4 research outputs found
Cumulative number of data packages in the Knowledge Network for Biocomplexity until 2007-06-21
This data set records the cumulative number of data packages in the Knowledge Network for Biocomplexity (KNB) data repository through 2007-06-21. A data package represents a set of data files and metadata files that together make a coherent, citable unit for some particular scientific activity. Each data package in the KNB is described by a scientific metadata document and can be composed of one or more data files that contain various segments of the data in question
Lanthanide(III) Di- and Tetra-Nuclear Complexes Supported by a Chelating Tripodal Tris(Amidate) Ligand
Syntheses,
structural, and spectroscopic characterization of multinuclear trisÂ(amidate)
lanthanide complexes is described. Addition of K<sub>3</sub>[NÂ(<i>o</i>-PhNCÂ(O)<i><sup>t</sup></i>Bu)<sub>3</sub>] to LnX<sub>3</sub> (LnX<sub>3</sub> = LaBr<sub>3</sub>, CeI<sub>3</sub>, and NdCl<sub>3</sub>) in <i>N</i>,<i>N</i>-dimethylformamide (DMF) results in the generation of dinuclear complexes,
[LnÂ(NÂ(<i>o</i>-PhNCÂ(O)<sup><i>t</i></sup>Bu)<sub>3</sub>)Â(DMF)]<sub>2</sub>Â(ÎĽ-DMF)
(Ln = La (<b>1</b>), Ce (<b>2</b>), NdÂ(<b>3</b>)),
in good yields. Syntheses of tetranuclear complexes, [LnÂ(NÂ(<i>o</i>-PhNCÂ(O)<sup><i>t</i></sup>Bu)<sub>3</sub>)]<sub>4</sub> (Ln = Ce (<b>4</b>), NdÂ(<b>5</b>)), resulted
from protonolysis of LnÂ[NÂ(SiMe<sub>3</sub>)<sub>2</sub>]<sub>3</sub> (Ln = Ce, Nd) with NÂ(<i>o</i>-PhNCHÂ(O)<sup><i>t</i></sup>Bu)<sub>3</sub>. In the solid-state, complexes <b>1</b>–<b>5</b> exhibit coordination modes of the
tripodal trisÂ(amidate) ligand that are unique to the 4f elements and
have not been previously observed in transition metal systems
Bonding Trends Traversing the Tetravalent Actinide Series: Synthesis, Structural, and Computational Analysis of An<sup>IV</sup>(<sup>Ar</sup>acnac)<sub>4</sub> Complexes (An = Th, U, Np, Pu; <sup>Ar</sup>acnac = Ar<i>N</i>C(Ph)CHC(Ph)<i>O</i>; Ar = 3,5‑<sup><i>t</i></sup>Bu<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)
A series of tetravalent AnÂ(IV) complexes with a bis-phenyl
β-ketoiminate
N,O donor ligand has been synthesized with the aim of identifying
bonding trends and changes across the actinide series. The neutral
molecules are homoleptic with the formula AnÂ(<sup>Ar</sup>acnac)<sub>4</sub> (An = Th (<b>1</b>), U (<b>2</b>), Np (<b>3</b>), Pu (<b>4</b>); <sup>Ar</sup>acnac = Ar<i>N</i>CÂ(Ph)ÂCHCÂ(Ph)<i>O</i>; Ar = 3,5-<sup><i>t</i></sup>Bu<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) and were synthesized through
salt metathesis reactions with actinide chloride precursors. NMR and
electronic absorption spectroscopy confirm the purity of all four
new compounds and demonstrate stability in both solution and the solid
state. The Th, U, and Pu complexes were structurally elucidated by
single-crystal X-ray diffraction and shown to be isostructural in
space group <i>C</i>2/<i>c</i>. Analysis of the
bond lengths reveals shortening of the An–O and An–N
distances arising from the actinide contraction upon moving from <b>1</b> to <b>2</b>. The shortening is more pronounced upon
moving from <b>2</b> to <b>4</b>, and the steric constraints
of the tetrakis complexes appear to prevent the enhanced U–O
versus Pu–O orbital interactions previously observed in the
comparison of UI<sub>2</sub>(<sup>Ar</sup>acnac)<sub>2</sub> and PuI<sub>2</sub>(<sup>Ar</sup>acnac)<sub>2</sub> bis<i>-</i>complexes.
Computational analysis of models for <b>1</b>, <b>2</b>, and <b>4</b> (<b>1a</b>, <b>2a</b>, and <b>4a</b>, respectively) concludes that both the An–O and
the An–N bonds are predominantly ionic for all three molecules,
with the An–O bonds being slightly more covalent. Molecular
orbital energy level diagrams indicate the largest 5f-ligand orbital
mixing for <b>4a</b> (Pu), but spatial overlap considerations
do not lead to the conclusion that this implies significantly greater
covalency in the Pu–ligand bonding. QTAIM bond critical point
data suggest that both U–O/U–N and Pu–O/Pu–N
are marginally more covalent than the Th analogues
Bonding Trends Traversing the Tetravalent Actinide Series: Synthesis, Structural, and Computational Analysis of An<sup>IV</sup>(<sup>Ar</sup>acnac)<sub>4</sub> Complexes (An = Th, U, Np, Pu; <sup>Ar</sup>acnac = Ar<i>N</i>C(Ph)CHC(Ph)<i>O</i>; Ar = 3,5‑<sup><i>t</i></sup>Bu<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)
A series of tetravalent AnÂ(IV) complexes with a bis-phenyl
β-ketoiminate
N,O donor ligand has been synthesized with the aim of identifying
bonding trends and changes across the actinide series. The neutral
molecules are homoleptic with the formula AnÂ(<sup>Ar</sup>acnac)<sub>4</sub> (An = Th (<b>1</b>), U (<b>2</b>), Np (<b>3</b>), Pu (<b>4</b>); <sup>Ar</sup>acnac = Ar<i>N</i>CÂ(Ph)ÂCHCÂ(Ph)<i>O</i>; Ar = 3,5-<sup><i>t</i></sup>Bu<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) and were synthesized through
salt metathesis reactions with actinide chloride precursors. NMR and
electronic absorption spectroscopy confirm the purity of all four
new compounds and demonstrate stability in both solution and the solid
state. The Th, U, and Pu complexes were structurally elucidated by
single-crystal X-ray diffraction and shown to be isostructural in
space group <i>C</i>2/<i>c</i>. Analysis of the
bond lengths reveals shortening of the An–O and An–N
distances arising from the actinide contraction upon moving from <b>1</b> to <b>2</b>. The shortening is more pronounced upon
moving from <b>2</b> to <b>4</b>, and the steric constraints
of the tetrakis complexes appear to prevent the enhanced U–O
versus Pu–O orbital interactions previously observed in the
comparison of UI<sub>2</sub>(<sup>Ar</sup>acnac)<sub>2</sub> and PuI<sub>2</sub>(<sup>Ar</sup>acnac)<sub>2</sub> bis<i>-</i>complexes.
Computational analysis of models for <b>1</b>, <b>2</b>, and <b>4</b> (<b>1a</b>, <b>2a</b>, and <b>4a</b>, respectively) concludes that both the An–O and
the An–N bonds are predominantly ionic for all three molecules,
with the An–O bonds being slightly more covalent. Molecular
orbital energy level diagrams indicate the largest 5f-ligand orbital
mixing for <b>4a</b> (Pu), but spatial overlap considerations
do not lead to the conclusion that this implies significantly greater
covalency in the Pu–ligand bonding. QTAIM bond critical point
data suggest that both U–O/U–N and Pu–O/Pu–N
are marginally more covalent than the Th analogues