Evolution of the dizincocene metal-metal bond in the series Zn2L2 where L = H, CH3, F, η5-C5H5

Ab initio plane-wave-based density functional calculations for the molecules Zn2L2 with the ligands L = H, CH3, F, η5-C5H5 (cyclopentadienyl Cp) show how the ZnZn and ZnL bonds evolve to dimetallocene from simple H to the electronically and spatially extended Cp ligand. The metal-metal bond distances (pm) decrease in the order: 240.2 (H), 239 (CH3), 230.4 (F), 230 (Cp) compared to distances: 266 (Zn metal), 246 (Zn22+), 230.5 (crystalline Zn2[C5(CH3)5]2). Analysis is supported by calculation of the total charge and partial charge density distributions and the electron localization function (ELF). In the dizinc region, the ELF consists of a separate ring (torus) and mid-bond axis basin. For molecules with the ligands H, CH3, and F, the mid-bond basin attractor appears on the bond axis at higher ELF followed at lower values by the ring. For Cp, the reverse is true. In the Cp compound, the bonding from ring to metal atom involves both sigma σ-contributions with s-, p-, and d-components and π-contributions with p- and d-components. In the Cp compound, the ELF shows some differentiation in the CC bonding within the C5 ring towards three single C-C and two double CC bonds.