Some studies on chlorocuprates

Abstract

The work in this thesis is concerned with alkylammonium chlorocuprates and their solid solutions. The stoichiometries and structures of various chlorocuprate anions are considered in terms of the influence of the size and shape of the cation on the compounds formed. The determination of the structure of (Me3NH)3 Cu2 C17 by X-ray crystallography is described; it is unusual because it contains two distinct chlorocuprate anions, CUC14 2-tetrahedra and (CUC13-)n chains. The symmetry of the CuC142- tetrahedron is approximately C3v, and this is attributed to the effect of the packing of (CuC13-)n chains, together with interactions between CuC142- and the cations. The CuC12- 2- 2- 4 ion in this compound is replaceable by CoC14 and ZnC14 ' while the (CuC13-)n chains are not disturbed. This led to a consideration of the possible effects of replacing the Jahn-Teller distorted ion in simple tetrachlorocuprates by ions not affected by this distortion, and hence to the preparation of solid 'solutions A2 (M,M' )C14.

The formation of solid solutions from a system of two salts having a common ion and a solvent is discussed, with particular emphasis on systems which deviate from ideal behaviour. The preparations of solid solutions (Me4N)2(Cu,Co)C14, (Me4N)2(Cu,Zn)C14 and Me4N)2(Co,Zn)Cl4 from ethanol and water are described, and related to the general conditions for solid solution formation. Solid solutions (Me3NH)3Cu(Cu,Co)C17 are also given.

Differential scanning calorimetry has been used in an attempt to elucidate the nature of the thermal transitions in (Me4N)2MC14 and in the solid solutions. The crystal structures of (Me4N)2CuC14, and (Me4N)2(Cu,Co)C14 (Cu:Co = 1:1) have been determined, and compared with that of (Me4N)2CoC14' It has been . 2- 2- shown that CuC14 and CoC14 each retain their characteristic configuration in the solid solution, so that CuC142- is the more distorted, because of the Jahn-Teller effect.