Authors: Christopher G. T. Price | Arpan Mondal | James P. Durrant | Jinkui Tang | Richard A. Layfield
Source: Inorganic Chemistry (article, 2023-06-14)
Field: Materials Science — Electronic, Optical and Magnetic Materials

Structural and Magnetization Dynamics of Borohydride-Bridged Rare-Earth Metallocenium Cations The structure and magnetic properties of the bimetallic borohydride-bridged dysprosocenium compound [{(η<sup>5</sup>-Cp<sup>ttt</sup>)(η<sup>5</sup>-Cp<sup>Me4t</sup>)Dy}<sub>2</sub>(μ:κ<sup>2</sup>:κ<sup>2</sup>-BH<sub>4</sub>)]<sup>+</sup>[B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]<sup>-</sup> ([<b>3</b><sub><b>Dy</b></sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>]) are reported along with the solution-phase dynamics of the isostructural yttrium and lutetium analogues (Cp<sup>ttt</sup> is 1,2,4-tri(<i>tert</i>-butyl)cyclopentadienyl, Cp<sup>Me4t</sup> is tetramethyl(<i>tert</i>-butyl)cyclopentadienyl). The synthesis of [<b>3</b><sub><b>M</b></sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] was accomplished in the 2:1 stoichiometric reactions of [(η<sup>5</sup>-Cp<sup>ttt</sup>)(η<sup>5</sup>-Cp<sup>Me4t</sup>)Dy(BH<sub>4</sub>)] (<b>2</b><sub><b>M</b></sub>) with [CPh<sub>3</sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], with the metallocenes <b>2</b><sub><b>M</b></sub> obtained from reactions of the half-sandwich complexes [(η<sup>5</sup>-Cp<sup>ttt</sup>)M(BH<sub>4</sub>)<sub>2</sub>(THF)] (<b>1</b><sub><b>M</b></sub>) (M = Y, Dy, Lu) with NaCp<sup>Me4t</sup>. Crystallographic studies show significant lengthening of the M···B distance on moving through the series <b>1</b><sub><b>M</b></sub>, <b>2</b><sub><b>M</b></sub>, and <b>3</b><sub><b>M</b></sub>, with essentially linear {M···B···M} bridges in <b>3</b><sub><b>M</b></sub>. Multinuclear NMR spectroscopy indicates restricted rotation of the Cp<sup>ttt</sup> ligands in <b>3</b><sub><b>Y</b></sub> and <b>3</b><sub><b>Lu</b></sub> in solution. The single-molecule magnet (SMM) properties of [<b>3</b><sub><b>M</b></sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] are characterized by Raman and Orbach processes, with an effective barrier of 533(18) cm<sup>-1</sup> and relaxation via the second-excited Kramers doublet. Although quantum tunneling of the magnetization (QTM) was not observed for [<b>3</b><sub><b>M</b></sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], it was, surprisingly, found in its magnetically dilute version, which has a very similar barrier of <i>U</i><sub>eff</sub> = 499(21) cm<sup>-1</sup>. Consistent with this observation, slightly wider openings of the magnetic hysteresis loop at 2 K are found for [<b>3</b><sub><b>M</b></sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] but not for the diluted analogue. The dynamic magnetic properties of the dysprosium SMMs and the role of exchange interactions in <b>3</b><sub><b>Dy</b></sub> are interpreted with the aid of multireference ab initio calculations. Chemistry ; Rare earth ; Borohydride ; Magnetization ; Crystallography ; Inorganic chemistry ; Mineralogy ; Organic chemistry ; Magnetic field Magnetism in coordination complexes ; Lanthanide and Transition Metal Complexes ; Advanced NMR Techniques and Applications