Structure and Hirshfeld surface analysis of two piperazine guest supramolecular inclusion complexes

Abstract Two piperazine guest supramolecular inclusion complexes, (1) [MePa][Zn(H2PO4)2] (MePa = methylpiperazine, C5H12N2) and (2) [Pa][PHBA]·H2O (Pa = piperazine, C4H10N2; PHBA = p-hydroxybenzoic acid, C7H5O3) has been investigated structurally in the solid state. The host [Zn(H2PO4)2]n in (1) forms a rigid grommet to wrap the guest [MePa] in the grommet channel. The host PHBA in (2) with water molecules form rectangular building blocks from four directions, leaving cylindrical channels to the guest Pa. The guest piperazine molecules in two complexes are all stabilized and orderly arranged by supramolecular acting force which displays high symmetry. This kind of inclusion without changing the guest molecular structure is helpful for the study of drug sustained-release agents. Hirshfeld surface analysis showed that there were strong intermolecular forces on the surface of the two supramolecular inclusion crystals, which made the crystal structure very stable. Thermogravimetric analysis showed that complexes (1) and (2) had better thermal stability.