[en] Mechanical mixtures of monocrystals of two polymorphous modifications of lutetium perrhenate tetrahydrate Lu(ReO₄)₃·2H₂O: the earlier described triclinic one and a monoclinic modification, isolated for the first time and belonging to a certain new structural type, are obtained by crystallization of Lu(ReO₄)₃ aqueous solution at 15-20 deg C above H₂SO₄. For monoclinic Lu(ReO₄)₃·4H₂O crystal structure is studied by the X-ray structural analysis method. The crystal lattice parameters are as follows: a = 7.273(1), b = 14.786(3), c = 13.093(2) A, β = 93.63(1) deg, Z = 4, sp. gr. P2₁/n. The structure consist of endless chains along [100], formed by interconnected LuO₈ polyhedrons and ReO₄ tetrahedrons. Chains are linked by hydrogen bond. (author)