Copper(II) complexes of [Et2N(N2O2)]- with tetradentate, tripodal ligands composed of 1,4,7-triazacyclononanes with pyridine (LPy), amide (LHAmH) or phenolate (LR2, R = Me or But phenolate substituents) groups as the fourth donor were prepared and characterized by spectroscopic and X-ray crystallographic methods. Bidentate O,O-coordination of [Et2N(N2O2)]- was observed in the complexes supported by LPy and LHAmH, but the stronger phenolate donor in LR2 induced novel monodentate coordination via the terminal oxygen atom, defined by X-ray crystallography for R = But. Comparison of the bonding parameters of [Et2N(N2O2)]- when bound bidentate versus when bound monodentate revealed subtle but significant differences in the N-O distances. The amount and rate of nitric oxide (NO) release from the compounds was measured using a chemiluminescence detection method. Despite the differences in [Et2N(N2O2)]- structural parameters resulting from the divergent coordination modes, insignificant variation of the rates of NO release therefrom were found.