Hydrogen bond mediated magnetism in [CuII(en)2(H2O)][CuII(en)2Ni2Cu2I(CN)10]·2H2O

Previous structural investigations of the title compound indicated that the paramagnetic copper ions are connected by extremely long paths built of covalent bonds and much shorter interionic connections formed by hydrogen bonds (HBs). Although the extended covalent pathway does not support detectable magnetic correlations, this paper reports on magnetic interactions, mediated by the HBs, between the paramagnetic copper ions. The corresponding magnetic properties have been investigated, including the experimental and numerical studies of the specific heat, magnetic susceptibility, isothermal magnetization, and electron paramagnetic resonance response. Given the geometry of the HBs present in the structure, the experimental data have been analyzed with a model of a planar tetramer with alternating ferromagnetic and antiferromagnetic interactions leading to a singlet ground state. The fact that the model does not provide a unique set of exchange coupling parameters for a detailed description of all experimental data indicates that the real system possesses a more complex geometry of magnetic interactions. However, despite the simplified approach used in the analysis, the magneto-chemical studies showed significant correspondence between the geometry of the HBs and the observed magnetic properties.