Search

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

Replacing a monoanionic cyclopentadienyl (Cp) ligand in dysprosium single-molecule magnets (SMMs) with a dianionic cyclobutadienyl (Cb) ligand in the sandwich complexes [(η 4 -Cb'''')Dy(η 5 -C 5 Me 4 t Bu)(BH 4 )] - (1), [(η 4 -Cb'''')Dy(η 8 -Pn † )K(THF)] (2) and [(η 4 -Cb'''')Dy(η 8 -Pn † )] - (3) leads to larger energy barriers to magnetization reversal (Cb''''=C 4 (SiMe 3 ) 4 , Pn † =1,4-di(tri-isopropylsilyl)pentalenyl). Short distances to the Cb'''' ligands and longer distances to the Cp ligands in 1-3 are consistent with the crystal field splitting being dominated by the former. Theoretical analysis shows that the magnetic axes in the ground Kramers doublets of 1-3 are oriented towards the Cb'''' ligands. The theoretical axiality parameter and the relative axiality parameter Z and Z rel are introduced to facilitate comparisons of the SMM performance of 1-3 with a benchmark SMM. Increases in Z and Z rel when Cb''' replaces Cp signposts a route to SMMs with properties that could surpass leading systems., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Intact transfer of the cyclobutadienyl ligand [C 4 (SiMe 3 ) 4 ] 2- to yttrium and dysprosium (M) produces the half-sandwich complexes [M{η 4 -C 4 (SiMe 3 ) 4 }(BH 4 ) 2 (THF)] - as coordination polymers with bridging sodium or potassium ions. The dysprosium versions are single-molecule magnets (SMMs) with energy barriers of 371(7) and 357(4) cm -1 , respectively. The pristine cyclobutadienyl ligands provide a strong axial crystal field that enhances the SMM properties relative to related cyclopentadienyl compounds.

Previous employment of the ligands 2-methoxy-6-[(methylimino)methyl]phenol (L 1 H) and 2-methoxy-6-[(phenylimino)methyl]phenol (L 2 H) has resulted in the self-assembly of pseudo metallocalix[6]arene complexes of general formulae: [M 7 (μ 3 -OH) 6 (L x ) 6 ](NO 3 ) y (M = Ni(ii), x = 1, y = 2 (1) and Co(ii/iii), x = 2, y = 3 (2)). Extrapolating upon this work, we report the coordination chemistry of ligands 2-methoxy-6-{[(2-methoxyphenyl)imino]methyl}phenol (L 3 H), 2-[(benzylimino)methyl]-6-methoxyphenol (L 4 H), 2-[(benzylamino)methyl]-6-methoxyphenol (L 5 H) and 2-[(benzylamino)methyl]-4-bromo-6-methoxyphenol (L 6 H), whose structures are modifications of ligands L 1-2 H. These ligands are employed in the synthesis and characterisation of the dimetallic complex [Ni(ii) 2 (L 3 ) 3 (H 2 O)](NO 3 )·2H 2 O·3MeOH (3); the monometallic complexes [Ni(ii)(L 4 ) 2 ] (4) and [Co(iii)(L 4 ) 3 ]·H 2 O·MeOH (5a); and the tetranuclear pseudo metallocalix[4]arene complexes: [(NO 3 )⊂Co(ii) 4 (μ 3 -OH) 2 (L 5 ) 4 (H 2 O) 2 ](NO 3 )·H 2 O (6), [(NO 3 )⊂Ni(ii) 4 (μ 3 -OH) 2 (L 5 ) 4 (H 2 O) 2 ](NO 3 )·H 2 O (7) and [Ni(ii) 4 (μ 3 -OH) 2 (L 6 ) 4 (NO 3 ) 2 ]·MeCN (8). The tetrametallic 'butterfly' core topologies in 6-8 are discussed with respect to their structural and topological relationship with their heptanuclear [M 7 ] (M = Co(ii), Ni(ii)) pseudo metallocalix[6]arene ancestors (1 and 2).