The structures of magnesium methoxide and magnesium methoxide fluoride obtained via the reaction of Mg(OCH(3))(2) with HF were investigated by single-crystal structure analysis and multinuclear solid-state NMR ((13)C and (19)F). The fluorolysis of magnesium methoxide transforms the cubane structure units in hexanuclear dicubane units containing micro(4)-fluorine atoms. The resulting Mg(6)F(2)(OCH(3))(10)(CH(3)OH)(14) compound crystallizes in two different crystalline modifications. Moreover by slow thermal decomposition of the compound Mg(6)F(2)(OCH(3))(10)(CH(3)OH)(14), it loses two outer CH(3)OH molecules and leaves crystal structure Mg(6)F(2)(OCH(3))(10)(CH(3)OH)(12). The thermal behavior of Mg(OCH(3))(2)(CH(3)OH)(3.55) and Mg(6)F(2)(OCH(3))(10)(CH(3)OH)(14) was investigated by DTA and XRD. Both compounds lose the solvated methanol completely by heating above 150 degrees C and form MgO above 600 degrees C as well as amorphous MgF(2) in the case of magnesium methoxide fluoride.