Yun-Hu Han

Highly chemical and thermally stable luminescent EuxTb1−x MOF materials for broad-range pH and temperature sensors

New luminescent Ln-MOFs, [Ln2(D-cam)(Himdc)2(H2O)2] (Ln = Eu 1, Tb 2, D-H2cam = D-camphoric acid, H3imdc = 4,5-imidazole dicarboxylic acid) have been synthesized via hydro(solvo)thermal reactions. X-ray single crystal structure analysis reveals that they are isomorphic and both crystallize in the orthorhombic space group Pna21. Compound 1 shows good chemical resistance to both acidity and alkalinity solutions with pH ranging from 2 to 13 and is highly stable in several boiling solvents, which make it potentially useful for wide-range pH sensors, especially in the physiological environment with pH = 6.8–8.0. Careful adjusting of the codoping ratio of Eu3+/Tb3+ into the same framework of 1 affords a mixed Ln-MOF, formulated as [Eu0.7Tb0.3(D-cam)(Himdc)2(H2O)2]3, which has demonstrated to be a viable probe for sensing temperature in a wide temperature range from 100 to 450 K.

A dual-walled cage MOF as an efficient heterogeneous catalyst for the conversion of CO2 under mild and co-catalyst free conditions

A novel 3D → 3D interpenetrated Zn-polyhedral MOF [Zn6(TATAB)4(DABCO)3(H2O)3]·12DMF·9H2O (1) (H3TATAB = 4,4′,4′′-s-triazine-1,3,5-triyl-tri-p-aminobenzoic acid, DABCO = 1,4-diazabicyclo[2.2.2]octane) based on a dual-walled icosahedral cage has been assembled by incorporating zinc paddlewheel units with nitrogen-rich tritopic carboxylate ligands. Owing to the high density of Lewis acid active sites and affinity to CO2 of the cage, this material exhibits an excellent catalytic efficiency in the cycloaddition of propylene oxide with CO2 into propylene carbonate under mild conditions (100 °C and ambient CO2 pressure) with a high yield of 99% over 16 h. Moreover, the catalytic reaction is environmentally friendly without any need for co-catalysts and solvents.

Td-MoTe2: A possible topological superconductor

We measured the magnetoresistivity properties of Td-MoTe2 single crystal under the magnetic field up to 33 T. By analyzing the Shubnikov–de Haas oscillations of the longitudinal resistance Δρxx, a linear dependence of the Landau index n on 1/B is obtained. The intercept of the Landau index plot is 0.47, which is between 3/8 and 1/2. This clearly reveals a nontrivial π Berrys phase, which is a distinguished feature of the surface state in Td-MoTe2 single crystal. Accompanied by the superconductivity observed at TC = 0.1 K, Td-MoTe2 may be a promising candidate of the topological superconductor and opens a door to study the relationship between the superconductivity and topological physics.

Synthesis, structures, and magnetic properties of a series of new heterometallic hexanuclear Co2Ln4 (Ln = Eu, Gd, Tb and Dy) clusters

A series of new Co–Ln heterometallic clusters formulated as [Co2Ln4(μ3-OH)2(piv)4(hmmp)4(ae)2]·(NO3)2·2H2O (Ln = Eu (1), Gd (2), Tb (3), Dy (4), H2hmmp = 2-[(2-hydroxyethylimino)methyl]-6-methoxyphenol, Hae = 2-aminoethanol, Hpiv = pivalic acid) were synthesized and characterized. X-ray crystallography reveals that each of them contains a heterometallic {Ln4Co2} core, which is supported by two μ3-hydroxide, four piv−, four hmmp2− and two ae− ligands. The magnetic investigation indicates that 2 exhibits weak antiferromagnetic interactions between GdIII ions, and a large MCE value of 24.9 J kg−1 K−1, while 4 shows a fast relaxation of magnetization. The TGA and VT-PXRD measurements suggest that all the compounds show good thermal stability and can be stable up to about 220 °C. In addition, to address the influence of the Gd–O–Gd angles on the magnetic properties, compound 2 was compared with a series of compounds involving different bridges between GdIII ions. The comparison reveals that the tiny difference in the Gd–O–Gd angles favors different magnetic coupling.

High proton conductivity in an unprecedented anionic metalloring organic framework (MROF) containing novel metalloring clusters with the largest diameter

An attractive anionic metalloring organic framework (MROF-1) containing unprecedented sextuply interlocked nanocages made up of original metalloring clusters with the largest diameter of ca. 21 A shows a high proton conductivity up to 1.72 × 10−2 S cm−1 at 70 °C and 97% RH, owing to plenty of counter cations (Me2NH2)+ located in the 1D channels.

An unprecedented anionic Ln-MOF with a cage-within-cage motif: spontaneous reduction and immobilization of ion-exchanged Pd(II) to Pd-NPs in the framework

An unprecedented microporous anionic Ln-MOF, [Me2NH2]24[Tb12(TATB)16(HCOO)12]·12DMF·48H2O (1) (H3TATB = 4,4′,4′′-s-triazine-2,4,6-tribenzoic acid), which is a rare cage-within-cage structure through interpenetration rather than covalent bonding, has been synthesized. Compound 1 contains a 3D net which is constructed using a large and a small Ln-carboxylate cage alternately arranged by sharing faces with each other. Interpenetration of two identical 3D nets occurs in such a way that each small cage of one net is encapsulated within the large cage of the other and vice versa, generating an overall 3D double-walled cage framework. Such interpenetration creates a unique structure of double-shelled hollow space to accommodate Pd nanoparticles (Pd-NPs), which could effectively prevent Pd-NPs from aggregation and leaching. Moreover, the ion-exchanged Pd(II) embedded in the framework can be readily reduced at room temperature with no requirement of any chemical or thermal treatments, affording Pd-NPs with uniform size and even distribution. As a result, the as-prepared Pd-NPs@1 exhibits excellent activity and cycling stability for the hydrogenation of styrene and its derivatives.

Resistivity plateau and large magnetoresistance in the charge density wave system TaTe4

Due to the time reversal symmetry, the metallic surface of the topological insulator (TI) survives and results in the resistivity plateau at low temperature, which is the transport signature of the metallic surface state. Such a universal character has been observed in many materials, such as Bi2Te2Se, SmB6, and so on. Recently, a similar behavior has also been found in the possible topological semimetal LaSb/Bi and the metallic compounds Nb/TaAs2. Herein, we have mainly explored the resistivity plateau and the magnetoresistance (MR) of TaTe4 single crystal with the charge density wave (CDW) transition temperature TCDW = 475 K. There are some interesting observations: (i) The large MR (MR is about 1200% in a magnetic field 16 T at T = 2 K) is observed at low temperature; (ii) A field-induced universal TI resistivity with a plateau at roughly T = 10 K and high quantum mobility of carriers in the plateau region are present; (iii) Quantum oscillations with the angle dependence of a two-dimensional Fermi surf...

Superconductivity in CaSn3 single crystals with a AuCu3-type structure

We report the superconductivity of CaSn3 single crystals with a AuCu3-type structure, namely cubic space group Pmm. The superconducting transition temperature TC = 4.2 K is determined by the magnetic susceptibility, electrical resistivity, and heat capacity measurements. The magnetization versus magnetic field (M–H) curve at low temperatures shows a typical-II superconducting behavior. The estimated lower and upper critical fields are about 125 Oe and 1.79 T, respectively. The penetration depth λ(0) and coherence length ξ(0) are calculated to be approximately 1147 nm and 136 nm by the Ginzburg–Landau equations. The estimated Sommerfeld coefficient of the normal state γN is about 2.9 mJ mol−1 K−2. ΔC/γNTC = 1.13 and λep = 0.65 suggest that the CaSn3 single crystal is a weakly coupled superconductor. Electronic band structure calculations show a complex multi-sheet Fermi surface formed by three bands and a low density of states (DOSs) at the Fermi level, which is consistent with the experimental results. Based on the analysis of electron–phonon coupling of AX3 compounds (A = Ca, La, and Y; X = Sn and Pb), we theoretically proposed a way to increase TC in the system.

Mobility spectrum analytical approach for the type-II Weyl semimetal Td-MoTe2

The extreme magnetoresistance (XMR) in orthorhombic W/MoTe2 arises from the combination of the perfect electron-hole (e-h) compensation effect and the unique orbital texture topology, which have comprised an intriguing research field in materials physics. Herein, we apply a special analytical approach as a function of mobility (μ-spectrum) without any hypothesis. Based on the interpretations of longitudinal and transverse electric transport of Td-MoTe2, the types and the numbers of carriers can be obtained. There are three observations: the large residual resistivity ratio can be observed in the MoTe2 single crystal sample, which indicates that the studied crystal is of high quality; we observed three electron-pockets and three hole-ones from the μ-spectrum and that the ratio of h/e is much less than 1, which shows that MoTe2 is more e-like; different from the separated peaks obtained from the hole-like μ-spectrum, those of the electron-like one are continuous, which may indicate the topological feature of electron-pockets in Td-MoTe2. The present results may provide an important clue to understanding the mechanism of the XMR effect in Td-MoTe2.The extreme magnetoresistance (XMR) in orthorhombic W/MoTe2 arises from the combination of the perfect electron-hole (e-h) compensation effect and the unique orbital texture topology, which have comprised an intriguing research field in materials physics. Herein, we apply a special analytical approach as a function of mobility (μ-spectrum) without any hypothesis. Based on the interpretations of longitudinal and transverse electric transport of Td-MoTe2, the types and the numbers of carriers can be obtained. There are three observations: the large residual resistivity ratio can be observed in the MoTe2 single crystal sample, which indicates that the studied crystal is of high quality; we observed three electron-pockets and three hole-ones from the μ-spectrum and that the ratio of h/e is much less than 1, which shows that MoTe2 is more e-like; different from the separated peaks obtained from the hole-like μ-spectrum, those of the electron-like one are continuous, which may indicate the topological feature o...

Anomalous Hall effect in two-dimensional non-collinear antiferromagnetic semiconductor Cr0.68Se

Cr0.68Se single crystals with two-dimensional (2D) character have been grown, and the detailed magnetization M(T), electrical transport properties (including longitudinal resistivity and Hall resistivity and thermal transport ones (including heat capacity Cp(T) and thermoelectric power (TEP) S(T)) have been measured. There are some interesting phenomena: (i) Cr0.68Se presents a non-collinear antiferromagnetic (AFM) semiconducting behavior with the Neel temperature TN = 42 K and the activated energy Eg=3.9 meV; (ii) It exhibits the anomalous Hall effect (AHE) below TN and large negative magnetoresistance (MR) about 83.7% (2 K, 8.5 T). The AHE coefficient RS is 0.385 cm-3/C at T=2 K and the AHE conductivity {\sigma}H is about 1 ohm-1cm-1 at T=40 K, respectively; (iii) The scaling behavior between the anomalous Hall resistivity and the longitudinal resistivity is linear and further analysis implies that the origin of the AHE in Cr0.68Se is dominated by the skew-scattering mechanism. Our results may be helpful for exploring the potential application of these kind of 2D AFM semiconductors.