Temperature-Dependent Semiconducting Behavior of an Organic Cocrystal Driven by the Stacking Mode of Interaction of a 4,4′-Bipyridine Molecule

Organic cocrystals based on H-bonding as well as π-stacking interactions between 4,4′-bipyridine–pyromellitic acid (1) and 4,4′-bipyridine–phthalic acid (2) are reported. Cocrystals 1 and 2 were fully characterized by single-crystal X-ray diffraction and NMR and IR spectroscopy. The single-crystal X-ray diffraction shows the H stacking pattern of the adjacent 4,4′-bipyridine molecules in the construction of a 3D chain structure for cocrystal 1. Cocrystal 2, however, formed a zigzag 3D chain where the adjacent 4,4′-bipyridyl molecules are involved in a J-stacking mode. Experimental conductivity measurements of the cocrystals 1 and 2 with a Keithley 4200 SCS parameter analyzer showed the temperature-dependent semiconducting behavior in the case of cocrystal 1, whereas cocrystal 2 remained as an insulator. The favorable H-stacking interaction of 4,4′-bipyridine molecules which is the prime origin of semiconductivity in cocrystal 1 may become out of phase due to the free rotation along the C–C bond of 4,4′-bipyridine with an increase in temperature. Although the semiconducting behavior of a material increases with increasing temperature and decreases in resistivity, in the case of cocrystal 1 due to the probable phase transition of the 4,4′-bipyridyl molecules the material became an insulator with an increase in temperature from 20 °C to higher temperature, whereas the semiconducting behavior was restored after cooling the crystals to 20 °C again. The theoretical study conducted with the optimized structures of 1 and 2 showed the higher electron hopping rate in the case of cocrystal 1 as compared to 2 which can account for the charge conduction in the case of 1

Terbium(III), Europium(III), and Mixed Terbium(III)–Europium(III) Mucicate Frameworks: Hydrophilicity and Stoichiometry-Dependent Color Tunability

Two 3D porous terbium­(III) mucicate frameworks, {[Tb₂(Mu^2–)₃(H₂O)₂]·4H₂O}_<i>n</i> (<b>1</b>) and {[Tb­(Mu^2–)­(Ox^2–)_0.5(H₂O)]·H₂O}_<i>n</i> (<b>2</b>), have been synthesized under hydrothermal conditions by changing the pH of the reaction medium. Isostructural europium­(III) and seven mixed terbium­(III)–europium­(III) mucicates were synthesized by doping different percentages of Eu^III under similar reaction conditions and unveiling different emission colors ranging from green to red under the same wavelength. Both dehydrated Tb^III metal–organic frameworks exhibit selective H₂O vapor sorption over other solvent molecules (MeOH, MeCN, and EtOH) of less polarity and bigger size and have been correlated to the highly hydrophilic pore surfaces decorated with −OH groups and O atoms from the carboxyl groups of mucicate

Terbium(III), Europium(III), and Mixed Terbium(III)–Europium(III) Mucicate Frameworks: Hydrophilicity and Stoichiometry-Dependent Color Tunability

Two 3D porous terbium­(III) mucicate frameworks, {[Tb₂(Mu^2–)₃(H₂O)₂]·4H₂O}_<i>n</i> (<b>1</b>) and {[Tb­(Mu^2–)­(Ox^2–)_0.5(H₂O)]·H₂O}_<i>n</i> (<b>2</b>), have been synthesized under hydrothermal conditions by changing the pH of the reaction medium. Isostructural europium­(III) and seven mixed terbium­(III)–europium­(III) mucicates were synthesized by doping different percentages of Eu^III under similar reaction conditions and unveiling different emission colors ranging from green to red under the same wavelength. Both dehydrated Tb^III metal–organic frameworks exhibit selective H₂O vapor sorption over other solvent molecules (MeOH, MeCN, and EtOH) of less polarity and bigger size and have been correlated to the highly hydrophilic pore surfaces decorated with −OH groups and O atoms from the carboxyl groups of mucicate

Bimodal Magneto-Luminescent Dysprosium (Dy^III)‑Potassium (K^I)‑Oxalate Framework: Magnetic Switchability with High Anisotropic Barrier and Solvent Sensing

We report synthesis, characterization, and properties of a multifunctional oxalate framework, {KDy­(C₂O₄)₂(H₂O)₄}_<i>n</i> (<b>1</b>) (C₂O₄^2– = oxalate dianion) composed of two absolutely different metal ions in terms of their size, charge, and electronic configuration. Dehydrated framework (<b>1′</b>) exhibits permanent porosity and interesting solvent (H₂O, MeOH, CH₃CN, and EtOH) vapor sorption characteristics based on specific interactions with unsaturated alkali metal sites on the pore surface. Compound <b>1</b> shows solvent responsive bimodal magnetic and luminescence properties related to the Dy^III center. Compound <b>1</b> exhibits reversible ferromagnetic to antiferromagnetric phase transition upon dehydration and rehydration, hitherto unknown for any lanthanide based coordination polymer or metal–organic frameworks. Both the compounds <b>1</b> and <b>1′</b> exhibit slow magnetic relaxation with very high anisotropic barrier (417 ± 9 K for <b>1</b> and 418 ± 7 K for <b>1′</b>) which has been ascribed to the single ion magnetic anisotropy of the Dy^III centers. Nevertheless, compound <b>1</b> shows a metal based luminescence property in the visible region and H₂O molecules exhibit the strongest quenching effect compared to other solvents MeOH, MeCN, and EtOH, evoking <b>1′</b> as a potential H₂O sensor

Bimodal Magneto-Luminescent Dysprosium (Dy^III)‑Potassium (K^I)‑Oxalate Framework: Magnetic Switchability with High Anisotropic Barrier and Solvent Sensing

We report synthesis, characterization, and properties of a multifunctional oxalate framework, {KDy­(C₂O₄)₂(H₂O)₄}_<i>n</i> (<b>1</b>) (C₂O₄^2– = oxalate dianion) composed of two absolutely different metal ions in terms of their size, charge, and electronic configuration. Dehydrated framework (<b>1′</b>) exhibits permanent porosity and interesting solvent (H₂O, MeOH, CH₃CN, and EtOH) vapor sorption characteristics based on specific interactions with unsaturated alkali metal sites on the pore surface. Compound <b>1</b> shows solvent responsive bimodal magnetic and luminescence properties related to the Dy^III center. Compound <b>1</b> exhibits reversible ferromagnetic to antiferromagnetric phase transition upon dehydration and rehydration, hitherto unknown for any lanthanide based coordination polymer or metal–organic frameworks. Both the compounds <b>1</b> and <b>1′</b> exhibit slow magnetic relaxation with very high anisotropic barrier (417 ± 9 K for <b>1</b> and 418 ± 7 K for <b>1′</b>) which has been ascribed to the single ion magnetic anisotropy of the Dy^III centers. Nevertheless, compound <b>1</b> shows a metal based luminescence property in the visible region and H₂O molecules exhibit the strongest quenching effect compared to other solvents MeOH, MeCN, and EtOH, evoking <b>1′</b> as a potential H₂O sensor