Volume 163, Issue 1-2

In this paper the structural relationships of compounds M 3 O[TO 4 ] are discussed. The crystal structures consist of [TO 4 ] tetrahedra, medium to large cations M, and oxygen atoms O not bonded to the tetrahedra. The basic structural unit is a trigonal layer with plane group p 3 m 1, a ≈ 7 Å and a thickness of about 3 Å. Layers of this type are stacked in the same way as the two-dimensional closest layers in close-packed structures, leading to a theoretically infinite number of stacking periodicities n . Examples are: (Cd,Pb) 3 O[SiO 4 ], for which a structure with n = 2 is proposed, Cd 3 O[SiO 4 ] with n = 3 and Ca 3 O[SiO 4 ] with n = 9. They may be considered as anti-structures of compounds ABX 3 , in which the large ions A and X form a close packing (as in perovskite). For each of the above structure types deformed varieties are known, the space group relations of which are presented.

The crystal structure of C.I. Pigment Yellow 3, α -(1-hydroxyethylidene)-2-chloro-acetanilide- α -azo-(4′-chloro-2′-nitrobenzene) has been determined by single-crystal X-ray diffraction techniques. It crystallises in the orthorhombic system with cell parameters a = 13.240 ± 0.073 Å, b = 30.206 ± 0.118 Å, c = 8.333 ± 0.025 Å. The space group is Pbca and there are eight molecules per unit cell. The structure was solved using direct methods and least-squares refinement has been completed on three-dimensional data, 1191 reflections (Cu Kα radiation). The hydrogen atoms have been found and included, but only those associated with the methyl group have been refined. The final residual is 7.2%. The molecule exists as the hydrazone tautomer and intramolecular hydrogen bonds keept the molecule approximately planar. The molecules are packed in planar chains parallel to the c axis with the molecules linked by hydrogen bonds, alternatively they may be thought of as packed in columns parallel to the a axis with alternate molecules antiparallel but with the molecules linked by van der Waals forces.

Two solid-state reactions can occur from a compound known in literature as “salt X”. The first is a topotactic reaction which leads to a salt having similar a and b parameters but with c three times the c of salt X. The second produces ferrinatrite, that is quite different both for its chemistry and structure from the parent compound and its topotactic product. The structure of salt X is known. Recently it has been refined to understand some structural details and the causes which lead salt X to change sometimes into ferrinatrite, sometimes into another compound. No appreciable crystallochemical differences have been noticed between salt X crystals showing different solid-state transformations, even if the presence of a merohedric twin has been pointed out. The presence or absence of this twin, seems the main cause which allows to understand the strange behaviour of salt X.

Different space groups for anisotropic grossular-andradite garnets are derived as an average result when crystal fragments are used to obtain diffraction intensity data. Ordering of aluminium and iron in the solid solution is considered to be controlled by steps on {110} faces. Since these steps are asymmetric, the eight coordinating polyhedra of Al and Fe with different orientation are considered non-equivalent in the growth process. The symmetry of the crystal volume grown under one step is then I [unk], which is considered the true symmetry for anisotropic grandites. Starting from occupancy factors given in the literature for I [unk] grandites, it is shown that all centrosymmetric subgroups of Fddd can be obtained from fragments of a pyramid of growth based on {110} faces. In general, all centrosymmetric subgroups of Ia 3 d can be obtained from fragments of a crystal with morphology {110}.

The crystal structure and electron density of tetraphenyl-silicon, (C 6 H 5 ) 4 Si, ( a 0 = 11.450(2), c 0 = 7.063(1) Å, P [unk]2 1 c , Z = 2) has been studied by single crystal X-ray diffraction. Data were collected up to 2 θ max = 70° ( s max = 0.81 Å −1 ). The final agreement factors of the all-data refinement were R overall = 0.027 and R w = 0.033 (omitting unobserved intensities). The electron redistribution due to chemical bonding was studied by calculating (X – X HO ) difference density maps with the atomic parameters from a semi-high-order (HO) refinement with reflections of s > 0.48 Å −1 . The deformation density distribution associated with the Si – C bond compares qualitatively well with the Si – O bonds found in forsterite, Mg 2 SiO 4 , and quartz, SiO 2 .

A series expansion distribution function of the structure amplitude | F | has been used to calculate the generalised cumulative distribution function N n ( z ) for a hypercentric crystal with n centres of symmetry. Modified expressions for moments have been derived considering the effect of hypercentrosymmetry for three different space groups P [unk], P 2/ m and Pmmm , which also take into account the effect of atomic heterogeneity in the crystal. The resultant change from the corresponding Wilson-type distribution is illustrated with the help of a hypothetical example and the effects of expansion terms have been discussed.

The structure of natrolite from Zeilberg, Oberfranken, Germany, Na 2 Al 2 Si 3 O 10 · 2H 2 O, is orthorhombic with space group Fdd 2, a = 18.319(4), b = 18.595(4), c = 6.597(1) Å, Z = 8 and D x = 2.22g cm −3 , and was refined to R (unweighted) = 0.032 and R (weighted) = 0.025 using 1661 non-equivalent reflections. The structure contains [SiO 4 ]tetrahedra (mean Si – O distance 1.629 Å), [AlO 4 ]tetrahedra (mean Al – O distance 1.723 Å), and [NaO 6 ]-polyhedra (mean Na – O distance 2.444 Å), and shows a partial Si/Al disorder of about 30% in all the tetrahedral sites.

The crystal structures of the title compounds ( 3 ) and ( 4 ) have been determined. ( 3 ): P 2 1 / c , a = 13.765(2), b = 6.012(1), c = 18.780(3) Å, β = 102.34(2)°, Z = 4, R = 0.038 for 2145 unique observed reflections. The ground state extension to 1.468 Ă of the bond to the leaving group (with respect to acetal hydrolysis) occurs without assistance from the lone pair electrons of the ring oxygen, since the endocyclic acetal bond length is unaffected. ( 4 ): P 2 1 / n , a = 12.989(3), b = 6.512(2), c = 18.701(5) Å, β = 97.23(2)°, Z = 4, R = 0.056 for 1739 unique observed reflections. This ring-opened isomer of ( 3 ) shows no ground state features connected with the ready transannular cyclisation.

The crystal structure of the title compound ( 3 ) has been solved and refined to R 0.045 [ P [unk]; a = 7.068(2), b = 7.468(2), c = 10.461(3) Å, α = 101.19(2), β = 101.97(2), γ = 105.79(2)°, Z = 2]. The length of the C – O bond to the leaving group (with respect to acetal hydrolysis) is 1.449(2) Å; comparison with related acetals shows that this bond length gives an indication of the intrinsic reactivity.

The structure of the title compound ( 2 ) has been determined [ R [unk], a = 37.600(15), c = 5.140(3) Å (hexagonal axes), Z = 18, R = 0.060]. The exocyclic acetal bond length C(1) – O(1) is 1.476(7) Å, within one e.s.d. of the value predicted by our previously published bond length/reactivity correlation. The endocyclic acetal bond length is almost 0.1 Å shorter. The tetrahydropyran ring is appreciably flattened around the acetal carbon C(1), consistent with progress in the ground state towards the postulated acetal hydrolysis intermediate, the oxocarbonium ion ( 4 ). The presence of a disordered cyclohexane molecule is responsible for the moderate accuracy of the structure.

The crystal structure of the title compound ( 2 ) has been determined [ P 2 1 / c , a = 8.986(2), b = 15.993(2), c = 9.000(2) Å, β = 94.42(2)°, Z = 4, R = 0.054]. ( 2 ) adopts the unexpected equatorial conformation. The exocyclic acetal bond is significantly shorter than the endocyclic [1.392(4), cf. 1.419(4) Å]. This is consistent with a system in which the transmission of electronic effects is unidirectional.

The structure of the title compound ( 2 ) has been determined [ P [unk], a = 11.792(3), b = 12.448(3), c = 15.686(5) Å, α = 95.58(2), β = 109.08(2), γ = 116.59(2)°, Z = 4, R = 0.047]. There are two molecules in the asymmetric unit, differing mainly in the torsion angles at the phosphate groups (maximum difference ca. 5°). C(5) – O(9), the C – O bond antiperiplanar to the bond to the phosphate leaving group, is in both molecules appreciably longer than in related acetals with poorer leaving groups. This is part of a trend consistent with the orbital-orbital interaction known as σ -conjugation. The expected shortening of the endocyclic CO – C(OX) bond [here C(1) – O(9)] is however not clearly established.

The structure of the title compound ( 2 ) has been determined [ P 2 1 / c , a = 10.957(3), b = 9.401(2), c = 11.181(3) Å, β = 113.19(2)°, Z = 4, R = 0.047]. ( 2 ) has a better leaving group (methanesulphonate) than any acetal derivative we have studied so far, as is reflected in the very long bond to the leaving group [C(1) – O(2) 1.478(3) Å]. The central C – O bond C(1) – O(9) shows a significant shortening compared with related equatorial acetals. This is consistent with our suggestion (preceding paper) that the C – O bond length patterns in these compounds are an expression of σ -conjugation.

The structure of (S 4 N 4 ) 2 SnCl 4 has been determined from single-crystal X-ray diffraction data. The crystals are orthorhombic, space group Pca 2 1 , a = 1244.3(7), b = 1153.7(6), c = 1204.3(7) pm, Z = 4, U = 1.7288 nm 3 and D x = 2.42 Mg m −3 . The structure was solved by Patterson and Fourier methods, and refined to R = 0.063 for 901 unique data with F > 4 σ ( F ). The tin atom is coordinated octahedrally by four chlorine and two trans -nitrogen atoms; the S 4 N 4 rings adopt an open saddle conformation.

The structure of [C 6 H 5 CH = NH – N = CHC 6 H 5 ] + [AsF 6 ] − has been determined from single-crystal X-ray diffraction data. The crystals are orthorhombic, space group Pca 2 1 , a = 19.183(12), b = 9.704(6), c = 8.568(6) Å, Z = 4, U = 1595.0 Å 3 and D x = 1.658 g · cm −3 . The structure was solved by Patterson and Fourier methods, and refined to R = 0.051 for 1353 unique data with F > 4 σ ( F ). The cation is nearly planar and adopts the transoid conformation. The planes of the phenyl rings are inclined by 7.1° to one another.

We analyse in the framework of the Landau theory of second order phase transitions the continuous structural transformation arising in KFeF 4 at 368°K. We note that in this case, the thermodynamic potential expansion against the order parameter contains a Lifchitz invariant, so that an incommensurate phase can be expected in this compound. It would arise between the phases of D 2 h 17 and D 2 h 13 symmetry, with a modulation wave vector directed along the crystallographic b axis.

The crystal structure of C.I. Pigment Yellow 6, α -(1-hydroxyethylidene)acetanilide- α -azo-(4′-chloro-2′-nitrobenzene) has been determined by single crystal X-ray diffraction techniques. It crystallises in the monoclinic system with cell parameters a = 7.462 ± 0.001 Å, b = 19.568 ± 0.002 Å, c = 11.175 ± 0.001 Å, β = 105.96 ± 0.01°. The space group is P 2 1 / n and there are four molecules per unit cell. The structure was solved using direct methods and least-squares refinement has been completed on three-dimensional data, 2504 reflections (Cu Kα radiation). The hydrogen atoms have been found and included, but only those associated with the methyl group have been refined. The final residual is 5.3%. The molecule exists as the hydrazone tautomer and intramolecular hydrogen bonds keep the molecule approximately planar, although the distortion in it is greater than in C.I. Pigment Yellow 3. The molecules are packed in columns parallel to the a axis with alternate molecules antiparallel and the molecules linked by van der Waals forces.

The crystal structure of zinc fumarate tetrahydrate, ZnC 4 H 2 O 4 · 4 H 2 O, has been determined using three-dimensional single crystal X-ray data. The crystals are monoclinic, space group P 2 1 / c , Z = 4, with a = 7.58(2), b = 14.46(3), c = 7.66(2) Å, β = 101.2(1)°. The structure was solved by the heavy-atom method and refined by least-squares using 692 independent observed reflexions to a final R -value of 0.12. The zinc atom is surrounded by six oxygen atoms, at the corners of a distorted octahedron. Both the carboxyl groups in the molecule are twisted out of the plane containing the carbon atoms by angles of 49.4° and 15.8°.

The crystal structure of manganese(II) succinate tetrahydrate, Mn(C 4 H 4 O 4 ) · 4H 2 O, has been determined from single crystal X-ray diffraction data. The crystals are triclinic, space group P [unk] with a = 5.50(1), b = 9.05(2), c = 5.26(1) Å, α = 96.1(5), β = 98.9(5), γ = 120.5(5)°, Z = 1. The structure was solved by the heavy-atom method and refined to a final R -value of 0.11 for all the 501 observed reflexions. The Mn 2+ ion is coordinated with six oxygen atoms with distances ranging from 2.18 to 2.24 Å. Both the carboxyl groups in the succinate anion are twisted out of the plane of the four carbon atoms by 7.7°.