A new monoclinic polymorph of 3-diethylamino-4-(4-methoxyphenyl)-1,1-dioxo-4H-1λ⁶,2-thiazete-4-carbonitrile

Abstract

A new monoclinic form of the title compound, C14H17N3O3S, has been found upon slow crystallization from water. Another monoclinic form of the compound was obtained previously from a mixture of dichloro­methane and diethyl ether [Clerici et al. (2002 ▶). Tetra­hedron, 58, 5173–5178]. Both phases crystallize in space group P21/n with one mol­ecule in the asymmetric unit. The formally single exocyclic C—N bond that connects the –NEt2 unit with the thia­zete ring is considerably shorter than the adjacent, formally double, endocyclic C=N bond. This is likely to be due to the extended conjugated system between the electron-donor diethyl­ammine fragment and the electron-withdrawing sulfonyl group. In the newly discovered polymorph, the meth­oxy group is rotated by almost 180° around the phen­yl–OCH3 bond, resulting in a different mol­ecular conformation.

A variable-temperature X-ray diffraction and theoretical study of conformational polymorphism in a complex organic molecule (DTC)

“… 22 The scarceness of the synthesized material 21 prevented further crystallization screenings. In the present study, the same specimen of the B phase employed in a previous work 22 was used.…”

“…The structure of the form A was originally solved in 2003, aer crystallizing freshly synthesized DTC by slow evaporation from a 1 : 1 CH 2 Cl 2 : Et 2 O mixture. 21,22 In 2010, the form B was discovered upon dissolution of the aged compound in warm distilled water and subsequent recrystallization by slow evaporation at RT. 22 The scarceness of the synthesized material 21 prevented further crystallization screenings.…”

“…21,22 In 2010, the form B was discovered upon dissolution of the aged compound in warm distilled water and subsequent recrystallization by slow evaporation at RT. 22 The scarceness of the synthesized material 21 prevented further crystallization screenings. In the present study, the same specimen of the B phase employed in a previous work 22 was used.…”

“…25 All the structural least-squares renements were performed by shelxl, 26 starting from the previously determined phases at room temperature. 21,22 Tables S1 and S2 in the ESI † show the main specs of data collections and renements.…”

“…In this work, a multi-temperature study of the two known conformational polymorphs [21][22][23] of 3-diethylamino-4-(4-methoxyphenyl)-1,1-dioxo-4H-1l 6 , 2-thiazete-4-carbonitrile (DTC, Scheme 1, C 14 H 17 N 3 O 3 S) is reported. The main objectives are (i) to study correlations between molecular conformation and interaction energetics in the two forms, providing a rationale for their relative stability, and (ii) to investigate how and why electrostatic interactions and the various NCI patterns depend on temperature.…”