Synthesis and Characterization of Cu(II) Substituted Hexa ...downloads.hindawi.com/journals/jchem/2008/719393.pdf · polyoxometalates formers as a result of the favorable combination

ISSN: 0973-4945; CODEN ECJHAO

E-Journal of Chemistry

http://www.e-journals.net 2008, 5(S1), 1021-1024

Synthesis and Characterization of Cu(II)

Substituted Hexa Tungstate and Molybdate of the

Anderson Type Anion [Xn+

M6O24]-(12-n)

K. C. DEY* and V. SHARMA

*Department of Chemistry, Jamshedpur Co-operative College,

Jamshedpur -831001, Jharkhand, India.

Department of Chemistry, RVS College of Engg and Technology,

Jamshedpur -831001, Jharkhand, India.

[email protected]

Received 31 January 2008; Accepted 20 March 2008

Abstract: Sodium salts of copper substituted heteropoly compounds

having molecular formula Na10[CuIIWVI6O24].22H2O(1) and

Na10[CuIIMoVI6O24].19H2O(2) analogous to the Anderson type anion

[Xn+M6O24]─(12-n) were synthesized according to the literature method.

Compound(1) was synthesized from aqueous acidic solution containing

sodium tungstate and copper chloride and compound(2) from sodium

molybdate and copper chloride solution. The elemental analyses show 1:6

atomic ratio of the heteroatom to the addenda in both the compounds. The IR

spectra for both the compounds are in good agreement with the reported

formulae. A small deviation in IR spectra are observed than that established for

Keggin anions. CuO6 acts as hetero group which replaces MO6 (M=W or Mo)

from the Anderson structure. The thermal analyses of the compounds show the

loss of the peripheral water molecules. The molecular weight of the compound

(1) and (2) have been found as 2212.5 and 1600.5 respectively

Keyword: Anderson anion, Tunstocuprate, Molybdocuprate, POM,

Introduction

Polyoxometalates (POM) belongs to large class of nanosized metal-oxygen cluster anion1-2

.

These compounds are formed by self assembly process, typically in an acidic aqueous

solution. POM species present a wide range of structures and with them the ideal frame

work for the development of a plethora of useful magnetic, catalytic, bioactive and

photochemical activities3. Keggin

4 and Anderson

5 established the structure of heteropoly

ions, [Xn+

M12O40]─(8-n)

and [Xn+

M6O24]─(12-n)

respectively having 12:1 and 6:1 atomic ratio of

1022 K. C. DEY et al.

addenda to heteroatom where addenda M=MoVI

and WVI

less frequently VV, Nb

V and Ta

V

or a mixture of these elements in their highest oxidation states. Almost all the elements of

the periodic table can act as heteroatom (X) except the rare gases6. The structures of

approximately 180 polyoxometalates have been reported7-10

. With the ever growing field of

polyoxometalates, molybdo(VI) and tungsto(VI) oxometalates systems occupy a special

place as being one of the most widely studied and quite well understood. These are the best

polyoxometalates formers as a result of the favorable combination of ionic radius and charge

and of the accessibility of the empty d orbitals for metal–oxygen π bonding. Important

possibilities attach to demonstration of potent anti-tumor and anti-viral of various

molybdates and tungstates11

. They are relatively low in toxicity and have high

thermodynamic stability. In contrast to the heteropoly oxometalates containing the

MnII,Fe

II,Co

II, Ni

II as the heteroatom(X) in the general formula [X

n+ M6 O24 ]

-(12-n) have been

extensively studied, only a little work has been done on the CuII analogous. The structure of

first copper derivative of tungsto-arsenate(III) was characterized in 198212

. In the present

paper, we report the synthesis and characterization of copper substituted tungsto and

molybdo sodium salts of Anderson heteropoly quasi complex.

Experimental

All the reagents used were of analytical grade purity. Distilled water was used to prepare the

solutions. The pH and the conductivity measurement were carried out by the EI digital pH

meter model 111E and EI Digital conductivity meter model 611. The copper, tungsten,

molybdenum and sodium metal present in the compounds were estimated by using

inductively coupled plasma atomic emission spectroscopy, (make Jobin Yvon France of

model JY Ultima -2) at IIT Powai, Mumbai. The IR spectra were recorded by Perkin Elmer

577 spectrophotometer in the region 4400-450 cm-1

.The thermal studies of heteropoly

compounds were carried out by thermogravimetric analysis and by heating between 42oC-

650oC at 10

oC/min using Perker Elmer USA of model Diamond TG-DTA followed by

solubility determination. The apparent molecular weights of the sodium salt of compounds

were determined cryoscopically using Beckmann’s thermometer.

Synthesis of sodium 6-tungstocuprate(II)

30 mL of copper chloride solution was prepared by dissolving 1g (6 mmol) of the solute, it is

added dropwise to 75 mL of sodium tungstate solution, prepared by dissolving 11.6 g, (35

mmol) of solute, with continuous stirring till constant pH 3.9. The conductivity of the final

mixture solution was found as 18.8 Ώ-1

.10 mL of glacial acetic acid was added to maintain the

acidic condition of the reaction mixture. The above mixture was refluxed for 4hrs and left

overnight, the glassy blue crystals were separated out which were washed with n-hexane and

preserved for the analysis. (Analysis: Na:10.5; Cu:2.9; W:50.5; O:17.9%(by diff).Calculated

for Na10[CuIIW

VI6O24].22H2O(1) is Na:10.6; Cu:2.9; W:51.03; O:17.3%; (by diff)).

Synthesis of sodium 6-molybdocuprate(II)

75 mL of sodium molybdate solution was prepared by dissolving 8.52 g, (35 mmol) of

solute. 30 mL of copper chloride solution was prepared by adding 1g, (6 mmol) of the

solute. Both the solutions are mixed drop wise with continuous stirring till to reach constant

pH 3.5.The conductivity of the mixture solution was found as 18.4 Ώ-1

.The acidic

environment of the reaction mixture was maintained by adding 10 mL of the glacial acetic

acid.. The above mixture was refluxed for 4h and left overnight. The dark blue crystals were

obtained, washed with n-hexane and preserved for analysis. (Analysis: Na:14.5; Cu:3.8;

Synthesis and Characterization of Cu(II) Substituted Tungstate Anion 1023

Mo:37.5; O:23.5%(by diff). Calculated for Na10[CuIIMo

VI6O24].19H2O(2) is Na:14.7;

Cu:3.9; Mo:35.9; O:23.8% (by diff)).

Results and Discussion

The compounds were prepared after taking the stoichiometric ratios of reagents on the basis

of the probable Anderson formula of the heteropoly complex [Xn+

M6O24]─(12-n)

. The mixture

of reagents were refluxed under pH 3.9 and 3.5 respectively in two different experiments.

The crystals of Na10[CuIIW

VI6O24].22H2O and Na10[Cu

IIMo

VI6O24].19H2O were separated

out. The elemental analyses show 1:6 atomic ratio of the heteroatom to addenda which are in

good agreement with the heteropoly compounds of the Anderson formula. The infrared

spectra exhibits characteristics metal oxo stretching bands between 4400-450 cm-1

. The

stretching of the Cu-O bonds in compounds occurs at lower frequencies than that in the

Keggin anion13

. It is due to the higher coordination number of the central heteroatom in the

Anderson system. Both the compounds show sharp peaks from 1141-1261cm-1

which may

be assigned to the terminal oxo stretching fundamentals υ(W-O) and υ(Mo-O).The broad

band from 833-888cm-1

may be due to the W-O-W and Mo-O-Mo bridge vibrations. The

medium bands in the region of 503-574cm-1

reveal the presence of Cu-O bond in both the

octahedral complexes. The compounds 1 and 2 show the broad bands for symmetrical

stretching of peripheral water molecules at υ(3513cm-1

) which is very prominent in the IR

curve. CuO6 octahedron replaces the WO6 and MoO6 respectively from [Xn+

M6O24]─(12-n)

(where M=Wor Mo).The structures of these heteropoly oxometalates consist of a slightly

flattened central CuO6 octahedron surrounded by an almost hexagonal planar array of

distorted six MO6 (where M=W or Mo octahedral). The TGA of compound 1 shows a

gradual well defined decomposition over the temperature range of 25-650oC. It depicts the

two step dehydration process. The first weight loss of 11% is observed between 150-200oC.

The second weight loss of 17% is observed from 270-350oC. Finally, the insoluble oxides

are given as the last product. The TG Curve for the compound 2 is also in good agreement

with compound 1 with a small difference in percentage weight loss of the water molecules in

two step dehydration process. No attempts were made to identify the products of the

decomposition. The apparent molecular weight of the compounds 1 and 2 have been found

out to be 2212.5 and 1600.5 as determined by cryoscopic method using Na2SO4.10H2O-

Water system as solvent14

against calculated molecular weight of 2340 and 1750.5.

Conclusion

We have synthesized two sodium salts of copper substituted 6-molybdo and 6-tungsto

heteropoly complex. The anions [CuIIW

VI6O24]

-10 and [Cu

IIMo

VI6O24]

-10 has typical Anderson

type of structure [Xn+

M6O24]─(12-n)

. Cu(II) forms CuO6 octahedra in both the compounds which

replaces one WO6 in compound (1) and one MoO6 in compound (2).The copper contents in

both the compounds are established by elemental analyses and spectroscopic characterization.

Acknowledgement

The authors are thankful to the SAIF, IIT Powai for the result of elemental analyses. One of

the authors (V. Sharma) is thankful to the Director RVSCET, JSR for providing the

resources for the synthetic work.

References

1. Souchey P, Ions Mineraux Condenses, Massons, Paris, 1964.

1024 K. C. DEY et al.

2. Pope M T, Heteropoly and Isopoly Oxometalates, Springer Berlin, 1983.

3. Pastor N C and Romero P G, Frontiers in Biosciences, 2004, 9, 1759-1770.

4. Keggin J F, Proc Roy Soc. London 1934, A144, 75.

5. Evans H T Jr, J Am Chem Soc.,1948, 70, 1291.

6. Pope M.T and Mullar A, Angew Chem Int Ed Engl.,1991, 30, 34.

7. Maksimov G M, Russ Chem Rev.,1995, 64, 445.

8. Roy S K and Dey K C, J Ind Chem Soc., 1991, 68, 462.

9. Roy S K and Dey K C, Ind J Chem., 1992, 31A, 64.

10. Roy S K, Jaiswal R and Dey K C, J Ind Chem Soc., 1993, 70, 705.

11. Pope M T and Mullar A, Ed. Polyoxometalates, From platonic solids to anti-retroviral

Activity, Kluwar Academic Publisher, Dordrecht, 1994, pp255-408.

12. Siedle A R and Golstein C, J Am Chem Soc., 1983, 105, 7447.

13. Bridgeman Adam J, J Wiley Inter Science, 2005, 12(7), 2094 – 2102.

14 Flynn C M and Pope M T, Inorg Chem., 1971, 10, 2526.

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Synthesis and Characterization of Cu(II) Substituted Hexa ...downloads.hindawi.com/journals/jchem/2008/719393.pdf · polyoxometalates formers as a result of the favorable combination