Self-assembled polymetallic square grids ([2 × 2] M<sub>4</sub>, [3 × 3] M<sub>9</sub>) and trigonal bipyramidal clusters (M<sub>5</sub>)—structural and magnetic properties
作者:Louise N. Dawe、Tareque S. M. Abedin、Timothy L. Kelly、Laurence K. Thompson、David O. Miller、Liang Zhao、Claire Wilson、Michael A. Leech、Judith A. K. Howard
DOI:10.1039/b602595a
日期:——
New self-assembled grids and clusters are reported, with square [2 à 2] M4 (M = Mn(II)4, Cu(II)4), trigonal-bipyramidal Mn(II)5, and square [3 à 3] M9 (M = Mn(II), Cu(II)) examples. These are based on a series of ditopic and tritopic hydrazone ligands involving pyridine, pyrimidine and imidazole end groups. In all cases the metal centres are bridged by hydrazone oxygen atoms with large (>125°) bridge angles, leading to antiferromagnetic exchange for all the Mn systems (J = â2 to â5 cmâ1), which results in S = 0 (Mn4), and S = 5/2 (Mn5, Mn9) ground states. The copper systems have a 90° alternation of the JahnâTeller axes within the Cu4 and Cu8 grid rings (Cu9), which leads to magnetic orbital orthogonality, and dominant ferromagnetic coupling. For the Cu9 grid antiferromagnetic exchange between the ring and the central copper leads to a S = 7/2 ground state, while for the Cu4 grids S = 4/2 ground states are observed. The magnetic data have been treated using isotropic exchange models in the cases of the Cu4 and Cu9 grids, and the Mn5 clusters. However due to the enormity of a fully isotropic calculation a simplified model is used for the Mn9 grid, in which the outer Mn8 ring is treated as the equivalent of an isolated magnetic chain, with no coupling to the central metal ion.
报道了一些新的自组装网格和簇,包括方形 [2 × 2] M4 (M = Mn(II)4, Cu(II)4)、三角双锥 Mn(II)5 以及方形 [3 × 3] M9 (M = Mn(II), Cu(II)) 的例子。这些基于一系列包含吡啶、嘧啶和咪唑末端基团的双位和三位肼酮配体。在所有情况下,金属中心由肼酮氧原子桥接,桥角大于125°,这导致所有 Mn 系统呈现反铁磁交换(J = -2 到 -5 cm⁻¹),最终结果为基态 S = 0 (Mn4),和 S = 5/2 (Mn5, Mn9)。铜系统在 Cu4 和 Cu8 网格环 (Cu9) 中表现出 Jahn-Teller 轴的 90° 交替,导致磁轨道正交性和主导的铁磁耦合。对于 Cu9 网格,环和中心铜之间的反铁磁交换导致 S = 7/2 的基态,而对于 Cu4 网格则观察到 S = 4/2 的基态。对于 Cu4 和 Cu9 网格以及 Mn5 簇,磁数据使用各向同性交换模型进行处理。然而,由于完全各向同性计算的复杂性,对于 Mn9 网格采用了简化模型,其中外层 Mn8 环被视作一个孤立磁链的等效体,与中心金属离子没有耦合。