A MnIII triplesalen-based 1D pearl necklace: exchange interactions and zero-field splittings in a C3-symmetric MnIII6 complex

Abstract

The reaction of the tert-butyl-substituted triplesalen ligand H₆talen^t-Bu₂ with 2.8 equivalents of Mn(OAc)₂·4H₂O in MeOH in the presence of NaBPh₄ results in the formation of the one-dimensional (1D) coordination polymer {[{(talen^t-Bu₂)Mn₃(MeOH)}₂(μ₂-OAc)₃](μ₂-OAc)}_n(BPh₄)_2n ({[Mn^III₆](OAc)}_n(BPh₄)_2n) which has been characterized by FTIR, elemental analysis, ESI-MS, single-crystal X-ray diffraction and magnetic measurements. The triplesalen ligand (talen^t-Bu₂)⁶⁻ provides three salen-like coordination compartments bridged in a meta-phenylene arrangement by a phloroglucinol backbone resulting in the trinuclear Mn^III base unit {(talen^t-Bu₂)Mn₃}³⁺. Two of these base units are bridged by three inner acetate ligands giving rise to the hexanuclear complex [{(talen^t-Bu₂)Mn₃(MeOH)}₂(μ₂-OAc)₃]³⁺ ([Mn^III₆]³⁺). These complexes are bridged by a single external acetate to form a 1D chain as pearls in a pearl necklace. Variable temperature-variable field and μ_effvs. T magnetic data have been analyzed in detail by full-matrix diagonalization of the appropriate spin-Hamiltonian consisting of isotropic exchange, zero-field splitting, and Zeeman interaction taking into account the relative orientation of the D-tensors. Satisfactory reproduction of the experimental data have been obtained for parameters sets J₁ = −(0.60 ± 0.15) cm⁻¹, J₂ = −(1.05 ± 0.15) cm⁻¹, and D_Mn = −(3.0 ± 0.7) cm⁻¹ with J₁ describing the exchange through the phloroglucinol backbone and J₂ describing the exchange through the inner acetates. The non-necessity to incorporate the bridging outer acetates correlates with the longer Mn–O bonds. The experimental data can neither be analyzed without incorporating zero-field splitting nor by the application of a single effective spin ground state.