Biomedical subjects

Frank H Herbstein

Publications and source records attributed to Frank H Herbstein.

4 recordsLinked to original sources

PubMed2006

On the mechanism of some first-order enantiotropic solid-state phase transitions: from Simon through Ubbelohde to Mnyukh.

The first (so-called) lambda transition in solids was found in the specific heat measurements for NH(4)Cl at 242 K by F. Simon in 1922 [Simon (1922). Ann. Phys. 68, 241-280]. Analogous phenomena found in many other solids gave rise to doubts (expressed most clearly by A. R. Ubbelohde some 50 years ago) about the applicability of classical thermodynamics to some phase transitions [Ubbelohde (1956). Brit. J. Appl. Phys. 7, 313-321]. However, Y. Mnyukh's studies of enantiotropic phase transitions in eight organic crystals showed that all proceed by a nucleation-and-growth mechanism [summarized in Mnyukh (2001), Fundamentals of Solid State Phase Transitions, Ferromagnetism and Ferroelectricity. 1st Books]. Nucleation is localized at defects in the parent phase; growth can be epitaxic and oriented if parent and daughter phases have closely similar structures, or random (not oriented) if there are substantial structural differences. This conclusion is supported by a critical review of Mnyukh's eight examples and other results published in the interim. It seems that Ubbelohde's invocation of "hybrid crystals" and "smeared transitions" can mostly be accounted for by lack of equilibrium in the phase-transition studies cited by him. However, the intermediate phase in 4,4'-dichlorobenzophenone appears to have structural resemblances to Ubbelohde's' "hybrid crystal".

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PubMed2003

5-Oxatricyclo[5.1.0.0(1,3)]octan-4-one, containing an enantiomorph and a racemate and not two polymorphs, is another example of a composite crystal.

This new example of a composite crystal adds to the small number previously reported among inorganic and molecular materials. Revision of the nomenclature used allows more fruitful comparison with the precedents.

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PubMed2002

Some errors from the crystallographic literature, some amplifications and a questionable result.

The space groups of [[Mo(2)(O(2)CCH(3))(4)('linker')](n)] are corrected from P1 to C2/m for 'linker' = pyrazine and 1,4-diazabicyclo[2.2.2]octane (dabco) and from P1 to C2/c for 'linker' = 4,4'-bipyridine. Also, [[tris-(2-pyridylmethyl)amine]BrV(mu-O)VBr[tris-(2-pyridylmethyl)amine]]Br.H(2)O is corrected from P1 to C2/c. These Laue class changes allow more reliable crystallochemical comparisons to be made among families of related structures. Space groups are corrected for 4-methyl-2,6-bis(4-methylbenzylidene)cyclohexanone, 2,6-bis(4-dimethylaminobenzylidene)cyclohexanone, K[Cr(tetramethylenediamine-N,N,N',N'-tetraacetate)].H(2)O and [bis(11,-11-dimethyl-3,4:8,9-dibenzobicyclo[4.4.1]undeca-3,8-diene)-(tetracyanoethylene)]. The conflicting reports for Cu(H(2)O)-(phenanthroline)(2)(X)(2), where X = ClO(4), NO(3) and BF(4), are resolved. Three related examples of open framework host-guest structures with space groups 'Cc or C2/c' are discussed. Adding centers to 2,2'-bi-1H-imidazolium dipicrate and [tris(2,2'-bi-1H-imidazole)bis[2-(2-1H-imidazolyl)-1H-imidazolium]bis(iodide)] corrects discrepancies of up to 0.38 A between chemically similar hydrogen-bond distances. Wrongly identified atoms are corrected in theta-[bis(ethylenedithio)tetrathiafulvalene](2) (CsCd)(SCN)(4) and (purported) diaquadihydroxotetrakis(m-nitrobenzenesulfonate)discandium(III). The reported difference between the crystal structure of (CH(3)NH(3))(4)YbCl(7) and those of the other members of this family of (CH(3)NH(3))(4)MX(7) (M = In, Fe, V; X = Cl, Br) structures is pointed out in the context of possibly different N-H...Cl hydrogen bonding in the Yb structure.

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PubMed2001

Some 60 new space-group corrections.

Some 60 examples of crystal structures are presented which can be better described in space groups of higher symmetry than used in the original publications. These are divided into three categories: (A) incorrect Laue group (33 examples), (B) omission of a center of symmetry (22 examples), (C) omission of a center of symmetry coupled with a failure to recognize systematic absences (nine examples). Category A errors do not lead to significant errors in molecular geometry, but these do accompany the two other types of error. There are 19 of the current set of examples which have publication dates of 1996 or later. Critical scrutiny on the part of authors, editors and referees is needed to eliminate such errors in order not to impair the role of crystal structure analysis as the chemical court of last resort.

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