Crystal Structure and Magnetic Properties of an Oxamato-Bridged Heterobimetallic Tetranuclear [(NiCuII)-Cu-II](2) Complex of the Rack Type

摘要

This work discusses a new heterobimetallic nickel(II)copper-(II) complex of the formula [Ni(tpa) Cu(opba)](2)center dot 6H(2)O (1) {H(4)opba = N, N'-1,2-phenylenebis(oxamic acid) and tpa = tris(2-pyridylmethyl)amine}. The molecular structure of 1 consists of neutral tetranuclear species with a 4R rack-type architecture featuring two (NiCuII)-Cu-II dinuclear units connected through two out-of-plane oxo(carboxylate-oxamate) atoms from the opba ligands. The crystal packing of 1 exhibits a supramolecular 1D arrangement of tetranuclear entities connected by hydrogen bonds and pi-pi stacking interactions. The dc magnetic properties of 1 were interpreted according to its dimer-of-dimer structure; the spin Hamiltonian being defined as {H = -J[S-Ni1 center dot S-Cu1 + S-Ni1i center dot S(Cu1)i - j(eff)(S-Cu1 center dot S-Cu1i)]}. The analysis of the magnetic data shows the occurrence of a strong intradimer antiferromagnetic coupling between the Ni-II and Cu-II ions [J = -115.2(4) cm(-1)] and a weak interdimer antiferromagnetic coupling between the Cu-II ions [j(eff) = -1.12(7) cm(-1)]. DFT-type calculations were performed to visualize the exchange pathway through the oxamate bridge and substantiate the value of J.