Tuning Electrocatalytic Water Oxidation Activity: Insights from the Active-Site Distance in LnCu6 Clusters

Atomically precise metal clusters serve as a unique model for unraveling the intricate mechanism of the catalytic reaction and exploring the complex relationship between structure and activity. Herein, three series of water-soluble heterometallic clusters LnCu6, abbreviated as LnCu6-AC (Ln = La, Nd, Gd, Er, Yb; HAC = acetic acid), LnCu6-IM (Ln = La and Nd; IM = Imidazole), and LnCu6-IDA (Ln = Nd; H2IDA = Iminodiacetic acid) are presented, each featuring a uniform metallic core stabilized by distinct protected ligands. Crystal structure analysis reveals a triangular prism topology formed by six Cu2+ ions around one Ln3+ ion in LnCu6, with variations in Cu···Cu distances attributed to different ligands. Electrocatalytic oxygen evolution reaction (OER) shows that these different LnCu6 clusters exhibit different OER activities with remarkable turnover frequency of 135 s-1 for NdCu6-AC, 79 s-1 for NdCu6-IM and 32 s-1 for NdCu6-IDA. Structural analysis and Density Functional Theory (DFT) calculations underscore the correlation between shorter Cu···Cu distances and improves OER catalytic activity, emphasizing the pivotal role of active-site distance in regulating electrocatalytic OER activities. These results provide valuable insights into the OER mechanism and contribute to the design of efficient homogeneous OER electrocatalysts.

Visible-Light Photocatalytic Overall Water Splitting on a B4C3/CxNy Z-Scheme Heterojunction: Role of Ultrafast Carrier Recombination-Transfer Kinetics

Herein, combining density functional theory (DFT) calculations with nonadiabatic molecular dynamics (NAMD), we built a computational framework to rationally screen from a series of 2D conjugated carbon nitrides (CNs) to match with B4C3, resulting in the excellent direct Z-scheme photocatalyst (B4C3/C6N6) for overall water splitting (OWS). Studies on interface engineering and ultrafast dynamics of carrier recombination-transfer show that in the B4C3/C6N6 system, compared with the slower interlayer migration process of carriers, strong nonadiabatic coupling and longer quantum decoherence time accelerates weak carrier interlayer recombination on a subpicosecond time scale, enabling simultaneous triggering of hydrogen evolution reaction (HER) with ΔG = -0.23 eV and spontaneous oxygen evolution reaction (OER) in the absence of sacrificial or cocatalysts. In general, our work will promote the design of efficient direct Z-scheme photocatalysts from an ultrafast dynamics perspective.

Conductive Lanthanide Metal-Organic Frameworks with Exceptionally High Stability

Electrically conductive metal-organic frameworks (MOFs) have been extensively studied for their potential uses in energy-related technologies and sensors. However, achieving that goal requires MOFs to be highly stable and maintain their conductivity under practical operating conditions with varying solution environments and temperatures. Herein, we have designed and synthesized a new series of {[Ln4(μ4-O)(μ3-OH)3(INA)3(GA)3](CF3SO3)(H2O)6}n (denoted as Ln4-MOFs, Ln = Gd, Tm, and Lu, INA = isonicotinic acid, GA = glycolic acid) single crystals, where electrons are found to transport along the π-π stacked aromatic carbon rings in the crystals. The Ln4-MOFs show remarkable stability, with minimal changes in conductivity under varying solution pH (1-12), temperature (373 K), and electric field as high as 800 000 V/m. This stability is achieved through the formation of strong coordination bonds between high-valent Ln(III) ions and rigid carboxylic linkers as well as hydrogen bonds that enhance the robustness of the electron transport path. The demonstrated lanthanide MOFs pave the way for the design of stable and conductive MOFs.

Correlation of the spin state and catalytic property of M-N4 single-atom catalysts in oxygen reduction reactions

The rational design of high-performance catalysts for oxygen reduction reactions (ORRs) is of great importance for large-scale applications in the field of proton-exchange membrane fuel cells and the green synthesis of H₂O₂. The effect of spin states of paramagnetic metal ions on the selectivity of ORRs is significant for single-atom catalysts (SACs). In this work, via spin-polarization density functional theory (DFT) calculations, we systematically investigated the popular paramagnetic metal-nitrogen graphene (M-N₄-C, M = Mn, Fe, and Co) SACs to mainly focus on the correlation of spin states and catalytic performance (e.g. activity and selectivity). Both thermodynamically and kinetically, it was found that Co-N₄-C (S = 1/2) has excellent 2e^- oxygen reduction performance (hydrogen peroxide production) with an ultralow overpotential of 0.03 V, and the hydrogenation of OOH* is the rate-determining step (RDS) with an energy barrier of 1.20 eV. The 4e^- ORR tends to occur along the OOH dissociation pathway (O* + OH*) on Co-N₄-C (S = 3/2), in which OOH* decomposition is the RDS with an energy barrier of 1.01 eV. It is proved that the spin magnetic moment is the key factor to regulate the ORR property via multi-angle electronic analysis. The spin states of catalysts play a crucial role in the activity and selectivity of ORRs mainly by manipulating the bond strength between OOH and catalysts. This will provide new insights for the rational design of ORR catalysts with magnetic metals.

Rational design of bimetallic MXene solid solution with High-Performance electrocatalytic N2 reduction

Electrocatalytic N₂ reduction reaction (eNRR) was an effective alternative method for green synthesis of NH₃. By combining the first-principal Density functional theory (DFT) calculations and Monte Carlo (MC) simulation, we systematacially investigated 24 types equal-ratio bimetallic MXene solid solution, involving 88 different catalysts. Our focus was on the catalytic performance of these materials in eNRR. The computational result indicate that MoW(3Mo) has high stability, selectivity (93.8 % against the hydrogen evolution reaction (HER)) and activity (U_L = -0.26 V), which is significantly better than that of monometal Mo₂CO₂ and W₂CO₂. This improvement in catalytic properties is attributed to the unique electronic structure (e.g. d-band center, charge) of bimetallic MXene solid solution. In explicit solvent conditions, the microenvironment of hydrogen bond in aqueous liquid thermodynamically promotes the catalytic property for eNRR and reduce the catalytic property of HER side reaction, but the kinetic barrier is also increased due to the effect of the hydrogen-bond microenvironment on proton migration. Overall, the obtained bimetallic MXene solid solution MoW(3Mo) exhibits excellent catalytic performance in eNRR.

Co-Dissolved Isostructural Polyoxovanadates to Construct Single-Atom-Site Catalysts for Efficient CO2 Photoreduction

We explored a co-dissolved strategy to embed mono-dispersed Pt center into V₂ O₅ support via dissolving [PtV₉ O₂₈ ]^7- into [V₁₀ O₂₈ ]^6- aqueous solution. The uniform dispersion of [PtV₉ O₂₈ ]^7- in [V₁₀ O₂₈ ]^6- solution allows [PtV₉ O₂₈ ]^7- to be surrounded by [V₁₀ O₂₈ ]^6- clusters via a freeze-drying process. The V centers in both [PtV₉ O₂₈ ]^7- and [V₁₀ O₂₈ ]^6- were converted into V₂ O₅ via a calcination process to stabilize Pt center. These double separations can effectively prevent the Pt center agglomeration during the high-temperature conversion process, and achieve 100 % utilization of Pt in [PtV₉ O₂₈ ]^7- . The resulting Pt-V₂ O₅ single-atom-site catalysts exhibit a CH₄ yield of 247.6 μmol g^-1  h^-1 , 25 times higher than that of Pt nanoparticle on the V₂ O₅ support, which was accompanied by the lactic acid photooxidation to form pyruvic acid. Systematical investigations on this unambiguous structure demonstrate an important role of Pt-O atomic pair synergy for highly efficient CO₂ photoreduction.

Magnetic and Dielectric Switchings Actuated by the Rotation of the Picoline Ligand in an Iron-Based Dinuclear Phase-Transition Complex

Multifunctional materials with switchable magnetic and dielectric properties are crucial for the development of memory and sensor devices. Herein, we report a methoxy-bridged dinuclear iron-pyridyl complex [Fe₂(4-picoline)₄(NCS)₄(μ-OCH₃)₂] (1), which shows simultaneous thermal-induced magnetic and dielectric switchings. Within the phase-transition temperature range, both magnetic switching and the dielectric anomaly were detected, in which the thermal hysteresis loops were 23 and 21 K, respectively. Detailed structural analyses revealed that these simultaneous switchings were rooted in the flexible rotatable ligands, which were actuated by readjusting the π-π intermolecular interactions between the pyridine ligands in the trans positions of the metal centers. These results were comprehensively investigated both experimentally and theoretically. This study presents a new guideline to control both the magnetic and dielectric properties of molecular complexes by external stimuli.

Construction of a High Nuclear Gadolinium Cluster with Enhanced Magnetocaloric Effect through Structural Transition

Starting from a dinuclear complex {Gd₂(L)₂(NO₃)₄(H₂O)₂}·2(CH₃CN) (1) based on 2,6-dimethoxyphenol (HL), a nonanuclear cluster {Gd₉(L)₄(μ₄-OH)₂(μ₃-OH)₈(μ₂-OCH₃)₄(NO₃)₈ (H₂O)₈}(OH)·2H₂O (2) was obtained via modulating the amount of the ligand and base. Both of them have been structurally and magnetically characterized. Complex 1 decorates the Gd₂ core bridged by double μ₂-phenoxyl oxygen atoms and coordinated neutral CH₃CN molecules, while 2 features the Gd₉ core with a sandglass-like topology. Magnetic investigations reveal that the weaker antiferromagnetic interactions between adjacent metal ions exist in complex 2 than in 1, which is in agreement with the theoretical results. Meanwhile, the magnetocaloric effect with a maximum -ΔS _m value changes from 27.32 to 40.60 J kg^-1 K^-1 at 2 K and 7 T.

W Single-Atom Catalyst for CH4 Photooxidation in Water Vapor

Solar-driven high-efficiency and direct conversion of methane into high-value-added liquid oxygenates against overoxidation remains a great challenge. Herein, facile and mass fabrication of low-cost tungsten single-atom photocatalysts is achieved by directly calcining urea and sodium tungstate under atmosphere (W-SA-PCN-m, urea amount m = 7.5, 15, 30, and 150 g). The single-atom photocatalysts can manage H₂ O₂ in situ generation and decomposition into ·OH, thus achieving highly efficient CH₄ photooxidation in water vapor under mild conditions. Systematic investigations demonstrate that integration of multifunctions of methane activation, H₂ O₂ generation, and decomposition into one photocatalyst can dramatically promote methane conversion to C1 oxygenates with a yield as high as 4956 µmol g_cat ^-1 , superior to that of the most reported non-precious photocatalysts. Liquid-solid phase transition can induce the products to facilely switch in from HCOOH to CH₃ OH by pulling the catalyst above water with CH₃ OH/HCOOH ratio from 10% (in H₂ O) to 80% (above H₂ O).

Family of Nanoclusters, Ln33 (Ln = Sm/Eu) and Gd32, Exhibiting Magnetocaloric Effects and Fluorescence Sensing for MnO4. Inorg Chem 2022;61:8861-8869. [PMID: 35653200 DOI: 10.1021/acs.inorgchem.2c00898]

A family of nanoclusters, [Ln₃₃(EDTA)₁₂(OAc)₂(CO₃)₄(μ₃-OH)₃₆(μ₅-OH)₄(H₂O)₃₈]·OAc·xH₂O (x ≈ 50, Ln = Sm for 1; x ≈ 70, Ln = Eu for 2) and [Gd₃₂(EDTA)₁₂(OAc)₂(C₂O₄)(CO₃)₂(μ₃-OH)₃₆(μ₅-OH)₄(H₂O)₃₆]·x(H₂O) (x ≈ 70 for 3; H₄EDTA = ethylene diamine tetraacetic acid), was prepared through the assembly of repeating subunits under the action of an anion template. The analysis of the structures showed that compounds 1 and 2 containing 33 Ln³⁺ ions were isostructural, which were constructed by three kinds of subunits in the presence of CO₃^2- as an anion template, while compound 3 had a slightly different structure. Compound 3 containing 32 Gd³⁺ ions was formed by three types of subunits in the presence of CO₃^2- and C₂O₄^2- as a mixed anion template. The CO₃^2- anions came from the slow fixation of CO₂ in the air. Meanwhile, one kind of high-nuclearity lanthanide clusters showed high chemical stability. The quantum Monte Carlo (QMC) calculation suggested that weak antiferromagnetic interactions were dominant between Gd³⁺ ions in 3. Magnetocaloric studies showed that compound 3 had a large entropy change of 43.0 J kg^-1 K^-1 at 2 K and 7 T. Surprisingly, compound 2 showed excellent recognition and detection effects for permanganate in aqueous solvents based on the fluorescence quenching phenomenon.

Nuclearity enlargement from [PW9O34@Ag51] to [(PW9O34)2@Ag72] and 2D and 3D network formation driven by bipyridines

The structural transformations of metal nanoclusters are typically quite complex processes involving the formation and breakage of several bonds, and thus are challenging to study. Herein, we report a case where two lacunary Keggin polyoxometallate templated silver single-pods [PW9O34@Ag51] (SD/Ag51b) fuse to a double-pod [(PW9O34)2@Ag72] by reacting with 4,4’-bipyridine (bipy) or 1,4-bis(4-pyridinylmethyl)piperazine (pi-bipy). Their crystal structures reveal the formation of a 2D 44-sql layer (SD/Ag72a) with bipy and a 3D pcu framework (SD/Ag72c) with pi-bipy. The PW9O349− retains its structure during the cluster fusion and cluster-based network formation. Although the two processes, stripping of an Ag-ligands interface followed by fusion, and polymerization, are difficult to envisage, electrospray ionization mass spectrometry provides enough evidences for such a proposal to be made. Through this example, we expect the structural transformation to become a powerful method for synthesizing silver nanoclusters and their infinite networks, and to evolve from trial-and-error to rational.

The synergetic effect of an aqua ligand and metal site on the performance of single-atom catalysts in H2O2 synthesis: a density functional theory study

Studying the effect of the coordination field on the catalytic property is critical for the rational design of outstanding electrocatalysts for H₂O₂ synthesis. Herein, via density functional theory (DFT) calculations and ab initio molecular dynamic (AIMD) simulations, we built an effective computational framework to identify the synergetic effect of an aqua ligand and metal ion on the 2e^- ORR catalytic performance under gas condition and aqua solvent. Specifically, the screening results of 29 single-atom catalysts (SACs), TM@C₆N₆ (TM = transition metal), indicated that Cu@C₆N₆ features excellent catalytic property with thermal stability, lowest 2e^- ORR overpotential (0.02 V) and high selectivity of 99.99%. Once an aqua ligand binds with the Cu site, the activity is reduced to the overpotential of 0.42 V and the selectivity decreased slightly (99.98%) due to the reduction of the adsorption strength for the reaction intermediates. A combination of geometric structures and electronic properties revealed that such changes are correlated with the charge of the Cu site. Furthermore, based on molecular orbital theory, the essence of the high catalytic property deeply lies in the effect of the moderate electron back donation bond (d_yz & d_xz→) between Cu and O₂. This work will provide a route to better design high-performance SACs for H₂O₂ synthesis effectively.

Enantioselective Recognition and Separation of C2 Symmetric Substances via Chiral Metal-Organic Frameworks

A promising route toward the enantioselective recognition and separation of racemic molecules is the design of chiral metal-organic frameworks (CMOFs) with high enantioselectivity and stability. Herein, we report porous CMOFs Δ- and Λ-RuEu-MOFs constructed from the D₃-symmetry helical chiral Ru(phen)₃-derived tricarboxylate ligand and Eu₂ units, which can be utilized as adsorbents for the enantioselective recognition and separation of 1,1'-bi-2-naphthol (BINOL) derivatives. Investigation of the circular dichroism enantiodifferentiation between the host and guest suggested that Δ- and Λ-RuEu-MOFs can be employed as chiral sensors to discriminate axial enantiomers due to their diastereomeric host-guest relationship. Density functional theory calculations reveal that chiral recognition is attributed to the distinguishing binding affinities stemming from N···H-O hydrogen bonds and π-π stacking between the host and guest. Moreover, the reticulate structure of Δ- and Λ-RuEu-MOFs can be readily recycled and reused for the successive enantioselective separation of BINOL up to 80% ee.

A new family of decanuclear Ln7Cr3 clusters exhibiting a magnetocaloric effect

Two dimeric Ln–Cr clusters with formula {Ln(H₂O)₈[Ln₆Cr₃(L)₆(CH₃COO)₆(μ₃-OH)₁₂(H₂O)₁₂]}·(ClO₄)₆·xH₂O (Ln = Gd, x = 35 for 1 and Ln = Dy, x = 45 for 2, HL = 2-pyrazinecarboxylic acid) were obtained by a ligand-controlled hydrolytic method with a mixed ligand system (2-pyrazinecarboxylic acid and acetate). Single crystal structure analysis showed that two trigonal bipyramids of [Gd₃Cr₂(μ₃-OH)₆]⁹⁺ worked as building blocks in constructing the metal-oxo cluster core of [Gd₆Cr₃(μ₃-OH)₁₂]¹⁵⁺ by sharing a common top – a Cr³⁺ ion. Additionally, compound 1 forms a three-dimensional framework with a one-dimensional nanopore channel along the a-axis through a hydrogen-bond interaction between the cationic cluster core and the free mononuclear cation [Gd(H₂O)₈]³⁺ and the π-bond interactions of the pyrazine groups on the two cationic cluster cores. Magnetic calculations indicated a weak ferromagnetic coupling interaction for Gd⋯Gd and Gd⋯Cr in compound 1, with its magnetic entropy change (−ΔS_m) reaching 21.1 J kg⁻¹ K⁻¹ at 5 K, 7 T, while compound 2 displayed an obvious frequency-dependency at H_dc = 2000 Oe.

Two decanuclear Ln–Cr clusters Ln₇Cr₃ were obtained, which formed a three-dimensional framework with one-dimensional nanopore channel through hydrogen-bond and π-bond interactions. Gd₇Cr₃ had a magnetic entropy change of 21.1 J kg⁻¹ K⁻¹ at 5 K, 7 T.

High-performance single-atom Ni catalyst loaded graphyne for H2O2 green synthesis in aqueous media

The electrochemical synthesis of hydrogen peroxide (H₂O₂) provides a greener and more efficient method compared with classic catalysts containing toxic metals. Herein, we used first-principles density functional theory (DFT) calculations to investigate 174 different single-atom catalysts with graphyne substrates, and conducted a three-step screening strategy to identify the optimal noble metal-free single atom catalyst. It is found that a single Ni atom loaded on γ-graphyne with carbon vacancies (Ni@V-γ-GY) displayed remarkable thermodynamic stability, excellent selectivity, and high activity with an ultralow overpotential of 0.03 V. Furthermore, based on ab-initio molecular dynamic and DFT calculations under the H₂O solvent, it was revealed that the catalytic performance for H₂O₂ synthesis in aqueous phase was much better than that in gas phase condition, shedding light on the hydrogen bond network being beneficial to accelerate the transfer of protons for H₂O₂ synthesis.

Role of the Auxiliary Ligand in the Spontaneous Resolution of Enantiomers in Three-Dimensional Coordination Polymers

Four pairs of chiral 3D coordination polymers (CPs), [Zn₂(BDC)(lac)(DMF)]·guest (2) (H₂BDC = benzene dicarboxylic acid; H₂lac = lactic acid; guest = 1.5DMF + i-PrOH), [Co₂(BDC)(lac)(DMF)]·guest (3) (guest = DMF + 2H₂O), [Fe₄(BDC)₃(lac)₂(DMF)₂](CO₃)·guest (4) (guest = DMF + 2H₂O), and {Zn₁₁(BPDC)₆(lac)₆[NH₂(CH₃)₂]₂}·guest (H₂BPDC = 3,3'-biphenyldicarboxylic acid; guest = 6DMF + 18H₂O) (5), are prepared through the reactions of racemic lactic acid (rac-H₂lac) with different metal ions and auxiliary ligands. Structural analyses and DFT calculations reveal that forming more and stronger coordination bonds between the auxiliary ligand and metal ions is more conducive to the spontaneous resolution of enantiomers in 3D CPs than simply increasing the entropy of the auxiliary ligand itself.

H-Bond-Mediated Selectivity Control of Formate versus CO during CO2 Photoreduction with Two Cooperative Cu/X Sites

It is highly desirable to achieve solar-driven conversion of CO₂ to valuable fuels with controlled selectivity. The existing catalysts are mainly explored for CO production but rarely for formate generation. Herein, highly selective photoreduction of CO₂ to formate (99.7%) was achieved with a high yield of 3040 μmol g^-1 in 10 h by hierarchical integration of photosensitizers and monometallic [bpy-Cu/ClX] (X = Cl or adenine) catalysts into a stable Eu-bpy metal-organic framework. However, replacing X with pyridine in [bpy-CuCl/X] significantly reduced formate production while increasing the CO yield to 960 μmol g^-1. Systematic investigations revealed that the catalytic process is mediated by the H-bond synergy between Cu-bound X and CO₂-derived species, and the selectivity of HCOO^- can be controlled by simply replacing the coordination ligands. This work provides a molecularly precise structural model to provide mechanistic insights for selectivity control of CO₂ photoreduction.

Thermally induced transformation of a Cu4I4-based cluster to a Cu2I2-based cluster under mild conditions

A reaction of 6,6'-bis((benzylthio)methyl)-2,2'-bipyridine (L) with CuI at room temperature led to one Cu4I4-based cluster, which could be thermally transformed to a Cu2I2-based one under mild conditions due to the formation of a Cu-S bond. Along with the structural transformation, remarkable changes in the color and luminescence have been triggered.

Integration of bio-inspired lanthanide-transition metal cluster and P-doped carbon nitride for efficient photocatalytic overall water splitting

Photosynthesis in nature uses the Mn₄CaO₅ cluster as the oxygen-evolving center to catalyze the water oxidation efficiently in photosystem II. Herein, we demonstrate bio-inspired heterometallic LnCo₃ (Ln = Nd, Eu and Ce) clusters, which can be viewed as synthetic analogs of the CaMn₄O₅ cluster. Anchoring LnCo₃ on phosphorus-doped graphitic carbon nitrides (PCN) shows efficient overall water splitting without any sacrificial reagents. The NdCo₃/PCN-c photocatalyst exhibits excellent water splitting activity and a quantum efficiency of 2.0% at 350 nm. Ultrafast transient absorption spectroscopy revealed the transfer of a photoexcited electron and hole into the PCN and LnCo₃ for hydrogen and oxygen evolution reactions, respectively. A density functional theory (DFT) calculation showed the cooperative water activation on lanthanide and O−O bond formation on transition metal for water oxidation. This work not only prepares a synthetic model of a bio-inspired oxygen-evolving center but also provides an effective strategy to realize light-driven overall water splitting.

Anion-Dependent Assembly of 3d-4f Heterometallic Clusters Ln5Cr2 and Ln8Cr4

A series of heterometallic Ln-Cr clusters with the formulas [Ln₅Cr₂(H₂L)₂(OAc)₆(μ₃-OH)₆(H₂O)₁₅](ClO₄)₇·xH₂O (Ln = Gd and x = 33 for 1 and Ln = Dy and x = 21 for 2) and [Ln₈Cr₄(H₂L)₄(OAc)₈(μ₃-OH)₁₆(μ₄-O)₁(H₂O)₈](Cl)(ClO₄)₅·10H₂O (Ln = Gd for 3 and Ln = Dy for 4) was obtained through the reaction of the acetate ligands 2,2-dimethylolpropionic acid (H₃L) and Ln(ClO₄)₃ in the presence of chromium salts with different anions under the same high pH conditions. X-ray analysis revealed that compound 1 contained a metal unit [Gd₃Cr₂] displaying the pentagonal bipyramid configuration and that compound 3 was templated by Cl^- and ClO₄^- as a mixed anion template featuring a quadrangular structure. In compound 3, the 12 metal atoms were arranged in a wheel-shaped metal skeleton [Gd₈Cr₄], which was produced by 4 tetrahedral metal units [Gd₃Cr] sharing vertices. The introduction of the mixed anion template increased the number of metal atoms in the Ln-Cr clusters. Magnetic calculations indicated that there was weak antiferromagnetic Gd···Cr coupling and weak ferromagnetic Gd···Gd coupling in 1, whereas both Gd···Cr and Gd···Gd in 3 exhibited weak antiferromagnetic interactions. Magnetothermal studies showed that compounds 1 and 3 displayed magnetic entropy changes of 25.2 J kg^-1 K^-1 at 5 K and 7 T and 33.8 J kg^-1 K^-1 at 2 K and 7 T, respectively.

A highly robust heterometallic TbIII/NiII-organic framework for C2 hydrocarbon separation and capture

The exquisite combination of hetreometallic [TbIIINiII(COO)3(H2O)] clusters with a designed hexatopic ligand generates one highly robust three-dimensional heterometallic TbIII/NiII-organic framework material {[TbNi(HTDP)(H2O)]·3DMF·2H2O}n (NUC-2; H6TDP = 2,4,6-tri(2,4-dicarboxyphenyl)pyridine). Gas adsorption measurements reveal that the activated NUC-2 exhibits ultrahigh C2H2 adsorption capacity but negligible uptake of C2H4, which is ascribed to its high stability and ultrahigh functional internal surface. Furthermore, dynamic breakthrough experiments confirm that NUC-2 can effectively fulfill the separation of a C2H2/C2H4 (1 : 99) mixture. Such excellent performance makes NUC-2 a promising adsorbent for practical C2H2/C2H4 separation and provides new insights into heterometallic MOFs for gas separation.

Syntheses, structures and magnetic properties of novel tetrameric Ln2Mn2 and ring-like Ln4Mn4 clusters

Two series of heterometallic Ln–Mn clusters Ln2Mn2 and Ln4Mn4 were successfully synthesized in the presence of alcohol ligands, and the magnetic coupling interaction between metal ions were characterized by theoretical calculations.

Temperature dependence of spherical electron transfer in a nanosized [Fe14] complex

The study of transition metal clusters exhibiting fast electron hopping or delocalization remains challenging, because intermetallic communications mediated through bridging ligands are normally weak. Herein, we report the synthesis of a nanosized complex, [Fe(Tp)(CN)3]8[Fe(H2O)(DMSO)]6 (abbreviated as [Fe14], Tp-, hydrotris(pyrazolyl)borate; DMSO, dimethyl sulfoxide), which has a fluctuating valence due to two mobile d-electrons in its atomic layer shell. The rate of electron transfer of [Fe14] complex demonstrates the Arrhenius-type temperature dependence in the nanosized spheric surface, wherein high-spin centers are ferromagnetically coupled, producing an S = 14 ground state. The electron-hopping rate at room temperature is faster than the time scale of Mössbauer measurements (<~10-8 s). Partial reduction of N-terminal high spin FeIII sites and electron mediation ability of CN ligands lead to the observation of both an extensive electron transfer and magnetic coupling properties in a precisely atomic layered shell structure of a nanosized [Fe14] complex.

Encapsulating a Ni(II) molecular catalyst in photoactive metal-organic framework for highly efficient photoreduction of CO2

Photocatalytic reduction of CO₂ to CO is a promising strategy for reducing atmospheric CO₂ levels and storing solar radiation as chemical energy. Here, we demonstrate that a molecular catalyst [Ni^II(bpet)(H₂O)₂] successfully encapsulated into a highly robust and visible-light responsive metal-organic framework (Ru-UiO-67) to fabricate composite catalysts for photocatalytic CO₂ reduction. The composite Ni@Ru-UiO-67 photocatalysts show efficient visible-light-driven CO₂ reduction to CO with a TON of 581 and a selectivity of 99% after 20-h illumination, because of the facile electron transfer from Ru-photosensitizer to Ni(II) active sites in Ni@Ru-UiO-67 system. The mechanistic insights into photoreduction of CO₂ have been studied based on thermodynamical, electrochemical, and spectroscopic investigation, together with density functional theory (DFT) calculations. This work shows that encapsulating molecular catalyst into photoactive MOF highlights opportunities for designing efficient, stable and recyclable photocatalysts.

Carboxylic acid stimulated silver shell isomerism in a triple core-shell Ag84 nanocluster

A unique triple core–shell Ag₈₄ nanocluster displaying isomerism, which is controlled by different carboxylic acids and a one-way transformation (SD/Ag84a and SD/Ag84b).

Isomerization is highly important in all aspects of science, yet it is rarely observed in nanoscience. Here, we synthesized a unique triple core–shell Ag₈₄ nanocluster displaying isomerism, which is controlled by different carboxylic acids and a one-way transformation (SD/Ag84a → SD/Ag84b). The innermost core is a rare Ag₁₀ nanocluster which comprises an Ag₆ octahedral unit as seen in face-centred cubic (fcc) silver metal and four capped Ag atoms. It templates two crescent-shaped polyoxometalate (W₇O₂₆)^10– shells which are then enclosed in a shell of silver shaped as rugby balls. The organic ligands (ⁱPrS^–, ⁿPrCOO^– and PhCOO^–) finally shield the metallic clusters. Due to slight differences in structure at two poles and the steric hindrance of ⁿPrCOO^– and PhCOO^–, SD/Ag84a and SD/Ag84b adopt the shapes of flat-headed and cuspidal prolate spheres, respectively. Interestingly, PhCOOH is dominant over ⁿPrCOOH whereby crystals of SD/Ag84b were isolated if PhCOOH is added during the synthesis of SD/Ag84a. This demonstrates that PhCOOH not only alters the organic coats but also induces metal shell re-organization. This work reveals carboxylate-controlled skeletal isomerism in silver nanoclusters for the first time, thus deepening the understanding of silver nanocluster assembly, flexibility and reactivity.

Unconventional Method for Fabricating Valence Tautomeric Materials: Integrating Redox Center within a Metal-Organic Framework

Due to the structural advantages displayed by Metal-Organic Frameworks (MOFs), integrating Valence Tautomerism (VT) systems within MOFs could be an effective strategy in order to break through the constraints of the traditional ones. Herein, we report the first successful integration of a VT system into a MOF termed VT-MOF-1. The structural characteristics of VT-MOF-1, such as dinuclear cobalt-catechol clusters and solvent-accessible pores, are both innovative and novel, potentially yielding new vitality within VT field. In addition, VT-MOF-1 exhibits specific behaviors responsive to temperature and different solvent molecules as n-butanol, tert-butanol, and isopropyl alcohol. The entropy values and configurations of the solvent molecules might be responsible for the tunable sensing behaviors.

Unusual fcc-structured Ag10 kernels trapped in Ag70 nanoclusters

A bioctahedral Ag₁₀ kernel is locked by a pair of Mo₇O₂₆^10– anions to form an inner Ag₁₀@(Mo₇O₂₆)₂ core which is further encapsulated by an outer Ag₇₀ shell to form three-shell Ag₁₀@(Mo₇O₂₆)₂@Ag₇₀ nanoclusters.

Controlled trapping atom-precise ultrasmall silver nanoparticles into silver nanoclusters is challenging; thus only limited progress has been made in this area. We are therefore inspired to isolate two novel silver nanoclusters, Ag₁₀@Ag₇₀ (SD/Ag80a and SD/Ag80b; SD = SunDi), where a novel fcc-structured Ag₁₀ kernel built from two single-edge opened Ag₆ octahedra by sharing one edge is trapped. The bioctahedral Ag₁₀ kernel is locked by a pair of Mo₇O₂₆^10– anions to form an inner Ag₁₀@(Mo₇O₂₆)₂ core which is further encapsulated by an outer Ag₇₀ shell to form three-shell Ag₁₀@(Mo₇O₂₆)₂@Ag₇₀ nanoclusters. Notably, the bioctahedral Ag₁₀ kernel has not been observed in silver nanoclusters ever before, thus representing a new embryo state of silver nanoparticles. SD/Ag80a emits in the near infrared (NIR) region (λ_em = 730 nm) at low temperature. This work will deepen our understanding on the atomic-level growth of silver nanoparticles and complicated three-shell self-assembly involving polyoxometalate (POM) and two different silver nanoclusters.

Photo-generated dinuclear {Eu(II)}2 active sites for selective CO2 reduction in a photosensitizing metal-organic framework

Photocatalytic reduction of CO2 is a promising approach to achieve solar-to-chemical energy conversion. However, traditional catalysts usually suffer from low efficiency, poor stability, and selectivity. Here we demonstrate that a large porous and stable metal-organic framework featuring dinuclear Eu(III)2 clusters as connecting nodes and Ru(phen)3-derived ligands as linkers is constructed to catalyze visible-light-driven CO2 reduction. Photo-excitation of the metalloligands initiates electron injection into the nodes to generate dinuclear {Eu(II)}2 active sites, which can selectively reduce CO2 to formate in a two-electron process with a remarkable rate of 321.9 μmol h-1 mmolMOF-1. The electron transfer from Ru metalloligands to Eu(III)2 catalytic centers are studied via transient absorption and theoretical calculations, shedding light on the photocatalytic mechanism. This work highlights opportunities in photo-generation of highly active lanthanide clusters stabilized in MOFs, which not only enables efficient photocatalysis but also facilitates mechanistic investigation of photo-driven charge separation processes.

Hierarchical tandem assembly of planar [3×3] building units into {3×[3×3]} oligomers: mixed-valency, electrical conductivity and magnetism

Electrical conductors are made from flat grid clusters of copper using mixed-valency and supramolecular interactions between the enveloping organic ligands.

A hierarchical tandem assembly – coordination, oligomerisation and supramolecular organization – is identified using MALDI-TOF of the solid products of the solvothermal reaction of 5,5′-pyridyl-3,3′-bi-1H-pyrazole with CuSO₄·5H₂O in CH₃OH–CH₃CN. The initial coordination leads to a [3×3] [CuI4CuII5(L)₆] (SO₄)·2CH₃OH (Cu₉) grid followed by oligomerisation to a 3×[3×3] [CuI6CuII21(L)₁₈(CN)₆(SO₄)](SO₄)₂·8CH₃CN (Cu₂₇) grid through bridging sulfate and in situ generated cyanide with time and subsequent supramolecular organization. The isolated silvery lustrous crystals, Cu₉ and Cu₂₇, are good electrical conductors, with conductivities of 3.2 × 10^–2 and 5.4 × 10^–3 S cm^–1, respectively, due to the mixed valency. Their magnetic properties are dominated by antiferromagnetic interactions. DFT and band structure calculations confirm their valence distribution and semiconducting behavior. The planarity of the large 3×[3×3] Cu₂₇ and its electro-activity renders it suitable for the development of large surface area molecular devices.

Multifunctional luminescent magnetic cryocooler in a Gd5Mn2 pyramidal complex

Magnetic cooling is a highly efficient refrigeration technique with the potential of replacing expensive and rare helium-3 in the field of ultra-low temperature cooling. However, the visualization of a cryogen at an extremely low temperature and in a strong magnetic field is challenging, but it is crucial for the precise positioning and in situ thermal probe measurements in potential practical applications. Here, the activation of a red-emissive Mn(ii) ion using 3d/4f chemistry produces a luminescent molecule cooler, [Gd5Mn2(LOMe)2(OH)4(Ac)6(MeOH)10Cl2]Cl3·2MeOH (1), with the core of an Mn(ii)-anchored heptanuclear [GdIII5MnII2] pyramid. The photoluminescence (PL) of the Mn2+ emission, with a large Stokes shift (λem ∼ 690 nm) from 4T1(4G) → 6A1(6S), shows not only a sensitive temperature sensing property but also reversible mechanoluminescence (ML). More attractively, these findings reveal a considerable magnetocaloric effect (MCE) coupled with a tunable emission window, opening up new opportunities in the multifunctional applications of PL, ML, and the MCE involving red-light sources, thermometers, and stress imaging. In particular, this provides a novel resolution to design visualized PL coolers.

Three Cd(ii) coordination polymers constructed from a series of multidentate ligands derived from cyclotriphosphazene: synthesis, structures and luminescence properties

By utilizing three ligands derived from cyclotriphosphazene, three novel cadmium-based coordination polymers have been successfully synthesized and structurally characterized, which exhibit the corresponding photo-chemical properties.

A hexadecanuclear silver alkynyl cluster based NbO framework with triple emissions from the visible to near-infrared II region

A hexadecanuclear silver alkynyl cluster based NbO framework with triple emissions from visible to near-infrared II region.

Structural, electrochemical and magnetic analyses of a new octanuclear MnIII2MnII6 cluster with linked-defect cubane topology

A new Mn^III₂Mn^II₆ coordination cluster from a hydroxymethyl-pyrazole ligand was isolated and its electrochemical and magnetic properties were studied in detail.

Ionothermal synthesis, magnetic transformation and hydration–dehydration properties of Co(ii)-based coordination polymers

A series of low-coordinated coordination polymers obtained under an ionic liquid medium exhibit interesting hydration–dehydration behaviour and magnetic transformations.