Chemical preparation, crystallographic characterization, thermal behavior and IR studies of two new cyclotriphosphates SrKP_3O_9 centre dot 3H_2O and SrKP_3O_9

摘要

Strontium and potassium cyclotriphosphate trihydrate, SrKP_3O_9 centre dot 3H_2O, was prepared by ion-exchange resin. It crystallizes in the orthorhombic system Pnma, Z = 4 with the following unit-cell dimensions a = 9.082(2)A, b = 8.133(2)A, c = 15.009(2)A and V= 1108.6(1)A~3. This salt is isotypic of SrRbP_3O_9 centre dot 3H_2O and SrNH_4P_3O_9 centre dot 3H_2O whose crystal structure is determined by X-ray diffraction. Its thermal behavior is studied, between 25 and 800 deg C, by infrared spectrometry, X-ray diffraction, thermal analyses TGA and DTA. SrKP_3O_9 centre dot 3H_2O leads, between 250 and 350 deg C, to the corresponding anhydrous phase, SrKP_3O_9. This new phase is characterized crystallographically as isotype of SrRbP_3O_9. The calcination, between 400 and 650 deg C, leads to a mixture of SrK_2P_4O_(12) crystallized and beta[Sr(PO_3)_2] amorphous phase in X-ray diffraction. This mixture is stable until its melting point at 696 deg C of SrK_2P_4O_(12). The kinetic characteristics of the dehydration of SrKP_3O_9 centre dot 3H_2O are determined. The vibrational spectrum of SrKP_3O_9 centre dot 3H_2O is examined and interpreted, in the domain of the valency frequencies, on the basis of the crystalline structure of its isotypic compounds SrM~IP_3O_9 centre dot 3H_2O (M~I = Rb~+, Tl~+) whose cycle has the site symmetry Cs. This infrared study is also made in the light of our results of the calculation of the IR frequencies and the successive isotopic substitutions of the equivalent atoms (3P, 3Oi and 6Oe belonging to the P_3Oi_3Oe_6 ring) of the P_3O_9~(3-) cycle with symmetry Cs.