Guo-Jun Yuan

A facile and efficient strategy for the design of ferroelectric and giant dielectric hybrids via intercalating polar molecules into noncentrosymmetric layered inorganic compounds

Taking into account that an intercalation reaction, an entropy and volume reducing process, can be promoted by increased pressure in a reactor, we developed a facile and efficient strategy for rapid preparation of DMSO and urea intercalated Kaolinites under mild reaction conditions by means of an autoclave, reducing the reaction time from several days to 6 h. The Kaolinite is a noncentrosymmetric layered inorganic host, the polar DMSO or urea molecules were inserted into the inter-layers of Kaolinite to create the hybrid ferroelectric or giant dielectric materials. Our results will shed light on the design and preparation of new hybrid functional materials with technologically important ferroelectricity and giant dielectric properties.

Grain size effect on magnetic and phase transition features in one-dimensional S = 1/2 Heisenberg spin chain molecular crystals

In this study, we prepared sub-micron crystals of one-dimensional (1D) spin-Peierls-type compounds, 1-(4′-R-benzyl)pyridinium-d5 bis(maleonitriledithiolato)nickelate (R = Br or Cl), using a facile method, namely, an acetonitrile solution of each compound was quickly mixed with excess water (an insoluble solvent). This facile method of preparation gave a uniform dispersion of sub-micron crystals with a typical dimension of <1.0 μm. We observed that the reduction in grain size affected the magnetic and phase transition features. With respect to the bulk crystal samples, the powder X-ray diffraction peaks are broadened, the transition temperature (TC) is up-shifted with ΔTC ≈ 1.2 K for R = Br vs. 1.0 K for R = Cl, and the changes of enthalpy and entropy of the phase transition are significantly decreased for the sub-micron crystal samples; in addition, reducing the crystal grain size leads to the onset of a strongly Curie–Weiss-type paramagnetic background and significant temperature-independent paramagnetism.

Phase Transition, Dielectrics, Single-Ion Conductance, and Thermochromic Luminescence of a Inorganic–Organic Hybrid of [Triethylpropylammonium][PbI3]

In this study, we used the facile solvent evaporation method to achieve the inorganic-organic hybrid crystals of [triethylpropylammonium][PbI3], which have been characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and differential scanning calorimetry as well as single-crystal X-ray structure analysis. The hybrid solid crystallizes in the monoclinic space group P21/c at room temperature and is composed of one-dimensional [PbI3]∞ chains, where the neighboring PbI6 coordination octahedra connect together via the face-sharing mode and the organic cations fall in the spaces between [PbI3]∞ chains. The hybrid exhibits a dielectric phase transition with a critical temperature of ca. 432 K, dielectric relaxation at frequencies below 107 Hz, and single-ion conducting behavior, the conductivity of which increases rapidly from 9.43 × 10-10 S cm-1 at 383 K to 4.47 × 10-5 S cm-1 at 473 K. The variable-temperature single-crystal and powder X-ray diffraction analyses revealed that the dielectric phase transition is related to the disorder-to-order transformation of cations in the lattice. The electric modulus and impedance spectral analyses further disclosed that the dielectric relaxation arises from the ionic displacement polarization and molecular dipole orientation of cations. The single-ion conductance is due to the migration of cations that fall in the spaces of rigid inorganic [PbI3]∞ chains. The phase transition gives rise to this hybrid showing switchable ion-conducting nature around the critical temperature of the phase transition. Besides the fascinating functionalities mentioned above, the hybrid also exhibits a thermochromic luminescence feature originating from the electron transition between the valence and conduction bands of the inorganic [PbI3]∞ chain.

An ion-pair complex [TTF][Pd(mnt)2]: synthesis, crystal structure, magnetic property, and electrical conductivity

A new ion-pair complex, [TTF][Pd(mnt)2] (1), where TTF+  = tetrathiafulvalene and mnt2− = maleonitriledithiolate, was synthesized and characterized structurally. Compound 1 crystallizes in triclinic space group P-1, with a = 8.008(5) Å, b = 11.333(8) Å, c = 11.373(6) Å, α = 108.112(7)°, β = 91.550(5)°, γ = 95.232(5)°, and V = 975.2(11) Å3. The [TTF]+ cations (C) and [Pd(mnt)2]− anions (A) form mixed stacks in …AACCAACC… fashion, and the neighboring mixed stacks are held together via van der Waals forces in the crystal. Compound 1 shows weak Curie/Weiss-type magnetic behavior from 2 to 370 K; theoretical investigation disclosed the existence of strongly antiferromagnetic coupling in both [Pd(mnt)2]2 2− and [TTF]2 2+ dimer pairs via frontier orbitals overlap mechanism and weakly ferromagnetic coupling between the face-to-face overlapped [TTF]+ and [Pd(mnt)2]− via spin polarization mechanism within a mixed stack. The powdered pellet electrical conductivity measurement indicated that 1 shows semiconductor character with activation energy of 1.1(3) eV.

CCDC 892060: Experimental Crystal Structure Determination

Related Article: Guo-Jun Yuan, Hao Yang, Shao-Xian Liu, Jian-Lan Liu, Xiao-Ming Ren|2014|Dalton Trans.|43|11908|doi:10.1039/C4DT00868E