Coaggregation of paramagnetic d- and f-block metal ions with a podand-framework amine phenol ligand

This report covers initial studies in the coaggregation of nickel (Ni2+) and lanthanide (Ln(3+)) metal ions to form complexes with interesting structural and magnetic properties. The tripodal amine phenol ligand H(3)tam (1,1,1-tris(((2-hydroxybenzyl)amino)methyl)ethane) is shown to be particularly accommodating with respect to the geometric constraints of both transition and lanthanide metal ions, forming isolable complexes with both of these ion types. In the solid-state structure of [Ni(H(2)tam)(CH3CN)]PF6.2.5CH(3)CN.0.5CH(3)OH (1), the Ni(II) center has a distorted octahedral geometry, with an N3O2 donor set from the [H(2)tam](-) ligand and a coordinated solvent (acetonitrile) occupying the sixth site. The reaction of stoichiometric amounts of H(3)tam with the Ni(II) ion in the presence of lanthanide(III) ions provides [LnNi(2)(tam)(2)](+) cationic complexes which contain coaggregated metal ions. These complexes are isolable and have been characterized by a variety of analytical techniques, with mass spectrometry proving to be particularly diagnostic. The solid-state structures of [LaNi2(tam)(2)(CH3OH)(1/2)-(CH3CH2OH)(1/2)(H2O)]ClO4.0.5CH(3)OH.4H(2)O (2), [DyNi2(tam)(2)(CH3OH)(H2O)]ClO4.CH3OH.H2O (6), and [YbNi2(tam)(2)(H2O)]ClO4.2.58H(2)O (9) have been determined. Each complex contains two octahedral Ni(II) ions, each of which is encapsulated by the ligand tam(3-) in an N3O3 coordination sphere; each [Ni(tam)](-)unit caps the lanthanide(III) ion via bridging phenoxy oxygen donor atoms. In 2, La3+ is eight-coordinated, while in 6, Dy(III) is seven- (to "weakly eight-") coordinated, and Yb(III) in 9 has a six-coordination environment. The complexes are symmetrically different, 2 possessing C-1 symmetry and 6 and 9 having CI symmetry. Magnetic studies of 2, 6, and 9 indicate that antiferromagnetic exchange coupling between the Ni(II) and Ln(III) ions increases with decreasing ionic radius of Ln(III).