Synthesis of mixed salts of the [Mo2O2(μ-S)2(SCN)6-n(L)n](4+n)− anion (n = 0–2); structures of [Mo2O2(μ-S)2(SCN)5(CH3CN)]3−, [Mo2O2(μ-S)2(CN)5]3−, and [Mo2O2(μ-S)2(CN)2(O)]2−, and probing the ligand exchange of thiocyanate and cyanide

Abstract

Aqueous coordination of cyanide and verification of the composition of the resulting coordination compound is important to ensure confidence in its coordination. Isothiocyanato compounds 1–7 were synthesized employing different synthetic routes and the complex, [Mo2O2(μ-S)2(SCN)5(CH3CN)]3−, 4, was structurally characterized. Ligand exchange reaction of 4 with cyanide forms 8, a cyano complex. Complex 8 was isolated as an organosoluble salt and fully characterized and confirmed as the major product formed in the aqueous ligand exchange reaction of 4–7 with cyanide. The crystal structure of 8 revealed the unusual [Mo2O2(μ-S)2(CN)5]3− anion where the two molybdenum(V) centers are unsymmetrically coordinated. A second unsymmetric cyano complex [Mo2O3(μ-S)2(CN)2]2−9, presumed hydrolysis product from an aqueous reaction, was isolated and structurally characterized revealing one square pyramidal Mo center and one tetrahedral Mo center in the binuclear core. Attempts to quantify the first order dissociative ligand substitution rate of thiocyanate in 4 to form 8 using the stopped-flow method gave an estimated minimum rate constant of 70 s−1. This confirms that the exchange reaction is sufficiently fast to be useful in aqueous coordination of cyanide.