The
coordination properties of the ligand 2,2′-bipyrimidine-4,4′-dicarboxylic
acid (H2
bpd) with lanthanide(III) ions
(Ln = Eu, Tb, or Lu) were investigated. The syntheses of the H2
bpd ligand and its salts, [K2(bpd)(H2O)2] (1) and [(AlkNH)Lu(bpd)2] (Alk = Et, Hex, or en), are described. In the presence of LnCl3 salts (Ln = Lu, Eu, or Tb), the formation of [Ln(bpd)2]− and [Ln(bpd)(H2O)
x
]+ species was assessed
by 1H nuclear magnetic resonance (NMR), spectrophotometry,
and spectrofluorometric titrations in aqueous solution. The solid
state structure of 1, [K(H2O)2][Lu(bpd)2] (2), and [(Et3NH)Lu(bpd)2] (3) could be
determined by X-ray diffraction, showing the ligand to act as a tetradentate
unit with formation of three five-membered chelate rings around the
central Ln(III). With the aim of building polynuclear assemblies,
the coordination between [Lu(bdp)2]− and [Lu(tta)3(H2O)] units (tta
= thenoyltrifluoroacetylacetonate) was also investigated. In methanol, 1H NMR titration experiments revealed the formation of complex
mixtures from which two new species could be identified, [Lu2(bpd)(tta)4] (4) and H[Lu(bpd)(tta)2] (5), as confirmed by
their solid state structure analysis. Using highly lipophilic cations
in chloroform, the octametallic complex [enH]4[Lu8(bpd)4(tta)18] (6) could be isolated
and its X-ray structure determined.