Synthesis, structural, and DFT studies of mixed ligand copper(II) malonates

Abstract

The synthesis, spectra, electrochemical studies, single crystal structures and DFT studies of two new mixed ligand copper(II) malonates viz. [Cu(H sub(2) O)(bpy(OH) sub(2))(mal)].H sub(2) O 1 and [Cu(H sub(2)O)(dmp)(mal)].2H sub(2) O 2 (bpy(OH) sub(2)) = 2,2'-bipyridine-6,6'-diol; dmp = 6,6'-dimethyl-1,10-phenanthroline; H sub(2) mal = malonic acid) are reported. The malonate, bpy(OH) sub(2) (in 1), dmp (in 2) function as bidentate ligands in the distorted square pyramidal Cu(II) compounds while the aqua ligand occupies the axial site in 1. In contrast, one N of dmp occupies the axial site in 2. ESR studies reveal the distorted coordination geometry of Cu(II) in 1 and 2. Extensive hydrogen bonding (O-H...O and C-H...O) is observed between the malonate oxygens, oxygens of water and the monomeric Cu(II) species resulting in the formation of hydrogen bonded network structure in 1 and 2. The neutral monomeric Cu(II) species and lattice water molecules in 2 are linked via O-H...O hydrogen bond forming a water dimer. Both compounds exhibit Pi...Pi stacking and carbonyl(lp)...Pi interactions (in 2) stabilize the structure. DFT studies reveal stronger hydrogen bond energy for 2 compared to 1, while Pi...Pi stacking energy is larger in 1 than in 2 and carbonyl(lp)...Pi interactions in 2 are found to be moderate. In a series of five coordinated mixed ligand Cu(II) malonates, compound 2 exhibits maximum deviation of the {CuN sub(2) O sub(3)} polyhedron from square pyramidal towards trigonal bipyramidal geometry.