Hydrothermal synthesis and characterization of a chromium(II) pyrophosphate, Na2CrP2O7 center dot 0.5H(2)O

The title compound, Na2CrP2O7. 0.5H(2)O, was synthesized hydrothermally usi ng chromium(II) acetate and tetrasodium pyrophosphate. The structure (P2(1) /n, a = 7.7033(2), b = 10.0798(2), c = 8.6667(2) Angstrom, beta = 100.284(1 )degrees, Z = 4) was solved from single-crystal data (R-1 = 0.0327, wR(2) = 0.0785 (I > 2 sigma(I))). The chromium is pentacoordinated by oxygen (4 1) with square pyramidal stereochemistry. Five of the seven oxygen atoms of the P2O74- ion are involved in the coordination of Cr2+. Each P2O74- ions acts twice as a chelating ligand to two Cr2+ ions forming two CrO3P2 rings. Thus, one-dimensional chains of alternating Cr2+ and P2O74- ions are forme d in which the chromium has a square-planar environment. These chains are c onnected to form sheets by coordination to an oxygen of an adjacent chain, thereby giving rise to the pentacoordinated stereochemistly of the Cr2+. Th e compound exhibits Curie-Weiss paramagnetism between 6 and 300 K. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.