Two new uncommon 3D cobalt-based metal organic frameworks: Temperature induced syntheses and enhanced photocatalytic properties against aromatic dyes

The reaction of 5-fluorine-3-(3,5-dicarboxylphenxoy)benzoic acid (H3L) with cobalt(II) salt in presence of 1,1'-(1,4-butanediyl)bis (imidazole) (bib) linker yielded two new metal–organic frameworks (MOFs) with compositions [Co4(μ3-OH)2(H2O)2(L)2 (bib)1.5(CH3CN)·3H2O·CH3CN] (1) and [Co8(μ3-OH)4(L)4 (bib)4·8CH3CN] (2). The single crystal X-ray diffraction revealed that 1 exhibited an unusual 3D 3,8-connected framework with 3,8T25 topology based on [Co4(μ3-OH)2] tetranuclear cobalt clusters as secondary building units (SBU) with a (43) (412·54·64·88) Schlafli symbol. In 2, by substituting the CH3CN with neutral N-ligand, a 3D 3,8-connected MOF with 3,10T9 topology and a point symbol of {418.624.83}.{43}2 has been obtained. This represents a highly connected uninodal network topology presently known for flexible carboxylate-based MOF systems. Both the MOFs have been used as photocatalysts for photodegradation of a model organic dye methyl violet (MV). The photocatalytic experiments demonstrated that both 1 and 2 displayed efficient photocatalytic performances to degrade MV under UV irradiation. The plausible mechanism through which both the MOFs displayed photocatalytic properties have been proposed by using band gap calculations.