Gas Adsorption of Mixed-Valence Trinuclear Oxothiomolybdenum Glycolates

Binuclear, tetranuclear and hexadecanuclear thio-oxomolybdenum(V/IV) glycolates with selective adsorptions of gases

By adjusting the pH values of the solutions, binuclear, tetranuclear and hexadecanuclear glycolato thio- and oxomolybdenum(V/IV) complexes [MoV2O₂(μ₂-O)(μ₂-S)(Hglyc)₂(Hpz)₂]·H₂O (1, H₂glyc = glycolic acid, Hpz = pyrazole), (Hdpa)[MoV2O₂(μ₂-S)₂(Hglyc)(glyc)(H₂O)] (2, dpa = 2,2'-dipyridylamine), (Hdpa)₄[MoV4O₄(μ₃-O)₂(μ₂-S)₂(glyc)₂(S₂O₃)₂] (3) and Na₂[MoIV4MoV12O₁₂(μ₂-O)₆(μ₂-OH)₂(μ₃-O)₁₂(glyc)₄(Hpz)₄(pz)₈]·28H₂O (4) have been obtained successfully. Here the glycolates existed in varying aggregates with different degrees of protonation and deprotonation in 1-4. The stable formations of 1 and 2 are attributed to strong hydrogen bonds formed between the molecules. In particular, the asymmetric unit in 2 is a tetramer linked by hydrogen bonding [2.574(9) Å] between α-hydroxy and α-alkoxy groups for further construction of unsaturated penta-coordination environments. Moreover, deprotonated glycolates act as bridging ligands to form tetra- and hexadecanuclear compounds 3 and 4, respectively. The smallest unit in 4 exhibits mixed valences of 4+ and 5+ simultaneously, where its gas adsorption experiments manifest that 4 is obviously beneficial for O₂ and CO₂ compared with no adsorption of N₂, CH₄ and H₂ at different pressures.

Chiral Supramolecular Microporous Thio-Oxomolybdenum(V) Tartrates for the Selective Adsorptions of Gases

Two pairs of enantiomerically pure hexanuclear and tetranuclear microporous molybdenum(V) d/l-tartrates, (H₂trz)₃[Mo₆O₆(μ₂-O)₃(μ₂-S)₃(d/l-Htart)₃(Htrz)₆]·8H₂O (abbreviated as d-1 and l-1; H₄tart = tartaric acid, Htrz = 1,2,4-triazole) and (H₂2-mim)₈[Mo₄O₄(μ₂-S)₄(d/l-tart)₂]₂·4H₂O (d-2/l-2; H2-mim = 2-methylimidazole), have been isolated in reduced media and well characterized. These enantiomers are observed to finish self-assemblies with single chiral configurations. Structural analyses indicate that tartrates adopt different coordination modes with α-carboxy and/or α-alkoxy groups in 1 and 2, which are further completed with nitrogen-containing ligands. There are two types of micropores that exist in 1 and 2, separately, which are all formed by the isolated molecules themselves. The significant roles of hydrogen bonding among lattice molecules, tartrates, and multi-azoles are suggested, where 1 and 2 exhibited interesting supramolecular networks only through intramolecular self-sorts. Adsorption tests show that 1 has good affinities toward CO₂ and O₂, while 2 is the most potential O₂ adsorbent compared with other common gases CO₂, H₂, CH₄, and N₂ under different pressures. In addition, IR, UV-vis, CD (circular dichroism), and solid-state ¹³C NMR spectroscopies have demonstrated the special chemical properties of these novel molybdenum d/l-tartrates.

Fluorescent Zn(II)-Based Metal-Organic Framework: Interaction with Organic Solvents and CO2 and Methane Capture

Adsorption of carbon dioxide (CO₂), as well as many other kinds of small molecules, is of importance for industrial and sensing applications. Metal-organic framework (MOF)-based adsorbents are spotlighted for such applications. An essential for MOF adsorbent application is a simple and easy fabrication process, preferably from a cheap, sustainable, and environmentally friendly ligand. Herein, we fabricated a novel structural, thermally stable MOF with fluorescence properties, namely Zn [5-oxo-2,3-dihydro-5H-[1,3]-thiazolo [3,2-a]pyridine-3,7-dicarboxylic acid (TPDCA)] • dimethylformamide (DMF) •0.25 H₂O (coded as QUF-001 MOF), in solvothermal conditions by using zinc nitrate as a source of metal ion and TPDCA as a ligand easy accessible from citric acid and cysteine. Single crystal X-ray diffraction analysis and microscopic examination revealed the two-dimensional character of the formed MOF. Upon treatment of QUF-001 with organic solvents (such as methanol, isopropanol, chloroform, dimethylformamide, tetrahydrofuran, hexane), interactions were observed and changes in fluorescence maxima as well as in the powder diffraction patterns were noticed, indicating the inclusion and intercalation of the solvents into the interlamellar space of the crystal structure of QUF-001. Furthermore, CO₂ and CH₄ molecule sorption properties for QUF-001 reached up to 1.6 mmol/g and 8.1 mmol/g, respectively, at 298 K and a pressure of 50 bars.

Spontaneous conversions of glutamine, histidine and arginine into α-hydroxycarboxylates with NH4VO3 or V2O5

Glutamine gets transformed to 2-hydroxy-5-oxoproline with NH₄VO₃ in a neutral solution as a product of 2,2'-bipyridine oxidovanadium(v) 2-hydroxy-5-oxoproline [V^V₂O₃(hop)₂(bpy)₂]·7H₂O [1, H₂hop = 2-hydroxy-5-oxoproline] with yields of 65.6%. Similarly, histidine and arginine are converted into the corresponding α-hydroxycarboxylates as 2,2'-bipyridine oxidovanadium(iv) 3-(1H-imidazolyl-5-yl)-2-hydroxyacrylate [V^IV₂O₂(imha)₂(bpy)₂]·bpy [2, H₂imha = 3-(1H-imidazolyl-5-yl)-2-hydroxyacrylic acid] and guanidinium oxidovanadium(v) 1-(aminoiminomethyl)-2-hydroxyproline (CN₃H₆)[V^VO₂(Haimhp)₂]·2H₂O [3, H₂aimhp = 1-(aminoiminomethyl)-2-hydroxyproline] with V₂O₅ in low yields respectively, where an aggregate of oxidovanadium(v) arginine (H₂arg)_n(V^VO₃)_n·½nH₂O (4, Harg = arginine) has been isolated preferentially in an initial experiment for 3. α-Hydroxycarboxylates chelate bidentately with vanadium viaα-alkoxy and α-carboxy groups in 1-3, as observed from structural analyses. Their racemizations have been observed after the conversions. There is no coordination in 4 based on solid-state ¹³C NMR spectra, and only strong hydrogen bonds exist in the anion chains (V^VO₃)^- and protonated arginines. 1 and 4 were fully characterized by elemental analysis, UV-vis, IR and solid-state ¹³C NMR spectroscopies, TG and X-ray structural analyses, and theoretical bond valence calculations (BVS). The conversions of glutamine, histidine and arginine occur spontaneously in a solution under ambient conditions.