Notes - NISCAIRnopr.niscair.res.in/bitstream/123456789/16137/1/IJCA 38A(12) 1244-1248.pdfNotes Metal malate hydrazinates-Precursors to fine particle oxide materials ... titration with

Indian Journal of Chemistry Vol. 38A, December 1 999, pp. 1 244- 1 248

Notes

Metal malate hydrazinates-Precursors to

fine particle oxide materials

S Yasodhai & S Govindarajan* Department of Chemistry, Bharathiar University,

Coimbatore 641 046, India

Received 5 April 1999; revised 25 June 1999

Metal complexes of malate with hydrazine possessing the stoichiometries, M(mal).2N2H4, (where M = Co, Ni and Zn and mal = -00C-CHOH-CH2-COO-), Cd(mal).2N2H4.2H20 and their solid solutions, M IIJCo2l3(mal).2N2H4 (where M = Ni or Zn) have been prepared and characterised by various physico­chemical techniques. Infrared spectral features show that the hydrazine moieties and the anion are present as bridging. bidentate ligands. Though the complexes exhibit different decomposition behaviour, the tinal step of decomposition is exothermic in all the cases. On decomposing the respective solid solution precursors, the cobaltite spinels, MC0204 (M = Ni or Zn) are formed. These precursors decompose exothermically at low temperatures (250-380°C) to give the respective spinel oxides through malate intermediates. The IR spectra of the oxides are characteristic of AB204 spinels. Fine particle nature of these spinels is evident from X-ray line broadening.

Metal carboxylate hydrazinates. are better potential precursors for fine particle metal or mixed metal oxides than their non-carboxylate counterparts t -4. The participation of the RC02- ion as an important ligand in inorganic and bioinorganic chemistry has created an increasing interest in the coordination chemistry of carboxylic acids. The extraordinary versatility of carboxylate ions on coordination is well-known and this together with hydrazine makes their thermal chemistry particularly interesting. Also, the interaction of hydrazine with the metal ion in presence of a carboxylate system has opened up a new area of coordination chemistry5- 14. As pait of our ongoing efforts on synthesis and characterisation of transition metal complexes involving hydrazine as the primary ligand, a metal and carboxylate system as secondary ligands as well as studies on low temperature preparation of spinel oxides using hydrazinate precursors, the new metal malate hydrazinates and their solid solutions have been prepared by us. There appear to be no reports in the literature on the preparation of these types of malate complexes to date. Thermal decomposition of metal

and mixed metal malate dihydrazinates have been investigated by TG and DTA and the respective mixed metal dihydrazinates have been used to obtain NiC0204 and ZnC0204. The formation of cobaltites have been identified by X-ray powder diffraction and IR spectral studies.

Experimental All the chemicals used were of AR grade and the

solvents were distilled before use. Hydrazine hydrate (99- 100%) was used in the reactions.

The composition of the malate complexes and precursors was determined by chemical analysis. The amount of hydrazine was estimated volumetrical ly by titration with 0.025 M KI03 solution under Andrews' condition l 5. The metal content in the complexes was determined by EDT A complexometric titration after decomposing a known weight of the sample with cone. nitric acid. The cobalt(m content in the precursors and cobaltites was estimated by precipitating cobalt as Co(CIOH60NOh using a­nitroso �-naphthoI 16. The filtrate containing divalent metal ion (Ni or Zn) after the separation of cobalt(m was treated with chloroform to remove excess a­nitroso �-naphthol, and the metal ions were estimated using standard EDT A solution.

The infrared spectra of the metal malate complexes, precursors a.nd cobaltites were recorded as KBr discs on a Shimadzu FfIR-820 1 PC spectrophotometer in the range 4000-400 em- I . Simultaneous TG-DTA studies were carried out on a STA 1 500 thermal analyser and the curves. were obtained in air using platinum cups as sample holders with 5- 1 0 mg of the samples at the heating rate of 10cC/min. The XRD powder patterns were recorded on a JEOL JDX 8030 X-ray diffractometer using Cu­Ka radiation . The 'a' values were calculated from the line broadening using Debye - Scherrer formula

17.

Preparation of the complexes The complexes of Co(II), Ni(II), Zn(II) and Cd(II)

were prepared by adding an aqueous solution (50 mL) of hydrazine hydrate and malic acid to the respective metal nitrate hydrates (50 mL) with constant stirring in a molar mixture ratio of I :2 :8 (metal nitrate :malic

/

NOTES 1 245

Zn X >--'iii c " -c

" > 18 "ii a:

Ni X

J

CoX

; " " '��� 3.0 13· 0 23· 0 33·0 43· 0 53·0 63·0 2 e ( Degrees)

Fig. l -XRD patterns of the metal malate hydrazinates. where X=(mal).2N2H4•

1246 INDIAN J CHEM, SEC. A, DECEMBER 1999

Table I-Analytical and Infrared data of the complexes

Compo Colour Yield, % Cobalt

Co(mal).2N2H4 Peach 90 (CoC4H120sN4)

Ni(mal).2N2H4 Pale blue 90 (NiC4H 1 2OsN4)

Zn(mal).2N2H4 Colourless 80 (ZnC4H 120sN4)

Cd(mal).2N2H4.2H2O Colourless 85 (CdC4H I �07N4)

Ni II3Co2l3(mal).2N2H4 Browni.sh red 90 14.80( 1 5.42)

(Ni I13C02l3C4H 120SN4)

Zn I/3Co2l3(mal).2N2H4 Peach 80 14.90( 1 5.28)

(Zn I/JC02lJC4H 1 20SN4)

b = broad

acid:hydrazine hydrate). The clear solutions were kept for crystallisation. The cadmium(II) complex was obtained immediately after the addition of the ligand solution, but the other complexes were obtained only after a day from clear solutions. The complexes formed were separated and washed with water, alcohol and ether and air-dried.

The mixed metal malate dihydrazinates · were prepared by reacting an aqueous mixture (50 mL) of malic acid (4.02 g, 0.03 mol) and hydrazine hydrate (6 mL, 0. 1 2 mol) with an aqueous solution (50 mL) containing cobalt nitrate hexahydrate (2.9 1 g, 0.0 1 mol) and respective metal nitrate hydrates (e:g., 1 .46 g of Ni(NO,h6H20), 0.005 mol). The resulting limpid solutions were allowed to crystallise at room temperature. The complexes precipitated as fine particles after 3 hours and were filtered, washed with water, alcohol and ether and dried in air.

All the complexes are insoluble in water and in common organic solvents. They are stable in air and insensitive to light.

The metal cobaltites were obtained as residues by the combustion of the precursors at 400°C in air. The combustion of the precursors was carried out by igniting them in a porcelain crucible at 400°C and allowing to decompose autocatalytically.

Results and discussion The metal complexes and the mixed metal

precursors have been prepared by a simple method from an aqueous solution containing the mixture of metal ions, malic acid and hydrazine hydrate in

Found (Calc.), % IR, cm-1

Metal Hydrazine VasyCOO' vsymCOO VN·N 22.80(23. 1 1 ) 24.90(25. 1 1 ) 1 650 1 390 970

22.70(23.04) 24.80(25. 1 3) 1 650 1 390 970

24.70(25.0 1 ) 1 8.60( 1 8.58) 1 650 1400 970

3 1 .90(32.64) 1 8.60( 1 8.58) 1 650(b) 1 400(b) 960

07.60(07.68) 24.40(25 . 1 1 ) 1 655 1 402 976

07.80(08.48) 24.20(24.89) 1 655 1 402 968

appropriate ratio. The composition of the complexes was determined by chemical analysis . (Table 1 ) . Comparison of X-ray powder diffraction patterns shows isomorphism among the anhydrous malate dihydrazinate complexes (Fig. 1 ) . The X-ray powder diffraction patterns of the precursors, MI/3C02/3(mal).2N2H4 are almost superimposable, augmenting the formation of solid solutions. It was observed that malic acid (hydroxy succinic acid) forms solid solutions, whereas succinic acid does not yield these types of solid solutions . Although, the metal succinate dihydrazinates were isomorphous among themselves, the desired homogeneity of the mixed metal complexes could not be achieved due to the immediate precipitation of metal succinate dihydrazinates.

The Co(ll) and Ni(II) complexes are paramagnetic and the Zn(m and Cd(II) complexes are diamagnetic. The corrected magnetic moment values for Co(II) and Ni(II) complexes are 4.55 and 3 .30 BM respectively, indicating a spin free octahedral ' geometry for both the complexes.

The electronic spectrum of cobalt malate dihydrazinate shows bands at 19,048 and 20,576 cm-I

which are assigned to the 4T,g(F)� 4T,iP) transition which is usually split due to spin-orbit coupling in the 4T,g(P) state. The nickel complex shows two bands at 17,544 and 27,778 cm-I which are assigned to the transitions 'A21i�3T'x(F) and 3A2g�'T,xCP), respectively. These electronic transItIOns are comparable to the spectra of the respective octahedral metal(II) complexes.

'"1"-

.'

NOTES 1247

Table 2-Thennal data of the complexes

Compo

Co(mal).2N2H4

Ni(mal).2N2H4

Zn(mal).2N2H4

Cd(mal ).2N2H4.2H2O

Ni 1I3Co2l.l(mal) .2N2H4

Zn 1I3Co2l.l(mal).2N2H4

(+) = endotherm, (-) = exotherm & d = doublet

DTA peak temp., oC

275(+) 348(-)

280(-) 332(-)

206(+) 453(-)

55(+) 1 96(+) 460(-)

283(+) 376(-)

27 1 (+) 363(-)

The important absorption frequencies are listed in Table 1 . The infrared spectra of all the anhydrous complexes show a band near 3400 cm- I indicating the presence of O-H stretching frequency of the hydroxyl group of the anion. The hydrated cadmium(1I) complex displays a broad band around 3500-3000 cm-I which is assigned to the O-H stretching of water with N-H stretching frequencies.The malate ion in the complexes coordinates to the metal ion as a bidentate l igand via both the carboxylate groups. The asymmetric and symmetric stretching frequencies of the carboxylate ions are seen at 1650 and around 1 400 cm -I , respectively with an average separation flv (vasy - vsym) of 250 cm-I , document.ing the monodentate coordination of both the carboxylate groups in the dianion. The N-N stretching frequency in these complexes appears in the range 960-980 cm-I

which is attributed to the bidentate bridging nature of the hydrazine moieties.

The thermal data of the complexes are given in Table 2. Though the metal complexes exhibit different decomposition patterns, the final step of decomposition is exothermic and the residue in all the compounds is invariably the metal oxide. Except cobalt dihydrazinate w�ich decomposes via oxalate intermediate, a l l the other complexes decompose through their respective metal malate intermediates.

Thennogravimetry Decomp. product Temp.range, Mass loss, %

°C Found(Calc.)

257 - 325 40.00(42.36) 325 - 353 67.00(68.52)

275 - 335 68.00(70.67)

1 69 - 250 22. 10(24.48) 250 - 465 69.00(68.86)

38 - 55 1 0.00(1 0.45) 1 86 - 203 26. 10(29.04) 203 - 490 65.00(62.72)

270 - 3 1 5 28.00(25. 1 1 ) 3 1 5 - 380 66.00(68.54)

262 - 280 23:00(24.89) 280 - 366 65.00(67.94)

COC204 C0304

NiO

Zn(mal) ZnO

Cd(mal).2N2H4 Cd (mal) CdO

NiCo2(malh NiC0204

ZnCo2(malh ZnCo204

The highly exothermic decomposition at low temperature « 400°C) of the similar anhydrous dihydrazinates are exploited for the preparation of mixed metal magnetic oxides using highly stable hydrazinate complexes of mixed metal malate precursors. This type of solid solution precursor method is advantageous and much more promising, since it achieves excellent stoichiometry and low impurity content.

The precursors decompose to afford metal cobaltites through malate intermediates (Table 2). An endothermic dehydrazination of the precursors in the first step yields the respective mixed metal malates. These intermediates are not stable for a particular temperature region as observed from continuous TG mass loss curves which show only a small break or an inflection in the curves. The exothermic disproportionation of the intermediates below 400°C give metal cobaltite residues of desired compositions. The actual mass losses reported in Table 2 for the decomposition processes of the complexes are less than the calculated mass losses . It may be due to the presence of carbon residue from the precursors. The atmospheric oxygen may not be sufficient to oxidise the fuel rich precursors completely.

The 2: 1 ratio of cobalt and metal in NiCo204 and ZnC0204 is evident from the chemical analyses of the cobaltites. The formation of these cobaltites from the

1248 INDIAN J CHEM, SEC. A, DECEMBER 1 999

precursors was further confirmed by infrared and x­ray powder diffraction studies. The infrared' spectra of the nickel and zinc cobaltite spinels register two absorption bands in the regions 650-660 and 550-570 cm-I due to the metal-oxygen stretchings in tetrahedral and octahedral sites, respectively l s. The 'a' values calculated from the patterns, (8.206A for NiCo204 and 8 . 1 33A for ZnCo204), are comparable with the reported values l9 of 8. 1 50 and 8 . 1 23A, respectively. The XRD lines are broad indicating the fine particle nature of these catalytically important oxide materials.

Acknowledgement S Y thanks the CSIR, New Delhi, for the award of

a senior research fellowship.

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