New ferroelectrics based on divalent metal ion alum

Tetra-kis(4-meth-oxy-anilinium) hexa-chloridobismuthate(III) chloride monohydrate

In the crystal of the title compound, (C₇H₁₀NO)₄[BiCl₆]Cl·H₂O, the Bi^III cation is located on an inversion center and coordinated by six Cl⁻ anions in a slightly distorted octa­hedral geometry; the uncoordinated Cl⁻ anion and lattice water mol­ecule are located on a twofold rotation axis. Two independent 4-meth­oxy­anilinium cations are linked to the Bi complex, the uncoordinated Cl⁻ anion and lattice water mol­ecule via N—H⋯Cl and N—H⋯O hydrogen bonds.

Bis(3-methyl-anilinium) hexa-chlorido-stannate(IV) dihydrate

In the title compound, (C₇H₁₀N)₂[SnCl₆]·2H₂O, the Sn^IV atom lies on a site with symmetry 2/m. One of the Cl atoms lies on a mirror plane and the 3-methyl­anilinium cation is also situated on a mirror plane. The water mol­ecule is located on a twofold rotation axis. The H atoms of the methyl and ammonium groups and the solvent water mol­ecule are disordered by symmetry. In the crystal, N—H⋯Cl, O—H⋯Cl and N—H⋯O hydrogen bonds connect the organic cations, the inorganic octahedrally shaped anions and the water mol­ecules.

Bis(2-hy-droxy-ethanaminium) terephthalate

The asymmetric unit of the title salt, 2C₂H₈NO⁺·C₈H₄O₄²⁻, comprises one crystallographically independent 2-hy­droxy­ethanaminium cation and one half terephthalate anion. In the crystal, hydrogen bonds involving the hy­droxy and ammonium groups of the cations and the carboxyl­ate O atoms of the terephthalate anions result in the formation of a three-dimensional network structure.

Bis(trimethyl-ammonium) naphthalene-1,5-disulfonate

The asymmetric unit of the title compound, 2C(3)H(10)N(+)·C(10)H(6)S(2)O(6) (2-), contains a half-anion, which is completed by inversion symmetry, and one cation. The cations and anions are associated via strong N-H⋯O(sulfonate) hydrogen-bonding inter-actions, forming cation-anion-cation groups. Secondary inter-actions such as C-H(ammonium)⋯O(sulf-on-ate) and van der Waals inter-actions link the cations and anions together in a three-dimensional crystal structure, with zigzag rows of cations lying between layers of anions.

Bis(3-hy-droxy-propanaminium) naphthalene-1,5-disulfonate

In the title molecular salt, 2C(3)H(10)NO(+)·C(10)H(6)O(6)S(2) (2-), the cations and anions are associated via N-H⋯O and O-H⋯O hydrogen-bonding inter-actions, giving rise to a three-dimensional structure with zigzag rows of cations lying between rows of anions. The asymmetric unit contains one cation and one half-anion, which is related to the remainder of the mol-ecule by an inversion center.

Tris(3-methyl-anilinium) tetra-chlorido-zincate chloride hemihydrate

The asymmetric unit of the title compound, (C₇H₁₀N)₃[ZnCl₄]Cl·0.5H₂O, consists of three 3-methyl­anilinium cations, one tetrahedral tetra­chloridozincate anion and one chloride anion and a water mol­ecule, which lies on a twofold axis. The components are linked into chains parallel to the a axis by N—H⋯Cl hydrogen bonds.

Diisopropylammonium chloride: a ferroelectric organic salt with a high phase transition temperature and practical utilization level of spontaneous polarization

A simple organic salt, diisopropylammonium chloride, shows the highest ferroelectric phase transition temperature among molecule-based ferroelectrics with a large spontaneous polarization, making it a candidate for practical technological applications.

Octa-kis(3-methyl-anilinium) hexa-chlorido-cadmate tetra-chloride

The asymmetric unit of the title compound, (C(7)H(10)N)(8)[CdCl(6)]Cl(4), contains four 3-methyl-anilinium cations, two chloride anions and half an octa-hedral hexa-chloridocadmate(II) anion, which lies on an inversion centre. In the crystal, numerous N-H⋯Cl and bifurcated N-H⋯(Cl,Cl) hydrogen bonds link the components.

catena-Poly[[bis-(1-ethyl-1H-imidazole-κN)cadmium]-di-μ-chlorido-[(1-ethyl-1H-imidazole-κN)cadmium]-di-μ-chlorido-[(1-ethyl-1H-imidazole-κN)cadmium]-di-μ-chlorido-[bis-(1-ethyl-1H-imidazole-κN)cadmium]]

The asymmetric unit of the crystal structure of the title compound, [Cd₂Cl₄(C₅H₈N₂)₃]_n, contains two Cd^II cations, three 1-ethyl-1H-imidazole ligands, and four Cl⁻ anions. The two Cd^II atoms have quite different coordination environments: one is octa­hedrally coordinated by four Cl atoms and two N atoms from two 1-ethyl-1H-imidazole ligands, and the second is in a severely distorted fivefold coordination by four Cl atoms and one N atom from a 1-ethyl-1H-imidazole ligand. Adjacent Cd^II cations are inter­connected alternately by pairs of chloride bridges, generating an infinite step-like chain along the a axis. One ethyl group of the 1-ethyl-1H-imidazole ligand is disordered over two sets of sites with a 0.668 (13):0.332 (13) site-occupancy ratio.

Di-μ(3)-chlorido-tetra-μ(2)-chlorido-dichloridobis(dimethyl-formamide-κO)hexa-kis-(1H-imidazole-κN)tetra-cadmium

The centrosymmetric mol­ecule of the title complex, [Cd₄Cl₈(C₃H₄N₂)₆(C₃H₇NO)₂], contains four Cd^II atoms, six imidazole, two dimethyl­formamide and eight chloride ligands. The structure shows a novel chloride-bridged tetra­nuclear cadmium quasi-cubane cluster. The coordination geometry of all Cd^II atoms is distorted octa­hedral, with the two metal atoms in the asymmetric unit in different coordination environments. One of the Cd²⁺ ions is coordinated by five Cl⁻ ions and by one N atom from an imidazole ligand, while the second is coordinated by three chloride ligands, two N atoms from two imidazole ligands and one O atom from a dimethyl­formamide mol­ecule. Inter­molecular N—H⋯Cl hydrogen bonds link the mol­ecules into a two-dimensional polymeric structure parallel to the ab plane.

4-(cyanomethyl)anilinium perchlorate: a new displacive-type molecular ferroelectric

A new organic ferroelectric compound, 4-(cyanomethyl)anilinium perchlorate, proceeds a second-order phase transition from a paraelectric phase (P2(1)/m) to a ferroelectric phase (P2(1)) at 184 K. A perfect ferroelectric hysteresis loop was observed even at 10 KHz. It is the first example of a molecule-based organic ferroelectric whose polarization can be switched at such a high frequency. The temperature dependent second harmonic generation effect shows that the second-order nonlinear coefficient is nearly zero above T(c) and proportional to the spontaneous polarization below T(c), suggesting the occurrence of symmetry breaking, in good agreement with crystal structural determination. The origin of ferroelectricity was ascribed to the displacements of -NH(3)(+) cations and ClO(4)(-) anions from the symmetric positions including a small part of the order-disorder behaviors of the ClO(4)(-) anions.

Large spontaneous polarization and clear hysteresis loop of a room-temperature hybrid ferroelectric based on mixed-halide [BiI3Cl2] polar chains and methylviologen dication

The search for hybrid organic-inorganic materials, which have the great advantage that they can be synthesized at moderate temperature (T < 200 °C), remains a great challenge in the field of ferroelectrics. Here, a room-temperature ferroelectric material with interesting characteristics, (MV)[BiI(3)Cl(2)] (MV(2+) = methylviologen), is reported. Its structure is based on polar inorganic chains resulting from a remarkable Cl/I segregation induced by methylviologen entities, which coincide with the fourfold polar axis of the tetragonal structure. Of great importance is that this room-temperature hybrid ferroelectric displays a clear electrical hysteresis loop with a large spontaneous polarization (>15 μC·cm(-2)).

Metal-organic complex ferroelectrics

Ferroelectric materials are of importance and interest in both fundamental scientific research and various technological applications. Metal-organic complexes (MOCs) represent a class of molecule-based ferroelectrics, which have shown various properties or functionalities due to their hybrid inorganic-organic nature. This tutorial review shows the recent development of the MOC ferroelectrics with particular emphases on the mechanism of ferroelectric-to-paraelectric phase transition, symmetry consideration, and multifunctionality.

4-Iodo-anilinium perchlorate 18-crown-6 clathrate

In the title compound, C₆H₇IN⁺·ClO₄⁻·C₁₂H₂₄O₆, the proton­ated 4-iodo­anilinium cation inter­acts with the 18-crown-6 through three N—H⋯O hydrogen bonds, forming a rotator–stator-like structure. The cation, anion and 18-crown-6 mol­ecule all have crystallographically imposed mirror symmetry.

4-Bromo-3-methyl-anilinium perchlorate 18-crown-6 clathrate

The reaction of 4-bromo-3-methyl-anilinium perchlorate and 18-crown-6 in methanol solution yielded the title compound, C(7)H(9)BrN(+)·ClO(4) (-)·C(12)H(24)O(6). The protonated 4-bromo-3-methyl-amine unit contains one -NH(3) (+) substituent, resulting in a 1:1 supra-molecular rotator-stator structure, (C(7)H(9)Br-NH(3) (+))(18-crown-6), through three bifurcated N-H⋯(O,O) hydrogen bonds between the ammonium group of the cation and the O atoms of the crown ether mol-ecule.

Mononuclear and dinuclear bromide-nitrite cadmium(II) complexes with related 1,4-diazabicyclo[2.2.2]octane ligands

The title compounds, di-μ-bromido-bis[bromido(1-carboxymethyl-4-aza-1-azoniabicyclo[2.2.2]octane-κN(4))(nitrito-κ(2)O,O')cadmium(II)] dihydrate, [Cd(2)Br(4)(C(8)H(15)N(2)O(2))(2)(NO(2))(2)]·2H(2)O, (I), and aquabromido(1-cyanomethyl-4-aza-1-azoniabicyclo[2.2.2]octane-κN(4))bis(nitrito-κ(2)O,O')cadmium(II) monohydrate, [CdBr(C(8)H(14)N(3))(NO(2))(2)(H(2)O)]·H(2)O, (II), are two-dimensional hydrogen-bonded metal-organic hybrid complexes. In (I), the complex is situated on a centre of inversion so that each symmetry-related Cd(II) atom is coordinated by two bridging Br atoms, one monodentate Br atom, one chelating nitrite ligand and one organic ligand, yielding a significantly distorted octahedral geometry. The combination of O-H···O and O-H···Br hydrogen bonds produces centrosymmetric R(6)(6)(16) ring motifs, resulting in two-dimensional layers parallel to the ab plane. In contrast, the complex molecule in (II) is mononuclear, with the Cd(II) atom seven-coordinated by two bidentate nitrite groups, one N atom from the organic ligand, one monodentate Br atom and a water O atom in a distorted pentagonal-bipyramidal environment. The combination of O-H···O and O-H···Br hydrogen bonds produces R(5)(4)(14) and R(3)(3)(8) rings which lead to two-dimensional layers parallel to the ac plane.

1-Cyanomethyl-1,4-diazoniabicyclo[2.2.2]octane tetrachloridocuprate(II)

In the crystal structure of the title compound, (C₈H₁₅N₃)[CuCl₄], the cations and anions, in which the Cu^II atom is tetra­hedrally coordinated, are linked via N—H⋯Cl hydrogen bonds into chains that are elongated in the c-axis direction.

4-Bromo-anilinium perchlorate 18-crown-6 clathrate

The reaction of 4-bromo­aniline, 18-crown-6, and perchloric acid in methanol yields the title compound, C₆H₇BrN⁺·ClO₄⁻·C₁₂H₂₄O₆, in which the protonated –NH₃⁺ group forms three bifurcated N—H⋯O hydrogen bonds to the O atoms of the crown ether.

4-[(2′-Cyanobiphenyl-4-yl)methyl]morpholin-4-ium nitrate

The title ion pair, C₁₈H₁₉N₂O⁺·NO₃⁻, features an N—H⋯O hydrogen bond linking the cation to the anion. The morpholine portion adopts a chair conformation; the aromatic rings of the biphenyl­ene portion are twisted [torsion angles for the four atoms involving the ar­yl–aryl bond = 35.1 (2)–40.4 (2)°].

4-Hydroxyanilinium perchlorate dihydrate

In the crystal structure of the title compound, C₆H₈NO⁺·ClO₄⁻·2H₂O, inter­molecular N—H⋯O and O—H⋯O hydrogen bonds occur. The protonated amine cations and the perchlorate anions are linked through the water mol­ecules, and the hy­droxy groups of the cations and the anions are linked through the water mol­ecules. The cations are connected to the perchlorate anions via inter­molecular N—H⋯O hydrogen bonds. In addition, the crystal structure exhibits weak inter­molecular C—H⋯π inter­actions.

4′-(Morpholinomethyl)biphenyl-2-carbonitrile

In the title compound, C₁₈H₁₈N₂O, the morpholine ring adopts a chair conformation and the dihedral angle between the aromatic rings is 49.16 (7)°. In the crystal, weak C—H⋯π inter­actions may help to establish the packing.

Bis(5-methyl-1-phenyl-1H-1,2,3-triazole-4-carboxylic acid) monohydrate

The crystal structure of the title compound, 2C₁₀H₉N₃O₂·H₂O, synthesized from azido­benzene and ethyl acetyl­acetate, is stabilized by O—H⋯O and O—H⋯N hydrogen bonds.

4-Ethoxyanilinium chloride

The title compound, C₈H₁₂NO⁺·Cl⁻, consists of an almost planar protonated 4-eth­oxy­anilinium cation with the N atom showing the biggest deviation from the plane formed by all non-H atoms of the cation [0.066 (1) Å]. In the crystal, N—H⋯Cl hydrogen bonds link cations and anions into chains along the a axis. Additional C—H⋯π and π–π inter­actions [centroid–centroid distance = 4.873 (2) Å] stabilize the crystal structure.

Bis(adamantan-1-aminium) tetrachloridozincate(II) 18-crown-6 monohydrate clathrate

The structure of the title compound [systematic name: bis(adamantan-1-aminium) tetrachloridozincate(II)-1,4,7,10,13,16-hexaoxacyclooctadecane-water (1/1/1)], (C(10)H(18)N)(2)[ZnCl(4)] x C(12)H(24)O(6) x H(2)O, consists of supramolecular rotator-stator assemblies and ribbons of hydrogen bonds parallel to [010]. The assemblies are composed of one protonated adamantan-1-aminium cation and one crown ether molecule (1,4,7,10,13,16-hexaoxacyclooctadecane) to give an overall [(C(10)H(18)N)(18-crown-6)](+) cation. The -NH(3)(+) group of the cation nests in the crown and links to the crown-ether O atoms through N-H...O hydrogen bonds. The 18-crown-6 ring adopts a pseudo-C(3v) conformation. The second adamantan-1-aminium forms part of ribbons of adamantan-1-aminium-water-tetrachloridozincate units which are interconnected by O-H...Cl, N-H...O and N-H...Cl hydrogen bonds via three different continuous rings with R(5)(4)(12), R(4)(3)(10) and R(3)(3)(8) motifs.

Reversible structural phase transition of pyridinium-4-carboxylic acid perchlorate

Pyridinium-4-carboxylic acid perchlorate (C6H6NO2·ClO4) was synthesized and separated as crystals. Differential scanning calorimetry measurement shows that this compound undergoes a reversible phase transition at about 122 K with a heat hysteresis of 1.8 K. A dielectric anomaly observed at 127 K further confirms the phase transition. The low-temperature (LT;T= 103 K) structure has space groupP21/cand cell parametersa= 17.356 (6),b= 13.241 (3),c= 16.161 (7) Å, β = 138.055 (17)°. The high-temperature (HT;T= 298 K) structure has space groupP21/cand cell parametersa= 5.5046 (11),b= 13.574 (3),c= 11.834 (2) Å, β = 99.35 (3)°, but can be re-described using new axesa′ =a,b′ =b,c′ = −2a+c,V′ =Vto give the cella′ = 5.5046 (11),b′ = 13.574 (3),c′ = 17.424 (3) Å, β′ = 137.92 (3)° and space groupP21/c. The associated coordinate transformation isx′ =x+ 2z,y′ =y,z′ =zand the associated reflection index transformation ish′ =h,k′ =k,l′ =l− 2h. The relationship between the two cells is 3a,b,c(HT) approximatesa,b,c(LT). The crystal comprises one-dimensional hydrogen-bonded chains of the pyridinium-4-carboxylic acid cations and perchlorate anions. A precise analysis of the main packing and structural differences as well as the changes in the intermolecular interactions between the HT phase and the LT phase reveals that the disorder–order transition of the perchlorate anions may be the driving force of the transition, and the hydrogen-bonding effect may contribute to the transition as a secondary parameter.

Dimethylammonium perchlorate 18-crown-6 monohydrate clathrate

The reaction of dimethyl­amine, 18-crown-6, and perchloric acid in methanol yields the title compound, C₂H₈N⁺·ClO₄⁻·C₁₂H₂₄O₆·H₂O. The dimethyl­ammonium cation and the water mol­ecule inter­act with the 18-crown-6 unit: N—H⋯O hydrogen bonds are formed between the ammonium NH₂⁺ group and four O atoms of the crown ether, while the water mol­ecule on the other side of 18-crown-6 ring forms O—H⋯O hydrogen bonds with two other O atoms of the crown ether. All conventional donors and acceptors in the cations are thus engaged in hydrogen bonding. The ClO₄⁻ anion is disordered over two sites, and occupancies for the disordered O atoms were fixed at 0.5. In the crystal, the cations and anions are arranged in alternating layers.

4-Methoxyanilinium hexafluorophosphate monohydrate

In the structure of the title compound, C₇H₁₀NO⁺·PF₆⁻·H₂O, the protonated 4-meth­oxy­anilinium cations and hexa­fluoro­phosphate anions are bridged by the water mol­ecule via N—H⋯O and O—H⋯F hydrogen bonds. The resulting zigzag chains extend along the c axis. In addition, C—H⋯π inter­actions are observed in the crystal packing.

Propane-1,3-diaminium tetrachloridozincate(II) 18-crown-6 clathrate

The reaction of propane-1,3-diamine hydrochloride, 18-crown-6 and zinc(II) chloride in methanol solution yields the title complex salt [systematic name: propane-1,3-diaminium tetrachloridozincate(II)-1,4,7,10,13,16-hexaoxacyclooctadecane (1/1)], (C(3)H(12)N(2))[ZnCl(4)] x C(12)H(24)O(6), with an unusual supramolecular structure. The diprotonated propane-1,3-diaminium cation forms an unexpected 1:1 supramolecular rotator-stator complex with the crown ether, viz. [C(3)H(12)N(2)(18-crown-6)](2+), in which one of the -NH(3)(+) substituents nests in the crown and interacts through N-H...O hydrogen bonding. The other -NH(3)(+) group interacts with the [ZnCl(4)](2-) anion via N-H...Cl hydrogen bonding, forming cation-crown-anion ribbons parallel to [010].

4-Methylmorpholinium bromide

The six-membered ring in the title salt, C₅H₁₂NO⁺·Br⁻, has a chair conformation. In the crystal, the cations are linked to the anions by N—H⋯Br hydrogen bonds.

4-(Cyanomethyl)anilinium chloride

The crystal structure of the title compound, C₈H₉N₂⁺·Cl⁻, is stabilized by N—H⋯Cl hydrogen bonds.

Benzyl-ammonium tetra-fluoro-borate 18-crown-6 clathrate

The reaction of benzyl­ammonium tetra­fluoro­borate and 18-crown-6 in a methano­lic solution yields the title compound, C₇H₁₀N⁺·BF₄⁻·C₁₂H₂₄O₆O6, which displays a supra­molecular structure. The –NH₃⁺ substituent of the benzyl­ammonium cation forms a 1:1 supra­molecular rotator–stator structure by N—H⋯O hydrogen-bonding inter­actions.

2,4-Dimethyl-anilinium chloride

In the crystal structure of the title compound, C(8)H(12)N(+)·Cl(-), all H atoms bonded to the ammonium N atom are hydrogen bonded to the chloride ions, with N⋯Cl distances in the range 3.080 (2)-3.136 (2) Å, resulting in 16-membered macrocyclic rings involving four formula units of the title compound.