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Conformational Polymorphism and Thermochemical Analysis of 5,5' ''-bis[(2,2,5,5-tetramethyl-1-aza-2,5-disila-1-cyclopentyl)ethyl]-2,2':5',2' ':5' ',2' ''-Quaterthiophene

Conformational Polymorphism and Thermochemical Analysis of 5,5' ''-bis[(2,2,5,5-tetramethyl-1-aza-2,5-disila-1-cyclopentyl)ethyl]-2,2':5',2' ':5' ',2' ''-Quaterthiophene

Hitoshi Muguruma, Shu Hotta

J Phys Chem B. 2006 Nov 23;110(46):23075-80.

PMID: 17107146

Abstract:

The titled compound exists as two polymorphic solid phases (denoted form-I and form-II). Form-I obtained by as-synthesized material is a more stable phase. Form-II is a less stable phase. Spontaneous solid-solid transformation from form-II to form-I is observed in the temperature range between room temperature and the melting point of form-I (Tm = 156.5 degrees C), and its activation energy is estimated to be 96 kJ mol-1 by Arrhenius plot. The solid-solute-solid transformation (recrystallization from solution) from form-II to form-I is also observed. In contrast, form-II is obtained only by a solid-melt-solid transformation from form-I. Therefore, the system of two polymorphs is monotropic. The solid-state NMR measurement shows that form-I has the molecular conformation of complete S-syn-anti-syn in the oligothiophene backbone, whereas form-II has that of S-all-anti. With the solution NMR data, the polymorphism could not be observed. Therefore, the polymorphs originate from the different molecular packing involving the conformational change of the molecule. This unique property is attributed to the extra bulky terminal groups of the compounds. However, despite the extra bulky terminal groups, the mentioned polymorphism is not observed in the titled compound analogue which has S-all-anti conformation (like form-II).

Chemicals Related in the Paper:

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AP132814916	3,3′′′-Dihexyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene	132814-91-6	Price
AP446043852	5,5′′′-Bis(tridecafluorohexyl)-2,2′:5′,2 ′′:5′′,2′′′-quaterthiophene	446043-85-2	Price
AP5632291	2,2′:5′,2′′:5′′,2′′′-Quaterthiophene	5632-29-1	Price

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