Conformation and Visual Distinction between Urea and Thiourea Derivatives by an Acetate Ion and a Hexafluorosilicate Cocrystal of the Urea Derivative in the Detection of Water in Dimethylsulfoxide.

Arup Tarai,Jubaraj B Baruah

doi:10.1021/acsomega.7b01217

Abstract

Structures of different solvates and solute–solvent interactions of 4-(3-(4-nitrophenyl)urido)benzoate (L1) and methyl-4-(3-(4-nitrophenyl)thiourido)benzoate (L2) with different solvents are analyzed. The solution of L1 with tetrabutylammonium acetate (TBAA) in dimethylsulfoxide (DMSO) is colorless, but a similar solution of L2 with TBAA is orange. On the other hand, respective solutions of these urea and thiourea derivatives with tetrabutylammonium fluoride (TBAF) in DMSO are orange. Urea derivative L1 facilitates the reaction of TBAF with glass to form tetrabutylammonium hexafluorosilicate, which on further interaction with L1 forms cocrystal 2L1·(TBA)2SiF6. Reorganization of hydrogen-bonded self-assembly of 2L1·(TBA)2SiF6 in DMSO caused by water is established by a dynamic light scattering study. With an increase in the amount of water in the solution, visual color changes from orange to colorless, and the color changes are reversed upon the addition of a dehydrating agent such as molecular sieves. Solvates of L1 with DMSO, dimethylformamide (DMF), and dimethylacetamide are quasi-isostructural. The respective self-assembly of these solvates differs due to orientations of aromatic rings and the carbomethoxy group across the thioamide/amide bond. Significant differences in self-assemblies of the respective DMSO solvate of L1 and L2 are observed; self-assembly of the former has dimeric subassemblies as repeat units, whereas the latter has monomeric subassemblies. DMF solvates of L1 and dimethylacetamide of L1 are built by dimeric subassemblies to form self-assembled structures, but these subassemblies differ in the orientation of the carbomethoxy group across the urea units.

Highlights

Urea- and thiourea-based molecules have a special status to form anion-guided noncovalent assemblies.[1−4] A thiourea derivative noncovalently bound to anions has higher stability than the corresponding urea derivative bound to the same anion.[5]
These absorptions are solventdependent; compound L1 dissolved in solvents such as acetonitrile, tetrahydrofuran, acetone, and 1,4-dioxane shows absorptions at 334−337 nm range, whereas the same compound dissolved in dimethylformamide (DMF) or DMSO shows absorption at 345−347 nm (Figure 2a)
DMSO prefers the stabilization of syn−syn geometry, whereas acetone favors the syn−anti forms of L1 or L2

Summary

Introduction

Urea- and thiourea-based molecules have a special status to form anion-guided noncovalent assemblies.[1−4] A thiourea derivative noncovalently bound to anions has higher stability than the corresponding urea derivative bound to the same anion.[5]. Solvents generally play an important role in guiding stabilization of a particular conformer of a urea derivative.[22,23] The present literature is not suggestive enough to provide integrated details regarding the differences in structures of solvates and their respective assembly in solution. The stabilization of different conformationally adjusted molecules (Figure 1c) in the solvate may replicate the solvent−urea/thiourea interactions in solution.

Results

Conclusion