CHAPTSR - I

INTRODUCTION

1

Sulphur and selenium being members of the

same group of periodic table resemble In most of the

properties and form structurally similar compounds.

Both elements are donors in a variety of ligands which

form complexes with metal ions. The complexlng ability

of donor and acceptor el an eats depends upon the nature

of the respective elements.

Ligands in which sulphur or selenium act as

donors have been classified as class ' b* donors by

Arhland, Chatt and Davies (1) and soft bases by

Pearson (2 ). 3uch ligands In which sulphur or selenium

atom is a doaor form more stable complexes with metal

ions which have low or aero positive charge, large size

and several easily excitable outer electrons and such

metal ions have been classified as d a 3S * b* acceptors( 1)

or soft acids (2 ).

Metal ions with d*° configuration, viz. Copper(l),

3ilver( I ) , Zinc( I I ) , Gactaium(Il) and mercury( II) and d^

metal ions namely nickel(Il), Palladium( II) and

i^latinumC II) show very high formation constants

particularly with sulphur ligands.Being class ' b‘ metal

ions they tend to fom strong sigaa bonds with these

ligands due to polarization of sulphur atom ( 3 ) or due

to greater covalent interaction (4 ) . A d* - d* bond

by back donation of electrons to vacant 3d orbitals of

sulphur atom is one of the reasons for the greater

stability of such complexes.

The sulphur and selenium ligands can be

broadly classified into two groups; inorganic and

organic compounds.

Amongst the important inorganic ligands are:-

(i) Julphidee and selenides.

(ii ) Trlthiocarbonates and t ri s eleno carbon at e 3 .

(i i i ) Thiocynates and selenocynates*

(iv) Thiosulphates and selenosulphates.

(v) Sulphite? and selenites.

The organic sulphur and selenium compounds

are of more varied type - the simple ones are

/ \ 0(i) Thils and selenols - one co-ordinating site.

(ii ) Thioethers and alkyl selenides- one coordinating site.

(i i i ) Mercaptoacids and selenol - acids, - two

bonding site^*

3

( iv) Thioketones and selenoketones, - thioacety-

acetone and selenoacetylacetone each have two

bonding sites.

The other class of compounds is represented by

thioureas and selenoureas, thiocarbamates and seleno-

carbamates; these ligands have each two bonding sites

nitrogen, sulphur or selenium act as donating atoms in

these ligands.

The formation of sulphur or selenium ligand

complexes of typical class * b* metal ions like

mercury(ll) and rsincCll) with hi^ti stabilities is quite

obvious.

The organic multidentate ligands like 2-mercapto-

propanoic acid and >* me reap to propanoic acid which are

isomers contain oxygen as well aB sulphur based

ft actional groups act as excellet chelating agents for

all * a' , * b' and borderline metal ions.

Similarly thioureas and selenoureas having

sulphur, nitrogen and selenium, nitrogen respectively

as donors form a variety of complexes with class • b’

and borderline metal ions.

4

The Important aspects of the studies on the

complexation are * (i ) physioo - chemical investigation

leading to understanding of nature of complex species

and their equilibria, (i i ) synthesis and determination

of structure of metal complexes (il i ) the analytical

applications. A review of literature reveals an intense

interest in all the three directions.

1. EQUILIBRIUM STUDIES ON MERGAPTOCAi-BOXYLATE

M3T,,L COMPLEXES •

Fernando aad Preiser (5) studied the chelating

properties of 3~mercaptopropanoic acid and determined

stepwise formation constants of Hickel(ll) and &Lnc(ll)

with the ligand and observed that Nickel(Il) complex is

less stable than zinc(ll) complex. With mercaptoacetic

acid as chelating agent they have determined the

relative stability of five and six membered ring chelates

using the relation ^ l o g K1 / / \ ^ aVt ^\log ILj is

decrease in value of first formation constant of the

chelates in going from five to six membered rings and

A p Kav is increase iQ arithmetic mean of negative

logarithm of acid dissociation constants of ligand

molecules, they found five membered rings are more

stable than six membered rings in each complex.

Leussing (6) reported the stability constants

of mangaese(ll), iron(ll), nickel(ll), and zinc(ll)

with thioglycolllc acid; only the formation of 1:1

and 1:2 (metal:ligand) complexes were reported and

zinc complex was found to be more stable than nickel

complex. The formation of polynuclear complexes between

nickel(ll) and thiogLycollic acid ions have been

described by Leussing and co-workers(7), they have

reported the formation of 2:2, 3:4, 4*6 (metal: ligand)

complexes with the metal ion.

Bear et al (8) have investigated potentiometrio-

all y the formation constants of lanthanide metal

complexes with 2-, and 3- mereaptopropanoic acids, they

have reported that both the acid anions function as

monodentate ligands. Sigam et al (9) have potentiometrically

studied metal complex of uranyl(VI) with 3-mercapto-

propanoic acid, i'he workers (10) have reported stability

constants of 1:1 complexes of copper(Il), cobalt(ll),

raercury(ll) and 1:2 con pi exes of nickel(ll), zinc(ll),

<LTi

palladium(ll), iron(lll), uranyl(Vl), zirconium(iv)

and thorium(iv) with thiol acetic acid using

potentiometric technique. In case of palladium, nickel,

zinc, the values of stability constants follow the

order Pd Hi Za. In case of eopper(ll) the value

is low* Saxena and Gupta (11) reported the composition

and stability constants of 3-mercaptopropaaoic acid

with 2inc(ll); 1:1 and 1*2 (metal:ligand ) complexes,

overall stability constant of 12.65 at 30°C has

been observed. Ihe workers (12) have investigated

potentiometrically the stability and composition of

thallium(l) with 3-merceotopropanoic add acid, 1*1

(metal;ligand) complex with logk value of 2.85 at 50°

is reported. Similar studies wer conducted with

nickel(ll) and 1*1 and 1:2 (a«tal*ligand) complexes

with the sme ligand with overall stability constant

value of 10.74 at 50°o were reported (13). Polarographic

studies of the same ligand with cadmiwa(ll) revealed

fo eh at ion of four complexes of 1*1, 1*2, 1*3 and 1*4

(metal*ligand) stoichiometry with overall stability

value of 17.19 at 30°C (14).

Bhattacharya sod Reddy (15) have investigated

the nickel (ll) and thallium(l) complex formation with

7

lactic acid and thiolactic acid by pH metric technique

and have reported that nickel(ll)-thiolactate complexes

are more stable than the lactate complexes and reverse

was the case with thallium(l). They have supported the

observations on the assumption that 3d Pi orbitals in

sulphur atom render metal to ligand Pi interactions

possible in case of nickel-thiolactate complex, and

such interactions were not existing in other complexes,

Bhattacharya and co-workers( 1 6) have also reported the

stepwise formation constants of complexes of

thioglycollic acid and thiolactic acid with 3e (Il),

Zn(ll) and Cd(ll), they have observed the stability

order : Gd ^>Zn }>Be and thlolacctic acid forms stronger

complexes than thioglycollic acid with these metal ions.

The stability of chelates is diseussed in terms of

metal - ligand Pi interactions, Nitriloacetic acid as

primary lirand and thioglycollic acid or thiol ®Aic acid

and thlomalie acid as secondary ligands with zlno(ll)

have also been studied by Bhattacharya et al (17).

They (18) also studied the mixed ligand systems of

copper(ll) and nlckel(ll) with nitrlloacetic acid as

primary ligand and a merceptoI'cid or an amino acid as

secondary ligand. Similarly phen ant hro line as primary

ligand and mereeptoacids as secondary ligands have

also been studied by Bhattacharya and co-workers (19).

The objective of these studies was to find out the effect

of Pi bonding, they concluded that the metal sulphur

covalent bond is strengthened and effect of Pi interaction

is not significant.

Tanaka and co-workers (20) have studied

potentiometrlcally the complex formation between phenyl

and methyl mercury and pencillamine and amino acids like

cysteine and reported a 1s2 (metal: ligand) complex

with the ligands. They have found that stability order

of the bonds decreased in the order:

MeHg -S >PhHg > PhHg -3 > MeHg - N

^>PhHg - 0.

They have also evaluated stability constants of

complexes of thiolactic acid and pencillamine with

Gr(lll) which foms 1:1 , 1*2 and 1:3 monomeric complexes

with thiolactic acid and 1:3 complexes are of regular

octahedral geometry. The complexes of pencillamine are

more stable than complexes of thiolactic a d d (21).

Van Pouke et a l .(22) have conducted

potentiometric and colorimetric studies of Mi(ll)

and 2n(Il) with thiolactic add and reported the

formation of mononuclear and polynuclear species of

the composition 1 :2 , 2:2, 3*4 (metal;ligand) with

stability constants 14.33* 17.29 and 34.92 respectively

The non-existence of 4 :6 complex is explained due to

presence of ateric hinderance by o£-methyl group

in thiolactic acid as the similar complexes are

existing in case of tfi(ll) and zn(ll) thioglycollic

acid. A similar study has been extended to the systems

of N i(Il) and sal(11) and 3-merceptopropanoic acid (23)

with 2n(ll) a number of species with 1:2, 3:4 , 4 :6

(metal:ligand ) stoichiometries have been observed and

in case of Hl(Il) complexes of 5:10, 6:9 and 6:12

(metal:ligand) stoichiometric ratios have been reported

2he absence of steric hinderance in 3-mercaptopropanoic

acid being responsible for the foumation of complexes

with such hi^i ligand ratios.

Sarin and Munshi (24) have investigated

potentiometric ally the complex formation of In (IIl)

with several mere ap to acids snd have reported that

stability of complexes with various li ands decrease

in order:

Thiolactic acid Thioglycollic add^>

Lactic acid Glycollic acid Alanine and

Glycine.

They have correlated these values with

stepwise formation constants of In(lIl)-3-mercapto-

propanoic acid complexes and have found these to b@

less stable than those of thiolactic acid and

thioglycollic acid and values of formation constants

decrease with increase in temperature. Stepwise

formation conatants of Ga(lII) complexes with thiolactic

acid, thiomalie a d d , thioglyoollic acid, lactic acid,

malic a d d and glycollic acid increase with increase

in temperature, and Ga(IIl) forms 1:1, 11 2, 1*3

(metal*ligand) complexes with thiolactic a d d . Ga(lll)-

thioglycollic acid complexes are more stable than those

of thiolactic a d d (25).

Cassasas and co-workers (26) have investigated

the Cd(II)-thiolactic system potentiometrlcally and

reported the existence of polynuclear species of the

composition,1 * 2, 2*3 and 3*4 (metal:ligand) with overall

formation constant, values of 15.04, 28.45 and 40.80

respectively. The acid sulph-hydryl group tends to

bridge metal ions in these complexes.

11

2. SOLID CGMPLiSXJS OP M̂ HCAP'JX) CA3BOXYLIC

ACIDS.

Fernando and Jfrleser (5) have reported complexes

of >-mercaptopropanoic a d d of ?b (ll), Cu(ll) and Ag(l),

the composition of these complexes reported is*

Pb(SCHgCHgCOO) f A d SCHgOHgCOO ) H^O,

Cu( SCHgCHgCOO ) and Cu( ESCHgCHgCOO),

Copper formed two types of complexes.

Shindo and Broun (27) have reported complexes

of L-cysteine, 3-methyl-L- cysteine and 3-mercapto-

propanoic acid with in(ll), Cd(ll), Hg(ll) and Pb(ll),

they have observed that Hg(ll) forms a number of

complexes with stoichiometrics -

Hg2 [SCH2CH(MH2)C02] 2 ,

Hg2 JTsCH gCH(HH 2 ) CO 2J 2 HCl,

Hg [SCH2 CH(*TH2)C02i 2 and

Hg5 [SCH2CH(NH^COgSj C l* ZHgO

12

Zinc and ca&nium form r-

C^4]2+M , M « 2n or Cd

L « S- CH2CH( IIHj) CO 2 # X * Cl~

The metal is hound to sulphur and earboxylate

oxygen, and sulphur atoms bridge the three metal atoms,

the other types of complexes reported are

The metal atom is bound to sulphur atom of sulphhydryl

group and nitrogen atom of amino group,

Mishra and STigera (9) have Isolated aid

characterized a uranyl complex of 3-mere apt op ropanoic

acid, its composition is reported to be *-

0oL2(H20 )2 (1 * -BCH2CH2C02 ) with octahedral

geometry has been reported (2S)| sulphur atom of -311

group and oxygen atom of -COOH group is involved in

bonding with Os>(ll) ion. Hi gam and co-workers (29) have

2-

[uOgLg ] 2H20 j L - -SCHgCHgCOgH.

A cobalt complex of the composition

isolated complexes of Ag(l), Cd(ll), Hg(Il) and

U02(VI) of 5-mercaptopropanoic a d d , the reported

composition of the complexes is

AgCC^OgSj.fflgO, CdtC^OgSj.aigO,

HgCC^OgSjg and UOgCG^Og.ffigO.

With Ag(l), Hg(ll) and Uranyl ions the ligand acts as

mono-negative bident ate ligand, co-ordinating through

oxygen atom of -COOH and sulphur atom of -SH group.

In case of cadmium the ligand acts in a binegative

bicentate fashion. Srlvastava and Higsra ( 30) have also

isolated the c cm pi exes of thiolactic a d d with Ag(l),

Cd(ll), Hg(ll) and Pb (II) with compositionsi-

H [lg(KL)] H20, Gd |hl] . 2H20

Sa2 [cdl2 ] .2 H 20, K2 QigL2 ] and

PbL.2H20 (L » C ^ O g S )

They have found that thiolactic a d d acts as bidentate

ligand co-ordinating through sulphur of -SH and oxygen

of -COOH groups. Complexes of Cr(IIl), Iln(ll), Co(ll),

and 'li(ll) with thiolactic a d d have been reported ( 3> ),

their compositions found are*-

14

H3 [cr ( C ^ 402S)3 ] , Mn [ (O ^ O g S ) (H ^O )^ 2H20

Ha2 [bo (C ^ O g S jg (H20 )2^|t

£»i (C ^ O g S ) (H20)4 ] and

Ua2 £ H tCC^OgSjg]

In these oomplexes the H a n d acts as bi dent ate

chelating agent co-ordinating throu^x sulphur of -3H

and oxygen of -COOH groups* They have suggested Mn(ll)

complex a square plannar geometry with ma&ietic moment

Of 4.51 B.M.

A trlnuclear complex of thiolactic acid with

Gu(ll) having composition-

CUj (GgH^OgS)^ 4.5 HgO has also been reported (32).

Mehrotra and co-workers (33) have reported

various complexes of Ti(lV) and Zr(lV) lsopropoxides

with 2-merc apto ethanol, thiolactic a d d and 3-mercap-

topropanolo acid.

Panchal and Bhattacharya (16) have prepared

complexes of Zn(Il), Cd(Il), Hg(ll) and Ag(l) with

thiolactic ad d and thioglycollio acid and compositions

of the complex©a is represented as i

2a( ZnI»2)2H20t Cd(0dL2), Hg( Hgl»2) and

Ag^( AgLg) t

L » C ^ O g S and -SCgHgOg

Horl (34) has reported the preparation of

mixed ligand complexes of 2-, and 3-mer captopropanoic

acids and ethylenediamine with Co(lll). The reported

composition of the complexes <S s-

Jco( SCHgCHgCOO) en2] x

[oo(CH3.S.CHOOO) en2 ] x

( en « ethylenedi amine, x * cl~ or 1“ )

complexes are mononuclear and the meroaptocarboxyllc

acids function as hi dentate ligands.

Coleman et al (35) have preoared the dialkyl-tin

complexes of merc&ptocarboxylic acids* the reported

composition of these complexes is t

(0H3) 2 Sal2.H20

3> -SCHgCOOH, -SOHgCHgCOgH and -SCH^CHCO^

16

From IE and i'fMR data they have suggested that tin

binds two groups of two ligand molecules, two alkyl

groups and a water molecule resulting in a penta-

coordinate tin atom.

3. SOLID COMPLEXES OP SELMO-, AND

THIOUREAS.

Podder et al (36) reported complexes of

mercury(ll) with guianyl-1hiourea, In which they have

shown co-ordination of the ligands throu$i nitrogen

and sulphur.

*- disubstituted selenoureas have been shown

to function as unidentate, Se-bonded ligands in Pd(ll)

and Pt(Il) complexes which are similar to corresponding

thiourea complexes but show an increased tendency to

form five co-ordinate complexes ( 37,38).

The selenourea complex of cadmium (I I ) has

analogous structure to its thiourea complex (39) and

its composition has been found to be s-

Cd( Su) 2 Clg ( Su « Selenourea )

Goddard et al (40,41 ) have determined the

stability constants of metal oomplexes of selenourea

and aelenosemicarbazides as well as of thiourea and

thiosemicarbazides with class 1 b' metal ions and have

reported the order of stability with

Be > S > 0

Domiano et al (42) have inferred from X-ray

powder data that bis ( selenourea) metal(ll) thiocynates

M(Su ) g(^CS)g (where II *» Co,Ni,Cd) are isoatructural

with corresponding thio urea complexes, having polymeric

structure consisting of chains of octahedra Joined by

two selenourea molecules which fora bridges between two

metal atoms. Selenourea complexes of Mo(V) have been

studied by e .s .r . Spectra (43).

Adducts of thiourea (l ) and selenourea ( I * ) to

1 , 6-dichlorobis ( ethylenediaaine) cobait( III) halides

have been characterized (44). 2he adducts bear following

compositions:

1,6- £coX2-en2 ’]x .n .L , i 1,6- [ 0oX2en2 "]x.1.5 I 1.5 l'

(X * 01, Br, n = 1 ,3 , en *= ethylene diamine)

In these complexes sulphur or selenium are not bonded

to cobalt atom.

Daraatelli and chlarl (45*46) have synthesized

polymethylene bis( phenylthiourea) and polymethylene

bis( phenylselenourea). On the basis of electronic spectra

and magnetic moments these complexes have been

characterized and bear the compositions -

M iL2X2*

L * polymethylene bie( phenyl thiourea), X * Cl,Br

IfiL Cl2 | L * trimethylene bis (phenylselenourea)

ITilg Br2 ; 1 «* octa©ethylene bis (phenylselenourea).

NiLj (C104 >4 ; L » tetramet> ylene bis( phenylselenourea)

In case of thiourea the HiS^ is square plannar and in

case of selenourSa both square plannar and octahedral

complexes have been found.

Various selenourea complexes of class ' b' metals

have been prepared (47), the reported composition of the

complexes ia

(GoL4 ) (C104 ) 2 , CoL5 (S04 )

and Hg 1 2 X2 ? ^ “ Selenourea, X *» Cl,Br.

19

3in^a and Gupta (48) have reported synthesis

and characterization of mixed ligand complexes of

LI,2J - dime tbylselenourea and pyridine with potassium

hexaisothiocynatoatannate (IV) and potassium hexai30thi0-

cynato tit annate (IV ), these complexes have coeapositiom

M * Co, Zn, Hg j L a ‘J , dimethyl-selenourea or

pyrldene.

H,H dibenzyl selenourea)

electronic spectra of these complexes has also been

reported,

Kubicki et al ( 50) have reported crystal and

molecular structure of tetrakis (selenourea) Pt(ll)

chloride- ( Pt (btO^Clg). Compound is monochinic,

In a el enourea complexes selenium is bonded to metal m '.

Rivero (49) has reported complexes of Co(Il)» »

■with - dibenzylthiourea and - dibenzyl selenourea

the composition of the complexes is -

CoL2C12, CoL2Br2 and CoL2(C104 )2

(L » £!,&' , dibeazyltbiourea or

selenourea Is bonded to platinum through, selenium;

PtSe^ is plannar with Pt-Se distance 2.439 %.

Proskina. (44) have reported mixed co-ordination

compounds of copper with heterocyclic amines acid

selenourea. The composition of complexes reported iss-

[cuL2q 1 (010^) 2 } L=2,2 “ dipyrldyl Q * Selenourea

[cuL Q( 010^ ) J t L o 1 ,10-phenanthroline

Co-ordination number is five in first oomplex with

trigond blpyranu'del geometry and later has co-ordination

number of four. Analogous thiourea derivatives have

also been reported.

4 . analytical applications of

mekoaptocarboxtlic a c id s .

Formation of metal complexes have been utilized

in qualitative and quantitative analysis of various

metal ions. Buscarons and Casaasas (51) have used

thiolactic ad d for detection of Pd and >ln. Solubilization

of hydroxides and sulphides of heavy cations with

thiolactic acid (52) as masking agent in -the

precipitation reactions of metallic hydroxides and

sulphides was used for separation of the cations -

As, Sb, Sn,Mo, Se, Te, Au, Pt, Mn, Mi and Co, which

are so stable that their sulphides do not precipitate.

They have used mereaptoethanol ; 2 ,3-dlmercaptopropanol

and mereaptosuccinic acid for such separations.

Busev and Baou (53) have suggested a photometric

method of determination of Palladium with

1-naphthylamide, 2-naphthylaraide $ o ,p - phenetidi de

derivatives of 1 -mereaptopropaaoic acid; ?d reacts

with the reagent in the ratio of 1:2 in presence of

large anount of (1000 fold) ?t(IV), Rh(IIl), Ir( I?)

and Os(IY) which do not interfere with the estimation

of Pd. The workers (54) have also determined Mo(V) and

Ho(Vl) with 1-mercaptopropanoic acid and its amide

derivatives like o,p - phenetidide, o,p-anisidide and

o,p-toluidide. Ho(V) and Mo(Vl) react with the reagents

in 1 :2 ratio over a wide pH range. Mo-1-mercaptopropionato-

phenetidide is extracted with 1 :1-isosmylalcohol: CHCl^

in presence of diphenylguaaidinium or benzylthiouronlum

in aqueous phase. Extraction photometric method was

developed to determine Mo in presence of W ,Cr(IIl)t

Ti,Co,Mi, 2n, Al,Fe( III) and V. Absorbance is measured

at 350-65 nm, in presence of tun gs ton at 430 run.

Shi geo Kara (55) determined cobalt colorime­

tric ally with 3-ra eroap to propanoic acid at pH 9,0 and

at 370 run. Beer* s law is obeyed, a 1*3 (metal:ligand)

complex is formed, interference of cooper is decreased

by adding potassium cynide, iron and nickel interfere.

Prlbil and Vesely (56) have determined zinc and

cadmium in presence of copper with >~m ereap to propanoic

acid as masking agent followed by direct titration of

zinc with t ri ethyl en e-tet ram in e hexar-acetic acid. After

addition of dianinocyclohexane tetra-acetic acid

cadmium is determined in directly by back titration with

2n(tf0j)2 solution, all the titrations are carried in

presence of xylenol orange as indicator in acidic medium,

iacu and coworkers (57) have used thiolactic acid for

gravimetric estimation of zirconium. Thi©lacotic acid

is added to zirconium salt at pH 4.5* Zr02 is

precipitated and dried. Sn( I I ), Hg(Il), Zn(Il), Gd(Il),

Ti(IV), Th(IV), Cu(Il), Pb(Il), Iii(II) and Ca(ll)

interfere in the estimation. Fritz and Beuuaan (58)

su©jested a rapid selective Spectrophotometric determination

of molybdeaura( XV) which is based on the formation

of a yellow molybdenum - thiolactic acid complex at

pH 1 .0-1 .6 and measuring absorbance at 365 nm.

In view of the literature cited it seems that

mercury(II) complexes of 3-, and 3-mercaptopropanoic

acids need further investigation. Besides this, it is

worthwhile to study the complexes of group IIB metals

with ligands having sulphur or selenium donors like

selenoureas and thioureas.

Therefore, the following studies have been

undertaken in the present work:-

(i) The physico-chemical investigation of mercury( I I )

meroaptopxopanoic acid systems leading to

calculation of stability constants and other

related parameters.

(ii ) Preparation and elucidation of structures of

anionic complexes of mercury( II) with a mercapto-

propanoic acids.

(iii) Determination of degree of dissociation of

soluble complexes and solubilities of less

soluble complex species.

24

(It ) Use of mercaptooarboxylie aoids as masking

agents for group I IB metal ions.

(▼) Preparation sod elucidation of structures of

complexes of N»N*-disubstituted seleno-, and

thioureas with mercury( II) and zLno(Il).

The sulphur and selenium containing ligands

whose ccmplexatlon with various metal ions is being

reported here, are t

(l) 2-Mercaptopropanoie aoid or

thiolactio a d d (abbreviated as HgTLA)

(i i ) 5-Meroaptopropanoio acldi

thiohydracrylic acid (abbreviated as H^MPA)

CHjCH COOH

SH

HSCHgCHgGOOH

( i i i ) JI - S TH r»V> Mtrl iial

( iv) HtN*«Dlbensyl Selenourea!

(abbreviated as DBSU) OgHgCHg.NH. C.SH.CHgCgF^

Se

or;r*J W

(v) N,M -Dibenzyl thiourea*

(abbreviated as DBTU)

5 . STABILITY COHSTASTTS

Stability of a complex refers to the extent of

dissociation of a complex species in solution form or

it is a measure of the extent to which a complex species

will form, or will be transformed into another species

under certain conditions whoa the system has reached

to equilibrium. A complex molecule is considered to

be formed from the free ligand (L) and a metal

ion (M)s-

, M + L = ML j ML + L - MLg and

ML + La m MLn+j | when the concentration of

metal ions and free ligand la considered and

the logarithmic ratios of products to

reactants give the stepwise stability

constants,

1 0 gK, . log

1 o #j5>I« « lo g

2 m s

. . ( i . i )

. . . ( 1 .2 )

0 6H5 0112#HE *G ,HH # GH2° 6H5

S

2G

log Kn - log(1 .3)

K-i] M• • •

Summation of log Kj, log Kg - - - log KQ values give

the overall stability constant log of a complex

species which can be evaluated directly also -

M is a metal ion and L may be either a charged ion

stability constant.

The logarithmic values of overall stability

constants at various ionic strengths extrapolated to

zero ionic strength give thermodynamic stability

constants, which are relted to free energy change,

enthalpy change and entropy change by the equation:-

• • • (1 .4 )

, e.f • •

A g° a -RTlnyg a * A h° - I As0 . . . . . ( 1 . 5 )

where T * absolute temperature.

R “ gas constant (1.987 aal.deg:1 mole”1 )

P * stability constant at zero ionic strength.

A g ° = Standard free energy change.

A h0 * standard enthalpy change

Atf° = standard entropy change.

The determination of enthalpy change and other

thermodynamic parameters from the stability constants

are helpful for thorough understanding©f the factors

influencing the complex formation (59). A number of

methods can be used for determination of stability

constants viz.,

(i) Potentiometry (pH metric method)

(il) Measurement of B.M.I.

( i i i ) Spectrophotometry.

( iv) Polaro graph y.

In the prescent work potentiometric technique

of measuring xS.M.F. of mercury ( I I ) ions in presence

of large excess of ligand has been used for determining

stability constants. A potentiometer with mercury

and saturated calomel electrodes is used to measure

of the concentration cell which contained

mercuric(Il) ions and large excess of ligand. The 3.1-!.?,

in a concentration cell arises due to the cell

reaction*-

Hg / 11 g If Hg2^2^ ^ • • • ( I • 6)

ro

The J3.M.F. of the concentration cell is

related to free Hg(ll) ion concentration by the relation*

0 + 2.292 RT to h _2+ _IS.M.F. - ^ l0* 3 . G . .

. . . ( 1 .7 )

where 2°jI^ Hg2+ » standard electrode potential of

mercury at 25°C (0.854 volts).

n ,, * Standard electrode potential of saturatedC* • v/ • 2i +calomel electrode at 25°C ( 0.242 volts).

lig4" » Free mercuric ( I I ) ion concentration or

activity of mercurie(ll) ions.

K - Gas constant ( 8 .3 U J molt1 )

F = Faraday constant (96,500 coulombs)

n « Valency ( 2 in case of mercury(II))

At temperatures other than 25°G , the relation

(1 .7 ) is modified (60) as*

S.M.F. - B ^ Hg2++ log Hg2+ - e“ . c. b/°-00076

(t- 25). . .(1 .8 )

t m temperature °G .

n.i;

0.03057 at 35°C (61)

•— « 0.02958 at 25°C and

In presence of large excess of ligand

mercury(ll) ione are supposed to exist as the hi^aest

co-ordinated species IIgLn . The pH of the reaction

mixture is adjusted above the pKn (dissociation

constant) of the ligand so that all the ligand exist

in completely dissociated fom ( HnL ^ nll+ + Ln'"‘ ) .

The overall stability constant was evaluated

with the help of exparimantally determined concentration

2+of free Hg ions using the relation: -

logjS Q= log -HeLnl

[Hg2+][x ,]n. . . (1 .9 )

The free ligand concentration La under the experimental

conditions is approximately equal to total ligand

concentration.

6. SOLID MI3R0APT0CAHB0XTLATE COMPLEXES OF Hg( I I ) .

(i ) Preparation aid opposition:

Sodium bis( 3-mercaptopropionato)-mercurate

and potassium bisthiolacetatomercurate were crystallized

9 ft«J

with ethanol from a solution of mercuric oxide and

respective mercaptoacid. Their other metal derivatives

were prepared from the solutions of sodium

bis(3-mercaptopropionato)-mercurate( I I ) and potassium

bls-thiolaotato mercurate( II) and respective salt

solutions of various metals.

The complexes were analysed for the metal,

sulphur and mercury content and thus composition was

established.

(ii) Structurest The infrared spectra of metal -

bis(mercaptooarbosylat3)iiicrcurates were reoorded between

4-000 cm"” ̂ - 600 using potassium bromide on

Pye unicam IR Spectrophotometer. Magnetic moments of

some complexes were measured at room temperature using

G-ouy balance. Proton magnetic resonance spectrum of

sodium-bis( j5-mercaptopropionato)-mercurat e( II) complex

was recorded on M-390 , 90 MHz Yarian LfMR Spectrometer.

XR, aagaetic moments and M R data were used to assign

structures to metal complexes.

(iii) Solubility : Com pi exam etri c and conductors etric

technique was used to determine solubility of less

soluble complexes in their saturated solutions at

different temperatures.

31

( iv) Other Investigations: The apparent molecular

weight and degree of dissociation of potassium

bisthlolaotatomercurate( II) and sodium bis(3-mercapto-

propionato)-mercurate( I I ) was determined by cryoscopic

method (62). The ionic mobilities of the anions -

[n g( TLa) 2 and [k g (MPA)2 "J 2 ware determined by

conductometric method.

(v) Analytical Applications* Use of thiolactic

acid and 3-mercaptopropanoic acid as masking agent

for group IIB metal ions in the estimation of

mag»esiua( II) has been studied.

7. 3TUBIBS OH Jm '-DISUBSTITUTSD SELM0-,

A'ID THIOUHBA COMPLiSXKS OF ZIHC(ll) A20

MSK,UHY(II).

( i) Preparation and composition* Complexes of• t- diphenyl selenourea, 31,51 -dibenzylselenourea and

1U,U - di benzyl thiourea have been prepared and their

composition established on the basis of elemental analysis.

(ii ) Structure lelucldatlon* The infrared spectra of

the complexes have been used in assigning the structures

for the complexes.

The work presented in this thesis comprises of

seven ohapters.

First chapter deals with the review of literature

and introduce the topics of the thesis.

Second chapter incorporates the studies of Hg( II)-

TLA and Hg( I I )—MPA systems leading to determination of

stabilities of Hg( I I ) complexes and evaluation of

relat ed thermodynamic parameters.

Third chapter includes the preparation of metal-

bis(mercaptocarboxylato)-mercuratee and chloro-

oomplexes of Hg( II) with 2-, and 5- mereaptopropanoic

acids, date m l nation of composition and structure of

these complexes*

Fourth chapter includes determination of degree

of dissociation and ionic mobilities and protonation

constants of alkali metal-bisthiolactato-mercurate and

bis( 5-meroaptopropionato)-mercrurate and solubilities

of other less soluble metal derivatives.

Fifth chapt er deals with analytical applications

of 2—, and >»mercapto propanoic acids.

Sixth ohapter incorporates preparation of Hg( II)

and Zn( II) complexes of BPSU, DBSU and DBTU, determination

of their composition and structure.

Seventh ohapter gives a summary of entire work.

3 ro

33

HBFERSTOSS

1 • Arhlsnd, s« i Chstt» J • • • •and Davles,N.

2* Pearson, R.G. , , ,

3. Jorgensen, C.E. . . .

4. Kloppman,G., . . .

5. Fernando,Q., and . . .Freiser,H.

6. Leus3lng,D.L. . . .

7. Leuasing,D.L. • • .Laramy,R. E ., and All>erts,G.3.

8 . Bear,J.L.,Chopin,G.R. . . . and QuagLiaao,J.V.

9 . Mishra,M.B.,NIgam, . . .H.L.

10. Srivastava,S.K., . . .Srivastava, P.C.and MIgam,H.L.

11. Saxena,R* S. and . . .Gupta,K.C.

Quart. Rev. (London), 12, 265(1958).

J.Am.Chera.Soc., 85, 3533 (1963).

Struct.Bond.3,106 (1967).

J.jys• Che®. Soc., 90,223(1968).

J.Am.Cham.Soc. 80, 4928-4931 (1958).

J.Aa.Chea.Soc. 80, 4180 (1958).

J.Am.Chem.Soc. 82, 4826 (I960).

J.Inorg.Hucl.Chea. 25* 513-18 (1963).

Acta Chim. (Budapest) 57(1), 1-4 (1968).

Indian J.Chon. 10(2), 223-4 (1972).

J.Inorg*Hucl.Chem. 30, 3368-3373 (19 68).

12. 3axena,R.S.,Gupta, . . . K.C. and Mittal,M.L.

Indian J.Chem., 7, 374 (1969).

1 3* b&X6Q&| S« | 8AdGupta*£. C •

14. Saxena,R.S., and Gupta,K.C.

15. Reddy,M.V., andBhattacharya, P.K.

16. Panchal,B.R., and Bhatt acharya,P.K.

17. Panchal,B.r . and Bhattacharya, P.K.

18. Joshl, <7. D», sQd Bhattacharya#P .K.

19. Jejurkar, C .R ., and Bhatt acharya, P.L.

20. HojO|Tt 1 Suglura, T . , . . .and Tanaka,H.

21. Ho j of X. ,*uglura,Y. , and Tanaka,H.

22. De Brabaader, H.Pj Geominne, A.M., and Van Pouke, L.G.

23. De Brabander,H«F., Creyft, H .S .,Qeomioae,A.M. , and VanPouke,L.C.

24. Sarin, R», and Munehi,K.I.

J.Ind.Chea.Soc. 46(3), 258 (1969).

J.Ind.Cham.Soc., 46(11), 1045 (1969).

Indian J.Chem. 7, 282(1969).

Acta Chim. (Budapest) 14(4), 399-403 (1972).

J .Inorg.Hucl.Chem.34(1 2), 3932-5 (1972).

J.Ind.Chem.Soc. 50(5), 344-6 (19 73).

Ind. J.Chem., 11(9), 946-7 (1973).

J.Inorg.ffucl.Chem. 38 ( 3), 641-4(19 7 6).

J . Inorg.Hucl. Chem. 39(10), 1859-63 (1977)

J. Inorg.Hucl. Chem. 37, 799-803 (1975).

Talanta, 23(5)* 405-7 (1976).

J • Inorg.Hucl. Chem. 35 » 201 (1973).

35

25 . Aabulkar, a. 3 ., and Munahi,K.N.

• Indian J • Chsut • 14A| 424-27 (1976).

26. Aguilar, M .vAlegret,S., and Casassaa,E.

. . . J . Inorg.ITucl • Chem.39(4), 733-37 (1977)

27. Shindo,Hj and Drown,2 .L.

• • J.Am.Chem.Soc. 87(9),1904-9 (1965).

28. Mishra,M.B., Hi gam,H .L . and Mehra,A.

J.Inorg. Nuol* Chem. 30(3), 881-3 (1968).

29. Mukand,B., Mishra, M .B ., and

l, H .L.

Indian J.Chaa. 9, 601(1971).

30. 8rivastava,S.K. and Nigam,H.L.

. . . Curr. Sci., 41 (16), 601-3 (1972).

31 . Srivastava,S.K., Panc.eya,K.B,, and Nigam,H.L.

■52 Sriv^stava#S .K .,* Penally*, K .B .,and

Hi gam,H .L .

33. Chatterjee ,S ., Sukhani, D. ,(lupt a,V .D . , and Mehrotra, H.C.

34. Hori,K.

. . . Indian J.Chem. 13(3), 498-500 (1975).

. . . J.Inorg. Chem.Lett. 11(3), 195-9 (1975)

. . . Indian J. Chem. 3 (4 ), 362-3 (1970).

. . . Bull. Chem. do c. , J ap. , 48(7), 2209-10 (1975).

35. Coleman,tf.M., III Guard,H.E., and Cobet, A.B.

. . . Inorg.Chto.Acta., 57(2), 223-6 (1982).

36

36. Poddar, S .H ., and Ray,B.P.

37. Purlani,C. and Tarantelli,T.

38. Tarantelli.T., and FurlanlfC.

39. Proskina,U.H., Chulbakya, S.M., Volodina, G .F ., and Ablov,A.V.

40. Goddard, D .ii.,Lodaaa, B. D ., A j ayi, S.0 . , and Campell, M.J.

41. Goddard, D .R ., and Ajayi, S.O.

42. Doaiano,P., . . . Hanfredoti, A .G ., 0ros3oni,G.,u ardelli ,M. and Tani, M.E.V.

43. I-larov, I.II., Belyaeva, . . . V .X ., Durbrov, Tu.!J.,and Emakov, A.N.

44. Ablov, A.V.,Proskina, . . . H.N.,and Simonov,Yu, A.

45. Tarantelli, 'J.

46. Tarantelll,T. and Cbiari,B.

J.Ind.Chem.Soc., 29, 279 (195 2).

Inorg. iTucl. Chem. Lett. 2, 391 (1966).

J.Chem.Soc., A. 1717(1968).

Zh. Struct. Khim. 9, 1095 (1968).

J.Chem.Soc., a*• 506(1969).

ibid, 2673 (1971 ).

Acta Cryst., 25B, 591 (1969).

Zh. IT eorg. .. hint. 1 6; 1 54 (1971).

Zh. leorf'. Khim. 19(1), 95-8 (1974).

J.Chem.Soc. (Dalton trans), 837 (1974).

J . Inorg. tfucl. Chem. 39(1), 33-6 (1977).

3?

47. Aittken,G.B.

48. Singh,P.P. and Gupta,A. K.

49. Itivaro,L.U.

50. Kubioki.M.M., Glowiak, T. 2.

51 • Bus carons, F ., and Casassas,E.

52. Buscarons, F ., and Casassas,2.

53. Busev,A*I*,H acu, A.

54. Busev, A. I. ,ilacu, A ., and Budzit,G.P.

55. Hara, S.

56. Pribil,i%., and Vesely,V.

57. Macu,Al., and Mocanu,R.

58. Fritz, J .S .and Beuxman,D.R.

59. Rossotti,F.J.G., Lewis,J. and

Wilkins,R.G,

. . . Inorg. Synth. 16, 83-7(1976).

. . . Indian J.Chem. H a , 688-91 (1976).

Phillip. Sci. 14,77-85(1977).

. . . Matter Sci. 3(1-2), 35-8 (1977).

. . . Anales real Soc, espan. fis.y . quia (Madrid) 55B, 655-662 (i960).

ibid. 55B, 663-8(1960).

. . . Zh. Anall t. Chia. 18(10),1 233-8 (1963).

. . . ibid 19(3), 337-45 (1964).

. . . Bunseki Kagaku 14(1), 42-5 (1965).

Talanta, 12(5), 475-8 (1965).

. . . An. Stint. Univ.”A l.I. Cuza" Iasi,Sect IC, 1 3(1), 4U (1967 ).

. . . Talanta, 19(3), 366-9(1972).

. . . "Modern co-ordinationchemistry”, Interscience publishers, Inc. JTew York, (1960).

33

60. 3tricks, W. , . . . J. Am. Chem. So c. ,76,Kolthoff,I.M. 1515 (1954).and. Heyndrickx,A*

61. Findlay,A* . . . "Practical PhysicalChemistry, ’’Longman. Sdn.9.p. 289 (1973;

62. Vogel,A.I. . . . "A Text Book ofQuantitative Inorganic Analysis" KLBS Edn. p .959 (1961 ).