[Be(NH ₃ ) ₁₆ ] ^[2] ⁺ Microsolvation: Structure, Energetics, and Temperature Effects

Abstract

Gas‐phase structural, energetic, and thermal properties of the [Be(NH 3 ) 16 ] 2 cluster are investigated by using the MP2/6‐311++G** level of theory. The relative stability of isomers is explained evidencing the long‐range electrostatic interactions and the spatial arrangement of NH 3 ligands around Be 2 + cation. The computed isomers binding strength and energies values are compared with that with beryllium cation coordinated from n = 1–6 ligands. A fitting approach yields an asymptotic binding energy of –32.2 kcal mol −1 . Clustering energies suggest a compact and strongly bound first solvation shell, with weaker, secondary interactions beyond four to five ligands. The cluster thermal behavior is probed through temperature‐dependent solvation enthalpies (Δ H ) and free energies (Δ G ) in gas phase. Results show that Δ G slightly decreases with temperature, while Δ H increases, emphasizing the role of entropy in thermal stabilization. Finally, Quantum Theory of Atoms in Molecules analysis reveals the coexistence of Be 2 + N coordination bonds and a network of NH…N hydrogen bonds. These cooperative noncovalent interactions significantly enhance both structural and energetic stability.