A new molecular complex of betaine with selenic acid, tetra(betaine) s
elenate, in the solid state and its deuterated analogue have been obta
ined. The phase transitions at ca. 135 K (the first order) and 150 K (
the second order) have been discovered by the DSC method. On deuterati
on the second order phase transition is shifted to higher temperature,
ca. 170 K. The dielectric properties and FTIR spectra of the title cr
ystal are reported as a function of temperature (300-11K).