Intramolecular Hydrolysis of Coordinated Acetonitrile in a Binuclear Complex of Cobalt(III): X-Ray Crystallographic Analysis of Salts of [(tren)Co(μ-NH₂,μ-L)Co(tren)]⁴⁺(L=OH, CH₃C(O)NH)

Abstract

A synthesis of [( tren )Co(μ-NH₂,μ-OH)Co( tren )]⁴⁺(3)( tren = tris (2- aminoethyl )amine) is reported along with a series of derivatives: [( tren ) XCo (μ-NH₂) CoX ( tren )]ⁿ⁺, where X = CF₃SO₃^- (n = 3)(4), X = CH₃CN (n = 5)(5), and [( tren )Co(μ-NH₂,μ-CH₃C(O)NH)Co( tren )]⁴⁺ (6). The substitution of (4) by CH₃CN to yield (5) was studied in CH₃CN at 20°C, k = 9.0×10^-3 s^-1, and the intramolecular hydrolysis of (5) to yield the bridging acetamide complex (6) was studied at various acid concentrations. The X-ray crystal structures were determined for (3b) (exafluorophosphate, dihydrate) and (6b) (dithionate, tetrahydrate ). Both crystals are monoclinic, respectively P2₁/n with a 11.082(2), b 10.402(2), c 15.611(2)Ǻ, β 99.13(2)°, Z 2, and C2/c with a 14.328(2), b 14.046(1), c 16.497(2)Ǻ, β 101.90(1)°, Z 4. For the salt of (3), 2389 data with 1 ≥ 2σ(I) were refined to R 0.070 ( Rw 0.066), and, for the salt of (6), 3087 data with I ≥ 3σ(I) were refined to R 0.041 ( Rw 0.056). Both ions lie on pseudo-symmetric sites involving disorder of the bridging ligands . The structures establish the binding mode of the acetamido ion and the orientation of the tren groups in the isolated complexes.