A C T A U N I V E R S I T A T I S L O O Z I E N S I S FOLIA CHIMICA 9, 1991
Joanna Maslowska*, J d ie f Szmich*
POTENTIOMETRIC INVESTIGATION OF HIXEO LIGAND COMPLEXES OF N i ( I I ) , C o ( I I ) AND Z n ( I I ) WITH THIOSALICYLIC ACIO
AND POLYETHYLENEPOLYAMINES
P o te n tio m e tric stu d ie s of the M ( II) - t h io s a lic y 1ic acidCH gA ^polyethylenepoliam ine ( E ) systems (where: M » N i, Co or Zn io ns, E-ethylenediam ine, d ie th y le n e tria m in e or trie th y le n e te tra a m in e ) in ethanol-w ater NaC10(, so lu tio n s (y = 0,1) re v e a ls the form ation of tern ary complexes of [MAE] 0 type. The log K forin and AG° values of these comp lexes were c a lc u la te d at 25°C. The c o n s titu tio n of formed complexes was determined as w e ll as the order of th e ir s ta b i l i t i e s in term of polyethylenepalyam ines and metal io n s.
T h io s a lic y lic acid (TSA) has two p o s sib le c o o rd in atio n s it e s , su lp h yd ryl (-SH) and carboxyl (-C00H) groups. Sulphur is known to form weak Ti M —► L bonds, whereas M —► 0 bonds are 6 in c h a ra c te r. Ligands w ith sulphur donor atoms are c l a s i f i e d as s o ft bases and those w ith oxygen donor atoms as hard bases [ l ] . This is the reason why the form ation of simple and mixed t r a n s it io n metal c h e la te s of TSA has gained an in t e r e s t in recent years [2-10]. In the present study an attempt has been made to in v e s tig a te the complex form ation of N i ( I I ) , C o ( I I ) and Z n ( I I ) w ith TSA and polyethylenepolyam ines such as: ethylenediam ine (e n ), d ie th y le n e tria m in e (d ie n ) and trie th y le n e te tra a m in e ( t r i e n ) .
I n s t it u t e of Ceneral Food Chem istry, Technical U n iv e r s ity of Lddź, Poland.
EXPERIMENTAL
Reagents
T h lo s a lic y l i e acid (Marck A. G .) was p u r ifie d by c r y s t a l l i z a tio n from methanol. Polyamines (en, d ien, t r ie n ) (Schuchardt A. G .) were p u r ifie d by vacuum d i s t i l l a t i o n and used as th e ir s a lt s with HC104 (en • 2HC104, dien • 3HC104 and tr ie n . 4HC104, resp .). (Ni/C104) 2, Co(C1 0 4 >2 stock s o lu tio n s were prepared according to procedure [ l l ] and stan d arised using EDTA [12, 13]. A l l the pH t it r a t io n s were c a rr ie d out with carbonate-free NaOH s o lu tio n . Ethanol-water 50 : 50
(V / V ) s o lu tio n s were used and constant io n ic strength (p » 0 .1 ) was m aintained by NaC104>
Apparatus
pH measurements were performed with p re c is io n , d ig it a l 0P-208 pH-meter R ad e lk is, equipped with a g la ss 0P-0718P and calomel
0P-0830P e le c tro d e s . R ad e lk i3 b u ffe rs of pH 2.15, 7.05 and 9.21 were employed. Po te n tio m e tric t it r a t io n s were performed under p u r i fie d n itrog en , supplied on to the bottom of the w ater-jacketed beaker at 25°.
Measurements and c a lc u la tio n procedure
The measurements were c a rrie d out as described in previous papers [14-16]. Seve ra l s e rie s of t i t r a t i o n curves were made. pK values of ligands c a lc u la te d from th e ir t i t r a t i o n curves by C h a-
b e r e k and M a r t e 1 1 method [ i 7] are presented in the
Tab. 1.
F ig u re 1 shows the t i t r a t i o n curves fo r the systems: 0.001 M (II)
- 0.01 TSA - 0.01 HC104 - 0.079 NaC104 - H20 (where M = N i, Co and Zn). From these c u rv e s , the s t a b i l i t y constants of simple complexes
have been c a l c u l a t e d using B j e r r u m method [18] modified
by C a l v i n and W i 1 s o n [19] (Tab. 2 ). Zinc ( I I ) com
T a b l e 1 Ligand acid d is s o c ia tio n constants
Ligand pKj pK2 pKj pk4 TSA H2A h pn2* 8 H,en 3+b Hjdien H ^ trie n 4* 5.1A 7.10 4.55 3.85 9.52 9.70 9.95 6.67 1 0. 10 9.20 9.92 a ’ b ’ c Ret. [14, 15, 16] - r e s p e c t iv e ly .
F ig . 1. P o te n tio m e tric t i t r a t i o n curves of TSA in absence and presence of M(1 1)
Curve 1: 0.01 M TSA - 0.01 M HC10t - 0.08 M NaCl04 . Curve 2: 0.001 M CoC I I ) - 0.01 M TSA - 0.01 M HC10t - 0.079 M HaC10; . Curve 3: 0.001 M N i ( I I ) - 0.01 M TSA - 0.01 M HC10k - 0.079 M NaCIO,,. Curve 4: 0.001 M
T a b l e 2 S t a b i l i t y constants of the binary TSA
complexes of [MA] and [MA2] type
Metal Ion log log ß2
C o ( II ) 5.8 ~ 0.2 4.1 - 0.2 Hi ( 11) 6.9 - 0.2 4.2 Í 0.2 Z n ( I I ) 8.2 ± 0.3
The p o ten tio m etric t i t r a t i o n curves have been determined fo r fo llo w in g mixed ligand systems:
1) 0.001 M ( I I ) - 0.01 TSA - 0.01 en - 0.02 HC104 - 0.059 NaC104, 2) 0.001 M ( I I ) - 0.01 TSA - 0.01 dien - 0.03 HC104 - 0.049 NaC104> 3) 0.001 M< 11) - 0.01 TSA - 0.01 trlen - 0.04 HC10. - 0.039 NaCIO,.
4 4
Fig u re 2 shows the curves fo r (1 ) system fo r M = N i, Co and Zn ( a - moles of NaOH per 1 mole of lig a n d ).
The comparison of the p o ten tio m etric t i t r a t i o n curves of (1-3) systems w ith those fo r systems without polyethylenepolyam ines, in d ic a te s form ation | of mixed ch e la te s by stepwise ad d itio n of both lig a n d s. I t is supported by the pH lowering in comparison to binary systems, the non-superimposable r.ature of the th e o r e tic a l and p rac t i c a l t i t r a t i o n curves as w e ll as d if f e r e n t colour of s o lu tio n s .
For example the F ig . 3 shows the curves fo r systems: C o ( I I ) - TSA and C o ( II ) - TSA - H2en2\
I f HjA is the formula of TSA and HnEn+ - polyethylenepolyam ines in form of th e ir s a lt s w ith HC104, the process of mixed ch e la te s form ation may be shown according to eqs. (1-2) :
M2+ ♦ H2A + 20H' = [MA] ♦ 2H20 (1 )
[MA] ♦ HnEn+ + nOH' = [MAE] + nH20 (2)
K , -M
e] .
F ig . 2. Po te n tio m e trie t i t r a t i o n curves o f systems: 0.001 M M ( I I ) - 0.01 M TSA - 0.01 M en - 0.02 M HC10t - 0.059 M NaC104, where M ( I I ) = C o ( I I ) (cu rve 5 ), Z n ( I I ) (cu rv e 6)
and N i ( I I ) (cu rve 7)
F ig . 3. P o te n tio m e tric t i t r a t i o n cu rve s: of 0.01 M TSA (c u rv e B ) and systems 0.01 M TSA ♦ 0.01 M C o ( I I ) (c u rv e 9) and 0.01 M TSA + ♦ 0.01 H C o ( I I ) + 0.01 M e n •2HC104 (c u rv e 10) 1 (» = 0 .1 )
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we have c a lc u la te d by the method of T h o m p s o n and L o- r a a s [2 0 ]. Free energy form ation values were c a lc u la te d from equation ( 4 ) :
AG° * RT In Kmae (4 )
The evaluated values are presented in Tab. 3.
T a b l e 3 Formation constants KMA£ and free energies of
formation AG° of mixed complexes
Complex lQ9 KMAE AG°[kJ/m ol-K]
[CoAen] 4.32 - 0.08 -24.64 [CoAdien] 5.47 i 0.17 -31.20 [CoAtrien] 7.02 - 0.12 -40.05 [NiAen] 5.78 - 0.10 -32.97 [NiAdien] 7.15 - 0.09 -40.79 [N iA trie n ] 9.31 - 0.18 -53.11 [ZnAen] 4.75 - 0.12 -27.10 [ZnAdien] 5.52 - 0.22 -31.49 [Zn A trien] 7.10 - 0.10 -40.50
The order of s t a b i l i t i e s of simple t i o s a lic y la t e s in term of m e ta lio n s i s : Z n ( I I ) > N i( I I ) > C o ( I I ) .
I t is in good agreement with I r v i n g-W i 1 1 i a ms con c lu s io n [2 1 ]. For the mixed ligand ch e la te s of [MAE] type the order is fo llo w in g : N i ( I I ) > Z n ( I I ) > C o ( I I ) .
The explanation for th is change is the d if fe r e n t a f f i n i t y of these ions to sulphur arid nitrogen atoms [22, 23] (c a tio n Z n ( I I ) with 3 d ^ e le c tro n co n fig u ra tio n shows le s s a b i l i t y for d -electrons engagement in the bond).
In term of polyamines the order is :
I t is in te r e s tin g , th at replacement of en by dien causes s m all er s t a b i l i t y in crease than replacement of dien by t r ie n . The ex pla n atio n may be th at complexes of [MA t r ie n ] type are in te r n a ly s a tu rate d , on co n tra ry to [MA en] and [MA dien] complexes, w ith four and f iv e bonds between metal ion and lig an d s r e s p e c t iv e ly .
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[17] S. C h a b a r s k J r . , A. M a r t e 1 i , J . Am. Chem. Soc., 74, 5052 (1952).
[18] J , 9 j e t c ii i , Metal Amraine Formation In Aqueous S o lu tio n , P. Haase and Son, Kopenhagen 1941.
[19] M. C a l v i n , K. W i l s o n , J . Am. Chem. S o c ., 67, 2003 (1945). [20] L. C. T h o m p s o n , J . A. L 0 r a a s, In org. Chem., 2, 89 (1963). [2 1] H. I r v i n g , R. J . P. W i l l i a m s , J . Chem. S o c . , 3533 (1953). [22] S. A h r 1 a n d, J . C h a t t , M. R. D a v i e s , Quart R e v., 12, 265 (1958). [23] R. M. T i c h a n e, W. E. B e n n e t , J . Am. Chem. S o c ., 79. 1293 (1957).
Joanna Masłowska, Jó z e f Szmich
P0IENCJ0METRYCZNE BAOANIA MIESZANYCH KOMPLEKSÓW N i ( I I ) , C o ( I I ) I Z n ( I I ) Z KWASEM TIOSALICYLGWYM
I POHETYLENOPOLIAMINAMI
Na podstawie potencjometrycznych badań układów: M (II)- k w as tio - s a lic y lo w y (H2A )- p o lietyle n o p o liam in a ( E ) (g d z ie : M = N i, Co i Zn, E-etylenodiam ina, d ie tyle n o tró jam in a i trie ty le n o te tra a m in a ) w wod- no-etanolowych roztworach NaClO^ (p = 0 ,1 ) w temp. 251 0,1*C s tw ie r dzono powstanie trójskładnikow ych kompleksów typu [MAE]0. Wyznaczo no ich skład oraz s t a łe tworzenia log K i w arto ści liczbowe e n e rg ii swobodnej tworzenia AG0. Określono także szereg trw a ło ś c i powsta jących kompleksów w zależności od p o lie ty le n o p o lia m in y i jonów me t a lu .
