Indian Journal of Chemistry Vol. 38A, December 1999, pp. 1286-1290

Synthesis and characterization of some lanthanide complexes of 2,6-diacetylpyridine

2-thenoylnicotinoyldihydrazone

B Singh* & T B Singh

Department of Chemistry, Faculty of Science, Sanaras Hindu University, Varanasi 221005 , India

Received 3 Jilly 1998; revised 4 Ocrober 1999

The complexes of the type [Ln(H2dapthnh)C1(H20hl­CI 2[Ln=La. Pr, Nd , Sm. Eu , Gd, Tb and Dy; H2dapthnh = 2,6-diacetylpyrid ine-2- thenoyl nicotinoyldihydrazonel have been synthesized by reacting [Ln(Hdapth)C1 2(H20 )31CI [Hdapth=2,6-diacetylpyrid inemono(2-thenoylhydrazone) with ni cotinoylhydra­zine in ethanol and characteri zed by analytical, molar conductance, IR , I H NMR , electroni c and FAS mass data. The \JOs iti on and shape of the hypersensitive transitions 4/w2 --1 4C 5/2 ,

-Cm Il1 the neodymium complex indicate eight coordinate geometry ~round the Ln(lll ) ion s. TIle symmetry of the eight coo rdi nate Eu( llI ) and Tb(l ll ) complexes has been determined from the emi ssion spectra.

Interes t in lanth an ide chemistry has been recently increas in g ow ing to the use of lanthan ide compounds as biological probes I , in materia ls2

-4 and chemjcal processes . These studies have produced technological developments in sc ienti fic and industrial applications. More recentl y, a fac ile generation of stable acyclic and mac rocyclic sc hiff bases using lan thanides as templating agents was found and a variety of complexes have been synthesized . In view of the above interesting aspects of the lanthan ide chemjstry, reaction of [Ln(Hdapth)CbCH20), ]CI with nicotinoy lh ydrazine has been carried out and the resul ting compounds have been characterized. The re:ults are reported in the present paper.

Experimental 2,6-Oi acety I pyrid i ne, 2-thiophenecarbox y I ichydra­

zide (Aldrich , Chemical Company, USA), ni cotin am ide (Sigma, USA) and hydrated lanthanide (III) chlorides (Indian Rare-Earth Ltd. , Kerala) were used as ohtained.

Preparation (~lligalld Nicotinoylhyd raz ine Cnh ) was prepared by reacting

ni coti namide and hydrazine following the literature

method5 It was characterized by m.pt.156-58°C (litS

160°C) and the hydrazine content 23.56 (23.32%). The 2,6-diacetylpyridinemono (2-thenoylhydra­

zone), Hdapth, has been synthesized and characte­rized6

. Hdapth was prepared in situ by adding an ethanolic solution (15 cm3

) of 2-thenoylhydrazine (0.5 mmol, 0.071 g) to a solution of 2,6-diacetyl­pyridine (0.5 mmol, 0.0815 g) in the same solvent (15 cm3

) and refluxing for - 2h on a water bath. The nicotinoylhydrazine (0.5 mmol, O. 0685g) in ethanol (10 cm3

) was added to the above reaction solution followed by a catalytic amount of concentrated acetic acid (0.5 cm3) and refluxed for - 3h . A solid compound separated during this time, which was cooled to the room temperature and fil tered off. The compound was recrystallized from hot ethanol, yield 0 .05g (25%). It was characterized by m.pt. (253-55°C), hydrazine content 15 .52 (15.74%), JR, 'H NMR and mass spectral data. The molecular ion (M+) peak appears at mlz = 406 in the mass spectrum and indicates formation of H2dapthnh. Some important peaks at mlz= 300, 176, 148, 130, 111, 78 , and 43 are attributed to the fragments C4H3SC(O)NHNC(CH,)CsH3NC(CH3)WNH, H3C-C5H3NC(CH,)NNHC+O, H3CC5H3NC(CH3)W NH,­NCC5H, NC+N, +OCC4H,S, C5H5N+ and C~NH, respectively.

Preparation of complexes The preparation and characterization of the

precursor complexes [Ln(Hdapth)C1 2(H20 h ]CI have been reported e lsewhere6

. The complexes Ln(H2dapthnh)C1(H20 h ]CI2 were obtained by reacting [Ln(Hdapth)Clz(H20h]CI (I mmol) with nicot inoylhydrazine (I mmol) in refluxing ethanol (25 cm') fo r -4h on a water bath. The reaction soluti on was concentrated to -3 cm' and addition of acetonitrile to it resulted in a gummy solid. It was separated by decantation. The maceration of the gummy solid with acetonitrile several times yielded a microcrystalline compound. It was filtered and washed with ethanol-acetonitrile (I :3 ,. v/v) and dried in desiccator under reduced pressure.

The La (111) or Pr(lII) chloride (1 mmol) in ethanol (10 cm' ) was added to a suspension of H2dapthnh ( I

NOTES 1287

Table I-Characterization data of Ln(III) complexes of H2dapthnh

Complex. % yield. colour. formula wt. m.p. (OC) C H

[La(H2dapthnh)CI(H20h]CI2• 90. 34.79 3.00 light yellow. 687 .82. 337 (34.93) (3.22)

[Pr(H2dapthnh)CI(H20 h ]CI2• 91. 34.75 3.40 yellow. 689 .82. 305 (34.83) (3.21)

[Nd(H2dapthnh)CI(H20 h ]CI2• 83. 34.49 3.10 yellow. 693 .15.305 (34.66) (3. 19)

[Sm(H2dapthnh)CI (H20 h ]CI2• 70. 34.30 3 .30 dark yellow. 699 .27 . 285 (34.36) (3 .17)

(Eu(H2dapthnh)CI(H20 )21CI2.95. 34.10 3.38 dark yellow. 700.87. 322 (34.28) (3 .16)

[Gd(H2dapthnh)CI (H20 h lCI2• 84, 33.82 3.00 dark yellow. 706.16. 330 (34.02) (3.14)

(Th(H2<1apthnh)CI(H20 )2]CI2. 90. 33 .78 2.95 dark yellow. 707 .84. 325 (33.94) (3 .1 3)

[Dy(H2dapthnh)CI(H20 h ]CI2. 91. 33 .59 3.30 yellow. 7 1 1:41 • 340 (33.77) (3.12)

mmol) in the same solvent ( 15 cm\ resulting in a clear solution which was refluxed for -4h on a water bath. The reaction solution was concentrated to - 3 cm3 and acetonitrile was added which resulted in a gummy solid. It was macerated with acetonitrile several times to get the microcrystalline compound. The compound was filtered and washed with ethanol­acetonitrile (1 :3, v/v) and dried in vacuo under reduced pressure.

The compounds, isolated from the above two different methods, have the same metal-ligand stoichiometry as shown by the analytical and molar conductance data. Thus, the compounds [Ln(H2dapthnh)CI(H20h]CIz resulted from the reaction of nicotinoylhydrazine with coordinated ligand Hdapth In the complexes [Ln(Hdapth)CI2(H20 )31CI .

The metal 7 and hydrazi ne8 were determined volumetrically . Chloride was determined8 gravimetri­cally . The analytical data and general behaviour of the complexes are given in Table 1.

Carbon, hydrogen and nitrogen contents were microanalysed on a Heraeus Carlo Erba 1108 analyser. The molar conductance was measured in

Found (Calcld). % Ilerr Molar

N M CI N2H4 8M conductance 0-1 cm2

mol-I

12.42 20.45 15 .25 9.50 0 185 (12.22) (20. 19) (15.46) (9.30)

12.05 20.70 15.21 9.45 3.36 210 (12.18) (20.43) (15.42) (9.28)

12.00 20.58 15.10 8.95 3.42 169 (12.12) (20.8 1) (15.34) (9.23)

12.19 21.25 14.95 8.95 2.59 169 (12.02) (21.50) (15.21) (9. 15)

12.19 21.30 15.35 9.40 3.64 200 (11.99) (2 1.68) ( 15.17) (9. 13)

11.75 22. 15 15.27 8.80 7.73 192 (1 1.90) (22.27) (15 .06) (9 .06)

11.69 22.25 14.85 8.85 9.50 181 (11.87) (22.45 ) (15 .02) (9 .04)

11.98 22.60 14.85 8.78 10.25 175 ( 11.8 1) (22 .84) (14.95) (8.99)

10-3 M methanol so lu tion on WTW conductivity meter. Mass spectrum of hydrazone and FAB mass spectrum of Nd(III) complex were obtained on a Jeol 0-300 C and Jeol SX-102/0A 6000 mass spectrometers, respectively. The TG and OTA studies were perfo rmed on a Stanton Red-craft STA-780 thermal analyse r in plantinum crucible and usi ng alumina as a reference. The compound was heated at a rate of 10DC/min in atomospheric air. Infrared spectra of the hydrazone and the complexes were recorded in KBr disc on a FJ'-IR Jasco-5300 spectrophotometer. I H NMR spectra of the hydrazone and its La(III) complex were obtained on Jeol FX 90 Q multinuclear spect rometer in OMSO-d6 solution . Room temperature magnetic susceptibility was measured on a Cahn-Faraday e lec trobalance using Hg[Co(NCS)41 ca li brant and was corrected for di amagneti sm') Electronic spectra were recorded in solid (nuj ol) and in 10-2 M ethanol solution on a Shimadzu UV-v is 160 A spectrophotometer. Emiss ion spectra of Sm(Im, Eu(III) and ' Tb(llI) complexes were obtained at liquid nitrogen temperature on a Perkin-Elmer MPF-44P f luorescence spectrophotometer after exci ting the compounds with 350 nm radiation .

1288 INDIAN J CHEM, SEC. A, DECEMBER 1999

Results and discussion Reaction of lanthanide(Ill) chlorides with

H2dapthnh and that of [Ln(Hdapth)CIz(H20)~]CI with nicotinoylhydrazine in ethanol in I: I stoichiometric ratio yielded the same compounds [Ln(H2dapthnh)­CI(H20)2]CIz . Since H2dapthnh is isolated in less yield, the complexes have been synthesized by following the latter method . They absorb moisture on prolong exposure to the atmosphere. They are insoluble in acetone, chloroform, diethylether and dichloromethane but are fairly soluble in ethanol, methanol, DMSO and DMF. The molar conductance values (Table I) in methanol indicate 1:2 electrolytic 10 nature of the complexes. During detennination of melting points of the complexes, colour changes from yellow to orange at 160-200°C, orange to brown at 250-270°C and melting with shrinking at 285-340°C are observed. These observations are attributed to phase transition of solid and escaping of some volatile moieties as shown by thermal analysis.

In the FAB mass spectrum of [Nd(H2dapthnh)CI(H20h]CI2, a base peak at mlz = 154 is observed which corresponds to the fragment CJI)SCONHNCt. The spectrum shows molecular ion (M+) peak at mlz = 6 19 which is indicative of the monomeric nature of the complex . Some prominent peaks observed are due to fragments [C5H4 NC(0)NHNC(CH))C5H)NC(CH))NNHC(0)C4H)SNd Cit 584, [C5H~C(0)NHNC(CH3)C5H3NC(CH3) NNHC(0)C4H)SNdt 548, [C5H~C(0)NHNd] 265, [C4H)SC(O)NHNCt 154, [C5H5Nt77, [C(O)NHt 43 .

The combined TG and DT A studies were performed on 7.85 mg of [Nd(H2dapthnh)­Cl(H20h]CIz complex. The TG curve shows 10 .1 9% weight loss in the temperature range 80-181 °C, attributed to elimination of two H20 and one HCl molecules which is accompanied by an endothermic peak at 145°C in the DTA thermogram. Further, 15 .28% loss in weight was observed in the temperature range 181-390°C which may be due to escaping of C5H~CO moiety via an exothermic process indicated by a peak at 380°C in the DTA thermogram. On increasin~ the temperature further, a loss in weight was observed upto 680°C through endothermic and exothermic processes . The observed weight losses are 10.83, 2.55 and 29 .29%, which are attributed to escape of CNNHCO, CH3 and C4H)S +

C j H4NCNCH, moieties at 480, 539 and 619°C, respectively . No weight loss was observed beyond the temperature 680°C, poss ibly due to formation of the metal ox ide.

Decomposition pattern of [Sm(H2dapthnh)-Cl(H20)2]Cl1 complex is a lmost similar to that of Nd(ITI) complex. The thermogravimetric curve shows the weight losses of 9.37, 15 .77, 9.14, 3.43 and 27.43% through endothermic and exothermic processes corresponding to the moieties indicated above.

The hyd razone ex hib its bands at 3180, 1660, 1643, 1515 and 1025 cm- I in the infrared spectrum of H1dapth nh whi ch are ass igned to v(N-H), amide J, v(C=N) , am ide II and v(N-N) modes, respectively . In the Ln(llT) complexes, the bands due to amide J, v(C=N), amide II and v(N-N) are observed at 1620-16 10, 1600-1595, 1504-1500 and 1050- 1045 cm- I

,

respect ively. Appearance of the bands due to amide I and v(C=N) at lower frequencies in the complexes, i mpl ies that both carbonyl oxygens and azomethine nitrogens are bonded to the metal ions. The coordination of azomethine nitrogens is also indicated from sh ift of amide II and v(N-N) modes to lower ( 1550- 1500) and higher frequencies ( 1050-1 040 cm- I

), respecti vely . The substituted pyridine ring vibrations observed at 640 (in-pl ane) and 410 cm- I

(out of plane) in the spectrum of H2dapthnh are observed at hi gher frequencies, 660-655 and 425-420 cm- I

, respectively, in the Ln(Ill) complexes, indicating invo lvement of the pyridine nitrogen in bonding.

The spectra of [Ln(H2dapthnh)CI(H20 h ]CIz complexes on compari ng with that of the parent complex [Ln(Hdapth)CI2(H26 h ]CI are similar in appearance except the band due to v(C=O) of the 2,6-diacetylpyrid ine which disappeared due to condensatioll with -N H2 of the nicotinoylhydrazine resu lting in >C=N group. The bands due to thiophene ri ng observed at 1420, I 195 and 905 cm - I ass igned to

ring stretching, C-H bending and Cring-Cexo stretching mvdes. respect ively, remain unchanged in the spectra of the co mplexes showing the non-involvement of th iophene sulphur in bonding. A band observed at 3400-3360 CI11-

1 in the spectra of the complexes are att ributed to v(O H) of H20 . The coordinated nature of water is shown by the presence of bands at 880-875 and 745-740 cm- I due to p, (H20) and pw (H20)

d . I II mo es, respective y .

NOTES 1289

The bonding of hyd~one to the metal ions is further ascertained by the PMR spectral analysis. The signals in free ligand were observed at D 11.26 (CsH~CONH), 11.13 (C4H 3SCONH), 3.69 (CH3), 8.0-8.29 (m) (pyridine), and 7.~3-7 .66(m)

(thiophene), protons, respectively. Two signals due to NH protons indicate two types of environment. The IH NMR spectrum of [La (H2dapthnh)Cl(H20)2]Ch exhibits signals at 0 11.85, 11.67 (NH) and 8.09-8.40 (m) (CSH3N) . The downfield shift in NH and pyridine protons indicates involvement of the carbonyl oxygens, azomethine nitrogens and pyridine nitrogen in bonding. The CH3 protons were observed at 0 3.83 showing downfield shift and suggest the coordination of azomethine nitrogen to the metal ion. The thiophene protons were observed at 0 7.29-7.66 (m) suggesting non-involvement of thiophene sulphur in bonding. The signal due to H20 protons overlaps with CH3 signal and appears as a broad signal. The integrated spectrum agrees with overlapping of CH3

and H20 protons and gives count for ten protons. The complexes except La(III) are paramagnetic in

nature. The magnetic moments of the complexes show little deviation from Van Vleck values 12

,

indicating little participation of 4f-electron in bonding. The relatively high !leff value obtained in case of Smell) complex is due to low J-J separation which leads to thermal population of next higher energy level s and shows susceptibility due to first order Zeeman effect.

The electronic spectrum of Nd (III) complex shows absorptions at 11454, 12115, 13550, 17182, 18796 and 19493 cm- I which are assinged to 4/9/2 ~ 4F312 , 4 FS/2, 4S3/2, 4CS/2, 2c m , 2 KI3/2 and 4C9f2, respectively. These bands occur at longer wavelengths as compared to aqua metal ions l3, which is known as nephelauxetic effect. The nephelauxetic ratio (~),

bonding (b' /2), Sinha (0%) and angular overlap covalency (11) parameters for Nd(III) complex were calculated from the solid state spectra. and tbeir values are 0.977,0.108,2.375 and 0.012, respectively. The nephelauxetic parameter is less than one and bonding, Sinha and angular overlap covalency parameters are positive for this complex showing covalent bonding between the metal ion and the hydrazone '4. The peculiar shape and position of the hypersensitive transitions 4/9/2~ 4CS/2 , 2Cm of the Nd(III) complex is similar to that of eight coordinate complex reported by Karrakerls

. The bands observed at 12484, 13531

and 17152 cm -I in the solution spectrum of Nd(III) complex are assinged to 4/9/2 ~ 4Fs12,4S312 and 4CS12 2Cm, respectively . The solution spectra of the complexes have similar appearance in position and band shape as in the solid state. This suggests no change in coordination number around metal ion due to solvent effed 6

The intensity of the f-f transitions at 12330-12594 (4/9/2 ~ 4 F5I2), 13297-13717 (4/9/2 ~ 4S3/2. 4 Fm ),

17006-17636 (4/9/2 ~ 4C512, 2C-m) and 19011 -20000 cm- I

( 4/1)f2 ~ 2K1 3/2 , 4C 9/2) of Nd(III) complex is calculated by area method ' 5, ' 6 and is presented as oscillator strength . The intensity of normal !-J transiti ons 'is found to be 10.55, 10.00, 13.89 and 8.8: x 106

, respectively and does not show much change whereas hypersensitive transitions 4/9/2~ 4C5/2 , 2Cm di splay large change as compared to the metal aqua ion l 7

. The increase in oscillator strength value for the hypersensitive transition is attributed to the dynamic coupling hetween f-electron quadrupole moments of metal ion and polarizability of ligand l8

.

The emission spectrum of Eu(m) complex shows strong emission lines. The 5Do ~ 7 FI transi tion consists of two components at 590 and 594 nm. The two components of the 5Do ~ 7 F2 transition appear at 6 I 6 and 620 nm, with an additional very weak band at 698 nm in the region of 5 Do ~ 7 F4 transition. The emission lines due to 5Do ~ TFO and 5Do ~ 7F3 transitions are not observed. The higher intensity of electric dipole allowed transition CDo ~ 7F2) compared to magnetic dipole allowed transition (5 Do ~ 7 F ,) suggests absence of ' inversion centre l 9

.

Appearance of two peaks due to each of 5Do ~ 7 FI and sDo~ 7 F2 transitions is consistent with the D2d site symmetr/ o and dodecahednil geometry for the Eu (lII) complex. The Tb(m) ion has two emitting levels CD3. sD4 ) and emission lines are observed at 468 , 482, 554, 588 and 616 nm due to the 5D3 ~ 7 F2,

5D4 ~ 7 F6, SD4 ~ 7 Fs, 5D4 ~ 7 F4 and 5D4 ~ 7F3

transitions, respectively. The emission lines observed . h . f 'D 7F d 5D 7F . . , In t e regIOn 0 " 4 ~ 4 an 4 -) 3 transitIOns are broad without any splitting and suggest higher symmetr/ I around Tb(Ill) ion . The Smell) complex does not fluoresce or fluoresce very weakly even at LNT. It is attributed to in ternal quenching through strong coupling of metal ion with crystal forces21

.

Therefore, no conclusion could be drawn regarding the symmetry around the metal ion .

1290 INDIAN J CHEM, SEC. A, DECEMBER 1999

(I)

Based on the above studies, Structure (I) IS

proposed for the complexes.

Acknowledgement Authors are thankful to Head, Dept. of Chemistry,

BHU for providing laboratory facilities. Recording of mass spectra from CDRI, Lucknow; emission spectra from Bose Institute, Calcutta and TG and DT A thermo grams from Dept. of Chemical Engineering, IT, BHU are gratefully acknowledged. Thanks are also due to UGC, New Delhi for providing financial assistance in the form of project ~o . F-12-58/93 (SR-I) .

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