John G. Brennan

Electron-transfer reactions of trivalent uranium. Preparation and structure of (MeC/sub 5/H/sub 4/)/sub 3/U = NPh and ((MeC/sub 5/H/sub 4/)/sub 3/U)/sub 2/(. mu. -eta/sup 1/,eta/sup 2/-PhNCO)

The chemical preparation of the isocyanate (1) and imide (2) complexes is described. The most important structural feature of 2 is the presence of the imido functional group with a U-N distance of 2.019 (6) A and a U-N-C angle of 167.4 (6)/sup 0/. Comparison of this bond distance with that of previously prepared tricyclopentadienyluranium complexes, this measurement is the shortest U-N length reported. The essentially linear U-N-C angle suggests that both lone pairs of electrons on the nitrogen atom are involved in bonding to uranium and the U-N bond is best interpreted as a triple bond. The most interesting structural feature of complex l is the (PhNCO)/sup 2 -/ unit which bridges the 2 tetravalent uranium, U(C/sub 5/H/sub 4/CH/sub 3/)/sub 3/, fragments in an nu/sup 1/(U(2)-0), nu/sup 2/(U(1)NC(1)) fashion. 15 references, 2 figures.The chemical preparation of the isocyanate (1) and imide (2) complexes is described. The most important structural feature of 2 is the presence of the imido functional group with a U-N distance of 2.019 (6) A and a U-N-C angle of 167.4 (6)/sup 0/. Comparison of this bond distance with that of previously prepared tricyclopentadienyluranium complexes, this measurement is the shortest U-N length reported. The essentially linear U-N-C angle suggests that both lone pairs of electrons on the nitrogen atom are involved in bonding to uranium and the U-N bond is best interpreted as a triple bond. The most interesting structural feature of complex l is the (PhNCO)/sup 2 -/ unit which bridges the 2 tetravalent uranium, U(C/sub 5/H/sub 4/CH/sub 3/)/sub 3/, fragments in an nu/sup 1/(U(2)-0), nu/sup 2/(U(1)NC(1)) fashion. 15 references, 2 figures.

Preparation of the first molecular carbon monoxide complex of uranium, (Me3SiC5H4)3UCO

Exposure of a solution of the metallocene (I) to CO at 1 atm and 20°C yields the title complex (II), which may be stored for at least 2 years at - 80°C. (I) also reversibly absorbs CO in the solid state.

Intense Near‐IR Emission from Nanoscale Lanthanoid Fluoride Clusters

Lanthanoid-doped fluoride glasses are intense near-IR (NIR) emission sources because of the low-energy phonon characteristics of fluoride lattices. These materials are particularly useful in optical applications, because fluorides are absolutely air-stable. Unfortunately, the extreme insolubility of lanthanoid ions in the presence of fluoride sources has always presented a barrier to developing alternative synthetic approaches to LnFx materials, particularly in media that would preclude the incorporation of NIR-emission-quenching OH groups. Herein we demonstrate that by using unconventional chalcogen-based ligands we can dramatically alter the solubility characteristics of lanthanoid cations in the presence of fluoride anions. We describe the synthesis, structural characterization, and exceptional NIR emission properties of the largest known lanthanoid cluster. Exposure of in situ prepared Ln(SePh)3 to fluoride sources does not result in the immediate precipitation of solid LnF3. Metathesis reactions of Ln(SePh)3 with HgF2, CsF, or Me4NF have yet to deliver crystalline products, but reactions of Ln(SePh)3 with NH4F in pyridine with subsequent filtration and saturation of the solution (either by layering with hexane or slow cooling) result in the crystallization, in 5–20% yields, of nanoscale lanthanoid fluoride clusters that were shown, by low-temperature single crystal Xray diffraction, to be [(py)24Ln28F68(SePh)16] (Ln=Pr 1, Nd 2 ; py= pyridine; Equation (1)). An ORTEP diagram of the

Covalent Bonding and the Trans Influence in Lanthanide Compounds

A pair of mer-octahedral lanthanide chalcogenolate coordination complexes [(THF)(3)Ln(EC(6)F(5))(3) (Ln = Er, E = Se; Ln = Yb, E = S)] have been isolated and structurally characterized. Both compounds show geometry-dependent bond lengths, with the Ln-E bonds trans to the neutral donor tetrahydrofuran (THF) significantly shorter than the Ln-E bonds that are trans to negatively charged EC(6)F(5) ligands. Density functional theory calculations indicate that the structural trans influence evidenced by the differences in these bond lengths results from a covalent Ln-E interaction involving ligand p and Ln 5d orbitals.

Lanthanide Compounds with Fluorinated Aryloxide Ligands : Near-Infrared Emission from Nd, Tm, and Er

Ln(OC(6)F(5))(3) form stable, isolable compounds with 1,2-dimethoxyethane (DME). Monomeric (DME)(2)Ln(OC(6)F(5))(3) (Ln = Nd, Er, Tm) adopt seven coordinate structures with two chelating DME and three terminal phenoxide ligands. Both (py)(4)Er(OC(6)F(5))(3) and (THF)(3)Yb(OC(6)F(5))(3) were also prepared and structurally characterized, with the latter being a mer-octahedral compound with bond lengths that are geometry dependent. Emission experiments on crystalline powders of the Nd(III), Tm(III), and Er(III) DME derivatives show that these compounds are highly emissive near-infrared sources.

Synthesis of bis(η-1,3,5-tri-t-butylbenzene) sandwich complexes of yttrium(0) and gadolinium(0); the X-ray crystal structure of the first authentic lanthanide(0) complex, [Gd(η-But3C6H3)2]

The vapours of yttrium and gadolinium react with 1,3,5-tri-t-butylbenzene to afford the metal(0) complexes [(M(η-But3C6H3)2], M = Y, Gd; the X-ray crystal structure of the gadolinium complex shows the molecule to possess the parallel ring sandwich structure.

Lanthanide Clusters with Chalcogen Encapsulated Ln: NIR Emission from Nanoscale NdSe(x).

Ln(SePh)(3) (Ln = Ce, Pr, Nd) reacts with elemental Se in the presence of Na ions to give (py)(16)Ln(17)NaSe(18)(SePh)(16), a spherical cluster with a 1 nm diameter. All three rare-earth metals form isostructural products. The molecular structure contains a central Ln ion surrounded by eight five-coordinate Se(2-) that are then surrounded by a group of 16 Ln that define the cluster surface, with additional μ(3) and μ(5) Se(2-), μ(3) and μ(4) SePh(-), and pyridine donors saturating the vacant coordination sites of the surface Ln, and a Na ion coordinating to selenolates, a selenido, and pyridine ligands. NIR emission studies of the Nd compound reveal that this material has a 35% quantum efficiency, with four transitions from the excited state (4)F(3/2) ion to (4)I(9/2), (4)I(11/2), (4)I(13/2), and (4)I(15/2) states clearly evident. The presence of Na(+) is key to the formation of these larger clusters, where reactions using identical concentrations of Nd(SePh)(3) and Se with either Li or K led only to the isolation of (py)(8)Nd(8)Se(6)(SePh)(12).

Electron localization in the bis-arene complexes [(η-C6H6)2Cr] and [(η-C6H5Me)2Mo]: an investigation by photoelectron spectroscopy with variable photon energy

Abstract Relative partial photoionization cross sections have been measured for the valence bands of [(η-C6H6)2Cr] and [(η-C6H5Me)2Mo] over the photon energy ranges 24–80 eV ([(η-C6H6)2Cr]) and 24–100 eV ([(η-C6H5Me)2Mo]). Both compounds show pronounced intensity increases of the metal-based ionizations (a−11g and e−12g) in the region of the np subshell ionization potentials, attribute to nd resonant photoemission following np→nd giant resonant absorption. Shape resonances are also observed in the cross sections of these bands. For [(η-C6H5Me)2Mo], the two resonance processes are almost coincident in photon energy, but can be distinguished more clearly in the [(η-C6H6)2Cr] cross sections. Evidence for metal d—carbon 2pπ covalency in the e1g set of molecular orbitals is found, with features in the cross sections of the metal-based bands correlating with those in the e−11g ionizations. The e−11u bands show an essentially monotonic cross section decrease with photon energy.

Zinc, Cadmium, and Mercury Complexes with Fluorinated Selenolate Ligands

Reductive cleavage of C(6)F(5)SeSeC(6)F(5) with elemental M (M = Zn, Cd, and Hg) in pyridine results in the formation of (py)(2)Zn(SeC(6)F(5))(2), (py)(2)Cd(SeC(6)F(5))(2), and Hg(SeC(6)F(5))(2). Structural characterization of the Zn and Cd compounds reveals tetrahedral coordination environments, while the Hg compound shows a complicated series of linear structures with two short, nearly linear Hg-Se bonds, up to two longer and perpendicular Hg...Se interactions, and no coordinated pyridine ligands. All three compounds exhibit well-defined intermolecular pi-pi-stacking interactions in the solid state. They are volatile and decompose at elevated temperatures to give MSe and either (SeC(6)F(5))(2) or Se(C(6)F(5))(2).

2,2′-Bipyridine complexes of the lithium chalcogenolates Li(EPh) and Li(NC5H4E-2)(E = S or Se)

2,2′-Bipyridine (bipy) forms stable crystalline co-ordination complexes with lithium benzeneselenolate and lithium pyridine-2-selenolate. The compounds are insoluble in aromatic hydrocarbons, slightly soluble in pyridine, and extremely soluble in tetrahydrofuran, from which they can be crystallized in ca. 70% yield. Both complexes have been characterized by elemental analysis, NMR, IR, and single-crystal X-ray diffraction. Compound [{Li(bipy)(SePh)}2]1[space group p21/m, a= 9.493(4), b= 16.866(5), c= 10.112(9), β= 114.53(6)° and Z= 4] is a dimer containing two lithium ions bridged by a pair of symmetric benzeneselenolate ligands, with bidentate bipy ligands bound to each lithium ion. In compound [{Li(bipy)(NC5H4Se-2)}2]2[space group P21/n, a= 10.361(5), b= 13.521(4), c= 11.062(5)A, β= 117.21(4)° and Z= 4] each lithium ion is bound to a bidentate bipy ligand, one bridging selenium atom, and the nitrogen atom from the second bridging pyridine-2-selenolate ligand, thus forming an eight-membered Li–Se–C–N–Li–Se–C–N ring. The analogous lithium thiolates have also been prepared in 70% yield; they are not isostructural with the selenolates.