Spotlighting main group elements in polynuclear complexes

François Gabbaï, Cameron Jones and Connie Lu introduce the Chemical Science themed collection on the topic of main group elements in polynuclear complexes.

Efforts towards the incorporation of main group elements in polynuclear motifs or in the coordination sphere of transition metals have been a prevalent theme of coordination chemistry, and one that has delivered notable advances in the area of structure and bonding. In the past decade, this field has witnessed an increased emphasis on the influence of the main group moiety over the reactivity or physical properties of the resulting constructs. Through a collection of both invited and selected articles, this themed issue puts the spotlight on this developing field, while at the same time illustrating far-reaching applications in the areas of small molecule activation, catalysis and molecular magnetism.A number of papers in this themed issue highlight the significant recent progress that has been made in the development of homo- and heterometallic systems incorporating s- and p-block elements, both in low oxidation states (often element–element bonded) and normal oxidation states. These have found particular use as low toxicity, earth abundant alternatives to late transition metal complexes in stoichiometric and catalytic transformations of small molecule substrates to value added products. This theme is introduced in primary articles dealing with the reactivity of magnesium-based systems. As shown by Jones, Maron and co-workers, magnesium(i) dimers (LMg–MgL, L = β-diketiminate) are activated by coordination of simple Lewis bases, and are subsequently able to reductively couple carbon monoxide to form the deltate and transient ethenediolate dianions (C_nO_n²⁻, n = 3 and 2, respectively; DOI: 10.1039/D0SC00836B). In another contribution, β-diketiminato-stabilised magnesium diboronates are shown by Hill, McMullin and co-workers to act as rare “masked” sources of nucleophilic boryl anions for the synthetic transformation of imines (DOI: 10.1039/C9SC02087J). These two papers integrate with the content of two reviews that highlight the unique structures and reactivity of polynuclear complexes containing low valent group 2, 13 and 14 elements. One of these reviews, by Inoue and co-workers, focuses on the structures of ditetrelenes (R₂E^II E^IIR₂, E = group 14 element) and ditetrelynes (RE^I E^IR), and their remarkable reactivity towards small molecules (DOI: 10.1039/D0SC03192E). Another review by Crimmin and co-workers explores the role that magnesium(i) and aluminium(i) reductants play in C–H bond activation reactions, and the synergy that may arise when the main group reagent is combined with a transition metal (DOI: 10.1039/D0SC03695A). Showcasing the value that s-block metals may display in their normal valence, Williams and coworkers describe macrocyclic Mg^II/Zn^II heterodinuclear complexes as highly effective catalysts for epoxide/CO₂ ring opening co-polymerization (DOI: 10.1039/C9SC00385A). The broader significance of this concept is developed in a review on heterobimetallic complexes containing s-block metals, in which Hevia and her co-worker highlight the unique ability of such complexes to support cooperative catalysis (DOI: 10.1039/D0SC05116K). The Lewis acidity of s-block cations can also be harnessed to manipulate the covalency of metal–ligand interactions, as elegantly demonstrated by Arnold, Love, Vitova, Schreckenbach and co-workers, who investigate a series of uranyl(v) complexes featuring U O–E motifs (E = group 1 or 2 element, DOI: 10.1039/C8SC05717F).Reduced polynuclear main group complexes can also provide new platforms for the discovery of atypical reactivity as illustrated by Kong and co-workers, who report mono-base-stabilized 1,2-diboranylidenehydrazines, a set of compounds that feature an unprecedented BNN-1,3-dipole that readily adds to arenes or small molecules such as CO₂ (DOI: 10.1039/D0SC02162H). In keeping with the theme of reactive diboron-containing units, Braunschweig and co-workers show in another captivating report that B–B triply-bonded diborynes can add to diboranes to afford B₄ chains, a transformation that could pave the way to new polymers with polyboron units in the main chain (DOI: 10.1039/C9SC02544H). The synthetic potential offered by low oxidation state main group elements comes to the fore in two additional reports, both dealing with Si₆ clusters. In the first one, Scheschkewitz and co-workers show that these silicon clusters can be functionalised with tetrylene substituents, and can act as ligands towards group 9 metal fragments, yielding complexes which act as catalysts for alkene isomerisations (DOI: 10.1039/D0SC02861D). A second report by Lips and co-workers describes highly unsaturated and structurally dynamic Si₆R₄ species (R = amide) with exposed silicon vertices (DOI: 10.1039/D0SC01427C). Exposed silicon moieties can also be appended to classical ligands as demonstrated by Roesky and co-workers who report on cyclopentadienyl ligands substituted by a silylene (R₂Si:). These ligands not only act as two-electron Si donors towards transition metal fragments but also undergo isomerization or deprotonation reactions leading to sila-fulvenes (DOI: 10.1039/D0SC04174B). Reduced group 14 elements can also be directly incorporated in the five-membered ring of cyclopentadienyl-like ligands as illustrated by Müller, Albers and co-workers in a contribution dealing with the germacyclopentadienediyl [K₂(:GeC₄R₄)] as an η⁵-ligand and its conversion into the first germaaluminocene, [Cp*Al(η⁵-:GeC₄R₄)] (DOI: 10.1039/D0SC00401D).As stated in the introductory paragraph, positioning main group elements in the coordination sphere of transition metals provides access to unusual reactivities, as in a contribution by Ozerov and co-workers (DOI: 10.1039/D0SC04748A) who demonstrate the reversible addition of ethylene to a boryl-based bis(phosphine) iridium pincer complex. A unique aspect of this contribution is the concomitant participation of the iridium and boron centres in the coordination of the hydrocarbon ligand. The ability of boron to cooperate with an adjacent transition metal centre is again a leading theme in two additional contributions selected for inclusion in this issue. The first one concerns the reversible addition of H₂ across an Ni–B bond, as elegantly documented by Rodríguez, Lledós and co-workers (DOI: 10.1039/D0SC06014C), who also used a boryl-based pincer as a supporting ligand. Exploiting the somewhat counter-intuitive reality that gold is more electronegative than boron, Yamashita, Lin and co-workers show that gold(i) diarylboryl complexes react as gold-based nucleophiles with organic reagents bearing C O and C N bonds (DOI: 10.1039/D0SC05478J). The unique reactivity of late transition metal–boryl linkages pervades in another contribution by Conejero, Lledós and co-workers who detail the highly choreographed addition of boranes such as HBpin and HBcat to a cationic, T-shaped, cyclometallated Pt(ii) bis-carbene complex (DOI: 10.1039/D0SC05522K). Isolated species include σ-BH Pt^II complexes, en route to the formation of T-shaped Pt^II bis-carbene complexes. Last, Tilley, Eisenstein and co-workers remind us of the importance of main group hydrides in catalysis in a contribution that pinpoints the intermediacy of dinuclear nickel–silyl species in an alkene hydrosilylation reaction mediated by a cationic nickel complex (DOI: 10.1039/D0SC00997K).Within the theme of heterometallic cooperativity, we highlight three articles where group 13 elements were introduced into transition metal complexes to promote small-molecule activation. In each report, a unique ligand design is used to juxtapose the transition metal centre with the group 13 element(s). Szymczak and co-workers appended two Lewis acidic borane groups to a pincer ligand via flexible linkers. The pendant boranes were critical for the stabilization of a rare high-spin Fe^II dihydride complex by forging Fe–H → B interactions (DOI: 10.1039/C9SC00561G). Upon exposure to an arylisocyanide, a good π-acid, the reductive elimination of H₂ ensued to form the iron(0) complex. Such a step is reminiscent of the E₄ intermediate in nitrogenase, which is proposed to release the obligatory H₂ equivalent upon binding of N₂ [see Chem. Rev., 2014, 114, 4041]. Envisioning a more active role for boranes, Harman and co-workers use the diboraanthracene platform, whose redox flexibility and dynamic Lewis acidity can be orchestrated to promote reactivity at the bound transition metal (DOI: 10.1039/C9SC02792K). The authors isolate a key Au borohydride intermediate that reduces CO₂ to formate, and close a synthetic cycle from CO₂ to formic acid using only proton and electron equivalents. Moving down the group 13 to the heavier congeners, Lu and co-workers show that the choice of the heavy group 13 ion (Al, Ga, or In) that is directly appended to a nickel(0) centre can significantly tune the Ni electronics (DOI: 10.1039/C9SC02018G). In comparing a triad of non-classical Ni(η²-H₂) adducts, the identity of the group 13 ion was found to perturb the free energy and activation energy of H₂ binding by ∼5 kcal mol⁻¹. Lastly, in a timely review, Takaya details the growing momentum of using main group/metalloid complexes as supporting ligands for transition metal-based catalysis (DOI: 10.1039/D0SC04238B). Takaya’s review presents illustrative examples to showcase the diverse main group elements (groups 13–15) and strategies that are being harnessed for transition metal catalysis.Moving down the periodic table to the f-elements, several articles explore heterometallic lanthanide and actinide complexes that fundamentally challenge our understanding of bonding and electronic structure. Using mixed arene π-ligands, Liddle and co-workers isolated an unusual bent Th “sandwich” complex that is stitched by K⁺ ions into a tetrathorium cluster (DOI: 10.1039/D0SC02479A). Diaconescu, Huang and co-workers report inverted sandwich complexes of Sm and Y featuring a bridging biphenyl ligand and bridging K⁺ ions (DOI: 10.1039/D0SC03555F). Depending on the lanthanide element, these inverted sandwiches feature Sm^III–arene–Sm^III or Yb^II–arene–K⁺ bonding interactions, where the biphenyl ligand is formally tetraanionic or dianionic, respectively. Freedman and co-workers conducted an in-depth study on the electronic structures of Sn-based heterometallics that contain a direct bond between Sn and a first-row transition metal that is varied from Mn to Ni (DOI: 10.1039/D0SC03777J). The authors make a striking comparison between the high-spin configurations of the 3d ions and those of typical Ln coordination complexes, wherein the coordinate bonds are more ionic. They rationalize that the Sn group behaves as an inverted, weak-field ligand due to the large energy mismatch between the Sn 5s/5p and 3d atomic orbitals [see Chem. Rev., 2016, 116, 8173]. Controlling spin states is only one of several requisites for the design of single molecule magnets (SMMs). Layfield, Mansikkamäki and co-workers report a triad of dinuclear dysprosium complexes, where the exogenous borohydride donor is varied in both number and coordination (terminal to bridging) (DOI: 10.1039/D0SC02033H). The authors observed a favourable increase in the effective energy barrier for a dinuclear dysprosium complex with a Dy : BH₄ ratio of 2 : 1. Lastly, Nippe, Chibotaru and co-workers explore magneto-structural relationships in a series of trigonal prismatic Ln^III complexes (Gd to Lu) that are scaffolded by three doubly deprotonated ferrocene (FeCp₂)²⁻ ligands and capped by Li⁺ ions (DOI: 10.1039/D0SC01197E). By virtue of its size and axis of anisotropy, the authors were able to engender SMM behaviour for the Ho^III complex. The authors demonstrate that the Ln size and the nature of the Li⁺ solvate both influence the twist angle, where the ideal trigonal prism geometry (twist angle of 0°) results in the large anisotropy that is conducive to SMM behaviour.To illustrate the diversity of the field, this themed issue also highlights several additional contributions dealing with atypical phosphorus-containing ligands. For example, Scheer and co-workers show that the four-membered cyclo-P₄ ligand of organometallic tantalum complexes can be used as a square building block for the construction of molecular capsules upon combination with silver cations and an appropriate template (DOI: 10.1039/D0SC03437A). Two additional contributions document recent trends at the confluence of traditional organophosphorus chemistry and coordination chemistry. Gessner and co-workers review the unique properties of phosphorus ylides and their ability to stabilize low-valent main group species, leading to the formation of new main group ligands for transition metal-based catalysis (DOI: 10.1039/D0SC03278F). The second contribution comes from Normand, Sosa Carrizo and co-workers who decipher the ambiphilic properties of bis(iminophosphoranyl)phosphide ligands and suggest that they be regarded as containing a triphosphenium coordinating unit (DOI: 10.1039/D0SC04736H).This themed issue was assembled with the intent of spotlighting the role played by main group elements in polynuclear complexes. We hope that those reading these articles will appreciate the topical diversity of this research field, its relevance to various areas of chemistry, and the numerous future research opportunities it presents.     

Chiral assembly of organic luminogens with aggregation-induced emission

Chirality is important to chemistry, biology and optoelectronic materials. The study on chirality has lasted for more than 170 years since its discovery. Recently, chiral materials with aggregation-induced emission (AIE) have attracted increasing interest because of their fascinating photophysical properties. In this review, we discussed the recent development of chiral materials with AIE properties, including their molecular structures, self-assembly and functions. Generally, the most effective strategy to design a chiral AIE luminogen (AIEgen) is to attach a chiral scaffold to an AIE-active fluorophore through covalent bonds. Moreover, some propeller-like or shell-like AIEgens without chiral units exhibit latent chirality upon mirror image symmetry breaking. The chirality of achiral AIEgens can also be induced by some optically active molecules through non-covalent interactions. The introduction of an AIE unit into chiral materials can enhance the efficiency of their circularly polarized luminescence (CPL) in the solid state and the dissymmetric factors of their helical architectures formed through self-assembly. Thus, highly efficient circularly polarized organic light-emitting diodes (CPOLEDs) with AIE characteristics are developed and show great potential in 3D displays. Chiral AIEgens are also widely utilized as “turn on” sensors for rapid enantioselective determination of chiral reagents. It is anticipated that the present review can entice readers to realize the importance of chirality and attract much more chemists to contribute their efforts to chirality and AIE study.

This review highlights the recent development of chiral materials with aggregation-induced emission properties, including their molecular structures, self-assembly and functions.     

Correction: A hybrid blue perovskite@metal–organic gel (MOG) nanocomposite: simultaneous improvement of luminescence and stability

Correction for ‘A hybrid blue perovskite@metal–organic gel (MOG) nanocomposite: simultaneous improvement of luminescence and stability’ by Samraj Mollick et al., Chem. Sci., 2019, 10, 10524–10530, DOI: 10.1039/C9SC03829A.

The authors regret that the formula used for the 2D perovskite EAPbBr₃ throughout the text is incorrect. The formula should read EA₂PbBr₄.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Assembly of the Thiolated [Au1Ag22(S-Adm)12]3+ Superatom Complex into a Framework Material through Direct Linkage by SbF6− Anions

Building framework materials with desirable properties and enhanced functionalities with nanocluster/superatom complexes as building blocks remains a challenge in the field of nanomaterials. In this study, the chiral [Au₁Ag₂₂(S-Adm)₁₂]³⁺ nanocluster/superatom complex (SC, in which S-Adm=1-adamantanethiol) was employed as a building block to construct the three-dimensional (3D) superatom complex inorganic framework (SCIF) materials SCIF-1 and SCIF-2 through inorganic SbF₆⁻ linkers. SCIF-1 is racemic due to the assembly of two SC enantiomers in a single crystal. In SCIF-2, the SC enantiomers are packed in separate crystals, thus producing larger channels and a circularly polarized luminescence (CPL) response. These two 3D SCIF materials exhibit unique sensitive photoluminescence (PL) in protic solvents. Our study provides a new pathway for creating novel open-framework materials with superatom complexes and a foundation for the further development of 3D framework materials for sensing and other applications.     

Correction: Effect of heterocycle content on metal binding isostere coordination

Correction for ‘Effect of heterocycle content on metal binding isostere coordination’ by Benjamin L. Dick et al., Chem. Sci., 2020, 11, 6907–6914, DOI: 10.1039/D0SC02717K.

The authors regret that a complete Conflicts of interest section was not shown in the original article. The correct Conflicts of interest section is shown below.     

Assembly of the Thiolated [Au1Ag22(S‐Adm)12]3+ Superatom Complex into a Framework Material through Direct Linkage by SbF6− Anions

Building framework materials with desirable properties and enhanced functionalities with nanocluster/superatom complexes as building blocks remains a challenge in the field of nanomaterials. In this study, the chiral [Au₁Ag₂₂(S‐Adm)₁₂]³⁺ nanocluster/superatom complex (SC, in which S‐Adm=1‐adamantanethiol) was employed as a building block to construct the three‐dimensional (3D) superatom complex inorganic framework (SCIF) materials SCIF‐1 and SCIF‐2 through inorganic SbF₆^? linkers. SCIF‐1 is racemic due to the assembly of two SC enantiomers in a single crystal. In SCIF‐2, the SC enantiomers are packed in separate crystals, thus producing larger channels and a circularly polarized luminescence (CPL) response. These two 3D SCIF materials exhibit unique sensitive photoluminescence (PL) in protic solvents. Our study provides a new pathway for creating novel open‐framework materials with superatom complexes and a foundation for the further development of 3D framework materials for sensing and other applications.     

Correction: Development of a structure-based computational simulation to optimize the blocking efficacy of pro-antibodies

Correction for ‘Development of a structure-based computational simulation to optimize the blocking efficacy of pro-antibodies’ by Bo-Cheng Huang et al., Chem. Sci., 2021, DOI: 10.1039/D1SC01748A.

The authors regret that a funding source was omitted from the original article. The following funding information should have been acknowledged: Ministry of Science and Technology, Taiwan (MOST 109-2627-M-037-001) and Kaohsiung Medical University, Taiwan (KMU-DK(B)11000-4).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Integrating Achiral and Chiral Organic Ligands in Zero-Dimensional Hybrid Metal Halides to Boost Circularly Polarized Luminescence

Chiral zero-dimensional hybrid metal halides (0D HMHs) could combine excellent optical properties and chirality, making them promising for circularly polarized luminescence (CPL). However, chiral 0D HMHs with efficient CPL have been rarely reported. Here, we propose an efficient strategy to achieve simultaneously high photoluminescence quantum yield (PLQY) and large dissymmetry factor (g_lum), by integrating achiral and chiral ligands into 0D HMHs. Specifically, three pairs of chiral 0D hybrid indium-antimony chlorides are synthesized by combing achiral guanidine with three types of chiral methylbenzylammonium-based derivatives as the organic cations. These chiral 0D HMHs exhibit near-unity PLQY and large g_lum values up to around ±1×10⁻². The achiral guanidine ligand is not only essential to crystallize these hybrid indium-antimony chlorides to achieve near-unity PLQYs, but also greatly enhances the chirality induction from organic ligands to inorganic units in these 0D HMHs. Furthermore, the choice of different chiral ligands can modify the strength of hydrogen bonding interactions in these 0D HMHs, to maximize their g_lum values. Overall, this study provides a robust way to realize efficient CPL in chiral HMHs, expanding their applications in chiroptical fields.     

Chiral Gold Nanoclusters: Atomic Level Origins of Chirality

Chiral nanomaterials have received wide interest in many areas, but the exact origin of chirality at the atomic level remains elusive in many cases. With recent significant progress in atomically precise gold nanoclusters (e.g., thiolate‐protected Au_n (SR)_m ), several origins of chirality have been unveiled based upon atomic structures determined by using single‐crystal X‐ray crystallography. The reported chiral Au_n (SR)_m structures explicitly reveal a predominant origin of chirality that arises from the Au–S chiral patterns at the metal–ligand interface, as opposed to the chiral arrangement of metal atoms in the inner core (i.e. kernel). In addition, chirality can also be introduced by a chiral ligand, manifested in the circular dichroism response from metal‐based electronic transitions other than the ligand's own transition(s). Lastly, the chiral arrangement of carbon tails of the ligands has also been discovered in a very recent work on chiral Au₁₃₃(SR)₅₂ and Au₂₄₆(SR)₈₀ nanoclusters. Overall, the origins of chirality discovered in Au_n (SR)_m nanoclusters may provide models for the understanding of chirality origins in other types of nanomaterials and also constitute the basis for the development of various applications of chiral nanoparticles.     

Photoresponsive Propeller-like Chiral AIE Copper(I) Clusters

A pair of propeller-like chiral trinuclear Cu^I clusters ( R/S-Cu3 ) with unique photoinduced fluorescence enhancement were prepared. R/S-Cu3 showed intense variable luminescence after UV light irradiation, which was attributed to the stepwise oxidation of ligand in the clusters. It exhibited typical aggregation-induced emission (AIE) (α_AIE=17.3). Mechanism studies showed that metal cluster-centered (MCC) and triplet metal-to-ligand charge-transfer (³MLCT) processes are the origin of the luminescence; the processes are regulated by a restriction of intramolecular motions mechanism in a different state. The chiral structure and AIE feature endow R/S-Cu3 with remarkable circularly polarized luminescence (g_lum=2×10⁻²) in the aggregated state. It shows good capability for producing reactive oxygen species. This work enriches the kinds of atomically precise AIE clusters, gains insight into their luminescence mechanism, and offers the prospect of application in multifunctional materials.     

Correction: SuFEx-enabled,chemoselective synthesis of triflates,triflamides and triflimidates

Correction for ‘SuFEx-enabled, chemoselective synthesis of triflates, triflamides and triflimidates’ by Bing-Yu Li et al., Chem. Sci., 2022, 13, 2270–2279, DOI: 10.1039/D1SC06267K.

The authors would like to correct the second sentence in the Acknowledgements section, which should read “For HPLC analyses, we kindly acknowledge Marcus Frings and the support from RWTH Aachen University.”The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: The morphology and surface charge-dependent cellular uptake efficiency of upconversion nanostructures revealed by single-particle optical microscopy

Correction for ‘The morphology and surface charge-dependent cellular uptake efficiency of upconversion nanostructures revealed by single-particle optical microscopy’ by Di Zhang et al., Chem. Sci., 2018, 9, 5260–5269, DOI: 10.1039/C8SC01828F.

In the Experimental section of the article, the concentration of citrate was incorrectly given as 0.05 M. The correct concentration of citrate is 2 M.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Photoresponsive Propeller‐like Chiral AIE Copper(I) Clusters

A pair of propeller‐like chiral trinuclear Cu^I clusters ( R/S‐Cu3 ) with unique photoinduced fluorescence enhancement were prepared. R/S‐Cu3 showed intense variable luminescence after UV light irradiation, which was attributed to the stepwise oxidation of ligand in the clusters. It exhibited typical aggregation‐induced emission (AIE) (α_AIE=17.3). Mechanism studies showed that metal cluster‐centered (MCC) and triplet metal‐to‐ligand charge‐transfer (³MLCT) processes are the origin of the luminescence; the processes are regulated by a restriction of intramolecular motions mechanism in a different state. The chiral structure and AIE feature endow R/S‐Cu3 with remarkable circularly polarized luminescence (g_lum=2×10^?2) in the aggregated state. It shows good capability for producing reactive oxygen species. This work enriches the kinds of atomically precise AIE clusters, gains insight into their luminescence mechanism, and offers the prospect of application in multifunctional materials.     

Correction: Graph neural network based coarse-grained mapping prediction

Correction for ‘Graph neural network based coarse-grained mapping prediction’ by Zhiheng Li et al., Chem. Sci., 2020, 11, 9524–9531, DOI: 10.1039/D0SC02458A.

The authors regret that eqn (5) was missing the adjacency matrix term. The correct form of eqn (5) is shown below:5where σ is the bandwidth and is set to σ = 1 in the experiment. denotes the adjacency matrix (Ẽ_ij = 1 if atom i and atom j are bonded, otherwise Ẽ_ij = 0).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Unprecedented Chiral Three-dimensional Hybrid Organic-Inorganic Perovskitoids

Chiral three-dimensional hybrid organic–inorganic perovskites (3D HOIPs) would show unique chiroptoelectronic performance due to the combination of chirality and 3D structure. However, the synthesis of 3D chiral HOIPs remains a significant challenge. Herein, we constructed a pair of unprecedented 3D chiral halide perovskitoids (R/S-BPEA)EA₆Pb₄Cl₁₅ ( 1-R/S ) (R/S-BPEA=(R/S)-1-4-Bromophenylethylammonium, EA=ethylammonium), in which the large chiral cations can be contained in the big “hollow” inorganic frameworks induced by mixing cations. Notably, 3D 1-R/S shows natural chiroptical activity, as evidenced by its significant mirror circular dichroism spectra and the ability to distinguish circularly polarized light. Moreover, based on the unique 3D structure, 1-S presents sensitive X-ray detection performance with a low detection limit of 398 nGy_air s⁻¹, which is 14 times lower than the regular medical diagnosis of 5.5 μGy_air s⁻¹. In this work, 3D chiral halide perovskitoids provide a new route to develop chiral material in spintronics and optoelectronics.     

Control of Axial Chirality by Planar Chirality Based on Optically Active [2.2]Paracyclophane

Optically active X-shaped molecules based on the planar chiral [2.2]paracyclophane building block were prepared, in which di(methoxy)terphenyl units were stacked on the central benzene rings. At 25 °C, anisolyl rings freely rotate in solution, while in the crystal form, they are fixed by intramolecular CH–π interactions, thereby leading to the expression of the axial chirality, i.e., propeller chirality was exhibited by the planar chiral [2.2]paracyclophane moiety. The X-shaped molecule exhibited good circularly polarized luminescence (CPL) profiles with moderate Φ_PL and a large g_lum value in the order of 10⁻³ at 25 °C, in solution. In contrast, at −120 °C, dual CPL emission with opposite signs was observed. According to the theoretical studies, the rotary motion of the anisolyl units is suppressed in the excited states, and so emission from two isomers could be observed. These results demonstrate that the axial chirality was controlled by the planar chirality, leading ultimately to propeller chirality.     

Enhanced Circularly Polarized Luminescence from Reorganized Chiral Emitters on the Skeleton of a Zeolitic Imidazolate Framework

A chiral zeolitic imidazolate framework (ZIF) showing circularly polarized luminescence (CPL) has been successfully constructed by blending binapthyl‐derived chiral emitters with ZIF‐8 rhombic dodecahedron nanoparticles. This approach solves a major trade‐off in CPL‐active materials: the large luminescence dissymmetry factor (g_lum) always suffers from suppression of luminescence efficiency. Compared to the optical properties of chiral emitters, the obtained chiral ZIF nanomaterials showed an enhanced fluorescence efficiency while the |g_lum| value is significantly amplified by one order of magnitude. Additionally, enantioselective fluorescence sensing in response to α‐hydroxycarboxylic acids has been enhanced in chiral ZIFs. Reorganization and conjunction of chiral emitters to the skeleton of ZIF nanoparticles can greatly improve both the luminescence quantum yield and circularly polarization, which facilitates the design of more efficient chiroptical materials.     

Correction: Mass spectrometric detection of fleeting neutral intermediates generated in electrochemical reactions

Correction for ‘Mass spectrometric detection of fleeting neutral intermediates generated in electrochemical reactions’ by Jilin Liu et al., Chem. Sci., 2021, 12, 9494–9499, DOI: 10.1039/D1SC01385H.

The authors regret that the details for ref. 15 and 17 were inadvertently swapped in the original article. The correct versions of ref. 15 and 17 are given below as ref. 1 and 2, respectively.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Dioxacyclophanes as a Scaffold for Silicon-based Circularly Polarized Luminescent Materials

Planar chiral dioxacyclophanes were designed and synthesized as a key scaffold for materials with circularly polarized luminescence (CPL). Representative planar chiral 1,12-dioxa[12](1,4)naphthaleneophane-derived organosilane compounds (?)-(R)-1, (+)-(R)-2, and (?)-(R)-3 were prepared by (+)-sparteine-mediated aryl metalation and an electrophilic reaction with chlorosilanes. The absolute configurations of the planar chirality were determined in the R form by single-crystal X-ray analysis. Optically active compound (+)-(R)-2 exhibited blue fluorescence and a CPL signal with a dissymmetry factor (g_lum value) of 0.001 in solution. The electronic structure was corroborated by DFT and TD-DFT calculations rationalizing the observed spectroscopic properties.