Size-dependent superhalogenicity and ring currents of tantalum doped platinum clusters TaPt n-1 -/0 (n = 2-21).

The anionic and neutral TaPt n-1 -/0 clusters, with n = 3-21, are systematically investigated using density functional theory (B3PW91/def2-TZVP). Their structural evolution is rationalized by four representative building units, TaPt3 -/0, TaPt7 -/0, TaPt13 -/0 and Ta@Pt18 -/0, corresponding to triangular, near triangular-pyramidal, basket-like and bipyramidal structures, respectively. The Ta dopant preferentially occupies a near-central site to maximize coordination and Ta-Pt bonding. An exohedral-to-endohedral transition occurs at n = 19, with full encapsulation established from Ta@Pt18 -/0 onward. Ta doping markedly increases binding energies relative to pure Pt n -/0 clusters, with the anionic series generally being more stable. Pronounced electron affinity values in the range of ∼3.0-3.4 eV are obtained for TaPt3, TaPt7, TaPt13 and Ta@Pt18, indicating a quasi-superhalogen character of these magic sizes. Charge redistribution is strongly geometry-dependent, shifting from Ta → Pt donation in the exohedral TaPt3 - to increasingly important Pt → Ta donation as the framework grows and Ta occupies an endohedral position in the TaPt7 -, TaPt13 - and Ta@Pt18 -. Extensive multicenter electron delocalization is consistent with coherent ring currents in TaPt13 -, confirming active Ta participation in the coherent electronic motion.