A Novel Sodium and Chromium Borophosphate Na{Cr[BP2O7(OH)3]}: Synthesis, Crystal Structure, Hydrogen Bonding, and Comparative Crystal Chemistry


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Abstract

A novel sodium and chromium borophosphate, obtained by hydrothermal synthesis in the Na2O–P2O5–B2O3–Cr2O3–Н2О system, has been investigated using X-ray diffraction and IR spectroscopy. The monoclinic cell parameters are found to be a = 10.4220(3) Å, b = 8.2468(2) Å, c = 9.2053(3) Å, β = 116.568(4)°, and V = 707.63(4) Å3; sp. gr. С2/с. The structure is interpreted and refined to the final reliability factor R1 = 2.23% in the anisotropic approximation of atomic displacements using 1311 reflections, I > 2σ(I). The novel compound is relative to the family of alkaline borophosphates with the general formula A{M[BP2O7(OH)3]} (A is an alkaline or alkaline-earth element; M is a transition метал) and is described by the crystallochemical formula (Z = 4) Na{Cr[BP2O7(OH)3]}, where the compositions of borophosphate anion and microporous framework are in square brackets and braces, respectively. The presence of alternative systems of strong symmetric hydrogen bonds is established; the localization of all hydrogen atomic sites has made it possible to analyze them in detail. An additional electron density peak is found, which can be interpreted as a statistically distributed proton H+. The IR spectrum is characteristic of compounds with strong hydrogen bonding; it confirms the statistical proton distribution over subsites around the inversion center. It is suggested that representatives of this family may possess proton conductivity.

About the authors

N. A. Yamnova

Moscow State University

Author for correspondence.
Email: natalia-yamnova@yandex.ru
Russian Federation, Moscow

S. M. Aksenov

University of Notre Dame

Author for correspondence.
Email: aks.crys@gmail.com
United States, South Bend

E. Yu. Borovikova

Moscow State University

Email: aks.crys@gmail.com
Russian Federation, Moscow

A. S. Volkov

Moscow State University

Email: aks.crys@gmail.com
Russian Federation, Moscow

O. A. Gurbanova

Moscow State University

Email: aks.crys@gmail.com
Russian Federation, Moscow

O. V. Dimitrova

Moscow State University

Email: aks.crys@gmail.com
Russian Federation, Moscow

P. C. Burns

University of Notre Dame

Email: aks.crys@gmail.com
United States, South Bend

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