Vergleich der Kristallstrukturen der Tetraammoniakate von Lithiumhalogeniden,LiBr·4NH3 und LiI·4NH3, mit der Struktur von Tetramethylammoniumiodid,N(CH3)4I

A Comparison of the Crystal Structures of the Tetraammoniates of Lithium Halides, LiBr·4NH₃ and LiI·4NH₃, with the Structure of Tetramethylammonium Iodide, N(CH₃)₄I Crystals of the tetraammoniates of LiBr and LiI sufficient in size for X‐ray structure determinations were obtained by slow evaporation of NH₃ at room temperature from a clear solution of the halides in liquid ammonia. The compounds crystallize in the space group Pnma (No. 62) with four formula units in the unit cell: LiBr·4NH₃: a = 11.947(5)Å, b = 7.047(4)Å, c = 9.472(3)Å LiI·4NH₃: a = 12.646(3)Å, b = 7.302 (1)Å, c = 9.790(2)Å For N(CH₃)₄I the structure was now successfully solved including the hydrogen positions of the methyl groups. N(CH₃)₄I: P4/nmm (No. 129), Z = 2, a = 7.948(1)Å, c = 5.738(1)Å The ammoniates of LiBr and LiI crystallize isotypic in a strongly distorted arrangement of the CsCl motif. Even N(CH₃)₄I has an CsCl‐like structure. Both structure types differ mainly in their orientation of the [Li(NH₃)₄]⁺ — resp. [N(CH₃)₄]⁺ — cations with respect to the surrounding “cube” of anions.     

Structural phase transition,thermal analysis,and spectroscopic studies in an organic–inorganic hybrid crystal: [(CH3)2NH2]2ZnBr4

An organic–inorganic hybrid compound [(CH₃)₂NH₂]₂ZnBr₄ has been prepared at room temperature under the slow evaporation method. Its structure was solved at 150 K using the single-crystal X-ray diffraction method. [(CH₃)₂NH₂]₂ZnBr₄ crystallizes in the monoclinic system – a = 8.5512 (12) Å, b = 11.825 (2) Å, c = 13.499 (2) Å, β = 90.358 (6)°, V = 1365 (4) ų, and Z = 4, space group P2₁/n. In the structure of [(CH₃)₂NH₂]₂ZnBr₄, tetrabromozincate anions are connected to organic cations through N–H⋯ Br hydrogen bonds. Differential scanning calorimetry (DSC) measurements indicate that [(CH₃)₂NH₂]₂ZnBr₄ undergoes four phase transitions at T₁ = 281 K, T₂ = 340 K, T₃ = 377 K, and T₄ = 408 K. Meanwhile, several studies including DSC measurements and variable-temperature structural analyses were performed to reveal the structural phase transition at T = 281 K in [(CH₃)₂NH₂]₂ZnBr₄. Conductivity and dielectric study as a function of temperature (378 < T [K] < 423) and frequency (10⁻¹ < f [Hz] < 10⁶) were investigated. Analysis of equivalent circuit, alternating current conductivity, and dielectric studies confirmed the phase transition at T₄. Conduction takes place by correlated barrier hopping in each phase.     

Crystal Structure,Phase Transition and Ferroelastic Properties of [N(CH3)4]3[As2Cl9]

The crystal structure of [N(CH₃)₄]₃[As₂Cl₉] is determined at 293 K. It crystallizes in trigonal space group P31c: a = 9.2199(8), c = 21.065(3)Å, Z = 2, R₁ = 0.0505, wR₂ = 0.1283. The crystal is built of the discrete bioctahedral [As₂Cl₉]^3— anions and the deformed tetramethylammonium cations. A structural phase transition in [N(CH₃)₄]₃[As₂Cl₉] is detected by the DSC and dilatometric techniques at 146/151 K (on cooling/heating). Dielectric relaxation studies in the frequency range 75 kHz — 5 MHz indicate reorientations of the tetramethylammonium cations within the high temperature phase. Optical observations show the existence of the ferroelastic domain structure below 146 K. The possible mechanism of phase transition is discussed on the basis of the presented results.     

Phase Transitions,Prominent Dielectric Anomalies,and Negative Thermal Expansion in Three High Thermally Stable Ammonium Magnesium–Formate Frameworks

We present three Mg–formate frameworks, incorporating three different ammoniums: [NH₄][Mg(HCOO)₃] ( 1 ), [CH₃CH₂NH₃][Mg(HCOO)₃] ( 2 ) and [NH₃(CH₂)₄NH₃][Mg₂(HCOO)₆] ( 3 ). They display structural phase transitions accompanied by prominent dielectric anomalies and anisotropic and negative thermal expansion. The temperature‐dependent structures, covering the whole temperature region in which the phase transitions occur, reveal detailed structural changes, and structure–property relationships are established. Compound 1 is a chiral Mg–formate framework with the NH₄⁺ cations located in the channels. Above 255 K, the NH₄⁺ cation vibrates quickly between two positions of shallow energy minima. Below 255 K, the cations undergo two steps of freezing of their vibrations, caused by the different inner profiles of the channels, producing non‐compensated antipolarization. These lead to significant negative thermal expansion and a relaxor‐like dielectric response. In perovskite 2 , the orthorhombic phase below 374 K possesses ordered CH₃CH₂NH₃⁺ cations in the cubic cavities of the Mg–formate framework. Above 374 K, the structure becomes trigonal, with trigonally disordered cations, and above 426 K, another phase transition occurs and the cation changes to a two‐fold disordered state. The two transitions are accompanied by prominent dielectric anomalies and negative and positive thermal expansion, contributing to the large regulation of the framework coupled the order–disorder transition of CH₃CH₂NH₃⁺. For niccolite 3 , the gradually enhanced flipping movement of the middle ethylene of [NH₃(CH₂)₄NH₃]²⁺ in the elongated framework cavity finally leads to the phase transition with a critical temperature of 412 K, and the trigonally disordered cations and relevant framework change, providing the basis for the very strong dielectric dispersion, high dielectric constant (comparable to inorganic oxides), and large negative thermal expansion. The spontaneous polarizations for the low‐temperature polar phases are 1.15, 3.43 and 1.51 μC cm^?2 for 1 , 2 and 3 , respectively, as estimated by the shifts of the cations related to the anionic frameworks. Thermal and variable‐temperature powder X‐ray diffraction studies confirm the phase transitions, and the materials are all found to be thermally stable up to 470 K.     

Coexistence of Three Ferroic Orders in the Multiferroic Compound [(CH3)4N][Mn(N3)3] with Perovskite‐Like Structure

The perovskite azido compound [(CH₃)₄N][Mn(N₃)₃], which undergoes a first‐order phase change at T_t=310 K with an associated magnetic bistability, was revisited in the search for additional ferroic orders. The driving force for such structural transition is multifold and involves a peculiar cooperative rotation of the [MnN₆] octahedral as well as order/disorder and off‐center shifts of the [(CH₃)₄N]⁺ cations and bridging azide ligands, which also bend and change their coordination mode. According to DFT calculations the latter two give rise to the appearance of electric dipoles in the low‐temperature (LT) polymorph, the polarization of which nevertheless cancels out due to their antiparallel alignment in the crystal. The conversion of this antiferroelectric phase to the paraelectric phase could be responsible for the experimental dielectric anomaly detected at 310 K. Additionally, the structural change involves a ferroelastic phase transition, whereby the LT polymorph exhibits an unusual and anisotropic thermal behavior. Hence, [(CH₃)₄N][Mn(N₃)₃] is a singular material in which three ferroic orders coexist even above room temperature.     

Equilibrium behaviour of exchange of [Coen3]3+ on vermiculite

Summary The cation exchange data of tris ethylene diamine cobaltic ion on H-vermiculite fit in with theLangmuir equation. The exchange of [Coen₃]³⁺ by different cations are in the order: Li < Na < NH₄ < K < Rb < H < Cs for the monovalent, Mg Ca < Ba for the bivalent and (C₂H₅)₄N < (CH₃)₄N CTA < CP for monovalent organic ions. Quaternary cations such as (C₂H₅)₄N⁺ exchange less than (CH₃)₄N⁺. This may be ascribed to the larger size of the former and also to the limitedc-axis expansion of vermiculite. By use of the equation ofKielland, thermodynamic equilibrium constants and standardGibbs free energy change have been evaluated. The plots of log (selectivity coefficient) vs. hydrated ionic radius and the reciprocal of theDebye Hückel parametera ⁰, suggest that the parametera ⁰ rather than the hydrated ionic radius may be found to correlate with the relative affinities of univalent cations for the vermiculite surface.     

Crystal structure,phase transitions and dielectric properties of the mixed compound [Cs0.92(NH4)0.08]2HgBr4

The crystal structure of [Cs_0.92 (NH₄)_0.08]₂HgBr₄ was determined by three-dimensional X-ray diffraction analysis. The space group is Pnma with a = 10.210(2), b = 7.928(1), c = 13.883(1)Å and Z = 4 at 293K. The structure was refined to R = 0.067. The distribution of atoms can be described as isolated HgBr₄²⁻tetrahedra , Cs⁺ and NH₄⁺ cations. The main feature of this structure is the coexistence of two types of bonds: Cs⁺  Br⁻ ionic bonds and NH…Br hydrogen bonds ensuring the cohesion of the crystal. Dicaesium-ammonium tetrabromomercurate exhibits three phase transitions at T₁ = 237K, T₂ = 244K and T₃ = 513K. These transitions were detected by differential scanning calorimetry and analysed by dielectric measurements using the impedance and modulus spectroscopy techniques. The phase change at high temperature is related with the orientational disorder of NH₄⁺ cations. Transport properties in this material appear to be due to a H⁺ ion hopping mechanism.     

Raman investigation of the order-disorder phase transitions in the 2[N(C3H7)4]SbCl4 compound

The Raman spectra of bis (tetrapropylammonium tetrachloroantimonate (III)) 2[(C₃H₇)₄N]SbCl₄ compound single crystals were studied in the wavenumber range from 3500 to 50 cm⁻¹ for temperatures between 300 and 415 K. Two phase transitions occurring at 343 (T_tr1) and 363 K (T_tr2) were observed and characterized. The strong evolutions of the Raman shift, half-widths and intensity of many lines associated with the organic cations were observed with discontinuities in the vicinity of the two phase transitions. The most important changes were noticed for the band at 307 cm⁻¹ (at room temperature) assignable to the torsion of CH₃ groups of the cations. The spectral characteristics of this band was analyzed and consistently described in the framework of an order–disorder model for the two phase transitions. They allowed us to obtain information relative to the activation energy, the correlation length, and the critical exponent of the mechanism. The decrease of the estimated activation energies for the band 307 cm⁻¹ with the increase in temperature has been interpreted in terms of a change in the reorientation motion of cations. The temperature dependence of the reduced peak intensity allowed for the determination of the critical exponents and evolution of the correlation length on approaching the transition.     

Structural phase transition,electrical and semiconducting properties in a lead-free 2D hybrid perovskite-like compound: [Cl-(CH2)2-NH3]2[CuCl4]

A new layered perovskite-type organic–inorganic hybrid compound: [Cl-(CH₂)₂-NH₃]₂[CuCl₄] ( 1 ), in which 2-chloroethylammonium cation occupies the space enclosed by the CuCl₆ octahedra, has been successfully synthesized. It is found that the compound exhibits the semiconducting properties with the optical band gap equal to 1.98 eV, confirmed by AC conductivity measurements, which varies between 10⁻⁵ and 10⁻⁴ Ω⁻¹ m⁻¹. Also, the low activation energy at low temperatures (0.26 eV) can indicate the electronic conduction of this material. Compound ( 1 ) displays phase transitions at T₁ = 281 K and T₂ = 380 K, confirmed by DSC, electrical and dielectric measurements. Single-crystal X-ray diffraction data at variable temperatures reveal that symmetry-breaking occurs from P2₁/c (at 296 K ˃ T₁) to P-1 (at 150 K ˂ T₁), originating directly from the [Cl-(CH₂)₂-NH₃]⁺ cation conformational changes and the distortions of CuCl₆⁴⁻ octahedra caused by the Jahn-Teller effect in the inorganic layers. Meanwhile, organic 2-chloroethylammonium moieties display some boat-like conformation below T₁, which transforms to a chair-like structure above T₁. This study paves the pathway to explore new lead-free hybrid perovskites with targeted properties for thermoelectric, supercapacitors, batteries, environmentally friendly processing and semiconductor applications.     

Crystal structure of 1-methyl-1,3,5,7-tetraazaadamantan-1-ium ammonium sulfate hydrate,a double salt containing puckered layers of hydrogen-bonded NH 4 + and SO 4 2− groups

The double salt [(CH₂)₆N₄CH₃](NH₄)SO₄·H₂O crystallizes in space groupP2₁/a, witha=12.994(2),b=6.319(1),c=15.082(2) Å, =93.78(2)^o, andZ=4. The structure was solved by the heavy-atom method and refined toR _F ²=0.051 for 2478 MoK data. The ammonium and sulfate ions are cross-linked by hydrogen bonds to form puckered layers disposed about the (001) family of planes. Each water molecule bridges a [(CH₂)₆N₄CH₃]⁺ ion and a sulfate group, so that the organic cations lying on both sides of a puckered layer have their methyl groups pointing inward and fitting into depressions. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82063 (18 pages).Carried out, in part, under contract DE-AC02-76CH00016 with the U.S. Department of Energy, Office of Basic Energy Sciences.     

Nuclear magnetic resonance study of the ferroelastic phase transition of order-disorder type in [N(C2H5)4]2CdCl4

This study uses nuclear magnetic resonance (NMR) techniques to examine the detailed changes in [N(C₂H₅)₄]₂CdCl₄ around its phase transition at the temperature T_C = 284 K. The chemical shifts and spin-lattice relaxation times in the rotating frame (T_1ρ) were determined from ¹H magic angle spinning (MAS) NMR and ¹³C cross-polarization (CP)/MAS NMR spectra. The two sets of inequivalent ¹H and ¹³C nuclei in CH₃ and CH₂ were distinguished. A ferroelastic phase transition was observed at T_C, without structural symmetry change. The phase transition is mainly attributed to the orientational ordering of the [N(C₂H₅)₄]⁺ cations, and the spectral splitting at low temperature is associated with different ferroelastic domains.     

Kraftkonstanten von Verbindungen des Typs (CH3)3ElCl+X− (El = N,P, As,Sb; X− = SbCl6−)

Force Constants of Compounds of the Type (CH₃)₃ElCl⁺X^?(El = N, P, As, Sb; X^? = SbCl₆^?) For the cations (CH₃)₃NCl⁺ ( 1 ), (CH₃)₃PCl⁺ ( 2 ), (CH₃)₃AsCl⁺ ( 3 ), and (CH₃)₃SbCl⁺ ( 4 ) a normal coordinate analysis using a general valence force field is performed by the method of Fadini. The force constants are discussed. Calculations of the potential energy distribution show, that the skeletal vibrations in 4 are all characteristic vibrations, but there is a strong coupling of vibrations in 1 .     

Synthesis,Characterization, and Crystal Structures of [N(CH3)4]2[B12H12] and [N(CH3)4]2[B12H12] · CH3CN

Bis(tetramethylammonium) dodecahydrododecaborate, [(CH₃)₄N]₂[B₁₂H₁₂], and bis(tetramethylammonium) dodecahydrododecaborate acetonitrile, [(CH₃)₄N]₂[B₁₂H₁₂] · CH₃CN, were synthesized and characterized via Infrared, ¹H and ¹¹B NMR spectroscopy. [(CH₃)₄N]₂[B₁₂H₁₂] crystallizes isopunctual to the alkali metal dodecaborates. The crystal structure of [(CH₃)₄N]₂[B₁₂H₁₂] · CH₃CN was determined from single crystal data and refined in the orthorhombic crystal system (Pcmn, no. 62, a = 898.68(8), b = 1312.85(9) c = 1994.5(1) pm, R(|F| , 4σ) = 5.9%, wR(F²) = 18.3%). Here, the geometry of the dodecaborate anion is that of an almost ideal icosahedron, less distorted than most other dodecaborates known. By low‐temperature Guinier‐Simon diffractometry phase transitions were detected for [(CH₃)₄N]₂[B₁₂H₁₂] and [(CH₃)₄N]₂[B₁₂H₁₂] · CH₃CN at –70 and –15 °C, respectively.     

Synthesis,Properties, and Structures of Salts with the Reineckate Anion, [CrIII(NCS)4(NH3)2]–, and Large Organic Cations

A series of 9 new Reineckate salts, A[Cr^III(NCS)₄(NH₃)₂] with various large organic cations A = tetraalkylammonium, [R₄N]⁺, R = n‐butyl, n‐dodecyl; 1‐alkyl‐3‐methylimidazolium, (RMIm)⁺: R = methyl, ethyl, iso‐propyl, n‐butyl, and n‐hexyl; A = 1,3‐dimethyl‐2,4,5‐triphenylimidazolium and A = 1,2,3,4,5‐pentamethylimidazolium was synthesized. The melting point of each compound was measured to see if any belongs to the group of metal‐containing Ionic Liquids with low melting points. Each compound was further characterized by elemental analysis, NMR, IR, and UV/Vis spectroscopy. From NMR investigations information about the magnetic behavior was derivedusing the Evans method. It has been found that every compound is paramagnetic with effective magnetic moments of spin‐only Cr^III. The structures of the Reineckates with A = tetra‐n‐butyl‐ammonium, tetra‐n‐dodecyl‐ammonium, 1‐ethyl‐3‐methylimidazolium, and 1,2,3,4,5‐pentamethylimidazolium were determined by single‐crystal X‐ray diffraction measurements: (nBu₄N)[Cr(NCS)₄(NH₃)₂]: monoclinic, C2/c (no. 15), a = 12.0818(8), b = 10.2425(8), c = 24.222(2) Å, β = 98.324(3)°, Z = 4, R1(F)/wR2(F²) = 0.0332/0.0871; {(C₁₂H₂₅)₄N}[Cr(NCS)₄(NH₃)₂]·0.85H₂O: triclinic, P$\bar{1}$ (no. 2), a = 8.4049(1), b = 20.1525(4), c = 20.7908(4) Å, α = 67.487(1)°, β = 81.328(1)°, γ = 78.040(1)°, Z = 2, R1(F)/wR2(F²) = 0.0533/0.1343; (EMIm)[Cr(NCS)₄(NH₃)₂]: orthorhombic, Pbcm (no. 57), a = 8.765(2), b = 15.888(3), c = 14.191(3) Å, Z = 4, R1(F)/wR2(F²) = 0.0466/0.1271; (PeMIm)[Cr(NCS)₄(NH₃)₂]: monoclinic, P2₁/n (no. 14), a = 6.0817(2), b =13.9811(5), c = 25.2902(9) Å, β = 90.075(2)°, Z = 4, R1(F)/wR2(F²) = 0.0405/0.1111.     

Structure and Phase Transitions in Ethylenediammonium Dichloride and its Salts with Antimony Trichloride

During the mixing of ethylenediammonium dichloride and antimony trichloride except of reported earlier [NH₃(CH₂)₂NH₃]₅(Sb₂Cl₁₁)₂ · 4 H₂O a new salt [NH₃(CH₂)₂NH₃](SbCl₄)₂ was obtained. The crystals are monoclinic at 295 K, space group C2/m, a = 13.829(3), b = 7.408(1), c = 7.588(2) Å; β = 103.18(3)°; V = 756.9(3) ų; Z = 2; d_c = 2.585, d_m = 2.56(2) g · cm^–3. The structure consists of anionic sublattice built of Sb₂Cl₈^2– units composed of two SbCl₅^2– square pyramids connected by edge. The ethylenediammonium cations are located in anionic cavities. The cations are disordered. Each methylene carbon atom is split between two positions. The X‐ray diffraction, DSC, TGA and dilatometric methods were used to investigate properties of ethylenediammonium dichloride and its two salts with antimony trichloride. In [NH₃(CH₂)₂NH₃]Cl₂ one phase transition of first order and of the order‐disorder type was found at 402 K. The [NH₃(CH₂)₂NH₃]₅(Sb₂Cl₁₁)₂ · 4 H₂O undergoes one transition at 355 K which is accompanied by the dehydration of the sample. In [NH₃(CH₂)₂NH₃](SbCl₄)₂ two phase transitions of the order‐disorder type: of first order at 238 K and of second order at 267 K were found. All those transitions in ethylenediammonium salts share common features. They were related to the changes in the molecular dynamics of ethylenediammonium cations. In the low temperature phases cations are ordered, while above T_c they are characterised by overall reorientations along the axis passing through opposite nitrogen atoms.     

Synthesen und Schwingungsspektren der homoleptischen Acetonitrilkomplex-Kationen [Au(NCCH3)2]+, [Pd(NCCH3)4]2+, [Pt(NCCH3)4]2+ und des Adduktes CH3CN · SbF5. Kristallstrukturen der Salze [M(NCCH3)4][SbF6]2 · CH3CN,M = Pd,Pt

The Syntheses and Vibrational Spectra of the Homoleptic Metal Acetonitrile Cations [Au(NCCH₃)₂]⁺, [Pd(NCCH₃)₄]²⁺, [Pt(NCCH₃)₄]²⁺, and the Adduct CH₃CN · SbF₅. The Crystal and Molecular Structures of [M(NCCH₃)₄][SbF₆]₂ · CH₃CN, M = Pd or Pt Solvolyses of the homoleptic metal carbonyl salts [M(CO)₄][Sb₂F₁₁]₂, M = Pd or Pt, in acetonitrile leads at 50 °C both to complete ligand exchange for the cations as well as to a conversion of the di-octahedral anion [Sb₂F₁₁]^– into [SbF₆]^– and the molecular adduct CH₃CN · SbF₅ according to: [M(CO)₄][Sb₂F₁₁]₂ + 7 CH₃CN → [M(NCCH₃)₄][SbF₆]₂ · CH₃CN + 2 CH₃CN · SbF₅ + 4 CO M = Pd, Pt The monosolvated [M(NCCH₃)₄][SbF₆]₂ · CH₃CN are obtained as single crystals from solution and are structurally characterized by single crystal x-ray diffraction. Both salts are isostructural. The cations are square planar but the N–C–C-sceletial groups of the ligands depart slightly from linearity. The new acetonitrile complexes as well as [Au(NCCH₃)₂][SbF₆] and the adduct CH₃CN · SbF₅ are completely characterized by vibrational spectroscopy.     

Crystal structure of tetramethylammonium hexafluoridoniobate(V) and hexafluoridotantalate(V)

Crystal structures of newly synthesized tetramethylammonium hexafluoridoniobate(V) and hexafluoridotantalate(V) (CH₃)₄N[МF₆] (M=Nb, Ta) have been determined; they crystallize in the tetragonal crystal system, sp. gr. P4/nmm. Crystal structures of isostructural compounds (CH₃)₄N[МF₆] (M=Nb, Ta) are formed by virtually regular tetrahedral tetramethylammonium cations (CH₃)₄N⁺ (NMe₄, TMA) and octahedral complex anions [МF₆]^– (M=Nb, Ta), fluorine atoms of the equatorial plane are statistically disordered over two positions. Ionic interactions and weak hydrogen bonds C–H???F join the cations and the complex anions in a 3D assembly.     

Complexation and Versatile Reactivity of a Highly Lewis Acidic Cationic Mg Complex with Alkynes and Phosphines

[(BDI)Mg⁺][B(C₆F₅)₄⁻] ( 1 ; BDI=CH[C(CH₃)NDipp]₂; Dipp=2,6-diisopropylphenyl) was prepared by reaction of (BDI)MgnPr with [Ph₃C⁺][B(C₆F₅)₄⁻]. Addition of 3-hexyne gave [(BDI)Mg⁺ ⋅ (EtC≡CEt)][B(C₆F₅)₄⁻]. Single-crystal X-ray analysis, NMR investigations, Raman spectra, and DFT calculations indicate a significant Mg-alkyne interaction. Addition of the terminal alkynes PhC≡CH or Me₃SiC≡CH led to alkyne deprotonation by the BDI ligand to give [(BDI-H)Mg⁺(C≡CPh)]₂ ⋅ 2 [B(C₆F₅)₄⁻] ( 2 , 70 %) and [(BDI-H)Mg⁺(C≡CSiMe₃)]₂ ⋅ 2 [B(C₆F₅)₄⁻] ( 3 , 63 %). Addition of internal alkynes PhC≡CPh or PhC≡CMe led to [4+2] cycloadditions with the BDI ligand to give {Mg⁺C(Ph)=C(Ph)C[C(Me)=NDipp]₂}₂ ⋅ 2 [B(C₆F₅)₄⁻] ( 4 , 53 %) and {Mg⁺C(Ph)=C(Me)C[C(Me)=NDipp]₂}₂ ⋅ 2 [B(C₆F₅)₄⁻] ( 5 , 73 %), in which the Mg center is N,N,C-chelated. The (BDI)Mg⁺ cation can be viewed as an intramolecular frustrated Lewis pair (FLP) with a Lewis acidic site (Mg) and a Lewis (or Brønsted) basic site (BDI). Reaction of [(BDI)Mg⁺][B(C₆F₅)₄⁻] ( 1 ) with a range of phosphines varying in bulk and donor strength generated [(BDI)Mg⁺ ⋅ PPh₃][B(C₆F₅)₄⁻] ( 6 ), [(BDI)Mg⁺ ⋅ PCy₃][B(C₆F₅)₄⁻] ( 7 ), and [(BDI)Mg⁺ ⋅ PtBu₃][B(C₆F₅)₄⁻] ( 8 ). The bulkier phosphine PMes₃ (Mes=mesityl) did not show any interaction. Combinations of [(BDI)Mg⁺][B(C₆F₅)₄⁻] and phosphines did not result in addition to the triple bond in 3-hexyne, but during the screening process it was discovered that the cationic magnesium complex catalyzes the hydrophosphination of PhC≡CH with HPPh₂, for which an FLP-type mechanism is tentatively proposed.     

High-temperature cubic modification of tetramethylammonium hexafluoridozirconate (N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>)<Subscript>2</Subscript>[ZrF<Subscript>6</Subscript>]

X-ray diffraction (XRD) and differential thermal analysis (DTA) methods are used to analyze tetramethylammonium hexafluoridozirconate of the composition [N(CH₃)₄]₂ZrF₆. In the temperature range between 96-110 °C, the crystals undergo a reversible phase transition from the low-temperature trigonal modification (space group R3 ) to the high-temperature cubic modification (space group Fm3m). The cubic phase is composed of regular [ZrF₆]²–octahedral and tetrahedral (CH₃)₄N⁺ cations linked by ionic interactions and the С–H???F hydrogen bonds.     

Darstellung,Schwingungsspektren und Kristallstrukturanalyse von Di- und Trifluor-tetramethylammonium-Salzen

Synthesis, Vibrational Spectra, and Crystal Structure Analysis of Di- and Trifluoro-tetramethylammonium Salts The tetramethylammonium salts (CH₃)₃NCH₂F⁺ ( II ), (CH₃)₃NCHF₂⁺ ( III ), and (CH₃)₃NCF₃⁺ ( IV ) were prepared by quaternation of the corresponding fluoromethylamines. III was also generated from (CH₃)₃N and Zn/CF₂Br₂/KF in acetonitrile. II , III , and IV were characterized by NMR and vibrational spectroscopy, a normal coordinate analysis being undertaken for IV . The crystal structures of the iodides of III and IV have been determined. In both cations the N? CH₃ distances are on the average ( III 1.508(2) Å; IV 1.514(5) Å) longer than the N? CF valencies ( III 1.497(4) Å; IV 1.491(6) Å).