Exploration of a new building block for the construction of cyano-bridged solvatomagnetic assemblies : $[Ni(cyclam)]^{3+}$

Two 1D CN-bridged coordination polymers based on the cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) complex of nickel in an unusual oxidation state III have been characterised in terms of structure and solvatomagnetic properties. The {[Ni(cyclam)][Cr(CN)6]·6H2O}n (1) and {[Ni(cyclam)][Fe(CN)6]·6H2O}n (2) chains are isostructural and crystallise in space group C2/m. They undergo reversible partial dehydration at 40 °C to {[Ni(cyclam)][Cr(CN)6]·3H2O}n (1d) and {[Ni(cyclam)][Fe(CN)6]·3H2O}n (2d), accompanied by marked changes in structure and magnetic properties. Strong ferromagnetic exchange interaction J along the chains, together with a much weaker inter-chain interaction, leads to magnetic ordering in the range from 2.4 to 5.8 K. Dehydration of 1 leads to a decrease in J from 32 to 18 K, while dehydration of 2 leads to an increase in J from 6.8 to 14.3 K (interaction Hamiltonian −2JSNiSM). The magnetic susceptibility for the CrIII–NiIII 3/2–1/2 spin alternating Heisenberg chain was analysed with the help of quantum Monte Carlo simulations, simultaneously including both intra- and inter-chain interactions for a bunch of chains. The compounds are the first bimetallic CN-bridged assemblies containing a magnetically coupled octahedral cationic building block of an LS d7 configuration.