From Mono- To Polynuclear Coordination Complexes With A 2,2 '-Bipyrimidine-4,4 '-Dicarboxylate Ligand

The coordination properties of the ligand 2,2'-bipyrimidine-4,4'-dicarboxylic acid (H(2)bpd) with lanthanide(III) ions (Ln = Eu, Tb, or Lu) were investigated. The syntheses of the H(2)bpd ligand and its salts, [K-2(bpd)(H2O)(2)] (1) and [(AlkNH)-Lu(bpd)(2)] (Alk = Et, Hex, or en), are described. In the presence of LnCl(3) salts (Ln = Lu, Eu, or Tb), the formation of [Ln(bpd)(2)](-) and [Ln(bpd)(H2O)x](+) species was assessed by H-1 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, H-1 NMR titration experiments revealed the formation of complex mixtures from which two new species could be identified, [Lu-2(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)[Lu-8(bpd)(4)(tta)(18)] (6) could be isolated and its X-ray structure determined.