Spin Helicity in Chiral Lanthanide Chains

We report here the
determination of the helical spin structure of three Ln-based chiral
chains of the formula [Ln­(Hnic)­(nic)2(NO3)]n (Hnic = nicotinic acid; Ln = Tb, Dy, and
Er) by means of cantilever torque magnetometry. While the Dy and Er
derivatives are strongly axial (easy-axis and easy-plane anisotropy,
respectively), the Tb derivative is characterized by a remarkable
rhombicity. In agreement with these findings, alternating-current
susceptibility reveals slow magnetic relaxation only in the Dy derivative.
Dilution of DyIII ions in the diamagnetic Y-based analogue
shows that the weak ferromagnetic intrachain interactions do not contribute
significantly to the energy barrier for the reversal of magnetization,
which is better described as a single-ion process. Single crystals
of the two enantiomers of the Dy derivative have also been investigated
using hard X-ray synchrotron radiation at the L-edge of the metal
revealing optical activity although with negligible involvement of
the 4f electrons of the DyIII ion.

本文报道了通过悬臂转矩磁强计法，对三种通式为[Ln(Hnic)(nic)₂(NO₃)]ₙ的镧系手性链状配合物的螺旋自旋结构进行的测定（其中Hnic代表烟酸，Ln为铽(Tb)、镝(Dy)和铒(Er)）。其中，镝和铒衍生物分别呈现强轴向各向异性（分别为易轴型和易平面型各向异性），而铽衍生物则表现出显著的菱面各向异性。与上述结果一致，交流磁化率测试仅在镝衍生物中观测到慢磁弛豫现象。将Dy³+离子掺杂至抗磁性钇基同构配合物中后发现，微弱的铁磁链内相互作用对磁化反转能垒的贡献并不显著，该过程更符合单离子弛豫机制。此外，研究人员还利用针对金属L边的硬X射线同步辐射技术，对镝衍生物的两种对映异构体单晶开展了表征，结果显示其具有光学活性，但镝(III)离子的4f电子对该活性的贡献可忽略不计。