Zhi-Peng Zheng

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.

A series of lanthanide complexes based on pyridine-3,5-dicarboxylate and succinate ligands: syntheses, structures and properties

Two different types of microporous lanthanide metal–organic frameworks based on pyridine-3,5-dicarboxylic acid (H2pydc) and succinic acid (H2suc), namely [Ln(pydc)(suc)0.5·3H2O]·2H2O (type I) [Ln = Pr (1), Eu (2), Tb (3), Er (4)] and [Ln(pydc)(suc)0.5·2H2O]·2H2O (type II) [Ln = Yb (5) and Lu (6)], have been successfully synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction, infrared spectroscopy (IR), elemental analysis, thermogravimetric analyses (TGA) and powder X-ray diffraction (PXRD). Complexes 1–4 (type I structure) are isomorphous, crystallize in the monoclinic P21/c space group and present three-dimensional (3D) pillar-layered frameworks constructed from two-dimensional (2D) [Ln(pydc)]− layers and suc2− pillars with 1D rhombic channels. The isomorphous compounds 5–6 (type II structure) crystallize in the triclinic P space group and feature a 2D layer made up of 1D ladder-like [Ln(pydc)]− chains and suc2− connectors with the water molecules occupying the interlayer spaces. The results show that structural variation from I to II may be attributed to the lanthanide contraction effect. Furthermore, the sorption ability of compound 2 and the luminescence properties of compounds 2–3 are also investigated.

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.

Two Schiff base ligands for distinguishing ZnII/CdII sensing—effect of substituent on fluorescent sensing

Two Schiff base ligands (HL1, HL2) were conveniently synthesised by one-step condensation between pyridine 2-ylmethanamine and 3-ethoxy-2-hydroxybenzenaldhyde (for HL1) or salicylaldehyde (for HL2) as fluorescent sensors for distinguishing sensing of Zn2+ or Cd2+. Both of the two fluorescent sensors present very weak emission at 463 nm (for HL1) or 453 nm (for HL2). For HL1, upon addition of Zn2+, the fluorescence intensity of HL1 enhanced and gradually red shifted to 493 nm with a green emission while addition of Cd2+ only induced enhancement of fluorescent intensity at 463 nm. For HL2, only addition of Zn2+ induced enhancement of fluorescence intensity, presenting a high Zn2+/Cd2+ selectivity. A Zn2+-induced red shift in fluorescent spectra of HL1 could be attributed to twisted intramolecular charge transfer (TICT) from the interaction between the Zn2+ ion and in situ formed ligand L1′ with the twisted structure in compound 1, which is absent in compound 2. The Zn2+/Cd2+ selectivity of fluorescent response for HL2 correlates with the Cd–HL2 and Zn–HL2 coordination bond distances. Obviously, introduction of ethoxyl groups onto the benzene ring as an electron-donating group facilitates the Zn-induced in situ dimerization of HL1 into new ligand L1′ with a twisted molecular structure, further resulting in a red shift of the fluorescence spectra.

A series of temperature-dependent CdII-complexes containing an important family of N-rich heterocycles from in situ conversion of pyridine-type Schiff base

An efficient method for the synthesis of a wide variety of N-rich heterocycles has been systematically explored. The synthetic protocol involves a solvothermal in situ metal–ligand reaction of pyridine-type Schiff base N-(2-pyridylmethyl)-pyridine-2-carbaldimine (L) with Cd2+ ions, resulting in the efficient formation of nine temperature-dependent CdII-complexes 1–9 supported by six types of N-rich heterocycles L1–6. To the best of our knowledge, both the synthetic strategy with solvothermal in situ CdII-mediated Schiff base-conversion and N-rich heterocycle rings L1–2 as well as cis-L6 are reported for the first time. Meanwhile, plausible in situ formation mechanisms of L1–6 are also proposed.

Two samarium(III) complexes with tunable fluorescence from in situ reactions of 2-ethoxy-6-((pyridin-2-ylmethylimino)methyl)phenol with Sm3+ ion

Two samarium(III) complexes showing different luminescent intensity, namely Sm(HL1)2·NO3·2H2O (1) and [SmL2(C2H5OH)2·NO3]2 (2), were constructed via the solvothermal in situ lanthanide metal–ligand reactions of 2-ethoxy-6-((pyridin-2-ylmethylimino)-methyl)phenol (HL) from pyridin-2-ylmethanamine and 3-ethoxy-2-hydroxybenzaldehyde with Sm3+ ion at different temperatures, in which H2L1 resulted from C–C coupling dimerization of HL, while H2L2 from C–C coupling of HL and pyridin-2-ylmethanamine.

CCDC 1003837: Experimental Crystal Structure Determination

Related Article: Zhi-Peng Zheng, Qin Wei, Wen-Xia Yin, Lin-Tao Wan, Xia Huang, Ying Yu, Yue-Peng Cai|2015|RSC Advances|5|27682|doi:10.1039/C5RA00987A