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Neat reaction between Hg[I.sub.2] and 1-methyl-2-(phenylazo)imidazole under microwave irradiation has synthesized [Hg[I.sub.2]][[RaaiR'].sub.2], where RaaiR' = 1-alkyl-2-(arylazo)imidazole, in which the layers of reactants are separately positioned in the crystal structure. The activation energy ([E.sub.a]) of cis-to-trans of free ligands are found to be much higher than that of halo-bridged Hg(II)-azomidazole complexes, whereas chloro-bridged Hg(II) complexes have shown lower [E.sub.a]'s than those of iodo-bridged complexes.

Energy is the center of importance for the survivability of civilization. Use of fossil fuel is going to be suspended, and renewable energy is technologically costlier. In the quest for new energy sources and to minimize fuel expenditure, the design of energy efficient devices is one of the solutions. Toward this objective, highly delocalized π-acidic N-hetreocycle pyrazine bridged Cd(II)-based coordination polymers (CPs), [Cd(tppz)(adc)(MeOH)] ( 1 ), [Cd(tppz)(trep)] ( 2 ), and [Cd(tppz)(2,6-ndc)] ( 3 ; tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) are synthesized in combination with π-accessible dicarboxylato linkers (acetylene dicarboxylic acid (H 2 adc), terephthalic acid (H 2 trep), and 2,6-naphthalene dicarboxylic acid (2,6 H 2 ndc)). The structures of the compounds, 1 - 3 , have been confirmed by single-crystal X-ray diffraction measurements. Analysis of electrical property demonstrates that light irradiation enhances the conductivity and follows the order 3 > 2 > 1 ; compound 3 possesses the highest conductivity (1.93 × 10 -3 (light), 1.12 × 10 -4 S m -1 dark)), than 2 (1.80 × 10 -4 (light), 1.10 × 10 -4 S m -1 (dark)) and 1 (5.06 × 10 -5 (light), 4.72 × 10 -5 S m -1 (dark)). This light-induced electrical conductivity can pave the way toward fabrication of an active electronic device by using the discussed materials.

Multidimensional applicability of functional materials is one of the focal attractions in today's scientific research. Highly stable and crystalline coordination polymers served as one of the active members in the club of multifunctional materials. Toward this concept, a 3-dimensional (3D) coordination framework, {[Zn 2 ( tdc ) 2 ( pcih ) 2 ] n } ( 1 ) ( tdc 2- , 2,5-thiophene dicarboxylate; pcih , pyridine-4-carboxaldehyde isonicotinoyl hydrazine), is designed and has been structurally well characterized by single crystal X-ray crystallography. One of the carboxylate groups of tdc 2- chelates to Zn(II), while the other carboxylato group (-COO) acts as bridging-O to neighboring Zn(II); the pcih serves as pyridyl-N bridging motif to two Zn(II) centers. The optical band gap, 3.83 eV (Tauc's plot), implies probable semiconducting ability of the material. Interestingly, the device fabricated using compound 1 measures the electrical conductivity, 2.21 × 10 -5 S cm -1 , and series resistance ( R s ), 807 Ω, at the dark phase, which are improved significantly to 6.36 × 10 -5 S cm -1 and 460 Ω, respectively, under illumination conditions. Isoniazid, used to synthesize pcih and hence the Zn(II) compound 1 , is a medicine; so, the medicinal efficiency of 1 is checked by measuring the anticancer activity against MDA-MB-231, HeLa, HCT-116, and HepG2 cells. It is observed that drug efficacy is highest on MDA-MB-231 cells (IC 50 : 19.43 ± 1.36 μM) than other cancer cells [IC 50 : 24.43 ± 2.02 μM (HeLa), 26.06 ± 3.48 μM (HCT-116), and 44.28 ± 3.04 μM (HepG2)]. Therefore, the material has significant contribution in the area of energy and health toward the sustainable development goals.

Pyridyl-substituted imidazoquinoline, a potent fluorescent framework, is advantageous to architect multifunctional coordination networks for sensing and fabricating emergent electrical conductors. In this work, a Cd(II)-based one-dimensional (1D) coordination polymer (1D CP), [Cd(glu) 2 ( pbiq ) 2 (H 2 O)] n ( 1 ), [ H 2 glu = glutaric acid and pbiq = 4-(6-(pyridin-4-yl)benzo[4,5]imidazo[1,2- c ]quinazoline)], has been structurally confirmed by single-crystal X-ray crystallography. The H-bonding and π···π interactions built a three-dimensional (3D) supramolecular structure that strongly emits at 416 nm in acetonitrile suspension. Potentially intrusive nitroaromatics (NAs) and trinitrophenol (TNP) selectively quench the strong emission of 1 , and the highest quenching is noted in the case of TNP. A detection limit (limit of detection (LOD)) of 1.51 × 10 -7 M for TNP is determined. The band gap (3.31 eV) of 1 recognizes semiconducting behavior, and an electronic device is fabricated. The correlation of current vs voltage ( I - V plot) reveals a substantial non-ohmic electrical conductivity of 1 (Λ: 1.10 × 10 -5 S m -1 ) along with a low energy barrier (Φ B : 0.69), and the series resistance ( R s ) becomes 6.21 kΩ.

Photoluminescence activity of coordination polymers (CPs) has evoked intricate applications in the field of materials science, especially sensing of ions/molecules. In the present study, 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 5-aminoisophthalate (HAIPA - ) coordinated to Cd(II) to architect a coordination polymer, {[Cd(HAIPA)(tppz)(OH)]·3H 2 O} n (CP 1 ) which unveils blue emission in an aqueous acetonitrile (98% aqueous) suspension. The emission is selectively quenched by Pd 2+ only without interference in the presence of as many as 16 other cations. The structure of CP 1 shows the presence of a free -COOH group, and the interlayer (-CO)O(2)···O(7) (OC-) distance, 4.242 Å, along with the π···π interactions (3.990, 3.927 Å), may make a cavity which suitably accommodates only Pd 2+ (van der Waal's radius, 1.7 Å) through the Pd(II)-carboxylato (-COO-Pd) coordination. The stability of the composite, [CP 1 + Pd 2+ ] may be assessed from the fluorescence quenching experiment, and the Stern-Volmer constant ( K SV ) is 7.2 × 10 4 M -1 . Therefore, the compound, CP 1 , is a promising sensor for Pd(II) in a selective manner with limit of detection (LOD), 0.08 μM. The XPS spectra of CP 1 and [CP 1 + Pd 2+ ] have proven the presence of Pd 2+ in the host and the existence of a coordinated -COO-Pd bond. Interestingly, inclusion of Pd 2+ in CP 1 decreases the band gap from 3.61 eV (CP 1 ) to 3.05 eV ([CP 1 + Pd 2+ ]) which lies in the semiconducting region and has exhibited improved electrical conductivity from 7.42 × 10 -5 (CP 1 ) to 1.20 × 10 -4 S m -1 ([CP 1 + Pd 2+ ]). Upon light irradiation, the electrical conductivities are enhanced to 1.45 × 10 -4 S m -1 (CP 1 ) and 3.81 × 10 -4 S m -1 ([CP 1 + Pd 2+ ]); which validates the highly desired photoresponsive device applications. Therefore, such type of materials may serve as SDG-army (sustainable development goal) to battle against the environmental issues and energy crisis.

The coordination polymer, (Zn(II)-CP, 1 ), {[Zn(2,6-NDC)(4-Cltpy)](H 2 O) 4 } ( 1 ) (2,6-H 2 NDC = 2,6-naphthalene dicarboxylic acid and 4-Cltpy = 4'-chloro-[2,2';6',2″]terpyridine) is structurally characterized by single crystal X-ray diffraction measurement and other physicochemical studies (PXRD, FTIR, thermal analysis, microanalytical data). 4-Cltpy acts as end-capping ligand, and NDC 2- is a carboxylato bridging motif to constitute ZnN 3 O 2 distorted trigonal bipyramid core that propagates to construct 1D chain. The coordination polymer, 1 , detects total iron (Fe 3+ and Fe 2+ ) in aqueous solution by visual color change, colorless to pink. Absorption spectrophotometric technique in aqueous medium measures the limit of detection (LOD) 0.11 μM (Fe 2+ ) and 0.15 μM (Fe 3+ ), and binding constants (K d ) are 6.7 × 10 4 M -1 (Fe 3+ ) and 3.33 × 10 4 M -1 (Fe 2+ ). Biocompatibility of 1 is examined in live cells, and intracellular Fe 2+ and Fe 3+ are detected in MDA-MB 231 cells. Zn(II) substitution is assumed upon addition of Fe III /Fe II solution to the suspension of the coordination polymer, 1 , in water-acetonitrile (41:1) (LZn II + Fe III/II → LFe III + Zn II , where L is defined as coordinated ligands), which is accompanied by changing from colorless to pink at room temperature. The color of the mixture may be assumed to the charge transfer transition from carboxylate-O to Cltpy via Fe(II/III) bridging center (carboxylate-O-Fe-CltPy). The product isolated from the reaction is finally characterized as Fe(III)@1 -CP. It is presumed that product Fe(II)@1 -CP may undergo fast aerial oxidation to transform Fe(III)@1 -CP. The Fe III exchanged framework ( Fe(III)@1 -CP) has been characterized by PXRD, IR, TGA and energy dispersive X-ray analysis (EDX)-SEM. The MTT assay calculates the cell viability (%), and the tolerance limit is 100 μM to total Fe 2+ and Fe 3+ .

A Zn(II) based two-dimensional metal-organic framework (2D MOF) [Zn 2 (suc) 2 (4-nvp) 2 ] ( 1 ) [H 2 suc = succinic acid and 4-nvp = 4-(1-naphthylvinyl)pyridine] exhibits a "photosalient effect" under UV light as well as sunlight along with the release of a stereoselective cyclobutane ligand, 1,3-bis(4'-pyridyl)-2,4-bis(naphthyl)cyclobutane ( rctt -4-pncb). Photolysis of in situ generated MOF in solution also leads to the formation of rctt -4-pncb crystals. Interestingly, compound 1 shows a high selectivity for Pd(II) sensing in aqueous medium.

A heteroporous metal-organic framework, [Cd 2 (2,2'-DSB) 2 (INH) 2 (H 2 O) 2 ] n ( 1 ), is fabricated by the reaction of CdI 2 , 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 (H 2 2,2'-DSBA) around the Cd(II) ion center. 2-MBAH has been in situ dimerized to the formation of 2,2'-DSB 2- (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.

A metal-organic compound [Cd(quin) 2 (4-nvp) 2 ] [1; Hquin = quinoline-2-carboxylic acid and 4-nvp = 4-(1-naphthylvinyl)pyridine] undergoes topochemical [2 + 2] cycloaddition by sunlight irradiation to generate a one-dimensional coordination polymer. This reaction is thermally reversible, and switching between two crystalline forms can be monitored by conductivity measurements.

A novel mixed ligand one-dimensional coordination polymer (1D CP), {[Cd 2 (adc) 2 (4-nvp) 6 ]·(MeOH)·(H 2 O)} n (1; H 2 adc = 9,10-anthracenedicarboxylic acid, and 4-nvp = 4-(1-naphthylvinyl)pyridine), has been synthesized and structurally characterized by single crystal X-ray crystallography. The 1D polymer undergoes supramolecular aggregation via hydrogen bonding, C-H···π, and π···π interactions. Interestingly, compound 1 shows increasing conductivity upon irradiation of light. Therefore, it has the potential to be used in optoelectronic devices. Moreover, the supramolecular assembly of 1 specifically detects Cr 3+ cation in the presence of other competitive analytes. Most importantly, compound 1 exhibits fascinating turn-on Cr 3+ sensing, which seems to be an ornament in the field of sensing application.

A pair of 4-(1-naphthylvinyl)pyridine (4-nvp) ligands has been successfully aligned in head-to-tail fashion in a one-dimensional (1D) double chain ladder polymer [Cd(adc)(4-nvp) 2 (H 2 O)] n (1; H 2 adc = acetylenedicarboxylic acid) that undergoes a photochemical [2 + 2] cycloaddition reaction accompanied by single-crystal to single-crystal (SCSC) structural transformation from a 1D chain to a 2D layer structure. These structural changes have a significant impact on the conductivity and Schottky nature of the compound.

Neat reaction between HgI2 and 1-methyl-2-(phenylazo)imidazole (Pai-Me) under microwave irradiation has isolated a novel compound whose structure shows intercalated HgI2 in the layers of Pai-Me. They exist independently in interpenetrated arrays. In a solution phase study, the same reaction has synthesized an iodo-bridged azoimidazole-Hg(II) complex, [Hg(RaaiR')(mu-I)(I)]2 (RaaiR' = 1-alkyl-2-(arylazo)imidazole). The structures have been characterized by X-ray diffraction studies. Chloro-bridged Hg(II) complexes of azoimidazoles, [Hg(RaaiR')(mu-Cl)(Cl)]2, are also known. These complexes upon irradiation with UV light show trans-to-cis isomerization. The reverse transformation, cis-to-trans isomerization, is very slow with visible light irradiation. Quantum yields (phi t-->c) of trans-to-cis isomerization are calculated, and the free ligand shows higher phi than their Hg(II) complexes. The cis-to-trans isomerization is a thermally induced process. The activation energy (Ea) of cis-to-trans isomerization is calculated by controlled temperature reaction. The Ea's of free ligands are much higher than that of halo-bridged Hg(II)-azoimidazole complexes. Chloro-bridged Hg(II) complexes show lower Ea's than those of iodo-bridged complexes. DFT calculation has been adopted to rationalize the experimental results.

The first azo-imine chelate system, Pd(N(H)C(R)NNPh)(2) (Pd(RA)(2)), has been isolated in the form of diamagnetic solids by the 6e(-)-6H(+) reduction of bis(phenylazooximato)palladium(II), Pd(N(O)C(R)NNPh)(2) (abbreviated Pd(RB)(2)), with ascorbic acid in a mixed solvent (R = Ph, alpha-naphthyl). Selected spectral features are described. The X-ray structures of Pd(PhA)(2) and Pd(PhB)(2) have revealed trans-planar geometry consistent with metal oxidation state of +2. Bond length trends within the chelate rings are rationalized in terms of steric and electronic factors. In Pd(PhA)(2) a total of 10 ligand pi electrons are present, each formally monoanionic ligand contributing five. Model EHMO studies have revealed that the filled HOMO (a(u)) in Pd(RA)(2) is a bonding combination of two ligand pi orbitals with large azo contributions. The LUMO (b(g)) is roughly the corresponding antibonding combination. The outer pi-electron configuration of Pd(RA)(2) is (a(u))(2)(b(g))(0). Four successive voltammetric responses, two oxidative and two reductive, are observed. The E(1/2) range is -1.3 to +0.8 V vs SCE for Pd(PhA)(2) in a 1:9 MeCN-CH(2)Cl(2) mixture (Pt electrode). EPR and electronic spectra of the electrogenerated one-electron-oxidized complex Pd(PhA)(2)(+) are described. The azo-imine system is compared with imine-imine and azo-azo systems. Crystal data for the complexes are as follows. Pd(PhA)(2): crystal system monoclinic; space group C2/c; a = 18.167(5) Å, b = 7.420(3) Å, c = 16.527(6) Å; beta = 92.70(3) degrees; V = 2225(1) Å(3); Z = 4; R = 2.61%, R(w) = 3.58%. Pd(PhB)(2): crystal system monoclinic; space group P2(1)/n; a = 5.735(5) Å, b = 10.797(6) Å, c = 18.022(11) Å; beta = 97.73(6) Å; V = 1105(1) Å(3); Z = 2; R = 3.37%; R(w) = 3.40%.