Symmetric Cations Research Articles

Conductivity and Dissociation Constants of Quaternary Ammonium Perchlorates and Picrates in 4-Methyl-pentan-2-one

The dissociation of 14 ionophores, namely, seven symmetrical (C1 to C7) and five asymmetrical quaternary ammonium perchlorates and two tetraalkylammonium picrates (all with linear hydrocarbon chains), in 4-methyl-pentan-2-one was studied at 25 °C (er = 12.92) using the conductance method. The values of the association constants of the quaternary ammonium cation, Ct+, with ClO4− vary from (7.4 ± 0.3)·103 L·mol−1 for tetramethylammonium to (2.4 ± 0.1)·103 L·mol−1 for tetrahexyl- and tetraheptylammonium; a distinct dependence on the size of the Ct+, especially for symmetrical cations, is evident. The values of the limiting molar conductivities Λ0/S·mol−1·cm2 vary from 122.8 to 90.0 (± 0.7). The plot of Λ0 versus the reciprocal cube root of the total van der Waals volume of the cations, VCt−1/3, is close to linear up to tetrapentylammonium and hexadecyltrimethylammonium, while for larger cations (with 21 to 28 carbon atoms) the Λ0 values stay practically constant. At the same time, symmetrical and asymmetrica...

Long-range corrected double-hybrid density functionals

We extend the range of applicability of our previous long-range corrected (LC) hybrid functional, omegaB97X [J.-D. Chai and M. Head-Gordon, J. Chem. Phys. 128, 084106 (2008)], with a nonlocal description of electron correlation, inspired by second-order Moller-Plesset (many-body) perturbation theory. This LC "double-hybrid" density functional, denoted as omegaB97X-2, is fully optimized both at the complete basis set limit (using 2-point extrapolation from calculations using triple and quadruple zeta basis sets), and also separately using the somewhat less expensive 6-311++G(3df,3pd) basis. On independent test calculations (as well as training set results), omegaB97X-2 yields high accuracy for thermochemistry, kinetics, and noncovalent interactions. In addition, owing to its high fraction of exact Hartree-Fock exchange, omegaB97X-2 shows significant improvement for the systems where self-interaction errors are severe, such as symmetric homonuclear radical cations.

Symmetry breaking in cationic polymethine dyes, part 1: Ground state potential energy surfaces and solvent effects on electronic spectra of streptocyanines

AbstractCharge localization and dynamics in conjugated organic molecules, as well as their spectral signatures are of great importance for photonic and photovoltaic applications. Intramolecular charge delocalization in polymethine dyes occurs through π‐conjugated bridges and contributes to the appearance of low‐energy excited states that strongly influence their linear and nonlinear optical (NLO) properties. When the chain length in symmetrical cations exceeds the characteristic size of the soliton, the positive charge may localize at one of the terminal groups of the molecule and induce symmetry breaking of both the electron density distribution and molecular geometry. This charge localization is coupled with molecular vibrations and solvent effects. We investigated the mechanism of symmetry breaking in a series of cationic streptocyanines with different conjugated chain length and qualitatively predicted their electronic absorption spectra. This class of organic molecules is chosen as a model system to develop methodology which can subsequently be used to evaluate more complicated compounds for NLO applications. Our calculations show that the minimum number of vinylene groups in the conjugated chain necessary to break the symmetry of streptocyanines is eight in the gas phase and six in cyclohexane. We constructed the ground state potential energy surface (PES) in two dimensions using symmetry breaking and symmetry adapted coordinates. These were defined as the difference and the sum of the two central carbon–carbon bonds, respectively. This PES was found to have two equivalent minima for systems with symmetry breaking. The energy barrier between these two minima was estimated in the gas phase and in solution, which was taken into account by the polarizable continuum model. Charge localization in each minimum was found to be asymmetric. It is additionally stabilized by the solvent reaction field, which increases the energy barrier. The electronic absorption spectrum in solution is red shifted as compared to the gas phase. As the symmetry breaks, additional excited states with large oscillator strengths appear in the electronic spectrum. Geometry optimization and spectral predictions were also performed in a uniform external electric field in order to simulate nonequilibrium solvation effects due to the finite relaxation time of solvent molecules. Two asymmetric minima with different depths appear on the resulting PES. The lower minimum has charge localized at one of the two molecular terminal groups which is additionally stabilized by the solvent field, while the higher one has charge localized on another terminal group. This finding demonstrates the possibility that two forms with different charge distributions coexist in polar solvents. Our results suggest that nonequilibrium solvation may be a cause of absorption band broadening and splitting. This work is a first step in a larger study aimed at the analysis of the linear and nonlinear properties of long π‐conjugated systems of interest for NLO applications and plastic photovoltaics. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

OHO Hydrogen Bond Geometries and NMR Chemical Shifts: From Equilibrium Structures to Geometric H/D Isotope Effects, with Applications for Water, Protonated Water, and Compressed Ice

AbstractHydrogen bond geometries and 1H NMR chemical shifts of OHO hydrogen‐bonded systems have been analyzed using an improved valence bond order model. This model predicts that the heavy atom hydrogen bond coordinate q2 = r1 + r2 is a function of the proton coordinate q1 = (r1 ‐ r2), where r1 and r2 represent the OH and the HO distances.In the first part, it is shown that this correlation reproduces published equilibrium geometries of the Zundel cation H5O2+ as well as those of water clusters in the gas phase and embedded in the fullerene C180. Using the example of the water hexamer, it is shown that changing the level of calculation shifts the calculated geometries along the correlation curve, but not away from the curve. In order to take quantum zero‐point vibrational effects (QZPVE) into account, an empirical correction is proposed. It is shown that this correction properly describes the calculated classical and quantum hydrogen bond geometries of compressed ice as well as calculated geometric H/D isotope effects. The improved valence bond order model is used to analyze a large number of OHO hydrogen bond geometries contained in the Cambridge Structural Database.In the second part, a relation between the geometries and the 1H NMR chemical shieldings of OHO hydrogen bonded systems is established using the valence bond order model. GIAO calculations of the isolated symmetric Zundel cation where H is located in the hydrogen bond center show only a small dependence of the chemical shifts on the O…O distance. This result is rationalized in terms of neighbor group effects and deshielding in the naked proton. The consequence is that the 1H NMR chemical shifts are not much affected by QZPVE. Calculations on water clusters indicate that the influence of the chemical environment of the OHO hydrogen bonds on their 1H NMR chemical shifts is smaller for the strong hydrogen bond regime but large for the weak hydrogen bond regime. A simple chemical shift vs. q1 relation is then used to calculate the average chemical shifts of water clusters in the regime of fast hydrogen bond exchange between hydrogen bonded and free OH groups. It is shown that average chemical shifts of about 6 ppm are possible as the clusters considered exhibit a broad distribution of stronger and weaker hydrogen bonds. The implications for water in organic solvents and for liquid water are discussed, based on published data on the 1H chemical shift distribution in the latter.

Confinement of Symmetric Tetraalkylammonium Ions in Nanoporous Carbon Electrodes of Electric Double-Layer Capacitors

We present a study on electric double-layer capacitors in organic electrolytes based on symmetrical bulky tetraalkylammonium cations, using activated carbons with adjusted pore size distribution. The results reveal that a close fit of electrode pore size distribution to the size of electrolyte ions can lead to a saturation of the active surface, observable as a decrease in capacitive current beyond the saturation point. This effect arises because of maximum cation loading being reached within the electrolyte voltage window following the trend: the longer the alkyl substituent, the lower the saturation voltage. In contrast, if the pore size distribution presents mostly pores significantly larger than the ion size, the saturation effect is not observed at the expense of the lower surface charge storage. The good correspondence between the maximum charge calculated on the basis of a distorted configuration of cations, Qmax, and the measured one, Qexp, suggests that cations use a wider range of pore sizes than would be possible at their unconfined and undistorted geometries. The saturation of the electrode porosity limits the usable voltage of a supercapacitor system and consequently the deliverable energy and power. In view of optimizing the electrochemical performance, the possibility of such an effect should be considered in adapting the sizes of electrode pores and electrolyte ions.

Effect of Cation Symmetry and Alkyl Chain Length on the Structure and Intermolecular Dynamics of 1,3-Dialkylimidazolium Bis(trifluoromethanesulfonyl)amide Ionic Liquids

In this article, the structure and intermolecular dynamics of 1,3-alkylmethylimidazolium bis(trifluoromethanesulfonyl)amides [C(n)mim][NTf(2)] with n = 2-5 are compared to those of 1,3-dialkylimidazolium bis(trifluoromethanesulfonyl)amides [(C(n))(2)im][NTf(2)] with n = 2-5. The structures of these room-temperature ionic liquids (RTILs) were studied by small-wide-angle X-ray scattering (SWAXS), and their intermolecular dynamics were studied by optical Kerr effect (OKE) spectroscopy. The SWAXS measurements indicate that, on a microscopic scale, the liquid structure of RTILs with symmetric cations is similar to that of RTILs with asymmetric cations. The OKE measurements indicate that the intermolecular dynamics of RTILs with symmetric cations are higher in frequency than those of RTILs with asymmetric cations. These results suggest that the local structure of RTILs with symmetric cations is more solid-like than that of RTILs with asymmetric cations. Further evidence for this difference in local structure on a mesoscopic spatial scale is that the width of the low-Q peak in the SWAXS data is narrower for [(C(5))(2)im][NTf(2)] than for [C(5)mim][NTf(2)]. Moreover, the structure and intermolecular dynamics of the RTILs with ethyl-substituted cations appear to be quite different from those of other RTILs within a given series. This difference is evidenced by a clear change in the dependence of the spectral parameters of the intermolecular part of the OKE spectrum on the alkyl chain length in going from n = 2 to n = 3. The dependence of the SWAXS and OKE data on alkyl chain length is discussed within the context of the nanoscale heterogeneities of RTILs.

(Solid + liquid) and (liquid + liquid) phase equilibria measurements and correlation of the binary systems {tri- iso-butyl(methyl)phosphonium tosylate + alcohol, or +hydrocarbon}

Phase diagrams for the binary systems {tri- iso-butyl(methyl)phosphonium tosylate ionic liquid ( i-B 3MPTOS + 1-alcohol, or n-alkane, or n-alkylbenzene} have been measured at atmospheric pressure by a dynamic method. (Solid + liquid) phase equilibria were measured for systems of alcohols (1-decanol and 1-dodecanol) and the ionic liquid and (liquid + liquid) phase equilibria for binaries containing hydrocarbons ( n-hexane, n-heptane, n-octane, n-nonane, n-decane, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene). The reduction of experimental data has been carried out by correlation using the Non-Random Two Liquid (NRTL) equation. The measured diagrams have been compared with analogous diagrams reported previously for systems with ionic liquids containing the symmetric quaternary phosphonium cation. The influence of the asymmetry of the cation on the phase behaviour of phosphonium ionic liquids has been discussed.

The structures of some (hexamethyl-1,5,9,13-tetraazacyclohexadecadiene)copper(II) compounds

The structure of the crystalline azamacrocyclic product formed by reaction of bis(propane-1,3-diamine)copper(II) perchlorate with acetone has been determined as N-rac-(6,8,8,14,16,16-hexamethyl-1,5,9,13-tetraazacyclohexadeca-5,13-diene)copper(II) · N-meso-(6,8,8,14,14,16-hexamethyl-1,5,9,13-tetraazacyclohexadeca-5,16(1)-diene)copper(II) perchlorate, with the cis, 5,16(1)-diene, and trans, 5,13-diene, isomeric cations co-crystallised. The structures of three compounds crystallised from solutions of this mixture have been determined. N-rac-(6,8,8,14,14,16-hexamethyl-1,5,9,13-tetraazacyclohexadeca-5,16(1)-diene)copper(II) tetrachlorozincate has an irregular flattened tetrahedral coordination geometry with trans-N-Cu-N angles of 139.27(8)° and 155.94(8)°. (Hexamethyl-1,5,9,13-tetraazacyclohexadecadiene)(thiocyanato- N)copper(II) perchlorate has twofold symmetrical square-pyramidal cations. A (μ-cyano)-tetracyanonickelate(II) compound has two (hexamethyl-1,5,9,13-tetraazacyclohexadecadiene)copper(II) cations each with a single axially coordinated tetracyanonickelate(II) group. The compounds, except for the tetrachlorozincate(II) salt, show disorder in the location of the imine functions and axial methyl substituents, attributed to co-crystallisation of enantiomers for the N-rac-trans isomer and/or of rotated arrangements of the N-meso-cis isomer. For the thiocyanato and tetracyanonickelato compounds this disorder precluded unambiguous assignment of configuration.

Effect of Polymethine Dyes with Various Electron-Donating Abilities of Terminal Groups on Thermopolymerization of Methylmethacrylate in Solutions

The process of radical thermo-initiated polymerization of DMF (dimethylformamide) MMA (methylmethacrylate) solutions is investigated kinetically. It is shown that the reaction occurs in the presence of symmetric cation polymethine dyes containing terminal groups of strong, moderate, and weak electron-donating abilities. It is established that, with growing the terminal group electron-donation, an increase of the monomer conversion occurs at the same reaction times. Using DFPH (diphenylpicrylhydrazyl), it is shown that the process is to be considered as a radical one.

A Density Functional Theory for Symmetric Radical Cations from Bonding to Dissociation

It has been known for quite some time that approximate density functional (ADF) theories fail disastrously when describing the dissociative symmetric radical cations R(2)(+). By considering this dissociation limit, previous work has shown that Hartree-Fock (HF) theory favors the R(+1)-R(0) charge distribution, whereas DF approximations favor the R(+0.5)-R(+0.5). Yet, general quantum mechanical principles indicate that both these (as well as all intermediate) average charge distributions are asymptotically energy degenerate. Thus, HF and ADF theories mistakenly break the symmetry but in a contradicting way. In this letter, we show how to construct system-dependent long-range corrected (LC) density functionals that can successfully treat this class of molecules, avoiding the spurious symmetry breaking. Examples and comparisons to experimental data is given for R = H, He, and Ne, and it is shown that the new LC theory improves considerably the theoretical description of the R(2)(+) bond properties, the long-range form of the asymptotic potential curve, and the atomic polarizability. The broader impact of this finding is discussed as well, and it is argued that the widespread semiempirical approach which advocates treating the LC parameter as a system-independent parameter is in fact inappropriate under general circumstances.

Nonpolar Dihydrogen Bonds—On a Gliding Scale from Weak Dihydrogen Interaction to Covalent HH in Symmetric Radical Cations [HnE‐H‐H‐EHn]+

The electronic structures and bonding patterns for a new class of radical cations, [HnE-H-H-EHn]+ (EHn=element hydride, E=element of Groups 15-18), have been investigated by applying quantum-chemical methods. All structures investigated give rise to symmetric potential energy minimum structures. We envisage clear periodic trends. The H--H bond length is shorter for elements toward the bottom of the periodic table of elements, and a short H--H bond corresponds to accumulation of electron density in the central H--H region. All [HnE-H-H-EHn]+ of Groups 15-17 are thermodynamically unstable towards loss of either H2 or H. The barriers for these dissociations are rather low. The Group 18 congeners, except E=Xe, appear to be global minima of the respective potential energy surfaces. The findings are discussed in terms of H2 bond activation, and a general mechanistic scheme for the standard reduction process 2H+ + 2e(-) --> H2 is given. Finally, it is proposed that some of the symmetric radical cations are likely to be observed in mass spectrometric or matrix isolation experiments.

Systematic optimization of long-range corrected hybrid density functionals

A general scheme for systematically modeling long-range corrected (LC) hybrid density functionals is proposed. Our resulting two LC hybrid functionals are shown to be accurate in thermochemistry, kinetics, and noncovalent interactions, when compared with common hybrid density functionals. The qualitative failures of the commonly used hybrid density functionals in some "difficult problems," such as dissociation of symmetric radical cations and long-range charge-transfer excitations, are significantly reduced by the present LC hybrid density functionals.

Local hybrid functionals based on density matrix products.

We present a novel similarity metric comparing exact and semilocal density functional theory (DFT) exchange holes in real space. This metric is obtained from the product of the one-particle density matrix and the uniform electron gas model density matrix. The metric is bound between 0 and 1, 1 in the uniform electron gas, 0 in regions asymptotically far from finite systems, and can detect delocalization of the exact exchange hole and effective fractional occupations. We also present a parameter-free local hybrid functional that uses this similarity metric to locally mix exact and semilocal DFT exchange energy densities. The resulting functional gives better thermochemistry and reaction barrier heights than our original local hybrids [Jaramillo et al., J. Chem. Phys. 118, 1068 (2003)], while retaining moderate accuracy for symmetric radical cation dimers.

On the Mechanism of Triclinic Distortion in Chevrel Phase as Probed by In-Situ Neutron Diffraction

This work presents, for the first time, a general mechanism of a rhombohedral (R)-triclinic (T) phase transition in Chevrel Phases (CPs) with small cations (radius<1 A), which was unclear in spite of intensive studies of these important materials in the past. In contrast to previous interpretation of the R<-->T transition in some CPs as cation ordering, T-distortion is regarded here as a particular case of general adaptation of the framework to cation insertion, which includes the deformations of the coordination polyhedra and their tilting. The research is based on a combination of experimental studies (in-situ neutron diffraction at different temperatures) for one model compound, MgMo6Se8, and structural analysis for a variety of known CPs. This analysis shows that the structure flexibility is fundamentally different for the R and T forms. As a result of the lower flexibility, in the R form, a strict correlation exists between the compression of the framework along the -3 symmetry axis and the cation position in the structure (the so-called 'delocalization'). The decreasing delocalization in the R-CPs, which occurs on cooling, leads to excessive repulsion within the cations pairs (R-Cu1.8Mo6S8 case) or undesirable asymmetry in the cation polyhedra (R-MgMo6Se8 case). The higher flexibility of the T framework allows for relaxation of these structural strains by increasing the cation-cation distances and forming a more symmetric cation environment, sometimes with higher coordination number (CN), like CN=5 in the T-Fe2Mo6S8 type. Thus, this work also proposes possible driving forces for T-distortion in CPs.

IR Spectrum of the H5O2+ Cation in the Context of Proton Disolvates L−H+−L

The H(5)O(2)(+) ion has been studied in chlorocarbon, benzene, and weakly coordinating anion environments to bridge the gap between the gas-phase and traditional condensed-phase investigations. Symmetrical cations of the type [H(5)O(2)(+) x 4Solv] are formed via H-bonding with the terminal O-H groups. In the infrared spectrum, the nu(s)OH and nu(as)OH vibrations behave in a manner similar to those of common water molecules: the stronger is the H-bonding interaction with the surroundings, the lower is the frequency shift. A consistent pattern of IR bands from the central O-H(+)-O group is identified, regardless of the strength of the interaction of H(5)O(2)(+) with its environment. Three intense bands develop: a (860-995 cm-1), b (1045-1101 cm(-1)), and c (1672-1700 cm(-1)), as well as two weak bands, d ( approximately 1300 cm(-1)) and e ( approximately 1400-1500 cm(-1)). These fingerprint bands are highly characteristic for vibrations of O-H-O group irrespective of formal charge. They are seen in symmetrical proton disolvates of the type L-H(+)-L, where L is an O-atom donor (alcohol, ether, ketone, phosphate, etc.), and in [A-H-A](-) acid salts (A(-) = oxyanion). The commonality is equivalency of the two O-atoms, a short O...O distance (ca. 2.40 Angstrom), and a flat-bottomed potential well for the bridging proton, that is, a short, strong, low-barrier H-bond. Assignments for bands a-e are suggested in an attempt to resolve inconsistencies between experimental and calculated data.

Syntheses and Properties of Fluorous Quaternary Phosphonium Salts that Bear Four Ponytails; New Candidates for Phase Transfer Catalysts and Ionic Liquids

AbstractThe fluorous tertiary phosphine [Rf6(CH2)2]3P [Rfn=CF3(CF2)n−1] and excess PhCH2Br, CH3(CH2)3OSO2CF3, or Rf6(CH2)2OSO2CF3 react (CF3C6H5, 45–110 °C) to give the phosphonium salts (PhCH2)[Rf6(CH2)2]3P+ Br− (2, 71 %), [CH3(CH2)3][Rf6(CH2)2]3P+ CF3SO3− (3, 65 %), or [Rf6(CH2)2]4P+ CF3SO3− (4, 83 %). The phosphines [Rf6(CH2)2]2[Rf8(CH2)2]P and [Rf8(CH2)2]3P are similarly elaborated with Rf6(CH2)2I, Rf8(CH2)2I, or Rf8(CH2)2Br (DMF, 115 °C) to [Rf8(CH2)2]4‐x[Rf6(CH2)2]xP+ I− (x=3, 7; 2, 8; 1, 9; 0, 10) or [Rf8(CH2)2]4P+ Br− (80–60 %). The salts exhibit melting points between 110 °C and 43 °C, with lower values favored by less symmetrical cations, Rf6 segments, and triflate and bromide anions. Solubilities decrease in the solvent sequence CF3C6F5 (all salts at least moderately soluble, room temperature)&gt;acetone&gt;THF&gt;CF3C6H5&gt;CF3C6F11&gt;CH3C6H5, Et2O, CH2Cl2, hexane (all salts insoluble at elevated temperatures); some appreciably increase upon heating. Partition coefficients are very biased towards fluorous phases (&gt;93:&lt;7). The salts can be quite efficient at extracting picrate from water into CF3C6F5 (97–86 % for 2, 4, 9, 10) or CF3C6H5 (85–66 % for 2‐4), demonstrating their potential for phase transfer catalysis. A CF3C6F5 solution of Rf8(CH2)3I and aqueous NaCl react at 100 °C in the presence (but not the absence) of 9 to give Rf8(CH2)3Cl.

On the crystallization mechanism of ETS-10 titanosilicate synthesized in gels containing TAABr

Thermal analysis of the products resulted during crystallization of ETS-10 by using starting co gels with molar composition 5.0 Na 2O–3.0 KF–TiO 2–6.4 HCl–TAABr–7.45 SiO 2–197.5 H 2O, where tetralkylammonium (TAA) are tetramethyl (TMA), tetraethyl (TEA), tetrapropyl (TPA) and tetrabutylammonium (TBA), was performed. The effect of TAA + cations (ionic radius in hydrated forms, shapes and hydrophilic/hydrophobic character) on the crystallization of ETS-10 is evident from the induction time, t i (TMA + ≪ TEA + < TPA + < TBA +), the rate of crystallization, R (TMA + < TEA + < TPA + < TBA +), morphology and size of crystallites. Organic cations play a “pore filling” role rather than as a “structure-directing” agent. The relatively flexible molecules of the symmetric tetraalkylammonium cations mixed with alkali cations (Na +, K +) participate directly at prenucleation and nucleation steps by their interaction with the silicate and titanate in aqueous colloidal dispersion.

Ab initio molecular dynamics and quasichemical study of H + (aq)

The excess proton in water, H(+)(aq), plays a fundamental role in aqueous solution chemistry. Its solution thermodynamic properties are essential to molecular descriptions of that chemistry and for validation of dynamical calculations. Within the quasichemical theory of solutions those thermodynamic properties are conditional on recognizing underlying solution structures. The quasichemical treatment identifies H(3)O(+) and H(2)O(5)(+) as natural inner-shell complexes, corresponding to the cases of n = 1, 2 water molecule ligands, respectively, of a distinguished H(+) ion. A quantum-mechanical treatment of the inner-shell complex with both a dielectric continuum and a classical molecular dynamics treatment of the outer-shell contribution identifies the latter case (the Zundel complex) as the more numerous species. Ab initio molecular dynamics simulations, with two different electron density functionals, suggest a preponderance of Zundel-like structures, but a symmetrical ideal Zundel cation is not observed.

Structure, magnetism and optical properties of achiral and chiral two-dimensional oxalate-bridged anionic networks with symmetric and asymmetric ammonium cations

A series of two-dimensional (2D) oxalate-based compounds, namely [N(n-C4H9)4][M(II)Cr(III)(ox)3] (M(II) = Mn, Fe; ox = C2O4(2-)) and [N(C2H5)(n-C3H7)(n-C4H9)(n-C5H11)][M(II)M(III)(ox)(3)] ((M(II), M(III)) =(Mn, Cr), (Fe, Cr), (Mn, Fe)) were synthesised starting from racemic tris(oxalato)metalate: rac-[M(III)(ox)3]3- (M(III) = Cr, Fe). For Cr(III), the synthesis has been undertaken starting from resolved (Delta)- or (Lambda)-[Cr(III)(ox)3]3-. The natural circular dichroism measurements assess the enantioselectivity of the synthesis. X-Ray powder diffraction analysis has revealed that, when racemic reagents are used to synthesise Mn(II) containing compounds, a R3c achiral space group is found. In contrast a P6(3) chiral space group is found when starting from (Delta)- or (Lambda)-[Cr(III)(ox)3]3-. Surprisingly, whatever the optical purity of the starting building block, all Fe(II) containing compounds crystallise in the P6(3) chiral space group. The magnetic properties of the synthesised compounds confirm that these compounds are ferromagnets for M(III)= Cr. For M(II)= Mn, Theta ranges between 9 and 11 K and T(c) equals 6 K. For M(II)= Fe, Theta ranges between 14 and 16 K and Tc between 11 and 12 K. [N(C2H5)(n-C3H7)(n-C4H9)(n-C5H11)][Mn(II)Fe(III)(ox)3] is an antiferromagnet with Theta = - 107 K and T(N) = 29 K.

Temperature dependence of viscosity for room temperature ionic liquids

We have measured the absolute viscosity of 23 room temperature ionic liquids (RTILs) (13 air/moisture-tolerant single salts and 10 air/moisture-sensitive binary salts) using a rolling-ball viscometer, which was constructed to enable the viscosity measurements to be performed outside a glove-box. The viscometer was non-destructive to the RTIL and the viscosity measurements were made under typical levels of O 2 and H 2 O of less than 1 ppm. The viscometer was calibrated with Milli-Q water and sucrose solutions (20, 40 and 60% w/w) at 14 temperatures (10 °C ⩽ T ⩽ 70 °C). Three balls of diameters 3.2, 4 and 5 mm were used for the calibration. We found that the ball with the smallest diameter (3.2 mm) was more accurate for measuring the viscosities. The activation energies for viscous flow ( E η ) for each RTIL were calculated, from the slopes of the Arrhenius plots. E η was correlated with changes in molecular structure of the RTIL; those containing high molar mass and less symmetric cations had higher E η values. The Arrhenius plot was not linear for the majority of the RTILs and some of these RTILs were better fitted with the Vogel–Tammann–Fulcher (VTF) equation. Those RTILs which obeyed the Arrhenius law typically contained asymmetric cations and the majority did not contain functional groups. Those RTILs which obeyed the VTF law contained small and symmetrical cations with low molar mass. Those RTILs which obeyed neither the Arrhenius nor the VTF law consisted of cations which were less symmetric, contained functional groups (e.g., OH and CO) and had higher molar mass. The glass transition temperatures T o (calculated from the VTF fittings) generally decreased with increasing size and molar mass of the cation and anion. The chloroaluminate RTILs containing oxygenated cations were more volatile than the corresponding de-oxygenated RTILs making them unsuitable for applications as solvents and/or electrolytes above ambient temperature.