Infrared and raman spectra of tetrachloro- and tetrabromodioxo-uranium(VI) complexes

INORG.

NUCL.

CHEM.

LETTERS

Vol.

10,

pp.

915-923,

1974.

Pergamon

Press.

Printed

in

Great

Britain.

INFRARED AND RAMAN SPECTRA OF TETRACHLORO- AND TETRABROMODIOXOURANIUM(VI) COMPLEXES. A.Marzotto Laboratorio di Chimica e Tecnologia dei Radioelementi del C.N.R., 35100 Padova, Italy. (Received 25 J ~ u a ~

1974)

INTRODUCTION

In previuos papers the preparation and properties of ionic complexes obtained by reaction of uranyl halides with the corresponding halides of substituted ammonium derivatives cations were reported (i-5). The structure of these compounds was shown to be L2UO2X 4 (L=thiamine, acetylcholine; X=CI-,Br -) on the basis of physico-chemical measurements culminating in the X-ray structure determination for [TH]2UO2CI 4 and[AcCh]2UOzBr4 (1,5). Since there are uncertainties and conflicts (6-9) ever the assignment of IR and Raman vibrational frequencies in the[UO2X ~ Z` anion an attempt to compare the spectral features of the[UO2Cl ~ 2. and

02Br 4 Moreover

anions in order

h a v i n g an i d e n t i c a l to investigate the

c a t i o n was u n d e r t a k e n , role of the organic

on t h e same ----IUO2X~2- a n i o n e i t h e r c h o l i n e o r i t s acetylderivative was used as cation and their characteristics compared. In this paper the electronic, IR, Raman and IH NMR spectra of bis(choline) tetrachloro- and tetrabromodioxouranium(VI) are reported in comparison with those found for the same anionic comcation

plexes

of acetylcholine.

EXPERIMENTAL The preparation and a few properties of [TH]2UOzCI4, EAcCI~2UO2CI4 and[AcCh]2UO2Br4 have been already reported (I-Z, 4-5). [Ch]2UO2CI 4 and [Ch]2UO2Br 4 have been prepared by the same Abbreviations: TH=protonated thiamine; AcCh=acetylcholine and Ch=choline. 915

916

Tetrachloro- and tetrabromodioxouranium(Vl) complexes

procedure from choline halide Schuchardt, MUnchen).

(BDH productJ

Vol. 10, No. 10

and uranyl halide

(T.

Elemental analysis is in agreement with CIoH28N206CI4U and CIoH28N206Br4 U respectively, Calcd: C, 19.36; II,4.55; N,4.51; CI, 22.86; U,38.38 - Found: C,19.25; H,4.48; N,4.48; CI,22.80; U,37.98 (m.p. 275°); Calcd: C,IS.05; H,3.53; N,3.51; Br,40.05; U,29.82 Found: C,15.03; H,3.55; N,3.48; Br,39.88; U,29.44 (m.p. 240°). Electronic absorption spectra of the solid compounds on KCI and KBr pellets were registered with a Perkin-Elmer photometer. IR spectra

356 spectro-

(4000-300 cm -I) were taken in Nujol mulls between

CsI plates or in KCI and KBr pellets (Perkin-Elmer 621 spectrophotometer). Far IR spectra (300-80 cm -I) were recorded in Nujol mulls between polyethylene plates (Beckman IR-II spectrophotometer). Raman spectra of the powders were taken on a Jarrell-Ash 25300 spectrometer using a Spectra Physics Model 125A He-Ne laser as exciting source. IH NMR spectra of 8% solutions

in D20 were registered with a

90 MHz Brucker spectrometer. TriMS ( 3-(trimethylsilyl)-propane-lsulfonate ) was used as internal reference.

RESULTS AND DISCUSSION The formation of bis(choline) tetrahalodioxouranium(VI) complexes is supported by elemental analysis, p.m.r., electronic and ir absorption spectra. The analytical analysis, is 4:1.

ratio X:U (X=CI-,Br-),

The visible absorption

recovered by elemental

spectra of the solid ujICh]zUO~X4 comple-

xes are shown in Figure together with the c o r r e s p o n d i n g l A c C ~ 2 U O 2 X 4 The shape, position and intensity of the vibrational structure of the electronic bands are very close to those found by Belyaev et a l (iO) and Vdovenko et al. (ii) for M2UO2CI 4 and M2UO2Br4, where M = (CIOH21)4 N ,respectively. Although the spectral region analysa-

Vol. 10, No. 10

Tetrachloro- and tetrabromodioxouranium(Vl) complexes

400

450

500

I

I

f

550

I

I

I

400

450

500 IB-

550

m

v

am

1 A. n m

Figure. Electronic absorption spectra at 25 ° of the solid complexes on KCI and KBr pellets respectively. a) [AcCh]z~UO~Cl.z ~; b) ~h]vU02Cl4; c) ~ h ] v U O 2 B r A and d) [AcChj2UO2Br4.Absorba~ce is expresse@ in a~bitrary unlts. -

ble for the bromide complexes is limited because the individual contributions are masked by an intense charge transfer 5and ( I ~ the maxima of the fine structure appear to be shifted by 5-10 nm in the direction of longer wavelengths with respect to the chloride complexes;

thus, as observed (ii) an increase in the size

of the anion causes a shift of the electronic transition in the lower frequency direction. At the same time no appreceable change in the position of the vibronic bands of the choline-uranyl derivatives is observed with regard to the acetyl-choline uranyl derivatives,

917

918

Tetrachloro- and tetrabromodioxouranium(Vl) complexes

Vol. 10, No. 10

These data, together with the results obtained by p.m.r, spectra, which indicate no significant difference in the resonance lines of hydrogens of the choline-uranyl derivatives in comparison to the choline alone, support the formation of the tetrahalodioxouranium(VI) complexes. The ir spectrum of the solid choline halide shows a broad -i absorption band at around 3250 cm which is shifted to about 3450 -I cm in the uranyl derivatives here reported. The 3250 cm -I vibration frequency is, very likely, due to the stretching of the alcoholic function of the choline molecule involved in intermolecular hydrogen bonds to form a polymeric association. The shift to 3450 cm

--i

-

in the uranyl-choline derivatives could be interpreted in

terms of destruption of this polymeric association by the complex formation. This is consistent with the lack of change in the O-C-CH 2 absorption frequency at 1050 cm -I which supports the formation of the tetrahalide complexes of uranyl and allows to exclude coordination to the choline molecule. In Table 1 are reported the asymmetric (Q3) and symmetric stretching frequency values of the O-U-O group observed for

('91)

[Ch]2UO2C14 and ICh] 2UO2Br4 together with those of the corresponding acetylcholine-uranyl compounds. As shown, the ~3 vibrational frequency in the ----IUO2Cl~2-anion

[u

]z- furthermoreL an

occur at 4-5 cm -I lower than that in O2Br 4 ; -i increase by 13-14 cm is noticeable within the same

uneglectable

anion on changing the acetylcholine witR the choline cation. The V 3 vibrational frequencies found for ECh]2UO~X4 are just the same reported for M2UO2CI 4 and M2UO2Br 4 (912 cm -~ and 918 cm-l), with M= (CIOH21)4 N , by Vdovenko et al.(ll). An even more remarkable increase (by about 20 cm -I) is observed in the symmetric stretching frequency Raman spectra.

(~i) values measured by

Table 1 shows also the values of the force constants calculated from the asymmetric and symmetric stretching frequencies according to the procedure described by Jones

(13) and the values of U-O

Vol. 10, No. 10

Tetrachloro- and tetrabromodioxouranium(V1)

bond distance using the Bagder's method

complexes

919

(14).

TABLE 1 Vibrational frequencies, force constants and U-O bond distance of tetrahalodioxouranium(VI) complexes. Compound

cCh 2UO2CI 4

~P3

~Pl

FUO o

(cm -I)

(cm -I)

FUO, UO '

(mdy~/A)

(mdyn/A)

RU-Oo (A)

900

826

6.58

-O.149

1.75

LCh] 2UO2C14

913

848

6.85

-0.074

1.74

[Ch] 2UO2Br 4

918

846

6.87

-O.128

1.74

tAn intense line at 824 cm of acetylcholine alone. The

far

iF a n d

Raman

-i

is also present in the Raman spectrum

spectra

of

r- -~ ~ Ch~ 2 U O 2 C I 4 a n d

f- -3 ~Ch~ 2 U O 2 B r 4 ~

together with the corresponding acetylcholine-uranyl derivatives, are shown in Table 2. An attempt of assignment of the vibrational frequencies was made. In all the compounds the strong ir band splitted in the 269-247 cm

-i

region should be assigned to the resolution of the doubly-degenerate UO~ + deformation since vibrational frequencies are present at 264~256 cm -I and 263p252 cm -I both in ~Ch]2UO2CI 4 and i n E A c C ~ U O z B r 4 According to other authors

(8,9), the absorption bands in the 269-,

256 cm -I region could be attributed to the e u U-C1 stretching mode and this should be in agreement with the presence of a hand at Z69-i 260 cm in the Raman spectrum. -i Whereas the resolved ir band shifted to 180-166 cm in the spectra of the bromide complexes is assigned to the U-Br stretching modes 9 the intense vibrational band~ which is also resolved in the

m=medium;

112 s

216 m 208 m

269 m

RAMAN

w=weak;

90 w

115 m

138 w 133 m

212 m

244 m 231 m

266 s

IR

180 s 173 s

206 w 202 w

263 s 252 s

IR

appreciably

100-80 b

173 sh 166 s

254 s 247 s

IR

183 w 163 w

RAMAN

EChl 2UO2Br4

complexes.

with those of the

168 m

198 w 190 w

RAMAN

EAcChl 2UO 2Br4

90-80 b

vw=very weak.

160 m

213 s

230 vw

267 w

RAMAN

LTHI 2U02C14

(300-80 cm-l) m of tetrahalodioxouranium(VI)

b=broad;

205 s

260 m

RAMAN

sh=shoulder;

105 w

137 sh 132 m

238 s 231 s

264 s 256 s

IR

Lch] 2U02C14

spectra

2

"The free ligands, AcCh and Ch, do not show bands interfering complexes both in the far IR region and in the Raman.

s=strong;

97 w

125 m

137 w 132 sh

186 m

214 m

248 sh 241 s

269 s 264 s

IR

EAcCh~ 2U02C14

Infrared and Raman

TABLE

$

9

Vol. 10, No. 10

Tetrachloro- and tetrabromodioxouranium(Vl) complexes

921

248-231 cm -I range and shown by the [UO2CI ~ 2 - anion alone and not by t h e UO2Br4 , s h o u l d s u p p o r t t h e a s s i g n m e n t to t h e U-C1 s t r e t c h i n g v i b r a t i o n modes in a g r e e m e n t w i t h t h e r e s u l t s o f Newbery ( 7 ) . M o r e o v e r , o n l y t h e --'[UO~Cl.| 2 - a n i o n shows a b s o r p t i o n s in t h e 138-i Z-l~J 132 cm and 125-115 cm regions. Newbery (7) and Wong et al. (9) -i assigned the 130-122 cm and the 116 cm -i vibrational frequencies to the e u bending mode of the ~_[UO2CI~ 2- anion. The Raman spectra of the ~~~O2C1412- anion show bands in the 269-260 cm -I, 208-205 cm -I and 124 cm -I regions. Newbery (7) assigned the 270-264 cm -i and 127 cm -i Raman lines to two U-C1 stret~ ching modes, and the 211-203 cm -I to a bending mode. The Raman spectra of the u~FUO2Br~2- anion show lines in the 198183 cm -i and 168-163 cm -i regions. Both Newbery (7) and Wong et al. (9) attributed the 198 cm -I line to the alg U-Br stretching mode and the c ~ 1 6 cm 5 -I line to b2g bending (7) or b2g stretching mode (9)

[

in

the L(CH3)4NJ2UO2Br4 compound~ The remaining lower absorption bands cannot be assigned unambigously because they are either attributed to vibration modes of the ionic species or to lattice modes. The ~2 bending values of the O-U-O group occur in the [JO~Br] 22 4 anion at lower w a v e n u m b e m than in the corresponding LUO2CI~ -,as well as the other ir and Raman lines, on changing the acetylcholine with choline cation. The resolution of the doubly-degenerate UO~ + and U-X v~brational modes points to a lower true point-group symmetry than D4h expecially for the ~~_~IUO2Br4|2- anion (14). Table 3 reports the resolved doubly-degenerate frequencies values (92) of the O-U-O group and the values of the U-O bond distance calculated according to the Ohwada's procedure ( i ~ . The results for U-O bond distance, shown in Table 1 and 3, are in a reasonable agreement with the value found by X-ray structure determination of [TH]2UO2CI 4 (1.78±O.O2 ~ (I) and [AcCh]2UO2Br4 (1.80±O.O3 A) (5). Once more, it is to be remarked that the U-O bond distance varies very little on changing both the equatorial

922

Tetrachloro- and tetrabromodioxouranium(Vl) complexes

Vol. 10, No. 10

halide ligands and the organic cation.

TABLE 3 Bending force constants and U-O bond distance calculated t h e ~ 2 bending frequency. Compound

~P2 (cm -I )

K~

RU_ 0

(mdyn. ~)

(~)

EAcCh] 2UO2C14

269 264

1.034 0.990

i. 86 1.85

EchJ 2u02c14

264 255

0.990 0.912

1.85 1.84

ETH] 2UO2CI 4 a

266

1.OO7

1.85

252

0.887

1.83

254 247

0.904 0.845

1.84 1.83

[Ch] 2UO2Br 4

a. Data reported in ref.

from

(3).

In conclusion, the present results suggest that the four U-X bonds in the ~ O 2 C I ~ 2 - and ~ O 2 B r ~ 2 - anions are not completely equivalent and therefore the U-O bending vibration is resolved. This conclusion seems to be consistent with the observed splitting of the halide-uranium and U-O vibrational modes helonging to two dimensional representations~ and is confirmedobY the X-ray structure analysis (1,5): the U-C1 (2.66 and 2.69 A) and U-Br (2.80 and 2.86 ~) distances are two by two eq~valent. The difference appears to be higher for U-Br than U-C1 owing to, probably, a more pronunced influence of the crystal lattice. In any case a true symmetry at least slightly lower than D4h pointgrpup is indicated for the considered ~ ~~O2CI2~ and -~O?Br41 -- 2anions.

Vol. 10, No. 10

Tetrachloro- and tetrabromodioxouranium(Vl) complexes

923

Finally) assuming that identical r ~LUOaX4jZ_ anions are structurally equivalent an influence of the cation field and a different chemical enviromentshould be postulated in order to explain the change of the vibrational frequencies of the O-U-O and U-X observed when substituting the acetylcholine with choline cation. Acknowledgements.

Thanks are due to Mr.F.Braga and Miss P.Destro for the careful technical assistance.

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AND S.DE JAEGERE,

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