction with inter­calation of the ester chains. The crystal studied was a two component twin with a refined BASF of 0.34961 (5). The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H⋯H (37.5%), H⋯C/C⋯H (24.6%) and H⋯O/O⋯H (16.7%) inter­actions. Hydrogen-bonding and van der Waals inter­actions are the dominant inter­actions in the crystal packing. Computational chemistry indicates that in the crystal, C—HPh⋯ODbt hydrogen bond energies are 38.3 and 30.3 kJ mol−1. Density functional theory (DFT) optimized structures at the B3LYP/ 6–311 G(d,p) level are compared with the experimentally determined mol­ecular structure in the solid state. The HOMO–LUMO behaviour was elucidated to determine the energy gap. Moreover, the anti­bacterial activity of the title compound has been evaluated against gram-positive and gram-negative bacteria.

The title complexes, (η4-cyclo­octa-1,5-diene)bis­(1,3-di­methyl­imidazol-2-yl­idene)iridium(I) iodide, [Ir(C5H8N2)2(C8H12)]I, (1) and (η4-cyclo­octa-1,5-di­ene)bis­(1,3-di­ethyl­imidazol-2-yl­idene)iridium(I) iodide, [Ir(C7H12N2)2(C8H12)]I, (2), were prepared using a modified literature method. After carrying out the oxidative addition of the amino acid l-proline to [Ir(COD)(IMe)2]I in water and slowly cooling the reaction to room temperature, a suitable crystal of 1 was obtained and analyzed by single-crystal X-ray diffraction at 100 K. Although this crystal structure has previously been reported in the Pbam space group, it was highly disordered and precise atomic coordinates were not calculated. A single crystal of 2 was also obtained by heating the complex in water and letting it slowly cool to room temperature. Complex 1 was found to crystallize in the monoclinic space group C2/m, while 2 crystallizes in the ortho­rhom­bic space group Pccn, both with Z = 4.

The title centrosymmetric NiII complex, [Ni(NCS)2(C15H22N2O2)2], crystallizes with one half mol­ecule in the asymmetric unit of the monoclinic unit cell. The complex adopts an octa­hedral coordination geometry with two mutually trans benzyl-2-(heptan-4-yl­idene)hydrazine-1-carboxyl­ate ligands in the equatorial plane with the axial positions occupied by N-bound thio­cyanato ligands. The overall conformation of the mol­ecule is also affected by two, inversion-related, intra­molecular C—H⋯O hydrogen bonds. The crystal structure features N—H⋯S, C—H⋯S and C—H⋯N hydrogen bonds together with C—H⋯π contacts that stack the complexes along the b-axis direction. The packing was further explored by Hirshfeld surface analysis. The thermal properties of the complex were also investigated by simultaneous TGA–DTA analyses.

Terbium oxychloride, TbOCl, was synthesized via the simple heat-treatment of TbCl3·6H2O and its structure was determined by refinement against X-ray powder diffraction data. TbOCl crystallizes with the matlockite (PbFCl) structure in the tetra­gonal space group P4/nmm and is composed of alternating (001) layers of (TbO)n and n Cl−. The unit-cell parameters, unit-cell volume, and density were compared to the literature data of other isostructural rare-earth oxychlorides in the same space group and showed good agreement when compared to the calculated trendlines.

The title compounds, 5-(2H-1,3-benzodioxol-5-yl)-N-cyclo­hexyl­penta-2,4-dienamide, C18H21NO3 (I), and 5-(2H-1,3-benzodioxol-5-yl)-1-(pyrrolidin-1-yl)penta-2,4-dien-1-one C16H17NO3 (II), are derivatives of piperine, which is known as a pungent component of pepper. Their geometrical parameters are similar to those of the three polymorphs of piperine, which indicate conjugation of electrons over the length of the mol­ecules. The extended structure of (I) features N—H⋯O amide hydrogen bonds, which generate C(4) [010] chains. The crystal of (II) features aromatic π–π stacking, as for two of three known piperine polymorphs.

The condensation of 2-furoic hydrazide and 4-dimethyl amino­benzaldehyde in ethanol yielded a yellow solid formulated as the title compound, C14H15N3O2·H2O. The crystal packing is stabilized by inter­molecular O(water)—H⋯O,N(carbohydrazide) and N—H⋯O(water) hydrogen bonds, which form a two-dimensional network along the bc plane. Additional C—H⋯O inter­actions link the mol­ecules into a three-dimensional network. The dihedral angle between the mean planes of the benzene and the furan ring is 34.47 (6)°. The carbohydrazide moiety, i.e., the C=N—N—C=O fragment and the benzene ring are almost coplanar, with an angle of 6.75 (9)° between their mean planes.

The structure of the title compound, [CrCl2(C10H24N4)][Cr(HCONH2)2(C10H24N4)][ZnCl4]2 (C10H24N4 = 1,4,8,11-tetra­aza­cyclo­tetra­decane, cyclam; HCONH2 = formamide, fa), has been determined from synchrotron X-ray data. The asymmetric unit contains two independent halves of the [CrCl2(cyclam)]+ and [Cr(fa)(cyclam)]3+ cations, and one tetra­chlorido­zincate anion. In each complex cation, the CrIII ion is coordinated by the four N atoms of the cyclam ligand in the equatorial plane and two Cl ligands or two O-bonded formamide mol­ecules in a trans axial arrangement, displaying a distorted octa­hedral geometry with crystallographic inversion symmetry. The Cr—N(cyclam) bond lengths are in the range 2.061 (2) to 2.074 (2) Å, while the Cr—Cl and Cr—O(fa) bond distances are 2.3194 (7) and 1.9953 (19) Å, respectively. The macrocyclic cyclam moieties adopt the centrosymmetric trans-III conformation with six- and five-membered chelate rings in chair and gauche conformations. The crystal structure is stabilized by inter­molecular hydrogen bonds involving the NH or CH groups of cyclam and the NH2 group of coordinated formamide as donors, and Cl atoms of the ZnCl42− anion as acceptors.

The title compound, C24H30Br2N4O2, consists of a 2-(4-nitro­phen­yl)-4H-imidazo[4,5-b]pyridine entity with a 12-bromo­dodecyl substituent attached to the pyridine N atom. The middle eight-carbon portion of the side chain is planar to within 0.09 (1) Å and makes a dihedral angle of 21.9 (8)° with the mean plane of the imidazolo­pyridine moiety, giving the mol­ecule a V-shape. In the crystal, the imidazolo­pyridine units are associated through slipped π–π stacking inter­actions together with weak C—HPyr⋯ONtr and C—HBrmdc­yl⋯ONtr (Pyr = pyridine, Ntr = nitro and Brmdcyl = bromo­dodec­yl) hydrogen bonds. The 12-bromo­dodecyl chains overlap with each other between the stacks. The terminal –CH2Br group of the side chain shows disorder over two resolved sites in a 0.902 (3):0.098 (3) ratio. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are from H⋯H (48.1%), H⋯Br/Br⋯H (15.0%) and H⋯O/O⋯H (12.8%) inter­actions. The optimized mol­ecular structure, using density functional theory at the B3LYP/ 6–311 G(d,p) level, is compared with the experimentally determined structure in the solid state. The HOMO–LUMO behaviour was elucidated to determine the energy gap.

The title compound, C22H17NO2·C3H7NO, was synthesized by condensation of an aromatic aldehyde with a secondary amine and subsequent reduction. It was crystallized from a di­methyl­formamide solution as a monosolvate, C22H17NO2·C3H7NO. The aromatic mol­ecule is non-planar with a dihedral angle between the mean planes of the aniline moiety and the methyl anthracene moiety of 81.36 (8)°. The torsion angle of the Car­yl—CH2—NH—Car­yl backbone is 175.9 (2)°. The crystal structure exhibits a three-dimensional supra­molecular network, resulting from hydrogen-bonding inter­actions between the carb­oxy­lic OH group and the solvent O atom as well as between the amine functionality and the O atom of the carb­oxy­lic group and additional C—H⋯π inter­actions. Hirshfeld surface analysis was performed to qu­antify the inter­molecular inter­actions.

The title compound, [Mn(C3H7NO)4(H2O)2][Cu5(C7H4NO3)4]·C3H7NO or cis-[Mn(H2O)2(DMF)4]{Cu[12-MCCu(II)N(shi)-4]}·DMF, where MC is metallacrown, shi3− is salicyl­hydroximate, and DMF is N,N-di­methyl­formamide, crystallizes in the monoclinic space group P21/n. Two crystallographically independent metallacrown anions are present in the structure, and both anions exhibit minor main mol­ecule disorder by an approximate (non-crystallographic) 180° rotation with occupancy ratios of 0.9010 (9) to 0.0990 (9) for one anion and 0.9497 (8) to 0.0503 (8) for the other. Each penta­copper(II) metallacrown contains four CuII ions in the MC ring and a CuII ion captured in the central cavity. Each CuII ion is four-coordinate with a square-planar geometry. The anionic {Cu[12-MCCu(II)N(shi)-4]}2− is charged-balanced by the presence of a cis-[Mn(H2O)2(DMF)4]2+ cation located in the lattice. In addition, the octa­hedral MnII counter-cation is hydrogen bonded to both MC anions via the coordinated water mol­ecules of the MnII ion. The water mol­ecules form hydrogen bonds with the phenolate and carbonyl oxygen atoms of the shi3− ligands of the MCs.

The title compound, C19H17ClN4O2, was obtained via a two-step synthesis involving the enol-mediated click Dimroth reaction of 4-azido­anisole with methyl 3-cyclo­propyl-3-oxo­propano­ate leading to the 5-cyclo­propyl-1-(4-meth­oxy­phen­yl)-1H-1,2,3-triazole-4-carb­oxy­lic acid and subsequent acid amidation with 4-chloro­aniline by 1,1'-carbonyl­diimidazole (CDI). It crystallizes in space group P21/n, with one mol­ecule in the asymmetric unit. In the extended structure, two mol­ecules arranged in a near coplanar fashion relative to the triazole ring planes are inter­connected by N—H⋯N and C—H⋯N hydrogen bonds into a homodimer. The formation of dimers is a consequence of the above inter­action and the edge-to-face stacking of aromatic rings, which are turned by 58.0 (3)° relative to each other. The dimers are linked by C—H⋯O inter­actions into ribbons. DFT calculations demonstrate that the frontier mol­ecular orbitals are well separated in energy and the HOMO is largely localized on the 4-chloro­phenyl amide motif while the LUMO is associated with aryl­triazole grouping. A Hirshfeld surface analysis was performed to further analyse the inter­molecular inter­actions.

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.

Total scattering measurements enable understanding of the structural disorder in crystalline materials by Fourier transformation of the total structure factor, S(Q), where Q is the magnitude of the scattering vector. In this work, the direct calculation of total scattering from a crystalline structural model is proposed. To calculate the total scattering intensity, a suitable Q-broadening function for the diffraction profile is needed because the intensity and the width depend on the optical parameters of the diffraction apparatus, such as the X-ray energy resolution and divergence, and the intrinsic parameters. X-ray total scattering measurements for CeO2 powder were performed at beamline BL04B2 of the SPring-8 synchrotron radiation facility in Japan for comparison with the calculated S(Q) under various optical conditions. The evaluated Q-broadening function was comparable to the full width at half-maximum of the Bragg peaks in the experimental total scattering pattern. The proposed calculation method correctly accounts for parameters with Q dependence such as the atomic form factor and resolution function, enables estimation of the total scattering factor, and facilitates determination of the reduced pair distribution function for both crystalline and amorphous materials.

A furnace that covers the temperature range from room temperature up to 2000 K has been designed, built and implemented on the D2AM beamline at the ESRF. The QMAX furnace is devoted to the full exploration of the reciprocal hemispace located above the sample surface. It is well suited for symmetric and asymmetric 3D reciprocal space mapping. Owing to the hemispherical design of the furnace, 3D grazing-incidence small- and wide-angle scattering and diffraction measurements are possible. Inert and reactive experiments can be performed at atmospheric pressure under controlled gas flux. It is demonstrated that the QMAX furnace allows monitoring of structural phase transitions as well as microstructural evolution at the nanoscale, such as self-organization processes, crystal growth and strain relaxation. A time-resolved in situ oxidation experiment illustrates the capability to probe the high-temperature reactivity of materials.

Hybrid photon-counting detectors are widely established at third-generation synchrotron facilities and the specifications of the Pilatus3 X CdTe were quickly recognized as highly promising in charge-density investigations. This is mainly attributable to the detection efficiency in the high-energy X-ray regime, in combination with a dynamic range and noise level that should overcome the perpetual problem of detecting strong and weak data simultaneously. These benefits, however, come at the expense of a persistent problem for high diffracted beam flux, which is particularly problematic in single-crystal diffraction of materials with strong scattering power and sharp diffraction peaks. Here, an in-depth examination of data collected on an inorganic material, FeSb2, and an organic semiconductor, rubrene, revealed systematic differences in strong intensities for different incoming beam fluxes, and the implemented detector intensity corrections were found to be inadequate. Only significant beam attenuation for the collection of strong reflections was able to circumvent this systematic error. All data were collected on a bending-magnet beamline at a third-generation synchrotron radiation facility, so undulator and wiggler beamlines and fourth-generation synchrotrons will be even more prone to this error. On the other hand, the low background now allows for an accurate measurement of very weak intensities, and it is shown that it is possible to extract structure factors of exceptional quality using standard crystallographic software for data processing (SAINT-Plus, SADABS and SORTAV), although special attention has to be paid to the estimation of the background. This study resulted in electron-density models of substantially higher accuracy and precision compared with a previous investigation, thus for the first time fulfilling the promise of photon-counting detectors for very accurate structure factor measurements.

The fact that a protein crystal can serve as a chemical reaction vessel is intrinsically fascinating. That it can produce an electron-dense tetranuclear rhenium cluster compound from a rhenium tri­carbonyl tri­bromo starting compound adds to the fascination. Such a cluster has been synthesized previously in vitro, where it formed under basic conditions. Therefore, its synthesis in a protein crystal grown at pH 4.5 is even more unexpected. The X-ray crystal structures presented here are for the protein hen egg-white lysozyme incubated with a rhenium tri­carbonyl tri­bromo compound for periods of one and two years. These reveal a completed, very well resolved, tetra-rhenium cluster after two years and an intermediate state, where the carbonyl ligands to the rhenium cluster are not yet clearly resolved, after one year. A dense tetranuclear rhenium cluster, and its technetium form, offer enhanced contrast in medical imaging. Stimulated by these crystallography results, the unusual formation of such a species directly in an in vivo situation has been considered. It offers a new option for medical imaging compounds, particularly when considering the application of the pre-formed tetranuclear cluster, suggesting that it may be suitable for medical diagnosis because of its stability, preference of formation and biological compatibility.

Advances in both non-resonant and resonant X-ray magnetic diffraction since the 1980s have provided researchers with a powerful tool for exploring the spin, orbital and ion degrees of freedom in magnetic solids, as well as parsing their interplay. Here, we discuss key issues for performing X-ray magnetic diffraction on single-crystal samples under high pressure (above 40 GPa) and at cryogenic temperatures (4 K). We present case studies of both non-resonant and resonant X-ray magnetic diffraction under pressure for a spin-flip transition in an incommensurate spin-density-wave material and a continuous quantum phase transition of a commensurate all-in–all-out antiferromagnet. Both cases use diamond-anvil-cell technologies at third-generation synchrotron radiation sources. In addition to the exploration of the athermal emergence and evolution of antiferromagnetism discussed here, these techniques can be applied to the study of the pressure evolution of weak charge order such as charge-density waves, antiferro-type orbital order, the charge anisotropic tensor susceptibility and charge superlattices associated with either primary spin order or softened phonons.

In this work, two methods of high-resolution X-ray data refinement: multipole refinement (MM) and Hirshfeld atom refinement (HAR) – together with X-ray wavefunction refinement (XWR) – are applied to investigate the refinement of positions and anisotropic thermal motion of hydrogen atoms, experiment-based reconstruction of electron density, refinement of anharmonic thermal vibrations, as well as the effects of excluding the weakest reflections in the refinement. The study is based on X-ray data sets of varying quality collected for the crystals of four quinoline derivatives with Cl, Br, I atoms and the -S-Ph group as substituents. Energetic investigations are performed, comprising the calculation of the energy of intermolecular interactions, cohesive and geometrical relaxation energy. The results obtained for experimentally derived structures are verified against the values calculated for structures optimized using dispersion-corrected periodic density functional theory. For the high-quality data sets (the Cl and -S-Ph compounds), both MM and XWR could be successfully used to refine the atomic displacement parameters and the positions of hydrogen atoms; however, the bond lengths obtained with XWR were more precise and closer to the theoretical values. In the application to the more challenging data sets (the Br and I compounds), only XWR enabled free refinement of hydrogen atom geometrical parameters, nevertheless, the results clearly showed poor data quality. For both refinement methods, the energy values (intermolecular interactions, cohesive and relaxation) calculated for the experimental structures were in similar agreement with the values associated with the optimized structures – the most significant divergences were observed when experimental geometries were biased by poor data quality. XWR was found to be more robust in avoiding incorrect distortions of the reconstructed electron density as a result of data quality issues. Based on the problem of anharmonic thermal motion refinement, this study reveals that for the most correct interpretation of the obtained results, it is necessary to use the complete data set, including the weak reflections in order to draw conclusions.

Model building into experimental maps is a key element of structural biology, but can be both time consuming and error prone for low-resolution maps. Here we present Namdinator, an easy-to-use tool that enables the user to run a molecular dynamics flexible fitting simulation followed by real-space refinement in an automated manner through a pipeline system. Namdinator will modify an atomic model to fit within cryo-EM or crystallography density maps, and can be used advantageously for both the initial fitting of models, and for a geometrical optimization step to correct outliers, clashes and other model problems. We have benchmarked Namdinator against 39 deposited cryo-EM models and maps, and observe model improvements in 34 of these cases (87%). Clashes between atoms were reduced, and the model-to-map fit and overall model geometry were improved, in several cases substantially. We show that Namdinator is able to model large-scale conformational changes compared to the starting model. Namdinator is a fast and easy tool for structural model builders at all skill levels. Namdinator is available as a web service (https://namdinator.au.dk), or it can be run locally as a command-line tool.

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.

Functional materials are of critical importance to electronic and smart devices. A deep understanding of the structure–property relationship is essential for designing new materials. In this work, instead of utilizing conventional atomic coordinates, a symmetry-mode approach is successfully used to conduct structure refinement of the neutron powder diffraction data of (1−x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics. This provides rich structural information that not only clarifies the controversial symmetry assigned to pure AgNbO3 but also explains well the detailed structural evolution of (1−x)AgNbO3–xLiTaO3 (0 ≤ x ≤ 0.09) ceramics, and builds a comprehensive and straightforward relationship between structural distortion and electrical properties. It is concluded that there are four relatively large-amplitude major modes that dominate the distorted Pmc21 structure of pure AgNbO3, namely a Λ3 antiferroelectric mode, a T4+ a−a−c0 octahedral tilting mode, an H2 a0a0c+/a0a0c− octahedral tilting mode and a Γ4− ferroelectric mode. The H2 and Λ3 modes become progressively inactive with increasing x and their destabilization is the driving force behind the composition-driven phase transition between the Pmc21 and R3c phases. This structural variation is consistent with the trend observed in the measured temperature-dependent dielectric properties and polarization–electric field (P-E) hysteresis loops. The mode crystallography applied in this study provides a strategy for optimizing related properties by tuning the amplitudes of the corresponding modes in these novel AgNbO3-based (anti)ferroelectric materials.

The local Fourier-space relation between diffracted intensity I, diffraction wavevector q and dose D, ilde I(q,D), is key to probing and understanding radiation damage by X-rays and energetic particles in both diffraction and imaging experiments. The models used in protein crystallography for the last 50 years provide good fits to experimental I(q) versus nominal dose data, but have unclear physical significance. More recently, a fit to diffraction and imaging experiments suggested that the maximum tolerable dose varies as q−1 or linearly with resolution. Here, it is shown that crystallographic data have been strongly perturbed by the effects of spatially nonuniform crystal irradiation and diffraction during data collection. Reanalysis shows that these data are consistent with a purely exponential local dose dependence, ilde I(q,D) = I0(q)exp[−D/De(q)], where De(q) ∝ qα with α ≃ 1.7. A physics-based model for radiation damage, in which damage events occurring at random locations within a sample each cause energy deposition and blurring of the electron density within a small volume, predicts this exponential variation with dose for all q values and a decay exponent α ≃ 2 in two and three dimensions, roughly consistent with both diffraction and imaging experiments over more than two orders of magnitude in resolution. The B-factor model used to account for radiation damage in crystallographic scaling programs is consistent with α = 2, but may not accurately capture the dose dependencies of structure factors under typical nonuniform illumination conditions. The strong q dependence of radiation-induced diffraction decays implies that the previously proposed 20–30 MGy dose limit for protein crystallography should be replaced by a resolution-dependent dose limit that, for atomic resolution data sets, will be much smaller. The results suggest that the physics underlying basic experimental trends in radiation damage at T ≃ 100 K is straightforward and universal. Deviations of the local I(q, D) from strictly exponential behavior may provide mechanistic insights, especially into the radiation-damage processes responsible for the greatly increased radiation sensitivity observed at T ≃ 300 K.

Reliable sample delivery and efficient use of limited beam time have remained bottlenecks for serial crystallography (SX). Using a high-intensity polychromatic X-ray beam in combination with a newly developed charge-integrating JUNGFRAU detector, we have applied the method of fixed-target SX to collect data at a rate of 1 kHz at a synchrotron-radiation facility. According to our data analysis for the given experimental conditions, only about 3 000 diffraction patterns are required for a high-quality diffraction dataset. With indexing rates of up to 25%, recording of such a dataset takes less than 30 s.

The present work reports on the charge and spin density modelling of YTiO3 in its ferromagnetic state (TC = 27 K). Accurate polarized neutron diffraction and high-resolution X-ray diffraction (XRD) experiments were carried out on a single crystal at the ORPHÉE reactor (LLB) and SPRING8 synchrotron source. The experimental data are modelled by the spin resolved pseudo-atomic multipolar model (Deutsch et al., 2012). The refinement strategy is discussed and the result of this electron density modelling is compared with that from XRD measured at 100 K and with density functional theory calculations. The results show that the spin and charge densities around the Ti atom have lobes directed away from the O atoms, confirming the filling of the t2g orbitals of the Ti atom. The dxy orbital is less populated than dxz and dyz, which is a sign of a partial lift of degeneracy of the t2g orbitals. This study confirms the orbital ordering at low temperature (20 K), which is already present in the paramagnetic state above the ferromagnetic transition (100 K).

The data quality requirements for charge density studies on actinide compounds are extreme. Important steps in data collection and reduction required to obtain such data are summarized and evaluated. The steps involved in building an augmented Hansen–Coppens multipole model for an actinide pseudo-atom are provided. The number and choice of radial functions, in particular the definition of the core, valence and pseudo-valence terms are discussed. The conclusions in this paper are based on a re-examination and improvement of a previously reported study on [PPh4][UF6]. Topological analysis of the total electron density shows remarkable agreement between experiment and theory; however, there are significant differences in the Laplacian distribution close to the uranium atoms which may be due to the effective core potential employed for the theoretical calculations.

Microcrystal electron diffraction (MicroED) combines crystallography and electron cryo-microscopy (cryo-EM) into a method that is applicable to high-resolution structure determination. In MicroED, nanosized crystals, which are often intractable using other techniques, are probed by high-energy electrons in a transmission electron microscope. Diffraction data are recorded by a camera in movie mode: the nanocrystal is continuously rotated in the beam, thus creating a sequence of frames that constitute a movie with respect to the rotation angle. Until now, diffraction-optimized cameras have mostly been used for MicroED. Here, the use of a direct electron detector that was designed for imaging is reported. It is demonstrated that data can be collected more rapidly using the Falcon III for MicroED and with markedly lower exposure than has previously been reported. The Falcon III was operated at 40 frames per second and complete data sets reaching atomic resolution were recorded in minutes. The resulting density maps to 2.1 Å resolution of the serine protease proteinase K showed no visible signs of radiation damage. It is thus demonstrated that dedicated diffraction-optimized detectors are not required for MicroED, as shown by the fact that the very same cameras that are used for imaging applications in electron microscopy, such as single-particle cryo-EM, can also be used effectively for diffraction measurements.

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.

Structural biology generally provides static snapshots of protein conformations that can provide information on the functional mechanisms of biological systems. Time-resolved structural biology provides a means to visualize, at near-atomic resolution, the dynamic conformational changes that macromolecules undergo as they function. X-ray free-electron-laser technology has provided a powerful tool to study enzyme mechanisms at atomic resolution, typically in the femtosecond to picosecond timeframe. Complementary to this, recent advances in the resolution obtainable by electron microscopy and the broad range of samples that can be studied make it ideally suited to time-resolved approaches in the microsecond to millisecond timeframe to study large loop and domain motions in biomolecules. Here we describe a cryo-EM grid preparation device that permits rapid mixing, voltage-assisted spraying and vitrification of samples. It is shown that the device produces grids of sufficient ice quality to enable data collection from single grids that results in a sub-4 Å reconstruction. Rapid mixing can be achieved by blot-and-spray or mix-and-spray approaches with a delay of ∼10 ms, providing greater temporal resolution than previously reported mix-and-spray approaches.

In this article, a method is presented to estimate a new local quality measure for 3D cryoEM maps that adopts the form of a `local resolution' type of information. The algorithm (DeepRes) is based on deep-learning 3D feature detection. DeepRes is fully automatic and parameter-free, and avoids the issues of most current methods, such as their insensitivity to enhancements owing to B-factor sharpening (unless the 3D mask is changed), among others, which is an issue that has been virtually neglected in the cryoEM field until now. In this way, DeepRes can be applied to any map, detecting subtle changes in local quality after applying enhancement processes such as isotropic filters or substantially more complex procedures, such as model-based local sharpening, non-model-based methods or denoising, that may be very difficult to follow using current methods. It performs as a human observer expects. The comparison with traditional local resolution indicators is also addressed.