Synthesis and Characterization of Cu(II) Substituted Hexa Tungstate and Molybdate of the Anderson Type Anion [X n+ M 6 O 24 ] -(12-n)

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1 ISSN: ; CODEN ECJHAO E- Chemistry , 5(S1), Synthesis and Characterization of Cu(II) Substituted Hexa Tungstate and Molybdate of the Anderson Type Anion [X n+ M 6 O 24 ] -(12-n) K. C. DEY* and V. SHARMA *Department of Chemistry, Jamshedpur Co-operative College, Jamshedpur , Jharkhand, India. Department of Chemistry, RVS College of Engg and Technology, Jamshedpur , Jharkhand, India. kcdey_ru@rediffmail.com Received 31 January 2008; Accepted 20 March 2008 Abstract: Sodium salts of copper substituted heteropoly compounds having molecular formula Na 10 [Cu II W VI 6O 24 ].22H 2 O(1) and Na 10 [Cu II Mo VI 6O 24 ].19H 2 O(2) analogous to the Anderson type anion [X n+ M 6 O 24 ] (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. CuO 6 acts as hetero group which replaces MO 6 (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 and respectively Keyword: Anderson anion, Tunstocuprate, Molybdocuprate, POM, Introduction Polyoxometalates (POM) belongs to large class of nanosized metal-oxygen cluster anion 1-2. 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 activities 3. Keggin 4 and Anderson 5 established the structure of heteropoly ions, [X n+ M 12 O 40 ] (8-n) and [X n+ M 6 O 24 ] (12-n) respectively having 12:1 and 6:1 atomic ratio of

2 1022 K. C. DEY et al. addenda to heteroatom where addenda M=Mo VI and W VI less frequently V V, 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 gases 6. The structures of approximately 180 polyoxometalates have been reported 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 tungstates 11. They are relatively low in toxicity and have high thermodynamic stability. In contrast to the heteropoly oxometalates containing the Mn II,Fe II,Co II, Ni II as the heteroatom(x) in the general formula [X n+ M 6 O 24 ] -(12-n) have been extensively studied, only a little work has been done on the Cu II analogous. The structure of first copper derivative of tungsto-arsenate(iii) was characterized in 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 cm -1.The thermal studies of heteropoly compounds were carried out by thermogravimetric analysis and by heating between 42 o C- 650 o C at 10 o C/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 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 Na 10 [Cu II W VI 6O 24 ].22H 2 O(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;

3 Synthesis and Characterization of Cu(II) Substituted Tungstate Anion 1023 Mo:37.5; O:23.5%(by diff). Calculated for Na 10 [Cu II Mo VI 6O 24 ].19H 2 O(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 [X n+ M 6 O 24 ] (12-n). The mixture of reagents were refluxed under ph 3.9 and 3.5 respectively in two different experiments. The crystals of Na 10 [Cu II W VI 6O 24 ].22H 2 O and Na 10 [Cu II Mo VI 6O 24 ].19H 2 O 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 cm -1. The stretching of the Cu-O bonds in compounds occurs at lower frequencies than that in the Keggin anion 13. It is due to the higher coordination number of the central heteroatom in the Anderson system. Both the compounds show sharp peaks from cm -1 which may be assigned to the terminal oxo stretching fundamentals υ(w-o) and υ(mo-o).the broad band from cm -1 may be due to the W-O-W and Mo-O-Mo bridge vibrations. The medium bands in the region of cm -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. CuO 6 octahedron replaces the WO 6 and MoO 6 respectively from [X n+ M 6 O 24 ] (12-n) (where M=Wor Mo).The structures of these heteropoly oxometalates consist of a slightly flattened central CuO 6 octahedron surrounded by an almost hexagonal planar array of distorted six MO 6 (where M=W or Mo octahedral). The TGA of compound 1 shows a gradual well defined decomposition over the temperature range of o C. It depicts the two step dehydration process. The first weight loss of 11% is observed between o C. The second weight loss of 17% is observed from o C. 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 and as determined by cryoscopic method using Na 2 SO 4.10H 2 O- Water system as solvent 14 against calculated molecular weight of 2340 and Conclusion We have synthesized two sodium salts of copper substituted 6-molybdo and 6-tungsto heteropoly complex. The anions [Cu II W VI 6O 24 ] -10 and [Cu II Mo VI 6O 24 ] -10 has typical Anderson type of structure [X n+ M 6 O 24 ] (12-n). Cu(II) forms CuO 6 octahedra in both the compounds which replaces one WO 6 in compound (1) and one MoO 6 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.

4 1024 K. C. DEY et al. 2. Pope M T, Heteropoly and Isopoly Oxometalates, Springer Berlin, Pastor N C and Romero P G, Frontiers in Biosciences, 2004, 9, Keggin J F, Proc Roy Soc. London 1934, A144, Evans H T Jr, J Am Chem Soc.,1948, 70, Pope M.T and Mullar A, Angew Chem Int Ed Engl.,1991, 30, Maksimov G M, Russ Chem Rev.,1995, 64, Roy S K and Dey K C, J Ind Chem Soc., 1991, 68, Roy S K and Dey K C, Ind J Chem., 1992, 31A, Roy S K, Jaiswal R and Dey K C, J Ind Chem Soc., 1993, 70, Pope M T and Mullar A, Ed. Polyoxometalates, From platonic solids to anti-retroviral Activity, Kluwar Academic Publisher, Dordrecht, 1994, pp Siedle A R and Golstein C, J Am Chem Soc., 1983, 105, Bridgeman Adam J, J Wiley Inter Science, 2005, 12(7), Flynn C M and Pope M T, Inorg Chem., 1971, 10, 2526.

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