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首页> 外文期刊>Bulletin of the Chemical Society of Japan >Theoretical Studies of Multiple Metal-Metal Bonds between Divalent Molybdenum Ions in Dimers, Tetramers, and Clusters
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Theoretical Studies of Multiple Metal-Metal Bonds between Divalent Molybdenum Ions in Dimers, Tetramers, and Clusters

机译：二聚体，四聚体和簇中二价钼离子之间多个金属-金属键的理论研究

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摘要

The multiple metal-metal bonds between divalent molybdenum (Mo(II)) ions in dimers and tetramers were investigated theoretically. The orbital energy gaps, occupation numbers of natural orbitals (NO) and effective bond orders for the naked Mo(II)_2 dimer (1) were calculated by ab initio UHF MO and density functional (DFT) methods. The effective exchange integrals (J_(ab)) of 1 were calculated by approximately spin-projected UHF and DFT methods, and the complete active space (CAS) CI by the use of UHF NO. The calculated J_(ab) values were discussed in relation to the temperature-dependent paramagnetism observed for the edge-sharing and face-sharing bioctahedral molybdenum complexes. The CAS CI calculations showed that the Heisenberg model is not appropriate for 1 under the condition that the Mo-Mo distance is shorter than 2.5 A. The UHF and DFT MO calculations were also performed for the linear naked Mo(II)_4 tetramer (2) to elucidate possible electronic structures of the d-d conjugated systems. The continuous changes from closed-shell diamagnetic) electronic structures to antiferromagnetic states were investigated by elongating the Mo-Mo distances. Similarities and differences between Mo(II)_2 (1) and naked Cr(II)-2 (3) or between Mo(II)_4 (2) and Cr(II)_4 (4) were examined and compared, since the nature of direct exchange couplings between divalent chromium ions in 3 and 4 was already studied extensively in relation to the electron correlation effect. The metal-insulator transitions induced by elongation of the Mo(II)-Mo(II) distance in Mo(II) clusters were discussed from the viewpoint of electron correlation and size effects in mesoscopic systems.
机译：理论上研究了二聚体和四聚体中二价钼离子之间的多个金属键。通过从头算UHF MO和密度泛函（DFT）方法计算了裸Mo（II）_2二聚体（1）的轨道能隙，自然轨道（NO）的占据数和有效键序。通过近似自旋投影的UHF和DFT方法计算出有效交换积分（J_（ab））为1，并通过使用UHF NO计算出完整的活动空间（CAS）CI。讨论了计算的J_（ab）值与边共享和面共享生物体面钼配合物的温度依赖性顺磁性有关。 CAS CI计算表明，在Mo-Mo距离小于2.5 A的条件下，Heisenberg模型不适用于1。还对线性裸Mo（II）_4四聚体（2）进行了UHF和DFT MO计算。 ）以阐明dd共轭体系的可能电子结构。通过拉长Mo-Mo距离，研究了从闭壳抗磁电子结构到反铁磁态的连续变化。由于性质，对Mo（II）_2（1）和裸露的Cr（II）-2（3）或Mo（II）_4（2）和Cr（II）_4（4）之间的异同进行了比较。关于3和4中二价铬离子之间的直接交换耦合的机理，已经广泛地研究了与电子相关效应的关系。从介电体系中的电子相关性和尺寸效应的角度，讨论了由于Mo（II）团簇中Mo（II）-Mo（II）距离的延长而引起的金属-绝缘体跃迁。

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