J. Phys. Chem. 1994, 98, 12856-12860
12856
Vibrationally Coupled Dioxygen in Dioxygen Adducts of Cobalt Porphyrin Complexes with Pyridine. Mode Specific Variations in Coupling Strengths Leonard M. Proniewicz,*Jy*Janusz Golus,’’* Halina Majcherczyk,’ Krzysztof Bajdor,tJ and James R. Kincaid**t Chemistry Department, Marquette University, Milwaukee, Wisconsin 53233, and Regional Laboratory of Physicochemical Analyses and Structural Research, Jagiellonian University, Krakow, Poland Received: June 4, 1994; In Final Form: October I, I994@
Resonance Raman spectra of I6O2 and lSO2 adducts of cobalt tetraphenylporphine complexes with pyridine and several deuteriated analogues are presented. It is shown that the bound 0 2 has a marked tendency to vibrationally couple with internal modes of the trans-axial pyridine. Moreover, it is shown that the inherent coupling strength varies depending upon the specific modes which are in a position to couple with the ~ ( 0 - 0mode. ) That is, throughout the series of complexes, specific modes associated with the given deuteriated pyridine couple to different extents. This variation of coupling strength presumably reflects differences in the precise mode formulations for the various ligands. In order to document the vibrational frequencies of the coordinated pyridine isotopomers, the spectra of the corresponding bispyridine ferrous tetraphenylporphine complexes were also acquired and are presented.
Introduction Resonance Raman spectroscopy has been used extensively to probe the active sites of heme proteins, providing spectral signatures of heme macrocycle structure and axial ligand disposition for several small exogenous ligands, such as CO, CN-, NO, and O Z . ~ In the case of the oxygen-transportproteins, hemoglobin (Hb) and myoglobin (Mb), attention is obviously focused on complexes with the physiologically relevant dioxygen molecules. While the v(Fe-0) mode is sufficiently resonance enhanced for the 0 2 adducts, the more structuresensitive ~ ( 0 - 0 mode ) is not observable with previously employed excitation lines in the case of the natural systems, although it has been observed for 0 2 adducts of certain model compounds.2 An important breakthrough was made by Tsubaki and Yu, who demonstrated that the ~ ( 0 - 0mode ) can be readily observed in RR spectra of the corresponding cobalt-substituted analogue^.^ Inasmuch as these derivatives maintain the gross structural and functional properties of the native (iron-containing) systems, they offer a valuable altemative strategy to investigate the structural details of 0 2 binding to the heme active site. Though intense RR active features associated with the bound dioxygen are indeed observed in the spectra of the cobaltsubstituted analogues, the interpretation is complicated by the appearance of multiple (oxygen) isotopic-sensitive features, this behavior initially being attributed to the presence of multiple conformer^.^ Fortunately, parallel studies being undertaken in this laboratory on 0 2 adducts of cobalt porphyrin complexes with nitrogen-containing trans-axial ligands revealed on interesting and remarkable propensity of bound dioxygen to be vibrationally coupled with internal modes of the trans-axial ligand so as to give rise to “extra” satellite bands and nonideal isotope shifts. In a series of extensive ~ t u d i e s wherein ,~ the inherent frequencies of the ~ ( 0 - 0mode ) and the intemal modes of the trans-axial ligand were systematically varied, this
* Regional Laboratory, Jagiellonian University. ’Marquette University.
8 Permanent address: Department of Chemistry, Jagiellonian University, Krakow, Poland. Permanent address: Institute of Industrial Chemistry, Warsaw, Poland. Abstract published in Advance ACS Abstracts, November 15, 1994. @
behavior was shown to conform to the well-known F e e resonance equation^,^ compliance with such being expected on theoretical grounds as shown by Veas and McHale.6 In fact, Bruha and KincaidM applied these concepts to the analysis of the RR spectra of cobalt-substituted hemoglobin (HbCo) and myoglobin (MbCo) and provided an altemative explanation of the complex spectral pattems which does not require the existence of multiple conformers. In an attempt to gain further insight into the factors which dictate efficient coupling of the ~ ( 0 - 0with ) modes of the trans-axial ligand, we have undertaken a systematic study of the pyridine complexes. We herein report the RR spectra for the 0 2 adducts of cobalt tetraphenylporphine complexes with a series of deuteriated pyridines. In order to help establish the inherent frequencies of the intemal modes of the bound pyridine ligands, the RR spectra of the corresponding bispyridine ferrous porphyrins, which are known to exhibit strongly enhanced pyridine mode^,^^^ were also acquired.
Experimental Section Compound Preparation. 5,10,15,20-Tetraphenylporphine (H2TPP) was purchased from Midcentury Chemical Co. (Posen, IL) and purified to remove traces of reduced porphyrine by refluxing with 2,3-dichloro-5,6-dicyano1,4benzoquinone @DQ) in toluene, extracting with sodium dithionite, and then chromatographing over dry alumina with c h l o r ~ f o m ./3-Pyrrole ~ deuteriated HzTPP (H2Tpp-d~)was synthesized from the cocondensation reaction of pyrrole-ds and benzaldehyde in propionic-dl acid.1° The iron was incorporated into H2TPP by refluxing the porphyrin in glacial acetic acid containing ferrous chloride, FeC12.” Fe(TPP)(pip)z, where pip = piperidine, was synthesized by reduction of Fe(TPP)Cl with piperidine in refluxing chloroform under a nitrogen atmosphereL2and used as a starting material for Fe(TPP)(py)z, where py = pyridine, preparation (see Spectral Measurements). The cobalt was incorporated into H2Tpp-d~by reaction of cobaltous chloride, CoC12, with the porphyrin in refluxing dry tetrahydrofuran (THF) in the presence of 2,6-lutidine under a nitrogen atmosphere and purified by chromatography on an alumina column according to a reported pr0~edure.l~
0022-3654/94/2098-12856$04.50/0 0 1994 American Chemical Society
J. Phys. Chem., Vol. 98, No. 49, 1994 12857
Dioxygen Adducts of Cobalt Porphyrin Complexes Pyridine and pyridine-ds were purchased from Aldrich Chemical Co., and distilled over solid sodium hydroxide prior to use. 3,5-Dichloro- and 2,6-dibromopyridine were sublimed before use. Pyridine-2-d, -3-d, and -4-d were prepared according to the method described previ0us1y.l~ Pyridine-3,5-d2 and -2,6d2 were prepared by a modified method originally given by Bak.ls In this preparation, 3,5-dichloro- or 2,6-dibromopyridine, respectively, was suspended in D2S04 (1 m o m ) and CH30D mixture (5:l) and refluxed under nitrogen while zinc dust (from Aldrich Chemical Co., 325 mesh) was added. Then the solution was refluxed for additional 3.5 h, and the reaction mixture was filtered and neutralized with sodium bicarbonate, NaHCO3. Deuteriated pyridine was distilled off carefully, dried over solid anhydrous sulfate, Na2S04, decanted, and distilled from phosphorus pentaoxide, P2O5. The yield was approximately around 70%. Isotopic purity, checked by NMR and MS, was higher than 95%. The solvents methylene chloride, CH2C12, and its deuteriated analogue, CD2Cl2, were purchased from Aldrich Chemical Co. and purified by refluxing over calcium hydride, CaH2. The gases 1 6 0 2 (isotopic purity greater than 99%, Amerigas) and 1 8 0 2 (isotopic purity greater than 97%, ICON) were used as supplied. Spectral Measurements. Pyridine and its deuteriated analogues were measured at room temperature in glass capillaries. Spectral measurements of the bispyridine complexes of Fe(TPP) and dioxygen adducts of Co(TPP-ds)(py) were carried out by using the "minibulb" technique.16 Fe(TPP)(py)z complexes were prepared by heating Fe(TPP)(pip)z in a minibulb at 180 "C for 2 h under vacuum of 1 x Torr to dissociate piperidine. Pyridine (or its deuteriated analogue) was then added by vacuum line transfer. The excess of pyridine was then removed by vacuum distillation while a minibulb was kept in a hot-water bath (80 "C). Next, dry and degassed CH2C12 was transferred through the vacuum line to dissolve the iron complex, the contents of the minibulb were frozen, and the bulb was sealed off. The RR spectrum was acquired at room temperature. Dioxygen adducts of Co(TPP-ds)(py) were prepared following a well-documented procedure. l7 The lU3 spectra were recorded on a Spex Model 1403 double monochromator equipped with a Hamamatsu R928 photomultiplier tube and a Spex DMlB computer. Pyridine, its deuteriated analogues, and the iron complexes were measured with excitation at 496.5 nm from a Spectra-PhysicsModel 2025 argon ion laser. Power at the sample was 15 mW. Dioxygen adducts of cobalt complexes were measured at 406.7-nm excitation accomplished with a Coherent Model 1100-K3 krypton ion laser. The power at the sample was kept below 5 mW. The accuracy of the frequency readings was zk1 cm-l. A CTI Model 21 closed-cycle helium refrigerator was used to maintain the samples of the cobalt complexes at the desired temperature (-90 "C) during the measurements.
Results and Discussion General Behavior. In a series of early studies, we had shown that the resonance-enhanced v ( 0 - 0 ) vibration of 0 2 adducts of cobalt porphyrin complexes with various axial ligands has a strong propensity to couple with internal modes of the transaxial ligand.4 In those studies, it was shown that the couplinginduced perturbations in the frequencies and relative intensities of the coupled modes were critically dependent on energy matching of the modes, the actual observed data being quantitatively consistent with the conventional Fermi-resonance equation^.^ Thus, for a given ligand mode, the magnitude of the observed perturbations for various 0 2 isotopomers could be quantitatively accounted for. However, the strength of the perturbation varies among different ligands and their internal
Co('l'YP-ds)(Iiy)(02) in CH2C12
I\ 5
P PY-dg
, A J L -
975
1100
Rainan sliirt
1225
(ci1i-l)
Figure 1. Resonance Raman spectra of 0 2 adducts of Co(TPP-d8) complexes with pyridine in CH2C12 (excitation at 406.7nm): (A) l602; (B)l6O2, CD2C12; (C) l 8 0 2 ; (D)l8O2, pyridine-ds.
modes (e.g., the coupling strength parameter for the 1108-cm-' mode of 4-methylimidazoleis different from that associated with the 1068-cm-' mode of pyridine). In an attempt to gain a better understanding of the factors which influence the strength of such coupling interactions, we have undertaken the present investigation of the complexes with a series of selectively deuteriated pyridines. Thus, within this series, the electronic structural factors are held constant while a number of different modes within the series of complexes are sufficiently energy matched to undergo coupling. The spectra given in Figure 1 nicely illustrate the general effects of this coupling interaction and serve to clarify the experimental strategies needed to reveal the essential data. In trace A, the "v(160-'60)" is observed as a strong band at 1144 cm-' accompanied by a shoulder of moderate intensity at 1157 cm-'. As was discussed in a previous work? the inherent frequency of the v ( ' ~ O - ' ~ Ois) actually 1149 cm-l (see trace B, obtained in CD2C12) but is lowered by interaction with the solvent (CH2C12), which has an internal mode at -1156 cm-'. Thus, to obtain the inherent v('~O-'~O)for the complex with a given deuteriated pyridine, the spectra are acquired in CD2Cl2 (which has an internal mode at 1050 cm-'). As can be seen by comparison of traces B and C, the most striking observation for this system is the appearance of two bands having significant intensity in the case of the 1 8 0 2 adduct. This is a direct consequence of vibrational coupling of ~ ( ' ~ 0 l80) with an internal mode of pyridine whose inherent frequency is 1069 cm-' (see trace A). As can be seen in trace D, this 1067-cm-l feature disappears when pyridine-d5 is used, and importantly, the frequency of the strong V ( ~ ~ O - ' ~mode O ) shifts 2 cm-' to lower frequency. From this set of spectra, it is clear that the inherent frequencies of the v ( ~ ~ O - ' ~and O) ~ ( ' ~ 0 leg)are 1149 and 1083 cm-', but the v(180-'80) couples with the 1069-cm-' pyridine mode to give perturbed frequencies at 1067 and 1085 cm-' (i.e., Av = f 2 cm-'). Furthermore, as we had shown elsewhere:' it should be emphasized that the total intensity of the 1067/1085-cm-' pair is equal to those of the 1149- and 1083-cm-' features in traces B and D and that
12858 J. Phys. Chem., Vol. 98, No. 49, 1994
Proniewicz et al.
i
I
975
1100
9775
1225
Raman shift (cm")
Figure 2. Raman spectrum of pyridine (excitation at 496.5 nm), trace A. Resonance Raman spectrum of Fe(TPP)(py)Zin CH2C12 (excitation at 496.5 nm), trace B. Resonance Raman spectra of dioxygen adducts of co(TPP-d~)(py)(excitation at 406.7 nm): (C) l 6 0 2 , CD2C12; (D) l 8 0 2 , CH2C12. Asterisks denote solvent bands. the relative intensities of the 1067- and 1085-cm-l features are in excellent agreement with those calculated by using the conventional Fermi-resonance equations. Specific Complexes. The spectra of all the members of the series of deuteriated pyridines in the region of interest (9751225 cm-l) are given in the A traces of Figures 2-7. In order to establish the frequencies of the coordinated ligands, the spectra of the corresponding bispyridine ferrous tetraphenylporphine, (py)2FeTPP, complexes were acquired and are given in trace B of each figure. Finally, in traces C and D of each figure are given the spectra of the 1 6 0 2 and l 8 0 2 adducts of the corresponding cobalt octadeuteriotetraphenylporphinecomplexes (Le., (py)CoTPP-ds). The deuteriated porphyrin was used in these cases in order to eliminate a porphyrin macrocycle mode which occurs at -1075 cm-' (see trace B) which would otherwise cause an unnecessary complication when interpreting the v ( ~ ~ O - ~behavior. ~O) Upon inspection of the spectra involving the natural abundance pyridine ligand (Figure 2), it is seen that the four A1 modes in this region are also observed in the spectrum of the iron complex. While the 1068-cm-l modes is essentially unshifted and only weakly enhanced, the 992(1013)-, 1031(1047)-, and 1217(1214)-cm-' modes are reasonably strongly enhanced, the two lower energy bands exhibiting relatively large shifts upon coordination. These data correspond very well to those presented earlier.7.8 However, in our case, we were able to observe the enhancement of the 1068-cm-' band of pyridine in the Fe(TPP)(py)z complex which has not been previously reported. The spectrum given in trace C shows weak enhancement of the 1012- and 1069-cm-l pyridine modes (the latter can be seen in trace A, Figure 1). As trace D clearly shows, the 1069-cm-' mode gains intensity and shifts to 1067 cm-l by virtue of the coupling interaction with ~ ( ~l 8 ~ 0 ) , as 0 previously mentioned. Furthermore, by inspection of traces C and D, it is clear that
1100
1225
Raman shift (an.')
Figure 3. Raman spectrum of py$dine-4-d, trace A. Resonance Raman spectrum of Fe(TPP)(py-4-& in CH2C12, trace B. Resonance Raman spectra of dioxygen adducts of Co(TPP-d~)(py-4-d):(C) I6O2, CH2Clz; (D) 1 8 0 2 , CH2C12. Spectral conditions as in Figure 2. Note that the 1031-cm-' band in trace A is due to trace of pyridine.
I/ I
975
F'yridine-2,6d2
1100
1225
Raman shift (cm?
Figure 4. Raman spectrum of pyridine-2,6& trace A. Resonance Raman spectrum of Fe(TPP)(py-2,6-d2)2in CH2Cl2, trace B. Resonance Raman spectra of dioxygen adducts of Co(TPP-&)(py-2.6-d2): (C) l 6 0 2 , CD2C12; (D) I8O2, CD2C12. Spectral conditions as in Figure 2. Note that the 1030-cm-' band in trace A is due to trace of pyridine-2-d. the 1012-cm-' band is stronger (relative to the adjacent 1004/ 994-cm-l porphyrin bands) in trace D, apparently because of coupling with v ( ~ ~ O - ~ ~ O ) . Inspection of the spectra given in the case of 4-2H1-pyridine (pyridine-4-4 reveals behavior which is consistent with that described above for the pyridine (py-NA) complexes (Figure 3). Thus, a similar pattern is observed for the Fe(TPP)(py-4-
Dioxygen Adducts of Cobalt Porphyrin Complexes
A
E'
I
41.idioe-3,5d2
1100
975
Pyridine-3d
1225
Figure 5. Raman spectrum of pyridine-3,5-d2, trace A. Resonance Raman spectrum of Fe(TPP)(py-3,5-d2)2in CH2C12, trace B. Resonance (c)I6O2, Raman spectra of dioxygen adducts of co(TPP-dE)(py-~,~-dZ): CDZClz; (D) l 8 0 2 , CH2C12. Spectral conditions as in Figure 2.
* B F-
m
z
1
I
1100
1225
Raman shift (cm?
Figure 6. Raman spectrum of pyridine-2-d,trace A. Resonance Raman spectrum of Fe(TPP)(py-2-6)2in CH2C12, trace B. Resonance Raman
spectra of dioxygen adducts of Co(TPP-d~)(py-2-d):(C) I6O2, CD2Spectral conditions as in Figure 2.
Clz; (D) L E 0 2 ,CH&.
complex, and the 1068-cm-' feature (trace C) is shifted and intensified in the 1 8 0 2 case (trace D). Though the 1005-cm-' feature may be expected to experience slight enhancement in the 1 8 0 2 case (similar to the 1012-cm-' mode for the py-NA complex), the presence of the relatively strong 1004-cm-' porphyrin mode complicates a determination of this minor issue. The spectra for the 2,6-2H2-pyridine (pyridine-2,6-d2) case reveal different behavior in the sense that the extent of
4 2
915
1100
1225
Raman shift (an.')
Raman shift (cm.')
975
J. Phys. Chem., Vol. 98, No. 49, 1994 12859
Figure 7. Raman spectrum of pyridine-3-d,trace A. Resonance Raman spectrum of Fe(TPP)(py-s-d)zin CH2C12, trace b. Resonance Raman spectra of dioxygen adducts of Co(TPP-d8)(py-%d): (C) I6O2, CH2C12; (D) I8O2, CH2C12. Spectral conditions as in Figure 2.
vibrational interaction appears to have diminished (Figure 4). Thus, the 1090-cm-' free ligand mode (trace A), which shifts to 1101 cm-' upon complexation (trace B), is in reasonably close proximity (18 cm-l) to the v(180-180)in the L802-~obalt complex (trace D). While there appeats to be a very slight increase in intensity of this mode in trace D (compared to trace C), the enhancement (coupling interaction) must be very weak, because neither it nor the v('~O-'~O)mode is shifted from its inherent frequencies. Obviously, this mode has a much lower capacity for coupling with the ~ ( 0 - 0than ) does the mode at 1068 cm-I in the spectra of the py-NA and py-4-d complexes. In both of those cases, the ligand mode and the Y ( ~ ~ O - ~ * O ) experience shifts of -2 cm-' and the ligand mode intensity is significantly enhanced. Thus, in terms of energy matching to the v(0-0), the 1101-cm-' mode is comparable to the 1068cm-' mode, yet the strength of the coupling interaction is much weaker. The opposite situation is encountered for the 3,5-2H2-pyridine (pyridine-3,5-d~)complexes presented in Figure 5 . In this case, the free ligand mode at 1174 cm-' (trace A), which shifts to 1172 cm-' for the 1 8 0 2 adduct of CoTPP-d8 (trace D), interacts fairly strongly with the v(l60-l6O), as can be seen in trace C. Thus, the inherent frequency of the ligand mode is 23 cm-' higher than the inherent frequency of the v('~O-'~O)(Le., Av = 1172-1149 = 23 cm-'), yet both bands are shifted by 2 cm-I and the intensity of the 1174-cm-' component is significantly enhanced (compared to that of the 1172-cm-I feature in trace D). Before considering the spectra of the monodeuteriated analogues, it seems necessary to comment on the unexpected appearance of two peaks in the Fe(TPP)(py-3,5-d2)~spectrum (trace B). Based on the general similarities of axial ligand frequencies in the CO(TPP-d8) and FeTPP spectra, it is expected that one axial ligand mode near 1172 cm-I should be observed in trace B, whereas actually two bands at 1167 and 1182 cm-' are observed. This observation is most reasonably explained by invoking a Fermi-resonance interaction between the funda-
12860 J. Phys. Chem., Vol. 98, No. 49, 1994 mental at -1 172 cm-' and the overtone of an IR-active mode which occurs at 589 cm-' (Le., '/2 of 1177 cm-') giving rise to two perturbed features which are shifted from their inherent frequencies by f 5 cm-'. While IR spectra for this complex are not available, we note that the strongest IR-active band for the free ligand is reported to occur at 592 cm-'.lsa The spectra for the 2-2H-pyridine (pyridine-2-6) complexes are given in Figure 6. First, it is interesting to note that the -1111-cm-l free ligand mode (trace A), though totally symmetric under C, symmetry, is correlated with the 1147-cm-' B2 mode of py-NA. Though it is reasonably well enhanced in the Fe(TPP)(py-2-6)2 spectrum (1119 cm-' in trace B), it is not appreciably enhanced in the cases of the cobalt complexes (traces C and D), though it may be obscurred somewhat by the 1121-cm-' macrocycle mode. The only clear evidence for coupling interactions involves the Y( l 8 0 - l80) and an internal mode of py-2-d which occurs at 1074 cm-' (both bands are shifted from their inherent frequencies by Jr2 cm-', i.e., 1085 - 1083 = 1074 - 1072 = 2 cm-'). This mode, which occurs at 1060 cm-' for the free ligand (trace A), is hidden by the -1075-cm-' macrocycle mode in the case of the Fe(TpP)(py2 4 2 complex (trace B). While quite weak, there does appear to be a slight interaction of Y ( ~ ~ O - ' ~with O ) the 1038-cm-' ligand mode, inasmuch as the intensity at 1038 cm-' is slightly greater in trace D than in trace C. Similar behavior is seen for the other monodeuteriated ligand, 3-2H-pyridine (pyridine-3-4, the relevant spectra being given in Figure 7. Again the 1113-cm-' mode (''B;' mode) experiences no detectable enhancement in the spectra of the 0 2 aducts, while the lower frequency mode (at 1051 cm-' in trace A) couples relatively efficiently with ~ ( ' ~l 800 )-, as witnessed by the 1-cm-I shift (i.e., 1084 - 1083 = 1067 - 1066 cm-') and significant intensity enhancement (comparing traces C and D). Somewhat surprisingly, the 1198-cm-' mode of the coordinated ligand (traces B, C, and D)apparently couples with the ~ ( ' ~ 0 l60), having slightly greater intensity in trace C than in trace D, even though it is separated from the inherent ~ ( ' ~ 0 - ' ~ 0 ) by 49 cm-'. The inherently strong coupling for this mode is consistent with the data for the py-3,5-d2 complex, where it was seen that the 1174-cm-' mode also strongly couples with ~(l~0-'~ The 0 )1043-cm-' . ligand mode may experience slight enhancement for the 1 8 0 2 adduct (compared to its intensity in trace C), although it is only marginal. Coupling Efficiency. The most interesting aspect of the present work is the demonstration that the strength of the coupling interaction between the ~ ( 0 - 0and ) an internal mode of the trans-axial pyridine varies for different ligand modes. For example, the mode occurring near 1200 cm-' couples relatively strongly in several cases, though the actual magnitude of the shifts and intensity borrowing are low because of the large energy mismatch with Y ( ~ ~ O - ~ ~However, O). according to published correlations,18-20in the case of py-2,6-d2, this mode is observed at 1090 (free ligand) and 1101 cm-' (complexed), yet it couples only very weakly with the Y ( ' ~ O - ' ~ O even ), though it is separated from it by only 18 cm-'. In contrast, the ligand mode occurring near 1069 cm-l in several of the complexes, where the separation from Y ( ~ ~ O - ' ~isOsimilar ) (Le., 14 cm-'), couples relatively strongly. Obviously it would be of interest to attempt to relate the observed coupling strength of the interactions with various pyridine modes to some property of those modes. This would require full descriptions of the relevant modes for each isotopomeric pyridine ligand. Unfortunately, while extensive spectral data have been c ~ m p i l e d and ~ ~ ~an' ~apparently reliable force field has been derived,2°,21no detailed descriptions of the modes are readily available for the various deuteriated derivatives. For
Proniewicz et al.
TABLE 1: Observed Frequencies and Enhancements COTPP(L)O2 pyridine 4-2H-pyridine 2,6-2H2-pyridine 3,5-2H2-pyridine 2-2H-pyridine 3-2H-pyridine
free ligand FeTPP(U2 1069 1068 1069 1067 1101 1087 1167/1182 1174
1060
N.O.'
1051
N.O.'
YLULY 1067(0.14) 1066(0.12) 1lOl(O.04) 1174(0.08) 1072(0.04) 1068(0.06)
~0~(10~)(1
1085(0.86) 1085(0.88) 1083(0.96) 1147(0.92y 1085(0.96) 1084(0.94)
IL and 1% are given as the fractional intensities of their sum. Note: Coupling is with Y ( ' ~ O - ' ~ O in)this case. Feature obscurred by overlap with the 1076-cm-l band of FeTPP.
example, the mode near 1200 cm-' for py-NA has been suggested to resemble the 9a vibrational of benzene (using Wilson numbers). However, upon deuteriation at the 2- and 6-positions, this mode shifts down to 1090 cm-' and presumably experiences unknown changes in the atomic displacements (relative to the displacementsfor the -1200-cm-' mode of pyrNA). Therefore, the application of such concepts to the data reported herein must await these detailed mode descriptions for each isotopomeric pyridine.
Acknowledgment. This work was supported by a grant from the National Institutes of Health (DK35153 to J.R.K.) and a grant from the Polish Committee for Scientific Research (2P 303 060 05 (to L.M.P.). References and Notes (1) Biological Applications of Raman Spectroscopy; Spiro, T. G., Ed.; Wiley-Interscience: New York, 1987; Vol. 3. (2) Wagner, W. D.; Paeng, I. R.; Nakamoto, K. J . Am. Chem. SOC. 1988, 110, 5565. (3) Tsubaki, M.; Yu, N. T. Proc. Natl. Acad. Sci. U S A . 1981, 78, 3581. (4) (a) Bajdor, K.; Kincaid, J. R.; Nakamoto, K. J . Am. Chem. SOC. 1984, 106,7741. (b) Kincaid, J. R.; Proniewicz, L. M.; Bajdor, K.; Bruha, A.; Nakamoto, K. Zbid. 1985,107,6775. (c) Proniewicz, L. M.; Nakamoto, K.; Kincaid, J. R. Zbid. 1988, 110, 4541. (d) Bruha, A.; Kincaid, J. R. Zbid. 1988, 110, 6006. (e) Proniewicz, L. M.; Bruha, A.; Nakamoto, K.; Kyuno, E.; Kincaid, J. R. Zbid. 1989, 111, 7050. (f) Proniewicz, L. M.; Kincaid, J. R. Zbid. 1990, 112, 675. (g) Proniewicz, L. M.; Bruha, A,; Nakamoto, K.; Uemori, Y.; Kyuno, E.; Kincaid, J. R. h i d . 1991,113,9100. ( 5 ) (a) Fermi, E. Z. Phys. 1931, 71, 250. (b) Herzberg, G. Molecular Spectra and Strucrure; Van Nostrand: New York, 1945; Vol. 2; p 215. (6) Veas, C.; McHale, J. L. J . Am. Chem. SOC. 1989, 111, 7042. (7) Wright, P. G.; Stein, P.; Burke, J. M.; Spiro, T. G. J. Am. Chem. SOC.1979, 101, 3531. (8) Schick, G. A.; Bocian, D. F. J. Am. Chem. SOC. 1984, 106, 1682. (9) Rousseau, K.; Dolphin, D. Tetrahedron Lett. 1974, 48, 4251. (10) Adler, A. D.; Longo, F.; Finarelli, J. D.; Goldmacher, J.; Assour, J.; Korsakoff, L. J. Org. Chem. 1967, 32, 476. (1 1) Chang, C. K.; DiNello, R. R.; Dolphin, D. In Inorganic Synthesis; Busch, D. M., Ed.; Wiley: New York, 1981; Vol. 20, p 157. (12) Epstein, L. M.; Straub, D. K.; Maricondi, C. Znorg. Chem. 1967, 6, 1720. (13) Collman, J. P.; Braumann, J. I.; Doxsee, K. M.; Halbert, T.; Hayes, J. E.; Suslick, K. S.J. Am. Chem. SOC.1978, 100,2761. (14) Bak, B.; Hansen, L.; Rastrup-Andersen, J. J. Chem. Phys. 1954, 22, 2013. (15) Bak, B. J. Org. Chem. 1956, 21, 797. (16) Nakamoto, K.; Nonaka, Y.; Ishiguro, T.; Urban, M. W.; Suzuki, M.; Kozuka, M.; Nishida, Y.; Kida,S . J. Am. Chem. SOC. 1982,104,3386. (17) Proniewicz, L. M.; Odo, J.; Goral, J.; Chang, C. K.; Nakamoto, K. J . Am. Chem. SOC. 1989, 111, 2105. (18) (a) DiLella, D. P. J . Raman Spectrosc. 1980, 9, 239. (b) DiLella, D. P.; Stidham, H. D. Zbid. 1980, 9, 90. (19) Sverdlov, L. M.; Kovner, M. A.; Krainov, E. P. Vibrational Spectra of Polyatomic Molecules; Wiley: New York, 1974 (Israel Program for Scientific Translations). (20) Pongor, G.; Puley, P.; Fogarosi, G.; Boggs, J. E. J, Am. Chem. SOC.1984, 106, 2765. (21) (a) Long, D. A.; Murfin, F. S.; Thomas, E. L. Trans. Faraday SOC. 1963, 59, 12. (b) Long, D. A,; Thomas, E. L. Trans. Faruday SOC. 1963, 59, 783.
