 T7 trisilanol cage

A corner-deficient cage ${\mathrm{R}}_7\mathrm{S}{\mathrm{i}}_7{\mathrm{O}}_9(\mathrm{OH}{)}_3$. Removing one silicon corner from a T8 cage leaves three silanol-bearing silicon sites, three further sites adjacent to those, and a unique opposite site: symmetry classes 3:3:1.