Zwitterionic 5-amino-2-naphthalenesulfonic acid

The crystal structure of 5-amino-2-naphthalene­sulfonic acid (1,6-Cleve's acid), C10H9NO3S, shows the presence of a sulfonate–aminium group zwitterion, viz. 5-ammonio-2-naphthalene­sulfonate. All aminium H atoms are involved in head-to-tail intermolecular hydrogen-bonding interactions with separate sulfonate O-atom acceptors, giving a three-dimensional framework polymer structure.