278
trans ligand; and that the two metal ions are differently sensitive to the influence of the trans ligand X in as far as it affects the 7~ interaction with the aryl ligand. Acknowledgments. We wish to thank Professor G. Costa and Dr. G. Mestroni for their advice. One of us (K. G. M.) thanks the Science Research Council for a research studentship and we are grateful to NATO for financial support. H. A. 0. Hill,* K. G. Morallee lnorganic Chemistry Laboratory, Oxford, England
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F. Cernivez, G. Pellizer Istituto di Chimica, Uniuersita di Trieste, Trieste, Italy Receioed August 19, 1971
9'Br
*/ISCN) 01
Structure and P h o t o c h e m i c a l Reactivity of Excited States of Halopentaamminerhodium(II1) Complexes'
Sir: The photochemical behavior of rhodium(II1)-ammine complexes is of interest both for its uniqueness and for its similarities to the behavior of other nd8 complexes. For example, features which seem common to the photochemistries of nd6 complexes (especially of cobalt, rhodium, and platinum) are wavelengthdependent product yields and oxidation-reduction reactions subsequent to the irradiation of charge transfer to metal bands. 2, A feature of great potential significance in the photochemistry of rhodium(II1) is the relatively high product yields which result from irradiation of ligand field absorption It is the purpose of this report to call attention to some unanticipated inferences which may be made based on the photochemical behavior which results from the ligand field excitation of Rh"'(NH3)BX(X = C1, Br, I) complexes. It has been reported that ligand field excitation of Rh(NH3)$12+ and Rh(NH3)J2+ results in predominantly (Le., >90 %) halide or ammonia aquation, respectively (eq 1 and 2). We have now found that Rh(NH&Br2+
/ /
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/
Q'CH,
/
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/
,"
01
pqSCN) / 901 / 9Q
100
L
120
110 .
A P P-FC6bCo((DO)(DOH)pn)X
Figure 1. Plot of the 1gF chemicals shifts (ppm) of (a) m-FCsH4Co{ (DO)(DOH)pn}X in (CH&SO 2s. m-FCBaPt(P(C&s)8)X in ( C H J K O and (b) p-FC6H,Co{(DO)(DOH)pn }X in (CHdnSO os. /I-FC~H~P~(P(C~H in ~(CH3)LD. )~)~X
a-donor properties of the ligand were mainly responsible for the observed lH chemical shifts. Differences between the Co(lI1) and Pt(l1) complexes are more apparent in A, values, since they include both a and P interactions (Figure 1b). The P-electron-effect paramTable 11, imply that the Co(II1) cometers, (A,-A,), plexes are better P donors (poorer 7r acceptors) than the Pt(I1) complexes and, interestingly, show a greater sensitivity to the trans ligand X. The donor properties of the metal complexes have different dependence on X: for Co(III), I > Br > SCN(NCS) > OCN(NC0) > CH3; for Pt(II), I > Br > OCN(NC0) > CH3 > SCN(NCS). The different orders may be accounted for if it is assumed that the thiocyanate ligand acts as a 7r donor in the Co(II1) complexes and a P acceptor in the Pt(1I) complexes. These results suggest that a-bonding effects in cobalt(111) and platinum(I1) complexes are similar ; that there is extensive P interaction with aryl ligands coordinated in complexes of both metals which is modified by the Journal of the American Chemical Society
94:l
1 January
0)
exhibits intermediate behavior, Le., Br-, NH4+, transRh(NH3)40H2Br2+,and Rh(NH3),0HZ3+result from the irradiation of the ligand field absorption bands of this complex (see Table I). All three halopentaammine complexes of rhodium(II1) quench the biacetyl phosphorescence but do not affect the fluorescence at room temperature. Stern-Volmer quenching plots are linear and consistent with similar studies of the sensitized photolysis of coordination ~omplexes.2'~'~ However, for these rhodium(II1) com(1) Support of this research by the National Science Foundation (Grant GP24053) is gratefully acknowledged. (2) For a comprehensive recent review, see V. Balzani and V . Carassitti, "The Photochemistry of Coordination Complexes," Academic Press, New York, N. Y., 1969. (3) (a) T. L. Kelly and J. F.Endicott, J . Amer. Chem. Soc., 92, 5733 (1970); (b) ibid., in press. (4) L. Moggi, Gazz. Chim. Ita/., 97, 1089 (1967). ( 5 ) (a) R. A. Bauer and F. Basolo, J . Amer. Chem. Soc., 90, 2437 (1968); (b) Inorg. Chem., 8 , 2231 (1969). (6) M. A. Scandola and F. Scandola, J . Amer. Chem. Soc., 92, 7278 (1970). (7) V. Balzani, R. Ballardini, M. T. Gandolfi, and L. Moggi, ibid., 93, 339 (1971).
12, 1972
279 Table I. Product Yields Resulting from the Ligand Field Photolysis of Rh’II(NH&X Complexes Wavelength irradiated,“ nm
Assignment*
X
T, “C
C1
25 75 25 75
350
‘Ai + ‘Ti
360
‘AI -* ‘A2
25
385
‘AI + ‘A2
Br I
75
Biacetyl sensitized product yieldsd
Direct photolysis product yieldsc 6x 6NHa 0.16 f 0.016 0.18 jz 0.01 0.019 f 0.001 0.021 f 0.001 0.01 0.01
4x 0.16
