Difluoro Complex Research Articles

Die Kristallstrukturen von zwei mononuklearen Peroxotitan (IV)‐dipicolinaten

AbstractThe crystal structures of two mononuclear peroxotitanium(IV) chelates, the triclinic, deep red, pleochroitic diaquoperoxotitanium dipicolinate [TiO2(C7H3O4N) (H2O)2]2H2O, and the monoclinic, orange difluoroperoxotitanium dipicolinate K2[TiO2(C7H3O4N)F2]2H2O, have been determined from X‐ray diffractometer data, and refined to R = 2.7% (3488 reflections) and R = 5.1% (2324 reflections) respectively. Analogous to a yellow‐orange dinuclear peroxotitanium dipicolinate described earlier, the utanium atoms are coordinated approximately pentagonal bipyramidally, with the peroxo group and the chelate ligand occupying the equatorial sites and with H2O or F‐ forming the apices. The OO bond length in the peroxo group is the same in all structures, but there is a very slight variation of the Ti‐peroxide distances apparently connected with the colours of the compounds. The more basic the apical ligands are (H2O → F− → μ‐oxygen), the higher is the frequency of the absorption band, the longer are the Ti‐peroxide distances, and the shorter are the apical bond lengths. Difference Fourier maps based on the final structures agree with this. The red diaquo complex shows highest residual peaks between titanium and the peroxo group, whereas the orange difluoro complex shows them near the apical TiF bonds. The packing of the complexes and hydrogen bonding are discussed. HO distances seem to indicate that the very acidic diaquo complex is near a transitional state towards a hydroxonium salt.