Structural diversity in silver salts of hexahalogenocarborane anions, Ag(CB11H6X6) (X = Cl, Br or I)

Abstract

Crystal structures have been determined for three Ag(CB 11 H 6 X 6 ) compounds (X = Cl, Br or I) crystallized from arene solvents. They are all one-dimensional co-ordination polymers in the solid state with hexahalogenocarborane anions acting as bridging ligands. The co-ordination geometries of these three salts are, however, unique. The type and number of donors to silver() varies from one to another and is not particularly predictable.Icosahedral carboranes constitute a new class of very weakly co-ordinating anions. 1,2 The 7-12 hexahalogenated derivatives CB 11 H 6 X 6 Ϫ (X = Cl, Br or I), are larger, more thermodynamically stable, more chemically inert, less co-ordinating and less nucleophilic than the parent CB 11 H 12 Ϫ ion. 3 They play a very important role in stabilizing co-ordinatively unsaturated cations such as the silylium ion (R 3 Si ϩ ) 4-7 and the four-co-ordinate 5,10,15,20-tetraphenylporphyrinatoiron() ion, [Fe(tpp)] ϩ . 8 Silver() salts of carborane anions are very useful halide metathesis reagents for introducing weakly co-ordinating anions into complexes and they are finding immediate applications in metathesis, catalysis and oxidation chemistry. 2-12 They are also of structural interest in their own right because they illustrate the subtlety and diversity of co-ordination chemistry when anions have comparable donor ability to solvent molecules. Examples of crystallographically characterized silver() carborane complexes include

Silver Phosphanes Partnered with Carborane Monoanions: Synthesis, Structures and Use as Highly Active Lewis Acid Catalysts in a Hetero-Diels–Alder Reaction

“…On first inspection, the silver(i) centre is coordinated with the carborane anion through two shorter (2.6963(5) ä and 2.8710(5) ä) AgÀBr interactions and one longer one (3.0953(5) ä), all of which fall comfortably within the sum of the van der Waals radii for silver and bromine. These bond lengths are of similar values to those previously reported for silver complexes of [CB 11 H 6 Br 6 ] À [31] and dibromoalkane complexes of silver. [52] The silver phosphane bond length (2.4032(10) ä) is slightly longer than that found in 1.…”

Carborane acids. New “strong yet gentle” acids for organic and inorganic chemistry

“…No band ascribable to a simple nX-H stretch is observed and, given the marked tendency of protons to be dicoordinate, 17 a polymeric structure with H + bridges between halogen substituents of the anions is proposed, similar to that observed in a number of Ag + salts of carboranes. 18 Carborane acids are so strong that they protonate (or react with) almost every solvent. In liquid SO 2 , one of the least basic solvents where good solubility is achieved (ca.…”

Silver and Copper Complexes with closo-Polyhedral Borane, Carborane and Metallacarborane Anions: Synthesis and X-ray Structure

“…. Br distance is 2.862(2) Å (Figure 67) [95]. In the crystals of {Ag[1-CB 11 H 6 -6,7,8,9,10,11,12-I 6 ]¨0.5(benzene)} n the silver atom is complexed by iodine atoms to one anion in bidentate fashion and to another in tridentate fashion adopting a square-pyramidal arrangement ( Figure 67) [95].…”