Previously, the 95 Mo and 139 La NMR study [1] confirmed complexation of heteropoly anion ( HPA ) of the type [ X IV Mo 9 O 32 ] 6-for X IV = Ni with Ln ions. It was shown that complex formation involves the cis -MoO 2 group of heteropoly ligand. The coordination active center is formed by two O atoms of the Mo 3 O 13 triplet and the O atom of the MoO 6 octahedron.This work was undertaken with the aim to study complexation of [ MnMo 9 O 32 ] 6-( HPA1 ) with Ln 3+ ions using electron and IR spectroscopies and X-ray diffraction analysis. EXPERIMENTALThe synthesis of the salts [ N ( CH 3 ) 4 ] 2 La [ HMnMo 9 O 32 ] · 6 H 2 O ( II ) and (NH 4 ) 6 [MnMo 9 O 32 ] · 8 H 2 O ( III ) was carried out following the procedures described in [2] and [3], respectively. In order to obtain single crystals of heteropoly complex ( HPC ) [ La 2 ( H 2 O ) 12 ( MnMo 9 O 32 )] · 2 H 2 O ( I ) , the analytical grade La chloride was added to a freshly prepared solution of ammonium salt of HPA1 with concentration ~2 × 10 -3 mol/l (Mn : La = 1 : 10). In 7-10 days, in the presence of the "pract" grade tetramethylammonium chloride ( c = 3-5 × 10 -3 mol/l), at room temperature, crystals I were formed as plates. In this case, crystals of the La salt [ N ( CH 3 ) 4 ] 2 La [ HMnMo 9 O 32 ] · 6 H 2 O, having the cubooctahedral form, were not formed. Note that tetramethylammonium ions do not enter the composition of a new HPC 1 , but their presence in a solution is necessary for the crystals of a complex to be formed.Crystals I were analyzed as follows. A weighed sample (0.2 g) was treated with a 5% NaOH solution. The precipitates of MnO 2 · x H 2 O and La 2 O 3 · y H 2 O formed on boiling were separated by subsequent dissolution of La(III) hydroxide in dilute HNO 3 (1 : 20). Lanthanum was determined by complexometric titration with methyl orange indicator [4,5]. The content of Mn was found by dissolving MnO 2 · x H 2 O in a titrated solution of the Mohr salt; an excess of Mn was determined by permanganatometric method [6]. A filtrate obtained after separation of Mn(IV) and La(III) was used to determine Mo as PbMoO 4 [7]. The water content was found by calcining a separate weighed sample at 500°ë .The electronic absorption spectra of I were recorded on a SF-4A spectrometer at 350-540 nm (UV spectra were referenced to a solution of HPA1 with La; the spectra in a visible region were referenced to water, l = 1 cm).The concentration of HPA1 solutions was 2 × 10 -3 mol/l in terms of a heteroatom. The Ln 3+ ions were added as solutions of Ce nitrate and La chloride with concentration 5 × 10 -2 mol/l. The titre of Ln(III) solutions was established by complexometric method [4,5]. The ratio HPA1 : Ln(III) solutions was 1 : 0.2 (at pH 4.23 for Ce(III) and pH 4.30 for La(III)), since at a higher amount of Ce, the study of complexation was difficult due to the formation of precipitates, characterized by For [La 2 (H 2 O) 12 (MnMo 9 O 32 )] · 2H 2 O Abstract -The properties of [MnMo 9 O 32 ] 6-heteropoly anion (HPA 1), as a macroligand with respect to the lant...
It is known [1, 2] that isopoly and heteropoly anions ( IPA and HPA ) can act as macroligands in the reaction of complex formation with transition metal ions. In this case, the central atom is coordinated to the terminal O atoms of IPA (HPA). Spectroscopic studies of complexation between the [ X III ( OH ) 6 Mo 6 O 18 ] 3-HPA and the d -metal ions in solutions showed that the central atom is coordinated to the terminal O atoms of the ligand cis -MoO 2 groups [3,4]. The assignment of the d -d transitions in [5] revealed that Fe(II) occurs in a high-spin octahedral state.The aim of this work was to synthesize crystals of novel heteropoly complexes ( HPC ) and to study their properties by IR and X-ray diffraction methods. EXPERIMENTAL Synthesis of heteropoly complexes, was performed as follows. Compounds I and III were obtained by the addition of the Na 2 SO 4 · FeSO 4 · 6 H 2 O crystals, synthesized by the procedure described in [6], to the solutions of Na 3 [ Cr ( OH ) 6 Mo 6 O 18 ] · 8 H 2 O ( IV ) and Na 3 [ Al ( OH ) 6 Mo 6 O 18 ] · 5 H 2 O ( V ) salt, respectively, with concentration 0.01 mol/l, until the ratio of X III : Fe = 1 : 4 was attained (X III = Cr, Al). The ( NH 4 ) 2 SO 4 · FeSO 4 · 6 H 2 O reagent was rejected in order to avoid oxidation of Fe(II) [7]. The required pH of the solutions (2.7-2.9) was reached using dilute sulfuric acid (0.02 N). Several days later, black-red, well faceted crystals precipitated in the form of the extended hexagons in the presence of CsNO 3 . To prevent Fe(II) oxidation, the working solutions were prepared in water, which was preliminarily freed of the dissolved oxygen. In order to avoid contact with the air oxygen, the solutions were kept under the hexane layer.Crystals II precipitated as hexagons of a light yellow color in the presence of CsNO 3 after the addition of MnSO 4 · 4 H 2 O to a solution of salt V ( c = 0.05 mol/l) at the ratio Al : Mn = 1 : 2 in 7-10 days.The pH of solutions was measured by a pH-300 potentiometer to an accuracy of ± 0.05 .Analysis of crystals I-III. The samples of the complexes ( ~0.2 g) were digested in a 0.1 M HCl with heating on a sand bath and then boiled with concentrated aqua ammonia (pH 6.5-7.0) to oxidize Fe(II) and to separate Fe(III), Cr(III), and Al(III) hydroxides from Mo and Mn [8]. In the case of I and III , the precipitates of hydroxides were dissolved in a 10% HCl solution, and the total content of Fe(III) and Cr(III) (or Al(III)) was determined by complexometric method [9, 10]. The content of Mo occurring as PbMoO 4 was determined in filtrate [11]. The water content was established by calcining a separate sample at 450°ë .In the case of II , after dissolving Al hydroxide in a 3% HCl solution, Al was determined photometrically with aluminon [12]. Manganese was determined using Abstract-Crystals of novel heterepoly complexes (HPC) Na 0.5 Cs 2 − x [H 0.5 − x X III (OH) 6 Mo 6 O 18 ] · 7-8H 2 O (M II = Fe, Mn; X III = Cr, Al) are synthesized. Crystal structures of the complexes Na 0.5 Cs 2 -x [H 0.5 -x Fe x Cr(OH) 6 Mo 6 O 18 ]...
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