Synthesis and crystal structure of double Ln(III) malonates with Co(NH3) 6 3+ in the outer sphere

Abstract

Double Ln(III) malonates of two different compositions crystallize from malonate solutions containing [Co(NH3)6]3+ ions. Lanthanides of the beginning of the series form compounds of the composition [Co(NH3)6][Ln(mal)2]3·6H2O (I) (Ln = La, Ce, Pr, Nd; mal = C3H2O2−), and those of the end of the series form compounds of the composition [Co(NH3)6]2[Ln3(mal)7(Hmal)(H2O)4]·nH2O (II) (Ln = Tb, Ho, Er, Tm). Structure I is based on trimeric anionic complexes [Ln3(mal)6]3− linked with each other to form a branched 3D network with [Co(NH3)6]3+ cations and water molecules accommodated in large voids. The coordination mode of malonate ions in I with the coordination capacity equal to 5 was unknown previously for lanthanide malonate compounds. The Ln(1) atom has the maximum possible for malonate compounds coordination number (CN) 12, and the Ln(2) atom has CN 9. The structure of II consists of anionic chains [Ln3(mal)7(Hmal)(H2O)4]n3− between which the [Co(NH3)6]3+ cations and water molecules are arranged. One independent malonate ion in the structure is coordinated in the bidentate chelate fashion to the Ln(1) atom, and the other independent chelate-bridging ligand is coordinated in the bidentate fashion to the Ln(2) atom and in the monodentate fashion to the Ln(1) atom. As a result, tetrameric fragments linked in anionic chains are formed in the structure of II. The Ln(1) and Ln(2) atoms have CN 8.