Pyridyl-Isonicotinoyl Hydrazone-Bridged Zn(II) Coordination Framework with Thiophenedicarboxylato Link: Structure, Biological Activity, and Electrical Conductivity.

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, {[Zn2(tdc)2(pcih)2]n} (1) (tdc2-, 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 tdc2- 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 (Rs), 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 (IC50: 19.43 ± 1.36 µM) than other cancer cells [IC50: 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.

Giant Enhancement of Second Harmonic Generation Accompanied by the Structural Transformation of 7-Fold to 8-Fold Interpenetrated Metal-Organic Frameworks (MOFs).

Interpenetration in metal-organic frameworks (MOFs) is an intriguing phenomenon with significant impacts on their properties, and functional applications. Herein, we show that a 7-fold interpenetrated MOF (1) is transformed into an 8-fold interpenetrated MOF by the loss of DMF in a single-crystal-to-single-crystal manner. This is accompanied by a giant enhancement of the second harmonic generation (SHG ca. 125 times) and two-photon photoluminescence (ca. 14 times). The strengthened π-π interaction between the individual diamondoid networks and intensified oscillator strength of the molecules aid the augment of dipole moments and boost the nonlinear optical conversion efficiency. Large positive and negative thermal expansions of 1 occur at 30-150 °C before the loss of DMF. These results offer an avenue to manipulate the NLO properties of MOFs using interpenetration and provide access to tunable single-crystal NLO devices.

Putting the squeeze on CH4 and CO2 through control over interpenetration in diamondoid nets.

We report the synthesis, structure, and sorption properties of a family of eight diamondoid (dia) metal-organic materials (MOMs) that are sustained by Co(II) or Zn(II) cations linked by one of three rigid ligands: 4-(2-(4-pyridyl)ethenyl)benzoate (1), 4-(pyridin-4-yl)benzoate (2), and 4-(pyridin-4-yl)acrylate (3). Pore size control in this family of dia nets was exerted by two approaches: changing the length of the linker ligand from 1 to 3, and using solvent as a template to control the level of interpenetration in nets based upon 1 and 3. The resulting MOMs, dia-8i-1, dia-5i-3, dia-7i-1-Zn, dia-7i-1-Co, dia-4i-3-a, dia-4i-3-b, dia-4i-2, and dia-4i-1, exhibit 1D channels with pore limiting diameters (PLDs) of 1.64, 2.90, 5.06, 5.28, 8.57, 8.83, 11.86, and 18.25 Å, respectively. We selected dia nets for this study for the following reasons: their 1D channels facilitate study of the impact of pore size on gas sorption parameters in situations where pore chemistry is similar (pyridyl benzoate-type linkers) or identical (in the case of polymorphs), and their saturated metal centers eliminate open metal sites from dominating sorbent-solvate interactions and possibly masking the effect of pore size. Our data reveal that smaller pore sizes offer stronger interactions, as determined by the isosteric heat of adsorption (Qst) and the steepness of the adsorption isotherm in the low-pressure region. The porous MOM with the smallest PLD suitable for physisorption, dia-7i-1-Co, was thereby found to exhibit the highest Qst values for CO2 and CH4. Indeed, dia-7i-1-Co exhibits a Qst for CH4 of 26.7 kJ/mol, which was validated through grand canonical Monte Carlo simulation studies of CH4 adsorption. This Qst value is considerably higher than those found in covalent organic frameworks and other MOMs with unsaturated metal centers. These results therefore further validate the critical role that PLD plays in gas adsorption by porous MOMs.

Oxygen-initiated stereoselective thermal isomerisation of a cyclobutane derivative in the solid state.

Solid-state [2+2] photochemical cycloaddition reactions have been extensively studied after the classical work of Schmidt in the 1960s. Of these, trans-1,2-bis(4'-pyridyl)ethylene (bpe) is one of the well-studied alkenes to synthesize tetrakis(4-pyridyl)cyclobutane (tpcb). However, almost all the solid-state [2+2] cycloaddition reactions of bpe yielded, almost exclusively, one of the four possible isomers, namely, the rctt-tpcb (r=regio c=cis and t=trans). Here we describe a stereoselective synthesis of the tetrahedrally disposed rtct-tpcb by the solid-state thermal isomerization of the rctt-isomer in atmospheric air. We propose that this isomerization occurs through a topochemical unimolecular mechanism by a radical chain pathway, initiated by molecular oxygen. This is supported by the nature of products formed in air and nitrogen, detection of a radical in ESR spectral studies, ESI-MS crossover experiments, VT PXRD studies along with QM, MD and docking calculations. The formation of a unique isomer by thermal isomerization may be a general phenomenon to quantitatively synthesize other useful stereoisomers from the existing isomers of cyclobutane derivatives.

Metal-organic organopolymeric hybrid framework by reversible [2+2] cycloaddition reaction.

Organic polymers are usually amorphous or possess very low crystallinity. The metal complexes of organic polymeric ligands are also difficult to crystallize by traditional methods because of their poor solubilities and their 3D structures can not be determined by single-crystal X-ray crystallography owing to a lack of single crystals. Herein, we report the crystal structure of a 1D Zn(II) coordination polymer fused with an organic polymer ligand made in situ by a [2+2] cycloaddition reaction of a six-fold interpenetrated metal-organic framework. It is also shown that this organic polymer ligand can be depolymerized in a single-crystal-to-single-crystal (SCSC) fashion by heating. This strategy could potentially be extended to make a range of monocrystalline metal organopolymeric complexes and metal-organic organopolymeric hybrid materials. Such monocrystalline metal complexes of organic polymers have hitherto been inaccessible for materials researchers.

Impact of halogen⋯halogen interaction on the mechanical motion of a 3D Pb(II) coordination polymer of elusive topology.

Herein, we report the synthesis of a Pb(II) based three-dimensional coordination polymer (3D CP), [Pb(DCTP)]n (1) [H2DCTP = 2,5-dichloroterephthalic acid] with an unprecedented topology, which exhibits a photomechanical effect wherein crystals show jumping upon UV irradiation. The Pb(II) CP forms a type II Cl⋯Cl interaction, which weakens further upon UV irradiation to resolve the anisotropic mechanical strain. The work presented here could be a beacon to the nascent field of photoactuating smart materials.

Thermal cleavage of cyclobutane rings in photodimerized coordination-polymeric sheets.

Three coordination polymers, [Cd(2)(pvba)(2)(tbdc)(dmf)(2)] (1), [Co(2)(pvba)(2)(tbdc)(dmf)(2)(H(2)O)(2)] (2), and [Ni(2)(pvba)(2)(tbdc)(dmf)(2)(H(2)O)(2)] (3) (H(2)tbdc = 2,3,5,6-tetrabromobenzenedicarboxylic acid, Hpvba = trans-2-(4'-pyridyl)vinylbenzoic acid), were synthesized by solvothermal methods. The solid-state structures of compounds 1 and 2 were determined by X-ray crystallography. In compounds 1 and 2, the bimetallic cores acted as secondary building units that connected the tbdc ligands in one direction and a pair of pvba ligands, which were aligned in a head-to-tail parallel manner, in the orthogonal direction to form sheet structures. The C=C bonds in these pvba ligand pairs in all three compounds were well-aligned to undergo quantitative [2+2] cycloaddition reactions in the solid state under UV irradiation, thereby yielding their cyclobutane derivatives. This photochemical reaction appeared to facilitate structural transformations from one 2D structure into another in the solid state. The photoreactive Co(II)- and Ni(II) coordination polymers exhibited a reversible dehydration-rehydration reaction that was accompanied by color changes from pink to purple and green to yellow, respectively, owing to a change in coordination number from six to five. Magnetic studies showed that compound 2 was an antiferromagnet, which displayed a field-dependent transition with a critical field (H(c)) of 40 kOe at 2 K; the antiferromagnetic interaction between the Co(2) units was strengthened and weakened by dehydration and UV irradiation, respectively. The cyclobutane ligand in the photodimerized products was cleaved on heating to yield a mixture of trans- and cis-isomers of pvba, as monitored by (1)H NMR spectroscopy. The Cd(II) coordination polymer underwent quantitative cleavage of the cyclobutane ring whilst the other two underwent partial cleavage.

Photoreactivity of polymorphs of a ladder polymer with criss-cross and parallel orientations of C=C bonds.

Two polymorphic forms of a ladder coordination polymer [Zn2(µ-O2C-p-Tol)2(O2C-p-Tol)2(bpe)2] have parallel and criss-cross alignments of the C=C bond pairs. Both polymorphs undergo 100% [2+2] cycloaddition reaction but the one with a parallel orientation of C=C bonds (thermodynamic product) retains its single crystallinity after the reaction.

Solid-state conversion of a MOF to a metal-organo polymeric framework (MOPF) via [2+2] cycloaddition reaction.

The bpeb ligands aligned in a slip-stacked manner in a two-fold interpenetrated non-porous metal-organic framework (MOF) [Zn2(bpeb)(bdc)(fa)2] undergo [2+2] cycloaddition reaction in a single-crystal to single-crystal manner to a non-interpenetrated 3D structure with a new topology comprising an organic polymer ligand and a 2D coordination polymer.

Mechanochemical reactions of coordination polymers by grinding with KBr.

Grinding of a one-dimensional (1-D) ladder coordination polymer (CP), [Zn(µ-CH(3)CO(2))(CF(3)CO(2))bpe] (1), and a hydrogen-bonded 1-D CP, [Cd(CH(3)CO(2))(2)bpe(H(2)O)] (2), with KBr resulted in the exchange of carboxylate by bromide ions and the formation of 1-D zigzag and 2-D CPs respectively.