Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(CpiPr5)Dy(Cp*)]+ (CpiPr5, penta-iso-propylcyclopentadienyl; Cp*, pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures. An effective energy barrier to reversal of the magnetization of Ueff = 1541 wave number is also measured. The magnetic blocking temperature of TB = 80 kelvin for this cation overcomes an essential barrier toward the development of nanomagnet devices that function at practical temperatures.

Abstraction of a chloride ligand from the dysprosium metallocene [(Cpttt)2DyCl] (1Dy Cpttt=1,2,4‐tri(tert‐butyl)cyclopentadienide) by the triethylsilylium cation produces the first base‐free rare‐earth metallocenium cation [(Cpttt)2Dy]+ (2Dy) as a salt of the non‐coordinating [B(C6F5)4]− anion. Magnetic measurements reveal that [2Dy][B(C6F5)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 2Dy 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 MJ value, with no significant mixing even in the higher doublets.

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Solid-state auride salts featuring the negatively charged Auion are known to be stable in the presence of alkali metal counter-ions. While such electron-rich species might be expected to be nucleophilic (cf. I -), their instability in solution means that this has not been verified experimentally. Here we report the two-coordinate gold complex (NON)AlAuP t Bu3 (3, NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) synthesised by the reaction of the potassium aluminyl complex [K{Al(NON)}]2 (1) with t Bu3PAuI, and which features a strongly polarized bond, Au(d-)-Al(d+). 3 has been studied computationally, with QTAIM charge analysis implying a charge at gold (-0.82) which is in line with the relative electronegativities of the two metals (Au: 2.54; Al: 1.61 on the Pauling scale). Consistently, 3 is found to act as an unprecedented nucleophilic source of gold, reacting with diisopropylcarbodiimide and CO2 to give the Au-C bonded insertion products (NON)Al(X2C)AuP t Bu3 (X = N i Pr, 4; X = O, 5).Transition elements are known to be able to access multiple oxidation states 1 , a property which underpins widespread application in fields such as small molecule activation and catalysis 2,3 . The vast majority of transition metal complexes however, feature cationic metals in positive oxidation states, ligated by neutral or anionic donors 1,4 . Systems featuring formal negative oxidation states, such as the tetracarbonylferrate 5 or bis(benzene)vanadium 6 anions are much less common, and usually require strong p-acceptor ligands, most frequently CO 7 . In this regard, gold is unique, being the only transition metal to give rise to a stable "naked" monoanion (Au -, auride) in the condensed phase 8 . In part, this is due to relativistic effects which contract the 6s orbital significantly, resulting in an electron affinity of 2.30 eV, the highest of any transition metal 9,10 .This value is more comparable to those of the chalcogens (e.g. S: 2.08 eV; Se: 2.02 eV) than to the lighter group 11 congeners (Cu: 1.23 eV; Ag 1.30 eV) 10 . The 12-electron auride anion is typically generated by the reduction of metallic gold with alkali metals, to give salts such as CsAu and RbAu 11,12 ; the solution chemistry of these salts, however, is restricted to liquid ammonia 13,14 .Reduction of organometallic gold compounds to give systems in low oxidation states (i.e. zero or below) has been attempted, but with limited success [15][16][17][18][19][20] . Thermodynamics typically drive the aggregation of molecular Au(0) systems to clusters of colloidal gold [15][16][17][18] . Recently however, electron-rich gold complexes have been reported by Bertrand and co-workers, by making use of strongly p-accepting cyclic(alkyl)(amino)carbenes (CAAC) ligands (I and II, Figure 1) 19 . In addition, a four-coordinate molecular 'boroauride' was reported by Harman and co-workers last year in which the gold centre is stabilized by a diboraanthracene-based scaffold (III, Figure 1) 20 .Notwithstanding these examples, and even though Auions...

Abstraction of a chloride ligand from the dysprosium metallocene [(Cpttt)2DyCl] (1Dy Cpttt=1,2,4‐tri(tert‐butyl)cyclopentadienide) by the triethylsilylium cation produces the first base‐free rare‐earth metallocenium cation [(Cpttt)2Dy]+ (2Dy) as a salt of the non‐coordinating [B(C6F5)4]− anion. Magnetic measurements reveal that [2Dy][B(C6F5)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 2Dy 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 MJ value, with no significant mixing even in the higher doublets.

Treatment of toluene solutions of the silylenes Si(SAr Me 6 ) 2 (Ar Me 6 = C 6 H 3 -2,6(C 6 H 2 -2,4,6-Me 3 ) 2 , 1) or Si(SAr Pr i 4

Reduction of the uranium(III) metallocene [(η5‐C5iPr5)2UI] (1) with potassium graphite produces the “second‐generation” uranocene [(η5‐C5iPr5)2U] (2), which contains uranium in the formal divalent oxidation state. The geometry of 2 is that of a perfectly linear bis(cyclopentadienyl) sandwich complex, with the ground‐state valence electron configuration of uranium(II) revealed by electronic spectroscopy and density functional theory to be 5f3 6d1. Appreciable covalent contributions to the metal‐ligand bonds were determined from a computational study of 2, including participation from the uranium 5f and 6d orbitals. Whereas three unpaired electrons in 2 occupy orbitals with essentially pure 5f character, the fourth electron resides in an orbital defined by strong 7s‐6d mixing.

Inducing magnetic coupling between 4f elements is an ongoing challenge.T oo vercome this formidable difficulty, we incorporate highly delocalized tetrazinyl radicals,w hich strongly couple with f-blockm etallocenes to form discrete tetranuclear complexes.S ynthesis,s tructure,a nd magnetic properties of two tetranuclear [(Cp* 2 Ln) 4 (tzC) 4 ]•3(C 6 H 6 ) (Cp* = pentamethylcyclopentadienyl;t z = 1,2,4,5-tetrazine; Ln = Dy,G d) complexes are reported. An in-depth examination of their magnetic properties through magnetic susceptibility measurements as well as computational studies support ah ighly sought-after radical-induced "giant-spin" model. Strong exchange interactions between the Ln III ions and tzC radicals lead to as trong magnet-like behaviour in this molecular magnet with alarge coercive field of 30 kOe.