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

Abstract

The complex Pd(μ-OOCMe)4Cu(OH2) · 2Pd3(μ-OOCMe)6 was synthesized and characterized by X-ray crystallography. In the heterometallic moiety of this complex, the PdII and CuII 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 PdIIMII(μ-OOCMe)4L (M = ZnII, NiII, CuII, CoII, FeII; L = OH2 and NCH) and their formate analogues PdIIMII(μ-OOCH)4L (M = ZnII, NiII, FeII) 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 [PdIII(μ-OOCMe)4NiIII]2+ type.