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 ML(2) 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)(NO(3))(H(2)O)(2), two monodentate triflate anions and one molecule of water in 2, Eu(L(1))(2)(OTf)(2)(H(2)O), and a bidentate and a monodentate nitrate anion in 3, Eu(L(2))(2)(NO(3))(2). Many strong H bonds are present in the crystalline network with H.O distances between 1.77 and 2.301 Å. 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.