Goutam Kumar Patra

Crystal Engineering of 2-D and 3-D Multiporphyrin Architectures − The Versatile Topologies of Tetracarboxyphenylporphyrin-Based Materials

This study explores diverse crystal engineering concepts in the formulation of a series of new porphyrin-based supramolecular arrays, utilizing tetrakis(4-carboxyphenyl)porphyrin as an effective building block. Different modes of the supramolecular assembly are demonstrated. They include: (a) self-assembly of the porphyrin units into extended networks through multiple hydrogen bonding, (b) intermolecular coordination assisted by external sodium ion auxiliaries which link between the carboxylic/carboxylate groups of several units, (c) formation of coordination polymers with the aid of bidentate ligands as bridges between the metal centers of the porphyrin molecules, and (d) various combination motifs of concerted hydrogen bonding and coordination features. The resulting multiporphyrin architectures obtained in this study illustrate the expression of several motifs (synthons) of noncovalent interaction in the construction of network solids, which can be potentially useful in the design of new porphyrin-based materials with attractive properties.

A ‘chromogenic’ and ‘fluorogenic’ bis-Schiff base sensor for rapid detection of hydrazine both in solution and vapour phases

A novel, convenient and rapid method has been developed, for the first time, for visual detection of hydrazine exploiting a simple, cost-effective Schiff base ligand, L as a fluorescent–colorimetric probe. The sensing behaviour is based on hydrogen bonding recognition. The probe could selectively distinguish hydrazine with an OFF–ON fluorescence signal change and the visible colour change from yellow to colourless at room temperature within 10 seconds. It exhibits exclusive selectivity towards hydrazine over different amines, metal cations and anions. The sensitivity of the fluorescence based assay (0.1 μM or 3.2 ppb) for hydrazine is far below the TLV (threshold limit value) set by the World Health Organization (WHO) and United States Environmental Protection Agency (USEPA). DFT and TDDFT calculations were performed on the molecule of L in order to get the structural information and to get better insight into the sensing mechanism. The probe can be successfully used for vapour-phase discrimination of hydrazine by the TLC plate technique and it shows good practical applicability in the detection of hydrazine in water and urine samples.

A new photoluminescent CuI2N6 chromophore

A novel CuI2N6 chromophore has been isolated with 2,2′-bis[(4R)-phenyl]-1,3-oxazoline (L) in the optically pure triple-stranded helicate [Cu2L3](ClO4)2, which displays photoluminescence in methanol at room temperature (emission maximum λem = 385 nm; quantum yield ϕ = 1.6 × 10−4; lifetime τ ≈ 2 ns) as well as at 77 K (λem = 430 nm; τ = 0.89 ± 0.13 s).

The synthesis and characterization of a series of bis-bidentate Schiff base ligands and their coordination complexes with silver(I), copper(I) and zinc(II) d10 metal ions

Three bis-bidentate Schiff base ligands 1, 2 and 3 have been prepared and thoroughly characterized, and their complexation behavior with d10 silver, copper and zinc ions was studied. The coordination assembly of Cu(I) and Ag(I) with ligands 1 and 2, afforded di-nuclear dimeric complexes [Ag2(1)2](ClO4)2 (1a), [Cu2(1)2](ClO4)2 (1b), [Ag2(2)2](ClO4)2 (2a) and [Cu2(2)2](ClO4)2 (2b), in which the metal ion auxiliaries adopted a pseudo-tetrahedral coordination environment. In these compounds the two ligands wrap around the metal ions in a twisted manner, forming box-like structures. Within these complexes each metal ion binds to two nitrogen sites of one ligand and two N-sites of the other ligand. The metal assisted self-assembly process is complemented by supportive π–π overlap interactions between the aromatic fragments of the assembly. In 1a and 2a the two silver ions lie close to one another at 3.1 A. On the other hand, zinc(II) yields a monomeric crystalline complex with 2, [Zn(2)(H2O)(CH3CN)](ClO4)2 (2c), interacting with four N-donors of the same ligand and complementing its octahedral coordination sphere with molecules of water and acetonitrile. The materials were characterized by UV-VIS, IR, MS, NMR, and X-ray diffraction analysis. Electrochemical behavior of the copper(I) compounds was also examined.

Supramolecular assembly of metalloporphyrins in crystals by axial coordination through amine ligands

Axial coordination to metalloporphyrins is an important tool in the supramolecular chemistry of these entities. Metalated 5,10,15,20-tetraphenylporphyrins can be axially linked to each other with the aid of amine and diamine ligands. Seven new crystalline materials consisting of such heterogeneous coordination oligomers and polymers of Zn(II)– or Mn(III)–tetraphenylporphyrins have been prepared and characterized by X-ray crystallography. Ligands of varying length have been used as bridging auxiliaries between the metal centers of the porphyrin species, effecting heterogeneous porphyrin-ligand oligomeric as well as polymeric assemblies. These correspond, respectively, to “wheel-and-axle” and “shish-kebab” type shapes of the supramolecular scaffolds. In addition, a uniquely structured homogeneous coordination polymer of a Zn(II)–tetrapyridylporphyrin derivative, is also reported.

Localized surface plasmon resonance of silver nanoparticles for sensitive colorimetric detection of chromium in surface water, industrial waste water and vegetable samples

Silver nanoparticles capped with tartaric acid (AgNPs/TA) are used as a localized surface plasmon resonance (LSPR) colorimetric sensor for the determination of chromium in real surface water (pond water and tube well water), industrial waste water and vegetable (cauliflower, tomato, spinach, green beans and cabbage) samples. The plasmon colorimetric sensing of chromium (+III and +VI) in samples was performed by measuring the change in the LSPR band in the UV-visible region of spectra. The reason for the change in the LSPR band was due to the aggregation of NPs induced by the coordination complex between chromium ions and tartaric acid present on the surface of NPs. The calibration curve gave a high level of linearity in the range of 5–100 μg L−1 for Cr(III) and 10–100 μg L−1 for Cr(VI) with a correlation coefficient of 0.996 and 0.995, respectively. The limits of detection (LODs) for Cr(III) and Cr(VI) were found to be 2 μg L−1 and 3 μg L−1, respectively, with the relative standard deviation percentage (RSD, %) in the range of 2.3–4.0%. The proposed method is found to be very simple, rapid and sensitive for the determination of trace levels of chromium present in surface water, industrial waste water and vegetable samples.

A reversible fluorescent-colorimetric chemosensor based on a novel Schiff base for visual detection of CO32− in aqueous solution

A reversible fluorescent colorimetric chemosensor for rapid detection of carbonate ion has been developed based on a novel bis-Schiff base. The chemosensor L employed here is easy to synthesize, eco-friendly and cost effective. It exhibits excellent selectivity and sensitivity towards carbonate ion by changes in both the absorption and fluorescence intensity. The anion recognition occurs indirectly through coordination of a counter metal ion to the Schiff base ligand exhibiting a colour change from colourless to yellow. Microstructural features of L and L + M+ have been investigated by SEM images. The sensitivity of the absorbance based assay (96 nM) for carbonate ion is the lowest ever reported in the literature. The chemosensor L providing rapid response time with sufficiently low detection limit may be useful as a valuable practical sensor for environmental analyses of carbonate ion.

A highly sensitive reversible fluorescent-colorimetric azino bis-Schiff base sensor for rapid detection of Pb2+ in aqueous media

A reversible fluorescent-colorimetric azino bis-Schiff based receptor for the detection of Pb2+ in aqueous medium has been developed for the first time. Receptor L exhibits an excellent selective fluorescent-colorimetric rapid response towards Pb2+. The sensitivity of the fluorescence based assay (8 nM) for Pb2+ is sufficiently low in comparison to that previously reported in the literature. From 1H NMR data, the Job plot measurement and the ESI-MS spectrum, 2 : 1 stoichiometric complexation between L and Pb2+ has been established. Microstructural features of L and L + Pb2+ have been investigated by using SEM images for better understanding the interaction between the chemosensor and Pb2+. Receptor L shows remarkable detection ability in a wide pH range of 4–10 and it has been successfully utilised in the determination of Pb2+ in aqueous solution of bovine serum albumin protein. The geometry of L has been optimized both by DFT calculations and single crystal X-ray studies and that of the Pb2+ complex has been optimized by DFT calculations.

Exploitation of a simple Schiff base as a ratiometric and colorimetric chemosensor for glutamic acid

A novel, exceptionally simple and rapid method has been developed for visual detection of L-glutamic acid (Glu) in aqueous solution. The chemosensor employed is easy to prepare and use with an added advantage of cost effectiveness. It exhibits an excellent selectivity and sensitivity towards Glu over other amino acids by changes in both absorption intensity and colour intensity. The chemosensor provides a fast response time, with an LOD of about 7.96 × 10−7 M suggesting that the chemosensor may be useful as a valuable practical sensor for environmental analyses of glutamic acid.

Effect of the size of discrete anions on the nuclearity of a complex cation

Reactions of 2,3-diphenylquinoxaline (L) with AgClO4·xH2O, AgCF3SO3, AgBF4, AgCF3CO2 and AgNO3 in equimolar proportions at room temperature yield, respectively, AgL·ClO4·2CH3OH (1), AgL2·CF3SO3 (2), AgL·BF4·H2O·½C2H5OH (3), AgL2·CF3CO2 (4) and Ag·½L·NO3 (5). From X-ray crystallography, complexes 1, 3 and 5 are found to be 1-D hybrid polymers while 2 and 4 are mononuclear. In these five structures, only the nitrate anion is found to be coordinating; other anions are more or less non-coordinating. For the non-coordinating anions, it is concluded that small anions lead to a polymeric cationic complex and larger ones exert a non-proliferating effect in the countercation. In 1 and 3 the polymerization in the complex cation is brought about by bidentate L. But in 5, the anion also becomes a part of the polymeric assembly. The nature of the solvent seems to have little effect on these general observations.