[en] By means of exchange reaction of nonachloro-(bromo) dimolybdates (3) of monoethanolammonium with tetraethylammonium chloride in acid medium (HCl or HBr) nonahalogenodimolybdates (3), containing cations of tetraethylammonium and hydrated protons, have been prepared. The compounds isolated are characterized by element analysis, methods of IR and electron spectroscopy, thermogravimetry, X-ray phase analysis. X-ray diffraction analysis of (Et₄N)₂(H₇O₃)[Mo₂Cl₉] is carried out. In crystal lattice of the compound two independent Mo₂Cl₉^3- ions with Mo-Mo distances 2.748(3) and 2.738(3)A are contained. Hydrates of H₉O₄⁺ and H₅O₂⁺ protons form hydrogen bonds with complex anions. Temperature dependence of magnetic susceptibility is investigated and exchange integral of the compounds prepared are calculated. Their thermal properties are studied and thermolysis processes are discussed