Many binuclear nickel complexes have NiNi distances suggesting NiNi covalent bonds, including lantern-type complexes with bridging bidentate ligands. This DFT study treats tetragonal, trigonal, and digonal lantern-type complexes with the formamidinate, guanidinate, and formate ligands, besides some others. Formal bond orders (ranging from zero to two) are assigned to all the NiNi bonds on the basis of MO occupancy considerations. A VB-based electron counting approach assigns plausible resonance structures to the dinickel cores. Model tetragonal complexes with the dimethylformamidinate and the dithioformate ligands have singlet ground states whose non-covalently bonded NiNi distances are close to those in their experimentally known counterparts. Trigonal dinickel complexes are unknown, but are predicted to have quartet ground states with NiNi bonds of order 0.5. The model digonal complexes are predicted to have triplet ground states, but the predicted NiNi bond lengths are longer than those found in their experimentally known counterparts. This could owe to inadequate treatment of electron correlation by DFT in these short NiNi bonds with their multiconfigurational character. All the NiNi bond distances here are categorized into ranges according to the NiNi bond orders of 0, 0.5, 1, 1.5, and 2, no NiNi bonds of order higher than two being identified. The NiNi bonds of given order in these lantern-type complexes are consistently shorter than the corresponding NiNi bonds in dinickel complexes having carbonyl ligands, attributable to the metalmetal bond lengthening effect of CO ligands.

中文翻译：

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灯笼型二镍配合物：探索镍-镍与桥联双齿配体键合的可能性

许多双核镍络合物具有 Ni  Ni 距离，表明 Ni  Ni 共价键，包括具有桥联双齿配体的灯笼型络合物。该 DFT 研究使用甲脒、胍盐和甲酸盐配体以及其他一些配体处理四方、三方和双方灯笼型配合物。基于 MO 占用考虑因素，将正式债券订单（从零到两个）分配给所有 Ni  Ni 债券。基于 VB 的电子计数方法将合理的共振结构分配给二镍核。具有二甲基甲脒和二硫代甲酸酯配体的模型四方络合物具有单线态基态，其非共价键合的 Ni Ni 距离接近于其实验已知对应物中的距离。三方二镍络合物未知，但预计具有四重基态，其中 Ni  Ni 键为 0.5。预测模型对角配合物具有三重态基态，但预测的 Ni  Ni 键长比在实验已知对应物中发现的长。这可能是由于 DFT 对这些具有多构型特征的短 Ni  Ni 键中的电子关联处理不充分。这里所有的 Ni  Ni 键距都按照 Ni  Ni 键的顺序 0、0.5、1、1.5 和 2 进行分类，没有 Ni 确定了高于两个的 Ni 键。这些灯笼型配合物中给定顺序的Ni  Ni 键始终比具有羰基配体的二镍配合物中相应的 Ni  Ni 键短，这归因于 CO 配体的金属金属键延长效应。