Inorganic Chemistry最新文献

With their rigid and preorganized skeleton, bispidine (3,7-diazabicyclo[3.3.1]nonane) chelators are very appealing for the preparation of metal complexes with high kinetic inertness. With the aim to develop new Tb(III)-based medical imaging probes, this study describes the synthesis and physicochemical properties of two novel terbium(III) complexes with octadentate bispidine-based ligands substituted with either pyridine-phosphonate (H₆L¹) or picolinate (H₄L²) subunits. Thermodynamic stability constants of the corresponding Tb(III) complexes have been determined by potentiometric, UV-visible absorption spectrophotometric and spectrofluorimetric methods. Despite their apparent similarity, these two octadentate ligands differ in their most stable conformation: chair-chair conformation for H₄L² and boat-chair conformation for H₆L¹, as confirmed by ¹H NMR studies and suggested by physicochemical investigations. This conformational change induces different protonation schemes for the two ligands. The kinetic inertness of the Tb complexes has been studied in various media and assessed by transmetalation and transchelation experiments. In particular, Tb(L²) displayed a remarkable kinetic inertness with no measurable dissociation over two months in mouse serum at 10^-5 M concentration. The complex was also very inert in the presence of a 50-fold excess of Zn(II) in H₂O at pH = 7.4 (7% of dissociation over two months). The complexes with ligand L¹ are significantly less inert, emphasizing the influence of the ligand conformation on the kinetic inertness of the Ln(III) complexes. Finally, the luminescence properties of the isolated complexes have also been investigated. A bright green luminescence was observed, especially for Tb(L²), which displays a high quantum yield value of 50% in H₂O (60% in D₂O; λ_exc = 263 nm). In addition, luminescence lifetimes of 1.9(2) and 1.7(2) ms have been measured for Tb(L¹) and Tb(L²), respectively, hence confirming the formation of nona-coordinated complexes with one inner-sphere water molecule. These data on a bispidine scaffold pave the way for developing bright, inert luminescent probes for bioimaging and for radiolabeling applications with Tb(III) radioisotopes.

The photosynthesis of hydrogen peroxide (H₂O₂), involving water oxidation and oxygen reduction, is crucial for optimizing light utilization. Here, a previously synthesized one-dimensional chain-like semiconductive uranyl coordination polymer (NDC-UCP) was used for the efficient overall photosynthetic reaction of H₂O₂ and its photocatalytic mechanism was systematically investigated. The excellent stability of NDC-UCP enables continuous H₂O₂ production for up to 96 h. Its unique hydrogen extraction capability enhances the photocatalytic performance, achieving a H₂O₂ production rate of 283.80 μmol g^-1 h^-1. Two mechanisms for H₂O₂ generation were revealed: efficient electron-hole separation in NDC-UCP facilitates a two-step one-electron oxygen reduction and direct water oxidation, while hydrogen abstraction of UO₂²⁺ generates hydroxyl (·OH) and hydroperoxyl radicals (HO₂^·), enhancing H₂O₂ photosynthesis. This study highlights the potential of uranyl coordination polymers in H₂O₂ production and their synergistic exciton dissociation and hydrogen abstraction functionalities in photocatalytic redox reactions.

There has long been a pursuit for a metal-organic framework (MOF)-based adsorbent for various hydrocarbon separations. Herein, we utilized simple trimesic acid and 1,2,4-triazole, together with the heterometallic strategy to produce two quaternary MOFs with a kgm-type structure. The cooperative coordination allows the immobilization of metal clusters into the pore channels, creating an appropriate pore size and high density of open metal sites. The resulting material shows excellent C₂H₂/CO₂ separation performance with good stability.

The ring-opening copolymerization (ROCOP) of epoxides with CO₂ or anhydrides is a promising strategy to produce sustainable polycarbonates and polyesters. Currently, most catalysts are reliant on scarce and expensive cobalt as the active center, while more abundant aluminum and iron catalysts often suffer from lower activities. Here, two novel heterodinuclear catalysts, featuring abundant Al(III), Fe(III), and K(I) active centers, are synthesized, and their performance in the polymerization of four different monomer combinations is compared to that of their Co(III) analogue. The novel Al(III)K(I) catalyst exhibits outstanding activities in the cyclohexane oxide (CHO)/CO₂ ROCOP, and at 1 bar CO₂ pressure it is the fastest aluminum-based catalyst reported to date. The M(III) site electronics for all three catalysts, Al(III)K(I), Fe(III)K(I), and Co(III)K(I), are measured using IR and NMR spectroscopy, cyclic voltammetry, and single crystal X-ray diffraction. A correlation between M(III) electron density and catalytic activity is revealed and, based on the established structure-activity relationship, recommendations for the future catalyst design of abundant Al(III)- and Fe(III)-based catalysts are made. The catalytic performances of both Al(III)K(I) and Fe(III)K(I) are further contextualized against the relative elemental abundance and cost. On the balance of performance, abundance, and cost, the Al(III)K(I) complex is the better catalyst for the carbon dioxide/epoxide ROCOP, while Fe(III)K(I) is preferable for anhydride/epoxide ROCOP.

Realizing ratiometric thermometers using single-component organic solid-state luminophores is attractive but challenging. Here, we synthesized a series of N,C-chelated tetra-coordinated organoboron compounds and characterized their structures. Among them, sample BN2Br can be used as a luminescent thermometer and exhibits a high temperature sensitivity (3.67% K^-1), a wide response range of 120-280 K, and good reversibility, which is mainly due to the temperature-dependent intermolecular stacking effect in the solid state. The proposed ratiometric thermometry protocol may provide new insights for developing photonic thermometers.

A methodology to access Z-1-silyl-2-aluminyl-disubstituted olefins is developed. It relies on the uncatalyzed ring opening of silacyclopropenes in the presence of a stoichiometric amount of trimethylaluminum. The resulting heterosubstituted alkenes exhibit a particular interaction between the electron-rich [Si-CH₃] moiety and the electron-deficient diorganoaluminyl group, resulting in similar geometrical features due to the proximity of these two centers. This interaction is rationalized using experimental and theoretical descriptors. The regioselectivity and functional tolerance of the methylalumination were also studied in the case of unsymmetrical silacyclopropenes, and the methodology ultimately transposed to the synthesis of a polymeric organoalane incorporating tricoordinated aluminum centers.

A novel heterometallic trinuclear cluster [Cu^II₂Mn^II(cpdp)(NO₃)₂(Cl)] (1) has been designed and synthesized by employing a molecular library approach that uses CuCl₂·2H₂O and Mn(NO₃)₂·4H₂O as inorganic metal salts and H₃cpdp as a multifunctional organic scaffold (H₃cpdp = N,N'-bis[2-carboxybenzomethyl]-N,N'-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol). This heterometallic cluster has emerged as an unusual ferromagnetic material and promising electrocatalyst for hydrogen evolution reaction (HER) in the domain of inorganic and materials chemistry. Crystal structure analysis establishes the structural arrangement of 1, revealing a butterfly-like topology with an unusual seven-coordinated Mn(II) center. Formation of this cluster is accomplished by a self-assembly process through functionalization of 1 with one μ₂:η¹:η¹-nitrate and two μ₂:η²:η¹-benzoate groups via the Cu^II(μ₂-NO₃)Cu^II} and {Cu^II(μ₂-O₂CC₆H₅)Mn^II} linkages, respectively. Variable-temperature SQUID magnetometry revealed the coexistence of ferromagnetic and antiferromagnetic interactions in 1. The observed magnetic behavior in 1 is unexpected because of a large Cu-O-Mn angle with a value of 132.05°, indicating that the correlation between coupling constants and the structural parameters is a multifactor problem. This cluster shows excellent electrocatalytic performance for the HER attaining a current density of 10 mA/cm² with a Tafel slope of 183 mV dec^-1 at a 310 mV overpotential value. Essentially, cluster 1 shows exceptional electrochemical stability at ambient temperature, accompanied by minimal degradation of the current density as examined by chronoamperometric studies. Density functional theory calculations establish the mechanistic insight into the HER process, indicating that the Cu^II-OCO-Mn^II site is the active site for formation of molecular hydrogen.

Catalytic applications of DNA duplexes containing Ag⁺-mediated cytosine-cytosine base pairs (C-Ag⁺-C) have not been well investigated. In this study, we demonstrate a novel approach for forming highly active DNA-capped Ag nanoparticle (DNA-AgNP) catalysts for the reduction of 4-nitrophenol (4-NP) using sodium borohydride (NaBH₄). This approach is based on the in situ generation of DNA-AgNPs from DNA duplexes containing C-Ag⁺-C (DNA duplex-Ag⁺). UV-vis spectroscopic analysis suggests that the DNA duplex-Ag⁺ complex acts as an excellent catalyst precursor for 4-NP reduction with NaBH₄. Transmission electron microscopy observations of the reaction solution after the 4-NP reduction reaction using DNA duplex-Ag⁺ provided detailed experimental insights into the mechanism of the catalytic activity of DNA duplex-Ag⁺ for 4-NP reduction. In the reaction solution, DNA-AgNPs were initially formed (DNA duplex-Ag⁺ + NaBH₄ → DNA-AgNPs) and then served as water-soluble catalysts for 4-NP reduction. Notably, the catalytic properties of the DNA-AgNPs generated in situ were affected by the DNA strand length and sequence. The properties of DNA duplex-Ag⁺ may provide a new application of DNA molecules containing metallobase pairs as water-soluble catalyst precursors.

Methane-propane coaromatization (MPCA) upgrades two abundant and inexpensive light alkanes into value-added aromatic products. While Ga-loaded MFI zeolites represent by far the most promising catalysts for MPCA reaction, they often contain a sizable portion of Ga species at the external surface of zeolites, which are remote from the Brønsted acid sites (BAS) within MFI pores and thus inefficient for MPCA. Here, we show that Ga can be introduced into MFI pores at fairly high loadings via a simple cocrystallization approach, yielding catalysts possessing well-dispersed Ga sites predominantly residing inside the pores and framework. Adjacency between Ga and BAS within the constraints of MFI channels makes these (Ga, Al)-H-MFI catalysts more active toward methane and propane activation and more selective toward aromatics compared to the Ga/MFI counterparts prepared by impregnation that inevitably leaves a large fraction of Ga at the external surface (i.e., without confinement and few adjacent BAS). Further, the effects of the Si/Al ratio on MPCA performance have been investigated for (Ga, Al)-H-MFI catalysts. Due to the multifold roles of BAS in the overall reaction sequence, an increased BAS concentration generally results in higher propane conversion and productivity of aromatics together with lower net methane conversion and severer coking.