The title compound Mn-5 (PO3 (OH))(2) (PO4)(2) (H2O)(4) was synthesized under hydrothermal condition. Its crystal structure was determined by single-aystal X-ray diffraction. DRS, IR, fluorescence and TGA spectra were used to characterize the title compound. As a result, the compound is formed by linking with PO4 and MnO6, and the oxygen in it can be divided to three categories, so in IR spectra the characteristic peaks of Mn-O and P-O are separated in to three, respectively. In DRS there are two peaks at 210 and 250 nm coresponding O-d-->Mn and O-b,O-c-->Mn. In fluorescence spectra the emission peaks are located at 354 and 413 nm when excited at 218 and 310 nm. Besides, thermal behavior of the compound is discussed by TGA diagrams. Finally, quantum chemistry calculation is performed to explain the structure characteristic. HF = - 4 558.659 555 1 a. u, HOMO(Alpha) = - 0.280 80a. u, LOMO(Alpha) = 0. 015 27a. u, DeltaE((Alpha)) = 0. 296 07 a. u; HOMO(Beta) 0.259 19 a. u, LOMO(Beta) = 0. 00108 a. u, DeltaE((Beta)) = 0. 260 72 a. u and Dipole = 4.208 2 Debye.