You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
sodium;[3-hydroxy-2,7-diiodo-6-oxo-9-(2-sulfonatophenyl)xanthen-4-yl]mercury(1+);hydroxide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C19H9HgI2NaO7S
assistant