pH‐Specific Synthesis and Structural and Spectroscopic Characterization of a Complex between Co II and N , N ‐Bis(phosphonomethyl)glycine: Cobalt–Phosphonate Interactions in the Solid State and in Solution

The presence of cobalt in biological systems has been associated with a variety of regulatory roles as an inorganic cofactor. Its involvement in (bio)chemical processes, where it contributes to the integrity of the physiology of humans, underscores its ability to promote (bio)chemistry with molecular targets of variable mass and biological properties. Given the fact that organic phosphonates are widespread substrates/ligands in biological fluids, we sought to investigate the relevant chemistry with CoII. With the organophosphonate ligand N,N-bis(phosphonomethyl)glycine (H5NTA2P) as the main metal ion binder, aqueous reactions with CoII were examined, ultimately leading to the isolation of the complex [Co(C4H9O8NP2)(H2O)2]·2H2O (1) at pH 1.5. This complex was characterized analytically, spectroscopically (FT-IR, UV/Vis, EPR), magnetically, and by cyclic voltammetry. X-ray crystallography shows that 1 is a compound with a molecular type of lattice. The complex consists of a mononuclear, octahedral CoII center coordinated by oxygen atoms belonging to the terminal phosphonate and carboxylate groups of H3NTA2P2–, the ligand nitrogen, and two bound water molecules. It should be emphasized that similar structural features have been observed in other metal organophosphonate lattices of materials with potential catalytic and chemical reactivity. The magnetic and EPR data for 1 suggest the presence of a high-spin octahedral CoII, with a ground state of an effective spin S = 1/2. The solution UV/Vis and EPR spectra suggest retention of the integrity of 1, which is consistent with the magnetization measurements in the solid state. Collectively, the data suggest a soluble CoII–organodiphosphonate species, not unlike those expected in bio-fluids containing the specific ligand or ligands structurally akin to H3NTA2P2–.The biological relevance of 1 to species in bio-fluids and the structural association with CoII–organophosphonate materials is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)