Magnetic and spectroscopic properties of chloride-bridged guanidinate dilanthanide complexes

The guanidinate ligand scaffold offers a unique combination of hard anionic charges, steric tunability, and electronic modulation, rendering it an ideal candidate for the molecular design of lanthanide complexes. Here, we present two dilanthanide chloride complexes [{(Me3Si)2NC(NiPr)2}2Ln(mu-Cl)]2 (Ln = Gd (1), and Tb (2)) where each metal ion is ligated to two guanidinate anions and bridged to the other metal ion by two chloride ligands. The isostructural complexes 1 and 2 were synthesized through salt metathesis reactions and characterized through single-crystal X-ray diffraction analysis, IR and UV-Vis spectroscopy, and SQUID magnetometry. The half-filled f-electron valence shell of GdIII ion allows an accurate study of magnetic coupling through fitting of the dc magnetic susceptibility data to a spin-only Hamiltonian, affording values of J = -0.0242 cm-1 and g = 2.0192. The operative superexchange coupling mechanism was confirmed through broken-symmetry density functional theory calculations, which additionally provide insight into the spectral analysis of 1.