161406-25-3Relevant academic research and scientific papers
Combination of metal-metal bonding and antiferromagnetic exchange interaction in the d2-d2 complex [V2O(SPh)4(Me2-bpy)2]·THF (Me2-bpy = 4,4′-dimethylbipyridine)
Dean, Norman S.,Bartley, Stuart L.,Streib, William E.,Lobkovsky, Emil B.,Christou, George
, p. 1608 - 1616 (2008/10/08)
Synthetic procedures leading to the preparation of VIII and VIV complexes of PhS- are described, including the mononuclear complex (NEt4)[V(SPh)4(bpy)] (1). Controlled aerial oxidation of its 4,4′-Me2-bpy (Me2-bpy) analogue generated in situ with 0.5 equiv of O2 leads to generation of [VO(SPh)3(Me2-bpy)]- that can be isolated as the NR4+ salts; (NMe4)[VO(SPh)3(Me2-bpy)] (2) has been structurally characterized and contains a distorted-octahedral anion with three equatorial PhS- groups and one Me2-bpy N atom of the chelate trans to the multiply-bonded O atom. Crystal data for 2: monoclinic, C2/c, a = 28.618(5) ?, b = 10.053(1) ?, c = 24.194(3) ?, β = 113.40-(1)°, Z = 8, T = -157°C, and V = 6387.8 ?3; R (Rw) = 5.85 (5.81)% for 3306 unique reflections with F > 3σ(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(Me2-bpy)]-, generated in situ, leads to isolation of V2O(SPh)4(Me2-bpy)2 (4) which has a [V2(μ-O)(μ-SPh)2]2+ core with a terminal PhS- and chelating Me2-bpy on each metal; the V-V separation of 2.579(3) ? is suggestive of a VIII-VIII single bond. Crystal data for 4: monoclinic, C2/c, a = 16.954(3) ?, b = 15.969(2) ?, c = 18.830(3) ?, β = 107.96(1)°, Z = 4, T = -173°C, and V = 4849.5 ?3; R (Rw) = 6.44 (6.46)% for 2115 unique reflections with F > 3σ(F). EHT calculations on the model complex V2O(SH)4(NH3)4 indicate a V-V σ bond arising from V dz2 overlap, with the HOMO and LUMO comprising δ and δ* orbitals, respectively, formed by V dxy orbitals. A small HOMO-LUMO gap (～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 (μeff/V2) of 1.35 μB at 330 K decreasing to 0.095 μB at 5.0 K. The data were fit to the Bleaney-Bowers equation for a d1-d1 dimer, and the obtained parameters were J = -355 ± 20 cm-1, g = 2.04, and TIP = 300 × 10-6 cm3 mol-1 with a 1.4% paramagnetic (VIII) impurity. Variable-temperature 1H NMR studies on complex 4 in d8-THF solution in the -90 to +50°C range were fit to the appropriate equation relating the 1H 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.
