Humidity-induced magnetization and magnetic pole inversion in a cyano-bridged metal assembly

In general, magnetic properties of bulk magnetic materials are independent of the humidity of the environment. To obtain a magnetic material that has humidity-sensitive characteristics, water vapour must penetrate the lattice and act on spin sites. Nanoporous materials composed of metal-assembled complexes^1,2,3,4 may be expected to display some humidity response because materials in this category can show functionalities such as gas storage and molecular recognition. Here, we demonstrate humidity-induced reversible variations in the magnetic properties of cyano-bridged cobalt(II)–manganese(II)–chromium(III) metal assemblies. The observed magnetic humidity response is due to adsorption and desorption of a ligand water molecule on the cobalt ion, which changes cobalt (II) between a 6- and 4-fold coordination geometry and switches the magnetic interaction between ferromagnetic coupling and antiferromagnetic coupling.