The mono-mu-hydroxo complex {[Cu-(tmpa)](2)-(mu-OH)}(3+) (1) can undergo reversible deprotonation at -30 degrees C to yield {[Cu(tmpa)](2)-(mu-O)}(2+) (2). This species is basic with a pK(a) of 24.3. 2 is competent for concerted proton-electron transfer from TEMPOH, but is an intrinsically poor hydrogen atom abstractor (BDFE-(OH) of 77.2 kcal/mol) based on kinetic and thermodynamic analyses. Nonetheless, DFT calculations experimentally calibrated against 2 reveal that [Cu2O](2+) is likely thermodynamically viable in copper-dependent methane monoxygenase enzymes.