sulfidecoordination

Sulfide coordination refers to the binding of sulfide ligands (S2−) to metal centers in coordination chemistry and related fields. Sulfide is a dianionic, soft to borderline two-electron donor that typically provides electrons to a metal through sulfide–metal bonds. In many complexes, sulfide binds terminally to a single metal, forming a direct M–S bond. It can also act as a bridging ligand, connecting two or more metal centers, with common bridging modes described as μ2-S, μ3-S, or higher, depending on the number of metals involved.

Sulfide ligands are prominent in complexes of late transition metals, including iron, cobalt, nickel, molybdenum, and tungsten, and they play a central role in many polynuclear metal-sulfur frameworks. They are especially important in bioinorganic chemistry, where sulfide bridges are key components of iron–sulfur clusters that participate in electron transfer and catalysis.

From an electronic viewpoint, sulfide is a relatively soft donor and often stabilizes lower oxidation states, contributing to strong metal–sulfur bonding and, in clusters, substantial metal–metal connectivity. In electron-counting terms, each sulfide bound to a metal typically contributes two electrons to that metal center.

Sulfide ligands can be introduced from sources such as Na2S or H2S and can undergo protonation to HS− or H2S, influencing ligand lability and reactivity. Sulfide coordination is distinct from thiolate coordination, the latter arising from deprotonated thiols (RS−) and often exhibiting different binding preferences and electronic effects.

Overall, sulfide coordination is a fundamental motif in inorganic chemistry, with relevance to catalysis, materials science, and biological systems.