Tetrahedral complexes containing the Fe(II)S4 core. The syntheses, ground-state electronic structures and crystal and molecular structures of the bis(tetraphenylphosphonium) tetrakis (thiophenolato)ferrate (II) and bis (tetrapheny lphosphonium) bis(dithiosquarato)ferrate (II) complexes. An analog for the active site in reducd rubredoxins (Rdred)