Two three-dimensional Fe(II) frameworks based on {P4Mo6} tetrameric clusters exhibiting efficient visible-light photocatalytic properties for the degradation of Cr(VI) and methylene blue

Two three-dimensional frameworks based on the {P4Mo6} unit, H(4,4'-bipy)(2)[Fe-4(PO4) (H2O)(4)Na-6][Fe-6(H2O)(4)][(Mo6O12)(HPO4)(3)(PO4)(OH)(3)](4)center dot 5H(2)O (4,4'-bipy = 4,4'-bipyridine) (1) and H-3(C12H14N2)(4)[Fe-4(PO4)(H2O)(4)Na-4][Fe-2(Mo6O12(HPO4)(3)(PO4)(OH)(3))(4)]center dot 6H(2)O (2) were successfully synthesized by varying the solvent. The extended structures of the two compounds were formed by transition metal Fe(II) ions bridging the {P4Mo6}-based tetrameric clusters around [NaXFe4(PO4)] (X = 6 (1), or X = 4 (2)) core. The 4,4'-bipy molecules and in situ generated methyl viologen cations as templates induce the formation of two three-dimensional structures, an 8-connected bcu topology framework for 1 and a 4-connected 2-fold interpenetrating diamond-like topological network for 2, respectively. Additionally, multiform hydrogen bonds are found in the framework and also play an important role in stabilizing the structure. The proton conduction mechanism of the two compounds can be mainly classified as the Grotthuss mechanism; the proton conductivity values are 1.06 x 10(-3) S cm(-1) for 1 and 3.13 x 10(-3) S cm(-1) for 2 at 75 degrees C under 98% relative humidity. The visible-light photocatalytic activity was evaluated by photocatalytic decomposition of Cr(VI) and MB dye, and the removal ratios can reach 95.6% (1) and 82% (2) for Cr(VI), and 98% (1) and 99% (2) for MB.

Automated summary

Two three-dimensional frameworks based on the {P4Mo6} unit were successfully synthesized by varying the solvent. The structures were formed by transition metal Fe(II) ions bridging the {P4Mo6}-based clusters, with templates inducing the formation of 8-connected and 4-connected frameworks. The compounds showed good proton conductivity and visible-light photocatalytic activity.