Electronic and bonding properties of mixed-ligand copper(II) complexes of N-(2-picolyl)picolinamide (pmpa). X-ray crystal structures of [Cu(pmpa)(4-methylimidazole)(H2O)](H2O)(ClO4) and [Cu(pmpa)(4-methylpyridine)(H2O)](H2O)(ClO4)

Mixed-ligand N-(2-picolyl)picolinamidocopper(II) complexes, [Cu(pmpa)(L)(X). nH(2)O] [pmpa = N-(2-picolyl)picolinamide anion; L = imidazole (n = 0, 1 or 2), N-methylimidazole (n = 0 or 1), 4-methylimidazole (4MImH) (n = 0 or 2), pyridine (n = 0), 2-methylpyridine (n = 0), 3-methylpyridine (n = 0), 4-methylpyridine (4Mpy) (n = 2), and NH3 (n = 2), X = ClO4- or BF4-], have been synthesized and characterized by elemental analyses, and electronic, vibrational, and EPR spectroscopic measurements. Molecular structures of [Cu(pmpa)(4MImH)(H2O)](H2O)(ClO4) (1) and [Cu(pmpa)(4Mpy)(H2O)](H2O)(ClO4) (2) have been determined by X-ray diffraction methods. Both complexes are square pyramidal with the pmpa and the heterocyclic unidentate ligands forming the basal plane and a H2O molecule on the apical position. The dihedral angles of the heterocyclic unidentate nucleus and the CuN4 basal plane are 79.3 degrees for 1 and 74.5 degrees for 2. The structures of other pmpa complexes are suggested to be square pyramidal or square planar based on their spectroscopic data. The sequence of d orbitals is assigned as d(x2-y2) much greater than d(z2) > d(yz) > d(xy) > d(xz), for the square pyramidal complexes and d(x2-y2) much greater than d(yz) > d(xy) > d(xz) > d(z2) for the square planar complexes. The significant rise in energy of the d(yz) orbital suggests that the central amido of the pmpa ligand is a strong pi-donor. Copyright (C) 1996 Elsevier Science Ltd