Abstract:Copper (I) halides (X = Cl, Br, I) were reacted with one mole of 4- cyanobenzaldehyde thiosemicarbazone (HL1 ) and two molar Ph3P to form complexes of general formula, [CuX(HL1 )(Ph3P)2] (1-3). However, the similar reaction with 4- methylbenzaldehyde thiosemicarbazone (HL2 ) did not give the same complex with copper (I) iodide and bromide. Instead of that X = I (A), Br (B) complexes of stiochiometry, [CuX(Ph3P)3] formed. No ligand gets attached to copper centre. Only the copper (I) chloride has formed complex of stiochiometry, [CuCl(HL2 )(Ph3P)2] 4. Conformation of formation of complexes was done by infra-red, ultra-violet and nuclear magnetic resonance spectroscopy. All these techniques support binding of thio- ligand to copper center in neutral mode. Binding of trihenylphosphine in these complexes is also confirmed by these techniques.