Response of CPO-27-Ni towards CO, N2 and C2H4

Abstract

Coordinatively unsaturated Ni²⁺ atoms in CPO-27-Ni form linear adducts with molecular nitrogen. The framework responds to the adsorption-modifying vibrational properties and local structure around adsorbing sites. The present paper deals with a fundamental infrared (IR) study of the interaction of gases on a microporous adsorbent metallorganic framework CPO-27-Ni containing, after solvent removal, coordinatively unsaturated Ni²⁺ atoms [Dietzel et al., Chem. Commun. 2006, 959]. CO, N₂ and C₂H₄ have been chosen. Notwithstanding the relative medium (CO and C₂H₄) and weak (N₂) adsorption enthalpies and the low equilibrium pressures adopted (100–10⁻³ mbar) the CPO-27-Ni framework responds promptly and reversibly to the adsorption process, modifying significantly both vibrational properties and local structure around Ni²⁺ adsorbing sites as determined by a parallel EXAFS investigation locating the N₂ molecule 2.27 ± 0.03 Å apart from Ni²⁺. For both N₂ and C₂H₄, IR spectra have been discussed and carefully compared with literature data. Isosteric heat of adsorption of the Ni²⁺⋯N₂ complex formation has been evaluated from temperature dependent IR study to be −ΔH_ads = 17 kJ mol⁻¹.