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Subject: Re: Old Chem in Britain Article on Wrong Structures and False Minima?? -- From: boyle@laue.chem.ncsu.edu (Paul D. Boyle)
Subject: Re: Old Chem in Britain Article on Wrong Structures and False Minima?? -- From: jvs@helix.nih.gov (James V. Silverton)

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Subject: Re: Old Chem in Britain Article on Wrong Structures and False Minima??
From: boyle@laue.chem.ncsu.edu (Paul D. Boyle)
Date: 30 Dec 1996 22:28:02 GMT
Lachlan Cranswick (lachlan@melbpc.org.au) wrote:
: I'm wondering if someone out there would remember the reference for
: (from Memory) a small Chemistry in Britain(?) (8 to 18 months old)
: article on Incorrect structures caused bya certain type of false minima.
: This was on organo-metalic singlecrystals and this problem was supposedly
: well known by a "previous generation" of crystallographers - but forgotten
: by people using new generation software(?).
I saw a summary of the article in Chemical and Enginerring News.
I think it was referring to a JACS article by G. Parkin.  The error
responsible for the false minima is the "polar dispersion error"
(PDE).  This comes from neglecting the anomalous dispersion terms in
the structure factor calculation when working in polar space groups (
I am away from the office, and don't have references handy, so I don't
want to say anything further which may be inadvertently misleading).
Happy New Year!
Paul
--
Paul D. Boyle			    |	boyle@laue.chem.ncsu.edu
Director, X-ray Structural Facility |	phone: (919) 515-7362
Department of Chemistry - Box 8204  |	FAX:   (919) 515-5079
North Carolina State University     | 
Raleigh, NC, 27695-8204
http://laue.chem.ncsu.edu/web/xray.welcome.html
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Subject: Re: Old Chem in Britain Article on Wrong Structures and False Minima??
From: jvs@helix.nih.gov (James V. Silverton)
Date: 3 Jan 1997 14:46:23 GMT
Paul D. Boyle (boyle@laue.chem.ncsu.edu) wrote:
: Lachlan Cranswick (lachlan@melbpc.org.au) wrote:
: : I'm wondering if someone out there would remember the reference for
: : (from Memory) a small Chemistry in Britain(?) (8 to 18 months old)
: 
: I saw a summary of the article in Chemical and Enginerring News.
: I think it was referring to a JACS article by G. Parkin.  The error
This may help...it is the result of a Dialog search.
 3/2/1
 DIALOG(R)File 313:CA SEARCH(R)
 (c) 1996 American Chemical Society. All rts. reserv.
   123326167    CA: 123(24)326167y    JOURNAL
     False Minima and the Perils of a Polar Axis in X-ray Structure Solutions:
     Molecular Structures of W(PMe3)4H2X2 (X = F, Cl, Br) and W(PMe3)4H2F2(H2O)
      AUTHOR(S): Murphy, Vincent J.; Rabinovich, Daniel; Parkin, Gerard
	LOCATION: Department of Chemistry, Columbia University, New York, NY,
	10027, USA
	  JOURNAL: J. Am. Chem. Soc.  DATE: 1995  VOLUME: 117  NUMBER: 38
	  PAGES:
	  9762-3 
	    CA275008 Crystallography and Liquid Crystals
	    CA278XXX Inorganic Chemicals and Reactions
	      IDENTIFIERS: mol structure tungsten methylphosphine halo hydrido
Best wishes,
Jim.
-- 
--                 Dr. James V. Silverton   jvs@helix.nih.gov
                   301-496-1515 (OFFICE)    301-402-3404 (FAX)
    NHLBI/LBC, 10/7N-307, 10 CENTER DR MSC 1676, BETHESDA MD 20892-1676  
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