Inversion Twin Research Articles

Tetra-kis(di-propyl-ammonium) tetra-kis(oxa-lato-κ(2) O (1),O (2))stannate(IV) mono-hydrate: a complex with an eight-coordinate Sn(IV) atom.

In the title salt, [(CH3CH2CH2)2NH2]4[Sn(C2O4)4]·H2O, the SnIV atom of the stannate anion is located on a special position with -42m symmetry. It is eight-coordinated by four chelating oxalate anions. The di­propyl­ammonium cation possesses mirror symmetry while the lattice water mol­ecule is disordered about a position with -42m symmetry and has an occupancy of 0.25. In the crystal, the anions and cations are linked by N—H⋯O hydrogen bonds, forming a three-dimensional network. This network is futher stabilized by weak O—H⋯O hydrogen bonds involving the water mol­ecules and oxalate O atoms. The crystal studied was refined as an inversion twin.

1,3,5-Tri-p-tolyl-pentane-1,5-diol.

In the title compound, C26H30O2, the central benzene ring forms dihedral angles of 14.85 (15) and 28.17 (14)° with the terminal benzene rings. The dihedral angle between the terminal benzene rings is 32.14 (13)°. The crystal packing exhibits two strong inter­molecular O—H⋯O hydrogen bonds, forming directed four-membered co-operative rings. A region of disordered electron density, most probably disordered ethyl acetate solvent mol­ecules, occupying voids of ca 519 Å3 for an electron count of 59, was treated using the SQUEEZE routine in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155]. Their formula mass and unit-cell characteristics were not taken into account during refinement. The structure was refined as an inversion twin [absolute structure parameter = −0.3 (4)].

Poly[tetrakis(μ-1,1,1,3,3,3-hexafluoropropan-2-olato)iron(II)dipotassium

The title compound, [K2Fe{OCH(CF3)2}4]n, was formed from the reaction of potassium hexa­fluoro­isopropoxide with iron(II) chloride in toluene. The FeII atom has a highly distorted tetra­hedral coordination environment. All four of the non-equivalent hexa­fluoro­isoprop­oxy O atoms link the FeII atoms to one of the K+ atoms in an alternating chain of Fe—O—K—O fused four-membered rings, with K—Fe distances of 3.715 (2) and 3.717 (2) Å. This K+ atom is also bridged to eight of the F atoms. The other K+ atom is bonded to only two of the O atoms, but has seven short K⋯F contacts, one of which links the chains into a three-dimensional arrangement. Weak hydrogen bonding between the lone H atoms on the hexa­fluoro­isoprop­oxy groups and F atoms is also present. The crystal studied was refined as an inversion twin.

Twinning and pseudosymmetry under high pressure

We review the available information on crystal twinning at high pressures and analyze the effect of hydro- static pressure on the pseudosymmetry of selected com- pounds. Twinning by merohedry, type I and II, as well as pseuomerohedral twinning at high pressures has been de- scribed. For twinning by merohedry type I (inversion twin- ning) a reliable characterization of the twin domains and volume fractions is difficult and largely depends on the ex- perimental conditions, i.e. the number of measured Friedel pairs and the chosen wavelength. For twinning by merohe- dry,typeII,andfor twinning bypseuodmerohedrytwinvol- ume fractions could be reliably determined for several cases. In noneof these a significant influence of hydrostatic pressure on the volume fractions of the individuals was ob- served. Pressure-induced twinning has been observed for compounds which undergo first-order phase transitions. The twinning operation in the described cases is related to the loss of rotational symmetry elements of the higher sym- metrical polymorph although the high and low pressure phases are not in group-subgroup relationship. The analy- sis of pseudosymmetry of several compounds as a function of pressure suggests that this parameter can be used to pre- dictthe(in)stabilityofcompounds. Inparticular, a decrease in pseudosymmetry seems to be strongly correlated with the occurrence of first-order phase transitions in which the crystal breaks or amorphizes. The effect of hydrostatic and chemical pressure on the pseudosymmetry of the crystal structurescanlead todifferentorevenoppositetrends,sug- gesting that the increase or decrease of pseudosymmetry cannotbe understoodasa pure volume effect.

A triclinic polymorph of (-)-(S)-N-benzyl-2-[(R)-6-fluoro-chroman-2-yl]-2-hy-droxy-ethanaminium bromide.

The title salt, C18H21FNO2 +·Br−, determined at 115 K, crystallizes in the triclinic space group P1. The previously reported polymorph occurs in the monoclinic space group P21 and has two independent mol­ecules in the asymmetric unit [Peeters et al. (1993 ▶). Acta Cryst. C49, 2157–2160]. In the title molecule, the pyran rings adopt half-chair conformations. The absolute configuration is S for the hy­droxy-bearing C atom and R for the asymmetric C atom in the di­hydro­pyran unit. In the crystal, the components are linked by N—H⋯Br and O—H⋯Br hydrogen bonds, forming chains along the c-axis direction. The crystal studied was refined as an inversion twin.

3-{[(E)-(2-Hydroxynaphthalen-1-yl)methylidene]amino}pyridinium perchlorate

In the title Schiff base salt, C16H13N2O+·ClO4 −, the pyridine ring and the naphthalene ring system are approximately co-planar [making a dihedral angle of 6.05 (12)°] and an intra­molecular O—H⋯N hydrogen bond occurs between the hydroxyl and imino groups. In the crystal, the cations and anions are linked by N—H⋯O and weak C—H⋯O hydrogen bonds, forming the supra­molecular layers parallel to (100). The crystal studied was an inversion twin refined with minor component = 0.43 (13).

2-Hydroxymethyl-1,3-dimethyl-1H-benzimidazol-3-ium iodide

In the cation of the title compound, C10H13N2O+·I−, all non-H atoms, with the exception of the O atom, are essentially coplanar, with a maximum deviation of 0.04 (1) Å. In the crystal, the cations and anions are arranged in layers parallel to (100). The cations are connected to the anions via an O—H⋯I hydrogen bond and there are significant π–π stacking inter­actions between cation layers, with centroid–centroid distances in the range 3.606 (5)–3.630 (5) Å. A weak intra­molecular C—H⋯O hydrogen bond is also observed. The crystal studied was an inversion twin with refined components of 0.52 (5) and 0.48 (5).

(Dimethylphosphoryl)methanaminium iodide–(dimethylphosphoryl)methanamine (1/1)

The asymmetric unit of the title structure, C3H11NOP+·I−·C3H10NOP, consists of one (di­methyl­phosphor­yl)methanamine (dpma) mol­ecule, one (di­methyl­phosphor­yl)methanaminium (dpmaH) ion and one iodide counter-anion. In the crystal, medium–strong to weak N—H⋯O and N—H⋯N hydrogen bonds connect dpmaH cations and dpma mol­ecules into strands along [001]. The iodide counter-anions form only very weak hydrogen bonds. The crystal used for the diffraction study was found to be an inversion twin with a ratio of 0.83 (2):0.17 (2). The title structure is isotypic to that of dpmaH[ClO4]·dpma [Buhl et al. (2013 ▶). Crystals 3, 350–362].

Use of intensity quotients and differences in absolute structure refinement

Several methods for absolute structure refinement were tested using single-crystal X-ray diffraction data collected using Cu Kα radiation for 23 crystals with no element heavier than oxygen: conventional refinement using an inversion twin model, estimation using intensity quotients in SHELXL2012, estimation using Bayesian methods in PLATON, estimation using restraints consisting of numerical intensity differences in CRYSTALS and estimation using differences and quotients in TOPAS-Academic where both quantities were coded in terms of other structural parameters and implemented as restraints. The conventional refinement approach yielded accurate values of the Flack parameter, but with standard uncertainties ranging from 0.15 to 0.77. The other methods also yielded accurate values of the Flack parameter, but with much higher precision. Absolute structure was established in all cases, even for a hydrocarbon. The procedures in which restraints are coded explicitly in terms of other structural parameters enable the Flack parameter to correlate with these other parameters, so that it is determined along with those parameters during refinement.

1-Allyl-2-aminopyridin-1-ium bromide

In the cation of the title salt, C8H11N2 +·Br−, the dihedral angle between the planes of the pyridinium ring and the allyl group is 79.4 (3)°. In the crystal, N—H⋯Br and weak C—H⋯Br hydrogen bonds link the cations and anions, forming chains of alternating R 2 1(7) and R 4 2(8) rings, which run parallel to the c-axis direction. The crystal studied was an inversion twin with components in a 0.753 (12):0.247 (12) ratio.

Tetraphenylphosphonium iodide–1,3,5-trifluoro-2,4,6-triiodobenzene–methanol (3/4/1)

The crystallization of a 1:1 molar solution of 1,3,5-tri­fluoro-2,4,6-di­iodo­benzene (TFTIB) and tetra­phenyl­phosponium iodide (TPPI) from methanol produced tetra­gonal needles of pure TPPI and tabular pseudo-hexa­gonal truncated bipyramids of the title compound, 3C24H20P+·3I−·4C6F3I3·CH4O or (TPPI)3(TFTIB)4·MeOH. The asymmetric unit is composed of six TPPI mol­ecules, eight TFTIB mol­ecules and two methanol mol­ecules, overall 16 constituents. The formation of the architecture is essentially guided by a number of C—I⋯I− halogen bonds (XB), whose lengths are in the range 3.276 (1)–3.625 (1) Å. Layers of supra­molecular polyanions are formed parallel to (10-1) wherein iodide anions function as penta-, tetra- or bidentate XB acceptors. The structure is not far from being P21/n, but the centrosymmetry is lost due to a different conformation of a single couple of cations and the small asymmetry in the formed supra­molecular anion. One methanol mol­ecule is hydrogen bonded to an iodide anion, while the second is linked to the first one via an O—H⋯O contact. This second methanol mol­ecule is more loosely pinned in its position than the first and presents very high anisotropic displacement parameters and a seeming shortening of the C—O bond length. The crystal studied was refined as a perfect inversion twin.

(2E)-1-(4-Chloro-phen-yl)-3-(4-nitro-phen-yl)prop-2-en-1-one.

In the title compound, C15H10ClNO3, a substituted chalcone, the dihedral angle between the benzene rings is 5.1 (7)°. The nitro group makes a dihedral angle of 12.5 (3)° with the benzene ring to which it is attached. In the crystal, weak C—H⋯O inter­actions link the mol­ecules into a one-dimensional array along [010]. The crystal studied was an inversion twin, with a refined ratio for the twin components of 0.6060 (9):0.3939 (1).

5-(Adamantan-1-yl)-3-[(4-fluoroanilino)methyl]-2,3-dihydro-1,3,4-oxadiazole-2-thione

In the title compound, C19H22FN3OS, the dihedral angle between the inclined oxa­diazole and benzene rings is 52.7 (3)°. In the crystal, helical supra­molecular chains along [100] are sustained by N—H⋯S hydrogen bonds supported by methyl­ene–benzene C—H⋯π inter­actions. The crystal studied was an inversion twin with the fractional contribution of the minor component being 0.33 (14).

3-(Adamantan-1-yl)-4-methyl-1-({4-[3-(trifluoromethyl)phenyl]piperazin-1-yl}methyl)-4,5-dihydro-1H-1,2,4-triazole-5-thione

In the title compound, C25H32F3N5S, two independent mol­ecules comprise the asymmetric unit and are related across a pseudo-centre of inversion. The piperazine rings have chair conformations with each N-bound substituent occupying an equatorial position so that the dihedral angles between the planes of the triazole and benzene ring are 78.20 (19) and 79.10 (19)° for the two independent mol­ecules, indicating that the mol­ecules have an L-shape. In the crystal, a three-dimensional architecture is stabilized by C—H⋯π inter­actions. The crystal studied was an inversion twin with the fractional contribution of the minor component being 0.27 (9).

2-(4-Methylphenyl)-3-oxo-4-phenyl-2,3,3a,4,9,9a-hexahydro-1H-benzo[f]isoindole-6-carbonitrile

In the title compound, C26H22N2O, one phenyl ring, one five-membered N-heterocyclic ring and one six-membered carbocyclic ring make up the hexa­hydro­benzo[f]iso­indole core. Another phenyl group is attached to the heterocyclic N atom as a substituent. The non-aromatic five- and six-membered rings both exhibit boat conformations. In the crystal, weak C—H⋯O and C—H⋯N inter­actions establish the observed three-dimensional structure. The crystal studied was refined as an inversion twin.

2-(4-Oxo-3-phenyl-1,3-thiazolidin-2-ylidene)malononitrile

In the title compound, C12H7N3OS, the essentially planar thia­zole ring (r.m.s. deviation = 0.022 Å) forms dihedral angles of 84.88 (9) and 1.8 (3)° with the phenyl ring and the –C(CN)2 group (r.m.s. deviation = 0.003 Å), respectively. The mol­ecule has approximate local C s symmetry. In the crystal, molecules are linked via C—H⋯N hydrogen bonds, forming chains propagating along [101]. The crystal studied was found to be an inversion twin with a refined 0.63 (1):0.37 (1) domain ratio.

8-Hydroxy-5,7-dimethylquinolin-1-ium hydrogen sulfate

The quinoline ring system of the title salt, C11H12NO+·HSO4 −, is essentially planar, with a maximum deviation of 0.054 (2) Å for all non H atoms. In the crystal, the cations and anions are linked via N—H⋯O, O—H⋯O and weak C—H⋯O hydrogen bonds, and are stacked respectively in columns along the a axis. π–π stacking inter­actions, with centroid–centroid distances of 3.5473 (12) and 3.6926 (12) Å, are also observed. The crystal studied was an inversion twin with refined components of 0.43 (7):0.57 (7).

Cis-Bis(2,2′-bipyridine-κ2N,N′)carbonylchloridoruthenium(II) hexafluoridophosphate

In the title compound, [RuCl(C10H8N2)2(CO)]PF6, the RuII atom is coordinated in a distorted octa­hedral geometry by four N atoms of the bipyridine ligands, a carbonyl C atom and a chloride ion. The carbonyl and chloride ligands in the cation adopt a mutually cis arrangement and these are disordered over two sets of sites with site occupancies of 0.721 (6) and 0.279 (6). The Ru—N bond length [2.117 (2) Å] trans to the carbonyl ligand is slightly longer than the average of the other Ru—N bond lengths (2.08 Å), which can be explained by the expected trans influence of the carbonyl group. In the crystal, weak C—H⋯F inter­actions are observed between the complex cation and the PF6 − anion, leading to the formation of a three-dimensional supramolecular structure. The crystal studied was an inversion twin with twin fractions of 0.78 (4) and 0.22 (4).

Crystal structure and formula revision of deliensite, Fe[(UO2)2(SO4)2(OH)2](H2O)7

AbstractThe crystal structure of deliensite, Fe[(UO2)2(SO4)2(OH)2](H2O)7, was solved by direct methods and refined toR1= 6.24% for 5211 unique observed reflections [Iobs> 3σ(I)], on a crystal that was found to consist of rotational and inversion (merohedral) twins, from Jeroným mine, Abertamy in the Czech Republic. The presence of four twin domains was taken into account in the refinement. The structure is orthorhombic, space groupPnn2, with unit-cell parametersa= 15.8514(9),b= 16.2478(7),c= 6.8943(3) Å,V= 1775.6(1) Å3andZ= 4. The crystal structure of deliensite contains uranyl-sulfate sheets with a phosphuranylite topology, consisting of dimers of edge-sharing uranyl pentagonal bipyramids linked by corner-sharing with sulfate tetrahedra. The sheets lie in the (100) plane and are decorated by [Fe2+O(H2O)5] octahedra; two weakly bonded H2O molecules are present in the interlayer. The [Fe2+O(H2O)5] octahedron is linked directly to the sheet via the uranyl oxygen atom. Adjacent sheets are linked by hydrogen bonds only. The sheet topology and geometrical isomerism is discussed and a comparison of the composition obtained from electron-probe microanalysis, powder-diffraction data, Raman and infrared spectra of deliensite samples from Mas d'Alary, Lodève, France; L'Ecarpière mine, Gétigné, France; and several localities at Jáchymov, Western Bohemia, Czech Republic is made.

A second polymorph of 2,4,6-tris(3,5-dimethyl-1H-pyrazol-1-yl)-1,3,5-triazine

The mol­ecule of the title compound, C18H21N9, is nearly planar, with the three pyrazole rings aligned at 2.40 (5), 9.27 (5) and 9.71 (5)° with respect to the triazine ring. The triazine ring is planar (r.m.s. deviation = 0.005 Å), the distortion from a hexa­gonal arrangement arising from the angles at the N [112.4 (1)–113.1 (1)°] and C [127.1 (1)–127.6 (1)°] atoms deviating from 120°. The crystal studied was an inversion twin.