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Scrutinizing negative thermal expansion in MOF-5 by scattering techniques and ab initio calculations.
MedLine Citation:
PMID:  23044752     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Complementary experimental techniques and ab initio calculations were used to determine the origin and nature of negative thermal expansion (NTE) in the archetype metal-organic framework MOF-5 (Zn(4)O(1,4-benzenedicarboxylate)(3)). The organic linker was probed by inelastic neutron scattering under vacuum and at a gas pressure of 175 bar to distinguish between the pressure and temperature responses of the framework motions, and the local structure of the metal centers was studied by X-ray absorption spectroscopy. Multi-temperature powder- and single-crystal X-ray and neutron diffraction was used to characterize the polymeric nature of the sample and to quantify NTE over the large temperature range 4-400 K. Ab initio calculations complement the experimental data with detailed information on vibrational motions in the framework and their correlations. A uniform and comprehensive picture of NTE in MOF-5 has been drawn, and we provide direct evidence that the main contributor to NTE is translational transverse motion of the aromatic ring, which can be dampened by applying a gas pressure to the sample. The linker motion is highly correlated rather than local in nature. The relative energies of different framework vibrations populated in MOF-5 are suggested by analysis of neutron diffraction data. We note that the lowest-energy motion is a librational motion of the aromatic ring which does not contribute to NTE. The libration is followed by transverse motion of the linker and the carboxylate group. These motions result in unit-cell contraction with increasing temperature.
Authors:
Nina Lock; Mogens Christensen; Yue Wu; Vanessa K Peterson; Maja K Thomsen; Ross O Piltz; Anibal J Ramirez-Cuesta; Garry J McIntyre; Katarina Norén; Ramzi Kutteh; Cameron J Kepert; Gordon J Kearley; Bo B Iversen
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-10-9
Journal Detail:
Title:  Dalton transactions (Cambridge, England : 2003)     Volume:  -     ISSN:  1477-9234     ISO Abbreviation:  Dalton Trans     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-9     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101176026     Medline TA:  Dalton Trans     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Center for Materials Crystallography, Dept. of Chemistry and iNANO, Aarhus University, 8000 Aarhus C, Denmark. bo@chem.au.dk.
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