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Stoichiometry of lanthanide(III) complexes with tripodal aminophosphonic ligand – a new solution of an old problem

Abstract

The Eu3+ and Gd3+ complexes with N-(methylene-2-pyridine)-N,N-di(methylenephosphonate) ligand (H4NP2py), an analogue of nitrilotri(methylphosphonic) acid (H6NTP), were synthesized and structurally characterized by the X-ray single crystal diffraction. The determined crystal structures ([C(NH2)3]5[Ln(NP2py)2]•12H2O) are the first example of a monomeric Ln3+ complex encapsulated by two tripodal aminophosphonic ligands. Each of the NP2py anions coordinates to Ln3+ through two oxygen atoms from each monodendate phosphonic group, amine nitrogen and pyridine nitrogen atoms, filling thus 8 coordination sites of Ln3+. Luminescence properties of [C(NH2)3]5[Eu(NP2py)2]•12H2O crystals were studied and compared with those of Eu–NP2py complexes in solution. Speciation analysis of Ln–NP2py complexes (Ln:NP2py = 1:2), performed by luminescence and potentiometric methods, showed that both [Ln(NP2py)]– and [Ln(NP2py)2]5– species may exist in solution. However, formation of the latter one occurs in alkaline solutions at pH as high as 8. By implementing the Specific Ion Interaction Theory (SIT) it was possible to calculate thermodynamic stability constants of the [Eu(NP2py)]– and [Eu(NP2py)2]5– complexes. The corresponding logb0(ML) and logb0(ML2) values are 16.3±0.11 and 19.5±0.15, respectively.

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Publication details

The article was received on 10 Apr 2017, accepted on 12 May 2017 and first published on 15 May 2017


Article type:
DOI: 10.1039/C7QI00191F
Citation: Inorg. Chem. Front., 2017, Accepted Manuscript
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    Stoichiometry of lanthanide(III) complexes with tripodal aminophosphonic ligand – a new solution of an old problem

    R. Janicki, J. Gałęzowska and A. Mondry, Inorg. Chem. Front., 2017, Accepted Manuscript , DOI: 10.1039/C7QI00191F

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