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

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, N-2 and C2H4 have been chosen. Notwithstanding the relative medium (CO and C2H4) and weak (N-2) 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 N-2 molecule 2.27 +/- 0.03 angstrom apart from Ni2+. For both N-2 and C2H4, IR spectra have been discussed and carefully compared with literature data. Isosteric heat of adsorption of the Ni2+center dot center dot center dot N-2 complex formation has been evaluated from temperature dependent IR study to be -Delta H-ads = 17 kJ mol(-1).