Synthetic Analogs of the Active Sites of Iron-Sulfur Proteins. XI. Synthesis and Properties of Complexes Containing the Fe2S2 Core and the Structures of Bis[o-xylyl-α,α′-dithiolato-μ-sulfido-ferrate(III)] and Bis[p-tolylthiolato-μ-sulfido-ferrate(III)] Dianions