The vibrational analysis of some potassium salts

Journal of Molecular Structure. 63 (1980) Q Elsevier Scientific PubIishing Company,

THE VIBRATIONAL

H. 0. DESSEYN,

ANALYSIS

B. J. VAN

13-24

Amsterdam -

OF SOME POTASSIUM

DER VEKEN,

A. J. AARTS

Labomtorium Anorganische Scheikunde, Rijksuniversitair Groenenborgerlaan 171, B 2020 Antwerpen (Belgium)

(Received 18 April 1979;

Printed in The Netherlands

SALTS

and M. A. HERMAN Centrum

Antwerpen,

in final form 30 May 1979)

ABSTRACT The IR, far-IR and Raman spectra of products with general formula X-COOK (X = -CONH,, -CONHCH, and -CSNH,) and the N-deuterated derivatives have been recorded, the fundamental vibrational frequencies assigned, and a valence force field calculated.

INTRODUCTION

In previous studies we have reported the vibrational analysis of a number of simple amides and thioamides [l-7] ; in this article we discuss the vibrational analysis of some products in which the amide or thioamide group is linked to a carboxylate function. Several vibrational analyses have been carried out on the simple salts X-COOK (X = H [S], CH2 [l, 9, lo], COOK [l, 11,123 and COOCH3 [13]) but little work appears to have been done on the compounds under investigation, though Wallace and Wagner [ 141 have recently published the IR spectra of oxamic acid, deutero oxamic acid and their salts. No discussion of the alkylated or thio compounds has been given, In general, the spectra show a number of bands which are easily recognized as characteristic features of one of the functional groupings present in the molecule. In such cases and for the sake of brevity, no complete discussion of the assignments will be given. STRUCTURE

Beagley and Small [15] have shown that the oxamate anion in ammonium oxamate is planar; no further structural work on the abovementioned compounds has been published. We have investigated -OOC-CONH, and -OOCCSNH, using CNDO/2 theory. Cartesian coordinates were calculated using standard bond lengths [l] and idealized valence angles, with planar amide and thioamide functions:Energies were calculated as a function of the dihedral angle between the carboxylate

11

and amide groups, and as a function of the C-C bond length. For both molecules, minimum energy was obtained for + = 90”, i.e. with the functional groups at right angles. The barriers to rotation around the C-C bond are 17.7 kJ mol-’ for the amide and 32.8 kJ mol-’ for the thioamide. The C-C equilibrium distances are 147.4 and 145.3 pm, respectively. This result is clearly in disagreement with the data given in ref. 15. It should be kept in mind, however, that the results were obtained with the molecule in completely different chemical surroundings_ The calculations suggest relatively low rotational barriers, so it is not impossible that the discrepancy could be explained on the basis of environmental effects. No reliable prediction of the solution conformation of the compounds can be made using these results. Some indications about the conformation may be obtained from the Raman solution spectra using symmetry considerations. An accurate study of the Raman solution spectrum of KOOCCOND, in DzO in the 1700-1600 cm-’ region was therefore carried out. The spectra were recorded in DzO to avoid the 6NH2 which gives rise to a band near 1600 cm-‘. Three bands appear in the region under consideration: at 1703 cm-’ (2 X z&C), 1667 cm-’ (vCO amide) and 1638 cm-’ (Y,,CO~-). For the model with 0 = 903 symmetry considerations show that v,,C02- must be completely depolarized, while for any other conformation the band may be polarized. The depolarization ratio however cannot be measured easily because in all cases v,,COZ- is strongly overlapped with other bands. The Ivv and Ivn components of the scattered light were measured individually under carefully controlled laser intensity conditions, using a spectrum digitizer and a tape punch. A band profile analysis was then performed for each spectrum, using Gauss-Lorentz sum functions. Despite the very strong overlap between vCO and z+&OZ-, especially in the I, spectrum, v&O,- is cal1 cm-‘), culated to lie at the same position in both the I vvandIvHspectra,(Av< which indicates the reliability of the analysis. The results are shown in Fig. 1. Using a similar analysis for the depolarized bands of Ccl4 in the same region of the spectrum, a calibration curve could be constructed [16]. This curve was used to correct the measured depolarization ratios for divergence and other instrumental effects. The results obtained are shown in Table 1. From this it is clear that the band at 1638 cm-’ has p = 0.478, far below the theoretical maximum of 0.750, showing that this band is polarized. Therefore, the dihedral angle in carboxy-amide in aqueous solution cannot be 90”. It would be expected that the depolarization ratio for conformations with r#~ close to 90” should approach 0.750; the clear evidence of polarization thus indicates that the dihedral angle is at least closer, if not equal, to O”. The experimental values of X(n + n*) and vCC for simple thioamides indicate that an elevated h (n + ?r*) value generally corresponds to an increased vCC, indicating some conjugation over the CC bond [5]. From the data given in this article it is clear that conjugation is present in KOOCCSNH, and KOOCCSNHCH3, indicating a planar structure for both molecules. The results given above and use of molecular models, allow us to conclude

15

Fig. 1. Experimental and simulated Raman spectra of KOOCCOND, in D,O solution. A: experimental IVV spectrum; B: experimental [VH spectrum; C: simulated ZVV and IVH spectra. TABLE 1 Depolarization

ratios

vf cm-’ )

Assignments

P

1638.0 1667.5 1703.3

vasco,UC0 2xLCc

0.478 0.239 0.069

that the earboxylates under investigation can be assumed to exist in a planar

conformation. As the number of polarized Raman bands does not exceed the number expected for a C, symmetry in any of the compounds investigated, the all-planar geometry was accepted in every case.

16 EXPERIMENTAL

The IR spectra were recorded on a Perkin-Elmer 580 grating instrument using KI-pellets and nujol mulls, which produced identical spectra. The KI pellets of the deuterated compounds were prepared in a dry box flushed with dry nitrogen. The far-IR spectra were recorded on a Beckman-RIIC FS 720M spectrometer as nujol mulls on polyethylene windows. The Raman spectra were recorded using a Coderg PHO equipped with a Spectra Physics model 164 argon ion laser. Liquids were contained in standard 300 ~1 cells and solids in capillaries. The valence force field was obtained with the matrix polynomial expansion model [ 171, using standard bond lengths [l] and the frequencies observed in the solution spectra, where possible. As detailed studies [18] on amides [ 151 have shown that the coupling between normal modes localized in methyl groupings are small, the methyl group in KOOCCONHCHJ was treated as a point mass. No F-matrices will be reproduced due to restrictions in space. Only contributions

to the PED greater than 5% are listed.

KOOCCONH2 was prepared by titrating HOOCCONHz (Aldrich o-920-4) with KOH; the product started to crystallize on adding alcohol to the aqueous solution, giving colourless crystals. Elemental analysis: Calculated (found): C, 18.89 (17-08); H, 1.59 (1.80); N, 11.02 (10.88); K, 30.75 (30.08). KOOCCONHCH3 was prepared by adding an equivalent of KOH to an alcoholic solution of CH300CCONHCH3 (3), giving colourless crystals. Elemental

analysis: Calculated (found): K, 27.69 (26.80).

C, 25.52 (23.85); H, 2.86 (2.81); N, 9.92 (9.36);

KOOCCSNH2 was prepared by titrating CpHSOOCCSNH2 [1] with KOH; the product crystallized on adding alcohol to the aqueous solution. Bright yellow crystals were obtained. Elemental analysis: Calculated (found): C, 16.77 (15.61); H, 1.41 (1.68); N, 9.78 (9.39); K, 27.30 (26.30). The elemental analyses were performed using standard procedures; potassium was determined gravimetrically as KB(C,H,), [ 191. VIBRATIONAL

ANALYSIS

The assignments for the amide and thioamide groups were made by comparison with literature data; the assignments for the carboxylate group were made by comparison with KOOCCOOCH, [ 131 and KOOCCSNHCHJ (CD,) [ 201. KOOCCONH:!

An article on this subject by Wallace and Wagner [ 141 was published soon after the completion of our study. For the sake of completeness this IR study of the oxamate ion will be compared with our results. The fundamentals for NaOOCCONH2 and the N-deuterated product are given in Table 2. The vibrational analysis, together with the PED values for the in-plane modes of KOOCCONH, and the N-deuterated derivative are also given in TabIe 2.

17

assignments given in this work are in general agreement with those discussed by Wallace and Wagner [14], with the exception of some skeletal deformation modes. They assigned the sodium oxamate IR band appearing at 864 cm-l to a 6C03- mode, and assumed the other skeletal in-plane deformations to lie in the 550 cm- I, 450 cm-’ and 330 cm-l regions, without giving any further details. The only K-oxamate band in the 850 cm-” region of the IR and Raman spectra is assigned to YCC; the presence of a split band in the Naoxamafe IIRspectrum at 864 cm-’ and 856 cm-’ could be due to crystal effects or Fermi resonance rather than to the SCO,- mode. We place the fourth inplane skeletal deformation mode in the 660 cm-’ region. Two bands can be distinguished in the 660 cm-’ region of the aqueous Raman spectra of KOOCCONH,. The 659 cm-’ band disappears on deuteration and is depolarized; this band is assigned to TNH*, in agreement with Wallace and Wagner [14f. The other band appears with very low intensity in the IR spectrum, and was not observed by Wallace and Wagner; it is more intense and polarized in the Raman and can be assigned to a skeletal deformation mode with some 6NC0 character. It should be noted that comparable masses, bond distances and bond strengths are present in the carboxylate and amide groups; consequently strong coupling in the deformation modes can be expected [ 31. This phenomenon is clearly demonstrated by the PED values given in the tables. The deformations can therefore be described as “delocalized frequencies”, and the assignments must. then be regarded as approximate descriptions of the true ~brations. The splitting in the vCN region, which was not observed by Wallace and Wagner, is caused by Fermi resonance with 6NCO; this has been noted for other primary amides [IS J. The great variation in the NH? and carbonyl frequencies between the Naand K-oxamate is probably due to the hydrogen bonding caused by the different crystal structures. The

KOOCC0NHCH3

The vibrational analysis for KOOCCONHCHZ, together with the PED values for the 13a’ vibration, are given in Table 3; Table 4 gives the data for the Ndeuterated derivative. The Y(NH) and the amide I (YCO), 11 (YCN t &NH), III (&NH -f- YCN), IV (6NCO) and V (aNH) were easily identified at 3283,1678,1533,1240, 767 and 800 cm-‘, respectively; pNC0 was assigned to the polarized Raman band at 433 cm-‘. The r&C can ~doubt~dly be assigned to the most intense polarized Raman band in the spectrum, at 883 cm-’ for the normal, and at 872 cm-l for the N-deuterated product; the carboxylate stretching frequencies have been assigned to the 1635 and 1385 cm-’ bands. The carboxyiate deformations are very weak and hard to detect, but converged values for the force constants of the a’

18 TABLE

2

Vibrational

analysis for NaOOCCONH,,

KOOCCONH,,

IR

RarrGZUI

IR

Raman

(Solid)

(Solid)

(Solid)

Solid

3426(5) 3377( 2)

3379 s

3X35( 3)br 1735( 3) 1687(5)

3216 s

vs w w vs sh vs

1662 vs 1586 vs

1667( 2) 1579( 2)br

1550 w 1449 vs

1453( 10)

1416 w 1358 m 1323 vs

and KOOCCOND,

KOOCCONH,

NaOOCCONH,

3426 3370 3280 3200 17 10 1697

NaOOCCOND,

1415( 2) (1360) (1320)

1698 1678 1632 1575

w vs ws w

Assignment, PED Hz0

9%stNH 2) 1741( 2) 1694( 2) 1661( 1) 1638( 2) 1572(l)

99usWH,)

1690( 2)P 1637( 3)P 1590( 2)

1439 sh 1433 s

1452( 10) 1443(l)

1442( 10)

1356 m

1343( 2)

1325( 3)

2 x .(CC) 5WCO), Blv(CN), lOp(NCO), 56(NH,) 814CO,), 5u(CO), 5p(CO,) 53a(NH,), 13u(CN), Su(CO), 8+&O,) 32v(CN), 26u,(CO,), 12a(NH,), 17a(NCO) 48+=,),

23v(CC), 1312 VW 1304 s

1322( 1) 1300( 1)

1306( 1)

1155 VW 1089 m

1153(l) 1067(l)

1093(5)P

WCN),

12a(NH,)

(1275) 1117 1050 864 856 799 695 565 555 485 455

m w ms ms ms,br s

1119(4) 1050( 2) 863(7)

s s m m

(560)sh 551(2) 472(3)

360 m 220 w 168 w (120)

690( 3)

370( 2)

856 s

858(4)

857(7)P

778 m 678 vs 665 vvw

778( 1) 672(l) 653(l)

672( 2)P 659( 1)

538 w 490 s 452 VW

563( 1)

333 224 166 136 120

s w w w w

451( 2)

(550)br 443( 5) 305( 1)

81p(NH,),

Su(CO),

Gu(CN)

43u(CC), 306(NCO), lOu(CN), 4v(CO) w0JH.z) 466(NCO), 15u(CC), 33s (CO,) TWH,) 68/.+X0), 27p(CO,) n(NCO) 726(CO,), lBv(CC), 106(NCO); sr(C0,) 85p(COz), 14p(NCO) T; u(N-H - - - 0), Lattice modes

species could be obtained by assigning the broad band at 426 cm-’ to pNC0 and pCO,-. The NR frequencies have, in agreement with recent literature data [lS], been located at 1157 (vRN) and 344 cm-’ (6NR). Of the five out-ofplane a” motions, one can be assigned at 800 cm-’ (nNH) and one at 617 cm-’

19

KOOCCOND,

NaOOCCOND, RalTMll (Solid) 3410 3230 3010 2870 2563 2372 2271 1710 1686 1656 1448

m w w w vs vs mw sh vs vs vs

1393 1356 1323 1253

m vs sh VW

1133 m 1030 w,br 939 m,br 850 m 843 vs 649 s

Ins ms ms w w

Assignment, PED

2 x v(C0)

2562( 5) 2350(5)

2543 s 2382 s

1710( 1) 1676(3) 1649(5) 1453( 10)

1697 1662 1621 1444

w ws vvs s

1395( 1) (1370)

1358 vs

(1250)

1255 w

1151(2) (1040) 940(6)

1120 w

855(3) 842(5) 640(3)

605 s

450 425 339 228 174

RaIIIa!I (D,O)

itolid)

455(5) 430 sh

~hs(ND,)

95vJND,),

1706( l)P 1670(3)P 1635( 1) 1453(1O)P

2 x v(CC) 58v(CO), lSu(CN), lOp(NC0) 88~&0,), 6&CO,) 27u(CN), 24v(CC), 5u(CO), 17v&!O,)

1345( 2)P

57+&O,),

(1252)

937( 8)P

850 835 777 666 627 595 538 529 516 472 450

852( 1) 838(4)P

315 222 174 162

15u(CC),

12s(ND,)

616(ND,), 14s(NCO), 8v(CN), Sv(CC)

1125(l)

917 s w s m

Su(CN)

7lp(NDz), S+O), 8s(NCO), 7u(CN) 48u(CC), 176(NCO), lWCO,), 8p(ND,) 50a(NCO), 306(CO,),

1Ou(CC)

m s s w w s VW m s mw w w

(120) 85 w

620( 2)

MND,) (540)

430( 2)

64p(NCO),

29p(CO,)

T(ND=) + n(NC0) SS(CO,), lSu(CC), n(CO,) 83p(CO,), T, v(N-D

10qNCO)

17pfNCO) - - - 0),

Lattice modes

(zNC0); the nNR and nC02- must arise in the 400-500 have both been assigned to the weak band at 490 cm-‘. must be present in the 300-170 cm-’ region, together and lattice vibrations.

cm-’ regions and The torsion mode with (N-H - 0) l

l

20 TABLE

3

Vibrational

analysis for KOOCCONHCH,

IR

Raman

(Solid)

Solid

3283 3180 3040 2990 2940 2890 1678 1656 1635 1533 1475 1440 1410 1385 1370 1300 1240 1157 1100

vs sb w VW w VW vs vs vs s w w ms s s VW rns m brw

1040 876 856 800 770 767 617 560 490 426

mw mw m wbr sh s VW mbr mwbr m

Assignment, PED I-W 99v(NH)

I

4CH,)

(1690)

(1690)P

1421(2)

1660brP 1540( 3)P 1465(5) 1454( 5)P 1420( 2)

1357(8)

1385(9)P

1242(5) 1155(8)

1240(4)P 1163(5)P 1120(l)

1637( 6) 1531(5) 1468(2)

1060( 2)br

344 300 284 275 234 211 170 144 120 108

m w VW VW sb w m m m w

874(10)

1021(9)P 883( 10)P 851(Z)

84u&CO,), lOp(C0,) 24u(CN), 17u(CO), 136 (NH),

186 (NCO)

WI-k)

546(NH), 70u(NR),

1

lOu(NR), 20a(NH)

14u(CN),

sS(NC0)

dCH,) 37v(CC),

146(NCO),

356(CO,)

n(NH) (770) (740) 558( 3) 498( 3) 437(7) 358( 2)

(750)

(550) 433(5)P 350(3)P

536(NCO), 2Ou(CC), 106(NR), m(NCO) 636(CO,), 31p(NCO)

8u(CN)

n(NR) + -(CO,)

48p(NCO), 346(NR), 6Op(CO,), 22u(CC) 7la(NR), 22p(NCO)

lOp(C0,)

- - - 0) ;N-H Lattice vibrations CH 3 torsion

KOOCCSNH, The strong fluorescence bands present in the Raman spectrum of the solid and the solution made it impossible to record useful Raman spectra, either

21

TABLE

4

Vibrational IR (Solid) 3010 2970 2940 2890 2453 2410 1677 1657 1635 1475 1444 1410 1370 1310 1168 1110 1055

analysis

for KOOCCONDCH,

Raman (D,O) ww w

1

VW

941 s 863 mw 849 w 760 s (58O)sb 560 mbr 490 mwbr

’ 97v(ND),

(1690)P 1650(3)br,P 1483( 10)P 1416(3)P 1360(5)P 1156(3)P 1068(5)P 1020( 6)P 940(7)P 872(9)P 850( 2) (760) (530) 433(5)P

342 m

300 284 260 236 210

w vw sb sbbr w

186 178 144 120 10s

m m m m w

PED

WH,)

w

s VW vs vs vs m w m sbr ww m w w

Assignment,

348( 3)P

57v(CO),

lv(CN) 24v(CN),

ll&CNO)

87%sWk), 7P(CO,) \ 24v(CN). 22v(CC), lOu(NR),

17a(NCO)

WH,) 57v&O,),

54v(NR), ACH,) 1 ’ 6WND), 37+X’),

lOv(CC),

5v(RN),

lOu(CN),

15v(CC)

16S(CO,)

6v(CC), 136(NCO), 8v(RN) 13s(NCO), 35p(NCO), 12p(CO,)

346(NCO), 25v(CC), 5u(CC), lOs(NR) n(ND) + n(NCO) 686(CO,), 186(NCO) n(NR) + rr(CO,) 40p(NCO), 18v(CC), 31p(CO,) 49p(CO,), 38p(NCO), 116(NR) 67s(NR), 27p(CO,)

{N-D - - - 0) Lattice vibrations CH, torsion

with the HeNe laser or with various lines of the Ar*-laser. The IR spectra, together with the assignments and PED values for the in-plane modes, are given in Table 5. The NH2 in-plane modes for the primary thioamide groups are situated at 3375,3240,1591 and 1232 cm-‘, and for the deuterated product at 2529,2363,1167 and 853 cm-‘. The NH, out-of-plane modes can appear as

22 TABLE 5 Vibrational analysisfor KOOCCSNH, and KOOCCSND, KOOCCSND,

KOOCCSNK, Assignment.

IR (Solid) 3375 3280 3240 3210 3158 1680 1631 1591 1426 f401 1368 1310 1246 1232 1136 Ill2 995 918 851 844 815 802 735 707 667 654 585 540 425 389 279 260 210 166 242 115 90

s nw m VW w w ws vvs VW w s w ww s m w mbr s vvw \rvw * ws VW VW sh s m vwbr w s iv sh w w w brvcv \v

89+scco,). 625(NH,).

PED

5~c0,). BOv(CN)

SIWZN). 59&WO,).

15~(cS). 23WW.

5l!HNH,).

Sv(CS).

41vfCC).

w(NH,) QNH,)

546(NCS).

22f’(CS>.

326(CO,)

736
- - - X) vibrations

Assignment,

IR (Solid)

BOS(NH,) 76 (coz)

llu,(COz).

Gu(CN>.

206(NCS)

206(COI)

3240 2970 2529 2461 2363 1624 1525 1499 1492 1462 1368 1221 1167 1140 1114 1072 993 920 853 834 809 800 758 747 700 688 599 579 568 535 500 470 403 372 355 280 262 230 165 740

w w vs vs vs sh m sh vs vs m s vvw m VW VW mw mw ms s m sh s wbr m VW w m s s sh m m s m m I w hrvw w

11.5 LX-VW

PED

98+&W,) 95v,(ND,). 84~~
4u
7P(C0,1

64U(CN). 7v~CS). 7V(CC) 64u,(CO,>. 2OY(CC). 86(CO,B 66S(ND,).

8u(CN).

Su(CC).

35v(CS). 65p(ND,

lOv(CN). ). 23WX).

l66(CO,) 9u(CC)

48v(CC),

13v
24&COz,

635(NCSL w(ND,)

106C

30S(COz)

7
54s(co2),

19&(NCSk

rr(NCS) + n(COZ) 6Op(NCS). 24P(C0,). 77p(CO,), 2lp
&-D Lattice

I3p(NCSl

86(C0,f

. - - X) vibrations

90 xv‘

split bands with variable intensity [S, 6] ; for this molecule they are situated in the 700 cm-’ region for the normal and in the range 550-600 cm-’ for the deuterated compound. Strong coupling between the vCC and vCS modes makes their assignment very difficult [ 1, 6] ; this has generally been achieved by comparison with the bands of complexes with “soft” metals, where YCS shows a large downward shift [ 211. However, on complexation of the present compound with Pd, a totally different spectrum was obtained. Two intense IR bands appear at 918 and 802 cm -I_ We calculated the force field twice, fiistl$ by assigning vCC to 918 cm-’ and YCS to 812 cm-’ and secondty with the opposite assignment. Converged vaIues were obtained only for the first of

23

these possibilities, and consequently this assignment was accepted. It may be seen from the PED data that considerable coupling occurs between vCC and YCS. The intense bands at 815 and 585 cm-’ could be due to overtones of the bands at 425 and 270 cm-‘, enhanced by Fermi resonance with the a’ modes at 802 and 654 cm-‘. For the deuterated products we observed these bands at 800 cm-’ and near 568 cm-’ in the ND2 out-of-plane region. The other bands arising in the low-frequency region can be ascribed to the torsion, (N-H - . . X) and lattice modes. CONCLUSION

In previous studies we have emphasized the characteristic features of amides [4], thioamides [ 63 and ester functions [ 221. We will therefore concentrate here on the carboxylate group. Only two bands due to this group are detected easily. They appear with typical profiles, frequencies and intensities and can be described as “group frequencies”. One band arises in the 1650-1600 cm-’ region, is very strong in the IR and of medium intensity in the Raman; the band has 80% v,,C02.and approximately 10% pCO,- character. The second band arises in the 13501400 cm-’ region, appears as an intense and polarized Raman band and is less intense in IR; this band consists of 60% Y$O~-, 20% vCC and 10% &CO,-. The deformations of the COZ- group appear as weak bands at different frequencies, due to strong coupling with other deformations in the molecules; they must consequently be regarded as “delocalized frequencies” and can hardly be described as characteristic. We calculated the bond order of the carboxylate C-O bonds from the force constants according to Siebert [22] as modified by Vansant [23], taking 144 pm as the length, and 5 mdyn A-’ [24] as the force constant for the CO single bond. The force constants and calculated bond orders are given in Table 6; we can see that, although the frequencies give no useful indications, the bond TABLE

6

Force constants and bond orders for some simple salts X-COOK

u&o,-

I&co,-

fco

(mdyn

X=CONH, COND, CONHCH, CONDCH, CSNH, CSND,

CSNHCH, CSNDCH, COOCH,

1610 1606 1636 1640 1631 1620 1633

1628 1642

1356 1354 1385 1365

9.75 9.68

1368 1346 1368 1368 1380

9.45

9.87 9.65 9.43

9.36 9.42

9.49

Bond order A-‘)

1.71 1.70 1.73 1.70 1.67 1.67 1.66 1.67 1.68

24

orders are slightly lower for molecules with thioamide groups. This can be explained by the conjugation effect, which occurs in compounds with the general formula XSCNHY, where X = primary or secondary amide, thioamide, nitrile or ester function and Y = H or R group [ 11. ACKNOWLEDGEMENT

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