L. Walz

Contributions to the chemistry of silicon-sulphur compounds—LX. Synthesis, molecular structure and properties of the dimeric cadmium(II) bis(tri-tert-butoxysilanethiolate) (t-C4H9O)3SiS2Cd2

Abstract The preparation and X-ray crystal structure of cadmium(II) bis(tri-tert-butoxysilanethiolate) from tri-tert-butoxysilanethiol and cadmium acetate are described. The compound forms a dimeric molecule (t-C4H9O)3SiS2Cd2 with a central four-membered Cd2S2 ring. According to the mass spectra the dimeric molecule is not preserved in the vapour phase. The compound is also characterized by 1H, 13C, 29Si NMR and UV spectra. Reactions with 1,10-phenanthroline and 2,2′-bipyridine afforded adducts with formal (RS)2,Cd(NN) stoichiometry. The central Cd2S2 kernel is folded with an angle of 150.6° at the CdCd diagonal. The cadmium atoms are three-fold bonded to thiolate sulphur atoms and the plane coordination is Cd(μ-SR)2(SR) with the mean distances of d(Cdμ-S) 256.0 pm and d(CdS) 240.8 pm. Additionally, there are weaker interactions with two oxygen atoms of two different tri-tert-butoxysilanethiolate ligands [d(CdO) 268 and 289 pm]. The comparison with the corresponding lead compound clearly shows the influence of the stereochemically active lone electron pair at lead(II).

Novel concepts in directed biaryl synthesis: XV. Chiral rhenium complexes [(η5-C5H5)Re(NO)(PPh3)(R,R-lactone)]+BF4− of lactone-bridged biaryls as ligands: s☆☆☆

Abstract The preparation is reported of the first series of (racemic) chiral rhenium complexes with “axially prostereogenic” biaryl lactone ligands, which a

Azobridges from azines, XVII1. Intra- and intermolecular [3+2] cycloaddition between nonstabilized azomethineimines and alkenes

Abstract Azo compounds 1 and 3 containing a CC-double bond in a parallel but distant position are quatemized by Me 3 OBF 4 to 1,MeBF 4 and 3,MeBF 4 , whereas MeI produces the cage compounds 2,HX and 4,HX . These [3+2] cycloadducts also are quantitatively formed from 1,MeBF 4 and 3,MeBF 4 with catalytic amounts of azo compounds. Intermolecular [3+2] cycloadditions occur with a mixture of DBH ( 5 ) or DBO ( 8 ), MeI and a variety of alkenes (→ HI) salts of ( 6, 7, 9 — 12 ). The intermediate azomethineimines, if stabilized by a fluorenylidene group, can be isolated ( 20, 22,24 ), but not, however, in the presence of a close parallel CC-bond ( 25 → 26 ).

Crystal structure of aluminium containing superconducting oxides: single crystal study of GdBa2Cu3−xAL x O6.88 (x=0.28) and ErBa2Cu3−yAl y O6.6 (y=0.14)

Following the discovery of the high temperature super-conductivity in YBa2Cu3O7−δ (Tc≃93 K) [1] it has been found that Y atoms can be substituted entirely by almost all of the rare-earth elements, except for Ce, Pr, and Tb, without changing the superconducting properties appreciably [2, 3]. The magnetic moments carried by the rare-earth atoms have apparently no influence on the superconducting properties. In Nd-, Sm-, Gd-, Dy- and Er-based compounds the rare earth moments order at low temperatures (0.025–2.2 K) [4–8] and the ordered antiferromagnetic state coexists with the superconducting state. We have investigated the antiferromagnetic ordering of these compounds by neutron diffraction both on powder and single crystal samples obtained from several laboratories [8–10]. Magnetic structures of all these compounds consist of antiferromagnetic (001) planes stacked ferro- or antiferromagnetically. There have been some controversies as to the stacking of antiferromagnetic (001) planes in GdBa2Cu3O7−δ.

[Al2P4]6-, [Al2As4]6-, [Ga2P4]6- und [Ga2As4]6-, Zintl-Anionen mit 1,3-Dimethylencyclobutan-Struktur / [Al2P4]6-, [Al2As4]6-, [Ga2P4]6- and [Ga2As4]6-, Zintl Anions with 1.3-Dimethylene-cyclobutane Structure

The compounds Cs6M2X4 (M = Al, Ga; X = P, As) were synthesized from stoichiometric mixtures of Cs, M and Cs4X6 in sealed Nb ampoules at 950 K. They are isotypic and crystallize in the monoclinic space group P21/c (No. 14) with Z = 4 formula units per unit cell. The anion partial structure is characterized by isolated [M2X4]6- units with relatively short distances for the terminal d(M–X) bonds corresponding to a Pauling Bond Order PBO = 1.5. The distances d(M–X) of the four-membered M2X2 rings correspond to single bonds. The FIR spectra have been interpreted on the basis of the [M2X4]6- units with 2/m 2/m 2/m-D2h, symmetry by considering a factor group splitting. The assignment of the observed frequencies is supported by a normal coordinate analysis.