Chapter 1

Introduction

chern~stry, the chemistry of metal complexes, is very rtch in

because of the fact that it plays a vital role in industry and in ltfe

processes The developmerit of our knowledge of complexes has been very slow.

gradual and cumulat~ve. The ~nvolvement of metal complexes in biologicd

systems IS an added impetus to the progress of coordinat~on chemistry. In a very

real sense coordination chemistry is a field that spawns fields like transition metal

organornetallic chemistry, homogeneous catalysis and bioinorganic chemistry. It 1s

also fundamental to other burgeoning fields, for example, solid state chemistry,

extended and rnesoscopic materials, photonic materials, models for solid surfaces,

separation science and molecular electronics. Because of the key roles rn new

fields, coordination chemistry has a foundational position in modern chemical

sciences.

In general, research, discoveries and innovat~ons in this field since 1930

have taken place at an ever-accelerating rate. The guiding star of Werner's

cootdinatron theory6 was accepted by most chemists and most of the 20th century

contributions are developments, extensions or conformations of it jModern

coordtnatlon chemistry has been characterised by increased enlphasis on

comprehensive theories of chenlical bonding that have served to explain the large

amount of experimental data. Notable characteristic of modern coordination

chemistry IS the increased reliance upon physicochemical methods unknown to

Werner and his contemporaries. With the introduction of. these newer techniques,

emphasis is shifted fiom structural and stereochemical studies to quantitative

studies b d on thernlodynamics, kinetics and reaction mechanisms.

Many biologically active compounds are complexes and even the simpler

type of complexes have served as model compounds in investigating bodily

processes. In fact, the field of bioinorganic chemistry is concerned largely with

coordination compounds. It is diacult to predict the future of coordination

chem~stry, In which the solution to any given problem usually opens up a number

of new research avenues and poses newer and more challengxng problems.

Moreover, the study of complexes has enabled the inorganic chemists to make

significant progress in refining the concept of chemicd bonding and to explain the

influence that bonding has on the various properties of the compounds.

1 .I. Iron - General chemistry

Compounds of iron in oxidation states from -2 (dlo) to +6 (d') are known.

I l e - 1 and +5 oxidation stares are rare and + I state is not common. The common

oxidation states of iron are +2 and +3. The relative stability of these two oxidation

states in acidic aqueous solution is defined by the standard electrode potential of

+0.77V for the F$'/F$~ couple7 This potential is such that the hydrated ~ e ' ' is

thermodynam~cally unstable with respect to atmospheric oxidation. The oxidation

is even more favourable in basic solution. It is apparent therefore that the

chemistry of iron including its importance in biology is closely associated with the

ready interconversion of these two oxidation states and with the dependence of the

redox potential on the ligand environment.

The small size and relatively high charge of ~ e " are responsible for its

strong tendency to hydrolyse tn aqumus solution. Thus, the hexaaqua ion is a

Brbnsted ac~d of moderate strength (ph = 3.05) and it exists in the undissociated

form below pH - 2. The high charge density of ~ e ~ ' is also responsible for its

strong affinity for donors such as oxygen and fluorine. It is for this reason that

~ e ~ ' , unlike ~ e ' + , forms few stable complexes with ligands such as ammonia or

simple amines which are also good Briinsted baser in aqueous solution. ~ d ' has a

d5 electronic configuration and it is high spin (S = 5/2) in most of its complexes.

There IS a possibility of the stabilisation of low spin (S = 112) ground state in strong

octahedral fields such as generated by CN- and in many bi or polydentate ligands

contaning unsaturated nitrogen. In addition, the intermediate spin state (S = 3/2)

may be p r o d u d in fields of lower symmetry. Magnetic susceptibility

measurement, ESR and Mossbauer spectra provide convenient means for

d~stlngu~shing the different possible spin states in most cases.

I f Fe(llJ-Cwdination chemistry

The various coordination geometries displayed by Fe(II1) complexes are

presented in Table I . I . The common coordinmon number of Fe(I1I) is six but a

range of other coordination numbers (three, four, five, seven and eight) are also

established.

Most of FHIII) complexes, particularly monomeric ones, are octahedral.

Fe(U1) has a little affinity for m i n e ligands but this is not the case with oxygen

donor ligands, where often bridl(ed species are formed in which there exists

antiferromagnetic coupling between the iron atoms. In pox0 dimers such as

[{Fe(~alen))~O] (five coordinate), [{Fe(porphyrin))20] (five coordinate) and

[ ( F ~ c I ~ ) ~ o ] ~ (four coordinate), the magnetic moment is considerably reduced to

around 2 BM/iron atom because of this antiferromagnetic coupling. The tendency

to form bridged complexes extends to sulphur species also, many of which are

biologically relevant. The complexes with very high field ligands are low spin

(e-g., [F~(cN)~]') and they have higher magnetic moment than the predicted value

due to the large orbital contrtbution that decreases at lower temperature.

Table 1.1 Various coordination geometries displayed by Fe(II1) complexes.

Fe(I1J) complexes are usually hneticdIy labile while the low spin

complexes are usually quite inert. Several complexes of Fe(l1i) display spin

crossover phenomena. For ~nstance, a variety of trigonally distorted octahedral

Coordination numbers

3

4

5

5

6

7

8

Geometry

Trigonal

Tetrahedral

Square pyramidal

Trigonal bipyrarnidd

Octahedral

Pentagonal bi pyramidal

Dodecahedra1

Example

[Fe{N(SiMe& 1 3 1

[FeCls]'

[ F ~ C t(dtck12-

F e f N d s l 2-

[Fe@henh13'

[Fe(EDTA)(H20)]'

[Few3)4] -

dithrocarbamate complexes [Fe(S2CNR2)3] can be high spin or low spin dependrng

an temperature.

7.1.2 Fe(III) - Electronic spectsa and magnetism

Little is known about the d-d transit~ons of Fe(II1) because thelr UV-visible

spcctra arc saamped by edges of intense UV charge-transfer bands. In h~gh sprn

octahedral Fe(Jl1) w~th a non-degenerate 'A, ground state, the magnetic moment 1s

given by the spln onIy (high spin) value of 5.92 BM which is ternpurature

~ndepndent Dev~at~on frorn t h ~ s value occurs by antiferromagnetic UI less

common I y a ferromagnet ~c t n terzct~on between the adjacent paramagnet~c centres

Because of the orbital slnglet nature of high spin FB(III), there are no

exc~ted states of the sane spin multiplicity and all d-d transitions are therefore spiri

forbidden as well as Laporte forbidden. The free-ion ground state 'S becomes "A,

4. In a c u b ~ c field while the first exclted s t a t e 4 ~ splits into two'I. states. I.e., 1'1 and

?2 and into a degenerate pair "1 and 4 ~ . The ligand field transitions for the high

spln d5 Mn are ~nd~cated as below.

Since these sextet-quartet l~ .ans~t~oi~s are both spin and parity fbrbldden, iiiter~sstles

of the transitions seldom exceed - 0.01 dmhmol-' cm-'. While in the caw ol'

tetrahedral symmetry, d-p mixing occurs and higher intensities for the transittori

usualtv ohscrved.

As a result of the spin and parity forbidden nature of the ligand field

transitions of the high spin d5 ion, many simple salts and complexes of Fe(ll1) have

little or no colour. The hexaaqua ion has a very pale violet colour while [ F ~ F ~ I ~ ' is

v~rtually colourless. But intense colour in certrun high spin Fe(1U) compounds can

be ass~gned to ligand-metal charge transfer transitions or due to interligand

transltlons.

1.2. Cobalt -- General chemistry

'The most common oxidation states of cobalt are +2 and t3. A few CO' and

CO' ' compounds exist.%xamplss are the golden yellow CslCoFs, which may be

prepared by fluorination of Cs2CoC14, and the red-brown BazCo04 which contains

discrete C O O J ~ units. Most of the simple d t s exist in the +2 oxidation state and

crystallise from aqueous solution as CoXz .6h0 or CoX2.4HzO. co2* salts or

complexes In aqueuus solution readily dissociate to give the CO(HZO)~~ ' . The blue

of ~ 2 0 ) 6 " IS possible In very strong acids which is rapidly reduced by water to

CO(&O)~", liberating oxygen. Complexing by NH3 and other amine ligands or by

CN- stabilises the +3 oxidation state. Great care must be exercised in preparing

co2. complexes to avoid alkaline conditions, atmospheric oxidation or the presence

of other oxidising agents especially when dealing with amine ligands.

Many cobalt mines are easily prepared by oxidising arnmoniacd solutions

of Co(I1) salts by a current of air. For example, if the solution contains CoCll and

NO; or CQ~" ion$ the brown Erdmann's salt, [Co(NHj)z(NOz)s]Nh or the red

[CO(NH~)~CO~]CI will be crystallised out. The cystals of the bridged salt

[mH3)5Co.02.CHNH3)s](SCN)4 are formed in a strongly ammoniacal solution of

Co(SCN)l which is kept exposed to the atmosphere. In such preparation, mixtures

of cobalt amlne Ions are formed, both mononuclear and polynuclear.

1.2 1 Co(II) - Cwinat ion chemistry

Four, five and six coordinations are found with d7 ion and usually

octahedral (often tetragond 1 y distorted) stereochemistry is favoured in water and

other coord~nating solvents and such systems are usually high spin. But ligand

distortion and extensive x-delocalisation can result in partial low spin octahedral

cmrd~nat~on."

Tetrahedral complexes are very common, especially with anionic ligands

(e .g . , ~0x4~~). With uncharged mixed complexes such as [CoX2L], the monomeric

tetrahedral structure is often found in equilibrium with octahedral dimeric or

polymeric [CoX2Lr] via X bridges. Thus [Co(Py)zC12] exists both as blue

monomeric tetrahedral complex and as rather a more stable polymeric violet

octahedral species. But [Co(acac)z]l however appears to be tetrameric with

octahedral coordination. tlgmd polarisability plays an important role in assigning

the stereochemistry . More polarisable Iigands like phosphine and arsine favour

monomeric tetrahedral structure while less polarisable mine donors prefer

octabedrd coordination.

Square planar structures are less numerous, but are known in [Co(salen)]

and other Schiff base complexes and also in [Co(porphyrin)j and

[Co(phthalocy mine)], where the stronger chelati rig ligand favours a low spin d7

configuration

Five coordination is less common and is found with trigonal b~pyramidal

geometry. Such structures are usually encouraged by the ligand stereochemistry

and are usudly hgh spin. Few square pyramidal Co(II) structures are known like

low spin ( N E ~ I P ~ ~ ~ [ C O ( C N ) ~ ] .

1.2.2 ColH) - Electronic spectra and magnetism

Octahedral Co(1I) complexes are usually pink to violet (absorption

- 500 om) in colow whereas tetrahedral complexes are usually blue (absorption

- 600 nm) in colour The colour of octahedral Co(1I) complexes are dominated by

the "I',&F) --+ ?,AP) trans~tron (v3) with the two lower energy transit~ons, m.,

? I ~ F ) -t ' T ~ F ) and 'T~AF) -+ 'A~&F) occurring in the near LR and visible

regjons respectively. '' The T ground term results in temperature dependent orbital

contr~butrons lo the magnetrc moment with values (4.8-5.2 BM) falling off

appreciably wrth dccreas~ng temperature. Tetrahedral Co(11) complexes are

dominated by the broad and intense v3 transition 4 ~ z + 4 ~ ~ ( ~ ) with lower energy

1 A? -+ ?z(F) transition ( V I ) and 4 ~ 2 -+ S,(F) transition (vl ) The spin only

moment of 3.87 BM for the tetrahedral I~gand field is modified by rnlxing the lower

energy ?T(F) level into the ground 4 ~ 2 term via spin orbit coupling, and this result

rn greater magnetlc moment than the spin only value depending on the ligand. The

magnet# moment is temperature independent in this case also.

1.3. Nickel -- General chemistry

Nickel features a range of oxidation states from 0 to 14, althougli

organometallic ~ i ' and N I ' species have been known The most common

oxidat~on state by far is NI' , although Ni(0) complexes are also well known ~ i ' '

and N 1' ' species are relative1 y rare, while ~ i ' " complexes are established for certain

types of' 11gands.

Most of the nickel compounds in the solid state and in the aqueous solution

contam the metal III the +2 oxidatio~~ state. Amongst the compounds of nickel in

low oxidation states (-1, 0, + I ) , the nickeI(0) complexes are by far the most

intensively studied1 while ~ i ' has been claimed to be formed only in a few

organomdlic compounds.'' The reported Ni(0) complexes are all diamagnetic

which show that the ligands stabilise the 3dI0 configuration relative to the other

ones ~ i ' - complexes are comparatively much less numerous than the Ni(0)

complexes. Mononuclear NI" complexes are paramagnetic (bR = 1.7-2.4 BM)

generally with four coordinate pseudotetrahedral or five coordinate trigonal

bipyramidal geometry.

NI'' and ~ i ~ ' complexes are well known even though they are not very

12 numerous. Majority of these complexes are formed by ligands with highly

electronegat~ve donor atoms such as F, O and N All the reported ~ i " complexes

have a spln doublet round state origlnnting from the 3d7 free ion configuration and

are paramagnetic while the ~ i " complexes have a singlet ground state originating

from 3d6 configuration and are dtamagnetic.

3 1 Ni(ll) - Cowdination chemisby

The literature on the coordination chemistry of ~ i ~ ' is immense. The most

common oxidation state of nlckel is +2 with a dhnfiguration. Four, five and six

coordinattons are common geometries of ~ i ' ' depending upon the ligands present.

Figure I . I shows the d-orb~tal splitting pattern for tetrahedral, square planar and

octahedral N i ' .

Free ioll Octahedron Tetrago~l distortion ssuare planar

Figure 1.1. d-orbital splitting pattern for tetrahedral, octahedral, tetragondly dstorted and square planar N2-

The coordination of hIi2 1s relatively common with tetrahedral and square

planar geometries representing the two extreme possibilities. Good rt-donor

ligands such as halides tend to stabilise tetrahedral geometries while n-acceptor

llgands such as CN- favour square planar geometrres. Planar coordinatron for N?'

1s common and is linked to the stabilisation of this geometry for d%etal ion. An

interestlnp feature In four coordinate ~ i ' ' is the interconversion of paramagnetic

tetrahedral and diamagnetic square planar These changes from

tetrahedral to square planar geometries are influenced by the steric bulk 01' the,

llgands with tetrahedral coordinat~on, which is generally favoured by htghly bulky

l~gands Another ~rnportmt feature of square planar N I ~ ' complexes is their ablllty I

to coordinate extra ligands in svlutlon to set up equilibria between four, f i ve and six

wordinate complexes. Thus diamagnetic square planar complexes can be

transformed to pararnagnet~c octahedral ~i~ ' species in coordinating solvents or in

the presence of extra ligands. These transformations can be monitored by

electron~c spectroscopy. Aggregation of planar units can also occur in both solid

state and in solution to form paramagnetic polymers.

Five coord~nate conlplexes usually incorporate polychelates or tripodal N, P

and As donor llgands "' It IS observed in simpler systems such zts [NI(cN)~] '- and

[NI( PPhMe2 )l(L-N h]. Interestingly [N~(cN)~] ' has been crystalllsed and

charactensed as square- based pyramidal and a tngonal bipyrmidal species.

Octahedral coordination IS the mast common geometry for ~ i ' ' and is

observed In most of the complexes with an extremely wide range of mono and

polydentate ligands. Octahedral ~ i * ' has a large zero-field splitting and these

complexes do not generally show ESR spectra, although paramagnetically shifted

NMR spectra are observed in many cases.

1.3.2 Ni(I1) - E I W n i c s p W m and magnetism

The electronic spectral features of nickel(I1) complexes have been

excellently re~ewed.'~'~' Tetrahedral complexes are usually highly coloured (blue

or green) owing to the three expected d-d trans~tions, viz., ' l r ( ~ ) -+ ''T~(F) (vl ),

'T](F) + 'AI(F) (v2) and 'T ,(F) + "TP) (v3), although the observed spectra tend

to be complicated by spln orbtt coupling effects. Simplified Orgel dragram for

tetrahedral and octahedral ~ i l ' is shown in Figure 1.2.

Figure 1.2. Orgel diagram for tetrahedral and octahedral ~ i ' '

-Tetrahedral Pii2- would be expected to have two unpaired electrons with

~ 4 8 in the range 3.2-4.2 BM consistent with a T ground state for a G4tz:

configurat~on. The observed values of for these complexes are related to the

degree of distortion from pure tetrahedral geometry. Square planar ~ i ' ' complexes

are typically yellow, red or brown a d are invariably diamagnetic with a spin paired

configuration, although there are recent reports of paramagnetic planar bii2*

species. The five coordinate complexes may be paramagnetic (high spin

m- = 3.2-3.5 BM) or d~amagnetic (low spin).

Three d-d transitions, vl, v l and v3 respectively due to ' A Z ~ F ) + ' T ~ F ) ,

3 A2dF) -t 3 ~ ~ d ~ ) and 3 ~ 2 & ~ ) -t 'TI ,(P) transitions would be expected for ~ i " in

an octahedral field. The magnetic moment values of octahedral ~ i " are typically

In the range 2.9-3.3 BM.

1.4. Copper - G e n d chemistry

Copper occurs In a range of oxidation states 0 to 4. The oxidation states

cover the range Cu(0) in the metal, Cu(1) in the cuprous compounds, Cu(U) in

cupric compounds, and CulIII) and Cu(IV). The Cu{O) and Cu(IV) states are

extremely limited. The Cu(lI1) oxidation state is s~gnificantly more common, but

has only been charactensed for few compounds.23 The Cu(1) and Cu(l1) oxidation

states we the most abundant oxidation states of copper. Cu(1I) is the more stable of

the two under normal conditions and foms a number of simple compounds and

complexes. The Cu(1) state is less extensive and is readily oxidised to the Cu(I1)

state. Cu(II) forms numerous complexes, capable of forming good crystals. The

latter circumstance has led to a w d t h of crystal structure determinations to

charwterise the various regular and distoned stereochemistries of Cu(E1) ion, which

are associated with the Jahn-Teller effect.24 The chemistry of Cu(1) is very much

less extensive then that of Cu(U) and a number of accounts occur which describe

the chemlsuy of simple compounds of Cu(l) with less emphasis on the formation of

its complexes. The Cu(1Z) ion is particularly stable in aqueous solution as

[cu(H~o)~]~- cation from which complexes may be prepared by the addition of the

appropriate ligand, usually in water or in nun-aqueous solvents. The Cu(l1) cation

may be stabilised by complex formation against reduction to Cu(I) by reducing

anions, such as iodide and cyanide. These ions will reduce Cu(1I) to Cu(1) in

aqueous solution along with the precipitation of Cull2 and CuCN respectively. The

addition of 'bipy' to the solution prior to the addition of the r or CN- anions

prevents the redcctlon and d l o . ~ s the preparat~on of [Cu(b~py)~LXj' cation

contaning coordinated 1' and CN- respectively. 25.26

Like all other first-row transition metal(1I) cations, Cu(ll) forms cornplexcs

w~th coordinaon numbers four, five and six. Unlike the other first-row transition

metal ions, the Cu(1l) complexes are characterised by a variety of d i s t o r t i ~ n . ~ ~ . ~ ~

Mqority of six coordinate Cu(iI) compIexes involve an elongated tetragonal or

rhombic octahedral structure, with few involving a compressed tetragonal structure.

The tetrahedral geometry of Cu(1l) ion always involves a significant compression

along the Sq symmetry axis. Only the square planar geometry is regular for Cu(l1)

tons, but even here it involves a slight tetrahedral distortion.

In five coordinate sjsterns, Cu(l1) ion rarely involves a regular square

pyramidal stereochemistry but generaliy involves both an elongation and a trigonal

in-plane d~stortion'~ or less frequently a tetrahedral distortion. The trlgonal

bipyrarn~dal stereochemistry of Cu(1l) may be regular, but is more frequently

involk ed in a distortion towards square pyramidal geometry.

7.42 Cu(1ij - Eleci~onic spectra and magnetism

Most of the Cu(I1) complexes are blue or green because of the d-d

absorption In the 600-900 nm region. There are exceptions in which there is strong

charge transfer bands taii~ng into the visible region causing a red or brown

appearance. As mentioned above Cu(11) is subjected to Jahn-Teller distortion and a

regular octahedral complex is not formed in all cases so that the formal E, and

Tz, terms get splitted. The spectra do not usually correspond to the simple

'E, + 'T?, excitati~n'~''~ but rather io one based upon the following Flgure 1.3

Figure 1.3. Splitting of 'E, and 'TZ, states in Cu(1I).

Four coordinate Cu(I1) complexes are common, but the strict tetrahedral or

square pt anar stereachemishes are rare. Rather, some intermediate stereoc hemi stry

of approximate D 2 d symmetry is more usual and four transitions between the

d-orbitals may be available,30a31 The spectra of such complexes often show two or

three more or less resolved bands below about 20000 cm". The polmisation

properties of these bands have been studied in some detail in cemn cases2932

assisting in the assignments of the transitions involved.

The magnetic moment values of simple Cu(U) complexes are generally in

the range 1.7-2.2 BM irrespective of stereochemi~try.~~ There are a number of

polynuclear compounds with magnetic anorna~ies.'~ In these compounds there

occurs a weak coupling of unpaired electrons with one on each Cu(Il) ion. As a

result the magnetic moment value will be lowered from the normal value.

1.5. Applications of transition rnetai complexes

The tratls~tion metal complexes find extensive application in technology,

~ndustry and medicine. In the production of carbon monoxide by coke gasification

for the use In blast-furnaces, zdditives are needed to enhance the reduction of any

carbon dioxide formed back to carbon monoxide. Trisoxalatoiron has been found

effect~ve for this Iron compounds are effective smoke retarders for some

polymers. Thus tri~acetylacetonato)iron, FeSOs, FBI(SO~)~ and Fez03 are dl used

roughly in equal in the combustion tests on poly(viny1 chloride).36 [ F ~ ( c N ) ~ ] ~ - as

the free acid has been used as a corrosion inhibitor for metal surfaces.37 It also acts

as combustion inhibitors for aromatic polymers.3g Also [Fe(S2CNM-)3] is used as

zn tmportant fungicide.39

A number of cobalt complexes are important as driers for the conversion of

l~quids to solids, in inks, peints, varnishes and in other surface coatings. Most

irriportant in this respect are the cobalt 'soaps' which are conlplexes of carboxylate

anions such as oleate, stearate, naphthenate, octanoate, etc. Cobalt octanoate and

naphthenate have been investigated as driers for linseed oil on paper.40 Both

bis(acetyIacetonata)cobalt(II) and tri s(acety1acetonato)m bdt(ILI) have been found

to possess fimgicidal activity." Also bis(salicyIa1dehyde)diimine complexes of

cobalt take up and release molecular oxygen and is used in the purification of

oxygen 42

Nickel complexes are of great importance and an excellent review43 is

available on the use of them In heterogeneous cdys i s , electroplating, pigments,

ceramics and in hydrogen storage. Nickel complex of benzoic acid derivative

acts a5 a stabiliser against oxidathn of polybutadiene." Nickel complex of

N-henzoyl-N'-(2-stn11nophenyl)thiocwbamide have been - shown to exhibit

antifungal a.ctlv~t~.~"he organisms, 'Fyncularia oryzae' which causes rice blast

and 'Helminthosponus oryzae', which causes brown leaf spot, can be controlled

with Ni(I1) complexes of l-phenyl-3-methyl-4-nitroso-2-pyrazolin-5-one and

3-methyl-4-n~troso-2-Pyazolin-5-one.46

The applications of copper complexes are extremely varied and of great

Importance. Copper complexes are widely used as polymer additives, fungic~des

and crop protectors. They are also used in antifouling paints. Copper(l1) soaps, i.e.,

the oleate and stwaie, find application in antifouling paints and as fungicides for

textiles. Bis(acetylacetonato)copper(I1) has been used as a source of copper in

copper-vapour lasers4' and ~t has also been investigated as a substitute for

silver iodide as an ice-nucleating agent for the initiation of rain Copper

phthalocyanine is more effective as a smoke retardant for polystyrene than such

complexes of other first row transition Bis(acetylacetonato)copper(11) is

employed in the protection of fabncs against fungicidal atta~k.~' Also copper

complexes of the Ilgand N-benzoyl-Nr-(2-aminopheny1)thiocarbamide are used as

effective

1.6. First row transition metal complexes of antipyrine and its derivatives: a review

The organic literature reveals that the 4-position of antipyrine is susceptible

to a wide variety of reactions and therefore, by introducing suitable functional

groups at that position, a large number of usef'ul derivatives can be prepared.

htipyrine acts as a unidentate ligand by coordinating through the ring carbonyl

oxygen, but the derivatives of antipyrine include unidentaie and multidentate

Iigands. Transition metals are capable of forming stable complexes with ant ipyrine

these complexes AAP acts as a neutral bidentate ligand, coordinating through the

amino nitrogen and the ring carbonyl oxygen with a tetragonal ~ r a m i d a l geometry

around the metal ion. The complexes of cobalt(IZ), nickel(I1) and zinc(l1) with AAP

have been reported.'' The complexes have the general formula M(AAPh(NCS),

(where M = Co, Ni or Zn) and Co(AAP)rBr2. An octahedral geometry 1s assigned

to all these complexes.

The complexes of cobaIt(ll), nickeI(1I) and zinc(1l) with 4-dirnethylamino-

ant~pynne (DAAP) have been reported.58 The complexes have the general formula

M(DM)z(N03)a(Hz0)2 and M(DAAP)z(SCN)2 (where M = Co or Ni). An

cictabedrd geometry is assigned to all these complexes. The chloride complexes of

iron(III), wbalt(II), copper(U) and Linc(Il) with 4dimethylaminomethyI-

antipynne (DMAMA) have been reported by Boopathy el a/. 59 The complexes are of

the compositions [Ft$DMAMA)3]C13. [Co(DMAMA)2]C12. [Cu(DMAMA)C12] and

[Zn(DMAMA)Clz]. h thesc: ampiexes DMAMA acts as a bidentate ligand

coordinatrng through the carbony! oxygen and the tertiary nitrogen.

Slngh er a1 reportedm the synthesis and structural investigation of

chrornlurn(IIl), iron(I11), copper(ll), nickeI(IZ), cobalt(Il), vanadyl(II), manganese(II)

and zlnc(I1) complexes of 4-aminoantipyrine dithiocarbamate (AAPD). The

complexes have the general formula [M(AAPD)3] (where M = Cr or Fe) and

[M(AAPDhJ (where M = Cu, Ni, Co, VO, Mo or Zn). For Fe(lI1) and Cr(l1l)

complexes, an octahedral geometry is assigned while for the Cu(1I) and Co(I1)

complexes, a square planar geometry is proposed. The Mn(I1) and Zn(II)

complexes are of tetrahedral geometry while in the case of vanadyl complex a

square pyramidal geometry 1s assigned.

RadhaLnshnan el al. have rePned6' the synthesis and characteri sat ion of

copper(l1) complexes of the ligands salicylal-4-aminoantipyrine (HSAAP) and

2- hydroxynap hthal-4-aminoantipyrine (FIN AAP). The complexes have the general

formulae Cu(SAAP)X and Cu(NAAP)X (where X = Clod', N o 3 - , CHJCOO-,

C1- or Br'). The chloride and bromide complexes of HSAAP have a

tetrahedral geometry whereas a square or distorted octahedral structure is

ass~gned to the rest of the complexes. Manganese(LI), cobalt(11) and nickel(i1)

complexes of HSAAP, HNW and 2,4-dihydroqbed-4-minoantipqne

(HDAAP) have been reported.62 The Mn(lT) complexes are of the

compositions [Mn(HSAAP)(H20)C12] .H20, [Mn(HNAAP)(H20)zCI]C1. H 2 0

and [M~(HDAAP)(H~O)CII]. H z 0 . For the cobalt(11) complexes, the

cornpos~tians are [CO(HSAAP)(H~O)C~Z] .HzO, [Co(HNAAP)(H20)2CIJCl

and [ C O ( H D A A P ) ( H ~ O ) C ~ ~ ] . H ~ ~ . In the case of nickel(I1) complexes, the

compositions are [Ni(HSAM)(H20)2Cl]CI.HZ0, [Ni(HNAAPHH20)3]C12.4H20

and ~I(HDAAP)(H~O)C~~] .~H~O. In all the complexes, the coordmon occur through

the cart>onyl oxygen of the pyrazolone ring, the quinonoid oxygen and the azornethme

tulqm. C o r n complexes wth bases ~-hydm~icy~a~4aminoanhpynne

(HOSAAP), 3-methoxysalicylal4~0antipyrrne (HMAAP) and HNAAP have been

repdedh3 7he complexes are of the mposltions [Cu(OSAAP)HIO]CI.l/LHfi,

[ C U ( W ) H ~ O ] C ~ . ~ H ~ C ~ and [ C u O AAPhClz]. H2O. In [Cu(OSAAP)H20]CI. '/&O

and [Cu(MAAP)H20]C1 .2Hz0, the ljgands HOSAAP and HMAAP coordinate

to the metal ion through the phenolic oxygen, imine nitrogen, carbonyl oxygen and

oxygen of waer, whereas HNAAP coordinate to the metal ion through the phenolic

oxygen, imine nitrogen and the carbonyl oxygen. A tetragonal geometry is assigned

for [Cu(OSPLAP)H20]C1. %H20 and [Cu(MAAP)H20]CI .2H20, whereas square

pyramidal geometry is proposed for [Cu2(NAAP)2C12] .H20.

Copper(l1) complexes of 3.5-dimethylsalicyld-4-aminoantiPyrine

(HDMSMP) have been reporred.6" The complexes have the general composition

Cu(DMSAAP)X (where X - Clod-, N ~ J - , OAc-, CI- or Br') with distorted

octahedral configuration. The 1R spectra reveal that HDMSAAP behaves as

a monovalent tridentate ligand coordinating through phenolic oxygen,

carbanyl oxygen and azomethine nitrogen. Copper(1l) compIexes of

4-(2-thienylmethy1ideneamino)antipyrine (TAAP) and 4-furfuryIidene

aminoantipyrine (FAAP) have been reported.65 The complexes are

formulated as [Cu(TAAP)](C104)1, [Cu(FAAP)2](ClO4)2, [Cu(FAAP)(OH)Br],

[CU(TAAP)Z(NO,>,I, [CufFAAP)2(N03hl, [CU(TAAP~XJ~.~HIO and

[CU(FAAP)~X~].~H~O (where X -- C1- or Br' and n = 1 or 2). Spectral studies

~ndlcate bidentate nature of both the ligands in all these cornpIaxes except

in [Cu(TAAP)J(C1O4)2 in whcih a tridentate coordination behavlour is

observed. The complexes of cobalt(I1) and nicket(I1) with

4-[N-(4-dimethylaminobenzyIidene)amino]antipyrine (DABAAP) have been

synthesis& and i n ~ e s t l ~ a t e d . ~ ~ The complexes have the general compositions

[M(DABAAP)2X2] and [M(DABAAP)3](C104)2 (where M = Co or Ni and X = CI-,

Br , I - , NO3- or NCS-). In dl the complexes, the coordination of D A B A N occurs

In a b~dentate fashion through the carbonyl oxygen and azomethine nitrogen with

an octahedral geometry.

The synthesis and characterisation of zinc(ll) complexes of

4-N-acetylammoant~py~ne (AAAP) have been repo~ted.67 The complexes have the

general composttlon [M(AAAP)lXzJ (where X = CI-, Bi, I-, NCS' or OAc-). In all

the complexes, the coordination of AAAP occurs bidentately resulting an

octahedral environment around the metal ion. Copper(I1) and nickel(11) complexes

of 4-(2-qutnolyimethyleneam1no)antrpyr1ne (HQAAP) have been prepared

and i n ~ e s t i ~ a t e d . ~ ' Elemental analysis, IR and mass spectral data suggest

that the complexes are of the composition M(QAAP)* (where M = Ni or

Cu). Copper(II), nickel(I1) andcobalt(I1) complexes of the ligand

4-(2-pyndylrnethylene)minoantip~1ne (PAAP) have been The

complexes have the general formula [M(PAAP)2J(ClO)d.HzO (where M =. Cu, Ni

or Co). In these complexes, the ligand acts as a terdentate one coordinating

through the pyndyl n~trogen, carbonyl oxygen and azomethine nitrogen with an

octahedral geometry around the metd ions. The complexes of copper(II), nickel(l1)

and cmbalt(I1) with 0-N-tosylamino(oxy, mercapto)-R-qlidene-4-aminoantipyrine

(HTAAAP) have been synthesrsd and investigated.70 The chelates are of the

composrtion M(ThMP)2 (where M - Co, Ni or Cu). The ligand functions either

as brdentate or as tridentate in these complexes.

Copper(I1) and nickel(I1) complexes of the t~gand

4-(2-hydroxynaphthylaro)mt~pyrine (HN AZAP) have been reported." '' 'fhe

copper complexes have the general formula Cu(NAZAP)X (where X = CIOi, CI-,

Bi, I-, N03-or SO JI-) and nickeljII) complexes are of the compositions

N I(~-IN AZAP)z(C104)z, N I(HNAZAP)(NAZAP)X (where X =- CI-, Br-, or SO J2-)

and NI~(NAZAP)~X (where X .= I-, N 0 i or CHJCOO'). A square planar geometry

IS assigned to all these Cu(l1) complexes. In the case of Ni(I1) complexes, all the - -

complexes are octahedral except the iodide complex, which is tetrahedral 411 nature.

A 1-2 md-l igand ratio is observed in the case of Co(II) complex with an * ,

octahedral geometry. Iron(II1) complexes of 4-(2-hydroxynaphthy1azo)antipyrine

(MN .&ZAP), (2,4-dihydroxypheny1azo)antipyrine (HRAAP) and

4-(2-hydroxy-4-methylphe~rylazo)antipyrn (HCAAP) have been synthesised and

~nvestlgated 72 The complexes have the general compositions [Fe(NMA P tz IX.

[E'~(RAAP)z]X and [F~(CAI\P)~]X (where X = C1-, B f , C104-or SC).J2-). In rhese

complexes, the coordination occurs in a monovalent tridentate fashion resulting in a

h ~ g h spln octahedral geometry Copper(Il), cobalt(ll), nickel(1l) and manganese(l1)

complexes of anbpynne-4-mo-alpha-naphthol (HAPAN) have been reported."

The complexes are of the cornpos~tion M(APANh (where M = Ni or Mn),

Cu~(APAN)X~(Q(OH).H20 (where X = CI' or OAd) and CO(APAN)(OAC)(H~O)I.

The synthes~s and characterisation of iron(IIl), nickel(l1) and

cobatt(I1) complexes of antipyrine-4-azo-beta-ethylcyanoacetate (HAPECA)

and an tlppne-4-azo-beta-aCety1acetone (HAPAAT) have been reported.74 The

ligands HAPECA and HAPAA?' behave as neutral bidentate with Fe(1II) and as

monovalent tridentate with Ni(Il), Co(1I) and Cu(l1). The Fe(Il1) and Cu(II)

complexes of W E C A and CdII) complex of HAPAAT are binuclear involving

chloride or enolic oxygen bridges. The complexes of manganese(II), cobaIt(1I) and

nickel(1I) with HAPECA and HAPAAT have been synthesised and in~esti~ated.~'

The complexes have the general compositions M(APECA)2 and M(APAAT)*

(where M == Mn, Co or Ni). In these complexes, the ligands behave in a

monovalent tridentate fashron resulting an octahedral geometry to the complexes.

lron(II1) complex of antipyrine-4-azo-2-(5,5-dimethyl- 1,3-cyclohexane-dione) have

been reported7' In this complex, the ligand acts as a monovalent tridentate one ~n

I ~ t s azo form establishing a 1 :2 metal-Iigand stoichiometry.

The synthesis and charactensation of cobdt(1IT) complex of the ligand

N-antipynnyl-N'-lmzqIt)Eio~~ea (HAPBT) have been reported.N 7he wmplex is of

the wmposrtron co(APl3T)~ in th~s complex, the coordination occurs through the

benzoyl oxygen and sulphur r a l t i n g an whbedral gmrneiry around the Co(11) ion.

Shoukry eta!. reprre~i'~ the mthesis md charactensation of ccpperfII) and n~ckel(ll)

complexes of N-antip~nnyl-N'-3-pheny1-2-propenoyl t h i In these corn~lcxes

the coordinat~on occur In a bidentate fashion through the carbonyl oxygen and

sulphul- atoms. Complexes of copper(1l) and ~ron(lII) wlth 2,Z1,?"-trl(4-oxy-

mt~pyrine)tr~ethylam~ne have been reported '" M aurya er al. reportedR' the synthesis

and structural ~nvest~ga.tron of ntckel(I1) complexes of the Schiff bases (SB) der~ved

from 4-antlpynne carboxaldehyde and o, p and rn-anisidme, o, p and ~n-toluldlnc,

2,b and 2,4-xylldine. All the complexes have the general cornpos~t~on

[NI{SB)~(UAC)IJ An octahedral geometry is ass~gned to these complexes.

The preparat~on and character~sation of copper(lI), nickeljII) and cobalt(I1)

complexes of N-anttpynnyl-N'-acryloylthiourea have been reported.82 A 1:1

(metaf-l~gand) ratlo IS established in the case of copper and nickel complexes

whereas a 1 :2 stoichtornetry is observed in the case of cobalt complexes. Costisor

et al reportedm the synthests and structural investigation of copper(li), cobal t(l1)

and nlckel(I1) complexes of N,Nt-tetra(4-antipyrylmethy1)- 1,2-diaminoethane

(TAMEN). The complexes have the general formula Mz(TAMEN)Cld (where M =

Cu, Ni or Co) . The ligand TAMEN bridges the two metal centres via carbonyl

oxygen and the 1,2-diaminoethane nitrogen with a tetrahedral geometry around the

metal ions. Binuclear complexes of copper(II), nickel(II), cobalt(II), iron(II1) and

zlnc(II1 w~th N,N-b~s(antipyrylm&hyI)pipermine (BAMP) have been reported.'"

The complexes are of the compvsrtions M2(BAMP)X4 (where M = Cu, Uo, Mn or

Zn), Fe2(BAMP)& and MZn(BAMP)C14 (where M = Cu and C o with X - ClOi,

I - , NC'S-. or CI-) El-Sawaf el a/. reportedR' the synthesis and structural investigation

of iron(III), cabala), nickel(ll), copperjlI) and zinc@) complexes of 4-formylantipyrine

thiosemlcarbazone. The l~gand binds to the metal bidentately via the azomethine

r~rtrogen and the thione or th~olato sulphur in some complexes and tridentately by

~ncluding the carbonyl oxygen of the pyrazolone ri~ig also in some other complexes.