Synthesis, Structure, and Magnetic Properties of 1D {[Mn^III(CN)₆][Mn^II(dapsc)]}_<i>n</i> Coordination Polymers: Origin of Unconventional Single-Chain Magnet Behavior

Two one-dimensional cyano-bridged coordination polymers, namely, {[Mn^II(dapsc)]­[Mn^III(CN)₆]­[K­(H₂O)_2.75(MeOH)_0.5]}_<i>n</i>·0.5<i>n</i>(H₂O) (<b>I</b>) and {[Mn^II(dapsc)]­[Mn^III(CN)₆]­[K­(H₂O)₂(MeOH)₂]}_<i>n</i> (<b>II</b>), based on alternating high-spin Mn^II(dapsc) (dapsc = 2,6-diacetylpyridine bis­(semicarbazone)) complexes and low-spin orbitally degenerate hexacyanomanganate­(III) complexes were synthesized and characterized structurally and magnetically. Static and dynamic magnetic measurements reveal a single-chain magnet (SCM) behavior of <b>I</b> with an energy barrier of <i>U</i>_eff ≈ 40 K. Magnetic properties of <b>I</b> are analyzed in detail in terms of a microscopic theory. It is shown that compound <b>I</b> refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the Mn^III–CN–Mn^II spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes [Mn^III(CN)₆]^3–. The prospects of [Mn^III(CN)₆]^3– complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed