25 research outputs found
A Highly Adjustable Coordination System: Nanotubular and Molecular Cage Species in Uranyl Ion Complexes with Kemp’s Triacid
No full textA unique example
of topology tailoring in a uranyl–organic
system is provided by the three-pronged Kemp’s tricarboxylate
ligand. While unexceptional one-dimensional polymers are formed with
uranyl alone under solvo-hydrothermal conditions, addition of Ni<sup>2+</sup> ions yields the nanotubular species [(UO<sub>2</sub>)<sub>2</sub>Ni(L)<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>]<sub>∞</sub>, with a hydrophilic inner cavity lined by hydrated Ni<sup>2+</sup> ions, and a hydrophobic outer surface. The further presence of 2,2′-bipyridine
brings about the trapping of Ni<sup>2+</sup> ions into counterions
and formation of the octanuclear pseudocubic cage [(UO<sub>2</sub>)<sub>8</sub>(L)<sub>6</sub>(H<sub>2</sub>O)<sub>6</sub>]<sup>2–</sup>
Lanthanide Ion Complexes with 2-, 3-, or 4-Sulfobenzoate and Cucurbit[6]uril
No full textThe reaction of lanthanide nitrate, trifluoromethanesulfonate,
or chloride salts with the three positional isomers of sulfobenzoic
acid (SBH<sub>2</sub>) in the presence of cucurbit[6]uril (CB6) under
hydrothermal conditions yielded 13 complexes which were crystallographically
characterized. The ortho isomer gave a series of one-dimensional polymeric
complexes of columnar shape, {[Ln(2-SB)(NO<sub>3</sub>)(H<sub>2</sub>O)<sub>2</sub>]<sub>2</sub>CB6}·<i>x</i>H<sub>2</sub>O [isomorphous for Ln = La (<b>1</b>) and Ce (<b>2</b>), <i>x</i> = 10 or 11], {[Nd(2-SB)(H<sub>2</sub>O)<sub>3</sub>][Nd(2-SB)(H<sub>2</sub>O)<sub>4</sub>]CB6}·2NO<sub>3</sub>·7.5H<sub>2</sub>O (<b>3</b>), and {[Ln(2-SB)(H<sub>2</sub>O)<sub>4</sub>]<sub>2</sub>CB6}·2NO<sub>3</sub>·<i>x</i>H<sub>2</sub>O [isomorphous for Ln = Eu (<b>4</b>), Dy (<b>5</b>), Er (<b>6</b>), and Yb (<b>7</b>), <i>x</i> = 5 or 6]. These compounds all comprise carboxylate-bridged
dinuclear units connecting the CB6 molecules through lanthanide–carbonyl
coordination, and they differ by sulfonate bonding and formation of
a chelate ring being only present in <b>1</b>–<b>3</b>. In contrast, [Lu(2-SB)(H<sub>2</sub>O)<sub>7</sub>]<sub>2</sub>·CB6·2NO<sub>3</sub>·7H<sub>2</sub>O (<b>8</b>) does not display sulfonate and carbonyl coordination, the carboxylate
group being monodentate and the complex species being held as a lid
over the CB6 portal by hydrogen bonding. The complexes obtained from
erbium trifluoromethanesulfonate and chloride salts, {[Er(2-SB)(H<sub>2</sub>O)<sub>4</sub>]<sub>2</sub>CB6}·2CF<sub>3</sub>SO<sub>3</sub>·2.5H<sub>2</sub>O (<b>9</b>) and [Er(2-SB)(H<sub>2</sub>O)<sub>7</sub>]<sub>2</sub>·CB6·2Cl·6H<sub>2</sub>O (<b>10</b>), present the same features as <b>4</b>–<b>7</b> and <b>8</b>, respectively. The meta
isomer is in the form of the carboxybenzosulfonate 3-SBH<sup>–</sup>, with the carboxylic acid retaining its proton, in the isomorphous
complexes {[Ln(3-SBH)(H<sub>2</sub>O)<sub>4</sub>]<sub>2</sub>CB6}·4NO<sub>3</sub> [Ln = Ce (<b>11</b>) or Nd (<b>12</b>)]. These
complexes display the feature, unusual in this series, of coordination
by the monodentate sulfonate group only. A columnar assembly is formed
by coordination of each metal ion to two CB6 molecules, the 3-SBH<sup>–</sup> ligand having no role in the polymer formation. Finally,
the para isomer is only coordinated by the chelating carboxylate group
in [Nd<sub>1.5</sub>(4-SB)(CB6)(NO<sub>3</sub>)(H<sub>2</sub>O)<sub>6.5</sub>]·4-SBH·4-SBH<sub>1.5</sub>·15H<sub>2</sub>O (<b>13</b>)
Uranyl Ion Complexes with Ammoniobenzoates as Assemblers for Cucurbit[6]uril Molecules
No full textThe crystal structures of the complexes formed under hydrothermal conditions by uranyl ions with 4-aminobenzoic (HL1), 4-amino-3-methylbenzoic (HL2), 4-(aminomethyl)benzoic (HL3), and 3-amino-5-hydroxybenzoic (HL4) acids, in the presence of cucurbit[6]uril (CB6), have been determined. These ligands have been chosen because, in their zwitterionic form, they display both a metal-complexing carboxylate group and an ammonium group able to associate with CB6 through ion-dipole and hydrogen bonding interactions. The complexes [H<sub>2</sub>NMe<sub>2</sub>]<sub>2</sub>[(UO<sub>2</sub>)<sub>2</sub>(L1)<sub>2</sub>O(OH)(H<sub>2</sub>O)]<sub>2</sub>·CB6·15H<sub>2</sub>O (<b>1</b>) and [H<sub>2</sub>NMe<sub>2</sub>]<sub>2</sub>[(UO<sub>2</sub>)<sub>2</sub>(L2)<sub>2</sub>O(OH)(H<sub>2</sub>O)]<sub>2</sub>·CB6·17H<sub>2</sub>O (<b>2</b>) were obtained in the presence of dimethylformamide, which gives dimethylammonium ions in situ. The latter are held at the CB6 portals, while the tetranuclear uranyl complex with the aminobenzoate anions is not bound to CB6. The neutral, ammonium-containing form of the ligand is present in [UO<sub>2</sub>(HL3)(OH)(HCOO)(H<sub>2</sub>O)]<sub>2</sub>·2CB6·2DMF·14H<sub>2</sub>O (<b>3</b>), in which the di(μ<sub>2</sub>-hydroxo)-bridged, dinuclear uranyl complex displays two diverging, monodentate HL3 ligands. The latter are associated with two CB6 molecules to give a dumbbell-shaped supramolecular assembly. Three CB6 molecules are assembled around a tetranuclear uranyl complex in [(UO<sub>2</sub>)<sub>4</sub>(HL3)<sub>2</sub>(L3)O<sub>2</sub>(OH)<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>]·2CB6·0.5CB8·HL3·NO<sub>3</sub>·20H<sub>2</sub>O (<b>4</b>), with two of them being bridging and giving rise to a one-dimensional, linear supramolecular architecture. Finally, the 3-amino substituted ligand HL4 gives the highly symmetric complex [UO<sub>2</sub>(HL4)(L4)<sub>2</sub>]·3CB6·16H<sub>2</sub>O (<b>5</b>), in which the uranyl ion is chelated by three carboxylate groups. Three CB6 molecules are assembled around the planar complex to give a triangular, discrete species. In compounds <b>3</b>–<b>5</b>, the usual packing of CB6 molecules into columns or layers is not retained as it is frequently in the presence of uranyl complexes. This is due to the CB6-assembling role of the heterodifunctional ligands, which hold the CB6 molecules at the periphery of mono-, di-, or tetranuclear uranyl complexes of quite usual, planar geometry
Increasing Complexity in the Uranyl Ion–Kemp’s Triacid System: From One- and Two-Dimensional Polymers to Uranyl–Copper(II) Dodeca- and Hexadecanuclear Species
No full textKemp’s
triacid (<i>cis</i>,<i>cis</i>-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic
acid, LH<sub>3</sub>) has recently been shown to be a versatile ligand
for the uranyl
ion, with the presence of additional nickel(II) cations allowing isolation
of nanotubular and cage species in particular. The high sensitivity
of the uranyl–LH<sub>3</sub> system to variations in the experimental
conditions was the incentive for the present investigation of different
solvents as organic components in solvo-hydrothermal synthesis methods
and of different additional species (metal cations, 2,2′-bipyridine).
Reaction of LH<sub>3</sub> with uranyl ions under purely hydrothermal
conditions gives [UO<sub>2</sub>(LH<sub>2</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·2H<sub>2</sub>O (<b>1</b>), an
unremarkable mononuclear complex. In the presence of manganese nitrate
and in water–THF or water–methanol, respectively, the
complexes [Hbipy][UO<sub>2</sub>(L)]·0.5H<sub>2</sub>O·0.25THF
(<b>2</b>) and [(UO<sub>2</sub>)<sub>3</sub>(MeL)<sub>2</sub>(OH)<sub>2</sub>(H<sub>2</sub>O)]·8MeOH (<b>3</b>) were obtained; <b>2</b> is a two-dimensional (2D) species,
while <b>3</b> is one-dimensional (1D) and contains the monoester
derivative of LH<sub>3</sub>, formed in situ. Another 2D compound,
[UO<sub>2</sub>Tb{(L)<sub>2</sub>H}(H<sub>2</sub>O)<sub>2</sub>] (<b>4</b>), crystallizes in the presence of terbium(III) nitrate.
The three complexes [(UO<sub>2</sub>)<sub>8</sub>{(L)<sub>6</sub>H<sub>2</sub>}(H<sub>2</sub>O)<sub>6</sub>]·H<sub>2</sub>O (<b>5</b>), [(UO<sub>2</sub>)<sub>8</sub>{(L)<sub>6</sub>H<sub>2</sub>}(H<sub>2</sub>O)<sub>6</sub>]·3H<sub>2</sub>O (<b>6</b>), and [Cu<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)(bipy)<sub>2</sub>(THF)<sub>2</sub>][(UO<sub>2</sub>)<sub>8</sub>{(L)<sub>6</sub>H}(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>·4H<sub>2</sub>O·7THF (<b>7</b>), which were obtained in the presence of copper(II) or nickel(II)
cations, all contain homometallic octanuclear cage-like species analogous
to that previously reported. The most interesting complexes in this
series, [(UO<sub>2</sub>)<sub>8</sub>Cu<sub>4</sub>(L)<sub>8</sub>(H<sub>2</sub>O)<sub>16</sub>]·9H<sub>2</sub>O (<b>8</b>) and [(UO<sub>2</sub>)<sub>10</sub>Cu<sub>6</sub>(L)<sub>10</sub>(OH)<sub>2</sub>(H<sub>2</sub>O)<sub>7</sub>] (<b>9</b>), were obtained together in water–THF and in the
presence of copper(II) cations. Compound <b>8</b> is a dodecanuclear
metallacycle comprising four (UO<sub>2</sub>)<sub>2</sub>Cu trinuclear
subunits, in which the central copper atom is bound to two uranyl
oxo groups, arranged in helical geometry. Compound <b>9</b> is
a large, hexadecanuclear cage-like species devoid of any crystallographic
symmetry. In both <b>8</b> and <b>9</b>, uranyl ions are
topologically sufficient for the formation of the cyclic or cage molecules,
and the hydrated copper ions are located inside. The curved shape
of the three-pronged Kemp’s tricarboxylate ligand appears well
suited to the formation of closed species (nanotubes, rings, and cages),
which are in all cases coated on the outside by the hydrophobic parts
of the ligands
Coordination Polymers and Cage-Containing Frameworks in Uranyl Ion Complexes with <i>rac</i>- and (1<i>R</i>,2<i>R</i>)-<i>trans</i>-1,2-Cyclohexanedicarboxylates: Consequences of Chirality
No full textRacemic
and enantiopure (1<i>R</i>,2<i>R</i>) forms of <i>trans</i>-1,2-cyclohexanedicarboxylic acid (H<sub>2</sub>chdc
and <i>R</i>-H<sub>2</sub>chdc, respectively) have been
used in the synthesis of a series of 13 uranyl ion complexes, all
obtained under solvo-hydrothermal conditions and in the presence of
additional metal cations and/or <i>N</i>-donor ligands.
While the homometallic complex [UO<sub>2</sub>(<i>R</i>-chdc)]
(<b>1</b>) was only obtained with the enantiopure ligand, complexes
[UO<sub>2</sub>(chdc)(THF)] (<b>2</b>), [UO<sub>2</sub>(chdc)(DMF)]
(<b>3</b>), and [UO<sub>2</sub>(chdc)(NMP)] (<b>4</b>),
with a coordinated solvent molecule, were obtained from the racemic
form only; all crystallize as two-dimensional (2D) assemblies. The
two complexes [UO<sub>2</sub>(chdc)(bipy)](<b>5</b>) and [UO<sub>2</sub>(<i>R</i>-chdc)(bipy)] (<b>6</b>), where bipy
is 2,2′-bipyridine, are isomorphous since <b>5</b> crystallizes
as a racemic conglomerate; they are both one-dimensional (1D) homochiral,
helical polymers. The heterometallic complexes [UO<sub>2</sub>Cu(chdc)<sub>2</sub>(bipy)(H<sub>2</sub>O)]·H<sub>2</sub>O (<b>7</b>) and [UO<sub>2</sub>Cu(<i>R</i>-chdc)<sub>2</sub>(bipy)]·3H<sub>2</sub>O (<b>8</b>) crystallize as a 1D or a 2D species, respectively,
while [UO<sub>2</sub>Cd(<i>R</i>-chdc)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·H<sub>2</sub>O (<b>9</b>) displays
a 2D arrangement with the unusual Cairo pentagonal tiling topology.
The four complexes [(UO<sub>2</sub>)<sub>2</sub>Na<sub>2</sub>(chdc)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>10</b>), [(UO<sub>2</sub>)<sub>2</sub>Ag<sub>2</sub>(chdc)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>11</b>), [(UO<sub>2</sub>)<sub>2</sub>Na<sub>2</sub>(<i>R</i>-chdc)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>12</b>), and [(UO<sub>2</sub>)<sub>2</sub>Pb(<i>R</i>-chdc)<sub>3</sub>(H<sub>2</sub>O)<sub>4</sub>] (<b>13</b>) are closely related, all of them containing tetranuclear,
pseudotetrahedral [(UO<sub>2</sub>)<sub>4</sub>(chdc/<i>R</i>-chdc)<sub>6</sub>]<sup>4–</sup> cage motifs, that
are assembled into a three-dimensional (3D) framework by bridging
counterions (Na<sup>+</sup>, Ag<sup>+</sup>, or Pb<sup>2+</sup>).
These cages define a new pathway to assembly of such species based
on the unique coordination geometry of uranyl ion, differing from
the widely exploited use of octahedral metal ions
Coordination Polymers and Cage-Containing Frameworks in Uranyl Ion Complexes with <i>rac</i>- and (1<i>R</i>,2<i>R</i>)-<i>trans</i>-1,2-Cyclohexanedicarboxylates: Consequences of Chirality
No full textRacemic
and enantiopure (1<i>R</i>,2<i>R</i>) forms of <i>trans</i>-1,2-cyclohexanedicarboxylic acid (H<sub>2</sub>chdc
and <i>R</i>-H<sub>2</sub>chdc, respectively) have been
used in the synthesis of a series of 13 uranyl ion complexes, all
obtained under solvo-hydrothermal conditions and in the presence of
additional metal cations and/or <i>N</i>-donor ligands.
While the homometallic complex [UO<sub>2</sub>(<i>R</i>-chdc)]
(<b>1</b>) was only obtained with the enantiopure ligand, complexes
[UO<sub>2</sub>(chdc)(THF)] (<b>2</b>), [UO<sub>2</sub>(chdc)(DMF)]
(<b>3</b>), and [UO<sub>2</sub>(chdc)(NMP)] (<b>4</b>),
with a coordinated solvent molecule, were obtained from the racemic
form only; all crystallize as two-dimensional (2D) assemblies. The
two complexes [UO<sub>2</sub>(chdc)(bipy)](<b>5</b>) and [UO<sub>2</sub>(<i>R</i>-chdc)(bipy)] (<b>6</b>), where bipy
is 2,2′-bipyridine, are isomorphous since <b>5</b> crystallizes
as a racemic conglomerate; they are both one-dimensional (1D) homochiral,
helical polymers. The heterometallic complexes [UO<sub>2</sub>Cu(chdc)<sub>2</sub>(bipy)(H<sub>2</sub>O)]·H<sub>2</sub>O (<b>7</b>) and [UO<sub>2</sub>Cu(<i>R</i>-chdc)<sub>2</sub>(bipy)]·3H<sub>2</sub>O (<b>8</b>) crystallize as a 1D or a 2D species, respectively,
while [UO<sub>2</sub>Cd(<i>R</i>-chdc)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·H<sub>2</sub>O (<b>9</b>) displays
a 2D arrangement with the unusual Cairo pentagonal tiling topology.
The four complexes [(UO<sub>2</sub>)<sub>2</sub>Na<sub>2</sub>(chdc)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>10</b>), [(UO<sub>2</sub>)<sub>2</sub>Ag<sub>2</sub>(chdc)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>11</b>), [(UO<sub>2</sub>)<sub>2</sub>Na<sub>2</sub>(<i>R</i>-chdc)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>] (<b>12</b>), and [(UO<sub>2</sub>)<sub>2</sub>Pb(<i>R</i>-chdc)<sub>3</sub>(H<sub>2</sub>O)<sub>4</sub>] (<b>13</b>) are closely related, all of them containing tetranuclear,
pseudotetrahedral [(UO<sub>2</sub>)<sub>4</sub>(chdc/<i>R</i>-chdc)<sub>6</sub>]<sup>4–</sup> cage motifs, that
are assembled into a three-dimensional (3D) framework by bridging
counterions (Na<sup>+</sup>, Ag<sup>+</sup>, or Pb<sup>2+</sup>).
These cages define a new pathway to assembly of such species based
on the unique coordination geometry of uranyl ion, differing from
the widely exploited use of octahedral metal ions
Ag<sup>I</sup> and Pb<sup>II</sup> as Additional Assembling Cations in Uranyl Coordination Polymers and Frameworks
No full textFive
mono- or polycarboxylic acids have been used to generate
a series of eight heterometallic uranyl complexes involving silver(I)
or lead(II) cations, all synthesized under (solvo)-hydrothermal conditions.
Pimelic acid (H<sub>2</sub>pim) gave complexes [Ag(bipy)<sub>2</sub>]<sub>2</sub>[UO<sub>2</sub>(pim)(NO<sub>3</sub>)]<sub>2</sub> (<b>1</b>) and [UO<sub>2</sub>Pb(pim)<sub>2</sub>(bipy)(H<sub>2</sub>O)]·0.5bipy·H<sub>2</sub>O (<b>2</b>) (bipy = 2,2′-bipyridine),
which both crystallize as one-dimensional (1D) polymers, but differ
in that the silver(I) cations are separate counterions, while carboxylate-bound
lead(II) cations are an essential component of the polymer. Only silver(I)-containing
species were obtained with all-<i>cis</i>-1,3,5-cyclohexanetricarboxylic
acid (H<sub>3</sub>chtc), [UO<sub>2</sub>Ag(chtc)(H<sub>2</sub>O)<sub>2</sub>] (<b>3</b>) and [Ag(bipy) (CH<sub>3</sub>CN)]<sub>2</sub>[UO<sub>2</sub>(chtc)]<sub>2</sub> (<b>4</b>); both contain
two-dimensional (2D) uranyl carboxylate subunits with honeycomb {6<sup>3</sup>} topology, these being united into a three-dimensional (3D)
framework with the lonsdaleite {6<sup>6</sup>} topology by bridging,
oxo-bound silver(I) cations in <b>3</b>. Both silver- and lead-containing
complexes were obtained with 3,3′,4,4′-biphenyltetracarboxylic
acid (H<sub>4</sub>bptc), [UO<sub>2</sub>Ag(bptc)(4,4′-bipyH)]
(<b>5</b>) and [UO<sub>2</sub>Pb(bptc)(bipy)<sub>2</sub>] (<b>6</b>) (4,4′-bipy = 4,4′-bipyridine), and they both
display a 2D uranyl carboxylate network with the {4<sup>4</sup>.6<sup>2</sup>} topology, the additional cations and <i>N</i>-donors
being decorating species. In this case, a higher dimensionality was
obtained not with an additional cation, but with a coordinated <i>N</i>-methyl-2-pyrrolidone (NMP) molecule, since [(UO<sub>2</sub>)<sub>2</sub>(bptc)(NMP)<sub>1.5</sub>(H<sub>2</sub>O)<sub>1.5</sub>]·1.5H<sub>2</sub>O (<b>7</b>) crystallizes as a three-dimensional
(3D) framework. In the presence of silver(I), 3-pyrimidin-2-yl-benzoic
acid (Hpyb) gave the complex [UO<sub>2</sub>Ag(pyb)<sub>3</sub>(H<sub>2</sub>O)<sub>2</sub>]·4H<sub>2</sub>O (<b>8</b>), in
which the two coordination sites are occupied in accord with Hard/Soft
Acid/Base (HSAB) principles, uranyl being chelated by three carboxylate
groups and silver(I) being bound to nitrogen atoms; the 1D polymer
formed bridges to another through silver–uranyl oxo bonding.
In contrast, the homometallic, molecular complex [UO<sub>2</sub>(pyb)<sub>2</sub>(bipy)] (<b>9</b>) was obtained in the presence of lead(II)
cations. The lead-containing complex with 2,6-pyridinedicarboxylic
acid (H<sub>2</sub>pydc), [UO<sub>2</sub>Pb<sub>2</sub>(pydc)<sub>2</sub>(phen)<sub>2</sub>(HCOO)<sub>1.5</sub>(NO<sub>3</sub>)<sub>0.5</sub>]·0.5H<sub>2</sub>O (<b>10</b>) (phen = 1,10-phenanthroline),
crystallizes as a 1D polymer in which uranyl is bound to two O,N,O-donors,
as usual with this ligand, polymerization being due to lateral double
lead(II) bridges. Variations in uranyl emission maxima positions appear
to be essentially related to the uranium coordination number within
the present series
Tetrahydrofurantetracarboxylic Acid: An Isomerizable Framework-Forming Ligand in Homo- and Heterometallic Complexes with UO<sub>2</sub><sup>2+</sup>, Ag<sup>+</sup>, and Pb<sup>2+</sup>
No full text(2<i>R*</i>,3<i>R*</i>,4<i>S*</i>,5<i>S*</i>)-Tetrahydrofurantetracarboxylic acid (H<sub>4</sub>thftc) has been
used as a ligand to synthesize five uranyl
ion complexes, three of them including additional silver(I) or lead(II)
metal cations. The complex [C(NH<sub>2</sub>)<sub>3</sub>]<sub>2</sub>[UO<sub>2</sub>(H<sub>2</sub>thftc)<sub>2</sub>] (<b>1</b>),
obtained in water at room temperature, is a discrete mononuclear species
in which the uranyl cation is bound to the tridentate coordination
site (involving the ether oxygen atom and the two adjoining carboxylate
groups) of two ligands, and extensive hydrogen bonding is present.
All the other complexes were obtained under (solvo)-hydrothermal conditions
giving rise to higher degrees of ligand deprotonation. [(UO<sub>2</sub>)<sub>3</sub>(Hthftc)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·2CH<sub>3</sub>CN (<b>2</b>) crystallizes as a two-dimensional (2D)
network with the V<sub>2</sub>O<sub>5</sub> topological type, whereas
in the heterometallic complex [(UO<sub>2</sub>)<sub>3</sub>Ag<sub>2</sub>(thftc)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·2H<sub>2</sub>O (<b>3</b>), similar 2D layers are assembled into a
three-dimensional (3D) framework by bridging Ag<sub>2</sub> moieties.
Lead(II) replaces uranyl in the tridentate coordination site in the
two complexes [UO<sub>2</sub>Pb(thftc)(H<sub>2</sub>O)] (<b>4</b>) and [UO<sub>2</sub>Pb(thftc)(H<sub>2</sub>O)<sub>2</sub>]·H<sub>2</sub>O (<b>5</b>), and the high connectivity of the ligand,
bound to seven metal cations through diverse chelating and bridging
interactions, ensures that both are 3D frameworks. Bonding of a uranyl
oxo group to either silver(I) or lead(II) is apparent in complexes <b>3</b> and <b>5</b>. The homometallic complexes [Ag<sub>3</sub>(Hthftc)] (<b>6</b>) and [Pb<sub>2</sub>(thftc)(H<sub>2</sub>O)] (<b>7</b>), devoid of uranyl cations, are both 3D frameworks
in which the ligand is bound to 11 or 9 metal cations, respectively.
Complex <b>6</b> is the single instance in this series in which
the ligand, originally in the <i>trans,cis,trans</i> form,
has undergone isomerization into the chiral <i>cis,trans,trans</i> (2<i>R*</i>,3<i>S*</i>,4<i>S*</i>,5<i>S*</i>) form through a process probably involving an ene-diol
intermediate. Only complexes <b>1</b>, <b>2</b>, and <b>4</b> display intense and well-resolved emission bands under excitation
at 420 nm in the solid state, the uranyl emission of complexes <b>3</b> and <b>5</b> being largely quenched
Uranyl Ion Complexes with all-<i>cis</i>-1,3,5-Cyclohexanetricarboxylate: Unexpected Framework and Nanotubular Assemblies
No full textall-<i>cis</i>-1,3,5-Cyclohexanetricarboxylic acid (LH<sub>3</sub>)
was reacted with uranyl nitrate under solvo-hydrothermal conditions,
either alone or in the presence of additional metal cations (Na<sup>+</sup>, K<sup>+</sup>, Ni<sup>2+</sup>, Cu<sup>2+</sup>, or Tb<sup>3+</sup>), resulting in the crystallization of a series of eight
complexes which were characterized by their crystal structures and
luminescence properties. The six complexes [UO<sub>2</sub>(H<sub>2</sub>O)<sub>5</sub>][UO<sub>2</sub>(L)]<sub>2</sub>·2H<sub>2</sub>O·3THF (<b>1</b>), [Ni(bipy)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>][UO<sub>2</sub>(L)]<sub>2</sub>·4H<sub>2</sub>O (<b>2</b>), [Ni(bipy)<sub>3</sub>][Ni(bipy)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>][UO<sub>2</sub>(L)]<sub>4</sub>·5H<sub>2</sub>O (<b>3</b>), [Ni(H<sub>2</sub>O)<sub>6</sub>][UO<sub>2</sub>(L)]<sub>2</sub>·2H<sub>2</sub>O (<b>4</b>), [Cu(H<sub>2</sub>O)<sub>6</sub>][UO<sub>2</sub>(L)]<sub>2</sub>·2H<sub>2</sub>O (<b>5</b>), and [Tb(H<sub>2</sub>O)<sub>8</sub>][UO<sub>2</sub>(L)]<sub>3</sub>·8H<sub>2</sub>O (<b>6</b>) all contain the
same {UO<sub>2</sub>(L)<sup>−</sup>}<sub>∞</sub> anionic
motif, in which the uranyl ion is tris-chelated by three L<sup>3–</sup> anions to give a two-dimensional assembly with hexagonal {6<sup>3</sup>} topology. The reaction of uranyl nitrate alone with LH<sub>3</sub> in water/<i>N</i>-methyl-2-pyrrolidone (NMP) yields
the complex [(UO<sub>2</sub>)<sub>3</sub>(L)<sub>2</sub>(NMP)<sub>2</sub>] (<b>7</b>), which crystallizes as a three-dimensional
framework. Finally, in the presence of Na<sup>+</sup>, K<sup>+</sup>, or even Kemp’s triacid (<i>cis</i>,<i>cis</i>-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid), the complex
[UO<sub>2</sub>(LH)] (<b>8</b>) is generated, the structure
of which displays a well-resolved nanotubular species possibly associated
with extremely disordered molecules or counterions of uncertain nature. These nanotubules
have {6<sup>3</sup>} topology and can be seen as resulting from the
folding of the two-dimensional assembly present in the former complexes.
Emission spectra measured in the solid state show the usual vibronic
fine structure, with various degrees of resolution and quenching
