Hydrogen-Bonded Networks of Ammonium Bis- and Tetrakisphosphonates—Synthesis, High-Throughput Screening and Structural Trends

Benzylbisphosphonic acid C6H5-CH(PO3H2)2, H4L, and 1,4-phenylenebis(methylidyne)tetrakis(phosphonic acid), H8L, were synthesized and characterized. In a combinatorial approach, their reactions with a library of amines were investigated. The crystal structures of (NH3CH2-C6H4-CH2NH3)1.5 [C6H5-CH(PO3)2H]·4H2O, 2(H4L)·3b, (C6H5-NH3)2[C6H5-CH(PO3)2H2], H4L·2c, (C5H10NH2)[C6H5-CH(PO3)2H3], H4L·i, (C5H5NH)[C6H5-CH(PO3)2H3], H4L·m, (NH3-C2H4-NH3)0.5[C6H5-CH(PO3)2H3)]·CH3OH, 2(H4L)·n, (C3N6H7)2[C6H5-CH(PO3)2H2]·4H2O, H4L·2s, and (NH3CH2-C6H4-CH2NH3)[H3(PO3)2CH-C6H4-CH(PO3)2H3]·1.5H2O, H8L·b, could be resolved and studied with special regard to the hydrogen-bonding of the molecular building blocks. Four different motifs of hydrogen bonding between the phosphonate groups could be observed: a single hydrogen bond, a dimeric R22(8) ring motif, the association of two bisphosphonate units into a dimer by two 2-fold hydrogen bonds, and an intramolecular hydrogen bond forming a six-membered ring. Cross-linking of the bisphosphonate groups via [O−H···O] bridges between phosphonates and in some cases solvent molecules generates two-dimensional networks. In the presence of a bifunctional organoammonium ion with a size-suitable rigid spacer unit, [N−H···O] bridges extend the network to the third dimension. All compounds provide structures with hydrophobic and hydrophilic regions.