Jl Deboer

MISFIT LAYER COMPOUNDS (MS)NTS2 (M = SN, PB, BI, RARE-EARTH ELEMENTS - T = NB, TA - N = 1.08 - 1.19), A NEW CLASS OF LAYER COMPOUNDS

Abstract A study by X-ray diffraction and electron microscopy is reported of the type of compounds that is usually designated as ternary sulphides “MTS 3 ” ( M = Sn, Pb, Bi, rare earth metals; T = Nb, Ta). They are misfit layer compounds built of alternating double layers of MS with M in distorted square pyramidal coordination by sulphur and sandwiches TS 2 with T is distorted trigonal-prismatic coordination by sulphur. One intralayer lattice constant of MS is incommensurate with that of TS 2 . Recent progress in the understanding of the crystallographic description is discussed and a unifying view based on about ten compounds is presented. Results of electrical transport measurements are briefly summarized.

STRUCTURE AND PHYSICAL-PROPERTIES OF (SNS)1.18NBS2,SNNBS3, A COMPOUND WITH MISFIT LAYER STRUCTURE

Abstract (SnS) 1.18 NbS 2 , “SnNbS 3 ”, is a compound with misfit layer structure consisting of two-atom thick layers of SnS with distorted NaCl type structure and three-atom thick sandwiches of NbS 2 as in 2H-NbS 2 , which alternate along the c axis. The lattices of SnS and NbS 2 both have C -centered orthorhombic unit cells which match along the b and c axes (respectively 5.751 A and 11.761 A) but not along the a axes, 5.673 A for SnS and 3.321 A for NbS 2 . The composition of the compound, (SnS) 1.18 NbS 2 , is determined by the mismatch along the a axes. The physical properties measured on single crystals (resistivity, Hall coefficient) and powder compacts (magnetic susceptibility and Seebeck coefficient) resemble strongly those of 2H-NbS 2 and intercalated 2H-NbS 2 : The Hall coefficient is positive, the thermoelectric power negative; the magnetic susceptibility is Pauli-paramagnetic.

CYCLOOCTATETRAENETITANIUM CHLORIDE AND ITS ADDUCTS WITH THF AND SOME AMINES

Abstract The syntheses and the results of mass spectrometry and infrared spectroscopy are reported of cyclooctatetraenetitanium chloride and its adducts with the donor molecules THF, diethylamine, pyrrolidine and pyridine. Single-crystal X-ray diffraction shows the chloride to be tetrameric, [C8H8TiCl]4, and the adduct with THF dimeric, [C8H8TiCl · THF]2.

CRYSTAL-GROWTH, STRUCTURE AND SOME PROPERTIES OF PBNBS3, SNSNBS3, LANBS3 AND RELATED MISFIT LAYER COMPOUNDS

Abstract Compounds with the assumed composition PbMS3, SnMS3 (M=Ti, V, Nb, Ta), known for about 20 years, were investigated by single crystal and powder X-ray diffraction. Since crystals were grown by vapour transport using Cl2, from (NH4)2PbCl6, as transport agent. The compounds may be classified as misfit layer compounds, built of alternately two-atom thick layers of SnS or PbS with distorted NaCl type structure and sandwiches MS2. This was proved by single crystal X-ray diffraction for “SnNbS3” which turned out to have the composition (SnS1.17NbS2; the NbS2 sandwiches have niobium atoms in trigonal prismatic coordination by sulfur like 2H-NbS2. Single crystals “LaNbS3” show a similar diffraction pattern which indicates a layered structure with units LaS and NbS2. The electrical transport properties of (PbS)1.14NbS2 resemble strongly those of 2H-NbS2. Crystals PbHfS3 and SnHfS3 obtained by vapour transport have the NH4CdCl3 structure.

Crystal structure and reactivity of C4Ph4TiCl3·Mg2Cl3(THF)6, a new type of organometallic complex

Reaction of TiCl3·3THF, diphenylacetylene and i-PrMgCl yields a blue complex of composition C4Ph4TiMg2Cl2·6THF. The complex is very sensitive to moisture. An X-ray diffraction study has shown that it consists of an ion pair (C4Ph4TiCl3)−, containing a planar cyclobutadiene ring, and (Mg2Cl3·6THF)+, in which the magnesium atoms are octahedrally surrounded by three bridging chlorine atoms and three disordered THF molecules.

Characterization, electrical transport and magnetic properties of the rare earth misfit layer compounds (TbS)(1.21)NbS2, (TbS)(1.20)TaS2, (DyS)(1.22)NbS2 and (DyS)(1.21)TaS2

Abstract X-ray powder and single-crystal X-ray diffraction of the title compounds showed that they are planar intergrowth compounds, built of alternating sandwiches TS2 (T ≡ Nb, Ta) and double layers LnS (Ln ≡ Tb, Dy), present in three orientational variants related by rotations of 120° around the c axis perpendicular to the layers. The TS2 and LnS subsystems are incommensurate along one of the in-plane axes. The LnS subsystem in each domain is face-centered orthorhombic. The stacking of the TS2 sandwiches shows disorder and the stacking type C or F could not be elucidated. The structures of the TbS subsystem and the common projection (TbS)1.21TaS2 were determined using single-crystal X-ray diffraction. The Tb-S distances are in agreement with trivalent Tb. The resistivity, Hall effect and thermopower measured for crystals and compacts point to conduction in an almost filled dz2 band of the NbS2 and TaS2 sandwiches corresponding to an electron donation of about 0.85 electron per T atom from LnS to TS2. Magnetic susceptibilities, measured in the range 4–300 K, are Curie-Weiss with effective magnetic moments close to those for free Ln3+ ions. The Curie temperatures are close to zero.

Thermoelectric power of N-dimethyl thiomorpholinium bis-tetracyanoquinodimethane, DMTM (TCNQ)2

Abstract The thermoelectric power of DMTM(TCNQ) 2 , where DMTM = N-dimethyl thiomorpholinium, was measured in the temperature range 77–400 K, a first order phase transition being observed at 272 K. These results together with conductivity data, are consistent with a splitting of the energy bands of the two chains in the unit cell by the crystal field, and a reduction of the energy gap.

Single crystal X-ray diffraction of the quasi crystal Al6CuLi3

Abstract Results of a single crystal X-ray diffraction study of the quasi crystal Al 6 CuLi 3 are presented. The positions of the reflections are accurately determined, and found to be in accordance with the icosahedral point group symmetry in very good approximation. The six reciprocal axes could uniquely be assigned, and a length of 0.4203 A -1 is determined. The intensities also show the icosahedral point symmetry, but a higher symmetry, for example a 6D hypercubic space group, could not be detected in the diffraction pattern.

CHANNELING IN QUASI-CRYSTALS

Ion-beam channeling has been observed in quasicrystals. For 1 MeV 4He+ ions in icosahedral AlCuFe the maximum effect found is 36%. The full width at half maximum of the observed dips is 1.3°. The effect persists up to great depths (> 200 nm), thus showing a high degree of ordering in this phase. The channeling effect is sensitive to radiation damage.

SUPPRESSION OF THE PEIERLS TRANSITION IN MEM(TCNQ)2 THROUGH DOPING WITH METM

Results of d.c-conductivity and X-ray measurements on a series of (METM)x (MEM)1-x (TCNQ)2, salts are presented. It is found that on adding METM the 4kF-phase transition temperature drops fast. A tentative interpretation is given in terms of the (thio-) morpholinium group.