To understand how the separation between the election and proton-accepting sites affects proton-coupled electron transfer (PCET) reactivity, we have prepared ruthenium complexes with 4' -(4-carboxyphenyl)terpyridine ligands, and studied reactivity with hydrogen atom donors (H-X). Ru ''(pydic) (tpy-phCOOH) (Ru '' phCOOH), was synchesized in one pot from [(p-cymene)Rucl(2)](2,) sodium 4' -(4-carboxyphenyl) -2,2':6'2" -terphyridine([Na center dot]tpy-phCOO(-)), and disodium pyridine-2, 6-dicarboxylate (Na(2)pydic). Ru '' PhCOOH plus (Bu4NOH)-Bu-n in DMF yields the deprotonated Ru(II) complex, (Bu4N)-Bu-n[Ru ''(pydic) (tpy-phCOO)] (Ru '' phCOO(-)). The Ru(III) complex (Ru'''phCOO) has been isolated by one-electron oxidation of Ru '' phCOO(-) with triarylaminium radical cations (NAr3..). The bond dissociation free energy (BDFE) of the O-H bond in Ru '' phCOOH is calculated from pK(a) and E-1/2 measurements as 87 kcal mol(-1), making Ru'''phCOO a strong hydrogen atom acceptor. There are 10 bonds and ca.11.2 angstrom separating the metal from the carboxylate basic site in Ru'''phCOO. Even with this separation Ru'''phCOO oxidizes the hydrogen atom donor TEMPOH (BDFE = 66.5 kcal mol(-1),Delta G degrees(rxn) = -21 kcal mol(-1)) by removal of an electron and a proton to form Ru '' PhCOOH and TEMPO radical in a concerted proton-electron transfer (CPET) process. The second order rate constant for this reaction is (1.1 +/- 0.1) * 10(5) M-1S-1 with k(H/)k(D) = 2.1 +/- 0.2, similar to the observed kinetics in an analogous system without the phenyl spacer, Ru'''(pydic) (tpy-COO-) (Ru'''COO). In contrast, hydrogen transfer from 2.6-di-tert-butyl-p-methoxyphenol ['Bu-2(OMe)ArOH] to Ru'''PhCOO is several orders of magnitude slower than the analogous reaction with Ru'''COO.