Regulating Magnetic Relaxation of Radical-Ln-Based Chains Involving Multidentate Nitronyl Nitroxides through Varying Spin Arrangement Motif and Local Symmetry around Ln Centers

Abstract

The reaction of a newly designed multidentate nitronyl nitroxide radical NIT-Ph-3,5-b-3PyO with Ln(hfac)3·2H2O led to two new 2p–4f chains {[Ln(hfac)3]2(NIT-Ph-3,5-b-3PyO)}n (LnIII = GdIII 1, DyIII 2; NIT-Ph-3,5-b-3PyO = 2-[3,5-bis(3-pyridinyloxy)-phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide). When the Cu(hfac)2 was introduced in the above reaction, the hetero-tri-spin 2p–3d–4f chains {Ln(hfac)3[Cu(hfac)2]2(NIT-Ph-3,5-b-3PyO)2}n (LnIII = GdIII 3, DyIII 4) were obtained. The crystal data show that the {4f–2p–4f} spin motif is involved in 2p–4f chains, while the {2p–4f–2p} arrangement of spins around Ln centers is found in 2p–3d–4f chains. Direct-current magnetic susceptibility investigations show that both Gd chains display the dominant GdIII–NO ferromagnetic exchanges. Alternating-current susceptibilities prove the existence of the field-induced slow magnetic relaxation behavior in 2, while no nonzero χ″ signals are observed for 4, which could be attributed to the distinct magnetic exchanges originated from different spin arrangements (4f–2p–4f versus 2p–4f–2p) and the different coordination geometry around the DyIII ions for two Dy derivatives (D4d of Dy1 center in 2 and D2d in 4).