Guo Dong, McCusker James K
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
Inorg Chem. 2007 Apr 16;46(8):3257-74. doi: 10.1021/ic070005y. Epub 2007 Mar 20.
The synthesis, physical, and spectroscopic properties of a series of metal complexes bridged by the redox-active chloranilate ligand are described. Compounds containing the (CAcat,cat)4- ligand, where (CAcat,cat)4- represents the fully reduced aromatic form of chloranilate, have been prepared by two different routes from H2CA and H4CA starting materials; the corresponding (CAsq,cat)3- analogue was obtained by one-electron oxidation with decamethylferrocenium tetrafluoroborate. Homo- and heterobimetallic complexes containing CrIII and GaIII with chloranilate have been prepared, yielding the following six complexes: Ga2(tren)2(CAcat,cat)2 (1), Ga2(tren)2(CAsq,cat)2(BF4) (2), GaCr(tren)2(CAcat,cat)2 (3), GaCr(tren)2(CAsq,cat)2(BF4) (4), [Cr2(tren)2(CAcat,cat)] (BPh4)2 (5), and Cr2(tren)2(CAsq,cat)2(BF4) (6) (where tren is tris(2-aminoethyl)amine). Single-crystal X-ray structures have been obtained for complexes 1, 3, and 5; nearly identical C-C bond distances within the quinoidal ligand confirm the aromatic character of the bridge in each case. Complex 2 exhibits a temperature-independent magnetic moment of microeff = 1.64 +/- 0.04 microB in the solid state between 4 and 350 K, consistent with the CAsq,cat formulation of the ligand and an S = 1/2 ground state for complex 2. Complex 3 exhibits a value of microeff = 3.44 +/- 0.09 microB that is also temperature-independent, indicating an S = 3/2 ground state. Complexes 4-6 are all influenced by Heisenberg spin exchange. The temperature-independent behavior of complexes 4 and 6 indicate the presence of strong antiferromagnetic exchange between the CrIII and the (sq,cat) bridging radical yielding well-isolated ground states of S = 1 and 5/2 for 4 and 6, respectively. In contrast, complex 5 exhibits a weak intramolecular antiferromagnetic exchange interaction between the two CrIII centers (J = -2 cm-1 for H = -2Jŝ1.ŝ2) via superexchange through the diamagnetic CAcat,cat bridge. The absorption spectra of the CAsq,cat-containing complexes exhibit a number of sharp, relatively intense features in fluid solution. Group theoretical arguments coupled with a qualitative ligand-field analysis including the effects of Heisenberg spin exchange suggest that several of the observed transitions are a consequence of exchange interactions in both the ground- and excited-state manifolds of the compounds.
描述了一系列由氧化还原活性氯冉酸配体桥联的金属配合物的合成、物理和光谱性质。含有(CAcat,cat)4-配体的化合物（其中(CAcat,cat)4-代表氯冉酸的完全还原芳香形式）已通过两种不同途径由H2CA和H4CA起始原料制备；相应的(CAsq,cat)3-类似物通过用四氟硼酸十甲基二茂铁进行单电子氧化获得。已制备了含CrIII和GaIII与氯冉酸的同双核和异双核配合物，得到以下六种配合物：Ga2(tren)2(CAcat,cat)2 (1)、Ga2(tren)2(CAsq,cat)2(BF4) (2)、GaCr(tren)2(CAcat,cat)2 (3)、GaCr(tren)2(CAsq,cat)2(BF4) (4)、[Cr2(tren)2(CAcat,cat)] (BPh4)2 (5)和Cr2(tren)2(CAsq,cat)2(BF4) (6)（其中tren是三(2-氨基乙基)胺）。已获得配合物1、3和5的单晶X射线结构；醌型配体内几乎相同的C-C键距离证实了每种情况下桥联的芳香性质。配合物2在4至350 K的固态下表现出与温度无关的磁矩，μeff = 1.64 +/- 0.04 μB，这与配体的CAsq,cat结构以及配合物2的S = 1/2基态一致。配合物3表现出μeff = 3.44 +/- 0.09 μB的值，该值也与温度无关，表明S = 3/2基态。配合物4 - 6均受海森堡自旋交换影响。配合物4和6与温度无关的行为表明在CrIII和(sq,cat)桥联自由基之间存在强反铁磁交换，分别为4和6产生了S = 1和5/2的良好隔离基态。相比之下，配合物5通过抗磁性的CAcat,cat桥联通过超交换在两个CrIII中心之间表现出弱的分子内反铁磁交换相互作用（对于H = -2Jŝ1.ŝ2，J = -2 cm-1）。含CAsq,cat的配合物的吸收光谱在流体溶液中表现出许多尖锐、相对较强的特征。群论论证以及包括海森堡自旋交换效应的定性配体场分析表明，观察到的一些跃迁是化合物基态和激发态流形中交换相互作用的结果。
