Self-assembly of d-f coordination frameworks based on 1H-benzimidazole-5-carboxylic acid: synthesis, structure and luminescence

By the addition of different secondary ligands [acetate (OAc), Br- and oxalate (ox)], or by the absence of such ligands, four different types of heterometallic coordination compounds were obtained by reaction of 1H-benzimidazole-5-carboxylic acid (H(2)bic) with transition metal (d) and lanthanide (f) ions under hydrothermal conditions, namely, [TbAg3(Hbic)(2)(bic)(2)]center dot 4H(2)O (1), [LnCu(2)(Hbic)(4)Br] [Ln = Er (2), Ln = Yb (3)], [EuAg2(Hbic)(2)(bic)(OAc)(H2O)] (4), [TbAg(Hbic)(3)center dot(ox)(0.5)] (5). Compounds 1, 2 and 3 stand out by having octahedrally coordinated lanthanide centers rather than the more usual 8 or 9 coordinated metal centers. Complex 1 exhibits an interesting 2D wave-like layered network constructed from infinite six-coordinated terbium carboxylate chains and Ag-3(Hbic)(2)(bic)(2) units. Isostructural compounds 2 and 3 display two-dimensional (2D) mildly ruffled sheets constructed by interconnecting mu(2)-Br ligands to adjacent ribbon-shaped Cu-2(Hbic)(4) chains. Addition of auxiliary acetate and oxalate ions led to lanthanide ions with normal coordination numbers, and Eu-2(OAc)(2) and Tb(ox) subunits are formed. Complex 4 is a 2D structure with a (4,4) net that is constructed by interlinking dinuclear Eu-2(OAc)(2) subunits with Ag-2(bic)(Hbic)(2)(H2O) subunits. Complex 5 represents a 2D heterometallic coordination framework with an (8,3) net that is constructed by interconnection of Ag(Hbic)(3) subunits and Tb(ox) subunits. The luminescence properties of 1, 4 and 5 are discussed.