COMBINATION OF METAL-METAL BONDING AND ANTIFERROMAGNETIC EXCHANGE INTERACTION IN THE D(2)-D(2) COMPLEX [V2O(SPH)(4)(ME(2)-BPY)(2)]CENTER-DOT-THF (ME(2)-BPY=4,4'-DIMETHYLBIPYRIDINE)

Synthetic procedures leading to the preparation of V-III and V-IV complexes of PhS(-) are described, including the mononuclear complex (NEt(4))[V(SPh)(4)(bpy)] (1). Controlled aerial oxidation of its 4, 4'-Me(2)-bpy (Me(2)-bpy) analogue generated in situ with 0.5 equiv of O-2 leads to generation of [VO(SPh)(3)(Me(2)-bpy)](-) that can be isolated as the NT4+ salts; (NMe(4))[VO(SPh)(3)(Me(2)-bpy)] (2) has been structurally characterized and contains a distorted-octahedral anion with three equatorial PhS(-) groups and one Me(2)-bpy N atom of the chelate trans to the multiply-bonded O atom. Crystal data for 2: monoclinic, C2/c, a = 28.618(5) Angstrom, b = 10.053(1) Angstrom, c = 24.194(3) Angstrom, beta = 113.40(1)degrees, Z = 8, T = -157 degrees C, and V = 6387.8 Angstrom(3); R (R(w)) = 5.85 (5.81)% for 3306 unique reflections with F > 3 sigma(F). The same oxidation reaction with the related ion [V(SPh)(2)(bpy)(2)](+) leads to [VO(SPh)(bpy)(2)](PF6) (3). Controlled hydrolysis of [V(SPh)(4)(Me(2)-bpy)](-), generated in situ, leads to isolation of V2O(SPh)(4)(Me(2)-bpy)(2) (4) which has a [V-2(mu-O)mu-SPh)(2)](2+) core With a terminal PhS(-) and chelating Me(2)-bpy on each metal; the V-V separation of 2.579(3) Angstrom is suggestive of a V-III-V-III single bond. Crystal data for 4: monoclinic, C2/c, a = 16.954(3) Angstrom, b = 15.969(2) Angstrom, c = 18.830(3) Angstrom, beta = 107.96(1)degrees, Z = 4, T = -173 degrees C, and V = 4839.5 Angstrom(3); R (Rw) = 6.44 (6.46)% for 2115 unique reflections with F > 3 sigma(F). EHT calculations on the model complex V2O(SH)(4)(NH3)(4) indicate a V-V sigma bond arising from V d(z)2 overlap, with the HOMO and LUMO comprising delta and delta* orbitals, respectively, formed by V d(xy) orbitals. A small HOMO-LUMO gap (similar to 0.02 eV) suggests the weak room-temperature paramagnetism is due to thermal population of the LUMO, Variable-temperature solid-state studies on 4 indicate an effective magnetic moment per dimer (mu(eff)/V-2) of 1.35 mu(B) at 330 K decreasing to 0.095 mu(B) at 5.0 K. The data were fit to the Bleaney-Bowers equation for a d(1)-d(1) dimer. and the obtained parameters were J = -355 +/- 20 cm(-1), g = 2.04, and TIP = 300 x 10(-6) cm(3) mol(-1) with a 1.4% paramagnetic (V-III) impurity. Variable-temperature H-1 NMR studies on complex 4 in d(8)-THF solution in the -90 to +50 degrees C range were fit to the appropriate equation relating the H-1 paramagnetic shifts to a number of parameters including J. The obtained value of J for 4 in solution was -280 +/- 20 cm(-1). The calculated singlet-triplet gaps for 4 are /2J/ = 710 and 560 cm(-1) for the solid and solution phases, respectively.