Petrie Simon, Stranger Robert
Department of Chemistry, The Faculties, The Australian National University, Canberra ACT 0200, Australia.
Inorg Chem. 2004 Apr 19;43(8):2597-610. doi: 10.1021/ic034525e.
Density functional theory (DFT) calculations are reported for 16 binuclear transition-metal complexes. Structural motifs studied include face-shared and edge-shared bioctahedra, carboxylate-bridged "paddlewheel" complexes, and nonbridged dimers possessing direct metal-metal bonds. Most of these structure types are represented both by multiply charged (tri- and tetra-anionic, and tetracationic) and by neutral or singly charged examples. Geometry optimizations for these species, in the vacuum phase, use the "broken-symmetry" approach coupled with nine different DFT methods. We find a clear dichotomy in the performance of different DFT approaches. For the eight neutral or singly charged complexes, orthodox gradient-corrected DFT methods such as BP and PBE perform generally very well in reproducing in vacuo the complex geometries obtained from X-ray crystallographic studies. In contrast, these orthodox approaches fail to reliably mimic the crystalline geometries for more highly charged complexes such as Mo(2)Cl(9)(3-), Cr(2)(CH(3))(8)(4-), and Rh(2)(NCCH(3))(10)(4+). Much closer agreement with experimental condensed-phase structures for the multiply charged dinuclear complexes is seen for two "local-density-approximation" approaches, X alpha and VWN, and for VWN+B-LYP, an unorthodox combination of the VWN local and B-LYP nonlocal density functionals. The very good performance of the latter approaches arises from an essentially fortuitous cancellation of errors: while the generally overbinding nature of these approaches suggests that they will not reliably describe true gas-phase structures, this overbinding compensates very well for the coulombic distortion expected when complexes are removed from the charge-stabilizing environment of the crystalline or solvated state. We recommend that, as an alternative to the (computationally expensive) incorporation of solvent-field corrections, VWN+B-LYP is the preferred method for structural characterization of triply or more highly charged dinuclear complexes, while orthodox approaches such as PBE perform best for neutral or mildly charged complexes.
报道了16种双核过渡金属配合物的密度泛函理论（DFT）计算。研究的结构单元包括面共享和边共享的双八面体、羧酸盐桥连的“桨轮”配合物以及具有直接金属-金属键的非桥连二聚体。这些结构类型中的大多数都有多重电荷（三价和四价阴离子以及四价阳离子）以及中性或单电荷的例子。在真空相中，对这些物种进行几何优化时，使用了“破缺对称性”方法并结合九种不同的DFT方法。我们发现不同DFT方法的性能存在明显的二分法。对于八个中性或单电荷配合物，传统的梯度校正DFT方法如BP和PBE在真空下重现从X射线晶体学研究获得的配合物几何结构时通常表现得非常好。相比之下，这些传统方法无法可靠地模拟更高电荷配合物（如Mo₂Cl₉³⁻、Cr₂(CH₃)₈⁴⁻和Rh₂(NCCH₃)₁₀⁴⁺）的晶体几何结构。对于多重电荷的双核配合物，两种“局域密度近似”方法Xα和VWN以及VWN + B - LYP（VWN局域和B - LYP非局域密度泛函的非传统组合）与实验凝聚相结构的一致性要好得多。后一种方法的良好性能源于误差的基本偶然抵消：虽然这些方法通常具有过度结合的性质，这表明它们不能可靠地描述真实的气相结构，但这种过度结合很好地补偿了配合物从晶体或溶剂化状态的电荷稳定环境中移除时预期的库仑畸变。我们建议，作为（计算成本高昂的）纳入溶剂场校正的替代方法，VWN + B - LYP是三重或更高电荷双核配合物结构表征的首选方法，而诸如PBE等传统方法对中性或轻度电荷配合物表现最佳。
