Synthesis and Structural Characterization of ... - Jacobs University

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Chapter 5 Unpublished Results anisotropically, while the O and Na atoms were refined isotropically. No H atoms were included in the models. The crystallographic data are summarized in Table 5.5. Table 5.5. Crystal Data and Structure Refinement for Na 34 [H 2 Te 24 Mo 44 O 198 ]·84H 2 O (Na-28). Code Na-28 Empirical formula H 2 Na 34 O 282 Te 24 Mo 44 MW 12748.8 Crystal system Triclinic Space group (no.) P1̅ (2) aÅ 17.301(11) bÅ 25.419(19) cÅ 36.150(3) ° 74.402(3) ° 77.461(2) ° 77.488(2) V/Å 3 14733.4(18) Z 2 T/ ºC -100(2) λÅ 0.71073 D/ Mg m -3 2.874 μ/ mm -1 4.304 R[I >2sigma(I)] a 0.110 R w (all data) b 0.263 a R = ∑|F o | – |F c | |∑| |F o |; b R w = {∑[w(F 2 o – F 2 c ) 2 ] / ∑[w(F 2 o ) 2 ]} 1/2 . 187
Chapter 5 Unpublished Results 5.A.2.4. Results and Discussion We performed a systematic study on the interaction of tellurium(IV) ions with sodium molybdate in neutral, aqueous medium, and at a ratio of 1 : 5 we were able to isolate crystals of Na 34 [H 2 Te 24 Mo 44 O 198 ]·84H 2 O (Na-28). Four reaction parameters are crucial for the successful formation and isolation of [H 2 Te 24 Mo 44 O 198 ] 34− (1) in a pure form: solvent, reaction temperature, molar ratio of reagents, and pH of the solution. Polyanion 1 is formed in water but the same reaction performed in 1M NaCl or sodium acetate buffer solution resulted in a different product based on FTIR which has not been characterized yet. Polyanion 1 is formed at room temperature, but if the solution is heated then a considerable amount of unidentified white precipitate was formed during the synthetic procedure which affects the yield observed. Thus, polyanion 1 also form upon heating, but the yield is much higher at room temperature. The ratio of the reagents TeO 2 and Na 2 MoO 4 should be 1: 5 to obtain a pure product and high yield. It is noteworthy that the ratio 1: 2 which is similar to that obtained in the structure (1: 1.8) gives a significant yellow precipitate during the synthetic procedure which gives a low yield at this ratio. Finally, the pH of the reaction solution affects the formation of 1 and yield of Na-28. A pH window of 6.1-6.9 resulted in a successful synthetic procedure, with pH 6.5 being optimal. A pH lower than 6.1 resulted undistinguished compound as the main product while at higher than 6.9 resulted Na 2 MoO 4·2H 2 O as the main product or as co-crystalline material with 1 as based on FTIR and single-crystal XRD. Interestingly, we discovered 1 when we were trying to crystallize the molydotellurate(IV) analogues of [H 2 Te 4 W 20 O 80 ] 22− or [NaTeW 15 O 54 ] 13− following the synthetic procedures that were used before. 8 Polyanion 1 crystallized as a hydrated sodium salt in the triclinic space group P1̅. The single-crystal X-ray analysis showed that 1 consists of 24 tellurium atoms coordinated to novel building blocks stabilizing the 44 isopolymolybdate. The structure of 188
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