Vanadium Hydridotris(pyrazolyl)borate Complexes of Diphenyl Phosphate. Homometallic Trimeric Complexes of the [LV{(PhO)2PO2}3]- Fragment

The synthesis and characterization of two linear trinuclear V(III) complexes are described: 1, [LV(μ-(PhO)2PO2)3-V-(μ-(PhO)2PO2)3VL]PF6, and 2, LV(μ-(PhO)2PO2)2(μ-OH)V(μ-(PhO)2PO2)2(μ-OH)VL]ClO4, where L = hydridotris(pyrazolyl)borate. Compound 1 consists of two terminal V(III) ions capped by a hydridotris(pyrazolyl)borate group and each linked to a central V(III) by three (μ-O, μ-O‘) diphenyl phosphate bridges. The structure of 2 is analogous but with a hydroxide bridge replacing a diphenyl phosphate in each link. X-ray crystal structural analysis of 1 and 2 gave the following parameters: 1, C98H92B2F6N16O24P7V3, P1̄, a = 14.191(6) Å, b = 14.338(4) Å, c = 14.471(3) Å, α = 76.41(3)°, β = 71.10(3)°, γ = 81.22(2)°, Z = 1, V = 2698.3(15) Å3; 2, C70H68B2ClN14O22P4V3, P21/n, a = 13.035(5) Å, b = 17.280(4) Å, c = 19.343(8) Å, β = 109.18(2)°, Z = 2, V = 4115(2) Å3. Magnetic measurements indicate that replacement of one phosphate bridge with a hydroxide leads to a change in the sign of the coupling between the terminal and central V(III) atoms from antiferromagnetic (AF) in 1 to ferromagnetic (FM) in 2. The similarity in structure between 2 and the previously reported [L2V2(μ-(PhO)2PO2)2(μ-OH)]ClO4 allows a comparison between their magnetic properties and confirms the previously postulated idea that the crossover from AF to FM coupling comes near a bridge angle of 133°.