Chemistry of 2,4,6-Trimercapto-1,3,5-triazine (TMT): Acid Dissociation Constants and Group 2 Complexes

The acid dissociation constants of 2,4,6-trimercaptotriazine (H3TMT, 1) were determined and now can be employed
in the preparation of complexes having specific M−TMT (M = divalent metal; TMT = 2,4,6-trimercapto-1,3,5-triazinide, C3N3S33-) ratios. For example, the combination of H3TMT (1) with Mg(OH)2 at pH 7.1 leads to the
crystallization of Mg(H2TMT)2·6H2O (4). With the appropriate pH adjustment, the contiguous series of compounds
Ba3(TMT)2·8H2O (3), Ba(H2TMT)2·7H2O (5), and BaHTMT·3H2O (6) can be isolated. The compounds were
characterized by mp, IR, TGA, elemental analysis, and, in the cases of 4, 5, and 6, crystallography. The comparison
of 4 with 5 and 6 offers an interesting view of the difference in hard and soft bonding with TMT. In the saltlike
Mg structure of 4, there is extensive hydrogen bonding, but in the Ba structures, 5 and 6, covalent Ba−S bonding
dominates.