Single-crystal and multi-frequency EPR studies on chemical analogues of Amavadin: V(IV)-doped Ca[Ti(hida)2]·6H2O, and Mo(V)-doped [PPh4][Nb(hida)2] and [NEt4][Ta(R,R-hidpa)2] [H3hida=2,2′-(hydroxyimino)diacetic acid, H3hidpa=2,2′-(hydroxyimino)dipropionic acid]

Abstract

Q-band single-crystal and powder EPR spectra at multiple frequencies (X, Q and 180 GHz) of V(IV)-doped Ca[Ti(hida)₂]·6H₂O and Mo(V)-doped [PPh₄][Nb(hida)₂] and [NEt₄][Ta(R,R-hidpa)₂] (H₃hida=2,2′-(hydroxyimino)diacetic acid; H₃hidpa 2,2′-(hydroxyimino)dipropionic acid) are reported. The Ti{V} system has the spin-Hamiltonian parameters g₁₁=1.910, g₂₂=1.987, g₃₃=1.990, A₁₁=176.4 G, A₂₂=53.5 G and A₃₃=46.3 G with non-coincidence between the principal axes of the g- and A-matrices. The Euler angles for the non-concidence are α=11.5°, χ=4.63° and γ=346.0°. The triclinic EPR symmetry is consistent with the low (C₁) point symmetry of the [Ti{V}(hida)₂]^2- anion in the solid state. The small angles of non-coincidence between the principal axes of the g and A matrices are also evident from the Q-band powder spectrum, but not the X-band spectrum. High-frequency (34–180 GHz) EPR measurements on powders of both the Nb{Mo} and Ta{Mo} systems reveal the presence of two magnetically distinct Mo centers in each case. The Nb{Mo} system has g-values of g_11(a)=1.9765, g_11(b)=1.9755, g_22(a)=1.9675, g_22(b)=1.9665, g_33(a)=1.8870 and g_33(b)=1.8840, while the Ta{Mo} system has g_11(a)=1.976, g_11(b)=1.974, g_22(a)=1.970, g_22(b)=1.967, g_33(a)=1.894 and g_33(b)=1.892.