Chapter 9 Interaction of Lewis-bases with Polymeric Metal ...shodhganga.inflibnet.ac.in/bitstream/10603/7190/15/15_chapter 9.pdf · 1,10-phenanthroline monohydrate, ethylenediamine

Chapter 9

Interaction of Lewis-bases with Polymeric Metal(II) Terephthalates

9.1 Intro

hthalic acid and its two other position isomers are yet another class of

compounds which are akin to oxalate systems in terms of their extended

conjugation. Not only these dicarboxylate systems have rigid framework

but also have extended conjugative interaction spanning from one carboxylate to

the other, through the two ends of the aromatic ring. While the carboxylate

moieties in all the three isomers can have the same versatile bonding features like

in any other carboxylate systems, the conjugatively coupled aromatic ring can

function as an interesting spacer moiety between the –COOH functions in them.

Among the three isomers, the 1,4-isomer terephthalic acid (H

duction

P

2tpa), HOOC-C6H4-

COOH, has got the two –COOH moieties disposed in opposite directions. It is easy

to understand that the dianion of 1,2- and 1,3- isomers will result in the formation

of zig-zag type polymer metal dicarboxylates. On the other hand, the 1,4-isomer

has the possibility of generating linearly coupled coordination polymers. Besides

the usual variations possible in the linking modes of the carboxylate moieties, the

phenylene function will act as a rigid and electronically interacting spacer unit

through its π-system, leading in polymeric metal terephthalates which can be

expected to have a metal–metal separation of about 12 Å.

Almost all metal-tpa complexes are binuclear or polymeric in nature except

in a few cases where they exist as discrete complexes.(1) Several metal

terephthalates with 1D-(2,3) and 3D-(4-6) framework structures have been

reported. Structural prediction of several interesting metal terephthalates of Mg,

Mn, Fe and Co have been carried out by Monte Carlo Simulated techniques.( 7)

In a layered complex, [Co2(OH)2tpa],( 3) two types of edge sharing CoO6 chains

connected to each other by -OH moiety (Co-O-Co bridges) exists which form

layers that are further joined together through terephthalate anion and exhibits

interesting magnetic properties from paramagnetism to metamagnetism and even

having collinear antiferromagnetism. However, [Co(H2O)2tpa](3) which contains

layers of octahedral CoO6 connected via Co-O-C-O-Co shows only paramagnetism.

Many copper and cobalt terephthalate complexes find wide applications as gas

adsorbents and as metamagnets.(8) Recently Dale and coworkers(9) reported a three-

dimensional complex, [Pb(tpa)(H2O)]n, wherein Pb geometry is seen to be

hemidirected seven-coordinate, having both monodentate and bidentate

402 Chapter 9 carboxylate coordination modes. Several interesting terephthalate bridged mixed-

ligand complexes with 1D zig-zag chain(10-17) and 3D supramolecular structures

with channels are known. Recently Xiao et al(21,22) have reported interesting 1D-

linear tpa bridged complexes of the type [M(tpa)Cl2(phen)2(H2O)n] [M= CoII or CuII;

n = 0, 2]. Several extended binuclear Fe(II) complexes, [Fe2(tpa)(L)4](X)n [L = 2,2'-bipy,

phen, n-phen, me-phen; X = SO4, ClO4; n = 1, 4], are known in which tpa

acts as bidentate linking ligand.(23) In the dinuclear [Cu2(tpa)(L)4](ClO4)2(24a,b) [L =

pn, dipn(N-(3-aminopropyl)-1,3-diaminopropane)], tpa functions as bis-

monodentate moiety while in [M2(tpa)(L)4](ClO4)2(24c,d) [M = Cu, Ni, Co; L = bipy,

phen], tpa is seen to be existing in bidentate linking mode. Recently Rogan et al(25)

reported an interesting one-dimensional polymeric Cu(II) complex,

[Cu(tpa)(phen)(H2O)]n in which tpa is found to be acting as bis-

monodentate species. Also reports are available on several interesting dinuclear

Mn(II) systems with composition [Mn2(tpa)(L)4](ClO4)2(24c,26) [L = phen, bipy] having

1D chain and showing antiferromagnetic behaviour. In the dinuclear Ni(II)

complexes [Ni2(L)(L')4](ClO4)2.nH2O(27) [L = xtpa or btpa (bromo or iodo

terephthalate dianion); L' = 2,2'-bipy, phen, n-phen; n = 0, 2] tpa functions as

bidentate bridging moiety whereas in [Ni2(tpa)(pn)4(Him)2](ClO4)2(24a) (Him =

imidazole), tpa acts as bis-monodentate function. In [M(L)4(H2O)2]tpa(28,29) [M

= Cu, Mn; L = imidazole], tpa is found to be non coordinated and links

the cations through H-bonding network. Recently Pang et al(30) reported an

interesting two-dimensional system [Ni(bipy)(H2O)4]tpa with sheet-like structure in

which tpa dianions are found to be non-coordinated. There also exist several 3D

complexes wherein this non-coordinated nature of tpa is seen.(31,32) Quite many

of the mixed-ligand tpa bridged complexes of Cu, Co, Ni, Fe and Mn are seen to

be showing predominantly antiferromagnetic property.(12,23,24,27) A 3D

supramolecular framework system, [Mn(tpa)(bipy)(H2O)]n, recently reported by

Zhang et al(33) are shown to have tpa as tridentate moiety. Yaghi et al(34) have also

reported an interesting cluster compound, [Zn4O(tpa)3].8DMF.C6H5Cl, which contains

[OZn4] clusters. This chapter focuses on some of metal terephthalates which are

polymeric in nature and their interaction with various Lewis-bases with an idea of

generating interesting mixed ligand complexes.

Interaction of Lewis-bases with Polymeric Metal(II) Terephthalates 403

9.2. Experimental

9.2.1 Reagents

Terephthalic acid, CuCl2.5H2O, NiCl2.6H2O, pyridine, 2,2'-bipyridine,

1,10-phenanthroline monohydrate, ethylenediamine and 1,3-diaminopropane used

were of Merck quality. Methanol, acetone, and diethyl ether were used after

purification by known procedure.(35)

9.2.2 Preparation of Terephthalate Complexes of Cu(II) and Ni(II)

(a) Copper(II) terephthalate complex, [(Cu(tpa)).H2O]n, 58

To an aqueous solution of disodium terephthalate (0.21g, 1mM),

cupric chloride (0.17g, 1mM) in 10 ml methanol was added slowly with stirring and

then digested on a water bath. The solution pH was adjusted to 6-7 by using

NaOH solution. Light blue coloured complex was formed which was washed repeatedly

with water followed by methanol. It was dried under vacuum over P2O5. (yield

: 85%)

(b) Nickel(II) terephthalate complex, [Ni(tpa)(H2O)2]n, 59

The preparative procedure adopted for this complex was also similar to that

employed for the copper(II) complex. A solution of nickel chloride (0.23g, 1mM)

was added slowly with stirring to 1mM aqueous solution of disodium terephthalate.

Its pH was adjusted to 6-7 by using NaOH solution. Light green complex was

precipitated out. It was washed repeatedly with water followed by methanol which

was then dried under vacuum over P2O5. (yield : 80%)

Attempt to prepare cobalt(II) terephthalate complex by above procedure was

not successful.

9.2.3. Preparation of Lewis-base adducts of copper(II) and nickel(II) terephthalates

404 Chapter 9 (a) [Cu(en)2]tpa.2H2O, 60

A solution of en (0.13ml, 2mM) in methanol was added dropwise to a

suspension of copper(II) terephthalate (0.24g, 1mM) in methanol with constant

stirring for about 1 h. A clear dark violet solution was obtained which was filtered

and concentrated to half of its volume and then cooled. The complex was

separated as violet solid and was filtered. It was repeatedly washed with ether and

dried under vacuum over P2O5. (yield : 80%)

(b) [Cu(bipy)2(H2O)2]tpa .4H2O, 61

About 0.31g (2mM) of 2,2'-bipy in methanol was dissolved in 10ml methanol

and was added to a suspension of copper(II) terephthalate (0.24g, 1mM) in

methanol. The mixture was kept under reflux for about 1 h. A clear blue solution

was obtained which was filtered and concentrated to half of its volume and cooled.

The complex separated out as blue solid which was filtered and repeatedly washed

with ether. It was dried in vacuo. (yield : 85%)

(c) [Cu(phen)2(H2O)2]tpa. H2O, 62

The method adopted for the preparation of this complex was almost similar

to that one employed for the 2, 2'-bipyridine adduct. Instead of 2,2'-bipyridine,

0.4g of phen in methanol was added to a copper(II) terephthalate suspension in

methanol. The complex was separated out as green powder and was repeatedly

washed with ether. It was dried under vacuo. (yield : 80%)


(d) [Cu(py)2tpa]n, 63

A solution of pyridine (0.48ml, 3mM) was added to a copper(II) terephthalate

(0.24g, 1mM) suspension in methanol with constant stirring. The reaction mixture

was refluxed for about 3h. The colour change of the parent complex gives clear

indication of the formation of new adduct. The sky blue complex formed was separated

out by filtration. It was washed repeatedly with methanol followed by ether. The

complex was dried in vacuo. (yield : 75%)

(e) [Cu(pn)tpa]n, 64

A solution of pn (0.27ml, 3mM) in methanol was added dropwise to a

suspension of copper(II) terephthalate (0.24g, 1mM) in methanol with constant

stirring for about 3 h. A clear blue solution was obtained from which bulk quantity

of blue solid was found to be thrown out from the solution. It was washed with

methanol followed by ether and dried in vacuo. (yield : 80%)

(f) [Ni(en)2(H2O)2]tpa, 65

A solution of en (0.13ml, 2mM) in methanol was added dropwise to a

suspension of nickel(II) terephthalate (0.25g, 1mM) in methanol with constant

stirring for about 3 h. A clear pinkish violet solution was obtained which was

filtered and concentrated to half of its volume and cooled. The complex was

separated as pinkish violet solid and was filtered. It was repeatedly washed with

ether and dried under vacuum over P2O5. (yield : 85%)

Attempts to prepare the other adducts of nickel(II) terephthalate with bipy,

phen, py and pn were met with failure by this method. Similarly none of the

cobalt(II) terephthalate adducts could also be separated.

9.3. Results and Discussion

9.3.1 Metal terephthalates of Cu(II) and Ni(II)

Even though the aliphatic dicarboxylic acid such as succinic, malonic and

oxalic acid form complexes with metals like Ni(II), Co(II) and Cu(II), the aromatic

dicarboxylic acid such as terephthalic acid was seen to be resistant in the complex

406 Chapter 9 formation with metal like Co(II) by conventional route. However it forms complexes

with Cu(II) and Ni(II). The composition of Cu(II) and Ni(II) complexes of terephthalic

acid obtained was determined by elemental analysis and the water content

determined by TG analysis. The data are tabulated in Table 9.1

Table 9.1 Elemental analytical data of metal(II) terephthalates

Elemental content (%) obsd (calcd) Complex

(Emp. formula) Formula weight

C H M

Colour

[(Cu(tpa)).H2O]n(CuC8H6O5)

58 245.54 39.10

(39.01) 2.50 (2.44)

25.9 (25.8)

Light blue

[(Ni(tpa)(H2O)2).H2O]n(NiC8H10O7)

59 276.69 34.71

(34.69) 3.65 (3.61)

21.3 (21.2)

Light green

The broad band at 3175 cm-1, ν(O-H) in the free ligand, [H2tpa] was found to

be absent in both the metal(II) terephthalate complexes. This was indicative of the

deprotonated form of the tpa group in the meal complexes. Broad peaks in the

range 3400-3380 cm-1 were seen in both complexes which gave a clear indication of

the presence of lattice water in the system. The peak seen at 3230 cm-1 was

assigned to coordinated water in nickel(II) tpa complex which was not seen in the

copper(II) tpa complex. The characteristic νas(CO2) bands were seen to appear in

these complexes in the region 1570-1560 cm-1 while their νs(CO2) peaks were found

in the range 1392-1385 cm-1. As mentioned earlier the band separation Δν around

180 cm-1 indicates bidentate coordination modes of both carboxylate groups of

tpa(36) (Table9.2).

Table 9.2. IR spectral data of metal(II) terephthalates (cm-1)

Complex ν(O-H) δ(O-H) νas(CO2) νS(CO2) Δν

H2tpa 3175 1610 1698 1463 235

[(Cu(tpa)).H2O]n 3380 1620 1570 1392 180


[(Ni(tpa)(H2O)2).H2O]n 3400 1630 1560 1385 175

The electronic spectra of metal(II) terephthalates could be recorded only in

the solid state because of their insoluble nature. The absorption values are given

in Table 9.3. The nickel(II) tpa complex gave characteristic peaks which are typical

of octahedral nickel(II) complex.(37,38) The copper(II) tpa complex showed a broad

absorption band at 13680 cm-1 which is expected for a square planar complex.(39,40)

408 Chapter 9

Table 9.3 Electronic spectral and magnetic data of metal(II) terephthalates

Complex Absor. max ν (cm-1)

Assignments μeff

(BM)

[(Cu(tpa)).H2O]n 13680 3B1g → 2A1g 1.49

[(Ni(tpa)(H2O)2).H2O]n

10820

14830

25640

3A2g(F) →3T2g(F) ν1

3A2g(F) →3T1g(F) ν2

3A2g(F) →3T1g(P) ν3

2.85

Magnetic measurements showed that both Ni(II) and Cu(II) terephthalate

complexes are paramagnetic in nature ( Table 9.3 ). The μeff value of

[(Ni(tpa)(H2O)2).H2O]n was found to be 2.85 BM indicating that the complex is

octahedral in nature while the μeff value for [(Cu(tpa))n.H2O]n was found to be 1.49

BM which is slightly lower than the value expected for typical Cu(II) complex . All

the foregoing data indicated the four coordinated character for copper(II) and six

coordinated character for nickel(II) complex. Based on the above observations and

high insolubility, the overall structure of the metal terephthalate complexes could

be considered as polymeric in nature.

9.3.2 Lewis-base mediated fragmentation of copper(II) terephthalates

The set of Lewis-bases chosen for the interaction studies with polymeric

copper(II) terephthalates, were the same as those used for other systems. We have

carried out the interaction of Lewis-bases with Cu(II) and Ni(II) terephthalates, under

various reaction conditions and stoichiometric proportions as earlier. However, to

isolate the new structural species we have employed some optimum reaction

conditions. These along with some salient features of the reactions and products

isolated are presented in Table 9.4. As indicated in Table 9.4 and in the preparative

section, the adduct formation and breaking up of the polymeric network occur with

comparative ease with en, bipy, phen and pn at the addition of the ligand itself.

However, py does not seem to depolymerise the metal terephthalates. The analytical

data shown in Table 9.5 confirm the 1:2 (copper(II) terephthalates : Lewis-base)

composition for all the adducts except for the pn adduct which was only 1:1.

Interaction of Lewis-bases with Polymeric Metal(II) Terephthalates 409Table 9.4 Interaction of metal(II) terephthalates with various Lewis-bases (LB)

Metal terephthalates +LB

(in MeOH) Conditions Observation Products Separated

58 + en (1:1) stirring, RT, (2h) partial dissolution to give light

violet solution no stoichiometric compound

58 + en (1:2) stirring, RT, (1h)

complete dissolution (clear violet solution)

[Cu(en)2]tpa.2H2O (60)

58 + bipy (1:1)

stirring under reflux, (2h)

partial dissolution (light violet solution)

no characterisable product

58 + bipy (1:2)

stirring under reflux, (1h)

complete dissolution (clear light violet solution)

[Cu(bipy)2(H2O)2]tpa.4H2O (61)

58 + phen

(1:1) stirring under

reflux, (2h) partial dissolution

(light violet solution) no stoichiometric compound

58 + phen


reflux, (1h) complete dissolution

(clear light violet solution) [Cu(phen)2(H2O)2]tpa.H2O (62)

58 + py


reflux, (3h) no observable change no characterisable product

58 + py


reflux, (3h)

slight colour change from blue to light blue

(incomplete reaction) no stoichiometric compound

58 + (py excess) stirring under reflux, (3h)

colour change from blue to sky blue (solution colourless) [Cu(py)2tpa]n. (63)

58 + pn

(1:1) stirring, RT, (2h)

partial dissolution

(light blue solution) no characterisable product

58 + pn

(1:2) stirring, RT, (3h) complete dissolution followed

by blue solid separation [Cu(pn)tpa]n (64)

59 + en

(1:1) stirring, RT, (2h) partial dissolution (light violet

solution) no stoichiometric compound

59 + en

(1:2) stirring, RT, (3h) complete dissolution (clear

violet solution) [(Ni(en)2(H2O)2].tpa (65)

Table 9.5 Elemental analytical data of Lewis-base adducts of copper(II) terephthalates

Complex (Emp. formula)

Formula weight

Elemental content % obsvd (calcd) Colour

410 Chapter 9

C H N M

[Cu(en)2]tpa.2H2O

(CuC12H24O6N4)

60

383.5 37.58

(37.54)

6.28

(6.30)

14.62

(14.60)

16.6

(16.5) Violet

[Cu(bipy)2

(H2O)2]tpa.4H2O

(CuC28H32O10N4)

61

647.9 51.84

(51.86)

4.95

(4.98)

8.60

(8.64)

9.7

(9.8)

Dark

blue

[Cu(phen)2(H2O)2]

tpa.H2O

(CuC32H30O9N4)

62

678.0 56.60

(56.64)

4.47

(4.46)

8.25

(8.26)

9.4

(9.3) Green

[Cu(py)2tpa]n

(CuC18H14O4N2)

63

385.7 55.97

(55.99)

3.66

(3.65)

7.22

(7.25)

16.5

(16.4) Blue

[Cu(pn)tpa]n

(CuC11H14O4N2)

64

301.6 43.70

(43.75)

4.70

(4.67)

9.30

(9.28)

21.1

(21.0) Blue


9.3.3 IR spectra of Lewis-base adducts of copper(II) terephthalate

The presence of Lewis-bases in all the adducts could be confirmed by the

appearance of their characteristic peaks in the IR spectra. The peaks due to

terephthalate moiety were also present with some shift in their position as compared

to the values in the parent metal terephthalates. The νas(CO2) stretching band

occurring at 1570 cm-1 in [(Cu(tpa)).H2O]n was found shifted to 1526–1568 cm-1 in its

adducts and the νs(CO2) band observed at 1392 cm-1 was found lowered to 1380-1390

cm-1 in its adducts.

The asymmetric and symmetric stretching vibrations of NH2 group of en in

[Cu(en)2]tpa.2H2O, 60, were observed at 3310 and 3240 cm-1 respectively. The

bending mode (δNH2) was seen at 1601 cm-1. The sharp band seen at 1040 cm-1 was

assigned to νC-N stretching. The νas(CO2) and νs(CO2) bands of carboxylate group were

observed at 1547 and 1389 cm-1 respectively and its non-bonded nature is confirmed

by their Δν value of 158 cm-1. The weak band seen at 3450 cm-1 indicates the presence

of lattice water in it.

The IR spectrum of the adduct [Cu(bipy)2(H2O)2]tpa.4H2O, 61, gave new peaks

at 775, 1020, 1450 and 1600 cm-1 indicating that bipy are coordinated to Cu through

both of its pyridyl nitrogens. The bands at 1545 and 1390 cm-1 are assigned to νas(CO2)

and νs(CO2) vibrations of carboxylate group of terephthalate moiety. The Δν value of

155 cm-1 again confirms the non-coordinated character of the carboxylate group. The

in-plane and out-of-plane ring deformation modes of bipy were observed at 650 and

440 cm-1 respectively. The strong band at 3230 cm-1 indicates the presence of

coordinated water and the weak band seen at 3400 cm-1 shows the presence of lattice

water in it.

For the adduct [Cu(phen)2(H2O)2] tpa.H2O, 62, new bands were observed at 724,

1470 and 1613 cm-1 respectively. The bands at 1470 and 1613 cm-1 were assigned to

the ring skeletal vibrations of phen and its ring deformation modes were observed at

640 and 435 cm-1 respectively. The asymmetric and symmetric bands of carboxylate

group of terephthalate moiety were seen at 1526 and 1380 cm-1. The Δν value of 146

412 Chapter 9 cm-1 show that the carboxylate moieties exist in ionic form. The bands at 3370 and

3220 cm-1 indicates the presence of lattice and coordinated water in the complex.

The IR spectrum of the adduct [Cu(py)2tpa]n, 63, shows peaks at 1600 and

1485 cm-1 which were assigned to C=C and C=N ring stretching skeletal bands of

pyridine. The νas(CO2) and νs(CO2) bands were seen at 1568 and 1388 cm-1

respectively. The Δν value of 177 cm-1 confirms the bidentate chelating nature of

the carboxylate group. The ring deformation modes of pyridine were observed at

690 and 432 cm-1.

For the adduct [Cu(pn)tpa]n, 64, two peaks were observed at 3300 and 3263

cm-1 which are characteristic of asymmetric and symmetric vibrations of NH2 groups of

pn. The δ(NH2) band of pn was observed at 1598 cm-1. The νas(CO2) and νs(CO2) bands

were seen at 1565 and 1391 cm-1 respectively. The Δν value of 175 cm-1 is

characteristic of the bidentate chelating nature of the carboxylate group in the

complex. All the other relevant absorption frequencies of copper(II) terephthalate and

their adducts are given in Table 9.6.

Like in the other systems we have monitored the trend in the changes of both

asymmetric and symmetric stretching frequencies of the carboxylate moiety. The order

for Δν among the various adducts were found to be 63 > 64 > 60 > 61 > 62. The

trend is seen to be almost dependent on the pKa value of the various Lewis-bases

chosen(41) and is consistent with the observations made in the adducts of other metal

dicarboxylates.

Table 9.6 IR spectral data of copper(II) terephthalate and its various Lewis-base adducts (cm-1)

Adducts 58 60 61 62 63 64

ν(O-H) 3380 3450 3400

3230

3370

3220 - -

νas(CO2) 1570 1547 1545 1526 1568 1565

νs(CO2) 1392 1389 1390 1380 1388 1390

Δν 180 158 155 146 177 175


C Cν

- - 1600 1613 1600 -

νC N

- - 1450 1470 1480 -

ν(C-N) - 1040 - - - 1036

ν(C-H) - - 775 724 - -

β(C-H) - - 1020 - - -

ν(NH2) - 3310 3240 - - - 3300

3263

δ(NH2) - 1601 - - - 1598

Ring deformation

(outplane)

(inplane)

-

-

-

-

440

650

435

640

432

690

-

-

414 Chapter 9 9.3.4 Electronic spectra and magnetic data of Lewis-base adducts of

copper(II) terephthalate

The electronic spectra of various adducts of copper(II) terephthalate were

recorded either in solid state or in solution (Fig 9.1). The data are presented in

Table 9.6. In the en adduct, 60, a broad band occurs in the region 17790 cm-1

assignable to the 2BB1g → A2 1g transition consistent with a square planar

geometry. Moreover n→π bands were found as blue shifted while π→π bands red

shifted compared to the parent complex. These bands were found to be appearing in

the region 34010 and 39520 cm respectively. In the tetragonally distorted octahedral

adducts of bipy, phen, py, pn broad band occurs in the region 14370-17240 cm

which is assignable to the B1g

(39,40) ∗ ∗

-1

-1

2B → 2A1g transition consistent with distorted octahedral

geometry in these adducts.(42,43) In addition n→ π∗ bands were found as blue shifted

and π → π∗ bands red shifted in comparison with the parent complex. These bands

appear in the region 33220-34010 and 39210-40000 cm-1 respectively. Further, all

the adducts exhibit an intense absorption band in the region 25970-28010 cm-1 which

could be assigned to charge transfer transition.

The magnetic moment values of the various copper(II) terephthalate complexes

vary in the range 1.53-1.80 BM. The μeff values for the polymeric adduct were found to

be lower than the monomeric species indicating the possibility of some metal-metal

interaction in the former. (44) In the adducts 63 and 64 which have a polymeric

structure the μeff values are seen to be comparatively lower than in others. Evidently

they (63 and 64) would be retaining some Cu-Cu interaction present in the parent

complex in them.


Fig 9.1 The electronic spectra of copper(II) terephthalate and its various Lewis-base adducts

(a) [(Cu(tpa)).H2O]n, 58 (b) [Cu(en)2]tpa.2H2O, 60

(c) [Cu(bipy)2(H2O)2]tpa.4.H2O, 61 (d) [Cu(phen)2(H2O)2] tpa. H2O, 62

(e) [Cu(py)2tpa]n, 63 (f) [Cu(pn)tpa]n, 64

416 Chapter 9

Table 9.7 Electronic spectral and magnetic moment data of Lewis-base adducts of copper(II) terephthalate

Adducts Absor.max ν (cm-1)

Assignments μeff

(BM)

[(Cu(tpa)).H2O]n

58

40650

32670

25440

13680

π→π∗

n→π∗

charge transfer

2B1g → 2A1g

1.49

[Cu(en)2]tpa.2H2O 60

39520

34010

25970

17790

π→π∗

n→π∗

charge transfer

2B1g → 2A1g

1.75

[Cu(bipy)2(H2O)2]tpa.4H2O 61

39060

33220

26450

14410

π→π∗

n→π∗

charge transfer

2B1g → 2A1g

1.79

[Cu(phen)2(H2O)2]tpa.H2O 62

40000

33333

26040

15170

π→π∗

n→π∗

charge transfer

2B1g → 2A1g

1.80

[Cu(py)2tpa]n

63

39680

33550

28010

14370

π→π∗

n→π∗

charge transfer

2B1g → 2A1g

1.53

[Cu(pn)tpa]n

64

39210

33440

26520

17240

π→π∗

n→π∗

charge transfer

2B1g → 2A1g

1.60

9.3.5 EPR spectra of Lewis-base adducts of copper(II) terephthalate

X-band EPR spectra of parent copper(II) terephthalate, 58, and its adducts

were either recorded in solution state (1:1 toluene-methanol mixture) at liquid

Interaction of Lewis-bases with Polymeric Metal(II) Terephthalates 417nitrogen temp or in solid state. The EPR traces are given in Fig 9.2-9.3. The

anisotropic features of the spectra in the case of 60, 61 and 62 which are recorded

in solution state are evident from the spectra in Fig 9.3. The various spin-

Hamiltonian parameters were calculated from the spectra using DPPH or TCNE free

radicals as the ‘g’ marker. The data are tabulated in Table 9.8.

Field (Gauss)

Fig 9.2 EPR spectra of copper(II) terephthalate and its polymeric adduct in solid state at 77 K (a) [(Cu(tpa)).H2O]n, 58 (b) [Cu(pn)(tpa)]n, 64

The spectra of parent copper(II) terephthalate, 58 and the pn adduct 64, are

not resolved enough to get the A⎜⎜ value. The spectra of 60, 61 and 62 in solution at

77 K (Fig 9.3) gave well resolved parallel components and unresolved perpendicular

components. The hyperfine constant A⎜⎜ for these adducts are moderately high at

190 G for 60, 160 G for 61 and 150 G for 62. The comparatively high A⎜⎜ for 60

suggests that the electron spin is more localised in Cu(II) dx2-y2 orbital(45) of en

adduct 60 than in bipy adduct 61 and phen adduct 62. It implies that in 61 and

62, there is more spin delocalisation onto the Lewis-base. This is very much

expected because en is totally σ-donor while bipy and phen can be considered as σ-

donor as well as π-acceptors because of their low-lying π* orbitals. As phen has

418 Chapter 9 better π-acceptor property than bipy, the electron spin gets delocalised more on

phen adduct 62 than in bipy adduct 61. The observed trend in σ-covalency factor,

α2Cu value is 60 > 61 > 62. This is also in consistency with the expected order. The

low G value of parent copper(II) terephthalate, 58 is an indication of moderate

exchange interaction while the G value for the adducts 60, 61 and 62 show

absolutely no interaction in them.(46) The nature of the ‘g’ tensor values g⎜⎜ > g⊥ >

2.0023 observed for all the Cu(II) adducts indicate dx2-y2 ground state for them.

(a) [Cu(en)2]tpa.2H2O, 60

(b) [Cu(bipy)2(H2O)2]tpa.4.H2O, 61

(c) [Cu(phen)(H2O)2]tpa.H2O, 62

Interaction of Lewis-bases with Polymeric Metal(II) Terephthalates 419Fig 9.3 EPR spectra of monomeric adducts of copper(II) terephthalate in solution (1:1 toluene-

methanol mixture) at 77 K

Table 9.8 The various EPR parameters of the Lewis-base adducts of copper(II) terephthalate

Complexes A⎜⎜

(gauss) A⊥

(gauss) g⎜⎜ g⊥ giso α2Cu G

[(Cu(tpa)).H2O]n 58 - - 2.22 2.07 2.12 - 3.14

[Cu(en)2]tpa.2H2O 60 190 53.33 2.23 2.02 2.09 0.8029 11.5

[Cu(bipy)2(H2O)2]tpa.4.H2O 61 160 46.66 2.27 2.04 2.12 0.7683 6.75

[Cu(phen)2(H2O)2]tpa.H2O 62 150 50 2.29 2.04 2.12 0.7605 7.25

[Cu(pn)(tpa)]n 64 - - 2.18 2.07 2.11 - 2.57

9.3.6 Thermal decomposition features of copper terephthalates and their adducts

The thermal characterisation of copper(II) terephthalates and their adducts

developed were carried out to study the ligation characteristics of the Lewis-bases

and the over all decomposition features and also to evaluate their thermodynamic

and kinetic parameters. The details are discussed below.

9.3.6.1 Phenomenological Aspects

(a) [(Cu(tpa)).H2O]n, 58

The decomposition of [(Cu(tpa)).H2O]n is seen to be starting at 400C (Ti) and

progressing till 900C (Tf) with a peak temperature of 600C (Ts). The weight loss

corresponding to this stage amounts to 7.4% which is in close agreement with the

calculated value of 7.3% for the loss of a mole of lattice water. The second stage is

seen commencing only at 2700C (Ti) and ending at 4000C (Tf) with a Ts of 3200C. The

mass loss corresponding to this stage was found to be 60.15% agreeing well with the

decomposition of [Cu(tpa)] unit to yield the final product of CuO (expected : 60.28%).

420 Chapter 9 Above 4000C, the residue was seen to be stable. The decomposition features are

summarized below and the data are tabulated in Table 9.9. The amount of final residue of

CuO obtained (32.45%) also confirms the initial stoichiometry and the nature of thermal

steps given in eqns 9.1 and 9.2.

[(Cu(tpa)).H2O]n

Δ N 2 ,

40 - 90 0C [Cu(tpa)]n + H2O↑ ………(9.1)

[Cu(tpa)]n

Δ N 2 ,

270 - 400 CO CuO + gaseous products↑…….(9.2)

Table 9.9 The thermal characteristics of [(Cu(tpa)).H2O]n

Weight loss (in %) Compound

Temp range (0C)

Peak temp. (0C)

Stages Found Calcd

Probable reaction

40-90 60 I 7.40 7.33 eq 9.1

270-400 320 II 60.15 60.28 eq 9.2 [(Cu(tpa)).H2O]nAbove 400 - - 32.45

(residue) 32.39

(residue) CuO

(b) [Cu(en)2]tpa.2H2O, 60

The thermogram of en adduct is given in Fig.9.4. The decomposition is seen

initiating at 650C (Ti) and progressing till 1050C (Tf). The peak temperature was

found to be 800C (Ts). The loss in mass observed for this decomposition stage

amounts to 9.57% indicating the loss of two moles of lattice water (expected

9.38%). The second stage is seen operating at 1050C (Ti) itself and ending at 2700C

(Tf) with a mass loss of 31.20%. This agrees well with the loss of two molecules of

en from the complex (expected : 31.29%). The third stage of decomposition is seen

initiating immediately at 2700C and ending at 4300C. This stage is attributed to the

decomposition of [Cu(tpa)]n to the final residue of CuO. The mass loss calculated

(38.59%) matches well with the observed value of 38.72%. The mass of the final

residue was found to be 20.51% which is in close agreement with the theoretical

value of 20.74%. The decomposition features are summarised below and the data

are tabulated in Table 9.10.


Fig 9.4 The thermogram (TG /DTG) of [Cu(en)2]tpa.2H2O in N2

[Cu(en)2]tpa.2H2O

Δ N 2 ,

65 - 105 0C [Cu(en)2]tpa + 2 H2O↑ ....... (9.3)

[Cu(en)2]tpa ,N2

o105 - 270 C [Cu(tpa)]n + 2 en ↑ ....................... (9.4)

[Cu(tpa)]n ,N2

o270 - 430 C CuO + gaseous products ↑ .............. (9.5)

Table 9.10 The thermal characteristics of [Cu(en)2]tpa.2H2O


Temp range (0C)

Peak temp (0C)

Stages Found Calcd

Probable reaction

65-105 80 I 9.57 9.38 eq 9.3

105-270 245 II 31.20 31.29 eq 9.4

270-430 303 III 38.72 38.59 eq 9.5 [Cu(en)2]tpa.2H2O

Above 430 - - 20.51

(residue) 20.74

(residue) CuO

(c) [Cu(bipy)2(H2O)2)]tpa.4H2O, 61

422 Chapter 9 Fig 9.5. gives the thermogram of the adduct. It shows a four stage decomposition

pattern starting from 400C and ending at 4200C. The first stage was observed in the

range 40-900C while the second stage was seen in the range 90-1150C. The third and

fourth stages were found to be in the ranges 115-2700C and 270-4200C respectively.

During the first stage the loss of four molecules of lattice water was seen to be taking

place. The mass loss corresponding to this stage was found to be 11.15% which is in

close agreement with the calculated value of 11.11% for the water loss. The second stage

can be attributed to the loss of two moles of coordinated water from the adduct. The

mass loss corresponding to this stage was found to be 5.55% which is in perfect match

with the calculated value of 5.56%. In the third stage the observed weight loss (23.98%)

was in agreement with the escape of one mole of bipy from the adduct (calculated value :

24.11%). In the fourth stage the loss of the remaining bipy moiety together with the

decomposition of tpa moiety takes place to yield CuO as the final product. The mass loss

corresponding to this stage was observed to be 47.10% agreeing well with the theoretical

value of 46.94%. Above 4200C, a residue (CuO) was formed which was seen stable even

at higher temperature. The mass of this residue was found to be 12.22% which was

also in good agreement with the expected value of 12.28%. The decomposition features

are summarized below and the relevant data are tabulated in Table 9.11.

Fig 9.5. The thermogram (TG/DTG) of [Cu(bipy)2(H2O)2)]tpa.4H2O in N2


[Cu(bipy)2(H2O)2)]tpa.4H2O , N2

040 - 90 C[Cu(bipy)2(H2O)2]tpa + 4 H2O↑ ..(9.6)

[Cu(bipy)2(H2O)2]tpa ,N2

090-115 C [Cu(bipy)2]tpa + 2H2O ↑ ......(9.7)

[Cu(bipy)2]tpa , N2

115-270 C [Cu(bipy)(tpa)]n + bipy ↑ .............(9.8)

[Cu(bipy)(tpa)]n

, N 2

0 420270 - CCuO + bipy + gaseous products↑...(9.9)

424 Chapter 9

Table 9.11 The thermal characteristics of [Cu(bipy)2(H2O)2)]tpa.4H2O

Weight loss (in %] Compound

Temp range (0C)

Peak temp (0C)

Stages Found Calcd

Probable reaction

40-90 50 I 11.15 11.11 Eqn 9.6

90-115 110 II 5.55 5.56 Eqn 9.7

115-270 195 III 23.98 24.11 Eqn 9.8

270-420 278 IV 47.10 46.94 Eqn.9.9

[Cu(bipy)2

(H2O)2)]tpa.4H2O

Above 420 - - 12.22

(residue) 12.28

(residue) CuO

(d) [Cu(phen)2(H2O)2]tpa.H2O, 62

The thermogram of the adduct is given in Fig. 9.6. The initial decomposition

starts at 400C and progresses till 800C with a peak temperature of 500C (Ts). The

loss in mass corresponding to this decomposition stage amounts to 2.80% which is

in close agreement with the calculated value of 2.65% for the loss of a mole of

lattice water. The second stage is seen operating at 800C and ending at 1700C with

a peak temperature of 1300C. The loss in mass during this stage amounts to

5.45% which is in close agreement with the theoretical value of 5.31% for the loss

of two moles of coordinated water. The third stage commences at 1700C and

progresses till 2800C with a peak temperature of 2550C. The weight loss observed

at this stage can be attributed to the loss of one mole of phen moiety from the

adduct (found: 29.3%; expected : 29.2%). The fourth stage starts at 2800C and ends

at 8400C, with a mass loss of 50.65%. In this stage the escape of the remaining

phen moiety together with the decomposition of tpa moiety can be expected to take

place to yield CuO as the final product. Above 8400C, the residue was seen to be

stable in the nitrogen atmosphere. The values are tabulated in Table 9.12 and the

reactions involved are given below.


Fig. 9.6 The thermogram (TG/DTG) of [Cu(phen)2(H2O)2]tpa.H2O in N2

[Cu(phen)2(H2O)2]tpa. H2O ,N2

40 - 80 C[Cu(phen)2(H2O)2]tpa + H2O↑ ..(9.10)

[Cu(phen)2(H2O)2]tpa, N2

80-170 C [Cu(phen)2]tpa + 2H2O↑ ........... (9.11)

[Cu(phen)2]tpa , N2

170-280 C [Cu(phen)(tpa)]n + phen ................... (9.12)

[Cu(phen)(tpa)]n , N2

280-840 C CuO + phen + gaseous products ↑ . (9.13)

426 Chapter 9

Table 9.12 Thermal decomposition features of [Cu(phen)2(H2O)2]tpa.H2O


Temp range (0C)

Peak temp (0C)

Stages Found Calcd

Probable reaction

40-80 45 I 2.80 2.65 eq 9.10

80-170 130 II 5.45 5.31 eq 9.11

170-280 255 III 29.30 29.24 eq 9.12

280-840 550 IV 50.65 51.07 eq 9.13

[Cu(phen)2(H2O)2] tpa. H2O

Above 840 - - 11.80

(residue) 11.73

(residue) CuO

(e) [Cu(py)2(tpa)]n, 63

The thermogram of the adduct is shown in Fig 9.7. It is seen to be thermally

stable upto 1700C indicated by a well defined plateau. The decomposition is seen

starting at 1700C (Ti) and gradually progressing till 3150C (Tf). The weight loss

corresponding to the stage amounts to 40.53% which indicates the loss of two

moles of py from the compound (expected : 41.01%). The second stage of

decomposition is seen commencing at 3150C and ending at 4030C with a mass loss

of 38.25%. This stage could be attributed to the decomposition of tpa moiety from

[Cu(tpa)]n to yield CuO. The residual mass of 21.22% agrees well with the

theoretical value of 20.62%.

Fig. 9.7 The thermogram (TG/DTG) of [Cu(py)2(tpa)]n in N2

Interaction of Lewis-bases with Polymeric Metal(II) Terephthalates 427 The decomposition features are summarized below and the data are

tabulated in Table 9.13.

[Cu(py)2(tpa)]n , N2

o170 - 310 C [Cu(tpa)]n + 2py ↑ ........................(9.14)

[Cu(tpa)]n , N2

o310 - 405 C CuO + gaseous products ↑ .................(9.15)

Table 9.13 Thermal characteristics of [Cu(py)2(tpa)]n


Temp range (0C)

Peak temp (0C)

Stages Found Calcd

Probable reaction

170-310 218 I 40.53 41.01 eq 9.14

310-405 325 II 38.25 38.37 eq 9.15 [Cu(py)2(tpa)]n

Above 405 - - 21.22

(residue) 20.62

(residue) CuO

428 Chapter 9

(f) [Cu(pn)(tpa)]n, 64

The thermogram of the adduct is shown in Fig 9.8. This compound is seen to

be stable upto 2150C indicated by a well defined horizontal plateau in the TG curve.

It shows only one decomposition stage. The weight loss is seen starting at 2150C

and ending at 3950C with a peak temperature of 2850C. The loss in mass

corresponding to this stage was found to be 73.55% which was in perfect match

with the theoretical value of 73.63% expected for the decomposition of the

compound to a final product of CuO. The decomposition features are given in Table

9.14.

Fig. 9.8: The thermogram (TG/DTG) of [Cu(pn)(tpa)]n in N2

[Cu(pn)(tpa)]n , N2

0215 - 395 C CuO + pn + gaseous products ↑ ...(9.16)

Table 9.14 Thermal characteristics of [Cu(pn)(tpa)]n in N2


Temp range (0C)

Peak temp (0C)

Stages Found Calcd

Probable reaction

215-395 285 I 73.55 73.63 eq 9.16 [Cu(pn)(tpa)]n Above

395 - - 26.45 (residue)

26.37 (residue) CuO

9.3.6.2 Kinetic and Mechanistic Aspects

The overall kinetics and the nature of mechanisms of thermal decomposition

of various Lewis-base adducts of copper(II) terephthalate were studied using non-

Interaction of Lewis-bases with Polymeric Metal(II) Terephthalates 429isothermal thermogravimetric techniques. Kinetic parameters for all the complexes at

various stages were calculated from the TG/DTG curves using Coats-Redfern

method.(47) The deduction of the possible mechanisms of reactions from non-

isothermal methods has been discussed by Sestak and Berggren.(48) From the nine

reaction mechanisms listed by Satava, the one which gives the best representation of

the experimental data is considered as the mechanism of the reaction. Linear plots

(Fig. 9.9) of nine forms of g(α)/T2 versus 103/T were drawn by the least square

method and the corresponding correlation coefficients were evaluated. The data are

presented later in Tables 9.16-9.19. The values of Ea and A were calculated

in each case from the slope and intercept respectively. The kinetic parameters

evaluated for different stages of decompositions of the adducts using non-

mechanistic equation are given in Table 9.15.

430 Chapter 9

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

-9.5

-9.0

-8.5

-8.0

-7.5 Lewis-base adducts of [(Cu(tpa)).H2O]n Stage I

ed

c

b

a

log

(g(α

)/T2 )

1000/T 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

-10.0

-9.5

-9.0

-8.5

-8.0Lewis-base adducts of [(Cu(tpa)).H2O]n Stage II

d

c

b

a

log

(g(α

)/T2 )

1000/T

(i) (ii)

1.5 1.6 1.7 1.8 1.9 2.0 2.1

-9.5

-9.0

-8.5

-8.0

-7.5 Stage IIILewis-base adducts of [(Cu(tpa)).H2O]

n

c

b

a

log

(g(α

)/T2 )

1000/T 1.0 1.2 1.4 1.6 1.8 2.0

-10.8

-10.4

-10.0

-9.6

-9.2

-8.8

-8.4

-8.0

-7.6

-7.2

c

b

Lewis base adducts of [(Cu(tpa)).H2O]n

StageIV

log

(g(α

)/T2 )

1000/T

(iii) (iv)

Fig 9.9 Log (g(α)/T2) Vs 1000/T plots for the thermal decomposition of Lewis-base adducts of

[(Cu(tpa)).H2O]n 58 : (i) Stage I (ii) Stage II (iii) Stage III and (iv) Stage IV; (a)

[Cu(en)2]tpa.2H2O 60 (b) [Cu(bipy)2(H2O)2]tpa.4H2O 61 (c)

[Cu(phen)2(H2O)2]tpa.H2O 62 (d) [Cu(py)2(tpa)]n 63 (e) [Cu(pn)(tpa)]n 64

Table 9.15 Kinetic parameters for the thermal decomposition stages of Lewis-base adducts of copper(II) terephthalate

Compounds Stages Kinetic

parameters [Cu(en)2]tpa. 2H2O 60 [Cu(bipy)2(H2O)2]tpa. 4H2O 61 [Cu(phen)2(H2O)2]tpa.H2O 62 [Cu(py)2(tpa)]n 63 [Cu(pn) (tpa)]n 64

Ea(kJ/mol) 89.19 99.72 36.03 46.04 117.85

A(s-1) 148.31 4595.62 7.39 × 10-2 2.30 × 10-2 39.71 I

ΔS(J/K/mol) -204.78 -175.54 -267.22 -280.32 -219.30

Ea(kJ/mol) 45.86 42.05 53.86 141.59 -

A(s-1) 0.034 5.29 × 10-2 6.82 × 10-2 44.88 - II

ΔS (J/K/mol) -277.27 -272.78 -269.89 -219.07 -

Ea(kJ/mol) 66.15 137.08 60.09 - -

A(s-1) 0.05 1031.39 6.44 × 10-2 - - III

ΔS (J/K/mol) -275.39 -191.92 -272.39 - -

Ea(kJ/mol) - 145.00 76.92 - -

A(s-1) - 925.05 6.42 × 10-3 - - IV

ΔS (J/K/mol) - -186.25 -295.37 - -

432

Table 9.16 Correlation coefficients calculated using the nine form of g(α) for the Lewis-base adducts of [(Cu(tpa)).H2O]n for stage I decomposition

Form of g(α) [Cu(en)2 ] tpa.2H2O 60

[Cu(bipy)2(H2O)2]tpa. 4H2O 61

[Cu(phen)2(H2O)2]tpa. H2O 62

[Cu(py)2

tpa]n 63 [Cu(pn)

(tpa)]n 64

α2 -0.996092 -0.991839 -0.995533 -0.992829 -0.991897

α+(1-α) ln(1-α) -0.996072 -0.991784 -0.995538 -0.993178 -0.992207

[1-(1-α)1/3]2 -0.994724 -0.989723 -0.991202 -0.979397 -0.988617

(1- 32 α)-(1-α)2/3 -0.996116 -0.991886 -0.995624 -0.993271 -0.992360

-ln(1-α) -0.995709 -0.990885 -0.993812 -0.990182 -0.991579

[-ln(1-α)]1/2 -0.994121 -0.988119 -0.985968 -0.967564 -0.987958

[-ln(1-α)]1/3 -0.992121 -0.985247 -0.952098 --0.721182 -0.981863

1-(1-α)1/2 -0.995597 -0.990854 -0.994069 -0.989399 -0.991001

1-(1-α)1/3 -0.995604 -0.990788 -0.993964 -0.989649 -0.991098

433

Table 9.17 Correlation coefficients calculated using the nine forms of g(α) for the Lewis-base adducts of [(Cu(tpa)).H2O]n for stage II decomposition

Form of g(α) [Cu(en)2 ]tpa.2H2O

60 [Cu(bipy)2(H2O)2]tpa.4H2O

61 [Cu(phen)2(H2O)2]tpa.H2O

62 [Cu(py)2(tpa)]n

63

α2 -0.989798 -0.992095 -0.996454 -0.985050

α+(1-α) ln(1-α) -0.990225 -0.992502 -0.996472 -0.985339

[1-(1-α)1/3]2 -0.975033 -0.981251 -0.992878 -0.979116

(1- 32 α)-(1-α)2/3 -0.990338 -0.992638 -0.996509 -0.985454

-ln(1-α) -0.986698 -0.990212 -0.995262 -0.983609

[-ln(1-α)]1/2 -0.963666 -0.972485 -0.990353 -0.976730

[-ln(1-α)]1/3 -0.806296 -0.866578 -0.965769 -0.965757

1-(1-α)1/2 -0.985724 -0.989265 -0.995181 -0.983077

1-(1-α)1/3 -0.986085 -0.989543 -0.995330 -0.983222

434

Table: 9.18 Correlation coefficients calculated using the nine forms of g(α) for the Lewis-base adducts of [(Cu(tpa)) (H2O)]n for Stage III decomposition

Form of g(α) [Cu(en)2 ]tpa.2H2O

60 [Cu(bipy)2(H2O)2]tpa.4H2O


62

α2 -0.993592 -0.988623 -0.984442

α+(1-α) ln(1-α) -0.993901 -0.988693 -0.985377

[1-(1-α)1/3]2 -0.984473 -0.986172 -0.962589

(1- 32 α)-(1-α)2/3 -0.993954 -0.989101 -0.985701

-ln(1-α) -0.991715 -0.986498 -0.981114

[-ln(1-α)]1/2 -0.977-066 -0.982603 -0.950455

[-ln(1-α)]1/3 -0.892917 -0.976777 -0.790610

1-(1-α)1/2 -0.991025 -0.987146 -0.979049

1-(1-α)1/3 -0.991304 -0.886975 -0.979817


Table. 9.19. Correlation coefficients calculated using the nine forms of g(α) for the Lewis-base adducts of [(Cu(tpa)).H2O]n for

Stage IV decomposition

Form of g(α) [Cu(bipy)2(H2O)2]tpa.4H2O


62

α2 -0.980421 -0.990543

α+(1-α) ln(1-α) -0.993492 -0.990613

[1-(1-α)1/3]2 -0.987253 -0.973829

(1- 32 α)-(1-α)2/3 -0.994789 -0.990686

-ln(1-α) -0.992042 -0.925616

[-ln(1-α)]1/2 -0.987926 -0.950408

[-ln(1-α)]1/3 -0.983520 -0.453627

1-(1-α)1/2 -0.991325 -0.985219

1-(1-α)1/3 -0.982762 -0.985340

The activation energies, Ea, in the first stage of thermal

decomposition of the Lewis base adducts of copper(II) terephthalate

were in the range 36-118 kJ/mol, but that of second, third and

fourth stages of decompositions are in the range 42-142 kJ/mol,

60-137 kJ/mol and 77-145 kJ/mol respectively.

The pre-exponential factors A vary in a wide ranges of values as

2.30×10-2 - 4596 s-1 for the first stage, 0.034-44.88 s-1 for the second

stage, 0.05-1031 s-1 for the third stage and 6.42×10-3 -925 s-1 for the

fourth stage of decompositions. The ΔS values are in the ranges -176

to -1280 J/K/mol, -219 to -277 J/K/mol, -192 to -275 J/K/mol

436 Chapter 9

and -186 to -295 J/K/mol respectively for these stages. The negative

values indicate that the activated complexes for all the stages of

decomposition have a more ordered structure than the reactants and

the reactions in these cases, may be described as slower than the

normal.(49-51) However, no definite trend is seen in the values of Ea or ΔS

for the various stages of thermal decomposition of the same complex.

From the correlation coefficients obtained from the kinetic

studies (Tables 9.16-9.19) it is evident that the rate controlling

process for all the four stages of decompositions is three

dimensional diffusion, spherical symmetry; obeying ‘Ginstling–

Brownshtein’ equation. The forms of g(α) with the highest value of

correlation coefficient for all the stages of thermal decomposition of

the complexes are given in Table 9.20.


Table 9.20 The form of g(α) with the highest value of correlation coefficients and the corresponding rate controlling processes

Stages Compound Form of g(α) Rate controlling process

[Cu(en)2]tpa.2H2O (1-2/3α) – (1-2)3/2

Three dimensional diffusion, spherical symmetry, Ginstling-Brownshtein equation

[Cu(bipy)2(H2O)2]tpa.4H2O (1-2/3α) – (1-2)3/2 ”

[Cu(phen)2(H2O)2]tpa.H2O (1-2/3α) – (1-2)3/2 ”

[Cu(py)2(tpa)]n (1-2/3α) – (1-2)3/2 ”

I

[Cu(pn)(tpa)]n (1-2/3α) – (1-2)3/2 ”

[Cu(en)2]tpa.2H2O (1-2/3α) – (1-2)3/2 ”

[Cu(bipy)2(H2O)2]tpa.4H2O (1-2/3α) – (1-2)3/2 ”

[Cu(phen)2(H2O)2]tpa.H2O (1-2/3α) – (1-2)3/2 ” II

[Cu(py)2(tpa)]n (1-2/3α) – (1-2)3/2 ”

[Cu(en)2]tpa.2H2O (1-2/3α) – (1-2)3/2 ”

[Cu(bipy)2(H2O)2]tpa.4H2O (1-2/3α) – (1-2)3/2 ” III

[Cu(phen)2(H2O)2]tpa.H2O (1-2/3α) – (1-2)3/2 ”

[Cu(bipy)2(H2O)2]tpa.4H2O (1-2/3α) – (1-2)3/2 ” IV

[Cu(phen)2(H2O)2]tpa.H2O (1-2/3α) – (1-2)3/2 ”

438 Chapter 9

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