Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Vill. S. Agata, Salita Sperone 31, I-98166, Messina, Italy.
Dalton Trans. 2010 May 21;39(19):4566-74. doi: 10.1039/b922626e.
In this paper we present an experimental and theoretical study to investigate the electronic structures of [ML₂]⁻ (M(III) = Cu, L = pdt and pds, pyrazine-2,3-dithiolate and -diselonate; M(III) = Au, L = pds) with the aim of elucidating the nature of the bonding and to establish the innocent-noninnocent character of the ligand in these complexes. Calculations based on DFT methods have been performed to obtain geometry optimizations, harmonic frequencies, IR intensities and Raman scattering activities. The experimental vibrational spectra are accurately reproduced by the calculations, which show that CC, CN, and CX (X = S, Se) vibrations are extensively mixed with other modes, and thus unsuitable to work as vibrational markers. Geometry optimization performed at the DFT level provides geometrical parameters in good agreement with the available structural data. The energetic sequence and nature of the redox-active molecular orbitals help to elucidate the observed electrochemical behaviour. Accordingly, the quasi-reversible redox couple for the reduction processes exhibited by [ML₂]²⁻ (L = pdt and pds), that appears at negative values and depends both on the ligand and on the metal, is related to the LUMO which is a σ antibonding combination of the ligand orbitals (sulfur or selenium atoms) and the 3d(xy) (Cu) and 5d(xy) (Au) metal orbitals. The HOMO is a π-orbital with a b(2g) symmetry, predominantly ligand in character with a small contribution of the nd(xz) atomic orbitals in antibonding combination with chalcogen atom orbitals. The low energy of the metal d-orbitals compared to the ligand orbitals, due to the high effective nuclear charge of the metals, explains their small participation to this orbital. Thus in [ML₂]⁻ the metals approach the oxidation state 3+ and the ligand a dichalcogenolate description and thus a prevalent innocent character. However the same ligand shows a noninnocent character in complexes with a different d⁸ metal such as Ni(II) whose d-orbitals lie at higher energies and mix at a higher extent with the ligand orbitals in the HOMO.
本文通过实验和理论研究，探讨了[ML₂]⁻（M(III) = Cu，L = pdt 和 pds，吡嗪-2,3-二硫醇和 -二硒醚；M(III) = Au，L = pds）的电子结构，旨在阐明键的性质，并确定这些配合物中配体的无辜-非无辜特征。基于 DFT 方法的计算已用于获得几何优化、简正频率、IR 强度和拉曼散射活性。实验振动光谱通过计算得到了准确的重现，结果表明 CC、CN 和 CX（X = S、Se）振动与其他模式广泛混合，因此不适合作为振动标记。在 DFT 水平上进行的几何优化提供了与可用结构数据非常吻合的几何参数。氧化还原活性分子轨道的能量序列和性质有助于阐明观察到的电化学行为。因此，[ML₂]²⁻（L = pdt 和 pds）还原过程中表现出的准可逆氧化还原对，出现在负值且取决于配体和金属，与 LUMO 有关，LUMO 是配体轨道（硫或硒原子）和 3d(xy)（Cu）和 5d(xy)（Au）金属轨道的σ反键组合。HOMO 是一个具有 b(2g)对称性的π轨道，主要是配体性质，并有少量 nd(xz)原子轨道与硫属原子轨道反键组合。由于金属的有效核电荷较高，金属 d 轨道的能量低于配体轨道，这解释了它们对该轨道的小贡献。因此，在[ML₂]⁻中，金属接近 3+氧化态，配体具有二硫代和二硒代描述，因此具有主要的无辜特征。然而，在具有不同 d⁸ 金属（如 Ni(II)）的配合物中，相同的配体表现出非无辜特征，其 d 轨道位于较高的能量，并在 HOMO 中与配体轨道混合得更高。
