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This paper summarizes brief perspectives on the historic process of establishing an African Crystallographic Association (AfCA) and includes representative references. It covers activities within four arbitrarily selected, approximate time slots, i.e., 1890s-1999, 2000-2013, 2014-2019 and 2020-2023. A genuine attempt is made to include appropriate role players, organizations and accompanying events within these periods. It concludes with the official admission of AfCA as the fifth Regional Associate of the IUCr at the 26th Congress and General Assembly of the IUCr in Melbourne, Australia in 2023. [ABSTRACT FROM AUTHOR]

The structures of 16 phosphane chalcogenide complexes of gold(I) halides, with the general formula R¹ 3-nR² nPEAuX (R¹ = t-butyl; R² = isopropyl; n = 0 to 3; E = S or Se; X = Cl, Br or I), are presented. The eight possible chlorido derivatives are: 1a, n = 3, E = S; 2a, n = 2, E = S; 3a, n = 1, E = S; 4a, n = 0, E = S; 5a, n = 3, E = Se; 6a, n = 2, E = Se; 7a, n = 1, E = Se; and 8a, n = 0, E = Se, and the corresponding bromido derivatives are 1b-8b in the same order. However, 2a and 2b were badly disordered and 8a was not obtained. The iodido derivatives are 2c, 6c and 7c (numbered as for the series a and b). All structures are solventfree and all have Z' = 1 except for 6b and 6c (Z' = 2). All molecules show the expected linear geometry at gold and approximately tetrahedral angles P--E--Au. The presence of bulky ligands forces some short intramolecular contacts, in particular H. . .Au and H. . .E. The Au--E bond lengths have a slight but consistent tendency to be longer when trans to a softer X ligand, and vice versa. The five compounds 1a, 5a, 6a, 1b and 5b form an isotypic set, despite the different alkyl groups in 6a. Compounds 3a/3b, 4b/8b and 6b/6c form isotypic pairs. The crystal packing can be analysed in terms of various types of secondary interactions, of which the most frequent are 'weak' hydrogen bonds from methine hydrogen atoms to the halogenido ligands. For the structure type 1a, H. . .X and H. . .E contacts combine to form a layer structure. For 3a/3b, the packing is almost featureless, but can be described in terms of a double-layer structure involving borderline H. . .Cl/Br and H. . .S contacts. In 4a and 4b/8b, which lack methine groups, Cmethyl--H. . .X contacts combine to form layer structures. In 7a/7b, short C--H. . .X interactions form chains of molecules that are further linked by association of short Au. . .Se contacts to form a layer structure. The packing of compound 6b/6c can conveniently be analysed for each independent molecule separately, because they occupy different regions of the cell. Molecule 1 forms chains in which the molecules are linked by a Cmethine. . .Au contact. The molecules 2 associate via a short Se. . .Se contact and a short H. . .X contact to form a layer structure. The packing of compound 2c can be described in terms of two short Cmethine--H. . .I contacts, which combine to form a corrugated ribbon structure. Compound 7c is the only compound in this paper to feature Au. . .Au contacts, which lead to twofold-symmetric dimers. Apart from this, the packing is almost featureless, consisting of layers with only translation symmetry except for two very borderline Au. . .H contacts. [ABSTRACT FROM AUTHOR]

The title compound, poly [bis(β-alaninium) [[dibromidoplumbate]-di-μ-dibromido]] {(C2H8NO2)2[PbBr4]}n or (β-AlaH)2PbBr4, crystallizes in the monoclinic space group P21/n. The (PbBr4)2− anion is located on a general position and has a two-dimensional polymeric structure. The Pb center is holodirected. The supramolecular network is mainly based on O—H⋯Br, N—H⋯Br and N—H⋯O hydrogen bonds. [ABSTRACT FROM AUTHOR]

The structures of seven gold(III) halide derivatives of general formula LAuX3 (L = methyl­pyridines or di­methyl­pyridines, X = Cl or Br) are presented: tri­chlorido­(2-methyl­pyridine)­gold(III), [AuCl3(C6H7N)], 1 (as two polymorphs 1a and 1b); tri­bromido­(2-methyl­pyridine)­gold(III), [AuBr3(C6H7N)], 2; tri­bromido­(3-methyl­pyridine)­gold(III), [AuBr3(C6H7N)], 3; tri­bromido­(2,4-di­meth­yl­pyridine)­gold(III), [AuBr3(C7H9N)], 4; tri­chlorido­(3,5-di­methylpyridine)­gold(III), [AuCl3(C7H9N)], 5; tri­bromido­(3,5-di­methyl­pyridine)­gold(III), [AuBr3(C7H9N)], 6, and tri­chlorido­(2,6-di­methyl­pyridine)­gold(III), [AuCl3(C7H9N)], 7. Additionally, the structure of 8, the 1:1 adduct of 2 and 6, [AuBr3(C6H7N)]·[AuBr3(C7H9N)], is included. All the structures crystallize solvent-free, and all have Z′ = 1 except for 5 and 7, which display crystallographic twofold rotation symmetry, and 4, which has Z′ = 2. 1a and 2 are isotypic. The coordination geometry at the gold(III) atoms is, as expected, square-planar. Four of the crystals (1a, 1b, 2 and 8) were non-merohedral twins, and these structures were refined using the 'HKLF 5' method. The largest inter­planar angles between the pyridine ring and the coordination plane are observed for those structures with a 2-methyl substituent of the pyridine ring. The Au--N bonds are consistently longer trans to Br (average 2.059 Å) than trans to Cl (average 2.036 Å). In the crystal packing, a frequent feature is the offset-stacked and approximately rectangular dimeric moiety (Au--X)2, with anti­parallel Au--X bonds linked by Au⋯X contacts at the vacant positions axial to the coordination plane. The dimers are connected by further secondary inter­actions (Au X or X X contacts, 'weak' C--H⋯X hydrogen bonds) to form chain, double chain ('ladder') or layer structures, and in several cases linked again in the third dimension. Only 1b and 7 contain no offset dimers; these structures instead involve C--H⋯Cl hydrogen bonds combined with Cl Cl contacts (1b) or Cl π contacts (7). The packing patterns of seven further complexes LAuX3 involving simple pyridines (taken from the Cambridge Structural Database) are compared with those of 1-8. [ABSTRACT FROM AUTHOR]

The crystal structures of two inter­mediates, 4-amino-3,5-di­fluoro­benzo­nitrile, C7H4F2N2 (I), and ethyl 4-amino-3,5-difluorobenzoate, C9H9F2NO2 (II), along with a visible-light-responsive azo­benzene derivative, diethyl 4,4′-(diazene-1,2-di­yl)bis­(3,5-difluoro­benzoate), C18H14F4N2O4 (III), obtained by four-step synthetic procedure, were studied using single-crystal X-ray diffraction. The mol­ecules of I and II demonstrate the quinoid character of phenyl rings accompanied by the distortion of bond angles related to the presence of fluorine substituents in the 3 and 5 (ortho) positions. In the crystals of I and II, the molecules are connected by N--H...N, N--H...F and N--H...O hydrogen bonds, C--H...F short contacts, and π-stacking inter­actions. In crystal of III, only stacking inter­actions between the molecules are found. [ABSTRACT FROM AUTHOR]

In the title compound, C19H17NO5S, the cyclo­hexene ring adopts nearly an envelope conformation. In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds, forming a three-dimensional network. In addition, C—H⋯π inter­actions connect the mol­ecules by forming layers parallel to the (010) plane. According to the Hirshfeld surface analysis, H⋯H (36.9%), O⋯H/H⋯O (31.0%), C⋯H/H⋯C (18.9%) and S⋯H/H⋯S (7.9%) inter­actions are the most significant contributors to the crystal packing. [ABSTRACT FROM AUTHOR]

Three organoplatinum(II) complexes bearing natural aryl­olefin and quinoline derivatives, namely, [4-meth­oxy-5-(2-meth­oxy-2-oxoeth­oxy)-2-(prop-2-en-1-yl)phen­yl](quinolin-8-olato)platinum(II), [Pt(C13H15O4)(C9H6NO)], (I), [4-meth­oxy-5-(2-oxo-2-propoxyeth­oxy)-2-(prop-2-en-1-yl)phen­yl](quinoline-2-carboxy­l­ato)platinum(II), [Pt(C15H19O4)(C10H6NO2)], (II), and chlorido­[4-meth­oxy-5-(2-oxo-2-propoxyeth­oxy)-2-(prop-2-en-1-yl)phen­yl](quinoline)­plat­inum(II), [Pt(C15H19O4)Cl(C9H7N)], (III), were synthesized and structurally characterized by IR and 1H NMR spectroscopy, and by single-crystal X-ray diffraction. The results showed that the cyclo­platinated arylolefin coordinates with PtII via the carbon atom of the phenyl ring and the C=Colefinic group. The deprotonated 8-hy­droxy­quinoline (C9H6NO) and quinoline-2-carb­oxy­lic acid (C10H6NO2) coordinate with the PtII atom via the N and O atoms in complexes (I) and (II) while the quinoline (C9H7N) coordinates via the N atom in (III). Moreover, the coordinating N atom in complexes (I)–(III) is in the cis position compared to the C=Colefinic group. The crystal packing is characterized by C—H⋯π, C—H⋯O [for (II) and (III)], C—H⋯Cl [for (III) and π–π [for (I)] inter­actions. [ABSTRACT FROM AUTHOR]

The cis- form of diaminodibenzocyclooctane (DADBCO, C16H18N2) is of interest as a negative coefficient of thermal expansion (CTE) material. The crystal structure was determined through single-crystal X-ray diffraction at 100 K and is presented herein [ABSTRACT FROM AUTHOR]

This study introduces bis­[hexa­kis­(nitrato-κ²O,O′)lanthanum(III)] tris­[hexa­aqua­nickel(II)] hexa­hydrate, [La(NO3)6]2[Ni(H2O)6]3·6H2O, with a structure refined in the hexa­gonal space group R... The salt com­prises [La(NO3)6]3− icosa­hedra and [Ni(H2O)6]2+ octa­hedra, thus forming an intricate network of inter­penetrating honeycomb lattices arranged in layers. This arrangement is stabilized through strong hydrogen bonds. Two successive layers are connected via the second [Ni(H2O)6]2+ octa­hedra, forming sheets which are stacked perpendicular to the c axis and held in the crystal by van der Waals forces. The synthesis of [La(NO3)6]2[Ni(H2O)6]3·6H2O involves dissolving lanthanum(III) and nickel(II) oxides in nitric acid, followed by slow evaporation, yielding green hexa­gonal plate-like crystals. [ABSTRACT FROM AUTHOR]

The synthesis, crystallization and characterization of a tri­fluoro­methane­sulfonate salt of 5,10,15,20-tetra­kis­(1-benzyl­pyridin-1-ium-4-yl)-21H,23H-por­phy­rin, C68H54N84+·4CF3SO3−·4H2O, 1·OTf, are reported in this work. The reaction between 5,10,15,20-tetra­kis­(pyridin-4-yl)-21H,23H-porphyrin and benzyl bromide in the presence of 0.1 equiv. of Ca(OH)2 in CH3CN under reflux with an N2 atmosphere and subsequent treatment with silver tri­fluoro­methane­sulfonate (AgOTf) salt produced a red–brown solution. This reaction mixture was filtered and the solvent was allowed to evaporate at room temperature for 3 d to give 1·OTf. Crystal structure determination by single-crystal X-ray diffraction (SCXD) revealed that 1·OTf crystallizes in the space group P21/c. The asymmetric unit contains half a porphyrin mol­ecule, two tri­fluoro-methane­sulfonate anions and two water mol­ecules of crystallization. The macrocycle of tetra­pyrrole moieties is planar and unexpectedly it has coordinated CaII ions in occupational disorder. This CaII ion has only 10% occupancy (C72H61.80Ca0.10F12N8O16S4). The pyridinium rings bonded to methyl­ene groups from porphyrin are located in two different arrangements in almost orthogonal positions between the plane formed by the porphyrin and the pyridinium rings. The crystal structure features cation⋯π inter­actions between the CaII atom and the π-system of the phenyl ring of neighboring mol­ecules. Both tri­fluoro­methane­sulfonate anions are found at the periphery of 1, forming hydrogen bonds with water mol­ecules. [ABSTRACT FROM AUTHOR]

The structural characterization is reported of the supra­molecular complex between the tetra­quinoxaline-based cavitand 2,8,14,20-tetra­hexyl-6,10:12,16:18,22:24,4-O,O′-tetra­kis­(quinoxaline-2,3-di­yl)calix[4]resorcinarene (QxCav) with benzo­nitrile. The complex, of general formula C84H80N8O8·2C7H5N, crystallizes in the space group P⥘ with two independent mol­ecules in the asymmetric unit, displaying very similar geometrical parameters. For each complex, one of the benzo­nitrile mol­ecules is engulfed inside the cavity, while the other is located among the alkyl legs at the lower rim. The host and the guests mainly inter­act through weak C—H⋯π, C—H⋯N and dispersion inter­actions. These inter­actions help to consolidate the formation of supra­molecular chains running along the crystallographic b-axis direction. [ABSTRACT FROM AUTHOR]

The title compound, [Co(NCS)2(C6H7N)4] or Co(NCS)2(4-methyl­pyridine)4, was prepared by the reaction of Co(NCS)2 with 4-methyl­pyridine in water and is isotypic to one of the polymorphs of Ni(NCS)2(4-methyl­pyridine)4 [Kerr & Williams (1977[Kerr, I. S. & Williams, D. J. (1977). Acta Cryst. B33, 3589-3592.]). Acta Cryst. B33, 3589–3592 and Soldatov et al. (2004[Soldatov, D. V., Enright, G. D. & Ripmeester, J. A. (2004). Cryst. Growth Des. 4, 1185-1194.]). Cryst. Growth Des. 4, 1185–1194]. Comparison of the experimental X-ray powder pattern with that calculated from the single-crystal data proves that a pure phase has been obtained. The asymmetric unit consists of one CoII cation, two crystallographically independent thio­cyanate anions and four independent 4-meth­yl­pyridine ligands, all located in general positions. The CoII cations are sixfold coordinated to two terminally N-bonded thio­cyanate anions and four 4-methyl­pyridine coligands within slightly distorted octa­hedra. Between the complexes, a number of weak C—H⋯N and C—H⋯S contacts are found. This structure represent a polymorphic modification of Co(NCS)2(4-methyl­pyridine)4 already reported in the CCD [Harris et al. (2003[Harris, J. D., Eckles, W. E., Hepp, A. F., Duraj, S. A., Hehemann, D. G., Fanwick, P. E. & Richardson, J. (2003). NASA Technical Reports, 211890.]). NASA Technical Reports, 211890]. In contrast to this form, the crystal structure of the new polymorph shows a denser packing, indicating that it is thermodynamically stable at least at low temperatures. Thermogravimetric and differential thermoanalysis reveal that the title compound starts to decomposes at about 100°C and that the coligands are removed in separate steps without any sign of a polymorphic transition before decomposition. [ABSTRACT FROM AUTHOR]

The title compound, C12H16N2O, is a hy­droxy-substituted mono­amine alkaloid, and the primary metabolite of the naturally occurring psychedelic compound psilocybin. Crystalline forms of psilocin are known, but their characterization by single-crystal structure analysis is limited. Herein, two anhydrous polymorphic forms (I and II) of psilocin are described. The crystal structure of polymorphic Form I, in space group P21/c, was first reported in 1974. Along with the redeterm­ination to modern standards and unambiguous location of the acidic H atom and variable-temperature single-crystal unit-cell determinations for Form I, the Form II polymorph of the title compound, which crystallizes in the monoclinic space group P21/n, is described for the first time. The psilocin mol­ecules are present in both forms in their phenol–amine tautomeric forms (not resolved in the 1974 report). The mol­ecules in Forms I and II, however, feature different conformations of their N,N-dimethyl ethyl­ene substituent, with the N—C—C—C link in Form I being trans and in Form II being gauche, allowing the latter to bend back to the hydroxyl group of the same mol­ecule, leading to the formation of a strong intra­molecular O—H⋯N hydrogen bond between the hydroxyl moiety and ethyl­amino-nitro­gen group. In the extended structure of Form II, the mol­ecules form one-dimensional strands through N—H⋯O hydrogen bonds from the indole group to the oxygen atom of the hydroxyl moiety of an adjacent mol­ecule. Form II exhibits whole-mol­ecule disorder due to a pseudo-mirror operation, with an occupancy ratio of 0.689 (5):0.311 (5) for the two components. In contrast, Form I does not feature intra­molecular hydrogen bonds but forms a layered structure through inter­molecular N—H⋯O and O—H⋯N hydrogen bonds. [ABSTRACT FROM AUTHOR]

The reaction of lithium hexa­methyl­disilyl­amide, [Li{N(Si(CH3)3)2}] (LiHMDS), with 4,4-dimethyl-2-phenyl-2-oxazoline (Phox, C11H13NO) in hexane produced colourless crystals of bis­(4,4-dimethyl-2-phenyl-2-oxazoline-κN)(hexa­methyl­disilyl­amido-κN)lithium, [Li(C6H18NSi2)(C11H13NO)2] or [Li{N(Si(CH3)3)2}(Phox)2] in high yield (89%). Despite the 1:1 proportion of the starting materials in the reaction mixture, the product formed with a 1:2 amide:oxazoline ratio. In the unit cell of the C2/c space group, the neutral mol­ecules lie on twofold rotation axes coinciding with the Li—N(amide) bonds. The lithium(I) centre adopts a trigonal–planar coordination geometry with three nitro­gen donor atoms, one from the HMDS anion and two from the oxazolines. All ligands are monodentate. In the phenyl­oxazoline units, the dihedral angle defined by the five-membered heterocyclic rings is 35.81 (5)°, while the phenyl substituents are approximately face-to-face, separated by 3.908 (5) Å. In the amide, the methyl groups assume a nearly eclipsed arrangement to minimize steric repulsion with the analogous substituents on the oxazoline rings. The non-covalent inter­actions in the solid-state structure of [Li{N(Si(CH3)3)2}(Phox)2] were assessed by Hirshfeld surface analysis and fingerprint plots. This new compound is attractive for catalysis due to its unique structural features. [ABSTRACT FROM AUTHOR]

The title compound, [Co(NCS)2(C6H7N)4] or Co(NCS)2(4-methyl-pyridine)4, was prepared by the reaction of Co(NCS)2 with 4-methyl-pyridine in water and is isotypic to one of the polymorphs of Ni(NCS)2(4-methyl-pyridine)4 [Kerr & Williams (1977). Acta Cryst. B33, 3589-3592 and Soldatov et al. (2004). Cryst. Growth Des. 4, 1185-1194]. Comparison of the experimental X-ray powder pattern with that calculated from the single-crystal data proves that a pure phase has been obtained. The asymmetric unit consists of one CoII cation, two crystallographically independent thio-cyanate anions and four independent 4-meth-yl-pyridine ligands, all located in general positions. The CoII cations are sixfold coordinated to two terminally N-bonded thio-cyanate anions and four 4-methyl-pyridine coligands within slightly distorted octa-hedra. Between the complexes, a number of weak C-H⋯N and C-H⋯S contacts are found. This structure represent a polymorphic modification of Co(NCS)2(4-methyl-pyridine)4 already reported in the CCD [Harris et al. (2003). NASA Technical Reports, 211890]. In contrast to this form, the crystal structure of the new polymorph shows a denser packing, indicating that it is thermodynamically stable at least at low temperatures. Thermogravimetric and differential thermoanalysis reveal that the title compound starts to decomposes at about 100°C and that the coligands are removed in separate steps without any sign of a polymorphic transition before decomposition. [ABSTRACT FROM AUTHOR]

The cis- form of diaminodibenzocyclooctane (DADBCO, C16H18N2) is of interest as a negative coefficient of thermal expansion (CTE) material. The crystal structure was determined through single-crystal X-ray diffraction at 100 K and is presented herein. [ABSTRACT FROM AUTHOR]

In the title compound, C20H17BrO5S, molecules are connected by intermolecular C--H...S hydrogen bonds with R22(10) ring motifs, forming ribbons along the baxis direction. C--H...π interactions consolidate the ribbon structure while van der Waals forces between the ribbons ensure the cohesion of the crystal structure. According to a Hirshfeld surface analysis, H...H (40.5%), O...H/H...O (27.0%), C...H/H...C (13.9%) and Br...H/H...Br (11.7%) interactions are the most significant contributors to the crystal packing. The thiophene ring and its adjacent dicarboxylate group and the three adjacent carbon atoms of the central hexene ring to which they are attached were refined as disordered over two sets of sites having occupancies of 0.8378 (15) and 0.1622 (15). The thiophene group is disordered by a rotation of 180° around one bond. [ABSTRACT FROM AUTHOR]

The title compound, ammonium trinickel(II) hydrogen arsenate arsenate dihydroxide, was synthesized under hydrothermal conditions. Its crystal structure is isotypic with that of K[Cu3(HAsO4)(AsO4)(OH)2] and is characterized by pseudo-hexagonal (001) 2∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]- layers formed from vertex- and edge-sharing [NiO4(OH)2] octahedra and [AsO3.5(OH)0.5] tetrahedra as the building units. The hydrogen atom of the OH group shows occupational disorder and was refined with a site occupation factor of 1/2, indicating the equal presence of [HAsO4]2- and [AsO4]3- groups. Strong asymmetric hydrogen bonds between symmetry-related (O,OH) groups of the arsenate units [O...O = 2.588 (18) Å] as well as hydrogen bonds accepted by these (O,OH) groups from OH groups bonded to the NiII atoms [O...O = 2.848 (12) Å] link adjacent layers. Additional consolidation of the packing is achieved through N--H...O hydrogen bonds from the ammonium ion, which is sandwiched between adjacent layers [N...O = 2.930 (7) Å] although the H atoms could not be located in the present study. The presence of the pseudo-hexagonal 2∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1 ]- layers may be the reason for the systematic threefold twinning of (NH4)[Ni3(HAsO4)(AsO4)(OH)2] crystals. Significant overlaps of the reflections of the respective twin domains complicated the structure solution and refinement. [ABSTRACT FROM AUTHOR]

The structures of fourteen halochalcogenylphosphonium tetrahalogenidoaurates(III), phosphane chalcogenide derivatives with general formula [R¹3-nR²nPEX][AuX4] (R¹ = t-butyl; R² = isopropyl; n = 0 to 3; E = S or Se; X = Cl or Br) are presented. The eight possible chlorido derivatives are: 17a, n = 3, E = S; 18a, n = 2, E = S; 19a, n = 1, E = S; 20a, n = 0, E = S; 21a, n = 3, E = Se; 22a, n = 2, E = Se; 23a, n = 1, E = Se; and 24a, n = 0, E = Se, and the corresponding bromido derivatives are 17b-24b in the same order. Structures were obtained for all compounds except for the tri-t-butyl derivatives 24a and 24b. Isotypy is observed for 18a/18b/22a/22b, 19a/23a, 17b/21b and 19b/23b. In eleven of the compounds, X...X contacts (mostly very short) are observed between the cation and anion, whereby the E--X...X groups are approximately linear and the X...X--Au angles approximately 90°. The exceptions are 17a, 19a and 23a, which instead display short E...X contacts. Bond lengths in the cations correspond to single bonds P--E and E--X. For each group with constant E and X, the P--E--X bond-angle values increase monotonically with the steric bulk of the alkyl groups. The packing is analysed in terms of E...X, X...X (some between anions alone), H...X and H...Au contacts. Even for isotypic compounds, some significant differences can be discerned. [ABSTRACT FROM AUTHOR]

The asymmetric unit of the title compound, C25H18N6.H2O, comproses two molecules (I and II), together with a water molecule. The terminal phenyl groups attached to the methyl groups of the molecules I and II do not overlap completely, but are approximately perpendicular. In the crystal, the molecules are connected by N--H...N, C--H...N, O--H...N and N--H...O hydrogen bonds with each other directly and through water molecules, forming layers parallel to the (001) plane. C--H...π interactions between these layers ensure the cohesion of the crystal structure. A Hirshfeld surface analysis indicates that H...H (39.1% for molecule I; 40.0% for molecule II), C...H/H...C (26.6% for molecule I and 25.8% for molecule II) and N...H/H...N (24.3% for molecules I and II) interactions are the most important contributors to the crystal packing. [ABSTRACT FROM AUTHOR]

Trichlorido(4-methylpiperidine)gold(III), [AuCl3(C6H13N)], 1, crystallizes in Pbca with Z = 8. Tribromido(4-methylpiperidine)gold(III), [AuBr3(C6H13N)], 2, crystallizes as two polymorphs, 2a in Pnma with Z = 4 (imposed mirror symmetry) and 2b, which is isotypic to 1. The Au--N bonds trans to Cl are somewhat shorter than those trans to Br, and the Au--Cl bonds trans to N are longer than those cis to N, whereas the Au--Br bonds trans to N are slightly shorter than the cis bonds. The methyl and AuX3 groups (X = halogen) occupy equatorial positions at the six-membered ring. The packing of all three structures involves chains of molecules with offset stacking of the AuX3 moieties associated with short Au...X contacts; for 1 and 2b these are reinforced by N--H...X hydrogen bonds, whereas for 2a there are no classical hydrogen bonds and the chains are interconnected by Br...Br contacts. [ABSTRACT FROM AUTHOR]

This paper summarizes brief perspectives on the historic process of establishing an African Crystallographic Association (AfCA) and includes representative references. It covers activities within four arbitrarily selected, approximate time slots, i.e., 1890s–1999, 2000–2013, 2014–2019 and 2020–2023. A genuine attempt is made to include appropriate role players, organizations and accompanying events within these periods. It concludes with the official admission of AfCA as the fifth Regional Associate of the IUCr at the 26th Congress and General Assembly of the IUCr in Melbourne, Australia in 2023.

The structures of 16 phosphane chalcogenide complexes of gold(I) halides, with the general formula R13-nR2nPEAuX (R1 = t-butyl; R2 = isopropyl; n = 0 to 3; E = S or Se; X = Cl, Br or I), are presented. The eight possible chlorido derivatives are: 1a, n = 3, E = S; 2a, n = 2, E = S; 3a, n = 1, E = S; 4a, n = 0, E = S; 5a, n = 3, E = Se; 6a, n = 2, E = Se; 7a, n = 1, E = Se; and 8a, n = 0, E = Se, and the corresponding bromido derivatives are 1b–8b in the same order. However, 2a and 2b were badly disordered and 8a was not obtained. The iodido derivatives are 2c, 6c and 7c (numbered as for the series a and b). All structures are solvent-free and all have Z′ = 1 except for 6b and 6c (Z′ = 2). All molecules show the expected linear geometry at gold and approximately tetrahedral angles P—E—Au. The presence of bulky ligands forces some short intramolecular contacts, in particular H...Au and H...E. The Au—E bond lengths have a slight but consistent tendency to be longer when trans to a softer X ligand, and vice versa. The five compounds 1a, 5a, 6a, 1b and 5b form an isotypic set, despite the different alkyl groups in 6a. Compounds 3a/3b, 4b/8b and 6b/6c form isotypic pairs. The crystal packing can be analysed in terms of various types of secondary interactions, of which the most frequent are `weak' hydrogen bonds from methine hydrogen atoms to the halogenido ligands. For the structure type 1a, H...X and H...E contacts combine to form a layer structure. For 3a/3b, the packing is almost featureless, but can be described in terms of a double-layer structure involving borderline H...Cl/Br and H...S contacts. In 4a and 4b/8b, which lack methine groups, Cmethyl—H...X contacts combine to form layer structures. In 7a/7b, short C—H...X interactions form chains of molecules that are further linked by association of short Au...Se contacts to form a layer structure. The packing of compound 6b/6c can conveniently be analysed for each independent molecule separately, because they occupy different regions of the cell. Molecule 1 forms chains in which the molecules are linked by a Cmethine...Au contact. The molecules 2 associate via a short Se...Se contact and a short H...X contact to form a layer structure. The packing of compound 2c can be described in terms of two short Cmethine—H...I contacts, which combine to form a corrugated ribbon structure. Compound 7c is the only compound in this paper to feature Au...Au contacts, which lead to twofold-symmetric dimers. Apart from this, the packing is almost featureless, consisting of layers with only translation symmetry except for two very borderline Au...H contacts.

The structures of ten phosphane chalcogenide complexes of gold(III) halides, with general formula R3-n¹R²nPEAuX3 (R¹ = t-butyl; R² = i-propyl; n = 0 to 3; E = S or Se; X = Cl or Br) are presented. The eight possible chlorido derivatives are: 9a, n = 3, E = S; 10a, n = 2, E = S; 11a, n = 1, E = S; 12a, n = 0, E = S; 13a, n = 3, E = Se; 14a, n = 2, E = Se; 15a, n = 1, E = Se; and 16a, n = 0, E = Se, and the corresponding bromido derivatives are 9b-16b in the same order. Structures were obtained for 9a, 10a (and a second polymorph 10aa), 11a (and its deutero-chloro-form monosolvate 11aa), 12a (as its di-chloro-methane monosolvate), 14a, 15a (as its deutero-chloro-form monosolvate 15aa, in which the solvent mol-ecule is disordered over two positions), 9b, 11b, 13b and 15b. The structures of 11a, 15a, 11b and 15b form an isotypic set, and those of compounds 10aa and 14a form an isotypic pair. All structures have Z' = 1. The gold(III) centres show square-planar coordination geometry and the chalcogenide atoms show approximately tetra-hedral angles (except for the very wide angle in 12a, probably associated with the bulky t-butyl groups). The bond lengths at the gold atoms are lengthened with respect to the known gold(I) derivatives, and demonstrate a considerable trans influence of S and Se donor atoms on a trans Au-Cl bond. Each compound with an isopropyl group shows a short intra-molecular contact of the type C-Hmethine⋯Xcis; these may be regarded as intra-molecular 'weak' hydrogen bonds, and they determine the orientation of the AuX3 groups. The molecular packing is analysed in terms of various short contacts such as weak hydrogen bonds C-H⋯X and contacts between the heavier atoms, such as X⋯X (9a, 10aa, 11aa, 15aa and 9b), S⋯S (10aa, 11a and 12a) and S⋯Cl (10a). The packing of the polymorphs 10a and 10aa is thus quite different. The solvent mol-ecules take part in C-H⋯Cl hydrogen bonds; for 15aa, a disordered solvent region at z ≃ 0 is observed. Structure 13b involves unusual inversion-symmetric dimers with Se⋯Au and Se⋯Br contacts, further connected by Br⋯Br contacts. [ABSTRACT FROM AUTHOR]

In the ten-membered 1,3,4,6-tetrahydro-2H-pyrido[1,2-α]pyrimidine ring system of the title compound, C17H15N5, the 1,2-dihydropyridine ring is essentially planar (r.m.s. deviation = 0.001 Å), while the 1,3-diazinane ring has a distorted twist-boat conformation. In the crystal, molecules are linked by N--H⋯N and C--H⋯N hydrogen bonds, forming a three-dimensional network. In addition, C--H⋯π interactions form layers parallel to the (100) plane. Thus, crystalstructure cohesion is ensured. According to a Hirshfeld surface study, H⋯H (40.4%), N⋯H/H⋯N (28.6%) and C⋯H/H⋯C (24.1%) interactions are the most important contributors to the crystal packing. [ABSTRACT FROM AUTHOR]

In the title compound, C21H15N5OS2, molecular pairs are linked by N--H…N hydrogen bonds along the c-axis direction and C--H…S and C--H…O hydrogen bonds along the b-axis direction, with R2²(12) and R2²(16) motifs, respectively, thus forming layers parallel to the (104) plane. In addition, C=S…π and C...N…π interactions between the layers ensure crystal cohe- sion. The Hirshfeld surface analysis indicates that the major contributions to the crystal packing are H…H (43.0%), C…H/H…C (16.9%), N…H/H…N (11.3%) and S…H/H…S (10.9%) interactions. [ABSTRACT FROM AUTHOR]

The title molecule, [Fe2(C5H5)2(C23H17ClN2)]⋅C3H7NO, is twisted end to end and the central N/C/N unit is disordered. In the crystal, several C--H…π(ring) interactions lead to the formation of layers, which are connected by further C--H…π(ring) interactions. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H…H (60.2%) and H… C/C…H (27.0%) interactions. Hydrogen bonding, C--H…π(ring) interactions and van der Waals interactions dominate the crystal packing. [ABSTRACT FROM AUTHOR]

The crystal structure of the tetraethylammonium salt of the non-steroidal antiinflammatory drug nimesulide (polymorph II) (systematic name: tetraethylammonium N-methanesulfonyl-4-nitro-2-phenoxyanilinide), C8H20N+-C13H11N2O5S-, was determined using single-crystal X-ray diffraction. The title compound crystallizes in the monoclinic space group P21/c with one tetra-ethylammonium cation and one nimesulide anion in the asymmetric unit. In the crystal, the ions are linked by C--H … N and C--H … O hydrogen bonds and C--H … π interactions. There are differences in the geometry of both the nimesulide anion and the tetraethylammonium cation in polymorphs I [Rybczyiiska & Sikorski (2023). Sci. Rep. 13, 17268] and II of the title compound. [ABSTRACT FROM AUTHOR]

Since its founding in 2013, the Young Crystallographers (YC) have become one of the most active working groups not only within their parent organization, the German Crystallographic Society (DGK), but also among other young crystallographers' groups in Europe and the world. The aim of the YC is and always has been to support early-career researchers in the diverse fields of crystallography and the rejuvenation of the field on a national scale. Over the past decade, we have curated events, platforms, and educational content tailored to foster collaboration and knowledge transfer among young crystallographers. In this article, we introduce our group and show how this active and diverse community has shaped the rejuvenation of crystallography in Germany, strengthened by the support of our national society. [ABSTRACT FROM AUTHOR]

In the crystal of the title compound, C6H9ClN2O, molecular pairs form dimers with an R²2(8) motif through N--H...O hydrogen bonds. These dimers are connect into ribbons parallel to the (100) plane with R44(10) motifs by N--H...O hydrogen bonds along the c-axis direction. In addition, π-π [centroid-tocentroid distance = 3.4635 (9) A ° ] and C--Cl... π interactions between the ribbons form layers parallel to the (100) plane. The three-dimensional consolidation of the crystal structure is also ensured by Cl...H and Cl...Cl interactions between these layers. According to a Hirshfeld surface study, H...H (43.3%), Cl...H/H...Cl (22.1%) and O...H/H...O (18.7%) interactions are the most significant contributors to the crystal packing. [ABSTRACT FROM AUTHOR]

In bis(4-methylpiperidine-N)gold(I) chloride, [Au(C6H13N)2]Cl (1), the methyl groups are, as expected, equatorial at the piperidine ring, but the Au atom is axial; this is the case for all five structures reported here, as is the expected linear coordination at the Au atom. Hydrogen bonding of the form N--H...Cl-...H--N leads to inversion-symmetric dimers, which are further connected by C--H...Au contacts. Bis(4-methylpiperidine-N)gold(I) dichloridoaurate(I), [Au(C6H13N)2][AuCl2] (2), also forms inversion-symmetric dimers; these involve aurophilic interactions and three-centre hydrogen bonds of the form NH(...Cl)2. Bis(4-methylpiperidine-N)gold(I) dibromidoaurate(I), [Au(C6H13N)2][AuBr2] (3), is isotypic to 2. The 1:1 adduct chlorido(4-methylpiperidine-N)gold(I) bis(4-methylpiperidine-N)gold(I) chloride, [Au(C6H13N)2]Cl·[AuCl(C6H13N)] (4), crystallizes as its dichloromethane solvate. The asymmetric unit contains two formula units, in each of which the chloride anion accepts a hydrogen bond from the cation and from the neutral molecule, and the two Au atoms are linked via an aurophilic interaction. A further hydrogen bond leads to inversion-symmetric dimers. The asymmetric unit of bis(2-methylpiperidine-N)gold(I) chloride, [Au(C6H13N)2]Cl (5), contains two 'half' cations, in which the Au atoms lie on twofold axes, and a chloride ion on a general position. Within each cation, the relative configurations at the atoms N and C2 (which bears the methyl substituent) are R, S. The twofold-symmetric dimer involves two N--H...Cl-...H--N units and an aurophilic contact between the two Au atoms. [ABSTRACT FROM AUTHOR]

The title compound, C10H11N5O2S2, consists of an unexpected tautomer with a protonated nitrogen atom in the triazine ring and a formal exocyclic double bond C N to the sulfonamide moiety. The ring angles at the unsubstituted nitrogen atoms are narrow, at 115.57 (12) and 115.19 (12)°, respectively, whereas the angle at the carbon atom between these N atoms is very wide, 127.97 (13)°. The interplanar angle between the two rings is 79.56 (5)°. The molecules are linked by three classical hydrogen bonds, forming a ribbon structure. There are also unusual linkages involving three short contacts (< 3 Å) from a sulfonamide oxygen atom to the C--NH--C part of a triazine ring. [ABSTRACT FROM AUTHOR]

In the title compound, C20H18O4, the dihedral angle between the 2H-chromen-2-one ring system and the phenyl ring is 89.12(5)°. In the crystal, the molecules are connected through C--H...O hydrogen bonds to generate [010] double chains that are reinforced by weak aromatic p-p stacking interactions. The unit-cell packing can be described as a tilted herringbone motif. The H...H, H...O/O...H, H...C/C...H and C...C contacts contribute 46.7, 24.2, 16.7 and 7.6%, respectively, to its Hirshfeld surface. [ABSTRACT FROM AUTHOR]

JUAMI, the joint undertaking for an African materials institute, is a project to build collaborations and materials research capabilities between PhD researchers in Africa, the United States, and the world. Focusing on researchactive universities in the East African countries of Kenya, Ethiopia, Tanzania and Uganda, the effort has run a series of schools focused on materials for sustainable energy and materials for sustainable development. These bring together early-career researchers from Africa, the US, and beyond, for two weeks in a close-knit environment. The program includes lectures on cuttingedge research from internationally renowned speakers, highly interactive tutorial lectures on the science behind the research, also from internationally known researchers, and hands-on practicals and team-building exercises that culminate in group proposals from self-formed student teams. The schools have benefited more than 300 early-career students and led to proposals that have received funding and have led to research collaborations and educational nonprofits. JUAMI continues and has an ongoing community of alumni who share resources and expertise, and is open to like-minded people who want to join and develop contacts and collaborations internationally. [ABSTRACT FROM AUTHOR]

Syntheses of the acyclic amidinium salts, morpholinoformamidinium hexafluoridophosphate [OC4H8N--CH NH2]PF6 or C5H11N2O+·PF6-, 1, and pyrrolidinoformamidinium hexafluoridophosphate [C4H8N--CH NH2]PF6 or C5H11N2 +·PF6-, 2, were carried out by heating either morpholine or pyrrolidine with triethyl orthoformate and ammonium hexafluoridophosphate. Crystals of 1 obtained directly from the reaction mixture contain one cation and one anion in the asymmetric unit. The structure involves cations linked in chains parallel to the b axis by N--H. . .O hydrogen bonds in space group Pbca, with glide-related chains pointing in opposite directions. Crystals of 1 obtained by recrystallization from ethanol, however, showed a similar unit cell and the same basic structure, but unexpectedly, there was positional disorder [occupancy ratio 0.639 (4):0.361 (4)] in one of the cation chains, which lowered the crystal symmetry to the non-centrosymmetric space group Pca21, with two cations and anions in the asymmetric unit. In the pyrrolidino compound, 2, cations and anions are ordered and are stacked separately, with zigzag N--H. . .F hydrogenbonding between stacks, forming ribbons parallel to (101), extended along the baxis direction. Slight differences in the delocalized C N distances between the two cations may reflect the inductive effect of the oxygen atom in the morpholino compound. [ABSTRACT FROM AUTHOR]