The vibrational spectra of molecular crystals of ferrocene, ruthenocene, osmocene and nickelocene

Journal of Molecular Structure, 19 (1973) 0 Elsevier Scientific Publishing Company,

329-346 Amsterdam

-

printed in The Netherlands

THE VIBRATIONAL SPECTRA OF MOLECULAR CRYSTALS OF FERROCENE, RUTHENOCENE, OSMOCENE AND NICKELOCENE

Ya.M.

KIMEL’FEL’D,

E.M. SMIRNOVA

institute of Elementoorganic Compounds, Academy gorodosk, Podolski Raion, Moscow Obl. (USSR)

of Sciences

of the USSR,

Akadem-

and V.T.

ALEKSANYAN

Institute of Elementoorganic Str. 28, Moscow (USSR)

Compounds,

Academy

of

Sciences

of the USSR,

Vavilov

ABSTRACT

Studies are presented of the infrared spectra (3200-400 cm-’ ) of monocrystal films of Fe (C5H5)2 Ru(C5H5)2; Os(C5H5)2 using polarized radiation, and of the laser-Raman spectra of solid samples of these compounds in the temperature range + 20” to -190°C. The samples were prepared by slow cooling of the melts. The infrared spectra of solid films of Ni(C5H5)2 made by deposition on a cold window, were also recorded. Assignments of the fundamental vibrational frequencies of these molecules are given. The fundamental modes of vibrations which are forbidden by symmetry appear in the spectra of the solid state. The vibrations of species El, and Ezu showed definite site group splitting. At the point of phase transition din the IR spectrum of Fe(C5H5)2 factor-group splitting to give 3-4 components for bands of species Al u and Azu and 6-8 components for bands of species El, and Egu was observed. Factor-group analysis is more consistent with Cl site symmetry of the low-temperature phase of the crystal of ferrocene than Ci, as was proposed earlier. IN‘I’RODUCTION The simple metallo-organic cene compounds have been studied intensively during the last fifteen years by spectral methods. The spectra of ferrocene has been investigated the most thoroughly. Lippincott and Nelson1 have assigned the fundamental vibrational frequencies on the basis of the infrared and Raman spectral data for fexrocene and its deuterium derivatives, and have calculated its thermodynamic functions. The normal coordinate treatment of ferrocene has also been carried out by Mayants et al. 2_ Winter et al. 3

330

have obtained the infrared spectrum of a single crystal of ferrocene using polarized radiation_ They observed some vibrational bands of symmetry species A,, and E,, which were not found in vapour and solution spectra, and site-group splitting for two doubly degenerate vibrations (850 and 1055 cm-l). Later the laser-Raman spectra of ferrocene and ferrocene-d10 were studied by Long and Huege4, and Bailey 5. These investigators confirmed the vibrational assignment of Lippincott and Nelson1 with one exception: the E,, C-C stretching mode was reassigned from 1560 to 1356 cm-l_ Finally, Bodenheimer et al. 6, while investigating the laser-Raman spectrum of a single crystal of ferrocene, observed the splitting of_ a number of the bands at a phase transition below 169” K, but they did not come to any conclusions about the change of the crystal structure of ferrocene at its phase transition. The vibrational spectra of ruthenocene have not been investigated in detail. The first assignment of the spectrum of ruthenocene was given also by Lippincott and Nelson 1. Recently, Bodenheimer 7 investigated the laserRaman spectra of a single crystal of ruthenocene at room temperature and at 80°K. He also suggested reassigningthe C-C stretching mode vZ6 E,,. There is as yet no detailed analysis of the spectra of osmocene and nickelocene in the literature. According to X-ray data, the space group symmetries of ferrocene and nickelocene differ from those of ruthenocene and osmocene8yg. Moreover, cene molecules are located at sites of lower symmetry than those of the free molecules. Therefore, we have carried out comparative investigations of the vibrational spectra of these four cenes as melts and in the solid state, different temperatures being used in order to obtain new data on the fundamental frequencies of these molecules and their lattice structure.

EXPERIMENTAL

Monocrystalline films of ferrocene, ruthenocene and osmocene of thickness 0.001 mm were grown between KBr plates in a special furnace lo; at the same time the IR spectra of the melts were measured, the first time this has been done. The cooling of the samples was carried out in a metal cryostat. The solid film of nickelocene, on the other hand, was made by deposition of the compound on a cold window. The IR spectrum of the ferrocene film deposited at liquid nitrogen temperature was identical to its spectrum obtained with the cooled melt. IR spectra were obtained with a Hitachi-225 spectrometer, the resolution being better than 2 cm-l. Raman spectra of polycrystalline samples, also grown in special tubes from melts, were studied with a Coderg Raman spectrometer. Spectra were obtained at room temperature and at 80°K with a He-Ne laser. The cene compounds investigated were obtained and purified by the methods given in refs. 11 and 12.

0

1052 1047 1044 -=G

1066 1062

P/d

(%)

Transmission

Transmlsslon

/

--s

6 ??

ai 8

,

644

654

1055 1045

t

Transmission

<

Transmission

P/d

P/d

I

6

::

a

z

332

antisymmetric vibration must have almost the same frequency. In fact Lippincott and Nelson 1 have concluded that the coinciding of the symmetric and antisymmetric modes involving displacements associated with the cyclopentadienyl rings are explained by their low degree of interaction. The spectrometer with better resolution did in fact allow us to observe a site group splitting (Fig. 1). The polarization effects in the monocrystal sample of Winter et al. 3 and in our films at room temperature are very slight. Winter et al. 3 have concluded that every antisymmetric vibration of ferrocene contains two factor group species A, and 23, of equal intensity, which is the consequence of the orientation of ferrocene molecules in a unit cell. The IR spectrum of ferrocene changes drastically at the points of phase transition, 158.0” K and 167.8% (ref. 13 gives the values 163.9”K and 169°K). After phase transi170

1241

mi’OC

860

840

I

I

cm4

C

Fig. 3. Polarization

spectra of ferrocene

at liquid nitrogen temperature.

1350

Fig. 4. Polarization

spectra of ruthenocene

at room temperature.

cm-1

333

tion the majority of bands undergo further splitting. The clearest pattern of splitting is observed near liquid nitrogen temperature; so the band at 816 cm-l (Vg,Azu) is split into four components: 806, 818, 823, and 834 cm-l (Fig. 2) and the band at 1255 cm-1 into three components. Both components of site splitting of the band at 1050 cm-l are split in turn into three components as seen in Fig. 2. The observable components have the oppositive polarization (Fig. 3). Thus the splitting observed is Davidov splittingl*. Edwards et al. l3 have measured the heat capacity of ferrocene in the region from 125°K to 200”K, and the X-ray diffraction of its single crystal at different temperatures_ The phase transition was classified as being if the X type. The authors have concluded that no gross change of the structure takes place at the phase transition point. It was suggested that the position of ferrocene above the phase transition point might consist of a mixture of two staggered arrangements, or alternatively of a mixture of one of the staggered configurations with one of the eclipsed forms, but that the low-temperature arrangement was a completely ordered lattice of staggered molecules. Unfortunately, it was not possible to confirm this suggestion since crystal distortion on cooling prevented a complete -analysis of the low-temperature structure. Our results contradict the conclusions of Edwards et al. l3 as the factorgroup analysis for two molecules in a unit cell with site symmetry Ci predicts only two components for non-degenerate vibrations, and four components for degenerate vibrations. In fact we observed the existence of twice as many components. The probable reasons for this are either that the unit cell comprises more than two molecules, or the site symmetry is Cl. However, results of the X-ray investigation10 indicate that there is no evidence of a sharp discontinuity in the unit cell constants at the phase transition. Therefore, one can accept the lowering of site symmetry to C, . It should be noted that the site symmetry C1 corresponds not only to the space group symmetry C2h, but also to C,. The spectral data are not in complete accordance with site symmetry C,, as the rule of mutual exclusion holds in all the regions of IR and Raman spectra. It is possible, however, that the forbidden bands of ferrocene are too weak to be observed in the crystal spectra. In fact the same picture is observed in the spectra of ruthenocene and osmocene, which have site symmetry C,. In the Raman spectra of the low-temperature phase of ferrocene neither we nor Bodenheimer 6 observed so many components in the bands. Apparently this is due either to the lower resolution of the Raman spectrometer or to the smaller value of Davidov splitting for Ramanactive vibrations. NICKELOCENE

The IR spectrum of a nickelocene film deposited at the temperature of liquid nitrogen contains half the number of components that ferrocene has. Such splitting is in accordance with factor-group analysis for the space group

334

ll\-

A

1095(m) 1105(s)

1176(w) 1190(w)

I, II I, II

I, II I, II

1095(m) 1105(s)

1176(w) 1190(w)

1110(s)

1185(m)

I, II I, II

I, II I, II

V31(E2~)

I II II>1 I<11 I>11 I, II

1044(s) 1047(w) 1052(s) 1069(m) 1062(vw) 1066(s)

I, II I, II

1046(w) 1055(w)

1068(m)

1096 (vs) 1102(m)

1058(m)

hb%l)

I, II I, II

995(s) 1005(s)

I, II

1002 (I)

1097 (m) 1102(m)

1050(w) 1060(s) 1065 (s)

1000(m)

V30(E2u)

V364,g)

VlO(A2ll)

v2 dE2g)

v, &!)

v2 7@2g)

1005 (6)

997(m)

900(m)

v33b%J

I, II I, II I, II

872(w) 882(w) 888(w)

I, II I, II

882(m) 902 (m)

336

h

J

s

337

338

I, II I, II I, II

1178(s) 1191(vw) 1199(vw)

I, II I, II

1176(m) 119O(vw)

1180(w)

I I I>11

1093(m) 1098(w) 1103(s)

1095(w) 1105(m)

1110(s)

I, II I, II

I, II

1075(w)

II I, II II I I I, II

1049(s) 1054 (w) 1057 (s) 1062(w) 1067(m) 1076 (m)

II II I

1049(m) 1053(w) 1065(w)

1050(w)

1185(m)

1100(s)

1045 (m) 1062(m)

1169(w) 1176(w) 1184(m) 1194(m) 1203(m) 1208(m)

1092(m) 1099(m) 1101(s)

1049(w) 1062(s) 1065(s) 1068 (9)

1g)

V24P2,)

V30(E2,)

WA

VlOb424)

ME2g)

V31(E2u)

Monocrystai 1246(w) 1255(s) 1342(s) 1365(w)

1394(w) 1405(s)

3074(m) 3083 (s) 3092(w) 3097(w) 3102(w) 3112(w)

I<11 I, II I, II

I>11

I II

I I, II

1252(s)

1340(w) 1365(m)

1405(s)

3074(m) 3084(s) 3090(s)

3101(m) 3108(m)

i340(wf

lliOS(s)

308!(s)

T = 77°K Polarization

T = 20°C

Monocrystal

Melt

XR’sp&a (cm-‘)

TAJ+E 2 (continued)

I>II I, u I>11 I, II I>11 I, II

I I, II

II>1 II I

Polarization

3109(w)

3100(s)

3090(w)

3075 (w) 3080(s)

1402(m)

1357(m)

Polycrystal

T = 20°C

-

3076 (w) 3083 (m) 3085(m) 3092(w) 3098(m) 3102(s) 3104(m) 3112(m)

1404(m) 1407 (m) 1411(w) 1414(m)

1359(m) 1365(m)

Polycrystal

T = 77°K

Raman spectra (cm-’ )

v2 3tE2&

v2Q(E2,)

V8(A2,)

w%J

VI&g)

v2o%J

V26@2g)

V32(E2u)

WA 1u)

Assignment

806(m) 814(w) 818(w) 822(w) 836(s) 838(s) 852(s) 860(m) 868(w) 872(m) 880(s)

I, II I, II I, II I, II I, II I I I>11 II

874(s) 874(m)

868(m)

856(w)

520(w) 526(w) 540(w)

I, II

532(w)

852(w) 870(s)

460(w) 484(w)

I, II

488(w)

814(w) 818(w) 832(s) 838(w) 846 (s)

416(m) 422(m) 436(s)

Monocrystal

I, II

Polarization

T = 77°K

430(c)

Monocrystal

824(s)

424 (VW)

Melt

T = 20°C

IR spectra (cm-‘)

TABLE 3 Infrared and Raman spectra of osmocene, OS(C+H~)~

I>11 II>1

I>11

I I<11 I, II I

I, II I, II I, II

I, II I, II

I, II I<11 I, II

Polarization

408(s) 411(w) 413 (s)

408 (s) 412(s)

597(w) 600(m)

356(s)

360(s)

600(m)

Polycrystal

T = 77°K

Polycrystal

T = 20°C

Raman spectra (cm-’ )

lb42u)

Vl9(W

V9@2,)

v2 fdE2,)

v2 IPI,)

V34(E2,)

v,

V16(El,)

V4W1,)

Assignment

992(w)

996 (vs)

1050(m)

902(m) 925(m)

1048(s) 1063 (8) 1059(m) 1062(w) 1064(w)

998(s)

896(m)

902(s)

Monocrystal

T= 20°C

‘90!(m) 924(m) 938(w)

Melt

IR spectra (cm-‘)

TABLE 3 (continued)

I<11 I I, II I, II

I I<11

1048(m) 1063(s) 1059(vw) 1063 (s) 1067(m) 1073(w) 1076(m)

I<11 I I, II I

I I II II I

990(w) 998(w) 995(w) 1000(s) 1004 (s)

I, II I, IX

I I, II I I>11

Polarization

899(m) 905(m) 914(w) 930(s)

Monocrystal

I>11 I>11 I, II

Polarization

T = 77°K

1049(w) 1060 (m)

991 (w) 996 (m) 1003(w)

1049(w) 1060(s) 1065(w)

991(m) 1000(s)

850(m)

850 (s)

900(w)

Polycrystal

T 177°K

Poiycrystal

T = 20°C

Raman spectra (cm”“‘)

l(E2lJ)

v2st*2g1

v,

V,,(J%gI

Vl2v4u)

v2 7vGg)

V33v4,~

~14bQJ

Assignment

139S(vs)

1340(w)

1096 (vs)

1337(m) 1340(w) 1342(s) 1366(w) 1362(s) 1364(m)

ICI1 I I>11

I>11

1336(w) 1341(s) 1367(w)

1376 (w)

1410(w)

I>11

1236(m) 1245(w) 1256(m)

I<11 I, II I, II

1230(m) 1240(m) 1266(m)

1393(m) 1396(w) 1400(s) 1398(w) 1406(s)

1180(m) 1195(m)

I, II I, II

1180(w) 1190(w)

1395(s)

1089(s) 1091 (w) 1096(w) 1098(s)

I<11 I<11 I

1089(m) 1098(m) 1096 (6)

I, II

I>11

I I I<11 I>11 I>11 I<11

I, II I>11 I>11

I, II I, II

I II I I< II

1362(m)

1190(w)

1092(w) 1096(s)

1362(m) 1366(w)

1190(w)

1092(w) 1096(s)

v2ob%l)

v2 #32&J

V,,(E,IJ

wAhl)

‘24tE2,)

V3Ov32”)

WA lg)

bob42,)

308O~vs}

Melt Monocrystal

3070(s) 3080(m) 3084 (s) 309O~s} 3104(s) 3112(s)

Polarization

I I>11 II I II

3074(m) 3086(m)

3092(m) 3104(w) 3112(m)

T = 77°K

Mono~~6t~

T = 20°C

IR spectra (cm-” ]

TABLE 8 (co~t~nued~

I>II I>11 I, II

I>II I>11

Polarization

3075(m) 3084{m~ 3088(w) 3092(w) 3104(s) 3113(m)

309O~w~ 3109(w)

1410(s) 1400(s)

1410(s)

3075(s) 308O(w~

Polycrystal

T = 77°K

Polycrystal

T = 20°C

Raman spectra (cm-’ f

%(A,,)

Vl,b%,)

v2 3iE26’)

t’29VW

~1’Iv-h)

v, svG,)

Assignment

345 TABLE 4 IR spectra of nickelocene (cm-‘), Polycrystal, T = 20°C

Ni(C,H&

Polycrystal, T = 77°K

500(w)

500(w)

776(s)

774(s) 780(w)

810(s)

804(s) 808(w) 810(m)

842(w)

840(w) 842(m)

Assignment v34(E2

u)

V9W2u)

V,d%t)

1000 (s)

998 (w) 1000(s)

1052(m)

1048(w) 1053 (m) 1056(m)

1110(m)

1098(w) 1110(m)

V,.(dz,)

1252(m)

1250(w) 1252(m)

Vs(A,,)

1335(w)

1335(w)

V32(E2,)

1422(m)

1422(m)

Vzo(~1,)

3075(m)

3070(s) 3080(m) 3084(s) 3090(s)

3085(m)

3104(s) 3112(s)

V12WlU) V3,(E2,)

VI7vw

v29tE2,)

346

symmetry of nickelocene at room temperature. Investigation of crystals allowed us to observe experimentally the vibrations of species E,, and A, u, forbidden in the IR spectrum of free nickelocene (Table 2). The same is true for the vibrational spectra of ruthenocene and osmocene (Tables 3 and 4). RDTHENOCENE

AND OSMOCENE

The vibrational spectra of ruthenocene and osmocene crystals are similar; this is because they have the same unit cell symmetry. The IR spectral bands of ruthenocene and OS; scene suffer site group and factor group splittings even at room temperature. In contrast to ferrocene the components of the site group splitting have different polarization. This character of the spectra conforms to site symmetry CS with symmetry plane au. In such a case the components of site group splitting of degenerate vibrations correlate with the different symmetry species A' and A" and, therefore, have different polarization. REFERENCES 1 2

3 4 5 6 7 8 9 10 11 12 13 14

E.R. Lippincott and R.D. Nelson, Spech-ochim. Acta, 10 (1958) 3307. L.S. Mayants, B.W. Lokshin and G.B. Shaltuper, Opt. Spektrosk. 13 (1962) 3317. W.K. Winter, B. Cumutte and SE. Whitcomb, Spectrochim. Actu, 12 (1959) 1085. T.V. Long and F.R. Huege, Chem. Commun., (1968) 1239. R.T. Bailey, Spectrochim. Acta, Part A, 27 (1971) 2199. J. Bodenheimer, E. Loewenthal and W. Low, Chem. Phys. Left., 13 (1969) 9715. J. Bodenheimer, Chem Phys. Lett., 6 (1970) 5519. B.G.L. Hardgrove and D.H. Templton, Acta C~ysfaZZogr., 12 (1959) 28. F. Jeliinek, 2. Nuturforsch. B, 14 (1959) 737. Ya.M. Kimel’fel’d, M.A. Moskaieva, G.N. Zhizin and W.T. Aleksanyan, Zh. Strukt. Khim., ll(l970) 4656. T.J. Koaly and P.L. Pauson, Nature, 168 (1951) 1039. A.F. Plate, in MS. Newman and J.D. Roberts (Eds.), Organic Syntheses, Vols. 40,41, 1960-1961. (Russian translation, Vol. 12, Mir, Moskow, 1964). 1-W. Edwards, G.L. Kington and R. Mason, Trans. Faraday Sot., 56 (1960) 5. Ya.M. Kimel’fel’d, M.A. Moskaleva, G.N. Zhizhin, W.P. Litvinov, S.A. Osolin’ and Ya.L. Gol’dfarb, Opt. Spektrosk., 28 (1970) 1112.