Novel Inclusion Compounds of Urea with Tetraalkylammonium Pentaborates

New crystalline inclusion compounds (n-C3H7)4N+[B5O6(OH)4]−·4(NH2)2CO·H2O (1) and (n-C4H9)4N+[B5O6(OH)4]−·2(NH2)2CO·B(OH)3 (2) have been prepared and characterized by X-ray crystallography. Crystal data, MoKα radiation: 1, space group P21, Z = 2, a = 8.343(2), b = 16.037(3), c = 13.343(3) Å, β = 104.75(3)°, RF = 0.079 for 1820 observed data; 2, space group P21/n, Z = 4, a = 11.582(3), b = 17.270(4), c = 17.819(5) Å, β = 96.85(3)°, and RF = 0.056 for 2291 observed data. Compound 1 has a channel-like host lattice built of urea molecules, pentaborate ions and water molecules, and the (n-C3H7)4N+ cations are arranged in a zigzag column within each channel. In compound 2 the host lattice comprises a stack of two-dimensional infinite layers of inter-connected urea molecules, pentaborate ions, and neutral B(OH)3 molecules. The (n-C4H9)4N+ cations are sandwiched between adjacent layers, while another most unusual guest component, namely a hydrogen-bonded planar ribbon formed by B3O3(OH)2 fragments belonging to different pentaborate ions, threads the central holes of macrocycles within the stacked layers.