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Infrared spectra and normal coordinate analysis of thiocarbonato complexes
Spectrochimica Acta, Vol. $0A,pp. 1059 to 1057. Pergamon Press 1974. Printed in Northern Ireland
T-t,ared spectra and normal coordi-Ate analysis o! thiocarbonato complexes Department
ALA~ COR)#I~R a n d ~ A z u o N ~ M O T O of Chemistry, Marquette University, Milwaukee, Wisconsin 53233, U.S.A. and
P. CHRISTOPHLIEMK a n d A c ~ MiYI~ER Institut fiir Chemie, Universitiit Dortmund, Dortmund, West Germany (Received 2 M a y 1973)
Almtract--The i.r. spectra of A~[-~(CSs)s] where M = 5sNi(II), 6~i(II), S4Zn(II) and 6SZn(II) and A = PPh4+, AsPh4+ and NMe4+ have been measured from 4000 to 33 cm-1. Normal coordinate analyses have been carried out on the planar [SSNi(CSs)2]z- ion and its 6sNi analog. The Ni--S stretching bands have been assigned at ca. 385 and 366 cm-1, and the corresponding f o r c e constant estimated to be 1.41 mdyn/A. In order to obtain good agreement between calculated and observed frequencies, it was necessary to modify the Urey-Bradley force field by adding s e v e r a l interaction constants. The low-frequency spectra of the Zn complexes have been assigned based on observed isotopic shifts due to the 64ZnJSZn substitution. INTRODUCTION RECENTLY, v i b r a t i o n a l spectra o f coordination c o m p o u n d s containing m e t a l ~ sulfur b o n d s h a v e been studied extensively. T h u s far, n o r m a l coordinate analyses h a v e been carried o u t on m e t a l complexes o f d i t h i o c a r b a m a t o [1, 2], x a n t h a t o [3], d i t h i o o x a l a t o [4], d i t h i o a c e t y l a c e t o n a t o [5] a n d dithiene complexes [6]. E x c e p t for t h e last complex, these calculations h a v e been m a d e on t h e 1 : 1 metal/ligand model. As s t a t e d p r e v i o u s l y [7], such a n a p p r o x i m a t i o n t e n d s t o o v e r e s t i m a t e t h e m e t a l - ligand stretching force c o n s t a n t in t h e U r e y - B r a d l e y force field since inter-ligand i n t e r a c t i o n s are ignored completely. I n order to estimate t h e m e t a l - - l i g a n d stretching force c o n s t a n t s accurately, i t is necessary t o c a r r y out a n o r m a l coordinate analysis on t h e whole molecule b y t a k i n g inter-ligand interactions into consideration. T h e m a i n p u r p o s e o f this investigation is t o d e m o n s t r a t e t h a t t h e m e t a l isotope d a t a [8] are indispensable in refining t h e m e t a l - l i g a n d a n d inter-ligand i n t e r a c t i o n force constants in a 1 : 2 metal/ligand model. R e c e n t l y , BURKE a n d I~ACKL~,R [9] r e p o r t e d t h e v i b r a t i o n a l spectra o f t h i o c a r b o n a t o complexes w i t h Ni(II), P d ( H ) a n d P t ( I I ) . H o w e v e r , n o m e t a l isotope studies n o r n o r m a l coordinate analysis such as t h a t described here h a v e been carried o u t previously. [1] E2] [3] [4] [5]
[6] [7] [8] [9]
K. ~TA~AMOTO,J. FUJlV~A,R. A. CO~V~T~ and Y. MO~IMOTO,J . Chem. Phys. 3 9 , 423 (1963). G. D ~ - ~ G ~ s ~ , D. N. S A T ~ Y A ~ A and C. C. P - ~ L , Can. J . Chem. 47, 631 (1969). V. A. LAwRH~ and P. B. RAo, Inorg. Chim. Aeta 2, 337 (1968). J. F(yJ~A and K. NAWAMOTO,BU/L Chem. Soe. J a p a n 37, 528 (1964). O. S~A~-~ and J. ~ s c o , !norg. Chem. 8, 1846 (1969). O. S I ] ~ * ~ and J. l ~ s c o , I~org. Chem. 10, 297 (1971). J. F u ~ , , A. E. M ~ t ~ T . and K. NA~A~OTO, J . Chem. Phys. 36, 331 (1962). K. NA~r*MOTO,.4ngew. Chem. Intern. Ed. 11, 666 (1972). J. M. B v ~ and J. P. FAO,rT~, I~torg. Chem. 11, 2744 (1972). 1059
1060
A. COI~IEI~, K. N~MOTO, P. CHRISTOPKLIEM.Kand A. MfrLLER EXPERIMENTAL
Preparation of compounds The preparation of the [Ni(CSa)~]~- salts with various cations have been reported by BURKE and FACKLER [9]. The [Zn(CSa)~]2- salts with various cations were prepared by the method reported by Mt2LLER et al. [10] The metal isotopes, 5sNi (99.98 ~o pure), 6~Ni(99.02 ~o pure), ~4Zn(99.66 ~ ) and eSZn(98.46 ~o) were purchased from Oak Ridge National laboratory. Infrared measurements The i.r. spectra from 4000 to 200 cm -1 were obtained on a Beckman IR-12 and those from 400 to 33 cm -1 were measured on a Perkin-Elmer-Hitachi FIS-3 i.r. spectrophotometer. For the former instrument CsI pellets were made at concentrations ranging from 0.5 to 4.0 mg sample per 200 mg CsI. For the latter instrument Nujol mulls with polyethylene plates were used. The instruments were calibrated by running the spectra of water vapor, polystyrene and 1,2,4-triehlorobenzene. The spectra of metal isotope compounds below 400 em -~ were recorded with a scanning speed of 1-2 cm-~/min to measure the isotopic shifts as accurately as possible. Furthermore, the reproducibility of the frequency reading and the isotopic shift were checked by multiple scans over the derived frequency region. NORMAL COORDINATE ANALYSIS A normal coordinate analysis has been carried out on the planar [Ni(CSa)2]2- ion of D2a symmetry shown in Fig. 1. The bond distances and angles were taken from the results of X-ray analysis [11]: d(l~i--S) = 2.21A, r(C--S)----1.70A, R(C----S) ---- 1.68A, fl(S~C--S) = 126.1 °, ~(S--C--S) = 107.9 °, ~,,(S--Ni--S) ---- 76.9 °, ?a(S--Ni--S') = 103.1 ° and 0(C--S--Ni) ---- 87.612 °. A minor adjustment was made for 0 to satisfy the ring redundancies in our calculations.
G
~
Sl
Sa
Se
S5
2
Fig. 1. Structure and i n t e r n a l coordinates o f the [Ni(CSa)~] -~ ion. [10] A. MffT,LER, P. C~ZSTOPHT,Z~,MK, I . TOSSIDZS and C. K . JORGE~S~.~, Z. Anorg. Allgem.
Chem., in press. [11] J. S. MCK~.CHNI~,S. L. MrES~.Land I. C. PAUL, Chem. Comm. 152 {1966).
Infrared spectra and normal coordinate analysis of thiocarbonato complexes
1061
Table 1. Symmetry coordinates Sym. species Au
S y m m e t r y coordinate
Mode of vibration~ ring torsion
Sx = T 1
Blu
1
* B~u
S , = ~ - ~ (Pl + O2)
ir(NiCS~)
$4 = e
~r(NiS 4)
~5 = ½(rl -- r2 + r3 -- r~)
v(C--S)
S s = ½(d 1 - - d a + d a - - da)
v(Ni--S)
g: ++
=
Ss = ½(01 - S, = ~
* Bau
Sxo = ~
1 1
0a - - 0a)
~(CSNi)
(~a - - 74)
~(S1NiSa)
( R x - - Rs)
V(C~S)
$11 = ½(r1 + r~ -- r~ -- r4)
v(C--S)
Sx2 ~ ½(d 1 + d~ - - d a - - d4)
v(Ni--S)
Sla = ~ $14 = ~ $15 = ~
1 1 1
(3~1 - - O1 - - 02 - - 71 - - 3a2 -~ Oa -~ 04 -~ ?B)
ring def.
(271 - - 27~ - - 01 - - 02 -{- 03 % 04)
r i n g def.
(~)x + (Xl + 01 + 0~, - - '~'z - - Ot~ - - 0 a - - 04)
Redundancy
1
S . . = ~ - ~ ( ~ + fl~ + fl~ - - ~ , - - fls - - fl,)
Redundancy
* Those symmetry blocks contain one redundant condition which gives one zero.frequency in the final result. v, s t r e t c h i n g ; (~, in.plane bending; It, out-of-plane bending.
The t w e n t y - o n e (3 × 9 -- 6) normal vibrations of the [ N i ( C S 3 ) 2 ] 2 - ion are classified into 4Ag + 3Big + 2B2~ + A~ + 3B1~ + 4B2, + 4B3~ under D ~ symmetry. Only the last eleven u-modes are i.r. active. Figure 1 illustrates the internal coordinates and Table 1 lists the s y m m e t r y coordinates used in our calculations. There are four out-of-plane bending modes of the terminal sulfur (¢), carbon (p), and nickel a t o m (e). The torsion (r) of one ring w i t h respect to the other is not shown. Since twelve s y m m e t r y coordinates were used to calculate eight in-plane uvibrations, this set includes four redundancies. Two of these are obvious in Table 1 ($15 and Sle). The other two redundancies were included in our calculations since t h e y cannot be eliminated easily. Final results gave t w o zero frequencies corresponding to these t w o redundancies. The potential energy was expressed b y using a modified U r e y - B r a d l e y force field:
v = X (K/rio(Ar,) + 1/2K~(Ar~)2) i
+ ]~ (H/r~(A~) + 1/2H,(Ao~,)2) i
+ Z (F,'q,o(Aq,) + I/2F,(Aq,) 2) i
+ 5 1/2(f~Ar,Ar,) + ~ 1/2f',j(Ar, Aa~) i
i
i
1062
A. COROneR, K. NA~A~OZO, P. CHRISTOPltLIEME and A. M~x.~r~
H e r e t h e s y m b o l s Ar, A a , a n d Aq a r e c h a n g e s i n b o n d l e n g t h s , a n g l e s , a n d n o n b o n d e d distances, respectively. The first three summation terms are the simple UreyB r a d l e y f o r c e f i e l d t e r m s [12]. T h e t e r m K i s a s t r e t c h i n g f o r c e c o n s t a n t , H is a b e n d i n g f o r c e c o n s t a n t , a n d 2 ' is a n o n - b o n d e d r e p u l s i v e f o r c e c o n s t a n t . T h e t e r m F' was taken as --1/10 F by assuming that the repulsive energy between non-bonded a t o m s is a p p r o x i m a t e l y p r o p o r t i o n a l t o - - 1 / r s. I n t h e f i n a l r e s u l t t h e t e r m s K ' a n d H' drop out since they can be expressed in terms of F'. Lastly the terms f,j, f,/and f , / ' w e r e a d d e d t o t h e s i m p l e U r e y - B r a d l e y f o r c e field a s a m o d i f i c a t i o n . T h e s e t e r m s a r e t h e i n t e r a c t i o n (off d i a g o n a l ) f o r c e c o n s t a n t s w h i c h a r i s e f r o m t h e g e n e r a l v a l e n c e f o r c e field. T h e i r v a l u e s s i g n i f y t h e d e g r e e a n d t h e t y p e o f i n t e r a c t i o n b e t w e e n o n e bond and its neighboring bond. Table 2 lists the best set of force constants obtained. Table 3 compares the o b s e r v e d f r e q u e n c i e s a n d i s o t o p i c s h i f t s w i t h t h o s e c a l c u l a t e d . T h e a g r e e m e n t is q u i t e s a t i s f a c t o r y . T h e m a x i m u m e r r o r is l e s s t h a n 1 p e r c e n t . T a b l e 4 l i s t s t h e Table 2. Force constants (mdyn/A) K(C~S) K(G--S) K(Ni---S) H(SI--C--S2) H(S,~---C--S1) H(C--S--Ni) H(SI--Ni--SI) H(Sr-Ni--S~)* H(~)
3.12 2.60 1.41 0.22 0.25 0.02 0.15 0.20 0.5
H(o)
--0.32 0.01 -- 0.21 0.45 0.07 --0.19 -
-
o.13
0.20 0.055 0.75 0.22 0.05 0.02
H(e)
H(r) F(S 1 . . . Ss) F(S 1 . . . S~) F(S 1 . . . St) F ( N i . . . C) *
f(r 1, o~1) f(r 1, fix) f(dp Yl) f(d 1, d~)* f(d t, da)* f(dl, ~a)*
Inter-ligand interaction constants
Table 3. Comparison of observed and calculated frequencies and b a n d assignments for the [Ni(CSs)2]2- ion (em-')* Observed
B2w
~(6SNi)
Art
fT(SSNi)
A~
Yl
--
--
25
0.0
v,
485.0
0.0
480 60 14 856.9 366.3 297.6 55.0 1010.3 506.1 383.9 185.5
0.0 1.0 0.0 0.0 5.0 1.6 0.4 O.0 0.I 7.1 1.3
~'s ~4 Bl**
Yi v, y~ vs
Bsu
Calculated
~0 Vie Yll v12
---
---
857.5 365.9 297.1
0.0 5.0 1.5
55.5
0.5
1010.0 507.0 384.7 185.7
0.0 0.5 7.2 2.0
Predominant mode Inter-ring torsion ~r(CSs) ~r(NiOSa) Ir(NS4) y(C--S) ~'(Ni--S) ~(S1GSa) v(S1NiS4) V(C~S) V(C---S) ~(Ni---S) ~(SI:N'iS~)
* PPht+ salt 1"A~ = ~(58Ni) -- ~(6~Ni) :~Not i.r. active. [12] T. SHD#AgOUCHI, J . Chem. Phys. 17, 245, 734 and 848 (1949).
Potential energy distribution $1(100~) Sz(92 %) ~a(55 ~ ) , H4(45 ~ ) S~(55 %), $a(45 ~ )
$5(80~) , S7(20%) ~q6(80~),S~(13%) $7(77 ~), $6(7 %), So(10~o) $9(72 %), Se(23 %) $10(64 %), $11(31%) $11(64~), $1o(29~) $12(90%) $14(55~), $18(40 %)
T a b l e 4. Observed frequencies of t h i o c a r b o n a t o complexes (cm-1) [Ni(CSa),]-* PPh~ + ¢(SeNi)
AsPh4+ ¢(SSNi)
1583(m) 1485(m)
1580(m) 1483(m)
1440(s)
1440(s)
[Zn(CS,)z]-* NMe4+ ~(Ni)
1480(s) 1445(m) 1405(m)
1340(w) 1315(w)
1338(m) 1312(m)
l190(w) 1165(w)
1185(m) 1165(m)
lllO(vs) 1075(vw)
1080(s)
1021(s, sh) 1010(vs) 995(s)
1022(s, sh) 1010(vs) 997(s)
965(m)
965(m)
926(vw) 898(vw) 880(vw) 857 (m) 841(w) 815(vw) 790(vw) 755(s) 725(vs) 690(s) 618(w)
925(vw) 897(w) 880(vw) 85___7(m) 840(m) 815(vw) 790(vw) 750(vs) 740(vs) 690(s) 618(w)
53O(vs) 50___5(w) 48...._5(w) 460(w) 394(sh) 38__5(vs) 36__8(m)
333(vw)
50_.7(w) 48....0(m) 468(s)
1013(vs)
904(w) 880(w) 8S_~5(s) 815(w) 790(vw)
50_~8(m) 4S....88(m)
38_~5(vs) 36~6(m)
1440(s)
1440(s)
1340(w) 1315(w)
1340(w) 1315(m)
l190(w) 1165(w) l130(w) lllO(vs) 1075(vw) 1050(vw) 1025(w)
l190(m) 1165(w) 1130(m)
334(vw) 308(w) 29__77(vw)
261(vw)
251 (vw)
246(vw) 241(w) 230(w) 188(w) 18._~5(m)
210(vw)
96(w)
1080(s) 1050(vw) 1023(w)
995(s) 982(s)
997(s) 98_55(vs)
930(vw)
925(vw)
8s0(vw) 860(m) 850(m) 810(vw)
882(vw) s6__5(m) 855(m) 805(vw)
760(s) 722(vs) 690(vs) 618(w) 600(vw) 575(w) 530(vs) 5o__._55(w,~a) 482(vw)
755(s) 745(vs) 690(vs) 618(w) 600(vw) 575(w) 528(w) 50_22(w,sh) 48O(m) 466(s)
450(m)
453(m)
37_~4(w)
372(w) 360(vs) 350(vs) 344(vs)
350(s) 345(s)
263(w) 256(w) 247(vw)
117(w) 92(w) 6_55(w) 52(vw)
1580(m) 1485(s)
945(s)
29.__66(vw) 284(w)
18_.44(m)
1585(m) 1484(m)
455(w) 3s___4(s) 36.~4(s)
AsPh4+ l~(*'Zn)
1285(w)
29._~7(vw) 284(vw)
203(w)
PPha+ ~(e'Zn)
31__~5(vw) 307(vw) 274(sh) 26__22(vs)
20___6(m) 18.._55(m) 152(vw) 116(vw) 5_66(w)
15__O(m) 134(w) 124(w) 1lO(w) 5_55(vw)
31._~5(vw) 26_~2(m) 241(m) 226(w) 20__8(m) 189(w) 15_.2(vw) 115(w) 96(w) 76(w)
(a) Only the bands due to the complex anion are underlined. An other bands are due to cations or non-fundsmental vibrations of the complex anions. (b) The frequency values were rounded off for brevity. (e) Abbreviations: vs(very strong); s(strong); re(medium); w(weak); vw(very weak); sh(shonlder). 1063
1064
A. CO~MIE~, K. NAKA-~OrO, P. CHRISTOPH]SIEMKand A. I~I~LL~R
observed infrared frequencies of the Ni(II) and Zn(II) thiocarbonato complexes with various cations. RESULTS AI~D DISCUSSION
Band assignments As is seen in Table 4, Figs. 2 and 3, the thiocarbonato complexes of Ni(II) and Zn(II) exhibit many bands, most of which are due to bulky cations. In order to distinguish complex anion bands from cation bands, we have measured the spectra of NMe4C1, PPh4C1 and AsPh4C1, and compared their spectra with those of metal complexes containing these cations. Variation of these cations for a fixed metal complex anion has aided the identification of cation bands. Observation of metal isotope shifts in the low-frequency region has given definitive evidence for assigning metal--ligand vibrations. As is shown in Table 3, the bands at 1010(~g) and 857(~5) are assigned to the C--~S stretching (S10) and C--S stretching ($5) modes, respectively. These bands correspond
(tiMe4)2 [M(cs3~
.Q <
!
(pph4)2 INi(CS..j)2]r ~
l
cpPh42nc i
~
i
1600
i
i
1400
i
L
1200
i
,
I000
Frequency,
,
,
i
800
,
600
,
,
400
2(X)
cm - I
Fig. 2. Infrared spectra of (N]~Ie4)~[Ni(CSa)2], (PPha)2[ssNi(OSa)2], and (PPh4) z[64Zn(CS3)2l in the high frequency region. Bands with asterisks are due to the complex anion.
Infrared spectra and normal coordinate analysis of thiocarbonato complexes
o
~'
1065
'~, (PPh4)2 [Ni(CS3)"
"
"-~.~&./.
"',,.,,"
(PPh4)2[Zn (CS3) ~
'..V / I /
400
i
[
I
I
I
I
l
I
I
I
I
300
I
[
{
Frequency,
[
[
I
[
I
[
200
i
i
I
i
i
i
i-{
[
[
I00
~
[
~
L
[
crn -I
Fig. 3. Infrared spectra of (NMe4)2[Ni(CS3)~,], (PPh4)~[ss'~Ni(CSs)~] and (PPh4) ~[~4"aSZn(CSs)2] in the low frequency region. Vertical lines indicate peak positions of metal isotope sensitive bands.
to the 905 cm -1 b a n d of t h e free CS3~- ion [13] which splits into two b a n d s u p o n c o m p l e x formation. A n o t h e r C - - S stretching m o d e (Su) is a t 507 cm -1 (~lO) which corresponds to t h e 520 cm -1 b a n d of the free ligand. T h e out-of-plane bending m o d e of the free ligand a t 505 cm -1 is n o w shifted t o 485 cm -1 (~2) in the Ni(II) complex. T w o new b a n d s a p p e a r a t 385 (~11) a n d 366 cm -1 (~s) which give large shifts (ca. 7 --~ 5 cm -1) b y t h e 5sNi--6~Ni substitution. These b a n d s m u s t be assigned t o t h e N i - - S stretching modes (S12 a n d Se, respectively). T h e b a n d s below 350 cm -1 h a v e n o t been assigned previously. I n b i d e n t a t e c a r b o n a t o complexes, the 710 cm -1 b a n d o f t h e free C03 ~- ion (OCO bending, E ' species) splits into two b a n d s a t ca. 760 a n d 670 cm -1 [14]. A similar f r e q u e n c y t r e n d m a y be e x p e c t e d for the 320 cm -1 b a n d (SCS bending, E ' species) of the free CS32- ion u p o n complex formation. H o w e v e r , t h e r e are a d d e d complications in t h e l a t t e r case. One o f the E ' c o m p o n e n t s is at 297 em -1 (~7) since it couples w i t h t h e N i m S stretching m o d e a t 365 cm -1 (~e). I n fact, t h e p o t e n t i a l e n e r g y distribution o f ~7 shows 7 % c o n t r i b u t i o n of t h e S s coordinate. This is also consistent with the [13] A. I~¢[]~LIJERand M. STOC~Bm~GF~,Z. Naturforsch. 20a, 1242 (1965); B. KREBS, A. ~VI~-LLER and G. GA~'row, Z. Naturforsch. 2{}b, 1124 (1965). [14] J. FUZITA, A. E. M.A~T~.T.Land K. NAXAMOTO,J. Chem. Phys. 86, 339 (1962).
1066
A. C o ~ ,
K. I~AlrA~VIOTO,P. CHRISTOPKLIEMK a n d A. MOLI~R
observation that this band gives an isotopic shift of 1.5 cm -1 by the 58Ni--6~Ni substitution. As is seen in Table 3, there is no band which strictly corresponds to the other E' component. According to Table 1, Sis is a ring deformation involving the change in the SCS angle. Table 3 shows, however, that $13 contributes only 40 per cent to the 186 cm -~ band ( ~ ) . Therefore, it is most reasonable to assign the band at 186 cm -1 to a ring deformation. Thus, a simple frequency correlation such as seen in carbonato complexes does not exist in thiocarbonato complexes. Although the nature of the weak band at 332 cm -1 is not obvious, we tentatively assign it to a g-type vibration which is weakly allowed by the crystal field effect. The strong band at 186 cm -1 (~12) gives a shift of 2.0 cm -1 by the 58Ni--62Ni substitution. According to our calculation, this band is predomluantly due to the S - - N i - - S bending ($14) mode. The lowest frequency band at 55 cm -1 (~s) has been assigned to the S - - N i - - S ' bending ($9) which involves the change in the inter-figand angle, ~. This mode gives a small metal isotope shift as expected. There are three out-of-plane bending vibrations which are not observed (~1, ~3 and ~4). These modes m a y be overlapped by other bands or their frequencies may be too low to be observed. According to our calculation, ~ was estimated to be 60 cm -1. The broadness of the 55 cm -1 band m a y suggest that ~3 is partially hidden or overlapped by ~8- The frequencies of ~1 and ~4 were estimated to be 25 and 14 cm -1, respectively, even with reasonable maximum values of force constants. Therefore, these bands are probably outside of our observable region. Previously, BURKE and I~ACKLER[9] stated that the low frequency vibrations of the [Ni(CS3)2]2- ion appeared to exhibit considerable mixing, and consequently, a direct correlation of the metal--sulfur stretching frequencies with bond strength could not be made. Our potential energy distribution (Table 3) shows, however, t h a t the Ni--S stretching modes (~11 and ~e) are surprisingly pure. The [Zn(CS3)~]2- ion belongs to the Vd(D2~) point group since the Zn atom is tetrahedrally coordinated by four sulfur atoms. Then, two Z n - - S stretching modes (B~ and E species) are i.r. active. As is seen in Fig. 3, two bands near 260 and 205 cm -1 give relatively large shifts (3 ~ 4 cm -1) by the e4Zn~SSZn substitution. The former is relatively sharp whereas the latter is broad. We tentatively assign these bands to the B 2 and E species, respectively. The frequencies of other vibrations are similar to those of the Ni(II) complex in the high frequency region.
Force constants Table 2 fists the best set of force constants obtained. I n order to fit calculated frequencies and isotopic shifts to observed values, it was necessary to modify the Urey-Bradley force field by adding six interaction constants. Among the latter, f(dj, de) is most important; its value significantly affects the value of K(Ni--S). Without this interaction constant, the value of K(Ni--S) becomes unreasonably small. I t also partly controls the magnitude of isotopic shifts of the Ni--S streteblng modes, f(dl, d3) mainly controls the separation of two Ni--S stretching frequencies. The magnitude of metal isotope shifts is mainly determined byf(dl, ~1) andf(dl, ~8). These two values were carefully adjusted to obtain a perfect fit for metal isotope shifts, f(rl, :h) andf(rl, ill) were added to obtain a perfect fit for the CS stretching modes.
Infrared spectra and normal coordinate analysis of thiocarbonato complexes
1067
Table 5. Comparison of Urey-Bradley force constants (mdyn/A) Bis (N,N-dimethyldithiocarbamato)niekel(II) (Ref. 2)
Bis (ethyl-xanthato) niekel(II) (Ref. 3)
Me
Force constant
NiJS1~N11 ~S~ y ~Me
K(~) K(I~i--S) H(S1--Ni--Sj) H(C---S--Ni) H(S1---C---S2)
2.78
1.69
2.60
2.02 0.3 0.1 0.52
P(S1
• • • S~)
0.62
. Ni)
0.1
2.24 0.65 0.6 0.4 0.4 0.3
1.41 0.15 0.02 0.22 0.22 0.02
P(C
. .
N i ~ S!"~.' " .C'~.•0. ~ S~>Y ~Et
This work
Table 5 compares the Urey-Bradley force constants obtained for similar systems. I t is seen t h a t the value of K(Ni--S) obtained in this work is smaller t h a t those obtained previously for other compounds. I t should be noted, however, t h a t these previous calculations have been done on the 1 : 1 metal/ligand model which entirely neglects the inter-ligand repulsive force, stretching-stretchln~ and stretching-bending interactions. Thus, the value of K(Ni--S) m a y be comparable to those obtained previously if the calculations were carried out on the 1 : 1 metal/ligand model.
Acknowledgments--This work was supported by an NATO research grant (No. 534).
T-t,ared spectra and normal coordi-Ate analysis o! thiocarbonato complexes Department
ALA~ COR)#I~R a n d ~ A z u o N ~ M O T O of Chemistry, Marquette University, Milwaukee, Wisconsin 53233, U.S.A. and
P. CHRISTOPHLIEMK a n d A c ~ MiYI~ER Institut fiir Chemie, Universitiit Dortmund, Dortmund, West Germany (Received 2 M a y 1973)
Almtract--The i.r. spectra of A~[-~(CSs)s] where M = 5sNi(II), 6~i(II), S4Zn(II) and 6SZn(II) and A = PPh4+, AsPh4+ and NMe4+ have been measured from 4000 to 33 cm-1. Normal coordinate analyses have been carried out on the planar [SSNi(CSs)2]z- ion and its 6sNi analog. The Ni--S stretching bands have been assigned at ca. 385 and 366 cm-1, and the corresponding f o r c e constant estimated to be 1.41 mdyn/A. In order to obtain good agreement between calculated and observed frequencies, it was necessary to modify the Urey-Bradley force field by adding s e v e r a l interaction constants. The low-frequency spectra of the Zn complexes have been assigned based on observed isotopic shifts due to the 64ZnJSZn substitution. INTRODUCTION RECENTLY, v i b r a t i o n a l spectra o f coordination c o m p o u n d s containing m e t a l ~ sulfur b o n d s h a v e been studied extensively. T h u s far, n o r m a l coordinate analyses h a v e been carried o u t on m e t a l complexes o f d i t h i o c a r b a m a t o [1, 2], x a n t h a t o [3], d i t h i o o x a l a t o [4], d i t h i o a c e t y l a c e t o n a t o [5] a n d dithiene complexes [6]. E x c e p t for t h e last complex, these calculations h a v e been m a d e on t h e 1 : 1 metal/ligand model. As s t a t e d p r e v i o u s l y [7], such a n a p p r o x i m a t i o n t e n d s t o o v e r e s t i m a t e t h e m e t a l - ligand stretching force c o n s t a n t in t h e U r e y - B r a d l e y force field since inter-ligand i n t e r a c t i o n s are ignored completely. I n order to estimate t h e m e t a l - - l i g a n d stretching force c o n s t a n t s accurately, i t is necessary t o c a r r y out a n o r m a l coordinate analysis on t h e whole molecule b y t a k i n g inter-ligand interactions into consideration. T h e m a i n p u r p o s e o f this investigation is t o d e m o n s t r a t e t h a t t h e m e t a l isotope d a t a [8] are indispensable in refining t h e m e t a l - l i g a n d a n d inter-ligand i n t e r a c t i o n force constants in a 1 : 2 metal/ligand model. R e c e n t l y , BURKE a n d I~ACKL~,R [9] r e p o r t e d t h e v i b r a t i o n a l spectra o f t h i o c a r b o n a t o complexes w i t h Ni(II), P d ( H ) a n d P t ( I I ) . H o w e v e r , n o m e t a l isotope studies n o r n o r m a l coordinate analysis such as t h a t described here h a v e been carried o u t previously. [1] E2] [3] [4] [5]
[6] [7] [8] [9]
K. ~TA~AMOTO,J. FUJlV~A,R. A. CO~V~T~ and Y. MO~IMOTO,J . Chem. Phys. 3 9 , 423 (1963). G. D ~ - ~ G ~ s ~ , D. N. S A T ~ Y A ~ A and C. C. P - ~ L , Can. J . Chem. 47, 631 (1969). V. A. LAwRH~ and P. B. RAo, Inorg. Chim. Aeta 2, 337 (1968). J. F(yJ~A and K. NAWAMOTO,BU/L Chem. Soe. J a p a n 37, 528 (1964). O. S~A~-~ and J. ~ s c o , !norg. Chem. 8, 1846 (1969). O. S I ] ~ * ~ and J. l ~ s c o , I~org. Chem. 10, 297 (1971). J. F u ~ , , A. E. M ~ t ~ T . and K. NA~A~OTO, J . Chem. Phys. 36, 331 (1962). K. NA~r*MOTO,.4ngew. Chem. Intern. Ed. 11, 666 (1972). J. M. B v ~ and J. P. FAO,rT~, I~torg. Chem. 11, 2744 (1972). 1059
1060
A. COI~IEI~, K. N~MOTO, P. CHRISTOPKLIEM.Kand A. MfrLLER EXPERIMENTAL
Preparation of compounds The preparation of the [Ni(CSa)~]~- salts with various cations have been reported by BURKE and FACKLER [9]. The [Zn(CSa)~]2- salts with various cations were prepared by the method reported by Mt2LLER et al. [10] The metal isotopes, 5sNi (99.98 ~o pure), 6~Ni(99.02 ~o pure), ~4Zn(99.66 ~ ) and eSZn(98.46 ~o) were purchased from Oak Ridge National laboratory. Infrared measurements The i.r. spectra from 4000 to 200 cm -1 were obtained on a Beckman IR-12 and those from 400 to 33 cm -1 were measured on a Perkin-Elmer-Hitachi FIS-3 i.r. spectrophotometer. For the former instrument CsI pellets were made at concentrations ranging from 0.5 to 4.0 mg sample per 200 mg CsI. For the latter instrument Nujol mulls with polyethylene plates were used. The instruments were calibrated by running the spectra of water vapor, polystyrene and 1,2,4-triehlorobenzene. The spectra of metal isotope compounds below 400 em -~ were recorded with a scanning speed of 1-2 cm-~/min to measure the isotopic shifts as accurately as possible. Furthermore, the reproducibility of the frequency reading and the isotopic shift were checked by multiple scans over the derived frequency region. NORMAL COORDINATE ANALYSIS A normal coordinate analysis has been carried out on the planar [Ni(CSa)2]2- ion of D2a symmetry shown in Fig. 1. The bond distances and angles were taken from the results of X-ray analysis [11]: d(l~i--S) = 2.21A, r(C--S)----1.70A, R(C----S) ---- 1.68A, fl(S~C--S) = 126.1 °, ~(S--C--S) = 107.9 °, ~,,(S--Ni--S) ---- 76.9 °, ?a(S--Ni--S') = 103.1 ° and 0(C--S--Ni) ---- 87.612 °. A minor adjustment was made for 0 to satisfy the ring redundancies in our calculations.
G
~
Sl
Sa
Se
S5
2
Fig. 1. Structure and i n t e r n a l coordinates o f the [Ni(CSa)~] -~ ion. [10] A. MffT,LER, P. C~ZSTOPHT,Z~,MK, I . TOSSIDZS and C. K . JORGE~S~.~, Z. Anorg. Allgem.
Chem., in press. [11] J. S. MCK~.CHNI~,S. L. MrES~.Land I. C. PAUL, Chem. Comm. 152 {1966).
Infrared spectra and normal coordinate analysis of thiocarbonato complexes
1061
Table 1. Symmetry coordinates Sym. species Au
S y m m e t r y coordinate
Mode of vibration~ ring torsion
Sx = T 1
Blu
1
* B~u
S , = ~ - ~ (Pl + O2)
ir(NiCS~)
$4 = e
~r(NiS 4)
~5 = ½(rl -- r2 + r3 -- r~)
v(C--S)
S s = ½(d 1 - - d a + d a - - da)
v(Ni--S)
g: ++
=
Ss = ½(01 - S, = ~
* Bau
Sxo = ~
1 1
0a - - 0a)
~(CSNi)
(~a - - 74)
~(S1NiSa)
( R x - - Rs)
V(C~S)
$11 = ½(r1 + r~ -- r~ -- r4)
v(C--S)
Sx2 ~ ½(d 1 + d~ - - d a - - d4)
v(Ni--S)
Sla = ~ $14 = ~ $15 = ~
1 1 1
(3~1 - - O1 - - 02 - - 71 - - 3a2 -~ Oa -~ 04 -~ ?B)
ring def.
(271 - - 27~ - - 01 - - 02 -{- 03 % 04)
r i n g def.
(~)x + (Xl + 01 + 0~, - - '~'z - - Ot~ - - 0 a - - 04)
Redundancy
1
S . . = ~ - ~ ( ~ + fl~ + fl~ - - ~ , - - fls - - fl,)
Redundancy
* Those symmetry blocks contain one redundant condition which gives one zero.frequency in the final result. v, s t r e t c h i n g ; (~, in.plane bending; It, out-of-plane bending.
The t w e n t y - o n e (3 × 9 -- 6) normal vibrations of the [ N i ( C S 3 ) 2 ] 2 - ion are classified into 4Ag + 3Big + 2B2~ + A~ + 3B1~ + 4B2, + 4B3~ under D ~ symmetry. Only the last eleven u-modes are i.r. active. Figure 1 illustrates the internal coordinates and Table 1 lists the s y m m e t r y coordinates used in our calculations. There are four out-of-plane bending modes of the terminal sulfur (¢), carbon (p), and nickel a t o m (e). The torsion (r) of one ring w i t h respect to the other is not shown. Since twelve s y m m e t r y coordinates were used to calculate eight in-plane uvibrations, this set includes four redundancies. Two of these are obvious in Table 1 ($15 and Sle). The other two redundancies were included in our calculations since t h e y cannot be eliminated easily. Final results gave t w o zero frequencies corresponding to these t w o redundancies. The potential energy was expressed b y using a modified U r e y - B r a d l e y force field:
v = X (K/rio(Ar,) + 1/2K~(Ar~)2) i
+ ]~ (H/r~(A~) + 1/2H,(Ao~,)2) i
+ Z (F,'q,o(Aq,) + I/2F,(Aq,) 2) i
+ 5 1/2(f~Ar,Ar,) + ~ 1/2f',j(Ar, Aa~) i
i
i
1062
A. COROneR, K. NA~A~OZO, P. CHRISTOPltLIEME and A. M~x.~r~
H e r e t h e s y m b o l s Ar, A a , a n d Aq a r e c h a n g e s i n b o n d l e n g t h s , a n g l e s , a n d n o n b o n d e d distances, respectively. The first three summation terms are the simple UreyB r a d l e y f o r c e f i e l d t e r m s [12]. T h e t e r m K i s a s t r e t c h i n g f o r c e c o n s t a n t , H is a b e n d i n g f o r c e c o n s t a n t , a n d 2 ' is a n o n - b o n d e d r e p u l s i v e f o r c e c o n s t a n t . T h e t e r m F' was taken as --1/10 F by assuming that the repulsive energy between non-bonded a t o m s is a p p r o x i m a t e l y p r o p o r t i o n a l t o - - 1 / r s. I n t h e f i n a l r e s u l t t h e t e r m s K ' a n d H' drop out since they can be expressed in terms of F'. Lastly the terms f,j, f,/and f , / ' w e r e a d d e d t o t h e s i m p l e U r e y - B r a d l e y f o r c e field a s a m o d i f i c a t i o n . T h e s e t e r m s a r e t h e i n t e r a c t i o n (off d i a g o n a l ) f o r c e c o n s t a n t s w h i c h a r i s e f r o m t h e g e n e r a l v a l e n c e f o r c e field. T h e i r v a l u e s s i g n i f y t h e d e g r e e a n d t h e t y p e o f i n t e r a c t i o n b e t w e e n o n e bond and its neighboring bond. Table 2 lists the best set of force constants obtained. Table 3 compares the o b s e r v e d f r e q u e n c i e s a n d i s o t o p i c s h i f t s w i t h t h o s e c a l c u l a t e d . T h e a g r e e m e n t is q u i t e s a t i s f a c t o r y . T h e m a x i m u m e r r o r is l e s s t h a n 1 p e r c e n t . T a b l e 4 l i s t s t h e Table 2. Force constants (mdyn/A) K(C~S) K(G--S) K(Ni---S) H(SI--C--S2) H(S,~---C--S1) H(C--S--Ni) H(SI--Ni--SI) H(Sr-Ni--S~)* H(~)
3.12 2.60 1.41 0.22 0.25 0.02 0.15 0.20 0.5
H(o)
--0.32 0.01 -- 0.21 0.45 0.07 --0.19 -
-
o.13
0.20 0.055 0.75 0.22 0.05 0.02
H(e)
H(r) F(S 1 . . . Ss) F(S 1 . . . S~) F(S 1 . . . St) F ( N i . . . C) *
f(r 1, o~1) f(r 1, fix) f(dp Yl) f(d 1, d~)* f(d t, da)* f(dl, ~a)*
Inter-ligand interaction constants
Table 3. Comparison of observed and calculated frequencies and b a n d assignments for the [Ni(CSs)2]2- ion (em-')* Observed
B2w
~(6SNi)
Art
fT(SSNi)
A~
Yl
--
--
25
0.0
v,
485.0
0.0
480 60 14 856.9 366.3 297.6 55.0 1010.3 506.1 383.9 185.5
0.0 1.0 0.0 0.0 5.0 1.6 0.4 O.0 0.I 7.1 1.3
~'s ~4 Bl**
Yi v, y~ vs
Bsu
Calculated
~0 Vie Yll v12
---
---
857.5 365.9 297.1
0.0 5.0 1.5
55.5
0.5
1010.0 507.0 384.7 185.7
0.0 0.5 7.2 2.0
Predominant mode Inter-ring torsion ~r(CSs) ~r(NiOSa) Ir(NS4) y(C--S) ~'(Ni--S) ~(S1GSa) v(S1NiS4) V(C~S) V(C---S) ~(Ni---S) ~(SI:N'iS~)
* PPht+ salt 1"A~ = ~(58Ni) -- ~(6~Ni) :~Not i.r. active. [12] T. SHD#AgOUCHI, J . Chem. Phys. 17, 245, 734 and 848 (1949).
Potential energy distribution $1(100~) Sz(92 %) ~a(55 ~ ) , H4(45 ~ ) S~(55 %), $a(45 ~ )
$5(80~) , S7(20%) ~q6(80~),S~(13%) $7(77 ~), $6(7 %), So(10~o) $9(72 %), Se(23 %) $10(64 %), $11(31%) $11(64~), $1o(29~) $12(90%) $14(55~), $18(40 %)
T a b l e 4. Observed frequencies of t h i o c a r b o n a t o complexes (cm-1) [Ni(CSa),]-* PPh~ + ¢(SeNi)
AsPh4+ ¢(SSNi)
1583(m) 1485(m)
1580(m) 1483(m)
1440(s)
1440(s)
[Zn(CS,)z]-* NMe4+ ~(Ni)
1480(s) 1445(m) 1405(m)
1340(w) 1315(w)
1338(m) 1312(m)
l190(w) 1165(w)
1185(m) 1165(m)
lllO(vs) 1075(vw)
1080(s)
1021(s, sh) 1010(vs) 995(s)
1022(s, sh) 1010(vs) 997(s)
965(m)
965(m)
926(vw) 898(vw) 880(vw) 857 (m) 841(w) 815(vw) 790(vw) 755(s) 725(vs) 690(s) 618(w)
925(vw) 897(w) 880(vw) 85___7(m) 840(m) 815(vw) 790(vw) 750(vs) 740(vs) 690(s) 618(w)
53O(vs) 50___5(w) 48...._5(w) 460(w) 394(sh) 38__5(vs) 36__8(m)
333(vw)
50_.7(w) 48....0(m) 468(s)
1013(vs)
904(w) 880(w) 8S_~5(s) 815(w) 790(vw)
50_~8(m) 4S....88(m)
38_~5(vs) 36~6(m)
1440(s)
1440(s)
1340(w) 1315(w)
1340(w) 1315(m)
l190(w) 1165(w) l130(w) lllO(vs) 1075(vw) 1050(vw) 1025(w)
l190(m) 1165(w) 1130(m)
334(vw) 308(w) 29__77(vw)
261(vw)
251 (vw)
246(vw) 241(w) 230(w) 188(w) 18._~5(m)
210(vw)
96(w)
1080(s) 1050(vw) 1023(w)
995(s) 982(s)
997(s) 98_55(vs)
930(vw)
925(vw)
8s0(vw) 860(m) 850(m) 810(vw)
882(vw) s6__5(m) 855(m) 805(vw)
760(s) 722(vs) 690(vs) 618(w) 600(vw) 575(w) 530(vs) 5o__._55(w,~a) 482(vw)
755(s) 745(vs) 690(vs) 618(w) 600(vw) 575(w) 528(w) 50_22(w,sh) 48O(m) 466(s)
450(m)
453(m)
37_~4(w)
372(w) 360(vs) 350(vs) 344(vs)
350(s) 345(s)
263(w) 256(w) 247(vw)
117(w) 92(w) 6_55(w) 52(vw)
1580(m) 1485(s)
945(s)
29.__66(vw) 284(w)
18_.44(m)
1585(m) 1484(m)
455(w) 3s___4(s) 36.~4(s)
AsPh4+ l~(*'Zn)
1285(w)
29._~7(vw) 284(vw)
203(w)
PPha+ ~(e'Zn)
31__~5(vw) 307(vw) 274(sh) 26__22(vs)
20___6(m) 18.._55(m) 152(vw) 116(vw) 5_66(w)
15__O(m) 134(w) 124(w) 1lO(w) 5_55(vw)
31._~5(vw) 26_~2(m) 241(m) 226(w) 20__8(m) 189(w) 15_.2(vw) 115(w) 96(w) 76(w)
(a) Only the bands due to the complex anion are underlined. An other bands are due to cations or non-fundsmental vibrations of the complex anions. (b) The frequency values were rounded off for brevity. (e) Abbreviations: vs(very strong); s(strong); re(medium); w(weak); vw(very weak); sh(shonlder). 1063
1064
A. CO~MIE~, K. NAKA-~OrO, P. CHRISTOPH]SIEMKand A. I~I~LL~R
observed infrared frequencies of the Ni(II) and Zn(II) thiocarbonato complexes with various cations. RESULTS AI~D DISCUSSION
Band assignments As is seen in Table 4, Figs. 2 and 3, the thiocarbonato complexes of Ni(II) and Zn(II) exhibit many bands, most of which are due to bulky cations. In order to distinguish complex anion bands from cation bands, we have measured the spectra of NMe4C1, PPh4C1 and AsPh4C1, and compared their spectra with those of metal complexes containing these cations. Variation of these cations for a fixed metal complex anion has aided the identification of cation bands. Observation of metal isotope shifts in the low-frequency region has given definitive evidence for assigning metal--ligand vibrations. As is shown in Table 3, the bands at 1010(~g) and 857(~5) are assigned to the C--~S stretching (S10) and C--S stretching ($5) modes, respectively. These bands correspond
(tiMe4)2 [M(cs3~
.Q <
!
(pph4)2 INi(CS..j)2]r ~
l
cpPh42nc i
~
i
1600
i
i
1400
i
L
1200
i
,
I000
Frequency,
,
,
i
800
,
600
,
,
400
2(X)
cm - I
Fig. 2. Infrared spectra of (N]~Ie4)~[Ni(CSa)2], (PPha)2[ssNi(OSa)2], and (PPh4) z[64Zn(CS3)2l in the high frequency region. Bands with asterisks are due to the complex anion.
Infrared spectra and normal coordinate analysis of thiocarbonato complexes
o
~'
1065
'~, (PPh4)2 [Ni(CS3)"
"
"-~.~&./.
"',,.,,"
(PPh4)2[Zn (CS3) ~
'..V / I /
400
i
[
I
I
I
I
l
I
I
I
I
300
I
[
{
Frequency,
[
[
I
[
I
[
200
i
i
I
i
i
i
i-{
[
[
I00
~
[
~
L
[
crn -I
Fig. 3. Infrared spectra of (NMe4)2[Ni(CS3)~,], (PPh4)~[ss'~Ni(CSs)~] and (PPh4) ~[~4"aSZn(CSs)2] in the low frequency region. Vertical lines indicate peak positions of metal isotope sensitive bands.
to the 905 cm -1 b a n d of t h e free CS3~- ion [13] which splits into two b a n d s u p o n c o m p l e x formation. A n o t h e r C - - S stretching m o d e (Su) is a t 507 cm -1 (~lO) which corresponds to t h e 520 cm -1 b a n d of the free ligand. T h e out-of-plane bending m o d e of the free ligand a t 505 cm -1 is n o w shifted t o 485 cm -1 (~2) in the Ni(II) complex. T w o new b a n d s a p p e a r a t 385 (~11) a n d 366 cm -1 (~s) which give large shifts (ca. 7 --~ 5 cm -1) b y t h e 5sNi--6~Ni substitution. These b a n d s m u s t be assigned t o t h e N i - - S stretching modes (S12 a n d Se, respectively). T h e b a n d s below 350 cm -1 h a v e n o t been assigned previously. I n b i d e n t a t e c a r b o n a t o complexes, the 710 cm -1 b a n d o f t h e free C03 ~- ion (OCO bending, E ' species) splits into two b a n d s a t ca. 760 a n d 670 cm -1 [14]. A similar f r e q u e n c y t r e n d m a y be e x p e c t e d for the 320 cm -1 b a n d (SCS bending, E ' species) of the free CS32- ion u p o n complex formation. H o w e v e r , t h e r e are a d d e d complications in t h e l a t t e r case. One o f the E ' c o m p o n e n t s is at 297 em -1 (~7) since it couples w i t h t h e N i m S stretching m o d e a t 365 cm -1 (~e). I n fact, t h e p o t e n t i a l e n e r g y distribution o f ~7 shows 7 % c o n t r i b u t i o n of t h e S s coordinate. This is also consistent with the [13] A. I~¢[]~LIJERand M. STOC~Bm~GF~,Z. Naturforsch. 20a, 1242 (1965); B. KREBS, A. ~VI~-LLER and G. GA~'row, Z. Naturforsch. 2{}b, 1124 (1965). [14] J. FUZITA, A. E. M.A~T~.T.Land K. NAXAMOTO,J. Chem. Phys. 86, 339 (1962).
1066
A. C o ~ ,
K. I~AlrA~VIOTO,P. CHRISTOPKLIEMK a n d A. MOLI~R
observation that this band gives an isotopic shift of 1.5 cm -1 by the 58Ni--6~Ni substitution. As is seen in Table 3, there is no band which strictly corresponds to the other E' component. According to Table 1, Sis is a ring deformation involving the change in the SCS angle. Table 3 shows, however, that $13 contributes only 40 per cent to the 186 cm -~ band ( ~ ) . Therefore, it is most reasonable to assign the band at 186 cm -1 to a ring deformation. Thus, a simple frequency correlation such as seen in carbonato complexes does not exist in thiocarbonato complexes. Although the nature of the weak band at 332 cm -1 is not obvious, we tentatively assign it to a g-type vibration which is weakly allowed by the crystal field effect. The strong band at 186 cm -1 (~12) gives a shift of 2.0 cm -1 by the 58Ni--62Ni substitution. According to our calculation, this band is predomluantly due to the S - - N i - - S bending ($14) mode. The lowest frequency band at 55 cm -1 (~s) has been assigned to the S - - N i - - S ' bending ($9) which involves the change in the inter-figand angle, ~. This mode gives a small metal isotope shift as expected. There are three out-of-plane bending vibrations which are not observed (~1, ~3 and ~4). These modes m a y be overlapped by other bands or their frequencies may be too low to be observed. According to our calculation, ~ was estimated to be 60 cm -1. The broadness of the 55 cm -1 band m a y suggest that ~3 is partially hidden or overlapped by ~8- The frequencies of ~1 and ~4 were estimated to be 25 and 14 cm -1, respectively, even with reasonable maximum values of force constants. Therefore, these bands are probably outside of our observable region. Previously, BURKE and I~ACKLER[9] stated that the low frequency vibrations of the [Ni(CS3)2]2- ion appeared to exhibit considerable mixing, and consequently, a direct correlation of the metal--sulfur stretching frequencies with bond strength could not be made. Our potential energy distribution (Table 3) shows, however, t h a t the Ni--S stretching modes (~11 and ~e) are surprisingly pure. The [Zn(CS3)~]2- ion belongs to the Vd(D2~) point group since the Zn atom is tetrahedrally coordinated by four sulfur atoms. Then, two Z n - - S stretching modes (B~ and E species) are i.r. active. As is seen in Fig. 3, two bands near 260 and 205 cm -1 give relatively large shifts (3 ~ 4 cm -1) by the e4Zn~SSZn substitution. The former is relatively sharp whereas the latter is broad. We tentatively assign these bands to the B 2 and E species, respectively. The frequencies of other vibrations are similar to those of the Ni(II) complex in the high frequency region.
Force constants Table 2 fists the best set of force constants obtained. I n order to fit calculated frequencies and isotopic shifts to observed values, it was necessary to modify the Urey-Bradley force field by adding six interaction constants. Among the latter, f(dj, de) is most important; its value significantly affects the value of K(Ni--S). Without this interaction constant, the value of K(Ni--S) becomes unreasonably small. I t also partly controls the magnitude of isotopic shifts of the Ni--S streteblng modes, f(dl, d3) mainly controls the separation of two Ni--S stretching frequencies. The magnitude of metal isotope shifts is mainly determined byf(dl, ~1) andf(dl, ~8). These two values were carefully adjusted to obtain a perfect fit for metal isotope shifts, f(rl, :h) andf(rl, ill) were added to obtain a perfect fit for the CS stretching modes.
Infrared spectra and normal coordinate analysis of thiocarbonato complexes
1067
Table 5. Comparison of Urey-Bradley force constants (mdyn/A) Bis (N,N-dimethyldithiocarbamato)niekel(II) (Ref. 2)
Bis (ethyl-xanthato) niekel(II) (Ref. 3)
Me
Force constant
NiJS1~N11 ~S~ y ~Me
K(~) K(I~i--S) H(S1--Ni--Sj) H(C---S--Ni) H(S1---C---S2)
2.78
1.69
2.60
2.02 0.3 0.1 0.52
P(S1
• • • S~)
0.62
. Ni)
0.1
2.24 0.65 0.6 0.4 0.4 0.3
1.41 0.15 0.02 0.22 0.22 0.02
P(C
. .
N i ~ S!"~.' " .C'~.•0. ~ S~>Y ~Et
This work
Table 5 compares the Urey-Bradley force constants obtained for similar systems. I t is seen t h a t the value of K(Ni--S) obtained in this work is smaller t h a t those obtained previously for other compounds. I t should be noted, however, t h a t these previous calculations have been done on the 1 : 1 metal/ligand model which entirely neglects the inter-ligand repulsive force, stretching-stretchln~ and stretching-bending interactions. Thus, the value of K(Ni--S) m a y be comparable to those obtained previously if the calculations were carried out on the 1 : 1 metal/ligand model.
Acknowledgments--This work was supported by an NATO research grant (No. 534).