Syntheses, crystal structures, and bond valence sum analyses of lanthanide complexes with a planar pentadentate ligand

The syntheses and X-ray crystal structures of the Eu, Gd, Dy, Ho, and Er nitrate complexes of the pentadentate ligand 2,6-diacetylpyridine bis acetic acid hydrazone, or H2dapaah, are reported. The complexes can be divided into 3 groups depending on the number of water molecules per metal ion. The Ln · 4H2O complexes with Eu, Gd and Dy are isomorphous, with the Ln ion being 10 coordinate. The Ln · 6H2O group includes Ho and Er, where the cation is 9 coordinate. The final complex Gd · 5H2O is 10 coordinate like the Eu, Gd and Dy complexes, but the additional water molecule has stabilized an ordered crystal. The bond valence sum method has been used to analyze the bonding in the complexes and has suggested that bond valence equalization in three dimensions may be an important concept.