Showing papers by "Sanjit Konar published in 2015"

Stable Multiresponsive Luminescent MOF for Colorimetric Detection of Small Molecules in Selective and Reversible Manner

Abstract: A novel Cu(I)-based two-dimensional (2D, 44 net) metal–organic framework (MOF) [Cu(L)(I)]2n·2nDMF·nMeCN (1); L = 4′-(4-methoxyphenyl)-4,2′:6′,4″-terpyridine; DMF = N,N-dimethylformamide, MeCN = acetonitrile) has been synthesized and found to behave as a colorimetric detector for the widest variety of small molecules such as different solvents, halobenzenes, N-heterocycles, amine, and nitroaromatic explosives all in vapor phase through a single crystal to single crystal (SCSC) transformation. The 2D 44 nets are interdigitated with each other to form a supramolecular 3D MOF having 1D pore. The interdigitated layers are stabilized by π···π interactions and CH···π interactions and provide extreme stability up to 380 °C. Interestingly, all guest exchange and encapsulation processes are reversible without loss of structural integrity. Positions of the guest molecules in the host–guest complex have been identified from the crystal structure and found to involve weak interactions with the framework. Notably, this...

Study of proton conductivity of a 2D flexible MOF and a 1D coordination polymer at higher temperature.

Abstract: We report the proton conduction properties of a 2D flexible MOF and a 1D coordination polymer having the molecular formulas {[Zn(C10H2O8)0.5(C10S2N2H8)]·5H2O]}n (1) and {[Zn(C10H2O8)0.5(C10S2N2H8)]·2H2O]}n (2), respectively. Compounds 1 and 2 show high conductivity values of 2.55 × 10–7 and 4.39 × 10–4 S cm–1 at 80 °C and 95% RH. The conductivity value of compound 1 is in the range of those for previously reported flexible MOFs, and compound 2 shows the highest proton conductivity among the carboxylate-based 1D CPs. The dimensionality and the internal hydrogen bonding connectivity play a vital role in the resultant conductivity. Variable-temperature experiments of both compounds at high humidity reveal that the conductivity values increase with increasing temperature, whereas the variable humidity studies signify the influence of relative humidity on high-temperature proton conductivity. The time-dependent measurements for both compounds demonstrate their ability to retain conductivity up to 10 h.

Nanoscopic molecular magnets

Abstract: Nanoscopic molecular magnets have attracted tremendous interest in recent years both from an experimental and a theoretical point of view because of their potential application in magnetic data storage devices, quantum computing and molecular spintronics. These molecules have crucial advantages over magnetic nanoparticles in terms of their perfectly mono-dispersed phase, chemical flexibility and high purity. This review discusses a few basic concepts that are needed to understand the magnetic properties observed in nanoscopic molecular magnets, a chemical approach for their synthesis and magneto-structural correlations. It includes a few selected examples and discusses the new trends in the field.

Tuning CO2 Uptake and Reversible Iodine Adsorption in Two Isoreticular MOFs through Ligand Functionalization

Abstract: The synthesis and characterization of two isoreticular metal-organic frameworks (MOFs), {[Cd(bdc)(4-bpmh)]}(n)center dot 2n(H2O) (1) and {[Cd(2-NH(2)bdc)(4-bpmh)]}(n)center dot 2n(H2O) (2) [bdc= benzene dicarboxylic acid; 2-NH(2)bdc= 2-amino benzene dicarboxylic acid; 4-bpmh= N, N-bis-pyridin-4-ylmethylene- hydrazine], are reported. Both compounds possess similar two-fold interpenetrated 3D frameworks bridged by dicarboxylates and a 4-bpmh linker. The 2D Cd-dicarboxylate layers are extended along the a-axis to form distorted square grids which are further pillared by 4-bpmh linkers to result in a 3D pillared-bilayer interpenetrated framework. Gas adsorption studies demonstrate that the amino-functionalized MOF 2 shows high selectivity for CO2 (8.4 wt% 273 K and 7.0 wt% 298 K) over CH4, and the uptake amounts are almost double that of non-functional MOF 1. Iodine (I2) adsorption studies reveal that amino-functionalized MOF 2 exhibits a faster I-2 adsorption rate and controlled delivery of I-2 over the non-functionalized homolog 1.

Influence of the coordination environment on slow magnetic relaxation and photoluminescence behavior in two mononuclear dysprosium(III) based single molecule magnets.

Abstract: The reaction of 2,6-bis(1-salicyloylhydrazonoethyl)pyridine [H4daps] with Dy(NO3)3·5H2O led to the formation of two new Dy(III) based complexes with formulae [Dy(H4daps)(H2O)3(NO3)] (NO3)2 (H2O) (1) and [Dy(H3daps)(H2O)2(NO3)] (NO3) (MeOH) (2). Complexes 1 and 2 were characterized by crystal structure determination, magnetic measurements and photoluminescence studies. In comparison with complex 1, complex 2 shows a slight difference of local symmetry around the Dy(III) center which is attributed to deprotonation of the ligand and also to different binding modes of the peripheral NO3− anion. AC magnetic susceptibility measurements reveal that both complexes exhibit single-molecule magnet (SMM) behavior, with the thermal energy barrier of 1 being higher than that of 2 (Ueff = 32.7 K for 1 and 23.8 K for 2). Our investigation discloses that small differences in the coordination environment around the metal centre played an important role in the difference in relaxation dynamics of the complexes. Solid state photoluminescence studies showed their photoluminescence behaviour with quantum yields of 0.98 and 1.44%.

Proton-Conducting Magnetic Coordination Polymers.

Abstract: Three isostructural lanthanide-based two- dimensional coordination polymers (CPs) {[Ln2(L)3(H2O)2]n⋅2n CH3OH)⋅2n H2O} (Ln=Gd(3+) (1), Tb(3+) (2), Dy(3+) (3); H2L=cyclobutane-1,1-dicarboxylic acid) were synthesized by using a low molecular weight dicarboxylate ligand and characterized. Single-crystal structure analysis showed that in complexes 1-3 lanthanide centers are connected by μ3-bridging cyclobutanedicarboxylate ligands along the c axis to form a rod-shaped infinite 1D coordination chain, which is further linked with nearby chains by μ4-connected cyclobutanedicarboxylate ligands to form 2D CPs in the bc plane. Viewing the packing of the complexes down the b axis reveals that the lattice methanol molecules are located in the interlayer space between the adjacent 2D layers and form H-bonds with lattice and coordinated water molecules to form 1D chains. Magnetic properties of complexes 1-3 were thoroughly investigated. Complex 1 exhibits dominant ferromagnetic interaction between two nearby gadolinium centers and also acts as a cryogenic magnetic refrigerant having a significant magnetic entropy change of -ΔSm=32.8 J kg(-1) K(-1) for ΔH=7 T at 4 K (calculated from isothermal magnetization data). Complex 3 shows slow relaxation of magnetization below 10 K. Impedance analysis revealed that the complexes show humidity-dependent proton conductivity (σ=1.5×10(-5) S cm(-1) for 1, σ=2.07×10(-4) S cm(-1) for 2, and σ=1.1×10(-3) S cm(-1) for 3) at elevated temperature (>75 °C). They retain the conductivity for up to 10 h at high temperature and high humidity. Furthermore, the proton conductivity results were correlated with the number of water molecules from the water-vapor adsorption measurements. Water-vapor adsorption studies showed hysteretic and two-step water vapor adsorption (182,000 μL g(-1) for 1, 184,000 μL g(-1) for 2, and 1,874,000 μL g(-1) for 3) in the experimental pressure range. Simulation of water-vapor adsorption by the Monte Carlo method (for 1) confirmed the high density of adsorbed water molecules, preferentially in the interlayer space between the 2D layers.

Synthesis and Characterization of Polyhedral-Based Metal–Organic Frameworks Using a Flexible Bipyrazole Ligand: Topological Analysis and Sorption Property Studies

Abstract: Six porous metal–organic frameworks (MOFs), {[Ni(BTC)0.66(BPz)2]·2MeOH·4H2O}n (1), {[Co(BTC)0.66(BPz)2]·2MeOH·4H2O}n (2), {[Mn(BTC)0.66(BPz)2]·2MeOH·4H2O}n (3), {[Cd(BDC)(BPz)(H2O)]·2MeOH·DMF}n (4), {[Cd2(NH2-BDC)2(BPz)(H2O)]·MeOH·H2O·DMF}n (5), and {[Co(BDC)(BPz)(H2O)]}n (6) (where H3BTC = 1,3,5-benzenetricarboxylic acid, H2BDC = 1,4-benzenedicarboxylic acid, NH2-H2BDC = 2-amino-1,4-benzenedicarboxylic acid, and BPz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole), were obtained through a solvent diffusion technique and characterized. The networks exhibit a variety of topologies: 1, 2, and 3 are isostructural and possess octahedral and cuboctahedra type cages and exhibit 3,6-c binodal net having loh1 topology, 4 is a two-dimensional MOF having one-dimensional open channels with a 4-c uninodal net having sql topology, 5 exhibits a three-dimensional (3D) porous MOF having a 3,3,4,8-c net with a new topology having the name, skr1, whereas 6 discloses a 3D nonporous network which exhibits a 4-c uninodal net having C...

A family of Fe3+ based double-stranded helicates showing a magnetocaloric effect, and Rhodamine B dye and DNA binding activities

Abstract: Herein, the synthesis, structural characterization, magnetic properties and guest binding activities of four Fe3+ based double-stranded helicates namely; [Fe2(L)2](ClO4)(Cl)·4(CH3OH)·2(H2O) (1), [Fe2(L)2](BF4)2·2(H2O) (2), [Fe2(L)2](NO3)2·3(CH3OH)·2(H2O) (3), and [Fe2(L)2](Cl)2·2(CH3OH)·4(H2O) (4) are reported. Complexes 1–4 have been synthesized using the hydrazide-based ligand H2L (H2L = N′1,N′4-bis(2-hydroxybenzylidene)succinohydrazide) and the corresponding Fe2+ salts. Each of the independent cationic complexes [Fe2(L)2]2+ shows double-stranded helicates from the self-assembly of the ligand and metal ions in a 2 : 2 ratio, where the individual Fe3+ centre is lying on a C2-axis and the ligand strands wrap around it. In 1–4, ligand L adopts “pseudo-C” conformations and forms a double-stranded dinuclear helicate with a small cage in between them. Moreover, in 1–4, each of the independent cationic complexes [Fe2L2]2+ is inherently chiral and possesses P for right-hand and M for left-hand helicity and as a consequence is a racemic solid. Detailed magnetic studies of all the complexes reveal that the Fe3+ centres are magnetically isolated and isotropic in nature. Estimation of the Magnetocaloric Effect (MCE) from magnetization data unveils a moderate MCE at a temperature of 3 K with magnetic entropy changes (−ΔSm) of 22.9, 27.7, 24.1, 26.5 J kg−1 K−1 at a magnetic field of 7 T for complexes 1–4, respectively. Also, the variation of the −ΔSm values was justified by considering the parameter of magnetization per unit mass. Stability of all the complexes in solution phase was confirmed by ESI-mass spectrometric analysis and liquid phase FT-IR spectroscopy. Further, the interaction of the complexes 1–4 with Rhodamine B dye was examined by UV-vis and fluorescence spectroscopic study. The observed blue-shift in the fluorescence study and hyperchromicity and hypochromicity with the appearance of two isosbestic points in the UV-vis study ascertain the interactions of the dye with the complexes. A DNA binding study by absorption spectral titration suggests the weak external intercalation of complex 1 within the nucleotide of calf thymus DNA. Computational study supports the isotropic nature of the metal centres and the consequent high spin multiplicity, which assists the complexes to show significant magnetic entropy changes.

Regulation of the pore size by shifting the coordination sites of ligands in two MOFs: enhancement of CO2 uptake and selective sensing of nitrobenzene

Abstract: Two metal–organic frameworks (MOFs), namely {[Cd2(sdb)2(4-bpmh)2(H2O)]}n·2n(H2O) (1), {[Cd2(sdb)2(3-bpmh)2]}n·3n(H2O)·n(C6H5NO) (2), [sdb = 4,4′-sulfonyl dibenzoic acid; 4-bpmh = N,N-bis-pyridin-4-ylmethylene-hydrazine, 3-bpmh = N,N-bis-pyridin-3-ylmethylene-hydrazine, C6H5NO = 3-pyridinecarboxaldehyde] have been synthesized by the solvent diffusion technique at room temperature. Structure determination reveals that compound 1 has 2D interdigitated architectures, whereas 2 is a 2-fold interwoven 3D porous network but both 1 and 2 have a common secondary building unit (SBU) [Cd2(sdb)4(L)4] [L = 4-bpmh (1) and 3-bpmh (2)]. Gas adsorption studies demonstrate that compound 2 shows high selectivity for CO2 over CH4 and the uptake amounts are almost double in comparison with compound 1 and both the compounds show high sensitivity for nitrobenzene via the fluorescence quenching mechanism.

Europium-Based Dinuclear Triple-Stranded Helicate vs. Tetranuclear Quadruple-Stranded Helicate: Effect of Stoichiometric Ratio on the Supramolecular Self-Assembly

Abstract: Two europium-based helicates, namely the dinuclear triple-stranded helicate [Eu2L3] (1) and tetranuclear quadruple-stranded helicate [Eu4L4(NO3)](3+) (2), were achieved by the self-assembly of the succinohydrazone derived bis-tridentate ligand (H2L) and Eu3+ ions in 1:1 and 1:2 ratios, respectively. Both the helicates were characterized by single-crystal X-ray analysis. Structural analysis of both the helicates revealed optically inactive 50:50 mixtures of left- (Lambda) and right-hand (Delta) helicates in one unit cell. In 1, both the europium centers lie along the three-fold axis whereas in 2, four europium centers are arranged in a triangular fashion around the four-fold axis, which passes through the center of the quadruple stranded helicate. In 2, the presence of a nitrate ion on the nucleation of the aesthetically pleasing tetranuclear quadruple stranded helicate is significant. Apart from the molar ratio, the role of the bridging modes of the ligand, anion and noncovalent interaction on the self-assembly of two helicates are also discussed.

Structural Adaptation of Ni4O4 Units To Form Cubane, Open Dicubane, Dimeric Cubane, and One-Dimensional Polymeric Cubanes: Magnetostructural Correlation of Ni4 Clusters

Abstract: The complexation reactions of a tripodal chelating ligand, [3,5-bis(2-amino-ethyl)-[1,3,5]triazinan-1-yl]-methanol (L), which is produced by the in situ transformation of 1,3,6,8-tetraazatricyclo[4.4.1.13,8]dodecane (L1) with Ni(NO3)2·6H2O has been explored in the presence of ammonium salts of inorganic and organic anions. These reactions resulted in four crystalline complexes [Ni4(L)2(μ3-OH)2(NCS)4]·4H2O (1), [Ni4(L)2(μ2-N3)4(N3)2]·2H2O (2), [Ni8(L)4(μ3-OH)4(BDC)3(H2O)4]·BDC·28(H2O) (3, BDC = 1,4-benzene dicarboxylate) and {[Ni4(L)2(μ3-OH)2(NDS)2(H2O)2]·NDS·11(H2O)}n (4, NDS = naphthalene-1,5-disulfonate). The crystal structure analyses of 1–4 reveal that all contain Ni(II) clusters, which act as secondary building units to generate higher order aggregates. The complexes 1, 3, and 4 contain exclusively Ni4 cubane units: a discrete cubane in 1, a dimer of cubanes linked by BDC in 3, and cubanes linked in one dimension by NDS to form a 1D-coordination polymer in 4. Interestingly, complex 2 exhibits an open...

Concomitant spin-canted antiferromagnetic ordering and proton conduction in homometallic and homoleptic coordination polymers

Abstract: Two unprecedented oxonate based 1D coordination polymers with FeII and CoII have been synthesized. A detailed magnetic investigation revealed that these complexes are the first oxonate based systems to exhibit spin canted antiferromagnetic ordering at low temperatures. Proton conductivity studies of the complexes showed good proton conduction ability at elevated temperatures and under high humidity conditions.

Exploration of the structural features and magnetic behaviour in a novel 3-dimensional interpenetrating Co(II)-based framework

Abstract: A new Co(II)-based three-dimensional (3D) framework having the molecular formula [Co(C4O4) (4-bpmh))H2O)2]n⋅ 2nH2O⋅2nMeOH ⋅(1) (4-bpmh = N, N-bis-pyridin-4-ylmethylene-hydrazine) has been synthesized using a mixed ligand system and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, single crystal X-ray diffraction and variable temperature magnetic study. The framework is constructed by the bridging squarate (C $_{\mathrm{4}}$O$_{\mathrm{4}}^{\mathrm{2-}}) $ and N, N-bis-pyridin-4-ylmethylene-hydrazine (4-bpmh) ligands and interpenetration of the 2D grid-like frameworks at definite angles gives rise to 2D → 3D inclined polycatenation with sql/Shubnikov tetragonal plane net topology. Extensive non-covalent interactions (H-bonding as well as π⋯π interactions) are also observed which stabilises the 3D arrangement. Additionally, complex 1 contains 1D channels of large dimensions (10.91 × 11.78 A2) that runs along the b-axis. Variable temperature DC magnetic susceptibility study reveals dominant spin–orbit coupling effect typical of the 4 T 1g ground state of octahedral high-spin Co(II) ion at a higher temperature range.