Temperature-Dependent Order-Disorder Phenomena in Crystal Structures Containing Dimers of Carboxylic Acids: The Crystal and Molecular Structure of 3,5-Dinitrobenzoic Acid at Room and Liquid Nitrogen Temperature and Statistics of tReport as inadecuate




Temperature-Dependent Order-Disorder Phenomena in Crystal Structures Containing Dimers of Carboxylic Acids: The Crystal and Molecular Structure of 3,5-Dinitrobenzoic Acid at Room and Liquid Nitrogen Temperature and Statistics of t - Download this document for free, or read online. Document in PDF available to download.

Croatica Chemica Acta, Vol.64 No.3 December 1991. -

3,5-dinitrobenzoic acid crystallizes in space group P2i-c with four molecules in the unit cell. At room temperature RT, the cell dimensions are a = 10.02374, b = 8.87283, c = 9.50904 A, = 95.681° and V = 841.566 A3 and at liquid nitrogen temperature LNT a = 9.7612, b = 8.91924, c = 9.4442 A -S = 97.551° and V = 815.12 A3. At both temperatures, the crystals contain the common centrosymmetric carboxylic acid dimers. At RT the carboxyl groups are partially disordered, as indicated by the C=0 1.2493 and C-0 1.2762A distances, C-C = 0 118.421 and C-C-0 116.42° angles and by the presence of disordered H atoms with occupancy factors of 0.63 and 0.37 in the O—O hydrogen bond.

At LNT, the acidic proton is ordered with a distance of 0.962 A from the donor hydroxyl O atom and the carboxyl group geometry is normal, with C=0 1.2322 and C-0 1.3052 A and C-C = 0 120.61 and C-C-O 114.41°.

The differences Ar distances and A of the C-C-O angles are 0.027 A and 2.0°, respectively, at RT and 0.073 A and 6.2°, respectively, at LNT, which indicates an increase of ordering with decreasing temperature. The mechanism of disordering most probably invokes a temperature-dependent concerted two-proton jump across the dimer hydrogen bonds. To test the relationship between Ar and A, a statistical analysis is performed on the C-0 distances and C-C-O angles of RT and LNT dimer and non-dimer structures retrieved from the Cambridge Structural Database. The analysis indicates that disorder in RT dimers is more frequent than in RT non-dimers and also that ordering is pronounced in both LT dimer and non-dimer structures.



Author: Jan A. Ranters - ; Bijvoet Center for Biomolecular Research, Laboratory for Crystal and Structural Chemistry, Rijksuniversiteit U

Source: http://hrcak.srce.hr/



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