Atomically Precise Core-Tailored Metal Chalcogenide Nanoclusters: Tuning the Electronic Structure and Magnetic Properties

Recent advances in the experimental and theoretical approaches have made it possible to design and synthesize small clusters and nanoparticles with desirable properties using atom-by-atom substitution. One of them is the well-defined superatomic cluster Co₆S₈L₆⁺(L = PEt₃). Herein, we present a synergistic study, involving theory and experiments, of the incorporation of the first-row transition metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co. Ni, Cu, and Zn) into the core of this cluster. We use the density functional theory to examine the effect of each of the substituted heteroatoms on the stability, electronic structure, and magnetic properties of the doped clusters. Experimentally, we use high-resolution electrospray ionization mass spectrometry and ion mobility spectrometry to examine metal incorporation into the cluster core and its effect on its structure. Theoretical calculations show that, except for Cu and Zn, it is energetically possible to replace a Co atom in the core with all 3d-transition metal atoms. However, with our synthetic method, only Mn, Ni, and Fe incorporation has been achieved experimentally. We propose that the incorporation of other metal atoms, while thermodynamically favorable, is hindered by side reactions. The high probability of formation of stable Co₅MnS₈L₆, Co₅FeS₈L₆, and Co₅NiS₈L₆clusters is found to be due to three types of molecular orbital overlap: 3d of the hetero atoms (Mn, Fe, and Ni) with Co 3d, S (sulfur) 3p, and P (phosphorus) 3p in Co₆S₈(L)₆. We further show that the incorporation of the 3d transition metal atoms into the Co₆S₈core can tune their magnetic properties as well as the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). While the bare core of the Co₆S₈cluster is magnetic with a large magnetic moment of 10 μ_B, the ligated Co₆S₈L₆cluster is nonmagnetic. Meanwhile, Co₅MnS₈L₆, Co₅FeS₈L₆, and Co₅NiS₈L₆carry finite magnetic moments. Similarly, the HOMO-LUMO energy gap in the ligated Co₅MS₈L₆clusters can be tuned in the range between 0.19 and 1.21 eV. This study identifies a strategy for tailoring the electronic and magnetic properties of stable metal chalcogenide clusters for potential applications in spintronics, catalysis, and molecular electronics.