Structural evolution and bonding within molybdenum-doped tin clusters, MoSnn (n = 2 – 15)

Tin clusters can form stable, hollow, cage-like structures which are attractive for the fine-tuning and the creation of new materials via the doping of these clusters with a variety of transition metals. Molybdenum is a particularly interesting possibility for doping due to its role in biological nitrogen fixation and its potential use in the improvement of the Haber–Bosch process. Hence, we address herein a detailed study of the structural, energetic, and electronic properties of molybdenum-doped tin clusters (MoSn_n (n = 2 – 15)), using genetic algorithms, density functional theory electronic structure calculations and quantum chemical topology wave function analyses. We considered the last-mentioned type of analyses, because although the properties of metallic nanoclusters depend ultimately on the chemical interactions among their constituent atoms, these studies are scarce. The Quantum Theory of Atoms in Molecules (QTAIM) shows that in MoSn_n clusters with $\mathrm{n\; \ge \; 6}$, the Mo atom undergoes electronic charge depletion, as opposed to expectations based on the relative electronegativities of Mo and Sn. This result indicates that the formation of Sn cages significantly increases their electronegativity compared to isolated tin atoms. The Interacting Quantum Atoms energy partition points that the addition of tin atoms to the system strengthen the interaction among themselves, via the covalent contribution of those Sn atoms which are not linked by QTAIM bond paths. Due to the potential use of Mo-doped clusters in nitrogen fixation, we also considered the adsorption of the N₂ molecule by selected clusters and we note that the considered MoSn_n complexes activate strongly the N  N bond. Altogether, this study illustrates how the examination of the evolutional structure and chemical bonding scenarios of bimetallic complexes might provide valuable insights for the design of custom-designed materials.