Indian Journal of Chemistry Vol. JIlA. August 1 999. pp. 833-838

Studies on lanthanide(III) complexes of nuclear substituted diphenylcarbazones

A H M Siddalingaiah· & H M Veerabhadra M Swamy Department of Chemistry, Karnatak University,

Dharwad S80 003. India Received 17 August 1998; revi�ed 19 March 1 999

La(I II). Ce( l l I ) . PrOlI). Nd(I1I), Sm(I1I), Dy(I1I) and Ho(II1) complexes of I .S-di(2.S-dimethylphenyl)carbazone and 1 ,S-di(Schloro-2-methylphenyl)carbazone have been synthesised and characterized on the basis of elemental analysis, molar conductances. magnetic moments and spectral studies (electronic absorption. infrared and \H-NMR spectra). The complexes conform to the composition Ln[(DPCh(N03hlN03·2H20. The substituted dipheny\carbazones act as neutral bidentate ligands and the complexes appear to be six-coordinated. The IR data suggest coordination of the ligand to the metal ions in the bidentate fashion through the oxygen of the carbonyl (>C=O) group and nitrogen of azo(-N=N-) group. Presence of two water molecules is indicated which are outside the coordination sphere. The antimicrobial screening of the ligands and their complexes has been carried oul. Proton-ligand and metal-ligand formation constants of the above complexes have also been determined pHmetrically in SO% (v/v) aqueous dioxane medium at 2So, 3So and 4SoC and ionic strength !l=D. 1 M (NaCI04). The thermodynamic parameters of complex formation have been evaluated. Stabilities (IogK\ values) of the chelates are found to increase with decrease in ionic radii of the metals. i.e., La(HI) L :::::O.02M) were prepared in AR grade dioxane which was further purified by the method of Freiser et aLIO. Carbonate-free sodium hydroxide solution was prepared by the method of Allen and Lowl I . The titrations against standard NaOH solution were carried out in an inert atmosphere in a specially designed double-walled reaction cell.

The metal ions contents in the solid complexes were estimated by oxinate methodJ2. The ligands and their complexes were analysed for their C, H and N contents on a Heraeus-CHN-Rapid Analyser. The magnetic moments at room temperature were measured on a Gouy magnetic balance using Hg[Co(SCN)4] as the cali brant. Molar conductances were measured in 1 0-3M OMF solution using an ELiCO conductivity bridge (type CM-82T) with a dip-type conductivity cell at room temperature. The electronic spectra of the ligands in DMF were recorded on a Hitachi 1 50-20 UV-VIS spectrophotometer using an optical cell of path length 1 0mm at room temperature in the region 9QO-200nm. IR spectra of the ligands and the complexes were recorded in 400-4000cm-1 region using a Nicolet 170

834 INDIAN J CHEM SEC A, AUGUST 1 999

FT-IR spectrophotometer as KBr pellets. IH-NMR spectra of l igands and La(III) complexes were recorded on a VXR 300 S Varian spectrometer at 300 MHz in CDCl, using TMS as the internal reference. The thermal analyses were performed on a Rigaku Thermal Analysis Station TAS 1 00 at a heating rate of l Oa/min in the temperature range 30°-800°C in nitrogen atmosphere. The antimicrobial activities of the synthesised compounds were determined by cup plate method with two different

' bacteria:

Pseudomonas aerugillosa (Gram -ve bacteria) and Bacillus cirraflagallous (Gram +ve bacteria) and two fungal spec ies; Aspergillus niger and Rhizoctonia bataticola on base layer medium containing peptone (0.6%) , yeast extract (0.3%) , beaf extract (0. 1 3%) and nutrient agar [prepared by dissolving definite volumes of peptone ( I %), yeast extract (0.6%), sodium chloride (0 .5%), potassium dihydrogen phosphate (0.3%) and glucose ( I %)] .

The cups were made by scooping out nutrient agar with steri l ized cork bore. The solutions of test compounds (0. 1 ml) were added to the cups by using sterile pipett�s and those plates were subsequently incubated at 37°C for 48 h. The antimicrobial activity was estimated on the basis of the size of inhibition zone formed around the holes on the seeded agar plates. The inhibjtion of the growth expressed in percentage was determined on the growth medium compound to the respective controls. This is expressed by the relation,

Relative inhibitions (%) of the test substance

= x - Y x I OO z - y

where, x = area of inhibition in test plate, y = area of inhibition in solvent (DMF) plate and z = area of inhibition in standard drug (Norfloxacin for bacteria, Griseofulvin for fungi)

Table I -Analytical . and magnetic moment data of the lanthanide(III) nitrate complexes of 1 ,5-di(2,5-dimethylphenyl)carbazone and 1 .5-di(5-chloro-2-methylphenyl)carbazone

Composition Found(Calcd). % !letT C H N M (8.M)

1 .5-Di(2.5-dimethylphenyl )carbazone C 17H10N4O 67.26 6.72 1 8 .74 (68.89) (6.80) ( 1 8.90)

La[(C I7H,,,N.O),( NO,hlNO,.2H2O 42.34 4.38 1 5.97 1 4.52

(42.90) ( 4.45) ( 1 6. 1 9) ( 1 4.60) Diamag

42.68 4.33 1 5 .78 1 4.78 Ce[ (C I 7H,nN40h( NO,),lNO,. 2H2O

(42.85) (4.44) ( 1 6. 1 6) ( 1 4.70) 2.42

Pr[ (C I 7H:"N4O)2( NO,h] NO,.2H2O 43.00 4.59 1 6.32 1 5 .00

(42.8 1 ) (4.43) ( 1 6. 1 5) ( 1 4.77) 3.58

Ndl (C I7H2"N40h( NO, hlNO,.2H20 42.86 4.38 1 5 .97 1 5 .22

(42.66) (4.42) ( 1 6. 1 0) ( 1 5.07) 3.66

Sm[(C I 7H,nN40h(NO,hlNO,.2H20 42.25 4.42 1 6. 2 1 1 5 .85

(42.39) (4.39) ( 1 5 .99) ( 1 5 .6 1 ) 1 .52

42.03 4.24 1 5 .54 1 6.42 Dy[(C I7H2oN40h(NO,),lNO,.2H20 (4 1 .87) (4.34) ( 1 5.79) ( 1 6.66)

1 0.34

Ho[(C I7H2"N40)z( NO,hlNO,.2H20 42.00 4.50 1 6.06 1 7. 0 1

(4 1 .76) (4.33) ( 1 5.76) ( 1 6. 8 1 ) 1 0.55

1 .5-Di(5-chloro-2-methylphenyl )carbazone 53.36 4. 1 5 1 6.20

CI�H I 4N40Cl2 (53 .42) (4. 1 8) ( 1 6.6 1 ) 34.72 2.88 1 4.80 1 3 .55

La[ (C l 5H 14N40CI2 ),( NO,hlNO,.2H20 (34.86) (2.92) ( 1 4.9 1 ) ( 1 3.44)

Diamag

34.67 2.78 1 4.72 1 3 .43 Ce[ (C I ,H 14N40CI2h(NO,hlNO,.2H20 (34.82) (2.92) ( 1 4.89) ( 1 3 .54)

2.50

34.70 2.83 1 4.96 1 3.48 Prl (C I �H 14N40Cl2 l2( NO,JzI NO,.2H2O (34.80) (2.92) ( 1 4.88) ( 1 3 .60)

3 .61

34.57 2.82 1 4.76 1 3 .74 Nd[(C 15H 1 4N40Cl,)2 (NO,hlNO,.2HzO

(34.68) (2.9 1 ) ( 1 4.83) ( 1 3 .88) 3.68

34.32 2.78 1 4.65 1 4.22 Sml (C l 5H 14N40Cl 2l2(NO,hlNO). 2HzO

(34.48) (2.89) ( 1 4.74) ( 1 4.39) 1 .57

32.06 2.75 1 4.48 1 5 .28 Dy[ (C I 5H 14N40CI2h( NO)h lN01.2H20

(34.08) (2.86) ( 1 4.57) ( 1 5.37) 1 0.40

33.28 2.73 . 1 4.42 1 5 .36 1 0.48 Hoi (C 15H 14N40Clzh( NO, h l NO,. 2HzO (34.0 1 ) (2.85) ( 1 4.54) ( 1 5 .56)

J.

�

�

NOTES 835

The areas of inhibition in test plate. solvent plate and standard plate were calculated by using the formula 1tr2 (r is the radius of the zon.e of inhibition).

The stabi l ity constants of the complexes were evaluated by Bjerrum-Calvin3 pH-metric t itration technique as modified by Irving and Rossotti4 using Schott-Gerate automatic titrator with the eombination of piston burette TI l 0, magnetic stirrer TM 1 20 and system pH-meter CG 804 with a combined glass electrode.

Synthesis of ligands The ligands ( structure I I) were synthesised by the

methods similar to those reported earlier' 3 . The carbazones obtained were purified by column

chromatography using sil ica gel as column and dry ether as solvent. The purity was tested by TLC. (i) 1 ,5-Di(2,5-dimethylphenyl)carbazone; yield : 64%, M.P: 1 78- 1 79°C; ( i i) 1 ,5-Di(5-chloro-2-methylphenyl)carbazone; yield: 69%, M.P: 158- 160°C.

Synthesis of complexes To a solution of lanthanon(III) n itrate (0.OO5M) in

doubly distil led water, an ethanolic solution of substituted diphenyICarbazone (0.01M) was added gradually at room temperature and the mixture was stirred magnetical ly. Dilute ammonia ( l : 20)

. was

added drop-wise to the mixture until pH of the solution mixture was == 6.5-7. The contents were stirred continuously for 3-4 h. The mass was filtered

Table 2-lmportant I H-NMR bands (ppm) of substituted diphenylcarbazones and their lanthanum(I1I) nitrate complexes

Compound Chemical Shifts (0. ppm) methyl phenyl amide aromatic (-CH) (-NH) (-NH) (-H)

1 ,S-Oi(2.5-dimethylphenyl)carbazone 2.25 s 2.70 s 6. 1 3 br 8.06 br 6.8-7.7 m .

La[(OPC)"(NO,h ]NO, 2H"O 2.28 s 2.65 s 6. 1 2 br 7.98 �r 6.7-7.7 m I ,5-0j( 5-chloro-2-methylphenyl )carbazone 2.3 s 2.5 s 2.7 s 6. 1 5 br 8 . 1 br 7.0-7.9 m La[(OPC)"(NO,)" ]NO, 2H2O 2.30 S 2.85 s 6.20 br 7.98 br 7.0-7.85 m

br : broad. III : multiplet. s : singlet.

Table 3-Metal-ligand stability constants and thermodynamic parameters of lanthanide(l I l ) nitrate complexes of 1 .5-di(2,5-dimethylphenyl)carbazone and I ,5-di(5-chloro-2-methylphenyl)carbazone at 11=0. 1 M (NaCI04)

Metal ion log�2 -�GO(kcal mol- I ) -/:Jr �So 25° 35° 45° 25° 35° 45° (kcal (e.u.)

mol-I )

La( l l l ) 10.9 1 9.92 9.79 7.58 1 7.4 1 8 7.227 6. 1 45 4.8 1 8 ( 1 0.65) (9.47) (9.27) (7.636) (6.736) (6.49 1 ) ( 1 8.502) (-32.463)

Ce( l I l ) 10.60 1 0.83 1 0.77 8. 1 68 7.691 7.595 8.754 -1 .966 ( 1 0.55) (9.97) (9.70) (7.677) (6.995) (6.750) ( 1 5.055) (-24.758) PrO I l ) 1 1 .2 1 1 0.92 1 0.97 8.236 7.759 7.704 8.226 0.033 ( 1 0.80) ( 1 0.45) ( 1 0.38) (7.69 1 ) (7.309) (7.2 1 3 ) (7.98 1 ) (-D.973) Nd( l I I ) 1 1 .36 1 1 . 1 8 1 1 . 1 0 8.31 8 8.004 7.745 8.792 - 1 .590 ( 1 0.86) ( 1 0.5 1 ) ( 1 0.44) (7.8 1 3) (7.43 1 ) (7.24 1 ) (9.24 1 ) (-4.79 1 ) Sm( l l l ) 1 2.02 1 1 .90 1 0.20 8.932 8.782 8.4 1 3 7.957 3.27 1 ( 1 0.33) ( 1 0.8 1 ) ( 1 0.46) (7.977) (7.568) (7.268) ( 1 0.375) (-8.046) Gd( 1 I 1 ) 1 2.48 1 2.07 1 1 .88 8.836 8.658 8.359 7.4 1 2 4.778 ( 1 0.5 1 ) ( 1 0.43) (9.80) (7.909) (7.5 1 3) (7.322) ( 1 0. 1 42) (-7.493) Oy( l l l ) 1 2 .98 1 2.35 1 2. 1 5 9. 1 22 8.727 8.427 1 0.68 1 -5.23 1 ( 1 1 .07) ( 1 0.99) ( 1 0.94) (7.977) (7.677) (7.58 1 ) (5.23 1 ) (9.2 1 4) Ho( l l l ) 1 3 .07 1 2.34 1 2. 1 9 9. 1 63 8.768 8.495 1 0.265 -3.697 ( 1 1 .45) ( 1 1 . 1 5) ( 1 1 .00) (8.045) (7.772) (7.58 1 ) (7.4 1 7) (2. 1 07 ) Er( l l \ ) 1 2.9 1 1 2.43 1 2.32 9.245 8.782 8.550 10.989 -5.852 ( 1 1 .78) ( 1 1 .30) ( 1 1 .2 1 ) (8. 1 95) (7.84 1 ) (7.704) (7.565) (2. 1 1 4) Yb( l l l ) 1 3 .20 1 2.99 1 2.27 9.259 9. 1 50 8. 1 4 1 1 0.269 -3.389 ( 1 1 .48) ( 1 1 .72) ( 1 1 .66) (8.29 1 ) (8. 1 1 3) (8.045) (3.952)' ( 1 4.560)

�e values given in the parentheses are those of the 1 .5-di(5-chloro-2-methylphenyl)carbozone complexes

836 INDIAN J CHEM SEC A, AUGUST 1 999

R 1 =2-methyl, R 1 =5-chloro,

R2=5-methyl R2=2-methyJ

under suction, washed with water and dried in vacuo at room temperature . All the metal complexes were purified by Soxhlet method l 4.

Results and discussion The analytical data presented in Table I indicate

that the complexes have 1 :2 stoichiometry (metalligand) . The water of crystall ization associated with these complexes is readily lost at - 1 10°C. Thermograms run for these hydrated samples also indicate ready loss of water in the temperature range SO- 1 00°C indicating that two water molecules are lattice-held and not coordinated. Finally, the complexes decompose to give Ln20, at >600°C.

All these complexes behave as I : I electrolytes in DMF (AM 87.%- 1 16 . 1 3) as compared to 6S-9S mho cm2 morl for I : I electrolytes l ) in DMF. The slightly higher molar conductance values observed are attributed to partial replacement of the coordinated nitrate ions by the solvent molecules l6 . The magnetic moment values reported in Table I are quite normal for the lanthanide complexes based on the i-values. Although the entire family of lanthanides could not be studied, it was however clear that the magnetic moments except for Sm(III) complexes show very l ittle deviation from Hund l ? and Vleck Frankl 8 values indicating little participation of 4f-e1ectrons in bonding as these electrons are well shielded by 5i Sp6 octet. The slightly higher magnetic moment values of Sm(III) complexes are due to the fact that the energy difference between the ground state level (6Hsl2) and the next i-level (6H7I2) being only of the order of kT leading to higher population in the higher energy levels and the susceptibilities due to the first order Zeeman effect l 9 .

I ,S-Di(2,5-dimethylphenyl)carbazone and 1 ,5-di(5-chloro-2-methylphenyl)-carbazones exhibited characteristic absorption maximum (A.m.x) at 295 and 298nm respectively. Their IR spectra exhibited characteristic medium intensity bands in the region 3000-3400 cm- I • The 3423cm-1 band is attributed to the intermolecular bonded V(N-H) vibration and the bands at 32S0, 3 1 50 and 30 1 Ocm-1 have been attributed to intramolecular bonded V(N-H) vibration20. A very strong band observed at I 690cm-1 is attributed to v(C=O) vibration. The bands at 1 597 and 1 604cm-1

are due to V(N=N) modes of respective l igands, similarly the corresponding bands for v(C=C)ar and N-H (bend) are observed at 1 480 and 856cm-1

respectively. • On complexation the, \I(c=O) band is shifted to the

region 1 600cm -I , showing that the carbonyl oxygen (>C=O) is involved in coordination. In the spectra of lanthanide c'omplexes V(N=N) band shifts to lower frequency region around l S I 0- I S60cm -I thereby indicating coordination of n itrogen of azo( -N=N-) group to the metal ions. The IR spectra of the metal complexes also exhibit two medium bands at 1 400 and 1 26Scm-1 which are assigned to V4 and V I stretching vibrations of coordinated nitrate groups. Since V4-V I is about I I Scm-

l , nitrate coordinates in a monodentate manner2 1 .22.

The M-O and M-N stretching vibrations are observed at about S80 and 4S0cm· 1 respectively in the spectra of the complexes23 .

The important IH-NMR spectral data of the l igands and their La(III) complexes are given in the Table 2 .

....

NOTES 837

Based on the r�s_ults of various physico-chemical studies structure lIII' is assigned to the complexes. The complexes have 1 :2 (metal-ligand) stoichiometry. The carbazone is bonded to the metal ions in bidentate fashion through the carbonyl oxygen (>C=O) and nitrogen of azo( -N=N-) groups.

We observed that all the compounds are more toxic towards fungi than the bacteria. Fairly high fungicidal activity of these compounds may be attributed to the fact that the ligands and the metal ion are more accessible to the fungal cel l than the bacterial cell . The compounds resist the fungal growth and act as toxic agents . Hence, it is concluded that though these compounds are not so good bactericides, they are good fungicides .

Proton-ligand formation constant The formation ( IlA Vs pH) curves of these ligands

are found to be single waves extending from 0 to 1 and the slope of the plot of IlA/( 1 - IlA) Vs pH is =0.99. Both these findings indicate that the ligands exist in monoprotic form, due to the presence of only one OH group in its enolic tautomeric form. From the titration curves the pKa values of the above ligands were determined fol lowing the procedure adopted by Siddalingaiah et al. 24. These were found to be 1 0.20 and 9. 1 4 respectively at 25°C. Methyl substitution in the aromatic nucleus enhances the donor strength on account of its electron repelling tendency25 . The pK. value of 1 ,5-di(2,5-dimethylphenyl)carbazone is higher than that of the parent OPC, in line with those of 2-methyl, 3-methyl and 2,4-dimethyl substituted derivatives25 . Further, this was examined by using the Hammett re\ationship26, log K1Ko=pcr, where, K and Ko are the ionization constants of the unsubstituted and substituted l igands respectively, 'p' is a constant relating to the sensitivity of the equilibrium constant to the changes in cr values of the substituents, while cr is the Hammett constant which gives a measure of electron donating or withdrawing power of the substituent. Using p(2.32) value and cr values evaluated by Siddalingaiah et at. 23, the pK. values of these ligands were calculated. These calculated values are in fairly good agreement with the experimental values.

Metal-ligand stability constants From the titration curves and pK. values, the n

(metal-ligand formation number) values of the metal

complexes were determined at various pH values. From these pK. and n values the corresponding values of pL and hence 10gK\ and logK2 were calculated by half-integral methods following procedures reported in the l iterature24,2s. The n and pL data were also subjected to the weighted leastsquares treatment developed by Sullivan et al.27 on a PC-XT computer to get Po values. TQe stability constants thus obtained are presented in the Table 3 . The following stability order is observed: La

838 INDIAN J CHEM SEC A, AUGUST 1 999

not unreasl l l lable to conclude that though the interactions between the cations and l igands are primarily e lectrostatic in nature, a partial covalent character \I cannot be ruled out.

The tl'mperature coefficient and Gibbs-Helmholtz equation were used to determine the overall changes of free energy (�GO), enthalpy (MlO) and entropy (.1S0). The total free energy change was obtained from the equation �Go = -RnnK . . where • KJ ' is the stabil ity constant. The values of enthalpy changes (MlO) were obtained by plotting 2.303 R 10gKJ against l iT, and overall entropy changes (.1S0) of the reactions were evaluated from the equation �so=(�Ho-�GO)/T. Al l the thermodynamic parameters so obtained are given in Table 2. The negative values of �Go indicate that the complexation reactions are spontaneous and metal chelates are thermodynamical ly stable. Negative values of Mlo indicate that the metal-ligand bonds are fairly strong and complexation reactions are spontaneous and metal chelates are thermodynamically stable. Negative values of �Ho indicate that the metal ligand bonds are fairly strong and complexation reactions are exothermic in nature and positive values of � suggest favourable chelation reactions.

Acknowledgement

One of the authors (H.M.V.S.) thank Mr. H. P. Dodmani, Department of Biochemistry, K. U. Dharwad for his help in the antimicrobial screening.

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