INDIAN J. CHEM .• VOL. 15A. OCTOBER 1977

complex) and 10'72% (for ~-nitroso complex)]. Themass loss data for the second stage of decompositioncorrespond to the conversion of the compound tothe residue Mn304 [Mass loss: Calc.: 83'37%.Found: 84'13% (e-nitroso complex) and 84'07%(~-nitroso complex)].

References1. GURRIERI. S. & SIRACUSA. G .• Inorg, chim. Acta, 5 (1971).

650.2. AMSTUTZ. HUNSBERGER. & CHESSICK,]. Am. chem,

Soc .• 73 (1951). 1220.3. DUTTA. R. L.. J. Indian chem. Soc .• 44 (1967). 381.4. JONASSEN. H. B. & DE MONSABERT. W. R.. ]. Am.

chem. Soc., 76 (1954). 6025.5. PATIL, S. V. & RAJu. J. R.. Indian J. Chern.• lZ (1974).

770.6. CHRISTENSEN. O. T.. Z. anorg, Chern.• 27 (1901). 325.7. NYHOLM. R. S. & SHARPE. A. G.• ]. chem. Soc., (1952),

3579.8. Cox, B. & SHARPE, A. G., J. chem. Soc., (1954), 1798.9. FIGGIS, B. N. & LEWIS, J., Progress in inorganic chemis-

try, Vol. 6 (Irrterscience Publishers, New York), 1964.10. NAKAMOTO, K., Infrared spectra of inorganic and co-

ordination compounds (John Wiley, New York). 1962.11. RAY, M. M .• DHYA. J. N. & PODDAR, S. N" Aust. J.

cu«,» (1966), 1737.

Molecular Association of PlatinumAcetylacetonate with Halogens

R. SAHAI* & V. N. BADONI

Department of Chemistry, V.S.S.D. CollegeKanp ur 208002

Received 9 September 1976; revised 9 February 1977;accepted 19 May 1977

Complexation of platinum acetylacetonate, Pt(acac).,with molecular halogens has been studied on the basisof infrared and electronic spectral measurements.Adducts of the type, Pt(acac).,X2 (X = Cl, Br or I),have been isolated in solid state and characterized.Possible geometries of these adducts have beendiscussed and a synergistic bonding scheme has beenproposed which involves It-donation from the highestoccupied MO orbital of the halogen molecule (It') toan empty d"", or dys orbital of the platinum togetherwith back a-donation from a filled d,,· platinum orbitalto the lowest empty MO of the halogens (a*). Theinteraction of Pt(acac). with 12 in CCI, has beenstudied spectrophotometr+cally at 25° and the forma-tion of a Charge-transfer complex has been proposedwith I..CT= 295 om and blue shifted iodine band at445 nrn,

MOLECULAR complexes of the donor-acceptortype have evoked considerable interest! during

the last two decades. The unexpected stabilityof some of the water insoluble metal acetylaceto-nates has been explained partly on the basisof benzenoid structures of the chelates=". Thesechelate rings show an important test for pseudo-aromaticity by undergoing electrophillic substitu-tion reactions with a variety of reagents2-I2. Re-cently Singh and Sahai+' have demonstrated that

*To whom all the correspondence should be addressed,

916

like aromaticsw-!", coordinatively saturated, neu-tral. monomeric metal acetylacetonates, Be(acacill'Al(acach. Sc(acacia. Zrjacac}, and Th(acac)4. formmolecular complexes with iod me , chelate rings actingas the electron donors. The results of our studieso,n the molecular association 01 halogens with pla-tinum acetylacetonates are reported in this note.

Platinum acetylacetonate, Pt(acac)2' reacts rapidlywith chlorine, bromine or iodine to torrn 1:1 mole-~ular complexes -. Pt(acach,X2 (X = 0. Br or I).III various organic solvents, The solid complexeshave, been isolated by mixing concentrated CUtsolutions ot pt(acac)2 and the respective halogenin a 1:1 molar ratio at room or lower temperatures.The products precipitated rapidly and almost quan-titat,ively from solution. The compounds readilysublime and have been characterized on the basisof elemental analysis and infrared spectra.

The infrared spectra of the solid compooundswere recorded in the region 4000-250 crrr! usingKBr discs. The electronic spectra were measuredon a Cary 14R spectrophotometer in the region250-700 nrn. Pttacacj, was prepared as reportedin the literature:". All the solvents used were ofspectroscopic purity grade,

The infrared spectra of the three compounds.Pt(acac)2.X2. are closely similar to each other andalso to that of pt(acac)2I7• except for four bandsthree in the region 1500-1000 ern+ [possibly due t~Pt(Clacac)2 and Pt(acac)(Clacac) impurities] andone at 362 and 316 cm-I exhibited by the chlorineand bromine compounds respectively. These datastrongly indicate that the three halogen complexeshave similar structures and that each contains anapproximately planar Pt(acac)2 moiety. The 316crrr- band in the bromine complex probably resultsfrom a predominantly \lBr-Br mode. Molecularcomplexes of Br2 with various Lewis bases exhibitan infrared active \lBr-Br mode around 300 crrr"(ref. 18). The chlorine compound does not exhibita band around 500 cnr! as expected in analogy withthe bromine compound and other molecular com-plexes at chlorine-". However. the predominantly\lO-Cl, mode might be masked by the vPt-017occurrmg at 485 crrr+, The band at 362 em? in thechlorine complex possibly results from a predomi-nantly \lPt-CI mode!". \11-1mode was not observedbut it would not be expected to lie above 250 crrr+,

The interaction of molecular halogens withPtjacac}, in solution was studied spectrophotometri-cally in the region 250-700 nm. Unfortunately in thesystems containing C12 and Br2, some halogenationot .the chelate rings occurs". No such complicationexists In the 12 system. At 25° addition of I to asolution of Ptfacac), in CCl4 [Pttacacj, = i-0-2'5xlO-5M. 12= 0'5xlO-q'Oxl0-3M] results in th.rapid appearance of intense bands at 295 and 445nm together with a band at 517 nm due to free I .Analysis of this data shows that a 1:1 complex isformed according to the reaction:

Pt(acac)2+ 12~Pt(acac)2.12

The equilibrium constant for this reaction has beenestimated to be 5'5xl04 litres mole:". No othercomplexes could be detected. The pt(acac)2.1t

NOTEScomplex rapidly reacts with excess EtaN to giveEtaN.I2 and with Bu4N to give the 13 ion in CCl,.All these data indicate that the iodine in thept(acac)2.12 complex is present in the molecular(12) form.

The electronic spectrum of pt(acac)2.12 in CC1,shows bands at 295, 325 (sh), 360 (sh) ano 445 nmwith Emax values 01 40600, 9890, 6250 and 12500 litresmole! crrr+ respectively. The solid state spectrum(nujol) shows bands at 292, 343 (sh) and 476 nm.The most interesting bands of the complex are thetwo high intensity bands at 295 and 445 nm. Theoscillator strengths] of both the bands are very high(jU5 = 0·665 and 1'45 = 0·155) which indicates thatthey result from strongly allowed transitions. The295 nrn band is probably due to a charge-transfertransition of a non-bonded platinum electron tothe lowest empty MO of iodine. The' band at 445nm may be due to the blue shift of the locally excited12 band present at 517 nm (in CC14). The largemagnitude of the oscillator strength (J445 = 0·155)and the heat of formation (-tlH = 5·66 kcal/mole):j:are both consistent w.th the appreciable stabilityof the Pt (acac)2.I2 complex.

The interaction of halogens with Pt(acac)2 isprobably not of the same type as reported by usIain the case of some other metal acetylacetonatesand iodine. In the first place the stability of thep~(acac)2.Iz complex is about 20 times greater thanthose of the most stable complexes of iodinereported earlier-", Moreover, the charge-transferbands of M(acac)n.lz (M=Pt), complexes all lie inthe narrow range of 350-370 nm'". These transitionsare distinctly different from the higher energy transi-tion in the case of pt(acach.12 at 295 nm.

It may be proposed that Pctacac), chelate ringsdo not act as electron donors in the presentcompounds which may instead have structures ofthe type (I) in which a linear pt-X-X arrangementcoincides with the principal axis of pt(acacl2 mole-cule. This is corroborated by the fact that thevBr-,Br band in Pl(acac)2.Br2 occurs at 316 em?which is identical with vBr-Br of free bromine. Thisstrongly suggests that Br2 and possibly C12and 12also bond to platinum by synergistic bonding. Aplausible bonding scheme involves -e-donation fromthe highest occupied MO of the halogen molecule(7t*) to an emptY'dxz or dyz orbital of the platinumtogether with back a-donation from a filled dz• Ptorbital to the lowest empty MO of the halogen (a*).

A detailed spectral study of acetylacetone-Lsystem in CCI, is in progress. Preliminary conduc-tomet ric and electronic s')ectral measurements ofthis system have indicat~d charge-transfer inter-action between iodine and acetylacetone but thesite of charge-transfer has not yet been absolutelysettled. A saturated solution of iodine in acetyl-acetone (0·4M in CC14) gave the NMR spectrumwhich is almost similar to the spectrum of acetyl-acetone except (i) low field shift in signals due to

tThe oscillator strengths have been calculated from theapproximate equation, f = 4·318 X 10-9 ernax ~\l112.

tThe heat formation (- ~H) of the complex was calcu-lated from the blue shifted iodine band (Ama:.: = 445 nm)using Ham approximation".

CR3

-OH, =CH-, -COCHa and =( protons ando

CH3

(ii) splitting of the -COCH3 and =< protons.o

These observations have recently been interpreted-"in terms of charge-transfer from the acetylacetonering to the anti bonding a*-orbital of iodine. How-ever, there is no distinct possibility of charge-transferin the present system from ketonic oxygen atomsbecause no effect on vC-'-'-'Omode was noticed. Wealso investigated the Pd (acac)z-12 system whichwould have probably behaved as the platinum systemif the iodine was bonded to chelate ring (s). How-ever, no interaction was detected between Pd(acac)2and 12 in CC14•

The authors are grateful to Prof. P. R. Singh,lIT, Kanpur, for providing necessary facilities andhelp during these investigations.References

1. (a) MULLIKEN, R. S. & PERSON, "V. B., Molecular com-plexes - a lecture and reprint volume (Wiley, New York),1969; (b) FOSTER, R., Organic charge transfer complexes(Academic Press, London). 1969; (c) YARWOOD, J.,Spectroscopy and structure of molecular complexes(Plenum Press, London), 1973; (d) ROSE, J., Molecularcomplexes (Pergamon Press, Oxford), 1967; (e) ANDREWS,L. J. & KEEFER, R. , Molecular complexes in organicchemistry (Holden-Day, San Francisco). 1964;(f) BRIEGLEB, G., Electronen-dmuitor-acceptor kom plex«(Springer-Verlag, Berlin), 1961.

2. COLLMAN, J. P., Adv. chem. Ser., 37 (1963). 78.3. COLLMA~, J. P., Angew Chern. Intern. Edn, 4 (1965). 132.4. COLLMAN, J. P., Transition metal cu«, 2 (1966). 1.5. SINGH, P.R. & SAHA!, R., Aust. J. Chem., 20 (1967), 639.6. SINGH, P.R. & SAHAI, R., Ausi. J. cu«, 20 (1967), 649.7. SINGH, P. R. & SAHAI, R., Lnorg, nucl. chem, Lett., 4

(1968), 513.8. SINGH, P.R. & SAHAI, R.,Inorg. chem. Acta, 2 (1968),102.9. SINGH, P.R. & SAHAI, R., Aust. J. Chem., 22 (1969). 263.

10. SINGH, P.R. & SAHAI, R., Indian]. cu-«, 7 (1969), 628.11. SINGH, P. R. & SAHAI, R., Aust. J. Chem., 22 (1969).

1169.12. SINGH, P. R. & SAHAI, R., J. Indian chem. Soc., 46

(1969), 945.13. SINGH, P.R. & SAHA!, R., Aust, J. Chem., 23 (1970). 269.14. BENESI, H. A. & HILDEBRAND, J. H., J. Am. chem. Soc.,

71 (1949), 2703.15. MULLIKEN, R. S., J. Am. chem, Soc., 72 (1950), 500,

4493.16. GRINBERG, A. A. & CHAPURSKII, I. N., Russ. J. inorg,

Chem. (Eng. Trans.), 4 (1959). 137.17. NAKAMOTO, K., Infrared spectra of inorganic and co-

ordination compounds (Wiley-Interscience, New York),1970, 247; NAKAMOTO, K., UDOVICH, C. & TAKEMOTO,J., J. Am. chem, Soc., 92 (1970). 3973.

18. MULLIKEN, R. S. & PERSON, W. B., Molecular complexes- a lecture and reprint volume (Wiley, New York),1969, 59 and references cited therein; FOSTER, R.,Organic charge transfer complexes (Academic Press,London), 1969, 94 and references cited therei n.

19. HAM, J., J. Am. chem, Soc., 76 (1954), 3875.20. SAHAI, R. & BADONI, V. N. (unpublished results).

917