Discrete Ion Pairs Research Articles

Cationic group 1 carbodiphosphorane complexes

Reactions of carbodiphosphorane (CDPR) ligands with equimolar quantities of group 1 and Fe(II) bis(trimethylsilyl)amides result in the isolation of discrete CDP-stabilized ion pairs, [M(CDPR)2]+[Fe{N(SiMe3)2}3]− (M = Li, Na; R = hexaphenyl, cyclopropyl-tetraphenyl). X-ray diffraction analysis revealed that the coordination sphere of the cationic group 1 center is provided by two CDPR ligands. In the solid state, we investigated the influence of the ligand substituents on the resulting architecture of the title complexes by utilizing different CDP ligands. In solution, we examined the stability of these complexes by variable temperature NMR spectroscopy. This study revealed that all title complexes show lability in solution due to dynamic processes: they are subject to a chemical exchange with the corresponding starting materials.

Voltammetry and Spectroelectrochemistry of TCNQ in Acetonitrile/RTIL Mixtures.

Understanding the solvation and ion-pairing interactions of anionic substrates in room-temperature ionic liquids (RTIL) is key for the electrochemical applications of these new classes of solvents. In this work, cyclic voltammetry and visible and infrared spectroelectrochemistry of tetracyanoquinodimethane (TCNQ) was examined in molecular (acetonitrile) and RTIL solvents, as well as mixtures of these solvents. The overall results were consistent with the formation of RTIL/acetonitrile nanodomains. The voltammetry indicated that the first electrogenerated product, TCNQ−, was not incorporated into the RTIL nanodomain, while the second electrogenerated product, TCNQ2−, was strongly attracted to the RTIL nanodomain. The visible spectroelectrochemistry was also consistent with these observations. Infrared spectroelectrochemistry showed no discrete ion pairing between the cation and TCNQ− in either the acetonitrile or RTIL solutions. Discrete ion pairing was, however, observed in the acetonitrile domain between the tetrabutylammonium ion and TCNQ2−. On the other hand, no discrete ion pairing was observed in BMImPF6 or BMImBF4 solutions with TCNQ2−. In BMImNTf2, however, discrete ion pairs were formed with BMIm+ and TCNQ2−. Density function theory (DFT) calculations showed that the cations paired above and below the aromatic ring. The results of this work support the understanding of the redox chemistry in RTIL solutions.

Tethered cationic alkaline earth - olefin complexes.

The aminofluoroalcohol N,N,N-(CH2[double bond, length as m-dash]CHCH2CH2-),(CH3OCH2CH2-),(HOC(CF3)2CH2-)N ({ROF}H) possessing both a methoxy and an olefin dangling side arms enables the preparation of the heteroleptic charge neutral alkaline earth complexes [{μ2-ROF}AeN(SiMe2H)2]2 (Ae = Ca, 1; Sr, 2). These O-bridged dinuclear complexes were characterised by NMR spectroscopy and X-ray diffraction crystallography. XRD analysis of 1 and 2 showed that both complexes are stabilised by intramolecular AeF-C and β-agostic AeH-Si secondary interactions, and that the olefin does not bind to the alkaline earths while the methoxy side-arm does. The discrete ion pairs [({μ2-ROF}Ae·(Et2O)2)2]2+·2[H2N{B(C6F5)3}2]- (Ae = Ca, 3a; Sr, 4a) were synthesised upon treatment of the parent complexes 1 and 2 by [H·(Et2O)2]+.[H2N{B(C6F5)3}2]-. NMR spectroscopy showed the presence of two coordinated Et2O molecules on each metal in these complexes. The water adduct [({μ2-ROF}Sr·(H2O))2]2+·2[H2N{B(C6F5)3}2]- (4b), presumably derived from 4a upon adventitious introduction of moisture during recrystallisation, was characterised by crystallographic methods. The dication [({μ2-ROF}Sr·(H2O))2]2+ exists as an O-bridged dinuclear species featuring very strong intramolecular SrF-C interactions in the range 2.788(5)-2.997(6) Å, and no interaction with the weakly coordinating anion. Perhaps more importantly, the tethered olefins are coordinated onto the metal cations, with short SrCπ interactions in the range 3.066(10)-3.092(10) Å; this represents the first example of a Sr-olefin cationic complex. Hence, cationisation of the charge neutral precursor to generate the discrete ion pair increases electron deficiency at the metal centre, resulting in the first observation of the binding of an olefin onto a well-defined cationic heavy alkaline earth. On the other hand, our attempts to produce Ae-olefin cations devoid of coordinated Lewis base with this strategy have met no success so far.

Influence of Molecular Organization of Ionic Liquids on Electrochemical Properties

Ionic liquids (ILs) are pure salts with melting points typically less than 100°C. ILs exhibit several advantages over conventional molecular liquids in disparate applications because of their remarkable physical properties, which include wide electrochemical stability windows, high ionic conductivity and negligible vapor pressure. IL applications, either already realized or currently under development, encompass many diverse areas such as analytics, catalysis, chemical synthesis, separation technologies, electrochemistry, capacitors, batteries, fuel cells, solar cells, and tribology. Many of these applications involve reactions at the IL/solid interface. Hence, a detailed understanding of the structure of this interface is important and cannot be overstated. ILs exhibit behavior that is very different from common molecular liquids. As ILs are composed entirely of charged species, they usually exhibit a more pronounced structure in the bulk and at surfaces than molecular liquids.1 ILs are subject to a range of cohesive interactions (Coulombic, van der Waals, hydrogen bonding and solvophobic forces), resulting in a well-defined nanostructure both in the bulk and at interfaces.2 The nanostructure of ILs evolves as a consequence of electrostatic interactions between charged groups that produce polar domains. Cation alkyl chains are solvophobically repelled3 from these charged domains and cluster together to form apolar regions, that in turn produce a sponge-like phase-separated nanostructure.4 This spongelike structure present in the bulk changes immediately adjacent to a smooth solid surface. Atomic force microscopy (AFM) force curves5,6 and reflectivity experiments7 both reveal the formation of discrete ion or ion pair layers immediately adjacent to the solid surface. This layered surface structure decays to the bulk sponge morphology over a length-scale of a few nanometers.8 The IL/solid interface has been the subject of extensive experimental and theoretical studies. Various spectroscopic and scattering methods have been applied to examine this interface.7,9-21 Electrochemical impedance spectroscopy (EIS) measurements have been used to study the structure and dynamics of ILs.22-24 Theoretical descriptions of the IL/electrode interface using molecular dynamics and Monte Carlo simulations,25-35 and mean field theory,36,37 have predicted “bell-” and “camel-” shaped capacitance curves and oscillating ion density profiles at the electrode surface, consistent with experimental results. However, a proper theoretical model of the electrified IL/solid interface does not yet exist and further experimental studies are required for better understanding the IL/electrode interfacial structure. During the last decade, in situ atomic force microscopy (AFM) and scanning tunneling microscopy (STM) have been extensively used to probe the IL structure at the IL/solid interface.1,5,8,38-50 The mechanism of operation of the AFM experiment is presented schematically in Fig. 1. The solid electrode substrate and the AFM tip and cantilever are completely immersed within the IL (Fig. 1a). The layers close to the surface are shown schematically as single (blue) layers. As the AFM tip moves towards the surface, it is deflected away due to the forces imparted by the interfacial IL

Tuning Binding of Rubidium Ions to Planar and Curved Negatively Charged π Surfaces

Two new rubidium salts of the bowl-shaped corannulene monoanion radical C20H10•– (1•–), [Rb(15-crown-5)2+][C20H10–] (2) and [Rb(dicyclohexano-18-crown-6)+][C20H10–] (3), have been synthesized and structurally characterized in this work. An excess of 15-crown-5 ether provided full encapsulation of the rubidium ion in [Rb(15-crown-5)2]+, which precluded metal-directed π interactions with the anionic surface of C20H10•– in the solid-state structure of 2. The use of more sterically demanding dicyclohexano-18-crown-6 ether prevented the formation of polymeric chains previously seen with 18-crown-6 ether and favored the isolation of the discrete contact ion pair 3. Complex 3 is built on a convex η6 coordination of Rb+ to C20H10•–, reaffirming the exo-binding preference of rubidium ions toward the singly charged corannulene bowl. A rubidium salt of the planar coronene monoanion radical C24H12•– (4•–), [Rb(18-crown-6)+][C24H12–] (5), has also been prepared and structurally characterized to reveal a new binding mo...

Dielectric relaxation and ultrafast transient absorption spectroscopy of [C6mim]+[Tf2N]−/acetonitrile mixtures

Mixtures of the ionic liquid (IL) [C(6)mim](+)[Tf(2)N](-) and acetonitrile have been investigated by a combination of dielectric relaxation spectroscopy (DRS) and ultrafast transient absorption techniques using the molecular probe 12'-apo-β-carotenoic-12'-acid (12'CA). Steady-state absorption spectra of the 12'CA molecule have also been recorded. The position of the probe's S(0)→ S(2) absorption maximum correlates linearly with the polarizability of the mixture, suggesting that the bulk composition is a good approximation to the local composition. The lifetime τ(1) of the S(1)/ICT state of 12'CA varies rather smoothly with composition between the value for pure acetonitrile (42 ps) and neat [C(6)mim](+)[Tf(2)N](-) (94 ps). At low IL contents there appears to be an influence of discrete ion pairs. Employing static dielectric constants from the DRS experiments, one finds that the lifetime of the probe in the IL mixtures is shorter than that in pure organic solvents with the same polarity parameter. This suggests an increased stabilization of the S(1)/ICT state in IL-containing mixtures, most likely due to IL-specific Coulombic interactions between the cation and the negative end of the probe's dipole. An ultrafast solvation component is observed which is ca. 0.5 ps in pure acetonitrile, and approaches the value for the pure IL (2.0 ps) already around x(IL) = 0.3. This is interpreted in terms of an efficient perturbation of the cooperative solvation response of acetonitrile by the presence of small amounts of IL and possibly also the viscosity increase when adding IL. This view is also supported by the increase of the average longitudinal relaxation time of acetonitrile upon addition of small IL amounts extracted from the DRS experiments.

How Hydrogen Bonds Influence the Mobility of Imidazolium-Based Ionic Liquids. A Combined Theoretical and Experimental Study of 1-n-Butyl-3-methylimidazolium Bromide

The virtual laboratory allows for computer experiments that are not accessible via real experiments. In this work, three previously obtained charge sets were employed to study the influence of hydrogen bonding on imidazolium-based ionic liquids in molecular dynamics simulations. One set provides diffusion coefficients in agreement with the experiment and is therefore a good model for real-world systems. Comparison with the other sets indicates hydrogen bonding to influence structure and dynamics differently. Furthermore, in one case the total charge was increased and in another decreased by 0.1 e. Both the most acidic proton as well as the corresponding carbon atom were artificially set to zero, sequentially and simultaneously. In the final setup a negative charge was placed on the proton in order to introduce a barrier for the anion to contact the cation via this most acidic hydrogen atom. The following observations were made: changing the hydrogen bonding ability strongly influences the structure while the dynamic properties, such as diffusion and viscosity, are only weakly changed. However, the introduction of larger alterations (stronger hydrogen bonding and antihydrogen bonding) also strongly influences the diffusion coefficients. The dynamics of the hydrogen bond, ion pairing, and the ion cage are all affected by the level of hydrogen bonding. A change in total charges predominantly influences transport properties rather than structure. For ion cage dynamics with respect to transport porperties, we find a good correlation and a weak or no correlation for the ion pair or the hydrogen bond dynamics, respectively. Nevertheless, the hydrogen bond does influence ion cage dynamics. Therefore, we confirm that ionic liquids rather consist of loosely interacting counterions than of discrete ion pairs. Hydrogen bonding affects the properties only in a secondary or indirect manner.

Hydrogen Bonding in Pyridinium Picrates: From Discrete Ion Pairs to 3D Networks

A series of 20 picrates of pyridine derivatives were synthesized and their crystal structures studied by X-ray diffraction. The characteristic pyridinium-picrate synthon I was found to be present in 15 structures. The geometry of the pyridinium-picrate ion pair was found to be governed by additional C–H···O and N–H···O hydrogen bonds with the o-nitro groups of the picrate. If additional hydrogen donors are present on the pyridine cation, hydrogen bonds between these donors and nitro groups of picrate anions of neighboring ion pairs connect the ion pairs into 1D, 2D, or 3D supramolecular architectures. Synthon I was absent in five structures, in two cases as a result of protonation of an amino substituent on the pyridine ring, and in two cases as a result of insertion of a water molecule between the pyridinium cation and the picrate anion.

Synthesis and structural characterization of mixed-metal complexes of CuI with MOS3 cores (M = Mo, W) and of an unusual polymeric AgI/mercaptoimidazole complex with five different AgI coordination environments

Reaction of (NH(4))(2)[MO(2)S(2)] (M = Mo or W) with KI, CuCl and 1,3-diazepane-2-thione (Diap) in acetone affords air- and moisture-stable mixed-metal cluster compounds [MOS(3)(CuDiap)(3)]I (1 and 2). Attempts to produce [WS(4)Ag(2)(Mim(Ph))(4)] (Mim(Ph) = 2-mercapto-1-phenylimidazole) led to the unexpected polymeric compound [Ag(5)I(5)(Mim(Ph))(4)](n) (4), subsequently obtained from a rational direct reaction between AgI and Mim(Ph) in chloroform. The complexes have been characterized by IR, (1)H and (13)C NMR spectroscopy, and single-crystal diffraction. 1 and 2 have crystallographic threefold rotation symmetry, with an incomplete distorted cube MS(3)Cu(3) core bearing terminal oxo and Diap ligands on M and Cu, respectively. The cube vertex opposite M is empty, giving an overall +1 cationic cluster and a separate I(-) anion too distant from the three Cu atoms to be considered as covalently bonded and resulting in discrete ion pairs in the crystal structures. This arrangement is different from previously reported related OMS(3)(CuL)(3)X complexes (L = monodentate ligand, X = halide), in which X, when present, is directly bonded to one, two or three Cu atoms. 4 has a one-dimensional polymeric chain structure in which silver displays five different approximately tetrahedral coordination environments, iodide ions serve as μ(2), μ(3) and μ(4) bridges, and the thione ligands are each either terminal or bridging. This unusually complex structure for a relatively simple chemical formula represents only the fifth example of a complex (AgI)(n)L(m) in which L is a neutral S-donor ligand, and the five structures display a wide range of individual features. In all three of the new structures, N-H···S and/or N-H···I hydrogen bonds are found.

ChemInform Abstract: Studies of Thermal Rearrangements of Methyl 3-Alkyl-3-methyl-3H- pyrazole-5-carboxylates. Concerted, Stepwise, and Unclassified Mechanisms.

Studies of the thermal rearrangements of five 3H-pyrazoles are described, in which the migrating groups were methorymethyl, tert-butyl, 1-adamantyl, p-methoxybenzyl, and benzyl. On the basis of reaction products, rearrangement of the (methoxymethyl)pyrazole in benzene, dichloromethane, and methanol at room temperature occurs by a stepwize mechanism, involving discrete ion-pair intermediates. Observed first-order rate constants, for the rearrangement of four of the 3H-pyrazoles in benzene-d 6 and acetone-d 6 at higher temperatures, were determined. The tert-butyl compound also rearranges by a stepwise mechanism in benzene-d 6 , acetone-d 6 , and methanol-d 6 based on the fact that isobutene and tert-butyl methyl ether (in methanol) are coproducts of rearrangement

Syntheses, Raman Spectra, and X-ray Crystal Structures of [XeF5][μ-F(OsO3F2)2] and [M][OsO3F3] (M = XeF5+, Xe2F11+)

Stoichiometric amounts of XeF(6) and (OsO(3)F(2))(infinity) react at 25-50 degrees C to form salts of the known XeF(5)(+) and Xe(2)F(11)(+) cations, namely, [XeF(5)][mu-F(OsO(3)F(2))(2)], [XeF(5)][OsO(3)F(3)], and [Xe(2)F(11)][OsO(3)F(3)]. Although XeF(6) is oxophilic toward a number of transition metal and main-group oxides and oxide fluorides, fluoride/oxide metathesis was not observed. The series provides the first examples of noble-gas cations that are stabilized by metal oxide fluoride anions and the first example of a mu-F(OsO(3)F(2))(2)(-) salt. Both [XeF(5)][mu-F(OsO(3)F(2))(2)] and [Xe(2)F(11)][OsO(3)F(3)] are orange solids at room temperature. The [XeF(5)][OsO(3)F(3)] salt is an orange liquid at room temperature that solidifies at 5-0 degrees C. When the salts are heated at 50 degrees C under 1 atm of N(2) for more than 2 h, significant XeF(6) loss occurs. The X-ray crystal structures (-173 degrees C) show that the salts exist as discrete ion pairs and that the osmium coordination spheres in OsO(3)F(3)(-) and mu-F(OsO(3)F(2))(2)(-) are pseudo-octahedral OsO(3)F(3)-units having facial arrangements of oxygen and fluorine atoms. The mu-F(OsO(3)F(2))(2)(-) anion is comprised of two symmetry-related OsO(3)F(2)-groups that are fluorine-bridged to one another. Ion pairing results from secondary bonding interactions between the fluorine/oxygen atoms of the anions and the xenon atom of the cation, with the Xe...F/O contacts occurring opposite the axial fluorine and from beneath the equatorial XeF(4)-planes of the XeF(5)(+) and Xe(2)F(11)(+) cations so as to avoid the free valence electron lone pairs of the xenon atoms. The xenon atoms of [XeF(5)][mu-F(OsO(3)F(2))(2)] and [Xe(2)F(11)][OsO(3)F(3)] are nine-coordinate and the xenon atom of [XeF(5)][OsO(3)F(3)] is eight-coordinate. Quantum-chemical calculations at SVWN and B3LYP levels of theory were used to obtain the gas-phase geometries, vibrational frequencies, and NBO bond orders, valencies, and NPA charges of the ion pairs, [Xe(2)F(11)][OsO(3)F(3)], [XeF(5)][OsO(3)F(3)], and [XeF(5)][mu-F(OsO(3)F(2))(2)], as well as those of the free ions, Xe(2)F(11)(+), XeF(5)(+), OsO(3)F(3)(-), and mu-F(OsO(3)F(2))(2)(-). The Raman spectra (-150 degrees C) of the salts have been assigned based on the ion pairs observed in the crystal structures and the calculated vibrational frequencies and intensities of the gas-phase ion pairs.

Spin Maximization from S = 11 to S = 16 in Mn7 Disk-Like Clusters: Spin Frustration Effects and Their Computational Rationalization

The use has been explored in Mn cluster chemistry of N(3)(-) or Cl(-) in combination with N-methyldiethanolamine (mdaH(2)) or triethanolamine (teaH(3)). The reactions of Mn(ClO(4))(2).6H(2)O, NEt(3), NaN(3), and either mdaH(2) or teaH(3) (1:2:1:2) in DMF/MeOH afford {[Na(MeOH)(3)][Mn(7)(N(3))(6)(mda)(6)]}(n) (1) and {Na[Mn(7)(N(3))(6)(teaH)(6)]}(n) (2), respectively, whereas the 2:1:1 reaction of MnCl(2).4H(2)O, mdaH(2), and NEt(3) in MeCN gives (NHEt(3))[Mn(7)Cl(6)(mda)(6)] (3). Similar reactions using NBu(n)(4)N(3) in place of NaN(3) gave (NHEt(3))[Mn(7)(N(3))(6)(mda)(6)] (4) and (NHEt(3))[Mn(7)(N(3))(6)(teaH)(6)] (5). The Mn(7) anions consist of a Mn(6) hexagon of alternating Mn(II) and Mn(III) ions surrounding a central Mn(II) ion. The remaining ligation is by six bridging and chelating mda(2-) or teaH(2-) groups, and either six terminal N(3)(-) (1, 2, 4, 5) or Cl(-) (3) ions. Each bridging mda(2-) or teaH(2-) ligand contains both mu- and mu(3)-O atoms, resulting in a similar, near-planar [Mn(7)(mu(3)-OR)(6)(mu-OR)(6)](5+) core for all three complexes. The Mn(7) anions of 1 and 2 are connected via Na(+) cations to yield one-dimensional zigzag chains and three-dimensional windmill-like "hexagons-of-hexagons", respectively. In contrast, the Mn(7) anion of 3 forms a strong hydrogen-bond between the NHEt(3)(+) cation and a terminal Cl(-) ion giving a discrete ion-pair. Variable-temperature, solid-state direct current (dc) and alternating current (ac) magnetization studies were carried out in the 5.0-300 K range. Fits of dc magnetization versus field (H) and temperature (T) data by matrix diagonalization gave S = 11, g = 1.95, D = -0.15 cm(-1) for 1, S = 16, g = 1.95, D = -0.02 cm(-1) for 2, and S = 11, g = 1.92, D = -0.13 cm(-1) for 3 (D is the axial zero-field splitting parameter). Complexes 4 and 5 were also found to possess S = 11 and S = 16 ground states, respectively. The different ground states of 1 and 2 were rationalized on the basis of the sign and magnitude of the various Mn(2) exchange parameters obtained from density functional theory (DFT) calculations. This analysis confirmed the presence of spin frustration effects, with the ground states being determined by the relative magnitude of the two weakest interactions. The combined results demonstrate the usefulness of N-based dipodal and tripodal alkoxide-based chelates as a route to structurally and magnetically interesting Mn clusters.

Bridging the Gap between Ionic Liquids and Molten Salts: Group 1 Metal Salts of the Bistriflamide Anion in the Gas Phase

Fourier transform ion cyclotron resonance mass spectrometry experiments showed that liquid Group 1 metal salts of the bistriflamide anion undergoing reduced-pressure distillation exhibit a remarkable behavior that is in transition between that of the vapor-liquid equilibrium characteristics of aprotic ionic liquids and that of the Group 1 metal halides: the unperturbed vapors resemble those of aprotic ionic liquids, in the sense that they are essentially composed of discrete ion pairs. However, the formation of large aggregates through a succession of ion-molecule reactions is closer to what might be expected for Group 1 metal halides. Similar experiments were also carried out with bis{(trifluoromethyl)sulfonyl}amine to investigate the effect of H(+), which despite being the smallest Group 1 cation, is generally regarded as a nonmetal species. In this case, instead of the complex ion-molecule reaction pattern found for the vapors of Group 1 metal salts, an equilibrium similar to those observed for aprotic ionic liquids was observed.

Synthesis, characterization and reactivity of heteroleptic rare earth metal bis(phenolate) complexes

The synthesis, characterization and reactivity of heteroleptic rare earth metal complexes supported by the carbon-bridged bis(phenolate) ligand 2,2'-methylene-bis(6-tert-butyl-4-methyl-phenoxo) (MBMP2-) are described. Reaction of (C5H5)3Ln(THF) with MBMPH2 in a 1:1.5 molar ratio in THF at 50 degrees C produced the heteroleptic rare earth metal bis(phenolate) complexes (C5H5)Ln(MBMP)(THF)n (Ln=La, n=3 (); Ln=Yb (), Y (), n=2) in nearly quantitative yields. The residual C5H5- groups in complexes to can be substituted by the bridged bis(phenolate) ligands at elevated temperature to give the neutral rare earth metal bis(phenolate) complexes, and the ionic radii have a profound effect on the structures of the final products. Complex reacted with MBMPH2 in a 1:0.5 molar ratio in toluene at 80 degrees C to produce a dinuclear complex (MBMP)La(THF)(micro-MBMP)2La(THF)2 () in good isolated yield; whereas complexes and reacted with MBMPH2 under the same conditions to give (MBMP)Ln(MBMPH)(THF)2 (Ln=Yb (), Y ()) as the final products, in which one hydroxyl group of the phenol is coordinated to the rare earth metal in a neutral fashion. The reactivity of complexes and with some metal alkyls was explored. Reaction of complex with 1 equiv. of AlEt3 in toluene at room temperature afforded unexpected ligand redistributed products, and a discrete ion pair ytterbium complex [(MBMP)Yb(THF)2(DME)][(MBMP)2Yb(THF)2] () was isolated in moderate yield. Furthermore, reaction of complex with 1 equiv. of ZnEt2 in toluene gave a ligand redistributed complex [(micro-MBMP)Zn(THF)]2 () in reasonable isolated yield. Similar reaction of complex with ZnEt2 also afforded complex ; whereas the reaction of complex with 1 equiv. of n-BuLi in THF afforded the heterodimetallic complex [(THF)Yb(MBMP)2Li(THF)2] (). All of these complexes were well characterized by elemental analyses, IR spectra, and single-crystal structure determination, in the cases of complexes , and -.

Synthesis and crystal structure of the trimetallic erbium tetrahydride complex [Li(THF)4] [{(ButCp)2Er(μ-H)}3-(μ3-H)

Reaction of [(ButCp)2Er(μ-Cl)]2 with ButLi in 1 : 1 molar ratio in THF at -78°C; after work-up, afforded the trimetallic erbium tetrahydride complex [Li(THF)4] [(Bu t Cp)2 Er(μ-H) 3(μ3-H)] (1) by ββ-hydrogen elimination reaction. Crystal structure determination reveals that complex 1 has discrete ion pair structure. The anion is composed of three (ButCp)2Er units to form a triangle array connected by three bridged hydrogen atoms, and the fourth hydrogen atom coordinated to three Er3+ ions. The coordination number for each Er3+ ion is 9.

Dimerization of a guanidiniocarbonyl pyrrole cation in DMSO that can be controlled by the counteranion.

In the presence of chloride anions cation 1 dimerizes in DMSO with a surprisingly high association constant of > 10(3) M(-1) whereas the addition of picrate disrupts these dimers by formation of even more stable discrete pi-stacked ion pairs.

3-Methyl-1-(1,2,3,4-tetrahydroisoquinolin-2-ylcarbonyl)imidazolium iodide

The title compound, C 14 H 16 N 3 O + .I - , crystallizes as discrete ion pairs with close (C)-H...I contacts of 3.04 and 3.06 A. The two C-N bonds of the urea functional group have significantly different bond lengths of : 1.327 (6) and 1.466 (6) A. This is the first crystal structure determination of a carbamoyl imidazolium salt.

Preparation and X-Ray Crystal Structures of Tetrahydrofuran-Complexed Rare Earth Chlorides — a Structurally Rich Series

Anhydrous lanthanoid metal chlorides LnCl3(thf)n (Ln = La, Ce, Nd, Sm, n = 2; Ln = Tb, Ho, n = 2·5; Ln = Dy, Tm, n= 2·7; Ln = Gd, Yb, Lu, n = 3; Ln = Er, n = 3·5) have been prepared in excellent yield by the direct reaction of the lanthanoid metal powders with hexachloroethane in tetrahydrofuran (thf), and (Ln = Eu, n = 0·8; Ln = La, n = 1·7; Ln = Pr, n = 2; Ln = Gd, n = 2·5; Ln = Er, n = 3) in good yield except for EuCl3(thf)0·8 from bulk metal. [YbCl3(thf)2]2 was prepared by prolonged treatment of solid YbCl3(thf)3 with pentane. The X-ray crystal structures of [LnC3(thf)2] (Ln = La, Ce or Pr), [LnCl3(thf)3.5] (Ln = Gd or Er), [YbCl3(thf)3] and [LaCl3(thf)(H2O)] have been determined. For [LaCl3(thf)2], a square antiprismatic single-stranded polymer, ... La(-Cl)3(thf)3La(-Cl)3(thf)2 ..., is the first eight-coordinate LnCl3(thf)n complex. The metal is surrounded by two sets of three bridging chlorines and cis thf oxygens. [LnCl3(thf)2] (Ln = Ce, Pr) have seven-coordinate structures with doubly chloride-bridged linear chains, ... LnCl(µ-Cl)3(thf)2LnCl(µ-Cl)2(thf)2 ... where the lanthanoid atom exists in a pentagonal bipyramidal environment, the pentagonal bipyramidal plane being defined by four chloride atoms and one oxygen atom of the thf ligand, and the axial positions being occupied by a chloride and a thf oxygen atom. [LnCl3(thf)3.5] (Ln = Gd, Er) crystallize as discrete ion pairs, [LnCl2(thf)5]+ [LnCl4(thf)2]¯. The lanthanoid atom in the cation displays pentagonal bipyramidal geometry with two apical chloride atoms and five equatorial thf ligands while the anion has quasi-regular octahedral stereochemistry with trans thf ligands. [LaCl3(thf)(H2O)] displays an eight-coordinate two-dimensional polymeric array with six bridging chlorides per lanthanum atom. Far-infrared spectra have been recorded for a number of products and used as a basis for structural proposals, particularly for products with fractional thf.

Crystal structure of [Pd(μ 3-2-propenyl)(dps)][Pd(μ 3-2-propenyl)Cl 2]. NMR evidence of binuclear μ 3-allyl palladium(II) species with bridging dps

The reactions of di-2-pyridyl sulfide (dps) with (μ 3-allyl)palladium chloride dimers gave the ionic compounds [Pd(μ 3-allyl)(dps)][Pd(μ 3-allyl)Cl 2] (allyl=2-propenyl ( 1), 2-methyl-2-propenyl ( 2), 2-butenyl ( 3)). The structure of 1 has been determined by X-ray diffraction methods. Crystals are triclinic, space group P 1 , with Z=2 in a unit cell of dimensions a=8.840(1), b=8.928(1), c=12.317(2) Å, α= 98.82(1), β=90.46(1), γ=95.46(1)°. The structure has been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least-squares on the basis of 3855 observed relections to R and R w values of 0.0269 and 0.0339, respectively. Compound 1 consists of discrete complex ion pairs, containing allyl groups coordinated to both the cationic and anionic palladium centres. In the cationic portion the dps acts as a chelate ligand and adopts an N,N inside conformation. The six-membered chelate ring shows a boat conformation. The cation and anion are connected by a short Pd2…Cl2 interaction (3.073(1) Å) which determines pseudo-five-coordination for the cation. At low temperature the 1H NMR spectra in CD 3OD of 1 and 2 confirm the presence of the cation and the anion while in CDCl 3 they also indicate the presence of a binuclear species with bridging dps. The 1H NMR spectra, at variable temperature, show that 1, 2 and 3 in solution undergo dynamic processes. In CDCl 3, a lower energy process makes the π-allyl groups equivalent at room temperature, a higher energy process determines the magnetic equivalence of syn and anti π-allyl protons at high temperature.

Syntheses of methylcyclopentadienyl derivatives of lanthanides (Ln = lanthanum-neodymium) and crystal structures of [(THF)2Li(.mu.-Cl)2]2[MeCpNd(THF)] and [Li(DME)3][MeCpLa(NPh2)3

The reaction of LnCl3.2LiCl with 1 equiv of MeCpNa in THF gives the complexes [(THF)2Li(mu-Cl)2]2[MeCpLn(THF)] (Ln = Nd (1), La (2)) in good yield. These precursors react further with 2 equiv of LiNPh2 to produce the new complexes [Li(DME)3][MeCpLn(NPh2)3] (Ln = La (3), Pr (4), Nd (5)). They have been characterized by elemental analyses and IR and NMR spectra, as well as by structural analyses of 1 and 3. The chloride 1 crystallizes in the monoclinic space group P2(1)/n (No. 14) with a = 12.130 (5) angstrom, b = 17.343 (5) angstrom, c = 17.016 (5) angstrom, beta = 108.54 (3)-degrees, V = 3393.87 angstrom3, Z = 4, and D(c) = 1.45 g/cm3. Least-squares refinement led to a final R value of 0.051 (I greater-than-or-equal-to 3-sigma(I(o))) for 2004 independent reflections. Complex 3 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 18.335 (6) angstrom, b = 16.576 (5) angstrom, c = 17.461 (6) angstrom, beta = 96.04 (3)-degrees, V = 5277.17 angstrom3, D(c) = 1.26 g/cm3, Z = 4, and R = 0.057 (I greater-than-or-equal-to 2.5-sigma(I(o))) for 3378 reflections. The structure of 3 consists of discrete ion pairs [Li(DME)3]+ and [MeCpLa(NPh2)3]- with average La-N and La-C(ring) distances of 2.459 (8) and 2.84 (1) angstrom, respectively.