Surface-Grafted Single-Atomic Pt-Nx Complex with a Precisely Regulating Coordination Sphere for Efficient Electron Acceptor-Inducing Interfacial Electron Transfer

Based on the electron-withdrawing effect of the Pt(bpy)Cl2 molecule, a simple post-modification amide reaction was firstly used to graft it onto the surface of NH2-MIL-125, which performed as a highly efficient electron acceptor that induced the conversion of the photoinduced charge migration pathway from internal BDC→TiOx migration to external BDC→PtNx migration, significantly improving the efficiency of photoinduced electron transfer and separation. Furthermore, precisely regulating over the first coordination sphere of Pt single atoms was achieved using further post-modification with additional bipyridine to investigate the effect of Pt-Nx coordination numbers on reaction activity. The as-synthesized NML-PtN2 exhibited superior photocatalytic hydrogen evolution activity of 7.608 mmol g-1 h-1, a remarkable improvement of 225 and 2.26 times compared to pristine NH2-MIL-125 and NML-PtN4, respectively. In addition, the superior apparent quantum yield of 4.01 % (390 nm) and turnover frequency of 190.3 h-1 (0.78 wt % Pt SA; 129 times compared to Pt nanoparticles/NML) revealed the high solar utilization efficiency and hydrogen evolution activity of the material. And macroscopic color changes caused by the transition of carrier migration paths was first observed. It holds profound significance for the design of MOF-Molecule catalysts with efficient charge carrier separation and precise regulation of single-atom coordination sphere.

Platinum(II) terpyridine-based supramolecular polymer gels with induced chirality

Metal-ligand binding plays a crucial role in regulating the photophysical properties of supramolecular gels. In this study, we designed 1-Pt complexes comprising a central benzene-1,3,5-tricarboxamide unit functionalized with three terpyridines, which can form supramolecular gels with Pt(II). The resulting supramolecular gel of 1-Pt exhibited strong orange emission, which was attributed to the metal-to-metal ligand charge transfer during gel formation. Furthermore, the temperature-dependent absorption spectrum changes of the supramolecular polymer 1-Pt exhibited a nonsigmoidal transition, following a cooperative pathway involving a nucleation-elongation mechanism. Additionally, the strategy for the co-assembling system involving 1-Pt with chiral molecules (D-form and L-form) induced the helical arrangement of 1-Ptvia chiral additives in supramolecular metallogels.

Photochromic and electrochromic properties of a viologen-based multifunctional Cd-MOF

A pair of novel multifunctional MOF materials [Cd₂(L)₂(D/L-Lm)(H₂O)₂]·5H₂O (denoted as D/L-Cd-MOF) has been synthesized by combining the viologen-functionalized ligand H₂L⁺Cl^- and chiral D/L-tartaric acid (H₂Lm) with a simple solvothermal method. Due to the unique photoelectric response properties of the viologen units, reversible photochromic and electrochromic properties have been combined in D/L-Cd-MOF, which points to a new way of designing and constructing multifunctional photoelectric materials.

Bacteria-Triggered Solar Hydrogen Production via Platinum(II)-Tethered Chalcogenoviologens

Multifunctional solar energy conversion offers a feasible strategy to solve energy, environmental and water crises. Herein, a series of platinum(II)-tethered chalcogenoviologens (PtL⁺ -EV²⁺ , E=S, Se, Te) is reported, which integrate the functions of photosensitizer, electron mediator and catalyst. PtL⁺ -EV²⁺ (particularly for PtL⁺ -SeV²⁺ )-based one-component solar H₂ production could be triggered not only by EDTA, but also by facultative anaerobic and aerobic bacteria relying on a simplified mechanism, along with efficient antibacterial activities. In addition, by using real pool water, PtL⁺ -SeV²⁺ achieved multiple functions, including H₂ production, antibacterial action and acid removal, which supplied a new strategy to solve various problems in real life via a single system.

Redox tuning in Pt(bpy)-viologen catalyst-acceptor dyads enabling photocatalytic hydrogen evolution from water

A Pt(ii)-based photo-hydrogen-evolving molecular device tethered to dimethyl-substituted viologens (Pt(bpy)(dmMV²⁺)₂), providing higher driving force for hydrogen evolution reaction (HER) than the non-methylated analogue (Pt(bpy)(MV²⁺)₂), is found to exhibit improved photocatalytic performance. The observed behaviors are explained by the multiple HER pathways taken by evolving H₂ by the doubly and triply reduced species generated via consecutive photo-driven steps. Although the activity is still killed by the Dexter-type energy transfer quenching, our results provide new design strategies towards the development of more finely tuned molecular devices controlling the photocatalytic HER.

Enhanced photoreduction of water catalyzed by a cucurbit[8]uril-secured platinum dimer

A cucurbit[8]uril (CB[8])-secured platinum terpyridyl chloride dimer was used as a photosensitizer and hydrogen-evolving catalyst for the photoreduction of water. Volumes of produced hydrogen were up to 25 and 6 times larger than those obtained with the corresponding free and cucurbit[7]uril-bound platinum monomer, respectively, at equal Pt concentration. The thermodynamics of the proton-coupled electron transfer from the Pt(ii)–Pt(ii) dimer to the corresponding Pt(ii)–Pt(iii)–H hydride key intermediate, as quantified by density functional theory, suggest that CB[8] secures the Pt(ii)–Pt(ii) dimer in a particularly reactive conformation that promotes hydrogen formation.

The cucurbit[8]uril macrocycle can secure a platinum terpyridyl complex into a particularly reactive dimer that catalyzes the photoreduction of water.

Conformational Effects of [Ni2 (μ-ArS)2 ] Cores on Their Electrocatalytic Activity

Two nickel complexes supported by tridentate NS₂ ligands, [Ni₂ (κ-N,S,S,S'-N^Ph {CH₂ (MeC₆ H₂ R')S}₂ )₂ ] (1; R'=3,5-(CF₃ )₂ C₆ H₃ ) and [Ni₂ (κ-N,S,S,S'-N^iBu {CH₂ C₆ H₄ S}₂ )₂ ] (2), were prepared as bioinspired models of the active site of [NiFe] hydrogenases. The solid-state structure of 1 reveals that the [Ni₂ (μ-ArS)₂ ] core is bent, with the planes of the nickel centers at a hinge angle of 81.3(5)°, whereas 2 shows a coplanar arrangement between both nickel(II) ions in the dimeric structure. Complex 1 electrocatalyzes proton reduction from CF₃ COOH at -1.93 (overpotential of 1.04 V, with i_cat /i_p ≈21.8) and -1.47 V (overpotential of 580 mV, with i_cat /i_p ≈5.9) versus the ferrocene/ferrocenium redox couple. The electrochemical behavior of 1 relative to that of 2 may be related to the bent [Ni₂ (μ-ArS)₂ ] core, which allows proximity of the two Ni⋅⋅⋅Ni centers at 2.730(8) Å; thus possibly favoring H⁺ reduction. In contrast, the planar [Ni₂ (μ-ArS)₂ ] core of 2 results in a Ni⋅⋅⋅Ni distance of 3.364(4) Å and is unstable in the presence of acid.

Intrinsic hydrogen evolution capability and a theoretically supported reaction mechanism of a paddlewheel-type dirhodium complex

The intrinsic capability of the paddlewheel-type dirhodium tetraacetate complex, [Rh₂(O₂CCH₃)₄(H₂O)₂] ([1(H₂O)₂]), as a hydrogen evolution catalyst (HEC) for photochemical hydrogen evolution from aqueous solution was illustrated. This was achieved by using an optimized artificial photosynthesis (AP) system with a cyclometalated iridium complex [Ir(ppy)₂(bpy)](PF₆) ([Ir-PS-1]) and triethylamine (TEA) serving as a photosensitizer (PS) and a sacrificial donor, respectively. The total amount of hydrogen evolution and the turnover number (TON) of catalysis using this AP system were 385.7 μmol and 3857 (per Rh ion), respectively; these values are higher than those of [Rh(dtBubpy)₃](PF₆)₃, which is the most efficient HEC among the mononuclear rhodium complexes, and RhCl₃. Moreover, the catalytic performance of [1(H₂O)₂] was further accelerated by using [Ir(ppy)₂(dtBubpy)](PF₆) [Ir-PS-3] as a PS; 9886 TON (H₂ per Rh ion) was verified after 12 h of irradiation. In addition, the detailed mechanism of hydrogen evolution catalyzed by [1(H₂O)₂] was clarified by combining electro- and photochemical analyses and DFT calculations. The optimized geometries of [1(H₂O)₂], [1], hydride intermediates [H-Rh₂(O₂CCH₃)₄] ([H-1]), and their reduced species were theoretically verified by DFT calculations. Moreover, their redox potentials were theoretically estimated and compared with the observed potentials. Their combination analyses indicated that (i) the formation of [1], which has an open-metal site for hydrogen evolution and can be reduced by the one-electron reduced species of [Ir-PS-1], is a trigger for hydrogen evolution; (ii) [H-1] and its reduced species, which are verified by CV analyses, are key intermediate species in this reaction; and (iii) photochemical hydrogen evolution catalyzed by [1(H₂O)₂] occurred by two-electron reduction processes.

Nickel(ii) PE1CE2P pincer complexes (E = O, S) for electrocatalytic proton reduction

The catalytic activity of a series of nickel complexes with different phosphinite/thiophosphinite ligands for electrocatalytic proton reduction strongly depends on the nature of the pincer ligands.

Luminescent properties of a 3,5-diphenylpyrazole bridged Pt(ii) dimer

We report the synthesis, electrochemistry, photophysics and electroluminescence of a highly luminescent pyrazolate-bridged platinum(ii) complex. Light-emitting electrochemical cells (LEECs) of this dimer complex were among the brightest and most efficient LEECs from dinuclear compounds to date.

Metal-complex chromophores for solar hydrogen generation

Solar H₂ generation from water has been intensively investigated as a clean method to convert solar energy into hydrogen fuel. During the past few decades, many studies have demonstrated that metal complexes can act as efficient photoactive materials for photocatalytic H₂ production. Here, we review the recent progress in the application of metal-complex chromophores to solar-to-H₂ conversion, including metal-complex photosensitizers and supramolecular photocatalysts. A brief overview of the fundamental principles of photocatalytic H₂ production is given. Then, different metal-complex photosensitizers and supramolecular photocatalysts are introduced in detail, and the most important factors that strictly determine their photocatalytic performance are also discussed. Finally, we illustrate some challenges and opportunities for future research in this promising area.

A Nickel Dithiolate Water Reduction Catalyst Providing Ligand-Based Proton-Coupled Electron-Transfer Pathways

A nickel pyrazinedithiolate ([Ni(dcpdt)₂ ]^2- ; dcpdt=5,6-dicyanopyrazine-2,3-dithiolate), bearing a NiS₄ core similar to the active center of [NiFe] hydrogenase, is shown to serve as an efficient molecular catalyst for the hydrogen evolution reaction (HER). This catalyst shows effectively low overpotentials for HER (330-400 mV at pH 4-6). Moreover, the turnover number of catalysis reaches 20 000 over the 24 h electrolysis with a high Faradaic efficiency, 92-100 %. The electrochemical and DFT studies reveal that diprotonated one-electron-reduced species (i.e., [Ni^II (dcpdt)(dcpdtH₂ )]^- or [Ni^II (dcpdtH)₂ ]^- ) forms at pH<6.4 via ligand-based proton-coupled electron-transfer (PCET) pathways, leading to electrocatalytic HER without applying the highly negative potential required to generate low-valent nickel intermediates. This is the first example of catalysts exhibiting such behavior.

Computational, electrochemical, and spectroscopic studies of two mononuclear cobaloximes: the influence of an axial pyridine and solvent on the redox behaviour and evidence for pyridine coordination to cobalt(i) and cobalt(ii) metal centres

[Co(dmgBF2)2(H2O)2] (where dmgBF2 = difluoroboryldimethylglyoximato) was used to synthesize [Co(dmgBF2)2(H2O)(py)]·0.5(CH3)2CO (where py = pyridine) in acetone. The formulation of complex was confirmed by elemental analysis, high resolution MS, and various spectroscopic techniques. The complex [Co(dmgBF2)2(solv)(py)] (where solv = solvent) was readily formed in situ upon the addition of pyridine to complex . A spectrophotometric titration involving complex and pyridine proved the formation of such a species, with formation constants, log K = 5.5, 5.1, 5.0, 4.4, and 3.1 in 2-butanone, dichloromethane, acetone, 1,2-difluorobenzene/acetone (4 : 1, v/v), and acetonitrile, respectively, at 20 °C. In strongly coordinating solvents, such as acetonitrile, the lower magnitude of K along with cyclic voltammetry, NMR, and UV-visible spectroscopic measurements indicated extensive dissociation of the axial pyridine. In strongly coordinating solvents, [Co(dmgBF2)2(solv)(py)] can only be distinguished from [Co(dmgBF2)2(solv)2] upon addition of an excess of pyridine, however, in weakly coordinating solvents the distinctions were apparent without the need for excess pyridine. The coordination of pyridine to the cobalt(ii) centre diminished the peak current at the Epc value of the Co(I/0) redox couple, which was indicative of the relative position of the reaction equilibrium. Herein we report the first experimental and theoretical (59)Co NMR spectroscopic data for the formation of Co(i) species of reduced cobaloximes in the presence and absence of py (and its derivatives) in CD3CN. From spectroelectrochemical studies, it was found that pyridine coordination to a cobalt(i) metal centre is more favourable than coordination to a cobalt(ii) metal centre as evident by the larger formation constant, log K = 4.6 versus 3.1, respectively, in acetonitrile at 20 °C. The electrosynthesis of hydrogen by complexes and in various solvents demonstrated the dramatic effects of the axial ligand and the solvent on the turnover number of the respective catalyst.

Photochemical H2 evolution from water catalyzed by a dichloro(diphenylbipyridine)platinum(ii) derivative tethered to multiple viologen acceptors

Enhanced hydrogen evolution from water photocatalyzed by a dichloro(diphenylbipyridine)platinum(ii) derivative tethered to multiple viologen acceptors is reported.

Improved photocatalytic hydrogen evolution driven by chloro(terpyridine)platinum(ii) derivatives tethered to a single pendant viologen acceptor

Chloro(terpyridine)platinum(ii) derivatives tethered to a single pendant viologen acceptor exhibit drastically improved turnover number in the photocatalytic H₂ evolution reaction from water.

Rational Design of an Electron-Reservoir Pt(II) Complex for Efficient Photocatalytic Hydrogen Production from Water

Herein we report a Pt(II) complex containing a 4,4'-bis[4-(triphenylsilyl)phenyl]-2,2'-bipyridine ligand as a molecular catalyst for water splitting. Systematic studies of the electrochemical and electronic properties of this catalyst, in comparison with two control complexes, reveal electron-reservoir characteristics upon two-electron reduction. A turnover number of 510,000 was recorded by employing this complex as a water reduction catalyst in combination with a state-of-the-art photosensitizer and N,N-dimethylaniline as a sacrificial electron donor, which represents a large improvement over the control complexes that do not contain the tetraphenylsilyl ligand substitution.

Ni–Cu alloy nanoparticles loaded on various metal oxides acting as efficient catalysts for photocatalytic H2 evolution

Catalysis of Ni–Cu alloy nanoparticles loaded on various metal oxides for photocatalytic H₂ evolution depends on preparation methods and supports.

A tricarboxylated PtCl(terpyridine) derivative exhibiting pH-dependent photocatalytic activity for H2 evolution from water

A ‘negatively charged’ PtCl(terpyridine) derivative was found to be the first example of a Pt(ii)-based molecular photocatalyst capable of driving H₂ evolution coupled with a PCET process at the ligand geometry.

Synergistic effects of Ni and Cu supported on TiO2 and SiO2 on photocatalytic H2 evolution with an electron donor–acceptor linked molecule

Ni and Cu supported on TiO₂ or SiO₂ synergistically acted as H₂ evolution catalysts in a photocatalytic system.

Pt(ii)-Catalyzed photosynthesis for H2 evolution cycling between singly and triply reduced species

A platinum(ii)-based single-component molecular photocatalyst for hydrogen evolution from water cycling between the singly and triply reduced forms is reported.