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 )(H 2 O) 2 ] ( 1 ) and [( Alk NH)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 )(H 2 O) x ] + species was assessed by 1 H nuclear magnetic resonance (NMR), spectrophotometry, and spectrofluorometric titrations in aqueous solution. The solid state structure of 1 , [K(H 2 O) 2 ][Lu( bpd ) 2 ] ( 2 ), and [(E 3 NH)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 (H 2 O)] units (tta = thenoyltrifluoroacetylacetonate) was also investigated. In methanol, 1 H 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.