STUDIES ON THE REACTIVITY OF S,N-DERIVATIVES OF NICKEL WITH N-DONOR BASES - CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF THE CUBANE CLUSTER TETRAKIS(MU-HYDROXO)TETRAKIS(MU-1,3-THIAZOLIDINE-2-THIONATO)TETRAKIS(PYRIDINE)-TETRANICKEL(II)-DIPYRIDINE

The reaction of polymeric [Ni(tzdt)2] (tzdt = 1,3-thiazolidine-2-thionate) with pyridine affords two different compounds depending on the conditions employed: [Ni(tzdt)2(py)2] in dry pyridine and [Ni4(OH)4(tzdt)4(py)4].2py with an excess of water. The former, mononuclear and paramagnetic, shows the nickel atom in an octahedral environment, while the latter has a cubanelike structure crystallizing in the tetragonal system: space group P42(1)cBAR, Z = 8, a = 11.969 (5) angstrom, c = 18.357 (9) angstrom, and V = 2629 (2) angstrom 3. The magnetic susceptibility of this cubane has been measured in the range 295-4 K showing that the compound has a diamagnetic ground state. The magnetic exchange among the four nickel atoms has been modeled with the use of three parameters, four ferromagnetic interactions (J1 = 17.5 cm-1) and two antiferromagnetic (J2 = J3 = -22 cm-1). These interactions are propagated by the hydroxo bridges and are dependent on the Ni-O-Ni angles. The antiferromagnetic behavior is explained in terms of the distortions induced in the cubane core by the tzdt bridging ligands leading to two different types of Ni-O-Ni, those of ca. 95-96-degrees and those of 103-degrees. It is proposed that the latter are associated with the antiferromagnetic couplings.