Synthesis of complexes with the polydentate ligand N,N '-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide

The pentadentate ligand N,N'-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide (POPYH4) has been used to prepare a variety of new complexes [HNEt3][Zn4Cl(POPYH)(3)] (2), [HNEt3][PdCl(POPYH2)] (3), [HNEt3][Ni(POPYH)] (4) and K[Ni(POPYH)] (5) which show the versatility of this multidentate ligand. The complexes have been characterised spectroscopically and their molecular and crystal structures have been determined by single crystal X-ray diffraction techniques. In these complexes the ligand exhibits different modes of coordination towards different transition metal ions. The structure of triethylammonium salt of the Zn(II) dianion 2 consists of an unusual tetra-zinc core supported by three POPYH ligands each one of which links two adjacent zinc centres through two oxygen and two nitrogen donor atoms. The salt of the square planar Pd(II) anion 3 contains one POPYH2 ligand which coordinates in a tridentate fashion through the two deprotonated amido groups and by the central pyridine nitrogen donor. The two Ni(II) salts 4 and 5 contain the same [Ni(POPYH)] anion in which the square planar Ni(II) centre is chelated by a POPYH ligand through the two deprotonated amido nitrogen atoms, the pyridine nitrogen and a deprotonated hydroxyl group.