Complexation of Ca X 2 With n NH 3 ( X  = H, F; n  = 1–3): Insight From Quantum Chemical and Vibrational Mode Analysis

Quantum chemical methods are employed to investigate the complexation of Ca X 2 with n NH 3 ( X = H, F; n = 1–3). In the presence of Ca X 2 , NH 3 molecules engage in several types of noncovalent interactions, namely, hydrogen bonding (HB), calcium bonding (CB), and dihydrogen bonding (DHB). The Ca X 2 : n NH 3 complexes are primarily stabilized by Ca···N interactions, though other noncovalent contacts also contribute in stabilizing or destabilizing different conformers. Closed ring conformers in Ca X 2 : n NH 3 complexes show high degree of cooperativity together with a consistent increase in Ca···N bond length and decease in H + ···H − / H + ···F − bond length with increasing number of NH 3 molecules. Fragment‐wise interaction energy analysis indicates that two‐body ammonia–metal hydride/fluoride (A i –Ca X 2 ) interactions dominate the total interaction energy, while nonadditive terms contribute up to ∼10% in certain heterotrimer conformers but diminish as the number of ammonia molecules increases. Vibrational mode automatic relevance determination analysis (VMARD) of Ca X 2 : n NH 3 complexes shows unequal contributions from atomic motions within the three different bonds in NH 3 molecule, revealing that complexation induces different intermolecular force constants, leading to loss in symmetry of NH 3 molecules. Pronounced redshift of the symmetric NH stretching mode is consistently observed, accompanied by symmetry lowering of the degenerate asymmetric NH stretching mode.