Initial employment of pyridine-2-amidoxime in zinc(II) chemistry: Synthetic, structural and spectroscopic studies of mononuclear and dinuclear complexes

Abstract

The first employment of pyridine-2-amidoxime [(py)C(NH2)NOH] in zinc(II) chemistry is reported. The syntheses, crystal structures, and spectroscopic characterization are described for complexes [Zn(O2CR)2{(py)C(NH2)NOH}2] (R=Me; 1, Ph; 2), [Zn2(acac)2{(py)C(NH2)NO}2] (3), and [Zn(NO3){(py)C(NH2)NOH}2](NO3) (4). The reactions between Zn(O2CR)2·2H2O (R=Me, Ph) or Zn(NO3)2·5H2O and two equivalents of (py)C(NH2)NOH in MeOH led to mononuclear compounds 1, 2 and 4, respectively. All three complexes contain two neutral N,N′-chelating (η2) (py)C(NH2)NOH ligands, coordinated through the Npyridyl and Noxime atoms. In contrast, the use of Zn(acac)2·H2O in place of Zn(O2CR)2·2H2O gives the dinuclear compound 3, which instead contains the anionic, η1:η1:η1:μ bridging form of the organic ligand; the ZnII atoms are doubly bridged by the diatomic oximate groups of the (py)C(NH2)NO− groups. Strong intra- and intermolecular hydrogen bonding interactions provide appreciable thermodynamic stability and interesting supramolecular chemistry for compounds 1–4. The photoluminescence properties of complexes 1–4 recorded in the solid state at room temperature are also presented.