Structural diversity of lanthanum saccharinates induced by 1,10-phenanthroline: A synthetic and X-ray crystallographic study

Abstract

Four new lanthanum(III) complexes of formulae [La(sac)3(phen)2(H2O)2]·(phen)(H2O)2 (1), [La(sac)3(phen)2(H2O)2]·(phen) (2), [La(sac)2(phen)(H2O)4]·(sac) (3) and [La(sac)2(phen)2(H2O)3]·(sac)(phen)(H2O) (4) (phen=1,10 phenanthroline, sac=saccharinate) have been synthesised and characterised by single crystal X-ray diffraction, IR, elemental analysis and thermogravimetric analysis. The binding mode of the sac anion was manipulated through the use of phen as structure inducer. In all four complexes the La(III) ion is in a nine-coordinate environment. The structures of 1 and 2 are similar, comprising of three sac anions coordinating in a monodentate fashion through the carbonyl O-atom, two bidentate phen and two water molecules coordinating directly to the same La(III) ion; a third, uncoordinated phen moiety also forms part of the unit cell. In addition, 1 is characterized by the presence of two crystallization water molecules which are absent in 2. In compound 3 the coordination sphere of La(III) is completed by a bidentate chelating sac through the N- and carbonyl O-atoms, a monodentate sac, a bidentate phen and four water ligands; a third, uncoordinated sac is also present in the crystal lattice. Compound 4 contains two bidentate phen, three water ligands and two monodentate O(carbonyl) sac ligands. The presence of three sac anions coordinating to the same lanthanide ion as well as a bidentate N–Ln–O chelating sac, confirmed by single crystal X-ray crystallography, is unprecedented for rare-earth saccharinates.