2576
Inorg. Chem. 1986,25, 2576-2582 Contribution from the Departments of Chemistry, Wayne State University, Detroit, Michigan 48202, and the University of Wisconsin-Eau Claire, Eau Claire, Wisconsin 54701
Characterization of Perchlorate Adduct Formation with Copper(I1)-Cyclic Polythia Ether Complexes and Determination of Corrected Stability Constants Ian R. Young,la L. A. Ochrymowycz,'b and D. B. Rorabacher*la Received October 8. I985 The conditional stability constants for the complexes formed between Cu(I1) and several cyclic polythia ether ligands have been determined spectrophotometricallyin the presence of perchlorate ion concentrationsof 0.010,0.025,0.050,0.10,0.25,0.50, and 1.00 M at 5, 15, 25, and 35 " C . The data indicate that the Cu(I1) complexes formed with [12]aneS4,[13]aneS4,and [16]aneS4 increase in apparent stability with increasing perchlorate as was earlier observed for Cu"([ 14]aneS4).By contrast, the conditional stability constant of CUI'([ 15]aneSs), the only pentathia ether complex studied, is virtually unaffected by varying perchlorate. The data for the tetrathia ether complexes can be interpreted as indicative of the formation of a 1:l adduct with the perchlorate anion. A linear mathematical expression is developed to permit the resolution of the thermodynamic stability constant, KcuLo, for the Cu(I1)-tetrathia ether complexes extrapolated to zero ionic strength. This mathematical treatment also yields values of an apparent equilibrium constant, Klxo,representing the interaction of a perchlorate ion with the Cu(I1)-tetrathia ether complexes (Le., for the reaction CuL2++ X- F? CuLX+). The resultant thermodynamic parameters characteristicof these two equilibrium constants and the activity-corrected 25 "C equilibrium constant values for each system are as follows (AHIX",ASlx", K I x ofor 25 "C, AHcULo,ASscuL",KcuLofor 25 "C): for C~'~([lZ]aneS~), -0.2 ( f l . 5 ) kcal mol-', 5 ( f 5 ) cal K-'mol-', 24 (i3)M-I, -0.6 (i1.0) kcal mol-', 13 ( 1 4 ) cal K-' mol-', 1.6 (f0.2) X lo3 M-I; for Cu"([13]aneS4),-1.8 (f0.5) kcal mol-', -0.2 (11.7) cal K-I mol-', 19 ( f l ) M-I, -1.5 (f0.3) kcal mol-', 9.4 ( f l . O ) cal K-'mol-', 1.44 (f0.09) X IO3 M-I; for Cu"([14]aneS4),-1.7 (*0.1) kcal mol-', 0.6 (10.4) cal K-' mol-', 24.2 (i0.5) M-I, -3.1 (f0.2) kcal mol-', 7.9 (f0.5) cal K-'mol-', 1.08 (f0.02) X IO4 M-I; for Cu"([lS]aneSs), no estimate, no estimate, 0 M-', -2.9 (f0.2) kcal mol-', 8.6 (f0.6) cal K-'mol-', 1.02 (f0.08) X lo4 M-I; for Cu"([16]aneS4), K l r o N 1 X 10 M-', KcvLo N 1.2 X lo2 M-'.
Introduction In recent years we have conducted extensive investigations into various aspects of the chemical behavior of copper(I1) complexes formed with macrocyclic polythia ethers, particularly as related to structural constraint^.^-^ Most of these studies have been carried out in aqueous solutions where the complexes are relatively weak (KcuL> C, (such that Cc, N [Cu']), we can combine eq 7-9 with eq 2 and rearrange them to yield the linear relationship of McConnell and Davidson:lo
By plotting bCL/A against l/Ccu for a series of solutions at constant temperature and perchlorate ion concentration, the value of eCuL' is obtained as the reciprocal intercept and Kc,L' as the (10) McConnell, H.; Davidson, N. J . Am. Chem. SOC.1950,72, 3164-3167. The spectrophotometric method described was initially reported by: Benesi, H. A,; Hildebrand, J. H. J . Am. Chem. SOC.1949, 71, 2703-2707.
Young et al.
2578 Inorganic Chemistry, Vol. 25, No. 15, 1986
Table I. Conditional Stability Constants and Molar Absorptivity Values for the Cu"([12]aneS4) Complex in Aqueous Solution as a Function of Perchlorate Ion Concentration and Temperature (A = 387 nm)"
[C1041, M param 10-3d, M-' cm-'
T, "C
5 15 25 35 5 15 25 35 25
10-3~~~ M-1 ~',
AHo', kcal mol-'
ASo',cal K-'mol-'
0.010 8.29 (23) 7.68 (20) 7.39 (16) 7.51 (16) 2.48 (16) 3.10 (21) 2.33 (11) 2.40 (11) -0.63 (112) 13.4 (39)
0.025 7.46 (18) 6.92 (8) 6.88 (13) 6.73 (11) 2.71 (6) 2.55 (14) 2.02(13) 2.34 (15) -0.84 (IO) 12.7 (3)
0.050 6.90(13) 6.86 (11) 6.84(5) 6.62 (14) 6.47 (260) 4.28 (101) 2.45 (16) 4.07 (119) -0.30 (50) 15.1 (17)
0.10 7.12 (13) 7.09 (11) 6.87 (5) 6.59 (9) 3.57 (22) 3.17 (16) 3.01 (7) 3.22 (15) -0.60 (50) 14.0 (7)
0.25 6.11 (1) 6.02 (1) 5.86 (1) 5.74(1) 5.75 (11) 5.52 (12) 5.67 (8) 5.26 (6) -0.41 (23) 15.7 (8)
0.50 7.30 (1) 7.12(1) 7.00 (1) 6.86 (2) 9.82 (27) 10.0 (2) 9.18 (33) 8.15 (41) -1.12 (42) 14.3 (14)
1 .o 7.60 (1) 7.49 (1) 7.32(1) 7.15 (1) 28.7(11) 21.4 (12) 21.9 (7) 19.5 (7) -1.92 (69) 13.4 (94)
"In this and the following tables, the values in parentheses represent the standard deviations in terms of the final digits listed for the accompanying experimental values as determined by linear regression analysis. Table 11. Conditional Stability Constants and Molar Absorptivity Values for the Cu"([13]aneS4) Complex in Aqueous Solution as a Function of Perchlorate Ion Concentration and Temperature (A = 390 nm)
param lO-)c', M-' cm-'
10-3Kcur', M-' cm-'
AHo', kcal mol-' ASo',cal K-' mol-'
T, O C 5 15 25 35 5 15 25 35 25
0.010 6.00 (3) 5.91 (6) 5.81 (16) 5.77 (7) 2.14 (2) 1.83 (3) 1.71 (7) 1.50(3) -1.92 (18) 8.3 (63)
0.025 7.05 (3) 6.94(2) 6.83 (2) 6.73 (3) 2.42 (3) 2.18 (2) 1.91 (2) 1.67 (2) -2.14 (12) 7.82 (41)
0.050 7.06 (2) 6.96 (1) 6.90(3) 6.75 (1) 2.86 (3) 2.51 (2) 2.24 (3) 1.94 (1) -2.19 (10) 7.97 (35)
[Clod, M 0.10 6.24 (2) 6.13(3) 6.07 (2) 5.95(2) 3.36(10) 2.96 (9) 2.59 (5) 2.17(3) -2.54 (13) 7.03 (44)
0.25 6.53 (1) 6.42(1) 6.32(1) 6.20(1) 5.48(6) 4.70 (7) 3.95 (4) 3.39 (4) -2.75 (8) 7.23 (27)
0.50 6.54 (1) 6.45 (1) 6.36 (1) 6.20 (1) 10.6(2) 8.32(11) 6.97 (12) 5.94 (4) -3.27 (16) 6.63 (56)
1 .o 6.98(1) 6.85(1) 6.78(1) 6.57(1) 32.6 (27) 25.4 (18) 17.7 (7) 14.2 (5) -4.87 (30) 3.17 (103)
Table 111. Conditional Stability Constants and Molar Absorptivity Values for the Cu"([16]aneS4) Complex in Aqueous Solution as a
Function of Perchlorate Ion Concentration and Temperature (A = 440 nm) [ClOJ, M param T, OC 0.010 0.10 1 .o 10-v, M-' cm-'
AH",
5 15 25 35
25 35 25
15.5 (44) 9.35 (32) 9.12(460) 8.87 (26) 8.24(20) 7.93 (12) 125 (35) 188 (7) 134 (67) 170 (5) 160 (4) 145 (3) -1.43 (9)
7.20 (9) 6.87 (6) 6.80(10) 6.44 (8) 2350 (120) 1840 (50) 1410 (50) 1170 (30) -4.03 (14)
kcal mol-' ASSO',
5.3 (3)
0.92 (49)
cal K-' mol-'
intercept/slope ratio (see Figure 3). For the Cu(I1) complexes formed with [ 12]aneS4, [ 13]aneS4, and [ 15]aneS5, plots of the type described above were constructed for perchlorate ion concentrations of 0.010, 0.025, 0.050, 0.10, 0.25, 0.50, and 1.0 M a t each of four temperatures: 5 , 15, 25, and 35 "C. For the C ~ ~ ~ ( [ l 6 ] a n esystem, S ~ ) the conditional stability constants were approximately 20-fold smaller, resulting in experimental data that were much more erratic. Therefore, data were obtained only for perchlorate concentrations of 0.010, 0.10, and 1.0 M. For all systems, the perchlorate ion concentrations were calculated to include the contribution from the C ~ ( C 1 0 ~ ) ~ - 6salt H ~used 0 (this contribution being significant for low perchlorate concentrations). The resolved KcuLfvalues are listed in Tables I-IV. For each Cu(I1)-ligand system, the temperature dependence of the KcuL'value a t constant perchlorate concentration can be used to calculate apparent enthalpy and entropy values according to the relationship AH" M0' -In KcuLf = -(11) RT R These values are included in Tables I-IV.
10-3/Ccu, M-'
Figure 3. Spectrophotometric data for the Cult([15]aneS5) system plotted in the form of eq 10 to yield the apparent molar absorptivity
value, ecu> [Hdbm], the rate law for the substitution reactions is expressed as rate = k,K[UO,(a~ac)~L][Hdbm]/(l + K[U0,(a~ac)~L]), where K = [U02(acac)2dbmH]/[U02(acac)2L][Hdbm]. The equilibrium constant K decreases as the basicity of ligand L increases. Rate constant k2 corresponds to that of proton transfer from coordinated Hdbm to leaving acac in UOz(acac)2dbmH,which is evidenced by the deuterium isotope effect on the rate and the linearity of the plot of log k2 vs. the reciprocal dielectric constant. The rate of the k2 path is accelerated in amphiprotic solvents. Rate constants (s-I) at 25 OC and activation parameters AH* (kJ mol-I) and AS* (J K-' mol-I) for the k2 path are 11.6 X 31.3 f 1.0, and -177 f 4 for U02(acac)2dmfand 2.31 X 50.2 f 0.4, and -127 14 for U02(acac)2tmp. These results are discussed in connection with those of the acac-exchange reactions in U02(acac)zLand Th(acac)+
*
Kinetics of exchange reactions between metal chelate complexes of various 8-diketonates (HB) and free ligands have been studied by the N M R line-broadening method,'-9 isotopic labeling method with 14C,1*12 and spectrophotometric method.I3 Although rates ~~
(1) Ikeda, Y . ;Tomiyasu, H.; Fukutomi, H. Inorg. Chem. 1984, 23, 3197. (2) Ikeda, Y . ;Fukutomi, H. Inorg. Chim. Acta 1986, 115, 223. (3) Fujiwara, N.; Tomiyasu, H.; Fukutomi, H. Bull. Chem. Soc. Jpn. 1984, 57, 1576. (4) Fujiwara, N.; Tomiyasu, H.; Fukutomi, H. Bull. Chem. Soc. Jpn. 1985, 58, 1386. (5) Folcher, G.; Keller, N.; Kiener, C.; Paris, J. Can. J . Chem. 1977, 55,
3559.
(6) Tanner, G. M.; Tuck, D. G.;Wells, E. J. Can. J. Chem. 1972,50, 3950. (7) Khvostik, G. M.; Sokolov, V. N.; Grebenshchikov, G. K.; Toropov, S. A.; Kondratenkov, G. P. Sou. J . Coord. Chem. (Engl. Trans/.) 1979, 5, 534. ( 8 ) Nixon, A. J. C.; Eaton, D. R. Can. J . Chem. 1978, 56, 1012. (9) Adams, A. C ; Larsen, E. M. Inorg. Chem. 1966, 5, 814.
0020-1669/86/1325-2582$01 S O / O
of the exchange reactions differ greatly with central metal ions, mechanisms so far proposed are classified into three types according to the rate-determining step: (1) breaking of one of the metal-oxygen bonds;" (2) formation of an intermediate containing a dangling unidentate ligand (B-) and an incoming ligand (HB in the enol f ~ r m ) ; ~(3) - ' ~intramolecular proton transfer from coordinated HB to leaving B-.3-7 In previous papers'*2we reported the kinetic study of exchange reactions of acac in U02(acac),L (acac = acetylacetonate; L = dimethyl sulfoxide (Me2SO), N,N-dimethylformamide (dmf)) in o-dichlorobenzene and proposed the mechanism of type 1. In this paper we report the kinetic results of substitution reactions of dibenzoylmethanate (dbm) for one acac in U02(acac)2L (IO) ( 1 1) (12) (13)
Watanabe, A.; Kido, H.; Saito, K. Inorg. Chem. 1981, 20, 1107. Kido, H. Bull. Chem. SOC.Jpn. 1980, 53, 82. Nishizawa, M.; Saito, K. Bull. Chem. SOC.Jpn. 1978, 51, 483. Sekine, T.; Inaba, K. Bull. Chem. SOC.Jpn. 1984, 57, 3083.
0 1986 American Chemical Society
