Chen-Xia Du

Hypersensitive dual-function luminescence switching of a silver-chalcogenolate cluster-based metal–organic framework

Silver(i) chalcogenide/chalcogenolate clusters are promising photofunctional materials for sensing, optoelectronics and solar energy harvesting applications. However, their instability and poor room-temperature luminescent quantum yields have hampered more extensive study. Here, we graft such clusters to adaptable bridging ligands, enabling their interconnection and the formation of rigid metal-organic frameworks. By controlling the spatial separation and orientation of the clusters, they then exhibit enhanced stability (over one year) and quantum yield (12.1%). Ultrafast dual-function fluorescence switching (<1 s) is also achieved, with turn-off triggered by O2 and multicoloured turn-on by volatile organic compounds. Single-crystal X-ray diffraction of the inclusion materials, obtained by single-crystal-to-single-crystal transformation, enables precise determination of the position of the small molecules within the framework, elucidating the switching mechanism. The work enriches the cluster-based metal-organic framework portfolio, bridges the gap between silver chalcogenide/chalcogenolate clusters and metal-organic frameworks, and provides a foundation for further development of functional silver-cluster-based materials.

Studies on the cyclometallation of ferrocenylimines

Abstract This review describes the cyclometallation reaction, including cyclomercuration, cyclopalladation and cycloplatination of Schiff base type of ferrocenylimines as well as the transmetallation reaction of cyclometallated ferrocenylimines and the stereochemistry associated with these reactions. The applications of cyclopalladated ferrocenylimines in several fields are also demonstrated in this review. The molecular and crystal structures of the products as well as the absolute configurations of optically active products were established by X-ray diffraction, NMR techniques, IR, UV–vis, etc. The general features of these reactions, especially the regioselectivity and the reaction mechanisms, are discussed. In addition, the structure–property relationships are discussed throughout this investigation. The transmetallation of optically pure cyclometallated ferrocenylimines with other metals such as mercury, tin and tellurium was found to proceed with complete retention of stereochemistry. This discovery led to a convenient method for the synthesis of optically pure cyclometallated organic compounds that are difficult to prepare by using conventional methods. Accordingly, a number of cyclometallated ferrocenylimines have been prepared in optically pure forms, which display surprisingly high angles of rotation.

A series of novel metal-ferrocenedicarboxylate coordination polymers: crystal structures, magnetic and luminescence properties

Novel two-dimensional layered lanthanide(III)-ferrocenedicarboxylate coordination polymers {[M(η 2 -O 2 CFcCO 2 -η 2 )(μ 2 -η 2 -O 2 CFcCO 2 -η 2 -μ 2 ) 0.5 (H 2 O) 2 ]· m H 2 O} n (Fc=(η 5 -C 5 H 4 )Fe(η 5 -C 5 H 4 ), M=Tb 3+ , m =2, 1 ; M=Eu 3+ , m =2, 2 ; M=Y 3+ , m =1, 3 ) with trapezium-shaped units and one-dimensional wave-shaped Cd(II)-ferrocenedicarboxylate polymer {[Cd(η 2 -O 2 CFcCO 2 -η 2 )(H 2 O) 3 ]·4H 2 O} n ( 4 ) have been prepared and structurally characterized by single crystal diffraction. In polymers 1 – 3 , each central metal ion (Tb(III), or Eu(III) or Y(III)) is located in a pseudo-capped-tetragonal prism coordination geometry, and ferrocenedicarboxylate anion ligands have two coordination modes (bidentate-chelating mode and tridentate-bridging mode). The magnetic behaviors for 1 and 2 are studied in the temperature range of 5.0–300 K. The results show that the paramagnetic behavior of 2 is mainly due to the effective spin–orbital coupling between the ground and excited states through the Zeeman perturbation, and the weak magnetic interaction between Eu 3+ centers can be observed. In addition, compared with sodium ferrocenedicarboxylate, the fluorescent intensities of the polymers 1 – 4 are enhanced in the solid state.

Highly pH-dependent synthesis of two novel three-dimensional dysprosium complexes with interesting magnetic and luminescence properties

Two novel Dy-based MOFs, namely, {[Dy2(PA)3(H2O)3(DMF)]·(DMF)2·(H2O)}n (1) and [Dy2(PA)3(H2O)2(DMF)2]·(DMF)3·(H2O)}n (2) (H2PA = pamoic acid), were solvothermally synthesized from the reaction of Dy(NO3)3 and H2PA at different pH values. Interestingly, both complexes can be obtained simultaneously within the pH range of 5.0–6.2, while higher pH values (6.2–7.0) promote the formation of compound 1 and lower pH values (2.0–5.0) tend to produce pure complex 2. Single-crystal X-ray diffraction studies indicate that 1 and 2 are both three-dimensional frameworks composed of dinuclear Dy(III) subunits featuring pcu networks with the point symbol of {412·63}. Significantly, their slight structure difference results in these two compounds showing completely different magnetic properties. Variable temperature magnetization measurements (χMT–T) demonstrate ferromagnetic interactions in compound 1, while possible antiferromagnetic interactions were observed in compound 2. Alternating current (ac) susceptibility measurements indicate that both the in-phase (χ′) and out-of-phase (χ′′) components showed frequency dependence in compound 1, suggesting that there is a slow relaxation behavior of the magnetization, which is typical of single-molecule magnets (SMMs), while no out-of-phase ac signal was noticed for 2. Furthermore, both 1 and 2 exhibit the characteristic luminescence of Dy3+ upon excitation at 365 nm, but with different intensities. The reasons for such magnetic and luminescence differences are discussed in detail.

Hierarchical assembly of a homochiral triple concentric helical system in a novel 3D supramolecular metal-organic framework: synthesis, crystal structure, and SHG properties.

The hierarchical assembly of a homochiral triple concentric helical system in a novel 3D metal-organic framework with SHG activity has been observed. The result also provides a better understanding of host-guest chemistry and the process of water transport in biological systems.

Two series of pH-dependent lanthanide complexes showing solvent-induced single crystal to single crystal transformation, sorption and luminescence properties

Two series of new lanthanide coordination polymers have been obtained by solvothermal reaction of Ln(NO3)3 and pamoic acid under different pH values. Both series of compounds show three-dimensional porous frameworks composed of dinuclear Ln(III) subunits. Series B demonstrates fascinating solvent-induced dynamic behaviors in an SCSC (single crystal to single crystal) manner. The capability of activated series B to absorb liquid acetone was investigated by means of 1H NMR spectroscopy, demonstrating the potential of Ln-MOFs as highly efficient and reusable liquid acetone sorbents. In addition, photoluminescence properties of Nd (3), Eu (5) and Yb (10) were measured and discussed. Lanthanide contraction effect also played a crucial role in the formation of each series of complexes. Analysis of the relations between the ionic radius (Ln3+) and the number of f electrons in these complexes indicates that lanthanide contraction effect in both series can be well described by the Raymond model.

Addition reactions of bis(trimethylsilyl)methyl- and 1-azzallyl-lithium with cyanoamines into triazines or β-diketiminatolithium compounds

Abstract Reactions of bis(trimethylsilyl)methyl lithium reagent Li[CHR2] (R=SiMe3) and 1-azaallyllithium, [ LiN(R)C(Bu t )C HR]2 with cyanoamines R′CN (R′=Me2N, 1-piperidyl or o, p-pyridyl) yielded β-diketiminatolithiums (1, 2, 5, 7, 8) or symmetrically and mixed substituted triazines (3, 4, 6, 9, 10), respectively. The mechanistic pathways involve silicotropic rearrangements from C to N or N to N and an unusual elimination of Li[CHR2]. The complexes 1, 6, 7, and 10 had been characterized by X-Ray diffraction.

Systematic Study of the Luminescent Europium-Based Nonanuclear Clusters with Modified 2-Hydroxybenzophenone Ligands

The reaction of 2-hydroxybenzophenone derivatives with europium ions has afforded a new family of luminescent nonanuclear Eu(III) clusters. Crystal structure analysis of the clusters reveals that the metal core comprises two vertex-sharing square pyramidal units. Most of these complexes show emissions typical of Eu(3+) ion under visible light excitation (400-420 nm) at room temperature. Photophysical characterization and DFT study reveal a correlation between luminescent efficiencies of Eu(III) complexes and the electronic features of the ligands, which can be tuned by the nature of substituents in the 4-position of the ligands. The ligands with a fluorine substituent possess more suitable triplet energy levels, resulting in more intensive luminescence.

Effect of lanthanide contraction on crystal structures of Ln(III) coordination polymers with dinuclear SBUs based on 3-(4-hydroxypyridinium-1-yl) phthalic acid and oxalic acid

A series of lanthanide coordination polymers, {[Ln(L)(OX)0.5(H2O)2]·3H2O}n (Ln = La 1, and Ce 2), [Ln2(L)2(OX)(H2O)3]n (Ln = Pr 3, Nd 4, Sm 5, Eu 6, Gd 7, Tb 8, Dy 9, Er 10, and Yb 11) (H2L = (3-(4-hydroxypyridinium-1-yl) phthalic acid, H2OX = oxalic acid), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction. The title compounds are crystallized in the same triclinic space group P but display different 2D layer structures with different dinuclear secondary building units (SBUs) due to the effect of lanthanide contraction. Furthermore, X-ray diffraction and thermogravimetric analysis of 1–11 are also studied, which demonstrate their high purities and good thermal stabilities. Luminescent measurements indicate that the Eu (6), Tb (8), and Dy (9) compounds exhibit ligand (L2−) sensitized emissions in red, green, and yellow light regions, respectively.

Strong optical limiting (OL) capability of the two-dimensional network cluster polymer [MoS4Cu6I4(py)4]n

The two-dimensional network compound [MoS4Cu6I4(py)4]n is the first example of a cluster polymer showing very large optical limiting effects; its nonlinear absorptive index α2 and nonlinear refractive value n2 are 1.5 × 10–9 m W–1 and –2.5 × 10–17 m2 W–1, respectively, in 6.5 × 10–5 mol dm–3 DMSO solution; the optical limiting threshold was determined to be 0.6 J cm–2, which is about three times better than that of C60.