Question

Experiment: Synthesis and Characterization of a Metal-Organic Framework (MOF)

Procedure:

In a 100 mL jar, dissolve 0.45 g (1.5 mmol) of zinc nitrate hexahydrate and 0.083 g (0.50 mmol) 1,4-benzenedicarboxylic acid (H₂BDC) in 49 mL of dimethylformamide (DMF) and 1 mL DI water. Screw the lid on the jar. Heat the reaction mixture in an oven at 100 °C for at least 7 h. Cool to room temperature.

In the hood, decant the solvent, and remove one or two crystals for XRD and IR characterization. Store these in a vial and flushed with nitrogen. Soak the remaining solid in 50 mL of CH2Cl2 for at least 8 h. Take an IR of one of the soaked crystals.

I)

After the DCM soak, what change(s) do you expect to observe in the IR spectrum? What causes the observed change(s)?

Answer 1

The reaction of zinc nitrate hexahydrate (Zn(NO₃)₂.6H₂O) and with 1,4-dicarboxylic acid will lead to 3-dimensional metal organic framework (MOF), where dimethyl formamide (DMF) will present inside the cavity as guest molecule.

when the metal organic framework heated in a oven at 100 deg C for 7 h, the DMF molecule present in the cavity may be liberated or evaporated.

therefore now the metal organic framework cavity is empty, as the MOF is soaked in DCM, the DCM molecule will trap inside the cavity as guest molecule and it will interact with carbonyl group of benzoate ligand

as a result in IR the carbonyl group of the MOF will be shifted and C-Cl str will be shifited for trapped DCM molecule due to interaction between guest (DCM) and host (MOF) molecules