Closing the Circle of the Lanthanide-Murexide Series: Single-Molecule Magnet Behavior and Near-Infrared Emission of the NdIII Derivative

Covalency versus magnetic axiality in Nd molecular magnets: Nd-photoluminescence, strong ligand-field, and unprecedented nephelauxetic effect in fullerenes NdM2N@C80 (M = Sc, Lu, Y)

Nd-based nitride clusterfullerenes NdM2N@C80 with rare-earth metals of different sizes (M = Sc, Y, Lu) were synthesized to elucidate the influence of the cluster composition, shape and internal strain on the structural and magnetic properties. Single crystal X-ray diffraction revealed a very short Nd-N bond length in NdSc2N@C80. For Lu and Y analogs, the further shortening of the Nd-N bond and pyramidalization of the NdM2N cluster are predicted by DFT calculations as a result of the increased cluster size and a strain caused by the limited size of the fullerene cage. The short distance between Nd and nitride ions leads to a very large ligand-field splitting of Nd3+ of 1100-1200 cm-1, while the variation of the NdM2N cluster composition and concomitant internal strain results in the noticeable modulation of the splitting, which could be directly assessed from the well-resolved fine structure in the Nd-based photoluminescence spectra of NdM2N@C80 clusterfullerenes. Photoluminescence measurements also revealed an unprecedentedly strong nephelauxetic effect, pointing to a high degree of covalency. The latter appears detrimental to the magnetic axiality despite the strong ligand field. As a result, the ground magnetic state has considerable transversal components of the pseudospin g-tensor, and the slow magnetic relaxation of NdSc2N@C80 could be observed by AC magnetometry only in the presence of a magnetic field. A combination of the well-resolved magneto-optical states and slow relaxation of magnetization suggests that Nd clusterfullerenes can be useful building blocks for magneto-photonic quantum technologies.

Oxalate-bridging NdIII-based arsenotungstate with multifunctional NIR-luminescence and magnetic properties

Oxalate bridged Nd-based arsenotungstate, K₁₄Na₆H₄[{(As₂W₁₉O₆₇(H₂O))Nd(H₂O)₂}₂(C₂O₄)]·64H₂O (1), was obtained from the reaction of K₁₄[As₂W₁₉O₆₇(H₂O)], oxalic acid, and NdCl₃·6H₂O in mildly acidic aqueous solution. The polyanion exhibits a dimeric structure in which the fully deprotonated oxalate ligands bridge two Nd^III cations and the arsenotungstate anions act as blocking ligands. The photoluminescence (PL) spectrum of 1 shows the characteristic emission peak of Nd^III in the near-infrared (NIR) region. However, the O → W charge-transfer transitions of arsenotungstate cannot effectively sensitize the emission of Nd^III cations as confirmed by the emission spectrum, due to the mismatch of the energy gap between ³T_1u → ¹A_1g (21.57 × 10³ cm^-1) of arsenotungstate components and ⁴F_3/2 → ⁴I_9/2 (11.43 × 10³ cm^-1) of Nd^III cations. Magnetic studies of 1 demonstrate its field-induced single-molecule magnet (SMM) behavior. Direct current magnetic susceptibility studies imply the weak ferromagnetic couplings present between the two neighboring Nd^III cations. In addition, the synergy between the coordination configuration of Nd^III cations and the intramolecular magnetic interaction was discussed.

Slow magnetic relaxation and luminescence properties in neodymium(iii)-4,4,4-trifluoro-1-(2-naphthyl)butane-1,3-dionato complexes incorporating bipyridyl ligands

A new series of eight-coordinated Nd(iii) complexes derived from 4,4,4-trifluoro-1-(naphthalen-2-yl)butane-1,3-dionate and bi-pyridyl ligands revealed multifunctional molecular materials as photoluminescent single-molecule magnets (SMMs).

High relaxation barrier in neodymium furoate-based field-induced SMMs

Two new neodymium molecular magnets of formula {[Nd(α-fur)₃(H₂O)₂]·DMF}_n (1) and {[Nd_0.065La_0.935(α-fur)₃(H₂O)₂]}_n (2), α-fur = C₄H₃OCOO, have been synthesized. In (1) the furoate ligands, in bidentate bridging mode, consolidate zig-zag chains running along the a-direction. Compound (2) is a magnetically diluted complex of a polymeric chain along the b-axis. Heat capacity, dc magnetization and ac susceptibility measurements have been performed from 1.8 K up to room temperature. Ab initio calculations yielded the gyromagnetic factors g_x* = 0.52, g_y* = 1.03, g_z* = 4.41 for (1) and g_x* = 1.35, g_y* = 1.98, g_z* = 3.88 for (2), and predicted energy gaps of Δ/k_B = 125.5 K (1) and Δ/k_B = 58.8 K (2). Heat capacity and magnetometry measurements agree with these predictions, and confirm the non-negligible transversal anisotropy of the Kramers doublet ground state. A weak intrachain antiferromagnetic interaction J'/k_B = -3.15 × 10^-3 K was found for (1). No slow relaxation is observed at H = 0, attributed to the sizable transverse anisotropy component, and/or dipolar or exchange interactions enhancing the quantum tunnelling probability. Under an external applied field as small as 80 Oe, two slow relaxation processes appear: above 3 K the first relaxation mechanism is associated to a combination of Orbach process, with a sizeable activation energy U/k_B = 121 K at 1.2 kOe for (1), Raman and direct processes; the second, slowest relaxation mechanism is associated to a direct process, affected by phonon-bottleneck effect. For complex (2) a smaller U/k_B = 61 K at 1.2 kOe is found, together with larger g*-transversal terms, and the low-frequency process is quenched. The reported complexes represent rare polymeric Nd single-ion magnets exhibiting high activation energies among the scarce Nd(iii) family.