CNRS, LCC, Laboratoire de Chimie de Coordination, 205, route de Narbonne, F-31077 Toulouse, France.
Dalton Trans. 2011 Feb 28;40(8):1700-6. doi: 10.1039/c0dt01253j. Epub 2011 Jan 19.
The syntheses, structural determinations and magnetic studies of tetranuclear Co(II)-Ln(III) complexes (Ln = Y, Gd, Tb) involving orthovanillin as main ligand are described. The structural studies demonstrate that centrosymmetric tetranuclear Co(2)-Ln(2) complex molecules with a defect-dicubane central core are obtained, with hexacoordinate Co ions in deformed octahedral environments and nine-coordinate lanthanide ions. The Co ions are linked by two hydroxo bridges and each Co ion is also involved in a double phenoxo-hydroxo bridge with the two Ln ions, so that each hydroxo group is triply linked to the two Co and one Gd ions. The four metal ions are coplanar. A ferromagnetic Co-Ln interaction operates in the Co(2)-Ln(2) complexes (Ln = Gd, Tb), along with a D zero-field splitting term for the cobalt ion and a weak ferromagnetic Co-Co interaction. The SMM behaviour of the Co(2)-Gd(2) complex is confirmed by observation of hysteresis loops, as a consequence of the slowing down of relaxation for this tetranuclear complex. The Co(2)-Tb(2) complex does not behave as a SMM, what could result from a subtractive combination of the Tb and Co anisotropies and an increased transverse anisotropy, leading to large tunnel splittings and quantum tunneling of magnetization.
描述了以邻香草醛为主要配体的四核 Co(II)-Ln(III)配合物（Ln = Y、Gd、Tb）的合成、结构测定和磁性研究。结构研究表明，获得了具有缺陷二立方烷中心核的对称四核 Co(2)-Ln(2)配合物分子，其中 Co 离子处于变形八面体环境中，镧系元素离子具有九配位。Co 离子通过两个羟桥连接，每个 Co 离子还与两个 Ln 离子形成双酚氧羟桥，从而使每个羟桥基团三重连接到两个 Co 和一个 Gd 离子上。四个金属离子共面。在 Co(2)-Ln(2)配合物（Ln = Gd、Tb）中存在 Co-Ln 铁磁相互作用，同时 Co 离子存在零场分裂项 D 和弱铁磁 Co-Co 相互作用。Co(2)-Gd(2) 配合物的 SMM 行为通过观察磁滞回线得到证实，这是由于这个四核配合物的弛豫减慢所致。Co(2)-Tb(2) 配合物不表现为 SMM，这可能是由于 Tb 和 Co 各向异性的相减以及横向各向异性的增加导致较大的隧道分裂和磁化的量子隧穿所致。
