Abstract
The aim of the work described in this thesis has been to prepare and study various ethylenediamine and propylenediamine chromium(III) phosphates and arsenates. A number of trisethylenediamine and trispropylenediamine tertiary phosphates and arsenates and also some acid phosphates and arsenates have been successfully prepared using silver phosphate or arsenate. These have been characterised by means of chemical analysis, spectrophotometric, thermogravimetric, infra-red and X-ray studies. Their thermogravimetric behaviour has been compared to that of the corresponding halides, thiocyanates and sulphates. Two principal types of behaviour have been observed. The first, in which there is a clear stage in the thermal decomposition corresponding to the reaction : [Cr en[3]]X[3] → [Cr en[2]X[2]]X + en, where X= Cl, Br I, SCN or n[Cr en[3]]AO[4] → [Cr en[2]AO[4]]on + n 'en', where A=P or As, and the second type in which such behaviour is not observed. The thermogravimetric studies have shown that the thermal stability of complexes depends (i) on the nature of the neutral ligand present initially in the co-ordination sphere, e.g. ethylenediamine compounds are more stable than the corresponding propylenediamine compounds; (ii) on the nature of the anion initially present outside the co-ordination sphere. The stabilities found in the present study agree for the known compounds with published work and provide information on the phosphate and arsenate compounds. The order of stabilities is given as follows : Cr~I > Cl > PO[4] > SCN > AsO[4]. It has been established that similar behaviour on thermal decomposition does not necessarily lead to identical products. Thus it has not proved possible to assign a definite structure to the compounds [Cr en[2]PO[4]]on and [Cr en[2] AsO[4]] on.