On the nature of the chemical bond in heterobimetallic palladium(II) complexes with divalent 3d metals

Abstract

The complex Pd(μ-OOCMe) 4 Cu(OH 2 ) · 2Pd 3 (μ-OOCMe) 6 was synthesized and characterized by X-ray crystallography. In the heterometallic moiety of this complex, the Pd II and Cu II atoms are at an extraordinary short distance (2.521(3) Å). DFT quantum-chemical calculations of the geometric and electronic structure of a series of heterobinuclear paddlewheel complexes Pd II M II (μ-OOCMe) 4 L (M = Zn II , Ni II , Cu II , Co II , Fe II ; L = OH 2 and NCH) and their formate analogues Pd II M II (μ-OOCH) 4 L (M = Zn II , Ni II , Fe II ) showed that the extraordinary short Pd⋯M distance in all these complexes is caused only by the tightening effect of carboxylate bridges rather than by the metal-metal bond. The direct Pd-M interaction becomes possible only after removal of electrons from the antibonding orbitals and formation of oxidized complexes of the [Pd III (μ-OOCMe) 4 Ni III ] 2+ type.