Complexes of Uranyl Ions with Aromatic di- and tetra-Carboxylates Involving [Ni(bipy)$_n$]$^{2+}$ (n = 2, 3) Counter-Ions
Résumé
Four di- and tetracarboxylate ligands based on aromatic platforms have been used to synthesize four uranyl ion complexes under solvo-hydrothermal conditions and in the presence of nickel(II) cations and 2,2ʹ-bipyridine (bipy). The four complexes [Ni(bipy)$_3$][(UO$_2$)$_2$(bdc)$_3$].4H$_2$O ($1$, bdc$^{2-}$ = 1,3-benzenedicarboxylate), [Ni(bipy)$_3$][(UO$_2$)$_2$(ndc)$_3$]×DMF×5H$_2$O ($2$, ndc$^{2-}$ = 2,6-naphthalenedicarboxylate), [UO$_2$(ntcma)(H$_2$O)$_2$].2H$_2$O ($3$, ntcma$^{2-}$ = 1,4,5,8-naphthalenetetracarboxylate-1,8-monoanhydride), and [UO$_2$Ni(hfdp)(bipy)$_2$(H$_2$O)].H$_2$O ($4$, hfdp$^{4-}$ = 4,4'-(1,1,1,3,3,3-hexafluoroisopropylidene)diphthalate) crystallize as two-dimensional assemblies. While separated [Ni(bipy)$_3$]$^{2+}$ counter-ions are present in 1 and 2, the Ni(bipy)$_2$$^{2+}$ groups in 4 are bound to carboxylate donors and are decorating species on the polymeric network, while nickel(II) is absent in the neutral complex 3. The networks in 1-3 have the {6$^3$} hcb topology and that in 4 the {4.8$^2$} fes one. Apart from Coulombic interactions in 1 and 2, OH$\cdots$ O and CH$\cdots$O hydrogen bonds are prominent interactions in the lattices, as shown by Hirshfeld surface analysis. Uranyl emission spectra in 1 and 4, in spite of almost complete quenching in the former, are in agreement with those measured in other polycarboxylate complexes with six and five equatorial donors, respectively.
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