fajThe kinetics and thermodynamics of reaction of O-2 with copper(I) complexes can provide fundamental information relevant to chemical and biological systems. Using diode-array variable-temperature (180-296 K) stopped-flow kinetic methods, we report detailed information on the O-2 reactivity (in EtCN) of dicopper(I) complex [(D-1)Cu-2(I)(RCN)(2)](2+) (2a) (R = Me or Et) [D-1 = dinucleating ligand with a -CH2CH2- group linking two tris(2-pyridylmethyl)amine (TMPA) units at a 5-pyridyl position of each tetradentate moiety]. A comparative study of mononuclear complex [(TMPAE)Cu(RCN)li (1a’) [TMPAE has a -C(O)OCH3 ester substituent in the 5-position of one pyridyl group of TMPA] has been carried out. The results are compared with data from the previously investigated complex [(TMPA)Cu(RCN)](+) (1a).