An atomic structure of complex Et4N[Eu(ТТA)4] (TTA is the thenoyltrifluoroacetonate anion, Et4N+ is the tetraethylammonium cation) possessing strong luminescence and triboluminescence was determined by X-ray crystallography. The crystal system of centrosymmetric crystals is monoclinic: a = 10.2495(1) Å, b = 20.2162(3) Å, c = 23.5788(3) Å, β = 102.551(1)°, space group P21/c, Z = 4, d calc = 1.625 g cm–3. The crystals of the compound have an isle structure, which comprises individual complex anions [Eu(TTA)4]– and tetraethylammonium cations Et4N+. The structural aspects of a possible model for the formation of triboluminescent properties were considered, the role of cleavage planes and disordering was discussed.