Tris(dialkylamino)cyclopropenium dialkylphosphate ionic liquids as lubricants.

Six new tris(dialkylamino)cyclopropenium dialkylphosphate ionic liquids (ILs), [C3(NR2)3]BEHP (NR2 = NEt2, NBuMe, NPr2, NBu2, NHex2, NDec2; BEHP = bis(2-ethylhexyl)phosphate), were prepared and characterised as potential lubricants. Thermophysical and thermochemical properties of these ILs were investigated, namely: viscosity, density, conductivity, miscibility, thermal stability and phase transitions. Miscibility studies indicated that [C3(NEt2)3]BEHP would not be suitable due to its water solubility and hexane immiscibility. [C3(NDec2)3]BEHP was not investigated as a lubricant due to its low purity (the chloride salt of this cation is also hexane miscible). Of the other four, [C3(NHex2)3]BEHP was found to exhibit significantly less wear for pin-on-disk test conditions than the standard phosphonium [P6,6,6,14]BEHP IL. The amount of wear was found to generally decrease with increasing molecular weight.

Highly-fluorinated Triaminocyclopropenium Ionic Liquids.

A series of highly-fluorinated triaminocyclopropenium salts, with up to six fluorous groups, were prepared and their properties as ionic liquids investigated. Reaction of pentachlorocyclopropane or tetrachlorocyclopropene with bis(2,2,2-trifluoroethyl)amine, HN(CH2 CF3 )2 , occurs in the presence of a trialkylamine, NR3 , to give cations with two fluorinated amino groups, [C3 (N(CH2 CF3 )2 )2 (NR2 )]+ (R=Et, Pr, Bu, Hex), with traces of [C3 (N(CH2 CF3 )2 )3 ]+ . Use of appropriate reagent ratios and reaction times and subsequent addition of a dialkylamine, HNR'R", gives cations with one fluorinated amino group, [C3 (N(CH2 CF3 )2 )(NR2 )(NR'R")]+ ((NR2 )(NR'R")=(NBu2 )2 , (NEt2 )(NPr2 ), (NBu2 )(NBuMe)). These cations were isolated as chloride salts and some of these were converted to bistriflamide, dicyanamide and triflate salts to provide ionic liquids. These salts were characterised by thermal (DSC and TGA) measurements and miscibility/solubility properties (determined in a range of solvents). Ionic liquids (ILs) were also characterised by density, viscosity and conductivity measurements where possible. X-ray diffraction studies of chloride salts showed the formation of fluorous regions and more hydrophilic ionic regions in the solid state.

Structures and Spectra of Halide Hydrate Clusters in the Solid State: A Link between the Gas Phase and Solution State.

This Review describes and assesses known solid-state examples of halide hydrates that are discrete in nature. Most of these are chloride hydrates, and most discrete clusters are dihalides, with very few mono- or multi-halide species found in the solid state. Polymeric chloride hydrates, on the other hand, are mostly 2D layered structures. We also observe that there is a gap in the chloride:water ratio between 8-20 waters per chloride. Isolated clusters can be found with 1-3 waters per chloride, 2D layers with 2-8 waters, and 3D semiclathrates with 20-38 waters. However, 1D chains comprise only 1-2 waters per chloride. [Cl(H2 O)]- is the only species found in both the solid state and gas phase and is also the only halide hydrate with a free OH group. Infrared spectra in the ν(OH) region are distinctive and useful for identification. Agreement between computed (gas phase) and experimentally-observed solid state structures and their vibrational spectra gives us confidence that discrete halide hydrate species observed in the solid state provide a useful link between gas phase species and structural motifs of halide hydrates in solution, especially microsolvated ion-pairs.

Discrete Oligomers and Polymers of Chloride Monohydrate Can Form in Encapsulated Environments: Structures and Infrared Spectra of [Cl4 (H2 O)4 ]4- and {[Cl(H2 O)]- }∞.

A discrete tetrachloride tetrahydrate cluster, [Cl4 (H2 O)4 ]4- , was obtained with a partially-fluorinated triaminocyclopropenium cation, [C3 (N(CH2 CF3 )2 )(NEt2 )(NPr2 )]+ . The cluster consists of a [Cl2 (H2 O)2 ]2- square with each Cl- coordinated by another H2 O bridged to another Cl- . A 1D polymer of chloride monohydrate, {[Cl(H2 O)]- }∞ , was obtained with [C3 (N(CH2 CF3 )2 )2 (NBuMe)]+ . The tetrameric and polymeric structures were found to be computationally-unstable in the gas phase which indicates that an encapsulated environment is essential for their isolation. DFT and DFTB calculations were carried out on gas-phase [Cl4 (H2 O)4 ]4- to assist the infrared assignments. Anharmonically-corrected B3LYP transition frequencies were in close agreement with experiment, but DFTB models were only appropriate for qualitative interpretation. Solid-state DFTB calculations allowed the vibrational modes to be assigned. The results found are consistent with "discrete" chloride hydrates.

Are "Bright-State" Models Appropriate for Analyzing Fermi-Coupled Bands in Molecular Vibrational Spectra?

Bright-state models are often applied to "deperturb" Fermi-coupled bands in molecular vibrational spectra, in cases where a harmonically forbidden transition "borrows" intensity from an energetically nearby allowed transition. However, forbidden transitions can also acquire intensity through anharmonic couplings on the potential energy surface ("mechanical anharmonicity") or dipole moment surface ("electrical anharmonicity") that are not accounted for within the bright-state model. In this work, we compare deperturbation shifts obtained by analysis of experimental data with those predicted using the bright-state model, for a series of discrete encapsulated chloride hydrate isotopomers. Predicted band center shifts and Fermi coupling matrix elements obtained using the bright-state model are larger than those estimated from experimental data.

A Discrete Chloride Monohydrate: A Solid-State Structural and Spectroscopic Characterization.

The solid-state structure of a discrete chloride monohydrate species, [Cl(H2O)]-, is reported for the first time. It was isolated as a salt of the tris(dipropylamino)cyclopropenium cation and has been structurally characterized by X-ray and neutron diffraction. Infrared (IR), far-infrared, and Raman spectroscopic studies were also carried out. Additionally, the D2O and HDO isotopomers were investigated. Of the six fundamental vibrational modes, only the out-of-plane bend ν3 was not observed as it forms an IR- and Raman-inactive local mode phonon.

A Series of Discrete Dichloride Dihydrates: Characterisation and Symmetry Effects.

A series of three discrete dichloride dihydrates [Cl2 (H2 O)2 ]2- have been isolated with different triaminocyclopropenium (TAC) cations and with different crystallographic symmetries. The cluster exhibits D2h symmetry with the tris(dimethylamino)cyclopropenium cation [C3 (NMe2 )3 ]+ , C2h symmetry with the fluorinated cation [C3 (N(CH2 CF3 )2 )(NBu2 )2 ]+ (containing two 2,2,2-trifluoroethyl substituents) and C2v symmetry with the more fluorinated [C3 (N(CH2 CF3 )2 )2 (NBu2 )]+ cation. The effect of symmetry on the infrared spectra of the dichloride ion-pair clusters, as well as deuterated analogues, has been investigated. The D2h - and C2h -symmetric clusters each exhibit two stretching bands in the infrared at 3427 and 3368 cm-1 for D2h symmetry and 3444 and 3392 cm-1 for C2h symmetry, whereas the C2v -symmetric cluster exhibits three bands at 3475, 3426 and 3373 cm-1 . Computational studies were carried out on a [Cl2 (H2 O)2 ]2- cluster with C2v symmetry to aid the infrared band assignments.

One water to bind a chloride-chloride ion pair: isolation of discrete [Cl2(H2O)]2- in the solid state.

A discrete dichloride ion pair in the form of a monohydrate, [Cl2(H2O)]2-, was isolated using the triaminocyclopropenium cation [C3(NHex2)(N(CH2CF3)2)2]+. Although this ion pair is calculated to be unstable in the gas phase, the ionic lattice and weak CH-Cl hydrogen bonds assist the stabilization of the cluster. The D2O and HDO isotopomers were also prepared and characterized.

A Discrete Dichloride Tetrahydrate Trapped by a Cyclopropenium Cation: Structure and Spectroscopic Properties.

A discrete dichloride tetrahydrate cluster, [Cl2 (H2 O)4 ]2- , was obtained as a salt of the bis(diphenylamino)diethylamino cyclopropenium cation [C3 (NPh2 )2 (NEt2 )]+ and characterized by single-crystal X-ray diffraction and infrared spectroscopy. This chloride-chloride ion-pair cluster consists of a [Cl2 (H2 O)2 ]2- square with opposite edges bridged by water molecules to give a chair-like structure of the non-hydrogen atoms. The solid-state structure is essentially the same as the calculated gas-phase structure. Infrared spectra were also collected on the deuterium analogue [Cl2 (D2 O)4 ]2- . Computational studies were carried out on gas-phase [Cl2 (H2 O)4 ]2- to confirm the infrared band assignments in the solid state. The structure and infrared spectrum are consistent with the discrete nature of the cluster.

Construction of Ternary Iodine-Bromine-Chlorine Octahalides.

A series of five ternary octanuclear iodine-bromine-chlorine interhalides, [I2 Br2 Cl4 ]2- (1), [I3 BrCl4 ]2- (2), [I4 Br2 Cl2 ]2- (3), [I2 Br4 Cl2 ]2- (4) and [I3 Br3 Cl2 ]2- (5), have been rationally constructed in two steps. Firstly, addition of a dihalogen (ICl or IBr) to the triaminocyclopropenium chloride salt [C3 (NEt2 )3 ]Cl forms the corresponding trihalide salt with [ICl2 ]- or [BrICl]- anions, respectively. Secondly, addition of a half-equivalent of a second dihalogen, followed by crystallization at low temperature, gives the corresponding octahalide: addition of Br2 and IBr to [ICl2 ]- gives 1 and 2, respectively, whereas addition of I2 , Br2 and IBr to [BrICl]- gives 3, 4 and 5, respectively. The five octahalides were characterized by X-ray crystallography and far-IR spectroscopy.

Rational Synthesis, Structures and Properties of the Ionic Liquid Binary Iodine-Bromine Octahalide Series [In Br8-n ]2- (n=0, 2, 3, 4).

A series of octanuclear iodine-bromine interhalides [In Br8-n ]2- (n=0, 2, 3, 4) were prepared systematically in two steps. Firstly, addition of a dihalogen (Br2 or IBr) to the triaminocyclopropenium bromide salt [C3 (NEt2 )3 ]Br forms the corresponding trihalide salt with Br3 - or IBr2 - anions, respectively. Secondly, addition to Br3 - of half an equivalent of Br2 gives the octabromine polyhalide [Br8 ]2- , whereas addition to IBr2 - of half an equivalent of Br2 , IBr or I2 gives the corresponding interhalides: [I2 Br6 ]2- , [I3 Br5 ]2- , and [I4 Br4 ]2- , respectively. The four octahalides were characterized by X-ray crystallography, computational studies, Raman and Far-IR spectroscopies, as well as by TGA and melting point. All of the salts were found to be ionic liquids.

The Binary Iodine-Chlorine Octahalide Series [In Cl8-n ]2- (n=3, 3.6, 4).

The octanuclear iodine-chlorine interhalides [I4 Cl4 ]2- and [I3 Cl5 ]2- were prepared in two steps. Firstly, addition of ICl to the triaminocyclopropenium chloride salt [C3 (NEt2 )3 ]Cl forms the trihalide ICl2 - salt, secondly, addition of half an equivalent of I2 or ICl, respectively, gave the desired products upon crystallization at low temperature. The non-stoichiometric octahalide [I3.6 Cl4.4 ]2- was obtained after heating a CH2 Cl2 solution of the ICl2 - salt to reflux for 2 hours followed crystallization. [I4 Cl4 ]2- is best described as two ICl2 - anions bridged by I2 , whereas [I3 Cl5 ]2- is best described as an [I2 Cl3 ]- pentahalide with a weak halogen bond to an ICl2 - trihalide. The octahalides were characterized by X-ray crystallography, computational studies, Raman and Far-IR spectroscopies, as well as by TGA and melting point.

Fluoride Ionic Liquids in Salts of Ethylmethylimidazolium and Substituted Cyclopropenium Cation Families.

A series of solvent-stabilized ionic liquid fluorides were prepared, [EMIM]F.nCH3COOH n = 1. 0, 1.6, 2.1, 2.4, and 3.2, either via exchange from the chloride salt using KF or AgF, or by neutralization of the hydroxide salt using HF. Azeotrope drying was used to remove water. Their viscosity, conductivity and density properties were determined. A diethanol solvate of the triaminocyclopropenium salt [C3(NPr2)3]F was found to be stable and its viscosity, conductivity and density properties were also determined. The monoethanol solvate, however, was found to be unstable with trace water present. Intramolecular stabilization of fluoride was achieved by using OH functionalized cations: [C3(NEt2)2N(CH2CH2OH)2]F, [C3(N(CH2CH2OH)2)3]F, and [Me3NCH2CH2OH]F.H2O, The first of these is an ionic liquid at ambient temperature and has a TGA mass loss onset at 175°C, indicating a useful range of liquid state stability.

Synthesis and physical properties of tris(dialkylamino)cyclopropenium dicyanamide ionic liquids.

The synthesis and properties of 16 tris(dialkylamino)cyclopropenium (TDAC) cations with the dicyanamide (DCA) anion, [N(CN)2]-, are described. D 3h- and C 3h-symmetric cations ([C3(NR2)3]DCA (R = Me, Et, Pr, Bu, Pent, Hex, Dec) and [C3(NRMe)3]DCA (R = Bu, St), respectively) were synthesised by reaction of C3Cl5H with the corresponding amine. Reaction of the alkoxydiaminocyclopropenium salt [C3(NEt2)2(OMe)]+ with amines led to a series of C 2v-symmetric salts [C3(NEt2)2(NR2)]DCA (R = Me, Bu, Hex) and two C s-symmetric salts and [C3(NEt2)2(NRMe)]DCA (R = Me, Bu). Similarly, [C3(NMe2)2(OMe)]+, was used to prepare the C s-symmetric salts [C3(NMe2)2(NRMe)]DCA (R = Pr, Bu). In addition to characterisation by NMR, mass spectrometry and microanalysis, the salts were characterised by DSC, TGA, density, viscosity, conductivity and miscibility/solubility studies. Comparisons have been made with similar series of bistriflimide (NTf2 -) salts that have been previously reported to see whether the same trends are observed with a different anion.

Cyclopropenium Cations Break the Rules of Attraction to Form Closely Bound Dimers.

The crystal structures of tris(ethylmethylamino)-cyclopropenium chloride and tris(diethylamino)-cyclopropenium iodide reveal the presence of closely bound dicationic dimers formed from two closed-shell monomer units. The distances between the C3 centroids of the staggered monomers are at the short end of those normally found in π-stacked neutral arenes, let alone charged aromatic rings. Computational analysis reveals that short-range interactions are dominated by strong dispersion forces, enabling metastable dicationic dimers to form without covalent intermolecular bonding. Surrounding counterions then provide a background source of charge balance, imparting strong thermodynamic stability to the system. Additionally, these counterions form a weak but attractive electrostatic bridge between the monomer units, contributing to the surprisingly short observed intermolecular C3-C3 centroid distance.

Structural, theoretical and spectroscopic studies of the dichloride hexahydrate cube [Cl2(H2O)6]2-.

The structure of the dichloride hexahydrate cube, [Cl(2)(H(2)O)(6)](2-), as a salt with the tris(diisopropylamino)cyclopropenium cation, [C(3)(N(i)Pr(2))(3)](+), has been determined by low-temperature X-ray and neutron-diffraction studies. H atoms not involved in O-H···Cl bonding are disordered over two 0.5 occupancy sites around the O(6) ring. Calculations of the dianionic cube in the gas phase show remarkably good agreement with the solid-state structures with the exception of short O-H bond distances around the O(6) ring that suggests the involvement of a dynamic process. The cluster was also characterised by single-crystal infrared spectroscopy, and vibrational wavenumbers were found to be in good agreement with hydrogen bonding distances. Dibromide and difluoride hexahydrates were also studied theoretically, and O···O distances were found to decrease in the order difluoride > dichloride > dibromide > (H(2)O)(6) and as O···O···O angles increased towards an almost planar ring in (H(2)O)(6). NMR spectra of a chloroform solution of the hydrated salt at -25 °C is consistent with cluster formation.

Triaminocyclopropenium salts as ionic liquids.

Salts of the charge-delocalised cations of the triaminocyclopropenium (tac) family bearing alkyl substituents have been prepared and shown to be air- and water-stable ionic liquids.