The bifunctional molecule tetrakis(methylthio)-1,4-benzenedicarboxylic acid (TMBD) interacts with the increasingly harder metal ions of Cu-I, Cd-II, and Zn-II to form the coordination networks of Cu2TMBD, CdTMBD, and Zn4O(H2O)(3)(TMBD)(3), where the carboxyl group consistently bonds to metal ions, while the softer methylthio group binds with preference to the softer metal ions (i.e., chelation to Cu+, single-fold coordination to Cd2+, and nonbonding to Zn2+). Diffuse-reflectance spectra show that the metal-thioether interaction is associated with smaller electronic band gaps of the solid-state networks.