Magnetically anomalous thio complexes of iron(III) and nickel(II)

Abstract

Thioxanthate complexes closely resemble the xanthates and the dithiocarbamates. Like the corresponding xanthates and dithiocarbamates, thioxanthates of iron(111), nickel(11), and copper(11) are black and those of cobalt(111) are dark green. In sufficiently dilute solutions, iron(111) and nickel(11) thioxanthates are more red than xanthates and dithiocarbamates which are brownish red. The pressure and temperature dependences of the magnetism show that the ferric thioxanthates exhibit a high-spin + low-spin electronic equilibrium, like the ferric dithiocarbamates and xanthates, though the low spin form predominates for the xanthates and thioxanthates. Pyridine forms green paramagnetic adducts in the solid with the nickel(11) complexes which lose pyridine if left in the open, while in solution a concentration dependent equilibrium is set up between the planar thioxanthates and its bis-pyridine adduct. In general the complexes are rather unstable at room temperature, but some kept fairly well if stored frozen in sealed tubes. The iron(111) thioxanthates Fe(S₂C-S-R)₃ are at least as stable as the corresponding xanthates. Analogously to the case of the xanthates, the stability of the thioxanthates decreases and the ability of the ligand to reduce the central metal atom increases with increasing chain length when R is an alkyl group. Some long-chain ligands are capable of reducing the central iron atom to form an iron(11) complex. Complexes with branched alkyl chains are more stable than the straight-chain analogues.