INDIAN J. CHEM., VOL. 16A, SEPTEMBER 1978

Ligand Replacement Reactions in Some MetalComplexes: Part I - Copper(II) Complexes

(Mrs) PADMA]A R. SHUKLA & (Miss) NEELAM VARMA

Chemistry Department, Lucknow University, Lucknow

Received 9 February 1978; accepted 31 March 1978

A number] of copper(lI) complexes containing threedifferent Iigands in their coordination sphere havebeen synthesized by ligand replacement reactions.Starting with tetraaquocopper(II) sulphate mono-hydrate, gradual addition of thiourea (T'u] followedby aromatic (am) or cbelating diamines (dam) resultsin the formation of complexes of the type [Cu(H.O).(Tu)(am)]SO. or [Cu(H20)(Tu)(dam)]SO.. Additionof potassium salt of a desired anion leads to the re-placement of sulphate ion frorn the complexes. T'h emagnetic and spectroscopic measurements suggestplanar structure for these complexes.

THE studies on the kinetic and mechanisticaspects of the ligand exchange reactions are

mostly confined to the octahedral and tetrahedralcomplexes of cobalt(II) and nickel(II), containingall equivalent ligandsv". In the present notean attempt is made to study the ligand substitutionreaction in some planar complexes of copper(II).

Preparation of complexe.s - (i) A known weightof tetraaquocopper(II) sulphate monohydrate wassuspended in n-butyl alcohol or ethanol, to this wasadded a calculated amount of thiourea in ethanoldropwise and the mixture refluxed. A little morethan the calculated quantity of amine (aromaticor chelating diamine) was also added and thereaction mixture further refiuxed for 3-5 hr. The

mixture was cooled when the crystalline complexseparated out, which was filtered and washed withacetone and dried over P4010'

(i) For reactions involving replacement of anionthe complex was suspended in absolute ethanoland the potassium salt of the corresponding anionwas added. This reaction mixture was refluxedfor 6 hr, the precipitated complex washed withabsolute ethanol and dried over P4010'

[CU(HZO)4]S04HZO (I) was chosen as the modelfour-coordinate Cu(II) complex. At least six diffe-rent types of complexes have been prepared, bythe substitution of coordinated water, in the abovecomplex, as shown below:

In method (i) adopted, complexes of the type[Cu(HzO)z(Tu) (am) JS04 (II) and [Cu(HzO) (Tu) (dam)]S04 (III) are obtained. This shows that theaddition of thiourea replaces only one water mole-cule from I, the second one is being replaced byaromatic amine to give the complex (II). Thethird water molecule can, however, be exchangedby chelating diamines only, which are stronger thanaromatic amines giving complexes of type (III).

If, on the other hand, an excess of aroma tic amineis added to I, complexes of type [Cu(HzOlaam]S04(IV) are formed, which remain unchanged on treat-ment with an ethanolic solution of thiourea.

Addition of ethylenediamine or propylenediamineto the complexes of type (II) results in the preci-pitation of a white solid (V) which appears to bea Cu(I) compound (due to its diamagnetic nature)but unfortunately has not been fully characterized.

Treatment of type (II) complexes with potassiumtungstate or chromate results in the simple replace-ment of anion and complexes of type [Cu(HzO)zTu(am)]W04 or Cr04 (VI) are obtained, whiletreatment with potassium oxalate, the remaining

TABLE 1 - CHARACTERIZATION DATA OF THE COMPLEXES

Compound Found (calc.), (%)

Cu S C H N

[(Cu(H.O),(PY) (Tu)]SO, 17-62 18'35 21·02 3·40 11'75(18'11) (18'28) (20'54) (3'70) (11'90)

[Cu(H.Oh(P-tol.) ]SO~ 19'29 10'58 27-10 5'00 5'20(19'81) (9·99) (26'21) (4-68) (4'36)

[Cu(H.O).(P-tol.) (Tu)] SO, 16'55 16'66 26·05 4·90 11·95(16'77) (16'92) (25-36) (4049) (11'09)

[Cu(H.O).(m-tol.) (Tu))SO. 16·07 16'26 26-05 4·60 11-90(16'77) (16'92) (25'36) (4049) (11'09)

[Cu(HPMan)] SO, 20·50 9·90 24'15 4'85 5'21(20'71) (10'45) (23-49) (4'24) (4'56)

[Cu(H.O).(an) (Tu)] SO. 17·97 17·80 24'15 4'62 12·25(17-41) (17'58) (23'04) (4'11) (11-51)

[Cu(H.O).(Dime-an) (Tu)]SO, 16'47 16'81 28'10 5·02 11-52(16'17) (16'32) (27'52) (4-83) (10'69)

[Cu (H.Olt(N -ethylan) (Tu)]SO, 16'52 15·74 28'15 5·05 10·99(16'17) (16'32) (27'52) (4'83j (10'69)

[Cu(H.O)(en)(Tu)]SO, 20'85 21'06 12·02 4·70 18'51(20'25) (20'43) (11'48) (4'46) (17'85)

[Cu(HaO)(pn)(Tu)]SO. 19·50 19·06 14·98 5·02 17·28(19'38) (19'56) (14-65) (4-88) (17'09)

[Cu(HP).(py) (Tu)]CrO, 14·51 15'24 19·80 3·25 15·95(14-81) (14'95) (19'60) (3-50) (16'33)

[Cu(H.O)z (py) (Tu)]WO, 13-30 6'25 14'05 2'50 9'02(12'64) (6'38) (14·34) (2'58) (8·36)

[Cu(py)(Tu)(C.O .)] 19·98 10'20 30·15 3-48 13-52(19'50) (9-87) (29'59) (3'39) (12'94)

SlNo.

2

3

4

5

6

7

8

9

10

11

12

13

810

NOTES

TABLE 2 - CONDUCTANCE, MAGNETIC MOMENT AND CRYSTAL FIELD ENERGY DATA OF THE COMPLEXES

S1 AM {J.eff Amax Frequency 10 DqNo. (mhos) in (BM) (nm) (cm'") (em-I)

nitrobenzene

30'0 1'897 710 14084- 140·84-930 sh

2 28'0 1'862 768 13020 130'20968 sh

3 25·6 1'824 702 14245 142·45932 sh

4 25·0 1·824 906 14164- 141·64935 sh

5 31'0 1-800 760 13157 131-57960 sh

6 Insoluble 1'873 700 14285 142'85968 sh

7 31·5 1'806 695 14388 143·88930 sh

8 Insoluble 1-816 702 14245 142'45935 sh

9 25'6 1'893 590 16949 169-49

10 26·05 1-895 593 16863 168'63

11 29'5 1·875 705 14184 141'84925 sh

12 Insoluble 1'859 702 14245 142·45-13 0'52 1'811 655 15267 152'67

two water molecules from II are also replaced alongwith sulphate ion (thiourea and amine remainingas such) forming the non-electrolytic complex [Cu(Tu)(am)(ox)] (VII) in which the oxalate ion (ox)is also coordinated to the metal.

Analytical data of the complexes, given in Table 1,show that at least three different ligands are co-ordinated to the metal, a fact which is furtherconfirmed by the shifts in the position of importantvibrational frequencies (in crrr") as follows:

In all the complexes except the ones of type(VII) the coordina tion of water is indicated by alarge lowering in the 'JOH, which is observed between3300 and 3350, and also by the appearance ofrocking and wagging bands in the range 860-690(ref. 4).

Thiourea is capable of being coordinated to themetal either through sulphur or nitrogen atom.However, the possibility of metal-nitrogen bondforma tion is less frequent due to the lowbasicity of thiourea 5. Bonding through sulphurdecreases the C-S bond order to the value for asingle bond, while that of C-N bond approachesdouble bond. In the present complexes the bandat 1412 of free thiourea is split and that at 730is both split and shifted to lower value, suggestingthe coordination of thiourea through sulphurs, Theabsorption at 3300 and 1617 which are due to 'JNH2stretching and deformation modes are unaffectedin the complexes, thus excluding the forma tion ofmetal-nitrogen bond".

The base pyridine is also coordinated to the metalwhich is evident from the observa tion tha t the bandsdue to C=C, C=N, ring stretchings, C-H in-planeand out-of-plane deforma tions, occurring in thefrequency ranges 1630-960 show positive shift, asan outcome of the tightening of the aroma ticring on coordinations".

In the case of complexes of aniline, Neethylaniline,m- and p-toluidines the coordination of the ligandto the metal is indica ted by a large negative shiftof NH and C-N stretching and a small positive shiftof NH deformation bandsIO-12•

The conductivity measurements on compoundsof types II and III show that these behave as 1:1electrolytes (Table 2) and hence the sulphate ion isnot coordinated to the metal. In the IR spectrathus only one band corresponding to 'Ja mode ofthe non-coordina ted sulphate ion is seen around1120, while the bands due to 'J2 and 'JI modes ofcoordina ted sulpha te ions are absent'P.

The oxalate ion is coordinated to the metal asshown by the positive shift of 'J7 and 'JI modes, andthe negative shift of V2 and 'Ja modes=.

The magnetic moments of the complexes fall inthe range 1·800-1·897 BM (Table 2). As the valueare very close to the spin only value, it is clear thatthe magnitude of the orbital contribution is not largein these complexes. This result has also been ob-served in the case of other square planar copper(II) complexes where the only orbital contributionto the moment is the one contributed in secondorder by spin-orbit coupling. The tetrahedral struc-ture has moment values around 2·20 BM15, and isthus excluded, for the present complexes.

The diffuse reflectance spectra of the complexesshow only one band in the visible region, consistentagain with the planar geometry of the complexest".The main band is observed around 750 and 570·nm for aromatic and chelating diamine complexes,respectively. As the position of this band is adirect measure of crystal field energy (10 Dq) itshows that aromatic amines are weaker ligand thandiamines.

One of us (N.V.) is thankful to UGC, New Delhi,for awarding junior research fellowship.

811

References

INDIAN J. CHEM., VOL. 16A, SEPTEMBER 1978

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13 (1968), 2496.3. RAY, S. K & SIDDHANTA, S. K, Indian J. Chem., 8

(1970), 552.4. GAMO, I., Bull. chem, Soc. Japan, 34 (1961), 760.S. SANDELL, E. B., Colorimetric determination of trace

elements (Irrterscience, New York), 1959, 199.6. YAMAGUCHI, A. et al., J. Am. chem, Soc., 80 (1958), 527.7. SWAMINATHAN, K. & IRVING, H. M. N. H., J. inorg.

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35 (1957). 1183.9. GREENWOOD, N. X. & \VADE, K., J. chem, Soc. A,

(1960), 1130.10. FOWLES, G. W. A., Proceeding Symposium Chem, Coord.

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(1970), 285.12. RAO, C. N. R., Chemical application of infrared spectro-

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M., J. Am. chem, Soc., 79 (1957). 490+.14. SINGH, G. P., SHUKLA, P. R. & SRIVASTAVA, L. N., J.

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Bis-chelate Complexes of Co(II) witha-(3,5-Dimethyl-l- pyrazolyl )acetohydrazide

NITYANANDA SAHA & DIPAK BHATTACHARYYA

Department of Pure ChemistryUniversity College of Science, Calcutta 700009

Received 22 December 1977; accepted 3 April 1978

The chelating behaviour of a-(3,5-dimethyl-l-pyra-zolyl) acetohydrazide (PAH) has been reported bycomplexation with cobalt(U) salts (halide, nitrate,sulphate and thiocyanate). Solid chelate bis-com-plexes of the type Co(PAH)2X2.nH20(X = Ct, Br, I,N03, SCN and iSO,; n = 0 or 2) have been charac-terized by elemental analysis, magnetic and con-ductivity measurements and IR and reflectancespectral data. Ali the cobalt(U) complexes are dis-torted octahedral as evident from electronic spectraldata and the corresponding ligand field parameterscalculated in terms of Oh symmetry. IR spectra ofcomplexes together with the ligand indicate thepyrazole-rfng nitrogen and the amide nitrogen(involving an • imidoI ' structure) of the hydraalderesidue as the points of attachment showing neutralbidentate function of the ligand.

THE coordination chemistry of pyrazole-basedligands has been investigated- extensively in

recent years, because of the biological implicationsof these heterocyclic bases. In continuation ofour studies=" on the coordinating properties ofsubstituted pyrazoles, we wish to report in this notethe synthesis and characterization of a few bis-chelates of cobalt(II) salts with 1X-[3,5-dimethyl-l-pyrazolyljacetohydrazide (I, herein after abbre-viated as PAH), the preparation of which has beenreported earlier'.

812

Preparation oj cobalt(II) complexes; Co(P AH)zXZ·nH20 (X = Cl, Br, J, NOa, i SO,,; n = 0, 2)-T~e. deep pink solution resulting (PH ~ 3) onrmxing aqueous ethanolic solutions of the ligand(0'01 mole) and the hydrated cobalt(II) salt (0·005mole), was heated on a water-bath for 10 min andthen kept at room temperature. On stirring well,a pink compound separated out in each case. Itwas suction-filtered, washed with ethanol and thendried over fused calcium chloride.

CIJ(PAHMNC5)z-Ethanolic solutions of hydratedcobalt(II) nitrate (0·005 mole) and KSCN (0'01mole) were mixed and the precipitated KNOafiltered off. The filtrate was evaporated on a water-bath to a smaller bulk and filtered directly into ahot ethanolic solution of the ligand root mole).The reaction mixture was stirred well at roomtemperature when a violet compound settled down.It was filtered off and collected as before.

Cobalt was estimated gravimetrically as anhydrousCoS04, halogens as silver halide and sulphate asBaS04• Nitrogen was estimated by Dumas' method.The conductance, electronic spectra in solution,diffuse reflectance and IR spectra and magneticsusceptibility in the solid state of the compoundswere carried out as described earlier'.

All these pink complexes are fairly soluble inwater and low molecular weight alcohols, exceptCo(PAH)zS04·2HzO which is sparingly soluble inorganic solvents; the aqueous and methanolic solu-tions are highly conducting (Table 1) which showthe ionic nature of the complexes [Co(PAH)z(solv)z]z+(for most of the compounds) at least in solutionof that solvent.

Magnetic data reveal that all the present cobalt(II)complexes are high spin (f!B = 4·6-4'8 BM at 29°;Table 1). The slightly lower magnetic momentvalues, as compared to those assigned for high spinoctahedral Co(II) cornplexes'' imply that the com-plexes probably belong to an orbital singlet groundstate with distorted octahedral environment". Thisis supported by electronic spectral data (Table 2).

The very much similar reflectance spectra of thecomplexes are characterized by two main bandsat .....,9000and ",,20000 crrr? (with shoulders on boththe sides) which may be assigned to Vt[4T uW)-+4T2g(F)] and Va[4Tlg-+4Ttg(P)J transitions respectivelyin an octahedral field.

However, the splitting of the Va bands into manycomponents in some of the cases makes the assign-ment difficult; these components may be due tolifting of the degeneracy of the 'Tu level either byspin-orbit splitting or by the presence of lowsymmetry (approximating to C2) components inthe ligand field. Alternatively, the components