COORDINATION MODES OF THE 1,3-DITHIOSQUARATE (1,3-DTSQ) LIGAND - SYNTHESES, CRYSTAL-STRUCTURES, AND MAGNETIC-PROPERTIES OF [NI(TREN)(1,3-DTSQ)(H2O)] AND [NI-2(TREN)(2)(1,3-DTSQ)](CLO4)(2) [TREN EQUALS TRIS(2-AMINOETHYL)AMINE]

The first X-ray crystallographic stucture determinations of metal comp lexes of the 1,3-dithiosquarate (1,3-dtsq, dianion of 3-hydroxy-4-merc apto-2-thioxo-3-cyclobuten-1-one) are reported herein. Compounds [Ni(t ren)(1,3-dtsq)(H2O)] (C10H20N4NiO3S) (1) and [Ni-2(tren)(2)(1,3-dtsq)] (ClO4)(2) (C16H36Cl2N8Ni2O10S2) (2) (where tren is tris(2-aminoethyl)a mine) both crystallize in the monoclinic system, space group P2(1)/c, with a = 8.519(1) Angstrom, b = 13.931(1) Angstrom, c = 13.587(3) Angs trom, beta = 106.705(8)degrees, and Z = 4 for 1 and a = 8.663(1) Angst rom, b = 14.496(2) Angstrom, c = 11.617(2) Angstrom, beta = 98.135(9)d egrees, and Z = 2 for 2. The structure of 1 consists of mononuclear, n eutral [Ni(tren)(1,3-dtsq)(H2O)] complex units, whereas that of 2 is m ade up of dinuclear dithiosquarate-bridged cations, [Ni-2(tren)(2)(1,3 -dtsq)](2+), and uncoordinated perchlorate anions. The nickel environm ent is distorted octahedral in both cases, the tren group acting as a tetradentate ligand through its four nitrogen atoms and the dithiosqua rate being monodentately coordinated through one of the sulfur atoms i n 1 and bridging bis-bidentate in 2. A water molecule which is hydroge n bonded to the neighboring carbonyl-oxygen atom of the dithiosquarate completes the octahedron around the metal atom in 1. The intradimer m etal-metal separation in 2 is 7.096(1) Angstrom. Variable-temperature magnetic susceptibility measurements of complex 2 reveal the occurrenc e of a weak intramolecular antiferromagnetic coupling. The ability of the 1,3-dithiosquarate ligand to transmit electronic effects between m etal ions has been analyzed through extended Huckel calculations. The theoretical influence of the position (1,2-dithiosquarate versus 1,3-d ithiosquarate) and the number of sulfur (1,2,3,4-tetrathiosquarate) at oms on the exchange coupling through bis-bidentate thiosquarates is al so considered.