Recent advances in metal-organic frameworks as adsorbent materials for hazardous dye molecules.

Water is vital for the sustenance of all forms of life. Hence, water pollution is a universal crisis for the survival for all forms of life and a hurdle in sustainable development. Textile industry is one of the anthropogenic activities that severely pollutes water bodies. Inefficient dyeing processes result in thousands of tons of synthetic dyes being dumped in water bodies every year. Therefore, the efficient removal of synthetic dyes from wastewater has become a challenging research field. Owing to their tuneable structure-property aspects, metal-organic frameworks (MOFs) have emerged as promising adsorbents for the adsorptive removal of dyes from wastewater and textile effluents. In this perspective, we highlight recent studies involving the application of MOFs for the adsorptive removal of hazardous dye molecules. We also classify the developed MOFs into cationic, anionic, and neutral framework categories to comprehend their suitability for the removal of a given class of dyes.

Effect of Substituents on the Crystal Structures, Optical Properties, and Catalytic Activity of Homoleptic Zn(II) and Cd(II) ß-oxodithioester Complexes.

Five novel zinc(II) and cadmium(II) ß-oxodithioester complexes, [Zn(L1)2] (1), [Zn(L2)2]n (2), [Zn(L3)2]n (3) [Cd(L1)2]n (4), [Cd(L2)2]n (5), with ß-oxodithioester ligands, where L1 = 3-(methylthio)-1-(thiophen-2-yl)-3-thioxoprop-1-en-1-olate, L2 = 3-(methylthio)-1-(pyridin-3-yl)-3-thioxoprop-1-en-1-olate, and L3 = 3-(methylthio)-1-(pyridin-4-yl)-3-thioxoprop-1-en-1-olate, were synthesized and characterized by elemental analysis, IR, UV-vis, and NMR spectroscopy (1H and 13C{1H}). The solid-state structures of all complexes were ascertained by single-crystal X-ray crystallography. The ß-oxodithioester ligands are bonded to Zn(II)/Cd(II) metal ions in an O∧S and N chelating/chelating-bridging fashion leading to the formation of 1D (in 2-4) and 2D (in 5) coordination polymeric structures, but complex 1 was obtained as a discrete tetrahedral molecule. Complex 4 crystallizes in the C2 chiral space group and has been studied using circular dichroism (CD) spectroscopy. The multidimensional assemblies in these complexes are stabilized by many important noncovalent C-H···π (ZnOSC3, chelate), π···π, C-H···π, and H···H interactions. The catalytic activities of 1-5 in reactions involving C-C and C-O bond formation have been studied, and the results indicated that complex 3 can be efficiently utilized as a heterogeneous bifunctional catalyst for the Knoevenagel condensation and multicomponent reactions to develop biologically important organic molecules. The luminescent properties of complexes were also studied. Interestingly, zinc complexes 1-3 showed strong lumniscent emission in the solid state, whereas cadmium complexes 4 and 5 exhibited bright luminescent emission in the solution phase. The semiconducting behavior of the complexes was studied by solid-state diffuse reflectance spectra (DRS), which showed optical band gaps in the range of 2.49-2.62 eV.

Spontaneous Resolution upon Crystallization and Preferential Induction of Chirality in a Discrete Tetrahedral Zinc(II) Complex Comprised of Achiral Precursors.

A pair of enantiomeric tetrahedral complexes (Λ-[Zn(L)2] and Δ-[Zn(L)2]) comprised of the achiral ligand methyl-3-hydroxy-3-phenyl-2-propenedithioate (L) have been synthesized by spontaneous resolution. Two chiral inducers, viz., d-(-)- and l-(+)-tartaric and mandelic acids, have been employed to achieve bulk homochirality and extend the generality of the present work. The work highlights the achievement of bulk homochirality using readily available chiral inducers in the synthesis of a spontaneously resolving chiral tetrahedral zinc(II) complex using achiral starting materials. These findings are established by 30 sets of single-crystal X-ray diffraction data with refined Flack parameters and circular dichroism spectroscopy.

Cooperative metal-ligand influence on the formation of coordination polymers, and conducting and photophysical properties of Tl(i) ß-oxodithioester complexes.

Eight novel Tl(i) ß-oxodithioester complexes, [TlL]n (1-8), with ligands, L = methyl-3-hydroxy-3-(2-furyl)-2-propenedithioate (L1), methyl-3-hydroxy-3-(2-thienyl)-2-propenedithioate (L2), methyl-3-hydroxy-3-(3-pyridyl)-2-propenedithioate (L3), methyl-3-hydroxy-3-(4-pyridyl)-2-propenedithioate (L4), methyl-3-hydroxy-3-(9-anthracenyl)-2-propenedithioate (L5), methyl-3-hydroxy-3-(4-fluorophenyl)-2-propenedithioate (L6), methyl-3-hydroxy-3-(4-chlorophenyl)-2-propenedithioate (L7) and methyl-3-hydroxy-3-(4-bromophenyl)-2-propenedithioate (L8), were synthesized and thoroughly characterized by elemental analysis, and IR, UV-Vis, 1H and 13C{1H} NMR spectroscopy, and their structures were ascertained by X-ray crystallography. Complexes 1 and 2 crystallized in P21 and P212121 chiral space groups, respectively, and were studied using Circular Dichroism (CD) spectra. Solid state structural analyses revealed that the ß-oxodithioester ligands are bonded to Tl(i) ions in (O, S) chelating and chelating-bridging modes, thereby forming different types of 1D and 2D coordination polymeric structures. By considering the metal-assisted bonding interactions, various coordination numbers of 5-8 and 10 are established around the metal centre. Except for 5 and 7a which have TlTl separations at 3.724(1) and 3.767(1), 3.891(1) Å respectively, the remaining complexes have no TlTl distances <4.0 Å. This indicates that the majority of structures contain only weak inter- and intramolecular thallophilic interactions. The structures of 1-8 highlight the role played by variations in substituents in the dithioester unit in the structure and properties of the complexes. The multi-dimensional assembly in these complexes rests on important non-covalent C-Hπ (TlOSC3, chelate), C-HX (X = F, Cl, O, N), C-Hπ, HH and rare TlH-C intermolecular anagostic interactions. The TlH-C anagostic interactions together with C-OTl and C-STl interactions formed 7-, 11- and 12-membered chelate rings about the metal centers. The anagostic interactions in 1, 2 and 7b were assessed by theoretical calculations. All the complexes showed bright green luminescent emissions in solution and solid phases. Time-resolved emission spectra revealed a triexponential decay curve and short mean lifetime for fluorescence behavior.

Impact of ligand framework on the crystal structures and luminescent properties of Cu(I) and Ag(I) clusters and a coordination polymer derived from thiolate/iodide/dppm ligands.

New homoleptic hexanuclear Ag(I) and heteroleptic trinuclear Cu(I) clusters and a Cu(I) coordination polymer (CP) of the formulas [Ag6(dtc)6] 1, [Cu3I2(dppm)3(dtc)] 2, and [Cu(ttc)I]∞ 3 (dtc = N-methylbenzyl-N-methyl-thiophenedithiocarbamate; dppm = 1,1-bis(diphenylphosphino)methane; and ttc = dimethyltrithiocarbonate) were synthesized and characterized by elemental analysis, IR, UV-vis, (1)H, (13)C, and (31)P NMR spectroscopies, and their structures were elucidated by X-ray crystallography. The complexes show interesting structures and luminescent properties. Complex 1, which is centrosymmetric, contains four short Ag···Ag interactions at 2 × 2.966(1) and 2 × 3.014(1) Å. There are also several Ag···Ag distances of 3.3-3.4 Å. The molecule shows hexagonal orientation with alternating silver and sulfur atoms of the overlapping Ag3S3 hexagons in the front and rear, along the a axis. Complex 2 is a rare trinuclear cluster complex of Cu(I); the Cu···Cu distances are 2.906(2), 3.551(2), and 3.338(2) Å, the foremost representing a substantial intermetallic contact. The Cu3I2P6S2 core is comprised of three fused distorted hexagonal rings with the I1 atom located at the center participating in all three rings. Complex 3 is an iodide-bridged CP with a "staircase"-like arrangement in which the Cu(I) is tetrahedrally surrounded by a sulfur atom from the ttc ligand and three iodine atoms. Unlike 3, which is nonluminescent, 1 and 2 are strongly luminescent in the solid and solution at room temperature. The time-resolved emission spectra reveal a triexponential decay curve and short mean lifetime characteristic of fluorescence behavior. Diffuse reflectance spectroscopy revealed semiconducting behavior with band gaps of 2.12, 3.01, and 2.18 eV for 1-3, respectively.

Influence of the ligand frameworks on the coordination environment and properties of new phenylmercury(II) ß-oxodithioester complexes.

New phenylmercury(II) complexes of the form [PhHg(L1), PhHg(L2) and PhHg(L3)] (L1 = methyl-3-hydroxy-3-(p-methoxyphenyl)-2-propenedithioate (1), L2 = methyl-3-hydroxy-3-(p-bromophenyl)-2-propenedithioate (2) and L3 = methyl-3-hydroxy-(3-pyridyl)-2-propenedithioate (3)) have been synthesized and characterized by elemental analysis, IR, UV-Vis, 1H and 13C NMR. The crystal structures of 1­3 reveal a linear geometry about the mercury atom via ipso-C and S11 atoms. 1 and 2 exhibited O,S-coordination whereas 3 preferred S,S-coordination. Intramolecular Hg∙∙∙O bonding interactions are also observed in 1 and 2 at distances of 2.638(14), 2.644(10) Å respectively. However in 3, incorporation of the 3-pyridyl substituent on the ligand enhanced the proximity of S13 and N14, giving rise to significant intramolecular Hg∙∙∙S and intermolecular Hg∙∙∙N interactions at 3.141(5) Å and 2.77(2) Å respectively generating a 1-D polymeric chain motif. The O,S- or S,S-coordination preference and Hg∙∙∙N interactions have been assessed by DFT calculations. All the complexes show metal perturbed ligand-centred luminescence characteristics in solution and in the solid phase. The band gap values 2.54, 2.66 and 2.61 eV for 1, 2 and 3, respectively, evaluated from the diffuse reflectance spectroscopy show the semiconducting nature of the complexes.

Investigation of crystal structure, vibrational characteristics and molecular conductivity of 2,3-dichloro-5,6-dicyno-p-benzoquinone.

Molecular geometries and vibrational spectra for the ground state of 2,3-dichloro-5,6-dicyno-p-benzoquinone (DDQ) and its anion (DDQ(-)) were computed using DFT method at the B3LYP level employing 6-311++G(d,p) basis set whereas for the first excited state (DDQ(∗)), these were calculated using TD-DFT at the B3LYP level employing the 6-311++G(d,p) basis set available with the Gaussian 09 package. The spectra have been experimentally investigated and the observed IR and Raman bands have been assigned to different normal modes on the basis of the calculated potential energy distributions (PEDs). XRD of single crystal has been investigated to determine molecular and crystal structures of DDQ. In order to elucidate the transfer of electrons, electronic structure and electronic absorption have been calculated with the TD-DFT method. Vibronic interaction and its role in the appearance of superconductivity in the DDQ, DDQ(-) and DDQ(∗) molecules have been investigated. The present XRD, molecular, electronic and vibronic studies indicate that mainly the ag C=O stretching and ring stretching modes participate in the charge transfer process.