基于配体场理论的锌铁合金异常共沉积机理

Mechanism of anomalous codeposition of zinc-iron alloys based on ligand field theory

结合配合物的化学键理论、晶体场理论和配体场理论,研究了碱性体系中锌离子和铁族金属离子配合物的结构和性质,及其中心离子的d电子轨道能级的分裂和配体场稳定化能,从量子化学及结构化学角度剖析了锌铁族合金的正常、异常共沉积,以及从正常共沉积到异常共沉积转变的本质原因。结果表明:[Fe(OH)4(TEA)2]2–中心离子Fe2+的d电子排布为42t2geg(弱场)或60t2geg(强场),[Zn(OH)4]2–中心离子Zn2+的d电子排布为46et2。弱场中,[Fe(OH)4(TEA)2]2–的配体场稳定化能大于[Zn(OH)4]2–的配体场稳定化能,Zn–Fe合金共沉积表现为正常共沉积;强场中,当配体的给电子能力强到一定程度(2.4Δ0>3P配)时,[Fe(OH)4(TEA)2]2–的配体场稳定化能小于[Zn(OH)4]2–的配体场稳定化能,Zn–Fe合金共沉积表现为异常共沉积。当电流密度增大时,配离子O和N的给电子能力增强,配合物中心离子d轨道的分裂能随之增大。当分裂能值大到一定程度时,[Fe(OH)4(TEA)2]2–和[Zn(OH)4]2–的稳定性会发生改变,Zn–Fe合金由正常共沉积转变为异常共沉积。

The structure and properties of the complexes of zinc ion and iron-family metal ions in alkaline system were studied based on valence bond theory, crystal field theory and ligand field theory. The energy level division of d orbit and the ligand field stabilization energy （LFSE） of the center ions were explored. From the point of quantum chemistry and structural chemistry, the essence of normal and anomalous codeposition of zinc and iron-family metal ions as well as the transition between normal and anomalous codeposition were illuminated. The results indicated that the electron arrangement in d orbit of the center ion Fe^2＋ in [Fe（OH）4（TEA）2]^2- are t2g^4eg^2 in weak field and t2g^6eg^0 in strong field, and that of Zn^2＋ in [Zn（OH）4]^2- is e^4t2^6. The LFSE of [Fe（OH）4（TEA）2]^2- is higher than that of [Zn（OH）4]^2- in weak field, resulting in a normal codeposition of Zn-Fe alloy; however, when the electron-donating ability of complex is strong enough （2.4△0 〉 3P） in strong field, the LFSE of [Fe（OH）4（TEA）2]^2- is lower than that of [Zn（OH）4]^2-, which causes an anomalous codeposition of Zn-Fe alloy. The electron-donating abilities of complexing ions O and N are enhanced and the division energy ofd orbit in center ion becomes larger with increasing current density. When the division energy is increased to a certain extent, the stability of [Fe（OH）4（TEA）2]^2- and [Zn（OH）4]^2- will change, and the transition from normal to anomalous codeposition happens.