Ethane-1,2-diphosphonic acid as a building block in supramolecular chemistry; a pillared-layer framework and framework-encapsulated cations

The 1:1 adduct of piperazine and ethane-1,2-diphosphonic acid is a salt [C4H12N2](2+). [C2H6O6P2](2-), in which both ions lie across centres of inversion in space group P2(1)/c. The anions are linked by a single type of O-H . . .O hydrogen bond [O . . .O, 2.562 (3) Angstrom; H . . .O, 1.73 Angstrom, O-H . . .O, 169 degrees] into (6, 3) nets built from a single type of R-4(4)(22) ring. The cations lie between these nets, linked to them by two types of N-H . . .O hydrogen bond [N . . .O, 2.635 (3) and 2.735 (3) Angstrom; H . . .O 1.72 and 1.82 Angstrom, N-H . . .O, 175 and 177 degrees] such that the cations link adjacent sheets, thus forming a pillared-layer framework. The aquated adduct formed between trimethylenedipiperidine and ethane-1,2-diphosphonic acid is also a salt [C13H28N2](2+). [C2H6O6P2](2-).2.8[H2O], in which there are 12 different types of hydrogen bond, eight O-H . . .O and four N-H . . .O. The anions are linked into chains by pairs of O-H . . .O hydrogen bonds and these chains are linked by the water molecules into a continuous three-dimensional framework. Within the anion/water framework are large voids which contain pairs of cations, linked to the framework by N-H . . .O hydrogen bonds.