UiO-66 Zr6O4 cluster framework without BDC linkers. Space group Fm-3m (225), a=20.700 Å. 56 atoms: 24 Zr at 24e positions, 32 O at 32f positions forming Zr6O4 octahedral clusters at 4a sites. Built from crystallographic data in Li & Ahlquist, npj Comput. Mater. (2026).