Abstract
Two Zn MOFs, MOF-645 and MOF-646, comprised of polarized 1,3-azulenedicarboxylate were synthesized. The guest free MOF-646 showed strong MOF-H-2 interactions (7.8-6.8 kJ mol(-1)), which revealed the significant impact of internally polarized azulene backbone to stabilized H-2 molecules in the framework.