Complexes of the tripodal nitrilotrimethylenetrisphosphonic (H6L) and P,P′,P″-triphenylnitrilotrimethylenetrisphosphinic (H3L°) acids with the copper(II) ion. Synthesis and characterization of [Hpy][Cu(H3L)(H2O)] and [Cu(HL°)(py)]2·2Me2CO

Abstract

The complexes [Hpy][Cu(H₃L)(H₂O)] 1 (L⁶⁻ = nitrilotrimethylenetrisphosphonate) and [Cu(HL°)(py)]₂·2Me₂CO 2 [(L°)³⁻ = P,P′,P″-triphenylnitrilotrismethylenetrisphosphinate)] have been isolated and characterized by X-ray crystallography, near IR-visible spectroscopy and magnetic measurements. The structure determination has shown the complexes to be constituted by monomeric and dimeric units respectively. In the monomer the metal atom is surrounded by the phosphonate ligand and a water molecule, with a geometry between a trigonal bipyramid and a square pyramid. The two copper atoms in the dimer are held together by an arm of the tripod ligand, with a pyridine molecule as additional ligand, and display octahedral geometry. The presence of monomeric and dimeric species in aqueous solutions of 1 and 2 has been shown by ESMS studies. The formation in water solution of the dimer [{Cu(H₃L)}₂]²⁻, as a minor species, has been supported by potentiometric measurements, whereas only the monomeric anion [CuL°]⁻ has been ascertained to be present. In general the ligand H₃L° forms less stable copper(II) complexes than H₆L.

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