Spin Helicity in Chiral Lanthanide Chains

Abstract

We report here the determination of the helical spin structure of three Ln-based chiral chains of the formula [Ln(Hnic)(nic)(NO)] (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 Dy 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 Dy ion.

Cantilever torque magnetometry on coordination compounds: from theory to experiments

“…These conclusions were supported by standard magnetization measurements performed on oriented single crystals. Moreover, only Dy 6 derivative shows slow relaxation of the magnetization, as expected for a strongly axial compound [100]. As a final remark, we notice that the anisotropy of these derivatives is opposite compared to the LnTRENSAL family, remarking the easy tunability of magnetic anisotropy by chemical design.…”

“…A second example of intramolecular noncollinearity studied via CTM is the spin helicity in chiral chains [100]. The structure of the studied complex, chemically described in Refs.…”

Hard X-ray magnetochiral dichroism in a paramagnetic molecular 4f complex

“…The intensity of the normalized XNCD is approaching 1%, which is signicantly larger than previously reported values for XNCD at the L-edge of chiral Ln complexes. 37,70 XNCD measures the mixing of electronic states with opposite parity in the ground state, which is at the origin of the non-linear optical properties of chiral systems. In the case of an L 3 absorption edge, the selection rules for theÊ 1 $Ê 2 interference term 39 allow only transitions to the intra-atomic (d, p) and (d, f) hybridized states.…”

Enantiomeric resolution and X-ray optical activity of a tricobalt extended metal atom chain

“… 6 Since then, a few other molecular systems have been studied, such as [Co(en) 3 Cl 3 ]·NaCl·6H 2 O and the 1D coordination polymers [Co(hfac) 2 NITPhOMe] ∞ and [Ln(Hnic)(nic) 2 (NO 3 )] ∞ . 7 Even though it is still in its infancy, this spectroscopy appears to be a very sensitive probe of the chiral molecular environment around the absorbing atom. An important aspect of XNCD originates from a not well-known electric dipole-electric quadrupole mechanism that exists only in oriented samples.…”