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

Abstract

Two polymorphous forms of the piperazinium zincophosphate (ZnPO) conditions from mixtures of ZnCl2, H3PO4 piperazine and H3BO3 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 (C4N2H12)[Zn2(HPO4 )3], space group P21/c, Z = 8) is reported for the first time, polymorph II (formulation (C4N2H12)[Zn2(PO4) (H1.5PO4)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 [H3O4(P)4] groupings (hydroxyl nests). A diprotonated piperazine molecule is enclosed in every [4668] 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 [H3O4(P)4] groupings. © 2002 Elsevier Science Inc. All rights reserved.