A. Chiesi Villa

Crystal, molecular, and electronic structure of catena-µ-oxalato-ammine-copper(II)

Crystals of formula Cu(NH3)(C2O4), obtained from very dilute ammonia solutions of copper(II) oxalate, are orthorhombic, space-group Pbca, with a= 11·19(1), b= 9·43(1), c= 8·38(1)A, Z= 8. The structure was refined by least-squares methods using 587 independent reflections, collected on a diffractometer, to a conventional R of 0·050. The structure is polymeric and co-ordination around copper is distorted square bipyramidal, with the ammonia molecule bonding in the more strict co-ordination plane. One oxygen of an oxalate group functions as a bridge between two atoms of copper, and this gives rise to strong antiferromagnetism, the magnetic moment at 302 K being 1·46 and at 94·5 K 0·53 BM. A superexchange mechanism operating through these oxygen atoms is invoked to explain this and a value for J of ca.–265 cm–1 is obtained. E.s.r. spectra of powders confirm this behaviour, and do not show the resonance at 3·1 cm characteristic of binuclear species such as copper(II) acetate. No bands other than those expected for the copper(II) chromophore itself could be found in the reflectance and single-crystal optical spectra. These latter could be interpreted in terms of ca. D4h symmetry, and it is found that the 2A1gâ†�2B1g transition lies at rather low energy, as expected from the relatively short axial copper(II)–oxygen bond lengths. Solution optical spectra indicate the possible existence of binuclear species.

Ni-Ni interaction in di-µ-ethylthiolatobis(ethyltrithiocarbonato)dinickel(II)

An X-ray three-dimensional analysis of di-µ-ethylthiolatobis(ethyltrithiocarbonato)dinickel(II) shows the compound to consist of dimers having a wedgeshaped conformation with square planar co-ordination of S around Ni and an intermetallic bond.

Crystal and molecular structures of the orthorhombic and monoclinic isomers of catena-di-μ-chloro-semicarbazidecopper(II)

The crystal structures of two isomeric complex compounds of formula [Cu(Cl)2(NH2NHCONH2)] have been determined by X-ray diffraction methods. The orthorhombic isomer has space groupPna21 and unit cell constants:a = 6·91(1),b = 8·30(1),c = 10·24(1) Å;Z = 4. The monoclinic isomer has space groupP21/c and unit cell constants:a = 6·91(1),b = 8·30(1),c = 11·32(1) Å, β = 117·1(2)°;Z = 4. In both complexes coordination around copper is octahedral, with chains of coordination polyhedra along [100]. In the monoclinic compound, the two semicarbazide molecules, which are present in two adjacent octahedra along the chain, have the oxygen and nitrogen atoms in thetrans configuration, one with respect to the other, and are correlated by a centre of symmetry. In the orthorhombic compound, the two semicarbazide molecules are in thecis configuration and there is no centre of symmetry. In both compounds packing is determined by the NH···Cl and NH···O hydrogen bonds which join the chains together.

The crystal and molecular structure of N′,N′-(2-chlorobenziliden)-histamine

SummaryThe crystal and molecular structure of the N′,N′-(2-chlorobenziliden)histamine has been determined and refined by Fourier and least-squares methods using three-dimensional X-ray data collected at room temperature by photographic techniques. Crystal data is as follows:a = 8·76(2),b = 13·82(1),c = 9·88(2) Å, β = 110·3(1) °,Z = 4. Space group:P21/c. The structure of the molecule is of the same tetrahydroimidazo[4,5-c]pyridine type found in spinaceamine. The benzene ring is rotated with respect to the other part of the molecule, which is formed by a non-planar tetrahydropyridine ring condensed with a planar imidazole ring. The bond distances and angles in these two rings are consistent with the observed distribution of the hydrogen atoms. Packing is mainly determined by a N-H ... N hydrogen bond, which joins the molecules in zig-zag chains running along [001].