Infrared spectra of various bivalent metal 8-selenoquinoline complexes formed at various pH values

J. inorg, nucl. Chem., 1974, Vol. 36, pp. 1003-1010. Pergamon Press. Printed in Great Britain.

INFRARED SPECTRA OF VARIOUS BIVALENT METAL 8-SELENOQUINOLINE COMPLEXES FORMED AT VARIOUS pH VALUES YOSHIYUKI MIDO, ISAMU FUJIWARA and EIICHI SEKIDO Department of Chemistry, Faculty of Science, Kobe University, Nada, Kobe 657, Japan (First received 23 January 1973; in revised Jbrm 27 June 1973) Abstract--The effect of acidity on the precipitation of various bivalent metal 8-selenoquinoline complexes

has been systematically studied by i.r. absorption spectrometry. Reasonable correlations between some metal-sens, bands and the structures of complexes were obtained. From the intensities of the metal-sens. bands for each complex and of the substituent-sens, bands for the diselenide, the percentage of regular chelate, other kind of complex and the diselenide were roughly estimated. Mn(ll), Co(ll) and Cu(1) compounds precipitated at a low pH value showed a tendency to give a larger percentage of each regular chelate than those obtained at a high pH value, but Zn(II), Cd(II), Pb(ll) and Ni(lI) compounds showed the inverse tendency. These two groups of metal chelates have been suggested to be in different structures.

INTRODUCTION

Trn~ EFFECT of acidity on the precipitation of various metal complexes of 8-selenoquinoline (selenoxine = SeQ) was systematically studied[I] and the i.r. spectra of SeQ and its metal complexes were reported[2]. They showed some possibility that the precipitate of some metal selenoxinates exists as a mixture of the regular chelate and something else. Precipitation of such a mixture seemed to be dependent on the pH value of the solution. The present study has been carried out for various samples precipitated from the different pH solutions to elucidate the relationships between some i.r. bands and the composition or its structure of a precipitate. A few i.r. studies related to the effect of acidity have been reported but only for metal oxinates[3-6]. EXPERIMENTAL

The samples were prepared by the previous method[l]. The i.r. spectrum was recorded on the same conditions and with the same instrument described before[7]. Each typical spectrum (4000-1000 cm- 1) for metal selenoxinates is shown in Fig. l(a~t and f), and the spectra of Zn- and Mn-selenoxinate were shown in Fig. 2 in[2]. The i.r. spectra in the 1000400 cm -1 region are shown in Figs. 2 8. The pH values of samples and their i.r. data were summarized in Tables 1 and 2. RESULTS A N D D I S C U S S I O N

There are no significant spectral differences in the 4000-1000 cm -1 region among various samples for a metal selenoxinate prepared in various pH solutions and among the spectra of the selenoxinates of various

metals, as seen in Fig. 1. The spectra in the 1000-400 cm-1 region will be discussed in the following. Mn-selenoxinate

Four samples listed in Table I are classified into two groups according to their spectral resemblance. Two spectra belonging to each group are shown by (b) and (c) in Fig. 2 and the spectrum (a) of the diselenide is added to the same figure in order to compare with them. By comparison among the three spectra, it is evident that the bands at 975, 776, 746 and 660 cm t originate from the metal chelate. The bands at 962, 788, 760, 756 and 642 c m - t may arise from the diselenide, since SeQ is apt to be oxidized to the diselenide by air, particularly in alkaline solutions; that is, the wave numbers for these bands agree with those of the diselenide and the band intensities of these bands in the spectrum (b) of the pH 10.0 sample are stronger than those in the spectrum (c) of the pH 5-2 sample. As metal selenoxinates do commonly exhibit three strong bands in the 85(~ 700 cm -1 region, the band at 818 cm - t observed in both spectrum (b) and (c) can be regarded as arising from both metal chelate and the diselenide, while the band at 784 c m - 1 from the diselenide alone. It is not necessary to take into account for any formation of a metal complex of the diselenide, because such a complex formation will certainly affect essentially on many vibrations of the diselenide. The 975 and 660 cm-~ bands are metal-sens, and the 962 and 642 cm-1 bands of the diselenide are substituent sens.E2]. F r o m the intensities of both sens. bands the rough percentage of the regular metal chelate containing in each sample is estimated to be ~ 4 0 per cent for the

1003

1004

YOSHIYUKI MIDO, ISAMU FUJIWARA a n d EIICHI SEKIDO

(d)

//'// (c) ]

iflq /

i

_ _

_ _ 2

5500 5000 2500

[

1600

_ J

1

•

1400

Wave number,

1

1200

.L IO00

3 5 0 0 3 0 ~0 0

cm - I

25~00

1600 ~

-

Wave

~

1400 ~

number,

,

1200 ~~

I000

cm - I

Fig. 1. Infrared spectra in the 4000-1000 cm -~ region of (a) Co-, (b) Ni-, (c) Cu-, (d) Cd-. (f) Pb-selenoxinate and (e) Cd-selenoxinate at pH -0.5.

-'--,;',m

.--"

.,

".. v

(a)

' m

~

~Lo .- ....

;~o,-,,". . . . . . . . . . . . . . '~', , . . . . . . . . . . . "'---', j---

, , - , " ~ c o ~-~-,

' ; ~

',4

]~

',2

i

1000

~

t

900

i

k

,

8 O0

i

,

700 W(]ve

number,

i

_ _

,

600

L

500

i

400

cm - I

Fig. 2. (a) T h e diselenide, (b) M n - s e l e n o x i n a t e o b t a i n e d a t p H 10.0 a n d (c) M n - s e l e n o x i n a t e at p H 5-2.

co co i

I000

i

900

86o Wave

7& 0

I

6&O

n u m b e r , cm - I

Fig. 3. C o - s e l e n o x i n a t e ; (a) p H 10.0, (b) p H 0-8.

5 0' 0

4 0' 0

I.R. spectra of 8-selenoquinolinecomplexes

1005

t~

i

I000

/

i

~

900

I

i

i

800

700

600

Wove n u m b e r ,

i

L

i

i

500

400

cm - I

Fig. 4. Ni-selenoxinate; (a) pH 9.7, (b) pH 1.0, (c) pH 0.3.

~-

I0' O0

9 0' 0

86 0 Wove

~o

.

. 700 .

number,

.

600 .

500

4(}0

cm - I

Fig. 5. Cu-selenoxinate: (a) pH 7.6, (b) pH 1-4.

pH 5.2 sample and ~ 10 per cent for the pH 10.0 sample using a base line method and by assuming almost equal extinction coefficients for these bands. Co-selenoxinate As previously described[l], cobalt(II) does not give a precipitate of a definite composition, but appears to precipitate as a mixture of C o R 2 . RH and C o R 2 o r as other complexes (e.g. CoR3), where R = C9H6NSe. In order to clarify the above question the samples prepared at pH 0.8 and 10.0, and the following three samples, A, B and C, at pH 4-0 were examined: A, the

sample corresponding to C o R 2 by the weight of precipitate; B, the sample to COR2, RH; C, the sample obtained from a solution containing excess cobalt(II) ion. Their spectra are classified into two types, as listed in Table 1 and shown in Fig. 3. Some characteristic bands of the diselenide, especially the substituent-sens, bands, appear strongly in the spectrum (b) but weakly in the spectrum (a). A shoulder seems to appear on the high frequency side of the metal-sens, band (660 cm-1), whereas near the higher metal-sens, band (978 ern-1) such one does not clearly. It was found that Co(III)-selenoxinate prepared by

YOSHIYUKI MIDO, ISAMUFUJIWARAand Ellcm SEKIDO

1006

Table 1. Infrared data (cm- 1). Metal

(D§)

pH~ complete ph++ sample

Figure

10-0 8-0

Mn

Co

5.90

1.66 10.0 0.8 4.0(A) 4.0(B) 4.0(C)

5.2 5.4

Ni

9-7 10.6

2(a)

2(b)

2(c)

3(a)

3(b)

4(a)

978 vw

978 w

975 m

978 m

962 vs

962 vs

962 s

819 vs 788 vs 784 vs

819 vs 788 vs 784 vs 778 sh 760 m 756 m 748 w 659 sh 642 vs

818 vs 788 sh 783 vs 776 vs 761 w 757 w 746 m 660 m 642 s

978 s 970 sh 962 w 954 sh 816 vs

979 s 970 sh 962 sh 955 sh 816 vs

760 s 756 s 642 vs

783 sh 775 vs 756 w 746 s 660 s 642 w

962 s 818 vs 789 sh 784 sh 776 vs 761 sh 757 sh 746 sh 662 m 642 s

774 vs 745 s 661 s 642 w

1.10 1.0 2.6 4-0

Cu

0.3

2.90 ( 7.6 3-0 4.0 10.0 10.2

0-89) 1.4 0.4 0.8 1.2 1.5

4(b)

4(c)

5(a)

979 s

979 m

971 s

962 s

962 s

962 vs

817 vs 789 sh 784 sh 774 vs 761 sh

818 vs 789 sh 784 vs 774 vs 76l m 756 m 746 m 661 m 642 s

816 vs

818 vs

782 vs

782 sh 777 vs

745 s 661 s 642 m

5(b) 971 s

760 s 756 s 656 m 642 s

757 sh 657 m 642 vw

* Intensity code: vs--very strong, s--strong, m--medium, w--weak, vw--very weak. [" The pH value at which complete precipitation begins, see ~1]. The pH value at which the sample measured was precipitated. The top sample is shown in each figure. § The diselenide of SeQ.

a conventional method has slightly higher metal-sens. bands (982 and 664 cm -1) than Co(II)-selenoxinate does. A characteristic medium band of Co(II1)selenoxinate appears at 757 c m - ~. The above facts suggest that the precipitate obtained from a solution containing excess cobalt(II) ion and at a pH value above 4.0 includes no diselenide but does a small quantity of Co(Ill)-selenoxinate. Any informations of CoR 2 . R H type complexes were not obtained from the observed spectra.

C u R . R H (above p H 3.0) were previously suggested from the composition of the precipitates[l] and from the low frequencies of the metal-sens, bands[2]. However, i.r. spectra in Fig. 5 seem to indicate that each sample prepared above p H 3.0 may not exist as a single c o m p o u n d of C u R . R H but rather as a mixture of CuR and the diselenide. A shoulder at 757 cm -1 in the spectrum (b), undoubtedly, is due to CuR but not the diselenide. Zn-selenoxinate

Ni-selenoxinate I.R. spectra of six samples are classified into three types as listed in Table 1. On the examination of some bands characteristic of the diselenide, it is found that the higher the pH value of precipitation is, the smaller the percentage of the diselenide becomes as seen from Fig. 4. A series of bands in the 980--950 c m - l range seems to be peculiar to Ni-selenoxinate and, also to Co- and Zn-~elenoxinate.

Cu-selenoxinate Many samples give roughly two types of their spectra and they are shown in Fig. 5. The reduction of copper(If) to copper(l) by SeQ and the resulting formation of precipitates as CuR (in the pH -0.89-2-0 range) or as

Three samples listed in Table 2 were examined and gave the same spectra except slight intensity-differences of the bands near 760 c m - 1 as shown in Fig. 6. The diselenide-characteristic bands, especially the 642 c m band, do not appear in the spectrum. The appearance of the 759 c m - l band ( C - C - C skeletal distortion) for the pH 0.5 sample suggests the coexistence of such a slightly incomplete chelate that it has two skeletons with different environment, probably as the structure V in[l], so that it should have two 6(C-C-C) vibrations. As will be discussed later, each of cadmium and lead samples precipitated from a strong acidic solution has a similar band to its lower counterpart (at 759 c m - 1 ) of the splitting and is suggested to have a structure of MR 2 . 2HC1 as represented by Formula I. It is concluded that zinc can always give single component precipitate of the 1 : 2 regular metal chelate in all pH range, though some precipitates formed in

I.R. spectra of 8-selenoquinoline complexes

1007

co

o~

~

1000

900

,

800

700

600

Wave number,

500

400

cm- I

Fig. 6. Zn-selenoxinate: (a) pH 10-5, (b) pH 3-9, (c) pH 0-5.

I'

[I

,I

~,, i

I!

'Ii

~,, 1/

, ,'

iI Ill

2 co ~

900

1000

800

700 Wave number,

600

500

400

cm - [

Fig. 7. Cd-selenoxinate: (a) pH 4.0, (b) pH 0.5, (c) pH -0.5.

, ,,"",,,-(d) ....,

,

~/,-''----'v'/-~ -,/

~

'~ A (4d,,.:

I

,',

"

li"

,'~

m

i

1000

m

900

~

8o0

76o Wave number,

~bo

s;o

4;0

cm - I

Fig. 8. Pb-selenoxinate : (a) pH 3.0, (b) pH 1.5, (c) pH -0-3, (d) pH 11.8, (e) pH 0-0, (f) 1 yr after the preparation of the sample of (c).

1008

YOSHIYUKI MIDO, ISAMUFUJIWARAand EIICHI SEKIDO

Table 2. Infrared data (cm-1) * Metal

(D§)

pHf complete pH~ sample Figure

Zn 0.75 0.5 3.9 10.5

2(a) 978 vw

6 980 vs

Cd

4.0 2.0 11.0

Pb

1.05 (0.60) 0.5 -0.5 0.6

7(a)

7(b)

971 vs

971 vs

7(c)

2.55 (2.20,0.70) 1.5 -0.3 (0.0) (0.7)

3.0 4.0 (11.8) 8(a)

8(b)

969 vs

969 s

968 w 962 vs 819 vs

962 vw 956 w 825 vs

962 m 816 vs

966 m 962 sh?

816

818 vs

819 s

810s.b 788 vs 784 vs 782 vs

777 vs

%0 s

787 sh 783 sh 777 vs 760 w

811 s.b 777 s. b

777 vs

758 s 756s 765m 668 s

745 s 657 vs

756w 745 s 657 vs

761 vs 756m.b 756b 745 sh 745 m 652 vs 659 vs 652 sh

645m 642 s

642m

8(c)

645m 642 sh

642 sh

* See footnotes in Table 1. the lower pH range may slightly include the incomplete chelate.

Cd- seleno xinat e

Cadmium reacts with SeQ to result in two forms; the red- and yellow--orange compounds precipitate in the pH -0.7~).6 and pH > 0.6 regions respectively[I]. The samples which give the latter compound exhibit the (a) type spectrum as shown in Fig. 7, whereas the pH 0.5- and - 0 . 5 samples, although both samples give the red-orange compound, exhibit different spectra, (b) and (c) respectively (see Table 2). A comparison of these spectra suggests that the sample giving the spectrum (a) exists as the regular metal chelate, while the sample giving the spectrum (b) exists as a mixture including a small amount of the diselenide. The spectrum (c) of the pH - 0 - 5 sample is quite different from the others, even in the 40(O-1000 c m - 1 region (cf. the spectrum (d) and (e) in Fig. 1). The appearance of the bands near 3050 and 1260 cm-1 assignable to v(N-H) and di(N-H) modes respectively, indicates the existence of N - H bonds[2]. The intensification of two bands near 1600 cm-1 and the appearance of a band near 1530 c m - 1 may occur due to the variation of environment of the C = C and C ~ N bondings[8]. The absence of the n(C-H) band near 780 cm-1 and the shift of the 6(C--C-C) band at 745 cm-~ (cf. the 759 c m - ~ band of the zinc pH 0-5 sample) may be caused from certain steric hindrance to neighboring C - H

groups by additional chlorine atoms to the N - H hydrogen atoms. The electronic change of the ring and the steric hindrance are capable of closely affecting such n(C-H) vibrations. The pH - 0 . 5 sample has lower metal-sens, bands (968 and 645 cm -1) than the regular chelate (971 and 657 cm-1) does. The lowering of the metal-sens, bands indicates the formation of linkage through only Cd-Se bond, but not the complete ring formation. The above facts support the previous conclusion[ll that the red-orange compound formed in a strong acidic solution is represented by Formula I.

Se HC1 \M M = Cd or Pb C1-H+ \Se

Formula l Also, it is indicated that the pH 0.5 sample, although it shows red-orange color as well as the p H - 0 . 5 sample, does not exist as the structure of Formula l but rather as a mixture of the regular metal chelate and the diselenide.

1009

I.R, spectra of 8-seIenoquinolinecomplexes Pb-selenoxinate

Lead, as well as cadmium, forms various precipitates with SeQ ; the red-orange, gray-green and dull-yellow compounds are obtained in the pH -0.75~).70, 0.902.20 and above 2.55 ranges respectively. The examined samples are roughly classified into three groups, as listed in Table 2 and shown in Fig. 8. The spectrum (a) and (b) for the pH 3.0 and 1.5 samples respectively, are similar to one another except the appearance of the band at 659 cm-1 in the latter (cf. the spectrum (e) for the pH 0.0 and 0.7 samples) and both show slightly the pattern of the diselenide. The 659 c m - 1 band is clearly exhibited also in the spectrum (f), of which sample was precipitated at pH - 0 . 3 and was re-examined after one year from its preparation. The 659 c m - ~ band may occur due to another kind of complex, so that the sample giving the spectrum (b) exists as a mixture. In the case of the spectrum (c) for the pH - 0.3 sample

the existence of P b R z . 2HC1 (Formula I) is explained along similar lines to that just discussed for the pH - 0 . 5 cadmium sample (cf. Fig. 7c). The same pH - 0 . 3 sample was re-examined after one year and it gave the spectrum (f) different from the early recorded spectrum

(c). By considering the positions of the metal-sens, bands and the above fact, it is suggested that with the lapse of time the pH - 0 . 3 sample represented by Formula I changes into a mixture of the diselenide and another kind of complex above mentioned. However, for the other metal selenoxinates, even for the pH - 0 . 5 cadmium sample, no spectral changes are observed by the lapse of time. Probably, Pb-selenoxinate may be less stable. Only the pH 11.8 sample gives some extraordinary bands near 1400 cm -1 and at 682 cm -1, as shown in Figs. l(f) and 8(d). The precipitate from the strong alkaline solution may have partially hydroxyl and/or carbonate groups since basic lead carbonate gives

Table 3. Estimation of each complex in various samples Mn-selenoxinate Sample (pH) Regular chelate

5.2 ~ 40 ~

10.0 ~ 10

Co-selenoxinate Sample (pH) Regular chelate*

0.8 ~ 90 ~'/o

10.0 ~ 50 °/o

* The value is estimated including the amount of Co(Ill)-selenoxinate. Ni-selenoxinate Sample (pH) Regular chelate

0.3 ~ 40 'Yo

1.0 ~ 60 ~

9.7 ~ 90 o/

Cu-selenoxinate Sample (pH) Regular chelate*

1-4 ~ 100 °/o

7.6 ~ 40 I~

* Cu(1)-selenoxinate, see text, Zn-selenoxinate Sample (pH) Regular chelate

0-5 ~ 100°/o*

3.9 ~ 100~*

10.5 ~ 100%o

* Including a slightly irregular chelate, see text. Cd-selenoxinate Sample (pH) Regular chelate

- 0-5 (Formula I)

0-5 ~ 70 o/,,

4.0 ~ 100 ~o

Pb-selenoxinate Sample (pH) Regular chelate

-0.3 (Formula I)

1.5 ~ 40 ~o irregular one 40To

3.0 ~ 80 ~o

1010

YOSH1YUKIMIDO, ISAMUFUJIWARAand EIICHI SEKIDO

similar bands and such a compound might exist in such an alkaline solution. Summary of metal selenoxinates

The percentage of regular chelate estimated roughly from band-intensities for each sample is summarized in Table 3. Several samples exist as a mixture of each regular chelate and the diselenide. Most transition metal complexes seem to give a larger percentage of the regular chelate when precipitated at a low pH value than they do at a high pH value. On the other hand, the typical element (d 1° metal) complexes show the inverse tendency. The difference in the behavior of two groups may be one of the characteristics of individual metal complex. It seems to occur due to different structures, transplanar and tetrahedral. Probably Ni-selenoxinate chelate may be of tetrahedral structure as well as those of d 10 metal chelates. There is a recent and favorable i.r. study[9] that Ni-oxinate exists in tetrahedral structure. Even in the sample precipitated at the most favorable pH or in the sample near the minimum pH for complete precipitation, the percentage of regular chelate for manganese is the lowest among the examined metal selenoxinates. This confirms that the stability of the complex is less than those of the other metal complexes.

On the other hand, zinc complex precipitates as only the regular metal chelate over the wide pH range. This complex seems to be the most stable in air among the examined metal complexes. The validity of the stability is supported by the previous studies on the minimum pH for complete precipitation[l] and the metal-sens. bands[2], and by some studies reviewed by H. Freiser

[10]. REFERENCES

1. E. Sekido, I. Fujiwara and Y. Masuda, Talanta 19, 479 (1972). 2. Y. Mido, I. Fujiwara and E. Sekido, J. inorg, nucl. Chem. 36., 537 (1974). 3. J. C. Fanning and H. B. Jonassen, J. inorg, nucl. Chem. 25, 29 (1963). 4. J.E. Tackett and D. T. Sawyer, lnorg. Chem. 3, 692 (1964). 5. R. J. Magee and L. Gordon, Talanta 12, 445 (1965). 6. T. J. Cardwell and R. J. Magee, Analytica Chem. Acta 36, 180 (1966). 7. Y. Mido and E. Sekido, Bull. chem. Soc. Japan 44, 2130 (1971). 8. H. F. Aly, F. M. A. Kerim and A. T. Kandril, J. inorg. nucl. Chem. 33, 4340 (1971). 9. N. Ohkaku and K. Nakamoto, Inorg. Chem. 10, 798 (1971). 10. H. Freiser, Japan Analyst 21, 1300 (1972).