Phenolic nitroaromatics detection by fluorinated metal-organic frameworks: Barrier elimination for selective sensing of specific group of nitroaromatics.

Many piesce of research have been performed to detect nitroaromatic-compounds (NACs) by metal-organic frameworks (MOFs). Despite extensive studies, there are still significant challenges like selective detection of specific NAC group in presence of other NACs. Here, we have integrated two functionalization strategies through decoration of pore-walls of the MOFs with trifluoromethyl groups and extension in π-conjugated system. Based on this idea, trifluoromethyl TMU-44 (with the formula [Zn2(hfipbb)2(L1)]n.DMF, H2hfipbb = 4,4'-(hexafluoroisopropylidene) bis(benzoic acid), L1 = N,N'-bis-pyridin-4-ylmethylene-benzene-1,4-diamine) and TMU-45 (with formula [Zn2(hfipbb)2(L2)]n.DMF, L2 = N,N'-bis-pyridin-4-ylmethylene-naphthalene-1,5-diamine) frameworks have been synthesized. The aromatic skeleton of TMU-44 is based on phenyl rings while TMU-45 aromatic skeleton is extended by replacement of phenyl with naphthyl core. Measurements reveal that these MOFs are highly sensitive to phenolic NACs especially 2,4,6-trinitrophenol (TNP) with high quenching efficiency of 90% for TMU-44 (KSV = 10,652 M-1, LOD = 6.9 ppm) and 99% for TMU-45 (KSV = 34,741 M-1, LOD = 2.07 ppm). The proposed detection mechanism can be associated with hydrogen bonding between OH group of phenolic NACs and trifluoromethyl groups of TMU-MOFs as well as π(rich)∙∙∙π(deficient) interaction between π-conjugated backbone of TMU-frameworks and π-deficient ring of NACs.

Size-Selective Urea-Containing Metal-Organic Frameworks as Receptors for Anions.

Anion recognition by neutral hosts that function in aqueous solution is an emerging area of interest in supramolecular chemistry. The design of neutral architectures for anion recognition still remains a challenge. Among neutral anion receptor systems, urea and its derivatives are considered as "privileged groups" in supramolecular anion recognition, since they have two proximate polarized N-H bonds exploitable for anion recognition. Despite promising advancements in urea-based structures, the strong hydrogen bond drives detrimental self-association. Therefore, immobilizing urea fragments onto the rigid structures of a metal-organic framework (MOF) would prevent this self-association and promote hydrogen-bond-accepting substrate recognition. With this aim, we have synthesized two new urea-containing metal-organic frameworks, namely [Zn(bpdc)(L2)]n·nDMF (TMU-67) and [Zn2(bdc)2(L2)2]n·2nDMF (TMU-68) (bpdc = biphenyl-4,4'-dicarboxylate; bdc = terephthalate; L2 = 1,3-bis(pyridin-4-yl)urea), and we have assessed their recognition ability toward different anions in water. The two MOFs show good water stability and anion affinity, with a particular selectivity toward dihydrogen arsenate for TMU-67 and toward fluoride for TMU-68. Crystal structure characterizations reveal 3-fold and 2-fold interpenetrated 3D networks for TMU-67 and TMU-68, respectively, where all single interpenetrated networks are hydrogen bonded to each other in both cases. Despite the absence of self-quenching, the N-H urea bonds are tightly hydrogen bonded to the oxygen atoms of the dicarboxylate ligands and cannot be directly involved in the recognition process. The good performance in anion sensing and selectivity of the two MOFs can be ascribed to the network interpenetration that, shaping the void, creates monodimensional channels, decorated by exposed oxygen atom sites selective for arsenate sensing in TMU-67 and isolated cavities, covered by phenyl groups selective for fluoride recognition in TMU-68.

Ultrasonic assisted synthesis of two urea functionalized metal organic frameworks for phenol sensing: A comparative study.

Two pillared metal-organic frameworks containing urea functional groups were synthesized by a sonochemical method and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analysis. The time of sonication and concentration of starting materials have been optimized to synthesize nanoparticles of TMU-31 and TMU-32. These two frameworks are interesting candidates for a comparative fluorescence study. Thus, their potential abilities for phenol sensing were investigated. This investigation revealed the prominent roles of hydrogen bond donating urea groups inside the pore cavity in the ability of these structures in phenol sensing.

Ultrasound-assisted synthesis of nano-structured Zinc(II)-based metal-organic frameworks as precursors for the synthesis of ZnO nano-structures.

A 3D, porous Zn(II)-based metal-organic framework {[Zn2(oba)2(4-bpmn)]·(DMF)1.5}n (TMU-21), (4-bpmn=N,N'-Bis-pyridin-4-ylmethylene-naphtalene-1,5-diamine, H2oba=4,4'-oxybis(benzoic acid)) with nano-rods morphology under ultrasonic irradiation at ambient temperature and atmospheric pressure was prepared and characterized by scanning electron microscopy. Sonication time and concentration of initial reagents effects on the size and morphology of nano-structured MOFs were studied. Also {[Zn2(oba)2(4-bpmn)] (TMU-21) and {[Zn2(oba)2(4-bpmb)] (TMU-6), 4-bpmb=N,N'-(1,4-phenylene)bis(1-(pyridin-4-yl)methanimine) were easily prepared by mechanochemical synthesis. Nanostructures of Zinc(II) oxide were obtained by calcination of these compounds and their de-solvated analogue as activated MOFs, at 550°C under air atmosphere. As a result of that, different Nanostructures of Zinc(II) oxide were obtained. The ZnO nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and FT-IR spectroscopy.

Urea Metal-Organic Frameworks for Nitro-Substituted Compounds Sensing.

Urea groups are known to form strong hydrogen bonds with molecules containing atom(s) that can act as hydrogen bond acceptor(s). Thus, urea is a particularly interesting building block for designing receptors for neutral or charged guests. In the quest for new sensors with enhanced performance for the detection of nitro-substituted compounds, two pillared metal-organic frameworks containing urea functional groups were synthesized and structurally characterized. The sensing properties of these frameworks toward nitro-analytes were investigated and compared to each other. The study clearly reveals the importance of urea groups orientation inside the pore cavity of MOFs, as well as the supramolecular interactions between the interpenetrated networks. This work is interesting as it represents the first example of urea-functionalized MOFs for nitro-analytes recognition.

Ultrasonic-assisted synthesis and structural characterization of two new nano-structured Hg(II) coordination polymers.

Two new Hg(II) coordination polymers containing N,N'-Bis-pyridin-3-ylmethylene-naphtalene-1,5-diamine ligand were synthesized by conventional and sonochemical methods, characterized by spectroscopic techniques (FT-IR and elemental analysis), and their X-ray crystallographic structures were determined. The crystal packing and supramolecular features of these coordination polymers were studied using geometrical analysis and Hirshfeld surface analysis. The crystal structure analysis revealed that H⋯H contacts, C-H⋯π and C-H⋯X (X = Cl for 1 and X = Br for 2) hydrogen bonding interactions are strong enough to govern the supramolecular architecture. The BFDH analysis helps us to compare the predicted morphology to that obtained under ultrasonication. This study may provide further insight into discovering the role of weak intermolecular interactions in the context of nano-supramolecular assembly.

The role of weak hydrogen and halogen bonding interactions in the assembly of a series of Hg(II) coordination polymers.

A series of eight new Hg(II) complexes based on the L4-X ligands, where L is (E) -4-halo-N-(pyridin-4-ylmethylene)aniline, were synthesized and characterized and their supramolecular crystal structures were studied by different geometrical and theoretical methods. Our study reveals the role of weak intermolecular interactions involving halogens, such as C­H∙∙∙X hydrogen bonds (in the cases of 1, 2, 3, 5, 6 and 7) and C­X∙∙∙X'­M halogen bonds (in the cases of 4 and 8), in the structural changes of supramolecular assemblies of coordination compounds. Complexes 1­8 were also synthesized by sonochemical irradiation and the morphology of the prepared complexes was investigated using FE-SEM. The BFDH analysis helps us to compare the predicted morphology to that obtained under ultrasonication. This study may provide further insight into discovering the role of weak intermolecular interactions in the context of metallosupramolecular assembly.

Influence of halogen bonding interaction on supramolecular assembly of coordination compounds; head-to-tail N···X synthon repetitivity.

In this study, N-(3-halophenyl)-2-pyrazinecarboxamide ligands, L(3-F), L(3-Cl), L(3-Br), and L(3-I), carrying a different halogen atom on the phenyl meta-position and N-phenyl-2-pyrazinecarboxamide ligand, L(H), have been employed for the synthesis of 12 mercury(II) complexes, [HgCl2(L(H))]n, 1, [HgCl2(L(3-Cl))]n, 2, [Hg2Cl4(L(3-Br))2], 3, [Hg2Cl4(L(3-I))2], 4, [Hg2Br4(L(H))2], 5, [HgBr2(L(3-F))], 6, [HgBr2(L(3-Cl))], 7, [HgBr2(L(3-Br))], 8, [HgBr2(L(3-I))], 9, [Hg2I4(L(H))2], 10, [HgI2(L(3-Br))], 11, and [HgI2(L(3-I))]n, 12. Interestingly, structural analysis clearly shows that, by the replacing of coordinated anions from chloride with bromide and iodide in each series containing the same ligand, the coordination geometry and structural motif of the resulting compounds have been dramatically affected. One of the common features in the crystal structures of these complexes is that there is a strong tendency to form halogen bonding synthons between adjacent halophenyl and pyrazine rings. The influence of these halogen bonding interactions on the supramolecular assemblies has been discussed with the help of geometrical analysis and theoretical calculations. The X···N halogen bonding distances are 2.5-9.4% shorter than the sum of the van der Waals radii of nitrogen and halogen atoms. Theoretical methods also show the halogen bonding energies within a range of -27.86 to -46.15 kJ·mol(-1). In all complexes synthesized here, the pyrazine ring is coordinated to the mercury(II) ion through the N atom syn to the carbonyl. Therefore, the second common feature of the crystal structures for complexes studied here is the selectivity of the metal ion coordination site. The halogen bond synthon repetitivity across these compounds and selectivity in the mercury(II) ion coordination site further point to application in the coordination crystal engineering research field.

2-Phenyl-1H-imidazole.

In the title compound, C(9)H(8)N(2), a mirror plane lies perpendicular to the phenyl and imidazole rings and passes through the bridging C-C bond, so that the imidazole ring is disordered over two sites about the mirror plane with the equal site occupancy; the asymmetric unit contains one half-mol-ecule. In the crystal, adjacent mol-ecules are linked via N-H⋯N hydrogen bonds.

catena-Poly[[bis-(pyrazine-2-carbox-amide-κN)mercury(II)]-di-µ-bromido].

In the crystal structure of the title compound, [HgBr(2)(C(5)H(5)N(3)O)(2)](n), the Hg(II) cation is located on an inversion center and is coordinated by two N atoms from the pyrazine rings and four bridging Br(-) anions in a distorted octa-hedral geometry. The Br(-) anions bridge the Hg(II) cations with significantly different Hg-Br bond distances of 2.4775 (8) and 3.1122 (8) Å, forming polymeric chains running along the a axis. Inter-molecular N-H⋯O and N-H⋯N hydrogen bonds are effective in the stabilization of the crystal structure.

catena-Poly[[bis-(pyrazine-2-carbox-amide)mercury(II)]-di-µ-chlorido].

In the polymeric title compound, [HgCl(2)(C(5)H(5)N(3)O)(2)](n), the Hg(II) atom (site symmetry ) adopts a distorted trans-HgN(2)Cl(4) octa-hedral coordination geometry. In the crystal, adjacent mercury ions are bridged by pairs of chloride ions, generating infinite [100] chains, and N-H⋯O and N-H⋯(N,N) hydrogen bonds help to consolidate the packing.