A metal-organic framework with rich accessible nitrogen sites for rapid dye adsorption and highly efficient dehydrogenation of formic acid.

MOFs with adequate free nitrogen sites have potential applications in dye adsorption and formic acid dehydrogenation. Here, we successfully synthesized a novel 3-D MOF 1 ([(CH3)2NH2][Cd(L)DMA]·0.5DMA·1.5H2O) with a special two-fold interpenetrating framework through a simple solvothermal reaction between CdCl2·1.5H2O and a nitrogen-rich triangular tricarboxylate-based linker (H3L, 4,4',4''-s-triazine-2,4,6-tribenzoic acid). After removing the guest molecules of dimethylacetamide (DMA) and H2O, including the coordinated DMA from 1 by vacuum activation at 423 K, a compound named 1' with a formula of [(CH3)2NH2][Cd(L)] and a similar interpenetrating framework structure was obtained. In comparison with compound 1, the total void volume of 1' is nearly doubled, and thus may provide higher potential for the adsorption of other guest molecules. Notably, the pyridine N atoms located in the middle of the triangular tricarboxylate-based linker are not involved in the coordination with Cd2+, and are all uniformly dispersed throughout the whole framework of the 3-D MOFs. Due to its unique structural features, the 3-D MOF 1' could effectively adsorb the cationic dye MB+ for recycling purposes. The rapid adsorption rate (0.7 × 10-2 g mg-1 min-1) and the relatively high capacity (900 mg g-1) for MB+ demonstrate the potential of 1' in dye adsorption. In addition, 1' may also be used as an effective support to immobilize PdAu NPs via the double-solvent method. The resultant catalyst Pd0.8Au0.2/1' exhibits decent catalytic activity for the dehydrogenation of formic acid with a TOF value of 1854 h-1 at 333 K. The existence of a large void volume and accessible pyridine N atoms provide a suitable environment for achieving a high dispersion of PdAu NPs, thereby leading to the formation of a catalytically active and stable supported noble-metal NP catalyst for H2 generation from formic acid decomposition.

Porous 3,4-di(3,5-dicarboxyphenyl)phthalate-based Cd2+ coordination polymer and its potential applications.

Porous coordination polymers with organic aminium as one of the guest species possess a potential application in dye adsorption and white-light material manufacture. Polycarboxylic acid with multiple COOH substituents tends to form this type of porous material (with metal ion). Here the solvothermal self-assembly between Cd2+ and a hexacarboxylic acid creates such a porous material [(CH3)2NH2]6[Cd3(L)2]·5DMF·3H2O (H6L = 3,4-di(3,5-dicarboxyphenyl)phthalic acid) 1. Total potential guest accessible void volume in 3-D 1 is found to be 4327 Å3. Based on its better porous structure and stability, the ability of 1 to adsorb organic dyes is investigated. It has been proved that (i) 1 can selectively adsorb cationic dyes as Azure A (AA+) and/or Methylene Blue (MB+), rather than neutral and anionic ones; (ii) the maximum adsorption capacity is 698.2 mg·g-1 for AA+ and 573.2 mg·g-1 for MB+, respectively; and (iii) to the adsorption of AA+, it can be recycled for at least five rounds. Also, it is utilized to fabricate the while-light emitting material. Based on the blue-light emission of 1, the trace Eu3+ and Tb3+ ions are introduced into the pores of 1 successfully, obtaining a white-light emitting material Eu3+/Tb3+@1 (CIE chromaticity coordinates: (0.33, 0.32)). Meanwhile, Eu3+/Tb3+@1 is found to be a potential fluorescence photochromic material, showing a yellow-white-blue light emission. According to these investigations, the relationship between material structure and its adsorption property for dyes, the points that should be paid attention to in the construction of white-light emitting materials as well as the potential adsorption mechanism for dyes and rare earth ions are deeply discussed.

New Cd2+, Pb2+ complexes with acylhydrazidate molecules from in situ acylation reactions.

Through employing the hydrothermal in situ acylation of N2H4 with aromatic dicarboxylic acids, four new acylhydrazidate-coordinated complexes, [Cd2(pth)4(phen)2(H2O)2]·H2O (pth = phthalhydrazidate; phen = 1,10-phenanthroline) 1, [Cd3(dcpth)6(phen)2(H2O)2] (dcpth = 4,5-dichlorophthalhydrazidate) 2, [Cd(pdh)2(H2O)2] (pdh = pyridine-2,3-dicarboxylhydrazidate) 3 and [Pb(sdpth)(phen)] (sdpth = 4,4'-sulfoyldiphthalhydrazidate) 4, were obtained. X-ray analysis revealed that (i) isomerization and deprotonation of acylhydrazide molecules also occurred; (ii) compound 2 possesses a one-dimensional (1-D) double-chain structure, in which dcpth exhibits three types of coordination modes; (iii) compound 4 shows a 1-D castellated single-chain structure; (iv) the adjacent uncoordinated acylamino groups form a hydrogen-bonded dimer, via which compounds 2-4 self-assemble into different two-dimensional (2-D) supramolecular networks. In the solid state, only compound 3 emits green light (λ(em) = 525 nm), while in an aqueous solution, compounds 1, 3 and 4 all emit light. Density functional theory (DFT) calculations indicate that the emission at 470 nm for compound 1 corresponds to a charge transfer within the phen molecule, whereas the emission at 400 nm for compound 3 corresponds to a charge transfer within the pdh molecule.

New thiocyanatocadmates templated by multi-dentate N-heterocyclic/diamine molecules.

With diverse multi-dentate N-heterocyclic/diamine molecules as the cations, the reactions between Cd(2+) and SCN(-) in C2H5OH/H2O solution acidified by H2SO4 created five new thiocyanatocadmates [H2(bim)][Cd(SCN)2(H2O)2]SO4 (bim = 2,2'-biimidazole) 1, [H2(pympip)]2[Cd2(SCN)4(SO4)2(H2O)4]·2H2O (pympip = 1-(2-pyrimidyl)piperazine) 2, [H2(tdpy)]2[Cd3(SCN)10] (tdpy = 4,4'-thiodipyridine) 3, [H2(badpm)][Cd(SCN)4] (badpm = 4,4'-biaminodiphenylmethane) 4 and [H2(pdma)][Cd2(SCN)4(SO4)] (pdma = 1,4-phenylenedimethanamine) 5. It is noteworthy that (i) in compounds 1, 2 and 5, SO4(2-) was incorporated into the organically templated thiocyanatocadmate frameworks; (ii) compound is a rare example, in which two types of chained thiocyanatocadmates are found, and (iii) compound shows an interesting layer structure, constructed up from the ribboned thiocyanatocadmates by µ2-mode SO4(2-). Photoluminescence analysis revealed that compounds 1, 2 and 5 in solid state emit blue light with the maximum at 425 nm for 1, 405 nm for 2 and 445 nm for 5, respectively.

New metal complexes with di(mono)acylhydrazidate molecules.

The simple hydrothermal self-assemblies between metal salts, organic polycarboxylic acids and N(2)H(4)·H(2)O, sometimes in the presence of phenanthroline (phen), created four di(mono)acylhydrazidate-coordinated compounds [Pb(2)(DPHKH)(2)(phen)(2)]·2H(2)O 1, [Cd(ODPTH)(phen)]·0.25H(2)O 2, [Pb(2)(MPTH)(4)(phen)(2)] 3, [Cd(2)(MPTH)(4)(phen)(2)]·H(2)O 4 as well as one diacylhydrazide molecule [H(2)(ODPTH)] 5 (DPHKH = 4,4'-diphthalhydrazidatoketone hydrazone, MPTH = 3-methylphthalhydrazidate, ODPTH = 4,4'-oxydiphthalhydrazidate). Note that the di(mono)acylhydrazidate molecules in the title compounds originated from the in situ acylation reactions between organic polycarboxylic acids and N(2)H(4)·H(2)O. Interestingly, another kind of ligand in situ reaction was found in the formation process of DPHKH in compound 1: the nucleophilic addition reaction of a ketone with N(2)H(4)·H(2)O.

New monoacylhydrazidate-coordinated Mn2+ and Pb2+ compounds.

By the simple hydrothermal self-assembly, four new monoacylhydrazidate-coordinated compounds [Mn(APTH)(2)(H(2)O)] 1, [Pb(APTH)(2)]·0.25H(2)O 2, [Pb(2)(EPDH)(4)(H(2)O)] 3 and [Pb(MPDH)(2)] 4 (APTH = 3-aminophthalhydrazidate, EPDH = 5-ethylpyridine-2,3-dicarboxylhydrazidate, MPDH = 6-methylpyrinde-2,3-dicarboxylhydrazidate) were obtained. It is noteworthy that APTH was derived from the in situ reduction reaction of NPTH (3-nitrophthalhydrazide) with N(2)H(4)·H(2)O as the reducer, whereas EPDH and MPDH were derived respectively from the in situ acylation reactions of epdca and mpdca (epdca = 5-ethylpyridine-2,3-dicarboxylic acid, mpdca = 6-methylpyridine-2,3-dicarboxylic acid) with N(2)H(4)·H(2)O. The photoluminescence analysis indicates that compounds 3 and 4 possess luminescence properties with maximum emissions at 531 nm for 3, and 600 nm for 4, respectively. The density functional theory (DFT) calculations indicate that the emission for compound 3 can be ascribed to a combination of the intra-ligand and inter-ligand charge transfers, while the emission for compound 4 is assigned to the intra-ligand charge transfer.

New photoluminescence acylhydrazidate-coordinated complexes.

Under the hydrothermal conditions, five new acylhydrazidate-containing compounds [Cd(EPDH)(2)(H(2)O)] 1, [Cd(MPDH)(2)] 2, [Zn(MPDH)(2)(H(2)O)(2)]·2H(2)O 3, [Pb(2)(ODPTH)(2)(phen)(2)(H(2)O)(2)] 4 and [Cd(2)(APTH)(4)(phen)(2)]·2H(2)O 5 (EPDH = 5-ethylpyridine-2,3-dicarboxylhydrazidate, MPDH = 6-methylpyridine-2,3-dicarboxylhydrazidate, ODPTH = 4,4'-oxydiphthalhydrazidate, APTH = 3-amiophthalhydrazidate, phen = 1,10-phenanthroline) were luckily obtained. Note that MPDH, EPDH and ODPTH were derived from the hydrothermal in situ acylation reactions between organic polycarboxylic acids and N(2)H(4)·H(2)O, whereas APTH originated from the hydrothermal in situ reduction reaction of NPTH (NPTH = 3-nitrophthalhydrazidate) in the presence of N(2)H(4)·H(2)O. The photoluminescence analysis indicates that all of the title compounds are fluorescent materials with maximum emissions at 530 nm for 1, 540 nm for 2, 517 nm for 3, 413 nm for 4 and 563 nm for 5, respectively. The density functional theory (DFT) calculations on the excited electronic states of compound 3 indicate that the emission is associated with the ligands, corresponding to the charge transfer from the π orbital of the acylhydrazidate ring to the π* orbital of the pyridine ring.