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.