A systematic first-principles study is performed to investigate the 20-electron transition metal complexes (C₅H₅)₂TM(E₁E₂)₂ (TM = Cr, Mo, W; E₁E₂ = CO, N₂, BF). For the thermodynamic stable (C₅H₅)₂TM(E₁E₂)₂ complexes (TM = Cr, Mo, W; E₁E₂ = CO, BF), their 20-electron nature is derived from their occupied nonbonding molecular orbital mainly donated by ligands. Furthermore, the nature of the TME₁ bond is thoroughly analyzed by the energy decomposition analysis (EDA) method. The absolute value of interaction energies (|ΔE_int|) between (C₅H₅)₂TM(E₁E₂) and E₁E₂ has the same trend as the corresponding bond dissociation energy and Wiberg bond orders of TME₁ bonds, following the order W > Mo > Cr with same ligands and BF > CO with same TM. The largest contribution to the ΔE_int values is the repulsive term ΔE_Pauli. Similar contributions from covalent and electrostatic terms to the TME₁ bonds are found, which can be described as the classic dative bond with nearly same σ and π contributions.

中文翻译：

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20 电子过渡金属配合物 (C5H5)2TM(E1E2)2（TM = Cr、Mo、W；E1E2 = CO、N2、BF）的理论洞察：稳定性、电子结构和键合性质

进行系统的第一性原理研究以研究 20 电子过渡金属配合物 (C ₅ H ₅ ) ₂ TM(E ₁ E ₂ ) ₂ (TM = Cr, Mo, W; E ₁ E ₂  = CO, N ₂ , BF)。对于热力学稳定的 (C ₅ H ₅ ) ₂ TM(E ₁ E ₂ ) ₂配合物（TM = Cr, Mo, W; E ₁ E ₂  = CO, BF），它们的 20 电子性质来自于它们占据的非键合分子轨道主要由配体提供。此外，TM 的性质 E ₁键通过能量分解分析（EDA）方法进行彻底分析。(C ₅ H ₅ ) ₂ TM(E ₁ E ₂ )和E ₁ E ₂之间相互作用能的绝对值(|Δ E _int |)与TM 对应的键解离能和Wiberg键级具有相同的趋势E ₁键，按照 W > Mo > Cr 的顺序，配体相同，BF > CO，TM 相同。对 Δ E _int值的最大贡献是排斥项 Δ E _Pauli. 发现共价项和静电项对 TM  E ₁键的贡献类似，可以将其描述为具有几乎相同的σ和π贡献的经典与键。