Effect of Coordinating Anions on the Kinetics and Thermodynamics of

2062

Inorg. Chem. 1990, 29, 2062-2067 Contribution from Ames Laboratory and the Department of Chemistry, Iowa State University, Ames, Iowa 5001 1

Effect of Coordinating Anions on the Kinetics and Thermodynamics of Oxygen Binding by a Macrocyclic Cobalt(11) Complex Andreja Bakac* and James H. Espenson* Received September 14, 1989 The macrocyclic cobalt(I1) complexes (X)L2Cot (X-= CI-, SCN-; L2 = C-meso-5,7,7,12,14,14-hexamethyl-1,4,8,1 l-tetraazacyclotetradecane) react with O2to yield (X)L2Co02t. The kinetics of the forward reaction in aqueous solution at 25 OC (X- = CI-, k = 1.80 X lo6 M-' s-'; X- = SCN-, k = 7.29 X lo6 M-l S-I) are similar to those for the unsubstituted, presumably diaquo complex L2C02*(k = 5.00 X 10" M-' s-l). The dissociation of O2from (X)L2CoOzt takes place with the rate constants of 3300 s-I and 3 4F:): no. of params refined

R' RWb

quality-of-fit indicatof largest shift/esd, final cycle largest peak, e/A3

'R = W ' a l

542.33 n i / n (No. 14) 8.396 (1) 9.149 ( I ) 15.385 (2) 97.449 (6) 1171.8 12) ., 2 1.537 0.27 X 0.28 X 0.31 10.06 Enraf-Nonius CAD4 Mo Ka (A = 0.71073 A) 25; 18.8-35.3 -20 w-2e 4-50 2050; 1573 142 0.0304 0.042 1 1.20