A novel mononuclear copper complex of the "NO-NOate" [Et(2)N(N2O2)](-) has been prepared and its X-ray crystal structure determined(shown). Comparison of rate constants for NO evolution from the complex and from Na[Et(2)N(N2O2)] revealed that the complex decomposes approximately half as fast as the sodium salt in aqueous Solution (pH 7.4, PBS buffer, 37 degrees C), implicating a decomposition mechanism for the complex different from that postulated for other reported polynuclear copper complexes of this NONOate.