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 Ni 2+ 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 C2H 4, 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 -ΔHads = 17 kJ mol-1.