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

Two unusual two-dimensional coordination networks, namely, {[Gd(hfac)₃]₃(NIT-Ph-3,5-bIm)₂}·2.25C₆H₁₄ (1) and {[Dy(hfac)₃]₃(NIT-Ph-3,5-bIm)₂}·2.5C₆H₁₄ (2), were obtained using 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 served as a tridentate linker, binding three Ln^III ions via one NO group and two imidazole units, resulting in unique zig-zag-shaped 2D networks with KIa topology. These coordination networks underwent a single-crystal-to-single-crystal transformation from a low-temperature non-centrosymmetric space group (P2₁) to a room-temperature centrosymmetric space group (P2₁/c) accompanied by the loss of helicity in chiral chains and an order-disorder transition of the Ln^III ions. Direct-current magnetic susceptibility studies of the Gd derivative showed dominant ferromagnetic Gd-NO exchange. Dynamic magnetic studies of the Dy analogue displayed temperature-dependent nonzero out-of-phase signals, indicating slow magnetic relaxation behavior.