Ionothermal Synthesis, Crystal Structure, and Magnetic Study of Co₂PO₄OH Isostructural with Caminite

A new framework cobalt­(II) hydroxyl phosphate, Co₂PO₄OH, was prepared by ionothermal synthesis using 1-butyl-4-methyl-pyridinium hexafluorophosphate as the ionic liquid. As the formation of Co₂PO₄F competes in the synthesis, the synthesis conditions have to be judiciously chosen to obtain well-crystallized, single phase Co₂PO₄OH. Single-crystal X-ray diffraction analyses reveal Co₂PO₄OH crystallizes with space group <i>I</i>4₁/<i>amd</i> (<i>a</i> = <i>b</i> = 5.2713(7) Å, <i>c</i> = 12.907(3) Å, <i>V</i> = 358.63(10) ų, and <i>Z</i> = 4). Astonishingly, it does not crystallize isotypically with Co₂PO₄F but rather isotypically with the hydroxyl minerals caminite Mg_1.33[SO₄­(OH)_0.66(H₂O)_0.33] and lipscombite Fe_2–<i>y</i>PO₄(OH) (0 ≤ <i>y</i> ≤ 2/3). Phosphate tetrahedra groups interconnect four rod-packed face-sharing _∞¹{CoO_6/2} octahedra chains to form a three-dimensional framework structure. The compound Co₂PO₄OH was further characterized by powder X-ray diffraction, Fourier transform–infrared, and ultraviolet–visible spectroscopy, confirming the discussed structure. The magnetic measurement reveals that Co₂PO₄OH undergoes a magnetic transition and presents at low temperatures a canted antiferromagnetic spin order in the ground state

Azobenzene-Based Organic Salts with Ionic Liquid and Liquid Crystalline Properties

Two sets of new azobenzene-based bromide salts are synthesized, and their thermal photochromic properties are studied. Both sets are based on the imidazolium cation. The first set (<b>1</b>) features a symmetric biscation where two imidazolium head groups (Im) with different alkyl chains (Cn) are connected to a central azobenzene unit (Azo): [Azo­(C1-Im-Cn)₂]; <i>n</i> = 6, 8, 10, 12, 14. The other one contains an <i>n</i>-alkyl-imidazolium cation (Cn-Im) bearing a terminal azobenzene unit (C1-Azo) substituted with an alkoxy chain (O-<i>Cm</i>) of either two (<b>2</b>) or six (<b>3</b>) carbon atoms: [C1-Azo-O-<i>Cm</i>-Im-Cn]; <i>m</i> = 2, <i>n</i> = 8, 10, 12 and <i>m</i> = 6, <i>n</i> = 8, 10, 12, 14, 16. For both cation classes, the influence of alkyl chains of varying length on the thermal phase behavior was investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). For five compounds (Azo­(-C1-Im-C12)₂ (<b>1d</b>), Azo­(-C1-Im-C12)₂ (<b>1e</b>), C1-Azo-O-C2-Im-C10 (<b>2b</b>), C1-Azo-O-C2-Im-C12 (<b>2c</b>), and C1-Azo-O-C6-Im-C16 (<b>3e</b>)), the formation of a liquid crystalline phase was observed. The biscationic salts (<b>1</b>) are all comparatively high melting organic salts (180–240 °C), and only the two representatives with long alkylchains (C12 and C14) exhibit liquid crystallinity. The monocationic salts with an O–C2 bridge (<b>2</b>) melt between 140 and 170 °C depending on the alkyl chain length, but from an alkyl chain of 10 and more carbon atoms on they form a smectic A liquid crystalline phase. The representatives of the third set with a O–C6 bridge qualify as ionic liquids with melting points less than 100 °C. However, only the representative with a hexadecyl chain forms a liquid crystalline phase. Representative single crystals for all sets of cations could be grown that allowed for single crystal structure analysis. Together with small-angle X-ray scattering experiments they allow for a more detailed understanding of the thermal properties. Through irradiation with UV-light (320–366 nm) all compounds undergo <i>trans–cis</i> isomerization, which reverses under visible light (440 nm)

Ionothermal Synthesis, Crystal Structure, and Magnetic Study of Co₂PO₄OH Isostructural with Caminite

A new framework cobalt­(II) hydroxyl phosphate, Co₂PO₄OH, was prepared by ionothermal synthesis using 1-butyl-4-methyl-pyridinium hexafluorophosphate as the ionic liquid. As the formation of Co₂PO₄F competes in the synthesis, the synthesis conditions have to be judiciously chosen to obtain well-crystallized, single phase Co₂PO₄OH. Single-crystal X-ray diffraction analyses reveal Co₂PO₄OH crystallizes with space group <i>I</i>4₁/<i>amd</i> (<i>a</i> = <i>b</i> = 5.2713(7) Å, <i>c</i> = 12.907(3) Å, <i>V</i> = 358.63(10) ų, and <i>Z</i> = 4). Astonishingly, it does not crystallize isotypically with Co₂PO₄F but rather isotypically with the hydroxyl minerals caminite Mg_1.33[SO₄­(OH)_0.66(H₂O)_0.33] and lipscombite Fe_2–<i>y</i>PO₄(OH) (0 ≤ <i>y</i> ≤ 2/3). Phosphate tetrahedra groups interconnect four rod-packed face-sharing _∞¹{CoO_6/2} octahedra chains to form a three-dimensional framework structure. The compound Co₂PO₄OH was further characterized by powder X-ray diffraction, Fourier transform–infrared, and ultraviolet–visible spectroscopy, confirming the discussed structure. The magnetic measurement reveals that Co₂PO₄OH undergoes a magnetic transition and presents at low temperatures a canted antiferromagnetic spin order in the ground state

Mesophase Stabilization in Ionic Liquid Crystals through Pairing Equally Shaped Mesogenic Cations and Anions

The synthesis and properties of a set of novel ionic liquid crystals with congruently shaped cations and anions are reported to check whether pairing mesogenic cations with mesogenic anions leads to a stabilization of a liquid crystalline phase. To that avail 1-alkyl-3-methyl-triazolium cations with an alkyl chain length of 10, 12, and 14 carbon atoms have been combined with <i>p</i>-alkyloxy-benzenesulfonate anions with different alkyl chain lengths (<i>n</i> = 10, 12, and 14). The corresponding triazolium iodides have been synthesized as reference compounds where the cation and anion have strong size and shape mismatch. The mesomorphic behavior of all compounds is studied by differential scanning calorimetry and polarizing optical microscopy. All compounds except 1-methyl-3-decyltriazolium iodide, which qualifies as an ionic liquid, are thermotropic ionic liquid crystals. All other compounds adopt smectic A phases. A comparison of the thermal phase behavior of the 1-methyl-3-decyltriazolium bromides to the corresponding <i>p</i>-alkoxy-benzensulfonates reveals that definitely the mesophase is stabilized by pairing the rod-shaped 1-alkyl-3-methyltriazolium cation with a rod-like anion of similar size

A Spin-Frustrated Trinuclear Copper Complex Based on Triaminoguanidine with an Energetically Well-Separated Degenerate Ground State

We present the synthesis and crystal structure of the trinuclear copper complex [Cu₃(saltag)­(bpy)₃]­ClO₄·3DMF [H₅saltag = tris­(2-hydroxybenzylidene)­triaminoguanidine; bpy = 2,2′-bipyridine]. The complex crystallizes in the trigonal space group <i>R</i>3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (<i>J</i>_CuCu = −324 cm^–1). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate <i>S</i> = ¹/₂ ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions