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The crystal and molecular structures of [Me2Etim]CI, [Me2Etim]2[CoCI4], and [Me2Etim]2[NiCI4] ([Me2Etim] § = 1,2-dimethyl-3-ethylimidazolium cation) all contain evidence that the H4 and H5 protons of the imidazolium cation enter into hydrogen bonds; the implications of this observation for the interactions in room-temperature chloroaluminate(lll) ionic liquids are considered.The nature of cation-anion interactions in the field of room-temperature halogenoaluminate(III) ionic liquids has been a major source of controversy. In dialkylimidazolium systems, the debate has centered around the involvement of ring protons in hydrogen bonding. Although attempts have been made to elucidate the structure of these ionic liquids using NMR [1] and IR [2] spectroscopy, there is a surprising paucity of crystallographic models of the system. The crystal structure of 1-methyl-3-ethylimidazolium iodide {[MeEtim]I} [3] shows the presence of a discrete hydrogen-bonded ion pair, with close contact [0.293(3) nm] between the proton on the C2 atom of the imidazolium ring and the iodide ion. There was no evidence of interaction between the protons at the 4-or 5-positions of the ring and the iodide ion. However, crystallographic studies [4] of [MeEtim]2[MC14] (M = Co or Ni) show that when more polarizing anions are present, contact distances between the protons at the 4-and 5-positions and the anion, though longer than those at the 2-position, are shorter than predicted from van der Waals radii.A series of 1,2-dimethyl-3-ethylimidazolium ([Me2Etim] +) salts has been prepared for structural determination (see Table 1), to facilitate the study of possible hydrogen-bonding of the C4 and C5 protons, *To whom correspondence should be addressed. in the absence of the most acidic C2 proton of the imidazolium ring. Crystals of [Me2Etim]2[CoCl4] and [Me2Etim]2[NiC14], prepared by the reaction of the appropriate anhydrous metal(II) chloride with [Me2Etim]C1in nitromethane, are isomorphous and hydrogen-bonded interactions are seen in both structures. Each cation forms short contacts from the ring protons to two different [MC14] 2-anions, and each chlorine atom forms one short contact to a ring proton (Figure 1, Tables 2-4). As might be expected, none of the hydrogen bonds are linear (see Table 3). The [MC14] z-anions are arranged in layers.[MezEtim]C1 (formed by the reaction of 1,2-dimethylimidazole and chloroethane) forms white monoclinic crystals (see Table 1); its structure reveals discrete dimers with short contacts between the C4 and C5 protons and the two chloride ions that bridge between two cations (Figure 2), at distances of r{H4...CI} = 0.253 nm and r{H5...C1} = 0.258 am (van der Waals contact = 0.300 rim). Assuming a hydrogen-bond acceptor radius for the chloride ion of 0.179 nm [5], this gives an average hydrogen-bond donor radius for the CH(4) and CH(5) groups (see Table 4) of 0.174 nm, only slightly larger than the values found for the CH(2) group in thiamine and its salts [6], a much more acidic group. Furthermore, the positive ion fa...

Previous studies of lethyl-3-methylimidazolium chloride-aluminium(II1) chloride (1 emim] Cl-AICI,) ionic liquids have been hampered by significant contamination of these liquids by oxide impurities. Treatment of these liquids with phosgene removes the oxide impurities, and the use of a specially constructed sample inlet system for airsensitive materials permitted them to be studied by fast atom bombardment mass spectrometry. The ions Cl-, [CI,l-, [AICI,]-, [AlzC171-, [emim]' and [(emim),X]+ (X = CI or AICI,) were observed for the basic ionic liquid. In addition, the anion [AI,CI,,]was observed for the acidic composition. Within the mass spectrometer, the hydrolyses of [ A13Cllo]to produce [ AI,CI,O]and of [ AI,CI,]to produce [ AI,CI,O]were observed. Comparison of these results with published '"0 NMR data suggests that the primary hydrolysis products in acidic ionic liquids are [AI,CI,O]-and [AI,CI,O]-and that the principal secondary hydrolysis product is [ AI,CI,(OH)] -.

The enzyme phenylalanine ammonia lyase taken orally has been found to reduce the rise in blood phenylalanine that normally occurs following a protein meal. Therefore the enzyme has a potential use in the management of the genetic disease phenylketonuria. The enzyme mediates the conversion of phenylalanine to cinnamic acid and its possible clinical future has necessitated a more detailed study of the product of its reaction. Cinnamic acid is a compound of low toxicity which is converted in the mammalian body primarily to hippuric acid. We have examined the kinetics of this process in a healthy male and in two patients with untreated phenylketonuria. In addition we have attempted to clarify the inconsistencies in earlier published work about the status of other, minor metabolites. Following an oral load of sodium (2H6) cinnamate there is an increase in urinary hippuric acid largely due to the excretion of (2H5) hippuric acid. In the subjects studied there was no major difference in the rate of elimination although the amount of cinnamic acid converted was less in those with phenylketonuria. This may reflect reduced first-pass absorption by the liver in untreated phenylketonuria enabling increased uptake to occur in other parts of the body.

A negative-ion fast-atom-bombardment mass spectrometric study of the room temperature chloroaluminate ionic liquids AIC1,-(MeEtim]Cl (IMeEtimJ' = 1-methyl-3-ethylimidazolium cation) has produced the first unambiguous experimental evidence for the existence of [A13Cl,,,J-.

Formation of Tns{ tetracbloroaluminate(III)}metallate(II)Anions, [ M(AlCI,), 1 -, in Acidic Ambient-temperature Ionic LiquidsMass spectrometry has been shown to be a powerful technique for the investigation of the structure of ambienttemperature chloroaluminate(II1) ionic liquids.', ' We report here the first use of fast atom bombardment (FAB) mass spectrometry to study solute species in an acidic? 1-ethyl-3-methylimidazolium chloride-aluminium(II1) chloride {[emim]C1-A1C1,} ionic liquid., Initial investigations of the structure of dissolved metal chloride species in acidic chloroaluminate(II1) ionic liquids, using electrochemistry4 and electronic absorption spectroscopy,5 yielded ambiguous and contradictory results. A recent EXAFS study6 showed that, in an acidic [emim]C1-A1C1, ionic liquid, the salts [emim]2[MC14] (M = Ni, CO or Mn) dissolve to form complexes with the metal centre bound to six chlorine atoms in the first coordination sphere, and with three aluminium atoms in the second coordination sphere. These data, together with the interatomic distances, were used to suggest that the dominant solute species was the tris{tetrachloroaluminate(III)}metallate(II) anion, [M(AlCl,),] -(see Fig. 1). However, powerful though the technique is, structure determination by EXAFS does not provide unambiguous structural identification: it is a best-fit method, and does not represent a unique solution. As a technique providing the only confirmation of the identity of an ion, it provides excellent, but not unequivocal, evidence. We now report here the first unambiguous evidence for the existence of [M(AlCI,),] -(M = Co or Ni).The ionic liquid was prepared as previously described.2 Concentrated solutions of anhydrous cobalt(I1) chloride (0.40 g, 3.1 mmol) or nickel(I1) chloride (0.30 g, 2.3 mmol) in acidic Figure 1. The proposed structure' for the tris(tetrachloroa1uminate(lll)}metallate(ll) ion, [M(AICI,),] -. t Chloroaluminate(II1) ionic liquids are called acidic if aluminium(II1) chloride is in excess over [emim]Cl; the precise composition is defined by the apparent mole fraction of AlCI, , {X(AlC13)}.(X(AIC1,) = 0.67) ionic liquid (7.3037 g and 7.4364 g, respectively) were prepared: the solutions were then treated with pho~gene,~ to remove oxide contamination.$ The addition of the metal(1I) chlorides to the ionic liquid caused a change in the composition of the ionic liquid. This can be accounted for by calculating the effect of the addition of two moles of chloride ions for every mole of the metal(I1) chloride dissolved in the ionic liquid. From this, it can be shown that the final compositions of the ionic liquids used in the experiment were X(AlC1,) = 0.60 for the cobalt(I1) chloride experiment and X(AIC1,) = 0.62 for the nickel(I1) chloride experiment, very similar to the compositions used for the EXAFS study.6Immediately after purification with phosgene, a sample of the solution was drawn into a sealable, gas-tight syringe (ex.S.G.E.), in which the sample was transferred to the spectrometer. The sample was then in...

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