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)(H 2O)](H 2O)(ClO 4) and [Cu(pmpa)(4-methylpyridine)(H 2O)] (H 2O)(ClO 4)

Abstract

Mixed-ligand N-(2-picolyl)picolinamidocopper(II) complexes, [Cu(pmpa)(L)(X) · nH 2O] [pmpa = N-(2-picolyl)picolinamide anion; L = imidazole ( n = 0, o 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 NH 3 ( n = 2); X = ClO 4 − or BF 4 −], have been synthesized and characterized by elemental analyses, and electronic, vibrational, and EPR spectroscopic measurements. Molecular structures of [Cu(pmpa)(4MImH)(H 2O)](H 2O)](H 2O)(ClO 4 ( 1) and [Cu(pmpa)(4Mpy)(H 2O)](H 2O)(ClO 4) ( 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 H 2O molecule on the apical position. The dihedral angles of the heterocyclic unidentate nucleus and the CuN 4 basal plane are 79.3° for 1 and 74.5° 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 x 2 − y 2 ⪢ d z 2 > d yz > d xy > d xz for the square pyramidal complexes and d x 2− y 2 ⪢ d yz > d xy > d xz > d z 2 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 π-donor.