Effect of the composition and structure of cobalt(III) complexes on their RF values obtained by thin-layer chromatography on silica gel

EFFECT OF THE COMPOSITION AND STRUCTURE OF COBALT@E) ON THEIR RF VALUES OBTAINED BY THIN-LAYER CHROMATOGRAPHY ON SILICA GEL

COMPF..EXES

M_ B.

&SAP*,

VOJSA

(Rec&-ed

March

GORDANA

VUk0V-l~

M_ J_ MALTiN=

T- J- JAW&

zmcl P_ N. RADE

18th, 1980)

SUMMARY

Thin-layer chromatographyon silica gel was used for the chromato_mphic separation of 7.5 cobalt(II1) complexes using 30 one-, two- and three-component solvent systems. It was observed that when chromatographingwith onc-component solvent systems, trmLs-isomers exhibit higher RF values than the correspondingcisisomers. In the other solvent systems some exceptionswere observed. A linear dependencebetweenthe number of five-memberedrings substitutedby six-membered ricgs and their & values has been established.Finally, it was found that an increase in the numberof carbon atoms in the aminocarboxylato@and resultsin an increasein the RF value of the complex and that thereis a linearcorrelationbetweenthis number and the & values of the complexes.

IN-liEtODUCTION

In eadier worklJ we studiedthe e&ct of the composition and the structureof cobalt(III) complexes on their RF values obtained by paper chromatography_Continuingtheseinvestigationsin this work, we have carriedout a systematicstudy of the eff&s of the follow5ngfactcrs on the RF values of the same complexesobtained by thin-layerchromatography:the geometricconfigurationof the complex, the siz of the chelatering and the size of the-branchedchain of the coordinatedamino acids. By comparing our earlier results obtained by paper chromatography’*’ with those obtained in the present work we wanted to establish which of the possible mechanismsprevailsin the cases studied. These investigationswere carriedout with compounds mainly prepared for the Grst time in our laboratory. EXPERIMENTAL

Synthesesof the complexes investigatedwere carriedout according to proceduresdescribedin the literatureflabIs III-VIr). 0021~%73~8O;IMOQd?W /x02.25

0 1980 EIse*

Lkiemsc Publishing CmEpiuIy

Chromatographic separations were performed by ascending thin-layer chromatography on silica gel G-RS (Carlo Erba, Milan, Italy) which contained 13 % of calcium sulphate. A suspension of silica gel (30 g) in water (70 cm? was applied on five~glass plates (19.5 x 13 x 0.5 cm), which had been washed !irst with a detergent solution and then with acetone-ethanol (1 :l). The layer thickness was 300 pm, In order to ensure that the layers were uniformly wetted in the course of the

development, silica gel pasted along the edges of the plates was removed. The plates

were dried-in air for 15 min and then heated in a drying cabinet at 110°C for 1 h. After this treatment the plates were kept in a desiccator over anhydrous calcium chloride; Aqueous solutions of the investigated complexes were applied in the form of small drops. The development was carried out in cylinders (13.5 x 19.5 x -23.5 cm). One hour before the development, the solvent mixture was placed in a cylinder in order to saturate it with solvent vapour. Solvent systems consisting of p.a grade solvents were used and their compositions are listed in Tables 1 and II. The solvent systems travelled about 10 cm and detection was performed by spraying the plates with 2 M ammonium sulphide solution. All investigations were performed at 20 & 2°C. TABLE I oNE-coMFoNENr No. ‘1 i 4 5 6 7

.

SOLVENT

SYSTEMS USED

COtl?pfJl&?ltt

Time of akvebpment(min)

DistilLi water Methanol E&ii01 EthyI&e gIyco1monomethyl ether Dimethyl sulphoxide N,N-Dimethylformamide AcetonitriIe 1,2-Propallediol 1,3-l?ropailediol

1.5 ii 55 45 25 30 16h 10h

RESLXIS AND DI%USSION Effect

of geotnetrfc conzjiguration on RF values of the investigated complexes

The investigations were carried out by chromatographing

16 cationic, anionic complexes (Tabks III and IV). The thin-layer chromatograpbic behaviour of the most of these complexes had not been investigated previously. Ckomatographic development was carried out by using 8 one-component and 14 multi-component solvent systems. It was established that with one-component systems the trams-isomers always exhibit higher RF values than the corresponding &s-isomers (Fable III). However, when using multi-component solvent systems, in 35% of cases the c&isomers were more mobile than the corresponding trmrs-isomers (Table rv). Qn the basis of the results it was concluded that with one-component soIvent systems the predominant process is adsorption or ionic exchange. As silica gel behaves as a weakly acidic cationic exchanger9 containing silanol groups, we believe that with and neutral cobalt(m)

10 11 12 I3 14 15 16 17 IS 19 21 22 23 24 25 26 27 28 29 30

30:70 5050 70:30 Sam 9O:IO z!z

45 30 25 55 40 25 10

40:60

35

ig.2

45 55

9@:10 ~5:15:1g per 104) IIll 15:15:70 30-2050 SO:30:20 7O:ZO:IO 70:25:5 9055 75:20:5 70:2&10

55 60 100 20 35 40 50 120 90 30 60

anionicor neutral complexestype hydrogenbonding to silicagel occurs, whereaswith cationic complexes type it is likely that ion exchange betweenthe silanol-group kydrogen and the cation also takes place. Moreover, the Iowermobikty of cis-isomersis in accordancewitk the fact tkat they are more polar than tke correspondingtramsisomersand tkat tkey are rkereforcmore stronglyadsorbedto the adsorbent With muk.i+zomponentsolvent systems containing water, in addition to adsorptionand ion exckange,the processof partitionis inevitableso tkat the sequenceof tke isomerson the platesdependson tke mechanismthat predominates. By comparing tke results obtained by paper ch.romatograpky*~’witk those obtained by thin-layerchromatographyfor tke same cobalt(IiI) complexes,it can be seen tkat the composition of mubicomponent systemska.sno efiit on the sequence of geometricalisomersin tke paperckromatograpkicseparation,where-asin the tkinlayerckromato_mpkicprocedurethe sequenceof isomersdependsOQthe composition of the solvent system-Ibis may be understoodin view of tke fact that in paper ckromatograpky tke predominantmechanismis that of partition, whereasin thin-layer ckromatograpkyseparationthe predominantmechanismdependson the composition of the mukicomponent solvent systems. On the basis of the above, it can be concludedtkat tke so far acceptedgeneral ru!ela-xztkat tr~~~~-isomers &r&it kigkcr RF values than the cossespondingcis-isomers is valid in tkin-layer ckromatograpkyon sikca gel only when one-component sO&nt systems are used. In addition, we consider that one shotid dif5erentiat.e between the results obtained with one-com&nent and multi-component solvent systems.Witk one-componentsolvent systems,wheresorption is dominating, a regu-

.~

”

‘.

,

‘:,

’

w?h1*

(NOZW

[Cotn(Il-ald(N+hl

[Cotngl)f~o~j~j.

1-n @-W W&d

[Co(NHA gb@JoJJ

D&W

KQn~ WOZW

[Cow

,;

;

8

8

71 79

_

83 90

-

-

6 6 7’

33 35

!i 5

4 4

:;I

‘,

=

60 78

22 36

,_

‘60 71 81 89

z

2 3 85 91

:

1:

4

15 25

E.

0 3 51 55

0 3

3 5

3

glycinc;j&H

72 75”‘s

,55 65

;;

_ -

3 6

4 6

;

” ti q~l,3diar&opro~ane; en ‘= 1,2&-uninocthanc; pn = 1,2diaminopropanc;glyH = “’ The coqpositiorisbf:theeolventsystemsarc givenin TableI, ‘,,, ‘,. :.,, ‘; ,’ .‘.: ‘, .,, .,

.

16 ‘_:‘., :‘trayNO; : .’

14

:

&N~~.~~uu.NH~ jr&N(-&

rru/~.NOz

d~-N02-rrans-NI&

,cls-N0#w~-NH~, NH, IfU/i$~IyO~

‘iyatk-frarwrans

c/s-NO&w.r-N

,clr-NOa 1rans~N0~

: ~&~p~0~.lrpns_NH1 .’

.‘I,

11,’ 12

13 ,’ 14 ”

:

:

:9 JO

8

.,s ,6 ‘7 :

Irur&N02

54 58

c/s-NOi

.3 3

3 4

[Cotnl(NOJl]+

39 43

(rawNO

cl*NC4

‘1 2,

2

Rp x 100”’

1

Ref.

‘.

Complex*

,,

:

homer

@&min$,

1

_ -.

z

15 23 _ -

;:

14 16

S‘

13

69 81 .88 ., ,92

9”:

12 .‘lS .i -

” ’

” 1: 7 ‘. :

‘8

:

88’. ‘,f “71 99 ‘86

73, 82 -, -.

iif

-82 89

4

30 38

6

-

,. .,’

:

“‘.

..

,.,

‘.

,’

,b,

::I’, $$ .,

1.::

::

i”.,

,; I_

‘8

$‘,’

1 I! “‘,m’ ps (,’

:. 77’ ~ ,@4,

‘72 80 1.84 -’ 88

88 g1-

,r: ” _ .. -

1:

7. 18

9

~~BALT@I),COMPLBXES ON THEIR RF VALUES &~UNED ‘.

ik

EFFkT OF Tti ~EOM&L&kL CONFIWRAT;ION 0~ THE tiw;O WITH ONECOMPONEN~ SOLVENT SYSTEMS’

~*ABLl$III,

:

.,

I..___I_ -_-_ ___. __.___._ _-_-10 11’ 13 14 15 16 18

-A”-

15 16

14

12 13

-_--_

-_-_

-._

(NOlhl _____

8 8

-----“-e-Y

49 61

57 60

8 8

’ Abbrcvintionsaa in Tnblc III. ” Tho compositionsof the ~olvcntsystemsurc given in Tnblo II,

_-_---_

Kotn(/l-ah)

41 53

33 50

7 7

1: 8 8

05 07

6 G

1 8

[Cow(P-ah)WOM

r:

;

5 6

11

4’

1

.-....-.. .- ---. --.-_._._-..I--___

:

. -. ..---..I-

2 5

-...“..-- _--. . 3 3

__..____.--__-_

:

,”

-..--_-..l_p 19 21 22

44 57

-

38 50

-

79 86

62

-

-

65 71

76 78

66 72

83 79

79 83

66 84

80 89

54 66

68 88

-.---

90 94

-

89 92

-

-

40 39

44 41

36 39

58 61

75 69

55 58

82 76

75 86

--

-

-

.___--.----_-

73 79

-

-

64 70 69 74

-

62 68

-s-w.

13 80

-

80 83

-

-

-

-

59 67

78 68

-

74 70

-

81 76

78 85

‘77 75

-

27

64 74

14 79

63 69

88 81

17 74

-

80 53 117 51

-

47 53

65 52 52 57

46 40

47 53 50 37

49 62

89 92

-

71 63

-

-

-

69 58

92 89

-

89 93

69 05

59 75

75 64

31 29

42 39

32 39

.._._. I_.._I-__._____

23

-

50 40

45 32

39 34

89 81

69 46

-

43 31

28

-

-

-

-

-

92 88

92 02

88 85

29

BPI%C!I’OP THE QEOMETRICALCONFIGURATIONOF THE MIXED CODALT(III) COMPLEXESON THEIR Rr VALUES OBTAINED WITH MULTI-COMPONENTSOLVENT SYSTEMS --.-.___-___-__-__.__--I_-__ -.-_----I. --_ Cotllplcxn RG~: RF x 100”’ Ismer No,

TABLE IV

:

@ala)2 KcNWY~

+-~~tru~-NH~ c&-O&m-NH2

P 8 ., /

4%alfl)2 Kw1~2 W2)21-

mGLhiis*tiatls ‘trats:trans-Wan8

.7.. 6,

Rr

4 8 :

[Co@nBlY (NO,)21 @ala) [Comly oUO2)21 (&ala)

cls-NO~mn,s~NH~ cl~~NO~mwNH~

ch-NO&wN& c/s-N02mwNH2

14 15

16 17

-.

7’

[Co(NH&gly(NO1)21 @ala)

12 &-~O&w;ls-NH~; tifi, 13‘ : :, .’ cl~~NO&m-NH~, NH,

14 1

(/I+-tla)

76 64

-

72 59

58

93 88

45 58

83 95

7

7,

81 89

_-

6

85

_ -

2

-

-

2

6

13 ‘, .13

fi; I ,X$erfdibn~l(l,2,6) ,‘:. ‘, j ‘; ,,Mor~dional(l,,2,6)~

[CoNH&y (NOhI’

NQJ

(p+-hl2

BwY2 (N0321'

61~@ala)

[Cosly (N02121a(&ala)

‘ci~~NO&ans.N cl~-N02m/s=N

I

&Np2-irans-N

,.‘,,

3 4 ,5

.’

32 18

72

44 ,I ‘9s

10 37

20 13.60

86 92

-

70

68 13

27 6

24

4

3

-

-

-

-_,

- -,

-

‘,, -

6

-i

-

-

-

5.,

‘EFFECT &THE CHELATE RING SIZE ON Rp VALUES OBTAINED WITH ONECOMPONkNT SOLVENT SYSTEMS Ref. x lOO”* Comph? No, Isomer., ,, ‘.

p3LEV

0

.,‘/

,;,I,’ - ” 63 87 .,

.,’

‘4

+,,, j:, -,

: 8

i7

--

_ ,‘;

.7

,

,j:. :>1

~ ;,’ <,,;,_

,,

‘,.. ,, ,-‘.

.i

mm-N rrms-N

C&.N C&.N

-

30 31

32 33

34 35

’

[CooxhlYa1-

Rcial (I,24 Pnclnl (I,24

27

28 29

18 I9

18 19

1s 17

15 I6 17

3”

4

4 3

8 8

20 20 __- _._..___.

---_._-Abbrcvintions08 in Tnblc 111, ” Tho composilions of the solvent systemsnrc given In Tnblc I.

[coox6~YJ@nln)r Eoox*BlY I” (Pal@ .~_-.__-._.--___.-

(IJdnh

[CJJhlYa1 (I)+W

Meridional(I ,2,6) Mcridionol(l,2,6) Mcridionnl(1,2,6)

::

E

cnln th [CohlYa1 BlY,(/)*nln) (Pnln)4

(NOAl+

Km

trms-NOi

22

mm-NOa rrm-NOI

Km% (NOW tnr

c/s-NOa &NO1

20 21

Pm& (NOJd Wnln)

rmns-NQa mm-NOI

18 19

;:

z 79

49 ::

58 10

79 73

__

._

32 28 23

24 34 30

16 18

73 69 28 27

32 25 lb

1: 13

12 7

89 83

7 13

6 12

2 0

-

; 27

13 23

12 16 -.----._--__

86 80 76

t!

-

-*

-

-

-

-

4 1

--

-

-

-

RI 72 46

::

8

-

92 88

Iarityin chromatographicbebaviow kto be expected;thisregularityoffersa possibility for the determinationof the geometricalcon&zjra~ion_oftheseComplexes.In contrast, when rm.Iti~rnponent solvent mixtures are used, the cotiposition of the solvent systemcontrolswhethersorptioqor partitionwill dominateand thereforethe sequence of isomersdependson the comp”osition of the solventsystem. ETect of chelate ring size OR RF values of the irrvestigtqed complexes

To investigatethe effect of the chelate ring size OQthe RF values of complex 12

a 14

/t

Q6

O-4

a2

0

/

24

-0.2

-0.4

a.6

-0.8.

-1.0

-1.2.

b)

Fig. 1.DepenaenCe of RM values on the number of five+membered riags substitited by the COTrespond&g six-membered rings. Compfexes: (a) 3-S; (b) 22-24; (c) Z-27 (see Tables V and VQ.

Thenumbers on thelinesreferto thesolventsysizmswed (seeTablesI andII).

TLC GF Cb(EE) WMlZEXt3

GS SILICA

GEL

67

compounds we chromatopphd 35 c0bdtcrr.I) cmqstexes (TableV) containing five- and/or six-membered tin~bo_9lato and/or d&nine &elate ligands_ The compkxes were cationic. anionic and neutral types. Cbromatographic separations were perfomed using 20 one- and multicomponent soivent systems (Tbles I and u). Ekvez~ groups of comp!ex compounds containing aminocarboxylato ligands, either with or without titro groups, were chromztograpkd by the use of eight onecomponent solvent systems (Table V, complexes l-19 and 25-29); it was found that the RF value decmsed with increasing &elate ring size. Contrary to these fIndings, three groups of compiexes with ox&to cfielate rings instead of nitro groups exhibited the opposite bekmiour (Table V, compkes 3U-35). None of these reguh-ities oc-

hl J26

s-

s-

I-

30

I-

7

Fa. 2. LkpaxW of RY w&e on tt# numb of casbonatoms iu one of the uwdinat& amino acXs in the (f&-&@IO& tmm@Q-[coAm:(compk. The nuriIbmson the linesreferto thesohhntsystefnstmi(sazTabkII).

.:

’

14 15

12 13

&NO&wr.+NH~ cl+NO&m.NHa

c/s-NO&wwNH~, NH, cls-NO~mn.+NH~,NH,

c/s-04rans-NH1 c/s-O+wNH~ Meridhnal(l,2,6) Meridional(1,2,6)

.8 9

10 11

transdrans-tram trans=friwtrans

ii 7

[cocOB'Y o\rodd

@ala)

ii

65 82

24’ 29 7’

id~W2121

WNW2 (P-m

ii

-

80

48

-

82

14 7

(/%ala)

W2hl’

75 23

73 86

ii

88

[CoNIWy

21 50

74 68

75

69 61

-

16

;

6”

6

t

49 10

12

RF x 100”

GO.aM2

PNWY~NO~I

@ah02

m%~Y2 W2M'

@ala)2

kdY@ala)

w02121-

13 13

IPxlY (NQ)41Z’

@WY2

Refi

,3 4 5

\

,

75 61

77 67

-

92 39

82 77

-

a

-

17

76 80

52 66

:;

48 67

23 45

-

99 80

-

-

-

iii! 48<-

-

_ _

-

22

J4

,

85 80

75 80

37 33

-

87 84

49 56

68 80 68

‘39

88

85 81’

30 55

!‘

-

24

,,I

/$‘,

5

1,, 1

:,

,

,5

”

65 *1-t54 -

64 5’.-

_,16

-’

-:

si ‘, : l 45 -

,I,

”

,,

20

’

.‘,

,B J),

,”

:

‘:,

‘,.

,* .’

II

’

,40 ~: 20

”

‘,

,

,‘(.L

33 * 25 : 1,

,, 36

:

%,

‘.”

-

‘$5 29

P;

: SO ‘, 40 ” fit

I

45 : 29

-L ’ io ig : ,: :” -k 29’ : 23 ” i,_‘,‘,

’ A

4i

_r ’ : $i

-

~,,

’

si,c 4j

25

*

i 711* - ,:, 56

71,

21

‘72 ‘75 .83, 68 *I39 8,61 41’ 67 882 65

86

-

65

a2

-

54 19

28 83 85 I-

13

_

-

-

JJ

,(,

VALUES ~BT~WED,~KHMIJLTI=C~MP~NENTSOLVENTSY~TEMS~

Complex*

U=W

homer

:

No,

EFFE~~OFTHE~HELATE~~N~~~~ONR~

TABLE VI

‘*

&m-N trrmN

30 31

34 35

[cooxJgly]*’ (/hIa)

[CW~Y ~1

20 20

18 19

18 19

1;

13 17 -

15 18

34 36

-

6 3

15 17 32 36

-

10 6 4

15 16 17

’ AbbrcvlntlonsPBIn Tublo111, " Tho compositioneof the solvent systems nro given in TAMO II,

lWal(1,2,3) Rciul(1,2,3)

28 29

32 33

Meridional(1,2,6) Meridional(1,2,6) Mcrldlonnl(1,2,6)

!

_. -

-

4

(CmnJ cntn 1111

mm-NO1 rruwN0, 1mwN0~ WQJ)JI+

4 3

tnJ

cls.NOa cl.~NOa

17 58 ;: I

46 31 :: _ -

8 8

ii

frms-NO1 ms~N0,

cls~NO~=frtwN&

cl~NO&mr~Nl-11

;: 27

:

22

;

19

18

16 17

13 39

30 55

38 46 61

51 57 61

50 56

;: ::, 39

50 44

80 75

81 48 58 50

54 35

25 29

31 35

76 78 69 72

5 34

_ _

18 27 10

43 48

36 52

-

76 65

; 54 _

69 71 73

64 71

74 72

78 67

a -

_

68 64 60

26 23 22

15 8

!I:

68 61

38 16 I

41 31 19

!! 74

_.

;;

74 61

6 10

10 14

;:

18 5

48 40

1

(-)-Meridional (1,2,6) cls.NOrtruns-NHz,NHa (-I-)-c&NOdruns-NHZ, NH, (+)-cls.NO&ws-NHa, NH3 rrawNO&s-NH3 tru/wNO~.cfs-NH, r/w/is-NO&-NH,

(-).Moridional

m%lYz (NO2hl’

8lY Lala ” a L=abu

[Cow%)? JI~Y~O2)11 L-ala L-abu

DN-WWMd L-ala tabu L-nva

WaO2

(L-ala)2 (i-abu)a (wva)?

[CoNH&aNOzl

(L-k)?

(L-h)2

14 14 14 14 7 7 7 7 7 7

7 7 25 25 25

24 24 24 24

(L-m2

24

(wal)l

F4

(bnv42

(t.-ala)l (L-abu)2 (ibu)3

68 73 75 78 24 27 55 34 39 45

25 41 54 68 70

35 46 59 55 73 69 80 78 76

88 92 95 97 82 86 88 33 69 90

37 71 84 94 94

-

28

31 38 43 51 33 37 47 24 33 40

7 14 28 35 43

14 20 25 22 44 42 60 62 59

26

90 93 97 99 81 86 89 -

-

-

-

-

14

:

51

25 48 67 73 81

_.

20

-

32 43 GO -, -

;;

84 87

25 64 90 98 99

-

-

11

48 53 49 57 65 50 53 56

35 42

55 67 73 75 89

z 75 76 77

:“8 55 57

22

82 86 88

-

-

-

70 81 90 93 95

82 81 89 85 91 92 94 94 91

13

46 59 67 59 73 71 81 71 76

21

87 90 93 78 84 89

-

14 76 68 13 77 48 71 81

65 70

43 42 62~ 61 76 74 85, 81 92 86

-

-

-

16

” calaH = calanine; x.-abuH= Gaminobutyricacid; LnvaH = L=norvalinc;tvalH = L-valinc;L&H = tnorleucine; ~1euH = tleucinc; L&H = xkiolcucinc. ” The compositionsof tha solvent systems are given in Table II. “* Sign of optical rotation at 589nm,

ii 24

19 20 21

Meridional(1,2,6)

15 16 17 18

(1,2,6) (-)-Meridional (1,2,6)

cis-O-truwNH2 (+)-cis.O.trunr-NH1 ( -I-)&O-trans.NH1 ($)-c/s-O-tram-NH1 (-I-)-c/s-0.tram-NH1

cls-NOa-truns-N (I_) ***-cis-NOz-rrurrs-N ( +)ds-NOa-trans-N ( -I-)&-NO#wwN ( +)d~-NOa-trans-N (+)&NO~-truns;N ( I_)&NOa-trans.N (I_)&-NOrtruns-N (I_)-cbNO~-trusts-N

10 11 12 13 14

i

2 3 4 5 6 7

30

EFFECT OF THE NUMBER OF CARBON ATOMS OF AMINOCARBOXYLATOLIOANDS ON RP VALUES OBTAINED WITH MULTICOMPONENT SOLVENT SYSTEMS No. Isonier Complex’ RF x lOO’* Ref:

TABLE VII

:’

%

a-9

’

g ‘w

3

curred for the remaining wmpkxes (IkbIe U, complexes 20-24) as well as when m&komponent solvent mixtures were used @able VI)_ However, in all instances where the groups contained three complexes each, a linear correlation was found between the number of five-membered rings substituted by the corresponding six-membered rings and the RX value of the complex (Fig_ I)_ Contrary to the results obtained by paper ehromat~graphy~, where this correlation was always negative, in thin-layer cbromato~phy on silica gel this correlation was found to be either posit&e or negative.

Eflect of branched chin sire of coordirra~edamino acids on RF values of the investigated conzpkxes It is known that in thin-layer chromatography there is a linear correlation between the nllm&r of carbon atoms in a homologous series of some organic compounds and their & valueS_ JursiP determined the RF values of some aminocarboxylatonickel(II) complexes by means of thin-layer chromatography on silica gel, using phenol-water (75:25) as the solvent system. He established that an increasing number of carbon atoms in a homologous series of coordinated amino acids results in an increase in the RF values of the complexes. With regard to these resuIts we wanted to establish (a) whether they represent part of a general n&a&y of the correlation between RF nlues of metal CompIexesand the number of carbon 2toms in coordin2ted RM 1.2

0.s

a4

234562

6.

2

3

4

and (b) whether there is a linear correlation between &e- ntimber of atoms in aminocarboxylato Iigands coordinated to cob&o and- ffie RM values of the comzsponding complexes. Therefore, we chromatogr$phed 24 anionic and neutral zminocarboxylatocobal@IQ complexes (Table VIE), divided &to five homologous series, by means of ten two- and &ree+muponen~ solvent systems, all compound% of each type being separaed by Ehe use of at least five d.i%kent solvent

amino acids, &bon

%!l a 0.6 8

‘-

1

:a

7

-0.8

-1.0

-1.2 46 -1.4

-Ls -Lo -1.8 -12

-I-

2

t

3

L :

:

:

”

23452234

c

NumksafCna~~

Fig. 4; Dependence of & value on ffie number of carbgi atomsin bne of the coo&a&d amino acids in tie (-)Ms_meridi~[~~~(NO&]~ compkx. The numbers on the lines refer to the solvent systems used (see Table II)-

htkse e.xgmimm% it pias establiskedthat an increasingnumber of carbon inthe& atoms in the branched chain of coordinatedamino acids causesan in= values of the complexesinvestigated.The increasetakes place regardlessof whether the carbon atoms belong to a straight or a branched chain of coordinated~chefate I&.&s. The diflkreuces in the RF vaks of complexes containing s*Aght and branchedchains witk the same numberof carbon atoms weresmall (Table VIE). l[naddition,we found a linear correlationbetweenthe number of carbon atoms in coordinatedaminocarboxylatoIigmds and ffie I& value of the complex (Figs. 2-6) ; tke correlationwas always negative-

Fig. 6. ikpezxm of & vake on the nr?mbcrof carbon atoms in one of the ax&hated amino acids in the rrzms(NO~,c~.H*[CoCo(NH~_4m~O~ c0mpkx. The nrunbers OQ the lines refer to the solvent s>-stemsus& (see Table IQ.

We assume that all of the above separationsof complexes are achievedby a partition mechanism,as the CH, group is known tc possss a very small adsorption eneq@, so that the separationcould not be effectedby an adsorption mechanismLikewise,ioo exchangecannot be taken as the cause of the separation,as the investigated complexeswereof anionic and neutraltypes, and silica gel behavesas a wetly acidic cationic exckanger.The fact that analogous resultsare obtained by partition paper chromatographysupportsthe postulatedmeckanism*-

74

M.B.&bU?etal.

ACKNOWLEDGEMENT The authors are grateful to the

SerbianRepublicResearchFund for financial

SUppXt.

REFERENCES

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