Synthesis and Characterization of Polyhedral-Based Metal–Organic Frameworks Using a Flexible Bipyrazole Ligand: Topological Analysis and Sorption Property Studies

Six porous metal–organic frameworks (MOFs), {[Ni­(BTC)0.66­(BPz)2]­·2MeOH­·4H2O}n (1), {[Co­(BTC)0.66­(BPz)2]­·2MeOH­·4H2O}n (2), {[Mn­(BTC)0.66­(BPz)2]­·2MeOH­·4H2O}n (3), {[Cd­(BDC)­(BPz)­(H2O)]­·2MeOH­·DMF}n (4), {[Cd2(NH2-BDC)2­(BPz)­(H2O)]­·MeOH­·H2O­·DMF}n (5), and {[Co­(BDC)­(BPz)­(H2O)]}n (6) (where H3BTC = 1,3,5-benzenetricarboxylic acid, H2BDC = 1,4-benzenedicarboxylic acid, NH2-H2BDC = 2-amino-1,4-benzenedicarboxylic acid, and BPz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole), were obtained through a solvent diffusion technique and characterized. The networks exhibit a variety of topologies: 1, 2, and 3 are isostructural and possess octahedral and cuboctahedra type cages and exhibit 3,6-c binodal net having loh1 topology, 4 is a two-dimensional MOF having one-dimensional open channels with a 4-c uninodal net having sql topology, 5 exhibits a three-dimensional (3D) porous MOF having a 3,3,4,8-c net with a new topology having the name, skr1, whereas 6 discloses a 3D nonporous network which exhibits a 4-c uninodal net having CdSO4 topology. Being isostructural, gas sorption studies of 1–3 show nearly the same CO2 sorption at 195 K of ∼90 mL g–1, whereas 4 and 5 show a maximum uptake of 42 and 37 mL g–1 at 195 K. Vapor sorption studies of 1–3 reveal stepwise uptake of water with a final amount reached to nearly 350 mL g–1, whereas 4 and 5 show maximum uptake of 110 and 90 mL g–1, respectively. Compared to the free ligand BPz, photoluminescence studies of 4 and 5 show red shifts and emit in the blue-green region with λmax at 430 and 472 nm for 4 and 5, respectively.