Raising the Spin-Reversal Barrier in Cyano-Bridged Single-Molecule Magnets: Linear Mn^III₂M^III(CN)₆ (M = Cr, Fe) Species Incorporating [(5-Brsalen)Mn]⁺ Units

Reactions between K3[M(CN)6] and [Mn(5-Brsalen)(H2O)2]+ (5-Brsalen = N,N‘-ethylenebis(5-bromosalicylidene)aminato dianion) in a mixture of methanol and water afford the compounds K[(5-Brsalen)2(H2O)2Mn2M(CN)6]·2H2O, with M = Cr (1) or Fe (2). The two compounds are isostructural, each containing a molecular cluster with a linear MnIII−NC−MIII−CN−MnIII core and tetragonally elongated coordination about the MnIII centers. Magnetic data indicate the presence of weak exchange interactions within the clusters, giving rise to ground states of S = 5/2 and 9/2 with significant zero-field splitting. Despite the proximity of spin-excited states, ac susceptibility data reveal frequency-dependent out-of-phase signals characteristic of single-molecule magnets with spin-reversal barriers of Ueff = 16 and 25 cm-1, respectively.