Bridging Ligand Research Articles

Bifunctional Metal–Organic Framework Synergistically Enhances Radiotherapy and Activates STING for Potent Cancer Radio‐Immunotherapy

AbstractThe activation of the stimulator of interferon genes (STING) protein by cyclic dinucleotide metabolites plays a critical role in antitumor immunity. However, synthetic STING agonists like 4‐(5,6‐dimethoxybenzo[b]thiophen‐2‐yl)‐4‐oxobutanoic acid (MSA‐2) exhibit suboptimal pharmacokinetics and fail to sustain STING activation in tumors for effective antitumor responses. Here, we report the design of MOF/MSA‐2, a bifunctional MSA‐2 conjugated nanoscale metal–organic framework (MOF) based on Hf6 secondary building units (SBUs) and hexakis(4′‐carboxy[1,1′‐biphenyl]‐4‐yl)benzene bridging ligands, for potent cancer radio‐immunotherapy. By leveraging the high‐Z properties of the Hf6 SBUs, the MOF enhances the therapeutic effect of X‐ray radiation and elicits potent immune stimulation in the tumor microenvironment. MOF/MSA‐2 further enhances radiotherapeutic effects of X‐rays by enabling sustained STING activation and promoting the infiltration and activation of immune cells in the tumors. MOF/MSA‐2 plus low‐dose X‐ray irradiation elicits strong STING activation and potent tumor regression, and when combined with an immune checkpoint inhibitor, effectively suppresses both primary and distant tumors through systemic immune activation.

Five novel Pb/Zn/Co metal-organic frameworks using 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene and carboxylate ligands: Synthesis, characterization, DFT calculation and catalytic PMS degradation of RhB

Five new metal-organic frameworks (MOFs), namely {Pb(atpt)(3-bpd)0.5}n (1); {Co(cbz)2(3-bpd)(H2O)2·2H2O}n (2); {Co(imdc)(3-bpd)(H2O)·H2O}n (3); {Co(tdca)(3-bpd)(H2O)2·DMF}n (4); {Zn(tdca)(3-bpd)(H2O)2·DMF}n (5), were assembled with metal ions Pb²⁺, Zn²⁺, and Co²⁺ using 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (3-bpd) as the main ligand, combined with 2-aminoterephthalic acid (H2atpt), 4-cyanobenzoic acid (Hcbz), 4,5-imidazoledicarboxylic acid (H2imdc), and thiophene-2,5-dicarboxylic acid (H2tdca) as auxiliary ligands via hydro/solvothermal methods. Their molecular structures were analyzed by single-crystal X-ray diffraction and characterized by FT-IR and PXRD. Complex 1 has a three-dimensional structure with a hepta-coordinated, semi-directed {PbNO6} metal center. The central metal ions in complexes 2–5 exhibit a six-coordinated {MN2O4} (M = Co or Zn) octahedral geometry. In complex 2, the carboxylate ligand does not function as a bridging ligand, resulting in a 1D chain structure, while complexes 3- 5 extend into 2D layered structures. Thermogravimetric analysis indicates good thermal stability for complexes 1–5. Then, the prepared complexes were used as catalysts to degrade Rhodamine B (RhB) during the monopersulfate (PMS) activation. Complexes 3 and 4 demonstrated significant efficiency, achieving degradation rates of 93.61 % and 98.56 % within 10 min. Radical scavenging experiments and EPR analysis identified that the activation of PMS for dye degradation by the two catalysts occurs through both radical and non-radical pathways, with SO4•− and •OH radicals being the dominant species. Density functional theory (DFT) calculations explained the superior catalytic performance of complex 4 compared to complex 3.

Stabilization of Ethane-like Dianionic Diborane(6) in Monometallic Titanium Complexes and its Subsequent B(sp3)-B(sp3) Bond Cleavage.

Treatment of [Cp*TiCl3] with [LiBH4∙THF] followed by thermolysis with [Ph2E2] (E = S or Se) resulted in the formation of classical diborane(6) complexes, [(Cp*Ti)(η4-B2H4LL')] (L = C6H4E; L' = C6H5E; 1a: E = S, 1b: E = Se), stabilized at titanium template. To the best of our knowledge, they are the first examples of mono-metallic classical diborane(6) complexes. The bonding analysis and theoretical studies suggest that the stabilization of these diborane(6) species is due to the presence of four bridging ligands in ĸ4-fashion, where two of them are phenyl thiolates/selenolates that provide more electrons to the electron-deficient titanium center. Reactions of these diborane(6) species with [M(CO)5∙THF] (M = Mo, W) led to the cleavage of electron-precise B(sp3)-B(sp3) bond that yielded ĸ3-hydridoborato complexes [(Cp*Ti)(ĸ3-BH3R)(μ-EPh)2{M(CO)4}] (2a-c: R = H, 3a-c: R = Ph). In an attempt to isolate the Te-analogue of 1a-b, a similar reaction was performed; however, the complex was too unstable to be isolated. Interestingly, the treatment of this unstable intermediate with [W(CO)5∙THF] yielded [(Cp*Ti)(ĸ3-BH3R)(μ-TePh)2{W(CO)4}] (2d: R = H, 3d: R = Ph) that are analogues of 2a-c and 3a-c, respectively. Formation of these species provide indirect evidence forexistence of unstable [(Cp*Ti)(η4-B2H4LL')] (L = C6H4Te; L' = C6H5Te; 1c).

Stabilization of Ethane‐like Dianionic Diborane(6) in Monometallic Titanium Complexes and its Subsequent B(sp3)‐B(sp3) Bond Cleavage

Treatment of [Cp*TiCl3] with [LiBH4∙THF] followed by thermolysis with [Ph2E2] (E = S or Se) resulted in the formation of classical diborane(6) complexes, [(Cp*Ti)(η4‐B2H4LL')] (L = C6H4E; L' = C6H5E; 1a: E = S, 1b: E = Se), stabilized at titanium template. To the best of our knowledge, they are the first examples of mono‐metallic classical diborane(6) complexes. The bonding analysis and theoretical studies suggest that the stabilization of these diborane(6) species is due to the presence of four bridging ligands in ĸ4‐fashion, where two of them are phenyl thiolates/selenolates that provide more electrons to the electron‐deficient titanium center. Reactions of these diborane(6) species with [M(CO)5∙THF] (M = Mo, W) led to the cleavage of electron‐precise B(sp3)‐B(sp3) bond that yielded ĸ3‐hydridoborato complexes [(Cp*Ti)(ĸ3‐BH3R)(μ‐EPh)2{M(CO)4}] (2a‐c: R = H, 3a‐c: R = Ph). In an attempt to isolate the Te‐analogue of 1a‐b, a similar reaction was performed; however, the complex was too unstable to be isolated. Interestingly, the treatment of this unstable intermediate with [W(CO)5∙THF] yielded [(Cp*Ti)(ĸ3‐BH3R)(μ‐TePh)2{W(CO)4}] (2d: R = H, 3d: R = Ph) that are analogues of 2a‐c and 3a‐c, respectively. Formation of these species provide indirect evidence for existence of unstable [(Cp*Ti)(η4‐B2H4LL')] (L = C6H4Te; L' = C6H5Te; 1c).

Bridge-Dependent Donor-Metal-Acceptor-Metal-Donor (D-M-A-M-D) Systems: From Charge Transfer to Electron Transfer in Dioxolene-Ge-Diimine Complexes.

Synthesis and structural characterization of a family of germanium-dioxolene complexes with ditopic N-donor ligands (L1-L5) (L1=1,2-bis(pyridin-2-ylmethylene)hydrazine L2=1,6-bis-(pyridin-2-yl)-2,5-diaza-1,5-hexadiene, L3=N,N-bis(pyridin-2-ylmethylene)-1,4-benzenediamine, L4=N,N-bis(pyridin-2-ylmethylene)-(biphenyl)-4,4-diamine, L5=2,2'-azopyridine) is reported. The reaction of germanium bis-catecholate with bridging ligands L1 - L4, differing by the nature of the linker between pyridine sites gives rise to dinuclear digermanium complexes (36Cat2Ge)2L1-4 (36Cat=dianion of 3,6-di-tert-butylcatechol) 1-4 of DMAMD type (donor-metal-acceptor-metal-donor) with a charge transfer in the UV-Vis region. In opposite, the interaction of the 36Cat2Ge with 2,2'-azopyridine (L5) results in the two-electron transfer from the donor 36Cat2- ligands to the azopyridine bridge forming stable open-shell complex 5 [(36SQ)(36CatGe)]2(L5)2- (36SQ=radical-anionic semiquinonate ligand). Molecular structures of compounds 3 and 5 were determined by single crystal X-ray diffraction analysis. Electronic structures of complexes 1-5 were studied by means of DFT calculations.

Benzo[1,2-b:4,5-b’]dithiophene diethynyl bridged bimetallic ruthenium complexes: syntheses and characterization, (spectro)electrochemistry combined with theoretical calculations

We have constructed isomeric triruthenium ethynyl complexes 1 and 2 linked by benzo[1,2-b:4,5-b’]dithiophene. The electronic properties of 1 and 2 were compared by (spectro)electrochemical and theoretical calculations. DFT (density functional theory) fully-optimized structures 1 and 2 showed that the ruthenium terminal groups both exhibit a similar pseudo-octahedral configuration as reported for the crystal structure of 1. With step-by-step oxidation, the bond length of Ru-C decreases and the bond length of C≡C increases, which indicated that the complexes undergo a transition from Ru-C≡C to Ru = C = C. The electrochemical results of 1 and 2 featured two consecutive single-electron redox processes, and the ΔE value of 2 (329 mV) was significantly higher than that of 1 (140 mV). The near-IR broad absorptions of 2 + from UV-Vis-NIR spectroelectrochemistry exhibited a blue shift relative to that of 1 +, which could be attributed to MLCT (metal to ligand charge transfer) absorptions and confirmed by TDDFT (time dependent) calculations. The results suggested that the bridge ligands are involved in the redox process. The ν(C≡C) stretch of 2 + from IR spectroelectrochemistry exhibited a strong single peak at 1969 cm-1, while the isomer 1 + showed three asymmetric peaks. These results showed excellent charge delocalization ability of 2.

Strong Antiferromagnetic Interactions in the Binuclear Cobalt(II) Complex with a Bridged Nitroxide Diradical

A binuclear cobalt–radical complex formed by the reaction of Co(hfac)2·2H2O (hfac = hexafluoroacetylacetonate) with the 2,2-bis(1-oxyl-3-oxide-4,4,5,5-tetramethylimidazolinyl) biradical (BR) has been synthesized. The complex {(hfac)CoII(BN)CoII(hfac)} crystallizes in the triclinic space group P1¯ : C34H28Co2F24N4O12, a = 11.1513(5) Å, b = 12.8362(7) Å, c = 18.2903(8) Å, α = 103.061(1)°, β = 100.898(2)°, γ = 102.250(1)°, Z = 2. The compound consists of two non-equivalent pseudo-octahedral CoII ions, each bearing two hfac ancillary ligands bridged by the tetradentate bis-nitroxide (BN). The temperature dependence of the magnetic susceptibility indicates a strong antiferromagnetic exchange between each of the Co2+ ions and the nitroxyl biradical, as well as between the spins within the bridging ligand, forming a spin-frustrated system. Micro-squid investigations, performed on a single crystal of {(hfac)CoII(BN)CoII(hfac)}, reveal a peculiarity of the M(H) graph at temperatures below 0.4 K displaying a step that is a result of ground and first excited levels mixing by the applied magnetic field due to a small energy gap between them, as inferred from ab initio calculation. The latter was also carried out for two models of mononuclear Co2+ complexes in order to obtain a set of initial parameters for fitting the experimental magnetic curves using the Phi program. Moreover, direct CAS(12,10)/def2-TZVP calculations of the magnetic dependences χT(T) and M(H) were performed, which satisfactorily reproduced the experimental ones.

A Pd(II) Complex Exhibiting Tetradentate NHC‐Phosphine Ligand: On Route to Unconventional Phosphonium Ylide Derivatives

AbstractUnusual open‐chain tetradentate NHC‐phosphine pre‐ligand [Ph2PCH(Ph)ImCH2ImC(H)PhPPh2](BF4)2 was prepared in a good yield by metal‐mediated approach starting from Mn(I) complex [Cp(CO)2Mn(η2‐Ph2P=C(H)Ph)](BF4) and bis(imidazole) derivative ImCH2Im. Its reaction with Pd(OAc)2 afforded dicationic Pd(II) complex of bis(NHC)bis(phosphine) ligand adopting κ4PĈĈP coordination mode as a mixture of two diastereomers. The deprotonation of the C(H)Ph ligand bridge in the latter using KN(SiMe3)2 as base provided stable complex exhibiting unconventional phosphonium ylide moiety, whereas all attempts to detect the corresponding bis(ylide) derivative failed.

Different Patterns of Pd-Promoted C-H Bond Activation in (Z)-4-Hetarylidene-5(4H)-oxazolones and Consequences in Photophysical Properties

This work aims to amplify the fluorescence of (Z)-4-hetarylidene-5(4H)-oxazolones 1 by suppression of the hula-twist non-radiative deactivation pathway by C^N-orthopalladation of the 4-hetarylidene ring. Different (Z)-4-hetarylidene-2-phenyl-5(4H)-oxazolones, 1a–1c, prepared by the Erlenmeyer–Plöchl method, have been studied. The orthopalladation of (Z)-2-phenyl-4-(5-thiazolylmethylene)-5(4H)-oxazolone (1a) takes place by C-H bond activation of the H4 of the heterocycle and C^N-chelation, giving the dinuclear trifluoroacetate derivative 2a. By further metathesis of bridging ligands in 2a, complexes containing the orthometalated oxazolone and a variety of ligands 3a–5a, were prepared. The study of the photophysical properties of 1a–5a shows that the bonding of the Pd metal to the 4-hetaryliden-5(4H)-oxazolone does not promote, in these cases, an increase in fluorescence. Interestingly, the orthopalladation of (Z)-2-phenyl-4-(4-thiazolylmethylene)-5(4H)-oxazolone (1b) gives orthopalladated 2b, where the incorporation of the Pd to the oxazolone takes place by C-H bond activation of the ortho-H2 of the 2-phenyl group, ring opening of the oxazolone heterocycle and simultaneous N,N-bonding of the N atoms of the thiazole ring and the generated benzamide fragment. This N^N^C-tridentate dianionic bonding mode is obtained for the first time in oxazolones. Despite a similar lock of the hula-twist deactivation, 2b does not show fluorescence.

Probing the performance of DFT in the structural characterization of [FeFe] hydrogenase models.

In this work, a series of DFT and DFT-D methods is combined with double-ζ basis sets to benchmark their performance in predicting the structures of five newly synthesized hexacarbonyl diiron complexes with a bridging ligand featuring a μ-S2C3 motif in a ring-containing unit functionalized with aromatic groups. Such complexes have been considered as [FeFe] hydrogenase catalytic site models with potential for eco-friendly energetic applications. According to this assessment, r2SCAN is identified as the density functional recommended for the reliable description of the molecular and crystal structures of the herein studied models. However, the butterfly (μ-S)2Fe2 core of the models demonstrates a minor deformation of its optimized geometry obtained from both molecular and periodic calculations. The FeFe bond length is slightly underestimated while the FeS bonds tend to be too long. Adding the D3(BJ) correction to r2SCAN does not lead to any improvement in the calculated structures.

2,3-Bis(2-pyridyl)thieno[3,4-b]pyrazine and its ruthenium(II) complexes: a new bidentate bridging ligand for enhanced metal-metal communication.

A new bidentate bridging ligand, bis(2-pyridyl)thieno[3,4-b]pyrazine is reported, along with its mono- and bi-metallic Ru(II) complexes as representative examples. Spectroscopic, electrochemical and X-ray crystallographic characterization of these species is reported, with the separation of the two Ru(III)/Ru(II) couples of the bimetallic complex suggesting better metal-metal communication than classical polypyridyl analogues.

Photoinduced Self-assembly: An Alternative Strategy for the Construction of Coordination Oligomers and Polymers.

Self-assembled oligonuclear and polynuclear complexes have numerous functionalities and potential applications. Generally, such compounds have been constructed by thermal substitution reactions with bridging ligands. Herein, we report bottom-up and photochemical construction of functional coordination oligomers and polymers by photosubstitution-induced self-assembly. The photosubstitution reactions of a ruthenium precursor complex with bridging ligands having pyrazole moieties afford mono-, di-, tri-, tetra-, and pentanuclear ruthenium complexes, Ru1-Ru5, which have one-dimensional architectures. Intramolecular hydrogen bonding between each bridging ligand is a key to construct the molecular nanowires. All the complexes have been isolated and thoroughly characterized. The photochemically synthesized ruthenium complexes act as synthons for longer metal-complex-based nanowires with a length of the order of tens-of nanometers. The multinuclear complexes are generated by photoinduced self-assembly in the presence of a base, and they undergo photoinduced disassembly in the presence of acid.

Bifunctional Metal-Organic Framework Synergistically Enhances Radiotherapy and Activates STING for Potent Cancer Radio-Immunotherapy.

The activation of the stimulator of interferon genes (STING) protein by cyclic dinucleotide metabolites plays a critical role in antitumor immunity. However, synthetic STING agonists like 4-(5,6-dimethoxybenzo[b]thiophen-2-yl)-4-oxobutanoic acid (MSA-2) exhibit suboptimal pharmacokinetics and fail to sustain STING activation in tumors for effective antitumor responses. Here, we report the design of MOF/MSA-2, a bifunctional MSA-2 conjugated nanoscale metal-organic framework (MOF) based on Hf6 secondary building units (SBUs) and hexakis(4'-carboxy[1,1'-biphenyl]-4-yl)benzene bridging ligands, for potent cancer radio-immunotherapy. By leveraging the high-Z properties of the Hf6 SBUs, the MOF enhances the therapeutic effect of X-ray radiation and elicits potent immune stimulation in the tumor microenvironment. MOF/MSA-2 further enhances radiotherapeutic effects of X-rays by enabling sustained STING activation and promoting the infiltration and activation of immune cells in the tumors. MOF/MSA-2 plus low-dose X-ray irradiation elicits strong STING activation and potent tumor regression, and when combined with an immune checkpoint inhibitor, effectively suppresses both primary and distant tumors through systemic immune activation.

Dinuclear zinc(II) acetate complexes derived from N,N',S-tridentate Schiff bases: synthesis, structural study and Hirshfeld surface analysis.

Three dinuclear zinc(II) acetate complexes of the general formula [Zn{Ln}(AcO)]2, namely, di-μ-acetato-κ4O:O'-bis[({2-[(pyridin-2-ylmethylidene)amino]phenyl}sulfanido-κ3N,N',S)zinc(II)], [Zn2(C12H9N2S)2(C2H3O2)2] (n= 1), 4, μ-acetato-1:2κ2O:O'-acetato-2κO-[μ-(2-{[1-(pyridin-2-yl)ethylidene]amino}phenyl)sulfanido-1κS:2κ3N,N',S][(2-{[1-(pyridin-2-yl)ethylidene]amino}phenyl)sulfanido-1κ3N,N',S]dizinc(II), [Zn2(C13H11N2S)2(C2H3O2)2] (n= 2), 5, and μ-acetato-1:2κ2O:O'-acetato-2κO-[μ-(2-{[phenyl(pyridin-2-yl)methylidene]amino}phenyl)sulfanido-1κS:2κ3N,N',S][(2-{[phenyl(pyridin-2-yl)methylidene]amino}phenyl)sulfanido-1κ3N,N',S]dizinc(II)-bis(2-aminophenyl) disulfide (2/1), [Zn2(C18H13N2S)2(C2H3O2)2]·0.5C12H12N2S2 (n= 3), 6·0.5(2-APS)2, were obtained from the reaction of 2-R-(pyridin-2-yl)benzothiazoline precursors (R= H, 1; R= Me, 2; R= Ph, 3) with zinc acetate dihydrate in a 1:1 ratio. All the complexes crystallized as dinuclear species and complex 6 cocrystallized with one molecule of bis(2-aminophenyl) disulfide (2-APS)2. The anionic Schiff base ligands {Ln}- displayed a κ2N,κS-tridentate coordination mode with the formation of two five-membered chelate rings. In 4, 5 and 6·0.5(2-APS)2, both ZnII ions are pentacoordinated and the coordination sphere of 4 was different with respect to those in 5 and 6·0.5(2-APS)2. For 4, the X-ray diffraction study showed a dinuclear complex containing two bridging acetate ligands linked to both ZnII ions. For 5 and 6·0.5(2-APS)2, the dinuclear complexes displayed one bridging acetate ligand linked to both ZnII ions, where the first ZnII ion includes a dative bond with one S atom from an adjacent anionic Schiff base {Ln}-, while the second ZnII ion is coordinated to one terminal acetate ligand. In each dinuclear complex, the geometry is the same for both ZnII metal centres. The local geometry of the ZnII cation in 4 is halfway between trigonal bipyramidal and square pyramidal local geometries; in 5 and 6, the local geometries are described as distorted square pyramidal. Hirshfeld surface analysis of 5 and 6 showed the predominance of H...H interactions, as well as the contribution of C-H...C, C-H...O and C-H...S noncovalent interactions to the cohesion of the crystalline network of the ZnII complexes.

Two mercury(II) halide coordination polymers with efficient photoluminescence

Two coordination polymers (CPs), [Hg(Bpbp)X2]n (X = Br (1), I (2), Bpbp = 4,4′-bis(4-pyridyl)-biphenyl), were synthesized via solvothermal synthesis methods, and were further fully characterized by single crystal X-ray diffraction, powder X-ray diffraction, elemental analyses, FT-IR spectroscopy, and thermogravimetric analyses. The two CPs exhibit similar one-dimensional zigzag chain structures constructed by Bpbp ligand connecting Hg(II) cations with halide ions as terminal ligands, while the zigzag chains show different configurations, symmetries and packing modes. The results of photoluminescence experiments and DFT calculations indicate that both the halide anions and conjugated Bpbp ligands show important roles in the emission process of CPs, and halide anions may tune the luminescence properties of CPs.

Water-soluble neutral octahedral chalcogenide tungsten and molybdenum {M6Q8} clusters with P(C2H4CONH2)3 ligand

Developing the chemistry of octahedral chalcogenide molybdenum and tungsten cluster complexes in the context of applications in biology and medicine, in this work a series of water-soluble neutral cluster complexes [{M6Q8}(P(C2H4CONH2)3)6] (M = Mo, W; Q = S, Se) have been obtained by simultaneous replacement of inner and terminal halide ligands in [{M6I8}I6]2− with chalcogenide and organic phosphine ligands and characterized by single-crystal X-ray diffraction analysis, 1H and 31P NMR spectroscopies, elemental analysis, and UV–vis spectroscopy. The amide groups of the organic ligands, on the one hand, contribute to the solubility of the resulting clusters in water and, on the other hand, are able to form an extensive network of hydrogen bonds, leading to the crystallization of the complexes from aqueous solutions. Despite this fact, the complexes have sufficient solubility and stability in aqueous solutions, which made it possible to demonstrate their low cytotoxicity on Hep-2 cells (IC50 were not reached even at concentration up to 4 mM). The resulting clusters are among the most biocompatible of the octahedral clusters studied to date and are the starting point for the development of a new family of X-ray contrast agents.

The Role of L‐Ligands in Silica‐Supported Ti Oxo/Imido Heterometathesis Catalysts

ABSTRACTWe report here the preparation and characterization of new well‐defined silica‐supported Ti imido complexes that present an L‐ligand variation in a structure of currently the most active oxo/imido heterometathesis catalyst (≡SiO)Ti(=NtBu)(Me2Pyr)(py)2 (1s), where py is replaced with stronger electron‐donating 4‐(N,N‐dimethylamino)pyridine (2s) or bidentate 2,2′‐bipyridine (3s). The materials were characterized with elemental and mass balance analyses and IR and solid‐state NMR that confirmed the selective formation of surface Ti species with terminal imido ligand. Evaluation of the catalytic oxo/imido heterometathesis activity of the obtained materials demonstrated that L‐ligands have a pronounced influence on the catalytic performance. In particular, the replacement of pyridine with stronger donating ligands resulted in a significant drop of activity. The catalytic results are discussed in view of the reaction mechanism and implications for further catalyst development.

Photo- and Electrocatalytic Hydrogen Evolution by Heteroleptic Dirhodium(II,II) Complexes: Role of the Bridging and Diimine Ligands.

A series of heteroleptic Rh2(II,II) complexes, cis-[Rh2(μ-DPhF)2(μ-bncn)2]2+ (1; bncn = benzo[c]cinnoline), cis-[Rh2(μ-DPhF)(μ-OAc)(μ-bncn)2]2+ (2), and cis-[Rh2(μ-OAc)2(μ-bncn)2]2+ (3), is presented, and the excited state and redox properties of each complex was characterized for the photo- and electrocatalytic production of H2. The oxidation potentials shift anodically from 1 to 3, consistent with a highest occupied molecular orbital (HOMO) with significant metal-ligand mixing, Rh2(δ*)/DPhF(π/nb). In contrast, modest differences in the first two bncn-localized reversible reduction potentials were observed in 1 - 3. The lowest energy metal/ligand-to-ligand charge transfer (1ML-LCT) transition, Rh2(δ*)/DPhF(π/nb) → bncn(π*), shifts from 633 nm in 1 to 553 nm in 2, and the metal-to-ligand charge transfer (1MLCT) Rh2(π*) → bncn(π*) absorption in 3 appears at 462 nm in CH3CN. Although the 3ML-LCT excited state of 2 is shorter lived than that of 1, 2.7 ns as compared to 19 ns, respectively, photocatalytic hydrogen generation is observed for the former upon 595 nm irradiation in the presence of 0.1 M TsOH (p-tolylsulfonic acid) and 0.1 M BNAH (1-benzyl-1,4-dihydronicotinamide). The temperature dependence of the 3ML-LCT lifetimes of 1 and 2 shows the presence of a thermally accessible deactivating state. In addition, the singly reduced intermediate, [2]-, is photoactive and able to generate hydrogen in the presence of TsOH. Importantly, the electrocatalytic currents generated by equimolar concentrations of 1 - 3 in CH3CN are nearly identical, consistent with a mechanism of catalysis that is localized on the bncn ligand and does not require a Rh-H hydride intermediate. This finding can be used to develop earth-abundant first-row transition metal complexes for photo- and electrocatalytic H2 production.

BOIMPY Scaffold: Accessing Ultrahigh Molar Extinction Coefficient AIEgen for SWIR Imaging‐Guided Photothermal Cancer Ablation

AbstractDespite the extensive reporting of versatile aggregation‐induced emission luminogens (AIEgens), boosting their molar extinction coefficient (MEC, ε ≈ 103–104 M−1cm−1) remains a formidable challenge, which poses a significant obstacle to achieving the ceiling of their output performance. In this work, an “aggrandizing absorption reservoir” approach is proposed to designing AIEgens with remarkable photons‐harvesting ability, ultimately enlarging its output performance in terms of short‐wave infrared (SWIR, 900–1700 nm) emission and photothermal effect. For the first time, the (bis‐(borondifluoride)‐8‐imidazodipyrromethene) (BOIMPY) unit, which provides sufficient rigidity and strong electron‐withdrawing ability by employing benzimidazole as a bridging ligand binding two BF2 units, is utilized to fabricate novel AIEgen (TPEB) that exhibits an ultrahigh MEC up to 1.29 × 105 M−1 cm−1 at 828 nm. To the best of knowledge, this is the highest MEC reported among AIEgens with near‐infrared absorption. Thanks to its remarkable photon‐harvesting ability, TPEB exhibits strong fluorescence in the SWIR region and a good photothermal effect. The as‐prepared TPEB NPs are successfully applied for SWIR imaging‐guided photothermal antitumor therapy. The proposed “aggrandizing absorption reservoir” approach provides a novel guideline for designing versatile AIEgens for biomedical applications.

Structural Diversity and Dimensionality of Three Cu(II)-dpds-C5O5 2- Coordination Polymers Controlled by the Coordination Sphere of Cu(II) Centers and the Coordination Modes of C5O5 2- (dpds = 4,4'-Dipyridyldisulfide).

Three supramolecular architectures, [Cu2(dpds)2(C5O5)2(H2O)4]·3H2O (1), [Cu(dpds)(C5O5)]·3H2O (2), and [Cu2(dpds)2(C5O5)2]·9H2O·C2H5OH (3) (dpds = 4,4'-dipyridyldisulfide and C5O5 2- (croconate) = dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione), have been synthesized and structurally characterized. Compound 1 contains two crystallographically independent Cu(II) ions, which are both distorted octahedral geometry with elongation along the croconate- and H2O-bound axial positions and bonded with two N atoms of two dpds, two O atoms of one C5O5 2-, and two H2O molecules. Two crystallographically independent dpds ligands, both adopting the bis-monodentate bridging mode, connect two Cu(II) ions to form a one-dimensional zigzag chain-like coordination polymer. In 2 and 3, there are two and three crystallographically independent Cu(II) ions, respectively, which are all distorted octahedral geometries with elongation along the croconate-bound axial positions six-coordinated and bonded with two N atoms of two dpds ligands in cis- or/and trans-forms and four O atoms of two C5O5 2- ligands. The dpds ligands in 2 and 3 all adopt the bis-monodentate bridging mode, and the C5O5 2- ligands act as bridging ligands with bridging bis-bidentate through three C5O5 2- oxygen atoms in 2 and bridging bis-bidentate through four adjacent C5O5 2- oxygen atoms in 3, respectively, linking the Cu(II) ions to generate a two-dimensional layered and a three-dimensional metal-organic framework, respectively. The structural diversity and dimensionality observed in 1-3 may be attributed to the cis- or/and trans-coordination sphere of Cu(II) centers with two dpds ligands and the coordination modes of croconate ligands. Thermal stability and in situ temperature-dependent structural variations of 1-3 have been verified by thermogravimetric analysis and powder X-ray diffraction measurements. Compounds 1 and 3 both exhibit water vapor capture behaviors with hysteresis isotherms.