A low-dimensional molecular spin system with two steps of magnetic transitions and liquid crystal property

Multi-step phase transition crystal with dielectric constant bistability and temperature-dependent conductivity

Here, we report the crystal structures, phase transitions, and thermal, dielectric, and conducting properties of an ion-pair compound [C4-bmim][Ni(mnt)2] (1). 1 undergoes a three-step phase transition with four phases before melting. A two-step dielectric constant bistability is also realized by the structural phase transition in 1 occurring among phases I, II, and III, which is due to the in-plane oscillations of the alkyl chain and crystal-to-mesophase transition, respectively. Moreover, 1 exhibits rare temperature-dependent conducting properties accompanying structural phase transitions, and conductivity is very high with 0.00186 S cm-1 at 413 K. The conduction properties of phase III (mesophase) arise from the dipole molecular motion.

Multi-step structural phase transitions with novel symmetry breaking and inverse symmetry breaking characteristics in a [Ag4I6]2- cluster hybrid crystal

In this study, a multi-step phase transition hybrid composed of (Pr-dabco)2Ag4I6 clusters (Pr-dabco+ = 1-propyl-1,4-diazabicyclo[2.2.2]octan-1-ium) has been prepared and characterized by microanalysis, IR and UV-vis spectroscopy, TG and DSC techniques, etc. This hybrid is thermally stable up to ∼486 K with five phases in the temperature region below 486 K. The phase transition shows symmetry breaking (SB) character between phases II (space group P21/c) and III (space group Pa3[combining macron]), while inverse symmetry breaking (ISB) between phases II and I (space group Pbca), and it is rather exceptional for matter to exhibit simultaneously SB and ISB nature in two successive phase transitions. Most importantly, each phase transition is associated with a dielectric anomaly, and phase V appears to be a plastic crystal with extra high ac conductivity (>10-2 S cm-1). Our work opens up new avenues to find a multi-phase transition material in silver halide hybrids.

Crystal structure of bis-(1-hexyl-N,N-di-methyl-pyridinium) bis-(maleo-nitrile-dithiol-ato)nickelate(II)

The asymmetric unit of the title compound, (C13H23N2)2[Ni(C4N2S2)2], consists of a 1-hexyl-N,N-di-methyl-pyridinium cation and one half of a [Ni(mnt)2](2-) dianion (mnt(2-) = maleo-nitrile-dithiol-ate) in which the Ni(2+) cation lies on a crystallographic inversion centre. The square-planar coordination about Ni(2+) comprises four S atoms from two bidentate chelate mnt(2-) ligands [Ni-S = 2.1791 (9) and 2.1810 (8) Å, and S-Ni-S bite angle = 91.93 (3)°]. The hydro-carbon chains of cations show trans-planar conformations and lie approximately parallel to the long mol-ecular axis of the [Ni(mnt)2](2-) anions, giving stacks along the c axis. The anions and cations form layers lying parallel to the bc plane. Only weak C-H⋯Ni and C-H⋯π associations are present in the crystal packing.

Ionic Liquid Crystals: Versatile Materials

This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

A two-dimensional anionic CdII polymer constructed through dicyanamide coordination bridges

In the search for potential ferroelectric materials, molecular-based one-, two- and three-dimensional cadmium(II) organic-inorganic compounds have been of interest as they often display solid-solid phase transitions induced by a variation in temperature. A new cadmium dicyanamide complex, poly[4-dimethylamino-1-ethylpyridin-1-ium [tri-μ-dicyanamido-κ(6)N(1):N(5)-cadmium(II)]], {(C9H15N2)[Cd(C2N3)3]}n, was synthesized by the reaction of 4-dimethylamino-1-ethylpyridin-1-ium bromide, cadmium nitrate tetrahydrate and sodium dicyanamide in aqueous solution. In the crystal structure, each Cd(II) cation is octahedrally coordinated by six terminal N atoms from six anionic dicyanamide (dca) ligands. Neighbouring Cd(II) cations are linked together by dicyanamide bridges to form a two-dimensional coordination polymer. The organic cations are not involved in the formation of the supramolecular network.

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 two-dimensional mixed-valence molecular crystal of [Ni(dmit)₂]₃⁻ shows a magnetic phase transition at ca. 77 K but absence of an electrical response in the same temperature interval.

Experimental and theoretical investigation of the magnetic and photoconductive nature of a novel two-dimensional, mixed-valence bis(2-thioxo-1,3-dithiole-4,5-dithiolato)nickelate molecular solid

A novel, two-dimensional mixed-valence [Ni(dmit)₂] molecular solid shows a rapid, clear and stable response of photoconductivity under UV irradiation.

Bis(1-ethyl-4,4′-bipyridin-1-ium) bis(1,2-dicyanoethene-1,2-dithiolato-κ2S,S′)nickelate(II)

In the anion of the title compound, (C₁₂H₁₃N₂)[Ni(C₄N₂S₂)₂], the Ni^II atom is coordinated by four S atoms from two 1,2-di­cyano­ethene-1,2-di­thiol­ate (mnt) ligands in a suqare-planar geometry. Weak C—H⋯N and C—H⋯S hydrogen bonds between the 1-ethyl-4,4′-bipyridin-1-ium cations and mnt anions and weak π–π inter­actions between the pyridine rings of the cations [centroid–centroid distances = 3.808 (3) and 3.972 (3) Å] lead to a two-dimensional network parallel to (010).

Observation of intramolecular vibrations cooperating with the magnetic phase transition in a nickel-bis-dithiolene compound

A new one-dimensional (1-D) ion-pair compound, [1,7-bis(1-methylimidazolium)heptane][Ni(mnt)(2)](2) (mnt(2-) = maleonitriledithiolate), was synthesized and characterized structurally and magnetically. This compound shows a spin-Peierls-type transition at around 235 K. Its crystal structure belongs to the monoclinic system with space group C2/c and the magnetic [Ni(mnt)(2)](-) anions form uniform stacks in the high-temperature (HT) phase. The crystal undergoes a transformation into the triclinic space group P1 accompanied by the magnetic transition and the anion stacks become dimerized in the low-temperature (LT) phase. The entropy changes (ΔS) are estimated to be 0.772 J K(-1) mol(-1) for the spin-Peierls-type transition, from DSC data, which is much less than the spin entropy change (ΔS = R ln 2 ≈ 5.76 J K(-1) mol(-1)), indicating that a substantial short-range order persists above the transition temperature. The variable temperature IR spectra showed that the peak positions and intensities for the bands near 1160 and 725 cm(-1), which correspond respectively to the ν(C-C) + ν(C-S) mode of the mnt(2-) ligands and the rocking vibration mode of the methylene group γ(r)(CH(2)) in the cation moiety, undergo an abrupt change at around 240 K, close to the transition temperature. This observation demonstrates that the intramolecular vibrations of both the anion and the counter-cation probably couple with the spins to cooperate with the spin-Peierls-type phase transition in this 1-D spin system.

Bis(4-dimethyl-amino-1-ethyl-pyridinium) bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κ(2)S,S')nickelate(II)

The asymmetric unit of the title complex, (C₉H₁₅N₂)₂[Ni(C₄N₂S₂)₂], comprises one 4-dimethyl­amino-1-ethyl­pyri­din­ium cation and one half of a [Ni(mnt)₂]²⁻ (mnt²⁻ = maleo­nitrile­dithiol­ate) anion; the complete anion is generated by the application of a centre of inversion. The Ni^II ion is coordinated by four S atoms of two mnt²⁻ ligands and exhibits a square-planar coordination geometry.