Polymorphism of the borophosphate anion in K(Fe,Al)[BP 2 O 8 (OH)] and Rb(Al, Fe)[BP 2 O 8 (OH)] crystal structures
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CTURE OF INORGANIC COMPOUNDS
Polymorphism of the Borophosphate Anion in K(Fe,Al)[BP2O8(OH)] and Rb(Al, Fe)[BP2O8(OH)] Crystal Structures O. V. Yakubovicha, I. M. Steeleb, and O. V. Dimitrovab a
Moscow State University, Moscow, Russia email: [email protected] b University of Chicago, Chicago, Illinois, 60637 USA Received March 24, 2010
Abstract—The crystal structure of two borophosphates, Rb(Al,Fe)[BP2O8(OH)] (a = 9.381(6), b = 8.398(5), c = 9.579(6) Å, β = 102.605(10)°, sp. gr. P21/c) and K(Fe,Al)[BP2O8(OH)] (a = 5.139(2), b = 8.065(4), c = 8.290(4) Å, α = 86.841(8)°, β = 80.346(8)°, γ = 86.622(8)°, sp. gr. P1 ), obtained by hydrothermal synthesis in the AlCl3 : FeCl3 : K3PO4(Rb3PO4) : B2O3 : H2O system has been established using Xray diffraction (Bruker Smart diffractometer, T = 100 K). Hydrogen atoms are located and their coordinates and thermal parameters are refined. It is shown that the polymorphism of the [BP2O8(OH)]4– borophosphate anion has a morphotropic nature and is related to the substitutions both in the cationic part of the structure and in the octahedral position of the anionic mixed framework. The synthesis of new isotypic triclinic compounds under hydrothermal conditions is predicted. DOI: 10.1134/S106377451005007X
SYNTHESIS OF CRYSTALS, XRAY EXPERIMENT, AND STRUCTURE INTERPRETATION
INTRODUCTION Crystals with anionic structures of a mixed type composed of phosphate and borate oxo complexes are a subject of intense and comprehensive study in view of their various physicochemical properties. Boro phosphates are used as catalysts and phosphors and have nonlinear optical and sorption properties; they are also promising anticorrosive and magnetic materi als [1–3]. Borophosphate phases with open microporous frameworks containing metal oxo com plexes have recently been intensively investigated. In view of the crystallochemical variety of these com pounds, one would expect them to have not only the important technological characteristics typical of zeo litelike crystals, but also interesting physical proper ties (antiferromagnetic, ferromagnetic, etc.) deter mined by the type of the metal cations that form, along with boron and phosphorus, such mixed frameworks [4–6]. A large number of compounds described by the general formula AM3+[BP2O8(OH)] have been synthe sized and studied over the last decade [7]. They are crystallized into two structure types, within either a monoclinic or triclinic system. Antiferromagnetic ordering was suggested in [8] for the monoclinic vana dium and iron terms of this group. In this paper, we report the results of studying the two new phases of mixed composition in this series of borophosphates based on lowtemperature experimental Xray data.
Crystals of Fe and Al borophosphates were synthe sized under hydrothermal conditions at Т = 280°С and Р = 70 atm in standard 4cm3 autoclaves lined with Teflon. The weight ratios of the initial compo nents of the AlCl3 : FeCl3 : K3PO4 : B2O3 : H2O and AlCl3 : FeCl3 : Rb3PO4 : B2O3 : H2O systems were 1 : 1 : 1 : 4 : 30
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