Inorg. Chem. 1985, 24, 4096-4100
4096
general usefulness of this type of relationship. From the N M R shifts obtained for the monobromo and monoiodo carboranes (Table I) appropriate additivity constants can be derived by comparing the chemical shifts of each boron position of the substituted carborane with the corresponding position of the parent C2BSH7.These additivity parameters, along with those derived from the corresponding fluoro2 and chloros compounds, are given in Table VI and are graphically displayed in Figure 7. The trends seen in this figure can be summarized as follows: (a) a downfield shift is obbserved for the boron atom directly attached to the halogen, with greater shifts observed for borons with smaller halogens; (b) an upfield shift is noted for the bororl atom antipodal (Le. 7-position) to the substituted 1-position, with greater antipodal-boron upfield shifts found when smaller halogens are attached to B( 1); (c) as might be reasonably expected, smaller effects are observed for other borons in the cage. The general utility of the additivity parameters to predict the chemical shifts of the dibromo- and diiodocarboranes in the present work is demonstrated by a comparison of experimental with calculated values in Table I (cf. chemical shifts "out-of-brackets" with chemical shifts "inbrackets", respectively). The differences between the observed and calculated shifts average ca. 0.4 ppm, with a slightly better
correspondence noted for the dibromo isomers than for the diiodo isomers.
Acknowledgment. The authors wish to thank the National Science Foundation (Grant CHE-8315951) and the MBRS (B.N., T.B.) and MARC (F.G.) programs, NIH, for partial support of this study. The PROPHET computer network was made available through an N I H biotechnology resources program DDR contract to the CSULA. Most of the IlB NMR data were obtained with a Bruker WM-500 instrument at the Southern California Regional N M R facility at the California Institute of Technology, funded by N S F Grant CHE-7916324; the assistance of Nancy Swick in obtaining some of the spectra is greatly appreciated. Registry No. 1-Br-2,4-C2BSH6,98821-51-3; 3-Br-2,4-C2BSH6, 98821-52-4;5-Br-2,4-C2BSH6, 27733-74-0; 1,3-Br2-2,4-C2BSHs, 9882153-5; 1,5-Br2-2,4-C2BSHs, 98821-54-6;3,5-Br2-2,4-C2BSH, 98821-55-7; 5,6-Br2-2,4-C2BSHS, 98821-56-8; 1-1-2,4-C2BsH6,98821-57-9;3-1-2,4CzBsH6, 98821-58-0; ~ - I - ~ , ~ - C , B 98838-28-9; SH~, 1,3-12-2,4-CzBSHS, 98821-59-1;1,5-12-2,4-CzBSHS,98838-29-0;3,5-12-2,4-CzBSHj,9634325-8; 5,6-12-2,4-C2BSHS,98821-60-4; l-F-2,4-C,BSH,, 55 124-16-8;3-F2,4-C2B~H6,55124-15-7;5-F-2,4-C,BsH6, 55124-17-9; ~ - C I - ~ , ~ - C $ S H ~ , 28347-69-5; 3-C1-2,4-C2BSH6,28347-93-5; 5-CI-2,4-CzBjH6,28347-92-4; 2,4-C2BjH,, 20693-69-0.
Contribution from the Department of Chemistry, Faculty of Science, Tohoku University, Aoba, Aramaki, Sendai 980, Japan
Photochemical and Thermal Decomposition of (AA,AA)-(p-Hydroxo)(p-peroxo)bis[bis(ethylenediamine)cobaIt(III)] Ions in Basic Aqueous Solution MASAHIRO KIKKAWA, YOICHI SASAKI,* SATOSHI KAWATA, YOSHIHIRO HATAKEYAMA, FUMIO B. UENO, and KAZUO SAITO*' Received January 31, 1985
The title ion in aqueous basic solution does not undergo deoxygenation in the dark, but it does on irradiation with ultraviolet light to give the photoinduced equilibration [ (en),Col"( r-OH,022-)Co"'(en),]3c
2 [ Co"(en),( H20),]*+
+ O2
The quantum yield determined in the presence of excess EDTA is ca. 2.2 X on irradiation at 366 nm at 5 OC and is virtually independent of pH (8.1-10.4). The yield on irradiation at 515 nm at ca. 25 OC is 270 nm (Figure 3a). An isosbestic point was observed at 264 nm during the first half (ca. 1 h) of the decrease in absorbance. Addition of 1.2 X M free ethylenediamine and 1.2 X M free diethylenetriamine increased the rate of spectral change by ca. 2 times (the pattern of the change is similar). The major product was [Co"'(dien)(en)(H,O)l3' (>70%), as found by ion-exchange chromatography. The photoinduced reactions of 2 are summarized in a reaction scheme similar to that of 1 except that there is a thermal pathway toward deoxygenation of 2. 3. Photochemical Reactions of 3. In the dark, the ion (AA,AA)-[(en)2C0111(p-NH2,022-)Co111(en)2]3+ (3) did not show any appreciable change in the absorption spectrum in basic aqueous solution (pH 8-1 1) after 5 h at room temperature both in the presence and in the absence of excessive EDTA. Neither did it show any change on continuous irradiation with light of the high-pressure mercury lamp for 3 h at pH 8.5 in the absence of EDTA ( [ C O ' ~ '= , ] 1 X IO4 M). A decrease in absorption was observed, however, in the range >270 nm (half-life ca. 1 h) when the solution contained 1.0 X M EDTA. The reaction products (20) Ebihara, M.; Sasaki, Y.; Aoki, H.; Saito, K., manuscript in preparation. (21) Sasaki, Y.; Tachibana, M.; Saito, K. Bull. Chem. SOC.Jpn. 1982, 55, -7651-3657 - - - - - - -. (22) Kanesato, M.;Ebihara, M.; Sasaki, Y.; Saito, K. J. A m . Chem. SOC. 1983, 105, 5711-5713.
Inorganic Chemistry, Vol. 24, No. 24, 1985 4099
Decomposition of (p-Peroxo)dicobalt(III) Complexes
Table 11. Identified Products and Their Yields for the Thermal Decomposition of (AA,AA)-[ (en),Colll(C1-OH,OzZ-)Colll(en),] 3 + (11) in Aqueous Solution
[lrl?/M
other ingredients6 (concn/M)
reacn conditions
identified products
yieldc/%
6.25 x 10-3 7.0 x 10-3 7.0 x 10-3 7.0 x 1 0 - 3 6.3 x 10-3
none none none
none en (0.125)
50 "C, 6 h 55 "C, 4 h 50 "C, 6 h 55 'C, 5.5 h 6 0 "C, 13.5 h
6.3 x 10-3
en (0.13); Co" (0.013)
65 "C, 21 h
126
6.3 x 10-3
en (0.13); CoII (0.013)
room temp, 1.5 months
64 166 30
i
[Co"'(en), (H,O),]
3f
64 78 62 69
61 25
Initial concentration of 11.
' en = ethylenediamine.
Yield per cobalt ion of the dimer (CoII added is not included).
separated by anion-exchange chromatography included [CO"'(edta)]- as well as [Corr(edta)lz-. The spectrum at pH 2.5 remained unchanged over a period of 5 h at room temperature in the dark. The solution showed a change (half-life ca. 5 h), however, on irradiation with light of the high-pressure mercury lamp. The products include [Co"'(en)z(Hz0)z]3' (ca.10% yield) as well as [ C O " ( H ~ ~ )(>67%). ~]~+ The change was accelerated by the presence of 1.0 X M EDTA (half-life 1.5 h). Complex 3 is photochemically much less reactive than 1 and 2, and the observed photochemical reactions of 3 appear to be complicated. N o simple deoxygenation reaction (corresponding to process i of Scheme I) takes place. If the deoxygenation occurred in basic solution in the absence of EDTA, the reverse oxygenation process (cf. process ii in Scheme I) would produce 1 rather than 3, and the photochemical irreversible decomposition of 1 would follow. Such a process was not observed. 4. Thermal Reactions of lr. (a) Change in the Absorption Spectrum in the Dark. Complex lr undergoes rapid deoxygenation (studied by the stopped-flow technique) in acid solution (pH
