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Nuclear magnetic resonance suffers from an intrinsically low sensitivity, which can be overcome by dynamic nuclear polarization (DNP). Gd(III) complexes are attractive exogenous polarizing agents for magic angle spinning (MAS) DNP due to their high chemical stability in contrast to nitroxide-based radicals. However, even the state-of-the-art Gd(III) complexes have so far provided relatively low DNP signal enhancements of ca. 36 in comparison to standard DNP biradicals, which show enhancements of over 200. Here, we report a series of new Gd(III) complexes for DNP and show that the observed DNP enhancements of the new and existing Gd(III) complexes are inversely proportional to the square of the zero-field splitting (ZFS) parameter D, which is in turn determined by the ligand-type and the local coordination environment. The experimental DNP enhancements at 9.4 T and the ZFS parameters measured with pulsed electron paramagnetic resonance (EPR) spectroscopy agree with the above model, paving the way for the development of more efficient Gd(III) polarizing agents., The Journal of Physical Chemistry C, 126 (27), ISSN:1932-7455, ISSN:1932-7447

Studies of the coordination chemistry between the diphenylamide ligand, NPh2, and the smaller rare-earth Ln III ions, Ln = Y, Dy, and Er, led to the structural characterization by single-crystal X-ray diffraction crystallography of both solvated and unsolvated complexes, namely, tris(diphenylamido-κN)bis(tetrahydrofuran-κO)yttrium(III), Y(NPh2)3(THF)2 or [Y(C12H10N)3(C4H8O)2], 1-Y, and the erbium(III) (Er), 1-Er, analogue, and bis[μ-1κN:2(η6)-diphenylamido]bis[bis(diphenylamido-κN)yttrium(III)], [(Ph2N)2Y(μ-NPh2)]2 or [Y2(C12H10N)6], 2-Y, and the dysprosium(III) (Dy), 2-Dy, analogue. The THF ligands of 1-Er are modeled with disorder across two positions with occupancies of 0.627 (12):0.323 (12) and 0.633 (7):0.367 (7). Also structurally characterized was the tetrametallic ErIII bridging oxide hydrolysis product, bis(μ-diphenylamido-κ2 N:N)bis[μ-1κN:2(η6)-diphenylamido]tetrakis(diphenylamido-κN)di-μ3-oxido-tetraerbium(III) benzene disolvate, {[(Ph2N)Er(μ-NPh2)]4(μ-O)2}·(C6H6)2 or [Er4(C12H10N)8O2]·2C6H6, 3-Er. The 3-Er structure was refined as a three-component twin with occupancies 0.7375:0.2010:0.0615.

Out of the 14 lanthanide (Ln) ions, molecular complexes of Ln(IV) were known only for cerium and more recently terbium. Here we demonstrate that the +IV oxidation state is also accessible for the large praseodymium (Pr) cation. The oxidation of the tetrakis(triphenysiloxide) Pr(III) ate complex, [KPr(OSiPh3)(4)(THF)(3)], 1-Pr-Ph, with [N(C6H4Br)(3)][SbCl6], affords the Pr(IV) complex [Pr(OSiPh3)(4)(MeCN)(2)], 2-Pr-Ph, which is stable once isolated. The solid state structure, UV-visible spectroscopy, magnetometry, and cyclic voltammetry data along with the DFT computations of the 2-Pr-Ph complex unambiguously confirm the presence of Pr(IV).

Synthetic studies of bimetallic uranium nitride complexes with the N(SiMe3)2 ligand have generated a new nitride complex of U(III), which is highly reactive toward C-H bonds and H2. Treatment of the previously reported U(IV)/U(IV) nitride complex [Na(DME)3][((Me3Si)2N)2U(μ-N)(μ-κ2:CN-CH2SiMe2NSiMe3)U(N(SiMe3)2)2] (DME = 1,2-dimethoxyethane), 1, with 2 equiv of HNEt3BPh3 yielded the cationic U(IV)/U(IV) nitride complex, [{((Me3Si)2N)2U(THF)}2(μ-N)][BPh4] (THF = tetrahydrofuran), 3, by successive protonolysis of one N(SiMe3)2 ligand and the uranium-methylene bond. Reduction of 3 with KC8 afforded a rare example of a U(III) nitride, namely, the U(III)/U(IV) complex, [{((Me3Si)2N)2U(THF)}2(μ-N)], 4. Complex 4 is highly reactive and undergoes 1,2-addition of the C-H bond of the N(SiMe3)2 ligand across the uranium-nitride moiety to give the U(III)/U(IV) imide cyclometalate complex, [((Me3Si)2N)2(THF)U(μ-NH)(μ-κ2:C,N-CH2SiMe2NSiMe3)U(N(SiMe3)2))(THF)], 5. Complex 4 also reacts with toluene at -80 °C to yield an inverse sandwich imide complex arising from C-H bond activation of toluene, [{((Me3Si)2N)2U(THF)}2(μ-N)][{((Me3Si)2N)3U(μ-NH)U(N(SiMe3)2)}2(C7H8)], 6. Complex 4 effects the heterolytic cleavage of the C-H of phenylacetylene to yield the imide acetylide [{((Me3Si)2N)2U(THF)}2(μ-N)][((Me3Si)2N)2U(η1-CCPh)(μ2-NH)(μ2-η2:η1-CCPh)U(N(SiMe3)2)2], 7. Complex 4 also reacts with H2 to produce an imide hydride U(III)/U(IV) complex, [{((Me3Si)2N)2U(THF)}2(μ-NH)(μ-H)], 9. These data demonstrate that nitride complexes of U(III) are accessible with amide ligands and show the high reactivity of molecular U(III) nitrides in C-H bond activation.

The redox chemistry of uranium is dominated by single electron transfer reactions while single metal four-electron transfers remain unknown in f-element chemistry. Here we show that the oxo bridged diuranium(iii) complex [K(2.2.2-cryptand)]2[{((Me3Si)2N)3U}2(μ-O)], 1, effects the two-electron reduction of diphenylacetylene and the four-electron reduction of azobenzene through a masked U(ii) intermediate affording a stable metallacyclopropene complex of uranium(iv), [K(2.2.2-cryptand)][U(η2-C2Ph2){N(SiMe3)2}3], 3, and a bis(imido)uranium(vi) complex [K(2.2.2-cryptand)][U(NPh)2{N(SiMe3)2}3], 4, respectively. The same reactivity is observed for the previously reported U(ii) complex [K(2.2.2-cryptand)][U{N(SiMe3)2}3], 2. Computational studies indicate that the four-electron reduction of azobenzene occurs at a single U(ii) centre via two consecutive two-electron transfers and involves the formation of a U(iv) hydrazide intermediate. The isolation of the cis-hydrazide intermediate [K(2.2.2-cryptand)][U(N2Ph2){N(SiMe3)2}3], 5, corroborated the mechanism proposed for the formation of the U(vi) bis(imido) complex. The reduction of azobenzene by U(ii) provided the first example of a “clear-cut” single metal four-electron transfer in f-element chemistry., Both a masked and the actual complex [U(ii){N(SiMe3)2}3]+ effect the reduction of azobenzene to yield a U(vi) bis-imido species providing the first example of a “clear-cut” metal centred four-electron reduction in f-element chemistry.

Oxide is an attractive linker for building polymetallic complexes that provide molecular models for metal oxide activity, but studies of these systems are limited to metals in high oxidation states. Herein, we synthesized and characterized the molecular and electronic structure of diuranium bridged U-III/U-IV and U-III/U-III complexes. Reactivity studies of these complexes revealed that the U-O bond is easily broken upon addition of N-heterocycles resulting in the delivery of a formal equivalent of U-III and U-II, respectively, along with the uranium(IV) terminal-oxo coproduct. In particular, the U-III/U-III oxide complex effects the reductive coupling of pyridine and two-electron reduction of 4,4 '-bipyridine affording unique examples of diuranium(III) complexes bridged by N-heterocyclic redox-active ligands. These results provide insight into the chemistry of low oxidation state metal oxides and demonstrate the use of oxo-bridged U-III/U-III complexes as a strategy to explore U-II reactivity.

Crystallographic characterization of complexes of the smaller rare-earth elements Y, Dy, and Er with the NPh2 ligand reveals monometallic, bimetallic, and tetra­metallic structures., Studies of the coordination chemistry between the di­phenyl­amide ligand, NPh2, and the smaller rare-earth Ln III ions, Ln = Y, Dy, and Er, led to the structural characterization by single-crystal X-ray diffraction crystallography of both solvated and unsolvated complexes, namely, tris­(di­phenyl­amido-κN)bis­(tetrahydro­furan-κO)yttrium(III), Y(NPh2)3(THF)2 or [Y(C12H10N)3(C4H8O)2], 1-Y, and the erbium(III) (Er), 1-Er, analogue, and bis­[μ-1κN:2(η6)-di­phenyl­amido]­bis­[bis­(di­phenyl­amido-κN)yttrium(III)], [(Ph2N)2Y(μ-NPh2)]2 or [Y2(C12H10N)6], 2-Y, and the dysprosium(III) (Dy), 2-Dy, analogue. The THF ligands of 1-Er are modeled with disorder across two positions with occupancies of 0.627 (12):0.323 (12) and 0.633 (7):0.367 (7). Also structurally characterized was the tetra­metallic ErIII bridging oxide hydrolysis product, bis­(μ-di­phenyl­amido-κ2 N:N)bis­[μ-1κN:2(η6)-di­phenyl­amido]­tetra­kis­(di­phenyl­amido-κN)di-μ3-oxido-tetra­erbium(III) benzene disolvate, {[(Ph2N)Er(μ-NPh2)]4(μ-O)2}·(C6H6)2 or [Er4(C12H10N)8O2]·2C6H6, 3-Er. The 3-Er structure was refined as a three-component twin with occupancies 0.7375:0.2010:0.0615.

The synthesis of lanthanides other than cerium in the oxidation state +IV has remained a desirable but unmet target until recently, when two examples of Tb-IV with saturated coordination spheres were isolated. Here we report the third example of an isolated molecular complex of terbium(IV), where the supporting siloxide ligands do not saturate the coordination sphere. The fully characterized six-coordinate complex [Tb-IV(OSiPh3)(4)(MeCN)(2)], 2-Tb-Ph, shows high stability and the labile MeCN ligands can be replaced by phosphinoxide ligands. Computational studies suggest that the stability is due to a strong pi(O-Tb) interaction which is stronger than in the previously reported Tb-IV complexes. Cyclic-voltammetry experiments demonstrate that non-binding counterions contribute to the stability of Tb-IV in solution by destabilizing the +III oxidation state, while alkali ions promote Tb-IV/Tb-III electron transfer.

[Y(N(SiMe3)2)3] reacts with (Ad,MeArOH)3mes to form the Y3+ complex [((Ad,MeArO)3mes)Y], 1-Y. This complex reacts with potassium metal in the presence of 2.2.2-cryptand to give a cocrystallized mixture of [K(2.2.2-cryptand)][((Ad,MeArO)3mes)Y], 2-Y, and [K(2.2.2-cryptand)][((Ad,MeArO)3mes)YH], 3-Y. The electron paramagnetic resonance spectrum of this crystalline mixture exhibits an isotropic signal at 77 K (giso = 2.000, Wiso = 1.8 mT), suggesting that 2-Y is best described as a Y3+ complex of the tris(aryloxide)mesitylene radical ((Ad,MeArO)3mes)4–. Evidence of the hydride ligand in 3-Y was obtained by 89Y–1H heteronuclear multiple quantum coherence NMR spectroscopy, and a coupling constant of JYH = 93 Hz was observed. A single crystal of 3-Y was also obtained in pure form and structurally characterized for comparison with the crystal data on the mixed component 2-Ln/3-Ln crystals. The origin of the hydride in 3-Ln is unknown, but further studies of the reduction of 1-La, previously found to form 2-La, r...

The magnetic properties and multi-electron reductive reactivity of the bimetallic inverse sandwich La2+ complex salt, [K(18-crown-6)(THF)2][(Cp″2La)2(μ-η6:η6-C6H6)]·THF, 1 (Cp′′ = C5H3(SiMe3)2), originally described by Lappert et al., have been examined. The compound was prepared by reduction of Cp″3La with potassium metal in benzene and crystallographically characterized. Compound 1 can be described as containing two 5d1 La(II) ions bridged by a planar (C6H6)1– benzenide bridged radical monoanion, with fits to its variable-temperature magnetic susceptibility data revealing strong antiferromagnetic exchange coupling, with JLa–C6H6 > |−400 cm–1|. The multi-electron reduction reactivity of 1 was explored in reactions with anthracene, naphthalene, and cyclooctatetraene. Compound 1 reduces anthracene to give Cp″2La(μ-η6:η6-C14H10)K(18-crown-6), 2, which contains a nonplanar anthracenide dianion with an end ring interacting with La(III) and the central ring interacting with potassium. The reaction of 1 with na...

Efforts to generate Ln2+ precursors suitable for reduction to Ln1+ compounds have provided the X-ray crystal structures of Cp″2Sm, 1-Sm, and Cptt2Ln, 2-Ln [Ln = Eu, Sm; Cp″ = C5H3(SiMe3)2; Cptt = C5H3(CMe3)2], allowing direct comparisons of these similar cyclopentadienyl rings in Ln2+ complexes. In the solid state, these complexes exhibit extensive intermolecular interactions. Bridging cyclopentadienyl ligands are found with both types of ligands and the Cp″ ligand engages in silyl-methyl-metal interactions. The compounds display bent metallocene structures with (ring centroid)–Ln–(ring centroid) angles ranging from 110.0° to 147.9°. Complex 2-Eu reacts with [HNEt3][BPh4] to form the mono(cyclopentadienyl) tetraphenylborate complex, (η5-Cptt)Eu(μ-η6:η1-Ph)2BPh2, 3-Eu, in which the Eu2+ ion is coordinated by three carbocyclic ligands in a nearly trigonal planar geometry.

To evaluate the effect of cyclopentadienyl ligand substitution in complexes of new +2 ions of the lanthanides, comparisons in reactivity and spectroscopic and magnetic properties have been made between [K(crypt)][Cp′3Ln], 1-Ln (Cp′ = C5H4SiMe3; crypt = 2.2.2-cryptand; Ln = La, Ce, Pr, and Nd), and [K(crypt)][Cp′′3Ln], 2-Ln [Cp′′ = C5H3(SiMe3)2]. The 2-Ln complexes (Ce, Pr, and Nd) were synthesized by reduction of Cp′′3Ln with potassium graphite in the presence of crypt and crystallographically characterized. The structures and UV–visible spectra of 2-Ln are similar to those of 1-Ln, as expected, but greater thermal stability for 2-Ln, expected from comparisons of 2-U and 1-U, was not observed. The magnetic susceptibilities of 2-Ce and 2-Pr were investigated because those of 1-Ce and 1-Pr did not match simple coupling models for 4fn5d1 electron configurations. The magnetic data of the 2-Ln complexes are similar to those of 1-Ln, which suggests that Ce2+ and Pr2+ complexes with 4fn5d1 electron configuration...

The synthesis of 4f n Ln3+ complexes of the tris(aryloxide) mesitylene ligand, ((Ad,MeArO)3mes)3-, with Ln = La, Ce, Pr, Sm, and Yb, and their reduction with potassium have revealed that this ligand system can be redox active with some metals. Protonolysis of [Ln(N(SiMe3)2)3] (Ln = La, Ce, Pr, Sm, Yb) with the tris(phenol) (Ad,MeArOH)3mes yielded the Ln3+ complexes [((Ad,MeArO)3mes)Ln] (Ln = La, Ce, Pr, Sm, Yb), 1-Ln. Single electron reduction of each 4f n complex, 1-Ln, using potassium yielded the reduced products, [K(2.2.2-cryptand)][((Ad,MeArO)3mes)Ln] (Ln = La, Ce, Pr, Sm, Yb), 2-Ln. The Sm and Yb complexes have properties consistent with the presence of Ln2+ ions with traditional 4f n+1 electron configurations. However, the La, Ce, and Pr complexes appear to formally contain Ln3+ ions and ((Ad,MeArO)3mes)4- ligands. Structural comparisons of the [((Ad,MeArO)3mes)Ln] and [((Ad,MeOAr)3mes)Ln]1- complexes along with UV-vis absorption and EPR spectroscopy as well as density functional theory calculations support these ground state assignments.

Electrocatalytic energy conversion with molecular f-element catalysts is still in an early phase of its development. We here report detailed electrochemical investigations on the recently reported trivalent lanthanide coordination complexes [((Ad,MeArO)3mes)Ln] (1–Ln), with Ln = La, Ce, Pr, Nd, Sm, Gd, Dy, Er, and Yb, which were now found to perform as active electrocatalysts for the reduction of water to dihydrogen. Reactivity studies involving complexes 1–Ln and the Ln(II) analogues [K(2.2.2-crypt)][((Ad,MeArO)3mes)Ln] (2–Ln) suggest a reaction mechanism that differs significantly from the reaction pathway found for the corresponding uranium catalyst [((Ad,MeArO)3mes)U] (1–U). While complexes 1−Ln activate water via a radical pathway, only upon a 1 e− reduction to yield the reduced species 2−Ln, the 5f analogue 1−U directly reduces H2O via a 2 e− pathway. The electrocatalytic H2O reduction by complexes 1–Ln is initiated by the respective Ln(III)/Ln(II) redox couples, which gradually turn to more positiv...

The Ln2+ complexes [K(2.2.2-cryptand)][Cp′3Ln] (Ln = La, Ce, Pr, Nd, Sm, Eu, Dy, Tm, Yb; Cp′ = C5H4SiMe3) were reacted with 1,3,5,7-cyclooctatetraene, C8H8, to determine if the reactivity of the complexes of 4fn+1 ions differed from that of 4fn5d1 ions. Crystallographically characterizable (C8H8)2– complexes were obtained only for the larger metals in the lanthanide series, and two types of products were obtained: [K(2.2.2-cryptand)][Cp′2Ln(C8H8)] (Ln = La, Ce) and [K(2.2.2-cryptand)][Ln(C8H8)2] (Ln = Ce, Pr, Nd, Sm). The expected co-products of the two-electron reduction of C8H8 by 2 equiv of [K(2.2.2-cryptand)][Cp′3Ln], namely, the tetrakis(cyclopentadienyl) complexes, [K(2.2.2-cryptand)][Cp′4Ln], were crystallographically characterized for six metals (Ln = Ce, Pr, Nd, Sm, Dy, Tm).

The synthesis of 4f

Electrocatalytic energy conversion with molecular f-element catalysts is still in an early phase of its development. We here report detailed electrochemical investigations on the recently reported trivalent lanthanide coordination complexes [((

The tris(cyclopentadienyl) yttrium complexes Cp3Y(THF), CpMe3Y(THF), Cp″3Y, Cp″2YCp, and Cp″2YCpMe [Cp = C5H5, CpMe = C5H4Me, Cp″ = C5H3(SiMe3)2] have been treated with potassium graphite in the presence of 2.2.2-cryptand to search for more stable examples of complexes featuring the recently discovered Y2+ ion first isolated in [K(18-crown-6)][Cp′3Y] and [K(2.2.2-cryptand)][Cp′3Y], 1-Y (Cp′ = C5H4SiMe3). Reduction of the tris(cyclopentadienyl) complexes generates dark solutions like that of 1-Y, and the EPR spectra contain doublets with g values between 1.990 and 1.991 and hyperfine coupling constants of 34–47 gauss that are consistent with the presence of Y2+. [K(2.2.2-cryptand)][Cp″2YCp], 2-Y, was characterizable by X-ray crystallography. Reduction of the Cp″3Gd, Cp″2GdCp, and Cp″2GdCpMe complexes containing the larger metal gadolinium were also examined. In each case, dark solutions and EPR spectra like that of [K(2.2.2-cryptand)][Cp′3Gd], 1-Gd, were obtained, and [K(2.2.2-cryptand)][Cp″2GdCp], 2-Gd, w...

© The Royal Society of Chemistry. A new option for stabilizing unusual Ln2+ ions has been identified in the reaction of Cp′3Ln, 1-Ln (Ln = La, Ce; Cp′ = C5H4SiMe3), with potassium graphite (KC8) in benzene in the presence of 2.2.2-cryptand. This generates [K(2.2.2-cryptand)]2[(Cp′2Ln)2(μ-η6:η6-C6H6)], 2-Ln, complexes that contain La and Ce in the formal +2 oxidation state. These complexes expand the range of coordination environments known for these ions beyond the previously established examples, (Cp″3Ln)1- and (Cp′3Ln)1- (Cp″ = C5H3(SiMe3)2-1,3), and generalize the viability of using three anionic carbocyclic rings to stabilize highly reactive Ln2+ ions. In 2-Ln, a non-planar bridging (C6H6)2- ligand shared between two metals takes the place of a cyclopentadienyl ligand in (Cp′3Ln)1-. The intensely colored (ε = ∼8000 M-1 cm-1) 2-Ln complexes react as four electron reductants with two equiv. of naphthalene to produce two equiv. of the reduced naphthalenide complex, [K(2.2.2-cryptand)][Cp′2Ln(η4-C10H8)].

A new option for stabilizing unusual Ln2+ ions has been identified in the reaction of (C5H4SiMe3)3Ln (Ln = La, Ce) with potassium graphite and 2.2.2-cryptand in benzene., A new option for stabilizing unusual Ln2+ ions has been identified in the reaction of Cp′3Ln, 1-Ln (Ln = La, Ce; Cp′ = C5H4SiMe3), with potassium graphite (KC8) in benzene in the presence of 2.2.2-cryptand. This generates [K(2.2.2-cryptand)]2[(Cp′2Ln)2(μ-η6:η6-C6H6)], 2-Ln, complexes that contain La and Ce in the formal +2 oxidation state. These complexes expand the range of coordination environments known for these ions beyond the previously established examples, (Cp′′3Ln)1– and (Cp′3Ln)1– (Cp′′ = C5H3(SiMe3)2-1,3), and generalize the viability of using three anionic carbocyclic rings to stabilize highly reactive Ln2+ ions. In 2-Ln, a non-planar bridging (C6H6)2– ligand shared between two metals takes the place of a cyclopentadienyl ligand in (Cp′3Ln)1–. The intensely colored (ε = ∼8000 M–1 cm–1) 2-Ln complexes react as four electron reductants with two equiv. of naphthalene to produce two equiv. of the reduced naphthalenide complex, [K(2.2.2-cryptand)][Cp′2Ln(η4-C10H8)].

Molecular uranium nitride complexes were prepared to relate their small molecule reactivity to the nature of the U & xe001;N & xe001;U bonding imposed by the supporting ligand. The U4+-U4+ nitride complexes, [NBu4][{(((BuO)-Bu-t)(3)SiO)(3)U}(2)(mu-N)], [NBu4]-1, and [NBu4][((Me3Si)(2)N)(3)U}(2)(mu-N)], 2, were synthesised by reacting NBu4N3 with the U3+ complexes, [U(OSi((OBu)-Bu-t)(3))(2)(mu-OSi((OBu)-Bu-t)(3))](2) and [U(N(SiMe3)(2))(3)], respectively. Oxidation of 2 with AgBPh4 gave the U4+-U5+ analogue, [((Me3Si)(2)N)(3)U}(2)(mu-N)], 4. The previously reported methylene-bridged U4+-U4+ nitride [Na(dme)(3)][((Me3Si)(2))(2)U(mu-N)(mu-kappa(2)-C,N-CH2SiMe2NSiMe3)U(N(SiMe3)(2))(2)] (dme = 1,2-dimethoxyethane), [Na(dme)(3)]-3, provided a versatile precursor for the synthesis of the mixed-ligand U4+-U4+ nitride complex, [Na(dme)(3)][((Me3Si)(2)N)(3)U(mu-N)U(N(SiMe3)(2))(OSi((OBu)-Bu-t)(3))], 5. The reactivity of the 1-5 complexes was assessed with CO2, CO, and H-2. Complex [NBu4]-1 displays similar reactivity to the previously reported heterobimetallic complex, [Cs{(((BuO)-Bu-t)(3)SiO)(3)U}(2)(mu-N)], [Cs]-1, whereas the amide complexes 2 and 4 are unreactive with these substrates. The mixed-ligand complexes 3 and 5 react with CO and CO2 but not H-2. The nitride complexes [NBu4]-1, 2, 4, and 5 along with their small molecule activation products were structurally characterized. Magnetic data measured for the all-siloxide complexes [NBu4]-1 and [Cs]-1 show uncoupled uranium centers, while strong antiferromagnetic coupling was found in complexes containing amide ligands, namely 2 and 5 (with maxima in the chi versus T plot of 90 K and 55 K). Computational analysis indicates that the U(mu-N) bond order decreases with the introduction of oxygen-based ligands effectively increasing the nucleophilicity of the bridging nitride.

Lanthanides (Ln) usually occur in the +3, or more recently the +2, oxidation states. The only example of an isolated molecular Ln(4+) so far remains Ce4+. Here we show that the +4 oxidation state is also accessible in a molecular compound of terbium as demonstrated by oxidation of the tetrakis(siloxide)terbium(III) ate complex, [KTb(OSi((OBu)-Bu-t)(3))(4)], 1-Tb, with the tris(4-bromophenyl) amminium oxidant, [N(C6H4Br)(3)] [SbCl6], to afford the Tb4+ complex [Tb(OSi((OBu)-Bu-t)(3))(4)], 2-Tb. The solid state structures of 1-Tb and 2-Tb were determined by X-ray crystallography, and the presence of Tb4+ was unambiguously confirmed by electron paramagnetic resonance and magnetometry. Complex 2-Tb displays a similar voltammogram to the Ce4+ analogue but with redox events that are about 1 V more positive.