A series of protonated and methylated Anderson-type molybdoperiodates as well as the unprotonated [IMo6O24]5- have been synthesized and structurally characterized as tetra-n-butylammonium salts: [(n-C4H9)4N]5[IMo6O24] [monoclinic, space group C2/c, a = 33.6101(3) A, b = 15.2575(1) A, c = 24.0294(2) A, beta = 126.9569(3) degrees , Z = 4], [(n-C4H9)4N]4[IMo6O23(OH)] [monoclinic, space group P21/c, a = 9.5587(1) A, b = 24.1364(2) A, c = 18.2788(2) A, beta = 90.1562(5) degrees , Z = 2], [(n-C4H9)4N]3[IMo6O22(OH)2].2DMF [monoclinic, space group P21/a, a = 17.6105(4) A, b = 15.5432(5) A, c = 29.3316(9) A, beta = 91.475(3) degrees , Z = 4], [(n-C4H9)4N]4[IMo6O23(OMe)].3H2O [orthorhombic, space group Pbca, a = 17.0679(4) A, b = 25.6998(6) A, c = 20.7428(4) A, Z = 4], [(n-C4H9)4N]3[IMo6O22(OMe)2] [monoclinic, space group P21/n, a = 10.4009(1) A, b = 14.6658(3) A, c = 23.5395(4) A, beta = 100.324(1) degrees , Z = 2]. In all of these compounds, the [IMo6O24]5- anion is protonated or methylated selectively at O atoms shared by two Mo atoms. The results have also revealed that the protonated Anderson-type molybdoperiodates readily react with methanol in a very selective manner, while the unprotonated [IMo6O24]5- anion does not react with methanol under similar conditions.