The differential magnetic relaxation behaviours of slightly distorted triangular dodecahedral dysprosium analogues in a type of cyano-bridged 3d–4f zig-zag chain compounds

Abstract

A class of cyano-bridged 3d–4f zig-zag chain compounds, {RE[TM(CN)₆] (PNO)₂(H₂O)₄}·(H₂O) {RE = Y^III, TM = [Fe^III]_LS (1); RE = Dy^III, TM = [Fe^III]_LS (2), Co^III (3)}, have been synthesized and characterized by single-crystal X-ray diffraction. The rare earth ions in these compounds are situated in a slightly distorted triangular dodecahedral (D_2d) coordination environment. The magnetic properties of compounds 1–3 have been comparatively studied in detail. Under a zero dc field, the temperature dependence of ac susceptibility measurements for YFe (1) indicates the absence of magnetic relaxation stemming from the single anisotropic [Fe^III]_LS ion. The dysprosium analogue DyFe (2) shows only magnetic relaxation behavior with a prominent QTM effect, while DyCo (3) exhibits SIM properties not completely covered by QTM, with an extracted energy barrier of 73 K under a zero dc field. The ab initio calculations indicate that both compounds 2 and 3 are SMMs with well-behaved magnetic relaxation properties primarily from the individual Dy^III ion. Therefore, the different magnetic behaviors exhibited by compound 2 compared to 3 may be ascribed to the stronger QTM effect caused by the extra weak interaction of [Fe^III]_LS ions in 2 as a fluctuating transverse field around the Dy^III ion. The QTM effect for both 2 and 3 is suppressed under an applied dc field with an effective energy barrier of 134 and 150 K, respectively. Compared with compound 2, the higher extracted U_eff/k_B and χ′′(T) peak temperature for 3 should be further attributed to its slightly higher single-ion axiality as calculated and the elimination of the transverse field from the [Fe^III]_LS ion.