Indian Journal of Chemistry Vol. 38A, April 1999, pp. 355 - 360

Studies on some lanthanide complexes of acyclic, asymmetrical and symmetrical schiff bases

B Singh· & T B Singh

Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, India

Received 2 January 1998; revised 4 January 1999

Some new complexes of Ln(I1I) chloride [Ln (I1I)=La, Pr, Nd, Sm, Eu, Gd, Th and Dy] with 2,6-diacetylpyridine mono (2-thenoylhydrazone) (Hdapth) and 2,6-diacetylpyridine bis (2-thenoylhydrazone) (H2dapth) have been synthesized. Their chemical compositions have been established as [Ln(Hdapth]CllH20)3]CI and [Ln(H2dapth]CI(H20h]CI2 from analytical , molar conductance and F AB mass data. The Hdapth and H2dapth are coordinated to the metal ions in tetrakis and pentakis fashion . The coordination number nine and eight around the metal ions are established from IR, NMR and electronic spectra, in Hdapth and H2dapth complexes, respectively. The emission spectra revealed symmetry of the ligand field around the metal ions in Sm(III), Eu(III) and Th(llI) complexes.

The 3d metal complexes of 2,6-diacetylpyridine based symmetrical aroyldrazones have been investigated and some interesting aspects have been reported for example, the versatility in the coordination number, the tendency to yield seven coordinate stereochemistry and the flexibility in assuming different confonnation. Pelizzi et al. prepared Hdapth l and H2dapth2 by reacting 2,6-diacetylpyridine and 2-thenoylhydrazine in 1: I and 1:2 molar ratios. The IR spectra and melting points reported by these workers appeared to be similar characteristics of Hdapth and thus complexes of only Hdapth have been reported. The H2dapth is fonned by the acid catalyzed condensation of 2,6-diacetylpyridine and 2-thenoylhydrazine. As the lanthanide ions have tendency to fonn complexes of higher coordination number it is aimed to synthesize the asymmetrical aroylhydrazones from 2,6-diacetylpyridine and to investigate structure and bonding in the resulting complex. The present paper describes the results of the investigations on La(IlI), Pr(III), Nd(III), Sm(III), Eu(III), Gd(UI), Th(III) and Dy(III) complexes of 2,6-diacetylpyridine mono (2-thenoylhydrazone) (I) and 2,6-diacetylpyridine bis (2-thenoylhydrazone) (II).

Materials and Methods 2,6-Diacetylpyridine and thiophene-2-carboxylic

acid hydrazide (Aldrich Chemical Company, USA) and hydrated lanthanide (III) chloride (Indian Rare­Earth Ltd., Kerala) were used as obtained.

Preparation of ligands 2,6-Diacetylpyridine mono (2-thenoylhydrazone)

(Hdapth) was prepared by adding an ethanolic

solution (15 cm3) of 2-thenoylhydrazine (10 mmol,

1.42g) to 2,6-diacetylpyridine (10 mrnol, 1.63 g) in the same solvent (10 cm3

) and refluxing for ca 2h on a water bath. A pale yellow compound separated on cooling the solution to room temperature. The compound was filtered and washed with ethanol. The compound was recrystallized from hot ethanol and dried in desiccator under reduced pressure. It was identified by m.pt. (222°C), hydrazine content 10.73 (11.13%) IR, NMR and mass spectra [mlz 287 (9 .8), 176 (91), 148 (82), 130 (70), 111 (100), 106 (15), 83 (7) and 44 (15%)] .

2,6-Diacetylpyridine bis(2-thenoylhydrazone) (H2dapth) was obtained by refluxing an ethanolic solution (20 cm3

) of 2-thenoylhydrazine (20 mmol , 2.84 g) and 2,6-diacetylpyridine (10 mmol, 1.63 g) in the presence of a catalytic amount (--0.5 cm3

) of acetic acid for -3h on a water bath. A yellow compound separated during reaction. The reaction mixture was cooled, filtered and the resulting compound was washed with ethanol and recrystallized from hot ethanol. It was characterized by m.pt. (270-75 0q,

356 INDIAN J CHEM. SEC A. APRIL 1999

hydrazine content 15.73 (15.55%) IR, NMR and mass spectra [m1z = 411 (3.3), 300 (49), 272 (8.1), 188 (12.6), 176 (100), 160 (2.5), 148 (93), 130 (52), 111 (82), 104 (28),83 (20) and 44 (23%).

Preparation of complexes The complexes [Ln(Hdapth)Ch (H20)3]CI were

prepared by ~ddir~g an ethanolic solution (10 cm3) of Ln (llI) chlonde (1. mmol) to a suspension of Hdapth (1 ~ol, 0.287 g) In the same solvent (20 cm3). The resulting clear solution was refluxed for -2h on a watt:r ~ath and concentrated to -5 ml. The compound precIpItated on adding acetonitrile, which was separated by filtration and washed with a mixture of ethanol-acetonitrille (1:3) and dried in desiccator under reduced pressure. ~e complex [Ln(H2dapth)CI(Hi»2]Ch were

obtaIned by reacting the lanthanidle (ill) chloride (1 mmol) and H2daplth (1 mmol) in ethanol following the above procedure. . ~e me~ls were estimated3 volurnetrically by

tItratIng agaInst EDT A. Chloride was determined4

gravimetrically as AgCI. Hydrazine wa!; determined4

volumetrically by titrating against KI03 solution after hydrolysing the complex for -2h in 4N HCl. Molar conductance was determined in 10.3 Methanol solution on a WTVI/ conductivity meter. Mass spectra of ligands were recorded on a Jeol D-300C mass spectrometer while F AB mass spectra of the metal complexes on ~l Jeol SX-I02tDA 6000 mass spectrometer. Thermal analyses were carried out on a Stanton Redcroft STA-780 thermal analyser in platinum crucible using Ah03 as the reterence in the 27-800 °C temperature range. Infrared spectra were recorded in the solid state as KBr disc on a FT-IR Jasco-5300 spectrophotometer. The IH and I3C NMR spectra were recorded on a Jeol FX-90 Q multinuclear spectrometer in DMSO-d6• Room temperature magnetic susceptibility was measured on a Cahn­Faraday electrqbalance using Hg[CO(NCS)4] calibrant and experimental magnetic sus(;eptibilities were corrected for diamagnetism. Electronic spectra of the neodymium and dysprosium complexes were obtained on Shimadzu 160 A spectrophotometer in nujol and 10.3 M ethanol solution. Emission spectra of solid complexes (Sm, Eu and Th) were reGorded on a Perkin-Elmer MPF-44B fluorescence spectro­photometer.

Results and Discussion Ln (III) chlorides react with Hdapthand H2dapth

and yield the addition compounds of the types [Ln(Hdapth) Ch (H20)3]CI and [Ln(H2dapth)CI (H20)2]Ch. Both types of the complexes absorb moisture on ~posure to atmosphere. They are insoluble in acetone, dichloromethane, chloroform and diethyl ether but are fairly ~luble in ethanol, methanol, DMF and DMSO. The Hdapth complexes are 1: 1 electrolytess in ethanol while H2dapth complexes are 1:2 electrolytess in methanol indicating that one and two of the. chloride ions are out of coordination sPhere, respectively. They decompose in the 300-350 °C temperature range.

The F AB mass spectrum of [Nd(Hdapth) Ch (H20)3]CI shows base peak at mlz = 43 which corresponds to the fragment CONHf. A peak at rnJz = 553 was observed for the molecular ion [M+] which indicates the monomeric nature of [Nd(Hdapth)Ch(H20)3]Cl. A peak due to molecular ion ~] appears at rnJz = 624 in the F AB mass spectra of [Nd(H2dapth)Cl(H20)2]Ch which is in favour of monomeric nature.

TIle combined TGA and DTA studies were made on 8.62 mg of [Nd(Hdapth)Ch(H20h]Cl. The TGA thermogram exhibits a loss in weight 6.96% in the temperature range 107-175 °C, involving three step endothermic processes as shown by three endothermic peaks at 120, 140 and 163°C in DTA thermogram. This is attributed to loss of two H20 molecules. Two endothermic peaks are also observed at 210 and 240 °C in the temperature range 175-315 °C showing escaping of CNNH moiety in two steps. When the temperature was further raised, a weight loss occurred via exothermic steps, at 370, 475, 575 and 705°C exliibiting loss of 11.02, 9.28, 3.48 and 11.02%, respectively. This may be due to excaping of 2HCl, COCH3, CH3 and CsH3N, respectively. No loss in weight is observed on heating beyond 705°C. It may be attributed to the formation of metal oxide as well as some stable non-stoichiometric residue.

The TGA thermogram of [Sm(Hdapth)Ch(H20)3]Cl shows the loss of three H20 and one HCI in the temperature range 120-315 °C involving the endothermic processes shown by the peaks at 140, 155, 169,240,263 and 292 °C in DTA thermogram. On further heating the loss in weight is observed at 375 (2CH3 and CN), 480 (Hel) and 580, 628, 705 °C (C~3S and NH) via the exothermic processes corresponding to the moieites shown. The endothermic peaks at 204 and 409°C and the exothermic peak at 375 °C in the DTA thermogram of

SINGH et al.: LANTHANIDE COMPLEXES OF SCHIFF BASES 357

Table I~erizatjon data of Ln(IIJ) complexes of Hdapth and Hzdapth

Complex Found (Calcd.). % Magnetic Molar-Formula weight C H N M CI N2H. moment conductance

BM ohm·1 cm2

mor l

(La(Hdapth)CIz ~zOh]CI 28.SO 3.18 7.27 23.45 lUI 5.67 0 33.6 586.62 (28.66) (3.26) (7.16) (23.68) (18.13) (5.46) [Pr(HcbIpdl)Clz (HzOh]CI 28.38 3.10 7.32 23.78 17.95 5.63 3.51 35.1 588.62 (28.56) (3.25) (7.14) (23.94) (18.06) (5.44) [Nd(Hdapth)CIz (HzOh]CI 28.25 3.09 7.20 24.08 17.49 5.88 3.58 37.5 591.95 (28.41) (3.23) (7.09) (24.37) (17.07) (5.41) (Sm(Hdapth)CIz.(HzOh]CI 28.31 3.05 6.82 25.34 18.00 5.53 2.86 39.0 598.07 (28.11) (3.20) (7.02) (25.14) (17.78) (5.35) [Eu(Hdapth)Clz (HzOh]C1 27.89 3.00 6.89 25.50 18.03 5.00 3.28 40.5 599.67 (28.04) (3.19) (7.00) (25.34) (17.74) (5.34) (Gd(Hdapth)CIz (HzOh]CI 27.65 3.31 6.76 26.10 17.80 5.54 8.60 39.9 604.96 (27.79) (3.17) (6.95) (25.99) (17.58) (5.29) [Tb(Hdapth)Clz (HzOh]CI 27.70 3.00 6.80 26.00 17.40 5.59 9.39 46.5 606.64 (27.72) (3.16) (6.93) (26.19) ( 17.53) (5.28) (Dy(Hdapth)CIz (Jf20 h]CI 27.39 3.05 6.75 26.89 17.64 5.36 10.72 47.0 610.21 (27.55) (3.14) (6.89) (26.63) (17.43) (5.24) (La(Hzdapch)CI (HzOh)CIz 33.15 2.90 10.25 20.28 15.00 9.00 0 158.0 692.80 (32.94) (3.06) (10.1 I) (20.05) (15.35) (9.24) [Pr(Hz dapth)C1 (HzOhJCh 32.79 3.12 9.85 20.54 15.42 9.43 3.38 162.0 694.79 (32.85) (3.05) (10.08) (20.28) (15.31) (9.21) [Nd(H~)C1 (H2Oh]CIz 32.50 3.16 10.19 20.54 15.44 9.28 3.52 160.0 698.13 (32.69) (3.03) (l0.03) (20.66) (15.23) (9.17) (Sm(Hzdapch)CI (HzOh)Ch 32.25 3.16 9.79 21.15 14.85 9.34 2.32 182.0 704.25 (32.40) (3.0T) (9.94) (21.35) (15.10) (9.08) [Eu(Hzdapth)C1 (HzOh]02 32.\0 2.80 9.82 21.70 15.38 9.40 3.28 190.0 705.85 (32.33) (2.99) (9.92) (21.53) (15.06) (9.07) (Gd(Hzdapth)CI (HzOh]CI1 32.23 3.18 9.63 22.32 15.20 8.78 7.75 199.0 711.14 (32.09) (2.98) (9.85) (22.11) (14.96) (9.00) (Tb(Hzdaptb)CI (H2Oh]CI1 32.00 3.09 9.69 22.40 14.70 9.21 9.18 175.0 712.82 (32.02) (2.97) (9.82) (22.29) (14.92) (8.98) [Dy(H:zdapth)CI (H20h]Ch 32.00 3.15 9.57 22.46 14.53 8.65 10.30 170.0 716.39 . (31.86) (2.95) (9.78) (22.68) (14.85) (8 .93) -The molar conquctance of [Ln(Hdapth) CI2 (H20h] CI in ethanol and that of [Ln(H2dapth)CI (H20h]CI2 in methanol

LNd(Hztiapth)Cl(H20)2]Ch show the loss in weight corresponding to 2H20, 2CH3 and C4H3S moieties, respectively. The compound shows the losses through exothermic process at 466 (2HC1), 592 and 610 (CSH3N and C.H3S) and via endothermic process at 539°C (CO). The decomposition of [Sm(H2dapth)CI(H20h]Ch occurs at 290 (2H20) and 539 (C.H3S) via endothermic and at 370 (2HCl and CQ) and 575°C (CSH3N, CNCH3 and C4H3S) via exothermic processes.

In the infrared spectrum of Hdapth the bands due to v(N-H), v(C=O)dap, amide I and amide II are observed at 3169, 1699, 1653 and 1518 em" , respectively. However, thev(C:::N) appears as a shoulder at 1618 em" . The amide I and v(C=O)dap apear as a composite band at 1635-1620 em-I in the spectra of the

[Ln(Hdapth)Ch(H20)3]CI complexes. The bands due to v(N-H), v(C=N) and amide II modes appear at 3157-3140, 1610-1599 and 1505-1500 em" in the Ln (III) complexes. The appearance of bands due to all the above modes at lower frequencies imply that both the carbonyl oxygens and azomethine nitrogen are bonded to the metal ions. The v(N-N) is observed at 1035 em" in the Hdapth, however in the complexes it appear at higher frequency (1060-1055 em"), which further supports the association of azomethin~

nitrogen with ·lanthanide ions. The involvement of pyridine nitrogen in bonding, is indicated from shifting of in-plane (640) and out-of plane (405 cm-') ring vibrations of the pyridine to the higher frequencies6 654-650 and 425-420 cm-', respectively. The bands due to thiophene ring obtained at 1421,

358 INDIAN J CHEM, SEC A. APRIL 1999

Table 2-Elcctron.ic spectral data ofNd(III) and Dy(III) complexes of Hdaptb and H2dapth

Band (em'l) Spectral S'LT Spectral Oscillator Complex Nujol mull Range (cm'l) Parameter Strength

EtOH soln (Px I 06)

[Nd(Hdapth)C12 (H20 )3]CI 111500 4F312 j3=0.996 t 12484 12269-12820 4FS12 b l12=0.0442 17.49 13-351, 13175-13869 4F7I2, 00/..=0.3915 14.43 13468 4S312

14705-15220 4F912 1')=0.0020 2.00 17152 16891-17825 °4GS12 ,2G712 20.57

19084,19531 19011-19569 4G7I2,4G912 6.59

[Dy(Hdapth.)CI2 (HZO)3)CI 10989 6F712 1F0.979 12405 4Fs12 b l12=0.102 25252 4F712 0%=2.145

1')=0.0111

[Nd(H2dapth)CI (HzO)2]CI2 11337-11686 .4F312 p=0.9855 3.55 12528 12239-12787 4Fs12 bI12=0.1204 12.66

1335 1,13531 13020-13831 4F7I2 , 4SJ/2 0%=1.4713 9.61

11=0.00733 15748-16155 2HlII1 0.873

17064 16835-18691 _4GS12, 2G712 14.19 19047 18903-19342 4G

712 6.91 19507 4G

912

[Dy(H2dapth)CI (H2Oh]CI2 10976 6F712 p=0.9885 12546 6F312 b I12=0.075 8 24813 4F712 0=1.1634

1')=0.0058 -Hypersensitive transition, Ground state of Nd(ilII) and Dy(lII) are 41912 and 6H ISI2 respectively.

1246 and 950 cm,l, assigned to ring stretching, C-H bending and Cring -Cexo respective:ly, remains unchanged in the spectra of complexes showing non­involvement of thiophene sulphur in bonding to the metal ions7. A broad band observed in the 3360-3400 cm'l region is attributed to YeO-H) of water. The coordinated nature of water is shown by the presence of bands at 740-730 and 660-675 cm'l due to Pr (H20) and Pw (H20) modes, respectivel/.

The IR spectrum of H2dapth exhi.bits bands at 3175 y(N-H), 1645 y(C=O) and y(C=N), 1515 (amide II), 1035 y(N-N), and 635, 405 ern' I (pyridine ring vibrations). In [Ln(H2dapth)Cl (H20)2]Ch complexes, bonding of both the carbonyl oxygens and azomethine

nitrogens to the metal ions is inferred from the shifting of YeN-H), [amide I + y(C=N)l-and amide II to lower frequencies 3150-3140, 1620-1595 and 1507-1500 cm'l, respectively. The involvement of azomethine nitrogens in bonding is also indicated from shifting of y(N-N) (1035 Cm'l) to higher frequency (1065-1045 em"). The pyridine nitrogen is found to bond the metal ions in all the complexes as the characteristic bands of pyridine ring vibrations [in- plane (635) and out of plane (405 cm")] are

observed at higher frequencies6 (655-645 and 420-418 cm"). The thiophene sulphur is not involved in bonding as no shift is observed in characteristic frequencies due to thiophene ring7. The coordinated nature of water molecules is shown by presence of band at 750-760 and 670-675 cm" due to Pr (H20) and Pw (H20) modes, respectivel/.

The hydrazone atoms bonded to the metal ions is further ascertained by IH NMR spectral data. 1fJe PMR spectrum of 2,6-diacetylpyridine mono (2-thenoylhydrazone) showed signals at 8 11.13, 8.20-

SINGH et af. : LANTHANIDE COMPLEXES OF SCHIFF BASES 359

8.55 (m) and 7.34-8.03 (m) which are assigned to N­H, pyridine and thiophene protons, respectively. The signals at 2.74 and 2.60 ppm are attributed to eH) protons, because of two different environments around eH). The PMR spectrum of [La(Hdapth)eI2 (H20»)]el showed signals at 11.85 (N-H) and 8.30-8.60 (m) (pyndine protons) ppm. The downfield shift in N-H and pyridine protons are attributed to involvement of the carbonyl oxygens, azomethine nitrogen and pyridine nitrogen in bonding. It was further supported from a down field shift in eH3 protons which are observed at 2.80 and 2.70 in the complex.

The 2,6-diacetylpyridine bis (2-thenoylhydrazone) exhibits signals at 8 11 .13 (N-H), 8.06-8 .34 (m) (eSH3N), 7.27-7 .37 (m) (e4H)S) and 3.40 (eH). The signals due to these protons are observed at 8 11.89, 8.1 0-8.44, 7.29-7 .36 and 3.50, respectively in the spectrum of La(III) complex. The downfield shift in N-H and pyridine signals suggest bonding of H2dapth through carbonyl oxygens, azomethine nitrogens and pyridine nitrogen . The downfield shift in e H) protons may be attributed to coordination through azomethine nitrogens. The signals due to thiophene protons p~mams almost unchanged, indicating non­involvement of the thiophene sulphur in bonding.

The 22.49 MHz proton noise-decoupled 13e NMR spectra of H2dapth and its La(III) complex were recorded in DMSO-d6 . The numbering scheme of e­atoms are shown in Structure II. The signals relating to e -atoms near the coordination sites are remarkably deshielded in comparison to the free ligand. In the spectrum of H2dapth, signals are observed at 161.28 (>e=O), 15 3.92 (>e=N, e2 , e6), 137.01 (e4 ), 120.76 (e3, es), 134.74 (e 2), ' 133 .55 (e), 126.88 (e4', e s) and 12.36 ppm (-e H). In the spectrum of [La(H2dapth)el (H20)2]e I2, the signal relating to carbonyl carbon is not observed because of high excitation energy and shielding effect. The signal due to e3' is also not observed. However, the other signals are observed at 155.50, 137.80, 121.00, 134.68, 126.93 and 12.72 ppm, respectively. The signal due to azomethine carbons shows a downfield shi ft suggesting bonding of azomethine nitrogens to the metal ion . The observed downfield shift in carbon resonance of pyridine imply the bonding of metal ion to the pyridine nitrogen as is inferred from proton NMR and infrared spectra.

The complexes except La (III) show paramagnetic behaviour. The room temperature magnetic moments,

slightly deviate from Van Vleck values9 (Table 1)., indicating little participation of 4felectrons in bonding. The Sm(III) complexes of Hdapth and H2dapth exhibit higher values of magnetic moment, due to thermal population of the next higher J levels of the metal ion, arising from first order Zeeman effecto.

The bands in spectr-a of complexes of Nd (III) and Dy (III) are observed. at lower wavenumbers compared to the corresponding absorption in metal aqua ions II . This has been attributed to the effect of crystal field upon inter-electronic repulsion parameter in the complexes. The hypersensitive absorption 4[912

~ 4G5/l, 2G 712 in Nd(III) complex has been used to probe the lanthanide-ligand interaction and coordination environment around the lanthanide ions. The spectral profiles of hypersensitive bands in [Nd(Hdapth)Ct2(H20)3]e l in ethanol solution is similar to that of solid state (nujol mull) . This indicates that complexes retained their identi ty in solution also l2 . The shape of hypersensitive transition of [Nd(H2dapth)el (H20)2]eI2 suggest coordination number eight around the metal ions l3. The various spectral parameters such as nephelauxetic ratio ((3) , bonding (b I/2), Sinha (8%) and covalency (11 ) (Table 2) have been calculated from the spectra of Nd(IJI) and Dy(IJI) complexes, of Hdapth and H2dapth. The r3 va lues are less than uni ty, b l /2 and 8% values are small and positive. These suggest weak covalent bonding between Ln(IIJ) and ligandsl4. The absorption intensities are presented as oscillator strengths and have been determined experimentally by area method I2,1), For most of bands, the experimental oscillator strength [P exp] (Table 2) are considerably higher than those of aqua ions ls, The considerable increase in intensity of the hypersensitive transition is due to dynamic coupling between quadrupole moment of the f -electrons and polarizability of the ligand l6 resulting in covalent nature of metal-ligand bond,

The emISSIOn spectrum of [Eu(Hdapth)eh (H 20»)]e l exhibit.:; bands at 5 88 , 612, 648 and 696 nm which are assigned to the SDO~7F), 5Do~7F2' SDO~7F3 and SDo~7F4' transitions respectively. The 5 Do~ 7 Fo, transition is absent. The higher intensity of electric dipole-allowe<:l transition CS Do~ 7 F2)

compared to magnetic dipole-allowed transition eDo~7FI) ' suggests absence of centre of symmetryl 7, The appearance of 5 Do~ 7 FI as doublet and the 5 Do~ 7 F2, transition as singlet suggests D3IJ

360 INDIAN J CHEM, SEC A, APRIL 1999

symmetry 18 around Eu(III) ion. The emISSIOn spectrum of [Eu(H2dapth)CI

(H20)2]CI2 shows int~nse component due to the 5Do~7F2' transition at 616 nm. Two more lines are also observed at 592 and 654 run due to 5 Do~ 7 F 1, and 5 Do~ 7 F3 , transitions, respecti vely. The 5 Do~ 7 Fo, transitions is absent suggesting absence of Cnv , Cll or Cs symmetry l9 and inversion centre. The higher intensity of 5Do~7F2' than 5Do~7F), 'indicates a sence of centre of symmetry I 7. The intensity and shape of the transition 5 Do~ 7 F 1, suggests that the actual · polyhedron may arise due to small distortion from more symmetrical arrangement. The appearance of two peaks for each of the 5Do~7F), 5Do~7Fl' transrtlOns are interpretated in temlS of Dld symmetry20 for the 8-coordinate complex.

The emission spectra of Sm(IIl) and Tb(m) complexes of Hdapth and H2dapth are indicative of tr.-, high symmetry of the electrostatic field of ligands slJ1Tounding the metal ions.

Thus it can be concl uded that the molecular fommlae [Ln(Hdapth)CllH20)3]CI and [Ln(H2dapth)Cl(H20h]CI2 have been established for the complexes possessing nine and eight coordi nate metal ions, respectively. The Schiff bases Hdapth and Hcoapth are bonded to the metal ions in tetradentate and pentadentate fashion, respectively, through carbonyl oxygcn(s) azomethine nitTogen(s) and pyridine nitrogen. The above coordination numbers have been also inferred from the electronic spectra of the Nd( fII) complex. A D3h symmetry for [Eu(Hdapth)CI2 (H20)3]CI and D2d symmetry for [Eu(i-hdapth)CI (HZO)2]CI2 and high symmetry for Tb(IIJ) and Sm(III) complexes of Hdapth and H2dapth are i'lferred from the emission spectra. The tentative Structures (III & IV) are proposed for the complexes.

Acknowledgement

Weare thankful to the Head, Dept. of Chemistry,

BHU, for laboratory facil ities. We are thankful to CDRl, Lucknow and Bose Institute, Calcutta for recording the mass and emission spectra, respectively and to the Department of Chemical Engineering, IT, BHU for recording TGA and DTA thermograms. Thanks are also due to the UGC, New Delhi, for providing financial assistance in the form of the research project No. F. 12-58/93 (SR-I).

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