Dehydration Induced a Structural Transformation into a One-Dimensional Hybrid Perovskite with Second Harmonic Generation and Dual Dielectric Switching.

Hybrid organic-inorganic perovskites with structural transformation have garnered continued interest in recent years for their potential as multifunctional materials in the field of optoelectronics and smart devices. Herein, we report a novel hybrid organic-inorganic halide, [C5NOH12]2[Cd1.5Cl5(H2O)] (1). Remarkably, the centrosymmetric compound 1 undergoes a structural transformation to a novel noncentrosymmetric hybrid perovskite [C5NOH12][CdCl3] (2) after dehydration. Accompanied by the chemical bond cleavage and reorganization, the zero-dimensional (0D) trinuclear cluster in compound 1 transforms into an intriguing one-dimensional (1D) hexagonal perovskite structure in compound 2, generating multiple optoelectronic switching behaviors. It is worth mentioning that compound 2 demonstrates successive structural phase transitions at 353 and 405 K, resulting in switchable second harmonic generation (SHG) and a dual dielectric response. In addition, compounds 1 and 2 both feature blue-light luminescence, with respective photoluminescence lifetimes of 0.73 and 1.42 ns. This work will offer a pioneering approach and expansive potential for the preparation and development of hybrid organic-inorganic perovskite materials with superior properties.

The proton conduction behavior of two 1D open-framework metal phosphates with similar crystal structures and different hydrogen bond networks.

Two open-framework zinc phosphates [C3N2H12][Zn(HPO4)2] (1) and [C6N4H22]0.5[Zn(HPO4)2] (2) were synthesized via hydrothermal reaction and characterized by powder X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Both compounds have a similar crystal structure and macroscopic morphology. However, the difference in equilibrium cations, in which the propylene diamine is for 1 and the triethylenetetramine is for 2, results in a significant distinction in the dense hydrogen grid. The diprotonated propylene diamine molecule in 1 is more favorable for forming a hydrogen-bond network in three dimensions than in 2, in which the twisted triethylenetetramine forms a hydrogen bond grid with the inorganic framework only in two dimensions owing to its large steric effect. This distinction further leads to a disparity in the proton conductivity of both compounds. The proton conductivity of 1 can reach 1.00 × 10-3 S cm-1 under ambient conditions (303 K and 75% RH) and then increase to 1.11 × 10-2 S cm-1 at 333 K and 99% RH, which is the highest value among the open-framework metal phosphate proton conductors operated in the same conduction. In contrast, the proton conductivity of 2 is four orders of magnitude smaller than 1 at 303 K and 75% RH and two orders smaller than 1 at 333 K and 99% RH.

Two chiral haloplumbate hybrids with thermochromism luminescence and application potential as luminescent thermometers.

Two noncentrosymmetric haloplumbate hybrids, [C6H10(NH3)2][PbCl4] (1) and [C6H10(NH3)2][PbBr4] (2), have been synthesized. Crystals of 1 and 2 belong to the chiral space group P212121. The inorganic parts comprise a one-dimensional chain structure for 1 and a two-dimensional sheet structure for 2. Both compounds exhibit thermochromic luminescence originating from dual emission and have potential applications as self-referencing luminescent thermometers.

Thermally Activated Transient Dipoles and Rotational Dynamics of Hydrogen-Bonded and Charge-Transferred Diazabicyclo [2.2.2]Octane Molecular Rotors.

We present here dielectric properties and rotational dynamics of cocrystals formed with either triphenylacetic acid (cocrystal I) or 9,10-triptycene dicarboxylic acid (cocrystal II), as hydrogen-bonding donors, and diazabicyclo[2.2.2]octane (DABCO), as a ditopic hydrogen-bond acceptor. While cocrystal I forms discrete 2:1 complexes with one nitrogen of DABCO hydrogen bonded and the other fully proton transferred, cocrystal II consists of 1:1 complexes forming infinite 1-D hydrogen-bonded chains capable of exhibiting a thermally activated response in the form of a broad asymmetric peak at ca. 298 K that extends from ca. 200 to 375 K in both the real and imaginary parts of its complex dielectric. The state of protonation in cocrystal II at 298 and 386 K was established by CPMAS 15N NMR, which showed signals typical of a neutral hydrogen-bonded complex. Taken together, these observations suggest a dielectric response that results from a small population of transient dipoles thermally generated when acidic protons are transiently transferred to either side of the DABCO base. A potential order-disorder transition further explored by taking advantage of the highly sensitive rotational dynamics of the DABCO group using line-shape analysis of solid-state spin echo 2H NMR and 1H NMR T1 spin-lattice relaxation showed no breaks in the Arrhenius plot or Kubo-Tomita 1H T1 fittings, indicating the absence of large structural changes. This was confirmed by variable-temperature single-crystal X-ray diffraction analysis, which showed a fairly symmetric hydrogen bond in cocrystal II at all temperatures, suggesting that both nitrogen atoms may be able to adopt a protonated state.

An Alkali Metal Ion-Exchanged Metal-Phosphate (C2H10N2) xNa1- x[Mn2(PO4)2] with High Proton Conductivity of 10-2 S·cm-1.

A two-dimensional layered inorganic-organic hybrid metal hydrogenophosphate (1) was treated with 0.1 M NaOH-ethanol solution, which resulted in a Na+-ion substitution product that exhibits excellent thermal and aqueous stability with 1, as well as much higher proton conductivity (σ = 10-2 S·cm-1) even at low temperature (283 K). This is because Na+ ions in aqueous solution make a more dense and extensive H-bonding network of water molecules, which enables protons to more easily transfer along the network.

Dielectric Relaxation and Beyond Limiting Behavior of Alternating-Current Conductivity in a Supermolecular Ferroelectric.

A cyclen-based hybrid supermolecule crystal, [(FeCl2 )(cyclen)]Cl (1), where cyclen=1,4,7,10-tetraazacyclododecane, was prepared using a liquid-liquid diffusion approach. The variable crystal structures exhibit that compound 1 belongs to an orthorhombic crystal system, Pna21 space group (point group C2V ) in the temperature range of 150-400 K. This hybrid supermolecule shows a dielectric relaxation behavior around room temperature, and the ferroelectric nature of 1 has been directly verified by hysteresis measurements. In addition, the AC (alternating current) conductivity study reveals that the 1 displays a beyond limiting behavior. These interesting findings are for the first time reported in the field of supermolecular ferroelectrics. This study may open a new way to construct supermolecular ferroelectrics and give insights into their conductor behavior.

[(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.

An inorganic-organic hybrid crystal with a two-step dielectric response and thermochromic luminescence.

An iodoplumbate-based hybrid crystal [C2-Apy][PbI3] (1) (C2-Apy+ = 1-ethyl-4-aminopyridinium) was synthesized and characterized structurally. Single crystal X-ray diffraction revealed that 1 crystallizes in the orthorhombic system with the space group Pnma at 150 K. Inorganic components form straight and face-sharing octahedral [PbI3]∞ chains and organic components form C2-Apy+ cations that are incorporated into the space between the inorganic chains. A temperature-dependent single crystal structure indicates that there exists an order-disorder transition of the cation. The dynamic motion of the cation strongly influences the dielectric and emission features of 1. 1 shows a two-step dielectric response. The first step dielectric response at a low frequency is caused by direct current conduction and electrode polarization which have been proved by impedance spectra. The second dielectric response at a high frequency (10 kHz to 10 MHz) is related to the order-disorder transition of the alkyl chain and the dynamic motion of pyridyl rings. In addition, 1 shows multi-band emission, and different emission bands show different trends with the temperature change, which makes 1 exhibit thermochromic luminescence properties.

Diffusion-Controlled Rotation of Triptycene in a Metal-Organic Framework (MOF) Sheds Light on the Viscosity of MOF-Confined Solvent.

Artificial molecular machines are expected to operate under conditions of very low Reynolds numbers with inertial forces orders of magnitude smaller than viscous forces. While these conditions are relatively well understood in bulk fluids, opportunities to assess the role of viscous forces in confined crystalline media are rare. Here we report one such example of diffusion-controlled rotation in crystals and its application as a probe for viscosity of MOF-confined solvent. We describe the preparation and characterization of three pillared paddlewheel MOFs, with 9,10-bis(4-pyridylethynyl)triptycene 3 as a pillar and molecular rotator, and three axially substituted dicarboxylate linkers with different lengths and steric bulk. The noncatenated structure with a bulky dicarboxylate linker (UCLA-R3) features a cavity filled by 10 molecules of N,N-dimethylformamide (DMF). Solid-state 2H NMR analysis performed between 293 and 343 K revealed a fast 3-fold rotation of the pillar triptycene group with the temperature dependence consistent with a site exchange process determined by rotator-solvent interactions. The dynamic viscosity of the MOF-confined solvent was estimated to be 13.3 N·s/m2 (or Pa·s), which is 4 orders of magnitude greater than that of bulk DMF (8.2 × 10-4 N·s/m2), and comparable to that of honey.

Insight into Understanding Dielectric Behavior of a Zn-MOF Using Variable-Temperature Crystal Structures, Electrical Conductance, and Solid-State 13C NMR Spectra.

A Zn-based metal-organic framework (MOF)/porous coordination polymer (PCP), (EMIM)[Zn(SIP)] (1) (SIP3- = 5-sulfoisophthalate, EMIM+ = 1-ethyl-3-methylimidazolium), was synthesized using the ionothermal reaction. The Zn2+ ion adopts distorted square pyramid coordination geometry with five oxygen atoms from three carboxylates and one sulfo group. One of two carboxylates in SIP3- serves as a µ2-bridge ligand to link two Zn2+ ions and form the dinuclear SBU, and such SBUs are connected by SIP3- ligands to build the three-dimensional framework with rutile (rtl) topology. The cations from the ion-liquid fill the channels. This MOF/PCP shows two-step dielectric anomalies together with two-step dielectric relaxations; the variable-temperature single-crystal structure analyses disclosed the dielectric anomaly occurring at ca. 280 K is caused by an isostructural phase transition. Another dielectric anomaly is related to the dynamic disorder of the cations in the channels. Electric modulus, conductance, and variable-temperature solid-state 13C CP/MAS NMR spectra analyses revealed that two-step dielectric relaxations result from the dynamic motion of the cations as well as the direct-current conduction and electrode effect, respectively.

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.

Dielectric response and anhydrous proton conductivity in a chiral framework containing a non-polar molecular rotor.

Herein, we report a chiral 3D framework with the formula [Co(HPO3)2][H2DABCO] (DABCO = 1,4-diazabicyclo[2.2.2]octane). This compound exhibits two distinct dielectric anomalies, one attributed to the transfer of protons between non-polar DABCO and the inorganic framework, and the other to the in-plane oscillatory fluctuation of the DABCO molecule. It also exhibits proton conductivity under high-temperature anhydrous conditions.

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.

Disorder-order transformation and significant dislocation motion cooperating with a surprisingly large hysteretic magnetic transition in a nickel-bisdithiolene spin system.

The compound [4'-CF3bzPy][Ni(mnt)2] (1) (where 4'-CF3bzPy = 1-(4'-(trifluoromethyl)benzyl)pyridinium and mnt(2-) = maleonitriledithiolate) was synthesized and displays a magnetic bistability with a surprisingly large thermal hysteresis loop (~49 K). X-ray crystallographic studies reveal that in the high-temperature (HT) phase the anions and cations form mixed stacks, with alternating anion dimers (AA) and cation dimers (CC) in an ...AACCAACC... fashion along the crystallographic a + b direction, and disordered CF3 groups in the cations are aligned into a molecular layer parallel to the crystallographic (001) plane. However, in the low-temperature (LT) phase, the c-axis length of the unit cell is roughly doubled, and the asymmetric unit switches from one [4'-CF3bzPy][Ni(mnt)2] pair in the HT phase to two [4'-CF3bzPy][Ni(mnt)2] pairs. Most interestingly, the CF3 group in the cations becomes ordered, and the conformation of one of two crystallographically different cations changes significantly. A dislocation motion between the neighboring molecular layers emerges as well. The analyses of the magnetic susceptibilities and the density functional theory calculations suggest that the antiferromagnetic exchange interaction within one of two types of [Ni(mnt)2]2(2-) dimers in the LT phase is much stronger than that within the [Ni(mnt)2]2(2-) dimer in the HT phase. The lattice reorganization during this phase transition is proposed to be responsible for the wide thermal hysteresis loop.

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.

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, (C(11)H(18)N(4))[Ni(C(4)N(2)S(2))(2)], the asymmetric contains one half-complex, with the cation placed on a twofold axis and the anion located on an inversion center. The Ni(II) ion in the anion is coordinated by four S atoms of two maleonitrile-dithiol-ate ligands, and exhibits the expected square-planar coordination geometry.

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.

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.

1-Butyl-pyridinium bis-(1,2-dicyano-ethene-1,2-dithiol-ato)nickelate(III).

The Ni(III) atom in the anion of the title complex, (C(9)H(14)N)[Ni(C(4)N(2)S(2))(2)], is coordinated by four S atoms of two maleonitrile-dithiol-ate ligands, and exhibits a square-planar coordination geometry.

1-Amino-pyridinium triiodidoplumbate(II).

The title complex, (C(5)H(7)N(2))[PbI(3)], consists of a 1-amino-pyridinium cation, disordered about a mirror plane, and a [PbI(3)](-) anion. The Pb(2+) ion (site symmetry ) is surrounded by six I atoms in a slightly distorted octa-hedral coordination. The PbI(6) octa-hedra share faces, building up (∞) (1)[PbI(6/2)] chains running along [010]. The cations are situated between the chains. Coulombic attractions and van der Waals inter-actions between the inorganic and organic components are mainly responsible for the cohesion of the structure.