Qing-Guang Zhan

Metal-directed assembly of two 2-D 4d–4f coordination polymers based on elliptical triple-deck cylinders hinged by meso-double helical chains

Two 2-D 4d–4f coordination polymers based on elliptical triple-deck cylinders hinged by meso-helical chains containing an isonicotinate ligand, namely, {[Ag2Ln(IN)4(H2O)2]·(NO3)·(H2O)}n (Ln = Sm and Eu, IN− = isonicotinate), have been successfully constructed through the transformation of a single-crystal to single-crystal (SC-SC) or different metal–organic polymer units, in which the recognition between the organic ligand and two types of metal ions direct the formation of the final productions.

Temperature-/solvent-dependent low-dimensional compounds based on quinoline-2,3-dicarboxylic acid: structures and fluorescent properties.

A series of 0-D, 1-D, and 2-D metal-organic compounds through reactions of quinoline-2,3-dicarboxylic acid (2,3-H(2)qldc) with transition metal salts MCl(2), namely, M(2,3-Hqldc)(2)(H(2)O)(2) (M = Co(1), Zn(4) and Cd(7)), [M(3-qlc)(2)(H(2)O)(2)](n) (M = Co(2), Zn(5) and Cd(8)), M(2-qldc-3-OCH(3))(2)(CH(3)OH)(2) (M = Co(3) and Zn(6)) and [Cd(2,3-qldc-OCH(3))(μ(2)-Cl)](2n) (9) (where, 3-Hqlc = quinoline-3-carboxylic acid and 2-qldc-3-OCH(3) = 3-(methoxycarbonyl)quinoline-2-carboxylic acid), were synthesized and characterized by elemental analysis, IR, thermogravimetric analysis (TG), and single-crystal X-ray diffraction. When the temperature ranged from room temperature to 70 °C, three isomorphous mononuclear complexes 1, 4 and 7 were obtained in H(2)O/H(2)O + CH(3)OH. As the temperature rose further to above 90 °C, due to the decomposition of 2-position carboxyl group in ligand 2,3-H(2)qldc, the same reactions, respectively, produced three isomorphous 2-D layer-like structures 2, 5 and 8 with 4(4) topology in water. By contrast, when the mixed solvent of H(2)O + CH(3)OH at a 1 : 1 ratio (v/v) was applied, the three above-mentioned reactions respectively gave compounds 3, 6 and 9 with the 3-position esterification of 2,3-H(2)qldc. Compounds 3 and 6 are mononuclear and isomorphous, while complex 9 has a 1-D double-stranded chain-like structure connected by two μ(2)-Cl bridges. Obviously, these results reveal that the reaction temperature and solvent play a critical role in structural direction of these low-dimensional compounds. Meanwhile, the photoluminescent property of the selected compounds is also investigated.

Syntheses and conversions of dinuclear cadmium(II) compounds containing N2O/N2O2 donor tridentate/tetradentate asymmetrical Schiff base ligands

Through different synthetic strategies, four dinuclear cadmium(II) complexes containing N2O/N2O2 donor tridentate/tetradentate asymmetrical Schiff base ligands have been synthesized and characterized. The two complexes [Cd(L1)(μ2-Cl)(CH3OH)]2 (1) and [Cd(L2)Cl]2·CH3OH (2) are constructed, respectively, from self-assembly of a Cd2+ ion with two asymmetrical Schiff base ligands, namely 2-((2-(dimethylamino)ethylimino)methyl)phenol (HL1) and 2-((2-(dimethylamino)ethylimino)methyl)-6-methoxyphenol (HL2). However, via single-crystal to single-crystal structural transformations driven by temperature, the other two corresponding compounds [Cd(L1)Cl]2 (1a) (1 → 1a) and [Cd(L2)Cl]2 (2a) (2 → 2a), with N2O2Cl and N2O3Cl donors, respectively, can be obtained. Obviously, the synthetic strategies presented in the text provide very effective methods for constructing the dinuclear CdII compounds with N2O/N2O2 donor tridentate/tetradentate asymmetrical Schiff base ligands. Meanwhile, the strong fluorescence emission of 1 and 2 makes them potentially useful photoactive materials.

Construction of three pH-dependent luminescent metal–organic frameworks with 3-(4-carboxyphen-yl)-1,3-benzoimidazole

Three luminescent metal–organic frameworks (MOFs) with 3-(4-carboxyphenyl)-1,3-benzoimidazole (HCPBm), named [Er(CPBm)3]n (1), [Zn(CPBm)2]n (2) and {Zn[Er(CPBm)(OH)(H2O)4]4·(ClO4)4·Cl2}n (3), have been synthesized using zinc(II) chloride, erbium(III) perchlorate and the ligand HCPBm under different pH conditions. Complex 1 obtained at pH = 5.5 exhibits a 1-D chain structure based on Er(III). At pH = 7.0, a 2-D Zn(II)-based layer 2 forms. The reaction at pH = 8.5 leads to a 2-D heteronuclear square grid layer 3 with a rare stacking fashion of ⋯ABCD⋯ in a 3-D supramolecular network. Compound 1 shows typical lanthanide Er(III) near-infrared emission, and compound 2 has strong fluorescent emission based on the ligand HCPBm. However, compound 3 presents sensitized near-infrared emission (λmax = 1500 nm) upon excitation of the Zn(II) unit in the visible region (400 nm) due to efficient energy transfer from the Zn(II) ion to the Er(III) units.

Anion-Dependent Assembly of Four Sensitized Near-Infrared Luminescent Heteronuclear ZnII–YbIII Schiff Base Complexes from a Trinuclear ZnII Complex

Four anion-dependent 0D Zn(II)-Yb(III) heterometallic Schiff base complexes, [YbZn2L2(OAc)4]·ClO4 (2), YbZnL2(NO3)3 (3), [(YbL)2(H2O)Cl(OAc)]2·[ZnCl4]2 (4), and YbZnL(OAc)4 (5), were assembled through central metal substitution or reconstruction from homotrinuclear Zn(II) complex {[(Zn(OAc)(H2O)L]2Zn}(ClO4)2·4H2O [1; HL = 2-ethoxy-6-[(pyridin-2-ylmethylimino)methyl]phenol] with different Yb(III)X3 salts [X = ClO4 (2), NO3 (3), Cl (4), and OAc (5)], in which the Zn(II)-sensitized near-infrared luminescent performances in the four complexes 2-5 are closely related to their structural models.

Single-crystal to single-crystal transformation from a 1-D chain-like structure to a 2-D coordination polymer on heating

The temperature-driven single-crystal to single-crystal transformation of a new erbium(III) coordination polymer with the ligand benzimidazole-5,6-dicarboxylic acid (H2bidc), {[Er(bidc)(ClO4)((H2O)3]·3H2O}n (1) to [Er(bidc)(ClO4)]n (2), has been reported and the structures of 1 and 2 were determined by X-ray crystallography. The thermal stability of compounds 1 and 2 were studied by thermogravimetric analysis (TGA). Powder X-ray diffraction experiments showed that the phase transitions described for single crystals also occur in the macroscopic powder samples and lead to monophasic products. Interestingly, with the loss of water molecules, the near infrared (NIR) emission of the Er(III) ion in compound 2 can be obviously enhanced compared to that in 1, which provides an effective strategy for enhancing the near infrared luminescence of lanthanide complexes.