Electronic and bonding properties of mixed-ligand copper(II) complexes of N-(2-pyridylethyl)picolinamide (pepa). Molecular structures of [Cu(pepa)(3-methyl-pyridine) (H 2O)](ClO 4), [Cu(pepa)(4-methylpyridine) (H 2O)](ClO 4) and [Cu(pepa)(4-methylimidazole) (H 2O)](H 2O)(ClO 4)

Abstract

Mixed-ligand N-(2-pyridylethyl)picolinamidocopper(II) complexes, Cu(pepa)(L)(H 2O) n (ClO 4) [pepa = N-(2-pyridylethyl)picolinamide anion; L = imidazole ( n = 0), N-methylimidazole ( n = 1), 2-methylimidazole ( n = 1), 4-methylimidazole (4MImH, n = 2), 3-methylpyridine (3Mpy, n= 1 and 2), and 4-methylpyridine (4Mpy, n = 1 and 2)], have been synthesized and characterized by elemental analyses, and electronic, vibrational and EPR spectroscopic measurements. Molecular structures of [Cu(pepa)(3Mpy)(H 2O)](ClO 4) ( 1), [Cu(pepa)(4Mpy)(H 2O)](ClO 4) ( 2) and [Cu(pepa)(4MImH)(H 2O)(ClO 4) ( 3) have been determined by X-ray diffraction methods. The structures of these complexes are square pyramidal with the pepa and a heterocyclic unidentate ligand forming the basal plane and an H 2O molecule on the apical position. The dihedral angles of the heterocyclic unidentate nucleus and the CuN 4 basal plane are 74.3° for 1, 66.8° for 2 and 77.7° for 3. The structures of other pepa complexes are suggested to be square pyramidal based on their spectroscopic data. The sequence of d orbitals was assigned as d x 2− y 2 ⪢ d z 2 > d yz > d xy > d xz for the square pyramidal complexes. The significant rise in energy of the d yz orbital suggests that the central amido of the pepa ligand is a strong π-donor.