Synthesis and Characterization
of Polyhedral-Based
Metal–Organic Frameworks Using a Flexible Bipyrazole Ligand:
Topological Analysis and Sorption Property Studies
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Abstract
Six
porous metal–organic frameworks (MOFs), {[Ni(BTC)<sub>0.66</sub>(BPz)<sub>2</sub>]·2MeOH·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>1</b>), {[Co(BTC)<sub>0.66</sub>(BPz)<sub>2</sub>]·2MeOH·4H<sub>2</sub>O}<i><sub>n</sub></i> (<b>2</b>), {[Mn(BTC)<sub>0.66</sub>(BPz)<sub>2</sub>]·2MeOH·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>3</b>), {[Cd(BDC)(BPz)(H<sub>2</sub>O)]·2MeOH·DMF}<i><sub>n</sub></i> (<b>4</b>), {[Cd<sub>2</sub>(NH<sub>2</sub>-BDC)<sub>2</sub>(BPz)(H<sub>2</sub>O)]·MeOH·H<sub>2</sub>O·DMF}<i><sub>n</sub></i> (<b>5</b>), and {[Co(BDC)(BPz)(H<sub>2</sub>O)]}<i><sub>n</sub></i> (<b>6</b>) (where H<sub>3</sub>BTC = 1,3,5-benzenetricarboxylic
acid, H<sub>2</sub>BDC = 1,4-benzenedicarboxylic acid, NH<sub>2</sub>-H<sub>2</sub>BDC = 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: <b>1</b>, <b>2</b>, and <b>3</b> are isostructural and possess octahedral
and cuboctahedra type cages and exhibit 3,6-c binodal net having <i><b>loh</b></i><b>1</b> topology, <b>4</b> is
a two-dimensional MOF having one-dimensional open channels with a
4-c uninodal net having <i><b>sql</b></i> topology, <b>5</b> exhibits a three-dimensional (3D) porous MOF having a 3,3,4,8-c
net with a new topology having the name, <i><b>skr</b></i><b>1</b>, whereas <b>6</b> discloses a 3D nonporous network
which exhibits a 4-c uninodal net having CdSO<sub>4</sub> topology.
Being isostructural, gas sorption studies of <b>1</b>–<b>3</b> show nearly the same CO<sub>2</sub> sorption at 195 K of
∼90 mL g<sup>–1</sup>, whereas <b>4</b> and <b>5</b> show a maximum uptake of 42 and 37 mL g<sup>–1</sup> at 195 K. Vapor sorption studies of <b>1</b>–<b>3</b> reveal stepwise uptake of water with a final amount reached
to nearly 350 mL g<sup>–1</sup>, whereas <b>4</b> and <b>5</b> show maximum uptake of 110 and 90 mL g<sup>–1</sup>, respectively. Compared to the free ligand BPz, photoluminescence
studies of <b>4</b> and <b>5</b> show red shifts and emit
in the blue-green region with λ<sub>max</sub> at 430 and 472
nm for <b>4</b> and <b>5</b>, respectively
