Synthese und Kristallstruktur des Bis(benzol)gallium(I)-tetrabromogallat(III)-Dimeren / Synthesis and Crystal Structure of the Bis(benzene)gallium (I) Tetrabromogallate(III) Dimer

Abstract

Anhydrous Ga[GaBr4] is readily dissolved in benzene. The resulting solutions show discrete 71Ga NMR signals for Ga(I) und Ga(III) centers. Narrow line-widths of the former indicate a small electric field gradient of the Ga(I) nucleus due to almost spherical shielding by the 4 s2 lone pair of electrons. Crystals obtained from the benzene solution on cooling have the stoichiometry [(C6H6)2Ga · GaBr4]2 ·3 C6H6, and are isomorphous with the analogous chloride compound: a = 9.390(2). b = 10.847(1), c = 13.118(2) Å; α = 85.54(1). β = 102.91(1). γ = 105.62(1)°; triclinic, space group Ρ1̄, Z = 1. The centrosymmetric dimers are composed of bis(benzene)gallium(I) and tetrabromogallate(III) units bridged by six bromine atoms. Only two bromine atoms are not engaged in coordinative bonding. The two benzene rings are both η6-bonded to the gallium(I) center, but not equidistant. They are enclined by 57.5°. The remaining benzene molecules are crystal benzene with no specific cation or anion contacts.