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N.Y., 1966, Chapter 9. F. A. Cotton, “Chemical Applications of Group Theory”, 2d ed, Wiley-Interscience, New York, N.Y., 1971. R. L. Belford and W. A. Yeranos, Mol. Phys., 6, 121 (1963). J. Josephson and C. E. Schaffer, Acta Chem. Scand., 24,2929 (1970). J. Selbin and J. C. Bailar, Jr., J . Am. Chem. SOC.,79, 4285 (1957). S. E. Rasmussen, Acra Chem. Scand., 13, 2109 (1959). S. H. Caldwell and D. A. House, J . Inorg. Nucl. Chem., 31,8 1 1 (1969). These conclusions hold regardless of whether the chloride in Cr(tren)CIH202+ is cis or trans to the tertiary nitrogen of tren. It is not clear at the present time which chloride is extremely labilized in aquation reactions. Conflicting views exist in the literature: the x-ray study of Ni(tren)(NCS)z43 and some recent NMR studies [R. J. West and S. F. Lincoln, Inorg. Chem., 12,494 (1973); S. F. Lincoln and R. J. West, J. Am. Chem. SOC.,96, 400 (1974)l support the labilization of the cis chloride, and other NMR and infrared studies support that of the trans>’ X-ray studies of some of these tren complexes would clarify the situation. J. L. Hoard, Proc. Int. Conf. Coord Chem., 8, 135 (1964). T. W. Swaddle, Coord. Chem. Reu., 14, 217 (1974). C. H. Langford and V. S. Shastri, M T P Int. Reu. Sci.: Inorg. Chem., Ser. One. 9 (1973). H K: L.’Powell,-jnorg. Nuel. Chem. Lett., 8, 891 (1972). W. V. Miller and S. K. Madan, Inorg. Chem., 10, 1250 (1971). C. Yang and M. Grieb, J . Chem. SOC.,Chem. Commun., 656 (1972). E. Kimura, S. Young, and J. P. Collman, Inorg. Chem., 9, 1183 (1970).
Contribution from the Department of Chemistry, Furman University, Greenville, South Carolina 296 13
Relaxation Pathways of Chromium(II1) Quartet Excited States N. A. P. KANE-MAGUIRE,* J. E. PHIFER, and C. G. TONEY Received July 29, 1975
AIC50555X
The photoracemization of ( + ) ~ - C r ( e n ) $ + in aqueous solution at 25 OC has been examined under ligand field excitation in the presence and absence of OH- ion as a specific 2Eg doublet-state quencher. For excitation wavelengths between 436 and 496.5 nm essentially constant percent reaction quenching by OH- ion was observed (57%). In contrast, a marked decrease in quenching occurred for irradiations a t 514.5 nm (38%) yielding a percent quenching ratio of 0.65 for 514.5 nm vs. 436 nm. The overall racemization quantum yield (&c) a t 25 OC remained constant (0.4) over this wavelength region and was identical with that observed for hydrolysis. These racemization results are interpreted on the basis of a model which indicates that 4Tzg 2Eg intersystem crossing competes successfully with 4Tzgvibrational equilibration. Independent support for this analysis comes from the relative phosphorescence yields (P) on 514 nm vs. 436 nm excitation (Psi4/P436 = 0.63), a value in close agreement with the percent reaction quenching ratio (0.65).
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Introduction It has been recently found that a limited number of Cr(II1) complexes display readily observable phosphorescence in room-temperature fluid solution.1J This knowledge has been subsequently applied with marked success3-6 to photoreactive excited-state identification, by comparing phosphorescence and photolysis quenching in the presence of specific doublet (2Eg) excited-state quenchers. Analysis of these quenching data for the Oh and D 3 systems so far examined strongly supports the contention that photoreaction originates solely out of the quartet (4T2g) excited level. We explore in this report a promising extension of this quenching technique which provides a clearer insight into the details of 4T2g excited state relaxation in aqueous solution (see Figure 1). Up to the present it has been generally assumed excitation, vibrational that subsequent to 4Azg equilibration of the 4T2g state is very rapid (
