In a wet scrubbing process, the addition of ethylenediamine cobalt(II) (Co(II)-en) to enhance the solubility of NO in aqueous solution may provide a good environmental control technology (coordination catalysis reactions absorption) for removal of NO, after the use of a SO2 scavenging process, that requires little capital when combined with a highly developed industrial wet desulfurization processes. Under anoxic conditions according to amount of time-dependent absorbed NO under different NO partial pressure, the mole ratio of reacted NO and Co(II)-en in the coordination reaction nNO + [Co(en)(3)](2+) double left right arrow [Co(en)(3)(NO)(n)](2+) was determined to be 1:1, that is n = 1. From this, the formula of the formed nitrosyl metal complex is derived to be [Co(en)(3)(NO)](2+). For the development of this scrubbing technological process, knowledge of thermodynamic equilibrium data of the reaction NO + [Co(en)(3)](2+) double left right arrow [Co(en)(3)(NO)](2+) over a range of temperatures is of prime importance. In the temperature range from (30 to 90) degrees C, the equilibrium constant has been determined, and the experimental data fit the following equation well: K-p = (3.3153 +/- 0.1160) x 10(-4) exp(4428.5 +/- 96.2/T)/bar(-1) where the reaction enthalpy is Delta H-0 = -(36.821 +/- 0.800) kJ.mol(-1).