Structure investigation of dimethyl-aluminium, -gallium and -indium O,OЈ-chelate complexes in solution and the solid state. Molecular structure of five-co-ordinated [Me 2 M( -OC 6 H 4 CO 2 Me-2)] 2 adducts

The reaction of trimethyl-aluminium, -gallium and -indium with an equimolar amount of methyl salicylate, 2-(HO)C 6 H 4 CO 2 Me (Hmesal), gives [Me 2 M(mesal)] n chelate complexes in high yield (where n = 1 or 2, M = Al 1 or Ga 2; n = 2, M = In 3). The resulting compounds have been characterised in solution by NMR and IR spectroscopy as well as by cryoscopic molecular weight determinations in benzene; their molecular structures in the solid state were determined by single-crystal X-ray diffraction techniques. All three compounds are dimeric in the solid state, with five-co-ordinated metal centres. The deformation of the metal centre co-ordination sphere is discussed. In solution compounds 1 and 2 are monomeric, four-co-ordinated chelate complexes while 3 retains its dimeric structure. On the basis of the structural observation resulting from this study and with respect to related compounds the following sequence of the Group 13 metal centre Lewis acidity, in four-co-ordinated diorganometallic O,OЈ-chelate complexes is proposed: In у Al > Ga. The past decade has brought a considerable increase in the number of examples of simple neutral monomeric five-and six-co-ordinated organometallic complexes of the Group 13 metals. 1, 2 The results indicate that the formation of compounds with higher co-ordination numbers is not limited to those containing macrocyclic ligands, and Group 13 organometallic chemistry has considerably broadened beyond the sphere of four-co-ordinated compounds that dominated previously. A large group of [R 2 M(O,X)] 2 -type chelate complexes (M = Al, Ga or In, and O,X = O, OЈ-or O,N-bidentate ligand), where diorganometallic alkoxides form oxygen-bridged dimers consisting of five-co-ordinated metal centres, are known. 3,4 These Group 13 organometallic chelate complexes potentially create interesting possibilities for comparative studies of the reactivity of four-and five-co-ordinated compounds. In a previous paper we discussed the influence of O,OЈ-bidentate ligands on the structure of dialkylaluminium O,OЈ-chelate complexes in solution and in the solid state. 4 Although this group of compounds has a tendency to form [R 2 Al(O,O)] 2 -type adducts with five-coordinated metal centres in the solid state, in solution they exhibit a considerably greater structural variety depending on the nature of the chelating ligand. For instance, we have elucidated the electronic factors determining the rearrangement from the five-co-ordinated adduct to the four-co-ordinated monomeric chelate complex upon dissolution (Scheme 1). 4 Such a rearrangement occurs for compounds with unsaturated O,OЈ-bidentate ligands, where the π interaction of the alkoxide oxygen lone electron pair with the chelate ligand unsaturated bond system considerably weakens the Lewis basicity of the bridging oxygen and simultaneously strengthens the basicity of the chelating oxygen owing to π delocalization. The role played by the nature of the bidentate ligand in related gallium and indium derivatives is less clear, because there are very few examples of structurally well characterised dialkylgallium O,Ochelate complexes 3l-3r and only two examples of related indium compounds. 3s,t In view of this, it is of interest to know whether the factors affecting the structure of dialkylaluminium chelate complexes can be extended to gallium and indium derivatives. In this paper we present the structural investigation of the † E-Mail: [email protected] Group 13 metal (M = Al, Ga or In) diorganometallic chelate complexes with the methyl salicylate anion (an unsaturated O,OЈ-bidentate ligand with a π conjugated system) in solution and in the solid state. Results and Discussion The interaction of Me 3 M (M = Al, Ga or In) with an equimolar amount of methyl salicylate (Hmesal) results in the quantitative evolution of methane and formation of diorganometallic O,OЈ-chelate complexes according to equation (1). We reported previously that the addition of 2 equivalents of Hmesal to Me 3 Al yielded a monomeric five-co-ordinated chelate complex MeAl(mesal) 2 . 2b It should be noted that when similar reactions were attempted under identical conditions with trimethylgallium and trimethylindium, only the products corresponding to a 1 : 1 stoichiometry were obtained. Compounds 1, 2 and 3 are stable as solids or in solution under an inert atmosphere. The resulting compounds have been characterised in solution by NMR and IR spectroscopy and by cryoscopic molecular weight measurements. The molecular structures of 1, 2 and 3 have been determined by X-ray crystallography; selected bond lengths and angles are given in Structure of [Me 2 Al(mesal)] n 1 Th

Measurement of the F2 structure function in deep inelastic e+^{+}p scattering using 1994 data from the ZEUS detector at HERA

We present measurements of the structure function \Ft\ in e^+p scattering at HERA in the range 3.5\;\Gevsq < \qsd < 5000\;\Gevsq. A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At \qsd < 35 \;\Gevsq the range in x now spans 6.3\cdot 10^{-5} < x < 0.08 providing overlap with measurements from fixed target experiments. At values of Q^2 above 1000 GeV^2 the x range extends to 0.5. Systematic errors below 5\perc\ have been achieved for most of the kinematic urray, W

Comparison of ZEUS data with standard model predictions for e+p→e+Xe^+ p \rightarrow e^+ X scattering at high xx and Q2Q^2

Using the ZEUS detector at HERA, we have studied the reaction e(+)p --> e(+)X for Q(2) > 5000 GeV2 with a 20.1 pb(-1) data sample collected during the years 1993 to 1996. For Q(2) below 15000 GeV2, the data are in good agreement with Standard Model expectations. For Q(2) > 35000 GeV2. two events are observed while 0.145 +/- 0.013 events are expected, A statistical analysis of a large ensemble of simulated Standard Model experiments indicates that with probability 6.0%, an excess at least as unlikely as that observed would occur above some Q(2) cut. For x > 0.55 and y > 0.75, four events are observed where 0.91 +/- 0.08 events are expected, A statistical analysis of the two-dimensional distribution of the events in x and y yields a probability of 0.72% for the region x > 0.55 and y > 0.25 and a probability of 7.8% for the entire Q(2) > 5000 GeV2 data sample. The observed excess above Standard Model expectations is particularly interesting because it occurs in a previously unexplored kinematic region

Measurement of Elastic ϕ\phi Photoproduction at HERA

The production of $\phi$ mesons in the reaction $e^{+}p \rightarrow e^{+} \phi p$ ($\phi \rightarrow K^{+}K^{-}$) at a median $Q^{2}$ of $10^{-4} \ \rm{GeV^2}$has been studied with the ZEUS detector at HERA. The differential$\phi$photoproduction cross section$d\sigma/dt$has an exponential shape and has been determined in the kinematic range$0.1<|t|<0.5 \ \rm{GeV^2}$and$60 < W < 80 \ \rm{GeV}$. An integrated cross section of$\sigma_{\gamma p \rightarrow \phi p} = 0.96 \pm 0.19^{+0.21}_{-0.18}$$\rm{\mu b}$has been obtained by extrapolating to {\it t} = 0. When compared to lower energy data, the results show a weak energy dependence of both$\sigma_{\gamma p \rightarrow \phi p}$and the slope of the$t$distribution. The$\phi$decay angular distributions are consistent with$s$-channel helicity conservation. From lower energies to HERA energies, the features of$\phi$ photoproduction are compatible with those of a soft diffractive process.Comment: 23 pages, including 6 post script figure

The self-assembly switching of the group 13 tetrahedral Schiff base complexes by changing the character of coordination centre

The reaction of Et 3 B with one equivalent of N-substituted salicylideneimine (HsaldR 0 ) yields the monomeric O,N-chelate complexes Et 2 B(saldR 0 ), where R 0 ¼ Me (1) or Ph (2). The crystal structure of the resulting complexes has been determined by X-ray crystallography. The molecular structure of these complexes consists of monomeric four-coordinate chelates and their primary arrangement in the crystal structure is determined by the C-HÁ Á ÁO aryloxide hydrogen bonds. An extended crystal structure analysis reveals that the adjacent monomeric moieties of 1 are interconnected by C-H imino Á Á ÁO hydrogen bridges resulting in a 1-D motif infinite H-bonded chain, whereas the crystalline complex 2 comprises dimeric molecules linked through a pair of intermolecular C-H arom Á Á ÁO interactions. The supramolecular arrangement of both compounds is discussed with relation to the structure of analogous aluminium and gallium complexes, and the role played by the coordination centre on the molecular assembly is analyzed. It is shown that the steric congestion at the hydrogen bond donor and acceptor sites, as a result of changes in the N-alkyl substituents or the coordination centre environment, affect the strength of the intermolecular C-HÁ Á ÁO hydrogen bonds and may lead to the self-assembly switching of the bidentate Schiff base complexes