Crystal structure Homeotypic

These concepts and their historical development were summarized in a contribution by Laves (1944), translated and reported by Hellner (1979), in which conditions for calling crystal structures equal (isotypism), similar (homeotypism) or different (heterotypism) are discussed and exemplified. 

Ryhlewska, U., and Warzajtis, B. Interplay between dipolar, stacking and hydrogen-bond interactions in the crystal structures of unsymmetrically substituted esters, amides and nitriles of (R,R)-0,0 -dibenzoyltartaric acid, Acta Cryst., Sec. B. 2001, B57, 415-427. Isostructuralism in a series of methyl ester/methylamide derivatives of (R,R)-0,0 -dibenzoyl tartaric acid inclusion properties and guest-dependent homeotypism of the crystals of (2R,3R)-0,0 -dibenzoyltartaric acid diamide, Acta Cryst., Sec. B. 2002,B58, 265-271. 

For the Classification of Minerals , crystal-structure determinations improved the definitions of mineral species and varieties, assisted in the development of the concept of crystal structure types, helped to establish isotypic series and homeotypic and heterotypic groups, and pointed to the recognition of much broader crystallochemical relationships. The X-ray method appreciably simplified the generally unique characterization of a mineral species and led to a reduction in varieties and the discreditation of many minerals accepted up to that time, thereby eliminating countless superfluous mineral names . 

Homeotypy. Homeotypic substances are those that have similar crystal structures, but with different crystallographic space groups and/or chemical compositions. 

Hellner, E. (1965). Descriptive Symbols for Crystal-Structure Types and Homeotypes Based on Lattice Complexes. Acta Ciyst. 19,703 - 712. lUPAC (1990). "Nomenclature of Inorganic Chemistry". Oxford Blackwell. 

BertheviUe B, Herrmannsdorfer T, Yvon K (2001) Structure data for K2MgH4 and Rb2CaH4 and comparison with hydride and fluoride analogues. J Alloys Compd 325 L13-L16 Hines J, Cambon O, Astier R et al (2004) Crystal structures of a-quartz homeotypes boron phosphate and boron arsenate structure-property relationships. Z Krist 219 32-37 Feldmann C, Jansen M (1995) Zurkristallchemischen Ahnlichkeit von Aurid- und Halogenid-lonen. Z anorg allgem Chem 621 1907-1912... 

This paper will give a survey of such an attempt for nearly all cubic structure types and their grouping in families main- and subdasses and homeotypic types it wfll further demonstrate the extension to crystal stmctures with non-cubic symmetry. 

Differences with respect to cell content (the number of atoms per unit cell). Crystals A and B are considered as homeotypic even then, if only parts of the Bau-verb3nde in A and B are equal from a topological point of view. These parts should be composed of those bondings, however, which are believed to be the most important for the structure types under consideration. 

ABSTRACT. Based on the nomenclature report of the lUCr (1990) the concepts of isopointal, isoconfigurational, Isotypic and homeotypic structures are described and illustrated by several examples. The notation proposed In this report for the crystal - chemical formulae is also developed, including the symbologies for close packings which are not closest, and for the condensation process of the structural units. 

In a report presented by Uma-de-Faria, Hellner, Liebau, Makovicky, Parth6 (1990) (henceforth denoted 1990 Report) a detailed analysis of this problem is made, and the following hierarchy of terms is proposed, based on the degree of stmctural similarity Isopointal, Isoconfigurational, crystal chemically Isotypic, and homeotypic structures ... 

Schubert (1989) points out that radius ratio considerations in LaFj would suggest coordination near LaFg, and the LaFj structure should therefore be homeotypic with CaFj. He then relates the LaFj structure to that of CaFj, compares the displacements to those of related structures, e.g., CaFj-YFj superstructures, and discusses crystal energetics. LaFj crystals were examined by DSC from 100 -500 K an anomaly which occurs in the Cp versus T curve is related to a phase transition in which the fluoride sublattice fuses (Aliev and Fershtat 1984). This phenomenon appears related to the high ionic conductivity of the tysonite-type fluoride phases. 

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