The digallium compound R(2)Ga-GaR(2) (1; R=CH(SiMe(3))(2)) reacts with citracinic acid by the release of two equivalents of bis(trimethylsilyl)methane and the formation of a unique oligofunctional cage compound (2). Four Ga-Ga bonds in a tetrahedral arrangement are bridged by four spacer ligands that are located on the faces of the tetrahedron and bridge the gallium atoms of three different Ga-Ga bonds. Four pyridinium groups result from the shift of one of the three acidic protons of four citracinic acid molecules to the nitrogen atoms of the aromatic rings. The N-H groups are arranged in pairs and are capable of acting as chelating acceptors for the coordination of THF molecules (2(THF)(2)) or the nitrogen atoms of 1-deazapurine (3(OEt(2))(4)). In particular, the last reaction verifies the potential applicability of this relatively water- and air-resistant acceptor compound for the generation of bioorganometallic hybrid molecules.
Treatment of the digallium compound R(2)Ga-GaR(2) [R = CH(SiMe(3))(2)] with benzotriazol-5-carboxylic acid afforded a large cage-like compound in which six Ga-Ga bonds are bridged by six trifunctional ligands. The central cavity encapsulated a THF molecule which cannot be removed in vacuo and does not show exchange with a large excess of the solvent.
Treatment of the digallium compound R2Ga-GaR2 1 [R = CH(SiMe3)2] with hydrogen fluoride or water in the presence of 2-aminonicotinic acid afforded the corresponding fluoride or hydroxide, R(X)Ga-Ga(X)R (X = F, OH), by substituent exchange and retainment of the Ga-Ga bonds. Both compounds form trimeric formula units in which three Ga-Ga bonds in a parallel orientation are bridged by six fluoro or hydroxo ligands.
Treatment of the tetraalkyldigallium(4) compound R 2 Ga−GaR 2 [1; R = CH(SiMe 3 ) 2 ] with the highly functionalized acids 3-and 4-carboxyphenylthiourea, 7azaindole-3-carboxylic acid, and 6-aminonicotinic acid afforded macrocyclic compounds in which two or four Ga−Ga bonds are bridged by the respective number of organic spacer ligands. In each reaction two equivalents of CH 2 (SiMe 3 ) 2 per formula unit of 1 were released. The Ga−Ga bonds of the products 2 to 5 are bridged by a carboxylato group and a chelating ligand containing two nitrogen donor atoms or the sulfur and nitrogen atoms of a thiourea group. The thiourea derivatives afforded different species with four or eight gallium atoms in the heterocycles (2 and 3) depending on their substitution patterns (1,3-versus 1,4-positions at the benzene rings). Supramolecular aggregates resulted that had up to 12 THF molecules encapsulated in the heterocycles or bonded to the surface of the molecules via hydrogen bonding or orthogonal dipolar interactions.
Treatment of the tetraalkyldigallium compound R2Ga–GaR2 [R = CH(SiMe3)2] (1) with a large number of different functionalized carboxylic acids afforded dicarboxylatodigallium compounds R2Ga2(μ‐O2C–R)2, in which two carboxylato ligands bridge the Ga–Ga bonds. The chelating ligands have additional nitrogen, oxygen or phosphorus donor atoms and may be suitable to act as Lewis‐bases to yield supramolecular aggregates in future investigations. Four compounds have been characterized by crystal structure determinations. One gave unprecedented dimeric formula units in the solid state by Ga–N interactions. The similar reaction with isonicotinic acid resulted in the cleavage of the Ga–Ga bond. A tetragallium compound was formed in which four isolated metal atoms were bridged by four organic ligands to give a square molecular core.
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