title: Alkaline Earth Metal Ion/Dihydroxy-Terephthalate MOFs: Structural Diversity and Unusual Luminescent Properties.
abstract: Alkaline earth (group 2) metal ion organic frameworks (AEMOFs) represent an important subcategory of MOFs with interesting structures and physical properties. Five MOFs, namely, [Mg2(H2dhtp)2(μ-H2O)(NMP)4] (AEMOF-2), [Mg2(H2dhtp)1.5(DMAc)4]Cl·DMAc (AEMOF-3), [Ca(H2dhtp)(DMAc)2] (AEMOF-4), [Sr3(H2dhtp)3(DMAc)6]·H2O (AEMOF-5), and [Ba(H2dhtp)(DMAc)] (AEMOF-6) (H4dhtp = 2,5-dihydroxy-terepthalic acid; DMAc = N,N-dimethylacetamide; NMP = N-methylpyrrolidone), are presented herein. The reported MOFs display structural variety with diverse topologies and new structural features. Interestingly, AEMOF-6 is the first example of a Ba(2+)-H2dhtp(2-) MOF, and AEMOF-5 is only the second known Sr(2+)-H2dhtp(2-) MOF. Detailed photoluminescence studies revealed alkaline earth metal ion-dependent fluorescence properties of the materials, with the heavier alkaline earth metal ions exhibiting red-shifted emission with respect to the lighter ions at room temperature. A bathochromic shift of the emission was observed for the MOFs (mostly for AEMOF-3 and AEMOF-4) at 77 K as a result of excited state proton transfer (ESIPT), which involves an intramolecular proton transfer from a hydroxyl to an adjacent carboxylic group of the H2dhtp(2-) ligand. Remarkably, AEMOF-6 displays rare yellow fluorescence at room temperature, which is attractive for solid state lighting applications. To probe whether the alkaline earth metal ions are responsible for the unusual luminescence properties of the reported MOFs, the potential energy surfaces (PESs) of the ground, S0, and lowest energy excited singlet, S1, states of model complexes along the intramolecular proton transfer coordinate were calculated by DFT and TD-DFT methods.
authors.affiliation: †Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece.
authors.forename: Antigoni
authors.initials: A
authors.lastname: Douvali
authors.affiliation: ‡Laboratory of Inorganic Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, Zografou 157 71, Athens, Greece.
authors.forename: Giannis S
authors.initials: GS
authors.lastname: Papaefstathiou
authors.affiliation: §Italian National Research Council (CNR), Institute for Organic Synthesis and Photoreactivity (ISOF), Via P. Gobetti 101, 40129 Bologna, Italy.
authors.forename: Maria Pia
authors.initials: MP
authors.lastname: Gullo
authors.affiliation: §Italian National Research Council (CNR), Institute for Organic Synthesis and Photoreactivity (ISOF), Via P. Gobetti 101, 40129 Bologna, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Barbieri
authors.affiliation: †Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece.
authors.forename: Athanassios C
authors.initials: AC
authors.lastname: Tsipis
authors.affiliation: ∥Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
authors.forename: Christos D
authors.initials: CD
authors.lastname: Malliakas
authors.affiliation: ∥Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
authors.forename: Mercouri G
authors.initials: MG
authors.lastname: Kanatzidis
authors.affiliation: ⊥Department of Materials Science and Technology, University of Crete, 71003 Heraklion, Greece.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Papadas
authors.affiliation: ⊥Department of Materials Science and Technology, University of Crete, 71003 Heraklion, Greece.
authors.forename: Gerasimos S
authors.initials: GS
authors.lastname: Armatas
authors.affiliation: #Department of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.
authors.forename: Antonios G
authors.initials: AG
authors.lastname: Hatzidimitriou
authors.affiliation: #Department of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.
authors.forename: Theodore
authors.initials: T
authors.lastname: Lazarides
authors.affiliation: †Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece.
authors.forename: Manolis J
authors.initials: MJ
authors.lastname: Manos