Synthesis and structural assessment of new mixed (n-heteroligand)fluoro complexes of cobalt(II). Evidence for ligand synthesis at the metal site

Abstract

Mixed-ligand fluorocobaltates(II), with N-donor co-ligands [Co(N₂H₄)₂F₂]. 2H₂O, [Co(dmpz)F₂(H₂O)₂] . 2H₂O, [phenH[CoF₃(phen)]. 8H₂O and [bipyH][CoF₃ (bipy)]. 6H₂O (dmpz = 3,5-dimethylpyrazole, PHEN = 1,10-phenanthroline and bipy 2,2'-bipyridine) have been synthesized from the reaction of a solution of Co(OH)₂ in 40% HF with hydrazine at pH ≤ 5. Attempts to synthesize the Co^II-dmpz-F complex with simultaneous synthesis of the ligand 3,5-dimethylpyrazole (dmpz) on a cobalt(II) centre involving reactions among Co(acac)₂, F^- and N₂H₄ or CoF₂(N₂H₄)2, F^- and acacH (acacH = acetylacetone) resulted in the formation of [Co(dmpz)F₂(H₂O)₂] . 2H₂O and CO(dmpz')₂ (dmpz' = dmpz - H), respectively, demonstrating the formation of the ligand on the metal. The comparative strength of the Co---N and Co---O bonds is discussed. The compounds have been characterized by elemental analyses, chemical determination of the oxidation state of cobalt, conductance and magnetic susceptibility measurements, pyrolysis, IR and electronic spectral studies. The complex ion in each case has a distorted octahedral structure, but discrete in [Co(N₂H₄)₂F₂], and polymeric containing F^- as the bridging ligand in other cases. Some of the differences of the fluorocomplexes from those of the other halides have been highlighted.