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The importance of proper crystal‐chemical and geometrical reasoning demonstrated using layered single and double hydroxides
Author(s) -
Richardson Ian G.
Publication year - 2013
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
eISSN - 2052-5206
pISSN - 2052-5192
DOI - 10.1107/s205251921300376x
Subject(s) - layered double hydroxides , hydroxide , chemistry , crystal structure , crystallography , divalent , crystal (programming language) , tetrahedron , rietveld refinement , thermodynamics , materials science , inorganic chemistry , computer science , physics , organic chemistry , programming language
Atomistic modelling techniques and Rietveld refinement of X‐ray powder diffraction data are widely used but often result in crystal structures that are not realistic, presumably because the authors neglect to check the crystal‐chemical plausibility of their structure. The purpose of this paper is to reinforce the importance and utility of proper crystal‐chemical and geometrical reasoning in structural studies. It is achieved by using such reasoning to generate new yet fundamental information about layered double hydroxides (LDH), a large, much‐studied family of compounds. LDH phases are derived from layered single hydroxides by the substitution of a fraction ( x ) of the divalent cations by trivalent. Equations are derived that enable calculation of x from the a parameter of the unit cell and vice versa , which can be expected to be of widespread utility as a sanity test for extant and future structure determinations and computer simulation studies. The phase at x = 0 is shown to be an α form of divalent metal hydroxide rather than the β polymorph. Crystal‐chemically sensible model structures are provided for β‐Zn(OH) 2 and Ni‐ and Mg‐based carbonate LDH phases that have any trivalent cation and any value of x , including x = 0 [ i.e. for α‐ M (OH) 2 · m H 2 O phases].