INTRAMOLECULAR HYDROLYSIS OF COORDINATED ACETONITRILE IN A BINUCLEAR COMPLEX OF COBALT(III) - X-RAY CRYSTALLOGRAPHIC ANALYSIS OF SALTS OF [(TREN)CO(MU-NH2,MU-L)CO(TREN)]4+(L=OH, CH3C(O)NH)

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(p-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 x l0-3 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) (hexafluorophosphate, 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) Å, β 99·13(2)°, Z 2, and C2/c with a 14·328(2), b 14·046(1), c 16·497(2) Å, β 101-90(1)°, Z 4. For the salt of (3), 2389 data with I ≥ 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. © 1990 ASEG.