Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Am Chem Soc. 2011 Jan 12;133(1):123-30. doi: 10.1021/ja108575t. Epub 2010 Dec 9.
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.
高磁各向异性构筑单元ReCl(4)(CN)(2)与Cu(MeCN)(6)和三(吡唑-1-基)硼酸盐(Tp(-))反应得到了锯齿链化合物(Bu(4)N)[TpCuReCl(4)(CN)(2)]。直流磁化率测量表明，每个链上的 Re(IV)和 Cu(II)中心之间存在铁磁交换耦合，拟合数据给出的交换常数为 J/k(B) = +41 K (+29 cm(-1))，这代表了通过氰化物观察到的最强铁磁耦合。在 11.4 K 以下和低于 3600 Oe 的外加磁场下，该化合物经历了一个从顺磁基态到反铁磁基态的相变，这源于较弱的π-π链间相互作用，其强度为 J(⊥)/k(B) = -1.7 K (-1.2 cm(-1))。这种超顺磁行为通过实验和理论方法得到了充分的阐明。此外，理论建模提供了对ReCl(4)(CN)(2)单元对应的局部各向异性张量的详细确定，并证明了 Re(IV)中心的锯齿排列显著降低了链的有效各向异性。这些结果证明了 Re(IV)-CN-Cu(II)键的实用性和各向异性自旋取向在设计强耦合系统中的重要性，这将有助于实现具有更高弛豫势的单链磁体，并构建具有更高有序温度的高维氰桥接材料。
