Introduction - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/4358/7/07_chapter 1.pdf · Chapter I Introduction 1.1 Introduction: Coordination chemistry of transition metal

Chapter I

Introduction

Chapter I Introduction

1.1 Introduction:

Coordination chemistry of transition metal complexes with Schiff base ligands is an

important and fascinating branch of chemistry. The coordination compounds

including Schiff base ligands are of significantly important and play a pivotal role in

industry, technology and life processes [1-4]. Due to their potential applications in

various fields it has always fascinated and inspired chemists in the world. This can be

evidenced by the vast prolificity and scope of research papers on the subject in recent

times and also by the diversity in which it has found applications [5-12]. A number of

reviews have been published in coordination chemistry of Schiff base metal

complexes [13-28].

Schiff bases are those organic ligands which contain azomethine (>C=N-) group

which play an important role in the coordination chemistry of many transition metals

due to the ease of their formation and versatility. Metal complexes of Schiff bases

found use in bioinorganic chemistry as models for metal containing sites in

metalloproteins, as catalysts for some organic reactions and in magneto chemistry

[29-31]. They can be readily synthesized by condensation of primary amines with

carbonyl components and this general approach allows access to ligand systems of

various denticity. The introduction of additional donor atoms increases the stability of

the formed metal complexes and gives the possibility to combine different ‘hard’ and

‘soft’ donor atoms in one chelating system which allows the formation of stable

complexes with transition metal ions [32].

The complexing properties of Schiff bases with metal have led to the formation of

various complexes. Scientists have ventured into the detailed study of these

complexes with the help of various physico-chemical methods. The introduction of

advanced techniques and the availability of sophaticated instruments of high precision

1


and capability have contributed immensely in the development of coordination

chemistry of metal complexes with Schiff base which now occupies a fundamental

position in modern chemical science.

1.2. Schiff base:

The Schiff bases are the organic ligands which contain azomethine group (R-C=N-).

The Schiff bases are generally prepared by condensation of primary amines (-NH2)

with active carbonyl compounds like aldehydes and ketones (>C=O). They are also

known as anils, imines, with general structure R.CH:N.R' where R and R' is alkyl,

aryl, cyclohexyl or heterocyclic radical which may be differently substituted. The

general reaction for formation of Schiff base can be represented as:

R–CHO + R' –NH2 RHC = N R' + H2O

R, R' = alkyl, aryl, cyclohexyl or heterocyclic group

1.2.1 General Characteristics:

The Schiff bases are weak bases and are readily hydrolyzed by mineral acids but

not by aqueous alkali. They form salts by co-ordination of the electrons on nitrogen

atom of azomethine group. The Schiff bases derived from lower aliphatic aldehydes

are less stable than those derived from aromatic aldehydes. Aliphatic Schiff bases are

difficult to isolate due to their tendency to polymerise. Schiff base derived from

formaldehyde exhibit tendency to undergo polymerisation.

Schiff bases which are effective as coordinating ligands bear a functional group

usually OH, sufficiently near the site of condensation that a five or six membered

chelate ring can be formed by the reaction with a metal ion. Because of great synthetic

flexibility of Schiff base formation, many ligands of diverse structural type can be

synthesized. The size of the chelate ring formed can be controlled by changing the

location of donor atoms and groups to explore the effect of substitution and steric

2


factors.These products have received considerable attention as model compounds for

theoretical studies and as precursor in the following reactions to heterocyclic

compounds.

1.2.2. Historical account of Schiff Bases:

Metal Schiff base complexes are known since the midnineteenth century [33] and

even before the general preparation of Schiff’s base ligands themselves [34]. In 1840,

dark green crystalline copper complex copper(II)bis(salicyladimine) (I) was prepared

by the reaction of cupric acetate, salicylaldehyde with aqueous ammonia by Ettling et al.

[34].

H

N

OCu/2

I

Further, Schiff [35] defined the composition of metal complex with this ligand by

establishing the 1:2 metal ligand ratio in copper complex derived from N-aryl-

salicylaldimine and prepared the complex from Schiff base derived from urea and

salicylaldehyde [36]. Delepine [37] in 1899 synthesized complex with R = methyl group

or benzoyl group by reacting the metal acetate, salicylaldehyde and primary amine in

alcohol and suggested 1:2 stoichiometry. Zelzsche et al. [38] reported the coloured

complexes of transition metals with Schiff bases of substituted salicylaldehyde. In 1931,

Dubsky and Sokol [39] synthesized N-N'-bis-salicylidene-ethylenediamino Cu(II) and

Ni(II) complexes. However, there was no comprehensive, systematic study until the

preparative work of Pfeiffer and associates [40-48] in the years 1931 to 1942. During this

period a systematic study was done on complexes of Schiff base derived from

salicylaldehyde, o-amino benzaldehyde (II) and pyrrole-2-aldehyde.

3


O

N N

OM

M = Cu(II), Ni(II)

II

1.2.3. Synthesis of Schiff base metal complexes:

Metal complexes of Schiff bases are synthesized by one of the following way

1) Reaction of metal salt, aldehyde and amine in solution.

2) The direct reaction of primary amine with a preformed aldehyde-metal complex.

3) The reaction of metal salt, usually in acetate, with a preformed Schiff base in

aqueous ethanol or similar solvent.

4) The reaction of primary amine complex of a metal with aldehyde. The

corresponding metal complexes of β–ketoamines are prepared in similar way.

The addition of alkali is necessary for some reactions. A base is often added to aid

in the removal of an acidic proton from the ligand if required. Potassium, Sodium or

Lithium alcoholate is used for removal of water in reaction. The preparative

procedure including the reaction period, temperature and the amount and kind of

solvent, vary both with the ligands and central metal ion. The preparation of β–

ketoaminato complexes is more difficult than the corresponding salicylideneiminato

complexes [49] and it is often necessary to carry out all procedure in an inert

atmosphere.

1.2.4. Applications of Schiff bases

The Schiff base metal complexes have occupied an important position in the

modern inorganic chemistry. The interest in these compounds arises from their

various applications in the field of bioinorganic chemistry [50-52]. The Schiff bases

are known for their biological importance as fungicides. The pharmacolgical activities

4


of Schiff bases such as anti-inflammatory activity [53], antibiotic activity [54] and

antimicrobial activity [55] have been studied thoroughly. Among the Schiff bases

containing thiazole moiety are biologically more active and its activity increases on

complexation. A number of Schiff base complexes are reported to be of great utility in

pharmacological and biological aspects [56, 57]. Metal complexes with sulphur

containing ligands show anticancer and antitumour activity [58].

Schiff base complexes possess an important property to take up molecular oxygen

reversibly [59-64]. The synthetic reversible oxygen carrying chelates [59, 65] are of

interest as model compounds in the study of reversible oxygenation mechanism

involved in very complex natural oxygen carriers. The Schiff base complexes carrying

molecular oxygen are useful in biological and industrial process because of

importance of molecular oxygen in these fields.

The Schiff base complexes have been found useful in organic synthesis, pigment

industry, polymer industry and textile industry. More recently azo dispersed dyes 2-

(6'-hydroxy Schiff base-5'-arylazolyl)-5-nitrobenzothiazole were synthesized and their

dyeing performance on polyester fibre were assessed [66]. The usefulness of

transition metal complexes in pigment and dyestuff industries [67, 68] is due to their

coloured nature. A number of Schiff base pigments or dyes are used in textile and

rubber industries and also in the manufacture of varnishes and printing inks.

Dey [69] has studied the use of cobalt and chromium mixed ligand complexes in

dyeing wool, silk and nylon. The Co(II), Cu(II), Ni(II), Fe(III) and Cr(III) complexes

of Schiff base triethylenetetramine 5-5'-sulphonyl-bis-salicylaldehyde and bis(2-pyridinal)-

biphenylene-4,4'-diamine are used as inorganic polymers in polymer industries [70, 71].

Schiff bases can also be used as analytical reagent for the analysis of transition

metals. Researchers [72,73] have made an attempt to utilize Schiff bases as an

5


important tool for separation and selection of trace amounts of metals like Cr3+, Fe3+,

Mn2+, Ni2+, Cu2+, Co2+, V5+, UO22+ and Th4+. The Schiff bases impart selectivity

towards metal leading to complex formation. These metals were estimated using

analytical techniques like HPLC or spectrophotometry. Literature [74-76] also reveals

that the transition metal complexes of Schiff bases have been found to be effective

catalyst for epoxidation of various olefins.

Schiff base complexes possess interesting properties of fluorescence. Aluminium,

Zinc, Tin and Yttrium complexes of Schiff base derived from salicylaldehyde and

ortho-aminophenol have green, bluish green or blue fluorescence. The Fluorescence

emission is utilized for the fluorometric determination of this metal ion [77-80]. The

Zn(II) and Co(II) complexes of 2-2'-dimethylthio-N-salicylidene ethylamine have

been studied which exhibit fluorescence.

The biological activity, catalytic activity and analytical applications can be

correlated to the structure of Schiff base and substituent group on it and the redox

potential of the metal ion.

1.3. Coordination Chemistry of Copper:

Copper [81] occupies a unique position in the periodic table. It is about 20th in

order of abundance and occurs at a concentration of about 100 g per ton of the

earthcrust [82]. It has an electronic configuration, [Ar]4s23d9 and naturally occurs as a

free element [83] but it is more commonly found in minerals such as malachite

CuCO3.Cu(OH)2 and azurite [2{Cu(CO3)2}.Cu(OH)2] [84].

Copper exists in a range of oxidation states and the ions readily form complexes,

yielding rich coordination chemistry. The oxidation states cover the range from

copper(0) in metal [85, 86], copper(I) in cuprous compounds [87], copper(II) in cupric

compounds [88] and copper(III) [89] as well as copper(IV) [90] that are rather

6


limited. The high potential, necessary for the oxidation state of +3, is responsible for

rather infrequent chemistry of Cu(III). But chemistry of Cu(III) is gaining increasing

interest because of it's occurrence as an intermediate in several organic reactions and

its association with biological chemistry [91]. The +1 and +2 oxidation states of

copper are the most common, out of which +2 is more stable than +1 [92, 93].

The key roles of copper have been widely recognized in various areas including

superconductivity [94], biological oxygenation [95] and organic synthesis [96-99].

The most important utility of copper in organic chemistry is in the form of

nucleophilic organocopper(I) reagents [100]. These reagents provide the most general

synthetic tools in organic chemistry for nucleophilic delivery of carbanions to

electrophilic carbon centers. The relevance of copper(I) with respect to its importance

in biology and chemistry have been short listed [101]:

1. Monovalent, stable, d10 configuration.

2. Not redox dead like Zn2+ and not too reactive like Ni(0).

3. Occurrence of multiple coordination numbers (Catalysis!).

4. No ligand field effect.

5. Flexible.

6. Supramolecular.

7. Preference for soft donors.

8. Weak π bonding.

9. Forms insoluble halides and sulfides.

10. Not reduced in physiological environment (unlike Ag+, Au+).

11. One electron oxidation at physiological potential.

12. Tolerates and stabilizes organic radicals.

13. Binds alkenes, alkynes and CO.

7


14. Activates dioxygen O2.

The chemistry of copper(I) is less extensive than that of copper(II). A number of

accounts [84, 89, 92, 93, 102, 103], describe the chemistry of simple compounds and

of copper(II) with less emphasis on the formation of coordination compounds of

copper(I) [89, 90, 93, 102]. During the past twenty five years, copper(I) species may

be involved as the precursor of the silent partner in the type III copper proteins has

resulted as a great development in the coordination chemistry of copper(I)

compounds. This is reflected in the text book of 'Advanced Inorganic Chemistry' by F.

A. Cotton and G. Wilkinson, wherein more emphasis has been given to copper(I) in

the recent editions as compared to the older ones. Interest has been increasing due to

the relevance of copper(I) in biological processes [104], catalysis [105] as well as

supramolecular chemistry [106]. Extensive reports have been published on studies

related to oxygen binding to copper(I) [101, 107].

Due to closed shell configuration in copper(I), the complexes are diamagnetic and

colorless, except where color results from the anion or charge transfer. Since

copper(I) ions are devoid of Crystal Field Stabilization Energy (CFSE), the steric

nature of the coordinating ligands, weak interactions present in the lattices and the

stoichiometry of the reaction decide the coordination number and the geometry

around copper(I) (Figure 1.1). In general, the most common coordination numbers

encountered in case of copper(I) are three and four. However, complexes possessing

lower coordination numbers have also been characterized. In coordination number

four, the metal either adopts a tetrahedral or a distorted tetrahedral geometry. With

coordination number of three, it is either T-shaped or Y-shaped. Linear geometry has

been observed with coordination number of two. Copper(I) is so flexible that small

perturbations can distort the regular geometry into a less symmetric geometry.

8


Cu Cu Cu

Cu Cu Cu

Linear T-shaped Y-shaped

Tetrahedral Trigonal Pyramidal See-saw

Fig. 1.1 Common Coordination Geometries of Copper(I).

Copper(I) being a soft acid [108] and is stabilized by soft bases. For example sulfur

and phosphorus donors are the most suited ligands for copper(I). Halides as well as

pseudohalides also form stable complexes with copper(I). Hard centers like nitrogen

and oxygen tend to stabilize copper(II). But there are stable copper(I) complexes of

nitrogen based ligands having sufficient π-character. Phosphines are the most common

ligands that are encountered in copper(I) chemistry [109]. These include tertiary

phosphines that serve as good σ-donors and moderate π-acceptors [110].

1.4. Schiff base Copper(I) Complexes: a brief literature review

Copper(I) complexes with various Schiff base ligands are of growing interest as most

of these complexes combine remarkable features like ease of preparation,

electrochemical behavior, light absorption in the visible spectral region; characteristic

structural flexibility, supramolecular architecture, long-lived electronically excited

states, and intense luminescence. They have ability to possess unusual configuration,

structural ability and sensitivity to molecular environment. Developments in these fields

are of great interest because of their various applications like solar energy conversion

supramolecular devices or catalytic activity in photo-redox reactions. Many excellent

9


works have been devoted to the exploration of new synthetic pathways and structural

aspects of the systems, highlighting the role of the ligands and to design a chemical

pathway capable of tuning the synthesis from mononuclear to multinuclear systems.

The literature survey reveals that extensive work has been done by S. Dehghanapour

and his coworkers on nitrogen donor Schiff base and their complexing behavior with

copper(I) [111-115]. The copper(I) complexes [Cu(Ca2men)2]ClO4 (1) and

[Cu(PhCa2dpen)2]ClO4 (III) (2) with Schiff base ligands N,N'-bis(3-phenylallylidene)-

propane-1,2-diamine (Ca2men) and 1,2-diphenyl-N,N'-bis(3-phenylallylidene)-ethane

1,2-diamine(PhCa2dpen) has been reported [111]. On the basis of X-ray crystallography

studies distorted tetrahedron is ascribed for the complexes. All the complexes show

quassireversible redox behavior (E1/2 = 0.71 and 0.83 V) at room temperature.

N

N N

Cu

N

Ph PhPhPh

X

+

_

R1

R1R2

R3R3

R3R3

R2

Complex R1 R2 R3 X

1 H CH3 H BPh4

2 Ph Ph Ph ClO4

III

The copper(I) complexes [Cu(mb2en)2]ClO4 (1) and [Cu(mb2en)(PPh3)2]BPh4 (2)

containing ligand N,N′-bis-(4-methoxy-benzylidene)-ethane-1,2-diamine (mb2en) have

also shows the coordination polyhedron about copper(I) with distorted tetrahedron on

the basis of X-ray crystallography studies [112,113]. The Schiff base ligands (4-

methyl-phenyl)-pyridine-2yl-methylene-amine (A), (2,3-dimethyl-phenyl)pyridine-2-yl-

methylene-amine (B), (2,4-dimethyl-phenyl)-pyridine-2-yl-methylene-amine (C), (2,5-

dimethyl-phenyl)pyridine-2-ylmethyleneamine (D) and their corresponding copper(I)

complexes [Cu(A)2]ClO4 (1a), [Cu(B)2]ClO4 (1b), [Cu(C)2]ClO4 (1c), [Cu(D)2]ClO4

10


(1d), [Cu(A)(PPh3)2]ClO4 (2a), [Cu(B)(PPh3)2]ClO4 (2b), [Cu(C)(PPh3)2]ClO4 (2c),

[Cu(D)(PPh3)2]ClO4 (2d) (IV) also show coordination polyhedron around the

copper(I) is distorted tetrahedron [114]. All these complexes show quassireversible

redox behavior at room temperature.

N

N

Cu

PPh3

PPh3

ClO4

R1 R2 R3 R4

R1

R2

R3

R4

+

_

Ligand

A

B

C

D

H H CH3 H

CH3 CH3

CH3 CH3

CH3 CH3

H H

H H

H H

IV

The copper(I) complexes of the type [Cu(Phca2en)(PPh3)X], [Phca2en = N,N-bis(β-

phenylcinnamaldehyde)-1,2-diiminoethane and X = Cl (1), Br (2), I (3), NCS (4), N3

(5)] shows that the coordination geometry around copper atom is a distorted

tetrahedron [115]. Furthermore, these copper(I) complexes exhibit supramolecular

motifs of the type multiple phenyl embraces resulting from attractive interactions

between phenyl rings of PPh3 moieties.

The coordination behavior of Schiff base ligands N, N'-bis(cinnamaldehyde-1,2-di-

iminoethane)(ca2en), and N,N'-bis(β-phenylcinnamaaldehyde-1,2-diiminoethane)(PhCa2en)

towards copper(I) is studied by Amirnasr and his coworkers [116]. The X-ray

crystallographic study of [Cu(PhCa2en)(PPh3)Br] and [Cu(PhCa2en)(PPh3)I] revealed

distorted tetrahedral geometry around copper(I). The reaction of CuI with the bidentate

Schiff base ligand bis[N,N'-bis(β-phenylcinnamaldehyde)]-2,2'-(diaminobiphenyl) (Phca2-

dab) afforded mononuclear copper(I) complex [Cu(Phca2-dab)2][CuI2] (V) [117]. The

structure of the complex shows that cationic moieties of CuI ion coordinated to four N

11


atoms of two PhCa2-dab ligands in a distorted tetrahedral fashion and isolated linear

diiodocuprate(I) anions. The Phca2-dab embrace involves two complexes attracted by

two edge-to-face (ef) interactions by the outer phenyl rings of the ligands.

N

N

PhPh

Ph Ph

N

N

Ph

PhPh

Ph

Cu

+

[ I -Cu -I]-

V

The single crystal analysis of mononuclear and dinuclear copper(I) complexes

[Cu(Phca2en)2][AgI2] (1), Phca2en = N,N'-bis(β-phenylcinnamaldehyde)1,2-diaminoethane

L), [Cu(Phca2-dab)2][CuI2] (2) Phca2-dab = N,N'-bis(β-phenyl-cinnamaldehyde)]-2,2'-

(diaminobiphenyl), [Cu2I2(L)2](3), L = N,N'-bis(3,3'-diphenyl-prop-2-ethylidene)-propane -

1,3-diamine, [Cu2I2(L)(PPh3)2].2CH3CN (4), L = {μ-bis[1-(pyridyl-2-yl) 2-ethylidene-

ethane-1,2-diamine-k.N,N'},[Cu(L)2]I3 (5), L = Bis[N,N'-bis-(3,3'-diphenyl-prop-2-

ethylidene)ethane-1,2-diamine-k.N,N'] are reported [117-122]. The X-ray crystallo-

graphic study of complexes (1) and (2) reveals the presence of cationic moieties of

copper(I) coordinated to ligands in distorted tetrahedral fashion and crystal packing

analysis represents the one dimensional array of supramolecular motif. In dinuclear

comolexes 3 and 4 the copper(I) atoms are coordinated with ligands and two I2 atoms

in 3 and two P atoms of PPh3 in 4, respectively, and shows distorted tetrahedral

geometry. In complex 5, copper(I) atom coordinated to four N atoms of two ligands

showing distorted tetrahedral geometry around copper(I). The complex [(Ca2Ph)Cu(µ-

I)2Cu(Ca2Ph)] {Ca2Ph = trans-cinnmaldehyde-o-phenylenediamine} has a dinuclear

12


structure with distorted tetrahedral geometry [123]. The reaction of bidentate Schiff

base ligand N,N′-bis(trans-cinnamaldehyde)-o-phenylenediamine with Cu(SCN)

afforded the coordinated polymers [Cu(L1)(SCN)]n and [Cu(L2)(SCN)]n (VI). Both the

complexes consists of an one dimentional polymeric chain in which copper(I) ions are

bridged by two thiocynate groups bonding in an end-to-end fashion [124].

N

R1

R2R3R3R2

R1

N

Cu

NCSn

SCN

VI

The mononuclear copper(I) complexes of type [Cu(ca2dapte)]ClO4 and dinuclear

copper(I) complexes of type [{Cu(PPh3)(X)}2(ca2dapte)] (X = I and Br) with

tetradentate N2S2 donor Schiff base ligand N,N′-bis(trans-cinnamaldehyde)-1,2-di(o-

iminophenylthio)ethane (ca2dapte) are reported (VII) [125]. The crystal structure

revealed that the coordination geometry around copper(I) is distorted tetrahedral. The

ligand ca2dapte is coordinated to copper(I) as a tetradentate ligand in mononuclear

complex while it acts as a bis-bidentate bridging ligand in dinulcear complexes.

CuN

S S

N

+

ClO4

_

VII

The X-ray structure of copper(I) complex of the flexible N2S2 Schiff base ligand

[Cu(ca2dapte)(NCS)], [ca2dapte = N,N,o-bis(cinnamaldehyde)-1,2-di(o-iminophenylthio)

13


ethane] reveals that the coordination polyhedron around the copper(I) center is best

described as a distorted tetrahedron [126]. The flexible N2S2 Schiff base ligand

ca2dapte acts as a tridentate ligand via two S atoms and one N atom, while the NCS-

ligand is coordinated to the metal ion through its nitrogen atom and apparently, the

coordination habits of the flexible ligand of this type can be altered in the presence of

other ancillary ligands.

The copper(I) complexes [Cu(Pyim)(PPh3)Cl] (1-2) and [Cu(Quin)(PPh3)Cl] (3-4)

are prepared by the condensation of aniline or α-methylbenzylamine with pyridine

carbaxaldehyde (Pyim) or 2-quinolinecarboxaldehyde (Quin) followed by the

treatment with [Cu(PPh3)3Cl] [127]. All the copper(I) complexes are proved to be

highly active in olefin cyclopropanation in the presence of ethyl diazoacetate. X-ray

crystallography of complex 2 reveals that the central copper atom possesses a slightly

distorted tetrahedral geometry.

The copper(I) linkage isomers of pyridine-2-carbaldehyde-2′-pyridylhydrzone

(papyH) [Cu(PPh3)2(Z-papyH)]ClO4, [Cu(PPh3)2(E-papyH)]ClO4 are synthesized

[128]. X-ray diffraction analysis indicate that the [Cu(PPh3)2(Z-papyH)]ClO4 consists

of discrete monomers of distorted tetrahedron geometry with the metal atom

coordinating to imino nitrogen and one of the pyridyl nitrogen atom of the coordinated

N

N

N

NH

Cu

PPh3Ph3P ClO4

+

_

VIII

ligand. The second pyridyl nitrogen is involved in an intramolecular hydrogen bond

with the hydrogen atom of the hydrazono moiety.

14


The neutral complexes of the type [(PPh3)2Cu(L)] (IX) are synthesized by the

reaction of (PPh3)2Cu(NO3) and Schiff base ligands 2-(benzylideneimino)phenol

(BimOH), 4-(benzylideneimino)resorcinolphenol (Bim(OH)2) and N(2,4-dihydroxy-5-

isopropylphenyl)acetamide (DipaH3) [129]. The ligands were designed to model

aminated intermediate forms of topaquinone cofactor in the enzymic cycle of copper

dependent amine oxidase. The ligands coordinate to the metal center through the

imine–N and phenolate-O donor atoms to form five membered chelate rings in

contrast to the six-membered chelate ring of salen-type Schiff base ligands. The

Bim(OH)O- ligand forms close to planar five membered chelate rings in the copper(I)

complex. The metal is coordinated in typical distorted tetrahedral fashion with small

N-Cu-O bite angles of 83° and two largely equivalent PPh3 ligands. The metal binding

by the unsymmetrical chelate Bim(OH)O- occurs with slightly longer bonds of Cu(I)

to the imine N than phenolate O centre.

N

OCu

PPh3

PPh3

IX

The reaction of 4(4′-methoxybenzaldehyde)3-methyl-1,2,4-triazole-5-thione and

4(3′-methoxybenzaldehyde)3-methyl-1,2,4-triazole-5-thione with [(PPh3)2CuCl]

afforded the complexes of type [(PPh3)2CuCl(L)] [130]. The reaction of 4-amino-5-

ethyl-2H-1,2,4-triozole-3(4H)-thione (AETT, L) with furfural in methanol led to the

Schiff base which on reaction with [Cu(PPh3)2]Cl in methanol gave neutral complex

[131]. The reaction of copper(I) halides with bidentate N,N′-bis(benzophenone)-1,2-

diiminoethane (bz2en) Schiff base form 1:1 adduct [Cu(bz2en)2][CuX2] (X = Cl, Br,

15


and I) [132]. The solid-state structure revealed ionic complexes containing a cation of

copper(I) ion coordinated to four nitrogen atoms of two bz2en molecules (distorted

tetrahedron) and a linear dibromocuprate(I) and a diiodo-dicuprate(I) anion for the

bromo and iodo adducts, respectively. The bromo adduct structure contains CH--Br

intermolecular hydrogen bonds. The copper(I) complex of the type [Cu(L)(PPh3)2].

0.5CH3OH, 0.25CHCl3, where L = 4-(4'-methoxybenzylideneamino)-5-methyl-2H-

1,2,4-triazole-3(4H)thione and 4-(4'-methoxybenzylideneamino)-5-methyl-2H-1,2,4-

triazole-3(4H)thione exhibit the tetrahedral geometry around the copper(I) atom

[133]. The reaction of copper(I) thiocynate (CuSCN) and triphenylphosphine (PPh3)

with a new bidentate Schiff base, N,N'-bis(2-nitro-cinnamaldehyde)ethylediamine

(NCa2en) resulted in the formation of a complex [CuSCN(NCa2en)(PPh3)](X) [134].

The X-ray crystal structure shows distorted tetrahedral geometry around copper(I).

NO2

N N

NO2

Ph3P

Cu

SCN

X

The mononuclear complexes [Cu(L)(CH3CN)2]ClO4 and [Cu(L)(PPh3)2]ClO4(XI), of

flexible polydentate diazine ligand butane-2,3-dione,bis(slicylhydrazone) (L) are

synthesized and their structural, photophysical, electrochemical properties and reactivities

are studied [135]. The phenolate oxygens did not take part in metal-coordination because of

the incompatibility of soft copper(I) ion with hard O- ion and also due to the free rotation of

N–N bond, the N,O donor atoms in the ligand moiety are disposed in a divergent fashion.

N N

OHOH

N N

Cu

Ph3P PPh3

XI

16


The crystal structure of two cationic copper(I) complexes of a Schiff base ligand in

two isomeric forms 2,6-bis-1[(imidazole-4ylethyl)imino)ethyl]pyridine[imidH]2 DAP]

and 4-methyl-4[6-Cl(2-imidzole-4-ylethyl)imino)ethylpyridine-2yl]-4,5,6,7-tetrahydro-

1H-imidazole[4,5,6]pyridine [(imid)DAP] (XII,XIII) have been reported [136]. The

pentacoordinated species shows distortion from idealized trigonal bipyramidal

geometry. The tetracoordinated structure described as flattened tetrahedron. The

pentacoordinated isomer form a dioxygen adduct at room temp in non aqueous

solution, under removal of dioxygen regenerate [CuI(imidH)2DAP].

NH

N

NH

N

NNCu

NH

N

N

N

NCu

XII XIII

The bimetallic copper(I) complex of dipyrromethane are synthesized from Schiff

base microcycles (XIV) [137]. Two different structural motifs are identified in

copper(I) complexes. The metal centers are found to have a distorted tetrahedral

NH

NH

N

N

NH

N

N

NH

Cl

Cl

CuCu

XIV

17


geometry and coordinated to two imine nitrogen on each side of the ligand. The

structural analysis revealed a copper-copper distance of 3.47 Å while SQUID

magnetic susceptibility data provide evidence for antiferromagnetic coupling between

two metal centers.

The reactivity of Schiff base ligand in the coordination sphere of copper(I) complex

[Cu(L)]PF6, (L = 2(acetyl)-6-[1-(diisopropylphenylimino)ethylpyridine] towards β-

diketones have been studied [138]. The X-ray single crystallographic analysis revealed,

a quite amazing structure corresponding to a 2:1 (L:Cu) stoichiometric 2,6-disubstituted

pyridine ligands. The asymmetric complex Cu(L2)PF6 is consistent with one [Cu(L)2]1

cation, one PF6 anion and one pentaendione molecule of crystallization for which a

strong disorder was observed. In the cation, the copper(I) atom is surrounded by two

transformed ligands according to distorted tetrahedral geometry defined by Cu-Npy

and Cu-Nimine bond lengths, respectively of 2.072(2), 2.118(3) and 2.003(2) Å and

N-Cu-N angles falling in the range 80.35(10)-135.69(11)0 .

The binuclear copper(I) complexes of the type [CuI(AEP)2IPAH]Cl2 (XV) and

[CuI(AEP)2IPAH]BF4 with the binucleating Schiff base ligand (AEP)2IPAH

synthesized by condensation of 2-hydroxy-5-methyliso-phthalaldehyde and 2-(2-

aminoethyl)pyridine [139]. Analytical, spectral and magnetic studies support the

N

N

Cu

X

Cu

O

CH3

N

N

2+

2Y_

XV

18


proposed formulation of these complexes. [CuI(AEP)2IPAH]+ reacts reversibly with

carbon monoxide in acetonitrile or dimethyl sulfoxide solution at room temperature to

form terminally bonded CO adduct.

The dimeric copper(I) complex of the type [(CuL)2(ClO4)2]DMF (XVI). (L = 1,8-

bis(2-pyridyl)-2,7-diazooctadiene-1,7) has helical structure with ligand L bridging

the two copper atoms to provide tetrahedral N4 coordination of each copper(I) [140].

In solution of [(CuL)2(ClO4)2, DMF showed solvent dependent dissociation.

N

NN

N

N

N N

N

CuCu

2+

-(ClO4)2

-

XVI

The X-ray crystallography stydy of dinuclear copper(I) complexes of 1,3-bis[N-(2

pyridylformimidoyl)]benzene, [Cu2(H-BPB-H)(CH3CN)2](BF4)2 as well as 5-nitro

derivative [Cu2(NO2-BPB-H)(CH3CN)2](BF4)2 shows the distorted tetraheral

geometry in the complexes [141].

The copper(I) complexes with N,N´-donor Schiff base ligand obtained from

vinylamine and α-diketone and form the complexes of the type [Cu(L)2]X.nH2O (X =

ClO4- ; n = 1.5; X- = PF6 n = 0) and [Cu(L)(PPh3)2]X (X- = ClO4, or PF6

-) [142]. The

copper(I) complexes show CuII/I potential in [Cu(L)2]X.nH2O is rather high, 0.92 V

vs. SCE in CH2Cl2 at a glassy carbon electrode. This indicates the ligand is a potential

π-acid which preferentially stabilises copper(I) much more than copper(II). This π

acidity of ligand arises because of the extensive conjugation. The complexes are

19


photoluminescent in fluid solution and its emission being somewhat quenched in

[Cu(L)2]X.nH2O. The copper(I) complexes of bis-bidentate Schiff base ligands

obtained from 2-quinolinecarboxaldehyde and ethylenediamine (L1) and benzyl-

dihydrazone (L2) afforded di-nuclear dimeric complexes [Cu2(L1)2](ClO4)2 (1b) and

[Cu2(L2)2](ClO4)2 (2b), in which the metal ion auxiliaries adopted a pseudo-

tetrahedral coordination environment [143]. In these complexes the two ligands wrap

around the metal ions in a twisted manner, forming box-like structures. Within these

complexes each metal ion binds to two nitrogen sites of one ligand and two N-sites of

the other ligand. Electrochemical behavior of the complexes reveals the more or less

similar type of quasireverssible CuI /CuII couple occurring at E1/2 = 1.28 and 1.35 V

and ∆Ep values are 235 and 220 mV, respectively.

The mononuclear neutral copper(I) complexes of the type [Cu(L1)](PPh3)(1)

(XVII), [Cu(L2)](PPh3)2 (2) (XVIII), (L1 = [{N(C6H3iPr2-2,6)C(H)}2C(Ph)]-, L2 =

[{N(C6H5)C(H)}2C(Ph)]-) have been synthesized and structurally characterized by X-

ray crystallography [144]. In complex 1, the copper(I) atom is in distorted three

coordinate trigonal planer environment, while in complex 2 with less sterically hindered

N

N

R

R

R

R

PPh3CuN

NCu

PPh3

PPh3

R = C(CH3)2 XVII XVIII

β-dialdinato ligand, the copper(I) atom is four coordinate distorted tetrahedron. At

room temperature complexes 1 and 2 in a film of PMMA exhibit green emission at

643 and 549 nm with lifetime of 528 and 532 ns.

20


The X-ray analysis of copper(I) complexes with [N,N'-bis(4-fluorobenzylidene)

ethylenediamine]bromo(triphenylphosphine) (XIX) shows that the coordination

polyhedron around the copper(I) is best described as distorted tetrahedron [145].

Photophysical investigation in solution of the time resolved spectral changes recorded

before and after irradiation show the transformation from syn to anti configuration of

the C=N bond.

Br

PPh3

N

N

Cu

F

F

XIX

The dinuclear copper(I) complexes derived from a diprotonated Schiff base

cryptand derived from the bicyclocondensation of tris(2-aminoethyl)amine with 2,6-

diacetylpyridine in the presence of acid have been reported [146]. The homodinuclear

copper(I) complex of the neutral cryptand was recovered. The crystal structures of the

two dinuclear complexes were determined. The Cu(I)--Cu(I) separation in the cryptate

complex is 6.25 Å. In the crystal, the complex [Cu2L6]4+ cations and BF4 two anions

are held together by several C-H-F hydrogen bonds and electrostatic interactions; the

partially occupied solvate species MeCN and H2O are all sited on crystallographic

symmetry axes and appear to have no significant short contacts [147].

The dimeric copper(I) complexes of the type Cu2(ClPhtrz)4(ClO4)2.2MeCN (1) and

Cu2(ClPhtrz)2(ClO4)2.2MeCN (2) with Schiff base containing triazole ligands N-[(E)-

(4-chlorophenyl)methylidene]-4H-1,2,4-triazol-4-amine (ClPhtrz) and N-[(E)-phenyl

21


methylidene]-4H-1,2,4-triazol-4-amine (Phtrz) are reported [148]. The complexes with

ClPhtrz form two different dimeric complexes. X-ray crystallography revealed that

each copper centre exhibits a planar trigonal coordination in 1, while the tetrahedral

coordination sphere of copper centre in 2 is completed by a solvent molecule. In

dimeric complexes the tetrahedral coordination of the copper(I) ions is formed by two

monodentate and two bidentate (bridging) Phtrz ligands.

The dicopper complexes of the type [Cu2(ibt)2(CH3CN)4][PF6]2.C6H12 (1),

[Cu2(ibt)2(CH3CN)4][PF6]2 (2) and [Cu2(ibt)2(CH3CN)4][ClO4]2 (3), (ibt = 4-isopropyl

idene amino-2,1,3-benzothiadiazole) are reported [149]. In complex 1 there are two

crystallographically independent monomeric units in each of which copper(I) is co-

ordinated by one N atom on the ring of ibt and two acetonitrile molecules; two units

are linked to each other by weak binding of the amino group of abt with copper(I) to

give a cyclic dinuclear complex. In complex 2 tetrahedral cooper(I) centers are

bridged by two ibt molecules in a head-to-tail fashion as in 1. Both complexes 1 and 2

have the same metallocyclophane skeletons showing an intramolecular stacking

interaction between two parallel aromatic rings and a considerably long Cu--Cu

separation. Following the same synthetic strategy as used for the synthesis of 2

another dicopper complex [Cu2(ibt)2][ClO4]2 3 are prepared which presents a

structural contrast with 2, two copper(I) centers are linearly coordinated by two ibt

molecules in a head-to-head arrangement which leads to a twisted conformation with

a shorter Cu--Cu distance of 2.699(2) Å.

The monomeric copper(I) complexes [Cu{PPh2CH(R)C(But)=NR}Cl]2 (1) and

complex [Cu{PPh2CH(R)C(But)=NR}2]ClO4 (2), with P,N ligands RN=C(But)C(H)

RPPh2 (R = SiMe3, H) are reported [150]. The presence of trace amounts of water

22


during the reaction resulted in the successive cleavage of the two trimethylsilyl groups

of the ligand and the formation of the monomeric chelate complexes [Cu{PPh=CH(R)

C(But)=NH}2]ClO4 (3) and [Cu{PPh2CH2C(But)=NH}2]ClO4 (4). Simple Cu(I)-chlorides

are frequently solvated by both P and N atoms resulting in dimeric complexes [PNCu(l-X)2

CuPN] with a tetrahedral coordination of the copper(I) atom and bridging Cl atoms.

The two-photon absorption of copper(I) complex with bis-cinnamaldiminato Schiff

base ligand, Cu(L)2(BF4), induce exceptionally large ó2 values on a Schiff base

through metal complexation [151]. The magnitude ó2 depends on the structure of the

complex as copper(I) enhances the electron-acceptor character of the central diamine

moiety. However, in the Schiff base ligand (L), the central diimine part possesses very

weak electron-withdrawing character. The high thermal stability as well as high TPA

cross sections makes theses complexes potential candidates for NLO applications.

The structural variation and spectroscopic properties of copper(I) complexes with

bis(Schiff base) ligands [(pyridine-4-carbaldehydeazine) (L1), 1,2-bis(4′-pyridylmethyl

eneamino)ethane (L2), pyridine-3-carbaldehydeazine (L3), (3′-pyridylmethyleneamino)

ethane (L4), pyridine-2-carbaldehydeazine (L5), 1,2-bis(2′-pyridylmethyleneamino)ethane

(L6)] in presence of PPh3 form complexes of the type [Cu2(L1)(PPh3)2I2].2CH2Cl2,

{[Cu2(L2)(PPh3)2]BF4}n, [Cu2(L3)(PPh3)4I2].2CH2Cl2, [Cu2(L4)(PPh3)4I2], [Cu2(L5)(PPh3)2I2]

and [Cu2(L6)(PPh3)2I2](XX) [152]. The ligand L1 and L2 gives infinite coordination

polymer chain. However, the ligand L3-L6 act as monodentate ligand and coordianate

N N

Cu

PPh3Ph3P

NN

Cu

PPh3Ph3P I

(CH2)n

-

+

XX

23


with two copper(I) atoms yielding a dimer. All the complexes exhibit photolumine-

scence in the solid state at room temperature.

A series of Schiff base copper(I) complexes have been synthesized with o-tert-

butylthiobenzaldehyde and terminal diamine (1,2-diaminoethane, 1,3-diaminopropape

and 1,4-diaminobutane) [153]. The complexes differ only in the length of the

methylene chain between the imine groups. This modification forces the copper centre

to shift the geometry from a planar (1,2-diaminoethane) to a more distorted

tetrahedral motif (1,4-diaminobutane). The S–Cu–N angles for each complex are

correlated against the respective redox potential allowing an analysis of the geometric

impact on the redox potential in soft copper centers. The redox potential is observed

to increase as the metal centre moves from a planar towards a tetrahedral motif.

The coordinated polymeric copper(I) complex [Cu(L)(PPh3)](ClO4) using di-

Schiff base ligand 1,2-bis(3’-pyridylmethyleneamino)ethane (L) are reported [154].

The crystal structure analysis revealed that the structure of the complex

[Cu(L)(PPh3)](ClO4) is an infinite zigzag chain and copper(I) atom has distorted

tetrahedral coordination geometry. The complexes show strong photoluminescence at

room temperature. The copper(I) complex [Cu(INHPy)(PPh3)2](ClO4) were synthesized

by the reaction of [Cu(MeCN)2(PPh3)2](ClO4) and Schiff base 2-pyridylcarboxaldehyde

isonicotinoyl hydrazone (INHPy) [155]. The single crystal X-ray analysis indicate

that copper(I) atom has distorted tetrahedral geometry.

The copper(I) complexes of the type [Cu(E3tren)]X (where E = O or S and X = I or

BPh4) with tripodal Schiff base ligands tris[4-(2-thienyl)-3-aza-3-butenyl]amine

(S3tren) and tris[4-(2-furyl)-3-aza-3-butenyl]amine (O3tren) are reported [156]. The

copper(I) geometry is trigonal pyramidal, with coordination occurring from the apical

24


tertiary amine N atom and the three azomethine N atoms of the tripodal Schiff base

ligand. The X-ray structure of copper(I) complex of tripodal Schiff base ligand,

[tris-{2-thienyl)-3-aza-3-butenyl}amine] indicate that the complex is monoclinic

and shows trigonal pyramidal geometry with coordination occurring from the

optical tertiary amine N atom and the three azomtehine nitrogen of the tripodal

Schiff base ligand [157].

The copper tripodal Schiff base complex {tris[4-(2-thienyl)-3-aza-kN-3-butenyl]

amine-kN}copper(I) tetrafluoroborate crystallizes with the cation residing in a general

position and two disordered tetrafluoroborate anions residing on 2-fold axes [158].

The cation has 3-fold symmetry and the copper(I) geometry is distorted trigonal

pyramidal with coordination from the apical tertiary amine N atom and the three

azomethine N atoms but not from the S atoms of the three thiophene moieties.

The dinuclear copper(I) complexes [Cu2(L)(X)2]; where L = N,N′-ethylenebis (acetone

-amine) (acacenH2) and X = CO(1), ButN (2) (XXI), [Cu2(L)(PPh3)4] (3) (XXII) and

[Cu2(L)(PPh3)4] (4) (XXIII), L = N,N’o-phenylene-bis(salycilaldemine (salophenH2)

have been reported [159]. The complexes 3 was analyzed with single crystal X-ray

crystallography and shows that the distortion about a center of symmetry and all the

phenyl rings are constrained to the regular hexagons in the complex.

N

N

O

O

Cu

CuL

L

CH3

CH3 CH3

CH3[Cu2(acacen) (L)2]

L=CO,ButNC

PPh3

PPh3

Ph3P

Ph3P

N

N

O

Cu

CH3

O

Cu

CH3

CH3

CH3

[Cu2(acacen)(PPh3)4]

PPh3

PPh3

PPh3

PPh3

N

N

O

O

Cu

Cu

[Cu2(salophen)(PPh 3)4]

XXI XXII XXIII

25


The copper(I) complexes [Cu(L)(PPh3)2]X, L = 4-fluorobenzaldehyde-thiosemi-

carbazone and N-methyl-thiosemicarbazone with N and S donor atoms shows that the

oxoanions NO3-, SO4

2- and CH3COO- play an important role in the structural

properties of the complexes [160]. Their oxygens are bad competitors with imino

nitrogen of the thiosemicarbazone moiety and moreover they form strong charge

assisted hydrogen bindings that stabilize the neutral form of the ligand.

In case of the copper(I) complexes [Cu(L)2]X (XXIV), different structural motifs

providing support for the coordination modes have been studied [161]. In all the

complexes the metal centers are found to have a distorted tetrahedral geometry and

coordinated to two imine nitrogens on each side of the ligand, with the exact structure

depending on the choice of Schiff base macrocycle.

O

N

Si(OEt)3

O

N

(EtO)3Si

Cu

XXIV

The X-ray crystallography study of complex, [Cu(L)2]ClO4, (XXV) L = (amino-N)2

(imino-N)2 chromophore suggests the perchlorate oxygen atom are disordered and all the

complexes exhibit photoluminescence in fluid solution at room temperature as well as in

frozen solution at 77 K [162].

Cu

Ph

N N

PhPh

NN

Ph

ClO4

+

_

XXV

26


The copper(I) complexes of Schiff bases derived from 2,6-aminopyridine with

phenyl methyl ester or tyrosine ethyl ester in solid state have mononuclear structure

in which the trimethine group act as tridentate ligand [163]. In methanol spectroscopic

properties suggest at least partial dissociation of one side arm leading to a two

ordinate copper(I) which interacts with a free imino nitrogen of the copper(I) orbital

with π* of the ligand and hence an increase in absorption intensities .

In copper(I) complexes [Cu2(L1)2 [BPH4]2; where L= Schiff base derived from 2,6-

diacetylpyridine and RNH2 R = (CH2)2CHCH2 (L1), CH2CHCH2 (L2), Bu (L3), Pr

(L4), (CH2)2SEt (L5), the X-ray diffraction study reveals that each copper atom is

bonded to the pyridine N and one imino N of ligand 1, and one imino N and one

alkene group of the ligand 2 in the distorted tetrahedral geometry [164].

The copper(I) iodide complexes with six-membered and four-membered metallocyclic

ligands, [Cu2(C4H3SCHNC5H4N)(I2-I)(I3-I)]n (1), [Cu2(3-Me-C4H2SCH NC5H4N)(I2-

I) (I3-I)]n (2) and two discrete chair-pyramidal shaped tetranuclear complexes, Cu4(5-

Me-C4H2SCHNC5H4N)2(I2-I)2(I3-I)2 (3) and Cu4(5-Br–C4H2SCHNC5H4N)2(I2-I)2(I3-I)2(4);

L = N-(2-thienylmethylidene)-2-pyridylamine derivatives R–Th–C=N–Py (R = H, 3-

Me, 5-Me, and 5-Br) are reported [165]. The molecular structures of 1, 2, 3 and 4 are

established in detail by single-crystal X-ray diffraction analysis. The polymer chain

structure of 2 is found to be extended into a two dimensional supramolecular network

through hydrogen-bonded interactions. In dinuclear complexes the effect of the

electron donating methyl or electron withdrawing bromo substituents on the α-

position of the thienyl ring was observed, while the steric hindrance of the substituent

might play an important role to limit the complex to a tetranuclear structure.

The structures of the copper(I) complexes with Schiff base derived polycatenar

ligands of pyridine-2-carboxaldehyde and substituted anilines, [Cu(L)n)2]BF4 (n = 1–

27


3) 1–3 reveals that the cis arrangement of the coordinated py-CHNN- fragment and

the trans conformation of the uncoordinated imino subunit, the overall ligand adopts

an almost planar geometry [166]. The four-coordinate tetrahedral copper(I) cation

shows Cu–N(py) and Cu–N(imine) distances of ca 2.085 and 2.021 Å, respectively

with chelate bite angles of 81.6 and 81.1°.

1.5. Redox Chemistry of copper(I) complexes:

There are three types of redox processes associated with the copper(I) complexes as

shown below.

(a) Electrolytic redox process:

Cu 0-e -

Cu + Cu 2+

+e -+e --e -

(b) Disproportionation:

2Cu+ Cu 0 + 2e -

(c) Oxidation with molecular oxygen:

Cu2+ + 2e- 2Cu+

O2 + 2e - O22-

The instability of copper(I) state in aqueous media is due to the disproportionation

reaction (b). This disproportionation tendency can be reduced by stabilizing copper(I)

via complexation. For example, soft copper(I) can be stabilized using soft bases or

ligands like phosphines, sulfur containing ligands etc. [167]. This enhanced stability is

generally reflected in an increase in the oxidation potential owing to higher stability

of copper in +1 state [168]. The redox potential of copper(I) complexes are sensitive

to the nature of the ligands present in the metal’s coordination sphere. In general the

electrochemical events are in the range of 0 to 1.4 V where the Cu(I) / Cu(II) redox

couple is usually observed for copper(I) phosphine complexes.

28


Cyclic voltammetric measurements of tetrameric complexes like [Cu4(μ-dppm)2(μ4-

S)](PF6)2, [169] [Cu4(μ-dppm)2(μ4-Se)](PF6) [169] {dppm = bis(diphenylphosphino)

methane} and [Cu4(μ-dtpm)2(μ4-S)](PF6)2 [170] {dtpm = bis[bis(4-methylphenyl)

phosphino]methane} in CH3CN have revealed four different oxidation waves within

the range of +0.29 V to 1.35 V.

No reduction waves observed for these complexes indicating that the oxidized forms

of these copper(I) clusters are unstable within the cyclic voltammetric time scale.

Whereas the trimeric structures with dppm [171] and diphosphinoamine ligand

systems {(PPh2)2N(R)} R = nPr, C6H5, C6H4-CH3-p, C6H4-F-p) [172] have showed

the presence of quasireversible oxidation couple, assignable to one electron oxidation

at the copper(I) center. The different acetylide capping ligands have been found to

have a pronounced effect on the metal’s redox potential. The acetylide group bearing

an electron rich substituent, results in a decrease in the oxidation potential. Whereas

electron withdrawing groups on the acetylide ligand increases the oxidation potential.

Similarly Leiva et al. have shown that an increase in the number of PPh3 ligands in

[Cu(CH3CN)4-n(PPh3)n]+ leads to a more anodic shift in the oxidation potential [173].

Origin of multiple peaks in multinuclear clusters have been attributed to electronic

communication between the metal centers in the case of copper(I) complexes of

bis(diphenylphosphino)amine (dppa) [174].

1.6. Scope of work:

The coordination chemistry of monovalent copper(I) complexes is currently

receiving much interest mainly due to their potential applications in various fields.

Due to the favourable soft acid-soft base interaction, the coordination chemistry of

this closed-shell d10 metal ion is largely based upon the coordination of the ligands.

29


The steric, electronic and conformational effects imparted by the coordinated ligands

play an essential role in stabilizing the copper(I) state and modifying the physical and

chemical properties of the prepared complexes. Copper(I) complexes with N, S, P as a

potentially donor ligands have been extensively studied due to their wide variation in

structural motifs and rich photophysical properties, however, only few complexes

with N,O-donor ligands are synthesized and structurally characterized.

Schiff base compounds particularly, are important because they can form different

types of coordination compounds with transition metals due to the several electron

rich donor centers with unusual structural and chemical properties. The literature

survey suggests that the structural chemistry of transition metal complexes of Schiff

base containing nitrogen, oxygen donor atom exhibit large variations. The studies can

further offer many variations in their properties by making the use of secondary

ligand which changes the structural aspects of metal complexes. Triphenylphosphine

and cis-1,2-bis(diphenylphosphino)ethane are most versatile phosphine ligands,

capable to stabilize a variety of complexes formed by transition metals especially in

low oxidation states and able to bind with metal atoms in variety of ways:

monodentate, chelating or bridging. They possess high covalency as well as ligand

field effect to enforce a drastic change in magnetic and other behaviour of the

resulting complexes.

The present work aim to study the structural aspects of copper(I) complexes

derived from the reaction of copper(I) salts CuCl, [Cu(MeCN)4]NO3,

[Cu(MeCN)4]ClO4 and [Cu(MeCN)4]BF4 with N,O-donor bidentate Schiff base

ligands in presence of triphenylphosphine (PPh3) and cis-1,2-bis(diphenylphosphino)

ethane (dppe) as coligands. The coordination behaviour of these ligands towards

30


copper(I) ions was investigated by microanalysis, IR, UV-visible and 1H NMR

spectral studies.

The present work aim to achieve the following points

1. Design and synthesis of copper(I) complexes with the N, O-donor Schiff base

ligands in presence of triphenylphosphine or cis-1,2-bis(diphenylphosphino)ethane.

2. To study the ligantional behaviour of Schiff base ligands in presence of

triphenylphosphine and cis-1,2-bis(diphenylphosphino)ethane by characterizing

the complexes with the help of microanalysis, physico-chemical and spectroscopic

methods.

3. To investigate the effects of coligands on the structural properties of the complexes.

4. To study the electrochemical behavior of the copper(I) complexes..

5. To study the photophysical properties of Schiff base ligands and their copper(I)

complexes.

31


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