721b although further ligation from the anion may

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Unformatted text preview: pto (r6-arene) complexes of Ga' and In' can be obtained from solutions of the lower halides (p. 240) in aromatic solvents, and some of these have surprisingly complex structures.(86) With bulky ligands such as CsMes simple adducts crystallize in which the cations [M(r6-C6Me6)l+ 'half-sandwich' structure shown in have the c(jv Fig. 7.21% e.g. [Ga(r6-C6Me6>1[GaC141 168" mP and [Ga(r6-C6Me,)l[GaBr41 mP 146'.(87) with less bulky ligands such as mesitylene (1,3,5C&Me3), a 2: 1 stoichiometry is possible to give cations [M(r6-C6H3Me3)21+ shown schematically in Fig. 7.21b, although further ligation from the anion may a1so Occur; e.g. [In(v6C6H3Me3121[InBr41 features polymeric helical chains in which bridging b - v ' ,V2-InBr41 units connect the cations as shown in Fig. 7.21c.(") With still less bulky ligands such as benzene itself, discrete dimers can be formed as in the solvated complex [Ga(q6-C6H&.] [GaC14].3C&j. This features tilted bis(arene)Ga' units linked through bridging GaC14 units to form the dimeric structure shown in Fig. 7.22a.@@ Mixed adducts can also be prepared. Thus, when 8 6H. SCHMIDBAUR, Angew. Chem. Int. Edn. Engl. 24, 893-904 (1985). 87 H. SCHMIDBAUR, . THEWALT and T . ZAFIROPOULOS, U Angew. Chem. Int. Edn. Engl. 23, 76-7 (1984). "J. EBENHOCH,. MULLER, . RIEDEand H. SCHMIDBAUR, G J Angew. Chem. Int. Edn. Engl. 23, 386-8 (1984). c6~ tructure characteristic of [Ga(q6-C6Me6)]+. (b) The 'bent-sandwich' s structure found in ions of the type [ h ~ ( q ~ - c ~ H ~ M e(c) )A ] ection of the helical chain in [In($~ ~ s+ . rne~)~][InBr~] showing the [p-q',q2-InBr4] unit bridging ions of the type shown in (b); the tilting angle is 133" a nd the ring-centres of the two arene ligands are almost equidistant from In (283 a nd 289 pm). 87.3.6 Organometalliccompounds 265 Figure 7.22 (a) Structure of the dimeric unit in the solvated complex [Ga(86-C6H6)2][GaC14].3C6H6 indicating the principal dimensions; the six benzene molecules of solvation per dimer lie outside the coordination spheres of the gallium atoms. (b) Structure of the ion-pair [Ga($'-[2.2.2] paracyclophane)][GaBr4]; the four Ga-Br distances within the tetrahedral anion are in the range 230.5-233.3 pm, the distance for Ga-Br, being 231.9pm; the Ga' . . . Br, distance is 338.8pm. dilute toluene solutions of Ga2C14 and durene (1,2,4,5-C&Me4) are cooled to 0 ", crystals containing the centrosymmetric dimer [(Ga(~j~-dur)(q~-tol)}GaCl4]2re obtained.(89) a The structure resembles that in Fig. 7.22a, with each Ga' centre $-bonded to one durene molecule at 264pm and one toluene molecule at 304 pm. These bent-sandwich moieties are then linked into dimeric units via three of the four C1 atoms of each of the two GaC14 tetrahedra. An even more remarkable structure emerges for the monomeric complex of Ga2Br4 with the tris(arene) ligand [2.2.2]paracyclophane (Fig. 7.22b):(") the Ga' centre is encapsulated in a unique q18 environment which has no parallels even in transition-met...
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