Complexes of di-2-pyridylketone—III: Some chelated products of metal-promoted hydration of the ketone

Abstract

Di-2-pyridylketone (DPK) exists either as the ketone-hydrate (i.e.) (C 5H 4N) 2C(OH) 2), abbrev. DPK·H 2O) or as the derived anion ((DPK·OH −) in the complexes [Co III(DPK·OH) 2]NO 3, [CO III(DPK·OH) 2]Cl·H 2O, [Co III(DPK·OH)(DPK·H 2O)](NO 3) 2, and [Co III(DPK·H 2O) 2](NO 3) 3· H 2O all of which possess pseudooctahedral trans N 4O 2 ligand fields provided by tridentate DPK·OH − or DPK·H 2O ligands. [Fe III(DPK·OH) 2]NO 3 has an analogous structure to the corresponding cobalt(III) complex but the compound with stoichiometry Fe(DPK) 2(OH) 2(NO 3(H 2O) 2 possibly has the structure [Fe III(DPK·H 2O) 2(OH) 2]NO 3 in which the DPK·H 2O units are bidentate. Both ferric complexes are in the low spin state. The ketone groups in the complex of stoichiometry Ni II(DPK) 2(OH) 2(H 2O) 4 have also suffered nucleophilic addition and a pseudo-octahedral N 4O 2 cation environment is indicated by spectral and magnetic evidence. The hydrated cobalt(II) complexes with stoichiometries Co II (DPK) 2 Y 2(H 2O) x in some cases ( Y=Cl, Br, I; x=2) contain one DPK and one DPK·H 2O ligand and in other cases ( Y= NO 3, ( SO 4) 1 2 ; x=3 ) both DPK units are hydrated. The cobalt(II) complexes show “anomalous” magnetic behaviour; in the temperature range 100–300°K the chloride and bromide are of predominantly high spin configuration whereas the iodide and sulphate are of predominantly low spin configuration and the nitrate shows “cross-over” behaviour from high spin to low spin as the temperature decreases.