bluuebunny/crossref_metadata_2025 huggingface dataset:
Applications of the Cambridge Structural Database in organic chemistry and crystal chemistry
Authors: Allen Frank H. , Motherwell W. D. Samuel
Published: July 2002

The Cambridge Structural Database (CSD) and its associated software systems have formed the basis for more than 800 research applications in structural chemistry, crystallography and the life sciences. Relevant references, dating from the mid-1970s, and brief synopses of these papers are collected in a database, DBUse, which is freely available via the CCDC website. This database has been used to review research applications of the CSD in organic chemistry, including supramolecular applications, and in organic crystal chemistry. The review concentrates on applications that have been published since 1990 and covers a wide range of topics, including structure correlation, conformational analysis, hydrogen bonding and other intermolecular interactions, studies of crystal packing, extended structural motifs, crystal engineering and polymorphism, and crystal structure prediction. Applications of CSD information in studies of crystal structure precision, the determination of crystal structures from powder diffraction data, together with applications in chemical informatics, are also discussed.
Two fluoradene derivatives: pseudosymmetry, eccentric ellipsoids and a phase transition. Erratum
Authors: Xia Aibing , Selegue John P. , Carrillo Alberto , Patrick Brian O. , Parkin Sean , Brock Carolyn Pratt
Published: July 2002

Numerous printing errors in the paper by Xia et al. [Acta Cryst. (2001), B57, 507–516] are corrected.
Relationship of three-dimensional structure of muscarinic antagonists to antimuscarinic activity: structure of thiodeacylaprophen hydrochloride
Authors: Karle J. M. , Karle I. L. , Gordon R. K. , Chiang P. K.
Published: July 2002

C20H28NS+.Cl−, 2-(diethylamino)ethyl 1,1-diphenylethyl sulfide hydrochloride (thiodeacylaprophen hydrochloride), Mr
= 349.9, orthorhombic, P212121, a = 8.933 (2), b = 11.710 (3), c = 18.934 (4) Å, V= 1980.6 (7) Å3, Z = 4, Dx
= 1.173 g cm−3, Cu Kα = 1.54178 Å, μ = 26.70 cm−1, F(000) = 752, room temperature, final R = 4.1% for 1417 reflections with \mid F_o \mid > 3 \sigma (F). Thiodeacylaprophen crystallized as a tertiary amine hydrochloride salt. The S—C—C—N+ segment adopts a trans configuration as does one of the Cphenyl—C—S—C segments. A comparison of the structure of thiodeacylaprophen with the crystal structures of potent antimuscarinic agents suggests that the relatively weak antimuscarinic activity of thiodeacylaprophen compared to atropine and aprophen may be substantially due to the short intramolecular S\cdotsN+ distance of 4.106 (6) Å. Other contributing structural factors may include the direction of the N+—H bond and restricted accessibility of the sulfur atom for interatomic interactions.
The compositional dependence of octahedral tilting in orthorhombic and tetragonal perovskites
Authors: Thomas N. W.
Published: July 2002

A new parameterization is defined for the quantitative description of octahedral tilting in orthorhombic and tetragonal perovskites. It contains six parameters, s
1, s
2, s
3, θx
, θy
and θz
. s
1, s
2 and s
3 refer to the lengths of the lines or `stalks' joining pairs of opposite octahedral vertices, and θx
, θy
and θz
to the angles subtended by these stalks with pseudo-cubic axes x, y and z. An equation is derived for the dependence of polyhedral volume ratio, Va
/ VB
, on these parameters: Va
/ VB
= 6cos2
θm
cos θz
− 1, where θm
= (θx
+ θy
)/2. To a good approximation, lengths s
1, s
2 and s
3 do not affect Va
/ VB
. The validity of this equation is tested by reference to the known crystal structures of 48 ternary oxide and fluoride perovskites, and its versatility demonstrated by application to the structures of some ternary palladium and platinum hydrides. The relationship of the approach to Glazer's system of nomenclature for octahedral tilting in perovskites is considered, in particular concerning the numbers of tilts operative in a given structure. A comparison is also made with the parameterization proposed for octahedral tilting and distortion in rhombohedral perovskites [Thomas & Beitollahi (1994). Acta Cryst. B50, 549–560]. Factors governing the choice of rhombohedrai or orthorhombic symmetry are discussed, with the significance of rhombohedral symmetry in obtaining ferroelectric properties brought out. Through the compilation of a table of AO12 and BO6 polyhedral volumes, the prospect is identified of predicting both the degree of octahedral tilting and the likelihood of ferroelectric behaviour for novel, hypothetical oxide compositions.
Crystal and molecular structures of 3-acetyl-5-[2-(3-ethyl-2-benzothiazolidene)]ethylidenerhodanine and its lithium and sodium salts. Layered organic–inorganic structures
Authors: Nüesch F. , Grätzel M. , Nesper R. , Shklover V.
Published: July 2002

An X-ray diffraction study of the crystals of 5-[2-(3-ethyl-2-benzothiazolidene)]ethylidenerhodanine N-acetic acid (1, solvate with dimethylsulfoxide), lithium 5-[2-(3-ethyl-2-benzothiazolidene)]ethylidenerhodanine N-acetate (2, solvate with water and dimethylformamide) and sodium 5-[2-(3-ethyl-2-benzothiazolidene]ethylidenerhodanine N-acetate (3, octahydrate) have been carried out at 295 K. Crystal data for (1): C16H14N2O3S3.C2H6OS, Mr
= 456.6, triclinic, a = 7.664 (6), b = 9.874 (8), c = 14.851 (8) Å, α = 101.71 (5), β = 90.45 (5), γ = 102.27 (5)°, V = 1074 (1) Å3, space group P{\bar 1}, Z = 2, F(000) = 476, Dx
= 1.412 g cm−3, μ(MoKα) = 0.469 mm−1, R = 0.0698 for 1688 reflections with F > 6σ(F); for (2): Li+.C16H13N2O3S−
3.2H2O.1.5C3H7NO, Mr
= 530.1, triclinic, a = 7.249 (5), b = 10.773 (6), c = 16.433 (13) Å, α = 87.66 (6), β = 85.22 (6), γ = 77.04 (6)°, V = 1246 (1) Å3, space group P1, Z = 2, F(000) = 556, Dx
= 1.413 g cm−3, μ(Mo Kα) = 0.342 mm−1, R = 0.0551 for 2360 reflections with F > 6σ(F); for (3): Na+.C16H13N2O3S−
3.8H2O, Mr
= 544.6, monoclinic, a = 46.209 (12), b = 7.005 (3), c = 16.583 (8) Å, β = 109.45 (4)°, V = 5061 (6) Å3, space group C2/c, Z = 8, F(000) = 2288, Dx
= 1.429 Mg m−3, μ(Mo Kα) = 0.365 mm−1, R = 0.0440 for 2680 reflections with F > 6σ(F). Crystals (1) and (2) are built up of stacks of head-to-tail oriented molecules and anions, respectively, which have alternating interplanar separations of 3.41 (1) and 3.46 (1) Å for (1), and 3.38 (1) and 3.45 (1) Å, for (2) (so-called H aggregation of dye). The Li+ cations and solvent molecules form the cationic layers in crystal (2), alternating with the anionic layers along the c direction. The shifted head-to-head oriented anions in crystal (3) form uniform stacks along the b axis at the interplanar separation of 3.39 (1) Å (so called J aggregation of dye). The stacks are arranged in bilayers with the O atoms on the outer surfaces of the bilayers. The inorganic layers situated between the anionic organic bilayers consist of extended chains of distorted edge-shared polyhedra of Na+ cations and water molecules. The O atoms on the outer surfaces of the bilayers do not participate in the direct ionic interactions with the Na+ cations. The structure and stability of layered organic inorganic structures with internal surfaces are discussed by means of the crystal structures of (1)–(3) and literature data.
Molecular and crystal structure of azadirachtin-H
Authors: Govindachari T. R. , Geetha Gopalakrishnan  , Rajan S. S. , Kabaleeswaran V. , Lessinger L.
Published: July 2002

Azadirachtin-H, isolated from the seed kernels of Azadirachta indica (neem), crystallizes in space group I4, Z = 8, with disordered ethyl acetate solvent filling channels along the fourfold rotation axes. The crystal structure determination showed that the previously reported molecular structure deduced from NMR studies was correct except for the stereochemistry at C(11). Azadirachtin-H, which belongs to a group of C-seco-tetranortriterpenoids (C-seco-limonoids) of great interest for their insect antifeedant and ecdysis-inhibiting activity, has some unusual features: the absence of a carbomethoxy group at C(11); the presence of a cyclic hemiacetal function at C(11); the α-orientation of the hydroxyl group on C(11), opposite to that in all other known azadirachtins with a hydroxyl group on C(11), except azadirachtin-I. There is no intramolecular hydrogen bonding. In this crystal the rotation of the two major moieties of the azadirachtin-H molecule about the single connecting C(8)—C(14) bond is quite different from that in azadirachtin-A, whose crystal structure has recently been determined.
The crystal packing modes of three sterically overcrowded imidazole derivatives
Authors: André C. , Luger P. , Lotz S. , Fehlhammer W.-P.
Published: July 2002

The crystal packing of racemic 4-cyclohexylamino-5-hydroxy-1,5-diphenyl-Δ3-imidazolin-2-one resembles the bilayered packing arrangements with alternating hydrophilic and hydrophobic layers observed in the crystal structures of lipids. The hydrophobic layers of the imidazolinone are built up individually by phenyl and cyclohexyl groups. In contrast, the corresponding 4-tert-butylamino derivative crystallizes optically resolved in a non-bilayer layer structure. This crystal packing is similar to the host-lattice of the inclusion compound formed by 9-(4-tert-butylphenyl)fluoren-9-ol and dioxane [Csöregh, Weber, Nassimbeni, Gallardo, Dörpinghaus, Ertan & Bourne (1993). J. Chem. Soc. Perkin Trans. 2, pp. 1775–1781]. The major building units of 4-tert-butylamino-1,5-diphenylimidazole are centrosymmetrical dimers in which the molecules display a `yin-and-yang'-like self-complementarity. The dimers pack in columns, which form a distorted hexagonal pattern.
Structure of Ce2Pt6Ga15: interplanar disorder from the Ce2Ga3 layers
Authors: Kwei G. H. , Lawson A. C. , Larson A. C. , Morosin B. , Larson E. M. , Canfield P. C.
Published: July 2002

The structure of the heavy fermion compound Ce2Pt6Ga15 has been determined from neutron powder and X-ray/neutron single-crystal diffraction. Examination of symmetry equivalence among the single-crystal data, as well as the good fit of the powder data to the final structural arrangement, with all the atoms on symmetry sites, suggests that the correct space group is P63/mmc. The structure is unusual in that Ce layers have 1/3 of the Ce atoms replaced by groups of three Ga atoms; distances between atoms in these planes suggest this substitution must occur in a concerted fashion. The refined occupancies lead to a stoichiometry near Ce2Pt6Ga15, consistent with such an arrangement. In addition, single-crystal neutron diffraction data show columns of weak diffuse scattering along the <001> axes, suggesting disorder arising from a lack of registration of successive Ce2Ga3 layers (lying half a cell length or 8.27 Å apart along z) and a 3 × 3 × 1 supercell. This disorder is very likely responsible for the low resistance ratio of approximately unity measured for single-crystal samples.
Sodalite, Na4Si3Al3O12Cl: structure and ionic mobility at high temperatures by neutron diffraction
Authors: McMullan R. K. , Ghose S. , Haga N. , Schomaker V.
Published: July 2002

Crystal data: Na4Si3Al3O12Cl, cubic, space group P43n, Z = 2, F(000) = 233.06 fm, μ

n
= 0.06 cm−1, lattice parameter ao
 (Å) [T] (K) at eight temperatures: 8.882 (1) [295]; 8.902 (2) [500]; 8.912 (1) [600]; 8.923 (1) [700] 8.951 (2) [800]; 8.971(1) [900]; 8.988 (1) [1000]; 9.037 (1) [1200]. The crystal structure has been determined at six temperatures (295 ≤ T ≤ 1200 K) based on neutron diffraction data with (sin θ/λ) < 0.80 Å−1. Besides conventional parameters, the least-squares refinement model included thermal tensor parameters up to fourth-order for sodium and chlorine (295 ≤ T ≤ 1200 K) and up to third-order for oxygen (T ≥ 700 K), together with the 1:1 coupled site occupancy factors of sodium and chlorine (T = 1200 K). The indices-of-fit, wR(F
2), are in the range 0.015–0.028 with observation-to-parameter ratios from 7.0 to 8.6. Bond lengths and angles in the aluminosilicate framework have average e.s.d.'s less than 0.002 Å and 0.08°. Between 295 and 1200 K, the observed Si—O (Al—O) bond lengths differ by −0.015 Å (−0.012 Å); corrections for librating rigid SiO4 (AlO4) groups change the difference to +0.004 Å (+0.006 Å), compared with the 295 K value of 1.620 Å (1.741 Å). The unique Si—O—Al angle increases from 138.24° (295 K) to 146.87° (1200 K), while the Si and Al valence angles are virtually unchanged. Between 295 and 1200 K the [Na4Cl] clusters expand with increases in the Na—Cl bond lengths of 0.200 Å, with simultaneous increases in Na—O bond lengths of 0.145 Å and decreases in the shortest Na...O contact distances of 0.126 Å. The thermal expansion of sodalite is attributed to the increasing amplitudes of coupled translational motion of the Na+ ions and the librational motion of the [Al/ SiO4] tetrahedra, leading to the untwisting of the aluminosilicate framework. Maps of the probability density functions for Na+ and Cl− indicate ionic diffusion paths along (111) directions. There is a finite probability of finding the Na+ ion within the plane of the next-nearest O atoms, suggesting that Na+ jumps from an occupied to an unoccupied site in the next-nearest cage through the six-membered ring of [Al/SiO4] tetrahedra.
Symmetry-modified conformational mapping and classification of the medium rings from crystallographic data. IV. Cyclooctane and related eight-membered rings
Authors: Allen F. H. , Howard J. A. K. , Pitchford N. A.
Published: July 2002

Crystallographic observations of eight-membered ring conformations, retrieved from the Cambridge Structural Database, have been mapped and classified using symmetry-adapted deformation coordinates, principal component analysis and cluster analysis. Seven subsets of eight-membered rings, containing 11–32 conformational observations, have been analysed: cyclooctane (dataset 8C1), cyclooctene (8C2), cycloocta-1,3-diene (8C3), mono-exo-unsaturated carbocycles (8C4), monohetero (8A1), 1,5-dihetero (8A2) and 1,3,5,7-tetrahetero rings (8A3). The energetically preferred (by ~7 kJ mol−1) boat-chair form is adopted by 26 of the 32 examples of 8C1, although varying degrees of twist are induced by fusion to rings of sizes three, four and five. Crystallographic results for other subsets also populate the lower-energy areas of the appropriate potential energy hypersurface, but the analyses are complicated by the effects of ring fusion and by the small numbers of relevant crystal structures in some cases.
Single-Crystal Neutron Diffraction Analysis of Anion–Cation Interactions in Perdeuteroacetylcholine Bromide at 100 K
Authors: Shankland N. , Florence A. J. , Wilson C. C.
Published: July 2002

The interaction of the neurotransmitter acetylcholine with receptor binding sites has been well studied over the years, but much is still unknown about how intermolecular forces govern the lock-and-key fit. Here we present an analysis of cation–anion hydrogen-bond interactions in a single-crystal of perdeuteroacetylcholine bromide, using pulsed neutron diffraction data to refine the X-ray crystal structure. The molecule crystallizes in space group P21/n, with a = 10.951 (4), b = 13.396 (8), c = 7.072(4) Å, β = 108.88(3)°, Z = 4. The final refinement included anisotropic temperature factors on all atoms and converged to wR(F) = 0.055 (244 parameters). The pyramidal configuration of C--D...Br− contacts observed in the crystal is in good agreement with ab initio molecular orbital predictions of favoured configuration and is consistent with a modest polarization of C--D bonds close to the N atom. There is evidence that close contact with Br− is hindered by the repulsive influence of the ester O atoms, dependent on the conformation of the acetylcholine cation. This is the most detailed picture to date of close interatomic contacts around the cation and analogies are drawn with the bonding of acetylcholine to its receptors.
Structures and Photochemistry of Inclusion Compounds of 9,10-Dihydro-9,10-ethenoanthracene-11,12-bis(diphenylmethanol)
Authors: Fu T. Y. , Scheffer J. R. , Trotter J.
Published: July 2002

Crystal structures have been determined for inclusion complexes of the host molecule 9,10-dihydro-9,10-ethenoanthracene-11,12-bis(diphenylmethanol), with acetone, ethanol and toluene as guest solvent molecules. The host molecule exhibits an intramolecular O--H...O hydrogen bond in each of the complexes, with intermolecular hydrogen bonds to the acetone and ethanol guests. Different photoproducts are obtained from solution and solid-state photolyses; the solid-state reaction involves a relatively small amount of molecular rearrangement, for which a mechanism is proposed.
Crystal Engineering Using Bisphenols and Trisphenols. Complexes with Hexamethylenetetramine (HMTA): Strings, Multiple Helices and Chains-of-Rings in the Crystal Structures of the Adducts of HTMA with 4,4'-Thiodiphenol (1/1), 4,4'-Sulfonyldiphenol (1/1), 4,4'-Isopropylidenediphenol (1/1), 1,1,1-Tris(4-hydroxyphenyl)ethane (1/2) and 1,3,5-Trihydroxybenzene (2/3)
Authors: Coupar P. I. , Glidewell C. , Ferguson G.
Published: July 2002

The 4,4′-bisphenols (1), X(C6H4OH)2 [a, X = nil; b, X = O; c, X = S; d, X = 502; e, X = CO; f, X = CH2; g, X = CMe2; h, X = C(CF3)2], when co-crystallized from alcoholic solutions with hexamethylenetetramine, (CH2)6N4 (HMTA), form 1:1 adducts (4a)–(h). 4,4′-Thiodiphenol–hexamethylenetetramine (1/1), (4c), C12H10O2S.C6H12N4, and 4,4′- sulfonyldiphenol–hexamethylenetetramine (1/1), (4d), C12H10O4S.C6H12N4, are orthorhombic, Pmn21, (4c) a = 15.029 (2), b = 9.7954 (8), c = 5.9817 (11) Å and (4d) a = 14.779 (2), b = 10.2558 (15), c = 5.9817 (8) Å, with Z = 2, and the structures consist of zigzag chains comprising strings of alternating bisphenol and HMTA units, each lying across mirror planes and linked by O—H...N hydrogen bonds. In addition, both (4c) and (4d) exhibit C—H...\pi(arene) hydrogen bonds with one CH2 group of the HMTA unit acting as a donor to two different arene rings; (4d) also exhibits multiple C—H...O=S hydrogen bonds with three C—H bonds in each HMTA unit acting as donors towards a single sulfone O atom. 4,4′-Isopropylidenediphenol–hexamethylenetetramine (1/1), (4g), C15H16O2.C6H12N4, is monoclinic, C2/c, a = 25.093 (6), b = 7.1742 (13), c = 23.612 (7) Å, \beta = 110.42 (2)°, with Z = 8, and again the structure is built from chains of alternating bisphenol and HMTA units linked by O—H...N hydrogen bonds, but these now form double helices around twofold rotation axes; the double helices are themselves linked into sheets by C—H...O hydrogen bonds. The trisphenol (2), CH3C(C6H4OH)3, forms three adducts (5a)–(c) with HMTA, having trisphenol:HMTA ratios of 1:2 (5a), 2:3 (5b) and 1:1 (5c). 1,1,1-Tris(4-hydroxyphenyl)ethane–hexamethylenetetramine (1/2), (5a), C20H18O3.(C6H12N4)2, is orthorhombic, P212121, a = 6.9928 (10), b = 14.0949 (15), c = 30.999 (4) Å, with Z = 4, and the trisphenol units and half the HMTA units form a triple helix around a 21 axis, in which each strand consists of alternating phenol and HMTA units, linked as usual by O—H...N hydrogen bonds. The remaining HMTA units, which are external to the triple helix, are connected to it by O—H...N hydrogen bonds and are formed into externally buttressing stacks. The triol (3), 1,3,5-C6H3(OH)3, forms a 2:3 adduct (6) with HMTA. 1,3,5-Trihydroxybenzene–hexamethylenetetramine (2/3), (6), C6H6O3.(C6H12N4)1.5, is monoclinic, C2/c, a = 23.598 (2), b = 7.136 (2), c = 19.445 (3) Å, \beta = 96.822 (11)°, with Z = 8, and the dominant structural motif consists of centrosymmetric rings containing two molecules each of (3) and HMTA, connected by O—H...N hydrogen bonds; these rings are themselves linked into a chain-of-rings by further HMTA units lying on twofold rotation axes. The hydrogen-bonding patterns are codified using the graph-set approach.
Structural Model of the Orthorhombic Non-Fibonacci Approximant in the Al12Fe2Cr Alloy
Authors: Sui H. X. , Liao X. Z. , Kuo K. H. , Zou X. , Hovmöller S.
Published: July 2002

Al5.103(Fe, Cr), orthorhombic, Imm2, a = 12.34, b = 12.41, c = 30.71 Å, V = 4701 Å3, atoms/cell = 305 (average), D

x
\simeq 3.4 g cm−3. A structural model of the non-Fibonacci approximant O-AIFeCr with composition Al5.103(Fe, Cr) found in an Al12Fe2Cr alloy has been derived from its high-resolution electron microscopy images and the structure of the hexagonal \mu-Al4Mn [Shoemaker, Keszler & Shoemaker (1989). Acta Cryst. B45, 13–20], being isostructural to \mu-Al4Cr. Among the 14 unique positions of transition metal (TM) atoms, 13 are icosahedrally coordinated: five of these icosahedra interpenetrate into each other, forming icosahedral chains along [010], and the remaining eight icosahedra with their twofold axis parallel to this axis. This structural model describes a (010) layer structure with a sequence P^{m}FP(P^{m}FP)_I, where a flat layer F (a mirror plane) is sandwiched between two puckered P and P

m
layers, and (P^{m}FP)I is related to P^{m}FP through a body-centred translation. The interatomic distances are 2.51–2.74 Å for TM—TM, 2.38–2.99 for TM—Al and 2.41–3.18 Å, for Al—Al. Simulated images and electron diffraction patterns calculated based on this structural model are comparable with the experimentally observed results.
Structure of Mn8Sn5
Authors: Elding-Pontén M. , Stenberg L. , Lidin S. , Madariaga G. , Pérez-Mato J.-M.
Published: July 2002

The title compound crystallizes as a slightly incommensurate modulation of the B8-type structure. In a basic NiAs structure, ∼60% of the trigonal pyramidal interstices are filled with Mn atoms in an ordered manner. The highest corresponding commensurate space group is Pbnm (Pnma, No. 62) with the cell parameters a = 21.9114 (4), b: 7.6003 (5), c = 5.5247  (5) Å. The four-dimensional superspace group of the incommensurate structure is Cmcm(α00)0s0 (No. 63.8), with the conventional setting Amam(00γ)0s0. The cell parameters for this incommensurate cell are a = 382 (1), b = 7.600 (2), c = 5.525 (2) Å, q = [0.616 (5), 0, 0]. The structural refinements were carried out on a multiply twinned specimen. The R-factors were 0.037 for the incommensurate refinement and 0.046 for one commensurate approximation. The refinements unambiguously show that the modulation is caused by the step-like modulation of one Mn site, which is accompanied by small displacive modulations of the basic lattice. The incommensurate nature of the modulation is manifested in a slight splitting of fifth-order satellites, visible in electron diffraction.
Influence of Chemical and Spatial Constraints on the Structures of Inorganic Compounds
Authors: Brown I. D.
Published: July 2002

The restrictions imposed by both chemistry and three-dimensional space on the structures of inorganic crystals can be analysed using the bond-valence model and space-group theory. The bond-valence model is used to construct a bond graph (connectivity table) from which the multiplicities and possible site symmetries of each atom can be assigned. These are matched to Wyckoff positions of the three-dimensional space groups, selecting the matching space group with the highest possible symmetry. High-symmetry structures such as NaCl, perovskite and garnet are readily derived from the chemical formula and, with a little more effort, the same can be done for structures of intermediate symmetry such as wurtzite, corundum and rutile. For other compounds a relationship between the site symmetry and the multiplicity of an atom can severely restrict the possible structures.
Radial Distribution of Electron Density in Magnetite, Fe3O4
Authors: Sasaki S.
Published: July 2002

Radial electron distributions and net atomic charges of magnetite Fe3O4 have been studied using single-crystal X-ray intensity data up to sin \theta/\lambda = 1.22 Å−1. The number of electrons, C(R), was calculated against the radius of an atomic sphere for each atom by the Fourier summation method from the observed crystal structure factors. The radial distribution function was then obtained by differentiating the C(R) curve to derive an electron distribution radius, r
ED, which can give a clear separation between neighboring atoms. The effective atomic charges of Fe ions thus obtained are +1.93 (4) e (A site) and +1.47 (4) e (B site), with r
ED = 1.13 and 1.19 Å, respectively. Fe ions occupying the A site are more ionic than those at the B site. The charge difference between sites A and B is +0.46 e, which is comparable to an ideal difference of +0.5 e between Fe3+ and [Fe2+Fe3+]. It suggests the existence of valence fluctuation between Fe2+ and Fe3+ in the B site. Crystal data: Fe3O4, M

r
= 231.54, cubic, Fd3m, a = 8.375 (2) Å, V = 587.4 (4) Å3, Z = 8, D

x
= 5.23 Mg m−3, \lambda(Mo K\alpha) = 0.7107 A, \mu(Mo K\alpha) = 14.88 mm−1, F(000) = 880, T = 296 K, final R = 0.016 wR = 0.010 for 78 reflections averaged out of 6049 within a hemisphere, with F > 3\sigma(F); u = 0.2555 (2).
Structures of the Phosphazenes [ClC(NPCl3)2]+PCl6
− and [CH3C(NPCl3)2]+SbCl6
− at 90 K
Authors: Belaj F.
Published: July 2002

The asymmetric units of both ionic compounds [N-(chloroformimidoyl)phosphorimidic trichloridato]trichlorophosphorus hexachlorophosphate, [ClC(NPCl3)2]+PCl^{-}_{6} (1), and [N-(acetimidoyl)phosphorimidic trichloridato]trichlorophosphorus hexachloroantimonate, [CH3C(NPCl3)2]+SbCl^{-}_{6} (2), contain two formula units with the atoms located on general positions. All the cations show cis–trans conformations with respect to their X—C—N—P torsion angles [X = Cl for (1), C for (2)], but quite different conformations with respect to their C—N—P—Cl torsion angles. Therefore, the two NPCl3 groups of a cation are inequivalent, even though they are equivalent in solution. The very flexible C—N—P angles ranging from 120.6 (3) to 140.9 (3)° can be attributed to the intramolecular Cl...Cl and Cl...N contacts. A widening of the C—N—P angles correlates with a shortening of the P—N distances. The rigid-body motion analysis shows that the non-rigid intramolecular motions in the cations cannot be explained by allowance for intramolecular torsion of the three rigid subunits about specific bonds.
Structure and Serotonin 5-HT2C Receptor Activity of ortho- and meta-Substituted Phenylpiperazines
Authors: Verdonk M. L. , Voogd J. W. , Kanters J. A. , Kroon J. , den Besten R. , Brandsma L. , Leysen D. , Kelder J.
Published: July 2002

The structural characteristics of ortho- and meta-substituted phenylpiperazines have been investigated in order to understand their actions at the serotonin 5-HT2c receptor. The crystal structures of the 4-methylated analogues of two phenylpiperazines that are already known as 5-HT2c ligands, 1-(1-naphthyl)-4-methylpiperazine (1NMP) and 1-[(3-trifluoromethyl)phenyl]-4-methylpiperazine (TFMPMP), and those of two novel 5-HT2c ligands, 1-(2-methoxyphenyl)piperazine (oMPP) and 1-(3-methoxyphenyl)piperazine (mMPP), are determined. Molecular mechanics calculations are performed to calculate the energy profiles of six phenylpiperazines for rotation about the central phenyl–nitrogen bond. The activities of several phenylpiperazines, in combination with their crystal structures and conformational characteristics, lead to the hypothesis that the conformation for which the piperazine ring and the phenyl ring are approximately co-planar should be the 5-HT2c receptor `activating' conformation. This hypothesis is then used to predict the activities of the two novel 5-HT2c ligands oMPP and mMPP. oMPP is predicted to be an antagonist at this receptor, whereas mMPP is predicted to be an agonist. As this prediction was confirmed by in vitro and in vivo tests, the proposed conformation is very likely to be responsible for the activation of the 5-HT2c receptor.
Channel-Type Crystal Packing in the Very Rare Space Group P4212 with Z' = 3/4: Crystal Structure of the Complex γ-Cyclodextrin–Methanol–n-Hydrate
Authors: Steiner T. , Saenger W.
Published: July 2002

The crystal structure of the title compound is discussed with focus on its unusual crystal packing mode. The γ-cyclodextrin molecules stack in columns which have internal channels and additional large channels are formed between the columns. Both types of channels are so wide that more or less free diffusion of water and small guest molecules is possible, preventing characterization of the solvent and guest arrangements. Although the space group P4212 (no. 90) and the unit-cell content Z′ = 3\over 4 are extremely rare in general, this is the favorite crystal packing arrangement of γ-cyclodextrin inclusion complexes. This space group has not been observed as yet for other purely organic compounds.
X-ray Diffraction Study of the Crystal Structure of the Tl Ternary Chalcogenides Tl2x
In2(1−x)Se2, x = 0.2, 0.3,...0.9
Authors: Hatzisymeon K. G. , Kokkou S. C. , Anagnostopoulos A. N. , Rentzeperis P. I.
Published: July 2002

A series of thallium ternary chalcogenides with the composition Tl2x
In2(1−x)Se2, x = 0.2, 0.3,...0.9, have been studied by X-ray powder and, for some of them, single-crystal diffraction. They are tetragonal, space group I4/mcm, Z = 4, and isostructural with the binary semiconductor TlSe. Their crystal structures have been solved by direct methods and refined by the Rietveld method to a precision which is satisfactorily comparable to single-crystal results. As x is changed from x = 0.2 to x = 0.9 the unit-cell parameters and volume decrease or increase following Kurnakov's law, which is valid for solid solutions. Refined positional parameters of Se, In—Se and Tl—Se bond lengths vary with x also according to the same law. The distribution of In and Tl cations in 4(a) and 4(b) sites depends on the stoichiometry x and the crystals are composed of [In3+Se2]_{\infty}^- chains along the c axis in which InSe4 tetrahedra share edges; the chains are interconnected with Tl+(In+) ions.
Cristobalite-Related Phases in the NaAlO2–NaAlSiO4 System. I. Two Tetragonal and Two Orthorhombic Structures
Authors: Thompson J. G. , Withers R. L. , Melnitchenko A. , Palethorpe S. R.
Published: July 2002

The crystal structures of five new cristobalite-related sodium aluminosilicates with four different structure types from the system Na2−x
Al2−x
Si
x
O4, 0 ≤ x ≤ 1 [Na1.95Al1.95Si0.05O4, P41212, a = 5.2997 (6), c = 7.0758 (9) Å; Na1.75Al1.75Si0.25O4, Pbca, a = 10.4221 (11), b = 14.264 (3), c = 5.2110 (5) Å; Na1.65Al1.65Si0.35O4, P41212, a = 10.3872 (7), c = 7.1589 (8) Å; Na1.55Al1.55Si0.45O4, Pbca, a = 10.385 (1), b = 14.198 (3), c = 5.1925 (6) Å; Na1.15Al1.15Si0.85O4, Pb21
a, a = 10.214 (2), b = 14.226 (7), c = 10.308 (1) Å], have been refined by the Rietveld method from X-ray powder diffraction data. Plausible starting models were derived for the x = 0.05, 0.25 and 0.45 structures by analogy. Starting models for the x = 0.35 and 0.85 structures, with previously unreported structure types, were derived from a modulation wave approach based on distortion of the ideal C9 structure type and assuming regular SiO4 and AlO4 tetrahedra.
Structures and magnetic properties of dimeric copper(II) benzoylformates. Erratum
Authors: Harada A. , Tsuchimoto M. , Ohba S. , Iwasawa K. , Tokii T.
Published: July 2002

The diagram which appeared as Fig. 3 on p. 660 was incorrect [Harada, Tsuchimoto, Ohba, Iwasawa and Tokii (1997). Acta Cryst. B53, 654–661]. The correct figure is shown below.
Prediction of Early- and Late-Growth Morphologies of Ionic Crystals
Authors: Soltzberg L. J. , Carneiro O. , Joseph G. S. , Khan Z. , Meretsky T. D. , Ng M. M. , Ofek S. A.
Published: July 2002

Comparison of early- and late-growth crystal morphologies of several water-soluble ionic materials suggests that early rapid growth is accompanied by a specific type of morphological distortion. This distortion, involving a change in the relative growth rate of just one growth direction, is consistent with our previously proposed mechanism for the transition from normal, polyhedral crystal growth to dendritic growth. Interpretation of this morphological distortion was aided by morphology prediction methods based on computed attachment energies.
Four-component intergrowth structures of the metal-ion cage complexes fac-(1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane)M
II diperchlorate hydrate, [M(C22H48N6)](ClO4)2.xH2O, M = Ni, Zn
Authors: Haller Kenneth J. , Rae A. David , Bygott Alexia M. T. , Hockless David C. R. , Ralph Stephen F. , Geue Rodney J. , Sargeson Alan M.
Published: July 2002

The crystal structures of (1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane-κ6
N,N′,N′′,N′′′,N′′′′,N′′′′′)nickel(II) diperchlorate–x(water) (x = 0.530), [Ni(C22H48N6)](ClO4)2.0.530H2O, and (1,5,9,13,20-pentamethyl-3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosane-κ6
N,N′,N′′,N′′′,N′′′′,N′′′′′)zinc(II) diperchlorate–x(water) (x = 0.608), [Zn(C22H48N6)](ClO4)2.0.608H2O, are isomorphic and each is described as an intergrowth of four substructures, consistent with different modulations of an idealized parent structure of space group C2/c. Two substructures correspond to alternative orientations of a C1¯ structure for which x = 0 in the general formula [M(C22H48N6)](ClO4)2.xH2O, and two substructures correspond to alternative origins of a P21/n structure for which x = 1. Twinning also occurs. An analysis of the pseudosymmetry, a description of the refinement and a description of the refined structures are presented. The MN6 coordination geometry is essentially octahedral, in contrast to the trigonal-prismatic geometry observed for the CdII and HgII complexes of the same ligand.
Crystal structures of [18]aneN6H2K[Co(CN)6].4H2O, [16]aneN4H2K[Co(CN)6] and [12]aneN4H3[Co(CN)6].2H2O. Insight into the electrostatic and hydrogen-bonding interaction in self-assembling supercomplexes
Authors: Zhou Ping , Xue Feng , Au-Yeung Steve C. F. , Xu Xiao-ping
Published: July 2002

The crystal structures of [18]aneN6H2K[Co(CN)6].4H2O [potassium dihydrogen hexacyanocobaltate–1,4,7,10,13,16-hexaazacyclooctadecane–water (1/1/4)], [16]aneN4H2K[Co(CN)6] [potassium dihydrogen hexacyanocobaltate–1,5,9,13-tetraazacyclohexadecane (1/1)] and [12]aneN4H3[Co(CN)6].2H2O [trihydrogen hexacyanocobaltate–1,4,7,10-tetraazacyclododecane–water (1/1/2)] have been determined. For these supercomplexes, the [Co(CN)6]3− binding with protonated polyammonium macrocycles is dominant in the binding competition between K+ and [Co(CN)6]3−. It is suggested that the binding of [Co(CN)6]3− with protonated polyammonium macrocycles is independent of the cavity size of the macrocycle, whereas that of K+ is size-match selective. For [18]aneN6H2K[Co(CN)6].4H2O, the formation of a two-dimensional lamella may be derived from a chain-like arrangement of four-, five- and eight-membered rings in the network through the mutual balance between electrostatic and hydrogen-bonding interactions. [16]aneN4H2K[Co(CN)6] is a novel example demonstrating the anchoring of cobalticyanide through hydrogen-bonding interactions inside a zeolite-type cavity in the three-dimensional network formed by K+ and the macrocycles through Coulombic interactions. Also, a three-dimensional network was formed mainly through hydrogen-bonding interactions between [Co(CN)6]3−, protonated macrocycles and water molecules in [12]aneN4H3[Co(CN)6].2H2O.
Structural investigation of the negative-thermal-expansion material ZrW2O8
Authors: Evans John S. O. , David W. I. F. , Sleight A. W.
Published: July 2002

High-resolution powder diffraction data have been recorded on cubic ZrW2O8 [a = 9.18000 (3) Å at 2 K] at 260 temperatures from 2 to 520 K in 2 K steps. These data have confirmed that α-ZrW2O8 has a negative coefficient of thermal expansion, α = −9.07 × 10−6 K−1 (2–350 K). A `parametric' approach to Rietveld refinement is adopted and it is demonstrated that a full anisotropic refinement can be performed at each temperature, despite using a data collection time of only 5 min. Examination of the resulting structural parameters suggests that the origin of the contraction with increasing temperature can be traced straightforwardly to the rigid-body transverse librations of bridging O atoms. α-ZrW2O8 undergoes a phase transition from P213 to Pa3¯ at 448 K that is associated with the onset of considerable oxygen mobility. The phase transition can be described in terms of a simple cubic three-dimensional Ising model. Unusual kinetics are associated with this phase transition. Hysteresis in the cell parameter through the phase transition is the opposite of that normally observed.
The crystal structure of the B-site ordered complex perovskite Sr(Yb0.5Nb0.5)O3
Authors: Yang Jae Ho , Choo Woong Kil , Lee Jin Ho , Lee Chang Hee
Published: July 2002

The room-temperature crystal structure of the B-site ordered complex perovskite strontium ytterbium niobate, Sr(Yb0.5Nb0.5)O3 [monoclinic, Z = 2, P21/n (set 2), a = 5.79095 (8), b = 5.82210 (7), c = 8.20358 (12) Å, β = 90.126 (1)°, with final R
wp = 0.0595, R
Bragg = 0.0203 for the neutron profile and R
wp = 0.0832, R
Bragg = 0.0193 for the X-ray profile, respectively], was determined by X-ray powder diffraction, high-resolution neutron powder diffraction and transmission electron microscopy. This compound shows a slight triclinic distortion from the prototype doubled cubic perovskite cell as a result of an a
−
a
−
c
+-type oxygen octahedral tilting distortion. It is also shown that the site ordering of the different species of B-site cations, Yb3+ and Nb5+, inherently leads to a difference between the volumes of the YbO6 and NbO6 octahedra. This volume difference is shown to inevitably inhibit the rigid rotation of octahedra.
The single-crystal structure of the organic superconductor βCO-(BEDT-TTF)2I3 from a powder grain
Authors: Madsen Dennis , Burghammer Manfred , Fiedler Stefan , Müller Harald
Published: July 2002

Synchrotron radiation diffraction data have been collected at 200 K on a microscopic single crystal (dimensions 12 × 10 × 2 µm) of the title compound, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene, C10H8S8. The quality of the diffraction data allowed a full structure refinement and enabled the determination of structural details such as the conformations of the ethylene groups as well as the occupancy of the triiodide sites. The compound was found to be slightly iodine-deficient and better described as βCO-(BEDT-TTF)2I3−x
[x = 0.014 (3)]. One of the ethylene groups of the BEDT-TTF cation is disordered at this temperature and exists in two distinct conformations with occupancies which are identical within the standard uncertainty.
Long-range Coulomb forces and localized bonds
Authors: Preiser Christoph , Lösel Jens , Brown I. David , Kunz Martin , Skowron Aniceta
Published: July 2002

The ionic model is shown to be applicable to all compounds in which the atoms carry a net charge and their electron density is spherically symmetric regardless of the covalent character of the bonding. By examining the electric field generated by an array of point charges placed at the positions of the ions in over 40 inorganic compounds, we show that the Coulomb field naturally partitions itself into localized regions (bonds) which are characterized by the electric flux that links neighbouring ions of opposite charge. This flux is identified with the bond valence, and Gauss' law with the valence-sum rule, providing a secure theoretical foundation for the bond-valence model. The localization of the Coulomb field provides an unambiguous definition of coordination number and our calculations show that, in addition to the expected primary coordination sphere, there are a number of weak bonds between cations and the anions in the second coordination sphere. Long-range Coulomb interactions are transmitted through the crystal by the application of Gauss' law at each of the intermediate atoms. Bond fluxes have also been calculated for compounds containing ions with non-spherical electron densities (e.g. cations with stereoactive lone electron pairs). In these cases the point-charge model continues to describe the distant field, but multipoles must be added to the point charges to give the correct local field.
Dimorphism and inclusion compounds of N,N′-di(benzenesulfonyl)-p-phenylenediamine
Authors: Nagel Norbert , Bock Hans , Eller Peter
Published: July 2002

Crystal structures of a new polymorph of N,N′-(p-phenylene)bis(benzenesulfonamide) (C18H16N2O4S2) and of two inclusion compounds with acetone [(CH3)2CO] and dimethylsulfoxide [2(CH3)2SO], respectively, have been determined at 150 K. For a more reliable comparison, the structure of the already known polymorph of N,N′-di(benzenesulfonyl)-p-phenylenediamine has been redetermined under identical conditions. In addition, the phase transformation behavior has been examined by differential scanning calorimetry and the crystallization conditions of both polymorphs including their formation by weathering of the inclusion compounds were investigated.
Determination of the modulated structure of Sr14/11CoO3 through a (3 + 1)-dimensional space description and using non-harmonic ADPs
Authors: Gourdon O. , Petricek V. , Dusek M. , Bezdicka P. , Durovic S.  , Gyepesova D. , Evain M.
Published: July 2002

Sr14/11CoO3 (i.e. Sr14Co11O33, tetradecastrontium undecacobalt tritriacontaoxide), a new phase in the hexagonal perovskite Sr
x
CoO3 system, has been prepared and its structure solved from single-crystal X-ray data within the (3 + 1)-dimensional formalism. Sr14/11CoO3 crystallizes in the trigonal symmetry, R3¯m(00γ)0s superspace group with the following lattice parameters: as
= 9.508 (2), cs
= 2.5343 (7) Å, q = 0.63646 (11)c

*
and Vs
= 198.40 (13) Å3. With the commensurate versus incommensurate test not being conclusive, the structure was considered as commensurate (P32 three-dimensional space group), but refined within the (3 + 1)-dimensional formalism to a residual factor R = 0.0351 for 47 parameters and 1169 independent reflections. Crenel functions were used for the oxygen and cobalt description and a Gram–Charlier expansion up to the third order of the atomic displacement parameter was employed for one Co atom. The structure is similar to that of Sr6/5CoO3, but with a different sequence of the octahedra and trigonal prism polyhedra along the [CoO3] chains. An interesting feature evidenced by the non-harmonic expansion is the displacement of the prismatic Co atoms from the site center, towards the prism rectangular faces.
The use of CCD area detectors in charge-density research. Application to a mineral compound: the α-spodumene LiAl(SiO3)2
Authors: Kuntzinger Sandrine , Dahaoui Slimane , Ghermani Nour Eddine , Lecomte Claude , Howard Judith A. K.
Published: July 2002

X-ray diffraction data sets collected on both Nonius and Siemens (Bruker) goniometers equipped with charge-coupled device (CCD) area detectors have been tested for the electron-density determination of the aluminosilicate mineral compound α-spodumene LiAl(SiO3)2, aluminium lithium silicon oxide. Data collection strategies, reflection intensity peak integration methods and experimental error estimates are different for the two instruments. Therefore, the consistency and quality of the two types of CCD measurements have been carefully compared to each other and to high-resolution data collected on a conventional CAD-4 point-detector diffractometer. Multipole density model refinements were carried out against the CCD data and the statistical factors analysed in terms of experimental weighting schemes based on the standard uncertainties of the diffraction intensities derived by the Nonius and Siemens software programs. Consistent experimental electron-density features in the Si–O–Si and Si–O–Al bridges were found from both CCD data sets. The net atomic charges obtained from the kappa refinements against each CCD data set are also in good agreement and quite comparable with the results of the conventional CAD-4 experiment.
Longitudinal positional ordering of n-alkane molecules in urea inclusion compounds
Authors: Weber Thomas , Boysen Hans , Frey Friedrich
Published: July 2002

The profiles of diffuse layers, which are present in diffraction patterns of urea inclusion compounds, are interpreted quantitatively by a longitudinal positional paracrystalline order of the alkane guest molecules within the channels of the urea-host framework structure, in agreement with the expected behaviour of a one-dimensional system. With decreasing temperature there is a gradual transition into long-range order behaviour. This ordering process remains unaffected by structural changes related to lateral correlations within and between both host and guest substructures, including a structural phase transformation. The differing behaviour of a mixed system (pentadecane/hexadecane) with average period almost commensurate with the urea host lattice is explained by the superposition of main and satellite layers. The distribution of both molecules within each tunnel is random.
Short N+—H...Ph hydrogen bonds in ammonium tetraphenylborate characterized by neutron diffraction
Authors: Steiner Thomas , Mason Sax A.
Published: July 2002

The crystal structures of ammonium tetraphenylborate, NH4
+·BPh4
−, are determined by neutron diffraction at 20 and 293 K. At both temperatures, all four N—H vectors of the ammonium ion are time-average-oriented at the midpoints of the phenyl rings of neighboring anions. The N—H...Ph distances, H...M 2.067 and N...M 3.023 Å, are exceptionally short (M = aromatic midpoint). Even at 20 K the ammonium ion performs large amplitude motions which allow the N—H vectors to sample the entire face of the aromatic system.
Bulk modulus and high-pressure crystal structures of tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 determined by X-ray powder diffraction
Authors: Dinnebier Robert E. , Carlson Stefan , van Smaalen Sander
Published: July 2002

The pressure dependence of the crystal structure of cubic tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 (TC) (P < 16.0 GPa, T = 298 K) is reported using high-resolution angle-dispersive X-ray powder diffraction. The compound has crystal structures with the molecules in a cubic-close-packed (c.c.p.) arrangement. It shows three phase transitions in the measured pressure range. At ambient conditions, TC has space group Fm{\bar 3}m (Z = 4) with a = 12.8902 (2) Å, V = 2141.8 (1) Å3 (phase I). Between 0 and 0.13 GPa TC exhibits a first-order phase transition into a structure with space group Pa{\bar 3} (phase II). A second first-order phase transition occurs between 0.2 and 0.28 GPa into a structure with space group P213 (phase III). Under non-hydrostatic pressure conditions (P > 10  GPa) a transformation is observed into a c.c.p. structure that is different from the face-centred-cubic structure at ambient conditions. A non-linear compression behaviour is observed, which could be described by a Vinet relation in the range 0.28–4.8 GPa. The extrapolated bulk modulus of the high-pressure phase III was determined to be K
0 = 7.1 (8) GPa. The crystal structures in phase III are refined against X-ray powder data measured at several pressures between 0.49 and 4.8 GPa, and the molecules are found to be fully ordered. This is interpreted to result from steric interactions between neighbouring molecules, as shown by analysing the pressure dependence of intramolecular angles, torsion angles and intermolecular distances. Except for their cell dimensions, phases I, II and III are found to be isostructural to the corresponding phases at low temperatures.