Complexes of lanthanide picrates with 1,4-pyrazine-dioxide

Complexes of hydrated lanthanide picrates with composition: [Ln(2)(pic )(2) (pyzDO)(H2O)(12)](pic)(4) (pyzDO)(2)(H2O)(4) (Ln=Pr, Nd, Sm, Eu; pic = picr ate; pyzDO = 1,4-pyrazine-dioxide) were synthesized by reaction of the hydr ated picrates in ethanolic solution with pyzDO in water solution. The compo unds that are all isomorphous, as determined by X-ray powder patterns, were characterized by CHN elemental analyses and complexometric titration with EDTA. The crystal structure of the Eu compound has been solved by single cr ystal X-ray diffraction. IR absorption spectra were interpreted in terms of coordination of bidentate picrate counter-ions, bonded through the oxygen of the phenoxo group and one oxygen of an ortho-nitrogroup. The parameters obtained from the absorption spectrum of the neodymium compound suggest the existence of small covalent character of the metal-ligand bonds. The Eu io n achieves a coordination number of nine by the bonding to one bidentate pi crate, six water molecules and an oxygen of bridging pyzDO moiety, in a tri capped trigonal prism fashion. The Eu ions linked in centrosymmetric dimers by bonded pyzDO and also more externally through two symmetry related brid ges formed by two hydrogen bonded water molecules which are in turn hydroge n bonded to coordinated waters. Two picrate anions and one pyzDO molecule a re out of the coordination sphere. (C) 2001 Elsevier Science B.V. All right s reserved.