Hydrothermal reversible interconversion of two zincophosphates with three-dimensional open frameworks containing diprotonated 1,4-diazacycloheptane molecules

A new zincophosphate (ZnPO), (C5H14N2)[Zn2(HPO4)3] (I), has been synthesized in the presence of 1,4-diazacycloheptane under mild hydrothermal conditions (160 °C) and the crystal structure determined by single-crystal X-ray crystallography. Corner-sharing ZnO4 and HPO4 tetrahedra are arranged into layers that are based on the 2D, three-connected 4.82 net and linked together by tetrahedral HPO4 pillars into the 3D interrupted open framework. The 3D intersecting channel system is filled with diprotonated amine molecules. It has been observed that I forms via hydrothermal transformation of a known ZnPO hydrate, (C5H14N2)[Zn2(HPO4)3]·H2O (II), with a closely related 3D open-framework structure, involving dehydration and reconstruction of Zn–O–P linkages. Interestingly, this transformation is completely reversible under hydrothermal conditions at temperatures between 100 and 160 °C with II and I being stable at low and high temperature, respectively. Also, I and II can be interconverted via solid–gas reactions. Crystal data for I: Orthorhombic, space group image, image, image, image, image, image.