Three Cyanide-Bridged One-Dimensional Single Chain CoIII-MnIIComplexes: Rational Design, Synthesis, Crystal Structures and Magnetic Properties

Abstract

Two pyridinecarboxamide dicyanidecobalt(III) building blocks and two mononuclear seven-coordinated macrocycle manganese(II) compounds have been rationally selected to assemble cyanide-bridged heterobimetallic complexes, resulting in three cyanide-bridged <TEX>$Co^{III}-Mn^{II}$</TEX> complexes. Single X-ray diffraction analysis show that these complexes <TEX>$\{[Mn(L^1)][Co(bpb)]\}ClO_4{\cdot}CH_3OH{\cdot}0.5H_2O$</TEX> (<TEX>$\mathbf{1}$</TEX>), <TEX>$\{[Mn(L^2)][Co(bpb)]\}ClO_4{\cdot}0.5CH_3OH$</TEX> (<TEX>$\mathbf{2}$</TEX>) and <TEX>${[Mn(L^1)][Co(bpb)]\}ClO_4{\cdot}H_2O$</TEX> (<TEX>$\mathbf{3}$</TEX>) (<TEX>$L^1$</TEX> = 3,6-diazaoctane-1,8-diamine, <TEX>$L^2$</TEX> = 3,6-dioxaoctano-1,8-diamine; <TEX>$bpb2^{2-}$</TEX> = 1,2-bis(pyridine-2-carboxamido)benzenate, <TEX>$bpmb2^{2-}$</TEX> = 1,2-bis(pyridine-2-carboxamido)-4-methyl-benzenate) all present predictable one-dimensional single chain structures. The molecular structures of these one-dimensional complexes consists of alternating units of <TEX>$[Mn(L)]^{2+}$</TEX> (<TEX>$L=L^1$</TEX> or <TEX>$L^2$</TEX>) and <TEX>$[Co(L^{\prime})(CN)2]^-$</TEX> (<TEX>$L^{\prime}=bpb2^{2-}$</TEX>, or <TEX>$bpmb2^{2-}$</TEX>), forming a cyanide-bridged cationic polymeric chain with free <TEX>$ClO_4{^-}$</TEX> as the balance anion. The coordination geometry of manganese(II) ion in the three one-dimensional complexes is a slightly distorted pentagonal-bipyrimidal with two cyanide nitrogen atoms at the trans positions and <TEX>$N_5$</TEX> or <TEX>$N_3O_2$</TEX> coordinating mode at the equatorial plane from ligand <TEX>$L^1$</TEX> or <TEX>$L^2$</TEX>. Investigation over magnetic properties of these complexes reveals that the very weak magnetic coupling between neighboring Mn(II) ions connected by the diamagnetic dicyanidecobalt(III) building block. A best-fit to the magnetic susceptibility of complex <TEX>${\mathbf}{1}$</TEX> leads to the magnetic coupling constants <TEX>$J=-0.084(3)cm^{-1}$</TEX>.