Postsynthetic Defect Formation in Three-Dimensional Hofmann-Type Coordination Polymers and Its Impact on Catalytic Activity

We report a systematic investigation of postsynthetic defect formation in Hofmann-type coordination polymers M(pz)[M'(CN)(4)] (M = Fe2+, Co2+, Ni2+; M' = Pd2+, Pt2+; pz = pyrazine). These compounds readily undergo selective ligand exchange at the pyrazine site when immersed in methanol (MeOH) at ambient temperature. The ligand exchange changes the chemical formula to M(pz)(1-x)(MeOH)(2x)[M'(CN)(4)] (0 < x < 0.3), affording a defective coordination environment around the M ions. The defect concentration is highly dependent on the combination of the metal ions and solvent species, reaching the defect concentration of ca. 30% (x similar to 0.3) at maximum. The magnetic state of one such coordination polymer gives an additional control of the defect formation, making the compound less susceptible to the ligand exchange at the low-spin state. Structures that form the defects at a high concentration function as catalysts and promote an acetalization reaction heterogeneously by providing Lewis acidic sites. The solvent-dependent character of the defect formation can be used to control the catalytic activity of the active compounds, demonstrating a facile defect engineering for functionalizing solid materials.

Automated summary

This study presents a systematic investigation on postsynthetic defect formation in Hofmann-type coordination polymers. The results show that the defect concentration is highly dependent on the combination of metal ions and solvent species, and the solvent-dependent character of defect formation can be used to control the catalytic activity of active compounds.