Jin-Ji Wu

Temperature-dependent supramolecular isomers of a tetranuclear macrocycle and a zigzag chain based on dicopper building blocks

Two new complexes [Cu4(2-OBPT)2(μ-OAc)4(μ-OH)2]·H2O (1) and [Cu2(2-OBPT)(μ-OAc)2(μ-OH)]·1.75H2O (2) (2-HOBPT = 4,6-bis(2-pyridyl)-1,3,5-triazin-2-ol) have been synthesized and characterized by single-crystal X-ray diffraction. Complex 1 is a tetranuclear macrocycle with a centrosymmetric space groupP, while complex 2 is a zigzag chain coordination polymer with a P21/c space group. They are supramolecular isomers based on the dicopper [Cu2(μ-OAc)2(μ-OH)] core and 2-OBPT ligand. Interestingly, each isomer can be afforded by control of the crystallization temperature. A mixture of complexes 1 and 2 were obtained in the range of 60–100 °C, while the unique 2 crystallized at 20 °C in a high yield of 82% and the sole 1 was afforded at 120 °C. Moreover, both the complexes are antiferromagnetic and the theoretical fit of the magnetic susceptibility data in the temperature range of 2–300 K gives J1/kB = −33.6(5) K, g = 2.26(1) for 1 and J1 = −29.1(6) K, g = 2.30(1) for 2.

Solvent-mediated crystal-to-crystal interconversion between discrete lanthanide complexes and one-dimensional coordination polymers and selective sensing for small molecules.

Two isostructural 1D coordination polymers {[Ln(OAc)2(H2O)(OBPT)]·3H2O}n (HOBPT = 4,6-bis(2-pyridyl)-1,3,5-triazin-2-ol, Ln = Eu(3+), 1; Tb(3+), 3) and two discrete complexes [Ln(OAc)2(DMF)2(OBPT)] (Ln = Eu(3+), 2; Tb(3+), 4) have been synthesized in H2O-MeOH or DMF solvents, respectively. Their structures were identified by powder X-ray diffraction. Single-crystal X-ray studies for complexes 1 and 2 revealed that the coordination geometries of the Eu(3+) ions are similar and can be described as a distorted tricapped trigonal prism with six oxygen atoms and three nitrogen atoms. The difference between them is that one aqua ligand and one oxygen atom from the OBPT ligand complete the coordination sphere in complex 1, whereas two DMF molecules complete the coordination sphere in complex 2. Interestingly, the solvent-mediated, reversible crystal-to-crystal transformation between them was achieved by immersing the crystalline samples in the corresponding solvent (H2O or DMF) or by exposing them to solvent vapor. Complex 1 shows a highly selective luminescence enhancement in response to DMF in comparison to that observed in response to other examined solvents such as acetone, ethyl acetate, ethanol, acetonitrile, methanol, and THF.

pH-Dependent formation of (6,3) and (10,3) hydrogen-bonded networks based on [Ru(H2biim)3]SO4: polymorphs and topological isomers

Two polymorphs formulated as [Ru(H2biim)3]SO4 (H2biim = 2,2′-biimidazole) have been solvothermally synthesized through changing the pH value of the reaction solution in an identical solvent at 120 °C. The α-[Ru(H2biim)3]SO4 (1) crystallizes in the monoclinic space groupP21/c with a = 8.1802(9) A, b = 21.293(2) A, c = 15.2116(14) A, β = 121.357(4)°, Z = 4. The β-[Ru(H2biim)3]SO4 (2) crystallizes in a chiral space groupI41 with a = 12.6267(10) A, c = 14.244(2) A, Z = 4. Complex 1 assembles into homochiral (Δ and Λ), (6,3) honeycomb two-dimensional layers, which further alternately stack in racemic, hydrogen-bonded networks, whereas 2 is a chiral, (10,3)-b 3-D network. Thus 1 and 2 are topological isomers. Importantly, their formations are much dependent on the pH value of the reaction solution. The data observed in this study seem to suggest that the diverse hydrogen bonding modes between the sulfate and H2biim ligand identified here play a crucial role in the formation of the polymorphs and topological isomers. The powder XRD patterns and infrared spectra also provide valuable information in the diagnosis of the polymorphs.

Spontaneous chiral resolution of mer-[CoII(N,N,O-L3)2] enantiomers mediated by π–π interactions

Six possible isomers of mer-[M(II)(N,N,O-L)(2)] complex were observed in the solid state, in which spontaneous resolution of S,S-Lambda and R,R-Delta enantiomers of mer-[Co(N,N,O-L3)(2)] was achieved via pi-pi interactions.

A nanocomposite gel based on 1D coordination polymers and nanoclusters reversibly gelate water upon heating

A stable nanocomposite metallogel was obtained by the addition of [Na(L)(H2O)]·2H2O (HL = 4,6-bis(2-pyridyl)-1,3,5-triazin-2-ol) to an aqueous solution of Cu2(OAc)4·2H2O in a molar ratio of Cu/L = 4 (5.6 wt% gelator concentration), from which 1D coordination polymers [Cu2L(μ-OAc)2(μ-OH)] (1) and coordination nanoclusters {[Cu9L4(OAc)7(OH)5]2+}2 (3) were afforded. The nanoclusters 3 stabilize the 1D coordination polymers 1 and inhibit crystallization of 1 from the system, generating a coordination-based heat-set nanocomposite hydrogel at room and higher temperatures that flows upon cooling to 4 °C, in sharp contrast to most supramolecular gels. Reversible thermo and pH responsive solution–gel phase transitions were observed. The results described herein may open a novel avenue for functional coordination nanocomposite materials.

Anion and pH induced spontaneous resolution of Δ- and Λ-[M(H2Biim)3]SO4 (M = Ru2+, Co2+, Ni2+, Mn2+, Fe2+, and Zn2+) enantiomers

The homochiral self-assembly of [M(H2biim)3]SO4 (M2+ = Ru, 1; Co, 2; Ni, 3; Mn, 4; Fe, 5; and Zn, 6; H2biim = 2,2′-biimidazole) complexes have been systematically observed. For complexes 1 and 2, the spontaneous resolution processes not only depend on the counter anion but are also impacted by the pH value of the reaction solution. The enantiomers Δ-1 and Λ-1, and Δ-2 and Λ-2 were isolated in acidic conditions, while rac-1 and rac-2·5H2O were obtained in neutral conditions, respectively. For complexes 3–6, however, the spontaneous resolution processes are independent on the pH value of the reaction solution. Single crystal X-ray diffraction analysis reveals the enantiomers Δ and Λ are homochiral (10,3)-b three-dimensional networks constructed by the hydrogen bonds between the sulfate and H2biim ligand, whereas rac-1 assembles into (6,3) two-dimensional layers (see CrystEngComm, 2009, 11, 1114–1121) and rac-2 into one-dimensional chains. The data observed here seem to suggest that the hydrogen bonding modes between the sulfate and H2biim ligand play a crucial role in spontaneous resolution of the enantiomers. Furthermore, the solid state CD spectra and powder XRD patterns were also used to diagnose the obtained complexes.

Liquid-assisted solid-state reaction: assembly of (6,3) and (10,3) hydrogen-bonded networks based on [M(Hbiim)3] by oxidation of [M(H2biim)3]2+ complexes in the presence of acetate anions

Two complexes [Ru(Hbiim)3] (1) and [Co(Hbiim)3]·3H2O (2) (H2biim = 2,2′-biimidazole) were synthesized quantitatively and rapidly via a “liquid-assisted” solid-state reaction approach. The reaction occurs within minutes of grinding together [Ru(H2biim)3](PF6)2 or [Co(H2biim)3]Cl2 and NH4OAc with a few drops of H2O2 as an oxidant and solvent, concomitant with colour changes. The structures of the compounds obtained from the solid-state reaction were confirmed by comparison of their PXRD patterns with simulations based on their single crystal structures. Complex 1 is a 3-fold interpenetrating three-dimensional hydrogen bonded polycatenate network based on a (6,3) net, complex 2 is a double-layer network linked by the lattice water molecules and the Hbiim ligands viahydrogen bonds. For comparison with the solid-state reaction, control reactions were also carried out in solution. Complex 1 was also afforded from the solution reaction. However, a new phase [Co(Hbiim)3]·0.5EtOH (3) was obtained from solution, rather than 2, although it also crystallized from an identical solution of EtOH–water. Complex 3 is a 4-fold interpenetrating three-dimensional hydrogen bonded polycatenate network based on a (10,3)-b net. Interesting, the [M(H2biim)3]2+ (M = Ru and Co) species can be oxidized to the corresponding [M(Hbiim)3] species by oxygen in the presence of acetate anions, which play a determined role in the redox reaction. The deprotonation of the [M(H2biim)3]2+ species triggered by the acetate anions greatly increases the electron density at the M(II) center and shifts the oxidation potentials of M(II) complex to a less positive value. This may provide an effective approach for the generation of high status metal complexes via supramolecular interactions.