A2BX4single crystals (A = Cs, Rb, N(CH3)4; B = Cd, Zn, Mn, Fe; X = C1, Br, I) with β−K2SO4type structure belong to the compounds with the different phase transitions (PT), including PT into incommensurate structure. The persistence of the transitions metals play an important role in the investigations of PT by the ligands field in the types of crystals, in particular, in the vicinity of phase transition. The nature of the corresponding phase transitions is closely connected with the tetrahedral complexes [B2+X4]2−bounded by A−cations. The Mn2+ions were chosen due ithe persistence of the five external d-electrons, which are highly sensitive to the external fields. The present work deal with experimental and theoretical investigation of the electronic band structure and optical parameters of [N(CH3)4]2MnCl4and Cs2CdI4single crystals.