A new layer type inclusion complex, (C₄H₉)₄N⁺[1,3,5 C₆H₃(COOH)₂(COO^-)]·2H₂O, has been prepared and characterized by X-ray crystallography. Crystal data: monoclinic, P2₁/c, a=1.3621(2) nm, b=1.3691(2) nm, c=1, 6094(2) nm, β=109.665 (3)°, V=2. 8261(7) nm 3, Z=4, R₁=0. 0508, wR=0. 1217. In the crystal structure of the title compound, trimesate anions are linked by single O-H...O hydrogen bonds to form a zigzag ribbon parallel to the b axis. The carboxylates C(3) and C(5) of two neighboring trimesate anions are further consolidated by a bridging water dimer formed by two independent water molecules via a single hydrogen bond to generate a trimesate water wide chain. Further hydrogen bonds between water dimer and carboxylate C(1) of adjacent ribbon are formed and two dimensional puckered layer parallel to the (001) family of planes is thus formed. The tetrabutylammonium cationic layers are located at c=0 and c=1/2 in the unit cell and sandwiched between adjacent hydrogen bonded trimesate water layers at c=1/4 and 3/4.

Key words: trimesic acid, tetraalkylammonium cation, hydrogen-bonding, inclusion compound, crystal structure