The monosulfoxide of cyclo-heptasulfur was reported along with cycloheptasulfur itself in 1977,[cite]10.1002/anie.197707161[/cite] along with the remarks that “ The δ modification of S 7 contains bonds of widely differing length: this has never been observed before in an unsubstituted molecule. and “the same effect having also been observed in other sulfur rings (S 8 O, S 7 I 1+ and S 7 O).”