Jian-Lan Liu

A rhombus channel metal–organic framework comprised of Sr2+ and thiophene-2, 5-dicarboxylic acid exhibiting novel dielectric bistability

A metal–organic framework (MOF) compound, comprised of Sr2+ and thiophene-2,5-dicarboxylic acid (H2TDA) with a formula of Sr(TDA)(DMF), was prepared via the solvothermal method, this MOF compound crystallizes in the monoclinic space group P21/c with unit cell parameters a = 6.0078(4) A, b = 16.9401(12) A, c = 13.0061(8) A, β = 116.158(3)° and V = 1188.10(14) A3. The spaces of rhombus channels in the MOF crystal are occupied by the disordered DMF molecules. The striking structural feature is that the connectivity between inorganic hendecahedron units of SrO7 and TDA2− ligands gives rise to the uncommon I1O2 type 3-D framework of 1. The dielectric relaxation and novel dielectric bistability behaviors were observed for this MOF compound in the lower frequency regime (f 160 °C), which originated from the orientation motion of the disordered polar DMF molecules under an ac electric field. This study suggested the possibility of dielectric bistability in the designed MOFs with pores or channels.

Ion-pair complexes with strong near infrared absorbance: Syntheses, crystal structures and spectroscopic properties

Three ion-pair complexes, [4-NH(2)-Py](2)[M(mnt)(2)] (4-NH(2)-Py(1+)=4-amino-pyridinium; mnt(2-)=maleonitriledithiolate; M=Pt (1), Pd (2) or Ni (3)), have been synthesized and characterized. In the crystal of 1, the strong H-bonding interaction was found from the protonated N-atom of pyridinium to the CN group of [Pt(mnt)(2)](2-) together with a weak Pt...H interaction between the anion and the cation. The crystals of 2 and 3 are isostructural with very similar lattice parameters and packing structures, which are distinct from the crystal of 1. Two kinds of strong H-bonding interactions are observed in the crystals of 2 and 3 between the CN groups of [M(mnt)(2)](2-) anion and the protonated N-atom of 4-NH(2)-Py(1+) cation as well as the CN groups of [M(mnt)(2)](2-) anion and the amino group of 4-NH(2)-Py(1+) cation. Complex 1 shows an intense near-IR absorbance in acetonitrile and solid state, such an absorption band is probably assigned to IPCT transition as well as a trace amount of [Pt(mnt)(2)](1-) species; complex 3 possesses a weak near-IR absorption band which can be attributed to the mixture of d-d transition in [Ni(mnt)(2)](2-) and IPCT transition as well as a trace amount of [Ni(mnt)(2)](1-) species.

Novel dielectric relaxation behaviors driven by host–guest interactions in intercalated compounds of kaolinite with aminopyridine isomers

Kaolinite (K), a polar and layered aluminosilicate mineral, was used as the host for three aminopyridine isomers: 2-aminopyridine (2-APy), 3-aminopyridine (3-APy), and 4-aminopyridine (4-APy). We inserted these isomers into the kaolinite interlayer to produce the intercalated compounds 2-APy-K, 3-APy-K, and 4-APy-K, respectively. These intercalated compounds show distinct ν(O–H) bands arising from the inner and inner-surface hydroxyl groups of kaolinite. They also have diverse deintercalation temperatures of about 112 °C for 2-APy-K, 136 °C for 3-APy-K, and 181 °C for 4-APy-K, indicating that the host–guest interaction is different for each of these intercalated compounds. One-step dielectric relaxation appears in 2-APy-K and 3-APy-K, while two-step dielectric relaxation appears in 4-APy-K in the low-frequency regime (f < 104 Hz). The dielectric relaxation in these compounds arises from the dipole motion of intercalatant molecules under an applied ac electrical field. Our results shed light on the design and preparation of new hybrid materials with technologically important physical properties using a host–guest chemical approach.

A bis(maleonitriledithiolato)nickelate charge-transfer salt with mixed stacks exhibiting novel non-ferroelectric-type dielectric phase transition and bistability

A charge-transfer salt consisting of 1,1′-dioctyl-4,4′-bipyridinium and bis(maleonitriledithiolato)nickelate is described. Its crystal is built from mixed stacks of the anion and cation, with the anions (A) and cations (C) adopting an …ACAC… fashion within a stack. This salt shows a novel non-ferroelectric-type dielectric phase transition at around 324 K and bistability.

Investigation of thermochromic photoluminescent, dielectric and crystal structural properties for an inorganic–organic hybrid solid of [1-hexyl-3-methylimidazolium][PbBr3]

The thermochromic photoluminescence, dielectric and impedance spectra, as well as temperature dependent crystal structures were investigated for the hybrid solid of [1-hexyl-3-methylimidazolium][PbBr3] (1). The hybrid crystal, belonging to a monoclinic system with the space group P21/c, is composed of one-dimensional [PbBr3]∞ chains where the neighboring PbBr6 coordination octahedra are connected via face-sharing mode; the organic cations are incorporated in the space of the inorganic chains. The dynamic motion of the cations strongly influences the dielectric and emission features of 1. The platform-type dielectric anomaly, accompanied by a thermal event, occurs at an onset temperature of around 250 K, which is related to the alkyl chain swing motion. The dielectric relaxation appears at temperatures above 240 K and results from the alkyl chain swing motion and imidazole ring libration motion. Another fascinating feature of 1 is its dual emissions, arising from the π ← π* transition within the imidazole ring and the exciton luminescence of the [PbBr3]∞ semiconducting chain. The two emission bands have different sensitivities to temperature, leading to 1 showing photoluminescent thermochromism, which may have a potential application in thermosensitive devices.

Insights into understanding water mediated proton conductivity in an intercalated hybrid solid of kaolinite at ambient temperature

In this study, an intercalated hybrid solid of kaolinite with L-alanine (abbr. K-Ala) was prepared, and the proton conductance of K-Ala has been investigated in both anhydrous and humid environments, respectively. The proton conductivity (σ) of K-Ala is 5.38 × 10−8 S cm−1 under an N2 atmosphere (anhydrous environment), while it is much enhanced under humid conditions and σ = 1.35 × 10−4 S cm−1 under 99% relative humidity (RH) at ambient temperature. With increasing temperature, the proton conductivity reaches 2.1 × 10−3 S cm−1 at 99% RH and 318 K, and this σ value is comparable to that recently reported in some of the high proton conducting MOF/PCP materials. DFT calculations were performed for the crystal structures containing different amounts of water molecules within the interlayer spaces of K-Ala, disclosing that the amounts of water molecules strongly influence the H-bond network. A denser H-bond network is formed when there are large amounts of water molecules in the interlayer spaces of K-Ala, providing an efficient proton transport pathway; as a consequence, the proton conductivity of K-Ala is much enhanced at high relative humidity.

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.

Observation of a magnetic phase transition but absence of an electrical response in a new two-dimensional mixed-valence nickel-bis-dithiolene molecular crystal

A new mixed-valence molecular crystal, [C3-Apy][Ni(dmit)2]3 (1) (dmit2− = 2-thioxo-1,3-dithiole-4,5-dithiolate and C3-Apy+ = 4-amino-1-propylpyridinium) was synthesized utilizing a facile solution process and a small size of counter-cation. This is distinct from the general strategy to obtain mixed-valence of [Ni(dmit)2] molecular crystal in which the large size counter-cation is desirable and the electrocrystallization method was used. The mixed-valence molecular crystal shows a magnetic phase transition around 77 K with a ca. 6 K thermal hysteresis loop. The crystal structure analysis at ambient temperature, the electronic band structure calculation based on the crystal structure, the variable temperature infrared spectra in 6–293 K, and the conductance measurements in 4–295 K were further performed, and the results revealed that 1 is a semiconductor and the magnetic phase transition is probably related to the electronic structure change in the {[Ni(dmit)2]3}1−.

Novel isomorphism of two hexagonal non-centrosymmetric hybrid crystals of M(en)3Ag2I4 (M = transition metal Mn2+ or main-group metal Mg2+; en = ethylenediamine)

In this study, two isomorphic hybrid crystals of iodoargentate, M(en)3Ag2I4 (M = transition metal Mn2+ (1) or main-group metal Mg2+ (2) ion), have been prepared through in situ self-assembly in DMF solution at ambient temperature and characterized by microanalysis, IR spectroscopy, thermogravimetric analysis and powder X-ray diffraction and single crystal X-ray diffraction techniques. The magnetic properties of 1 have been investigated. The crystals of 1 and 2 crystallize in the hexagonal non-centrosymmetric space group P6322 with rather similar lattice parameters. The metal complex M(en)32+ (M = Mn2+ or Mg2+) with the symmetry of D3 point group plays a crucial role in directing the formation of the three-dimensional hexagonal non-centrosymmetric framework of {Ag2I42−}∞. To the best of our knowledge, the hybrid Mg(en)3Ag2I4 is the first example of a main-group metal complex used as a structure directing agent for the formation of a hybrid crystal structure, and this is also the first instance where isomorphic hybrid crystals are obtained using transition and main-group metal complexes. These findings can provide a basis for broadening the utilization of metal coordination cations/anions as structure directing agents in the design and construction of novel hybrid crystal structures in more effective ways.

Two magnetic phase transitions, driven by symmetry breaking and isostructural phase transitions, in a nickel-bis-dithiolene spin system

A one-dimensional (1-D) magnetic chain compound, [(CD3)2CN-Py][Ni(mnt)2], where (CD3)2CN-Py+ = 1-(propan-d6-2-ylideneamino)pyridinium and mnt2− = maleonitriledithiolate, was synthesized and characterized. This compound undergoes two structural phase transitions, at around 267 K and 325 K. The three phases are sequentially labeled as α (below 267 K), β (between 267 and 325 K) and γ (above 325 K). The [Ni(mnt)2]− anions form irregular stacks, with two values of neighboring Ni⋯Ni distances. The cations align in a straight and regular arrangement along the crystallographic a-axis direction in the β phase. The asymmetric unit switches from one anion–cation pair to two anion–cation pairs in the transition from the β to the α phase. This leads to a doubling of the crystallographic axis length, parallel to the anion stack. It also results in the irregular anion stack showing three non-equivalent neighboring Ni⋯Ni distances, as well as making the straight cation arrangement irregular. The β and γ phases are isostructural and exhibit quite similar packing structures. The anion stack shrinks a little with increasing temperature, with all crystallographic axes showing small reduction from the β to γ phase. The two observed magnetic phase transitions are driven by these various structural phase transitions. A thermal hysteresis loop, with a separation of ∼8 K, appears in the transition between the β and α phases. However, this is absent in the transition between the β and γ phases. A dielectric anomaly appears across the phase transition between the β and γ phases but not between the β and α phases.