Photomagnetic Switching of Heterometallic Complexes [M(dmf)₄(H₂O)₃(μ‐CN)Fe(CN)₅]⋅H₂O (M=Nd, La, Gd, Y) Analyzed by Single‐Crystal X‐ray Diffraction and Ab Initio Theory

Abstract

Single-crystal X-ray diffraction measurements have been carried out on [Nd(dmf)(4)(H(2)O)(3)(mu-CN)Fe(CN)(5)].H(2)O (1; dmf=dimethylformamide), [Nd(dmf)(4)(H(2)O)(3)(mu-CN)Co(CN)(5)].H(2)O (2), [La(dmf)(4)(H(2)O)(3)(mu-CN)Fe(CN)(5)].H(2)O (3), [Gd(dmf)(4)(H(2)O)(3)(mu-CN)Fe(CN)(5)].H(2)O (4), and [Y(dmf)(4)(H(2)O)(3)(mu-CN)Fe(CN)(5)].H(2)O (5), at 15(2) K with and without UV illumination of the crystals. Significant changes in unit-cell parameters were observed for all the iron-containing complexes, whereas 2 showed no response to UV illumination. Photoexcited crystal structures have been determined for 1, 3, and 4 based on refinements of two-conformer models, and excited-state occupancies of 78.6(1), 84(6), and 86.6(7)% were reached, respectively. Significant bond-length changes were observed for the Fe-ligand bonds (up to 0.19 A), the cyano bonds (up to 0.09 A), and the lanthanide-ligand bonds (up to 0.10 A). Ab initio theoretical calculations were carried out for the experimental ground-state geometry of 1 to understand the electronic structure changes upon UV illumination. The calculations suggest that UV illumination gives a charge transfer from the cyano groups on the iron atom to the lanthanide ion moiety, {Nd(dmf)(4)(H(2)O)(3)}, with a distance of approximately 6 A from the iron atom. The charge transfer is accompanied by a reorganization of the spin state on the {Fe(CN)(6)} complex, and a change in geometry that produces a metastable charge-transfer state with an increased number of unpaired electrons, thus accounting for the observed photomagnetic effect.

A photo-induced excited state structure of a hetero-bimetallic ionic pair complex, Nd(DMA)4(H2O)4Fe(CN)6·3H2O, analyzed by single crystal X-ray diffraction

“…Accompanying theoretical analysis of NdFeDMF suggests that charge transfer from the cyanide ligands to the lanthanide atoms can explain the photomagnetic effect in good agreement with the observed structural changes. 20 Since all isostructural Fe compounds show a similar pattern of bond length changes, the same mechanism is expected to be responsible for the excitation of all the iron complexes and these complexes are therefore expected to show a similar photomagnetic behavior to that observed for NdFeDMF.…”

“…This was also observed in the related excited state structures of NdFeDMF, LaFeDMF, and GdFeDMF, where the exact same trends in Fe-ligand and cyanide bonds were found. 19,20 Significant changes are also observed around the Nd atom with an increase of 4% in the Nd-O3 bond. It is striking that this latter bond is exactly the Nd-O bond that points towards the Fe-moiety, and the O3-N6 distance changes from B2.75 A in the ground state to B2.71 A ˚in the excited state.…”

“…Photo-crystallographic studies have recently been reported 19,20 focussing on the structural consequences of the electronic transition resulting in the changed magnetic properties in the family of compounds related to the original 3d-4f cyanidebridged hetero-bimetallic complex with neodymium and iron, (Nd(DMF) 4 (H 2 O) 3 (m-CN)Fe(CN) 5 ÁH 2 O (DMF = dimethylformamide) (NdFeDMF) which exhibit a large increase (45%) of the magnetisation upon illumination with UV-light at low temperatures (T o B50 K). 21 The largest structural modifications were found in the Fe(CN) 6 -part of the structure, which indicated that this plays an important role in the excitation process.…”

Phase diagrams and critical behaviours of the mixed spin-5/2 and spin-7/2 Ising system

“…The generalization of the BC model for spin values larger than 1 has been investigated in detail through different approaches [4][5][6][7][8][9][10] (see [11] and references therein). Extension of the model to study two-sublattice mixed-spin systems with unequal magnetic moments or multiple layered structures of different magnetic substances has been a field of growing interest in recent years [12][13][14] due to their practical utilities such as in thermomagnetic recording, electronic and magneto-optical readout devices [15][16][17]. Indeed, many novel phenomena not observed in single-spin Ising systems were displayed, such as: giant magnetoresistance [18], surface magnetic anisotropy [19], etc.…”

Critical behavior of low dimensional magnetic systems

“…f -block lanthanide ions having large anisotropic magnetic moments yield hard magnets and long-range magnetic order in solids [4,[9][10][11]. Some of cyanobridged 4f -3d assemblies also exhibit field-induced magnetic relaxation [10], cooling-rate dependent magnetism [12], photo-induced magnetization [13], and humidity response [14] . Interactions between the ions/molecules determine the electronic and magnetic properties as well as dimensionality of the assembly.…”