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Fig. 4.7 a , b X-ray crystal structures of two representative complexes of o -TMeQ[6] with Nd 3 +
and Dy 3 +
cations, respectively; EDS of o -TMeQ[6] with 1:1 ratios of light: heavy lanthanides
supramolecular architectures and detailed interactions between the components, such
as a [PMo 12 O 40 ] 3 anion surrounded by (HO) 10 Q[5] molecules, and a (HO) 10 Q[5]
molecule surrounded by [PMo 12 O 40 ] 3 anions, in the K + /Ln 3 + /(HO) 10 Q[5]/
[PMo 12 O 40 ] 3 systems. Nine typical systems were selected as the representative
examples, such as Ce/Tb, Ce/Er, Ce/Yb, Nd/Tb, Nd/Er, Nd/Yb, Sm/Tb, Sm/Er, and
Sm/Yb, in aqueous HCl solution (1.0 mol/L), respectively, then the K + /(HO) 10 Q[5]/
[PMo 12 O 40 ] 3 system in aqueous HCl 1.0 mol/L was added to the mixtures of light
and heavy lanthanide nitrate salts with ratios of 1:1, respectively; energy dispersive
spectroscopy (EDS) data showed that the obtained crystals from the above systems
contained only or dominated light lanthanide [ 11 ].
Our another recent work showed the coordination in supramolecular assem-
blies by reacting a series of lanthanide cations (Ln 3 + ) and a new alkyl-substituted
cucurbituril, the ortho-tetramethyl substituted cucurbituril ( o -TMeQ[6]), in the
presence of cadmium nitrate as an inorganic structure directing agent in neutral
solution. X-ray diffraction analysis revealed that the coordination of lanthanide
cations gives rise to simple o -TMeQ[6]/Ln 3 + complexes (Ln 3 + = Gd 3 + , Tb 3 + ,
Dy 3 + , Ho 3 + , Er 3 + , Tm3 + , Yb 3 + and Lu 3 + ). Figure 4.7 a, b shows two representa-
tive o -TMeQ[6]/Ln 3 + complexes, TMeQ[6]/Nd 3 + and TMeQ[6]/Dy 3 + . Most
interestingly, no solid crystals were obtained for any compounds containing La,
Ce, or Pr, suggesting that these compounds may be suitable for the separation of
heavier lanthanide cations from their lighter counterparts [ 8 ]. In order to inves-
tigate this further, nine typical Ln 3 +
light Ln 3 heavy O TMeQ[6] Cd ( NO 3 ) 3 sys-
tems were selected as representative examples ( Ln 3 +
light Ln 3 heavy and La 3 + Ho 3 + ,
La 3 + Tm 3 + , La 3 + Yb 3 + , Ce 3 + Ho 3 + , Ce 3 + Tm 3 + , Ce 3 + Yb 3 + , Pr 3 + Ho 3 + ,
Pr 3 + Tm 3 + and Pr 3 + Yb 3 + ), all in 1:1 ratios. EDS showed that the crystals
obtained only heavy lanthanides, while the Ln 3 +
light lanthanides remained in the
mother liquor [ 12 ].
Not only smaller Q[ n ]s, such as Q[5]s and Q[6]s, but also larger Q[n]s, such
as Q[8], can present the potential application for isolation of lanthanide cati-
ons. X-ray diffraction analysis has revealed that the coordination of lanthanide
ions to Q[8] and corresponding supramolecular assemblies can be cataloged
into two isomorphous groups [ 13 ]. One group is characteristic of coordination
of Q[8] molecules with the light lanthanide cations, such as Ce 3 + , Nd 3 + , Sm 3 + ,
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