Formula with each discrete bonded residue or ion shown as a
               separate moiety. See the CHEMICAL_FORMULA category description
               for rules for writing chemical formulae. In addition to the
               general formulae requirements, the following rules apply:
                  (1) Moieties are separated by commas ','.
                  (2) The order of elements within a moiety follows general rule
                     (5) in the CHEMICAL_FORMULA category description.
                  (3) Parentheses are not used within moieties but may surround
                     a moiety. Parentheses may not be nested.
                  (4) Charges should be placed at the end of the moiety. The
                     charge '+' or '-' may be preceded by a numerical multiplier
                     and should be separated from the last (element symbol +
                     count) by a space. Pre- or post-multipliers may be used for
                     individual moieties.