By employing the pyridinium hexafluorophosphate task-specific ionic liquids 1-butyl-4-methylpyridinium hexafluorophosphate ([C₄mpyr][PF₆]) and 1-ethylpyridinium hexafluorophosphate ([C₂pyr][PF₆]) as the reaction medium, mineralizer, structure-directing agent, and, in the case of the smaller pyridinium cation, even a structural component, it was possible to obtain five new alkali metal iron phosphates featuring interconnected FeX₆ octahedra and PX₄ (X = F, O, or OH) tetrahedra. NaFe(PO₃F)₂ (1) is a dense 3D structure, RbFe(PO₃F)(PO₂(OH)F)(PO₂(OH)₂) (2) features 1D strands, (C₂pyr)LiFe(PO₃F)₃(PO₂F₂)F (3) has 2D layers, and LiFe(PO₃F)(PO₂F₂)F (4) as well as Cs_0.75Fe(PO_2.75(OH)_0.25F)(PO₂F₂)₂ (5) are 3D open frameworks. While in 1–2 as well as in 4 and 5, FeX₆ octahedra and PX₄ (X = F, O, or OH) tetrahedra alternate, 3 features octahedra dimers, Fe₂X₁₁ (X = F, O, or OH). The magnetic behavior of all compounds is governed by antiferromagnetic interactions. Interestingly, 3 exhibits a broad maximum in the temperature dependence of the magnetic susceptibility, characteristic of a low-dimensional magnetic system consistent with the presence of Fe–Fe dimers in its crystal structure. 

A new family of oxofluorophoshates, AFe(PO₃F)₂ (A = K, (NH₄)₂Cl, NH₄, Rb, and Cs), was synthesized via ionothermal methods using PF₆ ionic liquids. Single-crystal and powder X-ray diffraction reveal that AFe(PO₃F)₂ with A = (NH₄)₂Cl crystallizes in a trigonal structure, while AFe(PO₃F)₂ with A = NH₄, Rb, and Cs crystallizes in a triclinic structure. Dimorphic KFe(PO₃F)₂ crystallizes in both the trigonal and triclinic forms. The structures of all compounds feature Yavapaiite-like Fe(PO₃F)₂ slabs, which are characterized by triangular Fe layers, planar in the case of the trigonal structure and undulated in the case of the triclinic one. Magnetization measurements reveal all compounds to order antiferromagnetically at low temperatures. The trigonal phases AFe(PO₃F)₂ (A = K and (NH₄)₂Cl) display complex magnetic H–T phase diagrams. The observation of magnetization plateaus at M_sat/3 (M_sat = saturation magnetization) indicates the existence of the up–up–down (UUD) and V-phases at applied magnetic fields in the magnetically ordered state. Powder neutron diffraction measurements of KFe(PO₃F)₂ confirm the 120° spin structure at zero fields. Along c, the magnetic moments form a commensurate spiral since the spins in each plane are rotated by 90° with respect to the adjacent one. To our knowledge, this is the first time such a non-centrosymmetric version of the 120° spin structure with a 90° rotation between nearest planes has been reported.

Open framework materials such as zeolites and metalorganic frameworks are garnering tremendous interest because of their intriguing architecture and attractive functionalities. Thus, new types of open framework materials are highly sought after. Here, we present the discovery of completely new inorganic framework materials, where, in contrast to conventional inorganic open frameworks, the scaffold is not based on tetrahedral EO₄ (E = main group element) but octahedral MO₆ (M = transition metal) building blocks. These structural features place them closer to polyoxometalates than zeolites. The first representatives of this class of materials are [(R)₂₄(NH₄)₁₄(PO(OH)₂)₆]·[M₁₃₄(PO₃(OH,F))₉₆F₁₂₀] (M = Co, R = C₂Py = 1-ethylpyridinium and M = Ni, R = C₄C₁Py = 1-butyl-3-methylpyridinium) featuring interlinked fullerene-like nanosphere cavities. Having a transition metal building up the framework brings about interesting properties, for example, spin-glass behavior, and, with this particular topology, a hedgehog-like spin orientation.

The derivatives of the Li_1−xRE_5+xW₈O₃₂ series (RE = Dy–Lu) all crystallize C-centered in the monoclinic system (a = 1897–1909 pm, b = 560–562 pm, c = 1127–1152 pm, β ≈ 111.1°, Z = 2). In the crystal structures of all representatives there are atomic positions, which show a mixed occupation of Li⁺ and the respective RE³⁺ cations. For RE = Dy this ratio is determined to be 1:1, resulting in space group C2/c. For RE = Ho–Lu, two crystallographically distinguishable positions exhibit the aforementioned mixed occupation with one of these being preferably occupied with Li⁺ and the other with RE³⁺ cations, causing the inversion symmetry to be lost, thus, their structure solution is best performed non-centrosymmetrically in space group C2. Furthermore, in the overall structure a deficiency of lithium with respect to the ideal formula LiRE₅W₈O₃₂ was determined by both single crystal and neutron diffraction experiments and therefore the composition can be described better as Li_1−xRE_5+xW₈O₃₂. The resulting excess of positive charges in the formula is compensated by a partial reduction of the tungsten cations from their highest oxidation state, which is also indicated by the dark blue, almost black color of the compounds and was supported by magnetic susceptibility and electron paramagnetic resonance (EPR) measurements.

A new ionothermal synthesis utilizing 1-alkyl-pyridinium hexafluorophosphates [CxPy][PF6] (x = 2, 4, 6) led to the formation of highly crystalline single-phase ammonium cobalt trifluoride, (NH4)CoF3. Although ammonium transition-metal fluorides have been extensively studied with respect to their structural and magnetic properties, multiple aspects remain unclear. For that reason, the obtained (NH4)CoF3 has been investigated over a broad temperature range by means of single-crystal and powder x-ray diffraction as well as magnetization and specific heat measurements. In addition, energy-dispersive x-ray and vibrational spectroscopy as well as thermal analysis measurements were undertaken. (NH4)CoF3 crystallizes in the cubic perovskite structure and undergoes a structural distortion to a tetragonal phase at 127.7 K, which also is observable in the magnetic susceptibility measurements, which has not been observed before. A second magnetic phase transition occurring at 116.9 K is of second-order character. The bifurcation of the susceptibility curves indicates a canted antiferromagnetic ordering. At 2.5 K, susceptibility measurements point to a third phase change for (NH4)CoF3.

A set of imidazolium-based ionic liquids (ILs), 1-(2-hydroxyethyl)-3-methylimidazolium chloride (1), 1,3-bis-(2-hydroxyethyl)-imidazolium chloride (2), and 1-butyl-2,3,4,5-tetramethylimidazolium bromide (3), has been synthesized and their structural and thermal behavior studied. Organic halides are well-known IL formers with imidazolium halides being the most prominent ones. Functionalization of the imidazolium cation by enhancing its hydrogen bonding capacity, i.e. through introduction of -OH groups or by diminishing it, i.e. through substitution of the ring hydrogen atoms by methyl groups is expected to change the inter-ionic interactions. Consequently, the solid-state structures of 1-3 have been characterized with means of single X-ray diffraction to shed light on preferential inter-ionic interactions for obtaining valuable information on anti-crystal engineering, i.e. designing ion combinations that favor a low melting point and exhibit a low tendency for crystallization. The study reveals that endowing IL forming ions with an enhanced hydrogen bonding capacity leads to a depression in melting points and kinetically hinders crystallization. This study provides hints towards new design concepts for IL design, similar to the common strategy of employing conformationally flexible ions.

Pale yellow crystals of LnSb(2)O(4)Br (Ln = Eu-Tb) were synthesized via high temperature solid-state reactions from antimony sesquioxide, the respective lanthanoid sesquioxides and tribromides. Single-crystal X-ray diffraction studies revealed a layered structure in the monoclinic space group P2(1)/c. In contrast to hitherto reported quaternary lanthanoid(III) halide oxoantimonates(III), in LnSb(2)O(4)Br the lanthanoid(III) cations are exclusively coordinated by oxygen atoms in the form of square hemiprisms. These [LnO(8)](13-) polyhedra form layers parallel to (100) by sharing common edges. All antimony(III) cations are coordinated by three oxygen atoms forming psi(1)-tetrahedral [SbO3](3-) units, which have oxygen atoms in common building up meandering strands along [001] according to {[SbO2/2vO1/1t]-}infinity 1 (v = vertex-sharing, t = terminal). The bromide anions are located between two layers of these parallel running oxoantimonate(III) strands and have no bonding contacts with the Ln(3+) cations. Since Sb3+ is known to be an efficient sensitizer for Ln(3+) emission, photoluminescence studies were carried out to characterize the optical properties and assess their suitability as light phosphors. Indeed, for both, GdSb2O4Br and TbSb2O4Br doped with about 1.0-1.5 at-% Eu3+ efficient sensitization of the Eu3+ emission could be detected. For TbSb2O4Br, in addition, a remarkably high energy transfer from Tb3+ to Eu3+ could be detected that leads to a substantially increased Eu3+ emission intensity, rendering it an efficient red light emitting material.

The admixture of CeO2, Ce, CeCl3, and MoO3 with an excess of LiCl as flux in evacuated silica ampules leads to large black single crystals as well as a black microcrystalline powder of Ce3Cl3[MoO6] after tempering at 850 degrees C for three days. The title compound crystallizes in the hexagonal space group P6(3)/m (a=934.93(4), c=538.86(2) pm) with two formula units per unit cell. The crystal structure consists of rather unusual trigonal-prismatic [MoO6](6-) units besides Ce3+ ions in a tetra-capped trigonal-prismatic coordination, formed by four Cl- and six O2- ions. The black color is related to an optical band gap of 1.35(2) eV, which was determined by diffuse reflectance spectroscopy and confirmed by theoretical calculations. The low band gap between the 4f(1) state of cerium (HOMO) and the 5d(0) state of molybdenum (LUMO) gave rise to the idea of electronic excitation between these two states by IR irradiation, creating a drop in the resistivity of the material, which was detected by appropriate measurements.

The lanthanide(III) chloride oxidomolybdates(VI) with the empirical formula Ln(3)Cl(3)[MoO6] (Ln = La, Pr, and Nd) were synthesized by solid-state reactions utilizing the respective lanthanide trichloride, lanthanide sesquioxide (where available), and molybdenum trioxide together with lithium chloride as a fluxing agent. The title compounds crystallize in hexagonal space group P6(3)/m (a = 942-926 pm, c = 542-533 pm, Z = 2). Besides tetracapped trigonal prismatically coordinated Ln(3+) cations, noncondensed trigonal prismatic [MoO6]6(-) entities are found in the crystal structure. In addition to X-ray diffraction, the title compounds were also characterized by single-crystal Raman and infrared spectroscopy as well as measurements to determine their magnetic susceptibility and behavior at low temperatures. The most outstanding properties of the Ln(3)Cl(3)[MoO6] representatives (Ln = La, Pr, and Nd), however, are of an optical nature, because their band gaps, determined by diffuse reflectance spectroscopy, show a significant shift toward lower energies compared to those of other rare-earth metal chloride molybdates with a different polyhedral arrangement. This culminates in La3Cl3[MoO6]:Eu3+ exhibiting luminescence, which can be excited in the visible range of the electromagnetic spectrum by a blue light-emitting diode.

An ionothermal synthesis study of transition metal phosphates using the ionic liquid 1-butyl-4-methylpyridinium hexafluorophosphate [C(4)mpy] [PF6] yielded four new, different open framework manganese compounds, that is, K2Mn3 (HPO4)(2)(PO3F)F-2 (1), (NH4)(2)Mn-3 (HPO4)(2) (PO3F)-F-2 (2), KMn3 (H2PO4)(HPO4)(2)F-2 (3), and (NH4)Mn-3(H2PO4)(PO3F)(2)F-2 (4). The obtained products not only feature new framework topologies unprecedented in the family of phosphates but also interesting properties as the transition metal gives rise to both luminescent (rendering them potential nonrare earth containing red emitting phosphors) and unconventional magnetic properties governed by geometric frustrations. Aside from the structural analysis (powder and single-crystal X-ray diffraction, infrared spectroscopy), a variety of characterization methods (photoluminescence spectroscopy and magnetic measurements) were applied to study the material's properties. Single crystal X-ray studies reveal that 1 (P2(1)/c with a = 5.501(1), b = 14.203(3), c = 16.905(4) angstrom, beta = 108.65(3)degrees, V = 1251.4 angstrom(3), and Z = 4) and 2 (P2(1)/c with a = 5.587(1), b = 14.507(3), c = 17.364(3) angstrom, beta = 108.75(3)degrees, V = 1332.6(5) angstrom(3), and Z = 4) feature S-shaped 18-ring channels along [100], which are formed by trimer-Mn3O9F2 chains parallel to [100] and interconnecting PO3 (OH) and PO3F tetrahedra. The structure of compounds 3 (C2/c with a = 20.307(4), b = 7.635(1), c = 7.834(2) angstrom, beta = 103.26(3)degrees, V = 1182.2(4) angstrom(3), and Z = 4) and 4 (C2/c with a = 20.402(4), b = 7.673(1), c = 7.845(2) angstrom, beta = 103.56(3)degrees, V = 1193.8(4) angstrom(3), and Z = 4) are characterized by layers, which are built of Mn3O8F4 octahedra trimers, with Kagome topology parallel to the be plane featuring 3,6-ring channels. The layers are stacked according to a sequence of AA(i) along the a axis. Taking into account the [P(2)O-3(OH)/P(2)O3F] tetrahedra, the Kagome layers are replenished to a Mn3O2 (HPO4)/Mn3O2 (PO3F) composition, which are interlinked by [P(1)O-2(OH)(2)] forming 10-ring channels parallel to [001]. Charge compensation of the macroanions is achieved by K+ (1 and 3) and (NH4)(+) (2 and 4) cations. At room temperature, compounds 1-4 demonstrate a reddish orange emission ascribed to the spin-forbidden T-4(1g)((4)G) -> (6)A(1g) (S-6) transition of the Mn2+ ions. Upon lowering the temperature to 77 K, the emission of each compound is red-shifted and becomes pure red. Compounds 1 and 2 contain spin trimers with a presumable doubled ground state. The intertrimer magnetic coupling is relatively weak, and small ferrimagnetic domains are possible in 1. The magnetic behavior of 3 and 4 can be considered as antiferromagnetic. This can be understood as their staircase Kagome lattices are distorted, meaning that the intrinsic geometrical frustration is lifted.