Xiang-Guang Guo

Stoichiometry, temperature, solvent, metal-directed syntheses of metal–organic frameworks based on flexible V-shaped methylenebis(3,5-dimethylpyrazole) and various aromatic dicarboxylate acids

Seven new metal–organic frameworks (MOFs), namely, {[Cd2(NDC)2(H2MDP)](H2O)} (1), [Cd(NDC)(H2MDP)] (2), {[Cd2(NDC)(HNDC)2(H2MDP)2](H2O)0.5} (3), [Cd(NH2–BDC)(H2MDP)2] (4), [Cd(NH2–BDC)(H2MDP)2] (5), [Cd(H2MDP)(Br–BDC)0.5(Br–HBDC)] (6), {[Co(H2MDP)(Br–BDC)](H2O)0.5} (7) (H2MDP = methylenebis(3,5-dimethylpyrazole), H2NDC = 1,4-naphthalenedicarboxylic acid, NH2–H2BDC = 2-amino-1,4-benzenedicarboxylic acid, Br–H2BDC = 2,5-dibromo-1,4-benzenedicarboxylic acid) have been controllably synthesized with H2MDP and different aromatic dicarboxylic acids by tuning metal-to-ligand molar ratios, temperature, solvents and metal ions. Compound 1 is a 3D 2-fold interpenetrated pcu framework of 412·63 topology constructed from paddle-wheel SBUs and trans-conformation H2MDP pillars, while compound 2 exhibits a 3D 3-fold interpenetrated diamondoid framework formed by single metal nodes via linear NDC2− and trans-conformation H2MDP ligands. Interestingly, compound 3 contains two different types of binuclear subunits formed by a pair of Cd(II) ions with partly deprotonated HNDC− ligands, and these subunits are further linked by completely deprotonated NDC2− and cis-conformation H2MDP ligands to form a 2D (4,4) network. Compounds 4 and 5 are solvent-induced structural isomers based on 2D (4,4) layers, and therefore have different solvent-accessible voids. Compounds 6 and 7, synthesized with different metal salts under similar solvothermal conditions, are characteristic of a 3D hydrogen-bonded supramolecular network, and a 3D 3-fold interpenetrated diamondoid network with equal number of left- and right-handed helical {Cd(H2MDP)}n chains further bridged together by linear Br–BDC2− ligands, respectively. In addition, the luminescent properties of solids 1–6 have been investigated at room temperature.

Auxiliary ligand-directed synthesis of a series of Cd(II)/Co(II) coordination polymers with methylenebis(3,5-dimethylpyrazole): syntheses, crystal structures, and properties

Using a flexible methylenebis(3,5-dimethylpyrazole) ligand (H2MDP) with different aromatic carboxylate ligands, six new complexes {[Cd(H2MDP)(OPh)](H2O)}n (1), {[Cd(H2MDP)(MPh)](H2O)(1/10)}n (2), {[Cd(H2MDP)(PPh)](H2O)(3/2)}n (3), {[Co(H2MDP)(OPh)](H2O)2}n (4), {Co(H2MDP)(MPh)}n (5), {Co(H2MDP)(HBTC)}n (6) (H2OPh = phthalic acid, H2MPh = isophthalic acid, H2PPh = terephthalic acid, H3BTC = benzene-1,3,5-tricarboxylic acid) have been isolated under hydrothermal conditions. The crystal structure analyses reveal that complexes 1 and 4 feature two-dimensional undulated sheets with 4(4)·6(2) topology. Both complexes 2 and 3 contain M2L2-type metallocyclic motifs composed of two H2MDP ligands and two metal atoms, while complex 2 features a two-dimensional 4(4)·6(2) network constructed from binuclear cadmium units as four connected nodes, and complex 3 shows a two-dimensional network with 6(3)-hcb topology. Complex 5 affords a one-dimensional chain structure, and complex 6 shows a two-dimensional (4,4) network further connected into a 3D supramolecular structure connected by intermolecular hydrogen bonds and by π-π interactions. In addition, the luminescent properties of complexes 2 and 3 as well as the magnetic properties of 4 and 5 were studied.

Enantioselective inclusion of alcohols by solvent-controlled assembled flexible metal-organic frameworks.

Through judicious choice of the ligands and patient regulation of the solvent conditions, three unique chiral coordination polymeric isomers have been synthesized. Their structures, gas adsorption, and structural interconversion have been studied. One of the isomers displays dynamic behavior, and its use in the enantioselective separation of chiral alcohols has also been reported.

Construction of coordination polymers based on methylenebis(3,5-dimethylpyrazole) and varied aromatic carboxylic acids

Six new coordination polymers, namely, [Co(Cl-BDC)(H2MDP)]·0.5H2O (1), [Cd(Cl-BDC)(H2MDP)] (2), [Cd(OH-ip)(H2MDP)2]·H2O (3), [Mn(NO2-ip)(H2MDP)(H2O)] (4), [Cu(BTEC)1/2(H2MDP)] (5), and [Co(BTEC)1/2(H2MDP)]·H2O (6) (H2MDP = methylenebis(3,5-dimethylpyrazole), Cl-H2BDC = 2,5-dichloroterephthalic acid, OH-H2ip = 5-hydroxy-1,3-benzenedicarboxylic acid, NO2-H2ip = 5-nitro-1,3-benzenedicarboxylic acid, H4BTEC = 1,2,4,5-benzenetetracarboxylic acid) have been hydrothermally synthesized by using H2MDP as the main ligand and varying aromatic acids as auxiliary ligands, and characterized by single-crystal X-ray structure determination, FT-IR, elemental analysis, and powder X-ray diffraction. It was found that in complexes 2, 3, 4, and 6 the H2MDP ligands adopt a cis-conformation and tend to form M2L2-type metallocyclic units (SBU-1). These metallocyclic units further serve as linkers to connect the {metal–aromatic carboxylate}n chains to form two-dimensional frameworks with different structural features and topologies, i.e. 2D 63-hcb network for 2, (4,4) net for 3, undulated 63-hcb layered framework for 4, and dual (3,4)-connected net for 6 with point (Schlafli) symbol of (4·62)2(42·62·82). In complexes 1 and 5, the H2MDP ligands adopt a trans-conformation, and tend to link {metal–aromatic carboxylate}n chains into a higher dimensional framework, i.e. 3D triply interpenetrated dia network for 1 and dual (4,4)-connected double-layered structure for 5 with point (Schlafli) symbol of (54·62)(55·81)2. Moreover, the magnetic properties of complexes 1 and 6, and photoluminescent properties of 3 have also been investigated.

Postsynthesis Modification of a Metallosalen-Containing Metal–Organic Framework for Selective Th(IV)/Ln(III) Separation

An uncoordinated salen-containing metal-organic framework (MOF) obtained through postsynthesis removal of Mn(III) ions from a metallosalen-containing MOF material has been used for selective separation of Th(IV) ion from Ln(III) ions in methanol solutions for the first time. This material exhibited an adsorption capacity of 46.345 mg of Th/g. The separation factors (β) of Th(IV)/La(III), Th(IV)/Eu(III), and Th(IV)/Lu(III) were 10.7, 16.4, and 10.3, respectively.

A separation processing for industrial rare earth feed solution by phosphonium ionic liquid type saponification strategy

Abstract A novel ionic liquid type saponification processing based on quaternary phosphonium type bifunctional IL was developed for yttrium separation from ion-adsorbed rare earth deposit. The extractabilities of ([trihexyl(tetradecyl)phosphonium][sec-octylphenoxy acetate] ([P 6,6,6,14 ][SOPAA]) were pronouncedly higher than those of sec-octylphenoxy acetic acid (HSOPAA), a mixture of HSOPAA and [P 6,6,6,14 ]Cl for rare earth elements (REEs). The ion association extraction mechanism contributed to avoiding the numerous saponification procedures using alkali and resulting in saponification wastewater. After 13 stages of extraction and 6 stages of scrubbing sections, the Y(III) was successfully separated from industrial heavy RREs feed, the purity of Y(III) in raffinate was approximately to be 98.9%. Stripping by distilled water was effectively achieved for REEs, which contributed to the decreased consumption of acid to a considerable extent.

Enrichment of trace rare earth elements from the leaching liquor of ion-absorption minerals using a solid complex centrifugal separation process

A novel solid complex centrifugal separation (SCCS) process has been developed to enrich trace rare earth (RE) elements from the leaching liquor of ion-absorption RE minerals. When compared to liquid–liquid centrifugal extraction (LLCE), the proposed process employed 100% extractant without a volatile diluent for the RE enrichment process, which led to a much shorter equilibrium time of 5 min. Taking into account their ability to form solid complexes with RE ions from an aqueous phase, some alkyl phenoxy carboxylic acid derivatives, including p-tert-octylphenoxy acetic acid (POAA), iso-propanoic acid (POPA) and iso-butyric acid (POBA), were synthesized and used as the solid extractants. The SCCS process included the following steps: first, the solid extractants with a saponification degree of 80% were mixed with 0.5 g L−1 RE solution at a liquid/solid phase ratio of 200/1 to obtain the solid RE complexes. Second, the solid RE complexes were separated from the aqueous phase using a liquid/solid centrifugal separator. Finally, a high concentration of RE solution (>200 g L−1) was obtained by the stripping of solid RE complexes with concentrated HCl. In the SCCS process, a precipitation rate of more than 95.4% and a stripping rate of nearly 100% for RE could be achieved. Water solubilities of the as-prepared solid extractants in raffinate solution were tested to be lower than 32.8 ppm at 25 °C and the mass loss were determined as 0.6% for each cycle. The as-obtained high concentration RE solution with the purity of 96.9 wt% can be used directly as a feed solution for the next individual RE element separation.