LOW-LYING ELECTRONIC-ENERGY LEVELS IN A SERIES OF HETEROBINUCLEAR COMPLEXES CONTAINING OCTAHEDRAL NICKEL(II) AND TETRAHEDRAL METAL(II) (COPPER, COBALT, AND MANGANESE) SPECIES

A series of complexes of general formula Ni(CTH)MCI4 (CTH = dl-5,7,7,12,14,14-hexamethyl-1,4,I8-,te1t raazacyclotetradecane; M = Zn, Cu, Co, Mn) have been synthesized. An X-ray crystal structure determination was performed on the zinc derivative at room temperature. Ni(CTH)ZnC14 crystallizes in the monoclinic system, space group C2/c, with lattice constants a = 19.048 (3) A, b = 9.540 (3) A, c = 12.853 (3) A, p = 101.38 ( 5 ) ' , and Z = 4. Least-squares refinement of the structure led to a conventional R factor of 0.029. The structure consists of dinuclear units Ni(CTH)ZnCI, in which the nickel(I1) ion is octahedrally coordinated by four nitrogen atoms of the macrocyclic ligand and by two chlorine atoms. The latter are bridge-bonded to the Zn(I1) ion, which is tetrahedrally coordinated. Magnetic susceptibility measurements down to 4.2 K were performed with the copper, cobalt, and manganese derivatives. A ferromagnetic coupling was observed in the Ni-Cu derivative, a weak antiferromagnetic coupling was observed in the Ni-Mn derivative, and essentially no coupling was observed in the Ni-Co derivative. This behavior has been related to the available exchange pathways connecting the magnetic orbitals on nickel with those on the tetrahedral metal ions.