Hexacoordinated Sn(IV) porphyrin-based square-grid frameworks exhibiting selective uptake of CO2 over N-2

Abstract

We prepared porphyrin metal-organic frameworks with hexacoordinated Sn(IV) porphyrin trans-SnX2(TPyP), where X = Cl-, OH-; TPyP = 5,10,15,20-tetra(4-pyridyl)porphyrinato dianion, and Cu(II) acetate, namely {[SnCl2(TPyP)]center dot[Cu(OAc)(2)](4)}center dot 4DMF center dot 4H(2)O (1) and {[Sn(OH)(2)(TPyP)]center dot[Cu(OAc)(2)](4)}center dot xSolv (2). X-ray crystallographic analysis revealed that both materials consisted of the same square-grid two-dimensional (2D) sheet. The small difference in the trans-axial ligand coordinated to the Sn(IV) center creates distinctively different packing structures. As a consequence of the Cl center dot center dot center dot pi and Cl...Cl interactions between the adjacent layers in 1, squares of stacked 2D layers are well aligned, giving a single type of ordered porous channel. In contrast, adjacent 2D layers in 2 are stacked along the c-axis with an ABAB sequence with an average delamination of 7.05 angstrom. The coordination network structures of both materials provide large free voids without interpenetration. Gas sorption studies showed that both porous materials exhibit 10 times higher CO2 adsorption than N-2 at 273 K.