Hai-Bao Duan

Inorganic–organic hybrid compounds based on face-sharing octahedral [PbI3]∞ chains: self-assemblies, crystal structures, and ferroelectric, photoluminescence properties

Eight inorganic-organic hybrid compounds with a formula of [R-Bz-1-APy][PbI(3)] (R-Bz-1-APy(+) = mono-substituted benzylidene-1-aminopyridinium Schiff base derivative; R = m-CN (1), m-CH(3) (2), H (3), p-F (4), p-Cl (5), p-Br (6), o-Cl (7), o-Br (8)) have been synthesized and characterized structurally. The common characteristic of the crystal structures of 1-8 is that the inorganic components form straight and face-sharing octahedral [PbI(3)](∞) chains and the Schiff base cations surround the [PbI(3)](∞) chains to form molecular stacks. The substituent (R) on the phenyl ring of the Schiff base cation clearly influences the packing structures of 1-8, and the hybrid compound crystallizes in the space group P6(3) when R = CN (1) in the meta-position of the phenyl ring, and in a central symmetric space group when R is in the ortho- or para-position of the phenyl ring. The conformation of the Schiff base cation is related to the R position, and the dihedral angle between the phenyl and pyridyl rings increases in the order of para- < meta- < ortho-position substitution of the phenyl ring. The long molecular axis of the Schiff base cation adopts a manner approximately parallel to the straight inorganic [PbI(3)](∞) chain in the para-substituted hybrid compounds, and perpendicular to the straight inorganic [PbI(3)](∞) chain in the ortho-substituted hybrid compounds. 1 is second harmonic generation (SHG) active with a comparable response as that of urea and also exhibits ferroelectricity with larger P(s) and P(r) values; 1-8 emit multi-band luminescence in the 300-650 nm regions under the excitation of ultraviolet light.

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

A low-dimensional compound [C(6)-Apy][Ni(mnt)(2)] (1, where mnt(2-) = maleonitriledithiolate, C(6)-Apy(+) = 4-amino-1-hexylpyridinium) has been designed and synthesized, which has layer arrangement of anions and cations and shows two steps of magnetic transitions. The low temperature magnetic transition has an uncommon hysteresis loop, while the crystal structure investigations disclosed no structural transition with the magnetic transition. The high temperature magnetic transition exhibits two remarkable features: (1) it synchronously occurs with a crystalline-to-mesophase transition in the first heating process and (2) the structural changes that accompany the solid-mesophase transition are irreversible. A diamagnetic and isostructural compound, [C(6)-Apy][Cu(mnt)(2)], is further characterized by structure, DSC and POM techniques, which revealed also the existence of an irreversible crystalline-to-mesophase transition in the same temperature interval of [C(6)-Apy][Ni(mnt)(2)]. Therefore, the high-temperature magnetic transition in 1 is driven by release of the structural strains, but not magnetoelastic interactions. The mesophase exhibits the characteristic of smectic A phase, and the alkyl chain melting in the cation layers probably lead to the formation of mesophase. It is noticeable that the finding of a mesophase occurring in a hexyl hydrocarbon chain molecular system is in contrast to a suggested rule that at least a dodecyl chain is required. Our results will shed a light on the design and preparation of a new low-dimensional molecular system combining magnetic transition and liquid crystal properties.

Two in one: switchable ion conductivity and white light emission integrated in an iodoplumbate-based twin chain hybrid crystal

An iodoplumbate-based hybrid, [C7-Apy][PbI3] (1), where C7-Apy(+) = 1-heptyl-4-aminopyridinium, was prepared using a simple solution process. Three sequential phase transitions occur in the range of 402-443 K. In both the lowest and highest temperature phases, hybrid crystal 1 is composed of discrete [Pb2I6]∞ twin chains surrounded by C7-Apy(+) cations. The connectivity between PbI6 octahedra within a [Pb2I6]∞ twin chain and the arrangement of cations are quite difference between the lowest and highest temperature phases. Hybrid crystal 1 shows switchable ion conductivity due to the structural phase transition and white light emission attributed to the broad band semiconductor emission of the twin chain. The former functionality has potential application in ion conductor devices; the single-phase white light emitter is a useful material in low-cost, easily-made, high-efficiency white light-emitting diodes.

Nickel-Dithiolene Ion-Pair Compounds Showing Thermotropic Liquid Crystal Behaviors and Alkyl Chain Length Dependent Electrochemical Properties

Nine ion-pair compounds [Cn-Apy]2[Ni(mnt)2] (Cn-Apy+ = 1-alkyl-4-aminopyridinium, n = 2-10, corresponding to compounds 1-9; mnt2- = maleonitriledithiolate) were synthesized and characterized structurally. The hydrocarbon chain in the countercation adopts all trans-plane conformation when n < 7; otherwise, it adopts the mixed trans and gauche conformation. 1, 2, 8, and 9 show the layered packing structure of alternating anions and cations, whereas 3-6 display the mixed stacking structure of anions (A) and cations (C) in a … ACCA … manner. 3–9 exhibit the thermotropic liquid crystal behaviors. The redox couple of [Ni(mnt)2]−/[Ni(mnt)2]2- in the solid state depend on the hydrocarbon chain length in the cation. [Supplemental materials are available for this article. Go to the publisher’s online edition of Soft Materials to view the free supplemental file.]

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.

An amphidynamic inorganic–organic hybrid crystal of bromoplumbate with 1,5-bis(1-methylimidazolium)pentane exhibiting multi-functionality of a dielectric anomaly and temperature-dependent dual band emissions

Organic-inorganic hybrid crystals, [1,5-bis(1-methylimidazolium)pentane][PbBr3]2 (1), were achieved through the mutual diffusion of a bi-imidazolium based ionic liquid and PbBr2 solution of DMF in a glass tube. The hybrid solid crystallizes in the orthorhombic space group Fdd2 at room temperature; and is composed of one-dimensional [PbBr3]∞ chains where the neighbouring PbBr6 coordination octahedra are linked together via the face-sharing mode and the inorganic chains are surrounded by organic cations. The hybrid solid exhibits a dielectric anomaly around 443 K and dielectric relaxation above 400 K, the dielectric response mechanism was investigated using variable-temperature X-ray single crystal and powder diffraction as well as DSC techniques. Fascinatingly, this hybrid solid shows dual band emissions, moreover, the fluorescence nature of the two emission bands exhibits a distinct response to temperature, leading to a temperature-dependent fluorescence color, this feature has promising application in the emission temperature-sensing field.

Two spin systems based on [Ni(dmit)2]− building blocks exhibiting 1-D chain and 2-D sheet structures: crystal structures and magnetic properties

The crystal structures and magnetic properties for two ion-pair complexes, [MG][Ni(dmit)2] (1) and [RhB][Ni(dmit)2] (2) (MG+ = N-(4-((4-(dimethylamino)phenyl)(phenyl)methylene)cyclohexa-2,5-dienylidene)-N-methylmethanaminium, RhB+ = 9-(2-carboxyphenyl)-3,6-bis(diethylamino)xanthylium; dmit2− = 1,3-dithiole-2-thione-4,5-dithiolate), have been investigated. Complex 1 crystallizes in the monoclinic space group P21/c, the stacking interactions between the GM+ and [Ni(dmit)2]− lead to the anion exhibiting a banana-shaped molecular geometry; the neighboring anions form a 1-D alternating chain along the crystallographic [1 1 0] direction via intermolecular lateral-to-lateral and head-to-head S ··· S contacts. The temperature dependence of magnetic susceptibility from 2–350 K does not display the magnetic character of a 1-D chain; the magnetic susceptibility data were fit to the Curie–Weiss equation to give C = 0.351(15) emu K mol−1, θ = −3.51(28) K, and χ 0 = 8.00(3) × 10−5 emu mol−1. Complex 2 belongs to the triclinic space group P-1 with two crystallographic inequivalent [Ni(dmit)2]− anions, which exhibit perfect planar geometry. Two ethyl groups of RhB+ are disordered over two positions at 296 K, and one becomes ordered at 150 K. The [Ni(dmit)2]− anions form a 2-D molecular layer via intermolecular lateral-to-lateral and head-to-lateral S ··· S interactions with the anionic layer parallel to the crystallographic (0 1 −1) plane. The temperature variation of magnetic susceptibility from 2 to 350 K shows that antiferromagnetic coupling dominates in the anionic layer, and the disorder–order changes of cationic structure are not coupled to magnetic property.

[(18-Crown-6)K][Fe(1)Cl(1)4]0.5[Fe(2)Cl(2)4]0.5: A Multifunctional Molecular Switch of Dielectric, Conductivity and Magnetic Properties

Multifunctional materials that exhibit different physical properties in a single phase have potential for use in multifunctional devices. Herein, we reported an organic-inorganic hybrid compound [(18-crown-6)K][Fe(1)Cl(1)4 ]0.5 [Fe(2)Cl(2)4 ]0.5 (1) by incorporating KCl and FeCl3 into a 18-crown-6 molecule, which acts as a host of the six O atoms providing a lone pair of electrons to anchor the guest potassium cation, and [FeCl4 ]- as a counterion for charge balance to construct a complex salt. This salt exhibited a one-step reversible structural transformation giving two separate high and low temperature phases at 373 K, which was confirmed by systematic characterizations including differential scanning calorimetry (DSC) measurements, variable-temperature structural analyses, and dielectric, impedance, variable-temperature magnetic susceptibility measurements. Interestingly, the structural transformation was coupled to both hysteretic dielectric phase transition, conductivity switch and magnetic-phase transition at 373 K. This result gives an idea for designing a new type of phase-transition materials harboring technologically important magnetic, conductivity and dielectric properties.

Three-Dimensional Hydrogen Bonding Framework in the Crystal Structure of a Zinc(II) Complex of Imidazole Multicarboxylic Acid

An new compound, [Zn(H2EIDA)2(H2O)]·DMF (1), (H2EIDA = deprotonated 2-ethyl-4H-imidazole-4,5-dicarboxylic acid, DMF = N,N-dimethylform amide), has been synthesized and structurally characterized. Compound 1 crystallizes in monoclinic space group C2/c, an asymmetric unit contains one zinc ion, which is situated on a center of inversion, two crystallographically dependent deprotonated H2EIDA+ ligands, one coordinated water molecule and one DMF molecule. The Zn(II) ion is five-coordinated exhibiting distorted trigonal-bipyramidal geometry. The 1D chain was formed by H-bonding and O···O interactions between monodeprotonated H2EIDA+ ligand and DMF molecule, and bifurcated hydrogen bonding interactions link the 1D chain to form 3D framework.

3,3'-Dimethyl-1,1'-(propane-1,3-di-yl)diimidazol-1-ium bis-(1,2-dicyano-ethene-1,2-dithiol-ato-κS,S')nickelate(II).

In the title compound, (C11H18N4)[Ni(C4N2S2)2], the asymmetric contains one half-complex, with the cation placed on a twofold axis and the anion located on an inversion center. The NiII ion in the anion is coordinated by four S atoms of two maleonitriledithiolate ligands, and exhibits the expected square-planar coordination geometry.