The title compound, [Co(C(8)H(4)O(4))(C(13)H(14)N(2))(2)(H(2)O)(2)](n), was obtained by the reaction of CoCl(2), 4,4'-trimethyl-enedipyridine and terephthalic acid in a 1:1:1 ratio. The octa-hedrally coordinated cobalt ions are bridged by 4,4'-trimethyl-enedipyridine ligands, generating a chain. These chains are further linked by O-H⋯O and O-H⋯N hydrogen bonds, giving a three-dimensional network.

The asymmetric unit of title compound, C(8)H(6)O(4)·2C(4)H(9)NO, contains one half-mol-ecule (an inversion centre in P21/n generates the other half of the molecule) of terephthalic acid (TA) and one mol-ecule of N,N-dimethyl-acetamide (DMAC). The DMAC mol-ecules are linked to TA by strong O-H⋯O hydrogen bonds.

The asymmetric unit of the title compound, C(8)H(4)Br(2)O(4)·2H(2)O, contains one half-mol-ecule of 2,5-dibromo-terephthalic acid (DBTA) and one water mol-ecule. The DBTA mol-ecule is centrosymmetric. In the crystal structure, inter-molecular O-H⋯O hydrogen bonds link the mol-ecules, forming a three-dimensional framework.

A new thiol-specific reagent introduces a small bis(methylamino)terephthalic acid fluorophore into proteins. The noninvasive probe with distinct spectroscopic properties offers many advantages for protein labeling, purification, and mechanistic work promising to serve as a powerful tool in studies of protein folding and heme redox reactions.