Unusual zig-zag-shape Ln-radical coordination networks derived from a nitronyl nitroxide with two imidazole groups: single-crystal to single-crystal transformations and magnetic properties

Abstract

Two unusual two-dimensional coordination networks, namely, {[Gd(hfac)₃]₃(NITPh-3,5-bIm)₂}‧2.25C₆H₁₄ (1) and {[Dy(hfac)₃]₃(NITPh-3,5-bIm)₂}‧2.5 C₆H₁₄ (2), have been achieved utilizing the multidentate nitronyl nitroxide ligand containing two additional imidazole groups NIT-Ph-3,5-bIm (NIT-Ph-3,5-bIm = 2-[3,5-bis(1-imidazole)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; hfac = hexafluoroacetylacetonate). In these Ln-radical complexes, the multidentate nitronyl nitroxide radical ligand serves as a tridentate linker to bind three LnIII ions via one NO group and two imidazole units of the radical, resulting in unique zig-zag-shape 2D networks with KIa topology. These coordination networks can undergo a single-crystal to single-crystal transformation from low-temperature non-centrosymmetric space group (P2₁) to room temperature centrosymmetric space group (P2₁/c) accompanied by the helicity loss of chiral chains and an order−disorder transition of Ln^III ions. Direct-current magnetic susceptibility studies of the Gd derivative shows dominant ferromagnetic Gd-NO exchange. Dynamic magnetic studies of Dy analogs display temperature-dependent nonzero out of out-of-phase signals indicating slow magnetic relaxation behavior.