D. Thiery

Neutral penta-coordinate derivatives of bis(O-dioxophenylene) silicon—crystal structure of Si(O2C6H4)2(OPPh3) and Si(O2C6H4)2{OP(NC5H10)3} · CH2Cl2

The reaction of Si(OMe) 4 with catechol (1,2-(HO) 2 C 6 H 4 ) in toluene at 70°C yields a colourless compound, which we believe to be Si(O 2 C 6 H 4 ) 2 (MeOH) 2 ( 1 ). Compound 1 reacts with excess OPR 3 (R Ph, NC 5 H 10 ) in CH 2 Cl 2 yielding the penta-coordinate complexes Si(O 2 C 6 H 4 ) 2 (OPPh 3 ) ( 2) and Si(O 2 C 6 H 4 ) 2 {OP(NC 5 H 10 ) 3 } · CH 2 Cl 2 ( 3 ). Crystal structure investigations of 2 and 3 reveal a distorted trigonal bipyramidal environment for the silicon atom in 2 , while 3 shows a nearly square pyramidal coordination. In the mass spectrum, 1 , 2 and 3 exhibit ion peaks for monomeric Si(O 2 C 6 H 4 ) 2 and the donor ligand at temperatures above the melting points.

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.

Crystal structure of caesium potassium di-μ-arsenido-bis(arsenidogallate), Cs5.23K0.77Ga2As4

Source of material: The compound may be prepared from Κ As, GaAs and Cs (1:1:3) in a sealed Nb-ampoule at 950 K. The excess of alkali metals (Cs and K) is removed by high vacuum distillation at 525 K. The anionic partial structure of the compound is characterized by the slightly bent dimeric anions [Ga2As4]~ (see réf. 1 and ref. 2) with the average bond lengths (Ga-As)eio = 2.336(3) Â and d(Ga-As)end0 = 2.462(3) Â (see ref. 3).