Highly Polarizable Triiodide Anions (I3-) as Cross-Linkers for Coordination Polymers: Closing the Semiconductive Band Gap

From a hydrothermal reaction using CuI, KI, and 3,3'5,5'-tetramethyl-4,4'-bipyrazole (TMBP), the triiodide anion I-3(-) has been integrated into the water-stable 2D coordination polymer Cu(TMBP)I-3 (1). In contrast with other metal triiodide complexes, 1 features remarkably small distortions in the bond distances associated with the I-3(-) units (i.e., the Cu-I and I-I bonds), which effectively link up the copper(I) centers into infinite CuI3 chains. The electronic band gaps and electrical conductivity data are also found to be consistent with the I-3(-) ion acting as an effective linker across the copper(I) centers.