Xiao-Lin Qi

Pore Surface Tailored SOD‐Type Metal‐Organic Zeolites

Natural and synthetic zeolites are important microporous materials. [ 1 ] The highly ordered structures and tunable compositions of aluminosilicate frameworks are responsible for their extraordinary performances. After the discovery of zeolitic metal imidazolate frameworks, ranging from zeolite-like cobalt imidazolates [ 2 ] to the SOD-, ANA-, and RHO-type (three-letter codes of zeolite topologies) zinc benziimidazolate [ 3 ] and 2-alkylimidazolates, [ 4 ] these novel porous coordination polymers (PCPs) have blossomed in the past few years. [ 5 ] The similarity of the bended exo-bidentate coordination mode of imidazolate with that of the O atom in aluminosilicates has been considered as a determinative construction principle ( Figure 1 ). The rich structure-directing role of imidazolate side groups provides an additional variable for enumeration of new zeolitic structures. [ 3–5 ] Nevertheless, there seems to be some inherent difference between the inorganic and metal-organic counterparts. For example, inorganic zeolites are negatively charged aluminosilicate frameworks and their pore surface property can be routinely tailored by adjusting the Al/Si ratio and/or cation exchange. In contrast, PCPs (including metal-organic zeolites) are well-known to be completely ordered materials. Among the large family of known metal-organic zeolites, SOD-[Zn(mim) 2 ] (Hmim = 2-methylimidazole [ 4 ] ) is noteworthy for its high porosity and exceptional stability. The synthesis, porous property, sorption mechanism, and application of MAF-4 (the metal azolate framework 4) have attracted much attention. [ 6 ] However, MAF-4 only adsorbs many important gases, such as H 2 , CO 2 , and C 2 H 2 weakly, due to the lack of a strong adsorption site on its pore surface. While new functionalities of MAF-4 are still emerging, efforts have been devoted to the structural modifi cation of this prototype framework. Because imidazolates are almost the shortest linkers in PCPs, variation of the metal ion and/or substituent groups on the imidazolate linker can largely alter porosity (size or volume), change the framework, [ 5e–h ] and even alter the whole network topology. Metal ion substitution can effectively change the pore surface properties of PCPs functionalized with coordinatively unsaturated metal centers. [ 7 ] However, the tetrahedral

A Noble-Metal-Free Porous Coordination Framework with Exceptional Sensing Efficiency for Oxygen**

Oxygen sensors have a wide range of applications in food science, environmental analysis, space research, biochemistry among others. Luminescence quenching is a fast, high sensitivity, and simple oxygen sensing mechanism. To serve as optical oxygen sensors, luminescent dyes must be dispersed in gas-permeable porous matrices. According to the Stem– Volmer equation describing bimolecular collision quenching, long luminescence lifetimes (> 100 ns) are prerequisite for efficient quenching by oxygen, considering that the permeability of oxygen (i.e., the product of diffusion coefficient and solubility) is relatively low in common porous substrates. Therefore, phosphorescent (originating from triplet excited states) coordination complexes of precious-metal ions, such as Pt, Pd, Ru, Au, Ir, Re, have been widely used as oxygensensing luminescent dyes. Porous coordination polymers (PCPs) are highly ordered and porous matrices of metal complexes, which should be ideal for luminescent sensors. Lin et al. demonstrated that the highly oxygen-sensitive phosphorescent complex [Ir(ppy)3] (Hppy= 2-phenylpyridine) can be used as metalloligands to construct the first oxygen-sensing PCPs. To date, only a few oxygen-sensing PCPs have been reported, which are all based on phosphorescent noble metal complexes. While the sensitivities of phosphorescent PCPs are still moderate (< 88% quenching at 1 bar O2 or I0/I100< 8.3), [7,8]

A flexible metal azolate framework with drastic luminescence response toward solvent vapors and carbon dioxide

1H-Imidazo[4,5-f][1,10]phenanthroline (Hip) can be deprotonated to bridge Zn(II) ions, giving a flexible porous metal azolate framework [Zn7(ip)12](OH)2 (MAF-34) which shows not only drastic structural and luminescent changes for different solvent vapors, but also strong adsorption and quantitative luminescence response for low-pressure CO2.

Two temperature-induced isomers of metal-carboxylate frameworks based on different linear trinuclear Co3(RCOO)8 clusters exhibiting different magnetic behaviours

A pair of structurally isomeric metal-carboxylate frameworks (MCFs) with an identical formula of [Me2NH2]2[Co3(1,4-bdc)4]·4DMF (1 and 2, Me2NH2 = protonated dimethylamine, 1,4-bdcH2 = 1,4-benzenedicarboxylic acid and DMF = N,N′-dimethylformamide) have been synthesized from identical reactants at 160 °C and room temperature, respectively. Although both compounds feature the same bcg net (a uninodal eight-connected net) based on the Co3(OOCR)8 clusters as eight-connected nodes, the isomers exhibit different magnetic behaviours, owing to the slight difference of linear Co3(OOCR)8 clusters.

Two new polar coordination polymers with diamond networks: interpenetration and thermal phase transition

Two new polar coordination polymers, [Cu(Hmpc)2] (1) and [Cu2(mpc)2(DMA)] (2), were synthesized by solvothermal reactions of a ligand 3,5-dimethyl-1H-pyrazole-4-carboxylic acid (H2mpc) with Cu(NO3)2. Single-crystal X-ray analysis reveals that 1 crystallizes in the orthorhombic, polar space group Fdd2. Each square-planar coordinated Cu2+ ion is linked to four adjacent Cu2+ ions by mono-deprotonated Hmpc− ligands, resulting in a severely distorted 4-connected diamond network, inside which the methyl groups of the ligands are densely packed. In 2, non-centrosymmetric binuclear Cu2+ units serve as 4-connecting nodes, forming a non-porous polar structure consisting of 2-fold-interpenetrated diamond networks. A thermal structural phase transition was detected in 2 at around 323 K. At 298 K, 2 crystallizes in the tetragonal chiral space group P41 (2α), with a = 10.9931 (6) A, c = 18.0850(9) A, and Z = 4, whereas at a higher temperature (438 K) it is transferred to the tetragonal non-centrosymmetric space group P42nm (2β), with a = 10.9857(5) A, c = 9.1031(9) A, and Z = 2. By repeating in situ single-crystal X-ray diffraction, this phase transition was found to be reversible between a non-twinning non-centrosymmetric crystal (2β) and a racemic-twinning chiral crystal (2α). The symmetry of the diamond network was increased from C1 to D2d in the heating process, so that two fold interpenetrated networks become strictly parallel along the c-axis at about 323 K, and the c-axis was halved in 2β. At the same time, 2-fold disordered coordinated DMA molecules in 2α were found to be 8-fold disordered in 2β. According to aizu notation, 2 can be classified as 4mmF4 species, which are potentially secondary ferroic.

Syntheses, structures and gas sorption properties of two coordination polymers with a unique type of supramolecular isomerism

The solvothermal reaction of a short bridging ligand 1H-pyrazole-4-carboxylic acid (H2pc) and Zn(NO3)2 in a mixed solvent containing N,N-dimethylacetamide (DMA) at 110 °C produced two genuine supramolecular isomers [Zn2(pc)2(DMA)] (1) and [Zn2(pc)2]·DMA (2). Single-crystal X-ray diffraction studies showed that 1 is a densely packed layered structure with DMA molecules coordinated on the layered surface, and 2 is a porous three-dimensional framework structure with DMA molecules filled inside the pore without coordination to any metal ion, which represents a rare case of coordination-sphere isomerism in coordination polymers. Removal of the coordinated DMA molecules in 1 occurs at high temperatures, accompanying the irreversible formation of an unidentified nonporous phase. On the other hand, the guest DMA molecules in 2 can be readily removed under mild conditions to give a new porous phase [Zn2(pc)2] (2′). Gas-sorption measurements of 2′ revealed that the framework has significant flexibility and selective CO2 adsorption at room temperature.