Coordination modes of 3-hydroxypicolinic acid: synthesis and crystal structures of palladium(II), platinum(II) and rhenium(V) complexes

The new palladium and platinum complexes with 3-hydroxypicolinic acid (Hpic OH) [M(PPh3)(2)Cl(picOH)] . CHCl3, [M(bipy)(picOH)]Cl [M = Pd(II) or Pt(II) ], K[PdCl(picOH)(2)] and [Pt(picOH)(2)] and the new rhenium complexes [ReOI 2(PPh3)(picOH)] and [ReO(PPh3)(picOH)(2)]I have been prepared. The crystal structures of [M(PPh3)(2)Cl(picOH)] . CHCl3 [M = Pd(II) 1 or Pt(II) 2] and [ReOI2(PPh3)(picOH)] 3 were determined by X-ray diffraction. Complex 3 exhi bits a distorted octahedral geometry with the picOH(-) ligand showing N,O-c helation with a small bite angle O-Re-N of 74.8(3)degrees. In complexes 1 a nd 2 the metal centre is surrounded by a NP,CI donor set in a distorted squ are planar arrangement. Therefore, the picOH- ligand is bound through the n itrogen atom, but the distances found between the metal and the carboxylate oxygen [Pd...O(71) 2.773(5) Angstrom or Pt...O(71) 2.734(4) Angstrom] sugg est a [4 + 1] coordination consistent with N,O-chelation for palladium and platinum centres. Infrared, Raman, H-1 and C-13-{H-1} NMR spectroscopic dat a for the complexes are consistent with the crystallographic results. In th e solid state the complex units of 1 and 3 are aggregated in centrosymmetri c dimers based on C-H...Cl or C-H...O hydrogen bonding interactions between the chlorine of the Pd-Cl bond (in 1) or the phenolic oxygen of the picOH( -) anion (in 3) and a hydrogen atom of a phenyl group of a PPh3 ligand.