Retrieve compounds using the SMARTS query syntax.

Retrieve compounds with a molecular formula in the range specified by the query.

O3	3 oxygens exactly	O2-6	2-6 oxygens (inclusive)
O<6	less than 6 oxygens	O*	optional oxygens (≥0)
O>2	more than 2 oxygens

Special element symbols:

X	halogen	Q	heteroatom
M	any metal	R	any atom (not already specified)

Add H* or R* to allow any number of hydrogens or extra elements.