Entropy and crystal structure of hydrates of disodium hydrogen phosphate

Autor:	David H. Templeton, Helena Ruben, Allan Zalkin
Rok vydání:	1990
Předmět:	chemistry.chemical_compound Crystallography chemistry Proton Hydrogen bond Scattering X-ray crystallography General Engineering Crystal structure Physical and Theoretical Chemistry Triclinic crystal system Sodium phosphates Residual entropy
Zdroj:	The Journal of Physical Chemistry. 94:7830-7834
ISSN:	1541-5740 0022-3654
DOI:	10.1021/j100383a017
Popis:	Structures determined by X-ray diffraction are reported for crystals of Na{sub 2}HPO{sub 4}{center dot}xH{sub 2}O (x = 1, 2, 7, and 12). The new monohydrate phase is triclinic, space group P{bar 1}, a = 5.575 (1) {angstrom}, b = 7.949 (1) {angstrom}, c = 5.735 (1) {angstrom}, {alpha} = 103.83 (1){degree}, {beta} = 102.15 (1){degree}, {gamma} = 107.47 (1){degree}, Z = 2, R = 0.020 for 3329 independent reflections. The other structures are in agreement with independent determinations already published. For x = 1, 2, or 7 no disorder is observed, and there are unique configurations of protons in hydrogen bonds. The dodecahydrate (x = 12) has two kinds of disorder, randomness of phosphate ion orientations and of proton positions in hydrogen bonds. A model for this disorder gives 2.65 cal K{sup {minus}1} mol{sup {minus}1} as the residual entropy at low temperature, compared with 3.1 {plus minus} 0.5 and 3.5 {plus minus} 0.4 cal K{sup {minus}1} mol{sup {minus}1} derived from two thermodynamic cycles.
Databáze:	OpenAIRE
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