Protonation and Water-Mediated Anion Coordination in Organophosph(on)ate–Monourea Assemblies

Hydrogen-bond-directed self-assembly of organophosph(on)ates represents a versatile strategy for constructing functional supramolecular frameworks. To clarify how organophosph(on)ate anions direct urea-based assemblies, a mono(urea) ligand, 1,3-bis(4-nitrophenyl)urea (L), was coordinated with organophosph(on)ate salts to afford three crystalline structures (1–3). Single-crystal X-ray diffraction revealed that 1 and 2 exhibit a tendency to form anion–anion dimers, which assemble with the mono(urea) ligand into A2L2-type (A = anion, L = ligand) units. In contrast, controlled deprotonation in MeCN with trace water generated 3, in which a deprotonated phenylphosphonate (PhPO32–) forms an eight-hydrogen-bond coordination loop comprising three L donors and two water molecules. This multidentate environment resembles the dense hydrogen-bond network found in PTP1B–phosphate complexes. Comparative structural analysis demonstrates a protonation-controlled transition from self-dimerization to multipoint encapsulation, modulated by counter-cations and solvent interactions. These findings provide a molecular-level understanding of organophosph(on)ate-directed hydrogen-bond assembly and establish a readily accessible small-molecule platform for emulating phosphate-mediated recognition motifs relevant to both biomolecular regulation and functional material design.