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Coinage metal nanoclusters (NCs), comprising a few to several hundred atoms, are prized for their size-dependent properties crucial in catalysis, sensing, and biomedicine. However, their practical application is often hindered by stability and reactivity challenges. Thiacalixarene, a macrocyclic ligand, shows promise in stabilizing silver, copper, and bimetallic NCs, enhancing their structural integrity and chemical stability. This investigation delves into the unique properties of thiacalix[4]arene and their role in bolstering NC stability, catalytic efficiency, and sensing capabilities. The current challenges and future prospects are critically evaluated, underscoring the transformative impact of thiacalix[4]arene in nanoscience. This review aims to broaden the utilization of atomically precise coinage metal NCs, unlocking new avenues across scientific and industrial applications., (© 2024 Wiley‐VCH GmbH.)

The established capability of anion templates in precisely manipulating the size, geometry, and function of metal clusters is well acknowledged. However, the development of a systematic methodology for orchestrating the assembly of silver clusters, particularly those encompassing multiple distinct types of anion templates, remains elusive due to the formidable synthetic challenge. In this work, we report two novel silver clusters, Ag57 and Ag72, using two and three different anion templates, respectively. Ag57 features a gyroscope-like monovalent cation with an Ag 3 triangle core sandwiched by one [SiW 9 O 34 ] 10- and a triad of Cl - anion templates. By intentionally introducing the third anion template, SO 4 2- , the structure is expanded to the unprecedented Ag72 (with 15 silver atoms epitaxially grown on top of Ag57) resembling a tumbler, inside of which two Ag 3 layers are laminated by one [SiW 9 O 34 ] 10- , seven Cl - and one SO 4 2- anion templates in parallel with respect to longitudinal orientation. It is noteworthy that Ag72 exhibits remarkable structural complexity and represents a pioneering achievement as the first silver cluster incorporating three distinct types of anion templates. In addition, Ag72 demonstrates a significant advantage over Ag57, particular in terms of applications such as luminescent thermometers and remote laser ignition. This work not only broadens the horizon for precise control of the silver cluster structures through the integration of multiple types of hetero-anions but also lays a solid foundation for potential optical applications in the future., (© 2024 Wiley-VCH GmbH.)

Immobilizing molecular catalysts on electro-conductive supports (for example, multi-walled carbon nanotubes, CNTs) represent a promising way to well-defined catalyst/support interfaces, which has shown appreciable performance for catalytic transformation. However, their full potential is far from achieved due to insufficient utilization of the intrinsic activity for each immobilized molecular catalyst, especially at loadings that should allow decent current densities. In the present work, we discover host-guest interaction between tetra-crown ether substituted cobalt phthalocyanine and metal ions, for example K + ions, not only eliminate catalyst aggregation at immobilization procedures but also reinforce catalyst/support interactions by additional electrostatic attractions under operational conditions. Through simple dip-coating procedures, a successful single molecular dispersion is achieved. Such a catalyst/electrode interface is stable and can selectively catalyze CO 2 -to-CO conversion with Faradaic efficiency over 96%. Importantly, this interface maintains an almost unchanged turnover frequency (TOF) across all loading conditions, implying a full utilization of the intrinsic activity of supported molecular catalysts. Therefore, a simultaneous achievement of high TOF and high current density (TOF of 111 s -1 at 38 mA cm -2 ) is achieved, in an aqueous H-type electrolyzer at an overpotential of 570 mV., (© 2024 Wiley-VCH GmbH.)

Transition metal carbyne complexes are of fundamental importance in carbon-carbon bond formation, alkyne metathesis, and alkyne coupling reactions. Most reported iron carbyne complexes are stabilized by incorporating heteroatoms. Here we show the synthesis of bioinspired FeMo heterobimetallic carbyne complexes by the conversion of C 2 H 2 through a diverse series of intermediates. Key reactions discovered include the reduction of a μ-η 2 :η 2 -C 2 H 2 ligand with a hydride to produce a vinyl ligand (μ-η 1 :η 2 -CH = CH 2 ), tautomerization of the vinyl ligand to a carbyne (μ-CCH 3 ), and protonation of either the vinyl or the carbyne compound to form a hydrido carbyne heterobimetallic complex. Mechanistic studies unveil the pivotal role of H 2 O as a proton shuttle, facilitating the proton transfer that converts the vinyl group to a bridging carbyne., (© 2024. The Author(s).)

Plastic pollution is worsening the living conditions on Earth, primarily due to the toxicity and stability of non-biodegradable plastics (NBPs). Photocatalytic cracking of NBPs is emerging as a promising way to cleave inert C-C bonds and abstract the carbon atoms from these wastes into valuable chemicals and fuels. However, controlling these processes is a huge challenge, ascribed to the complicated reactions of various NBPs. Herein, we summarize recent advances in the CO 2 and carbon-radical-mediated photocatalytic cracking of NBPs, with an emphasis on the pivotal intermediates. The CO 2 -mediated cracking proceeded with indiscriminate C-H/C-C bond cleavage of NBPs and tandem photoreduction of CO 2 , while carbon-radical-mediated cracking was realized by the prior activation of C-H bonds for selective C-C bond cleavage of NBPs. Catalytic generation and conversion of different intermediates greatly depend on the kinds of active species and the structure of photocatalysts under irradiation. Meanwhile, the fate of a specific intermediate is compared with small molecule activation to reveal the key problems in the cracking of NBPs. Finally, the challenges and potential directions are discussed to improve the overall efficiency in the photocatalytic cracking of NBPs., (© 2024 Wiley-VCH GmbH.)

Herein is the first example of photocatalytic cross-coupling of alkenes with aldehydes by a single catalyst without an external photosensitizer and any additives. Irradiation of the aromatic aldehyde and cobaloxime catalyst results in the formation of an acyl radical, which undergoes radical addition with alkene or indole and subsequently β-H elimination to afford alkenyl ketone. The reaction features cheap and readily available raw materials, a broad substrate scope, and mild conditions, even for late-stage derivatization of bioactive compounds.

Represented herein is the first 1,3-difunctionalization of alkenes via photocatalysis. A single cobaloxime is used to carry out two catalytic cycles in which cobaloxime is used not only as a photocatalyst to initiate the reaction but also as a metal catalyst for the β-H elimination process. Electron-deficient alkenes, electron-rich alkenes, and unactivated alkenes could be directly converted to 1,3-bisphosphorylated products, even unsymmetric 1,3-bisphosphorylated products, with only H 2 as a byproduct under extremely mild reaction conditions.

Expanding the diversity of multi-macrocyclic nanocarbons, particularly those with all-benzene scaffolds, represents intriguing yet challenging synthetic tasks. Complementary to the existing synthetic approaches, here we report an efficient and modular post-functionalization strategy that employs iridium-catalyzed C-H borylation of the highly strained meta-cycloparaphenylenes (mCPPs) and an mCPP-derived catenane. Based on the functionalized macrocyclic synthons, a number of novel all-benzene topological structures including linear and cyclic chains, polycatenane, and pretzelane have been successfully prepared and characterized, thereby showcasing the synthetic utility and potential of the post-functionalization strategy., (© 2024 Wiley-VCH GmbH.)

Sb 2 S 3 has been extensively used as light absorber for photoelectrochemical cell. However, its p-type nature may result in the formation of Schottky junction with substrates, thus hindering the collection of photogenerated holes. Herein, an ultrathin Cu x S layer is successfully engineered as the bottom junction for Sb 2 S 3 for the first time. Capitalizing on its impressive electrical properties and superior optical properties, the Cu x S layer exhibits a high work function of 4.90 eV, which causes the upward band bending of p-type Sb 2 S 3 , forming a hole-transparent structure with ohmic contact. The transparency of the ultrathin Cu x S layer enables back-illumination of the Sb 2 S 3 /Cu x S platform, facilitating the integration of intricate catalyst layers for photoelectrochemical transformation. When modified with Pt nanoparticles, the photocurrent density reaches -5.38 mA cm -2 at 0 V vs. RHE, marking a fourfold increase compared to the photocathode without Cu x S layer. When introducing a molecular hybrid TC-CoPc@carbon black, a remarkable average photocurrent density of -0.44 mA cm -2 at the overpotential of 0 V is obtained for CO 2 reduction reaction, while the photocurrent density is less than -0.03 mA cm -2 without Cu x S., (© 2024 Wiley-VCH GmbH.)

The replacement of a CC unit with an isoelectronic BN unit in aromatic systems can give rise to molecules and materials with fascinating properties. We report here the synthesis, characterization, and reactivity of a 1,4,2,3-diazadiborole species, 2, featuring an unprecedented 6π-aromatic BN-heterocyclic moiety that is isoelectronic to cyclopentadienide (Cp - ). Bearing an unsymmetrical B=B entity, 2 exhibits reactivity toward oxidants, protic reagents, electrophiles, and unsaturated substrates. This reactivity facilitates the synthesis of a variety of novel mono- and bicyclic organoboron derivatives through mechanisms including ring retention, cleavage/recombination, annulation, and expansion. These findings reveal innovative synthetic routes to BN-embedded aromatic compounds via desymmetrization, affording unique building blocks for synthetic chemistry., (© 2024 Wiley-VCH GmbH.)

We report two bridging-diazene diiron complexes [Cp*Fe(8-quinolinethiolate)] 2 (μ-N 2 H 2 ) ( 1-N 2 H 2 ) and [Cp*Fe(1,2-Cy 2 PC 6 H 4 S)] 2 (μ-N 2 H 2 ) ( 2-N 2 H 2 ), synthesized by the reaction of hydrazine with the corresponding thiolate-based iron half-sandwich complex, [Cp*Fe(8-quinolinethiolate)] 2 ( 1 ) and Cp*Fe(1,2-Cy 2 PC 6 H 4 S) ( 2 ). Crystallographic analysis reveals that the thiolate sites in 1-N 2 H 2 and 2-N 2 H 2 can engage in N-H···S hydrogen bonding with the diazene protons. 1-N 2 H 2 is thermally stable in both solid and solution states, allowing for one-electron oxidation to afford a cationic diazene radical complex [ 1-N 2 H 2 ] + at room temperature. In contrast, 2-N 2 H 2 tends to undergo N 2 H 2 /N 2 transformation, leading to the formation of a Fe(III)-H species by the loss of N 2 . In addition to stabilizing HN=NH species through the hydrogen bonding, the thiolate-based ligands also seem to facilitate proton-coupled electron transfer, thereby promoting N-H cleavage.

The functionalization of polyoxovanadate clusters is promising but of great challenge due to the versatile coordination geometry and oxidation state of vanadium. Here, two unprecedented silsesquioxane ligand-protected "fully reduced" polyoxovanadate clusters were fabricated via a facial solvothermal methodology. The initial mixture of the two polyoxovanadate clusters with different colors and morphologies (green plate V 14 and blue block V 6 ) was successfully separated as pure phases by meticulously controlling the assembly conditions. Therein, the V 14 cluster is the highest-nuclearity V-silsesquioxane cluster to date. Moreover, the transformation from a dimeric silsesquioxane ligand-protected V 14 cluster to a cyclic hexameric silsesquioxane ligand-protected V 6 cluster was also achieved, and the possible mechanism termed "ligand-condensation-involved dissociation reassembly" was proposed to explain this intricate conversion process. In addition, the robust V 6 cluster was served as a heterogeneous catalyst for the synthesis of important heterocyclic compounds, quinazolinones, starting from 2-aminobenzamide and aldehydes. The V 6 cluster exhibits high activity and selectivity to access pure quinazolinones under mild conditions, where the high selectivity was attributed to the confinement effect of the macrocyclic silsesquioxane ligand constraining the molecular freedom of the reaction species. The stability and recyclability as well as the tolerance of a wide scope of aldehyde substrates endow the V 6 cluster with a superior performance and appreciable potential in catalytic applications.

Direct site-selective and enantioselective oxyfunctionalization of C(sp 3 )-H bonds to form alcohols with a general scope, with predictable selectivities, and in preparatively useful yields represents a paradigm shift in the standard logic of synthetic organic chemistry. However, the knowledge of either enzymatic or nonenzymatic asymmetric hydroxylation of tertiary C-H bonds for enantioenriched tertiary alcohol synthesis is sorely lacking. Here, we report a practical manganese-catalyzed enantio-differentiating hydroxylation of tertiary propargylic C-H bonds in acyclic systems, producing a wide range of structurally diverse enantioenriched tertiary propargyl alcohols in high efficiency with extremely efficient chemo- and enantio-discrimination. Other features include the use of C-H substrates as the limiting reagent, noteworthy functional group compatibility, great synthetic utilities, and scalability. The findings serve as a blueprint for the development of metal-catalyzed asymmetric oxidation of challenging substrates.

Near infrared (NIR) emitter with circularly polarized phosphorescence (CPP), known as NIR CPP, has emerged as a key part in the research of cutting-edge luminescent materials. However, it remains a challenge to obtain nanoclusters with NIR CPP activity. Here, we propose an asymmetric transformation approach to efficiently synthesize two pairs of chiral silver nanoclusters (R/S-Ag29 and R/S-Ag16) using an achiral Ag 10 nanocluster as starting material in the presence of different concentration chiral inducer (R/S)-1,1'-binaphthyl-2,2'-diyl hydrogenphosphate (R/S-BNP). R/S-Ag29, formed in the low-concentration R/S-BNP, exhibits a unique kernel-shell structure consisting of a distorted Ag 13 icosahedron and an integrated cage-like organometallic shell with a C 3 symmetry, and possesses a superatomic 6-electron configuration (1S 2 |1P 4 ). By contrast, R/S-Ag16, formed in the high-concentration R/S-BNP, features a sandwich-like pentagram with Ag I -pure kernel. Profiting from the hierarchically chiral structures and superatomic kernel-dominated phosphorescence, R/S-Ag29 exhibits infrequent CPP activity in the second near-infrared (975 nm) region, being the first instance of NIR-II CPP observed among CPL-active metal nanoclusters. This study presents a new approach to reduce the difficulty of de novo synthesis for chiral silver nanomaterials, and facilitates the design of CPP-active superatomic nanoclusters in NIR region., (© 2024 Wiley-VCH GmbH.)

The design of smart stimuli-responsive photoluminescent materials capable of multi-level encryption and complex information storage is highly sought after in the current information era. Here, a novel adamantyl-capped CsPbBr 3 (AD-CsPbBr 3 ) perovskite NCs, along with its supramolecular host-guest assembly partner a modified β-CD (mCD), mCD@AD-CsPbBr 3 , are designed and prepared. By dispersing these two materials in different solvents, namely, AD-CsPbBr 3 in toluene, mCD@AD-CsPbBr 3 in toluene, and mCD@AD-CsPbBr 3 in methanol, the three solutions exhibit diverse photoluminescence (PL) turn-on/off or PL discoloration response upon supramolecular stimulus. Based on these responses, a proof-of-principle programmable Multi-Level Photoluminescence Encoding System (MPLES) is established. Three types of four-level and three types of three-level information encoding are achieved by the system. A layer-by-layer four-level information encryption and decryption as well as a two-level encrypted 3D code are successfully achieved., (© 2024 Wiley‐VCH GmbH.)

Despite the discovery of a series of fullerenes and a handful of noncarbon clusters with the typical topology of I h -C 60 , the smallest fullerene with a large degree of curvature, C 20 , and its other-element counterparts are difficult to isolate experimentally. In coinage metal nanoclusters (NCs), the first all-gold fullerene, Au 32 , was discovered after a long-lasting pursuit, but the isolation of similar silvery fullerene structures is still challenging. Herein, we report a flying saucer-shaped 102-nuclei silver NC ( Ag102 ) with a silvery fullerene kernel of Ag 32 , which is embraced by a robust cyclic anionic passivation layer of (KPO 4 ) 10 . This Ag 32 kernel can be viewed as a non-centered icosahedron Ag 12 encaged into a dodecahedron Ag 20 , forming the silvery fullerene of Ag 12 @Ag 20 . The anionic layer (KPO 4 ) 10 is located at the interlayer between the Ag 32 kernel and Ag 70 shell, passivating the Ag 32 silvery fullerene and templating the Ag 70 shell. The t BuPhS - and CF 3 COO - ligands on the silver shell show a regioselective arrangement with the 60 t BuPhS - ligands as expanders covering the upper and lower of the flying saucer and 10 CF 3 COO - as terminators neatly encircling the edges of the structure. In addition, Ag102 shows excellent photothermal conversion efficiency ( η ) from the visible to near-infrared region ( η  = 67.1% ± 0.9% at 450 nm, 60.9% ± 0.9% at 660 nm and 50.2% ± 0.5% at 808 nm), rendering it a promising material for photothermal converters and potential application in remote laser ignition. This work not only captures silver kernels with the topology of the smallest fullerene C 20 , but also provides a pathway for incorporating alkali metal (M) into coinage metal NCs via M-oxoanions., (© The Author(s) 2024. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd.)

Herein, two atomically precise silver nanoclusters, Ag54 and Ag33, directed by inner anion templates (CrO 4 2- and/or Cl - ), are initially isolated as a mixed phase from identical reactants across a wide temperature range (20-80 °C). Interestingly, fine-tuning the reaction temperature can realize pure phase synthesis of the two nanoclusters; that is, a metastable Ag54 is kinetically formed at a low temperature (20 °C), whereas such a system is steered towards a thermodynamically stable Ag33 at a relatively high temperature (80 °C). Electrospray ionization mass spectrometry illustrates that the stability of Ag33 is superior to that of Ag54, which is further supported by density functional theory calculations. Importantly, the difference in structural stability can influence the pathway of 1,4-bis(pyrid-4-yl)benzene induced transformation reaction starting from Ag54 and Ag33. The former undergoes a dramatic breakage-reorganization process to form an Ag 31 dimer (Ag31), while the same product can be also achieved from the latter following a noninvasive ligand exchange process. Both the Ag54 and Ag33 have the potential for further remote laser ignition applications. This work not only demonstrates how temperature controls the isolation of a specific phase, but also sheds light on the structural transformation pathway of nanoclusters with different stability., (© 2024 Wiley-VCH GmbH.)

Mother nature accomplishes efficient ammonia synthesis via cascade N 2 oxidation by lightning strikes followed with enzyme-catalyzed nitrogen oxyanion (NO x - , x = 2,3) reduction. The protein environment of enzymatic centers for NO x - -to-NH 4 + process greatly inspires the design of glutathione-capped (GSH) quantum dots (QDs) for ammonia synthesis under visible light (440 nm) in tandem with plasma-enabled N 2 oxidation. Mechanistic studies reveal that GSH induces positive shift of surface charge to strengthen the interaction between NO x - and QDs. Upon visible light irradiation of QDs, the balanced and rapid hole and electron transfer furnish GS·radicals for 2e - /2H + alcohol oxidation and H·for 8e - /10H + NO 3 - -to-NH 4 + reduction simultaneously. For the first time, mmol-scale ammonia synthesis is realized with apparent quantum yields of 5.45% ± 0.64%, and gram-scale synthesis of value-added acetophenone and NH 4 Cl proceeds with 1:4 stoichiometry and stability, demonstrating promising multielectron and multiproton ammonia synthesis efficiency and sustainability with nature-inspired artificial photocatalysts., (© 2024 Wiley‐VCH GmbH.)

Represented herein is a simple thiol identified as an effective precursor to photochemically form a carbocation. Thanks to the thiyl radical rapid transformation to disulfide, which serves not only to stabilize the generated thiyl radical but also to allow the second electron transfer to form a carbocation. The resulting carbocations, including primary benzylic, secondary, and tertiary carbocations, can smoothly couple with nitrogen, oxygen, and carbon nucleophilic coupling partners as well as complex drug molecules, accompanied by elemental sulfur formation in air.

The highly strained, phenylene-derived organic cages are typically regarded as very rigid entities, yet their deformation potential and supramolecular properties remain underexplored. Herein, we report a pliable conjugated phenylene nanocage by synergistically merging rigid and flexible building blocks. The anisotropic cage molecule contains branched phenylene chains capped by a calix[6]arene moiety, the delicate conformational changes of which endow the cage with a remarkably deformable cavity. When complexing with fullerene guests, the cage showcases excellent guest-adaptivity, with its cavity volume capable of swelling by as much as 85 %., (© 2024 Wiley-VCH GmbH.)

"Improbable" rotaxanes consisting of interlocked conjugated components represent non-trivial synthetic targets, not to mention those with all-benzene scaffolds. Herein, a modular synthetic strategy has been established using an isolable azo-linked pre-rotaxane as the core module, in which the azo group functions as a tracelessly removable template to direct mechanical bond formations. Through versatile connections of the pre-rotaxane and other customizable modules, [2]- and [3]rotaxanes derived from all-benzene scaffolds have been accomplished, demonstrating the utility and potential of the synthetic design for all-benzene interlocked supramolecules., (© 2024 Wiley‐VCH GmbH.)

Atomically precise superatomic copper nanoclusters (Cu NCs) have been the subject of immense interest for their intriguing structures and diverse properties; nonetheless, the variable oxidation state of copper ions and complex solvation effects in wet synthesis systems pose significant challenges for comprehending their synthesis and crystallization mechanism. Herein, we present a solvent-mediated approach for the synthesis of two Cu NCs, namely, superatomic Cu26 and pure-Cu(I) Cu16 . They initially formed as a hetero-phase and then separated as a homo-phase via modulating binary solvent composition. In situ UV/vis absorption and electrospray ionization mass spectra revealed that the solvent-mediated assembly was determined to be the underlying mechanism of hetero/homo-phase crystallization. Cu26 is a 2-electron superatom with a kernel-shell structure that includes a [Cu 20 Se 12 ] 4- shell and [Cu 6 ] 4+ kernel, containing two 1 S jellium electrons. Conversely, Cu16 is a pure-Cu(I) Cu/Se nanocluster that features a [Cu 16 Se 6 ] 4+ core protected by extra dimercaptomaleonitrile ligands. Remarkably, Cu26 exhibits unique near-infrared phosphorescence (NIR PH) at 933 nm due to the presence of a superatomic kernel-related charge transfer state ( 3 MM (Cu) CT). Overall, this work not only showcases the hetero/homo-phase crystallization of Cu NCs driven by a solvent-mediated assembly mechanism but also enables the rare occurrence of NIR PH within the 2-electron copper superatom family.

Heteronuclear Fe(μ-H)Zn hydride Cp*Fe(1,2-Cy 2 PC 6 H 4 )HZnEt ( 3 ) undergoes reversible intramolecular C aryl -H reductive elimination through coupling of the cyclometalated phosphinoaryl ligand and the hydride, giving rise to a formal Fe(0)-Zn(II) species. Addition of CO intercepts this equilibrium, affording Cp*(Cy 2 PPh)(CO)Fe-ZnEt that features a dative Fe-Zn bond. Significantly, this system achieves bimetallic H 2 addition, as demonstrated by the transformation of the monohydride Fe(μ-H)Zn to a deuterated dihydride Fe-(μ-D) 2 -Zn upon reaction with D 2 .

Photoredox catalytic processes offer the potential for precise chemical reactions using light and materials. The central determinant is identified as interfacial charge transfer, which simultaneously engenders distinctive behavior in the overall reaction. An in-depth elucidation of the main mechanism and highlighting of the complexity of interfacial charge transfer can occur through both diffusive and direct transfer models, revealing its potential for sophisticated design in complex transformations. The fundamental photophysics uncover these comprehensive applications and offer a clue for future development. This research contributes to the growing body of knowledge on interfacial charge transfer in photoredox catalysis and sets the stage for further exploration of this fascinating area of research., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Titanium-oxide clusters (TOCs) are well-defined molecular models for TiO 2 materials and provide the opportunity to study the structure-activity relationships of TiO 2 . Here, we report a new Pb-doped TOC, Ti12Pb2, which resembles a two-layer decker of the {TiTi 6 } structural units of rutile TiO 2 with two Ti 4+ ions replaced by two Pb 2+ ions. Its electronic structure, photoresponse, and photocatalytic performances were investigated and compared with those of the Ti14 cluster, which is isostructural to Ti12Pb2. Our results indicate that Pb 2+ does not affect the electronic structure, but it greatly enhances the photocatalytic activity by improving the charge-separation and interfacial charge-transfer properties of the TOC. The successful synthesis of Ti12Pb2 highlights the roles of closed-shell heterometal ions in the construction of new TOCs. Our mechanism may be an inspiration for understanding the structure-activity relationships of closed-shell heterometal-doped TiO 2 .

Inspired by the drawstring structure in daily life, here we report the development of a drawstring-mimetic supramolecular complex at the molecular scale. This complex consists of a rigid figure-of-eight macrocyclic host molecule and a flexible linear guest molecule which could interact through three-point non-covalent binding to form a highly selective and efficient host-guest assembly. The complex not only resembles the drawstring structure, but also mimics the properties of a drawstring with regard to deformations under external forces. The supramolecular drawstring can be utilized as an interlocked crosslinker for poly(methyl acrylate), and the corresponding polymer samples exhibit comprehensive enhancement of macroscopic mechanical performance including stiffness, strength, and toughness., (© 2024 Wiley-VCH GmbH.)

Arylation of gold holds paramount importance in the domain of organometallic chemistry; however, the exploration of arylgold nanoclusters remains in its infancy primarily due to the synthetic challenge. Here, we present a facile and effective arylation strategy to directly synthesize two arylgold nanoclusters ( Au44a and Au44b ), by using tetraarylborates, capable of transferring aryl fragments to metal centers. X-ray crystallography reveals that both Au 44 nanoclusters contain an Au 44 kernel co-protected by six aryl groups, two tetrahydrothiophene, and 16 alkynyl-ether ligands, the latter is generated in situ through Williamson ether reaction during the assembly processes. Notably, Au 44 nanoclusters exhibit near-infrared (NIR) phosphorescence (λ max = 958 nm) and microsecond radiative relaxation at ambient condition, which is a thermal-controlled single/dual-channel phosphorescent emission revealed by temperature-dependent NIR, time-resolved emission, and femtosecond/nanosecond transition absorption spectra. This work represents a breakthrough in using aryl as protective ligands for the construction of gold nanoclusters, which is poised to have a transformative impact on organometallic nanoclusters.

Diels-Alder cycloaddition of anthracene with olefin is achieved in a homogeneous solution via energy transfer under visible light. A series of substrates including electroneutral styrene derivatives can be successfully converted into the corresponding cycloadducts in a head-to-head orientation with high to excellent yields. The high ortho-regioselectivity, mild condition, and broad substrate scope enable promising advances in organic transformation.

Photocatalytic redox reactions are important for synthesizing fine chemicals from olefins, but the limited lifetime of radical cation intermediates severely restricts semiconductor photocatalysis efficiency. Here, we report that Ag 3 PO 4 can efficiently catalyze intramolecular and intermolecular [2 + 2] and Diels-Alder cycloadditions under visible-light irradiation. The approach is additive-free, catalyst-recyclable. Mechanistic studies indicate that visible-light irradiation on Ag 3 PO 4 generates holes with high oxidation power, which oxidize aromatic alkene adsorbates into radical cations. In photoreduced Ag 3 PO 4 , the conduction band electron (e CB - ) has low reduction power due to the delocalization among the Ag + -lattices, while the particle surfaces have a strong electrostatic interaction with the radical cations, which considerably stabilize the radical cations against recombination with e CB - . The radical cation on the particle's surfaces has a lifetime of more than 2 ms, 75 times longer than homogeneous systems. Our findings highlight the effectiveness of inorganic semiconductors for challenging radical cation-mediated synthesis driven by sunlight., (© 2024. The Author(s).)

A cryptand-like Ti-coordination compound, namely Ti12Cs, comprising two Ti 6 -salicylate cages and hosting two Cs + ions, was synthesized by the solvothermal method. It exhibits strong visible-light absorption with an absorption band edge of 652 nm, attributed to the electron transition from salicylate ligands to Ti ions. Electrochemical impedance, visible-light transient photocurrent response, and photoluminescence spectra confirm that Ti12Cs has excellent visible-light response and charge-separation properties. Ti12Cs can be used as a heterogeneous and recyclable photocatalyst for CO 2 /epoxide cycloaddition, with high utilization efficiency of visible-light under mild conditions. The mechanism investigation points to a synergistic effect of photocatalysis and Lewis acid catalysis.

Exploration of molybdenum complexes as homogeneous hydrogenation catalysts has garnered significant attention, but hydrogenation of unactivated olefins under mild conditions are scarce. Here, we report the synthesis of a molybdenum complex, [Cp*Mo(Ph 2 PC 6 H 4 S-CH = CH 2 )(Py)] + (2), which exhibits intriguing reactivity toward C 2 H 2 and H 2 under ambient pressure. This vinylthioether complex showcases efficient catalytic activity in the hydrogenation of various aromatic and aliphatic alkenes, demonstrating a broad substrate scope without the need for any additives. The catalytic pathway involves an uncommon oxidative addition of H 2 to the cationic Mo(II) center, resulting in a Mo(IV) dihydride intermediate. Moreover, complex 2 also shows catalytic activity toward C 2 H 2 , leading to the production of polyacetylene and the extension of the vinylthioether ligand into a pendant triene chain., (© 2024. The Author(s).)

Polyoxometalates (POMs) represent crucial intermediates in the formation of insoluble metal oxides from soluble metal ions, however, the rapid hydrolysis-condensation kinetics of Mo VI or W VI makes the direct characterization of coexisted molecular species in a given medium extremely difficult. Silver nanoclusters have shown versatile capacity to encapsulate diverse POMs, which provides an alternative scene to appreciate landscape of POMs in atomic precision. Here, we report a thiacalix[4]arene protected silver nanocluster (Ag72b) that simultaneously encapsulates three kinds of molybdates (MoO 4 2- , Mo 6 O 22 8- and Mo 7 O 25 8- ) in situ transformed from classic Lindqvist Mo 6 O 19 2- , providing more deep understanding on the structural diversity and condensation growth route of POMs in solution. Ag72b is the first silver nanocluster trapping so many kinds of molybdates, which in turn exert collective template effect to aggregate silver atoms into a nanocluster. The post-reaction of Ag72b with AgOAc or PhCOOAg produces a discrete Ag 24 nanocluster (Ag24a) or an Ag 28 nanocluster based 1D chain structure (Ag28a), respectively. Moreover, the post-synthesized Ag28a can be utilized as potential ignition material for further application. This work not only provides an important model for unlocking dynamic features of POMs at atom-precise level but also pioneers a promising approach to synthesize silver nanoclusters from known to unknown., (© 2023 Wiley-VCH GmbH.)

As an interdisciplinary product, water-soluble gold nanoclusters (AuNCs) stabilized by ligands containing carboxyl (-COOH) group have garnered significant attention from synthetic chemists and biologists due to their immense potential for biomedical applications. However, revealing the crystallographic structures of -COOH-functionalized AuNCs remains a bottleneck. Herein, we successfully applied the salting-out method to obtain a series of high-quality single crystals of -COOH-functionalized Au 25 nanoclusters and revealed their crystallographic structures. Particularly, K 3 Au 25 (2-Hmna) 9 (mna) 6 ] - (Au25a) protected by 2-mercaptonicotinic acid features an unprecedented tetrameric Au 4 (SR S ) 3 (SR S,N ) 2 staple motifs surrounding the icosahedral Au 13 kernel, breaking the traditional perception on the structure of Au 25 (SR) 18 . Au25a exhibits a distinct near-infrared emission at 970 nm with long lifetime of 8690 ns, which have been studied by transient absorption spectroscopy and time-dependent density functional theory. This work compensates for the research gap in the experimental structure of -COOH-functionalized AuNCs and opens up a new avenue to explore their structure-property correlations., Competing Interests: Conflict of interest The authors declare that they have no conflict of interest., (Copyright © 2023 Science China Press. Published by Elsevier B.V. and Science China Press. Published by Elsevier B.V. All rights reserved.)

The subvalent silver kernel represents the nascent state of silver cluster formation, yet the growth mechanism has long been elusive. Herein, two silver nanoclusters ( Ag30 and Ag34 ) coprotected by TC4A 4- (H 4 TC4A = p - tert -butylthiacalix[4]arene) and TBPMT - (TBPMTH = 4- tert -butylbenzenemethanethiol) containing 6e and 4e silver kernels are synthesized and characterized. The trimer of the 2e superatom Ag 14 kernel in Ag30 is built from a central Ag 6 octahedron sandwiched by two orthogonally oriented Ag 5 trigonal bipyramids through sharing vertexes, whereas a double-octahedral Ag 10 kernel in Ag34 is a dimer of 2e superatoms. They manifest disparate polyhedron fusion growth patterns at the beginning of the silver cluster formation. Their excellent solution stabilities are contributed by the multisite and multidentate coordination fashion of TC4A 4- and the special valence electron structures. This work demonstrates the precise control of silver kernel growth by the solvent strategy and lays a foundation for silver nanocluster application in photothermal conversion.

Two Mo-Ti-mixed oxide clusters, Ti 6 Mo 4 and Ti 4 Mo 4 , which contain the {Mo 2 V } unit commonly observed in many polyoxomolybdates, were successfully synthesized. The introduction of a {Mo 2 V } dopant into a titanium-oxide cluster (TOC) results in a red shift of the absorption edge, hence leading to a substantial enhancement of visible-light absorption. The band gap electron transition mainly involves the ligand-to-metal charge transfer (LMCT, benzoate-to-Mo) and Mo V d-d transition. Both clusters show favorable visible-light responsiveness and charge-separation efficiency. Both serve as heterogeneous photocatalysts and exhibit excellent catalytic activity in CO 2 /epoxide cycloadditions under very mild conditions. The mechanism study suggests that the catalytically active sites are mainly Mo V , and the photogenerated electrons and holes are both involved. Ti 6 Mo 4 exhibits better photocatalytic activity than Ti 4 Mo 4 , demonstrating the crucial role of the titanium-oxide core, which corresponds to improved light absorption and charge-separation efficiency. Our findings highlight the potential of the {Mo 2 V } unit in constructing Mo-Ti-mixed oxide clusters with interesting topologies and excellent solar-light-harvesting activity.

Exploring bidirectional CO 2 /HCO 2 - catalysis holds significant potential in constructing integrated (photo)electrochemical formate fuel cells for energy storage and applications. Herein, we report selective CO 2 /HCO 2 - electrochemical interconversion by exploiting the flexible coordination modes and rich redox properties of a versatile iron-thiolate platform, Cp*Fe(II)L (L = 1,2-Ph 2 PC 6 H 4 S - ). Upon oxidation, this iron complex undergoes formate binding to generate a diferric formate complex, [(L - ) 2 Fe(III)(μ-HCO 2 )Fe(III)] + , which exhibits remarkable electrocatalytic performance for the HCO 2 - -to-CO 2 transformation with a maximum turnover frequency (TOF max ) ∼10 3 s -1 and a Faraday efficiency (FE) ∼92(±4)%. Conversely, this iron system also allows for reduction at -1.85 V (vs Fc +/0 ) and exhibits an impressive FE ∼93 (±3)% for the CO 2 -to-HCO 2 - conversion. Mechanism studies revealed that the HCO 2 - -to-CO 2 electrocatalysis passes through dicationic [(L 2 ) -• Fe(III)(μ-HCO 2 )Fe(III)] 2+ generated by unconventional oxidation of the diferric formate species taking place at ligand L, while the CO 2 -to-HCO 2 - reduction involves a critical intermediate of [Fe(II)-H] - that was independently synthesized and structurally characterized.

Catalytic asymmetric preparation of chiral 3-monosubstituted oxindoles represents a significant challenge in synthetic chemistry due to the ease of racemization of the tertiary stereocenter through enolization. Here, we describe a general titanium-catalyzed chemo- and enantioselective indole oxidation to produce a diverse set of chiral 3-monosubstituted oxindoles with up to 96% yield, 99% ee, and with a substrate/catalyst ratio of 10,000 by using the combination of a simple titanium(salan) catalyst with green and atom-economic terminal oxidant H 2 O 2 . The mild approach tolerates a broad range of functional groups, enabling late-stage asymmetric diversification of a series of commercial drugs and natural products together with late-stage asymmetric construction of a wide set of enzyme antagonists, all of which are difficult to achieve through existing methods.

Silver (Ag) undergoes a complex and dynamic Ag + /Ag 0 cycle under environmental conditions. The Ag + → Ag nanoparticles (AgNPs) transformation due to the combined actions of sunlight, O 2 , and dissolved organic matter has been a well-known environmental phenomenon. In this study, we indicate that this process may be accompanied by a pronounced accumulation of Ag(0) single atoms (Ag-SAs) on the minerals' surfaces. According to spherical aberration-corrected scanning transmission electron microscopy and high-energy-resolution X-ray adsorption fine structure analyses, humic acid (HA) and phenol (PhOH) can induce Ag-SAs accumulation, whereas oxalic acid causes only AgNPs deposition. Ag-SAs account for more than 20 wt % of total Ag(0) on the γ-Al 2 O 3 surfaces during HA- and PhOH-mediated photolysis processes. HA also causes Ag-SAs to accumulate on two other prevalent soil minerals, SiO 2 and Fe 2 O 3 , and the fractions of Ag-SAs are about 15 wt %. Our mechanism studies suggest that a phenolic molecule acts as a reducing agent of Ag + and a stabilizer of Ag-SAs, protecting Ag-SAs against autocatalytic nucleation.

We present the synthesis, structural characterization, and reactivity of alkylideneborane 2 , supported by π-donating N-heterocyclic imino and σ-donating N-heterocyclic carbene (NHC) ligands. The incorporation of these ligands effectively weakens the B═C bond strength, leading to enhanced reactivity. Consequently, selective cleavage of the B═C bond can be achieved using pyridine- N -oxide, sulfur, and selenium, resulting in the formation of 1,3-dioxa-2,4-diboretane 3 , thioxoborane 4 , and selenoborane 5 , respectively. Furthermore, intriguing B═C bond insertions with CO 2 and CS 2 are observed, affording zwitterionic borenium/fluorenide 6 and dithiaboretane 7 . The former species 6 is readily converted to transient oxoborane and imidazolium enolate, showcasing the bora-Wittig reaction of alkylideneborane. This investigation highlights the potential of alkylideneborane as a versatile building block for synthesizing novel organoboron compounds through unconventional transformations.

Tautomerization of C 2 H 2 at half-sandwich compound Cp*Fe(1,2-Cy 2 PC 6 H 4 S) exclusively produces an iron ethenylidene, Cp*Fe(=C=CH 2 )(1,2-Cy 2 PC 6 H 4 S) ( 2 ). Protonation of the ethenylidene causes nucleophilic attack of the C α by sulfur, affording a sulfur-tethered carbene complex, [Cp*Fe=C(CH 3 )SC 6 H 4 PCy 2 ] + ( 3 + ). This Fischer-type carbene complex undergoes an unusual isomerization by migrating a hydrogen atom from the β-CH 3 group to the α-C, leading to the formation of an olefin complex [Cp*Fe(η 4 -CH=CH 2 SC 6 H 4 PCy 2 ] + ( 4 + ). Compound 2 also displays diverse redox reactivities. It transforms to a neutral acetylide ferric complex ( 5 ) when reacting with free radical scavengers and to a cationic vinyl complex [Cp*Fe(η 3 -C(=CH 2 )SC 6 H 4 PCy 2 ] + ( 6 + ) upon 1e - oxidation. The interconversion between the vinyl and acetylide complexes can be realized through protonation/deprotonation reactions.

A novel smart fluorescent polymer polyethyleneimine-grafted pyrene (PGP) is developed by incorporating four stimuli-triggers at molecular level. The triggers are amphiphilicity, supramolecular host-guest sites, pyrene fluorescence indicator, and reversible chelation sites. PGP exhibits smart deformation and shape-dependent fluorescence in response to external stimuli. It can deform into three typical shapes with a characteristic fluorescence color, namely, spherical core-shell micelles of cyan-green fluorescence, standard rectangular nanosheets of yellow fluorescence, and irregular branches of deep-blue fluorescence. A quasi-reversible deformation between the first two shapes can be dynamically manipulated. Moreover, driven by reversible coordination and the resulting intramolecular photoinduced electron transfer, PGP can be used as an aqueous fluorescence ink with erasable and recoverable properties. The fluorescent patterns printed by PGP ink on paper can be rapidly erased and recovered by simple spraying a sequence of Cu 2+ and ethylene diamine tetraacetic acid aqueous solutions. This erase/recover transformation can be repeated multiple times on the same paper. The multiple stimulus responsiveness of PGP makes it have potential applications in nanorobots, sensing, information encryption, and anticounterfeiting., (© 2023 Wiley-VCH GmbH.)

The assembly of cluster-based π-stacked porous supramolecular frameworks presents daunting challenges, including the design of suitable cluster building units, control of the sufficient C-H···π interactions, trade-off between structural dynamics and stability as well as understanding the resulting collective properties. Herein, we report a cluster-based C-H···π interaction-stacked porous supramolecular framework, namely, Cu12a-π, consisting of Cu 12 nanocluster as a 6-connected node, which is further propagated to a dynamic porous supramolecular frameworks via dense intralayer C-H···π interactions, yielding permanent porosity. In addition, Cu12a-π can be transformed into cluster-based nonporous adaptive crystals (Cu12b-NACs) via ligand-exchange following a dissociation-reassembly mechanism. Moreover, Cu12a-π can efficiently remove 97.2% of iodine from saturated iodine aqueous solutions with a high uptake capacity of 2.96 g·g -1 . These prospective results positioned at cluster-based porous supramolecular framework and enlighten follow-up researchers to design and synthesize such materials with better performance., (© 2023. Springer Nature Limited.)

Chiral hydroxylamines are increasingly common structural elements in pharmaceuticals and agrochemicals, but their asymmetric synthesis remains challenging. Although enantioselective oxidation is the most straightforward method to prepare chiral oxides with a higher oxidation state, asymmetric and even nonasymmetric amine oxidation to hydroxylamines has been poorly addressed. We report a titanium-catalyzed asymmetric oxidation of racemic amines providing a broad range of structurally diverse chiral hydroxylamines with excellent chemo- and enantioselectivity. Notably, hydroxylamines bearing diverse substituent patterns on the stereocenters, including α,α-ester-alkyl, α,α-amide-alkyl, α,α-aryl-alkyl, α,α-alkynyl-alkyl, and α,α-dialkyl, are well tolerated with good functional group compatibility. Catalyst turnover numbers up to 5000 and selectivity factors up to 278 are observed. This finding offers a democratized platform to chiral hydroxylamines as design elements for drug discovery and provides insights into metal-catalyzed asymmetric oxidation of challenging substrates.

Due to the easy accessibility, chemical stability, and structural tunability of the macrocyclic skeleton, cobalt phthalocyanines immobilized on carbon supports offer an ideal research model for advanced electrochemical carbon dioxide reduction reaction (eCO 2 RR). In this work, an amphiphilic cobalt phthalocyanine (TC-CoPc) is loaded on multiwalled carbon nanotubes to reveal the roles of hydrophilic/hydrophobic properties on catalytic efficiency. Surprisingly, the resultant electrode exhibits a CO Faradaic efficiency (FE CO ) of 95% for CO 2 RR with turnover frequency (TOF) of 29.4 s -1 at an overpotential of 0.585 V over long-term electrolysis in a H-type cell. In the membrane electrode assembly (MEA) device, the boosted transport of water vapor to the catalyst layer slows down carbonate crystallization and enhances the stability of the electrode, with FE CO value of >99% over 27 h at -0.25 A, representing the best selectivity and stability among reported molecular catalysts in MEA devices. The amphiphilic cobalt phthalocyanine, which decreases interfacial charge and mass transfer resistance and maintains effective contact between active sites and the electrolyte, highlights the exceptional CO 2 conversion from a molecular perspective., (© 2023 Wiley-VCH GmbH.)

A nickel-based ultrathin catalyst film is assembled in situ from a solution of Ni(OAc) 2 and a Schiff-base ligand L. The resulting ultrathin catalyst film shows a low overpotential of 330 mV, a steady current of 7 mA cm -2 for water oxidation over 10 h.

Structural transformation of metal nanoclusters (NCs) is of great ongoing interest regarding their synthesis, stability, and reactivity. Although sporadic examples of cluster transformations have been reported, neither the underlying transformation mechanism nor the intermediates are unambiguous. Herein, we have synthesized a flexible 54-nuclei silver cluster ( Ag54 ) by combining soft ( t BuC≡C - ) and hard ( n PrCOO - ) ligands. The existence of weakly coordinated n PrCOO - enhances the reactivity of Ag54 , thus facilitating the dicarboxylic acid to induce structural transformation. X-ray structural analyses reveal that Ag54 transforms to Ag 28 cluster-based 2D networks ( Ag28a and Ag28b ) induced by H 2 suc (succinic acid) and H 2 glu (glutaric acid), whereas with H 2 pda (2,2'-(1,2-phenylene)diacetic acid), a discrete Ag 28 cluster ( Ag28c ) is isolated. The key intermediate Ag17 that emerges during the self-dissociation of Ag54 was isolated by using cryogenic recrystallization and characterized by X-ray crystallography. The "tandem transformation" mechanism for the structure evolution from Ag54 to Ag28a is established by time-dependent electrospray ionization mass spectrometry (ESI-MS) and UV-vis spectroscopy. In addition, the catalytic activity in the 4-nitrophenol reduction follows the sequence Ag28c > Ag28b > Ag28a > Ag54 due to more bare silver sites on the surface of the Ag 28 cluster unit. Our findings not only open new avenues to the synthesis of silver NCs but also shed light on a better understanding of the structural transformation mechanism from one cluster to another or cluster-based metal-organic networks induced by dicarboxylates.

High-valent iron-oxo species are appealing for conducting O-O bond formation for water oxidation reactions. However, their high reactivity poses a great challenge to the dissection of their chemical transformations. Herein, we introduce an electron-rich and oxidation-resistant ligand, 2-[(2,2'-bipyridin)-6-yl]propan-2-ol to stabilize such fleeting intermediates. Advanced spectroscopies and electrochemical studies demonstrate a high-valent Fe V (O) species formation in water. Combining kinetic and oxygen isotope labelling experiments and organic reactions indicates that the Fe V (O) species is responsible for O-O bond formation via water nucleophilic attack under the real catalytic water oxidation conditions., (© 2023 Wiley-VCH GmbH.)

This report unveils an advancement in the formation of a Lewis superacid (LSA) and an organic superbase by the geometrical deformation of an organoboron species towards a T-shaped geometry. The boron dication [2] 2+ supported by an amido diphosphine pincer ligand features both a large fluoride ion affinity (FIA>SbF 5 ) and hydride ion affinity (HIA>B(C 6 F 5 ) 3 ), which qualifies it as both a hard and soft LSA. The unusual Lewis acidic properties of [2] 2+ are further showcased by its ability to abstract hydride and fluoride from Et 3 SiH and AgSbF 6 respectively, and effectively catalyze the hydrodefluorination, defluorination/arylation, as well as reduction of carbonyl compounds. One and two-electron reduction of [2] 2+ affords stable boron radical cation [2]⋅ + and borylene 2, respectively. The former species has an extremely high spin density of 0.798e at the boron atom, whereas the latter compound has been demonstrated to be a strong organic base (calcd. pK BH + (MeCN)=47.4) by both theoretical and experimental assessment. Overall, these results demonstrate the strong ability of geometric constraining to empower the central boron atom., (© 2023 Wiley-VCH GmbH.)

Metalloligands provide a potent strategy for manipulating the surface metal arrangements of metal nanoclusters, but their synthesis and subsequent installation onto metal nanoclusters remains a significant challenge. Herein, two atomically precise silver nanoclusters {Ag 14 [(TC4A) 6 (V 9 O 16 )](CyS) 3 } (Ag14) and {Ag 43 S[(TC4A) 2 (V 4 O 9 )] 3 (CyS) 9 (PhCOO) 3 Cl 3 (SO 4 ) 4 (DMF) 3 ·6DMF} (Ag43) are synthesized by controlling reaction temperature (H 4 TC4A = p-tert-butylthiacalix[4]arene). Interestingly, the 3D scaffold-like [(TC4A) 6 (V 9 O 16 )] 11- metalloligand in Ag14 and 1D arcuate [(TC4A) 2 (V 4 O 9 )] 6 - metalloligand in Ag43 exhibit a dual role that is the internal polyoxovanadates as anion template and the surface TC4A 4- as the passivating agent. Furthermore, the thermal-induced structure transformation between Ag14 and Ag43 is achieved based on the temperature-dependent assembly process. Ag14 shows superior photothermal conversion performance than Ag43 in solid state indicating its potential for remote laser ignition. Here, we show the potential of two thiacalix[4]arene modified polyoxovanadates metalloligands in the assembly of metal nanoclusters and provide a cornerstone for the remote laser ignition applications of silver nanoclusters., (© 2023. Springer Nature Limited.)

Exploration of the metallomimetic chemistry of main group elements is of the utmost importance from the perspective of both fundamental research and potential applications. Here, we report the synthesis, bonding analysis, and reactivities of an isolable diiminoborane, Mes*B≡N─N≡BMes* (Mes* = 2,4,6-tri- tert -butylphenyl) ( 1 ), a BN analogue of butadiyne. This species is characterized by a conjugated B≡N─N≡B moiety, a structural feature that enables the controlled release of N 2 when it is exposed to organic nitriles. Furthermore, the N 2 unit in 1 could be reduced to an ammonium salt via cleavage of the BN triple bond. Our work shows a rare example of an unsaturated BN system, serving as a platform for both the release and reduction of N 2 . This discovery opens new pathways and holds substantial influence on the future design of functional main group N 2 species.