title: Influence of gas packing and orientation on FTIR activity for CO chemisorption to the Cu paddlewheel.
abstract: In situ Fourier-transform infrared (FTIR) spectroscopy is able to probe structural defects via site-specific adsorption of CO to the Cu-BTC (BTC = 1,3,5-benzenetricarboxylate) metal-organic framework (MOF). The temperature-programmed desorption (TPD) of CO chemisorbed to Cu-TDPAT (TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine) is virtually identical to Cu-BTC, suggesting CO chemisorbs to the open metal site at the axial position of the copper paddlewheel that is the building unit of both MOFs. Yet, despite an increased gravimetric CO : Cu ratio, CO chemisorbed to Cu-TDPAT is FTIR inactive. We rule out the presence of residual solvent, thermal degradation, adsorption temperature, and ligand-induced electronic effects at the adsorption site. TPD at increased pressure suggests the multiple CO per Cu site rearrange in Cu-TDPAT as a dynamic function of temperature and pressure. Thus, the FTIR inactivity of CO chemisorbed to Cu-TDPAT is attributed to orientation and/or packing of the CO relative to the Cu binding site. The results suggest dynamic chemisorption complicate extension of a site-specific in situ FTIR probe of gas adsorption. For both Cu-BTC and Cu-TDPAT, the in situ FTIR probe is a less sensitive probe of defects than X-ray photoelectron spectroscopy and nitrogen adsorption.
authors.affiliation: Departments of Energy and Mineral Engineering & Chemical Engineering, EMS Energy Institute, Pennsylvania State University, University Park, PA 16802, USA. adl11@psu.edu.
authors.forename: Cheng-Yu
authors.initials: CY
authors.lastname: Wang
authors.forename: Paramita
authors.initials: P
authors.lastname: Ray
authors.forename: Qihan
authors.initials: Q
authors.lastname: Gong
authors.forename: Yonggang
authors.initials: Y
authors.lastname: Zhao
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.forename: Angela D
authors.initials: AD
authors.lastname: Lueking