X-ray structure analysis of 2,3-diphenyl-5-thiomethyltetrazolium triiodide (123) shows that the phenyl rings at the 2- and 3-positions are out of
the plane of the tetrazolium ring by 69 and 58°, respectively. The bond distances in the tetrazolium ring are not equal. In contrast, 2,3-diphenyl-5- mercaptide shows extensive bond delocalization.209,2 1 0