Supersalts Na2MgX4 (X = F, Cl): Quantum Chemical Study of the Structure, Vibration Spectra and Thermodynamic Properties

The theoretical study of supersalts Na2MgX4 (X = F, Cl) has been performed. The formation of the supersalts was considered through association reactions between different building blocks: superalkalies and superhalogens, ionic (Na2X+ and MgX3−) and neutral (Na2X and MgX3), as well as dimers Na2X2 and traditional salts MgX2. The optimization of geometrical structures, and determination of vibrational spectra of supersalts and their respective building blocks was carried out by the DFT/B3P86 and MP2 methods; the McLean-Chandler basis set and the extended basis set (cc-pVTZ for Na, Mg; aug-cc-pVTZ for F, Cl) were used. Different possible geometrical configurations for Na2MgX4 were considered, among which two structures: two- cycled structure of D2d symmetry and polyhedral,C2v, were proved to be isomers; their relative concentrations in equilibrium vapour were evaluated. The energies and enthalpies of the association reactions were determined. The enthalpies of formation ∆fH°(0) of gas-phase supersalts found as follows: -1850± 30 kJ×mol-1(Na2MgF4) and -1170±40 kJ×mol-1(Na2MgCl4).