Ab-Initio Fully Periodic Characterization of MOF-74-M (M = Mg, Mn, Ni, Zn): Structures and Enthalpies of Adsorption
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Ab-Initio Fully Periodic Characterization of MOF-74-M (M = Mg, Mn, Ni, Zn): Structures and Enthalpies of Adsorption Loredana Valenzano1, Bartolomeo Civalleri2 and Warren F. Perger1 1 Michigan Technological University, Department of Physics, 1400 Townsend Dr, Houghton, MI 49331, U.S.A. 2 University of Turin, Department of Chemistry IFM and NIS Centre of Excellence, Via P. Giuria 7, Turin, 10125, Italy ABSTRACT As a part of a systematic study on cation-exchanged MOF-74-M, we report a partial snapshot of our recent work achieved via a fully periodic first principle approach. Structures are reported for bulk MOF-74-Mg, Mn, Ni, and Zn as computed at DFT-B3LYP level of theory; enthalpies of adsorption for CO and CO2 in interaction with MOF-74-Ni, and Zn are also investigated as obtained at B3LYP+D* level, which is able to take into account the long-range dispersion interaction between adsorbate and adsorbant, through an a-posteriori scheme. Results are discussed and compared with available experimental data. To the authors’ knowledge this represents the first description of MOF-74-Mn structure and of the interaction of the mentioned molecules with MOF-74-Zn. INTRODUCTION Metal organic frameworks (MOFs) have received wide attention in the last fifteen years due to their extremely high surface areas, and pore sizes and functionalization versatilities. The theoretically infinite number of possible structures that can be obtained by changing either the organic linker or the metallic brick opened a whole new window on the possibility for their use in gas storage, capture and separation, drug delivery, catalysis, electronical and optical applications, and sensing [1]. The systems in this investigation are MOF-74-M (M=Mg, Mn, Ni, Zn) also known as CPO-27-M, where 2,5-dihydroxyterephthalte linkers connect metallic MO5 bricks that helically arrange to form a 3D hexagonal packing (space group R-3, No. 148). The so obtained structure shows a 1D arrangement of parallel hexagonal channels of 15 Å in diameter, exhibiting the M2+ ion at the vertices of the hexagons formed by the organic linkers (Figure 1). All of the oxygen atoms of the carboxylate and hydroxy groups of the linkers coordinate the metal cation to give five oxygen atoms in the coordination sphere of each M2+ ion, which shows a sixth accessible coordination site that can be occupied by an adsorbed guest molecule. More details on the MOF74 structure can be found in Ref [2].
Figure 1. Honeycomb structure of MOF-74-M. Metal atoms, oxygens, carbons and hydrogens are reported in green, red, grey and white, respectively. THEORY Calculations were performed at the B3-LYP [3,4] level of theory with the periodic abinitio CRYSTAL09 program [5] where crystalline orbitals are represented as linear combinations of Bloch functions (BFs), and are evaluated over a regular three-dimensional mesh in reciprocal space. Each BF is expressed as local atomic orbitals (AOs) which are contractions of Gaussiantype functions (GTFs). All-electron basis sets (TZVP and TZP) were used for all the atoms
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