Synthesis and stabilization of a hypothetical porous framework based on a classic flexible metal carboxylate cluster

Abstract

By using pyridyl derivatives 4-cyanopyridine (4-pyCN) or nicotinate (na⁻) as terminal ligands (L^T) to decorate the flexible trigonal-prismatic trinuclear metal carboxylate M₃(μ₃-O/μ₃-OH)(RCOO)₆(L^T)₃ clusters, a theoretically predicted uninodal 6-connected flu-e network for [M₃(μ₃-O/μ₃-OH)(bdc)₃(L^T)₃] (H₂bdc = 1,4-benzenedicarboxylic acid) has been realized in three new porous coordination frameworks. The flu-e topology is isomeric to the uninodal 6-connected acs (MIL-88) and tetranodal 6-connected mtn-e (MIL-101) ones observed in the classic metal carboxylate framework materials, but comprises of unique cubic cages which require exceptional conformation for the trinuclear clusters. The weak coordinating 4-pyCN terminal ligands tend to leave the clusters during thermal activation, leading to framework distortion and reduction of the long-range order of the flu-e network, which can only be restored by 4-pyCN instead of other guest molecules. On the other hand, the carboxylate ends of the adjacent na⁻ ligands coordinate with additional metal ions to crosslink the coordination networks as new binodal 4,9-connected networks with remarkably enhanced thermal/chemical stability and porosity.