All tetraperoxo complexes studied exhibit an eight-fold coordination geometry, whereby the ligated oxygen atoms are arranged in a distorted dodecahedron, or equivalently a distorted tetrahedral arrangement of η 2 -O 2 2groups (Scheme 1). Although this geometry has been noted as less common, it is isostructural with the tetrakis(ethylene)metalates and is the natural expectation from VSPER theory. The overall charge on each species has been selected such that the metal Scheme 1: (a) Tetraperoxometalate complex where x = -4 for the Group IV metals (Ti, Zr, Hf); -3 for Group V (V, Nb, Ta); and -2 for Group VI (Cr, Mo, W). (b) 3D molecular rendering.