Thermal Conductivities and Figures of Merit of Tetracyanoquinodimethane-Based Thermoelectric Materials Consisting of Cations Exhibiting Order–Disorder Transitions

A reduction in thermal conductivity is a common challenge in the development of thermoelectric materials. The thermal conductivity of molecule-based crystals can be reduced by vibrating or disordered counter ions that scatter the heat-transporting phonons. In this work, the thermoelectric properties of five 1:2 salts of tetracyanoquinodimethane (TCNQ) were examined to study the effect of counter ions on the order–disorder transitions in thermal conductivity and on the thermoelectric figure of merit. The tetraethylammonium (TEA+) and dipropylammonium (DPA+) salts of TCNQ0.5–, which undergo the order–disorder transitions above 200 K, exhibited significantly low thermal conductivities compared to the quinolinium (Q+) salt, which does not undergo any order–disorder transition. Methyltriphenylphosphonium (MTPP+) and methyltriphenylarsenium (MTPAs+) salts also showed lower thermal conductivities than the Q+ salt, presumably because of the heavy P and As atoms. Despite the wide variation in thermal conductivities, the product of the phonon velocity v and mean free path l was minimized at similar temperatures, presumably because of the common vibronic property exhibited by the TCNQ0.5– stacks. A comparison between the power factors Pmax and zT revealed the improvement of the conversion efficiency by the vibrating counter cations. The Pmax value for the DPA+ salt was approximately 23 times smaller than that for Q+; however, the thermal conductivity of the DPA+ salt in the disordered phase was approximately a quarter that of Q+, and the zT value for DPA+ remained 7 times smaller than that for Q+

Superparamagnetic Behavior in an Alkoxo-Bridged Iron(II) Cube

Superparamagnetic Behavior in an Alkoxo-Bridged Iron(II) Cub

Superparamagnetic Behavior in an Alkoxo-Bridged Iron(II) Cube

Superparamagnetic Behavior in an Alkoxo-Bridged Iron(II) Cub

Highly Proton-Conducting Mixed Proton-Transferred [(H₂PO₄^–)(H₃PO₄)]∞ Networks Supported by 2,2′-Diaminobithiazolium in Crystals

Hydrogen-bonding organic acid–base salts are promising candidates for the chemical design of high-performance anhydrous proton conductors. The simple molecular crystals between the π-planar molecules of 2,2′-diaminobithiazolium (DABT) derivative and hydrogen-bonding H3PO4 formed the proton-transferred salts with proton conductivities above ∼10–4 S cm–1 and anisotropic behavior. Controlling the crystallization condition facilitated the formation of binary salts between di-cationic H2DABT2+ and (H3PO4–)2 or mixed proton-transferred (H2PO4–)2(H3PO4)2 with different hydrogen-bonding networks, including one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) networks. The structural isomers of 2,2′-diamino-4,4′-bithiazolium (2,4-DABT) and 2,2′-diamino-5,5′-bithiazolium (2,5-DABT) formed a different type of packing structure even with the same crystal stoichiometry of (H2DABT2+)­(H2PO4–)2 and/or (H2DABT2+)­(H2PO4–)2(H3PO4)2 where the latter salt had different protonated species of H2PO4– and H3PO4 in the hydrogen-bonding network. Four and 10 protons per H2DABT2+ molecule (H+: carrier concentration) were present in the (H2DABT2+)­(H2PO4–)2 and (H2DABT2+)­(H2PO4–)2(H3PO4)2 salts, respectively, which accounted for the highly proton-conducting behavior in the latter mixed protonated crystal. To design anhydrous intrinsic H+ conductors, both the mixed proton transfer state and uniform O–H···O hydrogen-bonding interaction are essential factors that must be considered

Cyanide-Bridged Iron(II,III) Cube with Multistepped Redox Behavior

A building unit of Prussian blue was isolated as a cyanide-bridged iron cube of [FeII4FeIII4(CN)12(tp)8]·12DMF·2Et2O·4H2O [tp− = hydrotris(pyrazolyl)borate]. A cyclic voltammogram showed quasi-reversible four-stepped redox waves, which correspond to [FeIII4FeII4]/[FeIII5FeII3]+, [FeIII5FeII3]+/[FeIII6FeII2]2+, [FeIII6FeII2]2+/[FeIII7FeII1]3+, and [FeIII7FeII1]3+/[FeIII8]4+ processes. Controlled potential absorption spectral measurements revealed two intervalence charge-transfer bands at 816 and 1000 nm, which were assigned to charge transfers from FeII ions to adjacent and remote FeIII ions, respectively, in the cube

Single-Molecule Magnets of Ferrous Cubes: Structurally Controlled Magnetic Anisotropy

Tetranuclear FeII cubic complexes were synthesized with Schiff base ligands bridging the FeII centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4]·2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4]·2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4]·MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1−6, the alkoxo groups of the Schiff base ligands bridge four FeII ions in a μ3-mode forming [Fe4O4] cubic cores. The FeII ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4−6 are shorter than those in 1−3. Dc magnetic susceptibility measurements for 1−6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, −0.64, −0.66, and −0.67 cm-1 for 1−6, respectively. Ac magnetic susceptibility measurements for 4−6 showed both frequency dependent in- and out-of-phase signals, while 1−3 did not show out-of-phase signals down to 1.8 K, meaning 4−6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4−6. The bridging ligands R-sap2- in 1−3 and R-sae2- in 4−6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn−Teller distortions at FeII centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry

Molecular Assemblies of Tetrahedral Triphenylmethanol and Triphenylamine Derivatives Bearing −NHCOC_<i>n</i>H_2<i>n</i>+1 Chains

Nonplanar three-fold symmetrical triphenylmethanol (1: n = 10 and 2: n = 3) and triphenylamine (3: n = 10 and 4: n = 3) derivatives bearing three alkylamide (−NHCO­CnH2n+1) chains were studied in terms of their phase transitions, molecular assemblies, nano- or meso-structures, and dielectric responses. Slight modification of the structural core from a hydroxyl moiety (C–OH in 1) to a nitrogen atom (N in 3) drastically changed the molecular assembly structures and physical properties in solids. The molecular assembly of 1 showed a glass–plastic crystal phase transition at ∼340 K, whereas 3 only displayed a direct solid–liquid phase transition. Uniform microscale spheres and nanowires with average diameters of 2 μm and 200 nm, respectively, were observed for the molecular assemblies of 1 and 3 on substrate surfaces, respectively, corresponding to amorphous glass and one-dimensional hydrogen-bonding columnar structures. An α-type frequency- and temperature-dependent dielectric relaxation was observed in amorphous 1 during the glass–plastic crystal phase transition, whereas no dielectric anomalies were observed for 3. This difference was attributed to the subtle chemical modification of the central core from C–OH to N

Highly Proton-Conducting Mixed Proton-Transferred [(H₂PO₄^–)(H₃PO₄)]∞ Networks Supported by 2,2′-Diaminobithiazolium in Crystals

Hydrogen-bonding organic acid–base salts are promising candidates for the chemical design of high-performance anhydrous proton conductors. The simple molecular crystals between the π-planar molecules of 2,2′-diaminobithiazolium (DABT) derivative and hydrogen-bonding H3PO4 formed the proton-transferred salts with proton conductivities above ∼10–4 S cm–1 and anisotropic behavior. Controlling the crystallization condition facilitated the formation of binary salts between di-cationic H2DABT2+ and (H3PO4–)2 or mixed proton-transferred (H2PO4–)2(H3PO4)2 with different hydrogen-bonding networks, including one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) networks. The structural isomers of 2,2′-diamino-4,4′-bithiazolium (2,4-DABT) and 2,2′-diamino-5,5′-bithiazolium (2,5-DABT) formed a different type of packing structure even with the same crystal stoichiometry of (H2DABT2+)­(H2PO4–)2 and/or (H2DABT2+)­(H2PO4–)2(H3PO4)2 where the latter salt had different protonated species of H2PO4– and H3PO4 in the hydrogen-bonding network. Four and 10 protons per H2DABT2+ molecule (H+: carrier concentration) were present in the (H2DABT2+)­(H2PO4–)2 and (H2DABT2+)­(H2PO4–)2(H3PO4)2 salts, respectively, which accounted for the highly proton-conducting behavior in the latter mixed protonated crystal. To design anhydrous intrinsic H+ conductors, both the mixed proton transfer state and uniform O–H···O hydrogen-bonding interaction are essential factors that must be considered

Highly Proton-Conducting Mixed Proton-Transferred [(H₂PO₄^–)(H₃PO₄)]∞ Networks Supported by 2,2′-Diaminobithiazolium in Crystals

Hydrogen-bonding organic acid–base salts are promising candidates for the chemical design of high-performance anhydrous proton conductors. The simple molecular crystals between the π-planar molecules of 2,2′-diaminobithiazolium (DABT) derivative and hydrogen-bonding H3PO4 formed the proton-transferred salts with proton conductivities above ∼10–4 S cm–1 and anisotropic behavior. Controlling the crystallization condition facilitated the formation of binary salts between di-cationic H2DABT2+ and (H3PO4–)2 or mixed proton-transferred (H2PO4–)2(H3PO4)2 with different hydrogen-bonding networks, including one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) networks. The structural isomers of 2,2′-diamino-4,4′-bithiazolium (2,4-DABT) and 2,2′-diamino-5,5′-bithiazolium (2,5-DABT) formed a different type of packing structure even with the same crystal stoichiometry of (H2DABT2+)­(H2PO4–)2 and/or (H2DABT2+)­(H2PO4–)2(H3PO4)2 where the latter salt had different protonated species of H2PO4– and H3PO4 in the hydrogen-bonding network. Four and 10 protons per H2DABT2+ molecule (H+: carrier concentration) were present in the (H2DABT2+)­(H2PO4–)2 and (H2DABT2+)­(H2PO4–)2(H3PO4)2 salts, respectively, which accounted for the highly proton-conducting behavior in the latter mixed protonated crystal. To design anhydrous intrinsic H+ conductors, both the mixed proton transfer state and uniform O–H···O hydrogen-bonding interaction are essential factors that must be considered