Ionothermal synthesis and characterization of a 3-D (4,8)-connected porous anionic metal–organic framework entrapped with 1-D [K2(H2O)6] chains

Pseudohalogen Chemistry in Ionic Liquids with Non-innocent Cations and Anions

Within the second funding period of the SPP 1708 "Material Synthesis near Room Temperature",which started in 2017, we were able to synthesize novel anionic species utilizing Ionic Liquids (ILs) both, as reaction media and reactant. ILs, bearing the decomposable and non-innocent methyl carbonate anion [CO3 Me]- , served as starting material and enabled facile access to pseudohalide salts by reaction with Me3 Si-X (X=CN, N3 , OCN, SCN). Starting with the synthesized Room temperature Ionic Liquid (RT-IL) [nBu3 MeN][B(OMe)3 (CN)], we were able to crystallize the double salt [nBu3 MeN]2 [B(OMe)3 (CN)](CN). Furthermore, we studied the reaction of [WCC]SCN and [WCC]CN (WCC=weakly coordinating cation) with their corresponding protic acids HX (X=SCN, CN), which resulted in formation of [H(NCS)2 ]- and the temperature labile solvate anions [CN(HCN)n ]- (n=2, 3). In addition, the highly labile anionic HCN solvates were obtained from [PPN]X ([PPN]=μ-nitridobis(triphenylphosphonium), X=N3 , OCN, SCN and OCP) and HCN. Crystals of [PPN][X(HCN)3 ] (X=N3 , OCN) and [PPN][SCN(HCN)2 ] were obtained when the crystallization was carried out at low temperatures. Interestingly, reaction of [PPN]OCP with HCN was noticed, which led to the formation of [P(CN)2 ]- , crystallizing as HCN disolvate [PPN][P(CN⋅HCN)2 ]. Furthermore, we were able to isolate the novel cyanido(halido) silicate dianions of the type [SiCl0.78 (CN)5.22 ]2- and [SiF(CN)5 ]2- and the hexa-substituted [Si(CN)6 ]2- by temperature controlled halide/cyanide exchange reactions. By facile neutralization reactions with the non-innocent cation of [Et3 HN]2 [Si(CN)6 ] with MOH (M=Li, K), Li2 [Si(CN)6 ] ⋅ 2 H2 O and K2 [Si(CN)6 ] were obtained, which form three dimensional coordination polymers. From salt metathesis processes of M2 [Si(CN)6 ] with different imidazolium bromides, we were able to isolate new imidazolium salts and the ionic liquid [BMIm]2 [Si(CN)6 ]. When reacting [Mes(nBu)Im]2 [Si(CN)6 ] with an excess of the strong Lewis acid B(C6 F5 )3 , the voluminous adduct anion {Si[CN⋅B(C6 F5 )3 ]6 }2- was obtained.

A soft chemistry approach to the synthesis of single crystalline and highly pure (NH4)CoF3 for optical and magnetic investigations

A new ionothermal synthesis utilizing 1-alkyl-pyridinium hexafluorophosphates [C_xPy][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.

Ionothermal Synthesis, Structures, and Magnetism of Three New Open Framework Iron Halide-Phosphates

A set of different open framework iron phosphates have been synthesized ionothermally using a task-specific ionic liquid, 1-butyl-4-methylpyridinium hexafluorophosphate, that acts in the synthesis as the reaction medium and mineralizer: (NH₄)₂Fe₂(HPO₄)(PO₄)Cl₂F (1) and K₂Fe₂(HPO₄)(PO₄)Cl₂F (2) exhibit similar composition and closely related structural features. Both structures consist of {Fe₂(HPO₄)(PO₄)Cl₂F}^2- macroanions and charge balancing ammonium or potassium cations. Their open framework structure contains layers and chains of corner-linked {Fe(1)O₂Cl₄} and {Fe(2)F₂O₄} octahedra, respectively, interconnected by PO₄ tetrahedra forming 10-ring channels. KFe(PO₃F)F₂ (3) is built up by {Fe[(PO₃F)_4/3F_2/2]}{Fe(PO₃F)_2/3F_2/2F₂} layers separated by K⁺ cations. Chains of alternating {FeF₂O₄} and {FeO₂F₄} octahedra, which are linear for 1 but undulated for 2, are linked to each other via corner-sharing {PO₃F} tetrahedra with the fluorine pointing into the interlayer space. The compounds were characterized by means of single crystal and powder X-ray diffraction, infrared spectroscopy, and magnetic measurements. 1 reveals a strong ground state spin anisotropy with a spin 5/2 state and a magnetic moment of 5.3 μ_B/Fe³⁺. Specific heat and magnetic data unveil three magnetic transitions at 95, 50, and 3.6 K. Compound 2 has a very similar crystal structure as compared to 1 but exhibits a different magnetic behavior: a slightly lower magnetic moment of 4.7 μ_B/Fe³⁺ and a magnetic transition to a canted antiferromagnetic state below 90 K. Compound 3 exhibits typical paramagnetic behavior close to room-temperature (5.71 μ_B/Fe³⁺). There are no clear indications for a phase transition down to 2 K despite strong antiferromagnetic spin-spin interactions; only a magnetic anomaly appears at 50 K in the zero-field cooled data.

Structure-directing effects of ionic liquids in the ionothermal synthesis of metal-organic frameworks

Traditional synthesis of metal-organic frameworks (MOFs) involves the reaction of a metal-containing precursor with an organic linker in an organic solvent at an elevated temperature, in what is termed a 'solvothermal' reaction. More recently, many examples have been reported of MOF synthesis in ionic liquids (ILs), rather than an organic solvent, in 'ionothermal' reactions. The high concentration of both cations and anions in an ionic liquid allows for the formation of new MOF structures in which the IL cation or anion or both are incorporated into the MOF. Most commonly, the IL cation is included in the open cavities of the MOF, countering the anionic charge of the MOF framework itself and acting as a template around which the MOF structure forms. Ionic liquids can also serve other structure-directing roles, for example, when an IL containing a single enantiomer of a chiral anion leads to a homochiral MOF, even though the IL anion is not itself incorporated into the MOF. A comprehensive review of ionothermal syntheses of MOFs, and the structure-directing effects of the ILs, is given.

An electron-transfer photochromic metal–organic framework (MOF) compound with a long-lived charge-separated state and high-contrast photoswitchable luminescence

A new photochromic MOF compound exhibits a charge-separated state with lifetime exceeding the reported values of the analogues and a luminescence contrast higher than those of most known pyridine derivative-based photochromic compounds.

Ionothermal synthesis of open-framework metal phosphates with a Kagomé lattice network exhibiting canted anti-ferromagnetism†Electronic supplementary information (ESI) available: Cif files, atomic parameters, X-ray diffraction patterns, IR spectra, TG curves, and thermal ellipsoid plot and atomic label schemes of compound . See DOI: 10.1039/c4tc00290cClick here for additional data file

Four open-framework transition-metal phosphates; (NH4)2Co3(HPO4)2F4 (1), (NH4)Co3(HPO4)2(H2PO4)F2 (2), KCo3(HPO4)2(H2PO4)F2 (3), and KFe3(HPO4)2(H2PO4)F2 (4); are prepared by ionothermal synthesis using pyridinium hexafluorophosphate as the ionic liquid. Single-crystal X-ray diffraction analyses reveal that the four compounds contain cobalt/iron-oxygen/fluoride layers with Kagomé topology composed of interlinked face-sharing MO3F3/MO4F2 octahedra. PO3OH pseudo-tetrahedral groups augment the [M3O6F4] (1)/[M3O8F2] layers on both sides to give M3(HPO4)2F4 (1) and M3(HPO4)2F2 (2-4) layers. These layers are stacked along the a axis in a sequence AA…, resulting in the formation of a layer structure for (NH4)2Co3(HPO4)2F4(1). In NH4Co3(HPO4)2(H2PO4)F2 and KM3(HPO4)2(H2PO4)F2, the M3(HPO4)2F2 layers are stacked along the a axis in a sequence AA i … and are connected by [PO3(OH)] tetrahedra, giving rise to a 3-D open framework structure with 10-ring channels along the [001] direction. The negative charges of the inorganic framework are balanced by K+/NH4+ ions located within the channels. The magnetic transition metal cations themselves form layers with stair-case Kagomé topology. Magnetic susceptibility and magnetization measurements reveal that all four compounds exhibit a canted anti-ferromagnetic ground state (Tc = 10 or 13 K for Co and Tc = 27 K for Fe) with different canting angles. The full orbital moment is observed for both Co2+ and Fe2+.

The layered structure of poly[[hexaaqua(μ4-benzene-1,2,4,5-tetracarboxylato)dicopper(II)] tetrahydrate]

In the structure of the title compound, {[Cu2(C10H2O8)(H2O)6]·4H2O}n, the benzene-1,2,4,5-tetracarboxylate ligand, (btec)(4-), is located on a crystallographic inversion centre in a μ4-coordination mode. The coordination environment of each pentacoordinated Cu(II) centre is square pyramidal (SBP), formed by three water molecules and two carboxylate O atoms from two different (btec)(4-) ligands. The completely deprotonated (btec)(4-) ligand coordinates in a monodentate mode to four Cu(II) atoms. The alternation of (btec)(4-) ligands and SBP Cu(II) centres leads to the formation of a planar two-dimensional covalent network of parallelograms, parallel to the ab plane. Hydrogen bonds between a basal water molecule and an apical one from an adjacent [Cu(btec)0.5(H2O)3] unit exist in the intralayer space. Hydrogen bonds are also present between the two-dimensional network and the water molecules filling the channels in the structure.