2-Pyridylmethylphosphonic acid: a flexible, multi-dentate ligand for metal phosphonates

Abstract

In a systematic investigation, 2-pyridylmethylphosphonic acid, 2PyCH₂PO₃H₂ (Py = pyridine), was reacted with specifically selected metal salts to examine the influence of the preferred metal geometry, role of the anion and coordination preferences of the ligand. From this study a series of metal phosphonates were isolated: [{M(2PyHCH₂PO₃H)(H₂O)}ClO₄]_n, M = Mn, 1 and Co, 2; a tetranuclear iron phosphonate cage, [Fe₄(2PyHCH₂PO₃)₄(H₂O)₁₂(Cl)(ClO₄)₇·xH₂O], 3, and two polymeric iron phosphonate chains: 4, [Fe₂(2PyHCH₂PO₃H)₂(ClO₄)]_n, and 5, [Fe(2PyHCH₂PO₃H)(H₂O)(ClO₄)]_n. Meanwhile, the stoichiometric reaction of Pb(NO₃)₂ and Ag(SO₃CF₃) with 2PyCH₂PO₃H₂ afforded a bimetallic Ag/Pb network, 6, [AgPb(2PyCH₂PO₃)(NO₃)]_n. The individual components of this reaction, Pb(NO₃)₂ and Ag(SO₃CF₃), when reacted with 2PyCH₂PO₃H₂ yielded [Pb(2PyHCH₂PO₃H)(NO₃)₂]_n, 7, and a luminescent silver polymer 8, [Ag₃(2PyHCH₂PO₃)(SO₃CF₃)₂]_n, that are used for structural comparison to 6. All products were characterized in the single crystal and bulk form. The electrochemical properties of 1, 2 and 3 were studied, and X-ray photoelectron spectroscopy (XPS) employed to investigate the bimetallic polymer, 6, and the tetrameric iron phosphonate, 3.