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.