Ligand Noninnocence in Nickel Porphyrins: Nickel Isobacteriochlorin Formation under Hydrogen Evolution Conditions

Porphyrin Aggregation under Homogeneous Conditions Inhibits Electrocatalysis: A Case Study on CO2 Reduction

Metalloporphyrins are widely used as homogeneous electrocatalysts for transformations relevant to clean energy and sustainable organic synthesis. Metalloporphyrins are well-known to aggregate due to π-π stacking, but surprisingly, the influence of aggregation on homogeneous electrocatalytic performance has not been investigated previously. Herein, we present three structurally related iron meso-phenylporphyrins whose aggregation properties are different in commonly used N,N-dimethylformamide (DMF) electrolyte. Both spectroscopy and light scattering provide evidence of extensive porphyrin aggregation under conventional electrocatalytic conditions. Using the electrocatalytic reduction of CO2 to CO as a test reaction, cyclic voltammetry reveals an inverse dependence of the kinetics on the catalyst concentration. The inhibition extends to bulk performance, where up to 75% of the catalyst at 1 mM is inactive compared to at 0.25 mM. We additionally report how aggregation is perturbed by organic additives, axial ligands, and redox state. Periodic boundary calculations provide additional insights into aggregate stability as a function of metalloporphyrin structure. Finally, we generalize the aggregation phenomenon by surveying metalloporphyrins with different metals and substituents. This study demonstrates that homogeneous metalloporphyrins can aggregate severely in well-solubilizing organic electrolytes, that aggregation can be easily modulated through experimental conditions, and that the extent of aggregation must be considered for accurate catalytic benchmarking.

Bifunctional porphyrin-based metal-organic polymers for electrochemical water splitting

Electrochemical water splitting offers the potential for environmentally friendly hydrogen and oxygen gas generation. Here, we present the synthesis, characterization, and electrochemical analyses of four organic polymers where metalloporphyrins are the active center nodes. These materials were obtained from the polymerization reaction of poly(p-phenylene terephtalamide) (PPTA) with the respective amino-functionalized metalloporphyrins, where M = Fe, 1; Co, 2; Ni, 3; Cu, 4. Scanning and transmission electron microscopy images (SEM and TEM) show that these polymers exhibit a layer-type morphology, which is attributed to hydrogen bonding and π-π stacking between the metalloporphyrin nodes. The synthesized materials were characterized by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), UV-Vis spectroscopy, and Fourier-transform infrared spectroscopy (FT-IR). Among the materials studied, the cobalt-based polymer, 2, demonstrates a bifunctional electrocatalytic activity for oxygen (OER) and hydrogen (HER) evolution reactions with overpotentials (η10) of 337 mV and 435 mV, respectively. The Fe, 1, and Ni, 2, polymers are less active for HER with maximum current densities (jmax) of 12.6 and 19.1 mA cm-2 and η10 678 mV, 644 mV. Polymer 2 achieves a jmax of 37.7 mA cm-2 for HER and 133 mA cm-2 for OER. The copper-based material, 4, on the other hand, shows selectivity towards HER with an overpotential (η) of 436 mV and a maximum current density (j) of 45.5 mA cm-2. The bifunctional electrocatalytic performance was tested in the overall water-splitting setup, where polymer 2 requires a cell voltage of 1.64 V at 10 mA cm-2. This work presents a novel approach to heterogenized molecular systems, providing materials with exceptional structural characteristics and enhanced electrocatalytic capabilities.

Hydride-Free Hydrogenation: Unraveling the Mechanism of Electrocatalytic Alkyne Semihydrogenation by Nickel-Bipyridine Complexes

Hydrogenation reactions of carbon-carbon unsaturated bonds are central in synthetic chemistry. Efficient catalysis of these reactions classically recourses to heterogeneous or homogeneous transition-metal species. Whether thermal or electrochemical, C-C multiple bond catalytic hydrogenations commonly involve metal hydrides as key intermediates. Here, we report that the electrocatalytic alkyne semihydrogenation by molecular Ni bipyridine complexes proceeds without the mediation of a hydride intermediate. Through a combined experimental and theoretical investigation, we disclose a mechanism that primarily involves a nickelacyclopropene resting state upon alkyne binding to a low-valent Ni(0) species. A following sequence of protonation and electron transfer steps via Ni(II) and Ni(I) vinyl intermediates then leads to olefin release in an overall ECEC-type pattern as the most favored pathway. Our results also evidence that pathways involving hydride intermediates are strongly disfavored, which in turn promotes high semihydrogenation selectivity by avoiding competing hydrogen evolution. While bypassing catalytically competent hydrides, this type of mechanism still retains inner-metal-sphere characteristics with the formation of organometallic intermediates, often essential to control regio- or stereoselectivity. We think that this approach to electrocatalytic reductions of unsaturated organic groups can open new paradigms for hydrogenation or hydroelementation reactions.

B12 and F430 models: Metal- versus ligand-centered redox in cobalt and nickel tetradehydrocorrin derivatives

DFT calculations with the well-tested OLYP and B3LYP* exchange-correlation functionals (along with D3 dispersion corrections and all-electron ZORA STO-TZ2P basis sets) and careful use of group theory have led to significant insights into the question of metal- versus ligand-centered redox in Co and Ni B,C-tetradehydrocorrin complexes. For the cationic complexes, both metals occur in their low-spin M(II) forms. In contrast, the charge-neutral states vary for the two metals: while the Co(I) and Co^II-TDC^•2- state are comparable in energy for cobalt, a low-spin Ni^II-TDC^•2- state is clearly preferred for nickel. The latter behavior stands in sharp contrast to other corrinoids that reportedly stabilize a Ni(I) center.

Characterization of paramagnetic states in an organometallic nickel hydrogen evolution electrocatalyst

Significant progress has been made in the bioinorganic modeling of the paramagnetic states believed to be involved in the hydrogen redox chemistry catalyzed by [NiFe] hydrogenase. However, the characterization and isolation of intermediates involved in mononuclear Ni electrocatalysts which are reported to operate through a Ni^I/III cycle have largely remained elusive. Herein, we report a Ni^II complex (NCHS2)Ni(OTf)2, where NCHS2 is 3,7-dithia-1(2,6)-pyridina-5(1,3)-benzenacyclooctaphane, that is an efficient electrocatalyst for the hydrogen evolution reaction (HER) with turnover frequencies of ~3,000 s^-1 and a overpotential of 670 mV in the presence of trifluoroacetic acid. This electrocatalyst follows a hitherto unobserved HER mechanism involving C-H activation, which manifests as an inverse kinetic isotope effect for the overall hydrogen evolution reaction, and Ni^I/Ni^III intermediates, which have been characterized by EPR spectroscopy. We further validate the possibility of the involvement of Ni^III intermediates by the independent synthesis and characterization of organometallic Ni^III complexes.

Substituent Effects in Iron Porphyrin Catalysts for the Hydrogen Evolution Reaction

For a future hydrogen economy, non-precious metal catalysts for the water splitting reactions are needed that can be implemented on a global scale. Metal-nitrogen-carbon (MNC) catalysts with active sites constituting a metal center with fourfold coordination of nitrogen (MN₄ ) show promising performance, but an optimization rooted in structure-property relationships has been hampered by their low structural definition. Porphyrin model complexes are studied to transfer insights from well-defined molecules to MNC systems. This work combines experiment and theory to evaluate the influence of porphyrin substituents on the electronic and electrocatalytic properties of MN₄ centers with respect to the hydrogen evolution reaction (HER) in aqueous electrolyte. We found that the choice of substituent affects their utilization on the carbon support and their electrocatalytic performance. We propose an HER mechanism for supported iron porphyrin complexes involving a [Fe^II (P⋅)]^- radical anion intermediate, in which a porphinic nitrogen atom acts as an internal base. While this work focuses on the HER, the limited influence of a simultaneous interaction with the support and an aqueous electrolyte will likely be transferrable to other catalytic applications.

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 i_c/i_p 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.

A rare polyoxometalate cluster [NiW12O44]14- based solid as a pre-catalyst for efficient and long-term oxygen evolution

Polyoxometalates (POMs) are an eminent class of metal oxide anionic clusters of early transition metals with huge structural diversity. Herein, a [NiW₁₂O₄₄]^14- cluster based solid, (C₅H₇N₂)₆[NiW₁₂O₄₄], has been reported (PS-78). The [NiW₁₂O₄₄]^14- cluster bridges the missing gap of 1 : 12 hetero-POMs of Keggin and Silverton together with a coordination number of 8 of the central heteroatom (Ni). Furthermore PS-78 has been explored as an efficient and highly sustained oxygen evolution pre-catalyst in alkaline medium with an overpotential of 347 mV to attain a current density of 10 mA cm^-2 and long-term stability up to 96 hours. Furthermore, mechanistic investigation showed that in situ generated NiO and WO _x (x = 1, 2) species act as active species for the oxygen evolution reaction. This study will open up new avenues for exploring POMs' new topologies and the potential of POMs as effective pre-catalysts in electrocatalytic applications.

Syntheses and Properties of Metalated Tetradehydrocorrins

The monoanionic tetrapyrrolic macrocycle B,C-tetradehydrocorrin (TDC) resides chemically between corroles and corrins. This chemical space remains largely unexplored due to a lack of reliable synthetic strategies. We now report the preparation and characterization of Co(II)- and Ni(II)-metalated TDC derivatives ([Co-TDC]⁺ and [Ni-TDC]⁺, respectively) with a combination of crystallographic, electrochemical, computational, and spectroscopic techniques. [Ni-TDC]⁺ was found to undergo primarily ligand-centered electrochemical reduction, leading to hydrogenation of the macrocycle under cathodic electrolysis in the presence of acid. Transient absorption (TA) spectroscopy reveals that [Ni-TDC]⁺ and the two-electron-reduced [Ni-TDC]^- possess long-lived excited states, whereas the excited state of singly reduced [Ni-TDC] exhibits picosecond dynamics. The Co(I) compound [Co-TDC] is air stable, highlighting the notable property of the TDC ligand to stabilize low-valent metal centers in contradistinction to other tetrapyrroles such as corroles, which typically stabilize metals in higher oxidation states.

Covalent Metalloporphyrin Polymer Coated on Carbon Nanotubes as Bifunctional Electrocatalysts for Water Splitting

Metalloporphyrins have exhibited excellent electrocatalytic activities for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In order to improve the efficiency and conductivity, these molecular catalysts need to be immobilized on conductive electrode materials. Herein, a facile "one-pot" strategy was developed to coat a covalent metalloporphyrin polymer on a carbon nanotube (CNT) as bifunctional catalysts [denoted as MTIPP@CNTs, H₂TIPP = 5,10,15,20-tetra(4-(imidazole-1-yl)phenyl)porphyrin)] for water splitting in alkaline solution. MTIPP@CNTs have shown excellent electrocatalytic activities for both the HER and OER when metalloporphyrin's central metal is optimized as well as the amount of catalysts that is loaded on the CNT. The overpotential (η₁₀) of NiTIPP@CNT-2 for the OER is only 320 mV at a current density of 10 mA cm^-2 in 1.0 M KOH, and CoTIPP@CNT-1 exhibited an excellent electrocatalytic activity for the HER (η₁₀ = 450 mV for 10 mA cm^-2). Furthermore, the remarkable bifunctional electrocatalytic performance (a cell voltage of 2.04 V with a current density of 10 mA cm^-2) was also explored in the overall water splitting test.

Proton-coupled electron transfer of macrocyclic ring hydrogenation: The chlorinphlorin

SignificanceThe chemical reduction of unsaturated bonds occurs by hydrogenation with H2 as the reductant. Conversely, in biology, the unavailability of H2 engenders the typical reduction of unsaturated bonds with electrons and protons from different cofactors, requiring olefin hydrogenation to occur by proton-coupled electron transfer (PCET). Moreover, the redox noninnocence of tetrapyrrole macrocycles furnishes unusual PCET intermediates, including the phlorin, which is an intermediate in tetrapyrrole ring reductions. Whereas the phlorin of a porphyrin is well established, the phlorin of a chlorin is enigmatic. By controlling the PCET reactivity of a chlorin, including the use of a hangman functionality to manage the proton transfer, the formation of a chlorinphlorin by PCET is realized, and the mechanism for its formation is defined.

Conductive metal and covalent organic frameworks for electrocatalysis: design principles, recent progress and perspective

Metal and covalent organic frameworks (MOFs/COFs) are emerging promising candidates in the field of catalysts due to their porous nature, chemically well-defined active sites and structural diversity. However, they are typically provided with poor electrical conductivity, which is insufficient for them to work as satisfying electrocatalysts. Designing and fabricating MOFs/COFs with high conductivity presents a new avenue towards special electrochemical reactions. This minireview firstly highlighted the origin and design principles of conductive MOFs/COFs for electrocatalysis on the basis of typical charge transfer mechanisms, that is "through space", "extended conjugation" and "through bond". An overview of conductive MOFs/COFs used in the electrocatalytic carbon dioxide reduction reaction (CO₂RR), water splitting and the oxygen reduction reaction (ORR) was then made to track the very recent progress. In the final remarks, the present challenges and perspectives for the use of conductive MOFs/COFs as electrocatalysts including their structural optimization, feasible applications and structure-activity correlation are proposed.

Electrocatalytic proton reduction by dinuclear cobalt complexes in a nonaqueous electrolyte

Two dinuclear CoII complexes 1 and 2 have been synthesized and characterized using various spectroscopic methods. Both the complexes were employed for H+ reduction in organic media. Faradaic efficiency of 82–90% was obtained for the H2 evolution.

Electrochemical Degradation of a Dicationic Rhenium Complex via Hoffman-Type Elimination

Electrocatalytic reduction of carbon dioxide (CO₂) by transition-metal catalysts is an attractive means for storing renewably sourced electricity in chemical bonds. Metal coordination compounds represent highly tunable platforms ideal for studying the fundamental stepwise transformations of CO₂ into its reduced products. However, metal complexes can decompose upon extended electrolysis and form chemically distinct molecular species or, in some cases, catalytically active electrode deposits. Deciphering the degradative pathways is important for understanding the nature of the active catalyst and designing robust metal complexes for small-molecule activation. Herein, we present a new dicationic rhenium bipyridyl complex capable of multielectron ligand-centered reductions electrochemically. Our in-depth experimental and computational study provides mechanistic insight into an unusual reductively induced Hoffman-type elimination. We identify benzylic tertiary ammonium groups as an electrolytically susceptible moiety and propose key intermediates in the degradative pathway. This investigation highlights the complex interplay between the ligand and metal ion and will guide the future design of metal-organic catalysts.

H2 Evolution from Electrocatalysts with Redox-Active Ligands: Mechanistic Insights from Theory and Experiment vis-à-vis Co-Mabiq

Electrocatalytic hydrogen production via transition metal complexes offers a promising approach for chemical energy storage. Optimal platforms to effectively control the proton and electron transfer steps en route to H₂ evolution still need to be established, and redox-active ligands could play an important role in this context. In this study, we explore the role of the redox-active Mabiq (Mabiq = 2-4:6-8-bis(3,3,4,4-tetramethlyldihydropyrrolo)-10-15-(2,2-biquinazolino)-[15]-1,3,5,8,10,14-hexaene1,3,7,9,11,14-N₆) ligand in the hydrogen evolution reaction (HER). Using spectro-electrochemical studies in conjunction with quantum chemical calculations, we identified two precatalytic intermediates formed upon the addition of two electrons and one proton to [Co^II(Mabiq)(THF)](PF₆) (Co_Mbq). We further examined the acid strength effect on the generation of the intermediates. The generation of the first intermediate, Co_Mbq-H¹, involves proton addition to the bridging imine-nitrogen atom of the ligand and requires strong proton activity. The second intermediate, Co_Mbq-H², acquires a proton at the diketiminate carbon for which a weaker proton activity is sufficient. We propose two decoupled H₂ evolution pathways based on these two intermediates, which operate at different overpotentials. Our results show how the various protonation sites of the redox-active Mabiq ligand affect the energies and activities of HER intermediates.

One to Find Them All: A General Route to Ni(I)-Phenolate Species

The past 20 years have seen an extensive implementation of nickel in homogeneous catalysis through the development of unique reactivity not easily achievable by using noble transition metals. Many catalytic cycles propose Ni(I) complexes as potential reactive intermediates, yet the scarcity of nickel(I) precursors and the lack of a general, non-ligand-specific protocol for their synthesis have hampered progress in this field of research. This has in turn also limited the access to novel, well-defined Ni(I) species for the development of new catalytic reactions. Herein, we report a simple, general route to access a wide variety of Ni(I)-phenolate complexes via an unusual example of an olefinic Ni(I) complex, [Ni(COD)(OPh*)] (COD = 1,5-cyclooctadiene, OPh* = O(^tBu)₃C₆H₂). This route has proven to be highly efficient for several coordination numbers and ligand classes enabling access to the following complexes: [Ni(IPr)(OPh*)] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), [Ni(dcype)(OPh*)] (dcype = 1,2-bis(dicyclohexylphosphino)ethane), [Ni(dppe)(OPh*)] (dppe = 1,2-bis(diphenylphosphino)ethane), and [Ni(terpy)(OPh*)] (terpy = 2,2':6',2″-terpyridine). Moreover, reacting [Ni(dcype)(OPh*)] with trimethylsilyl triflate has led to the isolation of a unique example of a cationic binuclear Ni(I)-arene complex. All these complexes have been characterized by single-crystal X-ray, DFT, and EPR analyses, thus providing crucial experimental and theoretical information about their coordination environment and confirming a d⁹ electronic structure for all complexes involved. Overall, this new synthetic approach offers exciting opportunities for the discovery of new stoichiometric and catalytic reactivity as well as the mechanistic elucidation of Ni-based catalytic cycles.

Influence of the proton relay spacer on hydrogen electrocatalysis by cobalt hangman porphyrins

A cobalt hangman porphyrin system with a phenyl spacer between the porphyrin ring and an internal carboxylic acid group as well as its non-hangman analogue were synthesized and utilized for the study of the proton-coupled electron transfer (PCET) kinetics attendant to electrocatalytic hydrogen evolution. Cyclic voltammetry (CV) together with simulations show that a short distance between the proton relay and the redox active cobalt center as well as the increased proton donating strength results in superior catalytic activity. The mechanism of hydrogen generation is at the nexus of proton transfer–electron transfer (PTET) and concerted proton–electron transfer (CPET), as opposed to an ETPT mechanism that is characteristic of hangman systems with longer proton relay networks.

Construction of Donor-Acceptor Heterojunctions in Covalent Organic Framework for Enhanced CO2 Electroreduction

Covalent organic frameworks (COFs) are promising candidates for electrocatalytic reduction of carbon dioxide into valuable chemicals due to their porous crystalline structures and tunable single active sites, but the low conductivity leads to unmet current densities for commercial application. The challenge is to create conductive COFs for highly efficient electrocatalysis of carbon dioxide reduction reaction (CO₂ RR). Herein, a porphyrin-based COF containing donor-acceptor (D-A) heterojunctions, termed TT-Por(Co)-COF, is constructed from thieno[3,2-b]thiophene-2,5-dicarbaldehyde (TT) and 5,10,15,20-tetrakis(4-aminophenyl)-porphinatocobalt (Co-TAPP) via imine condensation reaction. Compared with COF-366-Co without TT, TT-Por(Co)-COF displays enhanced CO₂ RR performance to produce CO due to its favorable charge transfer capability from the electron donor TT moieties to the acceptor Co-porphyrin ring active center. The combination of strong charge transfer properties and enormous amount of accessible active sites in the 2D TT-Por(Co)-COF nanosheets results in good catalytic performance with a high Faradaic efficiency of CO (91.4%, -0.6 V vs reversible hydrogen electrode (RHE) and larger partial current density of 7.28 mA cm^-2 at -0.7 V versus RHE in aqueous solution. The results demonstrate that integration of D-A heterojunctions in COF can facilitate the intramolecular electron transfer, and generate high current densities for CO₂ RR.

Mononuclear Mn complexes featuring N,S-/N,N-donor and 1,3,5-triaza-7-phosphaadamantane ligands: synthesis and electrocatalytic properties

Mononuclear Mn(i) carbonyl complexes incorporating 2-mercaptobenzothiazole or 2-mercaptobenzimidazole and phosphaadamantane ligands were evaluated as electrocatalysts for the HER both in acetonitrile and acetonitrile/water.

Enhanced Electrocatalytic Activity of a Zinc Porphyrin for CO2 Reduction: Cooperative Effects of Triazole Units in the Second Coordination Sphere

The control of the second coordination sphere in a coordination complex plays an important role in improving catalytic efficiency. Herein, we report a zinc porphyrin complex ZnPor8T with multiple flexible triazole units comprising the second coordination sphere, as an electrocatalyst for the highly selective electrochemical reduction of carbon dioxide (CO₂ ) to carbon monoxide (CO). This electrocatalyst converted CO₂ to CO with a Faradaic efficiency of 99 % and a current density of -6.2 mA cm^-2 at -2.4 V vs. Fc/Fc⁺ in N,N-dimethylformamide using water as the proton source. Structure-function relationship studies were carried out on ZnPor8T analogs containing different numbers of triazole units and distinct triazole geometries; these unveiled that the triazole units function cooperatively to stabilize the CO₂ -catalyst adduct in order to facilitate intramolecular proton transfer. Our findings demonstrate that incorporating triazole units that function in a cooperative manner is a versatile strategy to enhance the activity of electrocatalytic CO₂ conversion.

First-row transition metal porphyrins for electrocatalytic hydrogen evolution — a SPP/JPP Young Investigator Award paper

A series of first-row transition metal complexes of tetrakis(pentafluorophenyl)porphyrin (1), denoted as 1-M (M [Formula: see text] Mn, Fe, Co, Ni, Cu, and Zn), were synthesized and examined as electrocatalysts for the hydrogen evolution reaction (HER). All these transition metal porphyrins were shown to be active for HER in acetonitrile using trifluoroacetic acid (TFA) as the proton source. The molecular nature and the stability of these metal porphyrins when functioning as HER catalysts were confirmed, and all catalysts gave Faradaic efficiency of >97% for H2 generation during bulk electrolysis. Importantly, by using 1-Cu, a remarkably high turnover frequency (TOF) of 48500 s[Formula: see text] 1-Cu the most efficient among this series of metal porphyrin catalysts. This TOF value also represents one of the highest values reported in the literature. In addition, electrochemical analysis demonstrated that catalytic HER mechanisms with these 1-M complexes are different. These results show that with the same porphyrin ligand, the change of metal ions will have significant impact on both catalytic efficiency and mechanism. This work for the first time provides direct comparison of electrocatalytic HER features of transition metal complexes of tetrakis(pentafluorophenyl)porphyrin under identical conditions, and will be valuable for future design and development of more efficient HER electrocatalysts of this series.

Crystal structure of (15,20-bis-(2,3,4,5,6-penta-fluoro-phen-yl)-5,10-{(4-methyl-pyridine-3,5-di-yl)bis-[(sulfanediyl-methyl-ene)[1,1'-biphen-yl]-4',2-di-yl]}porphyrinato)nickel(II) di-chloro-methane x-solvate (x > 1/2)

The title compound, [Ni(C64H33F10N5S2)]·xCH2Cl2, consists of discrete NiII porphyrin complexes, in which the five-coordinate NiII cations are in a distorted square-pyramidal coordination geometry. The four porphyrin nitro-gen atoms are located in the basal plane of the pyramid, whereas the pyridine N atom is in the apical position. The porphyrin plane is strongly distorted and the NiII cation is located above this plane by 0.241 (3) Å and shifted in the direction of the coordinating pyridine nitro-gen atom. The pyridine ring is not perpendicular to the N4 plane of the porphyrin moiety, as observed for related compounds. In the crystal, the complexes are linked via weak C-H⋯F hydrogen bonds into zigzag chains propagating in the [001] direction. Within this arrangement cavities are formed, in which highly disordered di-chloro-methane solvate mol-ecules are located. No reasonable structural model could be found to describe this disorder and therefore the contribution of the solvent to the electron density was removed using the SQUEEZE option in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18].

Boosting hydrogen evolution by using covalent frameworks of fluorinated cobalt porphyrins supported on carbon nanotubes

A covalent framework using fluorinated cobalt porphyrins is synthesized and shows significantly improved efficiency for the hydrogen evolution reaction in aqueous solution.