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Structure of ice. V

Kamb, Barclay and Prakash, Anand and Knobler, Carolyn (1967) Structure of ice. V. Acta Crystallographica, 22 (5). pp. 706-715. ISSN 0365-110X.

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Ice V, the high-pressure ice phase stable at pressures of about 3 to 6 kbar, density 1.23 g•cm^(-3), has a structure involving 28 H_2O molecules in a monoclinic cell of dimensions ɑ = 9•22, b= 7•54, c = 10•35 Å, β = 109•2°, space group A2/ɑ. The structure is a single tetrahedral framework, rather than a 'self clathrate' as occurs in the denser forms ice VI and VII. Each oxygen atom is hydrogen bonded to 4 near neighbors at distances of 2•76-2•87 Å (average, 2•80 Å), and the shortest next-nearest neighbor distance is 3•28 Å. Distortion from ideal tetrahedral coordination is rather large, bond angles (at oxygen) ranging from 84 to 128 °, with a r.m.s, deviation of 18° from 109•5°. There is no indication of bifurcated hydrogen bonds. Proton ordering is not possible in the space group A2/ɑ indicated for the oxygen atoms. A proton-ordered structure is possible in space group Aɑ, but is considered unlikely on the basis of comparison with X-ray evidence for proton order in ice II. For the ice V structure to remain proton disordered on quenching to 120°K (the experimental conditions), the ordering energy must be less than 0•14 kcal.mole^(-1).

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Additional Information:© 1967 International Union of Crystallography. Received 20 July 1966. The crystallographic calculations were carried out with the CRYRM (IBM 7094) program written by R. E. Marsh, D. Duchamp, N. C. Webb, A. P. Kendig, C. M. Gramaccioli, T. A. Beineke, R. H. Stanford, and others. We are grateful to R. E. Marsh and R. Deverill for help with the computations. J. A. Doutt assisted in collecting the single-crystal data. The powder data at high pressure were obtained in collaboration with B. L. Davis.
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Deposited By: Ruth Sustaita
Deposited On:13 Sep 2016 23:17
Last Modified:03 Oct 2019 10:29

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