A. Meetsma

Polymorphism in pentacene

Pentacene, C(22)H(14), crystallizes in different morphologies characterized by their d(001)-spacings of 14.1, 14.5, 15.0 and 15.4 A. We have studied the crystal structure of the 14.1 and 14.5 A d-spacing morphologies grown by vapour transport and from solution. We find a close correspondence between the 14.1 A structure reported by Holmes, Kumaraswamy, Matzeger & Vollhardt [Chem. Eur. J. (1999), 5, 3399-3412] and the 14.5 A structure reported by Campbell, Monteath Robertson & Trotter [Acta Cryst. (1961), 14, 705-711]. Single crystals commonly adopt the 14.1 A d-spacing morphology with an inversion centre on both molecules in the unit cell. Thin films grown on SiO(2) substrates above 350 K preferentially adopt the 14.5 A d-spacing morphology, with a slightly smaller unit-cell volume.

Inversion symmetry in the spin-Peierls compound α'-NaV2O5

At room temperature, sodium pentaoxodivanadate, NaV2O5, was found to have the centrosymmetric space group Pmmm. This space group implies the presence of only one kind of V site, in contrast with previous reports of the non-centrosymmetric P21mn counterpart. This indicates a non-integer valence state of vanadium. Furthermore, this symmetry has consequences for the interpretation of the transition at 34 K, which was ascribed to a spin-Peierls transition of one-dimensional chains of V4+ ions.

Hexagonal LuMnO3 revisited

The crystal structure of hexagonal LuMnO3 at room temperature is isomorphous with YMnO3 and deviates in important details from the early work of Yakel et al. [Acta Cryst. (1963), 16, 957–962]. Mn is near the centre of its oxyxadgen coordination environment. On the threefold axes, the apical O—Lu bonds have alternating long and short bond lengths, leading to ferroelectric behaviour. The sample studied was composed of almost equal volumes of inversion twins.

Paramagnetic bis(amidinate) iron(II) complexes and their diamagnetic dicarbonyl derivatives

Reactions of two equivalents of the lithium amidinate salts Li[tBuC(NR)2] (R = iPr, cyclohexyl) with FeCl2 have been found to yield paramagnetic bis(amidinate) iron(II) compounds of the type [tBuC(NR)2]2Fe. In the case of R = cyclohexyl, the product has been characterized by single-crystal X-ray diffraction analysis as having a distorted tetrahedral geometry. The derivative with R = iPr is an oil, but its 1H and 13C NMR spectra indicate a similar monomeric structure. Both species have been found to react readily with CO to give the new diamagnetic FeII dicarbonyls [tBuC(NR)2]2Fe(CO)2. The compound with R = iPr has been structurally characterized, which showed it to have a strongly distorted octahedral structure with the carbonyls in a cis arrangement.

STRUCTURE OF 2H-TAS2

Tantalum disulfide, 2H-TaS2, Mr = 245.07, hexagonal, P63/mmc, a = 3.314 (1), c = 12-097 (1) A, V = 115.06 (5) A 3, Z = 2, Dx = 7.073 g cm-3, A(Mo K~) = 0.71073 A, /z = 485.3 cm-1, F(000) = 210, T= 295 K, RF = 0032 for 210 observed reflections with I> 2.5tr(/). The structure determination confirms the structure known from powder data. Ta is in trigonal-prismatic coordination by S and the Ta--S distances are 2.468 (2) A.

Structures of the misfit layer compounds (LaS)1.13TaS2, `LaTaS3' and (CeS)1.5TaS2, `CeTaS3'

(LaS)1.13TaS2 and the isostructural compound (CeS)1.15TaS2 are misfit layer compounds built of alternate double layers of MS (M = La, Ce), each approximately a {100} slice of NaCl-type MS, and sandwiches of TaS2 with Ta surrounded by distorted trigonal prisms of S. Both structural units are described in centered orthorhombic space groups, Cm2a for the MS part (Z = 4) and Fm2m for the TaS2 part (Z = 4) of the structure. lambda(Mo K-alphaBAR) = 0.71073 angstrom. For (LaS)1.13TaS2, M(r) = 438.3, D(x) = 6.63 g cm-3, mu = 367.3 cm-1; the LaS part: a = 5.813 (1), b = 5.773 (1), c = 11.526 (1) angstrom, V = 386.8 (1) angstrom 3, F(000) = 292, T = 295 K, R(F) = 0.038 for 255 unique reflections; the TaS2 part: a = 3.295 (1), b = 5.778 (1), c = 23.057 (1) angstrom, V = 439.0 (2) angstrom 3, F(000) = 420, T = 295 K, R(F) = 0.034 for 312 unique reflections; the layer stacking direction is c. For (CeS)1.15TaS2, M(r) = 443.1, D(x) = 6.78 g cm-3, mu = 328.8 cm-1; the CeS part: a = 5.737 (1), b = 5.749 (1), c = 11.444 (2) angstrom, V = 377.5 (1) angstrom 3, F(000) = 296, T = 295 K, R(F) = 0.062 for 427 unique reflections; the TaS2 part: a = 3.293 (1), b = 5.752 (1), c = 22.892 (2) angstrom, V = 433.6 (2) angstrom 3, F(000) = 420, T = 295 K, R(F) = 0.035 for 310 unique reflections. The composition is determined by the misfit along the a axes (the ratio a(MS)/a(TaS2)].

Structure determination of SnZrS3

The structure of tin zirconium trisulfide is of the NH4CdCl3 type with double columns of edge-sharing Zr octahedra. These columns are linked together by Sn atoms. Sn is coordinated to three S atoms at 2 x 2.619 (2) and 2.765 (2) angstrom; a fourth S atom is at 3.065 (2) angstrom. The zirconium coordination is approximately octahedral with six S atoms at 2.524 (2), 2 x 2.545 (2), 2.582 (2) and 2 x 2.592 (2) angstrom. Powder diffraction data were also collected; the JCPDS rue No. for tin zirconium sulfide is 44-1494.

Structure of tin hafnium sulfide and lead hafnium sulfide

SnHfS 3, M r = 393.36, orthorhombic, Pnma, a=9.139(1), b=3.694(1), c--13.875(4) A, V= 468.4 (2) ,/k 3, Z = 4, D x = 5.578 g cm 3, 2(Mo Kii) = 0.71073 ,~, g= 284.1 cm -~, F(000) 680, T= 298 K, R r=0.036 for 1301 observed reflections with I >_ 2.5tr(I). PbHfS 3, Mr = 481.88, orthorhombic, Pnma, a = 8.988 (2), b = 3-739 (I), c = 13.924 (2) ,~,, V=467.9(2)A 3, Z=4, Dx=6.840gcm ~, 2(MoK/i) =0.71073 A, g= 593-0cm ~, F(000)= 808, T= 298 K, R F = 0-036 for 1343 observed reflections with I>_2.5a(I). The compounds are isostructural with PbZrS 3 with modified NH4CdC13 structure. There are columns running along the b axis of double edgesharing octahedra (HfxS6)~; these columns are linked by Sn or Pb with coordinations typical for Sn 2+ and Pb 2+ with lone-pair s 2 electrons.

Domain structure and refinement of the triclinic superstructure of 1T-TaSe2 by single crystal X-ray diffraction

Abstract The 131/2a0 x 131/2a0 superstructure of 1T-TaSe2 at room temperature has been studied by singel-crystal X-ray diffraction. The basic structure has symmetry P3̅m1 with a0 = 3.4733 Å and c0 = 6.2715 Å. The superstructure has a pseudo hexagonal lattice, but it is triclinic with a 169-fold, 131/2a0 x 131/2a0 x 13c0 hexagonal supercell with 13 centering vectors. Structure refinements have been performed using space group P1̅ and the primitive unit cell with a basal plane 131/2a0 x 131/2a0 supercell, and with C = 2a0 + c0. Refinements converged to RF = 0.086 for 2327 observed reflections. Hexagram shaped clusters of 13 Ta atoms are the principle feature of this 13-fold superstructure, in accordance with the study of Brouwer and Jellinek (Physica B 99 (1980) 51). In the present refinement, significant deviations are found from local 6/m symmetry as it was assumed by Brouwer and Jellinek. The relative phase of the superstructure on neighbouring layers represents the most favourable packing of the buckled planes of Se atoms, and elastic coupling between Se atoms of consecutive layers is identified as the driving force for the observed inter-layer shift vector 2a0. The small deviations from trigonal symmetry of the clusters are responsible for the observation of an ordered superstructure, as it is opposed to a stacking of layers according a random selection of shift vectors (2a0, 2a0 + b0, and -a0 - 3b0) that are equivalent by the trigonal symmetry of the basic structure.

An Unexpected Trimethylstannylpyrrole from a Stannylated Derivative of Tosylmethyl Isocyanide (TosMIC) and Chalcone

The structure of the title compound, tert-butyl 3-benzoyl-4-phenyl-2-(trimethylstannyl)pyrrole-N-carboxylate, [Sn(CH3)3(C22H20NO3)], is one of the first in which the stannyl group is attached to a C atom of the pyrrole ring. There appears to be an intramolecular interaction between the Sn atom and the carbonyl O atoms of both the benzoyl and the tert-butoxycarbonyl substituents. The compound was prepared by a base-induced cycloaddition of a stannylated derivative of tosylmethyl isocyanide to chalcone.