Infrared absorption spectra of aquo complexes and the nature of co-ordination bonds

Spectroci~imica Acta, 1964, Vol. 20, pp. 430 to 439. Pcrgamon Prars Ltd.

Printed in Northern lrelanrl

Infraredabsorptionspectra of aquo complexes and the nature of co-ordination bonds ICHIRO NAKACJAWAand TAKEHIKO SHIMAN~UCHI Department

of Chemistry, Faculty of Science, The University Hongo, Tokyo, Japan (Rec&ed

17 May

of Tokyo,

1963)

Ab&ra&-The infrared spectra of aquo complexes, MSiF,.GH,O (M = Ni, Mn and Fe), NiCl,.GH,O, MnC1,.4H,O, MSO,.‘IH,O (M = Zn and Mg), CuS0,.6H,O and CrC1,.6H,O, and some of their deuterium compounds have been reported for the frequency range from 4000 to 270 cm-l. In addition to the OH stretching and OH, scissors frequencies of the co-ordinated water, there have been observed two or three absorpt,ion bands in the low-frequency range 1000-270 cm-l. The band of weak intensity observed in the range 9OCL600 cm-l and that of medium intensity observed in the range 650-450 cm--l have been assigned to the OH, rocking and wagging modes, respectively, because of the isot,opic shift of their frequencies. The broad band observed in the range 500-300 cm-’ has been assigned to the metal-oxygen stretching vibration. A normal co-ordinate treatment has been made for one complex ion of T, symmetry and for D, symmetry on the basis of Urey-Bradley t,ype pot,ential and the hond stretching force constants for the various metal-oxygen bonds have been calculated. The values for the force constants vary in the order Cr(I II) > Ni(II) > Mn(I1) w Fe(I1) >Cu(II) w Zn(I1) > M&II), showing that the degree of covalent character of the metaloxygen bonds decreases in the same order. The largest value of bond stretching force constants K(Cr-0) is 1.3 md/A, which is still smaller than those for the metal-nitrogen bonds of amino and nitro complexes and those for the metul-curbon bonds c.t’ cytmide complexes.

AMONGthe metal-ligand co-ordination bonds found in the cyanide, ammine, nitro and aquo complexes, the metal-oxygen bond of the last would be less covalent than those of the first three. However, this metal-oxygen bond is not purely ionic and is expected to have new modes of vibrations such as OH, wagging, twisting and rocking modes as well as the metal-oxygen stretching modes. These vibration frequencies may be observed below 1000 cm-l and be determined bot,h by the co-ordination effect and the outer-ion effect. The latter effect is mainly governed by the strength of hydrogen bonding to neighbour atoms in the crystal. Infrared spectra were reported by ELSKEN and ROBINSON [l] of mono- and dihydrates of alkali halides and alkaline earth halides, where the distance between the metal and oxygen atoms is pretty long. The absorption bands in the 300-600 cm-l region were interpreted as arising from the librational modes of the bound water molecules in the crystal. The librational frequencies are conipared with those of ice, of which the measurements of the infrared and Raman spectra were made by many researchers [2-41 and the normal co-ordinate analysis was made by KYOGOKU [S]. These frequencies described above are mainly determined by the outer-ion. effect. [l] J. VAN DER ELSKEN and D. W. ROBINSON, Spectrochim. dctu, 17, 1249 (1961). [2] N. OCKMAN and G. B. B. 11. SLJTHERLAND, Proc. Roy. Sot. (Lo&), A247, 434 (1958) [3] D. F. HORNIG, H. F. WHITE and E. P. REDING, Spectrochim. Acta, 12, 338 (1958) [4] I?. A. GICXJ~RE and K. B. HARVEY, Canad. J. Chem., 34, 789 (1966). [5] Y. KYOGOKU, Ni33ipon kagaku &ash& 81, 1648 (1960). 12

429

ICHIRO NAKAGAWA and

430

TAEEHIKOSHIMANOTJCHI

In the aquo complexes where the distance between the metal and oxygen is relatively short the co-ordination effect may be a more significant factor in determining the frequencies of the complex ion. So far a few attempts [6, 71 have been made to study the characteristic absorption bands of co-ordination water molecules. FUJITA et al. [6] found the absoprtion bands for Ni2+, Cu2+ and Cr3+ aquo complexes in the NaCl region and discussed them on the basis of the effects of co-ordination bonding. Recently GAMO [7] made similar studies. However, no systematic investigation has been made to study the nature of the metal-oxygen bond on the basis of the spectra including the lower frequency region as well as the normal co-ordinate analysis. In the present study the infrared spectra of aqua complexes, MSiF,.GH,O (M = Ni, Mn and Fe), MS0,.7H,O (M = Zn and Mg), NiC1,.6H,O, MnC1,.4H,O, CrC1,.6H,O and CuS0,.6H,O and some of their deuterium compounds have been investigated in the frequency range from 4000 to 270 cm-l. Raman spectra of ZnS01.7H20 have also been investigated in the aqueous solution. For these aqua complexes investigated the metal-oxygen bond is fairly covalent as evidenced by a relatively short bond distance and, therefore, the co-ordination effect may be a main factor in determining the frequencies. A normal co-ordinate treatment has been made for one complex ion and the nature of the metal-oxygen bond has been discussed on the basis of the calculated values of the force constants. The outer-ion effects have also been taken into account as an auxiliary factor of determining the frequencies. EXPERIMENTAL DETAILS AND RESULTS Preparation

of deuterium

compounds

The deuterium compounds were prepared by repeated recrystallization complexes of light water from heavy water and by freeze-drying. Measurement

of the corresponding

of spectra

The spectra in the NaCl region (4000-650 cm-l) were obtained by using a Hitachi EPI-2 Infrared Spectrophotometer. The wavelength calibration was made by the useof thesharp peaks of indene [S], 1,2,4-trichlorobenzene and polystyrene. The spectra in the lower frequency region (700-270 cm-l) were measured with a CsBr foreprism-grating spectrophotometer designed and adjusted in our laboratory [9]. The wavelength calibration was made by the use of the pure rotational lines of HsO vapour and the sharp peaks of 1,2,4-trichlorobenzene. Samples were prepared for examination by the KBr disk and the Nujol mull methods. The absorption bands are in general broad, especially in the case of Nujol mull methods. The frequencies measured by the KBr method are sometimes different from those by the Nujol mull method. The observed values of frequencies have been taken from those in the KBr disk method unless the difference from those in the Nujol mull method is large, because the former method gives less broad absorption bands. The measurement of Raman spectra has been made in the 20-30 per cent aqueous solution with or without the NaNO, filter by the use of the photographic spectrometer made by MIZUSHIMA[lo], exposed for 6 and 15 hr using Kodak Spectroscopic Safety Film Type 103-AJ. The typical infrared spectra below 1000 cm-l are shown in Fig. 1. [6] [7] [S] [9] [lo]

J. FUJITA, K. NAIUMOTO and M. KOBAYASHI, J. Am. Chem. Sot., 78, 3963 (1956). I. GAMO, Bull. Chem. Sot. Japan, 34, 760, 765 (1961). R. N. JONES, P. K. FAURE and W. ZAHARIAS, Rev. Univ. des Mines, 15, 417 (1959) T. SHIMANOUCRI, Y. KYOGOKU and T. MIYAZAKI, Spectrochim. Actu, 13, 451 (1963). S. MIZUSHIMA, Raman Effect, Hundbuch der Physik (Ed. S. Fhigge) Vol. 26, Springer, Berlin (1958).

Infrared absorption spectra of aquo complexes

431

Ni Si Fs*6H,O

Vi (H20)4Cl~ Ui Cl* -6HzO

Fig. la. Infrared spectra of aquo complex ions ‘(1000-270

cm-l).

P 20

I5 I

’

’

’

’

’

’

’

1

25 ’

’

’

’

’

30 ’

’

’

Fe(H20k2+

FeSiFG*GH,O

MnSi Fs*6H20

Mn(H,Ob CC2

Fig. lb. Infrared spectra of aquo complex ions (1000-270

cm-l).

’

’

ICHIRO NAKAOAWA and TAKEHIKO SHIMANOUCHI

432

Zn(H,O);+

!nS047H,O Roman

line

(except

SO,23

1

Mg(H,O,,‘+ MO str

!kjSO,;IH,O Roman

line (except

SOT)

1

I

Mg(D,O):+

Fig. lc. Infrared spectra of aquo complex ions (1000-270

cm-l).

DISCUSSION Norrr&

co-ordinate analysis

The X-ray and neutron diffraction studies [ 1 l-141 for some of the aquo complexes investigated in this study show that the metal-oxygen bond distance is 2.0-2.2 A. Therefore the co-ordination effect is considered to be much stronger than the solid state effect and a normal co-ordinate analysis can be made for one complex ion. The neutron diffraction study [14] for FeSiF,.6H,O shows that the H,O ligand is COordinated with its two-fold axis and the metal-oxygen bond colinear; the T, symmetry shown in Fig. 2 for M(H,O), and the D, symmetry for M(H,O), are adopted for the present treatment. The normal vibrations of these ions are shown in Table 1. Of these only F, species for T, symmetry and A,, and E, species for II,, symmetry are infrared active and the expressions for G- and F-matrices of the infrared active species are given in Table 2. Table 1 shows that only the OH, rocking and wagging and the metal-oxygen bond stretching vibrations are expected to appear in the frequency range 1000-270 cm-l in the infrared spectra, because the OR10 deformation frequencies should lie below 250 cm-‘. [ll] C. A. BEEVERS and H. LIPSON, Proc. Roy. Sot. (Lond.) A14t3, 570 (1934). [12] J. MIZUNO, K. UEEI and T. SUCAWARA, J. Phys. Sot. Jupun, 14, 383 (1959). 1131 R. A. PETERSON and H. A. LEVY, J. Chem. Ploys. 16, 220 (1957). [14] W. C. HAMILTON, Private communication to Prof. I. TSUJIKAWA, Unpublished

data.

Infrared absorption spectra of &quo complexes

0

Fig. 2. The structure of M(H,O),

Vib. mode

R:

A,:

R(P)

9,: S,: S,:

OH str. OH, miss. MO str.

A,: E,:

ia R(DP)

S,: Sg: Se: S,:

OH, OH OH, MO

E,:

ia

S,:

OH, twist

F,:

R(DP)

S9: OH str. S,,: OH, rock S,,: OH, wag S,,: OH, twist S,,: 0110 dcf.

Raman active; IR:

type ion (T,)

Species

- -

3’“: IR

Vib. mode sl,: S,,: S1,: S,,: Sls: &: E&,: Szl:

twist str. s&s. str.

OH str. (aym) OH str. (anti.) OH, miss. OH, rock. OH, wag. MO str. OMO def OMO dof.

______

Infrared active; P: Polarized; DP: Depolarized; ia: inactive.

Table l(b). The normal vibration of M(H,O), -

-____

H

type ion.

Table l(a). The normal vibrations of M(H,O), Speoies

433

Vib. mode

Species Al,:

R(P)

S1: OH str. S,: OH, miss. s,: MO xtr.

Al,:

ia

S,:

OH, twist.

A,,:

ia

S,:

OH, wag.

APU: IR

S,: OH Rtr. S,: OH, rock. s,: ant-of-plane def.

B1,:

R(DP)

S,: OH str. S,0: OH, s&s. S1,: MO atr.

B,,:

is

S,,:

OH, twist.

-

type ion (D,,)

Species

Vib. mode

Bp,,: R(DP)

S,,: S,,:

OH, wag. OMO def.

B,,:

S+ &: s,,:

OH str. OH, rock. out-of-plane dcf.

ia

E,:

R(DP)

S,,: OH str. S,,: OH, twist. Sal: OH, rock.

E,:

IR

El,,: S,,: Spa: S,,: Ss8:

OH str. OH, miss. OH, wag. MO str. OMO def.

434

IcmRO

NAKAGAWA and

TAKEHIKO

SHIMANOUCHI

Assignment of the observedfrequencies I n the fluosilicate complexes, [M(H~O)e]~+[SiFe]~-, the two strong absorption bands belonging to the [SiFe] ~- ion appear at 740 and 485 cm -1, which will be discussed later. There remains two broad bands to be assigned. The higher one, at 645 cm -1 for [Ni(H~O),] 2+, shows a frequency shift ratio of about 1/%/2 on deuterium substitution, while the lower one does not shift so much. In the complex [Ni(HsO)aCl~] where there is no disturbance by the absorption of [SiFt] ~- ion, another band a t 755 cm -1 has been observed. These facts show t h a t the lowest band near 400 Table

2(a). The

elements

i, j /z -}- 2/~lc 2

14, 14, 14, 14, 14, 15, 15, 15,

0 0 - - %/(2)plc 0 0 /~ -~- 2 ~ l s z

15, 18 15, 19

I5, ~o 15, 16, 16, 16, 16, 16, 16, 17, 17, 17, 17, 17, 18,

21 16 17 18 19 20 21 17 18 19 20 21 18

G- and

F-matrices

of F u species

~,~

14, 14 14, 15 14, 16 17 18 19 20 21 15 16 17

of the

0

- - 2~v/(3)//l~sc

0

F,~,~ K ( O H ) -~ (%~ - - 0 " I t ~ S ) F ( H . • • • M) -}- 2 % Z F ( H • • • H ) 0

f - - [lily/(3)] (s~t I - - 0 " I s l t , ) R F ( H - • • M) L + [3 V/(3)15] e o % r F ( H • • • H ) 0 0 V/(2) (sis 2 + 0.1 t l t 2 ) F ( H • • • M) 0 0 K ( 0 H ) -t- (s2~ - - 0-1tm2)F(H • • • M) - - 0-2toZF(H • • • H ) 0

- - 2~Is('r I ~- Tc)

(82g1 - - 0 - 1 s l t 2 ) R F ( H • • • M)

0 0

0 0

~/(2)/~-~s

for T a symmetry

o

- - ~/(2)px~'~s 3(p~ ~ -~- 2 p ~ s ~) 0 0 ~/(6)p~s 0 0 p ~ Q- 2 p ~ ( ~ -~ ~c) ~ -~- 4 ~ o ~ - - 2V/(2)/~o~'~~ 2%/(2)~o,r ~ - - %/{2)[4po'rl ~ -~- ~.~ITI("/"I"2C 7~)] %/(2)~I~'X(T1 -~ ~c) . f ( 1 / 2 ) p ~ % ~ / c ~ ~t./~1(~1 -Jr .rs/c)~

0 ( 2 / 3 ) J ( H O H ) -~ ( I ] 3 ) J ( H O M ) ~ F(seiss.) 0 0 - - [2/V/(6)] (s~t~ - - O . D ~ s ~ ) r F ( H . . • M) 0 0 J(HOM) ~ F(rock.) 0 0 0 0 H0r) ~ F(wag.)

18, 19 18, 20 18, 21

-- 2pov ~ 4pO~'l ~ -~ p l ~ ' l ( v l -~ vs/c) p~'r~O'~ -I- ~-s]c)

0 0 0

19, 19

2/~ o ~- / ~

19, 19, 20, 20, 21,

- - 4/~o~x 0 2(/~ -}- 4~uo~-~~) 0 2/~ ~ ~

20 21 20 21 21

t ÷ 2/~o~

~ , / ~ t , a n d ]~0: r e c i p r o c a l m a s s e s o f H , O, a n d M, r e s p . ~-~ lit ~ 1Jr(OH) ~rI ~ I / R = I / R ( M O ) c = cos (C(/2), s = sin (¢Z]2) ~: a n g l e o f H O H fl: a n g l e o f H O M

~+ 2~= 2~

~ K ( M 0 ) ~- 1 . 8 F ( O • • • 0 ) -~ 2(s~ 2 - - 0 . 1 $ ~ ) P ( H • • • M) t_---- F ( M O ) 0 . 9 R F ( O • • • O) 0 J(OMO) 0 J(OMO) so =

(r - - r c o s ~¢)lq, f l =

( R - - r c o s fl)lq"

% = (r - - R cos fl)lq, $1 = ~din o~/q', t o = r s i n ~ l q , t~ = R sin fllq" q = (r2-t- r l - - 2 r 2 c o s a ) i q" ~ ( R 2 "F r 2 - - 2 R r cos f l ) i J ( H O H ) = [ H ( H O H ) -t- (to~ ~ 0 " l s o g ) F ( t t " • • H ) ] r 2 J(HOM) ~ RrH(HOM) ~- R r ( t l t 2 -~- s1% × O . 1 ) F ( H • • • M) J ( O M O ) = [ H ( O M O ) ~- 0 - 5 5 F ( O . • • O ) ] R t

Infrared absorption spectra of aquo complexes Table 2(b). The elements of the Gi- and F-matrices

435

of IR active species for D,,, symmetry

K(OH) + (aa* - O*ltsa)P(H * . * H) (.Y& - O.lt,s,)RF(H * . . M) 0 J(HOM) s F(rock.) 0

O*2toPF(H * * . M)

J(a)

%

22,22 22, 23 22, 24 22, 25 22, 26 23.23 23, 24 23, 25 23, 26 24, 24 24, 25 24, 26 26, 25 25, 26 26, 26

K(OH) + (sac - O.lt,z)P(H . (1/2/3)&t, - O.ls,t,)RF(H t-+ (3~3/5)t,8,rF(H * * * H)

* * M) + . * * hi)

2QF(H.

* . H)

;~(R,J~ + O.lt,t,)P(H * . . M) 0 b]2/3)J(HOH) + (1/3)J(HOM) ES F(sciss.) ;

(2/d6)(8&

-

O~lt,s&F(H

* * . MM)

H(n) z: P(wag.) 0 0 {~Mo&

omqo

. * . 0) + 2(a,’ -

O.lt,‘)P(H

- * - M)

-(91/2/20)RF(O**.O) J(OM0)

cm-l is assigned to the metal-oxygen stretching vibration and the higher two bands to the OH, rocking and wagging vibrations. In this type of molecule the potential which governs the wagging frequency is of different nature from that for the rocking, unlike in the case of CH, wagging and rocking frequencies of the saturated compounds. Therefore the normal vibration calculation gives no information of the distinction between the wagging and rocking vibrations. We have assigned the stronger band to the wagging mode and the weaker one to the rocking mode from the following reason. N~YAZAWA showed [15] that the absorption band due to the librational mode about A axis is stronger that that about C axis for the bound water molecule in the nitrogen matrix, on the basis of the approximate intensity calculation assuming the fixed dipole moment. The librations about A- and C-axes correspond, respectively, to the wagging and rocking modes of the co-ordinated water molecule. (See Fig. 3.) So we can expect a stronger band for the wagging vibration of the aquo Moreover, the normal vibration calcomplex ion than for the rocking vibration. culation shows that the agreement between the observed and calculated frequencies is much better for the assignment where the rocking frequency is higher than the wagging. In the same way the observed bands are definitely assigned for all the complex ions investigated as shown in Fig. 1. The OH, rocking vibration of some complexes is not found probably because of the disturbance by the strong bands of the anion ( [SiPJ2- or [SOJ2-) or because of the inherent weakness of the intensity. We have also observed a broad Raman line near 380 cm-l for [Zn(H20)J2+, [IS] T. MIYAZAWA, BUZZ. Chem. Sot. Japan,34,202 (1961).

436

ICRIRO

and

NAKAGAWA

SHIMANOUCHI

in addition to those of [SO,]2- ion and MATHIEV [16] observed a polarized Raman line near 380 cm-l for [Mg(H20),12+. This Raman line arises from the tot&y symmetric metal-oxygen stretching vibration and this result of Reman effect is another support for the assignment of the metal--oxygen stretching vibration. Outer-

ion

effect

(X) 0

,’

l. *.

‘.H

H

0 (Xl

/-

lo/ M

Librotionol

modes

1, Wogging

Fig. 3. Librationel

Twisting

1, Rocking

modes and outer-ion effect.

Calculation of the force constants On the basis of these observed frequencies we have made the normal vibration calculation using the Urey-Bradley type potential [17] and obtained the force constants. In this kind of aquo complex ions the values of the diagonal elements of F-mat.rix for the symmetry co-ordinates corresponding to the appropriate vibrational modes are physically significant for the rocking and wagging OH, vibrations. The actua.1 procedure of the calculation is as the following. The repulsive constants E’(0 . * .O), F(H. - *H) and F(H** * M) were assumed to be O-20, O-10 and 0.07 mdyn/A, respectively. The diagonal element of F-matrix for the two OMO deformation modes, F(def.), was assumed to be 0.60 mdyn * A, from which the OMO deformation frequencies are calculated to be about 150 cm-l. Tsujikawa assumed this frequency to be 250 cm-l to explain the violet absorption lines of MnSiF,.6H20 [18]. We have no direct data for this vibration except we know that this should lie below 270 cm-l. The Jacobian matrix (&,/8Fi) shows that the value of F(def.) hardly affects the other frequencies than the OMO deformation vibrations. Therefore the force constants in which we are interested can be obtained reasonably, regardless with t,he OMO deformation frequencies. [lS] J. I’. MATHIEU, Corn@ Rend. Acarl. SC&, l’uris, 231, 896 (1950). 1171 T. SHIMANOTICHI,J. Chem. Phys., 17, 245, 734, 848 (1949). [18] I. TSUJIKAWA, International Symposium on Molecular Structure and Spectroscopy tember, 1962, Tokyo, Japan). See also S. KIODE and M. H. L. PRYCE, Phil. Mag., 3, 607 (1958).

(Sep-

Infrared

absorption

437

spectra of aquo complexes

By using the (i-matrix in Table 2 and the observed frequencies in Fig. 1, we obtained the results as shown in Table 3, where the force constants are expressed in terms of the diagonal elements of F-matrix, except the metal-oxygen bond stretching force constant for which both the diagonal elements and the Urey-Bradley force constants are given. The OH stretching and OH, scissoring frequencies are not included in this table, because they do not change at all with the central metal ion. The OMO deformation frequencies are also not shown because of the lack of the observed frequencies as described above. Table

3. The OH, rocking and wagging,

and MO st!retching frequencies and the corresponding force constant,5

OH, rock talc. ohs. --~-._..____.___.___._.__ LCr(H,O),]S+

[WH@,l*+

[Ni(&O),]“+ Wn(H,‘.X,l~+ [Pc(H,O),]a+ [~:u(H,O),)~+ [Zn( H a0),]2-+ [zn(I),o)J*+ [.llg(H,O),]e+ LMg(U,o),p+

800 (756)’ (656)‘f -( 887 85.5 467 -- ~. 474

MO ohs.

Dirrgonsl elements of F-matrix F(rock) P(wag) B(Mo md.A md.A md/A

a. talc.

UBFF K(Mo) md/A

823 752 560 OBH ti55 870

541 645 450 660 576 335

548 636 496 872 576 531

499 405 389 398 389 440

484 404 384 “‘$5 389 442

0.30 0.26 0.26 0.19 0.19 0.33

0.11 0.15 0.15 0.12 0.12 9.086

1.80 1.34 1.34 1.28 1.24 1.15

1.31 0.84 O-84 0.80 0.76 067

G20 4F4 607 45<5

541 392 460 391

347 429 471 374

364 358 310 -

364 342 320 299

0.17 0.17 0.16 0.16

0.11 0.11 0.08 0.08

1.12 1.12 0.80 0.80

0.64 0.64 0.32 0.32

* Ni(H,O),(‘l,; ** Tv~I~(H,O),(‘I, UI
-

of IJrey--Bradley field

When we look at tho results of Table 3, the agreement between the observed and calculated frequencies is quite satisfactory, except for the OD, wagging frequcncies of [Ni(D,O),]* + and [Zn(D,0)J2+, which will be discussed later. THE

NATURE

OF

THE

CO-ORDINATION

BONDS

The values for the metaLoxygen bond stretching force constants vary in the order Cr(TlI) > Ni(II) N Mn(I1) N Fe(I1) > Cu(I1) N Zn(II) > Mg(II), showing that the degree of covalent character of the metal-oxygen bonds decreases in the same order. The largest, value of bond stretching force constant,s K(@r-0) is l-3 mdyn/A, which is still smaller than those for the metal-ca;rbon bonds of cyanide complexes [I!)] and the metal-nitrogen bonds of nitro complexes [20] and some of the amine complexes [21-231, as shown in Table 4. We can conclude that t,he metal-oxygen bond of aquo complexes is much less covalent, even for those investigated in this study where the bond dista,nce is pretty short, comparing with the co-ordination bonds in the complex ions such as cyanide,.nitro and ammine complexes. [19] I. NAKAUAWA and T. SHIMANOUCHI, Speetrochim. Acta, 18,101 (1962). [20] I. NAKAGAWA and T. SHI~TANOUCHI. To be published. [21] T. SHIMANOXWIL and I. NAPAGAWA. To be published; See also Spectrochim. A& 89 (1962). [22] 8. MIZTXHIMA and I. NAKACAWA, IV@pon. &up&u .&s&i, 80, 124 (1959). 1231 S. MIZVSHIMA, I. NAKAGAWA and D. M. SWEENY, J. CILem. P&s., 25, 1106 (1956).

18,

438

ICEIRONAKAUAWA

and TAKEEIKOSEIMANOUOHI

Table 4. Force conskxntsof the co-ordination bon& Complex ion

[WCN),IzKWCN),14CWCV,I”-

[F&(CN),]”

i-‘%‘W,l’-

[Fe”I(CN),]J-

KWNO,),l*-

Foroe constants @d/A) Umy-Bradley 5oid

Metal-ligend atretching frequencies 605(IR); 664(IR) 660(IR) 685(IR); 665(IR); 511(IR);

465, 466(R)

K(Pt-C) K(Os-C) K(Ru--C) K(F&-C) K(Co-C) K(Fe=LC)

415(R) 409(R) 389(R)

= = = = = =

3.43 3.34 2.79 2.43 2.31 1.73

418(IR) (coupled with NO, rooking mode)

K(Co-N)

= 1.16

613(IR) 673(IR) 603(IR) 470(IR) 420(IR)

K(Hg-N) K(Hg-N) K(Co-N) K(Cr-N) K(Cu--N)

= 1.70 = 1.70 = 1.05 = 0.94 = 0.84

490(IR) IOS(IR) 395(IR) 389(IR) 440(IR) 364(IR); 310(IR);

K(Cr-0) K(Ni-0) R(Mn-0) K(Fe--0) K(Cu-0) K(Zn--0) K(Mg-0)

= = = = = = =

380(R) 380(R)

THE

OUTER-ION

Referenoee --

1.31 0.84 0.80 0.76 0.67 0.64 0.32

24-25 18-19 18-19 19, 26 19, 26 19, 26 20

22 23 21 20 20

the prosen t msesroh

EFFECTS

Even if the intramolecular potential of one complex ion is harmonic, the true potential by which the vibration frequencies are determined would not be harmonic, but perhaps could include a quartic potential opposing the libration in a more or less rigid frame formed by the outer atoms. In that case ~&n would be larger than If the potenthe value (&r/1n)1/2, expected on the basis of the harmonic potential. As pointed out previously, the ratio tial is I .re quartic, (V&J is (;1n/1,)2/3 [24]. observed of v&n for the wagging vibrations of Ni and Zn complexes is larger than that calculated on the basis of harmonic potential. This may be partly caused by the quartic term in the potential. It seems plausible that this discrepancy is found in the wagging vibration because this mode corresponds to the out-of-planelibration in a rigid frame as seen in Fig. 3. THE

VIBRATIONS

OF

ION

[SiFJ2-

Although the assignment of the two strong bands belonging to the P1, vibrations of [SiF,12- is of little doubt, we checked this by making the normal co-ordinate Table 5. Vibration frequenciesand force constants of rSiF,l+ ion Vibration mode SiF str. Y1(AI#) SiF atr. va(E,) SiF str. vJ(F1,,) FSiF def. v,(F,,)

[24] B. P.

BELL,

Obs.

Celo.

666(R) 610(R) 740(IR) 486(IR)

6.56 610 740 486

Proc. Roy. Sot. (Lond.), Al&

Force constants K(SiF) = 2.07 md/A P(F*** F) = 0.60 md/A f(def.) diagonal = 0.75 md/A k(Ar,h~~+~) = 957 md/A k’(Ar,Ars+l) = 0.04 md/A

328 (1945).

Infrared absorption spectra of “quo complexes

439

In this treatment the observed frequencies of Raman lines are also taken into account and the results are shown in Table 5. The values of the stretching force constants shows that the Si-F bond for the octahedral configuration should be appreciably covalent.

treatment.

Acknowledgement-The authors express their sincere thanks to Professor I. TSUJIKAWAof Tohoku University for his useful discussionsand for the generous offer of some of the samples and to Professor T. MIYAZAWAand Dr. J. FUJITAof Osaka University for their valuable discussions. [25] D. M. SWEENY,I. NAKAQAWA,S. MIZUSHIMA and J. V. QUAOLIANO, J. Am. Chem. Sot., 77, 6521 (1956). [ 261 K. NAEAMOTO,J. FUJITAand H. MURATA,J. Am. Chem. Sot., 80, 4817 (1958). [27] K. KAWAI. Private communication.