Preparation and identification of iridium bipyridine and phenanthroline complexes

J. ino~. nucl. Chem. Vol. 41, pp. 495-502 © PergamonPressLtd.. 1979. Printed in Great Britain

0022.-1902/7910401-0495I$02.0010

PREPARATION AND IDENTIFICATION OF IRIDIUM BIPYRIDINE AND PHENANTHROLINE COMPLEXES J. L. KAHL, KENNETH HANCK and KEITH DeARMOND Department of Chemistry, North Carolina State University, Raleigh, NC 27650, U.S.A.

(Received 28 July 1978; received for publication 20 September 1978) Abstract--The syntheses of the bis-, bisequis- and tris(2,2'-bipyridine (bpy) complexes of iridium(ill) and the bis-, bisesquis- and tris(l,10)phenathroline) (phen) complexes of iridium(HI)are described. The purification of these complexes using Cellex P and Sephadex LH-20 is presented. The identification of these complexes by the use of luminescence, 'H NMR, ~3CNMR and elemental analysis is also discussed.

INTRODUCTION The synthesis, separation and identification of diimine d 6 metal ion complexes have received little emphasis in the literature when the complexes contain Fe(II)[l-3], Ru(III)[2,4-7], Os(III)[2,7-9], Co(III)[10-12] and Rh(III)[13-16]. Now that the IrfllI) 2,2'-bipyridine (bpy) and 1,10- phenanthroline (phen) complexes are of spectroscopic interest the preparation has become a focal point of the literature[17-24]. The reaction of IrCl3 with bpy [25-28] leads primarily to [Ir(bpy)2Cl2] I÷ and an "impurity" which can only be removed by successive recystallization[18] or careful work with chromatographic columns[17]. As many as twenty-six recrystallizations have been used to purify this species[18], while other researchers have reported no purification upon recrystallization. Since these impurities are due to photoaquation of the bis dichloride [29], the ionization constant, dielectric constant and water content of the solvent as well as the lighting in the room have significant effects on the outcome of each recrystallization. For this reason ion exchange chromatography is preferred as the method of purification for the bis bpy and phen complexes[17]. The temperature and reaction time were increased for the IrCI3 and bpy melt reaction in an attempt to produce the tris bpy complex by forcing the third bpy to coordinate with the Ir[25, 36]. Extensive work with this reaction [22] shows an entire sequence of products: [Ir(bpy)z£1(H20)]2", [Ir(bpy)2(H2I)2] 3÷, [Ir(bpy)2(H2OXbpy)] 3÷ and the corresponding hydroxides. These compounds can be cycled between the acid or base. The bisesquisl" [Ir(bpy)2(OH)(bpy)]2÷ is also a product of the synthesis[19] of the difficult to synthesize [lr(bpy)3]3~ under controlled conditions. This monodentare bpy compound is of interest since it has been proposed as a stable reaction intermediate in iigand displacement reactions[22]. The successful syntheses[19] of the tris [Ir(bpy)3] 3" is carried out under controlled halide free conditions in an iridium sulfate-bisulfate fused salt medium. This reaction involves an Ir(I) hydroxide which inserts CO2 and HSO~[30]. Column chromatography is employed to separate the tris complex from the approximately ten other products [19]. The purpose of this work is threefold: (1) to describe

the separation of these Ir(III) complexes from the synthetic reaction mixture; (2) to present simple spectroscopic tools to guide the purification scheme; and (3) to present the ~H NMR and ~3C NMR spectra of each of the complexes and the emission spectra of the phen complexes.

EXPERIMENTAL All emission spectra were done in triply distilled ethanol and methanol from Fisher ScientificCo. 'H NMR and '3C NMR were done in Fisher Scientific Co. dimethyl suifoxide-ds(DMSO-dr) 99.5%. All complexes were synthesized using IrCl3.nH20 from Engelhard Industries, bpy and phen from Fisher Scientific Co. All other chemicals and solvents were reagent grade from Fisher Scientific Co. The glass columns were constructed with medium fritted glass disks and a teflon stopcock at the bottom. All reaction flasks, columns, beakers and glass rods were cleaned with hot concentrated nitric acid and rinsed repeatedly with deionized HzO. A 3M HNO3 slurry of Cellex P (Bio-Rad Laboratories) was packed into a 2.8 cm diameter glass column to a height of 30.0era. This column was eluted with I x 104 M HNO3until the elutant was pH 4.0. The Cellex P column was run at all times at a rate determined by gravity (10-20drops/min). A methanol slurry of Sephadex LH-20 (Pharmacia Fine Chemicals) was packed into a 2.0 cm dia. glass column to a height of 90.0 cm and eluted with methanol at a rate determined by gravity (60 drops/rain) for at least 8 hr before being used. All column work and sample handling thereafter was done in the dark. The prngress of the columns was monitored occasionally with a long wavelength (366nm)TLC lanp. Synthesis. The preparation of [Ir(bpy)2Cl2]+' has been de,;cribed in the literature[25-28]. The reaction mixture was dissolved in 100 ml of H20, the pH adjusted to 4.0 and chromatographed on Cellex P. This column was eluted with lx 10-'MHNO3, 0.01 M HNO3 and 0.05 M HNO3. The 0.05 M fraction was flash evaporated to dryness on a Rotovac with the additiov of 2propanol. This solid was dissolved in methanol and chromatographed on LH-20 at a rate of 30 drops/rain. This sample separated into four bands with the emission spectrum of the green luminescent band indicating the presence of [lr(bpy)2Cl:]~ This portion was chromatographed five additional times on LH-20 by the above procedure. The last application on LH-20 was done without using the UV lamp. The green luminescent band gave yellow crystals of [Ir(bpy2Cl.a]NO~upon addition of 2-propanol and flash evaporation. The [lr(phen)~Cl2]NO3.H20was prepared by an analogous procedure, [Ir(bpyh]3÷ was prepared by a method similar to that of Flynn and Demas[19]. A 11. beaker containing 2.0g of IrCl3.nH:O, 24g of KI-ISO4and 20 ml of H20 was heated slowly to dryness with stirring. This mixture was heated to the melting point of KHSO4

tBisesquis, a prefix meaning two and one-half. 495

496

J. L. KAHL el aL

(214°C) for 30 min with stirring (deep green) and then cooled to room temperature. The iridium bisulfate melt, 24.0g KzS2OT, 6.0 g bpy and 20 ml H20 were added to a new reaction flask. The temperature was held at 120°Cunder an N2 atmosphere until the H20 was removed. The temperature was raised to 180°Cand the N2 was replaced by CO2. The two layered melt (one brown, one yellow) was held at 230°Cfor 6 hr. The melt was fouled to room temperature and dissolved in 200 mi H20. The pH was adjusted to 7.0 with KHCO3, 800 ml of methanol added, cooled to 0°C for 2 hr and filtered to remove K2SO,. The filtrate was flash evaporated to 90 ml, cooled to 5°Cfor I hr and filtered to remove excess bpy. To the filtrate 600 ml of 0.2 M HNO~ was added, flash evaporated at 70°C to l0 ml and to dryness at 40°C. This yellow solid was dissolved in 600 ml of 0.2 M HNO3 and flash evaporated as above. The solid was dissolved in 100mi of H20. adjusted to pH 4.0 and chromatographedon Cellex P. This colunm was eluted with i×I0-4MHNO3. 0.05MHNO3 and 0.1MHNO3. The 0.1M fraction was neutralized, flash evaporated at 70°C to 100ml, checked for neutrality and flash evaporated at 40°C to dryness. The solid from the 0.1M fraction was dissolved in methanol and chromatographedon LH-20 at a rate of 25 drops/rain. This sample separated into five bands. The emission spectrum of the bright green luminescent band showed it contained [Ir(bpy)3]a+. This band was chromatographedfiveadditionaltimes on LH-20 by the above procedure. The last application on LH-20 was done without using the UV lamp. This portion gave pale yellow crystals of [Ir(bpy)3](NO~)r2H20 upon addition of 2.propanol and flash evaporation. The [lr(phen)~](NOj)3.3H20was prepared by an analogousprocedure. [Ir(bpy)-z(OH)(bpy)]2÷ was the mojor product of the [lr(bpy)3]3+ synthesis when the reaction time was shortened to 3hr[17]. Further purification was carried out as for [h~opy)d~* except that the 0.05MI-INO3 fraction from the Cellex P column contained the bisesquis complex. This fraction was also repeatedly chromatolp'aphedin methanol on the LH-20 column. The green luminescent band eluted from the column gave lightyellowcrystalsof [lr(bpy)2(OH)(bpy)](NO;)2on addition of 50ml of 2-propanol and flash evaporation, the [Ir(phen)2(OH)(phen)](NO~)2-5H20 was prepared by an analogous method. Each compound was stored in a blackened sample bottle in a blackened desiccator under a vacuum. Instrumentation. Emission spectra were obtained on an Aminco-Bowman Spectro-photofluorometer ~-8202 with a Hanovia Mercury lanp ~O01B0011, a RCA 11)21 P.M. tube, a Coming CS7-54 excitation filter and a Kodak ZA emission filter. 'H NMR spectra were obtained on a Varian HA 100 NMR Spectrometer, t3CNMR spectra were obtained on a JEOL Fourier Transform NMR Spectrometer ~JNM-FX60. RKSULTSAND DISCUSSION The elemental analysis data in Table I are in good agreement with the calculated values. In the past ele-

mental analysis has been the primary test of purity for the d e metal bpy and phen complexes. However experience with Ir complexes has shown elemental analysis alone to be of dubious value especially when waters of hydration are present. The picture can be distorted further when the product is the acid form of the bisesquis complex. The elemental analysis of [Ir(bpy)2(H20)(bpy)](NO3)3 cannot distinguish it from that of [lr(bpy)3](NO3)2.1H20. Consequently spectroscopic methods must be employed to verify purity and to identify the complex present. Emission at 77 K was chosen because spectra can be obtained on samples between separation steps with a minimum amount of sample and short analysis time. Figures i-.4 show the emission spectra of the bis, acid bisesquis, basic bisesquis and tris phen complexes Ir(III) in ethanol-methanol at 77 K. The emission spectra for the bis bpy, bis phen, acid bpy, basic bpy and tris bpy complexes have appeared in the literature[18,19,22,37]. The emission spectra were monitored to obtain three types of information. F'n'st, the maximum of the first vibrational band in neutral, 0.1 M HCI and 0.1 M NaOCH3 in ethanol-methanol was measured and compared with the values in Table 2. This was done to determine the major constituent in the given sample and to decide whicl~ bands were to be kept and purified further. When the major constituent was determined, Figs. 1-4 and the corresponding bpy spectra were used to monitor the number and relative intensity of v~rational bands in the emission spectrum. Secondly, the spectra were used to measure the intensity ratio l~olI,w as suggested by Ballardini et oA.[18]. This ratio was measured after each elution of the his complexes from the LH-20 column until the ratio was constant. Finally the emission band shape and relative intensity were monitored as a function of 365 nm excitation vs 313 nm excitation. The intensity ratio ( l ~ e ~ / l ~ , 3 ) was measured after each elution from the LH-20 until constant, therefore verifying the presence of a single component. This ratio was particularly useful when separating the tris and bisesquis complexes. This can be seen by comparing Fig.2 with Figs. 3 and 4 for the phen complexes. Since emission for most luminescent molecules in solvent media occurs from the lowest excited state of the molecule, emission band shapes are expected to be invariant to excitation wavelength. The spectra of these bpy and phen Ir(III) compounds using 313rim and 365 nm Fig lines for excitation are consistent with this

Tabk 1. Elemental --H, • - anaiy~s of bi~, bisesqui~, and tris-bpy and phen Ir(IID complexes Compound

CalCtLlatmd C

H

[

~u~ys£s

n

C1

C

H

N

Cl

llr(bpY)2C12]NO 3

37.68

2.53

10.99

11.12

37.53

2.33

10.73

10.99

[ I r (phe~) 2C12 ]NO3 • 1H20

40.97

2.58

9.95

10.08

40.59

2.68

9.99

10.18

[Ir(bpY)3](NO3)3"2a20

40.82

3.20

14.28

41.08

3.32

13.74

[Ir(phen)3](MO3)3"3H20

44.44

3.11

12.96

44.04

3.02

12.90

[Ir(bpy)2(OH)(bpy)](NO3) 2

44.94

3.14

13.98

44.54

3.14

13.25

[Ir(phen)2(OH)(phen)](RO3)2"5H20

44.86

3.66

11.62

44.92

3;00

11.56

497

Preparation and identification of iridium bipyridine and phenanthroline complexes Table 2. The emission maximum ot the first vibrational band for emission at 77 K in ethanol-methanolblass (nm) bpy

433

phen

459

[Ir(bpy)2Cl2]l+

473

[Ir(phen)2CZ2 ]I+

476

[Ir(bpy)3]3+

446

[Ir(phen)3 ]3+

447

[Ir(bpy)2(OH)(bpy)]2+

460

[Ir(bpy)2(H20)(bpy)] 3÷

470

[Zr(phen)2(OH)(phen)] 2+

479

[Ir(phen)2(H20)(phem)] 3+

452

expectation. Further, since emission quantum yields are normally independant of excitation wavelength, invariance of excitation spectra to successive purifications can be used as a criterion for purity. For convenience and maximum sensitivity, the Aminco spectrophotofluorometer was used only in the emission mode with Hg line excitation. Discrete line sources typically do not produce useful excitation spectra, but comparison of the emission band shapes and intensity ratios for 313 nm vs 365 nm excitation (Figs. 1-4) indicate that these spectra could be used in lieu of corrected excitation spectra to monitor purity. '3C NMR spectroscopy can also be used to characterize these complexes. Table 3. contains the chemical shifts in ppm vs TMS of the free ligands and the complexes dissolved in DMSO-d6. A '3C absorption I

should be seen for each nonequivalent carbon. Free bpy has five lines that correspond to the five distinct carbons (both sides of the bpy are equivalent). The his bpy complex however should show ten distinct carbons[19, 21] due to the fact that the complex has C2 symmetry but the '3CNMR has only six distinct resonance lines. The tris bpy having D3 symmetry shows the expected five distinct resonance lines. The '3C NMR spectrum of the bisequis bpy complex has ten resonance lines. This would correspond to the two and a half equivalent coordinated bpys (five lines) while the second half of the mondentate bpy gives five additional distince lines. The free phen and tris phen complex show the expected number of distince carbons(six). The bis phen '3C NMR spectrum shows only ten lines instead of the expected twelve resonance lines. Apparently the different external environments of the two bpy halves in the his complex have only a small effect on the carbons themselves, while the coordination of the nitrogen to the iridium and the resulting electron shifting in the ring have a much greater effect on the carbons in the bisesquis complex. The final spectroscopic tool used in this study was 'H NMR spectroscopy. Figures 5-8 show the proton resonance spectra and assignements of these complexes and the free ligands. The shifts in the resonance lines for each complex can be explained by the use of four basic principles [13]. (1) Protons adjacent to a hetro-atom of heterocyclic aromatic compounds absorb at higher 6 values than other positions. The portion next to the nitrogen (betroatom) has its resonance line at a higher 8 value (Figs. 5a and 7a). (2) Portions that are sterically held above or below the plane of an aromatic ring will be abnormally shielded because of ring current effects. This shielding results in absorption at a lower/~ value (Figs. 6a and 8a). (3) Electron withdrawing groups shift the aromatic proton absorption to lower field. Electron donating groups shift the aromatic proton absorption to higher field. Since Ir(III) removes some of the electron density I

|

I

>i

i

z Z

i
T: _.J

~00

500 WAVELENGTH (nm)

6OO

Fig. 1. Emission spectra of [Ir(phen)-~Cl2]~+ in ethanol-methanol glass at 77 K: (a) 313 nm excitation, Co) 365 run excitation; slits and meter settings identical.

J.L. KAHL ef a/.

498 I

'

I

I

100

"i

7

D--I

so __J

I

~

JlO0

500

I 600

WRVELENGTH (nm) Fig. 2. Emission spectra of [Ir(phan)3]3÷ in ethanol-methanol glass at 77K (a) 313nm excitation, (b) 365nm excitation; slits and meter settings identical.

I

100

)t,--

'

l'

I

'I

ia.J I-Z

so

7: _..1 ¢y

400

500

600

WAVELENGTH (nm) Fig. 3. Emission spectra of [Ir(phen)2(OH)(phen)]2÷ in ethanol-methanol glass at 77 K: (a) 313 nm excitation, (b) 365 nm excitation; slits and meter settings identical. from the ligands the result should be a shift to the higher 8 values relative to free bpy. This shift affects the ortho position the most, the paraposition somewhat less and the meta position the least (Figs. 6a and 8a compared to Figs. 5a and 7a). (4) The absorption of a proton is inversely proportional to the electronegativity of adjacent atoms. This effect is particularly important for the 3 position on bpy in the his complex. The 3 position is close to the electronegative chloride iigand and the proton (Fig.5a) is shifted to a much higher 8 value than the 3 position proton in bpy (Fig.5a). Figure5 shows the proton N M R of free bpy and the bis bpy complex. The proton resonance assignments of the free bpy are based on principle 1 and the splitting pattern while those for the his bpy complex are based on

the assignments of DeSim0ne and Drago[9]. The general shift to higher 8 values of all of the resonance lines (principle3), the shift to higher 8 values for position 3 (principle 4) and the shift to lower 8 values for positions 3' and 4' (principle 2) can be seen in the spectrum of the bis bpy complex (Fig. Yo). Figure 6 shows the proton NMR of the tris and bisequis bpy complexes. The assignments for the tris bpy complex are based on the splitting pattern and the [Os(bpy)3]2÷ proton NMR of DeSimone and Drago[9]. The general shift of all resonance lines to higher 8 value (principle 3) and the shift to a lower 8 value of the 3/Y positions (principle 2) can be seen in the spectrum of the tris bpy complex (Fig.6a). The resonance lines for the bisesquis bpy complex (Fig.6b) have not been assigned due to overlapping lines but general trends can be seen.

perparation and identification of iridium bipyridine and phenanthroline complexes I

'

I

I

499 I

I00

I

Z z

->

SO

-

~00

500

600

WAVELENGTH (nm)

Fig. 4. Emission spectra of [Ir(phen)2(O20)(phen)]3+ in ethanol-methanol glass at 77 K: (a) 365 nm excitation. Co) 313 nm excitation; slits and meter settings identical.

66 1 i/

4" ~ ~ 4 " S

1"

~1~,

/ ,4

I I0o

I 9.

I 8.0

L

I 7.0

Fig. 5. Proton NMR in Dmso-d6: (a) bpy 8.80, 8.56, 8.08 and 7.53; (b) [Ir(bpy)2C]2lI÷, 9.90, 9.09, 8.73, 8,38, 8.07 and 7.75 ppm vs TMS. The basic resonance lines of the tris bpy complex are present along with several small lines due to the uncoordinated half of the monodentate bpy. Figure 7 shows the proton NMR of free phen and the his phen complex. The assignments of the resonance lines of the his complex are based on splitting patterns

and the [Rh(phen)2Clz] ~÷ resonance assignments by Kulasingam et aL [32]. Figure 8 shows the proton NMR of the tris and bisesquis phen complexes. The assignments of the resonance lines of the tris complex are based on splitting patterns and the [Co(phen)3] ~÷ assignments of Miller and Price[33,34]. The shifts of the resonance lines

500

J. L. KAHL a aL Table 3. '3C NMR data for bis-, bisequis-, and tri~bpy and phen complexes of lr(IIl) in DMSOsd 6 in ppm vs TMS

bpy

155.2, 149.2, 137.1, 124.0, 120.4

phen

149.9, 136.2, 128.4, 127.8, 126.6, 123.3

[Ir(bpy)2C12 }1+

157.6, 151.0, 141.4, 140.8, 128.7, 125.1

[Ir(phen)2C12 ]I+

152.3, 148.5, 148.0, 140.5, 139.7, 131.2, 130.9 128.4, 127.0, 126.7

[Ir(bpy)3]3+

155.7, 151.1, 142.9, 130.1, 126.7

[Ir(phen)3]3+

153.1, 146.4, 141.8, 131.9, 128.9, 127.7

[Ir(bpy)2(OH)(bpy)]2+

156.9, 156.0, 154.3, 152.1, 150.2, 141.5, 139.6, 129.7, 125.8, 122.9

S

6

4

~

$

6" 4

S"

"

S"

J I

,,

I

i

b

I 10.0

Fig. 6. Proton ~

, 9.0

I 8.0

,

I

7.0

D1~LSO-d6;(a) [lr(bpy)3] 3÷, 9.28, 8.74, 8.14 and 8.08, (b) [Ir(bpy~OH)(bpy)] 2÷ in ppm vs TMS.

for these phen complexes can be explained by a method analogous to that used for the bpy complexes above. For the bis phen complex the general shift of all resonance lines to higher O values (principle 3) can be seen in Fig.7. The shift to higher 8 values for position 2 (principle 4) and the shift to lower 8 values for positions 8 and 9

(principle 2) can also be seen. The general shift of all resonance lines to higher 8 values (principle 3) and the shift of position 2/9 to a lower value (principle 2) can be seen in the spectrum of the tris phen complex (Fig.Sa). The resonance lines for the bisesquis phen complex (Fig.Sb) have not been assigned due to overlapping lines

Preparation and identification of iridium bipyridine and phenanthroline complexes

501

.__3~ o~

m

! 1 + Z

~c P~

Z

e~

JINC VoL 41, No. ~.---E

J. L. KAHL et a/.

502

but some structural features are evident. The spectrum of the bisesquis phen complex shows the basic resonance lines of the tris phen complex with several small lines due to the uncoordinated haft of the monodentate phen ligand. SUMMARY The identification of each of the Ix(HI) complexes is based on the distinctive structural features. The use of analytical tools such as luminescence, *HNMR and elemental analysis to elucidate these structural features has been demonstrated. Of particular interest to the synthetic work is the use of intensity ratios of luminescent bands as a criterion of purity. The use of chromatography to aid and simplify separations of prganometallic synthetic products has also been demonstrated. Ac~owledgmmts--Acknowledgement is made to Mrs. Margaret Bundy for running the ~HNMR spectra and Mr. Billy R. Roberts for running the '3C NMR spectra. This research was supported by the National Science Foundation (CF 40894 and CHE 7605716).

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(1968). 9. R. DeSimone and R. Drogo, Inorg. Chem. 8, 2517 (1969). 10. R. Bogucki, G. McLendon and A. Martell, Y. Am. Chem. Soc. ~ , 3202 (1976). 11. S. Margel, W. Smith and F. Anson, J. bTlectrochem. Soc.12& 241 (1978).

12. N. Tanaka and Y. Sato. Bull. Chem. Soc. Japan. 4l, 2059(1968). 13. J. Demas, E. Haris, C. Flynn,Jr. and D. Diemanti,J. Am. Chem. Sac. 97, (1975). 14. J. Demas, E. Harris and R. Mc Bride, J. Am. Chem. Soc. 99, 3547 (1977). 15. G. Kew, K, DeArmond and K. Hanck, J. Phys. Chem. 78, 727 (1974). 16. K. DeArmond and J. Hillis, Y. Chem. Phys. ~ , 2247 (1971). 17. J. Kahl, K. Hanck and K. DeArmond, J. Phys. Chem. 82, 540 0978). 18. R. Ballardini,G. Varani, L. Moggiand V. Balzani,J. Am. Chem. Soc. 99, 6881 (1977). 19. C. Flynn,Jr. andJ. Dcmas, Z Am. Chem. Sac. 96, 1959(1974). 20. R. Dallardini,G. Varuni,L. Mogsiand V. Balzani,/. Am. Chem. Soc. 9~, 7123 (1974). 21. C. Flynn, Jr. and J. Demas, Y.Am. Chem. Soc. 97, 1988(1975). 22. R. Watts, J. Harrington and J. Van Houten, J. Am. Chem. Soc. 99, 2179 (1977). 23. R. Watts, T. White and B. Griffith, J. Am. Chem. Sac. 97, 6914 (1975). 24. R. Watts, ]. Am. Chem. Sac. 96, 6186 (1974). 25. B. Martin and G. Wain& Y. Chem. Soc, 4284 (1958). 26. B. Martin, W. McWinnieand G. Waind, Y. lnorg. NacL Chem. 23, 207 (1961). 27. B. Chisweil and S. Livingstone, J. lnorg. NucL Chem. 26, 47 (1964). 28. R. Watts and G. Crosby, J. Am. C ~ n . Soc. 93, 3184 (1971). 29. R. Bagardini, G. Varuni, L. Mogsi, V. Blazani, K. Olsen, F. Scandola and M. Hoffman, J. Am. Chem. Soc. 97, 728 (1975). 30. B. Flynn, Ph.d. Thesis, Clarkson College of Technology, Potsdam, NewYork, (1976). 31. J. Dyer. In Applications of Absorption Spectroscopy of Organic Compounds (Edited by K. Rinehart, Jr.) pp. 82-89. Prentice-Hall, Englewood Cliffs, N. J. (19653. 32. G. Kulasingem,W. McWhinnieand J. Miller,J. Chem. Soc. 512 (1969). 33. J. Miller and R. Prince, J. Chem. Sac. 519 (1969). 34. J. Miller and R. Prince, J. Chem. Soc. 3185 (1965). 35. J. Huheey. In Inorganic Chemistry Principles of Structure and Reactivity, pp. 73-75. Harper & Row, New York. (1972). 36. K. Wunschel,Jr. and W. Ohnesorge, J. Am. Chem. Soc, g9, 2777 (1967). 37. J. KahI, Ph.d. Thesis, Nonh Carolina State University,Raleigh, N. C. (1978).