Structure of Co-crystals Formation from Imidazolium and Aromatic Ligands

In this study, two new co-crystals based on rigid imidazolium ligand （2,2＇-（（1,1’- biphenyl）-4,4＇-diyl）bis（2H-imidazo[1,5-a]pyridine-4-ium） hexafluorophosphate （L）） and 4,4＇- bipyridine （Bpy） and benzene （Ben）, formulated as L（Bpy）0.5 （co-crystal 1） and L（Ben） （co-crystal 2）, were obtained. Crystal data for 1： Pī space group with α = 10.921（4）, b = 16.998（6）, c = 17.666（6） A, α = 95.720（7）, β = 104.272（7）, γ = 93.340（6）°, V = 3150.5（19） A^3 and Z = 2; and crystal data for 2： monoclinic C2/m space group with α = 25.90（2）, b = 9.631（9）, c = 6.371（6） A, β = 95.26（2）°, V = 1583（2） A3 and Z = 2. Co-crystal 1 was dependent on hydrogen bonds and π···π stacking, while only hydrogen bonds are present in 2. Two new co-crystals were characterized by IR, NMR spectra, thermogravimetric and ultraviolet absorption analyses.

Two-dimensional Grid-type Zinc(Ⅱ) Coordination Polymer Constructed by a New Aromatic Carboxylate Ligand

A new aromatic carboxylate ligand,namely 5-（pyrrolidin-1-yl）-1,3-benzenedicar-boxylic acid（H2pybdc）,was synthesized and characterized by FT-IR and single-crystal X-ray diffraction analysis.It crystallizes in triclinic system,P1 space group with a = 10.05（5） ,b = 11.53（5）,c = 12.92（6） ,α = 112.11（6）°,β = 92.79（7）°,γ = 102.98（7）°,V = 1337.113,Z = 4,Mr = 253.25,Dc = 1.258 g.cm-3,μ = 0.099 mm-1,F（000） = 536,the final R = 0.0822 and wR = 0.2575 for 1893 observed reflections（I 2σ（I））.Based on it,a two-dimensional grid-type Zn（Ⅱ） coordina-tion polymer of {[Zn（pybdc）（bpy）（H2O）].2H2O.0.5CH3OH}n（1） was solvothermally synthesized,which crystallizes in triclinic,space group P1 with a = 10.218（5） ？,b = 11.176（5） ,c =11.350（5） ,α = 95.855（5）°,β = 94.248（5）°,γ = 101.421（5）°,V = 1257.9（2） 3,Z = 2,Mr = 524.84,Dc = 1.386 g.cm-3,μ = 1.024 mm-1,F（000） = 546,the final R = 0.0635 and wR = 0.1879 for 3913 observed reflections（I 2σ（I））.

The aromatic peptide protected gold nanoclusters with significant Stokes shift:Ligand-mediated two-step FRET

During the last decade,a great variety of ligand protected gold nanoclusters(AuNCs)have been synthesized,and their broad applications have been intensively reported.Although the spectroscopic properties of AuNCs have been comprehensively explored,the mechanism of the significant Stokes shift(>200 nm)and the specific role played by surface ligands have not been clearly explained yet.In this study,a series of fluorescent AuNCs with huge Stokes shift(up to 530 nm)were successfully prepared by employing the rationally designed tri-peptides as the protecting ligands,and their spectroscopic properties were systematically investigated.The detailed measurements on the example product,YCY-AuNCs(Tyr-Cys-Tyr liganded AuNCs),showed that the energy absorbed by the tyrosine(~250 nm)can be effectively transferred through the ligand-mediated two-step Förster resonance energy transfer(FRET)process and released as fluorescence emission in the near-infrared fluorescence(NIR)range(~780 nm),which resulted in the significant apparent Stokes shift.The YCY ligands play a critical role by offering the tyrosine groups(donor of the first FRET pair),generating the dityrosine-like structure on the AuNCs surface(acceptor of the first FRET pair and donor of the second FRET pair),and protecting the cores(acceptor of the second acceptor).The additional ligand exchange experiments and the investigation on the other AuNCs further demonstrated that the sufficient high density of the aromatic groups is also essential to mediate the two-step FRET and achieve the remarkable Stokes shift.We believe that the aromatic ligand-mediated FRET mechanism not only offers a new theoretical explanation for the huge Stokes shift exhibited in AuNCs,but also provides a general strategy for the construction of new materials with large Stokes shift.

Synthesis,Crystal Structure and Fluorescence of a Three-dimensional Cd(II) Coordination Polymer [Cd(μ_(1,3)- SCN^-)_2(μ-dmpo)]_n (dmpo = 3,5-Dimethylpyridine N-Oxide)

A three-dimensional complex [Cd（μ1,3-SCN）2（dmpo）]n has been synthesized with μ1,3-SCN^- and dmpo as mixed bridge ligands. The crystal belongs to monoclinic, space group C2/c with a = 15.648（2）, b = 15.126（2）, c = 11.9773（15） A, β= 112.416（2）°, V= 2620.7（6） ,A, Z= 8, C9H9CdN3OS2, Mr = 351.71, Dc = 1.783 g/cm^3, F（000） = 1376 and μ = 1.967 mm^-1. The structure was refined to R = 0.0260 and wR = 0.0647 for 2186 observed reflections （I 〉 2σ（I））. In the crystal the Cd（Ⅱ） ions are coordinated by ,μ1,3-SCN^- bridge ligands to form the crossing chains on the adjacent planes, and these chains are further joined by μ-dmpo mono-dentate bridge ligands leading to a three-dimensional structure. The complex exhibits strong fluorescent emission property.

Intramolecular stacking interaction in mixed-ligand complexes containing ATP4-and aromatic N-heterocyclic ligands

The stability constants of the binary ML2+ and ternary M(ATP)L2? complexes, where L=Iq (isoquinoline) or BIm (benzimidazole) and M=Zn2+ or Cd2+, have been determined by potentiometric pH titration in aqueous solution at I=0.1 mol/L (NaClO4), T=25°C. The stability of the ternary complexes characterized by ΔlogKM=logKM(ATP)LM(ATP)L- logKMML corresponding to the equilibrium M(ATP)2? + ML2+ = M(ATP)L2? + M2+ in higher than what would be expected on statistical grounds. The increase may be related to the stacking interaction between the aromatic ring of the ligands L and the purine moiety of ATP4–. 1H NMR studies of Zn2+/ATP4?/L confirm the presence of stacking in the ternary complexes. It is concluded that the strength of the intramolecular stacking interaction ia dependent on the structure of the aromatic ring of the ligand L and the formation of a metal ion bridge. Possible implications an discussed briefly.