Theoretical studies on the structures of one-dimensional Nin (n = 3, 5, 7) metal string complexes under the effect of electric field

Abstract

Metal string complexes Ni3(dpa)4C12(1), Ni5(tpda)4Cl2(2) and Ni7(teptra)4Cl2(3), have been investigated with density functional theory BP86 method by considering the effect of an external electric field (EF) along the Nin2n+ chain. With the increasing EF, the negative charge of Cl at the low potential end decreases, while that at the opposite end increases. There is no electron-transfer between the metal chain and the equatorial ligands. The spin densities of Ni and Cl at the high potential end decrease, while increasing at the opposite end. When the EF is larger than 2.056V·nm−1, the spin densities on Ni ions of Ni7(teptra)4Cl2 in the quintet state change significantly due to orbital mixing of δNi–N∗(3) and σ∗. The Ni–Cl distances at the high potential end and the Ni–Ni distances at the low potential end increase, while those at the opposite end decrease. Furthermore, the distributions of frontier occupied orbitals move toward the low potential end and their energies increase, whereas those of the unoccupied orbitals move to the opposite end and their energies decrease. Therefore, the HOMO–LUMO gaps decrease. These features are more pronounced with increasing metal chain length. Tuning the size of the metal string has a profound effect on the electron transport.