Stabilization of the Neutral [25]Hexaphyrin(1.0.1.0.1.0) Radical by Hetero-Bimetal-Coordination.

Stabilization of hexaphyrin(1.0.1.0.1.0) (named "rosarin") in its 25π radical state is achieved using a hetero-bimetal-coordination strategy. The antiaromatic BF2 complex B-1 was first synthesized, and then rhodium ion was inserted into B-1 to produce the BF2/Rh(CO)2 mixed complex Rh-B-1 as a highly air-stable radical. The structures of B-1 and Rh-B-1 were determined by single-crystal X-ray diffractions, and the antiaromatic or radical character was identified by various spectroscopy evidence and theoretical calculations. Rh-B-1 exhibits excellent redox properties, enabling amphoteric aromatic-antiaromatic conversion to their 24/26π states. Compared to the 24/26π conjugation systems on the same skeleton, Rh-B-1 has the narrowest electrochemical and optical band gaps, with the longest absorption band at 1010 nm. The ring-current analysis reveals intense paratropic currents for B-1 and co-existing diatropic-paratropic currents for Rh-B-1. This hetero-bimetal-coordination system provides a novel platform for organic radical stabilization on porphyrinoids, showing the prospect of modulating ligand oxidation states through rational coordination design.

Support Platform of Functionalized Sustainable Cellulose Self-Entanglement Monolithic Adsorbents for Efficient Adsorption of Cadmium(II) Ions.

Serious water contamination induced by massive discharge of cadmium(II) ions is becoming an emergent environmental issue due to high toxicity and bioaccumulation; thus, it is extremely urgent to develop functional materials for effectively treating with Cd2+ from wastewater. Benefiting from abundant binding sites, simple preparation process, and adjustable structure, UiO-66-type metal-organic frameworks (MOFs) had emerged as promising candidates in heavy metal adsorption. Herein, monolithic UiO-66-(COOH)2-functionalized cellulose fiber (UCLF) adsorbents were simply fabricated by incorporating MOFs into cellulose membranes through physical blending and self-entanglement. A two-dimensional structure was facilely constructed by cellulose fibers from sustainable biomass agricultural waste, providing a support platform for the integration of eco-friendly UiO-66-(COOH)2 synthesized with lower temperature and toxicity solvent. Structure characterization and bath experiments were performed to determine operational conditions for the maximization of adsorption capacity, thereby bringing out an excellent adsorption capacity of 96.10 mg/g. UCLF adsorbent holding 10 wt % loadings of UiO-66-(COOH)2 (UCLF-2) exhibited higher adsorption capacity toward Cd2+ as compared to other related adsorbents. Based on kinetics, isotherms, and thermodynamics, the adsorption behavior was spontaneous, exothermic, as well as monolayer chemisorption. Coordination and electrostatic attraction were perhaps mechanisms involved in the adsorption process, deeply unveiled by the effects of adsorbate solution pH and X-ray photoelectron spectroscopy. Moreover, UCLF-2 adsorbent with good mechanical strength offered a structural guarantee for the successful implementation of practical applications. This study manifested the feasibility of UCLF adsorbents used for Cd2+ adsorption and unveiled a novel strategy to shape MOF materials for wastewater decontamination.

Birnessite-Type MnO2 Modified Sustainable Biomass Fiber toward Adsorption Removal Heavy Metal Ion from Actual River Aquatic Environment.

In this work, a novel birnessite-type MnO2 modified corn husk sustainable biomass fiber (MnO2@CHF) adsorbent was fabricated for efficient cadmium (Cd) removal from aquatic environments. MnO2@CHF was designed from KMnO4 hydrothermally treated with corn husk fibers. Various characterization revealed that MnO2@CHF possessed the hierarchical structure nanosheets, large specific surface area, and multiple oxygen-containing functional groups. Batch adsorption experimental results indicated that the highest Cd (II) removal rate could be obtained at the optimal conditions of adsorbent amount of 0.200 g/L, adsorption time of 600 min, pH 6.00, and temperature of 40.0 °C. Adsorption isotherm and kinetics results showed that Cd (II) adsorption behavior on MnO2@CHF was a monolayer adsorption process and dominated by chemisorption and intraparticle diffusion. The optimum adsorption capacity (Langmuir model) of Cd (II) on MnO2@CHF was 23.0 mg/g, which was higher than those of other reported common biomass adsorbent materials. Further investigation indicated that the adsorption of Cd (II) on MnO2@CHF involved mainly ion exchange, surface complexation, redox reaction, and electrostatic attraction. Moreover, the maximum Cd (II) removal rate on MnO2@CHF from natural river samples (Xicheng Canal) could reach 59.2% during the first cycle test. This study showed that MnO2@CHF was an ideal candidate in Cd (II) practical application treatment, providing references for resource utilization of agricultural wastes for heavy metal removal.

Synthesis of Hybrid Porphyrin(2.1.2.1)s and Their Complexation.

Novel hybrid porphyrin(2.1.2.1)s and their boron and copper complexes were synthesized using the "toy bricks" synthetic method. Crystal data, frontier molecular orbital calculations, and electrostatic potential surface maps reveal that hybridization in the porphyrin(2.1.2.1) donor-acceptor unit controls the selective coordination of BF2.

Interface Engineering with the Coupling of a 3D Porous Structure Enables MoP2-NiCoP Heterostructure Nanosheets for Enhanced Alkaline Hydrogen Evolution Reaction.

One of the crucial parts of the electrochemically focused energy conversion and storage system is the hydrogen evolution reaction. The further exploration of electrocatalysts made of nonprecious metals could help to bring the technology closer to industrialization. Here, we present an effective hydrogen evolution reaction (HER) electrocatalyst that employs hydrothermal and phosphorization steps to create three-dimensional (3D) porous MoP2-NiCoP heterostructure nanosheets on nickel foam (MoP2-NiCoP/NF). H2O-dissociation and H-adsorption were effectively achieved due to the distinctive interface engineering between NiCoP and MoP2, which functions as a channel for immediate electron transfer. Compared to the single-component MoP2 and NiCoP, the synergistic interaction between the heterogeneous components coupling and the 3D porous structure enables MoP2-NiCoP/NF to exhibit satisfactory catalytic activity with an ultralow overpotential of 50 mV at 10 mA cm-2, which is close to the commercial Pt/C catalyst in alkaline media. More importantly, it exhibits good stability, with the ability to be electrolyzed in 1.0 M KOH electrolyte for 24 h without a significant change in overpotential. This study offers directions for the design of low-cost, high-activity, transition metal phosphides (TMPs)-based HER catalyst alternatives for future practical applications.

High-Density CoSe2 Sites Embedded within 2D Porous N-Doped Carbon for High-Performance Oxygen Reduction Reaction Electrocatalysis.

Designing and fabricating efficient and stable nonprecious metal-based oxygen reduction reaction (ORR) electrocatalysts is a pressing and challenging task for the pursuit of sustainable new energy devices. Herein, porous P-CoSe2@NC electrocatalysts with high-density carbon-coated CoSe2 sites were successfully fabricated based on a pyridyl-porphyrinic metal-organic framework (Co-TPyP MOF) via a molten salt-assisted synthesis method. The hierarchical pore and N-doping carbon substrate of P-CoSe2@NC promotes mass transfer and electron-transfer efficiency, which is beneficial to maximize CoSe2 site utilization. Well-designed P-CoSe2@NC exhibits efficient ORR catalytic activity with a high half-wave potential of 0.863 V and excellent catalytic stability. Meanwhile, rechargeable aqueous primary/quasi-solid-state ZABs based on a P-CoSe2@NC air cathode show a high peak power density and exceptional operating stability, catering to the demands of practical applications. The qualified performance and structure stability of the electrocatalytic system may be mainly attributed to the protection of the CoSe2 nanoparticle by the coated carbon layer. Given the rational design of the structure and the component of the electrocatalyst with enhanced ORR activity, we believe that this work has provided a reliable pathway to the development of high-performance transition-metal chalcogenides for energy-storage and -conversion devices.

Integrated Heterogeneous Engineering with the Vacancy Defect of Porous CoPv-MoxPv Nanosheets for an Accelerated Hydrogen Evolution Reaction.

Electrochemical water splitting is a possible way of realizing sustainable and clean hydrogen production but is challenging, because a highly active and durable electrocatalyst is essential. In this work, we integrated heterogeneous engineering and vacancy defect strategies to design and fabricate a heterostructure electrocatalyst (CoPv-MoxPv/CNT) with abundant phosphorus vacancies attached to carbon nanotubes (CNTs). The vacancy defects enabled the optimization of the electronic structure; thereby, the electron-rich low-valent metal sites enhanced the ability of nonmetallic P to capture proton H. Meanwhile, the heterogeneous interface between bimetallic phosphides and CNTs realized rapid electron transfer. In addition, the Co, Mo, and P active species in the electrocatalytic process exposed increased amounts of active sites featuring porous nanosheet structures, which facilitated the adsorption of reaction intermediates and thus enhanced the hydrogen evolution reaction performance. In particular, the optimized CoPv-MoxPv/CNT catalyst possesses an overpotential of 138 mV at a current density of 10 mA cm-2 and long-term stability for 24 h. This work offers insights and possibilities for the engineering and exploration of transition metal-based electrocatalysts through combining multiple synergistic strategies.

Electrocatalytic Oxygen Reduction Reaction of Peripheral Functionalized Cobalt Porphyrins(2.1.2.1).

Two peripheral functionalized clamp-shaped cobalt porphyrin(2.1.2.1) complexes were synthesized, and their electrocatalytic ORR abilities were investigated. The crystal data and optical and redox properties of them were revised by peripheral modification. The ORR capacities and DFT calculations of F5PhCo and F5NCo suggest superior selectivity for the 4e- ORR pathway. This work further confirms the clamp-shaped cobalt porphyrin complexes are ideal Co-N4 ORR catalysts.

Conflicting Aromaticity in Trirhodium(I) Rosarin.

Aromaticity is one of the most important and widely used concepts in chemistry. Among the various experimentally discovered and theoretically predicted compounds that possess different types of aromaticity, conflicting aromaticity, where aromatic and antiaromatic electron delocalization is present in one molecule simultaneously, remains one of the most controversial and elusive concepts, although theoretically predicted 15 years ago. In this work, we synthesized a novel conflicting aromatic trirhodium complex that contains a σ-aromatic metal fragment surrounded by the π-antiaromatic organic ligand and characterized it by nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry, and X-ray single crystal structure analysis. Experimental characterization and quantum chemical calculations confirm the unique conflicting aromaticity of the synthesized trirhodium molecule. Thus, this novel conflicting aromatic molecule expands the family of aromatic compounds. This discovery will enable researchers to develop and understand the phenomena of conflicting aromaticity in chemistry.

Electrocatalytic Hydrogen Evolution of Bent Bis(dipyrrin) Ni(II) Complexes.

Planar Ni(II) porphyrinoid complexes have been widely used in electrochemical carbon dioxide reduction reaction and oxygen reduction reaction as well as hydrogen evolution reaction (HER). However, nonplanar Ni(II) tetra-pyrrolic complexes have not been thoroughly investigated thus far. In this study, three highly bent bis(dipyrrin) Ni(II) complexes have been synthesized to investigate their structure, electronic property, and electrocatalytic HER activities. Cyclic voltammetry and thin-layer UV-visible spectroelectrochemistry studies revealed four redox processes, yielding two reduced species as the final products. The ic/ip values of phenyl- and pentafluorophenyl-bearing bis(dipyrrin) Ni(II) complexes were >30 when trifluoroacetic acid was used as the proton source, and their Faradaic efficiencies for H2 generation were >93%. Density functional theory calculations of the HERs revealed low endothermic energies of bent bis(dipyrrin) Ni(II) complexes.

Pt-Doped Biomass Carbon Decorated with MoS2 Nanosheets as an Electrocatalyst for Hydrogen Evolution.

It is necessary to develop an efficient hydrogen evolution catalyst to improve the efficiency of the hydrogen evolution reaction (HER). Herein, a MoS2 nanosheet is decorated on the Pt-doping biomass yeast cells (MoS2@Pt/YC) via a simple hydrothermal process. Reducing the noble metal loading without compromising its performance is a challenging task. The smooth surface of YCs is conducive to the growth of MoS2 nanosheets, and its functional groups provide attachment sites for metal Pt. The Pt/YC is covered with MoS2 nanosheets, thus improving the exposed active sites for HER. The obtained MoS2@Pt/YC delivers a competitive overpotential of 118 mV at the benchmark current density of 10 mA cm-2 and achieves a small Tafel slope of 74 mV dec-1, indicating the great HER performance of MoS2@Pt/YC. Moreover, MoS2@Pt/YC shows robust stability after 24 h of continuous operation toward HER in acidic solution. By introducing transition metal sulfides with high specific surface area, the loading of precious metals can be reduced without compromising properties. This work provides a method to design Pt-doping HER electrocatalysts through a simple method. The facile preparation process for MoS2@Pt/YC and its outstanding performance allow it to be a promising electrocatalyst for practical HER application.

Highly Robust and Antiaromatic Rhenium(I) Rosarin.

1ReH•Cl, a highly robust and antiaromatic rhenium(I) complex of triarylrosarin, is synthesized. The 1H NMR spectrum of 1ReH•Cl shows upfield-shifted pyrrole protons and highly downfield-shifted inner protons that confirm its antiaromatic nature, with density functional theory calculations strongly supporting this interpretation. Antiaromatic 1ReH•Cl absorbs from the UV to near-IR region of the optical spectrum; cyclic voltammetry, thin-layer UV-vis spectroelectrochemistry, and spin-density distributions clearly reveal that the rosarin backbone of 1ReH•Cl undergoes redox chemistry. The X-ray structure of 1ReH•Cl shows a fully coordinated and protonated inner cavity that effectively prevents proton-coupled electron transfer when treated with an acid. A remarkably negative NICS(0) value, clockwise anisotropy of the induced current density ring current, and the aromatic shielded inner cavity in the 2D ICSS(0) map reveal that the T1 state of 1ReH•Cl is aromatic based on Baird's rule.

Constructing a Functionalized Electrocatalyst of a Transition Metal Chalcogenide on Accordion-Like MXene to Boost the Hydrogen Evolution Reaction.

MXenes exhibit unique layered structures and excellent electrical conductivity, and their multiple surface termination groups are favorable for hosting impressive performance for electrochemical reactions. Therefore, a two-dimensional (2D) layered MXene-based catalyst may become a novel high-efficiency electrocatalyst to replace traditional noble metal electrocatalysts. In this work, a transition metal chalcogenide (MoS2/CuS) and MXene are combined to prepare a 2D electrocatalyst (MoS2/CuS/MXene) for the hydrogen evolution reaction (HER). MXene exhibited a large specific surface area in the shape of an accordion, which was very beneficial for the growth of nanomaterials. CuS/MXene promoted electron transfer and improved the exposed active site for HER. The exposed MoS2 edges exhibited a high chemical adsorption capacity, which is conducive to HER. Electrochemical tests reveal that the MoS2/CuS/MXene electrocatalyst can reduce the charge transfer resistance toward the HER and increase active sites for HER, leading to enhancing the catalytic performance. The MoS2/CuS/MXene electrocatalyst affords an efficient HER with a low overpotential (115 mV@10 mA cm-2). This work offers a new idea to create layered transition metal chalcogenide- and MXene-based electrocatalysts for HER.

Enhanced Four-Electron Oxygen Reduction Selectivity of Clamp-Shaped Cobalt(II) Porphyrin(2.1.2.1) Complexes.

The molecular structure, electrochemistry, spectroelectrochemistry and electrocatalytic oxygen reduction reaction (ORR) features of two CoII porphyrin(2.1.2.1) complexes bearing Ph or F5 Ph groups at the two meso-positions of the macrocycle are examined. Single crystal X-ray analysis reveal a highly bent, nonplanar macrocyclic conformation of the complex resulting in clamp-shaped molecular structures. Cyclic voltammetry paired with UV/Vis spectroelectrochemistry in PhCN/0.1 M TBAP suggest that the first electron addition corresponds to a macrocyclic-centered reduction while spectral changes observed during the first oxidation are consistent with a metal-centered CoII /CoIII process. The activity of the clamp-shaped complexes towards heterogeneous ORR in 0.1 M KOH show selectivity towards the 4e- ORR pathway giving H2 O. DFT first-principle calculations on the porphyrin catalyst indicates a lower overpotential for 4e- ORR as compared to the 2e- pathway, consistent with experimental data.

Near-Infrared Photoacoustic Probe for Reversible Imaging of the ClO-/GSH Redox Cycle In Vivo.

Homeostasis of the cellular redox status plays an indispensable role in diverse physiological and pathological processes. Hypochlorite anion (ClO-) and glutathione (GSH) represent an important redox couple to reflect the redox status in living cells. The current cellular redox probes that detect either ClO- or GSH alone are not accurate enough to monitor the real redox status. In this work, a reversible photoacoustic (PA) probe, DiOH-BDP, has been synthesized and applied for PA imaging to monitor the ClO-/GSH couple redox state in an acute liver injury (ALI) model. The near-infrared PA probe DiOH-BDP features significant changes in absorption between 648 and 795 nm during the selective oxidation by ClO- and the reductive recovery of GSH, which exhibits excellent selectivity and sensitivity toward ClO- and GSH with the limits of detection of 77.7 nM and 7.2 µM, respectively. Additionally, using PA770 as a detection signal allows for the in situ monitoring of the ClO-/GSH couple, which realizes mapping of the localized redox status of the ALI by the virtue of a PA imaging system. Therefore, the probe provides a potentially technical tool to understand redox imbalance-related pathological formation processes.

Hierarchical Coralline-like (NiCo)S2@MoS2 Nanowire Arrays to Accelerate H2 Release for an Efficient Hydrogen Evolution Reaction.

The hydrogen evolution reaction (HER) is significantly influenced by the evolved H2 bubble diffusion rate on the surface of the electrode, which involves the blocking and release of the active site at the catalytic interface. Rational design of nanostructured catalysts could not only sharply enhance the specific surface area but also provide large amounts of channels for gas release. Herein, NiCo-nanowire-derived multimetal chalcogenides grown in situ on carbon cloth [denoted as (NiCo)S2@MoS2/CC] are presented by serial hydrothermal methods. The obtained hierarchical nanowire array architecture affords abundant surface-active sites and is conducive to permeate electrolytes. The surface adsorption/desorption behavior of the heterostructure catalyst was optimized through regulating MoS2 concentration. Owing to the synergistic effect of metal Ni and Co and the interaction of the (NiCo)S2@MoS2 heterostructure, (NiCo)S2@MoS2/CC-2 delivers a relatively low overpotential of 74 mV at a current density of 10 mA cm-2 and displays a small Tafel slope of 54 mV dec-1 for HER catalysis, surpassing that of the recently reported MoS2-based electrocatalysts. Such a strategy through nanostructure optimization and electron interaction of the heterostructure could improve the electrocatalytic HER performance for multimetal chalcogenides in an alkaline medium.

ZIF-67-Derived (NiCo)S2@NC Nanosheet Arrays Hybrid for Efficient Overall Water Splitting.

Electrocatalytic water splitting is considered a promising approach to obtain clean and sustainable hydrogen energy. The integration of optimal nanoarchitecture and multicomponent synergy has been a significant factor for designing a bifunctional electrocatalyst to promote the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). In particular, the charge migration, mass transfer, and gas release rate in the catalyzing process are closely correlated with the architecture of the catalyst. Here, ZIF-67-derived N-doped carbon nanofiber-supported (NiCo)S2 nanosheet [(NiCo)S2/NCNF] as a bifunctional electrocatalyst was synthesized using electrospinning, template etching, and subsequent gas sulfidation method. The hierarchical hybrid nanofiber with inner hollow cubes and outer nanosheets provides easy electron penetration, high charge/mass transportation efficiency, and robust structure stability. Furthermore, the MOF-derived carbon-encapsuled bimetal-sulfide and the synergistic effect of double active centers are conducive to an exceptional performance, showing low overpotentials of 177 and 203 mV to drive a current density of 10 mA cm-2 and robust stability for the HER and OER, respectively. Meanwhile, the (NiCo)S2/NCNF electrodes exhibit a small voltage of 1.61 V for overall water splitting activity with an electrolyzer cell at current densities of 10 mA cm-2 over 12 h. This work presents novel insights into the bifunctional catalyst for promoting the overall water splitting via a MOF-derived nanoarchitecture and multicomponent synergy.

Synthesis, Characterization, and Electrochemistry of Copper Dibenzoporphyrin(2.1.2.1) Complexes.

Three copper dibenzoporphyrin(2.1.2.1) complexes having two dipyrromethene units connected through o-phenylen bridges and 4-MePh, Ph, or F5Ph substituents at the meso positions of the dipyrrins were synthesized and characterized according to their spectral, electrochemical, and structural properties. As indicated by the single-crystal X-ray structures, all three derivatives have highly bent molecular structures, with angles between each planar dipyrrin unit ranging from 89° to 85°, indicative of a nonaromatic molecule. The insertion of copper(II) into dibenzoporphyrins(2.1.2.1) induced a change in the macrocyclic cavity shape from rectangular in the case of the free-base precursors to approximately square for the metalated copper derivatives. Solution electron paramagnetic resonance (EPR) spectra at 100 K showed hyperfine coupling of the Cu(II) central metal ion and the N nucleus in the highly bent molecular structures. Electrochemical measurements in CH2Cl2 or N,N-dimethylformamide (DMF) containing 0.1 M tetrabutylammonium perchlorate (TBAP) were consistent with ring-centered electron transfers and, in the case of reduction, were assigned to electron additions involving two equivalent π centers on the bent nonaromatic molecule. The potential separation between the two reversible one-electron reductions ranged from 230 to 400 mV in DMF, indicating a moderate-to-strong interaction between the equivalent redox-active dipyrrin units of the dibenzoporphyrins(2.1.2.1). The experimentally measured highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps ranged from 2.14 to 2.04 eV and were smaller than those seen for the planar copper tetraarylporphyrins(1.1.1.1), (Ar)4PCu.

Binuclear Rhodium(I) Complex of a Dimethylvinylene-Bridged Distorted Hexaphyrin(2.1.2.1.2.1).

A highly distorted binuclear rhodium(I) complex, 2Rh, was successfully synthesized from hexaphyrin(2.1.2.1.2.1) containing dimethylvinylene-bridges between dipyrrin units. IR spectroscopy, 1H NMR spectroscopy, and X-ray crystallography revealed that the complex 2Rh consists of two rhodium(I) ions coordinated to two dipyrrin units. Rh complexation induced a transformation from a trans-/cis-/trans- to trans-/cis-/cis-conformation on the dimethylvinylene-bridges. This is the first example of rhodium(I)-ion-induced cis-/trans-isomerization in the porphyrin derivatives. Theoretical calculations of 2Rh predicted the presence of intramolecular charge-transfer absorption due to the distorted molecular structure.

Dynamically PEGylated and Borate-Coordination-Polymer-Coated Polydopamine Nanoparticles for Synergetic Tumor-Targeted, Chemo-Photothermal Combination Therapy.

Multifunctional nanomaterials with efficient tumor-targeting and high antitumor activity are highly anticipated in the field of cancer therapy. In this work, a synergetic tumor-targeted, chemo-photothermal combined therapeutic nanoplatform based on a dynamically PEGylated, borate-coordination-polymer-coated polydopamine nanoparticle (PDA@CP-PEG) is developed. PEGylation on the multifunctional nanoparticles is dynamically achieved via the reversible covalent interaction between the surface phenylboronic acid (PBA) group and a catechol-containing poly(ethylene glycol) (PEG) molecule. Due to the acid-labile PBA/catechol complex and the weak-acid-stable PBA/sialic acid (SA) complex, the nanoparticles can exhibit a synergetic targeting property for the SA-overexpressed tumor cells, i.e., the PEG-caused "passive targeting" and PBA-triggered "active targeting" under the weakly acidic tumor microenvironment. In addition, the photothermal effect of the polydopamine core and the doxorubicin-loading capacity of the porous coordination polymer layer endow the nanoparticles with the potential for chemo-photothermal combination therapy. As expected, the in vitro and in vivo studies both verify that the multifunctional nanoparticles possess relatively lower systematic toxicity, efficient tumor targeting ability, and excellent chemo-photothermal activity for tumor inhibition. It is believed that these multifunctional nanoparticles with synergetic tumor targeting property and combined therapeutic strategies would provide an insight into the design of a high-efficiency antitumor nanoplatform for potential clinical applications.