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The title compound, C40H64O12, crystallizes in a pseudo­merohedrally twinned primitive monoclinic cell with similar contributions of the two twin components. There are two symmetry-independent half-mol­ecules of nona­ctin in the asymmetric unit. Each mol­ecule has a pseudo-S 4 symmetry and resides on a crystallographic twofold axis; the axes pass through the mol­ecular center of mass and are perpendicular to the plane of the macrocycle. The literature description of the room-temperature structure of nona­ctin as an order–disorder structure in an ortho­rhom­bic unit cell is corrected. We report a low-temperature high-precision ordered structure of ‘free’ nona­ctin that allowed for the first time precise determination of its bond distances and angles. It possesses an unfolded and more planar geometry than its complexes with encapsulated Na+, K+, Cs+, Ca2+ or NH4 + cations that exhibit more isometric overall conformations.

A case of imperfect pseudo-merohedral twinning in monoclinic crystals of fungal fatty acid synthase is discussed. A space-group transition during crystal dehydration resulted in a Moiré pattern-like interference of the twinned diffraction patterns.

The recent high-resolution structures of fungal fatty acid synthase (FAS) have provided new insights into the principles of fatty acid biosynthesis by large multifunctional enzymes. The crystallographic phase problem for the 2.6 MDa fungal FAS was initially solved to 5 Å resolution using two crystal forms from Thermomyces lanuginosus. Monoclinic crystals in space group P21 were obtained from orthorhombic crystals in space group P212121 by dehydration. Here, it is shown how this space-group transition induced imperfect pseudo-merohedral twinning in the monoclinic crystal, giving rise to a Moiré pattern-like interference of the two twin-related reciprocal lattices. The strategy for processing the twinned diffraction images and obtaining a quantitative analysis is presented. The twinning is also related to the packing of the molecules in the two crystal forms, which was derived from self-rotation function analysis and molecular-replacement solutions using a low-resolution electron microscopy map as a search model.

In the cobaltocenium group of the title compound, [AuCo(C5H5)(C17H14P)Cl]PF6, the substituted cyclo­penta­dienyl (Cps) and the unsubstituted cyclo­penta­dienyl (Cp) ring planes are almost parallel, making a dihedral angle of 3.1 (3)°. The C atoms in Cp and Cps are in an eclipsed conformation. The AuI atom is coordinated by a P atom from the diphenyl­phosphanyl group and a Cl atom in an almost linear arrangement [P—Au—Cl = 178.15–(7)°]. Two hexa­fluorido­phosphate anions are each located on a twofold rotation axis. In the crystal, the complex cations and hexa­fluorido­phosphate anions are linked via inter­molecular C—H⋯F hydrogen bonds.

The title compound, [V2Cl4O2(CH3CN)4], is a centrosymmetric dinuclear VIV complex associated with four mol­ecules of acetonitrile. The coordination around both VIV atoms is essentially square-planar, involving three Cl atoms and one O atom [maximum deviation = 0.017 (3) Å for the O atom]. The augmented octahedral coordination of the metal atom is completed by the N atoms of acetonitrile ligands. The VIV atoms are linked by two Cl atoms, acting as bridging atoms. The crystal studied was a non-merohedral twin with a ratio of the two twin components of 0.8200 (3):0.1800 (3). Although Cl and O atoms are present as potential acceptors in the title compound, no hydrogen bonds were observed in the crystal structure.

The crystal structure of the title compound, C14H21NO2S, is a polymorph of the structure reported by Khan et al. [Acta Cryst. (2009), E65, o2867] which is also monoclinic (space group P21/c). The unit cell in the title structure is approximately half the volume of the previously reported polymorph and the asymmetric unit of the title compound contains one mol­ecule rather than two independent mol­ecules in the other polymorph. In the title mol­ecule, the cyclo­hexane ring is in the typical chair form. In the crystal structure, mol­ecules are linked via weak inter­molecular C—H⋯O inter­actions, forming a chain along the b-axis direction.

The title salt, C12H24N+·NCS−, represents a monoclinic polymorph of the previously reported ortho­rhom­bic form [Khawar Rauf et al. (2008 ▶). Acta Cryst. E64, o366]. Two independent formula units comprise the asymmetric unit with the major difference in their mol­ecular structures relating to the relative dispositions of the cyclo­hexyl rings [dihedral angles = 79.88 (6) and 67.72 (5)°]. Further, the independent anions form distinctive patterns of hydrogen-bonding inter­actions, i.e. 2 × N—H⋯N versus N—H⋯N and N—H⋯S. The resulting supra­molecular architecture is a supra­molecular chain along the c axis based on a square-wave topology.

The title compound, [Au(C9H10NOS)(C18H33P)], represents a monoclinic polymorph to complement a previously reported triclinic (P ) polymorph [Hall et al. (1993 ▶). Aust. J. Chem. 46, 561–570 (unit-cell data only)]. The AuI atom is coordinated within an S,P-donor set that defines a slightly distorted linear geometry [S—Au—P = = 175.43 (3)°], with the distortion due in part to a close intra­molecular Au⋯O contact [3.036 (2) Å]. In the crystal structure, mol­ecules are arranged into supra­molecular chains along the b axis mediated by C—H⋯π inter­actions.

The crystallization and preliminary X-ray diffraction analysis of sarcosine dimethylglycine methyltransferase from H. halochoris is reported.

Sarcosine dimethylglycine methyltransferase (EC 2.1.1.157) is an enzyme from the extremely halophilic anaerobic bacterium Halorhodospira halochoris. This enzyme catalyzes the twofold methylation of sarcosine to betaine, with S-­adenosylmethionine (AdoMet) as the methyl-group donor. This study presents the crystallization and preliminary X-ray analysis of recombinant sarcosine dimethylglycine methyltransferase produced in Escherichia coli. Mass spectroscopy was used to determine the purity and homogeneity of the enzyme material. Two different crystal forms, which initially appeared to be hexagonal and tetragonal, were obtained. However, on analyzing the diffraction data it was discovered that both crystal forms were pseudo-merohedrally twinned. The true crystal systems were monoclinic and orthorhombic. The monoclinic crystal diffracted to a maximum of 2.15 Å resolution and the orthorhombic crystal diffracted to 1.8 Å resolution.

The title complex, [Cu(C14H14N2O2)2]BF4, is a monomeric copper(I) species with linear two-coordinate geometry around the CuI atom. The asymmetric unit contains two half-cations that sit on crystallographic twofold rotation axes. The selected crystal was non-merohedrally twinned by a twofold rotation about an axis normal to the (100) family of planes. The ratio of the twin components refined to 0.4123 (6). Two 2-hydr­oxy-N-[2-(2-pyrid­yl)eth­yl]benzamide ligands coordinate to each CuI atom via the pyridyl N atom. Intra­molecular hydrogen bonding between the phenol OH groups and the amide O atoms imparts rigidity and planarity to the non-coordinating end of the ligand. The cationic complex is linked to the BF4 − anions via hydrogen bonding between the amide NH groups in the cations and BF4 − anions.

In the planar (r.m.s. deviation = 0.027 Å) title compound, [Hg(C7H5O2)Cl], the HgII atom shows a typical linear coordination by a C atom of the benzene ring and a Cl atom. Inter­molecular O—H⋯O hydrogen bonds are present in the crystal structure, resulting in chains propagating along the b axis. The crystal studied was a non-merohedral twin, with a twin ratio of 0.802 (2):0.198 (2).

In the title monomeric rare earth complex, [LiNd(C19H40N3Si2)2Cl2(C4H8O)2], the [(Me3Si)2NC(NCy)2]2Nd+ (Me is methyl, Cy is cyclo­hex­yl) and Li(THF)2 + units (THF is tetra­hydro­furan) are connected by two bridging Cl atoms. The Nd3+ ion is coordinated by two guanidinate ligands and two Cl atoms, forming a distorted chelating octa­hedral geometry. The Li+ ion is four-coordinated by two Cl atoms and two O atoms from THF mol­ecules in a distorted tetra­hedral geometry.

The title compound, [SnCl2(C5H4NS)2], is the product of reaction of 2,2′-dipyridyl disulfide with tin tetra­chloride. The SnIV atom adopts a distorted octa­hedral geometry, with the two bidentate pyridine-2-thiol­ate ligands forming two planar four-membered chelate rings. The two Sn—Cl, two Sn—N and two Sn—S bonds are in cis, cis and trans configurations, respectively. The crystal grown from acetonitrile represents a new monoclinic polymorph in space group C2/c with the mol­ecule having twofold rotational symmetry, the SnIV atom lying on the twofold axis. The mol­ecular structure of the monoclinic polymorph is very close to that of the triclinic polymorph studied previously in space group P-1, the mol­ecule occupying a general position [Masaki & Matsunami (1976 ▶). Bull. Chem. Soc. Jpn, 49, 3274–3279; Masaki et al. (1978 ▶). Bull. Chem. Soc. Jpn, 51, 3298–3301]. Apparently, the formation of the two polymorphs is determined by the different systems of inter­molecular inter­actions. In the crystal of the monoclinic polymorph, mol­ecules are bound into ribbons along the c axis by C—H⋯Cl hydrogen bonds, whereas in the crystal of the triclinic polymorph, mol­ecules form chains along the a axis by attractive S⋯S inter­actions. The crystal studied was a pseudo-merohedral twin; the refined BASF value is 0.221 (1).

The title compound, [Au2Cl2(C26H26N2P2)], is formed from a bidentate phosphine ligand complexed to two linearly coordinated gold(I) atoms. The gold(I) atoms are 3.4873 (7) Å apart. The mol­ecule exhibits a crystallographic twofold rotation axis.

The title complex, [AuCl{(C6H5)2P(OH)-κP}] or [AuCl(C12H11OP)], contains two independent mol­ecules in the asymmetric unit and is a polymorph of a previously reported structure [Hollatz et al. (1999 ▶) J. Chem. Soc. Dalton Trans. pp. 111–114]. The crystal structure exhibits inter­molecular Au⋯Au inter­actions with alternate distances of 3.0112 (3) Å and 3.0375 (2) Å. The Cl—Au—P bond angle varies between different mol­ecular units, depending on the degree of influence of the intra­molecular the O—H⋯Cl hydrogen bond; the angle thus varies between negligible distortion from linearity at 179.23 (3)° and more significant distortion at 170.39 (4)°, which differs from the previously reported polymorph in which both these angles are approximately 170°. The Au—Cl [2.3366 (9) and 2.3131 (10)Å] and Au—P [2.2304 (10) and 2.2254 (10) Å] bond lengths vary slightly between the two independent mol­ecules but overall, the bond lengths are in good agreement with those in the previously reported polymorph.

The title compound, C19H26N2O3, crystallizes with two independent mol­ecules in the asymmetric unit which differ in the twist of the phenyl rings with respect to the plane of the amide group [the C—C—C—O torsion angles are 121.5 (3) and −119.6 (3)° in the two mol­ecules. Both cyclo­hexane rings adopt chair conformations. In the crystal, weak C—H⋯O inter­actions occur. The crystal studied was a non-merohedral twin with a minor component of 4.8 (1)%.

The title compound, [Au2Cl2(C28H30N2P2)]·2C4H8O, was synthesized from a bidentate phosphine ligand complexed to two linear gold(I) chloride moieties. The Au(I) atom is in an almost linear coordination with a P—Au—Cl angle of 179.22 (4)°. The complex molecules reside on a twofold rotation axis.

In the title gold complex, [AuCl(C18H12F3P)], the P—Au—Cl unit is nearly linear, with an angle of 178.13 (5)°. The three phosphine-substituted benzene rings make dihedral angles of 77.7 (3), 84.4 (3) and 77.4 (3)° with each other. Two of the three F atoms are disordered over two positions, with refined site occupancies of 0.591 (11):0.409 (11) and 0.730 (12):0.270 (12). In the crystal structure, mol­ecules are linked into a three-dimensional network by inter­molecular C—H⋯Cl and C—H⋯F hydrogen bonds.

In the title structure, [CoRu(C5H5)(C17H26P)2Cl]PF6, the RuII atom is bonded to a cyclo­penta­dienyl ring, a Cl atom and two P atoms of the chelating 1,1′-bis­(dicyclo­hexyl­phosphino)cobaltocenium (di-cypc) ligand, leading to a three-legged piano-stool coordination. Part of the PF6 − counter-anion is disordered over two positions, with a site-occupancy ratio of 0.898 (7):0.102 (7). The components are linked by C—H⋯F and C—H⋯Cl hydrogen bonds.

The title compound, [(2S,5R,6S,9R)-6-isopropyl-9-methyl-1,4-dioxaspiro­[4.5]dec-2-yl]methyl 3,5-dinitro­benzoate, C20H26N2O8, was synthesized as part of a study of three-carbon stereochemical systems. The crystallographic assignment of the absolute stereochemistry is consistent with having started with (−)-menthone, the acetal carbon is R and the secondary alcohol is S. This brings the dinitro­benzoate into approximately the same plane as the menthyl ring and anti to the isopropyl group. Close inter­molecular C=O⋯NO2 contacts between neighboring mol­ecules [2.8341 (16) Å] contribute to the packing arrangement. The structure was refined as a pseudo-merohedral twin (monoclinic space group P21 emulating the ortho­rhom­bic space group C2221). Application of the twin law 100, 00, 0 gave a 2:1 ratio of twin moieties [refined BASF value = 0.3790 (7)].

The title compound, [Cu2Cl4(C14H14N2)2], is a new polymorph of a previously reported compound [Dehghanpour et al. (2011 ▶). Acta Cryst. E67, m1296]. The current polymorph was obtained from an acetonitrile solution of the title compound. Like the first polymorph, it is monoclinic (space group P21/c). The unique CuII ion in the title centrosymmetric dinuclear complex is in a distorted trigonal–bipyramidal coordination environment formed by the bis-­chelating N-heterocyclic ligand, two bridging Cl ligands and one terminal Cl ligand. In the crystal, weak C—H⋯Cl hydrogen bonds are observed in addition to π–π stacking inter­actions, with a centroid–centroid distance of 3.6597 (18) Å.

The title compound, [PtCl(C42H78OP4)]Cl·0.5CH2Cl2·4H2O, crystallizes as a contact ion-pair with two close inter­molecular C—H⋯Cl− contacts between CH acidic αH atoms of the phosphane ligand and the chloride anion. A chloride ligand together with three coordinating P ligand atoms create a slightly distorted square-planar coordination environment around the PtII center. An inter­molecular water O—H⋯Cl− and water O—H⋯OP hydrogen-bond network completes the coordination around the anion. In addition, a disordered CH2Cl2 solvent mol­ecule cocrystallized within a hydro­phobic cavity spanned by the dicyclo­hexyl­phosphane ligands.

The title compound, C26H28O4, lies about a crystallographic twofold rotation axis. The cyclo­hexane rings adopt a chair conformation. The two benzene rings form a dihedral angle of 40.82 (3)°. No significant intra- or inter­molecular inter­actions are observed in the crystal structure.

A review of published tetartohedrally twinned macromolecular structures is presented, together with details of the recent structure determination of triclinic tetartohedrally twinned crystals of human complement factor I.

Tetartohedral crystal twinning is discussed as a particular case of (pseudo)merohedral twinning when the number of twinned domains is four. Tetartohedrally twinned crystals often possess pseudosymmetry, with the rotational part of the pseudo­symmetry operators coinciding with the twinning operators. Tetartohedrally twinned structures from the literature are reviewed and the recent structure determination of tetartohedrally twinned triclinic crystals of human complement factor I is discussed.

In the title compound, (C5H7N2)2[CoCl4], the cobalt(II) ion is coordinated by four chloride ions in a slightly distorted tetra­hedral geometry. The crystal packing is stabilized by inter­molecular N—H⋯Cl hydrogen bonding, forming a three-dimensional network. The crystal was a non-merohedral twin emulating tetra­gonal symmetry, but being in fact ortho­rhom­bic.

In the title compound, [CuCl(C14H19N2O2)], the CuII ion is four-coordinated by one deprotonated N,N′,O-tridentate Schiff base and one chloride ion in a distorted square-planar geometry. In the crystal, adjacent mol­ecules are linked via C—H⋯Cl and C—H⋯O inter­actions, forming infinite layers parallel to the (100) plane. The structure was determined from a non-merohedrally twined crystal [twin ratio 0.777 (3):0.223 (3)].