Copper(II) complexes of tridentate selenobisphenolate ligand in mixed ligand environments: Synthesis, crystal structure, EPR and electrochemical studies

摘要

A series of square-pyramidal copper(II) complexes, [Cu(L-Se)(N boolean AND N)] (H2LSe = seleno-bisphenolate; N boolean AND N = bipyridyl, phenanthroline or N,N-dimethylethylenediamine) have been synthesized and characterized by elemental analyses, magnetic measurements, IR, EPR, and electronic spectral studies. Single crystal X-ray structures of [Cu(L-Se)(bpy)]center dot H2O (2), [Cu(L-Se)(phen)]center dot CH2Cl2 (3) and [Cu(L-Se)(N,N-Me(2)en)] (4) showed that all the complexes have approximately square-pyramidal geometry. In complexes 2 and 3, the square plane is occupied by O(1) O(2) N(1) and N(2) and the apical position by Se atom of L(Se 2-)ligand. The asymmetric unit of complex 4 contains two crystallographically independent discrete molecules A and B with CuN2OSe chromophore comprising the square plane and the axial position being occupied by another phenolate oxygen atom. Complexes 2, 3 and 4 are found to be paramagnetic and EPR parameters extracted are: g(parallel to) = 2.232, g(perpendicular to) = 2.069; < g(eff)> = 1.95; and g(parallel to) = 2.232, g(perpendicular to) = 2.083 for complexes 2, 3 and 4, respectively. Both the complexes 2 and 4 show three reduction processes: (a) a quasi-reversible reduction of Cu-II to Cu-I, (b) an irreversible reduction of Cu-I to Cu-0 with the release of free ligand, and (c) a reduction process occurs at this coordinated ligand. They also show a well-defined quasi-reversible oxidation of Cu-II to Cu-III and an irreversible oxidation peak at similar to 1.30 and 1.40 V vs. Ag/AgCl for 4 and 2, respectively, with no cathodic counterpart, and were attributed to the oxidation of the metal coordinated ligand. (c) 2006 Elsevier B.V. All rights reserved.