Structural characterization of pyridin-2-, -3-, and -4-yl functionalized (iminodimethanediyl)bis(phosphonic) acids: Insight into the cobalt(II) and copper(II) complexes of pyridin-2-yl derivative

Three representatives of a new family of C-functionalized derivatives of (iminodimethanediyl)bis(phosphonic) acid, namely pyridin-2-, 3-, and -4-yl derivatives (1–3, respectively) are characterized in solution by the NMR method and in the solid state by single crystal X-ray diffraction. Detailed crystallographic structural studies are provided for 1 and 2. For 3, the model of molecular structure is proposed. Compounds 1 and 2 crystallize as zwitterions with one and five water molecules in the asymmetric units, respectively. In 1, zwitterions are arranged into two-dimensional hydrogen-bonded layers parallel to (1 0 1) plane. In 2, one-dimensional chains running along a direction are observed. Hydrogen bonding mediated by water molecules hold above mentioned motifs into three-dimensional structures.The reaction of 1 with Co(II) and Cu(II) afforded two isomorphous crystals, namely, Co(LH2)·0.7H2O (1-a) and Cu(LH2)·0.9H2O (1-b). Both compounds are characterized by means of X-ray crystallography, NIR–Vis–UV spectroscopy, and their magnetic properties are reported.Compounds 1-a and 1-b reveal similar overall structures and packing schemes. Each M(II) ion is five-coordinate, displays distorted trigonal–bipyramidal geometry and is surrounded by three anions of 1. The five-coordination sphere of M(II) is formed by N2, N1 and O4 atoms of tridentate chelating dianion and O1, O2 oxygen atoms of two remaining dianions. Observed transition energies in the NIR–Vis–UV spectra and their assignments are consistent with distorted trigonal-bypyramid geometry found for [MN2O3] chromophore around M(II) center. The crystals of 1-a and 1-b comprise 1D coordination ribbon-like polymers running along a axis. The ribbons are assembled into layers parallel to (0 0 1) plane through O−H⋯O and N−H⋯O hydrogen bonds, and joined into 3D structures by means of weak C−H⋯O interactions and hydrophobic effects.Analysis of magnetic properties of 1-a provided evidence for the occurrence of weak antiferromagnetic interactions (J = −1.5 cm−1) between neighboring Co centers linked through O–P–O bridges.

Three C-functionalized (iminodimethanediyl)bis(phosphonic) acids, namely pyridyn-2-, -3-, and -4-yl substituted derivatives (1–3) were characterized by X-ray crystallography, and in solution by the NMR method. The reaction of Co(II) and Cu(II) with 1 afforded Co(LH2)·0.7H2O and Cu(LH2)·0.9H2O complexes (1-a and 1-b, respectively), which were characterized structurally, by means of NIR–Vis–UV spectroscopy, and magnetic studies. In both 1-a and 1-b, the M(II) ion is five-coordinate, displays distorted trigonal–bipyramidal geometry and is surrounded by three anions of 1. This results in 1D coordination polymers, joined into 3D structure by an array of hydrogen bonds and hydrophobic effects. Compound 1-a is shown to exhibit weak antiferromagnetic interactions between neighboring Co centers.Figure optionsDownload as PowerPoint slide