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Contrasting interpenetration in two isoreticular MOFs with bridged layers: role of 2D layer packing density in 3D
Jin Shuang Guo1,2,3, Yu Chuan Zhao4, Ran Liang1
1Shandong Provincial Engineering Research Center for Forensic Examination and, Information Technology in Public Safety, Shandong University of Political Science and Law, Jinan, Shandong 250014, People's Republic of China.
Abstract:
Single-crystal X-ray diffraction analysis of two isoreticular MOFs, poly[[(μ-4,4'-diazenediyldibenzoato)[μ-1,3-bis(pyridin-4-yl)propane]cadmium(II)] dimethylformamide tetrasolvate], {[Cd(C14H8N2O4)(C13H14N2)]·4C3H7NO}n or {[Cd(adc)(bpp)]n·4DMF}n (1), and poly[aqua(μ-4,4'-diazenediyldibenzoato)[μ-1,3-bis(pyridin-4-yl)propane]cobalt(II)], [Co(C14H8N2O4)(C13H14N2)(H2O)]n or [Co(adc)(bpp)(H2O)]n (2), obtained via one-pot solvothermal synthesis, reveals a counterintuitive relationship in interpenetration behaviour [adc = azobenzene-4,4'-dicarboxylate or 4,4'-diazenediyldibenzoate, bpp = 1,3-bis(pyridin-4-yl)propane and DMF = N,N-dimethylformamide]. MOF 1 crystallizes in the orthorhombic system (Pccn, Z = 8) and adopts a non-interpenetrating 3D architecture with a calculated solvent-accessible void volume of 40.4%. The [Cd(adc)]n sublayers in 1 exhibit twofold interpenetration, resulting in closely packed layers that prevent further 3D interpenetration upon bridging by flexible bpp ligands. In contrast, MOF 2 crystallizes in the space group P21/c (Z = 4) and adopts a twofold interpenetrated 3D framework with a reduced solvent-accessible void volume of 4.4%. This architecture originates from non-interpenetrated yet loosely packed [Co(adc)]n layers. Photoluminescence studies corroborate this structural dichotomy. Dense intralayer packing in 1 induces concentration quenching, whereas rigid non-interpenetrated layers in 2 preserve linker-based emission. This comparative crystallographic study demonstrates that the packing density of 2D layers dictates the propensity for higher-order catenation, highlighting interpenetration as a geometric constraint rather than a synthetic flaw.
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