One-pot general synthesis of metalloporphyrins

A new general one-pot method for the synthesis of various metalloporphyrins has been developed from pyrrole and substituted aldehydes using transition metal salts. This method allows higher working concentrations than those previously reported. Along with the reported metalloporphyrins, some new metalloporphyrins were synthesized in good yield.     

Modification of polystyrene maleic anhydride for efficient energy storage applications

Journal of Solid State Electrochemistry - The development of new energy storage devices has been gaining momentum in the wake of the energy crisis faced worldwide. New materials have been tried and...     

One-pot thioetherification of aryl halides with thiourea and benzyl bromide in water catalyzed by Cu-grafted furfural imine-functionalized mesoporous SBA-15

Surface functionalization of SBA-15 followed by its reaction with Cu(OAc)(2) has been carried out to develop a new Cu-grafted functionalized mesoporous material, which catalyzes one-pot three component coupling of different aryl halides with thiourea and benzyl bromide in aqueous medium to produce aryl thioethers in very good yields (80-88%).     

Enhanced ferromagnetic transition temperature in nanocrystalline lanthanum calcium manganese oxide (La0.67Ca0.33MnO3)

We report a novel, low temperature (450-600 °C) route for the synthesis of highly crystalline and homogeneous nanoparticles of lanthanum calcium manganese oxide La_0.67Ca_0.33MnO₃ (LCMO). The nanocrystallites, with average particle size of 30 nm, possess a ferromagnetic-paramagnetic transition temperature (T_c) of 300 K, which is about 50 K higher than that of a bulk single crystal. The transition temperature was found to be inversely proportional to the particle size. The Rietveld analysis of the powder X-ray diffraction data of the phase-pure nanopowders reveals that the particle size reduction leads to a significant contraction of the unit cell volume and a reduction of the unit cell anisotropy. We propose that these two lattice effects are responsible for the observed enhancement in T_c.     

Temperature dependence of the gap in the density of states near the Fermi level in a hole doped manganite

In this paper, we report a model-based quantitative analysis of temperature dependent scanning tunneling spectroscopy (STS) data taken on epitaxial thin films of the hole doped manganite La_0.7Ca_0.3MnO₃. The film, grown on lattice matched NdGaO₃ substrate, has a ferromagnetic transition temperature T_c=268 K. The analysis allows us to evaluate how the tunneling curve evolves across the transition temperature. We find that there is a gap Δ in the density of states (DOS), which peaks at T≈T_c. The gap closes in the ferromagnetic state following the evolution of the magnetization. The gap closing is gradual and not sudden at T=T_c. Above T_c the gap reduces from the peak value and reaches a limiting value of ≈75 meV for T/T_c≥1.1 which is close to the value of 60 meV seen from transport experiments.     

Syntheses, structures, and magnetic properties of three one-dimensional end-to-end azide/cyanate-bridged copper(II) compounds exhibiting ferromagnetic interaction: new type of solid state isomerism

The work in this paper presents the syntheses, structures, and magnetic properties of three end-to-end (EE) azide/cyanate-bridged copper(II) compounds [Cu(II)L(1)(μ(1,3)-NCO)](n)·2nH(2)O (1), [Cu(II)L(1)(μ(1,3)-N(3))](n)·2nH(2)O (2), and [Cu(II)L(2)(μ(1,3)-N(3))](n) (3), where the ligands used to achieve these species, HL(1) and HL(2), are the tridentate Schiff base ligands obtained from [1 + 1] condensations of salicylaldehyde with 4-(2-aminoethyl)-morpholine and 3-methoxy salicylaldehyde with 1-(2-aminoethyl)-piperidine, respectively. Compounds 1 and 2 crystallize in the monoclinic P2(1)/c space group, while compound 3 crystallizes in the orthorhombic Pbca space group. The metal center in 1-3 is in all cases pentacoordinated. Three coordination positions of the metal center in 1, 2, or 3 are satisfied by the phenoxo oxygen atom, imine nitrogen atom, and morpholine (for 1 and 2) or piperidine (for 3) nitrogen atom of one deprotonated ligand, [L(1)](-) or [L(2)](-). The remaining two coordination positions are satisfied by two nitrogen atoms of two end-to-end bridging azide ligands for 2 and 3 and one nitrogen atom and one oxygen atom of two end-to-end bridging cyanate ligands for 1. The coordination geometry of the metal ion is distorted square pyramidal in which one EE azide/cyanate occupies the apical position. Variable-temperature (2-300 K) magnetic susceptibilities of 1-3 have been measured under magnetic fields of 0.05 (from 2 to 30 K) and 1.0 T (from 30 to 300 K). The simulation reveals a ferromagnetic interaction in all three compounds with J values of +0.19 ± 0.01, +0.79 ± 0.01, and +1.25 ± 0.007 cm(-1) for 1, 2, and 3, respectively. Compound 1 is the sole example of a ferromagnetically coupled EE cyanate-bridged 1-D copper(II) system. In addition, a rare example of supramolecular isomerism and a nice example of magnetic isomerism have been observed and most interestingly a new type of solid state isomerism has emerged as a result of the comparison of the structure and magnetic properties of 2 with a previously published compound (2A) having the same composition and even the same crystal system and space group (New J. Chem.2001, 25, 1203-1207).     

Modulating Hierarchical Micro/Mesoporosity by a Mixed Solvent Approach in Al-MOF: Stabilization of MAPbBr3 Quantum Dots

Various hierarchical micro/mesoporous MOFs based on {[Al(μ-OH)(1,4-NDC)]⋅H₂O} ( MOF1 ) with tunable porosities (pore volume and surface area) have been synthesized by assembling Al^III and 1,4-NDC (1,4-naphthalenedicarboxylate) under microwave irradiation by varying water/ethanol solvent ratio. Water/ethanol mixture has played a crucial role in the mesopore generation in MOF1M₂₅ , MOF1M₅₀ , and MOF1M₇₅ , which is achieved by in situ formation of water/ethanol clusters. By adjusting the ratio of water/ethanol, the particle size, surface area and micro/mesopore volume fraction of the MOFs are controlled. Furthermore, reaction time plays a critical role in mesopore formation as realized by varying reaction time for the MOF with 50 % ethanol ( MOF1M₅₀ ). Additionally, hierarchical MOF ( MOF1M₅₀ ) has been used as a template for the stabilization of MAPbBr₃ (MA=methylammonium) perovskite quantum dots (PQDs). MAPbBr₃ PQDs are grown inside MOF1M₅₀ , where mesopores control the size of PQDs which leads to quantum confinement.     

Heterobridged dinuclear, tetranuclear, dinuclear-based 1-d, and heptanuclear-based 1-D complexes of copper(II) derived from a dinucleating ligand: syntheses, structures, magnetochemistry, spectroscopy, and catecholase activity

The work in this paper presents syntheses, characterization, crystal structures, variable-temperature/field magnetic properties, catecholase activity, and electrospray ionization mass spectroscopic (ESI-MS positive) study of five copper(II) complexes of composition [Cu(II)(2)L(μ(1,1)-NO(3))(H(2)O)(NO(3))](NO(3)) (1), [{Cu(II)(2)L(μ-OH)(H(2)O)}(μ-ClO(4))](n)(ClO(4))(n) (2), [{Cu(II)(2)L(NCS)(2)}(μ(1,3)-NCS)](n) (3), [{Cu(II)(2)L(μ(1,1)-N(3))(ClO(4))}(2)(μ(1,3)-N(3))(2)] (4), and [{Cu(II)(2)L(μ-OH)}{Cu(II)(2)L(μ(1,1)-N(3))}{Cu(II)(μ(1,1)-N(3))(4)(dmf)}{Cu(II)(2)(μ(1,1)-N(3))(2)(N(3))(4)}](n)·ndmf (5), derived from a new compartmental ligand 2,6-bis[N-(2-pyridylethyl)formidoyl]-4-ethylphenol, which is the 1:2 condensation product of 4-ethyl-2,6-diformylphenol and 2-(2-aminoethyl)pyridine. The title compounds are either of the following nuclearities/topologies: dinuclear (1), dinuclear-based one-dimensional (2 and 3), tetranuclear (4), and heptanuclear-based one-dimensional (5). The bridging moieties in 1-5 are as follows: μ-phenoxo-μ(1,1)-nitrate (1), μ-phenoxo-μ-hydroxo and μ-perchlorate (2), μ-phenoxo and μ(1,3)-thiocyanate (3), μ-phenoxo-μ(1,1)-azide and μ(1,3)-azide (4), μ-phenoxo-μ-hydroxo, μ-phenoxo-μ(1,1)-azide, and μ(1,1)-azide (5). All the five compounds exhibit overall antiferromagnetic interaction. The J values in 1-4 have been determined (-135 cm(-1) for 1, -298 cm(-1) for 2, -105 cm(-1) for 3, -119.5 cm(-1) for 4). The pairwise interactions in 5 have been evaluated qualitatively to result in S(T) = 3/2 spin ground state, which has been verified by magnetization experiment. Utilizing 3,5-di-tert-butyl catechol (3,5-DTBCH(2)) as the substrate, catecholase activity of all the five complexes have been checked. While 1 and 3 are inactive, complexes 2, 4, and 5 show catecholase activity with turn over numbers 39 h(-1) (for 2), 40 h(-1) (for 4), and 48 h(-1) (for 5) in dmf and 167 h(-1) (for 2) and 215 h(-1) (for 4) in acetonitrile. Conductance of the dmf solution of the complexes has been measured, revealing that bridging moieties and nuclearity have been almost retained in solution. Electrospray ionization mass (ESI-MS positive) spectra of complexes 1, 2, and 4 have been recorded in acetonitrile solutions and the positive ions have been well characterized. ESI-MS positive spectrum of complex 2 in presence of 3,5-DTBCH(2) have also been recorded and, interestingly, a positive ion [Cu(II)(2)L(μ-3,5-DTBC(2-))(3,5-DTBCH(-))Na(I)](+) has been identified.     

Dynamic Resolution of Piezosensitivity in Single Crystals of π-Conjugated Molecules

Targeted synthesis of piezoresponsive small molecules and in-depth understanding of their mechanism is of utmost importance for the development of smart devices. This work reports the synthesis, structure and piezosensitivity of a bola-amphiphile 1,4-bis(pentyloxy)-2,5-bis(2-pyridineethynyl)-benzene ( C5-PPB ). Depending on the rate of compression, two different phases in C5-PPB can be generated. The ambient-pressure α-phase is stable up to 0.8 GPa, beyond which it undergoes an isostructural transformation to β-phase, accompanied by a clearly visible elongation of the crystal. This α-to-β phase transition requires the sample to be compressed slowly. When quickly compressed, phase α persists to about 1.5 GPa, beyond which its amorphization starts, accompanied by the appearance of irregular grooves on the largest faces. Mechanical pressure also affects the optical property of C5-PPB , which shows reversible mechanochromism with a green to cyan transformation in the emission, associated with a 15 nm shift in the maxima. The conductivity of C5-PPB as a direct outcome of its crystal packing has also been studied.