Cs2CuP2O7, a novel low-density open-framework structure based upon an augmented diamond net

Abstract

Abstract The crystal structure of Cs2CuP2O7 [monoclinic, Cc, a=7.460(6), b=12.973(10), c=9.980(8) Å, β=111.95(2)°, V=895.8(12) Å3] prepared by solid-state reactions is based upon open framework formed by corner sharing between CuO4 distorted squares and P2O7 groups. The framework is porous and has a very low framework density of 13.4 Cu+P atoms per 1 nm3. Cs+ cations reside in large framework cavities. The heteropolyhedral network in the title compound is based upon three-dimensional (3;4)-connected net that has a three-membered CuP2 ring as its elementary unit. In terms of reticular chemistry, this net should be considered as an augmented diamond (dia) net. The Cu–P net can be obtained from the latter by the replacement of its nodes by the CuP2 triangles. This replacement is strongly non-centrosymmetric, since all CuP2 triangles are oriented along the same direction, which provides a crystal chemical explanation for the absence of a symmetry centre in the structure. Cs2CuP2O7 is the first compound in the A2CuP2O7 family (A=alkaline metal), which is based upon three-dimensional copper pyrophosphate framework.