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Using a dicarboxylic acid, [1,1′-biphenyl]-4,4′-dicarboxylic acid (H2L1) and an exobidentate ligand, (1E,1′E)-N,N′-(1,4-phenylene)bis(1-(pyridin-4-yl)methanimine) (L2), two 3D interpenetrated networks, {[Zn3(L1)3(L2)]·9H2O}n (Zn-MOF) and {[Co3(L1)3(L2)(DMF)]·0.5DMF}n (Co-MOF), have been prepared in good yields. The crystal structure analysis of Zn-MOF and Co-MOF revealed that both have a 3D pillared-layer structure based on pinwheel trinuclear metal–carboxylate clusters as secondary building units (SBUs). Furthermore, the structures also exhibited three-fold interpenetration. Although the overall networks in Zn-MOF and Co-MOF showed significant resemblances, there are marked differences in their crystal structures, which are associated with the coordination environment of the metal centre and the binding modes of the carboxylates. Gas adsorption studies (N2 at 77 K and 1 bar) indicated that Co-MOF is more porous than Zn-MOF. Magnetic measurements on Co-MOF indicate a significant antiferromagnetic interaction (45 K to 303 K) between trimeric Co(II) S = 3/2 spins through syn–syn carboxylato bridges. Both MOFs were studied for the Lewis acid catalyzed Knoevenagel condensation reactions between benzaldehydes and malononitrile with an active methylene group, where Zn-MOF was found to be a better catalyst than Co-MOF. This was supported by the Monte Carlo simulations indicating the better substrate binding ability of Zn-MOF than Co-MOF. [ABSTRACT FROM AUTHOR]

Utilizing the angular and rigid furan dicarboxylate (fdc2−) ion, a new series of four (1–4) metal–organic coordination networks (MOCNs) is synthesized in good yields through a one-pot self-assembly reaction in methanol under ambient conditions to demonstrate the effect of Cu2 dimetal subunits, connected by flexible polypyridyl bis(tridentate) ancillary ligands, tpxn, where x refers to the number of methylene groups connecting the alkyl nitrogen atoms in the ancillary ligands and is equal to 2, 4, 6, and 7. The solid-state molecular structures of 1–4 are determined by single-crystal X-ray diffraction. A change in the dimensionality of the resultant MOCN is observed from a 1D coordination polymer (CP) for 1, 2, and 3 to a molecular rectangle for 4. Furthermore, each unit of 4 contains one NaClO4. Using electrospray ionization (ESI) mass spectrometry, their structural integrity in solution and their purity of existence as a single product are confirmed. Further characterization of 1–4 by FTIR and UV-vis (in solution and solid-state) spectroscopy, and FESEM and TEM is also reported. The presence of unsaturated metal centers in 1–4 provided an opportunity to compare their Lewis acid catalytic activities for the Knoevenagel condensation reaction of malononitrile with various aldehydes. [ABSTRACT FROM AUTHOR]

Diverse ZnO nanostructures (ZnO_1 to ZnO_3) were synthesized by direct calcination of a chiral MOF precursor {[Zn4(μ3-OH)2(D -2,4-cbs)2(H2O)4]·5H2O}n (Zn-CBS) at three different temperatures of 600, 700 and 800 °C, respectively. On the basis of the field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses, 3D microflowers (ZnO_1), 3D polyhedrons (ZnO_2) and 1D nanorods (ZnO_3) are formed with an increase in temperature from 600 to 800 °C. The powder X-ray diffraction (PXRD), energy dispersive X-ray analysis (EDX), and elemental mapping confirmed their crystallinity and the wurtzite phase purity. Interestingly, only 3D microflowers (ZnO_1) comprising nanorods inherited the chiral nature of the parent MOF. Furthermore, only agglomerated ZnO microspheres without any diversity are obtained if Zn(OAc)2·2H2O is used as the precursor at three different temperatures, confirming the importance of innovative metal organic framework mediated synthesis (MOFMS). From the solid state diffuse reflectance spectra, the optical band gap values for ZnO nanostructures were found to be in the range of 3.10–3.17 eV. Their surface areas and pore sizes were determined by the N2 adsorption study at 77 K. On the other hand, their luminescence behaviour in the dispersed mode (solvent: water, methanol or ethanol) was noteworthy: nanorods showed a blue emission with a strong band at 531 nm, while only broad features were observed for microflowers and polyhedrons upon excitation at 380 nm. Utilizing such distinct properties, the as-synthesized ZnO nanostructures were studied for a comparative photocatalytic degradation of the organic pollutants: a cationic dye – methylene blue (MB) and an anionic dye – Congo red (CR) in water under UV light. The nanorods were found to be better than microflowers and polyhedrons for MB, while the microflowers showed an exceptional activity toward CR. In both cases, the degradation rates (first order for MB and pseudo second order for CR) were either comparable to or much better than the reported values. Their recyclability and photostability up to four cycles was very good. The detailed mechanism of their degradation is also discussed with support from the scavenger experiments carried out for ZnO_1 and ZnO_3. [ABSTRACT FROM AUTHOR]

Using a Cd(II) coordination polymer, [Cd2(bpma)2(adc)2]n (where bpma = N,N′-bis(pyridylmethyl) amine and adc = acetylene dicaboxylate), as the source of Cd2+ ions and thiourea as the source of S2− ions in various ratios (1 : 3, 1 : 5, 1 : 7, 1 : 10, 1 : 15 and 1 : 20) in water, CdS nanoparticles (CdS-1 to CdS-6) were synthesized under hydrothermal conditions without a template and an added surfactant. The size of nanoparticles increases with an increase in the concentration of thiourea. These nanoparticles were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectroscopy. The XRD results revealed the presence of both cubic and hexagonal forms in CdS-1 to CdS-6. Based on their UV–vis diffuse reflectance, the band gap energies were estimated to be 2.26, 2.20, 2.19, 2.18, 2.17 and 2.15 eV for CdS-1, CdS-2, CdS-3, CdS-4, CdS-5 and CdS-6, respectively. The photoluminescence spectra of CdS-1 to CdS-6 (excitation wavelength: 350 nm) displayed a blue emission in the wavelength range of 434–437 nm and a green emission in the range of 533–552 nm. The blue emission resulted from the recombination of excitons, whereas the green emission was caused by sulphur vacancies in CdS nanoparticles. Furthermore, the photocatalytic degradation of the methylene blue dye was carried out in water under visible light using CdS-1 to CdS-4, where the maximum degradation efficiency of 97% was obtained using 0.02 mol% of CdS-1. [ABSTRACT FROM AUTHOR]

Utilizing a bent bis(naphthalene) and hydroxy‐based dicarboxylate linker (mbhna) and two different tridentate polypyridyl ligands (bpma and bpta), four new coordination polymers (CPs) of Zn(II) and Cd(II) namely, [Zn(mbhna)(bpma)]n(1) {[Cd(mbhna)(bpma)].DMF}n(2) [Zn(mbhna)(bpta)]n(3) {[Cd(mbhna)(bpta)(CH3OH)]}n(4), are reported. Based on their solid‐state molecular structures determined by single‐crystal X‐ray diffractometry, all are found to be helical 1D CP; interestingly, 4 crystallizes in a chiral space group, showcasing the formation of a chiral CP from achiral components. For the presence of naphthalene moieties in mbhna, their excellent emissive nature is studied in different solvents and further utilized to selectively detect aromatic amines, particularly 4‐nitroaniline in water with detection limits at the ppm level. Utilizing the Stern‐Volmer plots, spectral overlap, and competitive test, their mechanism of action has been established. Furthermore, these are recyclable with good stability after sensing experiments. [ABSTRACT FROM AUTHOR]

The self-assembly of Mn(II), bis(tridentate) ligands and bent dicarboxylate linkers under ambient conditions has been exploited to generate a series of 1D coordination polymers in good yields. For a set of seven compounds, structural isomerization of these architectures is demonstrated through the variation of length and nature of the spacer between the tridentate capping sites of the bis(tridentate) ligands, such as tpbn (N,N′,N′′,N′′′-tetrakis-(2-pyridylmethyl)-1,4-diaminobutane), tphxn (N,N′,N′′,N′′′-tetrakis-(2-pyridylmethyl)-1,6-diaminohexane), and tpxn (N,N′,N′′,N′′′-tetrakis-(2-pyridylmethyl)-xylylamine) or by varying the bent dicarboxylate linker 4,4′-(dimethylsilanediyl)bis-benzoic acid (H2L1) or 4,4′-oxybis-benzoic acid (H2L2). These compounds have been structurally characterized by single-crystal and powder X-ray diffraction, FTIR, and thermogravimetric and elemental analyses. This study reveals that the supramolecular structural variation can be precisely controlled either by a judicious selection of reaction conditions or linker/ligand combinations. For example, the self-assembly of Mn(II), tpbn and H2L1 in DMF/EtOH/water affords a mixture of products (1 and 1a) while changing the solvent combination to EtOH/water results in the generation of a single isomer (1a) in a highly selective manner. On the other hand, for the Mn(II)-tphxn system, different structural isomers have been isolated by varying the dicarboxylates, H2L1 and H2L2 (2vs.5). Similarly, for the Mn(II)-H2L2 system, a variation in the spacer chain length of bis(tridentate) ligands, tpbn and tphxn resulted in the formation of different structural isomers (4vs.5). [ABSTRACT FROM AUTHOR]

Using Zn(II) coordination polymers, namely [Zn2(bpma)2(adc)2]n, [Zn2(bpea)2(adc)2]n and {[Zn2(bpta)2(adc)2]·2H2O}n, as precursors, a variation in the morphologies and dimensionalities of the ZnO nanostructures is demonstrated through three operating parameters: presence of different sacrificial ligands in the precursor, volume of water in a hydrothermal reaction mixture (0.5, 1 and 2 mL) and post synthetic-annealing of hydrothermally grown nanostructures. For example, microspheres and microflowers (3D), nanosheets (2D) and nanotubes (1D) have been obtained with a change in the precursor and volume of water. The growth mechanism of these materials during the hydrothermal synthesis has been elucidated in detail. The dimensionality change from 3D microflowers to 1D nanorods upon further annealing is discussed. The formation of 1D nanotubes is also explained based on the difference in the growth of the different planes of ZnO. Their structural composition and surface morphology were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). The XRD patterns have revealed that the as-synthesized ZnO nanostructures exhibit a hexagonal wurtzite phase. Based on the UV-vis diffuse reflectance spectra, the band gap energies for the as-synthesized nanostructures ZnO-1 to ZnO-9 were found to be in the range of 3.01–3.24 eV. Further, the photoluminescence spectra of these nanostructures displayed the maximum absorption band within the range of 430–490 nm originating from the defect states of zinc interstitials, zinc vacancies and oxygen vacancies. Also, a diminishing effect on the emission intensities was observed as a result of decrease in the concentration of precursors. [ABSTRACT FROM AUTHOR]

A 2D Cd(II) coordination polymer [Cd2(L1)4(H2O)4][ClO4]4·5(H2O), CP1, was synthesized with 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (L1) while the use of benzene-1,3-disulphonate (L2) along with L1 resulted in a novel 3D Cd(II) coordination polymer, [Cd(L1)2(L2)]·2(H2O)·(CH3OH), CP2. CP1 attained a threefold interpenetrated 2D staircase network where the channels are filled with H2O and ClO4− anions. CP2 has a 3D interpenetrated structure and has small pores. The chemical nature and size of the pores of CP1 and CP2 are effective in adsorbing organic dye molecules. Selective adsorption of upto 96% of methyl orange (MO) within 10 min was observed in CP1 and CP2. CP2 was also studied for the adsorption and desorption of iodine. CP1 and CP2 showed luminescence and their solid state PL has a strong emission peak at ∼484 nm. The structural analysis of L1 and [HL1][ClO4] showed the effect of ClO4− on the supramolecular assembly and geometry of the molecules of L1. [ABSTRACT FROM AUTHOR]

Abstract: The chemistry of Coordination Polymers (CPs) of an exo bidentate Schiff base ligand, L1b, 2,5‐bis‐(3‐pyridyl)‐3,4‐diaza‐2,4‐hexadiene, where two pyridyl moieties are separated by imine groups, is discussed. The reaction of ligand L1b and disodium succinate with Cd(ClO4)2 resulted in CP1, which is a 2D bilayer structure. Previously, it was reported elsewhere that the reaction of L1b with Cd(NO3)2 followed by the addition of disodium succinate resulted in a 3D network, while the similar reaction with Cd(ClO4)2 resulted in a different 3D network. The result from the current study establishes that reaction conditions and the anion in the metal salt can be crucial in obtaining diversified networks for the same combination of metal center and ligand. The effect of reaction conditions on network geometry is critically analyzed by comparing their single crystal structures and various other parameters. [ABSTRACT FROM AUTHOR]

Using Zn(II) and Cd(II), coordination architectures are synthesized and utilized in the fabrication of nanoparticles at different temperatures. • Synthesis of [Zn 2 (tpa) 2 (adc) 2 ].5H 2 O (1) and [Cd(tpa)(adc)] n (2) are reported. • Their single crystal structures indicate the formation of supramolecular networks. • Using 1 and 2 , ZnO and CdO nanomaterials, respectively, were fabricated. • A temperature-dependent diversification of size and morphology has been established. Using a tetradentate capping ligand, N,N, N -tris(2-pyridylmethyl)-amine (tpa) and acetylene dicarboxylic acid (H 2 adc), structural diversity is achieved with two group 12 divalent metal ions, Zn(II) and Cd(II). With a change in metal center, a discrete molecule [Zn 2 (tpa) 2 (adc) 2 ] . 5H 2 O (1) and a water soluble coordination polymer [Cd(tpa)(adc)] n (2) are isolated under the same reaction conditions. Furthermore, the formation of supramolecular networks of higher dimensionality in 1 and 2 has different associations: hydrogen bonding interactions between lattice water molecules and the uncoordinated oxygen atoms of adc are primarily involved in 1 , whereas π-π interactions between pyridyl moieties are responsible for it in 2. Both 1 and 2 are characterized by elemental analysis, IR spectroscopy, and thermogravimetric analysis (TGA), single crystal and powder X-ray diffraction. The exceptional thermal stability of 2 compared to 1 based on TGA is correlated to their structural differences. The template-free ecofriendly and efficient fabrication of 1 and 2 to the corresponding metal oxide nanomaterials (ZnO and CdO, respectively) was achieved via the direct calcination method but without any external reagent such as surfactants. Furthermore, a temperature-dependent (400–600 °C) diversification of size and morphology of both ZnO and CdO has established the value of such precursors. [ABSTRACT FROM AUTHOR]

Room temperature synthesis, crystal structures and properties of two new 2D metal-organic frameworks of Co(II) and Ni(II) and their fabrication to metal oxide nanomaterials are reported. [Display omitted] • Using a flexible cycloaliphatic dicarboxylic acid, two new isostructural 2D metal–organic frameworks of Co(II) and Ni(II) are prepared under ambient conditions. • Their single crystal structures are reported. The intermolecular and surface interactions using 3D Hirshfeld surface analysis and 2D fingerprint plots are considered. • Their spectroscopic and thermal properties are also reported. • Exploiting their thermal behaviour, the corresponding oxides Co 3 O 4 and NiO were obtained and characterized. For a combination of a semi-flexible cycloaliphatic dicarboxylic acid and a bis(tridentate) polypyridyl ligand with a semirigid spacer, two new isostructural two-dimensional (2D) metal–organic frameworks have been obtained under ambient conditions in yields > 80%: {[Co 2 (cdc) 2 (tpxn)(H 2 O) 2 ] · H 2 O} n (1) and {[Ni 2 (cdc) 2 (tpxn)(H 2 O) 2 ] · CH 3 OH} n (2) (where, cdc = cyclohexane-1,4-dicarboxylate and tpxn = N,N'-(1,4-phenylenebis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine)). Both 1 and 2 are characterized by elemental analysis, FTIR spectroscopy, thermogravimetric analysis (TGA), and single crystal X-ray diffraction. Each metal center in 1 and 2 is hexacoordinated with an N3O3 environment and contains a coordinated water molecule. The semirigid bis(tridentate) ligand binds with two metal ions and forms the dimetal subunit, which is extended further through two cdc2- carboxylates forming a 2D supramolecular net with a hcb topology. The dimension of the six-membered ring in the net is 19.500 Å × 23.013 Å and 19.423 Å × 22.903 Å (including van der Waals radii) for 1 and 2 , respectively. Additionally, the isostructurality of the reported Co(II) and Ni(II) compounds was revealed using Hirshfeld surface analysis supported by quantitative intermolecular interactions. Based on the thermal behavior established by TGA, the corresponding metal oxide nanomaterials (Co 3 O 4 and NiO for 1 and 2 , respectively) were fabricated under the template-free and surfactant-less direct calcination at 500 °C. [ABSTRACT FROM AUTHOR]