Calorimetric and Spectrophotometric Studies of Bromo Complexes of Copper(II) in N,N-Dimethylformamide

Abstract

Abstract Complexation of copper(II) with Br− ions has been studied by calorimetry and spectrophotometry in N,N-dimethylformamide (DMF) containing 0.16 mol dm−3 (C2H5)4NClO4, 1 mol dm−3 LiClO4, and 1 mol dm−3 NH4ClO4 as constant ionic media at 25 °C. Calorimetric titration curves obtained in each solution were well explained in terms of formation of [CuBrn](2−n)+ (n=1–4) and their formation constants, enthalpies and entropies were determined. Electronic spectra of individual copper(II) bromo complexes were also determined in the (C2H5)4NClO4, LiClO4, and NH4ClO4 DMF solutions over the range 260–500 nm, the spectra of each complex being kept practically unchanged in these solutions. The complexation of copper(II) with Br− ions is considerably weaker in the LiClO4 solution than in the (C2H5)4NClO4 one and is even more weakened in the NH4ClO4 solution due to the formation of LiBr and NH4Br ion pairs in the relevant solutions. The variation of the stepwise enthalpy and entropy values suggests that the coordination structure around copper(II) ion changes from octahedral to tetrahedral at the formation of [CuBr3]−. The result for the complexation between copper(II) and bromide ions thus obtained was compared with that for the complexation between the metal and chloride ions.