Rutile-related oxides of the formula LiMMoO(6) for M = Nb or Ta have been synthesized for the first time (a = 4.685(3), c = 9.25(1) Angstrom for M = Nb and a = 4.674(1), c = 9.23(1) Angstrom for M = Ta). These oxides undergo topochemical proton exchange in dilute HNO3, yielding layered HMMoO(6) . H2O that retain the rutile-like MMoO(6) slabs (a = 4.690(9), c = 25.75(8) Angstrom for M = Nb and a = 4.687(1), c = 26.71(1) Angstrom for M = Ta). The monohydrates undergo stepwise dehydration, yielding hemihydrates and anhydrous HMMoO(6). HMMoO(6) . H2O are strong Bronsted acids, intercalating a wide variety of organic bases, including pyridine (pK(a) = 5.3), aniline (pK(a) = 4.6), and pyrrole (pK(a) = 0.4).