Two polymorphs of a piperazinium zincophosphate with different interrupted SOD-type frameworks

Abstract

Two polymorphous forms of the piperazinium zincophosphate (ZnPO) (C 4N 2H 12)[Zn 2P 3O 12H 3] have been obtained under mild hydrothermal conditions from mixtures of ZnCl 2, H 3PO 4 piperazine and H 3BO 3 in ethylene glycol/water solvents. Single-crystal X-ray structure analyses revealed that both polymorphs possess an open-framework structure with sodalite (SOD) topology. While polymorph I (formulation (C 4N 2H 12)[Zn 2(HPO 4) 3], space group P2 1/c, Z=8) is reported for the first time, polymorph II (formulation (C 4N 2H 12)[Zn 2(PO 4)(H 1.5PO 4) 2], space group C2/c, Z=4) is a known phase. Its structure has been reinvestigated in order to unambiguously determine the hydrogen bonds. The interruptions in the ZnPO host structures possess the form of distorted tetrahedral [H 3O 4(P) 4] groupings (hydroxyl nests). A diprotonated piperazine molecule is enclosed in every [4 66 8] cage. The polymorphs differ in the host–guest N–H⋯O and C–H⋯O interactions, the degree of condensation of the distinct phosphate tetrahedra, the hydrogen-bonding systems in the interruptions, and the long-range ordering of interruptions in the host frameworks. Considerable differences are seen for the donor–acceptor O⋯O distances (ranging from 2.47 to 3. 14 Å) in the total of three distinct [H 3O 4(P) 4] groupings.