Crystal and molecular structure of bis(tetraphenylphosphonium) bis(1,2-dicyanoethylene-1,2-dithiolato)oxovanadate(IV). Its single-crystal electron spin resonance as a pure compound and diluted in the isomorphous molybdenum(IV) compound

Abstract

The crystal structure of [PPh₄]₂[VO(mnt)₂](mnt = 1,2-dicyanoethylene-1,2-dithiolate) has been determined at –154 °C by X-ray crystallographic methods. The compound crystallises in the monoclinic space group P2₁/n with a= 11.176(3), b= 15.254(5), c= 14.319(4)Å, β= 97.62(1)°, and Z= 2. The anion is disordered about the inversion centre with 50% occupancy of each site. The anion has approximately square-pyramidal geometry with dimensions: V–O 1.579(10), V–S(3′) 2.356(4), V–S(3) 2.372(3), V–S(4) 2.360(3), and V–S(4′) 2.407(3)Å. Single-crystal e.s.r. spectra at room temperature and Q-band frequencies gave the spin-Hamiltonian parameters; g₁= 1.970 ± 0.002, g₂= 1.987 ± 0.002, g₃= 1.988 ± 0.002, A₁=(–42.5 ± 1.0)× 10^–4, A₂=(–45.5 ± 1.0)× 10^–4, and A₃=(–136.6 ± 1.0)× 10^–4 cm^–1; g₁ and A₃ are coincident but g₂ and g₃ rotate by 6° from A₁ and A₂ respectively. Similarly for [PPh₄]₂[(Mo, V)O(mnt)₂]: g₁= 1.971 ± 0.001, g₂= 1.986 ± 0.001, g₃= 1.989 ± 0.001, A₁=(–40.3 ± 0.3)× 10^–4, A₂=(–47.4 ± 0.3)× 10^–4, A₃=(–136.3 ± 0.3)× 10^–4 cm^–1, and Q′= 3e²qQ/4I(2I– 1)=–(0.09 ± 0.05)× 10^–4 cm^–1; g₁ and A₃ are coincident and g₂ and g₃ rotated 5.5° from A₁ and A₂ respectively. The g and A tensors have been analysed via both angular overlap and by constrained minimisation of a composite function of the expressions for the spin-Hamiltonian parameters to estimate the d-orbital mixing in the complex.