Probing the role of weaker interactions in immobilization of solvents in a new class of supramolecular gelator

Abstract

A new class of thiazole based organogelator was synthesized and characterized by various techniques such as VT-NMR, IR, single crystal and powder X-ray diffraction. The role of unusual H-bond interactions such as C-H … N and van der Waals interactions were probed as driving forces for physical gelation of various polar and non-polar solvents. A structure-property correlation between various derivatives of thiazole was explored for their gelation or non-gelation behaviour.

Odd–even effect in a thiazole based organogelator: understanding the interplay of non-covalent interactions on property and applications

“…Our observations on the supramolecular assembly of amide containing thiazole compounds are well supported by the observation made by Aakero ¨y et al 18 in the seminal paper on amide functionality as robust synthon and the prospect of amideamide interactions (0-D or ladder type) in the presence of other probable hydrogen bonded supramolecular synthons (amideamide interaction is less probable in the presence of strong N-HÁ Á ÁN type cyclic H-bond). Interestingly, the CQOÁ Á ÁS (intramolecular) forces found in all the crystal structures of thiazole amide were reported in the present study as well as in our earlier work 11 irrespective of the presence-absence or position of the methyl functional group. The unusual non-bonded interaction, (carbonyl)CQOÁ Á ÁS(thiazole), appeared to force the long alkyl chain to have almost linear orientation with respect to the thiazole moiety.…”

“…On the other hand, the proximity of a methyl group to alkyl chains would disturb the overall packing pattern and probably lead to the 0-D dimensional hydrogen bonded network as observed in the structure of non-gelator 2d. Single crystal structures of 1b (even, n = 10) 11 and 1c (odd, n = 11) highlighted additional C-HÁ Á ÁO interaction in 1c leading to 2-D hydrogen bonded network in comparison to 1b, which is a 0-D network.…”

“…The synthesis, characterization, and gelation behaviour of thiazole amides (1a-1d, 2a-2d and 3a-3d) were reported earlier (n = 8, 10-12). 11 In the present study, gelation abilities of 1e-1h, 2e-2h and 3e-3h were examined in a variety of polar and non polar solvents (ESI, † Tables S1 and S2) by the systematic increase in the alkyl chain length (methylene functional group (n) = 13-16). Unsubstituted (1e-1h) and 5-methyl substituted (3e-3h) thiazole amides displayed excellent gelation properties towards various solvents such as methanol, ethanol, octadecane, etc.…”

“…The single crystal study of 2d supported the proposed mechanism for gelationnon-gelation that the strategic position of the methyl functional group may sustain or obstruct alkyl-alkyl chain interdigitation. 11 A suitable single crystal of gelator 1c was obtained from chloroform having a monoclinic (P2 1 /c) space group. The asymmetric unit displayed a single molecule of 1c joined together with another molecule through cyclic hydrogen bond One of the major challenges in these series of molecules is to understand the cause of gelation-non-gelation behaviour, due to odd-even number of methylene functional groups.…”

“…Recently, we discovered a new series of LMOGs based on thiazole amide derivatives (1a-1d, 2a-2d and 3a-3d) 11 (Scheme 1), which displayed the importance of position of a methyl group on a thiazole moiety in inducing gelation of solvent. For example, in the series of 5-methylthiazole amides (3b and 3d), gelation behaviour towards many solvents were observed, but gelation was completely absent in the series of 4-methylthiazole amides (2a-2d).…”