Theoretical study of manganese hydrides and halides, MnXn with X = H, F, Cl, Br and n = 1–4

Highlights: ► The B3P86 functional is found to be reliable in predictions of molecular structures and vibrational spectra. ► The hybrid B3LYP is more reliable for energetic parameters such as heats of formation. ► We also propose several new assignments for heats of formation and ionization energies of a number of species considered. - Abstract: Properties of a series of MnXn with X = H, F, Cl, Br and n = 1–4 are investigated using DFT, CCSD(T) and CASPT2 computations. The B3P86/6-311++G(3df,2d) method appears to be suitable for predicting their structures whose geometries and IR spectra are dependent on the charge state. While MnX2 are linear, MnX3 and MnX4 are characterized by high symmetry shape. The π-bonding type is observed for MnH30/+ and MnH40/+. In halides, a different type of bonds is formed as p-orbitals of halogens can overlap with empty metal d-orbitals allowing a more effective electron transfer and high spin ground electronic states. Vibrational frequencies and basic energetic quantities are computed and compared with available experiments. Several previous thermochemical quantities are re-evaluated, and the heats of formation of Mn-compounds can be determined with reasonable accuracy using the B3LYP functional. However, while calculated ionization energies are in agreement with experiment, electron affinities are obtained with large deviations.