Synthesis, structure, and solution studies of cyclohexantriol complexes of europium(III)

cis,cis-1,3,5-Trihydroxycyclohexane (L-1) and cis,cis-1,2,3-trihydroxycyclohexane (L-2) have been considered as ligands for the complexation of europium(III) in organic solvents. Three complexes were prepared and characterized by X-ray diffraction analysis, microanalysis, electrospray mass spectrometry, and proton NMR. Depending on the europium(III)-to-ligand ratio, ML or ML2 complexes were formed in organic solution. Complexes formed with ligand L-2 are stable in methanol solution, while those obtained from L-1 are stable only in nonprotic solvents. This difference is related to the amount of energy involved in the necessary chair-chair conversion prior to complexation of the europium(III) ion. In the solid state the coordination sphere including in each case two L-1 or L-2 molecules as tridentate ligands, is completed by a bidentate nitrate anion and one molecule of water in 1, [Eu(L-1)(2)(NO3)(H2O)](NO3)(2), two monodentate triflate anions and one molecule of water in 2, [Eu(L-1)(2)(OTf)(2)(H2O)](OTf), and a bidentate and a monodentate nitrate anion in 3, [Eu(L-2)(2)(NO3)(2)](NO3) Many strong H bonds are present in the crystalline network with H ... O distances between 1.77 and 2.301 Angstrom. Proton NMR studies have shown that a moderate lowering of the temperature is sufficient to observe the different species present in solution, the proportions of which depend on the metal-to-ligand ratio. Conductometric studies have also provided indication about the number of coordinated anion in methanol and acetonitrile solutions.