Crystal and molecular structure, electron spin resonance, and electronic spectrum of tetraphenylarsonium tetrachloro-oxomolybdenum(V)

Abstract

Crystals of the title compound are tetragonal, space group P4/n, with a= 12.766(7), c= 7.785(5)Å, Z= 2. The crystal structure was solved by the heavy-atom method and refined by full-matrix least-squares calculations to R 0.050 over 735 statistically significant reflections from diffractrometer measurements. The square-pyramidal [MoOCl₄]^– anion has 4mm(C_4v) symmetrywith Mo–O 1.610(10), Mo–Cl 2.333(3)Å, O–Mo–Cl 105.2(1)°. The [AsPh₄]⁺ cation has crystallographic (S₄) symmetry, with As–C 1.902(7)Å, end C–As–C angles of 105.3(3) and 111.6(3)°. The polarised single-crystal electronic spectra at room temperature and 5 K show that the first two bands at 1 5.4 and 22.5 kK are due to b₂*(4d_xy)→e*(4d_xz,yz, Mo–O_π*) and e(Mo–Oπ)→a₁*(Mo–O_a*) excitation respectively. The single-crystal e.s.r. parameters (g_∥ 1.967 ± 0.002, g⊥ 1.950 ± 0.002) and the Mo hyperfine parameters from solutions in CH₂Cl₂ and solid [AsPh₄][NbOCl₄], (Ā 47.9 × 10^–4 cm^–1, A‖ 72.8 × 10^–4 cm^–1), have been used in conjunction with the electronic spectrum to estimate the metal d-orbital contributions to the metal–ligand antibonding molecular orbitals.