pH-Specific synthetic chemistry, and spectroscopic, structural, electrochemical and magnetic susceptibility studies in binary Ni(II)-(carboxy)phosphonate systems

Nickel can play numerous roles in biological systems and in advanced abiotic materials. Supporting the diverse roles of Ni(II) in biological media are, among others, metal ion binding amino acids, their variably phosphorylated forms and/or exogenously administered organophosphonate drug substrates. In an effort to comprehend the aqueous chemistry of interactions between Ni(II) and organophosphonate substrates, research efforts were launched involving the ligands imino bis(methylenephosphonic acid) (H4IDA2P), H2O3P–CH2–NH2+–CH2–PO3H−, and N-(phosphonomethyl)glycine (glyphosate–H3IDAP), HOOC–CH2–NH2+–CH2–PO3H−. pH-Specific reactions of Ni(II) with H4IDA2P and H3IDAP led to the isolation of [Ni(C2H8O6NP2)2(H2O)2] (1) and [Ni(OOC–CH2–NH–CH2–PO3H)2]·[Ni(H2O)6]·3.3H2O (2), respectively. Compound 1 was characterized by analytical, spectroscopic techniques (UV–Vis, FT-IR), cyclic voltammetry, magnetic susceptibility measurements and X-ray crystallography. Compound 2 was characterized by elemental analysis, FT-IR spectroscopy, and X-ray crystallography. The structures of 1 and 2 reveal mononuclear octahedral Ni(II) assemblies bound by H3IDA2P− and water (1), and glyphosate (HIDAP2−) and water molecules (2), respectively. Magnetic susceptibility studies on 1 support the presence of high-spin octahedral Ni(II) in an oxygen environment, consistent with X-ray crystallography. The collective physicochemical features of the discrete Ni(II) assemblies in both species (a) shed light on aqueous binary Ni(II)–phosphoderivative interactions potentially influencing cellular physiology or toxicity, and (b) define the fundamental properties essential for the employment of such species in advanced materials synthesis and applications.

Graphical abstractpH-Specific reactions of Ni(II) with imino-diphosphonic and imino-carboxyphosphonic acids led to the isolation of new complexes [Ni(C2H8O6NP2)2(H2O)2] (1) and [Ni(OOC–CH2–NH–CH2–PO3H)2]·[Ni(H2O)6]·3.3H2O (2). Compounds 1 and 2 were characterized by analytical, spectroscopic, electrochemical, thermal, magnetic and structural studies. Their collective physicochemical profiles (a) reflect the pH-specific reactivity in aqueous Ni(II)–organophosphonate binary systems, and (b) project the nature of interactions in Ni(II)–organophosphonate species, participating in the requisite aqueous speciation, potentially influencing cellular events and/or materials synthetic processes.Figure optionsDownload full-size imageDownload as PowerPoint slide