Three-Dimensional Ni-MOF as a High-Performance Supercapacitor Anode Material; Experimental and Theoretical Insight.

A three-dimensional (3D) Ni-MOF of the formula [Ni(C4H4N2)(CHO2)2]n, has been reported, which shows a capacitance of 2150 F/g at a current density of 1A/g in a three-electrode setup (5.0 M KOH). Post-mortem analysis of the sample after three-electrode measurements revealed the bias-induced transformation of Ni-MOF to Ni(OH)2, which has organic constituents intercalated within the sample exhibiting better storage performance than bulk Ni(OH)2. Afterward, the synthesized MOF and reduced graphene (rGO) were used as the anode and cathode electrode material, respectively, and a two-electrode asymmetric supercapacitor device (ASC) setup was designed that exhibited a capacitance of 125 F/g (at 0.2 A/g) with a high energy density of 50.17 Wh/kg at a power density of 335.1 W/kg. The ASC further has a very high reversibility (97.9% Coulombic efficiency) and cyclic stability (94%) after 5000 constant charge-discharge cycles. Its applicability was also demonstrated by running a digital watch. Using sophisticated density functional theory simulations, the electronic properties, diffusion energy barrier for the electrolytic ions (K+), and quantum capacitance for the Ni(OH)2 electrode have been reported. The lower diffusion energy barrier (0.275 eV) and higher quantum capacitance (1150 µF/cm2) are attributed to the higher charge storage performance of the Ni-MOF-transformed Ni(OH)2 electrode as observed in the experiment.

Insight into the structure and transport properties of pyrrolidinium-based geminal dicationic-organic ionic crystals: unravelling the role of alkyl-chain length.

The present study has been undertaken with an aim to design and develop safer and more efficient all solid-state electrolytes, so that the issues associated with the use of conventional room temperature ionic liquid-based electrolytes can be tackled. To fulfil this objective, a series of geminal di-cationic Organic Ionic Crystals (OICs), based on C3-, C6-, C8- and C9-alkylbridged bis-(methylpyrrolidinium)bromide are synthesized, and the structural features, thermal properties and phase behaviours of these as synthesized OICs have been investigated. Additionally, a number of electro-analytical techniques have been employed to assess their suitability as an efficient electrolyte composite (OIC:I2:TBAI) for all solid-state dye sensitised solar cells (DSSCs). The structural analysis has revealed that along with excellent thermal stability and well-defined surface morphology, all thsese OICs exhibit a well-ordered three-dimensional network of cations and anions that can serve as a conducting channel for the diffusion of iodide ions. Electrochemical investigations have shown that OICs with an intermediate length of alkyl bridge (C6- and C8-alkyl bridged) show better electrolytic performance than those that are based on OICs with a relatively shorter (C3-) or longer (C9-) alkyl-bridge chain. A careful analysis of the above data has essentially demonstrated that the length of the alkyl bridge chain plays a significant role in determining the structural organisation, morphology and eventually the ionic conductivity of OICs. Overall, the comprehensive knowledge on OICs that has been extracted from the current study is expected to be helpful to explore further new types of OIC-based all solid-state electrolytes with improved electrolytic performance for targeted applications.

NiSe2 Nanoparticles Encapsulated in N-Doped Carbon Matrix Derived from a One-Dimensional Ni-MOF: An Efficient and Sustained Electrocatalyst for Hydrogen Evolution Reaction.

The spherical-type NiSe2 nanoparticles encapsulated in a N-doped carbon (NC) matrix (NiSe2-T@NC, temperature (T) = 400-800 °C) are derived from a 1D Ni-MOF precursor of the formula [Ni(BPY)(DDE)] [(BPY = 2,2'-bipyridyl), (DDE = 4,4'-dicarboxy diphenyl ether)] via a facile solvothermal technique followed by annealing at different temperatures and selenylation strategies. The combined effect of a NC matrix and the Ni nanoparticles has been optimized during varied annealing processes with subsequent selenylation, leading to the formation of the series NiSe2-400@NC, NiSe2-500@NC, NiSe2-600@NC, NiSe2-700@NC, and NiSe2-800@NC, respectively. The variation of annealing temperature plays a vital role in optimizing the catalytic behavior of the NiSe2-T@NCs. Among different high-temperature annealed products, NiSe2-600@NC shows superior electrocatalytic performance because of the unique spherical-type morphology and higher specific surface area (57.95 m2 g-1) that provides a large number of electrochemical active sites. The synthesized material exhibits a lower overpotential of 196 mV to deliver 10 mA cm-2 current density, a small Tafel slope of 45 mV dec-1 for better surface kinetics, and outstanding durability in an acidic solution, respectively. Consequently, the post stability study of the used electrocatalyst gives insight into surface phase analysis. Therefore, we presume that the synthesized 1D MOF precursor derived NiSe2 nanoparticles encapsulated in a NC matrix has excellent potential to replace the noble-metal-based electrocatalyst for enhanced hydrogen evolution through simple water electrolysis.

Temperature-Dependent Superhydrophobic Functionalized Coordination Polymers (SFCPs) for Selective Adsorption of C2H4 over C2H6.

We prepared two new superhydrophobic functionalized coordination polymers (SFCPs) [Zn4(OH)2(BTMB)2(4,4'-Bipy)2]∞ ⊃ solvent, 1, and [Cd4(OH)2(BTMB)2(4,4'-Bipy)3]∞ ⊃ solvent, 2, by solvothermal methods. For 1, the single-crystal XRD structure revealed that it contains two crystallographically distinct Zn2+ ions with two different types of coordination geometries of 4 and 6, exhibiting a unique superhydrophobic behavior with microporosity. Compound 1 exhibits superhydrophobicity with a contact angle of 155.5° (at 30 °C), which is stable even at high temperatures, whereas for the SFCP 2, all of the Cd2+ ions have only 6-coordination and exhibit a superhydrophobic character at room temperature with a contact angle of 156.7°(at 30 °C). However, surprisingly, this superhydrophobic character is stable only up to 60 °C, above which it is converted to hydrophilic nature, in contrast to the SFCP 1. Moreover, in this study, we also report a selective gas adsorption study of two C2 gases with similar kinetic diameters (∼3.9 Å) of ethylene over ethane.

Impact of Iron in Three-Dimensional Co-MOF for Electrocatalytic Water Oxidation.

The integration of iron (Fe) into a cobalt metal-organic framework (Co-MOF) tunes the electronic structure of the parent MOF as well as enhances their electrocatalytic characteristics. By using pyrazine and hydrofluoric acid, we have synthesized three-dimensional Co-MOF [CoFC4H4N2(SO4)0.5], (1), and Fe-MOF [FeFC4H4N2(SO4)0.5], (2), through a single-step solvothermal method. Further, a series of bimetallic (having both Co and Fe metal centers) MOFs [Co1-xFexFC4H4N2(SO4)0.5] were synthesized with variable concentrations of Fe, and their electrocatalytic performances were analyzed. The optimized amount of Fe significantly impacted the electrocatalytic behavior of the bimetallic MOF toward water oxidation. Particularly, the Co0.75Fe0.25-MOF needs only 239 and 257 mV of overpotential to deliver 10 and 50 mA/cm2 current density, respectively, in alkaline electrolytic conditions. The Co0.75Fe0.25-MOF shows a lower Tafel slope (42 mV/dec.) among other bimetallic MOFs and even the commercial RuO2, and it has excellent durability (with ∼8 mV increases in overpotential after 18 h of electrolysis) and 97.05% Faradaic efficiency, which further evident its catalytic excellency. These findings explore the intrinsic properties of MOF-based electrocatalysts and prospect the suitability for future water electrolysis.

Unusual CO2 Adsorption in ZIF-7: Insight from Raman Spectroscopy and Computational Studies.

Here, we use Raman spectroscopy to investigate temperature-dependent changes in the atomic-scale structure of the zeolitic imidazolate framework ZIF-7 in a CO2 atmosphere and uncover the mechanism of maximal CO2 adsorption at 206 K. At 301 K, the Raman spectra of ZIF-7 at various CO2 gas pressures reveal a narrow-pore (np) to large-pore (lp) phase transition commencing at 0.1 bar as a result of adsorption of CO2, as evident in the appearance of Fermi resonance bands of CO2 at 1272 and 1376 cm-1. Moreover, the Raman inactive bending mode of CO2 becomes active due to geometrical distortion of adsorbed CO2. It further splits into two peaks due to hydrogen bonding interactions between CO2 and the benzene ring of the benzimidazole linker ZIF-7, as supported by our computational studies. In addition, the interaction between CO2 molecules plays a key role. Upon reducing the temperature at 1 bar CO2 gas pressure, ZIF-7 exhibits softening of the imidazole puckering mode and the Fermi resonance CO2 band due to interactions between CO2 and the framework through hydrogen bonding. At 206 K, substantial modification in the lattice mode and disappearance of the Raman inactive CO2 bending mode confirm the changes in the size of the pore cavity through structural rearrangements of CO2.

Design and synthesis of purine connected piperazine derivatives as novel inhibitors of Mycobacterium tuberculosis.

A series of novel purine linked piperazine derivatives were synthesized to identify new, potent inhibitors of Mycobacterium tuberculosis. The compounds were designed to target MurB disrupting the biosynthesis of the peptidoglycan and exert antiproliferative effects. The first series of purine-2,6-dione linked piperazine derivatives were synthesized using an advanced intermediate 1-(3,4-difluorobenzyl)-7-(but-2-ynyl)-3-methyl-8-(piperazin-1-yl)-1H-purine-2,6(3H,7H)-dione hydrochloride (6) which was coupled with varied carboxylic acid chloride derivatives. Following this piperazine linked derivatives were also synthesized from 6 using diverse isocyanate partners. The anti-mycobacterial activity of the analogues was tested againstMycobacterium tuberculosis H37Rv which revealed a cluster of six analogues (11, 24,27, 32, 33 and34), possessed promising activity. In comparison, a set of these new compounds possessed greater potencies relative to current drugs used in the clinic such as Ethambutol. These results were also correlated with computational molecular docking analysis, providing models for strong interactions of the inhibitors with MurB providing a template for the future development of preclinical agents against Mycobacterium tuberculosis.

In Situ Transformed Cobalt Metal-Organic Framework Electrocatalysts for the Electrochemical Oxygen Evolution Reaction.

The development of an active and efficient electrocatalyst for the oxygen evolution reaction remains indispensable for the smooth running of an electrolyzer. Herein, we have synthesized two cobalt metal-organic frameworks (Co-MOFs) with the formulas [C6H6CoN2O4] (compound 1) and [C12H10CoN2O4] (compound 2) using pyrazine and 4,4'-bipyridine as linkers in dimethylformamide medium by a solvothermal method. Both Co-MOFs shows strong antiferromagnetic interactions with Θp = -70 and -61 K for compounds 1 and 2, respectively. The in situ transformation of both compounds catalyzes the OER efficiently in alkaline medium, affording a current density of 10 mA/cm2 at overpotentials of 276 ± 3 and 302 ± 3 mV by compounds 1 and 2, respectively. Moreover, compound 1 shows a very high turnover frequency (15.087 s-1), lower Tafel slope (56 mV/dec), and greater Faradaic efficiency of 95.42% in comparison to compound 2. The transformations of the Co-MOFs have been accessed by employing powder X-ray diffraction (PXRD), high-resolution transmission electron microscopic (HRTEM) analysis, and X-ray photoelectron spectroscopy, which reveal the formation of uniform hexagonal Co(OH)2 plates. Therefore, the as-developed Co-MOF is found to be an efficient pre-electrocatalyst for the OER in alkaline medium. These results not only reveal the preparation of OER electrocatalysts from a Co-MOF but also establish a method to derive a potentially active electrocatalyst to substitute for the traditional noble-metal-based materials.

A Dense I1O3 Hybrid Superhydrophobic Network, Pb(H-BTMB), Exhibits Selectivity toward CO2 Gas Sorption.

We achieved a dense I1O3 hybrid superhydrophobic porous coordination polymer (PCP), [Pb(H-BTMB)(DMF)] (1), by solvothermal methods. The single-crystal XRD structure of 1 indicated that it has a three-dimensional M-L-M framework with one-dimensional M-O-M connectivity leading to an I1O3 network. The new PCP obtained exhibited open metal sites (OMSs) by losing a coordinated DMF molecule. The degassed phase displayed selective adsorption of CO2 gas over N2, C2H6, and C2H4 gases. Additionally, it has a superhydrophobic surface with a contact angle of 156.4° at room temperature and it is stable even at 90 °C, displaying a contact angle of 135.3°.

Ruthenium-doped cobalt sulphide electrocatalyst derived from a ruthenium-cobalt Prussian blue analogue (RuCo-PBA) for an enhanced hydrogen evolution reaction (HER).

The designing of efficient electrocatalysts for hydrogen generation is essential for the practical application of water-splitting devices. With numerous electrochemical advantages, transition metal sulphides are regarded as the most promising candidates for catalysing the hydrogen evolution reaction (HER) in acidic media. In the present study, Ru-doped cobalt sulphide nanosheets, termed Co9S8/Ru@t (t = 24 h, 48 h, and 72 h), were obtained by varying the reaction time from 24 h to 72 h from a RuCo-PBA precursor. The role of the time period for the synthesis of Co9S8/Ru@48h is vital in increasing the number of electroactive sites and optimising the hydrogen adsorption-desorption phenomena leading to an increment in the HER activity. The electrochemical outcomes demonstrate that the optimized Co9S8/Ru@48h requires a low overpotential of just 94 mV to produce 10 mA cm-2 current density, and also exhibits a lower Tafel slope value of 84 mV dec-1 defining its faster reaction kinetics. The as-synthesized Co9S8/Ru@48h was stable for up to 20 h of constant electrolysis signifying its outstanding durability. The optimized synthetic approach and impressive electrochemical results make Co9S8/Ru@48h a suitable alternative to noble-metal-based electrocatalysts for the HER.

Ru Prussian blue analogue-derived Ru nanoparticles composited with a trace amount of Pt as an efficacious electrocatalyst for the hydrogen evolution reaction.

In this work, we designed a straightforward and highly reproducible synthetic methodology to prepare Ru0-Pt0 composites. We report a significant improvement in the electrocatalytic performance upon compositing Ru with a very trace amount of Pt. In particular, Ru nanoparticles were derived from a Ru-Prussian blue analogue (Ru PBA) and composited with (0.1, 0.5, and 1 mmol) metallic platinum following an optimized chemical reduction method. Interestingly, the composite with 0.5 mmol of Pt (Ru@C/Pt0.5) required low overpotentials of 32 and 140 mV to achieve current densities of 10 and 100 mA cm-2, respectively. Furthermore, Ru@C/Pt0.5 exhibited a smaller Tafel slope (26 mV dec-1), robust durability with 50 hours of long-term stability and a higher turnover frequency (TOF: 5.6 s-1@η10 mA cm-2) than commercial Pt/C (TOF: 4.1 s-1@η10 mA cm-2). First-principles calculations using density functional theory (DFT) revealed that the existence of Pt islands on the Ru nanoparticles weakened the strength of the adsorption of hydrogen at the Ru interstitials due to electrostatic repulsion caused by charge retention at Ru atoms near the corner of the islands, leading to rapid dissociation of hydrogen. This created a significant impact on the improvement of the electrocatalytic HER activity of the Ru@C/Pt0.5 electrocatalyst. It appears that restricting the concentration of Pt to trace amounts is a necessary condition for the observed catalytic efficiency, as the catalytic efficiency decreases with an increasing island size due to stronger binding of atomic hydrogen on peripheral Pt atoms and stabilization of adsorbed atomic hydrogen caused by softening of phonon modes with increasing island size. This study opens up a novel avenue for the exploration of highly efficient electrocatalysts for hydrogen evolution reactions.

Unraveling Multicopper [Cu3] and [Cu6] Clusters with Rare µ3-Sulfato and Linear µ2-Oxido-Bridges as Potent Antibiofilm Agents against Multidrug-Resistant Staphylococcus aureus.

In this research article, two multicopper [Cu3] and [Cu6] clusters, [Cu3(cpdp)(µ3-SO4)(Cl)(H2O)2]·3H2O (1) and [Cu6(cpdp)2(µ2-O)(Cl)2(H2O)4]·2Cl (2) (H3cpdp = N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol), have been explored as potent antibacterial and antibiofilm agents. Their molecular structures have been determined by a single-crystal X-ray diffraction study, and the compositions have been established by thermal and elemental analyses, including electrospray ionization mass spectrometry. Structural analysis shows that the metallic core of 1 is composed of a trinuclear [Cu3] assembly encapsulating a µ3-SO42- group, whereas the structure of 2 represents a hexanuclear [Cu6] assembly in which two trinuclear [Cu3] motifs are exclusively bridged by a linear µ2-O2- group. The most striking feature of the structure of 2 is the occurrence of an unusual linear oxido-bridge, with the Cu3-O6-Cu3' bridging angle being 180.00°. Whereas 1 can be viewed as an example of a copper(II)-based compound displaying a rare µ3:η1:η1:η1 bridging mode of the SO42- group, 2 is the first example of any copper(II)-based compound showing an unsupported linear Cu-O-Cu oxido-bridge. Employing variable-temperature SQUID magnetometry, the magnetic susceptibility data were measured and analyzed exemplarily for 1 in the temperature range of 2-300 K, revealing the occurrence of antiferromagnetic interactions among the paramagnetic copper centers. Both 1 and 2 exhibited potent antibacterial and antibiofilm activities against methicillin-resistant Staphylococcus aureus (MRSA BAA1717) and the clinically isolated culture of methicillin-resistant S. aureus (MRSA CI1). The mechanism of antibacterial and antibiofilm activities of these multicopper clusters was investigated by analyzing and determining the intracellular reactive oxygen species (ROS) generation, lipid peroxidation, microscopic observation of cell membrane disruption, membrane potential, and leakage of cellular components. Additionally, 1 and 2 showed a synergistic effect with commercially available antibiotics such as vancomycin with enhanced antibacterial activity. However, 1 possesses higher antibacterial, antibiofilm, and antivirulence actions, making it a potent therapeutic agent against both MRSA BAA1717 and MRSA CI1 strains.

Structure and magnetic properties of an amine-templated one-dimensional cobalt-fluoro-sulfate containing Co4F4 cubane and hydrogen evolution reaction (HER) performance of its derived carbon-wrapped CoSe2 nanorods.

Amine-templated 1D cobalt fluoro sulfate of the composition [(CH3)2NH2]2[Co4F4(SO4)3(C3N2H4)4], consisting of Co4F4 cubane-type secondary building unit, has been synthesized under solvothermal condition. The magnetic properties of the Co4F4 cubane chain exhibited a low-temperature magnetic ordering below 17 K (Tc) attributed to intra-cluster ferromagnetic coupling and did not show spin-glass freezing. The selenylation of the Co4F4 cubane chain leads to the formation of sphere-like CoSe2 in the hydrothermal route (CoSe2@HT). At the same time, nanorods of CoSe2 encapsulated with carbon matrix were obtained in a sealed tube method (CoSe2@ST). Moreover, CoSe2@ST exhibited a higher hydrogen evolution reaction (HER) activity than CoSe2@HT in an acidic medium with 177 mV overpotential to achieve the benchmark current density of 10 mA cm-2. The promising HER performance of derived CoSe2@ST could be attributed to an increase in the geometrical and specific activity due to the encapsulation of N-doped carbon matrix over the CoSe2 nanorods that facilitate faster charge transfer at the electrode-electrolyte interface and higher electrochemical conductivity than the derived CoSe2@HT. This work demonstrates a low-temperature, solvent- and reducing agent-free new synthetic approach for synthesizing framework-derived materials.

Electrochemically activated Co-Prussian blue analogue derived amorphous CoB nanostructures: an efficient electrocatalyst for the oxygen evolution reaction.

The oxygen evolution reaction is a kinetically sluggish half-cell reaction which plays an important role in tuning the efficiency of various electrochemical energy conversion systems. However, this process can be facilitated by manipulating the composition and morphology of the electrocatalyst. Here, by tuning the annealing temperature, a series of cobalt borides (CoB@300, CoB@450, CoB@550 and CoB@650) were synthesized from a metal-organic framework Prussian blue analogue (PBA) following boronization. The resulting borides were characterized systematically and we explored their electrocatalytic activity towards the oxygen evolution reaction (OER). In an alkaline electrolyte, the in situ surface transformation of the boride working electrode to the corresponding metaborite and cobalt oxyhydroxide took place which thereafter acted as the active catalytic sites for the OER. Interestingly, the amorphous form of cobalt boride (i.e., CoB@300) shows many fold increased catalytic activity compared to those of crystalline CoB and commercial RuO2 requiring only 290 mV overpotential to reach the benchmarked 10 mA cm-2 current density and the trend follows the order as CoB@300 > CoB@450 > CoB@550 > CoB@650 > PBA. The dominant catalytic activity of the amorphous cobalt boride nanostructure is attributed particularly to its amorphous nature and synergy between the in situ formed catalytically active centres (meta-borites and cobalt oxyhydroxide).

Revealing the electrochemical performance of a manganese phosphite/RGO hybrid in acidic media.

Transition metal phosphorous-based materials are considered as an ideal candidate for energy storage due to their robustness and durability. In this report, we present manganese phosphite, Mn11(HPO3)8(OH)6, an interesting inorganic material with spectacular structural features. A single step hydrothermal synthetic route was employed for the fabrication of a series of manganese phosphite/RGO hybrids (Mn-HPO/RGO-5, Mn-HPO/RGO-10, Mn-HPO/RGO-20). The as-synthesized hybrid (Mn-HPO/RGO-10) delivers a specific capacitance of 770 F g-1 when operated at 1 A g-1 current density in a three-electrode set-up with a rate capability of 66%. To broaden the practical applicability of the Mn-HPO/RGO-10 hybrid, an asymmetric supercapacitor (ASC) device was fabricated with MXene (Ti3C2) as a negative electroactive material and a Mn-HPO/RGO-10 hybrid as a positive active material. The as-fabricated device projects a specific capacitance of 108 F g-1 with an energy density of 34 W h kg-1 along with a power density of 508 W kg-1. Moreover, the ASC device retains a specific capacitance of 94% after 12 000 constant charge and discharge cycles, suggesting the excellent durability of the ASC device. These systematic investigations illustrate the potential of the Mn-HPO/RGO-10 hybrid as a high-performance energy storage device.

Metal-organic framework (MOF)-derived plate-shaped CoS1.097 nanoparticles for an improved hydrogen evolution reaction.

Metal-organic framework (MOF)-derived transition metal sulfides are viewed as reliable, cost-effective, and alternative hydrogen evolution reaction (HER)-efficient electrocatalysts. They have been used to replace platinum (and their alloys) for production of renewable energy carriers such as hydrogen. Progress towards development of non-precious transition-metal sulfides through different synthetic routes to obtain unique morphological nanostructures with enhanced HER activity is challenging. We introduced a transition-metal sulfide, cobalt sulfide (CoS1.097), derived from a cobalt MOF [Co-BPY-DDE] by following facile, one-step solvothermal sulfurization. By varying the sulfurization temperature (from 140 °C to 180 °C) during the solvothermal method, three cobalt-sulfide products were obtained: CoS1.097-140, CoS1.097-160, and CoS1.097-180, respectively. Temperature variation had a vital role in optimizing the HER activity of the electrocatalyst. Besides, notable plate-shaped cobalt sulfide nanoparticles (CoS1.097-160) required overpotential of 163 mV to deliver a current density of 10 mA cm-2 with a low Tafel slope of 53 mV dec-1, thereby demonstrating faster reaction kinetics during the evolution of molecular hydrogen. Furthermore, 25 h of long-term stability of the electrocatalyst reflected its practical applicability in acidic media. CoS1.097-160 had uniform plate-shaped morphology and large electrochemical active surface area, which contributed to enhanced electrochemical performance through water electrolysis.

Ancillary-Ligand-Assisted Variation in Nuclearities Leading to the Formation of Di-, Tri-, and Tetranuclear Copper(II) Complexes with Multifaceted Carboxylate Coordination Chemistry.

The self-assembly of a carboxylate-based dinucleating ligand, N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol (H3cpdp), and copper(II) ions in the presence of various exogenous ancillary ligands results in the formation of the new dinuclear complex [Cu2(cpdp)(µ-Hisophth)]4·2H2isophth·21H2O (1), trinuclear complex [Cu3(Hcpdp)(Cl)4] (2), and tetranuclear complex [Cu4(cpdp)(µ-Hphth)(µ4-phth)(piconol)(Cl)2]·3H2O (3) (H2phth = phthalic acid; H2isophth = isophthalic acid; piconol = 2-pyridinemethanol; Cl- = chloride). In methanol-water, the reaction of H3cpdp with CuCl2·2H2O at room temperature leads to the formation of 2. On the other hand, 1 and 3 have been obtained by carrying out the reaction of H3cpdp with CuCl2·2H2O/m-C6H4(CO2Na)2 and CuCl2·2H2O/o-C6H4(CO2Na)2/piconol, respectively, in methanol-water in the presence of NaOH at ambient temperature. All three complexes have been characterized by elemental analysis, molar electrical conductivity and magnetic moment measurements, FTIR, UV-vis spectroscopy, and PXRD, including single-crystal X-ray structural analyses. The molecular structure of 1 is based on a µ-alkoxide and µ-isophthalate-bridged dimeric [Cu2] core; the structure of 2 represents a trimeric [Cu3] core in which a µ-alcohol-bridged dinuclear [Cu2] unit is exclusively coupled with a [CuCl2] species by two µ:η1:η1-syn-anti carboxylate groups forming a triangular motif; the structure of 3 embodies a tetrameric [Cu4] core, with two copper(II) ions in a distorted-octahedral coordination environment, one copper(II) ion in a distorted-trigonal-bipyramidal coordination environment, and the other copper(II) ion in a square-planar coordination environment. In fact, 2 and 3 represent rare examples of copper(II)-based multinuclear complexes showing outstanding features of rich coordination chemistry: (i) using a symmetrical dinucleating ligand, trinuclear complex 2 is generated with four- and five-coordination environments around copper(II) ions; (ii) the unsymmetrical tetranuclear complex 3 is obtained by using the same ligand with four-, five- and six-coordination environments around copper(II) ions; (iii) tetracopper(II) complex 3 shows four different bridging modes of carboxylate groups simultaneously such as µ:η2, µ:η1:η1, µ3:η2:η1:η1, and µ4:η1:η1:η1:η1, the µ4:η1:η1:η1:η1 mode of phthalate being unprecedented. The formation of these [Cu2], [Cu3], and [Cu4] complexes can be controlled by changing the exogenous ancillary ligands and pH of the reaction solutions, thus allowing an effective tuning of the self-assembly. The magnetic susceptibility measurements suggest that the copper centers in all three complexes are antiferromagnetically coupled. The thermal properties of 1-3 have been investigated by thermogravimetric and differential thermal analytical (TGA and DTA) techniques, indicating that the decomposition of all three complexes proceeds via multistep processes.

Tetra germanium nonaselenide enwrapped with reduced graphene oxide and functionalized carbon nanotubes (Ge4Se9/RGO/FCNTs) hybrids for improved energy storage performances.

The development of multifunctional layered semiconductor materials and their carbonaceous hybrids as acceptable positive electrode materials for supercapacitor application is of key interest. Ternary germanium selenide (Ge4Se9) with reduced graphene oxide (RGO) and functionalized carbon nanotube (FCNT) hybrids were successfully synthesized by following a one-step hydrothermal approach, and their electrochemical energy storage performance toward supercapacitor (SC) applications was investigated. It was observed that the specific capacitance of Ge4Se9/RGO/FCNTs was 440 F g-1 at 1 A g-1 in an acidic (1 M H2SO4) medium. Further, the material showed 83% retention of its own initial value of capacitance with 98% coulombic efficiency after 5000 galvanostatic charge-discharge cycles. Considering the two-dimensional (2D) layered structures of MXenes with their greater stability, exceptional hydrophilicity, and pseudocapacitive behavior in aqueous electrolytes makes them an alternative for the fabrication of asymmetric SC devices. The above findings about MXenes suggest the design of an asymmetric device using MXene as the negative electrode material and as-prepared Ge4Se9/RGO/FCNTs as the positive electrode material in a similar electrolyte media. The fabricated Ge4Se9/RGO/FCNTs//MXenes displayed a higher specific capacitance of 102 F g-1 at 1 A g-1, with an acceptable energy density (E.D.) of 32 W h kg-1 and a power density (P.D.) of 1071 W kg-1. Furthermore, over long-term repeated 5000 GCD cycles the fabricated device retained 92% of its initial capacitance and good reversibility (96% coulombic efficiency), making the Ge4Se9/RGO/FCNT//MXenes assembly a preferable electrode material for enhancing asymmetric SC performance.

Synthesis, structure and the Hirshfeld surface analysis of three novel metal-tiron coordination complexes.

Three novel metal-tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) and other pillared ligand bpy (4,4'-bipyridyl)-centered coordination polymers of the formulae [Cd(tiron)(bpy)2(H2O)2]·0.5(H2O), 1, [Co3(tiron-bpy)2(bpy)(H2O)8]·(H2O)2, 2, and [Ba2(tiron-bpy)2(H2O)4][solvent], 3, were successfully synthesized under hydrothermal conditions. The as-synthesized materials were well characterized by complimentary techniques such as single-crystal X-ray diffraction, powder X-ray diffraction, Fourier-transform infrared spectroscopy and thermogravimetric analysis techniques. The as-synthesized coordination polymers of 1 and 2 featured 1D chains, while 3 shows a layered structure. Co-based 2 shows linear trinuclear Co(ii) ions and these Co(ii) ions have antiferromagnetic interactions among themselves. The structure of 1 features a zig-zag chain formed by the linkage between monodentate tiron ligands and octahedral Cd(ii) ions, interconnected by a twisted bpy ligand, 2 shows a linear chain constructed from corner-sharing trinuclear octahedral Co(ii) ions and coordinated with a tridentate tiron-bpy adduct ligand, whereas 3 shows nona-coordinated Ba(ii) ions sharing edges with other Ba(ii) ions and connected by hexadentate tiron-bridged structures resulting in a layered structure. In 2 and 3, the bpy nitrogen attacks at the ortho position of the tiron ligand and forms an in situ ligand adduct. The central metal ions show an octahedral geometry in 1 (Cd(ii) ions) and 2 (Co(ii) ions), but nona-coordination of Ba(ii) ions in 3. The short interatomic interactions in the crystal structures were evaluated by mapping the Hirshfeld surface process using pseudo-mirrored 2D fingerprint plots. The major short interatomic interactions H⋯H, O⋯H and C⋯H cover the Hirshfeld surfaces.

Enhanced Oxygen Evolution Reaction with a Ternary Hybrid of Patronite-Carbon Nanotube-Reduced Graphene Oxide: A Synergy between Experiments and Theory.

This work reports the hybridization of patronite (VS4) sheets with reduced graphene oxide and functionalized carbon nanotubes (RGO/FCNT/VS4) through a hydrothermal method. The synergistic effect divulged by the individual components, i.e., RGO, FCNT, and VS4, significantly improves the efficiency of the ternary (RGO/FCNT/VS4) hybrid toward the oxygen evolution reaction (OER). The ternary composite exhibits an impressive electrocatalytic OER performance in 1 M KOH and requires only 230 mV overpotential to reach the state-of-the-art current density (10 mA cm-2). Additionally, the hybrid shows an appreciable Tafel slope with a higher Faradaic efficiency (97.55 ± 2.3%) at an overpotential of 230 mV. Further, these experimental findings are corroborated by the state-of-the-art density functional theory by presenting adsorption configurations, the density of states, and the overpotential of these hybrid structures. Interestingly, the theoretical overpotential follows the qualitative trend RGO/FCNT/VS4 < FCNT/VS4 < RGO/VS4, supporting the experimental findings.