Sujata Kashyap

Anion directed supramolecular architecture of pyrazole based ionic salts

The reaction of 3,5-diphenylpyrazole (PzPh2H) with different inorganic acids affords salts viz., PzPh2H2+·H2PO4− (1), PzPh2H2+·NO3−·H2O (2), PzPh2H2+·Cl− (3), 8PzPh2H2+·4HSO4−·2SO4−2·3H2O (4) and PzPh2H2+·ClO4−·H2O·CH3OH (5) with different structures. The present study demonstrates that the formation of hydrogen bond between protonated pyrazoles and anions provides a sufficient driving force for the directed assembly of an extensive supramolecular frame work. Theoretical studies reveal that with the increase in the strength of the inorganic acid, the hydrogen bond interaction energy increases. Using Gaussview to analyse the optimized geometries obtained at DFT(B3LYP)/6-31G(d,p) level of theory further revealed that the orientation of molecules remained the same both in the solid and gaseous phases.

Supramolecular assemblies of benzene-1,3,5-tricarboxylic acid and 3,5-substituted pyrazoles: formation and structural analysis

Different supramolecular assemblies of benzene-1,3,5-tricarboxylic acid (H3BTC) with various substituted pyrazoles, viz., 3,5-dimethylpyrazole (PzMe2H), 3,5-diisopropylpyrazole (PziPr2H), 3-tert-butyl-5-isopropylpyrazole (PztBu,iPrH), 3-phenyl-5-methylpyrazole (PzPh,MeH), 3-cumenyl-5-methylpyrazole (PzCum,MeH), 3,5-diphenylpyrazole (PzPh2H) and 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (BPzH2) have been prepared. The present study demonstrates that the formation of hydrogen bond between protonated pyrazoles and anions provides a sufficient driving force for the directed assembly of varied supramolecular frameworks where H3BTC nicely adjusts its cavity dimensions to accommodate the guest. Theoretical studies were performed to analyze the effect of different substituents on hydrogen-bond interaction energy of the resultant salts and co-crystals. Energies of the various synthons were also calculated to correlate their stability and occurrence with the change of substituent on the pyrazole ring.

Effect of anions on supramolecular architecture of benzimidazole-based ionic salts

The reaction of N,N,N′,N′-tetrakis-(1H,benzimidazol-2ylmethyl) propane-1,3-diamine (L) with different inorganic acids affords salts viz., LH44+·4ClO4−·H2O (1), LH44+·4Cl−·2H2O (2), LH44+·2H2PO4−·H7P3O122−·3H3PO4 (3), LH44+·4NO3− (4), and 2LH+·2CF3COO−·5H2O (5). The X-ray crystallographic studies revealed that the proton transfer occurred from acid to the ligand. It also demonstrated that different type of hydrogen bond between protonated ligand and anions is responsible for the supramolecular framework. The colorimetric test showed color change upon the addition of acids in the solution of the ligand. The photo-physical experiments suggested the fluorescence properties of ligand in the presence of acids.

Interconversion of host–guest components in supramolecular assemblies of polycarboxylic acids and reduced Schiff bases

Eight supramolecular assemblies of benzene-1,3,5-tricarboxylic acid (H3BTC) and benzene-1,2,4,5-tetracarboxylic acid (H4BTtC) with reduced Schiff base of flexible backbone having phenolic and pyridyl groups, i.e., 1,2-bis(2-hydroxybenzylamino)ethane, 1,3-bis(2-hydroxybenzylamino)propane, 1,4-bis(2-hydroxybenzylamino)butane and 1,4-bis(4-pyridinylmethylamino)butane have been constructed by proton transfer reaction. H3BTC forms host–guest type assemblies with amines having phenolic functionality, while a layered structure was obtained with pyridyl functionalized amine. H4BTtC also formed host–guest assemblies with the diamines where reduced Schiff base acts as host and acid moiety acts as the guest. Different conformations of the diamines were observed in these assemblies. Theoretical studies were performed to analyze the effect of varied chain lengths of diamines on hydrogen bond interaction energy of the adducts.

High-spin iron(III) complexes: structural, spectroscopic, and photochemical studies

Reaction of FeCl3 with one equivalent of acac (acac = pentane-2,4-dionate) and KTpMe2 (TpMe2 = hydrotris(3,5-dimethyl-pyrazol-1-yl)borate) yielded TpMe2Fe(acac)Cl (3), which upon reaction with methanolic solution of sodium azide resulted in the formation of a six coordinate compound TpMe2Fe(acac)N3 (4) with a single azide. When the reaction of FeCl3 and KTpMe2 was performed with two equivalents of sodium azide and one equivalent of 3,5-dimethylpyrazole (PzMe2H), a six coordinate cis azide compound [TpMe2Fe(PzMe2H)(N3)2] (5) was obtained. These compounds were characterized by spectroscopic methods and single crystal X-ray crystallography. Electrochemical studies of 5 show that it can be irreversibly reduced at relatively lower potential than 4. The photolysis of 5 was performed at 77 K at different wavelengths (480, 419, and 330 nm) showing that 5 was photoreduced to a high-spin Fe(II) species instead of photooxidized to Fe(V).

Construction of Supramolecular Assemblies from Substituted Pyrazoles and Pyromellitic Acid: Rational Analysis of the Synthons and Theoretical Studies

AbstractSeven supramolecular assemblies of benzene-1,2,4,5-tetracarboxylic acid (pyromellitic acid, H4BTtC) and various pyrazoles viz., pyrazole (PzH), 3,5-dimethylpyrazole (PzMe2H), 3,5-diisopropylpyrazole (PziPr2H), 3-tert-butyl-5-isopropylpyrazole (PztBu,iPrH), 3-phenyl-5-methylpyrazole (PzPh,MeH), 3-cumyl-5-methylpyrazole (PzCum,MeH), 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (BPzH2) have been synthesized. Proton transfer was observed in all the cases except with 3-phenyl-5-methylpyrazole (PzPh,MeH). Theoretical studies were also performed to analyze the effect of various substituted pyrazoles on hydrogen-bond interaction energy of adducts. Energies of the resulted SOFs were also calculated to correlate their stability and occurrence with the different substituent present on the pyrazoles.Graphical AbstractSupramolecular assemblies of pyromellitic acid with pyrazoles have been synthesized.

Synthesis and structural studies of some copper-benzoate complexes

The reaction of CuCl2·2H2O with 3,5-diisopropylpyrazole (PziPr2H) in the presence of sodium parafluorobenzoate (Na-p-FBz) resulted in the formation of an oxo-chloro-bridged tetranuclear complex [Cu4(PziPr2H)4(μ-O)(μ-Cl)6] 1, whereas the reaction of Cu(NO3)2·3H2O with PziPr2H in the presence of different benzoates gave [Cu(PziPr2H)2(μ-OCH3)]2(NO3)22, [Cu(PziPr2H)3(NO3)(p-ClBz)]·CH3CN 3, [Cu(p-CH3Bz)2(PziPr2H)]2·2CH3CN 4, [Cu(p-OCH3Bz)2(CH3CN)]2·4CH3CN 5 and [Cu(p-CNBz)(CH3CN)]26. Single-crystal X-ray diffraction studies confirmed these formulations. DNA binding studies for these complexes were performed by means of UV-visible absorption titration and viscosity measurements. Gel electrophoresis studies showed that hydroxyl radicals are involved in DNA cleavage in the presence of the complexes.