Electron-Paramagnetic-Res Spectroscopy of a Trigonal Prismatic Vanadium Cage Complex - [1,8-Diammonio-3,6,10,13,16,19-hexaazabicyclo-[6.6.6]icosanato(3,6)vanadium(IV)](4+)

Abstract

An e.p.r . study of the cage complex [V^IVdi(amH)sar-2H]⁴⁺ gives spin Hamiltonian parameters g_X 1.974, g_y 1.967, g_Z 1.991, g_iso 1.977, A_X 92×10^-4 cm^-1, A_y 100×10^-4 cm^-1, A_Z 13×10^-4 cm^-1, A_iso 68×10^-4 cm^-1, viz. g_X ≈ g_y < g_Z ≈ 2.0 and A_X ≈ A_y > A_Z. This is consistent with the metal centre approaching a trigonal prismatic environment and a ²A₁ (D₃) ground state, viz. ...d1/z₂. Comparison of the spin Hamiltonian parameters from measurements in frozen and fluid solution, poly(vinyl alcohol) films and dilute powder [V^IVdi(amH)sar-2H]⁴⁺ doped into the lattice of the protonated Zn^II salt over a large temperature range indicates that the structures in solution and in the solid state are virtually identical. The results are discussed in relation to the known structure of the ion in the lattice [v^IVdi(amH)sar -2H](S₂O₆)₂, the sites of deprotonation of the coordinated amines and in relation to the trigonal and small rhombic distortions of the complex.