Entropy and crystal structure of hydrates of disodium hydrogen phosphate

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){de...

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Bibliographic Details
Published in:Journal of physical chemistry (1952) 1990-10, Vol.94 (20), p.7830-7834
Main Authors: Templeton, David H, Ruben, Helena W, Zalkin, Allan
Format: Article
Language:English
Subjects:
360602 - Other Materials- Structure & Phase Studies
360603 - Materials- Properties
ALKALI METAL COMPOUNDS
Chemistry
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DATA
DIFFRACTION
ENTROPY
Exact sciences and technology
EXPERIMENTAL DATA
INFORMATION
Inorganic chemistry and origins of life
MATERIALS SCIENCE
MEASURING METHODS
NUMERICAL DATA
OXYGEN COMPOUNDS
PHOSPHATES
PHOSPHORUS COMPOUNDS
PHYSICAL PROPERTIES
Preparations and properties
SCATTERING
SODIUM COMPOUNDS
SODIUM PHOSPHATES
THERMODYNAMIC PROPERTIES
TRICLINIC LATTICES
X-RAY DIFFRACTION
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Summary: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.
ISSN:0022-3654
1541-5740
DOI:10.1021/j100383a017