Tungstic acid
Tungstic acid refers to hydrated forms of tungsten trioxide, WO3. The simplest form, the monohydrate, is WO3·H2O, the dihydrate WO3·2H2O is also known. The solid state structure of WO3·H2O consists of layers of octahedrally coordinated WO5(H2O) units where 4 vertices are shared. The dihydrate has the same layer structure with the extra H2O molecule intercalated between the layers. The monohydrate is a yellow solid and insoluble in water. The classical name for this acid is 'acid of wolfram'.