Preparation of some thionitrosyl-type transition-metal complexes and their characterisation by infrared, optical, and electron paramagnetic resonance spectroscopy: [M(S₂N₂H)₂], [M(S₂N₂H)(S₃N)], and [M-(S₃N)₂](M = Co, Ni, Pd, or Pt)

The title compounds have been prepared by revision of the literature methods. Improved yields of many of the compounds have been obtained, as well as isolation of the previously unobtainable [Pd(S₂N₂H)(S₃N)] and preparation of pure samples of [Pd(S₂N₂H)(S₃N)] and [Pt(S₃N)₂]. Infrared data are reported for the [M(S₂N₂H)-(S₃N)] and [M(S₃N)₂] complexes and used to show that previous preparations for M = Pt have given impure products. The assignment of the spectra supports a cis square-planar geometry for all of the complexes reported. The optical absorption spectra of the complexes have been recorded, and show that the electronic transitions are mainly due to the ligands. Only the cobalt complexes give e.p.r. signals. Detailed studies of [Co(S₂N₂H)₂] at 10 K reveal the presence of a spin equilibrium between high-(S = 3/2) and low-spin (S = 1/2) cobalt(II).