4904
K. NAKAMOTO, J. F U j I T A ,
s. ‘TANAKA A N D &I. KOBAYASHI
platinum anode disappeared after the electrode had become oxidized. If the platinum anode is only partially oxidized an anodic chronopotentiometric wave is still observed but the transition time is smaller than for an unoxidized anode. This is demonstrated by the chronopotentiograms of iodide ion in Fig. 4 obtained with different degrees of prior oxidation of the anode. 1
Vol. 79
Acknowledgment.-Appreciation is expressed to Merck and Co. for sponsoring the Merck Graduate
1 0 5
0
10
0
10 2 0 0
20
40
Time, sec.
O C J
I 1 0
I
I
I
I
20
40
0
IO
J
Time, sec. Fig. 3.-Anodic chronopotentiograms for 0.094 milliformal potassium iodide in phosphate buffer a t pH 6.5 at a current density of 0.3 milliamp./cm.2: (1) with a previously reduced electrode; (2) resulted when the trial was repeated.
[CONTRIBUTION FROM
THE
Fig. 4-Anodic chroriopotentiograms for 0.094 milliformal potassium iodide in borax buffer a t pH 8.5 a t a current density of 0.3 milliamp./cm.2: (1) previously oxidized electrode; ( 2 ) oxidized electrode cathodized for 6 sec. a t 0.3 milliamp./cm.z; ( 3 ) oxidized electrode cathodized for 10 sec. a t 0.3 milliamp./cm.2; (4)oxidized electrode totally reduced by cathodizing for ca. 20 sec. a t 0.3 millianip./cm.2.
Fellowship in Analytical Chemistry held by one of us (F.C.A.). CAMBRIDGE, MASS.
DEPARTMENT OF CHEMISTRY, OSAKAUNIVERSITY]
Infrared Spectra of Metallic Complexes. IV. Comparison of the Infrared Spectra of Unidentate and Bidentate Metallic Complexes BY KAZUO NAKXMOTO, JUNNOSUKE FUJITA, SHIZUO TANAKA AND MASAHISA KOBAYASHI RECEIVED APRIL4, 1957 The infrared spectra of sulfato, carbonato, oxalato and acetato metallic complexes in which those ligands coordinate to the metal as an unidentate and as a bidentate have been measured in the range between 5000 and 400 cm.-’. From the comparison of the spectra of bidentate with that of unidentate complexes of the same ligands, it has been found that lowering of symmetry of the ligand or frequency shifts of the fundamentals due to coordination is, in general, more remarkable in the former than in the latter.
Introduction Studies of the effect of coordination on the infrared spectra of metallic complexes afford valuable information on the nature of the metal-ligand bond and the stability of the complex. Coordination usually causes (1) appearance of new bands and splitting of the degenerate modes due to lowering of symmetry, (2) frequency shifts of the bands, and (3) intensification of the spectra. In the previous works,l our attention was focussed to the frequency shifts of the ligand fundamentals caused by complex formation. However, a study of the effect of coordination on the symmetry of the ligand is also important. It is well known that the ligands such as COB-- and Cz04-- coordinate to the metal as an unidentate and as a bidentate. Therefore, comparison of the infrared spectra of unidentate and bidentate metallic complexes of those ligands will be of considerable interest. The present paper deals with the infrared spectra of sulfato, carbonato, oxalato and acetato complexes. In discussing the symmetry of the ligand from the spectra obtained in the crystalline state, site (1) J . F u j i t a , K. S a k a m o t o a n d hl. Kobayashi, THISJ O U R N A L . , 78, 6295, 3983 (1936); J . P h y s . C h e n i . , 61, 1014 (1957).
group or factor group analysis based on the knowledge of crystal structure is desirable. Unfortunately, for most of the compounds discussed here, crystal structural data are lacking. It is anticipated, however, that the effect of coordination upon the ligand absorption is much stronger than the effect of the over-all crystal field. Hence, ignorance of rigorous site group analysis niay be justified. By coordination, all the fundamentals are more or less shifted according to their modes of vibration. As the metal-ligand bond becomes stronger, their shifts to lower or higher frequencies increase. Furthermore, when coordination lowers the symmetry of the ligand, forbidden vibrations of the free ion are permitted, and degenerate vibrations are split. The stronger the metal-ligand bond, the larger the splitting of the degenerate mode. Therefore, frequency shifts, the magnitude of the splitting, and the intensity of newly permitted bands are useful as a measure of the effect of coordination. As to the change of relative intensity caused by complex formation, it is generally expected that newly developed fundamentals have weak or medium intensity, and other fundamentals active in
4905
SPECTRA OF UNIDENTATE AND BIDENTATE METALLIC COMPLEXES
Sept. 20, 1957
Cm.-'
the free ion increase their intensity. As is shown later, this anticipation is correct in the present series of the compounds. Since most of the compounds examined here are Co(II1) acido ammine complexes, they exhibit the bands characteristic of the acido group in question together with that of ammonia ligands. Therefore, care was taken not to confuse the former with the latter bands which are easily identified in the spectra. Experimental
1200
1100
1000
950
900
Preparation.-The compounds used in this work were prepared according to the literature which is given in Table I, 111, V and V I . Since most of the compounds studied here are typical metallic complexes, their purity was checked by comparing the ultraviolet spectra with the published data.2 However, the following two sulfato complexes which are comparatively difficult to prepare, were analyzed to examine their chemical composition. Anal. Calcd. for [ C O ( N H ~ ) ~ S O ~ C ] Bo ,~ :18.41; X, 21.88; Br, 24.97. Found: Co, 18.20; N, 21.95; Br, 25.01. For
( s H , j , C o ( ~ ~ ~ ) C o ( N H ~ ) ~ ] ( N O , ) , : Co, 21.35; K,
30.44. Found CO, 2i.20; N, 30.23. Absorption Measurements.-The infrared spectra were obtained by a Perkin-Elmer Model 21 double beam infrared spectrophotometer using NaCl and KBr prisms. The KBr disk method and Nujol mull technique were employed for the spectra of the S a c 1 and KBr regions, respectively. I
Results and Discussion Sulfato Complexes.-Free sulfate ion has (1) high symmetry of T d . Of the four fundamentals, only v3 and v4 are infrared active. If the ion is coordinated to the metal, the spectra will undergo marked change. Figure 1 and Table I indicate the spectra of 1200 900 an.-' region and the lo-
8
.
.
I
.
9
I
.
.
.
.
I
I
11
10 IJ.
Fig. l.-Infrared absorption spectra of: -- , [CO( N H ~ ) ~ ] ~ ( S O ~ ) ~ --------.~HZO , [Co ; (NH3),S04]Br ; -. -. - * ,
-
Co(NH3)4](N03)3; (KBr diskmethod).
[(NH~)ICO(;::>
TABLE I
THEINFRARED SPECTRA OF SULFATO COMPLEXES (Cra-1) Compound
Symmetry
Free SO4-- ion" [Co(NH3)8I2(S04)a.5K*Ob [Co(NH3),S04]Brc
Td
Td C3"
( NHI)~ C O < ~ ~ > O ( N H (1 ~ ) CZ" so4 (N02hd
u1
....
Y1
. . ./,U
E d
...
973(VW) 970 (M)
438(M)
995(M)
462(M)
~
1130 1032 1117 1050
--
{ -
VI
iJ4
1104(VS) 1140(0S) 1044(S) 1143(S) 1060(S) 1170(S) 1105(S)
613(S) 617(S)
6411:s) 6 101:s)
a G. Herzberg, "Infrared and Rainan Spectra of Polydtoniic Molecules," D. Van Nostrand Co., New York, E.Y . , 1945, p. 167. * S. M. Jorgensen, Z. anorg. Chem., 17, 457 (1898). S. M. Jorgensen, J . prakt. Chem., 31, 270 (1885). A . Werner, Ber., 40, 4610 (1907). e Raman, 981 em.-'. f 451 cm.-l. VS,very strong; S, strong; M, medium; w, weak; VW, very weak.
TABLE I1 CORRELATION TABLE'BETWEEN T d , "1
Y1
Ai (R) E (R) C3" Ai(I,R) E(I,R) CZ" Ai ( 1 3 ) Ai(I,Rl Az(R) I, infrared active; R, Raman active. Td
+
c3v
and C ~ V
Y1
Fz(I,R) Ai(I3) Ai(I,R)
+ E(I,R) + BI(I,R) + Bz(I,R)
YI
Fz(J,R) &(I,R) -t E(1,R) Ai(1,R) B>(I,R)
+
+ Bz(I,R)
cation of those four fundamentals in the free ion, In [ C O ( N H I ) ~ S O ~ ]however, B~, both V I and v 2 unidentate complex, and binuclear complex joined appear with medium intensity, and moreover, v3 - ~ H v4 ~ Osplit , by a sulfate bridge. In [ C O ( N H ~ ) B ] ~ ( S O ~ ) ~and into two bands, respectively. The v3 and v4 are strong, but V I is very faint and v Z is not correlation diagram of Table I1 suggests that this observed. Therefore, it is concluded that Tdsym- result can be interpreted reasonably only when we metry of the ion still holds although V I is weakly assume that Td symmetry of the ion is lowered to ~ ] ~ + C3" by complex formation. Thus we conclude allowed by the perturbation of [ C O ( N H ~ ) ion. (2) Y.Shimura, Bull. Chem. SOC.J a p a n , 29, 311 (1956). that one of the oxygens of the ion is different from
K. NAKAMOTO, J. FUJITA, s. TANAKA AND M. KOBAYASHI
4906
Vol. 79
Cm.-' 2000
5
1500
6
1400
1300
1200
8
7
1100
9
1000
10
P.
Fig. Z.-Infrared
absorption spectra (KBr disk method) of: . . . . . ., [ C O ( N H ~ ) ~ ]B ~ ~ ;, [ C O ( S H I ) G ] C ~ . C---------, O~; [Co(NH3)sC03]Br; , [CO(XH~)~CO~]C~.
others, and coordination occurs between this oxy- Thus, ~4 vibration which appears in calcite at 710 gen and the metal. The anomaly of the infrared em.-' splits into two bands in aragonite. Morespectrum of the sulfate ion a t 1100 cm.-' in [Co- over, totally symmetric vibration, vlr appears (NH3)&30~]C1was reported previously by Mizu- weakly a t 1080 cm.-l in the latter. As is shown shima and Q ~ a g l i a n owho, , ~ however, gave no de- in Table I11 and IV, these results are in complete tailed discussion. harmony with the prediction of site analysis. Since the effect of coordination is much stronger In (NH& C O < ~ ~ ~ C O ( ~ ~ ~both ) ~v1]and ( ~ Othan ~ ) the ~ ,effect of interaction between the ions, more v p appear with medium intensity, and v g and v4 split remarkable change of the spectra is expected when into three bands, respectively. This result together the ion is coordinated to the metal. In carbonato with Table I1 suggests that the symmetry of the complexes, Raman active vibrations of the free ion sulfate ion is once again lowered and probably re- will appear more strongly and the degenerate vibraduced to CZv. Hitherto, the following structure tions will split more markedly. Figure 2 and Table I11 show the spectra behas been assumed for the sulfate bridge. tween 2000 and 1000 cm.-l and location of the four co co fundamentals of the carbonate ion, respectively. 'o* o'* In [Co(NH3)6]CICO3,v1 does not appear, and 1.3 \ / and v4 do not split. Since the feature of the spec'S' trum is very similar to that of calcite, we conclude that the symmetry of the ion may be Ds. I n '0 ' 0 [ C O ( N H ~ ) ~ C O ~v 1] Bappears ~, very weakly and v.3 Our infrared study will present an evidence for the splits into two bands. The correlation diagram of above structure in which C2, symmetry is given. Table IV suggests that the symmetry of the carthe idea of (2) Carbonato Complexes.-Using site symmetry, Halford4 explained the difference bonate ion in this compIex is C2, a t the highest. of the spectra between calcite and aragonite which This result is consistent with the expectation that have the same chemical composition. According the ion is linked to the metal with one of its oxyto the site analysis, Dah symmetry of the free ion is gens. Similar trend is seen in the bidentate complexes lowered to D3 in calcite and to C, in aragonite. of [CO(NH~)~CO~]CI and [Co en2 CO31Br. How( 3 ) 5 hlizushima and J V Quaghano, THISJ O U R N A L , 7 6 , 4870 ever, v1 appears more strongly, and v3 splits more iI (1 57) markedly than in the case of the unidentate coin( - l i R 9 I I d f o r d J riletrr P / ~ \ s 1 4 , 8 (IQW,)
[
Sept. 20, 1957
SPECTRA O F
4907
UNIDENTATE AND BIDENTATE MET.4LLIC COMPLEXES
TABLE I11 THEINFRARED SPECTRA OF CARBONAT0 COMPLEXES (CM.-') Compound
Symmetry
n
VI
Y4
VI
. . . . , .h 879 (S) 1415(VS) 6m(S) Free COS-- ion" Dah 874(S) 1430(VS) 710(M) ......' Calciteb D3 1470(VS) 710(M), 6913(W) 855(S) C. 1080(W) Aragonite* 1390 1370(VS) 688(M) 868(S) D? ...... [CO(NH&]C1.COid 1450(S), 1370(S) 750(W) c2v 1070(VW) 848(S) [ Co(NH&COo]Bre 1592(S), 1255(S) 752(M) 837w [Co(NHo)4COa]Cl' CPV 1025(M) 1575(S), 1278(S) 757(M) 825 (S) CPV 1015(M) [ CoennC03]Br' G. Herzberg, "Infrared and Raman Spectra of Polyatomic Molecules," D. Van Nostrand Co., New York, N. Y., 1945, Synthesized, examined by X-ray powder photograph. p. 178. * Natural mineral, examined by X-ray powder photograph. d L. Jacobsen, Overs. Danske Selsk. Forb., 595 (1899). e A. Werner and N. Goslings, Ber., 36, 2381 (1903). f SI. N. Jorgensen, Z. anorg. Chem., 2, 283 (1892). 0 A. Werner and J. Rapiport, Ann., 386,73 (1912). * Raman, 1063 cm. -l; 1087 cm. -l.
-
TABLE IV TABLE BETWEEN Dah, DI, CORRELATION vi
A'i(R) Do Ai(R) CzV Ai(1,R) Cs A'(1,R) D3h
YI
A'a(1) Aa(I1 Bl(I,R) A"(1,R)
czv AND ca w
Y1
E'(I,R) E(I,R) Ai(1.R) A'(I,R)
+ Bt(1,R) + A'(1,R)
E'(I,R) E(I,R) AI(I,R) A'(1,R)
+ BdI,R) + A'(1,R)
plex. Therefore, we conclude that the symmetry of the ion does not differ whether it is an unidentate or a bidentate. This is in good accord with the chemical formula hitherto assumed. C?
' 0*
I
C
.O*
identified unambiguously. The CO stretching frequencies of the oxalato complexes are listed in Table V. It should be noted that the separation TABLE V
THE co
STRETCHING EkEQUENCIES OF 0XALA.rE COMPLEXES (CM.-l) Irred. rep. in Vh big bw k btu Free CIO# ion .O 163O(s) . . . d 1335,1316 ( C O ( N H I ) ~ C ~ O ~ ] B ~ ~ ~ & O.~ 1567(s) 1362(w) 1280(s) [Co(NHl)rC10r]Cl~ 1705(s) 1663(s) 1395(s) 1260(s) [CO(NHI)IHC,O~]B~;~ 1757(s) 1 6 7 % ~ ) 1396(s) 1250(s) Irred. rep. in C;v bi ai a1 bi
--
... . ..
..
"S. M. JBrgensen, Z . anorg. Chem.,
11, 425 (1896). Schramm, ibid., 180, 167 (1929). C R a m : ~ n ,1664 cm.-1. 1485 and 1450 cm.-l.
* W.
of the four bands is more remarkable in [Co(NHs)a H C 2 0 ~ ] B rthan z in [Co(NH& Cn04]Cl. .At first However, the effect of coordination undoubtedly is glance, this result seems contradictory to the genstronger in the bidentate than in the unidentate eral rule that the effect of coordination is stronger complex as is shown by the magnitude of the split- in the bidentate than in the unidentate complex. ting of the degenerate mode and the intensities of However, the oxalate ion in the former can be rethe Raman active vibrations. garded as a bidentate coordinated by hydrogen (3) Oxalato Complexes.-Free oxalate ion has and the metal. Furthermore, since the effect of high symmetry of v h and exhibits 12 fundamentals. 0-H bonding on the spectrum of the oxalate ion is Among those, 9 are in-plane and 3 are out-of-plane stronger than that of Co-0 bonding, the CO vibrations. The number of infrared active in- stretching frequencies of [CO(NH~)~HC!,O~]B~, plane modes is only 4 in Vh. If the symmetry is would undergo larger shifts than those of the bireduced to CrVby coordination, all the 9 modes be- dentate complex. come infrared active. (4) Acetato Complexes.-Free acetate ion has Three Co(II1) oxalato ammine complexes ex- 15 infrared active fundamentals. Among those, amined here show more than 9 bands in the region the vibrations due to COO- group are asym. CO between 1600 and 400 cm.-'. Therefore, it is stretching (1578 cm.-l), sym. CO stretching (1425 obvious that vh symmetry is destroyed by complex cm.-l), COz bending, C 0 2out-of-plane bending and how/ ~ H ~CO, O , rocking modes. formation. In [ C O ( N H ~ ) S C ~ O ~ ] B ~ . ~ ever, 4 or 5 bands which originate in g-type vibraIf the ion coordinates to the metal, the selection tions of Vh symmetry are very weak or almost van- rule does not differ since all the modes are already ished. Therefore, we suspect that the symmetry infrared active in the free ion. Therefore, we will of the ion in the unidentate complex may be ap- discuss the effect of coordination from the freproximated by Vh because of weak interaction. quency shifts caused by complex formation. The I n [Co(NH3)4C204]C1,all the 9 bands appear X-ray studiess indicate that CHaCOO- ion in Nistrongly. This result is expected from the follow- (CH3COO),.4H2Ois an unidentate whereas it is a ing structure of the bidentate in which Clv sym- bidentate in Cu2(CHsC00)4.2Hz0 in which the ion metry is assumed. is linked to two copper atoms. 0 0 Table VI gives the frequencies of the two CO stretching modes which can be assigned with cer*O> C - C d * tainty. It is seen that the separation of the two stretching frequencies is two times larger in the uni'.C0.' dentate Cos+ complex than in the Ni2+ complex. Since complete assignment is difficult, not all the It is expected that, as the metal-oxygen bond beobserved bands will be discussed. Therefore, we (5) J. N. van Niekerk and F. R. L. Schoeaing. Acta C r y ~ t .6, , 609, discuss only the CO stretching bands which can be 227 (1953). '0
-'o
4905
GEORGE 11'.
WATT,
D. >SOWARDS I.
comes stronger, two C-0 bonds of the acetate ion become uneven, and the separation of the two CO stretching frequencies may increase. If . . . . . . O 0 0O'\&/ \ /
+
AND
THR co
s. c. hfALHOTR.4 STRETCHISC
Vol. 79
TABLE VI FREQUESCIES PLEXES (CM.-') Asym
Thus we conclude that the effect of coordination is stronger in the Co3+comp1exthan in the Ni2+complex. This result surrrrests the imDortance of the
Free CI-IBCOO-ion Xi ( C H & 0 0 ) 2 ~ 4 H 2 0 CUZ(CH~COO)~.~HZO [Co(i'JHd5CHsCOOl (Clod?" = M. Linhard and R. Rau, (1953).
complex t h a n in ihe &identate
NAKANOSHIMA, KITA,OSAKA,JAPAN
I
C
I
CHa
CHI
[COXTRIBUTION FROM
Ni2+ complex.
THE
DEPARTMENT OF CHEMISlRY O F THEUSIVERSIlY
1578(s) l530(s) 1603(s) 1603(s) Z . nnorg.
OF
Sym.
Separation
1425(s) 153 1418(s) 112 1418(s) 186 223 1380(s) Chewz., 271, 121
TFXAS]
The Iodides of Thorium(III), (11) and (1)l BY
GEORGE 11'. L ~ A T T , D. M. SOWARDS AND
s. c. hf.lLHOTR.4
RECEIVED MAY20, 1957 The formation of iodides of thorium(III), (11) and (I) by the reduction of thorium(I\') iodide with excess elemental thorium a t 550' is described. Procedures for the separation of the five components of the resulting reaction mixture have been dcvised; the resulting data confirm the existence of Th13and provide evidence also for the existence of ThI2 and ThI.
Earlier efforts to provide evidence for the existence of Th
