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Nb₂©Au₆: a molecular wheel with a short Nb[triple bond, length as m-dash]Nb triple bond coordinated by an Au₆ ring and reinforced by σ aromaticity.

ABSTRACT: We report a photoelectron spectroscopy and high-resolution photoelectron imaging study of a bimetallic Nb₂Au₆ ^- cluster. Theoretical calculations, in conjunction with the experimental data, reveal that Nb₂Au₆ ^-/0 possess high-symmetry D _6h structures featuring a Nb-Nb axis coordinated equatorially by an Au₆ ring. Chemical bonding analyses show that there are two π bonds and one σ bond in the Nb₂ moiety in Nb₂©Au₆, as well as five totally delocalized σ bonds. The Nb[triple bond, length as m-dash]Nb triple bond is strengthened significantly by the delocalized σ bonds, resulting in an extremely short Nb-Nb bond length comparable to the quintuple bond in gaseous Nb₂. The totally delocalized σ bonding in Nb₂©Au₆ is reminiscent of σ aromaticity, representing a new bonding mode in metal-ligand systems. The unusually short Nb-Nb bond length in Nb₂©Au₆ shows that the Au₆ ring can serve as a bridging ligand to facilitate multiple bonding in transition metal dimers via delocalized σ bonding.

SUBMITTER: Jian T

PROVIDER: S-EPMC5694916 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Nb2©Au6: a molecular wheel with a short Nb[triple bond, length as m-dash]Nb triple bond coordinated by an Au6 ring and reinforced by σ aromaticity.

Jian Tian T Cheung Ling Fung LF Czekner Joseph J Chen Teng-Teng TT Lopez Gary V GV Li Wei-Li WL Wang Lai-Sheng LS

Chemical science 20170915 11

We report a photoelectron spectroscopy and high-resolution photoelectron imaging study of a bimetallic Nb2Au6 - cluster. Theoretical calculations, in conjunction with the experimental data, reveal that Nb2Au6 -/0 possess high-symmetry D 6h structures featuring a Nb-Nb axis coordinated equatorially by an Au6 ring. Chemical bonding analyses show that there are two π bonds and one σ bond in the Nb2</ ...[more]

PMID: 29163907

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Project description:In a natural environment, Fe(ii) adsorbed onto the surfaces of natural particles to form various surface complex species can influence the transformation of contaminants. The reductive reactivity of the [[triple bond, length as m-dash]Fe(iii)]/[[triple bond, length as m-dash]Fe(ii)] couples are close correlated with the surrounding conditions. In this study, we investigated the effects of Si(iv) on the reductive reactivity of [[triple bond, length as m-dash]Fe(iii)]/[[triple bond, length as m-dash]Fe(ii)] couples adsorbed onto γ-Al2O3. Experiments were conducted under different conditions to investigate the effects of Si(iv) on the reactivity of [[triple bond, length as m-dash]Fe(iii)]/[[triple bond, length as m-dash]Fe(ii)] couples for 2-nitrophenol (2-NP, selected as the model pollutant) reduction in γ-Al2O3 suspensions. Kinetics results revealed that chemical adsorption is the rate limiting step in Fe(ii) and Si(iv) adsorption processes and the reduction of 2-NP is an endothermic reaction. The linear correlations between the reduced peak oxidation potential (E p) (versus SCE) and 2-NP reduction rate (ln k), and between the adsorbed Fe(ii) density (ρ Fe(II)) and ln k, illustrated that E p and ρ Fe(II) are two key factors in the inhibiting effects of Si(iv) on the reductive reactivity of Fe(iii)/Fe(ii) couples on γ-Al2O3. The results of Fe K-edge X-ray absorption spectroscopy revealed that the increase of Si(iv) concentration resulted in the gradual change in the composition of the adsorbed Fe species from pure [triple bond, length as m-dash]AlOFe+ (γ-Al2O3 surface-bound Fe(ii) species with higher reductive reactivity) to a mixture of [triple bond, length as m-dash]AlOFe+ and [triple bond, length as m-dash]SiOFe+ (SiO2 surface-bound Fe(ii) species with lower reductive reactivity), leading to the decrease in ρ Fe(II), the positive shift in E p, the increase in activation energy (E a), and consequently the decrease in the reduction rate (ln k) of 2-NP.

Project description:A systematic, efficient approach to first complexes containing a triple bond between niobium and the elements silicon, germanium or tin is reported. The approach involves a metathetical exchange of the niobium-centered nucleophile (NMe4)[Nb(CO)4(κ2-tmps)] (1) (tmps = MeSi(CH2PMe2)3) with a suitable organotetrel(ii)halide. Compound 1 was obtained from (NMe4)[Nb(CO)6] and the triphosphane tmps by photodecarbonylation. Reaction of 1 with the disilene E-Tbb(Br)Si[double bond, length as m-dash]Si(Br)Tbb in the presence of 4-dimethylaminopyridine afforded selectively the red-brown silylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Si-Tbb] (2-Si, Tbb = 4-tert-butyl-2,6-bis(bis(trimethylsilyl)methyl)phenyl). Similarly, treatment of 1 with E(ArMes)Cl (E = Ge, Sn; ArMes = 2,6-mesitylphenyl) afforded after elimination of (NMe4)Cl and two CO ligands the deep magenta colored germylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Ge-ArMes] (3-Ge), and the deep violet, light-sensitive stannylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Sn-ArMes] (3-Sn), respectively. Formation of 3-Sn proceeds via the niobiastannylene [(κ3-tmps)(CO)3Nb-SnArMes] (4-Sn), which was detected by IR and NMR spectroscopy. The niobium tetrylidyne complexes 2-Si, 3-Ge and 3-Sn were fully characterized and their solid-state structures determined by single-crystal X-ray diffraction studies. All complexes feature an almost linear tetrel coordination and the shortest Nb-E bond lengths (d(Nb-Si) = 232.7(2) pm; d(Nb-Ge) = 235.79(4) pm; d(Nb-Sn) = 253.3(1) pm) reported to date. Reaction of 3-Ge with a large excess of H2O afforded upon cleavage of the Nb-Ge triple bond the hydridogermanediol Ge(ArMes)H(OH)2. Photodecarbonylation of [CpNb(CO)4] (Cp = η5-C5H5) in the presence of Ge(ArMes)Cl afforded the red-orange chlorogermylidene complex [Cp(CO)3Nb[double bond, length as m-dash]Ge(ArMes)Cl] (5-Ge). The molecular structure of 5-Ge features an upright conformation of the germylidene ligand, a trigonal-planar coordinated Ge atom, and a Nb-Ge double bond length of 251.78(6) pm, which lies in-between the Nb-Ge triple bond length of 3-Ge (235.79(4) pm) and a Nb-Ge single bond length (267.3 pm). Cyclic voltammetric studies of 2-Si, 3-Ge, and 3-Sn reveal several electron-transfer steps. One-electron oxidation and reduction of the germylidyne complex of 3-Ge in THF are electrochemically reversible suggesting that both the radical cation and radical anion of 3-Ge are accessible species in solution.

Dataset Information

Nb₂©Au₆: a molecular wheel with a short Nb[triple bond, length as m-dash]Nb triple bond coordinated by an Au₆ ring and reinforced by σ aromaticity.

Publications

Nb<sub>2</sub>©Au<sub>6</sub>: a molecular wheel with a short Nb[triple bond, length as m-dash]Nb triple bond coordinated by an Au<sub>6</sub> ring and reinforced by σ aromaticity.

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