Search

A simple azo-dye based bis-Schiff base chemosensor, L, has been designed, synthesized and characterized by NMR and IR spectroscopy, ESI-MS and elemental analysis. The chemosensor Lcan successfully detect sulfide ions both visually and spectro-photometrically in perfect aqueous medium as well as in an organic–aqueous mixture through a de-protonation mechanism. The detection limit reaches 16 μM in pure aqueous medium (1.7 μM by UV-vis titration and 3.35 × 10−7M by fluorescence titration in a 1 : 1 DMSO–H2O mixture), which is the lowest detection limit ever reported in the family of Schiff base chemosensors for sulfide ions. Other interfering anions (F−, Cl−, Br−, HSO3−, N3−, PO43−, NO3−, OAc−, CO32−and CN−) exhibited no interference for the detection of sulfide ions. The mechanism of interaction between Land sulphide ions has further been confirmed by DFT studies. The chemosensor Lhas also been applied for real sample analysis and in building a molecular logic gate.

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 (+iiiand +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−1for Cr(iii) and 10–100 μg L−1for 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−1and 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 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, Las 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 Lin 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 series of new imine ligands [1 (C12H12N2S2), 2 (C12H12N2S2), 3 (C24H18N4S2), and 5 (C30H27N7)] have been synthesized (1 and 2 are structural isomers). Cu^I and Ag^I complexes of the nonconjugated dithiophene-diimine ligands 1, 2 and the tripodal imine-amine ligand 5 have also been prepared and thoroughly characterized by spectroscopic techniques as well as by X-ray diffraction. In cyclic voltammetry at a glassy carbon milli electrode in anhydrous dichloromethane under dry N2, the corresponding Cu^I complexes [6 (2C12H12N2S2·CuClO4), 7 (2C12H12N2S2·CuClO4), and 12 (C30H27N7·CuClO4)] show quasi-reversible Cu^II/I couples with high redox potentials (1.001 V for 6, 0.958 V for 7, and 0.692 V for 12, vs. Ag/AgCl). This indicates that the π-acid ligands 1, 2, and 5 preferentially stabilize copper(I) over copper(II). The Cu^IN4 chromophores in the complexes 6, 7, and 12 display photoluminescence in dichloromethane at room temperature. The related silver complexes of the same three ligands 10 (2C12H12N2S2·AgClO4), 11 (2C12H12N2S2·AgClO4), and 13 [C30H27N7·Ag(CH3CN)ClO4] reveal similar structural features but lack specific photophysical properties. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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 Å. 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.

Three bis-bidentate Schiff base ligands 1, 2and 3have been prepared and thoroughly characterized, and their complexation behavior with d10silver, copper and zinc ions was studied. The coordination assembly of Cui and Agi with ligands 1and 2, afforded di-nuclear dimeric complexes Ag212ClO421a, Cu212ClO421b, Ag222ClO422a and Cu222ClO422b, 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 1aand 2athe two silver ions lie close to one another at 3.1 Å. On the other hand, zincii yields a monomeric crystalline complex with 2, Zn2H2OCH3CNClO422c, 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 copperi compounds was also examined.

A series of new multidentate imine building blocks [NC₅H₄(R)C&z.dbd;NCH₂CH₂N&z.dbd;C(R)C₅H₄N (R = H 1a, R = Me 1b) and NC₅H₄CH&z.dbd;N–N&z.dbd;C(R)–C(R)&z.dbd;N–N&z.dbd;CHC₅H₄N (R = Ph 2a, R = Me 2b)] have been synthesized, aiming at the formulation of extended coordination polymers with various transition metal ions. Formation of the corresponding metal–ligand complexes has been monitored and characterized by chemical and spectroscopic techniques. X-Ray diffraction analysis of the available single crystals revealed diverse polymeric patterns of the hybrid organic–inorganic supramolecular systems. Complexation of Cu(i) with 1a and 2a yielded one-dimensional and two-dimensional polymers, respectively, with tetrahedral geometry around the metal centers. Similar reactions of Ag(i) with 1b and with 2a led to three-dimensional and two-dimensional arrays, respectively. The former contains silver ions with tetrahedral as well as square-planar coordination environments, while in the latter case the metal species bind to the ligands in a tetrahedral manner. Related syntheses of coordination compounds between 2a and bivalent metal ions produced 1-D polymers with Cd(ii) and 2-D polymeric networks with Zn(ii), Co(ii) and Mn(ii).

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.

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.

Photochemical reaction between benzil and diethylenetriamine (dien) in anhydrous methanol in the presence of oxygen yields a novel triaza macrocycle 2,3-diphenyl-1,4,7-triazacyclonona-1,3-diene (L). It was characterised by FTIR, EI mass and NMR (¹H and ¹³C) spectra. A comparative study between the various physicochemical properties of L and the product (L₁; reported earlier by others) of the thermal reaction between benzil and dien is made in detail. L and L₁ can be regarded as isomers. While L₁ cannot be converted to L by UV radiation, L is transformed into L₁ upon refluxing in anhydrous methanol. The macrocycle L affords cationic copper(i) complexes of the type [CuL]X (X=ClO₄^- and PF₆^-). Cyclic voltammetry and coulometry at platinum electrodes in dimethylformamide under an N₂ atmosphere show that the Cu^II/I potential in [CuL]X is 0.25 V vs. SCE. This indicates that L is a weak π-acid. L is photoluminescent in methanol at room temperature (emission maxima λ_em=380 nm; quantum yield ϕ=1.96×10^-2). Its emission when in the form of [CuL]X in methanol is quenched considerably (λ_em=370 nm; ϕ=6.2–6.7×10^-3).

The title compound, [5,10,15,20‐meso‐tetrakis(4‐hydroxy­phenyl)­porphyrinato‐κ4N]­zinc(II) tris(dibenzo‐24‐crown‐8) methanol tetrasolvate, [Zn(C44H28N4O4)]·3C24H32O8·4CH4O, was synthesized and its molecular structure precisely charac­terized by low‐temperature single‐crystal analysis. All the components are involved in hydrogen bonding with each other, thus forming an extensively hydrogen‐bonded supramolecular lattice. The functionalized porphyrin moiety coordinates both equatorially and axially to the neighboring species.

Targeted synthesis of new supramolecular motifs of metalloporphyrins in crystals by a concerted mechanism of molecular recognition in three dimensions, aided by organic ligands, is presented; it involves induced assembly of [tetrakis(4-hydroxyphenyl)porphyrinato]zinc species by a combination of axial coordination through bridging bipyridyls and of lateral hydrogen bonding.