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An Exceptionally Stable, Porphyrinic Zr Metal-Organic Framework Exhibiting pH-Dependent Fluorescence Hai-Long Jiang, Dawei Feng, Kecheng Wang, Zhi-Yuan Gu, Zhangwen Wei, Ying-Pin Chen, and Hong-Cai (Joe) Zhou J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja406844r • Publication Date (Web): 28 Aug 2013 Downloaded from http://pubs.acs.org on August 29, 2013
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Journal of the American Chemical Society
An Exceptionally Stable, Porphyrinic Zr Metal-Organic Framework Exhibiting pH-Dependent Fluorescence Hai-Long Jiang,†,‡,§ Dawei Feng,†,§ Kecheng Wang,† Zhi-Yuan Gu,† Zhangwen Wei,† Ying-Pin Chen,† and Hong-Cai Zhou*,† † Department of Chemistry, Texas A&M University, College Station, Texas 77843, United States ‡ Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China ABSTRACT: A reaction between a ZrIV salt and a porphyrinic tetracarboxylic acid leads to a metal-organic framework (MOF) with two types of open channels, representing a MOF featuring a (4,8)-connected sqc net. The MOF remains intact in both boiling water and aqueous solutions with pH ranging from 1 to 11, a remarkably extensive pH range that a MOF can sustain. Given its exceptional stability and pH-dependent fluorescent intensity, the MOF can be potentially applied in fluorescent pH sensing.
INTRODUCTION In recent two decades, metal-organic frameworks (MOFs) have received tremendous attention due to their powerful attributes on structural and chemical versatility and tailorability.1 The rational design in their construction promises these porous materials tailored to specific functional applications, such as, gas storage/separation, catalysis, sensor, and drug delivery.2-5 Despite this, stability has being recognized as a crucial issue on the way to practical applications of MOFs. Thermally, MOFs usually stabilize up to 250 ºC and the best record demonstrates that the framework is able to maintain until even higher than 500 ºC, which are robust enough as porous functional materials.6 However, most of MOFs are more or less sensitive to moisture, which could be one of key limitations to meet the requirements of various applications. In addition, seldom MOFs were reported to be chemically resistant in an acidic or basic medium. Based on the previous reports, MOFs constructed by imidazole or pyrazolate derivatives are inclined to survive under alkaline conditions,6d,7 while carboxylate-coordinated MOFs would withstand an acidic environment.8 To target the MOFs with both thermal and chemical stabilities, our group have aimed at zirconium(IV) carboxylates. According to “soft and hard acids and bases” theory, zirconium(IV) cation and carboxylate anion belong to hard acid and hard base, respectively, which makes the coordination bonds between zirconium and carboxylic oxygens very strong and potentially tolerable to attack of water, acid and even base. However, the inert coordination bonds between Zr4+ cations and carboxylate anions make ligand exchange reactions extremely slow, which is unfavorable for defect repair in the process of crystal growth. Therefore, it is especially difficult to obtain single crystals of zirconium carboxylate MOFs and only a couple of them have been structurally characterized to date.6a,8b,9 During our persistent efforts in this research line, we have reported PCN-56 to -59 with UiO type structure that remain intact in dilute acid and base (2< pH
