133 research outputs found
Strong direct exchange coupling and single-molecule magnetism in indigo-bridged lanthanide dimers
The synthesis, structure and magnetic properties of the indigo-bridged dilanthanide complexes [{(η5-Cp*)2Ln}2(ÎŒ-ind)]nâ with Ln = Gd or Dy and n = 0, 1 or 2 are described. The gadolinium complexes with n = 0 and 2 show typically weak exchange coupling, whereas the complex bridged by the radical [ind]3â ligand shows an unusually large coupling constant of J = â11 cmâ1 (â2J formalism). The dysprosium complexes with n = 0 and 1 are single-molecule magnets in zero applied field, whereas the complex with n = 2 does not show slow magnetic relaxation
Interpreting molecular crystal disorder in plumbocene, Pb(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>: Insight from theory
Single-molecule magnet properties of a monometallic dysprosium pentalene complex
The pentalene-ligated dysprosium complex [(8-Pnâ )Dy(Cp*)] (1Dy) (Pnâ = [1,4-(iPr3Si)2C8H4]2â) and its magnetically dilute analogue are single-molecule magnets, with energy barriers of 245 cmâ1. Whilst the [Cp*]â ligand in 1Dy provides a strong axial crystal field, the overall axiality of this system is attenuated by the unusual folded structure of the [Pnâ ]2â ligand
Magnetic hysteresis up to 80 kelvin in a dysprosium metallocene single-molecule magnet
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 = 1,541 cmâ1 is also measured. The magnetic blocking temperature of TB = 80 K for this cation overcomes an essential barrier towards the development of nanomagnet devices that function at practical temperatures
Bimetallic synergy enables silole insertion into THF and the synthesis of Erbium singleâmolecule magnets
The potassium silole K2[SiC4â2,5â(SiMe3)2â3,4âPh2] reacts with [M(η8âCOT)(THF)4][BPh4] (M=Er, Y; COT=cycloâoctatetraenyl) in THF to give products that feature unprecedented insertion of the nucleophilic silicon centre into a carbonâoxygen bond of THF. The structure of the major product, [(ÎŒâη8 : η8âCOT)M(ÎŒâL1)K]â (1M), consists of polymeric chains of sandwich complexes, where the spiroâbicyclic silapyran ligand [C4H8OSiC4(SiMe3)2Ph2]2â (L1) coordinates to potassium via the oxygen. The minor product [(ÎŒâη8 : η8âCOT)M(ÎŒâL1)K(THF)]2 (2M) features coordination of the silapyran to the rareâearth metal. In forming 1M and 2M, silole insertion into THF only occurs in the presence of potassium and the rareâearth metal, highlighting the importance of bimetallic synergy. The lower nucleophilicity of germanium(II) leads to contrasting reactivity of the potassium germole K2[GeC4â2,5â(SiMe3)2â3,4âMe2] towards [M(η8âCOT)(THF)4][BPh4], with intact transfer of the germole occurring to give the coordination polymers [{η5âGeC4(SiMe3)2Me2}M(η8âCOT)K]â (3M). Despite the differences in reactivity induced by the group 14 heteroatom, the singleâmolecule magnet properties of 1Er, 2Er and 3Er are similar, with thermally activated relaxation occurring via the firstâexcited Kramers doublet, subject to effective energy barriers of 122, 80 and 91 cmâ1, respectively. Compound 1Er is also analysed by highâfrequency dynamic magnetic susceptibility measurements up to 106 Hz
Identification of oxidation state +1 in a molecular uranium complex
The concept of oxidation state plays a fundamentally important role in defining the chemistry of the elements. In the f block of the periodic table, well-known oxidation states in compounds of the lanthanides include 0, +2, +3 and +4, and oxidation states for the actinides range from +7 to +2. Oxidation state +1 is conspicuous by its absence from the f-block elements. Here we show that the uranium(II) metallocene [U(η5-C5iPr5)2] and the uranium(III) metallocene [IU(η5-C5iPr5)2] can be reduced by potassium graphite in the presence of 2.2.2-cryptand to the uranium(I) metallocene [U(η5-C5iPr5)2]- (1) (C5iPr5 = pentaisopropylcyclopentadienyl) as the salt of [K(2.2.2-cryptand)]+. An X-ray crystallographic study revealed that 1 has a bent metallocene structure, and theoretical studies and magnetic measurements confirmed that the electronic ground state of uranium(I) adopts a 5f3(7s/6dz2)1(6dx2-y2/6dxy)1 configuration. The metal-ligand bonding in 1 consists of contributions from uranium 5f, 6d, and 7s orbitals, with the 6d orbitals engaging in weak but non-negligible covalent interactions. Identification of the oxidation state +1 for uranium expands the range of isolable oxidation states for the f-block elements and potentially signposts a synthetic route to this elusive species for other actinides and the lanthanides
Carbonyl back-bonding influences the rate of quantum tunnelling in a dysprosium metallocene single-molecule magnet
The isocarbonyl-ligated metallocene coordination polymers [Cp*2M(ÎŒ-OC)W(Cp)(CO)(ÎŒ-CO)]â were synthesized with M = Gd (1, L = THF) and Dy (2, no L). In a zero direct-current field, the dysprosium version 2 was found to be a single-molecule magnet (SMM), with analysis of the dynamic magnetic susceptibility data revealing that the axial metallocene coordination environment leads to a large anisotropy barrier of 557(18) cmâ1 and a fast quantum-tunnelling rate of âŒ3.7 ms. Theoretical analysis of two truncated versions of 2, [Cp*2Dy{(ÎŒ-OC)W(Cp)(CO)2}2]â (2a), and [Cp*2Dy(OC)2]+ (2b), in which the effects of electron correlation outside the 4f orbital space were studied, revealed that tungsten-to-carbonyl back-donation plays an important role in determining the strength of the competing equatorial field at dysprosium and, hence, the dynamic magnetic properties. The finding that a classical organo-transition-metal bonding scenario can be used as an indirect way of tuning the rate of quantum tunnelling potentially provides an alternative chemical strategy for utilizing the fast magnetic relaxation properties of SMMs.peerReviewe
Coupling of nitric oxide and release of nitrous oxide from rare-earth-dinitrosyliron complexes
Addition of Lewis acidic [Cp*2M]+ (M = Y, Gd) to the dinitrosyliron complexes (DNICs) [(NacNacAr)Fe(NO)2]â (Ar = mesityl, 2,6-diisopropylphenyl) results in formation of the isonitrosyl-bridged DNICs [(Cp*)2M(ÎŒ-ON)2Fe(NacNacAr)]. When Ar = 2,6-diisopropylphenyl, coupling of the NO ligands and release of N2O occur. Two factors contribute to this previously unobserved DNIC reactivity mode. First, the oxophilic rare-earth elements drive the formation of isonitrosyl bonds, forcing the DNIC nitrogen atoms into proximity. Second, the bulky substituents further squeeze the DNIC, which ultimately overcomes the barrier to NO coupling, demonstrating that N2O elimination can occur from a single iron center
Synthesis and single-molecule magnet properties of a trimetallic dysprosium metallocene cation
The dimetallic fulvalene-bridged dysprosium complex [{Dy(Cp*)(Ό-BH4)}2(Fvtttt)] (1, Cp* = C5Me5) is converted into the trimetallic borohydride-bridged species [{Dy(Cp*)(Fvtttt)}2Dy(Ό-BH4)3] (2). In turn, 2 is reacted with a silylium electrophile to give [{Dy(Cp*)(Ό-BH4)(Fvtttt)}2Dy][B(C6F5)4] ([3][B(C6F5)3]), the first trimetallic dysprosocenium cation. Compound [3][B(C6F5)3] can also be formed directly from 1 by adding two equivalents of the electrophile. A three-fold enhancement in the effective energy barrier from 2 to 3 is observed and interpreted with the aid ofab initiocalculations
Benzotriazolate cage complexes of tin(II) and lithium: halide-influenced serendipitous assembly
The one-pot reactions of the tin(II) halides SnX2 (X = F, Cl, Br, I) with lithium hexamethyldisilazide, [Li(hmds)], and benzotriazole, (bta)H, produce contrasting outcomes. Tin(II) fluoride does not react with [Li(hmds)] and (bta)H, the outcome being the formation of insoluble [Li(bta)]â. Tin(II) chloride and tin(II) bromide react with [Li(hmds)] and (bta)H in toluene to produce the hexadecametallic tin(II)-lithium cages [(hmds)8Sn8(bta)12Li8X4]·(ntoluene) [X = Cl, 3·(8 toluene); X = Br, 4·(3 toluene)]. The reaction of tin(II) iodide with [Li(hmds)] and (bta)H in thf solvent produces the ion-separated species [{(thf)2Li(bta)}3{Li(thf)}]2[SnI4]·(thf), [5]2[SnI4]·(thf), the structure of which contains a cyclic trimeric unit of lithium benzotriazolate and a rare example of the tetraiodostannate(II) dianion
- âŠ