Valence-Electron Control of Mono-, Di-, and Tri-Noble-Gas (He-Kr) Binding to Electron-Deficient Main-Group Centers.

The interactions of noble gases Ng = He, Ne, Ar, Kr with highly electron-deficient main-group fragments are systematically investigated by using high-level CCSD and CCSD(T) calculations. A broad set of electrophilic acceptors is considered, spanning six-electron (O, S, F, Cl, Br, OH, SH, NH), four-electron (BF, AlF), and two-electron (BeF, MgF) centers. Optimized geometries, interaction energies, and electronic descriptors reveal a continuous evolution of Ng binding behavior across the series from weak polarization-dominated interactions for He and Ne, to donor-acceptor bonding for Ar, and to strongly covalent-like coordination in Kr complexes. The analysis, supported by natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), symmetry-adapted perturbation theory (SAPT), and molecular electrostatic potential (MESP) descriptors, demonstrates that the strength and multiplicity of Ng binding are governed primarily by the electrophilicity and valence-electron deficiency of the acceptor fragment with noble-gas polarizability modulating the interaction strength. Within this context, a unified 2e-4e-6e valence-electron framework is employed as a descriptive tool to rationalize why six-electron centers preferentially bind one Ng atom, four-electron centers stabilize two Ng atoms, and highly electron-deficient two-electron centers accommodate three Ng atoms. Among the multi-noble-gas complexes examined, BeF and MgF are found to stabilize tri-noble-gas adducts across the He-Kr series, with KrBeF exhibiting the strongest overall binding. Trihelium coordination to BeF, with interaction energies of several kcal mol per He atom, highlights the remarkable stabilization that can arise in extreme electron-deficient environments. Overall, the results provide a unified and internally consistent framework for organizing mono-, di-, and tri-noble-gas binding motifs across the noble-gas series, clarifying the electronic factors that govern noble-gas coordination in highly electrophilic chemical regimes.