Synthesis, Structure, and Magnetic Properties of 1D {[MnIII(CN)6][MnII(dapsc)]} n Coordination Polymers: Origin of Unconventional Single-Chain Magnet Behavior

Two one-dimensional cyano-bridged coordination polymers, namely, {[MnII(dapsc)]­[MnIII(CN)6]­[K­(H2O)2.75(MeOH)0.5]} n ·0.5n(H2O) (I) and {[MnII(dapsc)]­[MnIII(CN)6]­[K­(H2O)2(MeOH)2]} n (II), based on alternating high-spin MnII(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 I with an energy barrier of U eff ≈ 40 K. Magnetic properties of I are analyzed in detail in terms of a microscopic theory. It is shown that compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the MnIII–CN–MnII spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes [MnIII(CN)6]3–. The prospects of [MnIII(CN)6]3– complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed.