Syntheses, Crystal Structures and Kinetic Mechanisms of Thermal Decomposition of Rare Earth Complexes with Schiff Base Derived from o-Vanillin and p-Toluidine

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JOURNAL OF RARE EARTHS 24 (2006) 268 - 275

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Syntheses, Crystal Structures and Kinetic Mechanisms of Thermal Decomposition of Rare Earth Complexes with Schiff Base Derived from o -Vanillin and p -Tohidine

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Zhao Guoliang , Feng Yunlong (;$??&,)lvz, Wen Yihang (%-&)'" ( 1 . College of Chemistry and L$? Science , Zhejiang Normal University, Jinhua 321004 , China; 2 . Zhjiang Key Laboratory for Reactive Chemistry on Solid Su&ces , Jinhua 321004, China ) Received 15 September 2005; revised 12 November 2005

Abstract: Three complexes, [Pr(N03)3(HL)2] ( I ) , [Nd(NO,),(HL)z] ( 2 ) and [Er(N03)3(HL)2].0.5H20 ( 3 ) , were synthesized from the reaction of a Schiff base ligand 2-[ (4-methylphenylimino) methyl]-6-methoxyphenol ((215 HIS NO2 , HL) with Ln( N 0 3 ) 3 -6Hz0 (Ln = Pr , Nd , Er) . Characterization by single-crystal X-ray diffraction technique, elemental analysis, molar conductance, FT-IR, UV-Vis , 'H NMR and thermal analysis shows the title complexes are neutral molecules where the central Ln( 1 ) ion is ten-coordinated in biapical anti-hexahedron prism geometry, with four oxygen atoms of the phenolic hydroxy and methoxy groups in the two bidentate Schiff base ligands and six oxygen atoms provided by the three bidentate NO3 - anions. Additionally, the kinetic mechanism of thermal decomposition of complex 3 was determined with a TG-DTG curves by both integral and differential methods. The functions of thermal decomposition reaction mechanism and the equation of kinetic compensation effect were obtained.

Key words : o -vanillin; p -tohidine ; Schiff base; crystal structure; kinetic mechanism of thermal decomposition; rare earths

CLC number: 0614.33; 0641.4

Document code: A

With the increasing application of rare earth metals in a variety of fields, rare earth ions continually intrude into general environment and further into the bodies of plants, animals and human beings. It is therefore of significance to investigate the physiological action and long-term effect of rare earth ion on biological bodies. Various studies have shown that Schiff bases derived from salicylaldehyde and its derivatives have considerable biological importance partly because such ligands have many donor atoms ( N , 0)and are analogous to biological environment to some extent. They have been widely used in the fields of biology, pharmacology, catalysis, organic synthesis, chemical, analysis, and so Much attentions have been *-

Article JD: 1002 - 0721(2006)03 - 268 - 08

paid to these Schiff bases because of the stability of the ligands and various properties of their metal c o m p l e ~ e s [ ~ -Liu ' ~ ~ and . co-workers["9'21reported the reaction between rare earth nitrate and Schiff base derived from o -vanillin and p -tohidine afforded corresponding complexes and the proposed structures were characterized, but studies concerning the crystal structure of complexes derived from rare earth nitrate and the Schiff base remain unexplored. In view of this, , Nd ( Er three complexes of rare earth (Pr ( nitrate with the ligand of Schiff base 0-vanilly-ptoluidine were synthesized in absolute alcohol. Their crystal structures were determined by single-crystal X-

(a))

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a),

Corresponding author (E-mail: [email protected]) Foundation item: Project supported by Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces (0507) Biography: Zhao Guoliang (1963 - 1, Male, Master, Associate professor; Research field: Coordination chemistry Copyright 02006. by Editorial Committee of Journal of the Chinese Rare Earths Society. Published by Elsevier B . V . All rights reserved.

Zhao G L et a1 . Syntheses, Crystal Structures and Kinetic Mechanisms of Thermal Decomposition of RE Complexes

ray diffraction technique, and were characterized by elemental analysis, molar conductance, FT-IR, UV-Vis , 'H NMR and thermal analysis. The thermal decomposition mechanism functions of complex 3 were obtained from the analysis of TG-DTG curves by integral method of Achar and differential method of Coats-Redfern .

1 Experimental 1.1 Reagents and instruments All the reagents were of A. R . grade and were used without further purification. Ln ( N o 3 ) 3 6H20 (Ln = Pr, Nd, Er ) were prepared by dissolving Pr60,,, Nd203 and Er203( 9 9 . 9 5 % ) in concentrated nitric acid and crystallizing the salts by evaporating the solution on a steam bath. The metal contents were determined by the weight of the complex residue after thermal decomposition. Elemental analysis ( C , H , N ) were performed on an analyzer made in Germany. Elementar Vario EL The molar conductance of the complexes in DMF mol*L-') was measured using (25 T, 1 . 0 x DDS-1 1A conductivity bridge made by Shanghai China. FTIR spectra were recorded on a Nicolet NEXUS 670 FTIR spectrophotometer using KBr discs in the range of 4000 400 cm- ' . UV-vis spectra were surveyed in methanol at concentration 1 . O X 10-4mol*L-' (200- 800 nm) by Shimadzu UV-2501 PC. The 'H NMR spectra were recorded at 400 MHz on a Bruker400 spectrometer using d6-DMS0 solutions, chemical shifts are expressed as 6 (pg g - ' ) with respect to tetramenthylsilane as an external reference. Single crystal structure was determined on a Rigaku R-AXIS RAPID Weissenberg IP . Thermogravimetric analysis was carried out on A Mettler Toledo thermal analyzer TGA/SDTA 85 1".

m

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1.2 Synthesis of Schiff base ligand o-vanillin ( 1 .52 g , 10 mmol) in 20 ml ethanol was added dropwise into the solution of p-toluidine (1.07 g, 10 mmol) in absolute ethanol ( 2 0 ml) with continuous stirring, then the orange crystals were obtained after 10 min. The product ( Fig. 1 ) was filtered, washed with absolute alcohol, dried in air (yield: 8 0 % ) , m . p . 99.9- 100.3 "c. The Schiff base ligand was recrystallized in absolute alcohol

Fig. 1 Structure of Schiff base ligand

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beforeused. (Found: C , 7 4 . 6 2 % ; H , 6 . 3 1 % ; N , 5 . 7 7 % . Calcd. for Cl5HI5NO2:C , 7 4 . 6 6 % ; H , 6 . 2 7 % ; N , 5 . 8 1 % ) . IR ( c m - I , KBr pellet): v 0 - H 3451(w, b r ) ; ~ ~ = ~ 1 (6s ,1 s7h ) ; ~ ~ - ~ 1 2( v6s , 0 s h ) . 'H NMR ( 6 p g - g - ' , d6-DMSO): 13.38 ( s , l H , - O H ) , 8.94 (s, l H , - C H = N - ) , 7.32 (dd, 2H, J = 8 . 3 Hz, MePh-H), 7 . 2 6 ( d d , 2H, J = 8.0 Hz, MePh-H), 7 . 2 2 6.87 ( m , 3H, Ph - H ) , 3.81 ( s , 3H, -OCH3), 2 . 3 3 ( ~ ,3H, -CH3).

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1.3 Synthesis of complexes Complex 1 : A ethanol solution ( 10 ml) of Pr (NO3)3*6H20 ( 1 . 0 mmol, 0.44 g ) was added dropwise into an ethanol solution (40 ml) Schiff base ligand ( 2 . 0 mmol , 0.48 g ) with continuous stirring and refluexed for 2 h , then the clear orange red mixture solution was formed. The orange red crystals of complexes ( 1 ) suitable for structure determination were isolated at room temperature 8 d later, washed with absolute ethanol, dried in air (Yield : 45 % ) . (Found : C, 4 4 . 3 8 % ; H , 3 . 7 9 % ; N , 8 . 6 1 % ; Pr, 17.22%. Calcd. for C30HBN5013Pr:C , 4 4 . 5 1 % ; H , 3 . 7 4 % ; N , 8 . 6 5 % ; Pr, 17.41%). IR ( e m - ' , KBr pellet): ~ o - H 3 4 1 8 ( ~b,r ) ; ~c,N1638 (VS, s h ) ; uC-01235 ( s , s h ) ; uNO,- 1500 ( V S , s h ) , 1291 ( s , s h ) , 1024 (w, s h ) , 818 ( w ) , 731 ( w ) ; ~ R - ~ 4 8( w8 ) . 'H NMR ( 6 pg g - ' , d6-DMSO): 13. 39 ( s , l H , - O H ) , 8.95 (s, l H , - CH = N - ) , 7 . 3 3 ( d d , 2H, J = 8 . 0 Hz, MePh-H), 7.27(dd, 2H, ] = 8 . 0 Hz, MePh-H) , 7 . 2 4 6.88 ( m , 3 H , Ph-H) , 3.82 ( s , 3H, -OCH3), 2.34 ( s , 3 H , - C H 3 ) . Complex 2 was synthesized with the same method as 1 except for replacing Nd ( N 0 3 ) 3* 6 H 2 0 with Pr ( NO3 )3 * 6 H 2 0 , single crystals were obtained after 7 d , (Yield: 4 0 % ) . (Found: C, 44. 2 0 % ; H , 3 . 6 8 % ; N , 8.50%; Nd, 1 7 . 4 2 % . Calcd. for Cm HBN5NdOl3: C, 44.33%; H , 3 . 7 2 % ; N , 8 . 6 2 % ; Nd, 1 7 . 7 5 % ) . IR ( c m - ' , KBr pellet): ~O-H3420 ( w , br); v C = N 1 6 4 0 ( V S , s h ) ; ~ c - 01237 ( s , s h ) ; uNO3-1503(vs, s h ) , 1288 ( s , s h ) , 1024 ( w ) , 818

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( w ) , 729 ( w ) ; vNd-o489 ( w ) . 'H NMR ( 6 p g - g - ' , d6-DMSO): 13.38 (s, I H , - O H ) , 8 . 9 5 (9, I H , - C H = N - ) , 7.33 (dd, 2H, J = 8 . 4 H z , MePhH ) , 7.27 ( d d , 2H, J = 8 . 4 H z , MePh-H), 7 . 2 3 6.88 ( m , 3 H , Ph-H), 3.82 ( s , 3 H , - OCH3), 2 . 3 4 ( ~ ,3 H , - CH3). Complex 3 was also prepared with the same method as 1 except for replacing Er( N 0 3 ) 3 6H20 with Pr ( NO3 ), 6 H 2 0 , single crystals were obtained after 10 d , (Yield: 50%). (Found: C , 42. 5 4 % ; H ,

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3 . 6 0 % ; N , 8 . 1 2 % ; Er, 1 9 . 6 2 % . Calcd. for C30 H31ErN5013,5: C, 4 4 . 6 4 % ; H , 3 . 7 0 % ; N , 8 . 2 9 % ; Er, 19. 80%). IR ( c m - ' , KBr pellet): uo-H3421 ( w , b r ) ; ~c,N1642 (s, sh);Yc-o 1239 ( 5 , s h ) ; u N O 3 - 1504 (vs, s h ) , 1297 ( s , s h ) , 1025 ( w ) , 819 w )4. 'H 9 NMR 0 (6 pg-g-', ( w ) , 739 ( w ) ; ~ ~ ~ - ( ~ d6-DMSO): 13.37 ( s , l H , - O H ) , 8 . 9 5 ( s , l H , - C H = N - ) , 7.33 ( d d , 2H, 5 = 7 . 6 Hz, MePhH ) , 7 . 2 7 (dd, 2H, J = 7 . 6 H z , MePh-H), 7 . 2 3 6.88 ( m , 3H, Ph-H), 3 . 8 2 ( s , 3H, - OCH3), 2.34 ( s , 3H, -CH3).

1.4 Thermal analysis Thermal decomposition of the complexes was carried out by a heating rate of 10 "c nmin-' from 30 to 900 "c with N, ( 30 ml min- ' ) as protective gas and 02(50 ml*min-I) as reactive gas. The kinetic parameters were obtained from the analysis of TG-DTG curves by integral and differential methods.

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1.5 Single-crystal structure determination

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Intensity data for the complexes 1 3 were measured with a Rigaku R-AXIS RAPID Weissenberg IP diffractometer with graphite-monochromated Mo Ka ra-

diation ( A = 0 . 0 7 1073 nm) at 293 K. Empirical absorption corrections were applied by use of the SADABS program. The structure was solved by direct method and successive Fourier difference syntheses and all calculations were performed with the aid of the SHELXL PC program. The structures were refined by full-matrix, least-squares minimization of C( F , - F,)' with anisotropic thermal parameters for all atoms except H atoms. The H atoms except phenolic hydroxy were positioned geometrically. The crystallographic data of the complexes 1 3 and the parameters of data collection are summarized in Table 1, selected bond lengths and angles in Tables 2 4.

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2 Results and Discussion 2.1

Chemical composition, IR spectra and 'H NMR spectra of ligand and the complexes

The title complexes are stable in air and have no melting point, they are easy soluble in polar organic solvents ( methanol, ethanol, acetone, Py , DMF , DMSO ) and slight soluble in nopolar solvents (benzene, cyclohexane) . The C , H , N , Ln contents

Table 1 Crystallographic data for complexes Complexes

1

Empirical formula

C~OH~ONJOI~~

G O H ~ O NdO N S 13

C3oH31k E d i 3 . 5

Formula weight Crystal dimensionslmm

809.50 0 . 1 2 x 0.08 x 0 . 0 6

812.83 0 . 1 0 x 0 . 1 0 x 0.10

844.86 0.30~0.18~0.12

Crystal system

Monoclinic

Monoclinic

Triclinic

Space group

c21c 1.9756(4) 0.92528( 18) 1.8783(4)011.8903(4) 90.00 94.88(3) 90.00 3.4209 ( 12 ) 4 1.572 1.495 1632 293(2) 15827 3908 2920 0.0564 223 I . 103 0.0527 0.1435 1107; - 1981

c2tc 1.9826(4) 0.92291 ( 18) 1.8451(4) 90.00 94.86(3) 90.00 3.4464( 12) 4 1.567 1.577 1636 293(2) 3906 3906 3291 O.OO0 223 1.012 0.0455 0.1141 1006; - 871 e - n m - '

alnm blnm clnm

Yl(O) V/nm3 0

L

D,/(kg*m-3) pImm-'

F (OOO) Temperature/K Reflections collected Independent reflections Observed data [ I > 2 u ( f ) ] Rint

Parameters Goodness-of-fit on F2

R1 [ f > 2 u ( f ) ] wR2 Maximum and minimum peak in difference map

2

3

Pi 0.9786(2) 0.9986(2 ) 98.36( 3 ) 101.54(3) 106.14(3) 1.6579(6) 1

1.692 2.606 844 293(2) 16472 7524 6263 0.0304 45 1 1.056 0.0414 0.1076 756; -0.562 e - n m - '

Zhao G L et a1 . Syntheses , Crystal Structures and Kinetic Mechanisms of Thermal Decomposition of RE Complexes

Table 2 Selected bond lengths ( nm) and angles Pr(l)-O(l) Pr(l)-O(4) O(1 )-Pr(1 )-O( 1) # 1 O(l)-Pr(l)-O(4) # 1 O(1) # l-~dl)-O(4) # 1 O( 1 )-Pr( 1 )-0(4) O(1) # l-Pr(l)-O(4) O(4) # l-Pr(1)-0(4) O(l)-Pr(1)-0(3) # 1 0(1)#1-Pr(l)-0(3)# 1 O(4) # l-Pr(l)-O(3)# 1 0(4)-Pr(l)-0(3) # 1 O(l)-Pr(l)-O(3) O(1) # l-Pr(l)-O(3) O(4) # l-Pr(l)-O(3) 0(4)-Pr(l)-0(3) O(3) # l-Pr(l)-O(3)

0.2363(3) 0.2501(8) 160.35(19) 77.7(3) 86.6(3) 86.6(3) 77.7(3) 74.3( 10) 104.73(15) 73.29(15) 51.0(4) 118,3(4) 73.29(15) 104.73(15) 118.3(4) 51.0(4) 168.8(3)

('1

for complex 1

Pr( 1 )-O( 3) Pr( 1 )-0(6) O(l)-Pr(l)-O(6) O(1) # l-Pr(l)-O(6) O(4) # l-Pr(1 )-O(6) 0(4)-Pr( 1 )-0(6) O(3) # 1-Pr(1 )-0(6) O( 3 )-Pr(1 ) -O( 6) O(l)-Pr(l)-0(6) # 1 0(1)#l-Pr(1)-0(6)#1 O(4) # 1-Pr(1 )-0(6)# 1 0(4)-Pr(1 )-0(6)# 1 O(3) # l-Pr(lbO(6) # 1 0(3)-Pr(l)-O(6)# 1 0(6)-Pr(l)-0(6) # 1 O(1 )-Pr(1)-0(2) # 1 O(1) # l-Pr(l)-O(2)# 1

0.2549(5) 0.2550(4) 80.61(14) 118.25(14) 149.1(5) 126.1(4) 115.57(19) 75.27(18) 1 18.25( 13) 80.61(14) 126.1(4) 149.10) 75.27(18) 115.57(19) 49.4(2) 131.68(12) 59.12(11)

Pr( 1 ) -0(2)

0.2838(4)

O(4) # l-Pr(l)-O(2) # 1 0(4)-Pr(l)-0(2) # 1 0(3)#1-Pr(l)-0(2)# 1 0(3)-Pr(l)-0(2) # 1 0(6)-Pr(l)-0(2)# 1 O(6) # l-Pr(l)-O(2)# 1 O( 1 )-Pd1 ) -0(2) 0(1)#l-Pr(l)-0(2) O(4) # l-Pr( 1 )-O(2) 0(4)-Pr(l)-0(2) O(3) # l-Pr(l)-O(2) 0(3)-Pr(l)-0(2) 0(6)-Pr( 1)-0(2) O(6) # l-Pr(l)-0(2) O(2) # l-Pr(l)-O(2)

143.2(4) 84.7(5) 121.15(15) 64.50(16) 67.19(12) 65.21(13) 59.12(1 1 ) 131.68(12) 84.7(5) 143.2(4) 64.50(16) 121.15(15) 65.21 ( 13) 67.19(12) 127.26(19)

Nd(l)-0(6)

0.2539(3)

Table 3 Selected bond lengths (nm)and angles (") for complex 2 Nd(1)-O(1) Nd(l)-0(2) 0(1)-Nd( 1 )-O( 1) # 1 0(1)-Nd(l)-0(4) # 1 O(1) # l-Nd(l)-0(4) # 1 0(1)-Nd(l)-0(4) O(1) # l-Nd(l)-0(4) O(4) # l-Nd( 1 )-0(4) O(l)-Nd(l)-0(3)# 1 0(1)#1-Nd(l)-O(3)#1 O(4) # l-Nd(l)-0(3) # 1 0(4)-Nd( 1 )-O(3)# 1 O( 1 )-Nd( 1 )-0(3) O( 1) # 1-Nd(1 )-0(3) O(4) # l-Nd(1)-0(3) 0(4)-Nd( 1 )-0(3) O(3) # l-Nd(l)-0(3)

0.2373(3) 0.2843(3) 160.27(15) 77.7(2) 86.5(3) 86.5(3) 77.7(2) 73.0(9) 105.14(12) 72.89(12) 51.8(4) 117.6(4) 72.89(12) 105.14(12) 117.6(4) 51.8(4) 168.9(2)

Nd(l)-0(3) Nd( 1)-0(4) 0(1)-Nd(1)-0(6) O(1)# l-Nd(l)-0(6) O(4) # l-Nd(1 )-0(6) 0(4)-Nd( 1 )-0(6) O(3) # 1-Nd(1 )-O(6) 0(3)-Nd(1)-0(6) O(l)-Nd(1)-0(6) # 1 O(l)#l-Nd(1)-0(6)#1 O(4) # 1-Nd(l)-0(6)# 1 0(4)-Nd(l)-0(6) # 1 O(3) # l-Nd(l)-0(6)# 1 0(3)-Nd( 1 )-0(6) 1 0(6)-Nd(l)-0(6) # 1 O( 1)-Nd(l)-0(2) O(1) # l-Nd(l)-O(2)

0.2537(4) 0.2476(8) 80.09(10) 118.80(10) 149.4(4) 126.4(4) 116.01(14) 74.67(14) 118.80(10) 80.09(10) 126.4(4) 149.4(4) 74.67(14) 116.01(14) 50.67(16) 59.20(9) 131.57(10)

O(4) # l-Nd(l)-O(2) 0(4)-Nd(l)-0(2) O(3) # l-Nd(l)-0(2) 0(3)-Nd(l)-0(2) 0(6)-Nd(l)-0(2) 0(6)# l-Nd(l)-O(2) 0(1)-Nd(l)-0(2)# 1 0(1)#1-Nd(l)-0(2)# O(4) # l-Nd(l)-O(?) # 0(4)-Nd(l)-0(2)# 1 O(3) # 1-Nd(l)-0(2)# 0(3)-Nd(l)-0(2) # 1 0(6)-Nd(l)-O(2) # 1 0(6)# l-Nd(l)-0(2)# . 0(2)-Nd( 1)-0(2) # 1

1 1 1

1

85.1(5) 142.8(4) 64.63(13) 120.91( 12) 65.36(1 1 ) 67.49(10) 131.57(10) 59.20(9) 142.8(4) 85.1(5) 120.91(12) 64.63(13) 67.49(10) 65.36(11) 127.48(15

Table 4 Selected bond lengths (nm) and angles ("1 for complex 3 Er( 1 )-O( 1 ) Ed1 )-O(2) Er( 1 )-0(3) Er(l)-0(4) 0(3)-Er( 1 )-O(2) 0(3)-Er( l)-O(12) O( 2)-Er(1 )-O( 12) 0(3)-Er(l)-0(5) 0(2)-Er(l)-0(5) 0(12)-Er(1)-0(5) 0(3)-Er(l)-0(8) 0(2)-Er(l)-O(8) 0(12)-Er(1)-0(8) 0(5)-Er( I )-0(8) 0(3)-Er(l)-0(9) 0(2)-Er( 1 )-O(9) 0(12)-Er(1 )-0(9) 0(5)-Er(l)-O(9) 0(8)-Er(l)-0(9)

0.2736(4) 0.2328(3) 0.2319(3 0.2743(3) 157.41(13) 124.17(12) 75.73(13) 77.47(13) 81 . 1 1 ( 13) 129.82(14) 117.90(12) 74.25(12) 76.93(13) 137.24(13) 68.38(12) 115.18(12) 115.82(14) 114.28(13) 5 1 .43(12)

Er( 1 )-0(5 ) Er(l)-0(6) Er( 1 )-O( 8)

0.2475(4) 0.2581(4) 0.2482(3)

Ed1 )-0(9) Ed 1 )-O( 11) Er( 1 )-O( 12)

0.2484(4) 0.2538(4) 0.2444(4)

0(3)-Er(l)-O(ll) 0(2)-Er(l)-O(ll) O( 12)-Er(1 )-O( 1 1 ) 0(5)-Er( 1 1-O( 11) O( 8)-Er( 1 )-O( 1 1 ) 0(9)-Er( 1 )-O( 1 1 0(3)-Er(l)-0(6) 0(2)-Er(l)-0(6) 0(12)-Er(1)-0(6) 0(5)-Er(l)-0(6) 0(8)-Er(l)-0(6) 0(9)-Er(l)-0(6) O(ll)-Er(l)-0(6) 0(3)-Er( 1)-0( 1) 0(2)-Er( l)-O(1 )

82.00(13) 120.59(13) 5 1 .30(15) 151.97(14) 69.81( 13) 74.52(15) 100.71(13) 70.14(12) 80.16(15) 50.05(13) 141.35(13) 163.73(14) 117.04(14) 104.09(10) 61.41(10)

0(12)-Er(1)-0(1) 0(5)-Er( 1 )-0(1) 0(8)-Er( 1 )-O( 1 ) 0(9)-Er(l)-O(1) O( 11 )-Ed1 )-O( 1 ) 0(6)-Er(l)-O( 1) 0(3)-Er(l)-0(4) 0(2)-Er( 1 )-0(4) 0(12)-Er(1)-0(4) 0(5)-Er(l)-0(4) 0(8)-Er(l)-O(4) 0(9)-Er(l)-0(4) O(ll)-Er( 1 )-0(4) 0(6)-Er(l)-0(4) O( l)-Er( I )-0(4)

129.42(11 ) 70.57(13) 67.03(13) 66.15(12) 133.77(13) 106.88(12) 61.21(10) 125.21(1 1) 71.49(12) 87.55(13) 135.20(12) 118.31(11) 65.74(13) 61.98(12) 156.43(11)

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of both theoretically calculated values and measured values are in accordance with their formula of the complexes, and it shows that the Schiff base ligand is neutral. Their molar conductance in DMF solvent (25 % , l . O ~ 1 0 - ~ m o l * L - are ' ) 18.0 ( l ) , 19.0 ( 2 ) , and 18 . 3 ( 3 ) S cm2 mol - ' , respectively , suggesting that the complexes are all non-ele~trolytes['~] . The broad absorption band at 3451 cm-' due to the hydroxy group in the IR spectra of the free ligand appears at lower frequency in the corresponding complex, viz., 3418 c m - ' ( l ) , 3420 c m - ' ( 2 ) , and 3421 cm-'( 3 ) , showing coordination of oxygen atom of the phenolic hydroxy with the central Ln ( III ) ion. The shift of the C - 0 stretching vibration of the phenolic part of o-vanillin from 1260 cm-' (free ligand ) to 1235 cm-'( 1 ) , 1237 cm-' ( 2 ) , and 1239 c m - ' ( 3 ) also supports the coordination of oxygen atoms. However, a strong band in the free Schiff base ligand occurring at 1617 cm-' due to C = N stretching is found shifted to higher frequency, viz. , 1638 cm-' ( 1 ) , 1640 c m - ' ( 2 ) , and 1642 c m - ' ( 3 ) , but the nitrogen atom of azomethine was regarded as no complex with Ln( )[159161. And also, a new band at 488 cm-'( l ) , 489 c m - ' ( 2 ) , and 490 c m - ' ( 3 ) was Ln - 0 stretching vibration[l7], whereas there was no such a band for the ligand. Among the five absorption peaks at 1500 cm-' ( v , ) , 1297 cm-'( v 4 ) , 1024 cm-' ( v 2 ) , 818 c m - ' ( v 3 ) and 739 c m - ' ( u 5 ) , Au ( v , v 4 ) = 203 cm-I in the spectra of complexes are indicative of coordinated nitrates which behave as bidentate ligand[18.191 , corresponding to the results of the deter-

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mination of single crystal structures. The 'H NMR spectra of the complexes indicate that the proton of phenolic hydroxy of Schiff base ligand in complexes was not deprotonated.

2.2 UV/vis spectra UV/vis data of the ligand and the complexes are listed in Table 5 . Three absorption peaks of the free Schiff base ligand appears at 3 1 8 . 0 , 277.5 and 227.5 nm in the range of 200 -400 nm. The band of 318.0 nm may be assigned to a n-x transition of conjugation between lone-pair electron of p orbital of N atom in C = N group and a conjugated x bond of benzene ring. A peak at 277.5 nm is assigned to a x-x * transition of conjugation system of Schiff base. Uv/vis spectra of three complexes are very similar and almost the same as that of Schiff base ligand.

2.3 Crystal structure of complexes The X-ray diffraction analysis shows that complexes 1 and 2 are allomers. Comparably, complex 3 contains more half a free water molecule. Fig. 2 shows the molecule structure and the coordination environment of center Nd atom of complex 2. The crystal structure of complex 2 consists of a Nd ( ) cation, two Schiff base ligands and three nitrate anions. The Nd atom displays a distorted biapical anti-hexahedron prism geometry, and each Nd atom is ten-coordinated by six 0 atoms [ Nd - 0 distances in the range of 0.2476( 8 ) 0. 2539 ( 3 ) n m ] from three nitrate groups and four 0 atoms from two Schiff base ligands,

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Table 5 UV/vis swctra of k a n d and comdexes HL 1

2 3

318.0 317.5 317.5 317.5

14625 28980 27855 30615

277.5 276.5 276.0 277.5

10560 22635 21570 24180

227.5 223.3 224.3 224.5

20985 57090 50370 59265

Fig. 2 Molecular structure of complex 2 and coordination environment of Nd atom

Zhao G L et a1 . Syntheses, Crystal Structures and Kinetic Mechanisms of Thermal Decomposition of RE Complexes

with Nd - 0 distances 0.2373 ( 3 ) and 0.2843 ( 3 ) nm, respectively. Eight 0 atoms [ 0 ( 1 ) , 0 ( 2 ) , 0 ( 3 ) , 0 ( 6 ) , O ( l A ) , 0 ( 2 A ) , 0 ( 3 A ) , and O ( 6 A ) ] form an anti-hexahedron prism polyhedron, while the other two 0 atoms occupy the apical positions. The dihedral angels defined by coordinated nitrate 0 atoms and Nd atoms are 35.67’, 36.73’, and 36.73’, respectively. Although the Schiff base ligand has three coordination sites, only two 0 atoms bond to the Nd atom in complex 2. All C atoms from a Schiff base ligand nearly lie in one plane and the angle of two adjacent planes is 83.16’.

2.4 Thermogravimetric analysis The process of thermal decomposition of the title complexes are very similar and four stages of decomposition were observed, the residues are rare earth oxides. No weight loss was observed of complexes 1 and 2 below 230 “c, indicating that there are not any small molecules of solvent in the complexes. The TGDTG curves of complex 3 are shown in Fig. 3 . The first step of decomposition of the complex starts at 53.5 “c to 100. 6 “c , the observed weight loss (1.17%) corresponds to the elimination of 0. 5 mol crystal water (theoretical loss is 1.07% ) . The second step decomposition temperature is in the range of 231.1 283.8 “c with a mass loss of 16.62% which corresponds to the loss of three NO2 (theoretical loss is 16.33%). The third weight loss 12.37% (calc. 12.44% ) at 283.8 340.6 “c corresponds to the decomposition of p-toluidine of the Schiff base ligand. The forth step of decomposition at 340.6 587.1 “c with a weight loss 47.93% , accompanied with the

-

-

-

........................................... 100 200

300 400

500 600

TIK

Fig. 3

TG-DTG curves of complex 3

decomposition of o-vanilly , is the decomposition of another Schiff base ligand (calc . 47.21 % ) . The residue weight 21.91% corresponds to Er2032 2 . 6 4 % . This result is in good accordance with the composition of the complex. The kinetic mechanisms of thermal decomposition from the second stage to the fourth stage of the complex were investigated by integral and differential methods. The kinetic equations were confrmed by : methods of non-isothermal ACHARL201 l n [ g ( a ) / T * ] = ln(AR/PE)-E/RT and non-isothermal COATS-REDFERNIZO1:

(1)

In[ ( d a l d t ) / f ( a ) ]= lnA/P-E/RT (2) where a is the fraction of conversion, d a / d T is the rate of conversion, T is the absolute temperature, A is the pre-exponential factor, R is the gas constant, E is the apparent activation energy, P is the linear heating rate, g ( a ) and f(a ) are the integral and differential mechanism functions respectively. The basic parameters of a , T and d a /d T obtained by the TG-DTG

Third stage a,

I

700 800

tl “C

Table 6 Base data for complex 3 obtained from TG-DTG curve from the second to the fourth stages’ Second stage

273

Fourth stage

(da/dt),

T/K

a,

(da/dt),

TIK

a,

( d a / d t ),

0.03802 0.06844 0.09886 0.13308 0.17110 0.21673 0.27757 0.35741 0.46768 0.54753 0.62357 0.69582 0.76046 0.82129 0.88213

0.00659 0.0069 0.0072 0.00762 0.00884 0.01128 0.01518 0.02214 0.02007 0.01711 0.01605 0.01501 0.01404 0.01312 0.01246

527.87

0.0707 1

0.00786

560.98

0.095238

0.01372

629.85

531.6 536.71 541.29 545.65 549.48 553. I6

0.12121 0.30303 0.52525 0.73737 0.86869 0.94950

0.02753 0.03913 0.06417 0.04295 0.02601 0.01651

565.15 569.42 573.76 578.08 582.28 586.36 590.34 594.27 598.18 602.11 606.04 609.98

0.174603 0.285714 0.396825 0.507937 0.587302 0.666667 0.730159 0.793651 0.84127 0.873016 0.920635 0.952381

0.01547 0.01698 0.0171 0.01576 0.01348 0.01111 0.00916 0.0078 0.00697 0.00653 0.00631 0.00619

641.87 653.91 666.01 678.32 690.93 703.77 716.88 728.93 740.45 752.27 764.67 776.1 787.98 799.82

JOURNAL OF RARE EARTHS, Vol. 2 4 , No.3 , Jun . 2006

274

curves are listed in Table 6 . Plotting In [ g ( a ) / T2] and In[ (da/dT)/f( a ) ] vs. 1/TL211 respectively and using a linear least squares method, the linear regression of the data in each thermal decomposition process is carried out. Calculated kinetic parameters E , A and linear correlation coefficients r are listed in Table 7 . When the values of E and A obtained by the two

Table 7 and dealing 1nA-E with linearity fitting by least squares fit, we can get a l = 0.218, bl = -6.2835, r = 0. 9985; a 2 = 0. 2225, 6 2 = - 0.4345, and r = 0.9997 for the second step, and a l = 0.2061, b l = - 8 . 8313, r = 0.9984; a 2 = 0.2096, b2 = - 0.6095, and r = 0.9985 for the third step, and a l = 0.1615, b l = - 10.09, r = 0.9909; methods are approximately equal, the linear correlaa2 = 0.1646, b2 = - 1.3944, and r = 0.9659 for the tion coefficient is better and the values of E and 1nA fourth step. So the expiatory effect expression of inteobeys the universal law, it can be concluded that the gral kinetics and differential kinetics are lnAl = relevant function is the probable thermal decomposi0.218E -6.2835 and lnA2 = 0.2225E - 0.4345 for tion mechanism of the complex. For the second stage the second stage, 1nA = 0.2061 E - 8.83 13 and 1nA 2 of decomposition of the complex 3 , it can be suggested = 0. 20966 - 0. 6095 for the third stage, lnAl = that the functions of the possible mechanism are g ( a ) = [ 1 / ( 1 - a ) 1 / 3 - 1 ] 1 / 2 a n d f ( a ) = 3 / 2 ( 1 - ~ 1 ) ~ / ~ 0.1615E - 10.09 and lnA2 = 0.1646E - 1.3944 for the fourth stage respectively. [ 1/( 1 - 1 1 - l of function No.6 based on the data in Table 7. The kinetic equations of this process are

In= { [ l- ( 1 - 1]1/2/T2/ = ln(AR/PE) - E / RT and da/dT = A e 3/2 ( 1 - a )4/3 [ 1/( 1 - 1 ] - I . The decomposition mechanism was governed by three-dimensional diffusion (4D3). By the same way, the functions of thermal decomposition and kinetic equations for the third and fourth stages of complex 3 are the same as the second stage. By using the expiatory effect expression[20*u1 1nA = aE + b ( a , b are expiatory parameters) and integral kinetic parameters and differential parameters in Table 7

Fitted data for the second stage of thermal decomposition of complex 3

D1 506.CB75 M 56o.m

1D3 s84.m 2D3 634.m

104.4237 0.9381 D1 51.W31

10.834

0.oBll

116.2341 0.9566 M

156.8928

34.073

0.549

1 2 O w . 0.9612 ID3

m.m

44.212

0.m

1 3 1 . m 0.9768 2D3 2 . m - 0 7

0.0018

0.8991 0.0060 4m 560.974 M.15 0.9333 A1 60.9916 14.378 0.m A1.5 -5.8E-07 0.0018 0.4100 A2 - 5 . E - 0 8 0.0019 O.ClD3 A3 -3.3E-07 0.0018 0.8738 A4 -3.3E-07 0.0019 0.932 R2 -R.@B - 1 6 . B 0 . m R3 -3.3E-07 0.0019 0 . B P1 -206.213 -45.188 0.7934 P2 -1.X-07 0.0019 0.9233 P3 -377.889 -84.818 0.9508 P4 -399.345 -@.% 0.9585 C2 I.=-07 0.0019 0.m C1.5 3 . m - 0 7 0.0019 0.8675

3m 460.m 91.76682 0 . m 3m -13.3~1

4m

8l2.W

A1 M.IM A1.5 23.0955 A2 172.5733

172.2856 0 . m

71.i337 44.5955 30.88192 A3 1 1 2 . m 17.07314 A4 81.797&2 10.07015 R2 2H.m 51.3%

R3 312.8532 PI 348.5272 P2 119.772 p3

76.8567

P4 5 . m C2 5a.m c1.5 m.6251

0.9900 0.W 0.W 0.9888

0.W 0.m

61.15187 0.9761 47.41e 0.9360

18.53568 O.%I3

8.7oB8ro O.%l l . m 0.m 108.7107 0.9952

20.70B41 0 . W

-6.16

References : Schiff bases and their uses [ J ] . J . Scient . Ind. Res., 1974, 33: 76. [ 21 Dhar D N , Taploo C L. Schiff bases and their applications [ J ] . J. Scient. Ind. Res., 1982, 41: 501. [ 3 ] Liu X L, Liu Y H, Shi Y C, et al. Application of Schiff's bases in organic synthesis [ J ] . Chinese Journal of Organic Chemistry (in Chin.), 2002, 22(7): 482. 41 Hodnett E M , Dunn W J . Structure-antitumor activity correlation of some Schiff bases [ J ] . J . Med. Chem.,

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1970, 13(4): 768. 51 You X Z , Meng Q J , Han W S. Progress in Coordination Chemistry [ M ] . Beijing : Higher Education Press, China, 2000. 24. 61 Costes J P, Dahan F, Nicodene F. Structure-based description of a step-by-step synthesis of homo- and heterodinuclear (4f, 4f') lanthanide complexes [.I.]Inorg. Chem., 2003, 42: 6556. 71 Golcu A , Turner M , Demireli H , et al. Cd( fl ) and Cu( 1 ) complexes of polydentate Schiff base ligands: synthesis, characterization, properties and biological activity [ J ] . Inorg. Chim. Acta., 2005, 358: 1785. 8 1 Vigato P A , Fenton D E . Schiff base complexes of lanthanides and actinides [.I] . Inorg. Chim . Acta, 1987,

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ment of Crystal Structure [ M I . Germany: University of Gottingen, 1997. Geary W J . Use of conductivity measurements in organic solvents for the characterization of coordinate compounds [ J ] . Coord. Chem. R e v . , 1971, 7: 81. Koen B , Yury G G , Rik V D , et al. Rare-earth-containing magnetic liquid crystals [ J ] . J . Am. Chem. soc., 2000, 122: 4335. Xie W H , Heeg M J , Wang P G. Formation and crystal structure of a polymeric La ( H2 salen) complex [ J ] . Inorg. Chem., 1999, 38: 2541. Liu G F, Zhao Y N , Liu X X . Preparation and characterization of coordination compounds on rare earth nitrate with Schiff base derived from o-vanillin and 1-naphthylamine [ J ] . Acta Chim. Sinica, 1992, 50(5): 473. Nakamoto K. Translated by Huang D R , Wang R Q.

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Infrared and Raman Spectra of Inorganic and Coordination Compounds [ M 1 . Beijing: Chemical Industrial Press, China, 1986. 251. Liang Y Q, Zhao Y N , Zhang S G , et a l . Raman and infrared spectra of rare earth crown ether complexes [ J ] . Acta Chim. Sinica, 1983, 4 1 ( 3 ) : 198. Chen J H , Li C R . Thermal Analysis and Application [ M I . Beijing: Science Press, China, 1985. 128. Li Y Z . Thermal Analysis [ M 1. Beijing: Tsinghua University Press, China, 1987. 74. Hu R Z , Yang Z Q , Liang Y . The determination of the most probable mechanism function and three kinetic parameters of exothermic decomposition reaction of energetic materials by a [ J ] . Thermochim. Acta, 1988, 123: 135.

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Synthesis and Properties of Ternary Europium Complexes with Aromatic Carboxylic Acid and Nitrogen-Containing Heterocyclic Ligand Ma Ruixia' , Wang Ruifen' * , Wang Shuping' , Zhang Jianjun2( 1 . College of Chemistry and Material Science , Hebei Normal University, Shijiazhuang 050016, China ; 2 . Experimental Center, Hebei Normal University , Shijiazhuang 050016 , China ) Abstract: Seven ternary Eu (

m

) complexes were and luminescence spectra of the title complexes reveal synthesized with aromatic carboxylic acid ( benzoic acthat the fluorescence of the complexes in which 1 , l o id, phenylacetic acid, phenylpropionic acid and cinphenanthrolin as the second ligand are more intensive namic acid) as the first ligand and 1,lO-phenanthrothan those complexes in which 2,2'-dipyridyl as the second ligand . The order of the strongest emission line or 2,2'-dipyridyl as the second ligand . The ternary Eu( 1) complexes were characterized by elemental peak of seven ternary complexes is: E ~ ( p - P P A ) ~ p h e n analysis, IR and TG-DTG methods. In these complex> E ~ ( B A ) ~ p h e>nE ~ ( p L A ) ~ p h e>nE ~ ( B A ) ~ b i p>y es, the Eu( ) ions are bonded to the oxygen atoms Eu(PLA),bipy > E ~ ( C A ) ~ p h e n . H>~E0 ~ ( C A ) ~ b i p y of carboxylate and the nitrogen atoms of neutral li(BA: benzoic; PLA: phenylacetic; P-PPA: phenylgands . Four complexes whose second ligand is 1 10propionic ; CA : cinnamic ; phen :1 , lo-phenanthroline phenanthrolin have fine thermal stability. Excitation and bipy : 2 , 2'-dipyridyl) . Key words: aromatic carboxylic acid ; europium ; ternary complex; thermal decomposition; fluorescence spectra; rare earths

m

(See J . Chin. RE. Soc. (in Chin. ), 2006, 24(3) : 274 for full text)