Structures of the magnesium Grignard complexes CH3MgF, CH3MgMgF, CH3MgF(Mg), and CH3MgF(Mg-2) have been studied by ab initio methods of quantum chemistry, including self-consistent-field, many-body perturbation theory, and density functional theory techniques, Electronic distributions have been analyzed by means of natural bond orbital analysis. It has been found that magnesium atoms can be attached to the Grignard reagent CH3MgF, leading to a dimagnesium complex CH3MgF(Mg) and the trimagnesium species CH3MgF(Mg-2). The energy of the CH3MgF(Mg) complex is found to be lower than that of the previously known CH3MgMgF compound.