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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.)

The potassium cyclobutadienyl [K 2 {η 4 -C 4 (SiMe 3 ) 4 }] (1) reacts with MCl 3 (THF) 3.5 (M=Y, Dy) to give the first rare-earth cyclobutadienyl complexes, that is, the complex anions [M{η 4 -C 4 (SiMe 3 ) 4 }{η 4 -C 4 (SiMe 3 ) 3 -κ-(CH 2 SiMe 2 }] 2- , (2 M ), as their dipotassium salts. The tuck-in alkyl ligand in 2 M is thought to form through deprotonation of the "squarocene" complexes [M{η 4 -C 4 (SiMe 3 ) 4 } 2 ] - by 1. Complex 2 Dy is a single-molecule magnet, but with prominent quantum tunneling. An anisotropy barrier of 323(22) cm -1 was determined for 2 Dy in an applied field of 1 kOe, and magnetic hysteresis loops were observed up to 7 K., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Abstraction of a chloride ligand from the dysprosium metallocene [(Cp ttt ) 2 DyCl] (1 Dy Cp ttt =1,2,4-tri(tert-butyl)cyclopentadienide) by the triethylsilylium cation produces the first base-free rare-earth metallocenium cation [(Cp ttt ) 2 Dy] + (2 Dy ) as a salt of the non-coordinating [B(C 6 F 5 ) 4 ] - anion. Magnetic measurements reveal that [2 Dy ][B(C 6 F 5 ) 4 ] is an SMM with a record anisotropy barrier up to 1277 cm -1 (1837 K) in zero field and a record magnetic blocking temperature of 60 K, including hysteresis with coercivity. The exceptional magnetic axiality of 2 Dy is further highlighted by computational studies, which reveal this system to be the first lanthanide SMM in which all low-lying Kramers doublets correspond to a well-defined M J value, with no significant mixing even in the higher doublets., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Reducing hexaazatrinaphthylene (HAN) with potassium in the presence of 18-c-6 produces [{K(18-c-6)}HAN], which contains the S=1/2 radical [HAN](.-) . The [HAN](.-) radical can be transferred to the cobalt(II) amide [Co{N(SiMe3 )2 }2 ], forming [K(18-c-6)][(HAN){Co(N'')2 }3 ]; magnetic measurements on this compound reveal an S=4 spin system with strong cobalt-ligand antiferromagnetic exchange and J≈-290 cm(-1) (-2 J formalism). In contrast, the Co(II) centres in the unreduced analogue [(HAN){Co(N'')2 }3 ] are weakly coupled (J≈-4.4 cm(-1) ). The finding that [HAN](.-) can be synthesized as a stable salt and transferred to cobalt introduces potential new routes to magnetic materials based on strongly coupled, triangular HAN building blocks., (© 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

In the presence of stoichiometric or catalytic amounts of [M{N(SiMe3 )2 }2 ] (M=Fe, Co), N-heterocyclic carbenes (NHCs) react with primary phosphines to give a series of carbene phosphinidenes of the type (NHC)⋅PAr. The formation of (IMe4 )⋅PMes (Mes=mesityl) is also catalyzed by the phosphinidene-bridged complex [(IMe4 )2 Fe(μ-PMes)]2 , which provides evidence for metal-catalyzed phosphinidene transfer., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)