Keeping of MVO(XO4)(2) under saturated vapor pressure at room temperature resulted in the synthesis of a number of isostructural complexes M[VO2(XO4)(H2O)(2)] center dot H2O, where X = S, M = K, Rb, NH4, Tl and X = Se, M = K, Rb, NH4. The conclusion about the isostructural nature of the synthesized sulfate and selenate compounds was based on X-ray diffraction and vibrational spectroscopy data. Characteristic features of the thermal decomposition of M[VO2(XO4)(H2O)(2)] center dot H2O on heating in air were identified. It was shown that K[VO2(SeO4)(H2O)(2)] center dot H2O tends to undergo spontaneous dehydration under ambient conditions to give the monohydrate K[VO2(SeO4)(H2O)].