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

Abstract

Crystals of the title complex are tetragonal, space group P4/n, with a= 13.090(7), c= 7.440(5)Å, Z= 2. The crystal structure has been solved by the heavy-atom method and refined by full-matrix least-squares calculations to R 0.054 over 750 statistically significant reflections from diffractometer measurements (Mo-K_α radiation). The distorted octahedral [MoCl₄O(OH₂)]^– anion has 4mm(C_4v) symmetry with Mo–O 1.672(15), Mo–O(OH₂) 2.393(15), and Mo–Cl 2.359(3)Å, and O–Mo–Cl 99.0(9)°. The [AsPh₄]⁺ cation has crystallographic (S₄) symmetry, As–C 1.900(9)Å, and C–As–C angles of 105.5(4) and 111.5(4)°. The polarized single-crystal electronic spectra at room temperature and 5 K show that the first two bands at 13 200 and 22 800 cm^–1 are xy polarized; these absorptions are assigned to the transitions b₂*(4d_xy′Mo–Cl π*)→e*(4d_xz′yz′ Mo–O π*) and e(4d_xz′yz′ Mo–O π)→b₂*(4d_xy′Mo–Cl π*), or a₁*(4d_z²′Mo–O σ*) respectively. The single-crystal e.s.r. parameters, g_‖ 1.970 ± 0.002 and g⊥ 1.935 ± 0.002, and the Mo hyperfine parameters measured for solutions in concentrated HCl and for polycrystalline [AsPh₄][NbCl₄O(OH₂)], A 45.5 × 10^–4 and 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.