Synthesis and characterization of two new types of oxovanadium complexes with pyrazole as ligand.

At room temperature, two new different oxovanadium complexes with simple pyrazole (C3H4N2) as ligand were synthesized. VO(pz)₄(SO₄)·H₂O (1) (pz: pyrazole) is a mono-nuclear oxovanadium complex with pyrazole as terminal ligands. V₂O₂(μ-pz)(μ-OOSO₂)(μ-OCH₃)(pz)₄ (2) is bi-nuclear oxovanadium complex containing three different bridges, which are pyrazolate, sulphate and methoxy, respectively. The two complexes were characterized by IR, elemental analyses, thermal analyses and X-ray diffraction. The crystal structural data of the complexes 1 and 2 are given as follows: Complex 1, orthorhombic, Pna2₁, a =14.547(2) Å, b =10.895(2) Å, c =11.835(2) Å; α=β=γ=90°; V=1875.8(5) ų, Z = 4, R₁ = 0.0485, _wR₂= 0.1092. Complex 2, triclinic, P1, a =8.377(2) Å, b =9.928(2) Å, c = 16.527(3) Å, α = 85.54(3)°, δ = 80.92(3)°, γ = 87.92(3)°, R₁= 0.1461, _wR₂ = 0.4444. The study of non-thermal kinetic de- composition shows that, for complex 1, the possible reaction mechanisms of the two steps are nucleation and growth n=1/3, and three-dimensional pervasion n=2, respectively, and the kinetic equations may be expressed as da/dT = (A/β)exp(-E/RT){1/3(1-α)[-ln(1-α]^-2} and da/d T = (A/β)exp(-E/RT){3/2(1-α)^2/3 [1-(1-α)^1/3]^-1}, respectively; for complex 2, the possible reaction mechanisms of the two steps are chemical reaction, and three-dimensional pervasion n=2, respectively; the kinetic equations may be expressed as da/dT = (A/β)exp(-E/RT)[(1-α)ଡ], and dα/d T = (A/β)exp(-E/RT){3/2(1-α)^2/3[1-(1-α)^1/3]^-1}, respectively. [ABSTRACT FROM AUTHOR]