Portal de Periódicos da CAPES

Thermally‐Triggered Crystal Dynamics and Permanent Porosity in the First Heptatungstate‐Metalorganic Three‐Dimensional Hybrid Framework

2017; Wiley; Volume: 23; Issue: 59 Linguagem: Inglês

10.1002/chem.201703585

1521-3765

Jagoba Martín‐Caballero, Beñat Artetxe, Santiago Reinoso, Leire San Felices, Óscar Castillo, Garikoitz Beobide, José Luis Vilas‐Vilela, Juan M. Gutiérrez‐Zorrilla,

Advanced Nanomaterials in Catalysis

Abstract The hybrid compound [{Cu(cyclam)} 3 (W 7 O 24 )] ⋅ 15.5 H 2 O ( 1 ) (cyclam=1,4,8,11‐tetraaza‐cyclotetradecane) was synthesized by reacting the {Cu(cyclam)} 2+ complex with a tungstate source in water at pH 8. Compound 1 exhibits an unprecedented three‐dimensional covalent structure built of heptatungstate clusters linked through metalorganic complexes in a POMOF‐like framework that displays water‐filled channels. This dynamic architecture undergoes two sequential single‐crystal‐to‐single‐crystal transformations upon thermal evacuation of water molecules to result in the partially dehydrated [{Cu(cyclam)} 3 (W 7 O 24 )] ⋅ 12 H 2 O ( 2 ) and anhydrous [Cu(cyclam)] 0.5 [{Cu(cyclam)} 2.5 (W 7 O 24 )] ( 3 ) crystalline phases. These transitions are associated with cluster rotations and modifications in the Cu II coordination geometries, which reduce the dimensionality of the original lattice to layered systems but preserving the porous nature. Phase 3 reverts to 2 upon exposure to ambient moisture, whereas the transition between 1 and 2 proved to be irreversible. The permanent microporosity of 3 was confirmed by gas sorption measurements (N 2 , CO 2 ), which reveal a system of parallel channels made of wide cavities connected through narrow necks that limit the adsorption process. This observation is in good agreement with Grand Canonical Monte Carlo simulations.