The cyanate and azide ions as bridging ligands in transition-metal complexes of 3- and 4-cyanopyridines

Abstract

Complexes of the type ML_x(NCO)₂ are described (M = Mn, Fe, Co, Ni, or Zn; L = 3- or 4-cyanopyridine; x= 2 or 4). It is shown from spectra and magnetic and X-ray measurements that, with the exception of M = Zn, all the ML₂(NCO)₂ complexes contain six-co-ordinate metal ions. I.r. spectra establish that the nitrile function of the cyanopyridine is not co-ordinated and therefore that the NCO group is bonded to two metal ions. Evidence is presented, mainly from i.r. spectra, for a single-atom (nitrogen) bridge, M–N–M in the cyanato-complexes (and also in some isomorphous azides) rather than the three-atom bridge, M–NCO–M, which occurs in bridged thiocyanato-complexes.

The magnetic moments of the MnL₂(NCO)₂ and MnL₂(N₃)₂ complexes are anomalously low and also temperature-dependent. It is suggested that these effects are due to weak antiferromagnetic exchange between the paramagnetic centres in the non-magnetically dilute bridged structure M–N–M.