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Study of molecular dynamics and the solid state phase transition mechanism for unsymmetrical thiopyrophosphate using X-ray diffraction, DFT calculations and NMR spectroscopy.

Potrzebowski MJ, Bujacz GD, Bujacz A, Olejniczak S, Napora P, Heliński J, Ciesielski W, Gajda J

Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Łódź, Poland. marekpot@cbmm.lodz.pl

Differential scanning calorimetry (DSC) and low-temperature X-ray diffraction studies showed that 2-thio-(5,5-dimethyl-1,3,2-dioxaphosphorinanyl)2'-oxo-dineopentyl-thiophosphate (compound 1) undergoes reversible phase transition at 203 K related to the change of symmetry of the crystallographic unit. Solid state NMR spectroscopy was used to establish the dynamic processes of aliphatic groups and the phosphorus skeleton. 13C and 31P variable temperature NMR studies as well as T1 and T1rho measurements of relaxation times revealed the different mode of molecular motion for each neopentyl residue directly bonded to phosphorus. It is concluded that molecular dynamics of aliphatic groups causes different van der Waals interactions in the crystal lattice and is the driving force of phase transition for compound 1. Finally, we showed that very sharp phase transition temperature makes compound 1 an excellent candidate as a low-temperature NMR thermometer in the solid phase.

Published 13 February 2006 in J Phys Chem B Condens Matter Mater Surf Interfaces Biophys, 110(2): 761-71.
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