The coordination compounds of copper(I) with nitrogen and sulphur-containing ligands are well known; the coordination number in these complexes usually varies 1'2 from 1 to 3. A few tetra-coordinated complexes have also been reported such as cyano, substituted phosphine and arsine complexes. The latter are formed by coordination through bridging and occur more frequently with iodide 3. It has been reported that copper(I) may also form stable mixed ligated complexes with four coordination through substitution and addition reactions. Interesting examples 4 of such types of compounds are the products formed by the substitution or addition ofheterocyclic amines to copper(I) thiourea complexes, e.g. [ C u ( T u ) 3 Py] I, [Cu(Tu)33-Pic] I, and [Cu(Tu)2Dipy ] I. Mixed ligand chloro and iodo copper(I) complexes have also been investigated potentiometrlcally 5. The stereoch.emistry of such coordination complexes is explained on the basis of the formation of a drc~/rc bond, due to the availability of a vacant d-orbital in the ligand which may also act as an acceptor drc-orbital by taking the excessive charge from the metal. The present study is an extension of the earlier work carried out on the mixed ligand complexes of copper(I). This study includes investigations by a potentiometric method on the composition of the complex species formed in solution and their reaction mechanism.
EXPERIMENTAL
The silver-silver sulphide electrode used in the potentiometry was prepared by depositing silver metal on a platinum wire. The platinum wires were immersed in a solution of potassium argentocyanide and subjected to electrolysis using a 2 V accumulator. The silver coated wire was then dipped in dilute H2S water for about 12-18 h until a uniform dark grey coating of AgzS was obtained. The reversibility of the electrode was tested by measuring the potentials of thiourea solutions of varying concentrations. From the concentration-potential calibration curve the concentration of the known thiourea solution was checked.
Tristhiourea copper(I) chloride and iodide complexes, were prepared as described earlier 4,5. Thiourea, pyridine, 2,2-dipyridyl and phenylarsonic acid were all E. Merck products and purified before use.
Potentiometric measurements were made with a Toshniwal potentiometer type CL06 using Ag-Ag2S and calomel as indicator and reference electrodes, respec-