Isomerization mechanisms of stereolabile tris- and bis-bidentate octahedral cobalt(II) complexes: X-ray structure and variable temperature and pressure NMR kinetic investigations.

The isomerization dynamics of five labile octahedral Co(II) compounds have been investigated by variable temperature and pressure (1)H and (19)F NMR spectroscopy in dichloromethane solution. The X-ray crystal structure of the two tris-chelates, [Co(HFA)(2)bpic] (1) and [Co(TTFA)(2)bpy] (2), show a distorted octahedral arrangement of the 4 oxygen and 2 nitrogen donor atoms, with bidentate ligand bite angles smaller than 90 degrees. On the other hand, in the three bis-chelates, trans(N)-[Co(HFA)(2)(CH(3)py)(2)](3), cis(N)-cis(CF(3))-trans(S)-[Co(TTFA)(2)(CH(3)py)(2)](4), and trans(N)-trans(CF(3))-[Co(TTFA)(2)(CF(3)py)(2)](5), the replacement of the bidentate nitrogen donor ligands by two monodentate Rpy ligands leads to relaxed structures with almost regular octahedral arrangements of the donor atoms (HFA = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato anion; TTFA = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato anion; bpy = 2,2'-bipyridine; bpic = 4,4'-dimethyl-2,2'-bipyridine).

Mechanism of pyridine-ligand exchanges at the different labile sites of 3d heterometallic and mixed valence mu3-oxo trinuclear clusters.

The syntheses and single crystal X-ray structural analysis of five novel hetero- and homometallic mu 3-oxo trinuclear cluster with the formula [Fe (III) 2M (II)(mu 3-O)(mu-O 2CCH 3) 6(4-Rpy) 3]. x(4-Rpy). y(CH 3CN) where R = Ph for 1(Fe 2Mn), 2(Fe 2Fe), 3(Fe 2Co), 4(Fe 2Ni) and R = CF 3 for 5(Fe 2Co), are reported.

Richness of isomerism in labile octahedral Werner-type cobalt(II) complexes demonstrated by 19F NMR spectroscopy: structure and stability.

The cobalt(II) complexes [CoL2(R2-Py)2] (1-4) where HLA = 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione, R2-Py = 4-methylpyridine (1), HLB = 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione, R2-Py = 4-methylpyridine (2), 4-phenylpyridine (3) and S-(-)-1-(4-pyridyl)ethanol (4) were prepared by two-step reactions. X-ray structure analysis of [CoLA2(CH3-Py)2] revealed the {trans(N)-trans(CF3)-trans} configuration for the complex obtained by crystallization from ethanol. A dynamic equilibrium between the five possible stereoisomers was observed for each complex 1-4 in solution by 19F NMR spectroscopy.