Bíró L, Tóth B, Lihi N, Farkas E, Buglyó P. Interaction between [(η
6-
p-cym)M(H
2O)
3]
2+ (M
II = Ru, Os) or [(η
5-Cp*)M(H
2O)
3]
2+ (M
III = Rh, Ir) and Phosphonate Derivatives of Iminodiacetic Acid: A Solution Equilibrium and DFT Study.
Molecules 2023;
28:molecules28031477. [PMID:
36771142 PMCID:
PMC9918899 DOI:
10.3390/molecules28031477]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 01/29/2023] [Accepted: 01/31/2023] [Indexed: 02/05/2023] Open
Abstract
The pH-dependent binding strengths and modes of the organometallic [(η6-p-cym)M(H2O)3]2+ (MII = Ru, Os; p-cym = 1-methyl-4-isopropylbenzene) or [(η5-Cp*)M(H2O)3]2+ (MIII = Rh, Ir; Cp* = pentamethylcyclopentadienyl anion) cations towards iminodiacetic acid (H2Ida) and its biorelevant mono- and diphosphonate derivatives N-(phosphonomethyl)-glycine (H3IdaP) and iminodi(methylphosphonic acid) (H4Ida2P) 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 IdaP3- and Ida2P4- 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. The replacement of one carboxylate in Ida2- by a phosphonate group (IdaP3-) resulted in a significant increase in the stability of the metal complexes; however, this increase vanished with Ida2P4-, which was most likely due to some steric hindrance upon the coordination of the second large phosphonate group to form (5 + 5) joined chelates. In the phosphonate-containing systems, the neutral 1:1 complexes are the major species at pH 7.4 in the millimolar concentration range that is supported by both NMR and ESI-TOF-MS.
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