Structural evolution and gas-induced electronic, vibrational, and magnetic responses in Mo-centered boron nanoclusters.

Mo-centered boron nanoclusters emerge as a striking platform where multicenter bonding and metal-boron hybridization enable programmable nanoscale functionality. We uncover a coordination-driven structural transition in MoBn clusters from planar molecular wheels (n = 8-10) to highly coordinated double-ring drums (n = 16-20), accompanied by enhanced thermodynamic stability and widening electronic gaps. MoB10 and MoB20 stand out as exceptionally robust motifs, combining high symmetry with large HOMO-LUMO gaps of up to 2.5 eV. Gas adsorption reveals strongly analyte-specific responses: in MoB10, CO and NO induce opposite band-gap shifts, enabling clear electronic discrimination, whereas MoB20 preserves its gap while exhibiting adsorption-site-dependent behavior ranging from strongly chemisorbed to highly reversible binding. Distinct red shifts of the C-O and N-O stretching modes generate unambiguous spectroscopic fingerprints of adsorption strength and geometry. Remarkably, adsorption on MoB9 quenches its intrinsic magnetic anisotropy, directly linking chemical binding to spin-orbit-driven magnetic behavior. These results establish Mo-centered boron wheels and drums as multifunctional nanoscale building blocks that integrate structural tunability, electronic selectivity, vibrational detectability, and magnetic responsiveness within a single borometallic framework.