Single-Crystal-to-Single-Crystal Transformation of Two Copper(II) Metal-Organic Frameworks Modulated by Auxiliary Ligands

The single-crystal-to-single-crystal (SCSC) transformations of metal-organic frameworks (MOFs) are fascinating because we can directly observe the change of the crystal structure during the transformation process. It also greatly helps to understand the delicate interaction between the guest molecules and the skeleton framework and therefore fosters a deep understanding of gas storage and separation within the frameworks. Herein, we report two novel MOFs, [Cu-8(BCB)4(mu(3)-OH)(2)(mu O-3)(H2O)(8)(Py)(5)]center dot 16DMF center dot 52H(2)O (1) and [Cu-3(BCB)(2)(Py)(6)]center dot DMF center dot 11H(2)O (2) (Py = pyridine; DMF = N,N'-dimethylformamide), which were constructed through the self-assembly of Cu2+ and 4,4',4 ''-benzenetricarbonyltribenzoic acid (H3BCB) by a solvothermal reaction. Although the structure and coordination patterns of compound 1 are pretty different from those of 2, the two Cu-MOFs were prepared from identical ligands and similar reaction conditions. Interestingly, compound 1 will change to 2 wholly and gradually after the addition of a certain amount of Py with a small amount of dilute hydrochloric acid. This conversion represents a scarce example of SCSC transformation involving transition-metal-based MOFs. Moreover, with its microporous nature, compound 2 shows large carbon dioxide (CO2) uptake capability and good selectivity for CO2/N-2 separation. Furthermore, both compounds 1 and 2 could be used as excellent heterogeneous catalysts toward the cyanosilylation reaction under solvent-free conditions.

Automated summary

The single-crystal-to-single-crystal transformations of metal-organic frameworks (MOFs) are fascinating and help understand gas storage and separation. Two novel MOFs were reported, which can undergo complete transformation and exhibit excellent gas adsorption and separation properties, as well as catalytic activity.