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

Article abstract of DOI:10.1021/ic991171b

This report covers initial studies in the coaggregation of nickel (Ni²⁺) and lanthanide (Ln³⁺) metal ions to form complexes with interesting structural and magnetic properties. The tripodal amine phenol ligand H₃tam (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(H₂tam)(CH₃CN)]PF₆·2.5CH₃CN·0.5CH₃OH (1), the Ni(II) center has a distorted octahedral geometry, with an N₃O₂ donor set from the [H₂tam]^- ligand and a coordinated solvent (acetonitrile) occupying the sixth site. The reaction of stoichiometric amounts of H₃tam with the Ni(II) ion in the presence of lanthanide(III) ions provides [LnNi₂(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)]Cl0₄·0.5CH₃OH·0.5CH₃CH ₂OH·4H₂O (2), [DyNi₂(tam)₂(CH₃OH)(H₂O)]ClO₄·CH₃H·H₂O (6), and [YbNi₂(tam)₂(H₂O)]ClO₄·2.58H₂O (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 C₂ symmetry and 6 and 9 having C₁ 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).