Figure 2.

Ball and stick representation of (A) classical Dawson type anion P₂${\text{Mo}}_{18}^{6-}$ (Briand et al., 2002); (B) anion in P₂O₇${\text{Mo}}_{18}^{4-}$ (Kortz and Pope, 1994); (C) anion in ${\text{AsW}}_{18}^{7-}$ (Jeannin and Martin-Frere, 1979). Color code: addenda atom Mo (B) or W (C), dark blue spheres; heteroatom P (B) or As (C), yellow spheres; O, red spheres.