Magneto-structural correlations in dinuclear Mn(iii) compounds with formula [{Mn(L)(NN)}(μ-O)(μ-2-RC6H4COO)2{Mn(L′)(NN)}]n+

Abstract

Three dinuclear Mn(III) compounds with oxo and carboxylato bridges have been synthesized and characterized by X-ray diffraction: [{Mn(L)(NN)}(μ-2-ClC₆H₄COO)₂(μ-O){Mn(L′)(NN)}]ⁿ⁺ with NN = 2,2′-bipyridine (1 and 2) or 1,10-phenanthroline (3). The counteranion is either NO₃⁻ (1 and 3) or ClO₄⁻ (2) and the monodentate positions (L, L′) could be occupied by molecules of water or the counteranion. For compound 1, L = H₂O and L′ = NO₃⁻; compound 2 shows two different dinuclear units and L and L′ could be H₂O or ClO₄⁻, and for compound 3 both monodentate positions are occupied by nitrate anions. The magnetic properties of the three compounds have been analyzed using the Hamiltonian H = −JS₁·S₂. Compound 1 exhibits a dominant ferromagnetic behavior, with J = 3.0 cm⁻¹, |D_Mn| = 1.79 cm⁻¹, |E_Mn| = 0.60 cm⁻¹ with intermolecular interactions zJ′ = −0.18 cm⁻¹. Due to the anisotropy of the Mn(III) ions, the ground state S = 4 shows ZFS with |D₄| = 0.58 cm⁻¹. Compounds 2 and 3 show antiferromagnetic couplings, with J = −10.9 and −0.3 cm⁻¹, respectively. The magnetic interaction in this kind of compound depends on several structural factors. In the present work, the distortion around manganese ions, the torsion angle between the phenyl ring and the carboxylate group and the relative disposition of the coordination octahedra have been analyzed.