Of eleven possible isomers for neutral S-4, rectangular S-4 has been proposed theoretically as one of the most stable forms. There has, however, been no consensus as to the S-4 ground-state geometric structure despite much effort over recent years, because of the lack of direct structural information from experimental work due to lack of preparation in a pure state. The principal question is whether the ground-state geometry is rectangular D-2h, or open planar C-2v. Our group found first rectangular S-4 in coordination compounds of Rh and Ir tetranuclear complexes as a ligand and disclosed mysterious rectangular S-4 by X-ray analysis and theoretical studies. Here, the newly developed chemistry of rectangular S-4 complexes together with the related tetrasulfur species is introduced both from experimental and theoretical view points. In addition, more accurate argument of the principal question mentioned above is also described using results obtained from recent high-level theoretical calculations.