Borohydride as Magnetic Superexchange Pathway in Late Lanthanide Borohydrides

Abstract

The magnetic characteristics of a series of borohydride‐based systems, including binary α‐/β‐Ln(BH4)3 phases (Ln = Gd, Tb, Dy, Ho, Er, and Tm) with direct Ln–HBH–Ln bridges and selected mixed‐metal systems, LiYb(BH4)4, NaYb(BH4)4, KHo(BH4)4, RbTm(BH4)4, with isolated Ln3+ ions embedded in [Ln(BH4)4]– anions are described for the first time using SQUID magnetometry and DFT+U calculations. Crystal field effects as well as the nature and strength of magnetic superexchange interactions via BH4– ligands are established based on a ligand field theory approach. We find Auzel's scalar crystal field strength parameter (Nv, the weighted quadratic mean of the ligand field parameters Bkq) for these systems to be substantial, in particular for α‐Ho(BH4)3, indicating a significant covalent component in the Ho···H bonding. The BH4– anion is capable of mediating both weakly ferro‐ or antiferromagnetic superexchange. Quantum mechanical DFT+U calculations, even when including spin‐orbit coupling effects, do not reliably describe the sign and the size of the magnetic superexchange constants in these systems.

Inclusion of Neon into an Yttrium Borohydride Structure at Elevated Pressure – An Experimental and Theoretical Study

“…[ 1–3 ] This has been manifested in significant growth of the number of known solvent‐free borohydrides, strongly supported by the development of the synthetic methods, in parallel with the structural identification of the products. [ 4–11 ] Besides the storage of hydrogen and their traditional use in reduction processes, borohydrides are studied in the context of solid‐state ion conduction, [ 12–15 ] magnetic and luminescent properties, [ 16–19 ] or as porous materials, capable for loading of guest molecules. [ 20 ]…”

Synthesis, Polymorphism and Thermal Decomposition Process of (n-C4H9)4NRE(BH4)4 for RE = Ho, Tm and Yb

“…The observed absorption bands are also similar to those reported for the related derivatives of yttrium borohydride [ 57 ], where the DFT calculations for [(CH 3 ) 4 N][Y(BH 4 ) 4 ] confirmed 12-fold coordination of Y 3+ in the [Y(BH 4 ) 4 ] − complex. [ RE (BH 4 ) 4 ] − complex anion in such geometry is found in numerous RE 3 + borohydrides, also in all the known mixed-cation derivatives of RE (BH 4 ) 3 , RE = Ho, Tm, Yb, namely K[Ho(BH 4 ) 4 ] [ 38 ], Rb[Tm(BH 4 ) 4 ] [ 23 ], [Ph 4 P][Tm(BH 4 ) 4 ] [ 58 ], and M [Yb(BH 4 ) 4 ], M = Li [ 11 ], Na, K [ 39 ], as well as in the related compounds of Sc and Y [ 34 , 57 , 59 , 60 ].…”

“…Although most of studies focus on examining of the process of hydrogen release, several reports indicate at least some degree of reversibility of such systems, which is crucial for their application, e.g., [ 10 ]. Various borohydrides can also serve as precursors of metal borides [ 11 , 12 , 13 , 14 , 15 ] or boron nitride [ 16 ], and some of them have been explored as prospective solid-state electrolytes in Li + batteries [ 17 , 18 , 19 , 20 , 21 ] or luminescent and magnetic materials [ 22 , 23 ], while the borohydride complexes of rare-earth elements were also tested for organic catalysis [ 24 , 25 ].…”

“…These compounds can be conveniently prepared and are thermally stable, therefore they may serve as precursors towards new mixed-cation borohydrides of the RE mentioned above, which would be performed according to Equation (1). Notably, only a limited number of inorganic, solvent-free borohydrides of RE = Ho, Tm, and Yb is currently known, including KHo(BH 4 ) 4 [ 38 ], RbTm(BH 4 ) 4 [ 23 ] and M Yb(BH 4 ) 4 , where M = Li [ 11 ], Na, K [ 39 ]. It is worth to mention that although a few (n‑C 4 H 9 )N RE (BH 4 ) 4 compounds have been reported before [ 40 ], only two of them, RE = Y [ 41 ] and Sc [ 42 ], were fully identified on a basis of their crystal structures.…”

Fulvalene as a platform for the synthesis of a dimetallic dysprosocenium single-molecule magnet

“… 42 This proposal is consistent with a recent study of magnetic exchange in [Ln(BH 4 ) 3 ] (Ln = Gd–Tm), in which it was found that {HBH} bridges between the metal centres allow antiferro- or ferro-magnetic exchange, albeit with very small coupling constants. 43 …”