No abstract

The porous materials are efficient storage and exchange systems of small molecules and ions. Some of the porous materials may be used as an efficient storage system of iodine. Herein, a honeycomb (hcb)-type 2D+2D (2D = two-dimensional), parallel polycatenated Porous Polycatenated Coordination Polymer (PPCP) {[Cd2I2(BDC)2(INH)2]·(2DMF)­(H2O)} n , 1 (INH, isoniazid; H2BDC, terephthalic acid; DMF, dimethylformamide) is characterized that reversibly uptakes I2 from organic medium (more than 98%). The single-crystal X-ray structure determination reveals the CdIN2O3 distorted octahedral geometry, and the microporous channel (∼1.7 nm) is generated by polycatenation along with the supramolecular interaction. On thermal treatment at 120 °C the polymer, 1, loses solvents, while the crystalinity is reserved. The solvent-free activated state of the coordination polymer, [Cd2I2(BDC)2(INH)2] n , 1′, adsorbs N2, and the adsorption–desorption analysis displayed the increase in porosity to mesoporous range (∼14.7 nm) with very high specific Brunauer–Emmett–Teller surface area, which may be due to the rise in interparticle void space. Iodine (I2) sorption studies of mesoporous architecture of 1′ show high I2 removal efficiency (98.9%), which is revealed from the reversible iodine uptake kinetics study. Typically, uptake of three moles of I2 per unit cell associated with color change from colorless to brown is discernible from thermal analysis. Interestingly, the iodine-loaded polymer (I 2 @1′) shows ∼1.5 times enhancement in electrical conductivity compared to 1′ only. The optical band gap obtained from density functional theory (DFT) calculation and the experimental values are 1, 3.48 eV (DFT), 3.70 eV (experimental) and I 2 @1′, 3.19 eV (DFT), 3.50 eV (experimental). The lowering of band gap after I2 sorption is presumably due to the interaction of I2 with Cd–I (Cd–I···I–I) in hcb core, which was evidenced from Raman spectra analysis.

Tris(abpy) complexes of types mer-[Cu(II)(abpy)3][PF6]2 (mer-1(2+)[PF6(–)]2) and ctc-[Cu(II)(abpy)2(bpy)][PF6]2 (ctc-2(2+)[PF6(–)]2) were successfully isolated and characterized by spectra and single-crystal X-ray structure determinations (abpy = 2,2′-azobispyridine; bpy = 2,2′-bipyridine). Reactions of mer-1(2+) and ctc-2(2+) ions with catechol, o-aminophenol, p-phenylenediamine, and diphenylamine (Ph–NH–Ph) in 2:1 molar ratio afford [CuI(abpy)2](+) (3(+)) and corresponding quinone derivatives. The similar reactions of [Cu(II)(bpy)3](2+) and [Cu(II)(phen)3](2+) with these substrates yielding [Cu(I)(bpy)2](+) and [Cu(I)(phen)2](+) imply that these complexes undergo reduction-induced ligand dissociation reactions (phen = 1,10-phenanthroline). The average −N═N– lengths in mer-1(2+)[PF6(–)]2 and ctc-2(2+)[PF6(–)]2 are 1.248(4), while that in 3(+)[PF6(–)]·2CH2Cl2 is relatively longer, 1.275(2) Å, due to dCu → πazo* back bonding. In cyclic voltammetry, mer-1(2+) exhibits one quasi-reversible wave at −0.42 V due to Cu(II)/Cu(I) and abpy/abpy(•–) couples and two reversible waves at −0.90 and −1.28 V due to abpy/abpy(•–) couple, while those of ctc-2(2+) ion appear at −0.44, −0.86, and −1.10 V versus Fc(+)/Fc couple. The anodic 3(2+)/3(+) and the cathodic 3(+)/3 redox waves at +0.33 and −0.40 V are reversible. The electron paramagnetic resonance spectra and density functional theory (DFT) calculations authenticated the existence of abpy anion radical (abpy(•–)) in 3, which is defined as a hybrid state of [Cu(I)(abpy(0.5•–))(abpy(0.5•–))] and [Cu(II)(abpy(•–))(abpy(•–))] states. 3(2+) ion is a neutral abpy complex of copper(II) of type [Cu(II)(abpy)2](2+). 3 exhibits a near-IR absorption band at 2400–3000 nm because of the intervalence ligand-to-ligand charge transfer, elucidated by time-dependent DFT calculations in CH2Cl2.

Naphtheledicarboxylato ((NDC 2− ) bridged coordination polymers (CPs) along with (E)-1-methyl-2-(p-chlorophenylazo)imidazole (ClPai-Me) coordination to Co(II), [Co(∝-NDC) 0.5 (∝ 4 -NDC) 0.5 (ClPai-Me)]•0.5H 2 O (1), and to Zn(II), [Zn(∝-NDC) 0.5 (∝ 4 -NDC) 0.5 (ClPai-Me)]•0.5H 2 O (2), have been characterized. In the single crystal X-ray structure of 1, ClPai-Me chelates to the Co(II) ion by N(azo) and N(imidazolyl), whereas in compound 2, it acts as a monodentate N(imidazolyl) donor to the Zn(II) ion. The coordination atmosphere around Co(II) in the 1 ion is distorted octahedral CoN 2 O 4 , whereas in the case of 2, it is distorted square pyramidal ZnNO 4 . Compounds 1 and 2 exhibit the righthanded (P) and left-handed (M) one-dimensional helical chain. NDC −2 is serving as a bridge between two M(II) ions to constitute μ-NDC and four M(II) ions to construct μ 4 -NDC to assemble threedimensional polymers. Upon UV light (369 nm) irradiation, compound 2 shows trans-to-cis isomerization of -NN−C 6 H 4 −Clp both in the solid and solution state but 1 remains silent. Prolonged light irradiation in the solid state (film phase) does not change the coordinated ClPai-Me in complexes 1 and 2, whereas the free stage of ClPai-Me undergoes photoreduction of the −NN− bond and forms azo radicals with a concomitant permanent color change. The persistence of the radical has been characterized by electron paramagnetic resonance spectroscopy in the solid state at g = 2.009. The effective magnetic moment of 1 is 4.17 μ B at 300 K, Co(II) ion of S = 3/2.

A one-dimensional coordination polymer (1D CP), [Cd­(bpe)­(p-brba)2] n (1), has been synthesized by the slow diffusion method keeping the mixture of Cd­(NO3)2·6H2O and 1,2-bis­(4-pyridyl)­ethylene (bpe) ligand along with para-bromobenzoic acid (p-brba) in the dark. Interestingly, the compound 1 undergoes a single-crystal to single-crystal (SCSC) photochemical [2 + 2] cycloaddition reaction to generate dimerized 1D CP [Cd­(rctt-tpcb)1/2(p-brba)2] n (2) [rctt-tpcb = rctt-tetrakis­(4-pyridyl)­cyclobutane]. As a result, π···π stacking interactions among p-brba ligands of adjacent chains have been removed in the dimerized product. This structural transformation has a significant effect on the conductivity of the materials.

A new mixed-ligand divalent one-dimensional coordination polymer (1D CP) [Zn(adc)(4-nvp) 2 (H 2 O) 2 ] n , ( 1 ) [H 2 adc = acetylenedicarboxylic acid and 4-nvp = 4-(1-naphthylvinyl)pyridine] has been synthesized and well characterized by elemental analysis, infrared spectrum, single-crystal X-ray crystallography, powder X-ray diffraction pattern, and thermogravimetric analysis. The compound 1 constructs a 3D supramolecular network by the combination of hydrogen bonding, C–H···π, and π···π interactions. Interestingly, the material shows Schottky behavior which is exclusively analyzed with the help of thermionic emission and space charge-limited current theory. In addition, the Schottky barrier diode parameters for compound 1 demonstrate better device performance after light soaking. Hence, the compound has applicability in the fabrication of optoelectronic devices.

o-Imino-p-R'-benzosemiquinone anion radical (L(R')(IS)(˙-)) complexes of oxidovanadium(IV) of type [(L(1)(R-))(VO(2+))(L(R')(IS)(˙-))] (R = H, R' = H, 1; R = H, R' = -CMe(3), 2; R = -CMe(3), R' = H, 3 and R = -CMe(3), R' = -CMe(3), 4) incorporating the redox-innocent tridentate NNO-donor L(1)(R-) ligands (L(1)(R)H = 2,4-di-R-6-{(2-(pyridin-2-yl)hydrazono)methyl}phenol) were isolated and substantiated by elemental analyses, IR, mass, NMR and UV-vis spectra including the single crystal X-ray structure determinations. The V-O(phenolato) (cis to the V=O) lengths spanning 1.905(3)-1.9355(15) Å in 1-4 are consistent with the coordination to the [VO](2+) state. The V-O(IS) (trans to the V=O) lengths, 2.1505(17)-2.1869(15) Å, in 1-4 are longer due to the trans influence of the V=O bond. The V-N(IS) lengths, 1.906(3)-1.924(2) Å, in 1-4 are comparatively shorter due to the higher affinity of the paramagnetic [VO](2+) ion towards the L(R')(IS)(˙-) anion radicals. Density functional theory (DFT) calculations using B3LYP, B3PW91 and PBE1PBE functionals on 1 and 2 authenticated that the closed shell singlet (CSS) solutions (dianionic o-amido-p-R'-phenolates (L(R')(AP)(2-)) coordinated to VO(3+), Type I) of 1-4 are unstable with respect to the open shell singlet (OSS) perturbations. Broken symmetry, BS (1,1) M(s) = 0 (L(R')(IS)(˙-) coordinated to the VO(2+) ion, Type III) solutions of 1-4 are stable and reproduce the experimental bond parameters. Frozen glasses EPR spectra of [1-4](+) ions (e.g. g(||) = 1.948, g(⊥) = 1.978, A(||) = 184 (22 G), A(⊥) = 62(15 G) for [2](+)) and unrestricted DFT calculations on [1](+), [2](+), [1](-) and [2](-) ions using doublet spin state elucidated that the reversible anodic waves at [0.15-0.31] V of 1-4 complexes are due to the oxidation of L(R')(IS)(˙-) generating [(L(1)(R-))(VO(2+))(L(R')(IQ))]+ complexes (L(R')(IQ) = o-imino-p-R'-benzoquinone) coordinated to the [VO](2+) ion (Type V) while the irreversible cathodic waves at -[1.08-1.49] V are due to the formation of unstable [(L(1)(R-))(VO(2+))(L(R')(AP)(2-))](-) complexes (Type II). The second anodic waves at [0.76-0.89] V are assigned to a [VO](3+)-[VO](2+) couple affording diamagnetic [(L(1)(R-))(VO(3+))(L(R')(IQ))](2+), [1-4](2+) complexes (Type VI) which are identified by UV-vis spectra, DFT and time dependent (TD) DFT calculations. Spectro-electrochemical measurements and TD DFT calculations on 1 and 2 disclosed that lower energy electronic absorption bands of 1-4 are due to the LMCT and CSS-OSS perturbation which disappear in [1-4](+) ions. [1-4](+) absorb at 600-650 nm due to d-d transitions and MLCT which are absent in VO(3+) complexes, [1-4](2+).

A heteroporous metal–organic framework, [Cd2(2,2′-DSB)2(INH)2(H2O)2] n (1), is fabricated by the reaction of CdI2, 2-mercaptobenzoic acid (2-MBAH), and isoniazid (INH). The X-ray structure of the compound 1 shows the bridging INH and 2,2′-disulfanediyldibenzoic acid (H22,2′-DSBA) around the Cd­(II) ion center. 2-MBAH has been in situ dimerized to the formation of 2,2′-DSB2– (S–S-bonded dianion), which has further extended to form the 2D network. However, supramolecular assembly via π···π and hydrogen bonds strengthens the structural motif within the 3D array. Optical stimulation generated the thiol radical under an argon environment followed by the electron paramagnetic resonance (EPR) study, but upon exposure to air, the EPR signal gradually disappeared by the formation of the S–S bond, which was commonly known as a self-healing property. Again, compound 1 exhibited as a semiconducting material with a band gap of 3.7 eV. The I–V characteristics of 1 show that the conductivity is intensified by an optical response. The Schottky diode property of 1 shows a lower barrier height, a lower resistance, and a higher conductivity upon illumination at 360 nm.