Synthesis, characterization and supramolecular structure of three new Cu(II) and Ni(II) complexes with the potentially bidentate ligand 2-amino-6-methylpyrimidin-4(1H)-one (AMPO)

Three binuclear Cu(II) and Ni(II) perchlorate complexes with the potentially bidentate ligand 2-amino-6-methylpyrimidin-4(1H)-one (AMPO) [Cu(AMPO)4][Cu(H2O)5](ClO4)4·6H2O (1), [Cu2(AMPO)4(H2O)3](ClO4)4·½H2O (2) and[Ni(AMPO)4][Ni(H2O)6](ClO4)4·5H2O (3), have been prepared and were characterized by single crystal X-ray diffraction, IR spectroscopy and elemental analysis. Structural and IR data indicate that the ligand is present in its tautomeric form protonated at nitrogen in position one and metal coordinated at position three. The basic coordination pattern of the AMPO coordinated metal cations in all three complexes is square planar by four pyrimidyl nitrogen atoms of four different AMPO ligands. The coordination sphere is augmented by weak M⋯O interactions between the metal centers and AMPO keto oxygen atoms. Bond valence calculations indicate the M⋯O interactions to be most pronounced for nickel compound (3), and least for copper complex (2). The structural and geometrical differences between compounds (1) and (3) on the one hand and compound (2) on the other can to a large part be traced back to the lack of available water in the crystallization solvent in (2) which starves the cation not coordinated to AMPO nitrogen atoms of water molecules to saturate its coordination sphere, thus forcing two of the AMPO ligands in (2) to act as a bridging ligands, while the other AMPO ligands in the three structures are mostly monodentate with the coordination mode of the AMPO ligand being completed by weak secondary chelating M⋯O interactions.

Graphical abstractThree binuclear Cu(II) and Ni(II) perchlorate complexes with the potentially bidentate ligand 2-amino-6-methylpyrimidin-4(1H)-one (AMPO) have been prepared. Structural and IR data indicate that the ligand is present in its tautomeric form protonated at nitrogen in position one and metal coordinated at position three. The basic coordination pattern of the AMPO coordinated metal cations in all three complexes is square planar by four pyrimidyl nitrogen atoms of four different AMPO ligands. The coordination sphere is augmented by weak M⋯O interactions between the metal centers and AMPO keto O atoms.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The basic coordination pattern of the AMPO coordinated metal cations is square planar. ► The coordination sphere is augmented by weak metal⋯O interactions. ► The AMPO ligand is present in its nitrogen protonated tautomeric form. ► The bond length features are consistent with an imino resonance.