Chapter-5

MAGNETIC PROPERTIES OF COMPLEXES, ELECTRONIC SPECTRA AND ELECTRONIC STRUCTURE

131

Chapter-5

MAGNETIC PROPERTIES OF COMPLEXES AND ELECTRONIC

SPECTRA AND ELECTRONIC STRUCTURE

Section A: MAGNETIC PROPERTIES OF COMPLEXES

5A.1. INTRODUCTION

Magnetochemistry emerged in 1850s by Michel Faraday'. The primitive

applications of magnetochemistry were experimented and developed by Curie,

Langevin, Weiss and PascaP'^. Lewis during early 1920s identified the relationship

between the magnetic moment and molecular structure of the compounds^'*.

The magnetic properties of complexes of furan, benzofuran and naphthofuran

refers to the bonding of the central metal ion with the surrounding donor atoms in a

square planar, tetrahedral or octahedral geometry. The study of the magnetic

behavior of chemical compounds gives information about the magnetically

interesting atoms and its immediate surroundings. However, it fails to give any

information on the rest of the molecule.

A review of literature revealed that magnetic behavior of some complexes of

benzofuran derivatives have been studied'"". However there is no information on the

magnetic studies of complexes of naphthofuran derivatives.

In the present chapter the results of the investigation on magnetic properties

of Cu(II), Co(II), Ni(II), Cd(ll), Hg(Il) and Zn(ll) complexes of various

naphthofuran derivatives are presented.

132

5A.2. EXPERIMENTAL

5A.2.1. Materials

The ligands 2-acetylnaphthofuran(ANF), its oxime(ANFO), its

hydrazone(ANFH) and its semicarbazone(ANFSC) were synlhcsiscd by the method

described in the chapter-2. Similarly other ligands namely 2-benzoyl naphthofuran

oxime(BNFO), 2-benzoyl naphthofuran hydrazone(BNFH), 2-benzoyi naphthofuran

semicarbazone(BNFSC) and ethyl naphthofuran-2-carboxylate(ENFC) were

synthesised (chapter-2). All these ligands were complexed with Cu(II), Co(II),

Ni(II), Cd(II), Hg(II) and Zn(II) under appropriate conditions as described in earlier

chapter. In the measurements of magnetic susceptibility, mercury tetrathiocyanato

cobaltate(II), Hg[Co(CNS)4], was used as a calibrant and it was prepared by the

method described elsewhere . However a brief procedure is outlined here.

Aqueous solution of Analar cobalt sulphate heptahydrate (5.6 g) and Analar

ammonium thiocyanate (6.0 g) (both in 10 ml of distilled water) were added at the

boiling point at a stretch, to a filtered boiling solution of Analar mercuric chloride

(5.4 g) in distilled water (60 ml) with vigorous stirring. The mixture was boiled for

two more minutes with constant stirring. The product was washed several times with

water collected by filtration and dried at 120°C for 30 minutes.

5A.2.2. Instrument

The Gouy magnetic balance consisting of type NP-53 electromagnet with an

MP-1053 type DC power supply unit and semimicro electronic balance supplied by

AND Electronics Japan was used. A Gouy tube of internal diameter 8 mm and

133

length 20 cm was used throughout the experiment. All measurements were made on

solid complexes.

5A.2.3. Determination of magnetic properties

The clean, dry and empty Gouy tube was suspended using a thin glass rod

between the poles of the powerful electromagnet with its lower tip at the center of

the pole gap. Its weight was recorded. A current of 1.0 Amp, which in the specified

experimental set up produced a magnetic field of 1.27 k Gauss in the pole gap of

2.7 cm of the electromagnet, was passed for two minutes and the weight recorded.

The decrease in weight due to the diamagnetism of the glass tube was readily

observed on the digital scale of the balance. Care was taken to avoid prolonged

passage of current, which produced heating effects and there by produced bouyancy

errors in weighing. The weights were recorded by increasing the field strengths to

1.71, 2.58, 3.44, 4.27 and 4.68 k Gauss by passing the corresponding higher currents

of 1.5, 2.5, 3.5 4.5 and 5.0 Amperes respectively.

The instrument was turned off for an hour and the Gouy tube was filled with

double distilled water exactly upto a certain mark and its weight was recorded when

the field was off Mercury tetrathiocyanato cobaltate(II) in the form of fine powder

was filled into the clean and dry Gouy tube up to the same mark to which water was

taken by adding small amount of complex and tapping the bottom of the tube at each

time, carefully on a wooden surface to ensure the close packing without any air gap.

The Gouy tube filled with compound was then suspended in between the poles of the

magnet and weight was recorded in the absence of the magnetic field. The magnetic

field in the increasing order as practiced earlier was applied by allowing sufficient

134

time to attain stable field in the intervals and the corresponding weights were

recorded for each of the magnetic field applied.

The Gouy tube was emptied, cleaned, dried thoroughly and filled with fine

and dry powder of the naphthofuran complexes whose magnetic susceptibility XM

and moment ^eir was to be determined. The same procedure of increasing field

strength up to the values as applied for empty tube and reference compound was

followed to record the corresponding change in weight. The average values of three

independent trials were used for calculation of magnetic susceptibilities and

moments in different magnetic fields. The results are summarised in Tables 5A. 1 and

5A.2

From the apparent change in weight (F), the total pull (F) on the sample was

calculated as follows

F'= F - 6

Where 6 is the pull (a negative quantity) on the Gouy tube.

The gram magnetic susceptibility Xgof the sample was calculated from the relation

Xg = (a + PF')/w

where a and p are the constants for a particular Gouy tube,

a = 0.029 X specific volume

P = tube calibration constant

W = weightof the sample.

Magnetic moment of a particular sample is evaluated in terms of molar

magnetic susceptibility XM •

XM =Xg ^ molecular weight of the sample.

135

The molar susceptibility was corrected for the diamagnetism of the

constituents of the complex using Pascal's constants'^. The effective magnetic

moment, fieir (B.M.) was computed from the equation,

^elT=2.84[xM"^T]'^

Where T = absolute temperature at which the measurement is made and

XM - corrected molar susceptibility.

The Gouy tube was calibrated by using Hg[Co(SCN)4] as the standard. Xg of

the standard complex at 20° C is 16.44 X 10'* CGS units (decreases by 0.05 degree"'

rise of temp.).

5A.2.4. Basis for the calculation of magnetic susceptibility

The magnetic moments of the complexes can be used to diagnose their

stereochemical configurations. The magnetic susceptibility may be used in

conjunction with electronic spectra to establish the structure of the complexes'''. The

paramagnetism of a substance is due to the presence of unpaired electrons. Two

properties of an unpaired electron, the spin and orbital moments, contribute to the

magnitude of paramagnetic moment. The 'spin only' value of the magnetic moment

(is is given by the relation,

^s= [n(n+2)]"2

Where n = number of unpaired electrons.

The discrepancy between the measured magnetic moment and that calculated

from the above equation is due to the removal of orbital degeneracy of 'd' orbitals by

the ligands. For example, in Ni(II) complex the 'spin only' value is 2.83 B.M. and

136

the experimental magnetic moment fleir lies in the range 2.8 - 4.0 B.M. in octahedral

configuration.

From the magnetic point of view, the Ni(II) complexes can be classified into

three categories.

1. Six coordinated paramagnetic octahedral complexes,

2. Four coordinated paramagnetic tetrahedral complexes and

3. Four coordinated diamagnetic square planar complexes.

In octahedral (Oh)paramagnetic complexes, the orbital contribution to the

magnetic moment due to orbital degeneracy is absent. Due to spin-orbit coupling

between the first excited state T2g and the ground state A2g the observed

magnetic moments obey the relation,

U =2.83 / 'off 'eff 10Dq

Where X, is the spin-orbit coupling constant. If X, is -315 cm'' ( the value for free

Ni(II)), the expected magnetic moment will be 10% higher than the 'spin only'

value of 2.83 B.M for an Oh Ni(II) complex. Usually octahedral Ni(ll) complexes

therefore have the magnetic moments in the range 2.9 to 3.3 B.M'^ On the other

hand four coordinated tetrahedral Ni(II) complexes with ground state ^T|(F) have

some orbital contribution to the observed magnetic moment. In addition to this,

spin-orbit coupling also causes a mixing of T2g(F) with T| (F) ground state as in Oi,

complexes. Hence tetrahedral Ni(II) complexes show an increased magnetic

moments as compared to the octahedral ones. The observed magnetic moments

generally lie in the range 3.6 - 4.1 B.M.'^. The four coordinated Ni(II) complexes

137

with planar configuration are invariably diamagnetic with spin singlet ground state

'A,g.

The magnetic susceptibility for a given material consists of contributions for

paramagnetic and diamagnetic susceptibilities, the former being much greater.

However, for molecules containing a large number of diamagnetic atoms per

paramagnetic atom (as in a metal complex with large organic ligands), the

diamagnetic contribution is appreciable. Hence measured susccplibilily should be

corrected by subtracting the diamagnetic contribution from it. It is known that

diamagnetism is an additive property and diamagnetism of a molecule can be

obtained by adding the diamagnetism of each atom in the molecule.

Paramagnetism = Measured susceptibility - Diamagnetic susceptibility.

This formula leads to a positive correction to the measured susceptibility

because the value of diamagnetic susceptibility is negative. The paramagnetic

susceptibility is converted into magnetic moment by using the equation,

|leff= 2.84[x'gXT]"^

Where T = absolute temperature at which the measurements are made,

X'g = corrected magnetic susceptibility for diamagnetic effects and

|ien"= corrected magnetic moment (B.M.) of the material.

5A.3. RESULTS AND DISCUSSION

The binding force among various atoms within the complex in naphthofuran

derivatives could be the cause of electrostatic forces and covalcnt bonding or

combination of both. The bonds operating between the donor atoms of naphthofuran

138

derivatives of the ligand and the central metal ion Cu(II), Co(II), Ni(Il), Cd(ll),

Hg(II) and Zn(II) are essentially covalent in nature. For bond formation, it is

essential to have bonding atoms to possess stable orbitals having electrons with

opposite spins. Such bonds are commonly called covalent and are characteristic of

having definite direction in space. It is possible to deduce the nature of orbitals

involved and spatial configuration of the complex with the knowledge of number of

electrons used in covalent bond formation. Magnetic properties of the complex

depend more on the electronic structure of the central metal ion rather than the nature

of the ligand. The outer orbital electronic configurations of Co(II), Ni(II) and Cu(II)

complexes of naphthofuran derivatives is diagrammatically represented as shown in

theFigSA.l.

The magnetic moment resulting from the motion of the electrons constitute a

major part in the measured magnetic properties of the substances. When a substance

containing paired sets of electrons in all the orbitals is subjected to experience a

magnetic field, field induced motion of electrons generate a magnetic field as

opposed to the applied field. As a result, the substance will be repelled by the applied

magnetic field and such materials are said to be diamagnetic. Diamagnctic effect is

absent in the absence of magnetic field but this effect is exhibited when the

substance is subjected to a magnetic field. Permanent magnetic moment is exhibited

by the substances containing one or more unpaired electrons. When such materials

are placed in an external magnetic field, the magnetic moments align themselves in

the direction of the applied field and are attracted to it. Such substances are known

as paramagnetic. The magnitude of paramagnetic effect is one or two limes higher

139

than that of the diamagnetic effect. Therefore, a paramagnetism dominates over the

diamagnetism in all the materials containing unpaired electrons. As mentioned

earlier total paramagnetic moment consist of two parts, one is spin-only magnetic

moment and the other one is orbital contribution to it.

Hence experimentally determined values of magnetic moments usually differ

from the spin-only values calculated by using equation mentioned in page no. 135 .

If the orbital motion makes its full contribution to the magnetic moments, the

magnetic moment is given by,

^n+L = ^ 4 n ( n + l ) + L(L+l)

where L represents the orbital angular momentum quantum number of the electrons.

Spin-orbital coupling involves electron occupation of equivalent degenerate orbilals

which enable the electron to revolve around an axis. The values of 1.1 are often

observed to exceed [Xn, but indeed are as high as )in+L- This may be due to partial or

total quenching of the orbital moments

The present assignment of structures of complexes, in relation with magnetic

susceptibilities measurements is based upon similar kind of observations made by

different authors which have been summarized below.

Pate! et al'^ assigned octahedral geometry to Cu(II) complex which showed

magnetic moment value between 1.77 and 1.88 B.M, close to spin only value

1.73 B.M. expected for an unpaired electron. Cotton et al'* found that magnetic

moment values of Cu(II) complexes are in between 3.2 and 3.22 B.M. which are in

good agreement with high spin octahedral geometry. All the Cu(M) complexes arc

found to be paramagnetic and the magnetic moment values are coincided with that of

140

corresponding one unpaired electron with spin only value of 1.73 B.M. by Mrudula

Rao et al". KJiare et al^" observed magnetic moment value of Cu{ll) complexes in

the range of 2.05 B.M. and assigned octahedral geometry. Complexes of Cu(II) have

been assigned octahedral geometry with the 'magnetic moment value around

2.05 B.M ' . Characteristic distorted tetrahedral coordination sphere was assigned

to Co(II) complexes showing magnetic moment in the range of 4.5 to 4.8 B.M ''' '*.

Octahedral geometry was assigned to ketonic complexes of Co(II) showing magnetic

moment value of 5.2 B.M. by Lever^'and Allan^*. Octahedral geometry for Ni(II)

complex was confirmed by Sharma et al '' and Moharana et al * depending upon the

effective magnetic moment values of these complexes in the range of 2.8 to 3.0 B.M.

Figgis et al assigned octahedral structure for Ni(II) complexes depending upon the

magnetic moment values which fall in the range of 3.39 to 3.62 B.M. Similarly

Mayadevi et al , Nawar et al"" and Madhu et aP^ assigned distorted tetrahedral

geometry to the complexes of Ni(II) with 2,l-Di(imimo- 4'-antipyrinyl)ethane and

4-N-(4'-antipyromethylidene)amino antipyrine, the magnetic moment value of which

is observed to be 4.1.B.M.

Depending upon these observations, the different geometries have been

assigned to Cu(II), Ni(II) and Co(II) complexes of different naphthofuran derivaties

as shown in the Table 5A.2.

All the complexes of Cd(II), Hg(II) and Zn(II) obtained from various

naphthofuran derivatives are found to be diamagnetic, expected of such d'° system.

In all these cases magnetic suceptibility values are found to be negative as shown in

the Table 5A.3

141

Co 2 +

NJ .2+

Cu 2 +

Co

Ni

2+

2+

Cu 2+

U1M 1 1

1L1M 1 1

11 11 11 1

1MM 1 1

11 11 11 1 T]

11 11 11 11 1

B B B B B B

• • I t

• • • •

• • • t

sp^d^

sp^d^

SP'

SP'

SP'

Figure 5A. 1. The diagrammatic representation of the electronic configuration of the

outer orbital of the metals. The black dots represent electrons donated

by ligand.

142

Table 5A. 1. Magnetic susceptibility data for the Cu(II), Ni(II) and Co(II) complexes

of naphthofuran derivatives

SI. Complexes Field strengh Magnetic |ic(T No. K Gauss susceptibility

XMXIO-**

(B.M.)

1.27 1531.20 1.98

1.71 1490.63 1.93

1 CuANF 2.58 1506.32 1.92

3.44 1604.73 1.90

4.27 1422.15 1.88

4.68 1459.17 1.86

1.27 4769.61 3.69

1.71 5427.76 3.64

2 NiANF 2.58 4576.94 3.41

3.44 5586.03 3.40

4.27 4459.84 3.34

4.68 4731.93 3.30

1.27 5288.62 4.90

1.71 6819.54 4.89

3 CoANF 2.58 5553.05 4.63

3.44 6123.66 4.40

4.27 6443.76 3.99

4.68 6808.61 4.80

1.27 1603.65 2.22

1.71 1548.90 2.10

4 Cu ANl'O 2.58 1564.55 2.05

3.44 1736.65 2.00

4.27 1556.72 1.98

4.68 1642.76 1.92

143

Table 5A. 1 .continued

1.27 2338.79 3.45

1.71 2503.24 3.40

5 Ni ANFO 2.58 2620.57 3.35

3.44 2659.70 3.20

4.27 2698.81 3.15

4.68 2464.13 2.99

1.27 3113.40 4.90

1.71 4341.72 4.70

6 Co ANFO 2.58 3935.27 4.66

3.44 4240.11 4.59

4.27 4304.77 4.26

4.68 4387.90 3.98

1.27 2271.00 2.74

1.71 2189.64 2.50

7 Cu ANFH 2.58 2180.16 2.35

3.44 3090.60 2.31

4.27 2565.79 2.30

4.68 1836.20 2.12

1.27 4678.44 3.73

1.71 5329.61 3.69

8 Ni ANFH 2.58 5694.26 3.64

3.44 5586.03 3.60

4.27 4731.93 3.40

4.68 5427.76 3.38

1.27 6143.50 4.50

1.71 6531.20 4.38

9 Co ANFH 2.58 6710.14 4.20

144

Table 5A. 1 .continued

3.44 5815.45 4.12

4.27 6262.79 4.20

4.68 5964.56 3.90

1.27 1368.67 1.99

1.71 1353.62 1.87

10 CuANFSC 2.58 1396.03 1.84

3.44 1371.50 1.83

4.27 1433.26 1.82

4.68 1629.68 1.80

1.27 4022.40 3.61

1.71 3984.17 3.30

11 Ni ANFSC 2.58 4158.73 3.26

3.44 5344.42 3.18

4.27 4476.94 3.13

4.68 4348.31 3.10

1.27 5842.20 4.44

1.71 5868.88 4.40

12 Co ANFSC 2.58 5949.27 4.38

3.44 5225.71 4.10

4.27 5198.91 3.90

4.68 5493.69 3.88

1.27 1656.87 2.02

1.71 1600.54 2.01

13 CuBNFO 2.58 1559.91 2.00

3.44 1700.33 1.97

4.27 1576.94 1.96

4.68 1639.08 1.92

145

Table 5A. 1.continued

1.27 4474.50 3.34

1.71 4067.72 3.30

14 Ni BNFO 2.58 4338.90 3.27

3.44 4433.81 3.26

4.27 4528.72 3.30

4.68 4420.24 3.00

1.27 5694.78 4.42

1.71 5288.01 4.41

15 Co BNFO 2.58 5979.51 4.39

3.44 5993.06 4.20

4.27 5952.83 4.10

4.68 5559.59 3.90

1.27 1490.63 1.98

1.71 1604.73 1.93

16 Cu BNFH 2.58 1506.32 1.92

3.44 1422.15 1.90

4.27 1490.63 1.90

4.68 1531.20 1.86

1.27 2459.43 3.15

1.71 2324.55 3.10

17 Ni BNFH 2.58 2261.08 3.10

3.44 2380.10 3.00

4.27 2459.43 2.93

4.68 2499.00 2.85

1.27 3133.66 4.25

1.71 3252.65 4.22

18 GO BNFH 2.58 3332.00 4.20

146

Table 5 A. 1 .continued

3.44 3078.13 4.10

4.27 3371.66 3.95

4.68 3371.60 3.88

1.27 1478.50 2.06

1.71 1486.33 2.02

19 CuBNFSC 2.58 1490.63 1.97

3.44 1603.59 1.90

4.27 1740.84 1.90

4.68 1700.33 1.89

1.27 4576.94 3.34

1.71 4474.50 3.30

20 Ni BNFSC 2.58 4338.90 3.28

3.44 4348.31 3.27

4.27 4411.76 3.26

4.68 4386.00 3.20

1.27 5204.17 4.20

1.71 5365.13 4.10

21 Co BNFSC 2.58 4828.61 4.00

3.44 5633.37 3.95

4.27 5499.24 3.88

4.68 5298.04 3.60

1.27 2009.97 2.21

1.71 1591.21 2.00

22 Cu ENFC 2.58 1630.63 1.97

3.44 1527.45 1.93

4.27 1491.44 1.90

4.68 1410.89 1.85

147

Table 5A. 1 .continued

1.27 3441.15 3.40

1.71 4731.93 3.34

23 Ni ENFC 2.58 4576.94 3.30

3.44 4348.31 3.26

4.27 4474.50 3.10

4.68 4203.30 2.90

1.27 5898.14 4.50

1.71 5396.45 4.40

24 Co ENFC 2.58 5965.94 4.35

3.44 5559.17 4.10

4.27 5260.87 3.98

4.68 6101.52 3.88

48

Table 5A.2. Geometry assigned to different complexes

SI No Complexes HcffB.M Geometry assigned

I CuANF 1.92 Octahedral

2 CoANF 4.90 Octahedral

3 NiANF 3.40 Octahedral

4 Cu ANFO 2.00 Octahedral

5 CoANFO 4.70 Octahedral

6 Ni ANFO 3.40 Octahedral

7 Cu ANFH 2.30 Tetrahedral

8 Co ANFH 4.50 Tetrahedral

9 Ni ANFH 3.60 Tetrahedral

10 Cu ANFSC 1.80 Octahedral

11 Co ANFSC 4.40 Tetrahedral

12 Ni ANFSC 3.10 Octahedral

13 Cu BNFO 1.92 Octahedral

14 Co BNFO 4.20 Tetrahedral

15 Ni BNFO 3.00 Octahedral

16 Cu BNFH 1.92 Octahedral

17 Co BNFH 4.20 Tetrahedral

18 Ni BNFH 3.00 Octahedral

19 Cu BNFSC 1.90 Octahedral

20 Co BNFSC 4.00 Tetrahedral

21 Ni BNFSC 3.20 Octahedral

22 Cu ENFC 1.85 Octahedral

23 Co ENFC 4.40 Tetrahedral

24 NiENFC 3.10 Octahedral

149

Table 5A.3. Magnetic susceptibility data for the Cd(II), Hg(II) and Zn(II) complexes

of naphthofuran derivatives.

SI. Complexes Field strengh No. K Gauss

Magnetic susceptibility XMXIO-**

Men-B.M.

1. CdANF 2.58 -233.18

2. HgANF 2.58 -280.34

3. ZnANF 2.58 -360.70

4. Cd ANFO 2.58 -340.50

5. Hg ANFO 2.58 -302.64

6. Zn ANFO 2.58 -198.03

7. Cd ANFH 2.58 -253.73

8. Zn BNFO 2.58 -220.19

9. Cd ENFC 2.58 -399.90

10. Zn BNFH 2.58 -223.29

11. Cd BNFSC 2.58 -340.76

12. Hg ANFSC 2.58 -305.25

13. Zn BNFSC 2.58 -280.34

14. Hg BNFSC 2.58 -253.73

15. Cd BNFH 2.58 -307.50

16. Hg ANFH 2.58 -320.40

17. Cd ANFSC 2.58 -218.50

18. Cd BNFO 2.58 -320.58

150

5A.4. REFFRENCES

1. M. Faraday, "Experimental Researches", Vol III, Tailor and Francis,

London(1855).

2. P. Curie, Am. Chim. Phys., 5, 289(1895).

3. P. Langevin, Am. Chim. Phy., 5, 70(1905).

4. P. Langevin, Am. Chim. Phy., 4, 678(1905).

5. P. Weiss, Phys., 6,353(1907)

6. P. Pascal, Am. Chim. Phys.. 147, 56, 242, 742(1908)

7. G.N. Lewis, "Valence and the Structure of Atoms and Molecules ", Chemical

Catalog Co., New York(1923).

8. G.N. Lewis, Chem. Rev., 1, 231(1924).

9. F.A. Cotton and G. Wilkinson, " Advanced Inorganic Chemistry", Wiley

Eastern, New Delhi( 1972).

10. F.M. Iskandar, A.M. EL. Agan, L.S. Refaat and S.EL. Sayed, Inorg. Chim.

Acta., 14, 167(1975).

11. N.S. Biradar, B.R. Patil and V. H. Kulkami, Monatsh Chem., 107,251 (1976).

12. B.N. Figgis and R.S. Nyholm, J. Chem. Soc, 4190(1958).

13. P.W. Selwood, "Magnelochemistry", Interscience, New York( 1960).

14. R.S. Drago, "Physical Methods in Inorganic Chemistry", Reinhold

Plublishing Corporation, New York(1965).

15. L. Sacconi, Trans. Metal Chem., 4,199(1968).

16. B.N. Figgis, J. Lewis, F.B. Mabbs and G.A. Webbs, Nature, 203,

1138(1964).

151

17. B.K. Patel and M.M. Patel, J. Indian Chem. Soc, 67.186(1990).

18. F.A. Cotton and M. Goodgame, J. Phys. Chem., 65. 191 (1961).

19. B.V. Mrudula Rao, G. Venkatanarayana and P. Lingaiah, Indian J. Chem.,

27A, 261(1988).

20. Mahima Khare and A.P. Mishra, J. Indian Chem. Soc, 11,256(2000).

21. A.B.P. Lever, '^Inorganic Electronic Spectroscopy 2"'' Ed. Elsevier,

Amsterdam(1984).

22. R.L. Dutta and A. Syamal, "Elements of Magnetochemistry", 2" Ed.

Affiliated East West, New Delhi(1993).

23. B.N. Figgis and J. Lewis, "The Magnetic Properties of Transtition Metal

Complexes", in "Progress in Inorganic Chemistry", Ed. F. A. Cotton,

Interscience, New York, 6, 179(1964).

24. 0. Costisor, M. Mracec, Z. Jori, I. Labadi and W. Linert, Synth. React. Inorg.

Met-Org Cftem., 30(8), 1489(2000).

25. A.B.P. Lever, "Inorganic Electronic Spectroscopy ", Elsevier, New

York(1968).

26. J.R. Allan, D.H. Brown, R.H. Nutlal and D.W.A. Sharp, J. Inorg Nucl.

Chem., 26, \S65i\964).

27. C.L. Sharma and M.S. Isalm, Synth. React. Inorg. Met-Org. Chem., 10,

553(1986).

28. S.N. Moharana and K.C. Dash, Indian J. Chem., 8,1023(1970).

29. B.N. Figgis and J. Lewis, Prog Inorg. Chem., 4,185(1964).

152

30. S. Mayadevi and K.M.M. Yusuff, Synth. React. Inorg. Met-Org. Chem., 27,

319(1997).

31. N. Nawar, M.A. Khattab, M. M. Bekheit and A.H. El- Kaddah, Indian J.

C//em.,35A, 308(1996).

32. N.T. Madhu and P.K. Radhakrishnan, Synth. React. Inorg. Met-Org. Chem.,

30, 1561(2000).

153

Section B: ELECTRONIC SPECTRA AND ELECTRONIC STRUCTURE

5B.1. EXPERIMENTAL

The Stock solutions of 1X10''' M concentrations of the complexes were

prepared by weighing and dissolving the required amount of sample in extra pure AR

diniclliyl formamidc. Solutions of suitable concentrations were prepared by

appropriate dilution of the stock solution in dimethyl formamide the. A UV-visible

spectrophotometer UV-160A from Shimadzu corporation, Japan with 1 cm matched

cells and JASCO model UVIDEC - 610 double beam spectrophotometer were used

for the electronic spectral measurements.

5B.2. THEORETICAL BACKGOUND

Molecular absorption in the ultraviolet (200-400 nm) and the visible (400-

800 nm) regions of the electromagnetic radiation is dependent on the valence shell

electronic structure of the molecule. Absorption of energy resulting in the transition

of electrons from orbitals in the ground state to the higher orbitals in an excited state

of the molecule is quantized. The total energy of a molecule is the sum of its

electronic, vibrational and rotational energies. The change in energy AE, of a

molecule upon absorption of ultraviolet-visible radiations is accompanied by changes

in vibrational and rotational energies. The spectra of ions or molecules in solutions

generally contain broad bands arising partly from the superimposition of vibrational

and some times rotational energy changes. For an electronic transition to take place

a very short time (about 10"' sec) is required. The following selection rules arc

pertinent to electronic absorption spectroscopy.

154

1. Transitions between states of different multiplicity are forbidden i.e.,

electron transitions in which spin of electron changes are not allowed.

2. In a molecule which has center of symmetry, transitions between two

gerade or two ungerade states (i.e., g—>g or u->u ) are Laporte

forbidden. The allowed transitions are g->u and u->g.

3. Simultaneous excitation of more than one electron is forbidden.

The principle characteristics of an absorption band are its position and

intensity. The position of an absorption corresponds to the wavelength of radiation

whose energy is equal to that required for an electronic transition. Intensity of

transition is largely dependent on two factors: the probability of interaction between

the radiation energy and the electronic system to raise the ground level to an excited

state and polarity of the excited state. The probability of transition is proportional to

the square of the transition moment or dipole moment of transition. The dipole

moment of transition is proportional to the change in the electronic charge

distribution occurring during excitation. Intense absorption occurs when transition is

accompanied by a large change in the transition moment. Absorptions with Enin.x>

10'' are considered as very strong absorptions and strong absorptions correspond to

Gmnx values from about 10 to lO"*. Absorptions with Zmax <10^ arc considered to be

forbidden transitions.

The wavelength of maximum absorption, X^ax. and intensity of absorption

must be measured accurately in order to obtain useful information from the

electronic spectrum of a compound. The compound should be dissolved in some

suitable solvent that does not itself absorb light in the wavelength region under

155

investigation. The electronic spectrum can be obtained mostly by plotting absorbance

verses wavelength (nm). Beer's law gives a convenient relationship of absorption

intensity with concentration. The relationship is mathematically expressed as

A = ebc = log (I/T)

Where A = absorbance,

8 = molar absorptivity (ImoP' cm"'),

b = the path length (cm),

c = concentration of the solute (mol/1),

T = transmittance = I / lo,

I = intensity of the transmitted light,

lo = intensity of the radiant energy.

For a particular compound, the molar absorptivity at a given wavelength is

constant and is most commonly expressed as Emax. There are six types of electronic

transitions n -> n*, n-> n*, n -> a*, o -> a*, charge transfer and ligand field out

of which o -^ a* is of less importance as it occurs in far ultraviolet region

(<200 nm).

Full discussion on the electronic spectroscopy with respect to the

fundamental, theoretical and applied aspects can be found in the literature'"^.

The electronic spectra of the selected complexes have been studied to procure

an additional support for the conclusion adduced from the magnetic data.

156

5B.3. RESULTS AND DISCUSSION

The observed band maxima for the complexes are systematized in Table

5B.1, 5B.2 and 5B.3 along with the calculated ligand field parameters. These band

maxima have been assigned to various transitions observed for Co(II), Ni(II) and

Cu(II) complexes.

5B.3.1. Cobalt(II) complexes.

Hexa coordinated cobalt(II) complexes.

Cobalt(II) is a d ion having "F ground state and hence gives rise to three

transitions viz., ''Tig-^ ''Tag (F) /Tig-* ^Aj^ (F) and ""Tig- ''Tig (P) in an octaliedral

field. These transitions are sensitive to the nature of the interacting ligands and show

variations. This is obvious from the range of data available. These transitions are

reported to occur respectively in the following regions i.e. 8,000-10,000 cm'' ''T|g->

"Tzg (F), around 12,000 cm'' ''T,g-> "AjgCF) and around 20,000 cm'' "Tjg^ "TigCP).

The ''T|g-> ''Tig (P) transition some times occurs as a shoulder to the high intensity

charge transfer band. Patel et. al^ have reported three bands at 9,200 cm'' 17,900 cm"

' 19,600 cm'' assignable to "Tig-^ %^ (F), "Tig-^ "Ajg (F) and ''T|g-> "Tig (P) for

cobalt(II) complexes of Salicylideneanthranilic acid 2,2-bipyridylaminc. According

to Grag et. al^. cobalt(II) complexes of bidentate Schiff base display three bands

around 9,010 cm'', 1,8181 cm'' and 18,948 cm ' attributable to "Tig^ "Tag (F),

' 'Tig^ ''A2g (F) and ''Tig-> ''Tig (P) transitions suggestive of octaliedral geometry

around cobalt(II). Ligand field parameters such as ligand field stabilisation energy

(Dq), Racah parameter (B) and inter electronic parameter (P) have been calculated as

per the standard method delineated for one of the cobalt(ll) complexes at the end of

157

the chapter. The V2/V1 ratio for hexa coordinate cobait(II) complexes lies in the range

of 2.1-2.2 and it is closure to Ihc range il" Ihc complex is more ionic, l-or the

complexes under study (he V2/V1 rallo is around 2.08 indicating (hat the complexes

are closure to the ionic system. For octahedral cobalt(II) complexes the Dq/B ratio

approximately lies around 1.3 and in weak ligand field it shows variation indicating

distortion (i.e. tetragonal distortion). The observed ratio of Dq/B for these complexes

lies around 1.11 as against 1.3 suggesting lower order of symmetry, p and p% lie in

the range (Table 5B.1) expected for hexa coordinated cobalt(II) complexes. All these

observations pin point that the cobalt(ll) have hexa coordinate structure.

Tetrahcdral cobalt(II) complexes

Various transition observed for tetrahedral cobalt(ll) complexes under study

are listed in Table 5B. 1.

Cobalt(II) complexes in tetrahedral ligand fields exhibit two bands belonging

to ' ' A 2 - > ' ' T | (F) and ' 'A2-> ' 'TI ( P ) which appear in the near infrared and visible

regions as multi component bands. The transition occurring in the visible region

(1,500-2,500 cm'") has high intensity and large band width and is too larger to be

accounted for spin orbit coupling. For the complexes listed in the Table 5B.1 two

multi component bands of high intensity have been observed and they have been

assigned to various transitions (Table 5B.1). The transition ' ' A 2 - ^ ' ' T | (P) occurs in the

range of 22,000 - 23,280 cm"' and the other band is found in the range of 8,403-

10,100 cm"'and is attributed to the ' 'A2-> ' 'TI ( F ) transition. These assignments

suggests that in these complexes cobalt(ll) has tetrahedral geometry. These

observations supplicates the conclusions achieved in the Chapter 5A. Further these

158

(assignments) have gained supports in the assignment by Khare and Mishra' for

cobalt(Il) tetrahedral complexes. They have assigned ' 'A2^ ' 'T2 (F) and ' 'A2->''TI (P)

at 14,531 cm''and 19,455 cm''.

5B.3.2. Nickel(II) complexes

llcxa coordinate nickcl(II) complexes

Nickel(Il) is a d ion with F2 ground state and displays three transitions

namely A2g -^ ^T2g(F), A2g -> ^Tig(F) and A2g -^ ^T|g(P), of these the third

transition most of the time occurs at the tail end of the charge transfer band as a

shoulder. The other bands occur either as weak or medium intensity bands. These

three bands appearing in the following regions: 9,000 -11,000 cm"', 14,000-18,000

cm"' and 25,000-30,000 cm"' are attributed to A2g -^ ^T2g(F), A2g -> ^T|g(F) and

•'A2g-> ^Tig(P)*. Patel and Co-workers' observed three bands around 10,525 cm"',

16,970 cm"' and 25,000 cm"' for Ni(II) complexes of schiff bases, in the other

incident the same authors report 10,000 cm"', 18,000 cm"' and 24,000 cm"' forNi(II)

complexes and attribute these bands to ''A2g -> ^T2g(F), A2g -^ ''Tig(F) and A2g ->

^Tig(P). In view of all these observations the bands found in the regions 8,000-9,800

cm"'(vi), 12,900 - 15,380 cm"' (va) and around 25,000 cm"' (V3) are assigned

respectively to the A2g -^ •'T2g(F), A2g -> ^Tig(F) and A2g -> ^Tig(P) transitions.

The calculated parameters (Table 5B.2) suggest that in these complexes Ni(II) has

tetragonally distorted octahedral geometry. The values observed are lower than the

theoretical values suggesting that these complexes have distorted octahedral

geometry.

159

5B.3.3. Coppcr(II) complexes

Copper(ll) is a d' ion aiid looked upon as a liole equivalent to d and hence

one can expect copper(ll) spectra akin to Ti(IIl) with inverted energy levels, thus the

spectrum should have been simple. But the copper(II) complex are subjected to

considerable distortion that renders the absorption spectra quite complex. ^D ground

state of copper(II) splits into ^Eg and ^T2g in an octahedral field and ^Eg is subjected

to considerable Jahn-Teller distortions. Copper(II) complexes which are green or

blue are letragonally distorted with four short bands in xy plane and two metal -

ligand longer bands along z axis above and below the xy plane. In the extreme case

of distortion the octahedral geometry terminates into four coordinate square-planar

geometry. Such complexes give rise to one absorption band in the region near 16,000

cm''. Rama Rao et.al'°. have reported two bands around 16,670 cm'' and 21,740 cm'

for copper(II) complexes of 4-hydrazone-benzofuro[3,2-d]pyrimidine with

2-hydroxy-l-naphthaldehyde and have concluded that the complexes possess

distorted octahedral geometry. Hiremath et.al". observed a single broad band in the

region 13,332-16,670 cm'' and attribute same to the ^Eg ->^T2g transition. They

attribute the broadness of the band to the dynamic Jahn-Teller distortion. A few other

authors'^'''' report a broad band in the region 16,393-12,658 cm'' in copper(ll)

complexes and assigned this to Eg -> T2g transition. In view of all these

observations the broad band observed in the region 12,500-14,080 cm'' is regarded

as due to ^Eg —> T2g transition and complexes have distorted octahedral structure.

160

Calculation of Dq, B and p for octahedral Co(II) complexes

For Co(II), in an octaliedral field, ligand field stabilization energy (Dq),

Racah parameter (B) and inter-electronic parameter (P) have been calculated as

follows.

' T , g ^ % ( F ) ( v , ) =8,100

'T,g->%g(F)(v2) =16,900

'T,g-)>'T,g(P)(v3) =19,800

V| = 8Dq = 8,100

Dq= 1,012.5

V3 = 15B + 6Dq= 19,800

153 + 6X1012.5 = 19,800

158 + 6075=19,800

153=13,725

3 =915 cm''

tJcomplcx

P

P =

D free metal

915

917

p = 0.947

P% = (1-P)X100

p% = (1-0.942) X 100

P% = 5.8.

161

Calculation of Dq, B and P for tetrahedral Co(II) complexes

For Co(II), in tetrahedral field, ligand field stabilization energy (Dq), Racali

parameter (B) and inter-electronic parameter (P) have been calculated as follows.

% - > "12 (F) (V,) =10,100

% - > "T, (F) (V2) =19,250

% - ^ % ( P ) ( v 3 ) =23,250

Vi = 10Dq= 10,100

Dq=1010

V3=15B+12Dq = 23,250

15B +12X1,010 = 23,250

158+12,120=23,250

15B= 11,130

B =742 cm"'

tJcomplex

P =

P =

B free tnelal

742

917

P = 0.809

P%=(1-P)X100

P% = (1-0.809) X 100

P%=19

162

Calculation of Dq, B and P for octahedral Ni(II) complexes

For Ni(II), in an octaliedral field, ligand field stabilization energy (Dq),

Racah parameter (B) and inter-electronic parameter (P) have been calculated as

follows.

% g - > % ( F ) . ( v , ) =9,800

%g^'T,g(F)(v2) =15,380

%g->'T,g(P)(v3) =25,000

vi = 10Dq = 9,800

Dq = 980

V3=15B + 12Dq = 25,000

153+12X980 = 25,000

153+11,760=25,000

153 =13,240

B = 882.66 cm"'

P "complex

P 1 free metal

P 882.66

1080

P = 0.817

p% = (1-P)X100

P% = (1-0.817) X 100

P%=18.3

163

ca ON 00 VC rn ir> •—1

OS <N 0 0 o6 0 0

ON ON oo ON O 00

ca

00

00 o

0 0 00 o

m

O O NO • " ^ NO rn

ON

iri

ON 00 ON

00 ON

(L> >

> •n

Q

<o ro (N rn

O^ r-H » — » ON

o o

m o ro >n TT (N (1 oo ON ON

O

5 c«

<u

6 o o

o

o

X )

13 i3 o <u ex o

•a o

w

OQ

ca H

CO O

00

o o o ON

O CT)

Tf

ri (N ,—4 .—< -^ .-I (N

O O o O O O o O O 00 >n o 00 o •^ 00 (N (N o <N o o" ON rn ( (N m ro (N (N (N (N CM (N

OS

o o O N

NO"

O

ON

(/I (U X

"a, 6 o O

o

o"

O ON^ o

OS

O o 00^ ON"

O rj- O o O ro o O NO o ri t — « O r^ U~t (N (N o" •<4; <N (N oo" oo" ON" > — ' oo" ON" ON"

^-v u ,,- / O ^ o CO O X C/5 U pLt PL, tu lu u- MH Pi-z Z Z z Z Z Z <^ < ^ S m 03 PJ \ ^ o ^ o '5' "o' o o U u U O U U U

164

>

Id >

•a u 73

O

-3 a, c

to (U X

o

o

I t3

o (U V) O •a o tl o u W CN CQ >o

o O m t-~ o o o 00 o o I^

ea rf vo •—I •—' •—' o\

CO.

m

<,

X

e o U

(N

ON 0\ oo o

OS OO

OS ON

m o ON

00 OO

m o

o ri ON

ON NO 0\ O 00 CN • * t^ NO (N

O OO VO O r~ «n 00 ON 1—1 0\ ON

ON

00

ON O 00

O OO ON

r-' 00 00

r<-i 00 OO

NO ON

00

ON O OO

o (N r~- m o o r- • ^ m •5t 00 r-~ in m f<

as 00 OO OO

U^ O

5 OO o X

(JL, U-,

z 2 PQ OQ

o •3

c

V) u X

"5, B o o

165

CO.

OQ

>

> Q

3

o o

• * - •

o u OH

O

•a o a a (L)

w OQ

oa H

^

o o O o O O O oo m r- o O O r~-o ro </-> ON tn ON U-(

ro <N (N CN

(U X

'a, E o

O

^ 5" o' £ u 00

u (Jl PH P-, PH PL, Pu pH

z 5 :^ z Z "Z, s <; <, 5 CQ CQ CQ w —-' 3 ^ 'H' 3 3 3 'H' u u u O u u u

166

6.4. REFERENCES

1. J.R. Dyer, "Applications of Absorption Spectroscopy of Organic

Compounds", Prentice - Mall of India Pvt. Lid., New Delhi(197l).

2. E.D. Olsen, "Modern Optical Methods of Analysis", McGraw - Hill Book

Company, New York(1975).

3. D.A. Skoog and M.D. West, "Principles of Instrumental Analysis", 2"'' Ed.

Holt - Saunders International Ed., New York(1980).

4. W. Kemp, "Organic Spectroscopy", ELBS Macmillan, Hong Kong(1985).

5. M.S. Patel, R.P. Patel and J.R. Shah, J. Indian Chem. Soc, 57, 120(1980).

6. B.S. Grag, V. Kumar and M.J. Reddy, Indian J. Chem., 32(A), 726(1993).

7. M. Khare and A.P. Mishra, J. Indian Chem. Soc, 77,256(2000).

8. F.A. Cotton and G. Wilkinson, "Advanced Inorganic Chemistry", 3' Ed.

Wiley Eastern, New Delhi(1972).

9. K.C. Patel and D.E. Goldberg, J. Inorg Nucl. Chem., 34, 637(1972).

10. N. Rama Rao, S.D.Rao and M.C. Gandrakar, Indian J. Chem., 21(A),

839(1982).

11. A.C. Hiremath, Proc. Nat. Acad Sci. India, 68(A), 111(1998).

12. K.M. Reddy, M.B. Halli and A.C. Hiremath , Nat. Acad. Sci. Letter, 14,

7(1991).

13. V. Srivastava, S.K. Srivastava and A.P. Mishra, Proc. Nat. Acad. Sci. Sect A.,

65,247(1995)

14. R.L. Datta and A. Syamal "Elements of Magnetochemistry" 2"*" Ed.

Affiliated East West, New Delhi 1993.