Monday, October 30, 2017

Structural diversity, single-crystal to single-crystal transformation and photocatalytic properties of Cu(II)-metal-organic frameworks based on 1,4-phenylenedipropionic acid


Four Cu(II)-MOFs containing 1,4-phenylenedipropionic acid have been reported.
The effect of N,N′-donor coligand is critical in the arrangement of polymeric structure.
The 3D framework of 3 is transformed to 4 upon heating in a single-crystal-to-single-crystal manner.
All compounds are photo-catalytically active for the decomposition of MB.


A series of four new copper(II) based metal-organic frameworks containing 1,4-phenylenedipropionic acid and different N,N′-donor coligands, namely, [Cu(ppa)(bpy)]n(1), {[Cu(ppa)(azp)(H2O)](H2O)}n (2), {[Cu(ppa)(tdp)(H2O)](H2O)2}n (3), and {[Cu(ppa)(tdp)](H2O)}n (4), (H2ppa = 1,4-phenylenedipropionic acid, bpy = 4,4′-bipyridine, azp = 4,4′-azobipyridine, tdp = 4,4′-thiodipyridine) have been successfully synthesized and structurally characterized by elemental analysis, IR, UV–vis, TGA, XRPD and single-crystal X-ray diffraction. Compound 1 containing a short and rigid bpy coligand displays a 2D square lattice (sql) topology while 2 and 3 which contain more flexible and longer azp and tdp coligands possess two-fold interpenetrating diamond-like (dia) 3D framework. Finally, the thermal-induced compound 4 is transformed from compound 3 by heating, through single-crystal-to-single-crystal transformation, adopting a CdSO4-like (cds) 3D framework. Additionally, the solid stated compounds 14 exhibit the energy band gaps of 3.50, 3.16, 3.53 and 3.31 eV, respectively. Thus, the photocatalytic properties of 14have been investigated. Approximately 84.9% for 1, 93.3% for 2, 82.0% for 3 and 85.4% for 4 of methylene blue were decomposed within 105 min.

Graphical abstract
Four new Cu(II)-MOFs have been synthesized in the presence of 1,4-phenylenedipropionic acid (ppa) and different N,N′-donor ancillary ligands. The structural diversity indicates that the effect of N,N′-donor ancillary ligand is critical in construction of polymeric arrangement.

Image for unlabelled figure