Ligation modes of dioxygen in metal complexes

M=0 [VO]2+, V=0 bond length (155 to 168 pm) has partial triple-bond character. 

M—O—M Linear, ReC 3 Re—O—Re forms the edges of cubic unit cell. 

Coordination modes of dioxygen metal complexes (a) -superoxo, 

The stretching frequencies attributed to the 0-0 vibration are closely related to the structural type. Type I complexes show 0-0 stretching vibrations around 1125 cm-1 and type II around 860 cm-1. This sharp difference enables the O-O stretching frequency as measured by infrared or Raman spectroscopy to be used for structure type classification. Table 16.2.2 lists the structural data of dioxygen metal complexes. 

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