1869 H. E. Roscoe (new ed.) xxiii. 236 The metal is a grey substance, which oxidises on heating in air to molybdenum trioxide, MoO3, a yellow powder which acts as an acid, forming with bases salts called molybdates.
1983 S. P. Parker 632/1 Molybdenum trioxide reacts with strong acids..to form complex cations, such as molybdenyl, MoO22+, and molybdyl, MoO4+.