Homoleptic copper(II) complexes of an osazone. Reversal of the coordination ability of hexafluorophosphate and perchlorate anions

Abstract

Using the 1:1 condensate of benzil and 2-hydrazinopyridine as the ligand LH (H: dissociable proton), three copper(II) complexes of the type [Cu(L)(LH)]ClO4 (1), Cu(L)(LH)PF6 (2) and CuL2 (3) are synthesized. From the X-ray crystal structures, it is found that 1 is distorted square pyramidal, whereas complex 2 in distorted octahedral via coordination of PF6− anion to the metal with a Cu(II)F bond distance of 2.722(3)Å. Although ClO4− is more coordinating than PF6−, a reversal of their coordinating ability is observed here. The CuN bond trans to CuF is somewhat longer (2.304Å). Complex 3 is a distorted octahedral homoleptic neutral mer complex. In 3 two axial CuN bond lengths are shorter (1.967Å and 1.978Å) than the equatorial one giving rise to a compressed octahedron. EPR spectrum of 1 is isotropic (g=2.057), but g|| (2.138)>g⊥ (2.027) in 2 showing Jahn-Teller elongation. On the other hand, in 3, g||<g⊥ (1.986, 2.112), which is another type of manifestation of the Jahn-Teller effect. In the density functional theory calculations, the SOMO of 2 shows a (dx2−y2)1 ground state in contrary to 3 where (dz2)1 is the ground state. Thus experimental and theoretical results are in one-to-one-correspondence. In cyclic voltammetry at an Au electrode whose surface is modified by thiocyanate, 3 displays an irreversible one-electron oxidation with an anodic peak potential of 0.98V vs normal hydrogen electrode.