Rational design of efficient electrode materials for fuel cell, water oxidation, and the metal-air battery is now cutting–edge activity in renewable energy research. In this regard, tuning the activity at...

Conformational adjustments in 1-(n-methylthiazol-2-yl)-3-naphthalen-1-yl-thiourea (n = 4, 5) through carbon-nitrogen bond rotation over an intramolecular hydrogen bonded synthon were established. Isosteric homodimeric hydrogen bonded synthons were analysed in their respective self-assemblies. The corresponding urea derivatives, namely, 1-(n-methylthiazol-2-yl)-3-naphthalen-1-yl-urea (n = 4, 5) also had similar homodimeric sub-assemblies in each of their respective assemblies. However, these two positional isomers of a urea derivative did not show polymorphism, which was observed in the corresponding thiourea counterpart. On the other hand, 1-(5-methylthiazol-2-yl)-3-naphthalen-1-yl-thiourea underwent a facile cyclisation reaction, whereas 1-(5-methylthiazol-2-yl)-3-naphthalen-1-yl-urea formed hydrated salts upon reaction with different inorganic acids. Self-assembly of chloride salt had a bifurcated hydrogen bond between two N-H of the urea moiety with chloride ion, whereas perchlorate salt had a similar bond with the oxygen atom of a water of crystallization, making a difference in the type of heterosynthon. Thus, heterosynthons of these salts were found to be anion dependent. Each salt has a cation differing in conformational adjustments guided by anions. Multi-component hydrated and anhydrous crystals of 1-(5-methylthiazol-2-yl)-3-naphthalen-1-yl-urea with tetrabutylammonium chloride were formed concomitantly. These are examples of anion-guided assemblies of thiazole based compounds containing a neutral host. The different naphthyl group orientations of the heterosynthon resulted in two polymorphic hydrated cocrystals.

Orientations of the phenyl group and the intramolecular hydrogen bond play prime roles in the packing patterns of three conformational polymorphs of an unsymmetrical thiourea derivative, 1-(5-methylthiazol-2-yl)-3-phenylthiourea (PTH1). Self-assembly of each polymorph is composed of hydrogen-bonded dimeric motifs held together in head-to-tail arrangement but packed in different manners. Each has an intramolecular N−H•••N hydrogen bond between an amide N−H and the nitrogen atom of the 5-methylthiazole unit. The packing pattern of 1-(4-methylthiazol-2yl)-3-phenylthiourea (PTH2) is composed of dimeric assemblies of PTH2 in head-to-tail fashion. PTH2 is monomorphic as there are intermolecular C−H•••S interactions between a C−H bond of the phenyl ring of each molecule and the sulfur atom of the thiocarbonyl group of a neighboring molecule. Such interactions lock the orientation of phenyl group in the solid state. The syn−anti conformation across the thiourea group, originally present in the positional isomers PTH1 and PTH2, is invariably transformed to syn−syn conformation in their salts. The extent of hydration of anions in the salts of PTH1 or PTH2 is dependent on the cation as well as the anion. The chloride salt of PTH1 has a large difference in packing patterns in comparison with the corresponding chloride salt of PTH2; they also differ in the numbers of symmetry-nonequivalent molecules in their respective unit cells. The anhydrous salt of PTH1 with hydrogen bromide having a 1:1 ratio of cation and anion is formed, whereas the bromide salt of PTH2 is a hydrate of composition (HPTH2) 2 (Br) 2 •6H 2 O. This salt has bromide−water clusters in its crystal lattice. Nitric acid reacts with PTH1 under different conditions to form hydrated or anhydrous salts. The hydrated salt (HPTH1) 2 (NO 3 ) 2 •H 2 O has anions bridged by water molecules. The anhydrous nitrate salts of PTH1 and PTH2 are structurally similar in having nitrate•••nitrate interactions. The deprotonation of polyacids by PTH1 and PTH2 is selective. The ability to abstract a proton from sulfuric acid to form crystalline salts by PTH1 and PTH2 differs. The sulfate salt (HPTH1) 2 (SO 4 ) is formed by reaction of sulfuric acid with PTH1, but PTH2 forms the bisulfate salt (HPTH2)HSO 4 •H 2 O. PTH1 forms the corresponding dihydrogen phosphate salt upon reaction with orthophosphoric acid; the dihydrogen phosphate anions are held together in the form of cyclic hydrogen-bonded hexameric assemblies in the lattice. Water loss from the assemblies of hydrated salt was determined by thermogravimetry and differential scanning calorimetry and showed that dehydration from anion-assisted assemblies was guided by the cationic host and the type of assembly.

Six new Dy(III)-containing coordination polymers (CPs) have been synthesized emphasizing the role of solvent molecules in directing the formation of the Dy(III) coordination sphere which in turn influences the dimensionality of the coordination polymer, thermal stability, and emission properties. An isophthalate-based flexible ligand 5-[(anthracen-9-ylmethyl)amino]-isophthalic acid (H 2 L) with different solvents such as dimethylformamide (DMF), dimethylacetamide (DMA), dimethyl sulfoxide (DMSO), diethylformamide (DEF), and N-donor linkers phen (1,10-phenanothroline) and pyridine (py) was employed to o b t a i n s i x d i ff e r e n t c o o r d i n a t i o n p o l y m e r s , 5), and [Dy(L)(NO 3 )(py) 2 •py] n (6), respectively. All the compounds were characterized by IR spectroscopy and thermogravimetric analysis, and unambiguously characterized by single crystal X-ray crystallography. The bulky anthracenyl group of the linker H 2 L in combination with the solvent molecules significantly alters the coordination symmetry of the Dy(III) coordination sphere in the polymers in the manner: D 2d in 1, C 2v and D 4d in 2, C 4v and C s in 3, C 5v in 4, D 4d in 5, and D 2d in 6. The coordination symmetry plays an interesting role in sensitization of lanthanide emission. The emission maxima of compounds 1−6 vary from the blue region to the yellow region significantly due to coordination symmetry expressed by the Dy(III) centers, which in turn depends upon the coordinated solvent molecule. The thermogravimetric profile indicates the thermal stability of the solvent free compounds up to 300 °C.

Intriguing reactivities of positional isomers 1-(5-methylthiazol-2-yl)-3-(4-nitrophenyl)thiourea (L 1 ) and 1-(4-methylthiazol-2-yl)-3-(4-nitrophenyl)thiourea (L 2 ) towards environment polluting ions such as mercuric, fluoride, bromide and solvents provide scope to study various self-assemblies formed under different conditions and allied applications. The solid state structures of L 1 and L 2 revealed that both adopt the imine form. However, the number of symmetry independent molecules in asymmetric units as well as the packing patterns of these two compounds have distinguishable features. The asymmetric unit of L 1 has three symmetry non-equivalent molecules. The packing patterns of these two positional isomers differ as L 1 has two arrays of dimeric self-assemblies in contrast to the single array found in the packing of L 2 . The reactivity of L 1 and L 2 with solvents was explored through crystal structure elucidation. The compound L 1 forms solvates with N,N′-dimethylacetamide or dimethylsulphoxide. The structural analysis of solvates of L 1 provided avenues to study conformational adjustments. An unusual example of a metastable solvate of L 1 with N,N′-dimethylacetamide was isolated. A ring-opening reaction of 1,8-diazabicyclo [5.4.0] undec-7-ene with L 1 has been observed. The compound L 2 underwent hydrolysis cum bromination with hydrobromic acid in dimethylsulphoxide. The reactivities of L 1 and L 2 towards mercuric and fluoride ions contributed to chemodosimetric signal transductions. The study establishes the impact of subtle changes in structure, reaction and crystallization conditions, which can influence pre-designed crystal engineering.

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As a general outline to show anion guided conformational adjustments of an uncommon conformer found in self-assembly of 2-[(5-methylthiazol-2-ylamino)-methyl]-phenol (1) and subsequent protonation leading to reversal of conformer is shown. On formation of nitrate salt (1 c) the anti conformer of 1 transformed to syn conformer. Whereas conformational adjustments in the corresponding syn conformer of the organocation of the chloride (1 a) and bromide (1 b) took place to adopt orientations that are different from the parent compound or nitrate salt.