282
J . Phys. Ckem. 1985, 89, 282-285
Resonance Raman of Singly Reduced Tris( bipyrldine)iron( I I ) S. M. Angel, M. K. DeArmond,* R. J. Donoboe, and D. W. Wertz* Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204 (Received: June 4, 1984; In Final Form: August 13, 1984)
The resonance Raman of the singly reduced tris(bipyridine)iron(II) complex is reported and compared to the resonance Raman of the unreduced compound. The presence of both shifted and unshifted bipyridine vibrational energies indicates that there are two distinct chromophores in the reduced complex, consistent with a localized model of the redox orbital. The 600-nm absorption band of the reduced complex is assigned as metal-to-ligand charge transfer. This assignment implies a shift of that transition 2500 cm-l to lower energy upon reduction. The 524-nm absorption band in the reduced compound is assigned as a bipyridine anion T*-T* transition.
Introduction The nature of the excited electronic states of the d6 metal tris(bipyridine) complexes (M(bpy)t') has been a subject of much theoretical and experimental interest.' The F e ( b p ~ ) complex ~~+ (hereafter referred to as FB2) displays some characteristics which make it unique in comparison to its osmium and much-studied ruthenium analogues. Of primary interest is the lack of observable emission for the iron complex. Further, although the cyclic voltammetric patterns of the three complexes are similar, the second and third reduction products of the iron complex have not been successfully isolated, whereas those of the ruthenium and osmium complexes have. Finally, FB2 has a much stronger resonance Raman (RR) overtone spectrum. The R R study of FB2 was first reported by Nakamoto and co-workers.2 Their discussion presumed the metal-to-ligand charge transfer (MLCT) assignment of the absorption in the visible spectrum. Their polarization studies indicated that, with one possible exception, all of the observed R R lines above 900 cm-I are polarized, which indicates that only totally symmetric modes are resonance enhanced. It should be noted that the R R spectrum is dominated by ligand vibrations; none of the features observed a t low energy have been definitively assigned to metal-ligand vibrations. Initially, it was assumed that the MLCT excited state of the M ( b ~ y ) complexes ~~+ retained the D3 symmetry of the ground state.Ia* More recent results, notably the discussion of highresolution photoselection experimentss8 in clarification of earlier data,3b.cand the time-resolved R R studies of Woodruff et show that the excited electron is more properly described as single-ring localized. The ESR data on the iron complex indicate that the reduced species and the excited-state molecule are similar in nature, Le.:
We have undertaken the R R studies of the reduction products of the M ( b ~ y ) complexes.6 ~~+ Herein we report the results of (1) (a) Harrigan, R. W.; Crosby, G . A. J . Chem. Phys., 1973, 59, 3468. (b) Hager, G . D.; Crosby, G . A. J . Am. Chem. SOC.1975, 97, 7031. (c) Hager, G . D.; Crosby, G . A. J . Am. Chem. Soc. 1975,97, 7042. (d) Felix, F.; Ferguson. J.; Gudel, H.; Ludi, A. J. Am. Chem. Soc. 1980,102,4096. (e) Ferguson, J.; Herren, F. Chem. Phys. Lett. 1982,89, 371. (f) Braterman, P. S.;Harriman, A.; Heath, G. A.; Yellowless, L. J. J. Chem. Soc., Dulton Trans. 1983, 1801. (g) Heath, G . A.; Yellowlea, L. J.; Braterman, P. S. J . Chem. Soc., Chem. Commun. 1981, 287. (h) Kober, E. M.; Meyer, T.J. Znorg. Chem. 1983,22,1614. (i) DeArmond, M. K. Acc. Chem. Res. 1974,7,309. (2) Clark, R. J. H.; Turtle, P. C. Strommen, D. P.; Streusand, B.; Kincaid, J.; Nakamoto, K. Znorg. Chem. 1977, 16, 84. (3) Carlin, C. M.; DeArmond, M. K. Chem. Phys. Letr. 1982,79,297. (b) Fujita, I.; Kobayashi, H. Inorg. Chem. 1973,12, 2758. Hipps, K. W. Znorg. Chem. 1980,19, 1390. (4) Bradley, P. G.;Kress, N.; Hornberger, B. A.; Dallinger, R. F.; Woodruff, W. H. J . Am. Chem. SOC.1981, 103, 7441. ( 5 ) Motten, A. G.; Hanck, K.; DeArmond, M. K. Chem. Phys. Lett. 1981, 79, 41.
TABLE I: Location and Approximate Extinction Coefficients of the Bands in the Absorption Spectrum of Fe(bpy),+
cm-'
nm
€*
16600 19 100 20 400 27 000 28 700 33 500 54 500
602 524 490 370 348 298 290
6 540 12 200 8 200 18700 10400 54 300 57 000
"dm3 mol-' cm-I.
our study of the singly reduced iron complex F e ( b ~ y ) ~(hereafter + referred to as FBI).
Experimental Section Synthesis and Purification. Fe(bpy)3(C104)2was prepared by a previously published procedure' and recrystallized from acetone and water three times. The acetonitrile (Aldrich, Gold Label) was dried by vacuum distillation three times over PzOs and never exposed to air. Tetrabutylammonium hexafluorophosphate (TBAH) (Kodak) was recrystallized and dried in a vacuum oven. Procedure. The singly reduced species was prepared by a previously described bulk electrolysis technique8 in a Model H E 43-2 Vacuum Atmospheres glovebox under a nitrogen atmosphere. The samples were approximately 1.3 mM in complex and 0.1 M in TBAH with the dried acetonitrile as a solvent. One-milliliter aliquots were transferred to NMR cells equipped with ground glass joints and subsequently flame sealed upon leaving the box. The R R spectra were obtained with the 135' backscattering technique. An N M R spinner was adapted to spin the samples. R R spectra obtained a t 77 K employed a similar geometry, but the sample was spun inside a liquid nitrogen dewar designed with a transparent "finger" for spectroscopic studies. The frequencies were measured relative to the 918-cm-' peak in CH3CN. Instrumentation. The Raman excitation energy was provided by a Spectra Physics Model 171-17 Ar+ ion laser either alone or pumping a Spectra Physics Model 375 dye laser using Coumarin 540 or Rhodamine 590 laser dye (Exciton). All Ar+ laser lines were filtered with 1-nm band-pass filters (Ealing) and the dye laser output was passed through a SPEX Lasermate in order to remove background fluorescence. Laser power at the samples was 50-200 mW. The scattered radiation was scanned by a Jarrell Ash Model 25-300 monochromator and detected by a cooled RCA Model C31034/76 photomultiplier tube. The signal was sent as photon counts to an MTU-130 computer for storage and treatment. The absorption spectrum was obtained on a Cary 14 spectrophotometer at 0.5 mM concentration in 1-mm path length cells. (6) Angel, S. M.; DeArmond, M. K.; Donohoe, R. J.; Hanck, K. W.; Wertz, D. W. J. Am. Chem. SOC.1984, 106, 3688. (7) Palmer, R. A.; Piper, T.S. Znorg. Chem. 1966, 5, 864. (8) Morris, D. E.; Hanck, K. W.; DeArmond, M. K. J. Electroanal. Chem. 1983, 149, 115.
0022-3654/85/2089-0282$01.50/0
0 1985 American Chemical Society
Resonance Raman of Singly Reduced Tris(bipyridine)iron(II)
The Journal of Physical Chemistry, Vol. 89, No. 2, 1985 283 TABLE II: Wavenumbers of the Peaks Observed in the RR Spectra of Fe(bpy):+ (FB2) with 514-nm Excitation and Fe(bpy)3+ (FB1) with 600-nm and 525-nm Excitation'
,\ 22
21
20
19
18
17
16
15
cm-1x 10-3 Figure 1. The absorption spectrum of Fe(bpy)3+ in the visible region. See Experimental Section for details.
FB2 514 1014 w 1023 m 1031 w 1170 m
FB1 600 1012 m 1026 w 1167 s 1209 w
FB1 525d 1009 m 1019 m 1029 w 1163 m 1210mw
1272 w 1318 s 1486 vs 1558 s 1601 ms
1268 w 1317 s 1482 vs 1482 vs 1601 s
1280 w 1360 m 1491 vs 1506 m 1557 m
RB-1' 1007 1022 1163 1220 1269 1282 1358 1486 1505 1558
bDVC
952 982 1033 1151 1205 1273 1357 1478 1497 1558
'The lines observed in the RR of Ru(bpy),- (RB-1) and the prominent lines in the RR of bpy- are included for comparison. bSee ref 6. CSeeref 9. dWeak peaks found at 1319 and 1600 cm-' which are due to unreduced bipyridine have been omitted (see text). the 600-nm band, and that in which the degree of resonance enhancement essentially "mapped out" the entire visible absorption spectrum. There were no vibrations which showed their greatest enhancement at excitation energies other than those corresponding to absorption maxima.
1+
u525 , ( J L w I nm
.000
120$m-1 1400
16L
Figure 2. The RR spectra from 950 to 1625 cm-' of Fe(bpy)32+with
514-nm excitation (top) and Fe(bpy)p+with 600-nm (middle) and 525nm (bottom) excitation. X indicates a solvent peak.
Results The absorption spectrum of FB1 in the visible region is shown in Figure 1. The energies and approximate extinction coefficients of the bands shown, as well as the bands observed in the UV, are listed in Table 1. The primary features of the visible spectrum of FB2 consist of the major absorption band a t 19.1 X lo3cm-l and a shoulder a t 20.7 X lo3 cm-1.2 The R R spectra of FB1 were taken with exciting lines corresponding to the three absorption maxima in the visible as well as numerous intermediate lines in an effort to detect any underlying absorption bands. Those R R spectra obtained by employing excitation corresponding to the absorption features at 19.1 X lo3 cm-' and 16.6 X lo3 cm-' are shown in Figure 2. RR spectra obtained at 20.5 X lo3 cm-I were similar to those at 19.1 X lo3 cm-l but were very weakly resonance enhanced. The R R spectrum of FB2 has been reported elsewhere2 but is included in Figure 2 for comparison. Table I1 lists the observed R R peak frequencies for these spectra along with those observed in the R R of the triply reduced tris(bipyridine)ruthenium(II) (RB-1)6 and the prominenent features observed in the R R of the bipyridyl anion (bpy-) as reported by Forster and H e ~ t e r . ~ The excitation profiles of the RR lines observed in our spectra were determined from 15 separate excitation energies between 476 and 625 nm. The low-intensity, overlapping of peaks and sample instability made reliable profiles impossible to obtain. However, there were three general categories which could clearly be ascribed to the R R enhancement of each vibration: that in which the vibration showed R R enhancement only in the 524-nm absorption band, that in which the greatest enhancement was in (9)
Forster, M.; Hester, R. E. Chem. Phys. Lett. 1981, 81, 41.
Discussion The Redox Orbital. R R spectroscopy provides an excellent method for investigating the extent of localization of the redox electron in FB1. In keeping with earlier results, it is presumed that the redox orbital is largely ligand antibonding in n a t ~ r e . ~ - * * l ~ If the redox orbital extends throughout the three ligands, the R R spectrum should exhibit vibrational frequencies characteristic of b ~ y - ' / ~In . contrast, if the orbital is localized on one of the ligand rings, the observed R R lines should be characteristic of either bpy or bpy- (or both) depending on the nature of the electronic transition(s) in resonance with the Raman excitation. An inspection of Figure 2 and Table I1 reveals the presence of lines in the R R of FB1 with 600-nm excitation which are essentially identical with those seen in the R R of FB2 with 514-nm excitation. However, the R R of FB1 obtained with 525-nm excitation exhibits several peaks which are unique to the reduced species. In a previous study: a correlation of the R R frequencies of RB-1 with those observed in the R R of bpy- was presented (see Table 11). More recent results on the R R of RB-1 in CH3CN show that the R R spectrum of FB1 observed with 525-nm excitation is nearly identical with the R R of R E 1 in this wavenumber range. We conclude that the R R of FBI at 525-nm contains peaks at frequencies characteristic of bpy-. Thus, the R R spectra of FB1 display both bpy and bpy- vibrations. This is definitive evidence for the localized description of the redox orbital on the R R time scale, Le., any interligand hopping of the redox electron is slower than the R R experiment. In the group theoretical description of the number and symmetry of the vibrations expected for these complexes, restriction of consideration to one ligand at a time is appropriate since one would expect very little vibrational coupling between the separate rings. The C,, symmetry of the ligand leads to a prediction of 11 totally symmetric modes with energies between 1000 and 1650 cm-I. There are at least eight peaks in the R R of FB1 obtained at 600 nm which exhibit depolarization ratios (p = 0.3 to 0.4) characteristic of AI modes. The RR of FB1 with 525-nm excitation displays at least five new peaks (1506, 1491, 1360, 1280, and 1163 cm-')which also have depolarization ratios in the 0.3-0.4 range. Thus there are at least two more totally symmetric vibrations in this wavenumber range than would be predicted if the rings were equivalent, again supporting the localized description of the redox orbital. Absorption Band Assignments. The frequencies of the lines observed in R R spectroscopy are those of the electronic ground(10) Morris, D. E.; Hanck, K. W.; 1983, 105, 3032.
DeArmond, M. K. J . Am. Chem. SOC.
284 The Journal of Physical Chemistry, Vol. 89, No. 2, 1985
state vibrations. When these vibrations are A,, as in our experiments, the R R intensity is dictated by differences in the geometries of the ground and excited states. An inspection of Figure 2 provides some insight into the nature of the transitions in the visible spectrum shown in Figure 1. The frequencies and relative intensities of the lines seen in the R R of FB1 observed with 600-nm excitation are, with one exception (-1000 cm-I), nearly identical with those seen in the R R of FB2 probing the absorption assigned to MLCT. This leads us to assign the 600-nm absorption band in FBI as being MLCT (where the accepting orbital is on an unreduced ligand). The extinction coefficient of this band is consistent with that reported by Nakamoto et al. for the unreduced compound.* That the MLCT is shifted down 2500 cm-' relative to its location in the parent compound can be rationalized as being due to the effect of the localized redox electron on the ionization potential of the metal center. In this rationale, the redox electron destabilizes the d orbital on the iron. Consistent with this assignment, Heath et al. have assigned the MLCT in the singly reduced ruthenium complex to be 800 cm-' lower than the MLCT of the parent compound.'g Finally, the shape of the absorption spectrum in Figure 1 indicates that there may be an additional absorption feature located between the two prominent bands at 602 and 524 nm. As noted previously, the MLCT in FB2 contains a high-energy side band. The broad, flattened region between the two main features in Figure 1 may be the result of an analogous side band of the 602-nm MLCT in FB1. The predominance of bpy- vibrations in the R R of FB1 taken with 525-nm excitation implies that the geometry of the excited state for this transition is distorted along the normal coordinates of a reduced bipyridine. As a result, the 524-nm absorption band is assigned to a bpy- transition, although there appears to be some MLCT intensity there as well (vide infra). In keeping with the assignments of Heath et al.'g for the reduced ruthenium complex, we label this bpy- transition as a*-a*. As mentioned earlier, our data showed very little resonance enhancement for the R R spectra obtained at 490 nm. It appears that what little enhancement is observed may be due to the 524-nm transition. Therefore, the 490-nm absorption band cannot be assigned on the basis of this R R data. However, it should be noted that the absorption spectrum of bpy- has two prominent bands in the visible region at 527 and 558 nm." Thus, the remaining absorption band may be tentatively assigned as a bpy- a*-a* transition. Vibrational Analysis. i. 920 to 1650 cm-'. For convenience we refer to the R R spectrum of FB1 obtained with 525-nm excitation as F1-525, that of FB1 obtained with 600-nm excitation as F1-600, and that of FB2 obtained with 514-nm excitation as F2-5 14. It is difficult to convincingly correlate the RR lines arising from two separate chromophores, primarily because the excited states responsible for the observed R R intensity may be quite different for the two sites. In addition, there is the possibility that the additional electron may cause bonding and geometry changes in the two chromophores which may result in different normal coordinate descriptions of some or all of the vibrations. Our proposed correlations may be obtained from Table 11. A brief discussion of some of our conclusions follows. The 1600- and 1319-cm-, peaks in F1-525 are assigned as unreduced bipyridine vibrations arising either from unreduced complex or as a result of resonance enhancement due to the MLCT of FBI which may have appreciable intensity at 525 nm (vide supra). These two peaks show their greatest enhancement at 600 nm. Conversely, the 1557-cm-' peak in F1-525 shows its greatest enhancement at 525 nm and is assigned as a bpy- vibration which has shifted from 1601 cm-' in F2-514. It has sometimes been tacitly assumed that the presence of an electron in an antibonding bpy orbital leads to a lowering of all vibrational frequencies. However, as Forster and Hester have noted: there appears to be a shift of some vibrational energies to higher energy upon addition of an electron to the lowest antibonding orbital. Our correlations involve several peaks which (11) Mahon, C.; Reynolds, W. L. Inorg. Chem. 1967, 6, 1927.
Angel et al.
w
400
600
800
cm-1
Figure 3. The RR spectra from 200 to 950 cm-I at 77 K of Fe(bpy)32+ (top) and Fe(bpy),+ (bottom) with 514-nm excitation. X indicates a
solvent peak. may shift upward or remain at approximately the same energy upon reduction. Of special interest is the peak at 1491 cm-' in F1-525. That this peak is unique to the RR of FB1 in the 524-nm absorption band has been verified by careful scanning of the 1400-1 550-cm-l region with 555-nm excitation, Le., between the 524- and 602-nm absorption bands. These R R spectra clearly show three peaks: one at 1480 cm-' corresponding to a line in F1-600, and one at 1490 cm-' along with one at 1505 cm-' both of which correspond to lines observed in F1-525. Further support of this is provided by the R R data for the reduced ruthenium species,6 where three peaks are clearly visible in this frequency range. We correlate the 1491-cm-' line in F1-525 with the 1486-cm-' line in F2-514. This conclusion is based on the relative intensities of these lines. Throughout our studies on the osmium, ruthenium, and iron tris(bipyridine) complexes, the most intense Raman peak upon excitation in the visible absorption bands has been within 5 cm-' of 1486 cm-I. This has been the case regardless of the number of additional redox electrons or assignment (MLCT or bpy- a*-a*)of the absorption band. In keeping with a previous study: the 1360-cm-l line in F1-525 has been correlated with the 1318-cm-' line in F2-514. The assignment of that frequency as being largely inter-ring stretch and its upward shift upon reduction are in accord with a recent description of the LUMO of bipyridine which indicates an increased electron density in this bond.14 The 1163-cm-' line in F1-525 is associated with the 1170-cm-' line in F2-514. This small shift is in keeping with its assignment as a C-H d e f o r m a t i ~ n ' ~and J ~ the assumption that the electron density of the C-H bonds will not significantly change upon reduction. The three peaks at 1009, 1019, and 1037 cm-l in F1-525 are associated with the assymmetric peak at 1023 cm-l in F2-514. Two of these three peaks are attributed to C-H deformations while the third is likely due to the ring breathing. Finally, the 1210-~m-~ peak in F1-525 is assigned to the remaining C-H deformation which is unseen in F2-514 but is present in F1-600. ii. 200 to 1000 cm-'. The R R of FB1 at room temperature in the region from 200 to 1000 cm-' shows two weak features at -660 and 740 cm-' and a peak at -370 cm-' which is partially obscured by a solvent vibration. To attain greater resolution, we obtained the RR of FBI at 77 K. The result is seen in Figure 3, along with the R R of FB2 obtained under identical conditions. The low-energy region of the R R spectra at 77 K showed a number of peaks which were not observed in the room temperature R R (the high-energy region showed no new bipyridine peaks at 77 K). The new features observed in the R R at 77 K are not due to solvent or decomposition of the reduced species. There does appear to be some reoxidized complex present, a measure of which is provided qualitatively by the intensity of the 658-cm-' peak, which is a bpy vibration.2 It should be noted that the relative (12) Strukl, J. S.; Walter, J. L. Spectrochim. Acta 1971, 27, 209. (13) Basu, A.; Gafney, H.D. Strekas, T. C. Inorg. Chem. 1982, 21, 2231. (14) Ohsawa, Y.; Whangbo, M.-H.; Hanck, K. W.; DeArmond, M. K. Inorg. Chem., in press.
J . Phys. Chem. 1985,89, 285-289 intensities of the R R lines observed at 77 K varied slightly from scan to scan. This variation probably arises due to inhomogeneity of the sample upon freezing. It is clear, however, that there are several strong lines and a multitude of weaker lines which are due to the FB1 complex. Of these, the strong feature at 745 cm-' and weaker 807-cm-I peak have been seen in the excited-state R R of the ruthenium complex3 and the R R of bpy-? The 519-cm-I peak has not been reported previously and appears to be a bpy- vibration. It is very interesting to note that the peak at 366 cm-' does not appear to shift upon reduction. The large increase in its intensity upon reduction relative to that of the 658-Cm-' peak argues in favor of attributing it to both the FBI and FB2 complexes. We attribute the emergence of the RR lines observed upon freezing to a matrix effect, rather than a fortuitous shifting of the absorption spectrum resulting in heretofore unseen resonance enhancement.
Conclusions The R R of the F e ( b ~ y ) ~complex + clearly supports a localized model of the redox orbital. The presence of unshifted bpy vi+ with 600-nm excitation brations in the RR of F e ( b ~ y ) ~obtained
285
is consistent with the MLCT assignment of the 602-nm absorption band. The 524-nm absorption band of Fe(bpy),+ is assigned as being largely bpy- ?T*-T*as a result of the bpy- vibrations observed in the R R obtained at 525 nm. There is good correlation of the peaks seen in the R R of F e ( b ~ y ) ~with + those seen in the R R of F e ( b ~ y ) , ~ +The . shift of the vibrational energies upon reduction is consistent with the previous assignments of the vibrations considered along with the LUMO description of bpy. Some of the shifts are to higher energy. An interesting and possibly quite useful effect was observed in the R R of the reduced complex in the low-energy region upon freezing the sample. Acknowledgment. The authors are grateful to Mr. D. Brent MacQueen for obtaining the absorption spectrum. We also thank Dr. David Morris and Dr. Yasuhiko Ohsawa for their expert advice on electrochemical technique. Finally, we thank Dr. Don Segers for many helpful discussions. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research. Registry No, Fe(bpy),z+, 15025-74-8; Fe(bpy),+, 51383-17-6.
Adsorbate Exchange and Insertion Reactions at Metal Surfaces: Hydroquinone and Naphthohydroquinone at Smooth Polycrystalline Platinum in Aqueous Solutions Manuel P. Soriaga,* Dian Song, and Arthur T. Hubbard* Department of Chemistry, University of California,Santa Barbara, California 93106 (Received: June 14, 1984: In Final Form: October 3, 1984)
Coadsorption processes analogous to ligand-exchange and ligand-insertion reactions investigated at smooth polycrystalline platinum electrodes are described. Electrodes pretreated with an oriented layer of one aromatic compound were placed in contact with aqueous 1 M HC104 electrolyte containing another aromatic compound at room temperature. Hydroquinone (HQ) and 1,4-naphthohydroquinone(NHQ) were the compounds studied. Adsorptionfdesorption measurements were based on thin-layer electrochemical techniques. No reactions were noted when flat or vertically oriented HQ (or NHQ) was exposed to NHQ (or HQ) solutions of concentrationbelow 0.3 mM. However, flat-adsorbedHQ or NHQ reacted with more concentrated NHQf HQ solutions (12 mM), resulting in adsorption (insertion) of HQ/NHQ. Insertion induced flat-tevertical reorientation, without desorption, of preadsorbed material. When vertically oriented adsorbed HQ/NHQ was exposed to concentrated NHQfHQ solutions at open circuit for 180 s, displacement of about 5% of the preadsorbed material was observed. The extent of exchange increased as the electrode potential was made less positive, HQ being the more readily displaced; up to 50% of the preadsorbed HQ was displaced by NHQ after 180 s at sufficiently negative potentials.
Introduction Studies based on thin-layer electrochemistry,' Auger electron spectroscopy,2 and surface infrared spectroscopy3 have demonstrated that aromatic compounds spontaneously and irreversibly displace weakly coordinating solvents (such as water) or anions (such as ClO;, PF;, SO:-, PO4>, and F)from smooth platinum surfaces to form intermediates bound in specific orientational statese4 These states, which depend upon various factor^,^ have (1) (a) Soriaga, M. P.; Hubbard, A. T. J . Am. Chem. Soc. 1982, 104, 2735. (b) Soriaga, M. P.; Hubbard, A. T. J. Am. Chem. Soc. 1982,104,3937, (c) Soriaga, M. P.; Hubbard, A. T. J. Electroanal. Chem. 1984, 167, 79. (2) Chia, V. K. F.; Stickney, J. L.; Soriaga, M. P.; Rwasco, S. D.; Salaita, G. N.; Hubbard, A. T.; Benziger, J. B.; Pang, P. K.-W. J. Electroanal. Chem. 19114 - - - ., -163 - - , 4137 .- . . (3) Pang, P. K.-W.; Benziger, J. B.; Soriaga, M. P.; Hubbard, A. T. J . Phys. Chem. 1984.88, 4583. (4) Soriaga, M. P.; Binamira-Soriaga, E.; Hubbard, A. T.; Benziger, J. B.; Pang, P. K.-W. Inorg. Chem., in press.
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been shown to influence the chemical reactivity of the surface coordination compounds.6 Ligand substitution reactions involving the heavier halides and diphenolic compounds have recently been inve~tigated.'~~ ( 5 ) (a) Soriaga, M. P.; Wilson, P. H.; Hubbard, A. T.; Benton, C. S. J . Electroanal. Chem. 1982, 142, 317. (b) Soriaga, M. P.; White, J. H.; Hubbard, A. T. J . Phys. Chem. 1983,87,3048. (c) Soriaga, M. P.; Hubbard, A. T. J . Am. Chem. SOC.1982, 104,2742. (d) Soriaga, M. P.; Chia, V. K. F.; White, J. H.; Song, D.; Hubbard, A. T. J. Electroanal. Chem. 1984,162, 143. (e) Soriaga, M. P.; Hubbard, A. T. J. Phys. Chem. 1984.88, 1089. ( f ) Chia, V. K. F.; Soriaga, M. P.; Hubbard, A. T.; Anderson, S . E. J . Phys. Chem. 1983,87, 232. (g) Chia, V. K. F.; Soriaga, M. P.; Hubbard, A. T. J . Electroanal. Chem. 1984, 167, 97. (h) White, J. H.; Soriaga, M. P.; Hubbard, A. T. J . Electroanal. Chem. 1984, 177, 89. (6) (a) Soriaga, M. P.; White, J. H.; Song, D.; Chia, V. K. F.;Arrhenius, P. 0.; Hubbard, A. T. Inorg. Chem., submitted for publication. (b) Soriaga, M. P.; Hubbard, A. T. J . Electroanal. Chem. 1983, 159, 101. (c) Soriaga, M. P.; Stickney, J. L.; Hubbard, A. T. J. Electroanal. Chem. 1983,144, 207. (d) Soriaga, M. P.; Stickney, J. L.; Hubbard, A. T. J . Mol. Catal. 1983, 21, 21 1. (e) Stickney, J. L.; Soriaga, M. P.; Hubbard, A. T.; Anderson, S. E. J. Electroanal. Chem. 1981, 125, 73.
0 1985 American Chemical Society
