New kind of electride sandwich complexes based on the cyclooctatetraene ligand M 1 2 (η 8 -C 8 H 8 ) 2 M 2 2 (M 1 = Na, K and M 2 = Ca, Mg): a theoretical study

In the present study, the electronic structures of a series of binuclear sandwich complexes based on the cyclooctatetraene ligand M (η -C H ) M (M = Na, K and M = Ca, Mg) are studied theoretically. Each cyclooctatetraene ligand binds with the metal in the η binding mode. The M -M bond length agrees well with the reported bimetallic covalent Ca and Mg bond lengths. The Wiberg bond index (WBI) also indicates the presence of covalent M -M bonds, which gives additional stability to the complex. A non-nuclear attractor (NNA) is found in-between the M -M bond and the negative Laplacian of the electron density is found at the NNA. Noncovalent interaction (NCI) plot shows that electron density is localized at the M -M bond. Based on the performed analysis, we have concluded that the designed sandwich complexes are electrides. We herein report, for the first time, the electride sandwich complexes of the cyclooctatetraene ligand. Due to the presence of a diffuse electron system, the electride complexes exhibit higher values of the static second hyperpolarizability within the range of 2.6 × 10 to 1.4 × 10 a.u. Among the studied complexes, M (η -C H ) Ca exhibit a higher value of static second hyperpolarizability.