([2.2]Paracyclophane)gallium(I) Tetrabromogallate(III): Its Synthesis and Novel Structural Features

[2.2]Paracyclophane forms 1:1 complexes (1,2) with Ga₂Cl₄and Ga₂Br₄, respectively, in benzene at ambient temperature. The products are insoluble in common organic solvents. The crystal and molecular structure determination shows compound 2 to form an intricate highly symmetrical three-dimensional network (orthorhombic, space group Pnma with a = 12.836 (4) Å, b = 10.004 (3) Å, c = 14.943 (4) Å, V = 1918.9 ų, d_calcd⁼ 2.310 g/cm³for Z = 4, R_w = 0.038 for 106 refined parameters and 1352 unique reflections with F_o≥ 4.0σCF_o)). Each Ga(I) center is complexed by two [2.2]paracyclophane molecules, whose parallel pairs of aromatic rings are tilted relative to each other by 56.7°. The 1:1 stoichiometry implies that each paracyclophane in turn is bonded to two Ga(I) atoms which are situated nearly centrically above each of the arene rings at a distance of 2.72 Å. The polydecker chains of alternating gallium(I) ions and paracyclophane molecules thus formed are cross-linked by tetrahedral GaBr₄^-anions, each of which provides one bromine atom to bridge two Ga(I) centers. Thereby the latter adopt a strongly distorted pseudo-tetrahedral coordination geometry.