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 Cu 2TMBD, CdTMBD, and Zn 4O(H 2O) 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 Cd (2+), and nonbonding to Zn (2+)). Diffuse-reflectance spectra show that the metal-thioether interaction is associated with smaller electronic band gaps of the solid-state networks.