Structural studies of complex compounds of 6,6'-diacetyl-2,2'-bipyridine dioxime with copper(I/II), platinum(II), and palladium(II) metal ions

Abstract

The tetradentate ligand 6,6'-diacetyl-2,2'-bipyridine dioxime (L) was obtained in high yield by the condensation reaction of 6,6'-diacetyl-2,2'-bipyridine with hydroxyl amine in alkaline solution. Density functional calculations and 3D modeling of the structure at the B3LYP/6-31G(d) level of theory for L revealed that the energy difference between the global trans conformer (trans-L), which possesses the C_{2h} point group, and the distorted cis conformer (cis-L) was 5.214 kcal/mol. Synthesis and characterization of the metal complexes with Cu(I), Cu(II), Pt(II), and Pd(II) metal ions were reported. L acted as a N_4-donor ligand to coordinate to the metal centers via N atoms of the 2,2'-bipyridine and the imine moieties to afford tetrahedral complex [Cu^IL]PF_6 (1), distorted octahedral complex [Cu^{II}L(OH_2)_2](NO_3)_2 (2), and square-planar complexes [Pt^{II}L]Cl_2 (3) and [Pd^{II}L]Cl (4), respectively. The CHN analysis for 1 implies that L coordinated to 2 copper(I) ions as a bridging ligand to form a dinuclear metal complex, [Cu_2L_2]^{2+}, due to the twisting of the coordinated bonds exposed by the tetrahedral geometry preference for the metal ion. The ligand formed intramolecular hydrogen bonds between the oxime groups in 4, as revealed by the spectroscopic studies. The most stable conformations of the compounds were obtained by using the molecular mechanics optimization feature in CAChe software with an augmented MM2 force field.^1