Synthesis, characterization and crystal structure of a novel mononuclear peroxotungsten(VI) complex with an acetone peroxide ligand

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<ul><li><p>ruto</p><p>R, Zoge</p><p>Article history:Available online 6 August 2009</p><p>recognition of his great contribution to the</p><p>A new mononuclear peroxo complex of tungsten of the formula (gu)2[WO(O2)2CO(O)2(CH3)2](CH3)2CO+ +</p><p>by X-ray diffraction indicates that the side-on peroxo groups and the bidentate acetone peroxide ligandbind the W(VI) centre leading to an hepta coordination mode. The guanidinium ion occurring as a coun-terion and the hydrogen-bound interactions stabilize the complexes. The stability of the complex in aque-ous solution was determined by Raman and NMR spectroscopies.</p><p> 2009 Elsevier Ltd. All rights reserved.</p><p>been used both as stoichiometric and effective catalytic oxidantsof different organic and inorganic substrates [1]. Peroxo com-pounds generate dioxygen in its rst excited singlet state (1O2),which is a regio- and stereo-selective oxidant [7]. Peroxide metalcomplexes described in the literature contain one or more O22 li-gand(s) in different bonding modes. It is possible to substitute theone or two peroxo groups by (a) co-ligand(s) (monodentate, biden-tate, tridentate) [8]. In our previous work the synthesis and charac-</p><p>Ugo et al. also reported the formation of a platinum complex com-pound with the same ligand (acetone peroxide), obtained from thereaction of a platinum oxygen complex with acetone [13].</p><p>The complex compound reported in this work is consisted by anacetone peroxide ligand coordinated to a tungsten metal ionW(VI).The guanidinium counterions utilized during the synthesis of thecompound are characterized by thermodynamical stability andalso favour the stabilization of the crystal network by extensivehydrogen bonding [15]. The above compound was generated bythe reaction of sodium tungstate occurring with Y2O2 in acetonesolution and the formation reaction is illustrated in Scheme 1.</p><p>* Corresponding author. Tel.: +30 210 7274456; fax: +30 210 7274435.</p><p>Polyhedron 28 (2009) 34003406</p><p>Contents lists availab</p><p>e</p><p>.eE-mail address: akaraliota@chem.uoa.gr (A. Karaliota).1. Introduction</p><p>Hydrogen peroxide readily associates with transition metalssuch as Mo(VI), V(V), Nb(V) andW(VI), forming a number of peroxocomplexes whose nature depends on the pH and relative concen-tration of the reagents [1]. In the last decades, peroxo species ofearly transition metals (i.e. Mo, W, V, Nb) have attracted consider-able attention because of their extended coordination chemistry[2]. Transition metal complexes have an important role in indus-trial, pharmaceutical and biological processes [36]. They have</p><p>terization of peroxo niobate and tungstate complexes wasreported. The tetraperoxo (gu)3[Nb(O2)4], triperoxo (gu)2[Nb(O2)3(quin-2-c)] and dioxo diperoxo (gu)2[WO2(O2)2], (gu)[WO(O2)2(quin-2-c)] (where, quin-2-c is quinoline-2-carboxylate), ion com-plexes, respectively [8,9].</p><p>A quite rare group of peroxo metal complexes consists of these,which incorporate a molecule of acetone peroxide as a ligand. Toour knowledge, only two complexes with this structure are re-ported so far. Bordner and co-workers reported the formation of3,3-dyhydro-5,5-dimethyl-3,3-triphenyl-1,2,4,3-trioxastibolane [12].advancement of inorganic chemistry inGreece through single-crystal X-raycrystallography.</p><p>Keywords:Acetone peroxidePeroxotungsten(VI)ComplexMononuclearHepta coordination modeTransition metalsGuanidinium ionTriacetone triperoxide0277-5387/$ - see front matter 2009 Elsevier Ltd. Adoi:10.1016/j.poly.2009.07.056This paper is dedicated to Dr. Aris Terzis in</p><p>(where gu = guanidinium ion, CN3H6 ion) has been synthesized and characterized by infrared, Raman,and 1H NMR spectroscopies. The crystal structure of (gu)2[WO(O2)2CO(O)2(CH3)2](CH3)2CO determinedSynthesis, characterization and crystal stperoxotungsten(VI) complex with an ace</p><p>Vasilis Tsitsias a, Adamantia Maniatakou a, Catherinea Inorganic Chemistry, Department of Chemistry, University of Athens, Panepistimiopolisb Institute of Materials Science, NCSR Demokritos, Aghia Paraskevi Attikis 15310, Greec</p><p>a r t i c l e i n f o a b s t r a c t</p><p>Polyh</p><p>journal homepage: wwwll rights reserved.cture of a novel mononuclearne peroxide ligand</p><p>aptopoulou b, Alexandra Karaliota a,*</p><p>rafou 15771, Greece</p><p>le at ScienceDirect</p><p>dron</p><p>l sevier .com/locate /poly</p></li><li><p>The coordination sphere about the tungsten atom consists of se-</p><p>Table 1Crystal data and structure renement for (gu)2[WO(O2)2CO(O)2(CH3)2](CH3)2COcomplex.</p><p>(gu)2[WO(O2)2CO(O)2(CH3)2](CH3)2CO</p><p>Formula C8H24N6O9WFormula weight 532.18Space group P212121T (C) 10k () 1.54178a () 10.5039(1)b () 12.4161(2)c () 13.5584(2)a () 90b () 90c () 90V (3) 1768.25(4)Z 4qcalc (g cm3) 1.999l(Cu Ka) (mm1) 12.625R1/wR2a 0.0268/0.0633b</p><p>a w = 1/[r2(F2o) + (aP)2 + bP] and P = (max(F2o,0) + 2F</p><p>2c )/3; R1 =</p><p>P(|Fo| |Fc|)/P</p><p>(|Fo|) and wR2 = {P[w(F2o F2c )2]/</p><p>P[w(F2o)</p><p>2]}1/2.b For 2729 reections with I &gt; 2r(I).</p><p>Table 2Selected bond lengths () and angles () for the complex.</p><p>Bond distances Bond Angles</p><p>WO5 1.733(4) O5WO3 102.5(2) O4O3W 69.3(3)WO3 1.943(5) O5WO1 101.7(2) O3O4W 65.7(2)WO1 1.948(5) O3WO1 84.5(2) OXO6 W110.6(3)WO2 1.985(4) O5WO2 96.0(2) C2O7W 117.1(3)WO4 1.994(4) O3WO2 129.1(2) C2OXO6 105.2(4)WO7 2.005(4) O1WO2 45.1(2) OXC2O7 107.7(5)WO6 2.087(4) O5WO4 96.7(2) OXC2C4 104.3(6)O1O2 1.509(7) O3WO4 44.9(2) O7C2C4 110.3(6)O3O4 1.505(7) O1WO4 129.0(2) OXC2C3 110.9(6)O6OX 1.472(5) O2WO4 166.98(19) O7C2C3 111.1(5)O7C2 1.431(8) O5WO7 88.77(15) C4C2C3 112.2(7)OXC2 1.429(7) O3WO7 137.4(2) N3C8N1 118.8(7)C2C3 1.506(9) O1WO7 133.8(2) N3C8N2 121.6(9)C2C4 1.505(9) O2WO7 89.38(19) N1C8N2 119.5(7)C8N3 1.296(9) O4WO7 93.38(19) N5C9N4 122.5(7)C8N1 1.300(9) O5WO6 165.29(15) N5C9N6 119.0(8)C8N2 1.309(10) O3WO6 87.8(2) N4C9N6 118.4(8)C9N5 1.306(10) O1WO6 89.5(2) O11C11C12 120.6(11)C9N4 1.332(9) O2WO6 85.2(2) O11C11 122.7(11)C9N6 1.339(9) O4WO6 83.1(2) C12C11C13 116.5(9)O11C11 1.180(8) O7WO6 76.57(15)C11C12 1.414(11) O2O1W 68.7(2)C11C13 1.433(14) O1O2W 66.2(2)</p><p>rma</p><p>dron2. Experimental</p><p>2.1. Materials and methods</p><p>Sodium tungstate, and guanidinium carbonate obtained fromAldrich were used without further purication. Hydrogen peroxide(30%) obtained from Merck was used as received and de-ionizedand distilled water was used throughout this study. Deuteratedsolvents for use in the NMR, D2O, and DCl were purchased fromMerck. IR spectra were recorded using a KBr pellet on a Perkin El-mer 880 IR spectrophotometer. High-frequency Raman spectrawere recorded with a PerkinElmer GX Fourier 514.5 nm usingan Ar+ laser with a JobinYvon (T64000) triple spectrometer asthe excitation source. The UVVis absorption spectra in the range900200 nm were recorded using a Cary 3E spectrophotometer.NMR spectra were recorded with a Bruker Avance 500 MHz instru-ment and were processed by X-WIN MR 2.6 (Bruker AnalytikGmbH).</p><p>2.2. Preparation of (gu)2[WO(O2)2CO(O)2(CH3)2](CH3)2CO</p><p>A solution of sodium tungstate (1.08 g, 3.3 mmol) in 30% H2O2(20 mL) was treated with (gu)2CO3 (1.35 g, 7.5 mmol) in 20 mL dis-tilled water. The clear yellow solution was stirred for a few min-utes and the pH solution was recorded to be 8.7. 120 ml ofacetone were slowly added and a white precipitate was formedimmediately after the addition of acetone. The solid was lteredoff. The ltered solution was cooled at 4 C and colourless crystalssuitable for X-ray diffraction were obtained after 7 days. Anal. Calc.for: C. 18.06; H, 4.55; N, 15.79. Found: C, 18.26; H, 4.49; N, 15.85%.</p><p>2.3. X-Ray diffraction</p><p>Slow crystallization from acetone yielded colourless prismaticcrystals. A crystal with approximate dimensions0.29 0.42 0.56 mm was taken from the mother liquor andimmediately cooled to 10 C. Diffraction measurements weremade on a Rigaku R-AXIS SPIDER Image Plate diffractometer usinggraphite monochromated Cu Ka radiation. Data collection (x-scans) and processing (cell renement, data reduction, Numericaland Empirical absorption correction) were performed using theCRYSTALCLEAR program package [19]. The structure was solved by di-rect methods using SHELXS-97 [20] and rened by full-matrix least-squares techniques on F2 with SHELXL-97 [21]. Further experimentalcrystallographic details for the complex: 2hmax = 130; reectionscollected/unique/used, 10 537/2843 [Rint = 0.0539]/2843; 223parameters rened; (D/r)max = 0.007; (Dq)max/(Dq)min = 0.689/0.588 e/3; R1/wR2 (for all data), 0.0281/0.0644. All hydrogen</p><p>Scheme 1. The proposed mechanism for the fo</p><p>V. Tsitsias et al. / Polyheatoms were introduced at calculated positions as riding on bondedatoms. All non-hydrogen atoms were rened anisotropically.</p><p>3. Results and discussion</p><p>3.1. Crystal structure</p><p>The crystal data for the complex are given in Table 1 and se-lected bond lengths and angles in Table 2. The structure of themonomeric oxo diperoxo complex is depicted in Fig. 1.tion reaction of the acetone peroxide complex.</p><p>28 (2009) 34003406 3401ven oxygen atoms arranged in a pseudotrigonal bipyramid geome-try with the oxo ligand O(5) and an oxygen atom of the ligand O(6),in the axial positions. The two peroxo groups and the oxygen O(7)of the ligand lie in the equatorial plane. Similar structural data forperoxo complexes of tungsten W(VI) are reported in a more recentreview published in 2008 by Sergienko [18]. The complex com-pound has a similar structure with the heteroleptic tungsten com-plex with the quinaldinic ligand reported in our work as it can beseen by the bond angles [9]. The oxo atom, the bond (COW) andthe peroxo group of the acetone peroxide ligand are almost copla-</p></li><li><p>the quinaldinic ligand does [9]. Raczynska et al. reported the rich-ness of intermolecular interactions in guanidinium salts. These arehydrogen bonds, Coulomb and Van der Waals interactions. In par-ticular, the highly symmetric and planar guanidinium ion with sixequivalent protons, is a hydrogen bond donor. Since the H-bonddonor and acceptor are charged species, the electrostatic interac-tions in the crystal lattice may additionally modify the hydrogenbond network [15]. The selected hydrogen bond lengths are re-ported in Table 3.</p><p>3.2. Infrared and Raman data</p><p>The infrared spectrum of the complex revealed the characteris-tic spectral pattern main vibrations of which are summarized inTable 4. The spectrum of the complex illustrated in Fig. 3 exhibitsa strong sharp band at 929 cm1 consistent with the presence ofthe W@O bond vibration Two strong and sharp bands packing at869 and 828 cm1 are ascribed to the OO vibration [14]. Theoccurrence of two bands indicates the presence of different peroxogroups side-on bound to the metal. Additional bands in the rangeof 690540 cm1 belong to mas(WO2) and ms(WO2) [10]. Thebands at 1551 and 1363 are assigned to the methyl group bendingmotion, and the band at 1227 corresponds to the CO stretch [16].The peaks at 3417 and 3182 cm1 are attributed to the asymmetricvas(NH2) and symmetric vs(NH2)vibrations. Drozd et al. in a theo-retical vibrational spectra study of guanidine selenate (GUSE) andguanidinium sulphate (GUS), reported that the bands at 35743511 cm1 and at 35753502 cm1 are assigned in mas(NH2)vibra-tions in (GUS) and (GUSE), respectively, and the symmetric vibra-tions ms(NH2) at 3103 and 3315 for (GUS) and (GUSE). In the IR</p><p>Fig. 1. Structure and atom numbering of (gu)2[WO(O2)2CO(O)2(CH3)2](CH3)2CO(where gu+ = guanidinium ion, CN3H6+ ion). Thermal ellipsoids are drawn at the 50%</p><p>3402 V. Tsitsias et al. / Polyhedron 28 (2009) 34003406nar and perpendicular to the plane of the peroxo oxygen atoms.The acetone peroxide bidentate chelating ligand is coordinated tothe metal atom by the oxygen atoms of the oxygencarbontung-sten bond (COW) and by two peroxo oxygen atoms and closesthe ve membered metallocycle WOCO2. The angle between them(O5WO7) is 88.7(15) which is close to the angle between the oxoatom the tungsten ion and the oxygen of the quinolinium ring ofthe quinaldinic tungsten complex [9]. The distance of the W@Odouble bond is 1.733 (4), whereas the W@O distance is 1.698 respectively in the quinaldinic complex. The OO bond lengths(1.509(7)1.505(7) ). The WO(peroxo) bond lengths are in therange 1.943(4)1.994(5) , which suggests that they are bondedasymmetrically. These data are also in accordance with those re-ported in our previews work except that the lengths of the OO(1.509(7)1.505(7)) bonds are noticeably longer comparing to thequinaldinic complex reported previously [9]. The crystal packingof the complex is dominated by intermolecular OH O hydrogenbonds. The co crystallized acetone molecule and the guanidinium</p><p>probability level.N atoms participate in 8 hydrogen bonds of each molecule(Fig. 2) (in) the same way (as) the peroxo tungstate complex with</p><p>Fig. 2. Crystal packing of (gu)2[WO(O2)2CO(O)2(CH3)2](CH3)2CO. Hydrogen bondsare represented by dotted lines, and selected donor and acceptor atoms are labelled.Table 4IR and Raman data of the (gu)2[WO(O2)2CO(O)2(CH3)2](CH3)2CO complex.</p><p>Assign.W@O IR 929</p><p>Raman 896m(OO) IR 869, 828</p><p>Raman 839, 823ms(WO2) IR 541</p><p>Raman 526mas(WO2) IR 687Table 3Distances and bending angles for hydrogen bonds in structure of the complex.</p><p>DH A DH H A DH A </p></li><li><p>3.3. Raman in solution</p><p>The Raman spectra of the complex in aqueous solution both inabsence and presence of hydrogen peroxide at different pH values,is extremely useful for the identication of the different peroxospecies formed and the data are summarized in Table 5. In orderto obtain valuable conclusions a strictly specic procedure was fol-lowed. Firstly, a spectrum, obtained 20 min after the dissolution ofthe complex in water, exhibits two main bands at 1013 and932 cm1 corresponding to the CN and W@O vibrations,respectively.</p><p>After the addition of an appropriate quantity of H2O2, capable toprepare a solution with an excess of H2O2, a second spectrum ob-tained which is depicted in Fig. 5. In that spectrum the appearanceof four new bands at 876 main, 858 shoulders, 795 broad band, and573 cm1, not present before indicates the interaction of H2O2 withthe complex compound. The band at 876 corresponds to the OOvibration of the free H2O2 and the two bands at 858 and795 cm1 to the coordinated H2O2. The band at 573 cm1 is attrib-uted to the WOC vibration [16]. Another interesting differencebetween the two spectra is the absence of the band at 932 cm1</p><p>in the second spectrum. All the peaks mentioned above exceptfor the peak at 573 cm1 appeared in the solid state. The abovendings are in accordance with those reported in our work withperoxo tungsten complexes [9]. The disappearance of the band at932 cm1 indicates the absence of theW@O bond to the compoundin the presence of an excess of H2O2. Under these conditions a tri-peroxo form of the complex is dominant. This assertion becomesstronger due to the appearance of the bands at 858 and</p><p>V. Tsitsias et al. / Polyhedron 28 (2009) 34003406 3403spectra reported here the corresponding peaks are shifted due tothe hydrogen bonding of the guanidinium cation. Also the bandat 3417 cm1 is characterized by higher intensity comparing tothe band at 3182 cm1. This nding is in contrast to Drozd et al.who supported that the ms(NH2) is the stron...</p></li></ul>

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