7 research outputs found
The sparse Blume-Emery-Griffiths model of associative memories
We analyze the Blume-Emery-Griffiths (BEG) associative memory with sparse
patterns and at zero temperature. We give bounds on its storage capacity
provided that we want the stored patterns to be fixed points of the retrieval
dynamics. We compare our results to that of other models of sparse neural
networks and show that the BEG model has a superior performance compared to
them.Comment: 23 p
Uranyl and/or Rare-Earth Mellitates in Extended OrganicāInorganic Networks: A Unique Case of Heterometallic CationāCation Interaction with U<sup>VI</sup>ī»OāLn<sup>III</sup> Bonding (Ln = Ce, Nd)
A series of uranyl and lanthanide (trivalent Ce, Nd)
mellitates
(<i>mel</i>) has been hydrothermally synthesized in aqueous
solvent. Mixtures of these 4f and 5f elements also revealed the formation
of a rare case of lanthanideāuranyl coordination polymers.
Their structures, determined by XRD single-crystal analysis, exhibit
three distinct architectures. The pure lanthanide mellitate Ln<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub>(<i>mel</i>) possesses
a 3D framework built up from the connection of isolated LnO<sub>6</sub>(H<sub>2</sub>O)<sub>3</sub> polyhedra (tricapped trigonal prism)
through the mellitate ligand. The structure of the uranyl mellitate
(UO<sub>2</sub>)<sub>3</sub>(H<sub>2</sub>O)<sub>6</sub>(<i>mel</i>)Ā·11.5H<sub>2</sub>O is lamellar and consists of 8-fold coordinated
uranium atoms linked to each other through the organic ligand giving
rise to the formation of a 2D 3<sup>6</sup> net. The third structural
type, (UO<sub>2</sub>)<sub>2</sub>LnĀ(OH)Ā(H<sub>2</sub>O)<sub>3</sub>(<i>mel</i>)Ā·2.5H<sub>2</sub>O, involves direct oxygen
bondings between the lanthanide and uranyl centers, with the isolation
of a heterometallic dinuclear motif. The 9-fold coordinated Ln cation,
LnO<sub>5</sub>(OH)Ā(H<sub>2</sub>O)<sub>3</sub>, is linked to the
7-fold coordinated uranyl (UO<sub>2</sub>)ĀO<sub>4</sub>(OH) (pentagonal
bipyramid) via one Ī¼<sub>2</sub>-hydroxo group and one Ī¼<sub>2</sub>-oxo group. The latter is shared between the uranyl bonding
(Uī»O = 1.777(4)/1.779(6) Ć
) and a long LnāO bonding
(CeāO = 2.822(4) Ć
; NdāO = 2.792(6) Ć
). This
unusual linkage is a unique illustration of the so-called cationācation
interaction associating 4f and 5f metals. The dinuclear motif is then
further connected through the mellitate ligand, and this generates
organicāinorganic layers that are linked to each other via
discrete uranyl (UO<sub>2</sub>)ĀO<sub>4</sub> units (square bipyramid),
which ensure the three-dimensional cohesion of the structure. The
mixed UāLn carboxylate is thermally decomposed from 260 to
280 Ā°C and then transformed into the basic uranium oxide (U<sub>3</sub>O<sub>8</sub>) together with UāLn oxide with the fluorite
structural type (ā(Ln,U)ĀO<sub>2</sub>ā). At 1400 Ā°C,
only fluorite type ā(Ln,U)ĀO<sub>2</sub>ā is formed with
the measured stoichiometry of U<sub>0.63</sub>Ce<sub>0.37</sub>O<sub>2</sub> and U<sub>0.60</sub>Nd<sub>0.40</sub>O<sub>2āĪ“</sub>
Uranyl and/or Rare-Earth Mellitates in Extended OrganicāInorganic Networks: A Unique Case of Heterometallic CationāCation Interaction with U<sup>VI</sup>ī»OāLn<sup>III</sup> Bonding (Ln = Ce, Nd)
A series of uranyl and lanthanide (trivalent Ce, Nd)
mellitates
(<i>mel</i>) has been hydrothermally synthesized in aqueous
solvent. Mixtures of these 4f and 5f elements also revealed the formation
of a rare case of lanthanideāuranyl coordination polymers.
Their structures, determined by XRD single-crystal analysis, exhibit
three distinct architectures. The pure lanthanide mellitate Ln<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub>(<i>mel</i>) possesses
a 3D framework built up from the connection of isolated LnO<sub>6</sub>(H<sub>2</sub>O)<sub>3</sub> polyhedra (tricapped trigonal prism)
through the mellitate ligand. The structure of the uranyl mellitate
(UO<sub>2</sub>)<sub>3</sub>(H<sub>2</sub>O)<sub>6</sub>(<i>mel</i>)Ā·11.5H<sub>2</sub>O is lamellar and consists of 8-fold coordinated
uranium atoms linked to each other through the organic ligand giving
rise to the formation of a 2D 3<sup>6</sup> net. The third structural
type, (UO<sub>2</sub>)<sub>2</sub>LnĀ(OH)Ā(H<sub>2</sub>O)<sub>3</sub>(<i>mel</i>)Ā·2.5H<sub>2</sub>O, involves direct oxygen
bondings between the lanthanide and uranyl centers, with the isolation
of a heterometallic dinuclear motif. The 9-fold coordinated Ln cation,
LnO<sub>5</sub>(OH)Ā(H<sub>2</sub>O)<sub>3</sub>, is linked to the
7-fold coordinated uranyl (UO<sub>2</sub>)ĀO<sub>4</sub>(OH) (pentagonal
bipyramid) via one Ī¼<sub>2</sub>-hydroxo group and one Ī¼<sub>2</sub>-oxo group. The latter is shared between the uranyl bonding
(Uī»O = 1.777(4)/1.779(6) Ć
) and a long LnāO bonding
(CeāO = 2.822(4) Ć
; NdāO = 2.792(6) Ć
). This
unusual linkage is a unique illustration of the so-called cationācation
interaction associating 4f and 5f metals. The dinuclear motif is then
further connected through the mellitate ligand, and this generates
organicāinorganic layers that are linked to each other via
discrete uranyl (UO<sub>2</sub>)ĀO<sub>4</sub> units (square bipyramid),
which ensure the three-dimensional cohesion of the structure. The
mixed UāLn carboxylate is thermally decomposed from 260 to
280 Ā°C and then transformed into the basic uranium oxide (U<sub>3</sub>O<sub>8</sub>) together with UāLn oxide with the fluorite
structural type (ā(Ln,U)ĀO<sub>2</sub>ā). At 1400 Ā°C,
only fluorite type ā(Ln,U)ĀO<sub>2</sub>ā is formed with
the measured stoichiometry of U<sub>0.63</sub>Ce<sub>0.37</sub>O<sub>2</sub> and U<sub>0.60</sub>Nd<sub>0.40</sub>O<sub>2āĪ“</sub>
Single Crystal Synthesis Methods Dedicated to Structural Investigations of Very Low Solubility Mixed-Actinide Oxalate Coordination Polymers
Two crystal growth methods dedicated to very low solubility
actinide
coordination polymers have been developed and applied to the synthesis
of mixed actinideĀ(IV)āactinideĀ(IV) or actinideĀ(IV)āactinideĀ(III)
oxalate single crystals of a size (typically 100ā300 Ī¼m)
suitable for isolating them and examining their crystal structure.
These methods have been optimized on mixed systems composed of UĀ(IV)
and lanthanide (surrogate of trivalent actinides) and then assessed
on UĀ(IV)āAmĀ(III), PuĀ(IV)āAmĀ(III), and UĀ(IV)āPuĀ(IV)
mixtures. Three types of single crystals characterized by different
structures have been obtained according to the synthesis and the chemical
conditions. This is the first time that these well-known or recently
discovered key compounds are formed by crystal growth methods specifically
developed for actinide crystal handling (i.e., in glove boxes), thus
enabling direct structural studies on transuranium element systems
and acquisition of basic data. Characterization by X-ray diffraction,
UVāvisible solid spectroscopy, thermal ionization mass spectroscopy
(TIMS), energy-dispersive X-ray spectroscopy (EDS), and inductively
coupled plasma atomic emission spectroscopy (ICP-AES) demonstrates
the potentialities and complementarity of the two crystal growth methods
for obtaining the targeted mixed oxalates (actinide oxidation state
and presence of both metallic ions in the crystal). More generally,
this development opens broad prospects for single crystal synthesis
of novel actinide organic frameworks and their structural description
Crystal Growth and First Crystallographic Characterization of Mixed Uranium(IV)āPlutonium(III) Oxalates
The mixed-actinide uraniumĀ(IV)āplutoniumĀ(III)
oxalate single crystals (NH<sub>4</sub>)<sub>0.5</sub>[Pu<sup>III</sup><sub>0.5</sub>U<sup>IV</sup><sub>0.5</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ā·H<sub>2</sub>O]Ā·<i>n</i>H<sub>2</sub>O (<b>1</b>) and (NH<sub>4</sub>)<sub>2.7</sub>Pu<sup>III</sup><sub>0.7</sub>U<sup>IV</sup><sub>1.3</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>5</sub>Ā·<i>n</i>H<sub>2</sub>O (<b>2</b>) have been prepared by the diffusion of different ions through membranes
separating compartments of a triple cell. UVāvis, Raman, and
thermal ionization mass spectrometry analyses demonstrate the presence
of both uranium and plutonium metal cations with conservation of the
initial oxidation state, U<sup>IV</sup> and Pu<sup>III</sup>, and
the formation of mixed-valence, mixed-actinide oxalate compounds.
The structure of <b>1</b> and an average structure of <b>2</b> were determined by single-crystal X-ray diffraction and
were solved by direct methods and Fourier difference techniques. Compounds <b>1</b> and <b>2</b> are the first mixed uraniumĀ(IV)āplutoniumĀ(III)
compounds to be structurally characterized by single-crystal X-ray
diffraction. The structure of <b>1</b>, space group <i>P</i>4/<i>n</i>, <i>a</i> = 8.8558(3) Ć
, <i>b</i> = 7.8963(2) Ć
, <i>Z</i> = 2, consists of
layers formed by four-membered rings of the two actinide metals occupying
the same crystallographic site connected through oxalate ions. The
actinide atoms are nine-coordinated by oxygen atoms from four bidentate
oxalate ligands and one water molecule, which alternates up and down
the layer. The single-charged cations and nonbonded water molecules
are disordered in the same crystallographic site. For compound <b>2</b>, an average structure has been determined in space group <i>P</i>6/<i>mmm</i> with <i>a</i> = 11.158(2)
Ć
and <i>c</i> = 6.400(1) Ć
. The honeycomb-like
framework [Pu<sup>III</sup><sub>0.7</sub>U<sup>IV</sup><sub>1.3</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>5</sub>]<sup>2.7ā</sup> results
from a three-dimensional arrangement of mixed (U<sub>0.65</sub>Pu<sub>0.35</sub>)ĀO<sub>10</sub> polyhedra connected by five bis-bidentate
Ī¼<sup>2</sup>-oxalate ions in a trigonal-bipyramidal configuration
Crystal Growth and First Crystallographic Characterization of Mixed Uranium(IV)āPlutonium(III) Oxalates
The mixed-actinide uraniumĀ(IV)āplutoniumĀ(III)
oxalate single crystals (NH<sub>4</sub>)<sub>0.5</sub>[Pu<sup>III</sup><sub>0.5</sub>U<sup>IV</sup><sub>0.5</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ā·H<sub>2</sub>O]Ā·<i>n</i>H<sub>2</sub>O (<b>1</b>) and (NH<sub>4</sub>)<sub>2.7</sub>Pu<sup>III</sup><sub>0.7</sub>U<sup>IV</sup><sub>1.3</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>5</sub>Ā·<i>n</i>H<sub>2</sub>O (<b>2</b>) have been prepared by the diffusion of different ions through membranes
separating compartments of a triple cell. UVāvis, Raman, and
thermal ionization mass spectrometry analyses demonstrate the presence
of both uranium and plutonium metal cations with conservation of the
initial oxidation state, U<sup>IV</sup> and Pu<sup>III</sup>, and
the formation of mixed-valence, mixed-actinide oxalate compounds.
The structure of <b>1</b> and an average structure of <b>2</b> were determined by single-crystal X-ray diffraction and
were solved by direct methods and Fourier difference techniques. Compounds <b>1</b> and <b>2</b> are the first mixed uraniumĀ(IV)āplutoniumĀ(III)
compounds to be structurally characterized by single-crystal X-ray
diffraction. The structure of <b>1</b>, space group <i>P</i>4/<i>n</i>, <i>a</i> = 8.8558(3) Ć
, <i>b</i> = 7.8963(2) Ć
, <i>Z</i> = 2, consists of
layers formed by four-membered rings of the two actinide metals occupying
the same crystallographic site connected through oxalate ions. The
actinide atoms are nine-coordinated by oxygen atoms from four bidentate
oxalate ligands and one water molecule, which alternates up and down
the layer. The single-charged cations and nonbonded water molecules
are disordered in the same crystallographic site. For compound <b>2</b>, an average structure has been determined in space group <i>P</i>6/<i>mmm</i> with <i>a</i> = 11.158(2)
Ć
and <i>c</i> = 6.400(1) Ć
. The honeycomb-like
framework [Pu<sup>III</sup><sub>0.7</sub>U<sup>IV</sup><sub>1.3</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>5</sub>]<sup>2.7ā</sup> results
from a three-dimensional arrangement of mixed (U<sub>0.65</sub>Pu<sub>0.35</sub>)ĀO<sub>10</sub> polyhedra connected by five bis-bidentate
Ī¼<sup>2</sup>-oxalate ions in a trigonal-bipyramidal configuration
Crystal Growth and First Crystallographic Characterization of Mixed Uranium(IV)āPlutonium(III) Oxalates
The mixed-actinide uraniumĀ(IV)āplutoniumĀ(III)
oxalate single crystals (NH<sub>4</sub>)<sub>0.5</sub>[Pu<sup>III</sup><sub>0.5</sub>U<sup>IV</sup><sub>0.5</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ā·H<sub>2</sub>O]Ā·<i>n</i>H<sub>2</sub>O (<b>1</b>) and (NH<sub>4</sub>)<sub>2.7</sub>Pu<sup>III</sup><sub>0.7</sub>U<sup>IV</sup><sub>1.3</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>5</sub>Ā·<i>n</i>H<sub>2</sub>O (<b>2</b>) have been prepared by the diffusion of different ions through membranes
separating compartments of a triple cell. UVāvis, Raman, and
thermal ionization mass spectrometry analyses demonstrate the presence
of both uranium and plutonium metal cations with conservation of the
initial oxidation state, U<sup>IV</sup> and Pu<sup>III</sup>, and
the formation of mixed-valence, mixed-actinide oxalate compounds.
The structure of <b>1</b> and an average structure of <b>2</b> were determined by single-crystal X-ray diffraction and
were solved by direct methods and Fourier difference techniques. Compounds <b>1</b> and <b>2</b> are the first mixed uraniumĀ(IV)āplutoniumĀ(III)
compounds to be structurally characterized by single-crystal X-ray
diffraction. The structure of <b>1</b>, space group <i>P</i>4/<i>n</i>, <i>a</i> = 8.8558(3) Ć
, <i>b</i> = 7.8963(2) Ć
, <i>Z</i> = 2, consists of
layers formed by four-membered rings of the two actinide metals occupying
the same crystallographic site connected through oxalate ions. The
actinide atoms are nine-coordinated by oxygen atoms from four bidentate
oxalate ligands and one water molecule, which alternates up and down
the layer. The single-charged cations and nonbonded water molecules
are disordered in the same crystallographic site. For compound <b>2</b>, an average structure has been determined in space group <i>P</i>6/<i>mmm</i> with <i>a</i> = 11.158(2)
Ć
and <i>c</i> = 6.400(1) Ć
. The honeycomb-like
framework [Pu<sup>III</sup><sub>0.7</sub>U<sup>IV</sup><sub>1.3</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>5</sub>]<sup>2.7ā</sup> results
from a three-dimensional arrangement of mixed (U<sub>0.65</sub>Pu<sub>0.35</sub>)ĀO<sub>10</sub> polyhedra connected by five bis-bidentate
Ī¼<sup>2</sup>-oxalate ions in a trigonal-bipyramidal configuration