[Zr6O4(OH)4(benzene-1,4-dicarboxylato)6]n: a hexagonal polymorph of UiO-66

Since its discovery in 2008, the paradigmatic UiO- 66 has behaved as the germ that has prompted the chemistry of group- 4 metal based metal- organic frameworks, all of them featuring outstanding thermal and chemical stability. Herein we present the first polymorph of UiO- 66 and the key conditions that led to its formation.