Synthesis and structural characterization of bis(tetraphenylphosphonium) bis(diethyldithiocarbamato)bis(thiophenolato)tetrakis(.mu.3-sulfido)tetraferrate(2II, 2III), (Ph4P)2[Fe4S4(SPh)2(Et2dtc)2]. A "cubane" type cluster with mixed terminal ligands and two different modes of ligation on the Fe4S4 co