Interaction between [(η--cym)M(HO)] (M = Ru, Os) or [(η-Cp*)M(HO)] (M = Rh, Ir) and Phosphonate Derivatives of Iminodiacetic Acid: A Solution Equilibrium and DFT Study.

The pH-dependent binding strengths and modes of the organometallic [(η--cym)M(HO)] (M = Ru, Os; -cym = 1-methyl-4-isopropylbenzene) or [(η-Cp*)M(HO)] (M = Rh, Ir; Cp* = pentamethylcyclopentadienyl anion) cations towards iminodiacetic acid (HIda) and its biorelevant mono- and diphosphonate derivatives N-(phosphonomethyl)-glycine (HIdaP) and iminodi(methylphosphonic acid) (HIda2P) was studied in an aqueous solution. The results showed that all three of the ligands form 1:1 complexes via the tridentate (O,N,O) donor set, for which the binding mode was further corroborated by the DFT method. Although with IdaP and Ida2P in mono- and bis-protonated species, where H might also be located at the non-coordinating N atom, the theoretical calculations revealed the protonation of the phosphonate group(s) and the tridentate coordination of the phosphonate ligands.