Theoretical Studies on the Structures of Metal String Complexes Cr(L)Cl ( = 3, 5, 7; L = Oligo-α-Pyridylamide) under the Effect of an Electric Field.

To study the electronic structures and properties of [Cr(L)Cl] ( = 3, L = dpa: di(2-pyridyl)amido; = 5, L = tpda: tripyridyldiamido; = 7, L = teptra: tetrapyridyltriamine) metal string complexes, the BP86 method was used by considering the influence of the electric field (EF) applied parallel to the metal axis. As the EF increases, the migration of more positively charged Cr is more significant than that of Cr, which results in alternating long-short Cr-Cr bonds. This happens because of the natural charges on the Cr of -, which are more electropositive than those on Cr. The electrons are pulled to the Cr and Cl() atoms at the high-potential side from Cl() at the low-potential side by the EF, which leads to asymmetrical FMOs. After the critical electric field (), the configuration turns into a remarkably asymmetric one with alternating Cr-Cr quadruple bonds and weak interactions. The electrons are transferred from equatorial ligands (L) to metal chains. In the meantime, the asymmetry of the FMOs increases and the delocalization is further reduced, which affects the conductivity. Especially for [Cr(teptra)Cl], the delocalized electrons of HOMO are completely transformed into a localized model after the critical electric field. It is observed that this supports the electric switching phenomenon ascribed to the conformations of delocalized and localized electrons. In addition, the longer the length of the metal chain, the smaller the and the easier is for the complexes to be polarized by the EF.