Hg–Hg bonding and its influence on the stability of (HgS)n clusters

Abstract

Pulsed laser ablation of a HgS_(s) precursor shows the formation of small cluster ions, (HgS)_n=2–4⁺, together with HgS_n=1–8^± and [(HgS)_n + S_m]^±. The computed structure, atomization energy, and HOMO–LUMO gap energy values of the lowest energy ring singlet show stable (HgS)_n=2–8. However, the computed bond conductance of the Hg–Hg bond in (HgS)_n shows a high value for (HgS)_n=2–4 (ξ = 1.072–0.122), whereas it is low for (HgS)_n=5–8 (ξ = 0.039–0.006) and decreases significantly as the ring expands, indicating that (HgS)_n≥5 is unstable. It evidences that the weak chemical bonding between Hg²⁺–Hg²⁺ closed shell (5d¹⁰–5d¹⁰) electrons plays a significant role in the stability of ring (HgS)_n=2–4. Thus, it validates the experimental observation of stable cluster ions up to (HgS)₄⁺. In contrast, the low energy chain triplet (HgS)_n=2–8 shows a progressive increase in stability and bond conductance with chain length, indicating sustained mercurophilic interactions in long chain clusters like its crystal structure. Furthermore, the lowest/low energy isomers of HgS_n=1–8 have been computed for their energetics, HOMO–LUMO gaps, and electron affinity using DFT-B3LYP/PBE0 methods.