Calcium and Magnesium Bicarboxylates Combined with Tetrathiafulvalene Moiety

Four coordination compounds of calcium and magnesium with tetrathiafulvalene (TTF) bicarboxylate ligand have been synthesized and characterized by single-crystal analysis. As well-studied bicarboxylate complexes, the carboxylate groups in this ligand coordinate to alkaline earth metal ions in multidentate modes forming compounds 1−4. Calcium compounds [CaL(DMF)2] (1) and [Ca2L2(H2O)2(EtOH)]·MeOH (2) take a seven-coordinated sphere with a pentagonal bipyramid geometry, while magnesium compounds [Mg2L2(H2O)7]·EtOH·4H2O (3) and [Na2(DMF)2(H2O)9][MgL2(DMF)2] (4) are six-coordinated with an elongated octahedral geometry. The effect of metal ion radii on the coordination structure is clearly exhibited. The molecules of these alkaline-earth metal complexes are assembled to a sandwiched structure with hydrophobic layers of a sulfur-rich TTF matrix and hydrophilic layer of the metal carboxylate. Equilibriums of the metal coordination, acid dissociation, and ligand oxidation have been studied in the solution systems of these compounds. At a neutral state of the TTF moiety, TTF-carboxylate is an appropriate ligand for Ca(II) ion, but when the TTF moiety is oxidized, it switches the alkaline earth metal ion to the solution.