Field-induced slow magnetic relaxation of monoand dinuclear dysprosium(III) complexes coordinated by a chloranilate with different resonance forms

We synthesized the dinuclear and mononuclear dysprosium(III) complexes [{Dy(Tp)₂}₂(Cl₂An)]˙ 2CH₂Cl₂ (1) and [Co(Cp)₂][Dy(Tp)₂(Cl₂An)] (3), where Cl₂An^2- and Tp^- are the chloranilate and hydrotris(pyrazolyl)borate ligand, respectively. In addition, the magnitude of the magnetic coupling between the lanthanide centers through the Cl₂An^2- bridge has been probed through the synthesis of [{Gd(Tp)₂}₂(Cl₂An)]˙ 2CH₂Cl₂2 (2), which is a gadolinium(III) analogue of 1. Complexes 1-3 were characterized by infrared (IR) spectroscopy, elemental analysis, single-crystal X-ray diffraction, and SQUID measurements. IR and single-crystal X-ray structural analyses confirm that the coordination environments of the lanthanide(III) centers in 1 and 3 are similar to each other; i.e., eight-coordinated metal centers, each occupied by an N₆O₂ donor set from two Tp^- ligands and one Cl₂An^2- ligand. The coordination geometries of the lanthanide(III) centers in 1 and 2 are distorted triangular dodecahedral, while that in the mononuclear complex 3 is square antiprismatic, where the Cl₂An^2- ligand takes the bi-separated delocalized form in 1 and 2, and the o-quinone form in 3. Alternating-current (AC) magnetic studies clearly reveal that both 1 and 3 exhibit field-induced slow relaxations of magnetization that occur via Raman and direct processes. Complexes 1 and 3 exhibit different spin relaxation behavior, which reflects the coordination geometry around each Dy^III center and its nuclearity, as well as the molecular packing in the crystal lattice. Although the magnetic analysis of 2 revealed negligible magnetic coupling, Cl₂An^2- bridges with small biases may form in the dinuclear complexes, which play roles in the spin relaxation dynamics through dipolar interactions.