Coordinatively unsaturated Ni(2+) 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, N(2) and C(2)H(4) have been chosen. Notwithstanding the relative medium (CO and C(2)H(4)) 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 Ni(2+) adsorbing sites as determined by a parallel EXAFS investigation locating the N(2) molecule 2.27 +/- 0.03 A apart from Ni(2+). For both N(2) and C(2)H(4), IR spectra have been discussed and carefully compared with literature data. Isosteric heat of adsorption of the Ni(2+)...N(2) complex formation has been evaluated from temperature dependent IR study to be -DeltaH(ads) = 17 kJ mol(-1).