Spectroscopic studies on copper(II) halide complexes with isomeric benzoylpyridines: Electronic and electron spin resonance spectral evidence for five-coordinate copper(II) species in solution

Abstract

Coordination compounds formed by copper(II) chloride and bromide with 2-, 3- and 4-benzoylpyridines (BOP)Cu(2-BOP)Cl 2 , Cu(3-BOP) 2 Cl 2 , Cu(4-BOP)Cl 2 , Cu(2-BOP) 2 Br 2 , Cu(3-BOP) 2 Br 2 and Cu(4-BOP) 2 Br 2 —have been characterized by elemental analyses, molar conductance, magnetic moments, electronic, IR and ESR spectral studies. It is suggested that Cu(2-BOP)Cl 2 is monomeric tetrahedral, Cu(3-BOP) 2 Cl 2 and Cu(4-BOP)Cl 2 are dimeric octahedral and tetrahedral structures, respectively, bridging through chlorines while all the bromo complexes are polymeric octahedral structures with bridging bromine atoms in the solid state. Powder ESR data reveal rhombic symmetry for all the chloro complexes. Cu(2-BOP) 2 Br 2 is suggested to have an axial symmetry while the other bromo complexes are isotropic in nature. Electronic and ESR spectral studies in DMSO solution suggest the interaction of solvent molecules with copper(II) ions in the axial plane. The solution spectral data are almost comparable suggesting same local symmetry for all the compounds consistent with five-coordinate square pyramidal geometry in each case. ESR spectra also suggest considerable CuCu interactions in Cu(3-BOP) 2 Cl 2 . Various Spin—Hamiltonian parameters calculated from ESR data indicate the presence of an unpaired electron in the d x 2 − y 2 orbital of the copper(II) ion in an axial symmetry.