Suman Mukhopadhyay

Copper–organic frameworks assembled from in situ generated 5-(4-pyridyl)tetrazole building blocks: synthesis, structural features, topological analysis and catalytic oxidation of alcohols

Two new metal-organic compounds {[Cu3(μ3-4-ptz)4(μ2-N3)2(DMF)2](DMF)2}n (1) and {[Cu(4-ptz)2(H2O)2]}n (2) {4-ptz = 5-(4-pyridyl)tetrazolate} with 3D and 2D coordination networks, respectively, have been synthesized while studying the effect of reaction conditions on the coordination modes of 4-pytz by employing the [2 + 3] cycloaddition as a tool for generating in situ the 5-substituted tetrazole ligands from 4-pyridinecarbonitrile and NaN3 in the presence of a copper(ii) salt. The obtained compounds have been structurally characterized and the topological analysis of 1 discloses a topologically unique trinodal 3,5,6-connected 3D network which, upon further simplification, results in a uninodal 8-connected underlying net with the bcu (body centred cubic) topology driven by the [Cu3(μ2-N3)2] cluster nodes and μ3-4-ptz linkers. In contrast, the 2D metal-organic network in 2 has been classified as a uninodal 4-connected underlying net with the sql [Shubnikov tetragonal plane net] topology assembled from the Cu nodes and μ2-4-ptz linkers. The catalytic investigations disclosed that 1 and 2 act as active catalyst precursors towards the microwave-assisted homogeneous oxidation of secondary alcohols (1-phenylethanol, cyclohexanol, 2-hexanol, 3-hexanol, 2-octanol and 3-octanol) with tert-butylhydroperoxide, leading to the yields of the corresponding ketones up to 86% (TOF = 430 h(-1)) and 58% (TOF = 290 h(-1)) in the oxidation of 1-phenylethanol and cyclohexanol, respectively, after 1 h under low power (10 W) microwave irradiation, and in the absence of any added solvent or additive.

PtII-Promoted [2 + 3] Cycloaddition of Azide to Cyanopyridines : Convenient Tool toward Heterometallic Structures

The [2 + 3] cycloaddition reactions (which are greatly accelerated by microwave irradiation) of the di(azido)platinum(II) compounds cis-[Pt(N(3))(2)(PPh(3))(2)] (1) with cyanopyridines NCR (2) (R = 4-, 3-, and 2-NC(5)H(4)) give the corresponding bis(pyridyltetrazolato) complexes trans-[Pt(N(4)CR)(2)(PPh(3))(2)] (3) [R = 4-NC(5)H(4) (3a), 3-NC(5)H(4) (3b), and 2-NC(5)H(4) (3c)]. Compound 3c has been characterized as the N(1)N(2)-bonded isomer in the solid state by X-ray crystallography and represents the first bis(tetrazolato) complex of this kind. Complexes 3a and 3b have been used as metallaligands to generate heteronuclear coordination polymers in the presence of copper nitrate. A one-dimensional supramolecular architecture was obtained as the exclusive product, {trans-[Pt(2)(N(4)CR)(4)(PPh(3))(4)Cu](n)(NO(3))(2n).nH(2)O (4.nH(2)O) (R = 4-NC(5)H(4)), when 3a was employed, whereas with 3b the heteronuclear square complex trans-[Pt(N(4)CR)(2)(PPh(3))(2)Cu(NO(3))(2)(H(2)O)](2) (5) (R = 3-NC(5)H(4)), composed of Pt/Cu ions, was obtained. All the isolated complexes were characterized by IR, elemental, and (for 3b, 3c, 4, and 5) X-ray structural analyses. Complexes 3 were additionally characterized by (1)H, (13)C, and (31)P {(1)H} NMR spectroscopies.

Polymer encapsulated scorpionate Eu3+ complexes as novel hybrid materials for high performance luminescence applications

N,N,N-Tri(1-pyrazolyl)methane europium complexes, [Eu{HC(pz)3}(H2O)6]Cl3, encapsulated with polymethyl methacrylate (PMMA) gel, polyvinyl acetate (PVA) gel or hexagonal mesoporous silica–PVA (HMS–PVA), have been synthesized, by using a sol–gel technique, as hybrid materials. The geometric structure of the new Eu complex has been confirmed by single crystal X-ray analysis. The hybrid Eu–PVA sample has performed the most effective unit mass luminescence emission with a longer lifetime 444 μs, higher quantum efficiency, greater thermal stability and better exposure durability in comparison to the other Eu–PMMA (379 μs) and Eu–HMS–PVA (55 μs) samples. The characterization results support that these hybrid polymers have made a proper network structure with the Eu3+ complex and act as antennae for the transfer of energy to the central Eu3+ ions, and could be use for enhanced OLED light.

Copper complexes with a flexible piperazinyl arm: nuclearity driven catecholase activity and interactions with biomolecules

Abstract Three new Cu(II) complexes, [Cu(HL1)(pyridine)(H2O)](ClO4)2·2MeOH (1), [Cu2(HL1)2(NO3)2](NO3)2·3H2O (2) and [Cu(HL2)(NO3)2]·MeCN (3), have been synthesized from two Schiff base ligands [HL1 = 1-phenyl-3-((2-(piperazin-4-yl)ethyl)imino)but-1-en-1-ol and HL2 = 4-((2-(piperazin-1-yl)ethyl)imino)pent-2-en-2-ol] using the chair conformer of a flexible piperazinyl moiety. Structural analysis reveals that 1 and 3 are monomeric Cu(II) complexes consisting of five- and six-coordinate Cu(II), respectively, whereas 2 is a dinuclear Cu(II) complex consisting of two different Cu(II) centers, one square planar with the other distorted octahedral. Screening tests were conducted to quantify the binding of 1–3 towards DNA and BSA as well as the DNA cleavage activity of these complexes using gel electrophoresis. Enzyme kinetic studies were also performed for the complexes mimicking catecholase-like activities. Antibacterial activities of these complexes were also examined towards Methicillin-Resistant Staphylococcus aureus bacteria. The results reflect that 2 is more active than the monomeric complexes, which is further corroborated by density functional theory study.

Greener Selective Cycloalkane Oxidations with Hydrogen Peroxide Catalyzed by Copper-5-(4-pyridyl)tetrazolate Metal-Organic Frameworks

Microwave assisted synthesis of the Cu(I) compound [Cu(µ4-4-ptz)]n [1, 4-ptz = 5-(4-pyridyl)tetrazolate] has been performed by employing a relatively easy method and within a shorter period of time compared to its sister compounds. The syntheses of the Cu(II) compounds [Cu3(µ3-4-ptz)4(µ2-N3)2(DMF)2]n∙(DMF)2n (2) and [Cu(µ2-4-ptz)2(H2O)2]n (3) using a similar method were reported previously by us. MOFs 1-3 revealed high catalytic activity toward oxidation of cyclic alkanes (cyclopentane, -hexane and -octane) with aqueous hydrogen peroxide, under very mild conditions (at room temperature), without any added solvent or additive. The most efficient system (2/H2O2) showed, for the oxidation of cyclohexane, a turnover number (TON) of 396 (TOF of 40 h−1), with an overall product yield (cyclohexanol and cyclohexanone) of 40% relative to the substrate. Moreover, the heterogeneous catalytic systems 1–3 allowed an easy catalyst recovery and reuse, at least for four consecutive cycles, maintaining ca. 90% of the initial high activity and concomitant high selectivity.

Nickel tetrazolato complexes synthesized by microwave irradiation: Catecholase like activity and interaction with biomolecules

Abstract 1,3-Dipolar cycloaddition between nickel-ligated azide in [NiL(N3)] [HL = 3-(2-diethylamino-ethylimino)-1-phenyl-butan-1-one] and two different organonitriles furnished two new square-planar complexes viz. [NiL(5-phenyltetrazolato)] and [NiL{5-(4-pyridyl)-tetrazolato}]. Both the complexes have been characterized by spectroscopic tools and single-crystal X-ray crystallography. Interaction with different biomolecules revealed that both complexes bind strongly to serum albumin proteins and show moderate catecholase-like activity by catalyzing the oxidation of 3,5-ditertbutylcatechol (3,5-DTBC). Identification of intermediates formed in catechol oxidation has been explored by ESI-MS spectrometry.

The effect of remote substitution on the formation of preferential isomers of cobalt(III)-tetrazolate complexes by microwave assisted cycloaddition

The 1,3-dipolar cycloaddition reaction of cis-[Co(N3)2(en)2]NO31 with different organonitriles (NCR) under focussed microwave irradiation produced bis-tetrazolate complexes [Co(N4CR)2(en)2](NO3). Interestingly, in the case of 3-cyano pyridine the reaction produced both cis- and trans-isomers (cis-2 and trans-2), whereas for 4-cyano pyridine the compound obtained was exclusively cis (cis-3) and for 4-bromobenzonitrile it was only the trans- (trans-4) compound which was isolated. This indicates a probable role of remote substitution of the phenyl ring in dictating the formation of the preferential isomer. When starting from the trans-isomer of the diazido complex (trans-[Co(N3)2(en)2]ClO4, 1a), upon reacting with different nitriles a mixture of cis- and trans-isomers of [Co(N4CR)2(en)2]ClO4 was produced in each case, with a greater preference towards cis-geometry [R = 4-NC5H4 (cis-5 and trans-5), 4-BrC6H4 (cis-6 and trans-6) and C6H5 (cis-7 and trans-7)]. The preferential formation of the cis-analogue of compound trans-4 when starting from the trans-precursor was quite curious. A theoretical investigation of compounds trans-4 and cis-6 reveals that the greater stability of the trans-complex 4 may arise from additional van der Waals interactions in the solid state because of the presence of an extra DMF molecule as solvent of crystallization. However, an interacting counter-anion and a probable halogen–halogen interaction may also contribute to the formation of preferential isomers for cycloaddition complexes, even in the solution state.

Targeted synthesis of cadmium(II) Schiff base complexes towards corrosion inhibition on mild steel

Three ligands L1 [N,N-dimethyl-N′-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine], L2 [2-morpholino-N-(1-(pyridin-2-yl)ethylidene)ethanamine] and L3 [(2-(piperidin-1-yl)-N-(1-(pyridin-2-yl)ethylidene)ethanamine)] were introduced to prepare five Cd(II) Schiff base complexes [Cd(L1)2](ClO4)2 (1), [Cd(L1)(Cyanoacetate)(OAc)] (2), [Cd2(L1)2(N3)4] (3), [Cd(L2)(N3)2]n (4), [Cd2 (L3)2(N3)4]n (5) and the corrosion inhibition properties of these complexes on mild steel upon treatment with 15% HCl have been examined where azide complexes have shown corrosion inhibition properties as revealed by electrochemical impedance spectroscopy and potentiodynamic polarization. Field emission scanning electron microscopy (FE-SEM) images show that the mild steel surface was protected by cadmium complexes. Among azido complexes polymeric complexes have higher inhibition activity which was further explained using density functional theory. So finally a new bridge between nuclearity driven coordination inorganic chemistry and materials as well as corrosion engineering was established by this observation.

Fine tuning through valence bond tautomerization of ancillary ligands in ruthenium(II) arene complexes for better anticancer activity and enzyme inhibition properties

Four new ruthenium arene PTA type complexes have been synthesized using substituted picolinamide derivatives as ancillary ligands and characterized by spectroscopic methods. In one of the complexes, the ancillary ligand has shown an unprecedented valence-bond tautomerization in the presence of an ammonium salt to act as a polar neutral donor ligand making the ligand more prone towards substitution. The same compound has shown remarkable antiproliferative activity against three cancer cell lines with GI50 values comparable to Adriamycin, a known therapeutic drug. Along with this it also strongly inhibits the action of thioredoxin reductase, which might be a probable reason for the enhanced proliferative action of the valence-bond tautomerized compound.

Discotic Organic Gelators in Ion Sensing, Metallogel Formation and Bioinspired Catalysis.

Two organogelators G2 and G3 with a carboxamide group have been synthesized and characterized with different spectroscopic tools. Dimethylformamide or dimethyl sulfoxide solutions of both the compounds upon the addition of a minute quantity of water show the tendency to form gels. Supramolecular self-assembly for gel formation paves the way for aggregation-induced emission enhancement (AIEE) phenomena for both the gelator molecules. Introduction of metal ions in organogels strengthens the gel property without much affecting the fluorescence behavior. However, the introduction of Ag+, Fe2+, and Fe3+ ions in the G2 organogel separately results in total quenching of AIEE, making it possible to sense that particular cation in the gel state. The G3 organogel shows a similar behavior with the Fe2+ ion. Remarkably, other metallogels such as Ni(II)G2 and Co(II)G2 can sense sulfide ion and Cu(II)G2 can sense iodide ion by switching off the fluorescence even in multianalyte conditions. Furthermore, the copper-based metallogel Cu(II)G2 can be utilized as a catalyst and reaction medium for aerobic oxidation of catechol to quinone. To the best of our knowledge, this is the first attempt known so far to utilize a metallogel material for bioinspired catalysis such as catechol oxidation.