Structure and magnetic exchange in heterometallic 3d–3d transition metal triethanolamine clusters

Abstract

Synthetic methods are described that have resulted in the formation of seven heterometallic complexes, all of which contain partially deprotonated forms of the ligand triethanolamine (teaH₃). These compounds are [Mn^III₄Co^III₂Co^II₂O₂(teaH₂)₂(teaH)_0.82(dea)_3.18(O₂CMe)₂(OMe)₂](BF₄)₂(O₂CMe)₂·3.18MeOH·H₂O (1), [Mn^II₂Mn^III₂Co^III₂(teaH)₄(OMe)₂(acac)₄](NO₃)₂·2MeOH (2), [Mn^III₂Ni^II₄(teaH)₄(O₂CMe)₆]·2MeCN (3), [Mn^III₂Co^II₂(teaH)₂(sal)₂(acac)₂(MeOH)₂]·2MeOH (4), [Mn^II₂Fe^III₂(teaH)₂(paa)₄](NO₃)₂·2MeOH·CH₂Cl₂ (5), [Mn^IIMn^III₂Co^III₂O(teaH)₂(dea)(Iso)(OMe)(F)₂(Phen)₂](BF₄)(NO₃)·3MeOH (6) and [Mn^II₂Mn^IIICo^III₂(OH)(teaH)₃(teaH₂)(acac)₃](NO₃)₂·3CH₂Cl₂ (7). All of the compounds contain manganese, combined with 3d transition metal ions such as Fe, Co and Ni. The crystal structures are described and examples of ‘rods’, tetranuclear ‘butterfly’ and ‘triangular’ Mn₃ cluster motifs, flanked in some cases by diamagnetic cobalt(III) centres, are presented. Detailed DC and AC magnetic susceptibility and magnetization studies, combined with spin Hamiltonian analysis, have yielded J values and identified the spin ground states. In most cases, the energies of the low-lying excited states have also been obtained. The features of note include the ‘inverse butterfly’ spin arrangement in 2, 4 and 5. A S = ⁵/₂ ground state occurs, for the first time, in the Mn^III₂Mn^II triangular moiety within 6, the many other reported [Mn₃O]⁶⁺ examples having S = ½ or ³/₂ ground states. Compound 7 provides the first example of a Mn^II₂Mn^III triangle, here within a pentanuclear Mn₃Co₂ cluster.