A novel polyoxometalate cluster, i.e., Na1.5H4.5[(CH3)4N]2{[Mn(CO)3]4(Se2W11O43)}·9H2O (1), has been successfully synthesized under moderately acidic conditions. Compound 1 contains four electron-donating {Mn(CO)3}+ organometallic entities, which are grafted over an unprecedented heteropolytungstate electron-acceptor group. Compound 1 was further structurally characterized by various physicochemical techniques like elemental analyses, inductively coupled plasma (ICP) analyses, IR and UV-vis spectroscopy, electrochemistry, and single-crystal X-ray diffraction, and so on. The polyoxoanion of 1 comprises a novel {Se2W11} fragment, which is obtained from molecular assembly of rare {SeW3} and {SeW8} species. Evaluation of the data from solution-state IR spectrum showed excellent agreement with the solid state IR spectrum, indicating the intact clusters in the CH3CN/Na2SO4 solvent. Also, negative electrospray ionization mass spectrometry (ESI-MS) was an alternative tool to verify the stability of 1 in the mixed solvent. Additionally, the resulting hybrid can act as a catalyst for cyclic carbonate formation from the reactants epoxides and CO2 under modest reaction conditions in conjunction with a 1-ethyl-1-methylpyrrolidinium bromide (2). The good activity can be substantiated due to the cooperative influence of polyoxoanion and Br- ions. Complex 1 can also be easily recycled and reused three times without obvious decrease of catalytic activity.