Record Ferromagnetic Exchange through Cyanide and Elucidation of the Magnetic Phase Diagram for a CuIIReIV(CN)2 Chain Compound

Reaction of the high-magnetic anisotropy building unit [ReCl4(CN)(2)](2) with [Cu(MeCN)(6)](2+) and hydrotris(pyrazol-1-yl)borate (Tp(-)) affords the zigzag chain compound (Bu4N)[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 pi-pi: interchain interactions of strength J(perpendicular to)/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 [ReCl4(CN)(2)](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 R-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 highdimensional cyano-bridged materials exhibiting higher ordering temperatures.