Transition metal dithioacetylacetonates are coordination complexes containing dithioacetylacetonate ( ligands, abbreviated SacSac-) and related ligands. Analogous to the situation for acetylacetonate complexes, SacSac- ligands bind to the metal to form a six-membered MS2C3 chelate ring. The simplest complexes have the formula M(SacSac)3 and M(SacSac)2. Mixed-ligand complexes are also known, e.g. .
Synthesis Dithioacetylacetone is not well-characterized, so complexes are prepared by indirect methods. In one approach, a solution of acetylacetone is treated with a mixture of hydrogen sulfide and hydrochloric acid prior to the addition of a metal halide. SacSac- complexes can also be prepared by reduction of a 1,2-dithiolium salt with sodium borohydride followed by treatment with a metal salt. A common unsymmetrical version of HSacSac pro-ligand is the thionoester , which can be prepared from O-ethylthioacetate.
Examples Square planar complexes of the type M(SacSac)2 are known for Ni (red), Pd (red), Pt (violet), Co (violet). A tetrahedral bis(dithiochelate) has been characterized by X-ray crystallography for . In contrast with these structures, M(acac)2 are dimeric or oligomeric for M = Co, Ni, Mn, Cd, Zn. The octahedral complex Fe(SacSac)3 is low-spin, in contrast to Fe(acac)3.
Related ligands Complexes are also well known for monothioacetylacetone (HSacac). The free ligand is readily obtainable as a distillable liquid, which facilitates the preparation of its complexes. In contrast to low-spin Fe(SacSac)3, derivatives of the type exhibit spin crossover behavior.
References