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A series of dilanthanide benzene inverse sandwich complexes of the type (Cp iPr5 Ln) 2 (μ-η 6 :η 6 -C 6 H 6 ) ( 1-Ln ) (Ln = Y, Gd, Tb, Dy, Tm) are reported. These compounds are synthesized by reduction of the respective trivalent dimers Cp iPr5 2 Ln 2 I 4 (Ln = Y, Gd, Tb, Dy, Tm) in diethyl ether with potassium graphite in the presence of benzene, and they feature an unusual linear coordination geometry with a highly planar benzene bridge as verified by single-crystal X-ray diffraction. The Ln-Bz centroid distances of 1-Ln are the shortest distances observed to date, ranging from 1.943(1) Å for 1-Tm to 2.039(6) Å for 1-Gd . Structural, spectroscopic, and magnetic analyses together with density functional theory calculations support the presence of a rare, unsubstituted tetraanionic benzene in each compound, which is stabilized by strong covalent δ bonding interactions involving the filled π* orbitals of (C 6 H 6 ) 4- and vacant d xy and d x 2 -y 2 orbitals of the Ln 3+ ions. Notably, 1-Ln are the first examples of compounds of the later lanthanides to feature an unsubstituted tetraanionic benzene.

The actinide elements are attractive alternatives to transition metals or lanthanides for the design of exchange-coupled multinuclear single-molecule magnets. However, the synthesis of such compounds is challenging, as is unraveling any contributions from exchange coupling to the overall magnetism. To date, only a few actinide compounds have been shown to exhibit exchange coupling and single-molecule magnetism. Here, we report triangular uranium(III) clusters of the type (Cp i Pr5 ) 3 U 3 X ( 1-X ; X = Cl, Br, I; Cp i Pr5 = pentaisopropylcyclopentadienyl), which are synthesized via reaction of the aryloxide-bridged precursor (Cp i Pr5 ) 2 U 2 (OPh t Bu ) 4 with excess Me 3 SiX. Spectroscopic analysis suggests the presence of covalency in the uranium-halide interactions arising from 5f orbital participation in bonding. The dc magnetic susceptibility data reveal the presence of antiferromagnetic exchange coupling between the uranium(III) centers in these compounds, with the strength of the exchange decreasing down the halide series. Ac magnetic susceptibility data further reveal all compounds to exhibit slow magnetic relaxation under zero dc field. In 1-I , which exhibits particularly weak exchange, magnetic relaxation occurs via a Raman mechanism associated with the individual uranium(III) centers. In contrast, for 1-Br and 1-Cl , magnetic relaxation occurs via an Orbach mechanism, likely involving relaxation between ground and excited exchange-coupled states. Significantly, in the case of 1-Cl , magnetic relaxation is sufficiently slow such that open magnetic hysteresis is observed up to 2.75 K, and the compound exhibits a 100-s blocking temperature of 2.4 K. This compound provides the first example of magnetic blocking in a compound containing only actinide-based ions, as well as the first example involving the uranium(III) oxidation state.

Mixed-valence dilanthanide complexes of the type (Cp iPr5 ) 2 Ln 2 I 3 (Cp iPr5 = pentaisopropylcyclopentadienyl; Ln = Gd, Tb, Dy) featuring a direct Ln-Ln σ-bonding interaction have been shown to exhibit well-isolated high-spin ground states and, in the case of the Tb and Dy variants, a strong axial magnetic anisotropy that gives rise to a large magnetic coercivity. Here, we report the synthesis and characterization of two new mixed-valence dilanthanide compounds in this series, (Cp iPr5 ) 2 Ln 2 I 3 ( 1-Ln ; Ln = Ho, Er). Both compounds feature a Ln-Ln bonding interaction, the first such interaction in any molecular compounds of Ho or Er. Like the Tb and Dy congeners, both complexes exhibit high-spin ground states arising from strong spin-spin coupling between the lanthanide 4f electrons and a single σ-type lanthanide-lanthanide bonding electron. Beyond these similarities, however, the magnetic properties of the two compounds diverge. In particular, 1-Er does not exhibit observable magnetic blocking or slow magnetic relaxation, while 1-Ho exhibits magnetic blocking below 28 K, which is the highest temperature among Ho-based single-molecule magnets, and a spin reversal barrier of 556(4) cm -1 . Additionally, variable-field magnetization data collected for 1-Ho reveal a coercive field of greater than 32 T below 8 K, more than 6-fold higher than observed for the bulk magnets SmCo 5 and Nd 2 Fe 14 B, and the highest coercive field reported to date for any single-molecule magnet or molecule-based magnetic material. Multiconfigurational calculations, supported by far-infrared magnetospectroscopy data, reveal that the stark differences in magnetic properties of 1-Ho and 1-Er arise from differences in the local magnetic anisotropy of the lanthanide centers.

The recent discovery of metal-metal bonding and valence delocalization in the dilanthanide complexes (Cp iPr5 ) 2 Ln 2 I 3 (Cp iPr5 = pentaisopropylcyclopentadienyl; Ln = Y, Gd, Tb, Dy) opened up the prospect of harnessing the 4f n 5d z 2 1 electron configurations of non-traditional divalent lanthanide ions to access molecules with novel bonding motifs and magnetism. Here, we report the trinuclear mixed-valence clusters (Cp iPr5 ) 3 Ln 3 H 3 I 2 ( 1-Ln , Ln = Y, Gd), which were synthesized via potassium graphite reduction of the trivalent clusters (Cp iPr5 ) 3 Ln 3 H 3 I 3 . Structural, computational, and spectroscopic analyses support valence delocalization in 1-Ln resulting from a three-center, one-electron σ bond formed from the 4d z 2 and 5d z 2 orbitals on Y and Gd, respectively. Dc magnetic susceptibility data obtained for 1-Gd reveal that valence delocalization engenders strong parallel alignment of the σ-bonding electron and the 4f electrons of each gadolinium center to afford a high-spin ground state of S = 11. Notably, this represents the first clear instance of metal-metal bonding in a molecular trilanthanide complex, and the large spin-spin exchange constant of J = 168(1) cm -1 determined for 1-Gd is only the second largest coupling constant characterized to date for a molecular lanthanide compound.

A small but growing number of molecular compounds have been isolated featuring divalent lanthanides with 4f n 5d z 2 1 electron configurations. While the majority of these possess trigonal coordination geometries, we previously reported the first examples of linear divalent metallocenes Ln(Cp iPr5 ) 2 (Ln = Tb, Dy; Cp iPr5 = pentaisopropylcyclopentadienyl). Here, we report the synthesis and characterization of the remainder of the Ln(Cp iPr5 ) 2 ( 1-Ln ) series (including Y and excluding Pm). The compounds can be synthesized through salt metathesis of LnI 3 and NaCp iPr5 followed by potassium graphite reduction for Ln = Y, La, Ce, Pr, Nd, Gd, Ho, and Er, by in situ reduction during salt metathesis of LnI 3 and NaCp iPr5 for Ln = Tm and Lu, or through salt metathesis from LnI 2 and NaCp iPr5 for Ln = Sm, Eu, and Yb. Single crystal X-ray diffraction analyses of 1-Ln confirm a linear coordination geometry with pseudo- D 5 d symmetry for the entire series. Structural and ultraviolet-visible spectroscopy data support a 4f n +1 electron configuration for Ln 2+ configuration for the other lanthanides ([Kr]4d n 5d z 2 1 configuration for the other lanthanides ([Kr]4d z 2 1 for Y 2+ ). Characterization of 1-Ln (Ln = Y, La) using electron paramagnetic resonance spectroscopy reveals significant s-d orbital mixing in the highest occupied molecular orbital and hyperfine coupling constants that are the largest reported to date for divalent compounds of yttrium and lanthanum. Evaluation of the room temperature magnetic susceptibilities of 1-Ln and comparison with values previously reported for trigonal Ln 2+ compounds suggests that the more pronounced 6s-5d mixing may be associated with weaker 4f-5d spin coupling.

Magnetic effects of lanthanide bonding Lanthanide coordination compounds have attracted attention for their persistent magnetic properties near liquid nitrogen temperature, well above alternative molecular magnets. Gould et al . report that introducing metal-metal bonding can enhance coercivity. Reduction of iodide-bridged terbium or dysprosium dimers resulted in a single electron bond between the metals, which enforced alignment of the other valence electrons. The resultant coercive fields exceeded 14 tesla below 50 and 60 kelvin for the terbium and dysprosium compounds, respectively. —JSY

The divalent metallocene complexes Ln(Cp iPr5 ) 2 (Ln = Tb, Dy) were synthesized through the KC 8 reduction of Ln(Cp iPr5 ) 2 I intermediates and represent the first examples of neutral, linear metallocenes for these elements. X-ray diffraction analysis, density functional theory calculations, and magnetic susceptibility measurements indicate a 4f n 5d 1 electron configuration with strong s/d mixing that supports the linear coordination geometry. A comparison of the magnetic relaxation behavior of the two divalent metallocenes relative to salts of their trivalent counterparts, [Ln(Cp iPr5 ) 2 ][B(C 6 F 5 ) 4 ], reveals that lanthanide reduction has opposing effects for dysprosium and terbium, with magnetic relaxation times increasing from Tb III to Tb II and decreasing from Dy III to Dy II . The impact of this effect is most notably evident for Tb(Cp iPr5 ) 2 , which displays an effective thermal barrier to magnetic relaxation of 1205 cm -1 and a 100-s blocking temperature of 52 K, the highest values yet observed for any nondysprosium single-molecule magnet.

The partially fluorinated oxo-alkoxide tungsten(VI) complexes WO(OR)4 [4; R = C(CH3)2CF3, 5; R = C(CH3)(CF3)2] have been synthesized as precursors for chemical vapour deposition (CVD) of WOx nanocrystalline material. Complexes 4 and 5 were prepared by salt metathesis between sodium salts of the fluoroalkoxides and WOCl4. Crystallographic structure analysis allows comparison of the bonding in 4 and 5 as the fluorine content of the fluoroalkoxide ligands is varied. Screening of as a CVD precursor by mass spectrometry and thermogravimetric analysis was followed by deposition of WOx nanorods.

Tungsten nitrido complexes of the form WN(NR2)3 [R = combinations of Me, Et, (i)Pr, (n)Pr] have been synthesized as precursors for the chemical vapor deposition of WN(x)C(y), a material of interest for diffusion barriers in Cu-metallized integrated circuits. These precursors bear a fully nitrogen coordinated ligand environment and a nitrido moiety (W≡N) designed to minimize the temperature required for film deposition. Mass spectrometry and solid state thermolysis of the precursors generated common fragments by loss of free dialkylamines from monomeric and dimeric tungsten species. DFT calculations on WN(NMe2)3 indicated the lowest gas phase energy pathway for loss of HNMe2 to be β-H transfer following formation of a nitrido bridged dimer. Amorphous films of WN(x)C(y) were grown from WN(NMe2)3 as a single source precursor at temperatures ranging from 125 to 650 °C using aerosol-assisted chemical vapor deposition (AACVD) with pyridine as the solvent. Films with stoichiometry approaching W2NC were grown between 150 and 450 °C, and films grown at 150 °C were highly smooth, with a RMS roughness of 0.5 nm. In diffusion barrier tests, 30 nm of film withstood Cu penetration when annealed at 500 °C for 30 min.