Data type: char
Example: '[Co Re (C12 H22 P)2 (C O)6].0.5C H3 O H'
Formula expressed in conformance with IUPAC rules for inorganic and metal-organic compounds where these conflict with the rules for any other _chemical_formula_ entries. Typically used for formatting a formula in accordance with journal rules. This should appear in the data block in addition to the most appropriate of the other _chemical_formula_ data names. Ref: IUPAC (1990). Nomenclature of Inorganic Chemistry. Oxford: Blackwell Scientific Publications.