A series of bis-alkyltrimethylammonium dichromates (CnH2n+1(CH3)(3) N)(2) Cr2O7. x H2O (where n = 8, 10, 12, 14, 16, 18, and 0 less than or equal tox less than or equal to2) compounds (ATMACr) was synthesized from alkyltrimethylammonium bromide and K2Cr2O7. The phase transitions and mesogenicity of these substances were studied by X-ray diffraction, DSC measurements, and FT-IR observations. In the series of hydrated ATMACr compounds, the decreasing of the DeltaS(Sm-I) phase transition values with the alkyl chain length n increase, suggest that the disorder in the smectic A phase is dependent on the carbon. From the temperature dependence of DTMACr IR spectra, the increase of the CH2 stretching vibrations frequency and the bandwidth accompanied by a lowering of the peaks intensity can be ascribed to the introduction of a high degree of conformational and motional disorders into the alkyl chain.