Strong Effect of Organic Ligands on the Electronic Structure of Metal-Chalcogenide Clusters

It is shown that multiple ionization energies of metal-chalcogenide clusters can be substantially reduced by adding ligands that form charge transfer complexes. We demonstrate this intriguing phenomenon by considering metal-chalcogenide clusters including cases where a cluster has a filled electronic shell with a large gap between the occupied and unoccupied states reminiscent of stable species. The studies include a Co₆Se₈ core ligated with tri-ethylphosphine (PEt₃) ligands forming a stable Co₆Se₈(PEt₃)₆ species. All of the ligated clusters have a first ionization energy in the range for alkali atoms and multiple ionization energies that are considerably lower than those for the non-ligated clusters. The change in electronic behavior upon ligation can be associated with a shift in the electronic spectrum via a crystal field like effect due to attaching ligands that form charge transfer complexes. We also show that metal-chalcogenide species can be programmed by proper ligand replacement to promote dimerization by first forming the Co₆Se₈(PEt₃)_<i>n</i>(CO)_6‑<i>n</i> (<i>n</i> = 0–6) clusters where the CO ligands could be replaced by diisocyanide (CNC₆H₄NC) ligands. The diisocyanide ligand acts as a rigid linker between the metallic cores, enabling the formation of a Co₆Se₈(PEt₃)₅(CNC₆H₄NC)­Co₆Se₈(PEt₃)₅ superatomic molecule (SM), and we examine the electronic and magnetic properties of the recently synthesized SM via studies on an analogous SM with smaller ligands