Exploration of a new building block for the construction of cyano-bridged solvatomagnetic assemblies: [Ni(cyclam)]

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 ]·6H 2 O} n ( 1 ) and {[Ni(cyclam)][Fe(CN) 6 ]·6H 2 O} n ( 2 ) chains are isostructural and crystallise in space group C 2/ m . They undergo reversible partial dehydration at 40 °C to {[Ni(cyclam)][Cr(CN) 6 ]·3H 2 O} n ( 1d ) and {[Ni(cyclam)][Fe(CN) 6 ]·3H 2 O} 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 −2 JS Ni S M ). The magnetic susceptibility for the Cr III -Ni III 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 d 7 configuration. In the bimetallic {[Ni III (cyclam)][M III (CN) 6 ]· n H 2 O} n (M = Cr, Fe) chains, magnetic exchange of an LS d 7 ion through CN-bridges is observed for the first time.