SUMMARY

The coordination chemistry comprises a large body of inorganic chemistry. It is

mainly the chemistry of metal complexes and has fascinated and inspired the chemists all

over the world. The modern theory of coordination chemistry which is one of the most

rapidly growing branch of inorganic chemistry has proved very efficient in the study of

structural backbone, biological and pharmacological aspects of modern chemistry and has

been found to play crucial role in chemical evolution. Further interest in this field, has shown

because of the complex compounds formation and their biochemical aspects. Coordination

complexes thus formed has stimulated the interest as well as generated the curiosity in their

studies with various angles. Academic and industrial researches in coordination chemistry are

flourishing and their outputs are growing exponentially that is why it has experienced an

impressive renaissance. Two approaches for the synthesis of new molecules currently are first

to synthesize molecule hitherto unknown in the literature and secondly to study out their

biological importance. A considerable amount of work has been done previously and reported

for large number of simple and complex molecules having organic ligands with nitrogen,

oxygen and sulphur as effective donor sites and their analytical aspects have been worked

out.

The present thesis entitled “Synthesis and Characterization of Some Platinum

Metal Complexes with Multidentate Ligands [Ru(III), Rh(III) and Ir(III)]” work describes

the complexing ability of Schiff bases derived from isatin, sulpha drugs, dithiooxamide,

isonicotinoyl hydrazide and substituted mercaptotriazoles with some platinum group metals

like ruthenium(III), rhodium(III) and iridium(III). For this purpose ruthenium(III),

rhodium(III) and iridium(III) complexes with series of ligands were synthesized and

characterized well with elemental analysis, spectral analyses (IR, UV-VIS, 1H NMR, FAB

mass), magnetic measurements and thermal investigations to explore the possibility of

structure elucidations. The work comprised in the thesis has divided into eight chapters, the

salient features of which are summarized below:

CHAPTER 1

This chapter deals with introduction of the coordination chemistry and chemistry of

ruthenium(III), rhodium(III) and iridium(III) along with their biological and other

applications utmost importance.

CHAPTER 2

This chapter entitled “Review of Literature” covers the relevant and an up to date

historical review of the ruthenium(III), rhodium(III) and iridium(III) complexes of nitrogen,

oxygen, sulphur, mixed nitrogen-oxygen, mixed nitrogen-sulphur donor ligands and

macrocyclic ligands containing nitrogen, oxygen and sulphur donor atoms.

The syntheses of these complexes along with the various physicochemical techniques

used for the elucidation of their structures and also some of their biological importance have

been described here. This chapter has been concluded with the justification for undertaking

the present study.

CHAPTER 3

This chapter describes the quality and source of various materials used

throughout this investigation. The details of preparation of the various ligands used for the

syntheses of ruthenium(III), rhodium(III) and iridium(III) complexes have also been

mentioned. There have been several crucial experiments carried out ingeniously with respect

to earlier investigations; it is proposed to carry out systematic reactions of some platinum

metal complexes with the following ligands for present study-

Schiff bases derived from isatin and various sulpha drugs

Schiff bases derived from sulpha drugs and various aldehydes

Schiff bases derived from substituted isatin and dithiooxamide

Schiff bases derived from isonicotinoyl hydrazide and various aldehydes/ ketones

Schiff bases derived from substituted mercaptotriazoles and pyridine-2-

carboxaldehyde/ thiophene-2-carboxaldehyde

A brief outline of various physicochemical methods such as elemental analyses,

melting point determinations and physical measurements including spectral analyses,

magnetic studies and thermal studies are also described.

CHAPTER 4 Ruthenium(III) complexes with Schiff bases derived from isatin and

various sulpha drugs

A systematic study of reactions of the ruthenium(III) chloride with Schiff bases (LH)

derived from isatin and various sulpha drugs (molar ratio 1:2) in ethanol may be represented

by the following equation.

RuCl3 + 2LH → [Ru(L)2(H2O)2]Cl + 2HCl

Where; LH = IShAH, IShMH, IShGH, IShDH, IShAcH and IShPH

All the complexes are coloured and powdered form and soluble in THF, DMF and

DMSO. The Schiff bases were expected to behave as a bidentate with oxygen and nitrogen as

donor atoms or coordination sites. All the ruthenium(III) complexes being d5 (low spin), S =

1/2 behave as paramagnetic. The molar conductance of the complexes in DMF indicates the

1:1 electrolytic behaviour.

Magnetic moments are often used in conjunction with electronic spectra to

gain information about the oxidation number and stereochemistry of the central metal ion in

coordination complexes. At the room temperature the magnetic moment of the ruthenium

complexes lie between 1.80-2.10 B.M. That is very close to the spin only value, suggesting

the octahedral geometry around ruthenium ion. The values thus obtained correspond to the

presence of one unpaired d electron leading to +3 oxidation state for ruthenium.

The electronic spectrum of the low spin ruthenium(III) complexes recorded in

DMSO displays three spin allowed transitions. The low spin ruthenium(III) is a d5 system

with ground state 2T2g and first excited doublet levels in the order of increasing energy are

2A2g and 2A1g, which arises from t2g4 eg1 configuration. These bands are characteristic of

an octahedral geometry. Spectra of all ruthenium(III) complexes displayed bands at 13908-

15356 cm-1 and 17241-20202 cm-1 assigned to 2T2g →4T1g and 2T2g→4T2g. The two lowest

energy absorptions corresponding to 2T2g→4T1g and 2T2g→4T2g were frequently observed as

shoulder to charge transfer bands. The bands in the region 26525-31250 cm -1 has been

assigned to 2T2g→2A2g transition in ruthenium complexes.

The infrared Spectra of the Schiff base ligands were compared with that of metal

complexes to obtain the information about the binding mode of ligands in the complexes. The

ligands can act either in keto or in enolic form, depending upon the conditions (e.g. pH of the

medium, oxidation state of the metal ion). This fact was further supported by the bands

including azomethine nitrogen ν(C=N) at 1615–1694 cm-1 in ligands and the lowering of this

band by 20-35 cm-1 in complexes results in chelation of the nitrogen to metal ion. In the

spectra of the ligands the presence of bands at 3040-3200 cm-1 and 1672-1680 cm-1 assigned

to ν(N-H) and ν(C=O) vibrations of isatin moiety respectively. These bands disappear in

ruthenium(III) complexes, which may be due to enolization of keto group. The spectra of

free Schiff bases show a medium band at ca. 3140 cm-1 due to ν(N-H), which persists almost

at the same position in the complexes indicating the non-involvement of this group in bond

formation. The band at ca. 1370 and ca. 1150 cm-1 are assigned to νasym(SO2) and νsym(SO2),

respectively. Further no shift in the absorption bands of SO2 has been observed thereby

indicating the nonparticipation of sulphonamide oxygen in the bonding. The band in the

range 1615-1694 and 1480-1500 cm-1 in the spectra of ligands may be assigned to ν(C=N)

and ν(C=C) (phenyl) vibrations, respectively. The coordination modes are further confirmed

by the presence of bands in the range 450-490 cm-1 and 440-460 cm-1 in complexes spectra

assigned to ν(Ru-N) and ν(Ru-O) vibrations, respectively. In addition, all complexes show

broad band at 3400 cm-1 due to ν(OH) of coordinated water molecules. The Schiff base

ligands behave as monobasic bidentate ligands coordinating through one azomethine nitrogen

and one enolic oxygen through deprotonation.

The proton magnetic resonance spectra of the ligands were recorded in

deuterated dimethylsulphoxide. The ligand has protons in different chemical environments.

The spectra of ligands show the expected signals due –NH, aromatic protons and –CH3. The

following conclusions can be derived by spectra of the ligands. The signals of ligands

observed for N-H protons appeared at δ8.06-8.69 ppm. The chemical shift of certain aromatic

protons appeared as broad multiplets in the range of δ6.96-7.85 ppm, but in ligands which is

highly diagnostic for their environment. In IShMH and IShDH the methyl protons appear as

singlet in the region δ1.86-2.24 ppm.

The mass spectra of the ligands and complexes are compared. Their fragmentation

revealed the exact composition of the compounds formed. Mass spectra of the ligands namely

IShAH, IShMH, IShGH, IShDH, IShAcH and IShPH show molecular peak at m/z = 301,

393, 343, 379, 343 and 378 which corresponds to their molecular weight. The molecular ion

peaks for the complexes of ruthenium(III) are observed at m/z = 773, 957, 857, 929, 857 and

927 they are in good agreement with their molecular weights.

Thermal studies of the Schiff base complexes were carried out in order to get (i)

information about thermal stability of new complexes, (ii) to decide whether the water

molecule is inside or outside of the coordination sphere of central metal ion and (iii) to

propose a general scheme for thermal decomposition of these chelates. The numbers of

chelates rings as well as the type of chelates rings around the metal ion play an important role

in thermal stability and decomposition of the complexes. Thermogravimetry data reveals that

the ruthenium(III) complexes decompose in two steps. The presence of water molecules

suggested from infrared spectra is confirmed by TG and DTG data. Although decomposed

weight loss, the complete decomposition of the ligand occurred at ~620˚C in all the

complexes. At the end of the final step, i.e., 680-720˚C, stable metallic oxides Ru2O3 were

formed. On the basis of spectral studies the following structures are suggested for the

complexes.

Proposed structure of complex

CHAPTER 5 Ruthenium(III) complexes with Schiff bases derived from sulpha drugs

and various aldehydes

The ruthenium(III) chloride with Schiff base ligands were synthesized in

combination of hydroxyl aromatic aldehydes and sulpha drugs (sulphanilamide or

sulphamerazine) in 1:1 molar ratio in ethanol. The complexes of type [Ru(L)2(H2O)Cl] are

obtained according to the following reaction.

RuCl3·3H2O + 2LH → [Ru(L)2(H2O)Cl] + 2HCl

LH = oVSaH, oVSmrzH, SdSaH, SdSmrzH, 2hNSaH, 2hNSmrzH

All the complexes are found to be stable in air and non-hygroscopic microcrystalline

salts. Complexes exhibit good solubility in DMF, DMSO, THF and poor solubility in diethyl

ether, acetone and water. Complexes are sparingly soluble in methanol and ethanol. The very

low conductance values in DMF (10-3M) solution indicate the non-electrolytic nature of the

complexes.

Magnetic susceptibility measurements of the complexes were performed at room

temperature lie in the range 1.82- 1.96 B.M., which expected to be lower than the predicted

value of 2.10 B. M. The spin-only values were calculated using the equations µRu = 2[SRu(SRu

+ 1)]1/2 for complexes are markedly equal to/ or higher than spin-only value for one unpaired

electron for low spin t2g5 ruthenium(III) in an octahedral environment.

The electronic spectra of low spin ruthenium(III) is a d5 system with ground

state 2T2g and first excited doublet levels in the order of increasing energy are 2A2g and 2T1g,

which is arises from t42geg1 configuration. In most of UV-spectra of ruthenium(III) complexes

only charge transfer bands occur. These bands are characteristic of an octahedral geometry.

Spectra of all ruthenium(III) complexes displayed bands at 13550-14100 and 17240-18230 cm-1

assigned to 2T2g→4T1g and 2T2g→4T2g. The bands in the region 23660-23860 cm-1 has been

assigned to 2T2g→2A2g transition in ruthenium complexes.

The infrared spectra of the Schiff base ligands display a strong and sharp band in the

region 1615-1635 cm-1 which is due to ν(C=N) azomethine band. This band shifts to lower

frequency by 10-25 cm-1 in the spectra after complexation, indicating the coordination of

azomethine nitrogen to metal ion. In the spectra of ligands, exhibit two broad peaks in the

region 3040-3400 cm-1 due to the hydrogen bonded OH and NH. In the spectra of complexes,

the band due to OH gets shifted to the higher wave number region showing the coordination of

the ligand through the phenolic oxygen after deprotonation. However, the νΝH band remains

approximately at the same position, which clearly indicates the non involvement of NH in

complexation. This is further substantiated by the appearance of ν(C-O) phenolic at lower

frequencies (compared to 1355-1370 cm-1 in the ligands) in the range 1340-1350 cm-1, after

complexation. The coordination of azomethine nitrogen and phenolic oxygen is further

supported by the appearance of bands at 480-500, 440-460 cm-1 and 355-380 cm-1 due to ν(Ru-

N), ν(Ru-O) and ν(Ru-Cl), respectively in all complexes. A broad band in the region 3400-3295

cm-1 is arising from overlap of stretching vibrations of coordinated water molecule with ν(N-H)

of ligands are observed in almost all of the complexes. Schiff base ligands are uninegatively

bidentate, coordinating through phenolic O and azomethine N.

The proton magnetic resonance spectrum of Schiff bases ligands were recorded in

CDCl3 solution using tetramethylsilane (TMS) as internal standard. The signals due to

phenolic-OH protons of the ligands appear at δ12.86-12.94 ppm. The signals at δ8.09-8.64 ppm

appear due to azomethine protons (-CH=N). The ligands show a complex multiplet in the

region δ6.84-7.86 ppm for the aromatic protons. In addition, signals appear in the ligands due

to various groups e.g. at δ10.22-10.52 ppm due to NH protons and at δ3.22- 3.34 due to protons

of methoxy group.

The mass spectra of the ligands and complexes are compared. Their fragmentation

revealed the exact composition of the compounds formed. Mass spectra of the ligands namely

oVSaH, oVSmrzH, SdSaH, SdSmrzH, 2hNSaH and 2hNSmrzH show molecular peak at m/z

= 306, 398, 276, 368, 326 and 418 which corresponds to their molecular weight. The

molecular ion peaks for the complexes of ruthenium(III) are observed at m/z = 768, 952,

708, 892, 808 and 988 they are in good agreement with their molecular weights. Therefore

above fragmentation pattern complemented the exact composition of the various compounds

and described the stoichiometry in which complexes has been formed.

The aim of the thermal study was to obtain the information concerning presence of one

water molecule and chloride ion in the coordination sphere of the complexes suggested from

infrared spectra was confirmed by TG and DTG data. Ruthenium(III) complexes lose their

weight and become stable in the temperature range 150-260˚C corresponding to one water

molecule and from 280-330˚C a mass loss is attributed to the loss of chloride ion. Although

decomposed fragments of the ligand could not be approximated owing to continuous weight

loss, the complete decomposition of the ligand occurred at ~630˚C in all the complexes. The

final decomposition favours a mixed residue of Ru2O3- RuO2 at 680-695˚C.

On the basis of the above spectral studies the following structures are suggested.

Where,

R” = H;

Proposed structure of metal complexes

CHAPTER 6 Ruthenium(III) and rhodium(III) complexes with Schiff mannich bases

derived from substituted isatin and dithiooxamide

In this chapter focus our interest on the compounds has been achieved by the

reaction of Schiff mannich bases precursor of isatin followed by condensation with

dithiooxamide. All the ruthenium(III) and rhodium(III) complexes are brown to blackish

brown in color. They are soluble in ethanol, tetrahydrofuran, dimethylformamide and

dimethylsulphoxide while insoluble in water. The molar conductance values of the complexes

were measured in DMF (10-3M) solutions showing the 1:1 electrolytic nature.

RuCl3∙3H2O + 2LH → [Ru(LH)2Cl2]Cl

RhCl3∙3H2O + 2LH → [Rh(LH)2Cl2]Cl

Where, LH = MrdtoII, DpdtoII, NMydtoII, NAydtoI, NBydtoI

The Ruthenium(III) complexes were found lie in the range 1.80-2.02 B.M., which are

expected to be lower than the predicted value of 2.10 B.M. They are near spin only value

suggesting t2g5 (low spin, d5, S = 1/2) configuration with one unpaired electron. The

complexes of rhodium(III) are diamagnetic (low spin, d6, S = 0) as expected. This is

consistent with an octahedral arrangement of nitrogen and sulphur atoms producing a strong

field.

Ruthenium(III) complexes act as paramagmetic one and rhodium(III) complexes are

diamagnetic. The electronic spectra of all ruthenium(III) complexes show three d-d bands,

corresponding to transitions 2T2g → 4T1g, 2T2g →

4T2g, 2T2g → 2A2g, 2T1g display bands at 13510-

14000, 17240-18300 and 23460-23800 cm-1. The electronic spectra of the rhodium(III)

complexes exhibited bands at 17060-17640, 20220-20890 and 27300-28590 cm -1 in the

spectrum. The ground state in rhodium(III) complexes in an octahedral field is 1A1g. Thus, the

possible transitions in the rhodium(III) complexes are 1A1g → 3T1g,

1A1g → 1T1g and l A1g →

1T2g

of d-d origin. The general pattern of the spectra indicates octahedral geometry around the

metal ions.

The infrared spectra of the ligands exhibit display two sharp bands in the region 3210-

3260 cm-1 and 3320-3430 cm-1 assignable to νsym and νasym vibrations of the NH2 group,

respectively. The IR spectra showed that the ligands exhibited vibrational modes of νC=N of

azomethine group, (νC–N, νNH), (νC–N, νC–S), νC–S, and νC=S of dithiooxamide moiety.

The position of the bands assigned to νNH vibrations of the cyclic rings was dependent on

their environment, νNH of ligands were observed at lower frequencies compared with that of

ligands. The complexes showed additional shifts in νNH to lower frequencies while no

significant changes were observed on vibration modes of C=O group which rules out

coordination with carbonyl oxygen. Shifts of thioamide bands were observed in the spectra of

complexes and were attributed to coordination of metal ion with sulphur atom. The

appearance of medium intensity bands at ca. 530, 435 and 312 cm -1 region assignable to νM-

N, νM-S and νM-Cl vibrations, respectively. The appearance of the non-ligand bands further

support the bonding of the ligands to the metals through the nitrogen, sulphur and chloride.

The proton magnetic resonance spectra of ligands and their corresponding

rhodium(III) complexes have been recorded in DMSO-d6. The -NH2 group gives a sharp

singlet at δ2.48-2.60 ppm in the free ligands. The signal due to NH protons appeared in the

lower field at δ9.84-10.62 ppm as singlet. The multiplets in the range of δ6.40-7.82 ppm

assigned to aromatic protons have been observed in ligands as well as in complexes

The following structure may be tentatively proposed for ruthenium(III) and

rhodium(III) complexes:

Where,

M = Ru(III), Rh(III)

R = , , H, ,

Proposed structure of complexes

CHAPTER 7 Ruthenium(III) and iridium(III) complexes with hydrazones derived

from isonicotinoyl hydrazide and various aldehydes/ ketones

In this chapter we reported the synthesis of heterocyclic hydrazones viz. 2-

hydroxybenzaldehyde isonicotinoylhydrazone (HBINH), o-vanilllin isonicotinoylhydrazone

(o-VINH), 2-hydroxyacetophenone isonicotinoylhydrazone (2-HAINH), 5-

chlorosalicylaldehyde isonicotinoylhydrazone (5-CSINH) and its ruthenium(III) and

iridium(III) complexes. The metal complexes formed between metal trichloride and

hydrazones have stoichiometry [Ru(L)(H2O)Cl]2 and [Ir(L)(H2O)Cl]2. The metal complexes

are condensation reaction in 1:1 ratio reactions are as follows:

2MCl3∙3H2O + 2LH2 → [M(L)(H2O)Cl]2 + 4HCl

Where,

M = Ru(III), Ir(III); LH2 = HBINH, o-VINH, 2-HAINH, 5-CSINH

All the complexes exhibit good solubility in DMF, DMSO, THF and poor solubility

in water. These complexes were sparingly soluble in methanol and ethanol. All complexes of

isonicotinoyl hydrazones were obtained in good yield and are stable in solid and liquid phase.

Electrical conductances in DMF solution were indicated non-electrolytic nature of the

complexes.

The spin-only values were calculated using equation µRu-Ru = 2[µRu2 + µRu

2)]1/2 and it lie

in the range 0.72-1.02 B.M. range. These low values might be indicative of metal-metal

interactions in the dimeric structure. The effective magnetic moment of complexes agreed

well with that predicted for a low-spin d5 configuration. This possibility mainly arisen due to

the metal-metal interaction between ruthenium ions suggested dinuclear configuration.

Iridium(III) complexes shows zero magnetic moment at room temperature and suggested

diamagnetic structure with d6 paired electron (low spin, d6; S = 0 ) as expected this with an

octahedral arrangement of donor atoms producing strong field.

The electronic spectra of all ruthenium(III) complexes were recorded in DMF

solution. All the ruthenium(III) complexes are paramagnetic indicating the central metal atom

in its +3 oxidation state. Dimeric complexes showed three bands in the region of 13900-

31260 cm-1. Ligand → metal charge transfers exhibit high intensity bands and are observed at

13908-15350 cm-1. Such high intensity bands generally obscure the weak d-d transitions of

the metal centers. Other bands observed in ruthenium(III) complexes are in range 17260-

20120 cm-1 and 26520-3120 cm-1 assigned to 2T2g → 4T2g and 2T2g → 4A2g transitions in

increasing order of energy. Complexes have shown the nearest coordination sphere with

microsymmetry octahedral. Since ruthenium(III) is a d5 system it has relatively high oxidizing

properties, the charge transfer bands of the Lπy → t2g type are prominent in the lower energy

region and it obscure the weaker bands due to d-d transition. The data concerning

interpretation of the absorption spectra of ruthenium(III) coordination compounds revealed

low spin states in all the complexes. Three charge transfer bands in close proximity with data

also proposed that central ion configuration d5 causes low spin states. Electronic spectra of all

iridium(III) complexes exhibited bands at 18620-20490 cm-1, 29410-32154 cm-1 and 39840-

41600 cm-1 corresponding to 1A1g → 3T1g, 1A1g →

1T1g, and 1A1g → 1T2g transitions in increasing

order of energy.

The infrared spectra of the ligands and its binuclear ruthenium(III) and iridium(III)

complexes have been studied carefully. The presence of medium to weak intensity broad

band centered at 3430 cm-1 in the ligand corresponds to phenolic ν(OH). In the spectra of the

complexes, ν(OH) remain absent while it is difficult to trace the disappearance of ν(OH)

because the range of ν(OH) group occurred at the same zone where ν(N-H) is located. This

indicates the deprotonation of the hydroxyl group and its coordination with metal ion and

confirmed out the mononegative behaviour of ligands. The broadening of ν(OH) vibrations

may be due to the overlapping with absorption due to coordinated water. The band in

binuclear complexes shift to lower frequency due to azomethine ν(C=N) by 20-45 cm -1

suggest bonding through azomethine nitrogen. Coordination of the nitrogen to the metal atom

would be expected to reduce the electron density in the azomethine links and this cause a

shift in the ν(C=N) band. ν(N-N) band in complexes exhibits the small shift to higher

frequency at ca. 1050 cm-1 and further indicated participation of azomethine nitrogen in

coordination. In support of this further structure was confirmed by the coordination of the

ligands to metal atom by appearance of the ν(M-N), ν(M-O) and ν(M-Cl) at range 480-520,

430-445 and 350-380 cm-1 , respectively as additional evidence. In the ligands bands at 1460-

1500 cm-1 due to the pyridine ring nitrogen remain unchanged on complexation, indicating

non involvement of the ring nitrogen in complex formation. The overall infrared spectral

studies suggested that the ligands are tridentate coordinating through amide oxygen,

azomethine nitrogen and phenolic oxygen forming a five membered chelate ring.

The proton magnetic resonance spectra of the ligands and their iridium(III) complexes

were recorded in a DMSO-d6 solution. 1H NMR spectrum of the ligand shows signal due to

OH at ca. δ12.26 ppm. This disappears in the spectra of iridium complexes indicating

deprotonation and phenolic oxygen is involved in complexation. A singlet at ca. δ10.50 ppm

in the free ligand due to NH disappears in the complexes and a signal at ca. δ8.68 ppm

observed in the spectrum of the free ligand had shifted to ca. δ8.82 ppm indicating

coordination through azomethine nitrogen. This downward shift may be due to the reduction

of electron density at the azomethine C-H. The methoxy protons of the ligand and complexes

appear at ca. δ3.80-3.92 ppm. The aromatic protons appear as multiplets at ca. δ7.18-7.86

ppm (isonicotinic 4H). A sharp singlet at δ2.34-2.51 ppm due to the methyl protons attached

to azomethine of the ligands undergoes a downfield shift due to the coordination of the

azomethine nitrogen.

Dynamic TG data with the percent weight loss at different steps and their probable

assignments are observed here. The reaction of the ligands HBINH, o-VINH, 2-HAINH and

5-CSINH with ruthenium(III) and iridium(III) afforded complexes [Ru(HBINH)(H2O)Cl]2,

[Ru(o-VINH)(H2O)Cl]2, [Ru(2-HAINH)(H2O)Cl]2, [Ru(5-CSINH)(H2O)Cl]2 and [Ir(HBINH)

(H2O)Cl]2, [Ir(o-VINH)(H2O)Cl]2, [Ir(2-HAINH)(H2O)Cl]2, [Ir(5-CSINH)(H2O)Cl]2

respectively. The TG studies were done for the complexes where the complexes show a

weight loss of 3.5-3.8% in the temperature range 170-230˚C attributed to two water

molecules. A weight loss of 7.5-7.8% shown by the complexes in the temperature range 270-

340˚C was attributed to elimination of two Cl-. On increasing temperature the decomposition

continues with gradual mass loss and stops at 620-670˚C with the formation of Ru2O3 and

Ir2O3.

The following structure has been proposed for the ruthenium(III) and iridium(III)

complexes.

M = Ru(III), Ir(III)

The proposed structure of complex

CHAPTER 8 Ruthenium(III) complexes with Schiff bases derived from substituted

mercaptotriazoles and pyridine-2-carboxaldehyde/ thiophene-2-

carboxaldehyde

The reactions of ruthenium(III) chloride with monobasic Schiff bases (L1H and L2H)

derived from substituted mercaptotriazoles with thiophene-2-carboxaldehyde or pyridine-2-

carboxaldehyde in molar ratio 1:2 respectively. The ligands formed by condensation of

substituted various acids i.e. 4-methoxybenzoic acid, salicylic acid, 2-chlorobenzoic acid;

forming substituted mercaptotriazoles with thiophene-2-carboxaldehyde or pyridine-2-

carboxaldehyde in ethanolic medium. They exhibited the complexes of the type

[Ru(L1)2(H2O)2]Cl and [Ru(L2)2]Cl. The reaction can be represented by the following

equations:

RuCl3∙3H2O + 2L1H [Ru(L1)2(H2O)2]Cl + 2HCl

L1H = ATMTH; STMTH; CTMTH

RuCl3∙3H2O + 2L2H [Ru(L2)2]Cl + 2HCl

L2H = APMTH; SPMTH; CPMTH

Complexes are non hygroscopic microcrystalline salts were coloured having a

template methods which exhibit cyclization through ligands. As mercaptotriazoles are

potentially active exhibit tautomeric systems. The coloured microcrystalline powders, quite

stable in air and are soluble in dimethylformamide (DMF), tetrahydrofuran (THF),

dimethylsulphoxide (DMSO), but found insoluble in ethanol, methanol, ether, acetone, CHCl3

and water. The molar conductivities of complexes in DMF (10-3 M) solution exhibited 1:1

electrolytic nature.

Magnetic moment measurements provide information regarding the structure of the

complexes. The room temperature magnetic moments showed that the complexes are one

electron paramagnetic, in the range 1.69-1.82 B.M; lower than the predicted normal values

(2.10 B. M.) Corresponding to +3 oxidation state of ruthenium, suggesting a low spin 4d 5 , S =

1/2 around octahedral ruthenium(III) with t2g5 configuration.

The electronic absorption spectra of ruthenium(III) complexes have been recorded in

dimethylsulphoxide and the bands obtained and their corresponding assignments. The

ruthenium(III) complexes showed bands which are observed lie in visible region in the range of

13500-13890 cm-1, 17440-18223 cm-1 and 23200-23800 cm-1 assigned as 2T2g → 4T1g (ν1), 2T2g →

4T2g (ν2) and 2T2g → 2A2g, 2T1g (ν3). The strong field electrostatic matrices of Tanabe and Sugano

predict eight transitions from the (t2g5, eg

0) ground state to the (t2g4eg

1) doublet state configuration

and two transitions from the ground state to the t2g4eg

1 quartet states. These d-d transition may

be expected from the 2T2g ground state and occur in increasing order of energy. However many

low energy charge transfer bands of L (π) → metal (t2g) types are also possible.

In the spectra of the free ligands the presence of bands at 3060-3210 cm-1 and 2440-

2560 cm-1 due to ν(N-H) and ν(S-H) respectively, clearly give an evidence of establishment of

this type of thione thiol tautomeric system. In the spectra of complexes, however, all the

thioamide bands disappeared indicating that the mixing of ν(C-N), δ(N-H) and ν(C=S)

vibrations may be absent. The deprotonation of thiol group and complexation through sulphur

atom is indicated by absence of the band at 2440-2560cm-1 (due to ν(S-H) in the spectra of

complexes. In the spectra of complexes appearance of a new band at 650-700 cm -1 due to

conversion of C=S into C-S further supported the coordination through sulphur atom. The ν(M-

S) vibration appear at 365-380 cm-1 in the spectra of complexes. The band at 1600-1625 cm-1

corresponding to azomethine ν(C=N) of free ligands, shifts to lower wave numbers on complex

formation by 15-20 cm-1 hence, the nitrogen atom of the azomethine group is coordinating to

metal ion in all complexes. This coordination mode was further confirmed by the presence of a

band at 470-490 cm-1 in complexes assigned to ν(M-N) vibrations. This indicated involvement

of the azomethine linkage in coordination. The spectra of the ligands STMTH and SPMTH

show bands at ca. 3400 cm-1 due to ν(O-H). In the parent complexes these bands persist

indicating the non coordination of phenolic oxygen to metal. As additional evidence in

complexes derived from L1H band in range 520-540 cm-1 assigned to ν(M-O) of coordination

water molecule to metal ion. In the spectrum of ligand (L2H) due to the pyridine ring vibration

is also appeared at ca. 1476 cm-1 and ca. 1476 cm-1. In the spectra of complexes the band shifted

is shifted to lower wave number side indicating coordination through nitrogen of the pyridine

ring. The band corresponding to the coordinated pyridine ring is also observed in the region

240-260 cm-1 in the ruthenium(III) complexes derived from ligand (L2H).

The proton magnetic resonance spectra of the ligands and ruthenium(III) complexes

were recorded in deuterated dimethylsulphoxide (DMSO). In the spectra of the ligands

APMTH, SPMTH and CPMTH a multiplet was observed at δ7.60-7.76 ppm. It include

probably for both the aromatic protons of the phenyl and pyridine ring. For ligands ATMTH,

STMTH and CTMTH three multiplets are observed in the region δ5.84-6.76 ppm along with

multiplets of aromatic protons. This could be due to thiophene protons. The other signals

appeared in the spectra of ligands at ca. δ3.46 ppm due to –OCH3 group and at ca. δ9.46 ppm in

the spectra of ligands STMT and SPMT may be assigned to phenolic proton.

FAB mass spectra of the ligands namely ATMTH, APMTH, STMTH, SPMTH,

CTMTH and CPMTH show molecular ion peak at m/z = 316, 311, 302, 297, 288 and 315

which corresponds to their molecular weight. Complexes of ruthenium(III) with composition

[Ru(L)2(H2O)2]Cl shown peaks because of fragmentation of coordination water molecule. In

[Ru(CPMT)2(H2O)2]Cl, the molecular ion peak is m/z = 860 respectively.

In complexes presence of water molecule and chloride ion in the coordination sphere

was confirmed by dynamic TG and DTG data. In the investigating decomposition involves two

step; first step indicates loss of two water molecules at temperature range 140-240˚C. Second

loss observed at 260-300˚C range due to one chloride ion. The organic moieties such as ligand

decompose in gradual manner with increasing of temperature which confirmed by mass loss of

31.15-31.50% at this stage. Although thermal degradation of organic moiety could not be

approximated, thus complete decomposition of ligand occurred at ~580-600˚C in all the

complexes. Another mole of triazole moiety was lost between 370-500˚C with a mass loss of

62.30-63.05% on TG curve. At the final step as the end product stable metal oxide as Ru2O3

On the basis of above given studies following structures have been proposed.

L1H = ATMTH, STMTH, CTMTH

Fig: 1

L2H = APMTH, SPMTH, CPMTH

Fig: 2