Record ferromagnetic exchange through cyanide and elucidation of the magnetic phase diagram for a Cu(II)Re(IV)(CN)2 chain compound.

Reaction of the high-magnetic anisotropy building unit ReCl(4)(CN)(2) with Cu(MeCN)(6) and hydrotris(pyrazol-1-yl)borate (Tp(-)) affords the zigzag chain compound (Bu(4)N)[TpCuReCl(4)(CN)(2)]. Dc magnetic susceptibility measurements reveal the presence of ferromagnetic exchange coupling between Re(IV) and Cu(II) centers along each chain and a fit to the data gives an exchange constant of J/k(B) = +41 K (+29 cm(-1)), representing the strongest ferromagnetic coupling yet observed through cyanide. Below 11.4 K and at applied fields of less than 3600 Oe, the compound undergoes a phase transition to an antiferromagnetic ground state, stemming from weak π-π interchain interactions of strength J(⊥)/k(B) = -1.7 K (-1.2 cm(-1)). This metamagnetic behavior is fully elucidated using both experimental and theoretical methods. In addition, theoretical modeling provides a detailed determination of the local anisotropy tensors corresponding to the ReCl(4)(CN)(2) units and demonstrates that the zigzag arrangement of the Re(IV) centers significantly reduces the effective anisotropy of the chain. These results demonstrate the utility of the Re(IV)-CN-Cu(II) linkage and the importance of anisotropic spin orientation in designing strongly coupled systems, which will aid in both the realization of single-chain magnets with higher relaxation barriers and in the construction of high-dimensional cyano-bridged materials exhibiting higher ordering temperatures.