Fluoride binding and crystal-field analysis of lanthanide complexes of tetrapicolyl-appended cyclen

Lanthanide complexes of tetrapicolyl cyclen display remarkably high affinities for fluoride (log K ~ 5) in water, and are shown to form 1:1 complexes. The behaviour of these systems can be rationalised by changes to the magnitude of the crystal field parameter, B02. However, such changes are not invariably accompanied by a change in sign of this parameter: for early lanthanides the N8 donor set with a coordinated axial water molecule ensures that the magnetic anisotropy has the opposite sense to that observed in the analogous dehydrated lanthanide complexes.