COM MUNICA TIONS

I-

~ 4

6

3

21-+I I

(a)

40 80 1206Hads • kJ mol-1

I I

6 6C>

4 ~+'".'- 5 +*. 7bIf) 2

0: 4

<J + (b)3 L- ~

Fig, 2-(a) Plot of the metal (d)-ft· (CO) charge-transfer energyagainst the heat of adsorption [(i) Ag(Ill); (2) Cu(3]])(3) wuoou (4) Ni(lIO) ; (5) Ni(I00) ; (6) Pt(11l) and Pt(100);and(7) Ni(IIl)] (b) Plot of the ft· (CO) orbital energy againstthe heat of adsorption [(1) Cu(311); (2) Pt(Ill) and Pt(IOO);(3) W(1OO); (4) Ni(lll); (5) Ni(IlO); (6)Pd(I00); and(7) Ni(I00)].

References1. ANDERSSON.S.• Solid State Commun .• 21 (1977). 75.2. SEXTON.B. A .• Chern. Phys. Lett .• 63 (1979). 451.3. THOMAS.G. E. & WEINBERG.W. H .• J. chem. Phys .• 70

(1979). 954.4. F'ROITZHEIM.H .• IBACH.H. & LEHWALD.S.• Surf Sci .• 63

(1977). 56.5. KUPPERS. J.• J. Electron Spectrosc. Rei. Phenom., 1 (1972),

186.

6. KUPPERS, J., Surf Sci .• 36 (1973). 53.7. AKIMOTO.K., SAKISAKA.Y., NISHInMA, M. & ONCHI, M.,

Surf Sci .• 88 (1979), 109.8. SAKISAKA,Y., AKlMOTO,K., NISHIJIMA,M. & ONCHI, M.,

Solid State Commun., 29 (1979), 121.9. RUBLOFF,G. W. & FREEOUF,J. L., Phys. Rev., B17 (1978),

4680.10. PAPP, H., Surf s«., 63 (1976), 182.11. PAPP, H. & PRITCHARD,J., Surf sa.. 53 (1975), 371.

12. McELHINEY, G., PAPP, H. & PRITCHARD, J., Surf Sci.,54 (1976), 617. .

13. CHESTERS.M. A., HOPKINS, B. J. & WINTON,R. 1., Surfsa.. 59 (1976), 46.

14. BADER,S. D., BLAKELY,J. M., BRODSKY,M. B .• FRIDDLB,R. J. & PANOSH,R. L., Surf sa.. 74 (1978). 405.

15. NETZER.F. P. & MATHEW,J. A. D., Surf Sci., 81 (1979).L651.

16. NETZER. F. P., WILLIE, R. A. & MATHEW,J. A. D., SolidState Commun., 21 (1977), 97.

17. SOMORJAI.G. A., Surf sa.. 89 (1979). 496.

I

18. BAKER, J., M. & EASTMAN,D. E., J. Vac. Sci. Tech., 10(1973), 223.

19. NORTON,P. R. & TAPPING, R. L.. Chern. Phys. Lett., 38(1974). 207.

20. ERLEY.W:, WAGNER.H. & IBACH,H .• Surf Sci .. 80 (1979),612. .

21. BERTOLINI~J. c., DALMAI-IMELI~.G. & ROUSSEAU,J .. SurfSci .. 68(1977). 539.

•.•. 22. HOPSTER,H. & IBACH.• H., Surf Sci., 77 (1978), 109.23. FROITZHEIM.H., HOPSTER,H., IBACH, H. & LEHWALD,S.,

Appl. Phys .. 13 (1977), 147.24. DUBOIS,L. H. & SOMORJAI,G. A., Surf. Sci., 91 (1980)

514. '25. LEHWALD.S. & IBACH.H., Surf Sci .• 89 (1979).425.26. IBACH. H. & LEHWALD.S .• J. Vac. Sci. Tech .• 15 (1978),

407. '27. IBACH.Ht• LEHWALD.S. & SEXTON.B. A .• Appln Surf. Sci .•

1 (1977}. 1.28. IBACH. H.. HOPSTER. H. & SEXTON.B. A .• Appl. Phys.,

14 (1977). 21.29. BERTOLINI,J. C. & ROUSSEAU,J .. Surf Sci .• 89 (1979) .467.30. LEHWALD.S .• IBACH, H. & DEMUTH. J. E., Surf. Sci., 78

(1978) • 577.

Identification of a One-electron Redox Process inFe(ID) , Co(IIl) & Cu(II) Complexes of I-Ethyl-3-

phenyltriazene I-Oxide

R. N. MUKHERJEE& A. CHAKRAVORTY·Department of Inorganic Chemistry, Indian Association for

the Cultivation of Science, Calcutta 700 032

Received 13 October 1980; accepted 29 October 1980

The existence of a nearly reversible one-electron transferreaction MLp + e ¢ ML; (M = Fe, p = 3; M = Co,p = 3; M = Cu, P = 2; L = l-ethyl-3-phenyltriazene I-oxide)is established using cyclic voltammetry, phase sensitivealternating current voltammetry and coulometry. Formal elec-trode potentials in acetonitrile at hanging mercury drop electrodeare : Fe, -0.71 V; Co, -0.52 V; Cu, -0.79 V vs SeE.

MANY substituted triazene I-oxides bind anumber of transition metal ions giving com-

plexesof variable stereochemistryv>, There is thus anopportunity to establish trends pertaining to varia-tions of ligand substituent, central metal ion and com-plex stereochemistry on electron transfer reactions.In this communication the occurrence of such areaction is identified for a group of three complexesof general formula MLp (M=Fe, Co or Cu) usingelectrochemical techniques in acetonitrile solutionwhich is 0.1 M in tetraethylammonium perchlorate(supporting electrolyte). Results are collected inTable 1 and Fig. 1.

MLp

M= Fe) ~::J

M = Co; P';"JM = ell, p= 2

73

INDIAN J. CHEM., VOL. 20A, JANUARY 19S1

'",I ,I • \I \I \, \

\\\\\\,,,... L(jlA)

The FeL3 complex was also studied (Fig. 1) usingphase sen~itive. alternating current voltammetry atHMDE (sinusoidal frequency, 35 Hz; modulationamplitude, 10 mY; d.c. scan rate 5 mY sec-I). Thepeak potential (-0.73 Y) agrees well with Eg98(-0.71 Y). The observed width at half height is120 mY showing" that the electrode process is nearlya.c. reversible.

Financial help received from the Department ofAtomic Energy, Government of India, BombayIndia is gratefully acknowledged. '

References

1. ZACHARIAS,P. S. & CHAKRAVORTY,A., Inorg. Chem., 10(1971), 1961; ZACHARIAS,P. S. & CHAKRAVORTY,A.,Inorg. chim. Acta, 6 (1972), 673; ZACHARIAS.,P. S. &CHAKRAVORTY,A., Inorg. chim. Acta, 11 (1974) 122and references therein. '

2. RAJASEKHARAN,M. V., VARUGHESE,K. I. & MANOHARANP. T., Inorg. Chem., 18 (1979), 2221. '

3. UNDERKOFLER,W. L. & SHAIN,I., Analyt, Chem., 37 (1965).21S; BOND, A. M., O'HALLORAN, R. J., RUZIC,I. &SMITH, D. E., Analyt Chem., 48 (1976), S72.

0.9 0.7

- E (V) v s 5.C.E

Fig. 1 - Cyclic voltammograrn (--) and phase sensitivea. c. voltammogram (- - -) of FeL3 [Conditions of measure-

ment are stated in the text]

•....._--

'.' 0.5

TABLE 1 - CYCLICVOLTAMMETRICDATA (29SK) AT HMDE IN Reactions of TrithiazyItrichloride with RhodiumACETONITRILE Nitrosyl Complexes

[Acetonitrile solution is 0.1 M in tetraethylammonium per-chlorate used as supporting electrolyte; solute cone, = ~ I0-3 M;scan rate 50 mVsec="; all potentials are referenced to

saturated calomel electrode]

Epc(V) Ep.(V) t:,.Ep(mV)0

Complex Em(V)

EeLs -0.75 -0.67 SO -0.71CoL, -0.57 -0.47 100 -0.52CuL2 -0.S3 -0.75 SO -0.79

At hanging mercury drop electrode (HMDE)FeL3 affords a well-defined cyclic voltammogram(Fig. 1) with characteristic cathodic (Epe) andanodic (Epa) peaks. For a one-electron process thepeak-to-peak separation (6Ep) should be 58 mY.The observed separation is 80 rnv showing that theprocess is quasireversible. The cathodic and anodicpeak currents are nearly equal. The cobalt(IU)complex is also reduced in a one-electron processwhich is less reversible (higher 6Ep) than that ofFeL3; on the other hand the one-electron transferprocess for CuL2 is very nearly reversible (Table 1).That the number of electrons transferred (n) is equalto 1 was confirmed in each case by constant potentialcoulometric studies at potentials 200 mY morenegative than Epe (Found: n = 1 ± 0.1). Thegeneral electrode reaction is thus,

MLp + e ~ MLp .. (1),

The formal electrode potential Eg98 (Table 1) forreaction (1) taken as the average of the two peakpotentials in each case shows that the thermodynamicease of reduction follows the order COL3> Fel., >CuL2• Studies on a large group of triazene l-oxidecomplexes are underway in order to establish varioustrends.

74

i/

K. K. PANDEY& U. c. AGARWALA*Department of Chemistry, Indian Institute of Technology,

Kanpur 20S 016,

Received 3 November 1980

The rhodium nitrosyl complexes Rh(NO)X.(PPha). (X=CI, Br) react with (NSCI). in THF to give the bridged thionitrosylcomplexes [Rh(NS)X.(PPh3)1. which, with excess of triphenyl-phosphine and triphenylarsine, give complexes [Rh(NS)X.(PPh3)L](L=PPh3 or AsPh3) containing terminal thionitrosyl group.Their tentative geometries have been proposed on the basis ofvarious physicochemical methods.

'SYNTHETIC and structural studiesv< on metalthionitrosyl complexes reveal that in all the

complexes, thionitrosyl ligand is terminally bonded.-Recently, we have synthesized first bridged thio-nitrosyl compex" of rhodium. Herein we Wish to-report the syntheses of a few bridged thionitrosylrhodium complexes, [Rh(u-NS)X2.(PPh3)]z'

A green solution of (NSCI)3 (O.lg) (ref. 6) in THF(15 ml) was added dropwise to a stirred solution ofRh(NO)CI2(PPh3)iO.2g) in THF (20 ml) orCCI4-CHC13 at 10°C under argon atmosphere. Afterthis addition was complete, the mixture was stirredfor I hr, solvent evaporated under reduced pressureand the residue extracted with benzene. On theaddition of petroleum ether to the benzene extract,a brown complex precipitated out which was washed'with petroleum ether-hexane and water, dried inair, and recrystallized as brown crystals of [Rh(wNS)CliPPh3)]2 (1) (m.p. > 210) from toluene-dichloro-.methane (I: I). The brown crystalline complex[Rh(f'-NS)Br::(PPh3)]2.(2) was prepared by a similarprocedure.