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

Abstract

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 ∼ 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.