Transition metal dithioacetylacetonates
Class of chemical compounds
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Transition metal dithioacetylacetonates are coordination complexes containing dithioacetylacetonate (CH3CSCHCSCH−3, abbreviated SacSac-) as a bidentate ligand. Dithioacetylacetonate complexes are analogous to acetylacetonate complexes: both sulfur atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(SacSac)3 and M(SacSac)2. Mixed-ligand complexes are also known, e.g. Fe(SacSac)2(CO)2.[2]
Synthesis
Dithioacetylacetone is 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.[3] A common unsymmetrical version of a HSacSac ligand is C6H5C(SH)=CHC(=S)OC2H5, which can be prepared from O-ethylthioacetate.[4]
Examples
Square planar complexes of the type M(SacSac)2 are known for Ni (red),[1] Pd (red), Pt (violet), Co (violet). Tetrahedral M(SacSac)2 are isomorphous for M = Mn, Zn, Cd.[5] In contrast with these structures, M(acac)2 are dimers or oligomeric for M = Co, Ni, Mn, Cd, Zn. The octahedral complex Fe(SacSac)3 is low-spin, in contrast to Fe(acac)3.[6]
Complexes are also well known for monothioacetylacetone (HSacac). The free ligand is readily obtainable as a distillable liquid,[7] which facilitates the preparation of these coordination complexes. Fe(Sacac)3 exhibits spin crossover behavior.