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)A, 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)A. 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.