A novel Co based metal organic anion framework, {(H2N(CH3 )(2)]][Co-2 (BDC)SO4 F(H2O)11 with highly exposed S0(4)(2-) on the {001} facets has been synthesized under hydrothermal condition by 1,4-H-2 BDC (1,4-benzenedicarboxylic), CoSO4 .7H(2)O and HF. Notably, F- and S0(4)(2-) both have made great contributions to the construction of the anion framework. Due to the anion framework and the highly exposed S0(4)(2-), the Co-MOF could be developed as an active electrochemical sensor by the modification on the GCE and could realize the enhanced detection of Fe3+. The typical redox potentials at 0.37 V and 0.64 V on cyclic voltammograms (CV) curves provide the qualitative detection of Fe3+, and the linear I-c (current-concentration) equation makes the quantitative detection available. The lowest quantitative detection limit could be down to 0.1 mu M The detection mechanisms have been explored in details through the analyses of X-ray single crystal diffraction, scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDX) and X-ray photoelectron spectroscopy (XPS). The SO42- groups mainly exposed on the {001} facets of the cubic Co-MOF, and the interactions between the "hard acid" Fe (3+) and the "hard base" SO42- on the highly exposed facet {001} play the vital role in helping sensing Fe3+, which finally makes the Co-MOF into an active sensor for Fe3+.