Crystal structure of a host-guest complex of the tris-urea receptor, 3-(4-nitro-phen-yl)-1,1-bis-{2-[3-(4-nitro-phen-yl)ureido]eth-yl}urea, that encapsulates hydrogen-bonded chains of di-hydrogen phosphate anions with separate tetra--butyl-ammonium counter-ions.

The title compound, CHNO·CHN·HPO (I) or (CHNO)·(-BuN)·(HPO ) (systematic name: 3-(4-nitro-phen-yl)-1,1-bis-{2-[3-(4-nitro-phen-yl)ureido]eth-yl}urea tetra-butyl-ammonium di-hydrogen phosphate), comprises a tris-urea receptor (), a di-hydrogen phosphate anion and a tetra--butyl-ammonium cation. It crystallizes with two independent formula units in the asymmetric unit. The conformations of the two tris-urea receptors are stabilized by N-H⋯O and C-H⋯O intra-molecular hydrogen bonds. Each di-hydrogen phosphate anion has two O-H⋯O inter-molecular hydrogen-bonding inter-actions with the other di-hydrogen phosphate anion. Inversion-related di-anion units are linked by further O-H⋯O hydrogen bonds, forming a chain propagating along the -axis direction. Each di-hydrogen phosphate anion makes a total of four N-H⋯O(HPO ) hydrogen bonds with two ureido subunits from two different tris-urea receptors, hence each tris-urea receptor provides the two ureido subunits for the encapsulation of the HPO hydrogen-bonded chain. There are numerous inter-molecular C-H⋯O hydrogen bonds present involving both receptor mol-ecules and the tetra--butyl-ammonium cations, so forming a supra-molecular three-dimensional structure. One of the butyl groups and one of the nitro groups are disordered over two positions of equal occupancy.