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A novel organotellurium halide with tellurium presenting mixed oxidation states: Synthesis and structural characterization
Inorganica Chimica Acta 365 (2011) 492–495
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Note
A novel organotellurium halide with tellurium presenting mixed oxidation states: Synthesis and structural characterization Gleison Antônio Casagrande a,⇑, Cristiano Raminelli a, Ernesto Schulz Lang b, Sebastião de Souza Lemos c a
Laboratório de Síntese e Caracterização Molecular, Universidade Federal da Grande Dourados, Rod. Dourados/Itahum, Km 12, 79.804-970, Douradosm, MS, Brazil Departamento de Química, Universidade Federal de Santa Maria, 97.105-900 Santa Maria, RS, Brazil c Instituto de Química, Universidade de Brasília, 70.904-970, Brasília, DF, Brazil b
a r t i c l e
i n f o
Article history: Received 21 July 2010 Received in revised form 16 September 2010 Accepted 27 September 2010 Available online 8 October 2010 Keywords: Organotellurium halides Mixed oxidation state Secondary bonds
a b s t r a c t In this work we have investigated the reaction for the obtention of an uncommon complex salt of the organotellurium bromide class. The reaction was carried out without the isolation of the synthetic intermediates in one-pot procedure. The complex salt obtained presents the tellurium atoms with mixed oxidation states (TeII and TeIV). The cationic unit [5-Br-2-CH3O–C6H3Te(ETU)]+ presents the TeII atom with a ‘‘T” shape coordination geometry, and the anionic unit [4-CH3O–C6H4TeBr4] presents the TeIV atom with an octahedral coordination geometry considering the TeBr interaction of 3.600(6) Å from the dimeric arrangement presented in the solid state. Intermolecular (TeBr) secondary bonds, built up the crystalline/molecular structure. Solution NMR data are presented and discussed in the light of the X-ray structure. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction In recent years, the rich and extensive chemistry of organotellurium halides have obtained special attention due to structural features presented in the solid state, for example, the possibilities in the participation of dimeric, polymeric and supramolecular arrangements via secondary bonds of the type TeX [1–3]. Organotellurium halides are very reactive compounds which have been widely applied in several types of reactions in the field of organic synthesis such as arylation of olefins, detelluration of organotellurium halides with the formation of new C–C bonds, replacement of the tellurium halides moieties by other functionalities, etc. [4]. Reactions concerning halogenation of organotellurium species for giving compounds of tellurium in low oxidation states were reported in pioneering works by Klar and Schulz [5,6], as well as the complexation of this species with thiourea derivatives were reported by Foss and Maartmannmoe [7]. Complex salts showing aryltellurinates anions of the type [ArTeX4] (Ar = Ph, mO2NC6H4, p-NCC6H4; X = Cl, Br, I) stabilized for cations of the pyridinium type have been widely investigated and fully characterized by X-ray diffraction studies [8,9]. Moreover, telluronium cations of the type [Ar3Te]+ (Ar = Ph, Mes) stabilized for anions I3 and SbF6 were also characterized in early works [10,11]. Organochalcogen halides containing chalcogen atoms with mixed oxidation states in the same molecule are very rare and
⇑ Corresponding author. Tel.: +55 67 3410 2114; fax: +55 3410 2112. E-mail address: [email protected] (G.A. Casagrande). 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.09.053
few examples were reported in the literature so far. It is very difficult to access this class of molecule due to relative instability of the synthetic intermediates as, for example, the monohalides of organotellurium. Occurrences of disproportionation reactions were reported in previous work of our research group [12]. In recent work, we have demonstrated the synthesis and structural characterization of some symmetrical examples of molecules of this nature [13]. We demonstrated that the structural organization in the solid state is more related to steric effects than electronic effects of the organic groups bonded in the chalcogen atom [14]. Recently, Beckmann and co-workers have investigated the halogenation reaction of two diarylditellurides aiming to the obtention of the new diarylditellurides with mixed oxidation states. The obtained products RX2TeTeR (R = Ph, 2,6-Mes2C6H3; X = Cl, Br) were characterized in the solid state by X-ray diffraction and structural details revealed a dimeric organization from TeX secondary bonds [15]. Secondary bonds of type TeX and XX play an important role in supramolecular self-assembling of anions of the type [RTeX4] (R = organic groups; X = Cl, Br, I), which are present in various salt complexes described in the literature [9,16]. Alcock has introduced the ‘‘secondary bond” term in the literature for classifying chemical bonds that have borderline forces between the classic covalent bonds and weak van der Waals interactions [17]. The supramolecular synthesis considers the self-assembling of the molecular entities based on the secondary bonds, and calls ‘‘tectons” the single unities which acts in the formation of the supramolecular arrays by secondary bonds [18]. In this work we present the synthesis and structural characterization of a rare unsymmetrical salt complex of the organotellurium
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halide family. The new salt complex presents the tellurium atoms with mixed oxidation states in the same molecule. The dimeric association via secondary bonds TeBr are present in the solid state but the NMR 125Te features suggest that such interactions are not sustained in acetone-dimethylsulfoxide solution. Multinuclear magnetic resonance has been used to demonstrate that such interactions, when present in solution, induce a considerable low-field shifting of the 125Te nucleus [19,20].
Bruker Tensor-27 spectrometer using KBr pellets. Elemental analyses were obtained in a Perkin–Elmer CHN 2400 equipment. 2.2. Preparation of the salt complex The salt complex was synthesized exploring a one-pot procedure in agreement with the outline below: ðiÞBr2
ðiiÞETU
R0 TeTeR0 ! R0 TeBr ! R0 TeðETUÞBr ðBrownÞ
ðiiiÞR00 TeBr3
2. Experimental
ðiÞ rt=5 min:
2.1. Chemicals and measurements
ðiiÞ Ethylenethiourea ðETUÞ; rt=15 min: ðiiiÞ R00 TeBr3 ; 45 C=1:5 h:
All manipulations were conducted under nitrogen by the use of standard Schlenk techniques. Br2 and ethylenethiourea are analytical grade reagents (Sigma–AldrichÒ) and were used without purification. Organotellurium derivatives were synthesized according to the literature methods [4,21] and methanol was dried with Mg/I2 and distilled prior to use [22]. The X-ray structural determinations were collected with a Bruker APEX II CCD area-detector diffractometer and graphite-monocromatized Mo Ka (0.7107 Å) radiation. The structure was solved by direct methods using SHELXS and SHELXL package implemented in the WINGX 2002 program [23]. All refinements were made by full-matrix least-squares on F2 with anisotropic displacement parameters for all non-hydrogen atoms. Hydrogen atoms were included in the refinement in calculated positions. Crystal data and more details of the data collections and refinements are shown in Table 1. All NMR spectra were recorded on a Varian Mercury plus spectrometer (7.05T) operating at 94.74 MHz for 125Te. 125Te spectra were acquired in a mixture of acetone-d6 and DMSO-d6 (9:1 by volume) and were externally referenced to Me2Te checked against Te2Ph2 in CDCl3 (d = 450 ppm) [24]. The sample temperature was maintained at 300 K during the acquisitions. The IR measurements were acquired in a
!
½R00 TeðETUÞ½R0 TeðBrÞ4
ðYellowÞ
ðYellowÞ
R0 ¼ p-CH3 O—C6 H4 ; R00 ¼ 5-Br-2-CH3 O—C6 H3 Initially, Br2 (0.032 g, 0.2 mmol) was added to a red solution of (4-CH3O–C6H4Te)2 (0.094 g, 0.2 mmol) in methanol (20 mL). After stirring for 5 min, it was produced a brown solution of 4-CH3O– C6H4TeBr. Afterwards, ethylenethiourea (0.0204 g, 0.2 mmol) was added and the solution quickly turned yellow. To this solution the organotellurium tribromide (0.088 g, 0.2 mmol) was added and maintained under stirring at 45 °C for 1.5 h. After cooling at room temperature the mixture was filtered and the slow evaporation of the solvent gave yellow needle crystals. Properties: crystalline air stable substance; C17H19Br5N2O2STe2 F.W. (970.15); Yield: 0.192 g (82%) based on the ditelluride used; Melting point: 121–123 °C; Anal. Calc. C, 21.05; H, 1.97; N, 2.89. Found: C, 21.22; H, 1.92; N, 2.92%; 1H NMR: d 8.67 (sbroad, 2H, NH), 6.8–8.4 (m, 7H, C–Harom.), 3.92–3.85 (m, 10H, CH2, OCH3); 13 C{1H} NMR: d 176.66 (C@S), 138.4, 138.00, 137.50, 115.90, 115.70, 115.30, 114.10, 113.00 (Carom), 57.00, 55.85 (OCH3), 46.17, 42.60 (CH2); IR (KBr, m/cm1) 1579, 1522, 1462 (ms-N–C@S) [25], 1252 (ms-C–O) [26], 3292 (ms-N–H) [26]. 3. Results and discussion
Table 1 Crystal data and structure refinement for the complex. Empirical formula Formula weight Temperature(K) Radiation; k (Å) Crystal system Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) Volume (Å3) Z/density calculated (g cm3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm) Range for data collection h (°) Index ranges
Reflections collected Reflections unique Completeness to theta maximum (%) Absorption correction Maximum and minimum transmission Data/restraints/parameters Goodness-of-fit F2 Final R indices [I > 2r(I)] R indices (all data) Largest difference in peak and hole (e Å3)
3.1. X-ray studies C17H19Br5N2O2STe2 970.15 295(2) Mo Ka; 0.71073 triclínic P 1 9.3936(6) 11.7872(8) 13.2069(9) 109.531(4) 96.464(4) 104.259(4) 1304.96(15) 2/2.469 9.987 892 0.32 0.32 0.26 1.67 a 32.15 14 6 h 6 14 15 6 k 6 17 19 6 l 6 16 27041 9057 99.7 semi-empirical 0.1810 and 0.1423 9057/0/262 1.062 R1 = 0.0489 wR2 = 0.1210 R1 = 0.0781, wR2 = 0.1468 1.747 e 1.112
The crystal X-ray data and the experimental conditions of the analyses for the complex are given in Table 1. Table 2 summarizes selected bond distances and angles for the title complex. Fig. 1 shows the molecular structure present in the crystallographic asymmetric unit. Fig. 2 shows the dimeric association from the secondary bond present in the solid state, the secondary interactions are identified by dashed lines. To the best of our knowledge, this complex salt is the first organotellurium halide reported in the literature containing unsymmetric organic groups bonded in the chalcogen atoms with mixed oxidation states. The structure consists of one cationic unit [5-Br-2-CH3O–C6H3Te(ETU)]+ containing the TeII atom and one anionic unit [4-CH3O–C6H4TeBr4] containing the TeIV atom. These units interact with each other through one interionic secondary bond Te(2)Br(1) of 3.2900(7) Å, this interaction is in agreement with the value of 3.1757(13) Å for a similar compound [13]. On the other hand, the anionic units interact with each other through Table 2 Bond lengths (Å) and angles (°) selected for the complex. Bond lengths S(1)–Te(2) Br(1)–Te(2) Te(1)–Br(2)#1 Br(1)–Te(1) Br(2)–Te(1)
Angles 2.4467(13) 3.2900(7) 3.6000(6) 2.7221(7) 2.6650(6)
S(1)–Te(2)–Br(1) C(11)–Te(1)–Br(2)#1 C(11)–Te(1)–Br(4) C(21)–Te(2)–S(1) Br(2)–Te(1)–Br(4)
170.09(2) 170.25(12) 89.91(12) 96.19(12) 178.97(2)
Symmetry transformations used to generate equivalent atoms: #1 x, y, z 1.
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crystallographic space group. This inversion center is located P1 in the middle point of the square formed by Te(1), Br(2), Te(1)#1, Br(2)#1 atoms. 3.2.
Fig. 1. Molecular structure of the complex with emphasis in the secondary bond Te(2)Br(1) of 3.2900(7) Å (all H-atoms have been omitted for clarity). Thermal ellipsoids are drawn at the 50% probability level.
one secondary bond Te(1)Br(2)#1 of 3.600(6) Å, this interaction is less than the sum of van der Waals radii for the same atoms (Te and Br 4.00 Å) [27]. The latter secondary bond completes the octahedral coordination sphere of the Te(1) atom, and is responsible by dimeric array organization of the structure in the solid state. The analysis of the bond angles between S(1)–Te(2)–Br(1) of 170.09(2)° and C(21)–Te(2)–S(1) of 96.19(12)° for the Te(2) atom, present in the cationic unit, shows that this atom has a ‘‘T” shape coordination geometry and this is in agreement with other compounds already mentioned in the literature [28]. Finally the dimeric array is correlated by one inversion center belonging to
125
Te NMR studies
Due to the low solubility of the title complex crystals in conventional organic solvents such as chloroform, benzene, and hexane, our investigations for the solution behavior studies were elaborated employing acetone-d6 and DMSO-d6 in a 9:1 proportion, respectively. Moreover our attention was focused on 125Te NMR once the 1H and 13C NMR spectra do not show significant structural features for the dimeric complex in solution. Two peaks were detected in the 125Te NMR spectra of the complex in solution. One sharp peak appears in d = 1210.9 ppm and one broad signal appears in d = 931.5 ppm. When the same experiment is carried out for the standard compound [Et4N][PhTeBr4] only one sharp signal is observed at d = 1199.8 ppm, this signal is assigned for the anionic unit [PhTeBr4]. For comparison purposes, we have recorded the same experiment for the neutral compound PhTeBr3, and in this case two sharp signals appeared in d = 1202.3 and d = 824.8 ppm. These results show that the PhTeBr3 ionizes in DMSO-acetone solution according to the equation: 2PhTeBr3 + DMSO ? [PhTeBr4] + [PhTe(DMSO)Br2]+ [13]. In the light of these results and supported by the performed experiments we propose that our complex ionizes in solution generating the corresponding cationic and anionic units. Accordingly, the sharp peak that appears in d = 1210.9 ppm corresponds to the anionic unit [4-CH3OC6H4TeBr4], and the broad signal that appears in d = 931.5 ppm is related to the cationic unit [5-Br-2CH3O–C6H3Te(ETU)]+. Based on this behavior, we conclude that in solution occurs the disruption of the secondary bonds (TeBr) responsible for the dimeric association represented by dashed lines in the Fig. 2. It is worth mentioning that in the complex [p-CH3O(C6H4)Te(ETU)][pCH3O(C6H4)TeI4] the 125Te NMR spectrum showed a broad signal at 933.5 ppm, attributed to the [p-CH3O(C6H4)Te(ETU)]+ cation
Fig. 2. Molecular structure and dimeric arrangement for the complex. Interionic secondary interactions are depicted in dashed lines (all H-atoms have been omitted for clarity). Thermal ellipsoids are drawn at the 50% probability level. Symmetry transformations used to generate equivalent atoms: #1 x, y, z 1.
G.A. Casagrande et al. / Inorganica Chimica Acta 365 (2011) 492–495
[14]. Thereby, the dimeric structure that we have in the solid state does not maintain its arrange in solution. 4. Conclusion The title complex presenting mixed oxidation states was synthesized in a one-pot procedure in a good yield. The data refined from the X-ray diffraction reveal the dimeric association of the molecular entities formed via secondary bonds which are present in the solid state. The comparison between 125Te NMR and X-ray data show that the structure present in the solid state is not kept in solution, moreover all secondary interactions (TeBr) are broken in solution. Acknowledgments We gratefully acknowledge the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and the FUNDECT (Fundação de Apoio ao Desenvolvimento do Ensino, Ciência e Tecnologia do Estado do Mato Grosso do Sul) for financial support. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2010.09.053. References [1] J.Z. Schpector, I. Haiduc, Phosphorus, Sulfur, Silicon 171 (2001) 73. [2] G.M. Oliveira, G.A. Casagrande, E.S. Lang, R.M. Muzzi, S.S. Lemos, J. Organomet. Chem. 694 (2009) 2463.
495
[3] J. Beckmann, S. Heitz, M. Hesse, Inorg. Chem. 46 (2007) 3274. [4] Petragnani, Nicola, Tellurium in Organic Synthesis, Academic Press, Inc. San Diego, CA, 1994. [5] G. Klar, P. Schulz, Z. Naturforsch. B 30 (1) (1975) 43. [6] G. Klar, P. Schulz, Z. Naturforsch. B 30 (1) (1975) 40. [7] O. Foss, K. Maartmannmoe, Acta Chem. Scand. A 41 (1987) 121. [8] J. Beckmann, A. Duthie, C. Mitchell, Organometal. Chem. 19 (11) (2005) 1196. [9] E.S. Lang, G.M. Oliveira, R.M. Fernandes Jr., E.M.V. Lopez, Inorg. Chem. Commun. 6 (2003) 869. [10] W.W. Du Mont, J. Jeske, F. Rhute, P.G. Jones, L.M. Mercuri, P. Deplano, J. Inorg. Chem. 7 (2000) 1591. [11] W.W. Du Mont, J. Jeske, P.G. Jones, Phosphorus, Sulfur, Silicon 185 (2010) 1243. [12] G.N. Ledesma, E.S. Lang, E.M. Vázquez-Lopez, U. Abram, Inorg. Chem. Commun. 7 (2004) 478. [13] E.S. Lang, G.A. Casagrande, G.M. Oliveira, G.N. Ledesma, S.S. Lemos, E.E. Castellano, U. Abram, Eur. J. Inorg. Chem. (2006) 958. [14] G.A. Casagrande, E.S. Lang, G.M. Oliveira, S.S. Lemos, V.A.S. Falcomer, J. Organomet. Chem. 691 (2006) 4006. [15] J. Beckmann, M. Hesse, H. Poleschner, K. Seppelt, Angew. Chem., Int. Ed. 46 (2007) 8277. [16] N.W. Alcock, W.D. Harrison, J. Chem. Soc., Dalton Trans. (1983) 2015. [17] J.M. Alcock, Adv. Inorg. Chem. Radiochem. 15 (1972) 1. [18] J. Simard, J. Am. Chem. Soc. 113 (1991) 4696. [19] M. Iwaoka, S. Tomoda, J. Am. Chem. Soc. 118 (1996) 8077. [20] C.S. Menon, B.S. Harkesh, J.M. Jasinski, R.J. Butcher, Organometallics 15 (1996) 1707. [21] J.V. Comasseto, A.T. Omori, F.T. Toledo, P. Castelani, R.L.O.R. Cunha, J. Organomet. Chem. 689 (2004) 3631. [22] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemicals, third ed., Pergamon Press, Oxford, EUA, 1988. [23] G.M. Sheldrick, SHELXS-97 and SHELXL-97 Programs for Crystal Structure Solution and Refinement, University of Gottingen, Germany 1997. [24] M. Asahara, M. Tanaka, T. Erabi, M. Wada, J. Chem. Soc., Dalton Trans. 15 (2000) 3493. [25] C.N.R. Rao, R. Venkataraghavan, Spectroquim. Acta 18 (1962) 541. [26] R.M. Silverstein, G.C. Bassler, T.C. Morrill, Spectrometric Identification of Organic Compounds, fifth ed., John Wiley and Sons, 1991. [27] A. Bondi, J. Phys. Chem. 68 (1964) 441. [28] G.N. Ledesma, U. Abram, E.S. Lang, J. Organomet. Chem. 689 (2004) 2092.
Contents lists available at ScienceDirect
Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Note
A novel organotellurium halide with tellurium presenting mixed oxidation states: Synthesis and structural characterization Gleison Antônio Casagrande a,⇑, Cristiano Raminelli a, Ernesto Schulz Lang b, Sebastião de Souza Lemos c a
Laboratório de Síntese e Caracterização Molecular, Universidade Federal da Grande Dourados, Rod. Dourados/Itahum, Km 12, 79.804-970, Douradosm, MS, Brazil Departamento de Química, Universidade Federal de Santa Maria, 97.105-900 Santa Maria, RS, Brazil c Instituto de Química, Universidade de Brasília, 70.904-970, Brasília, DF, Brazil b
a r t i c l e
i n f o
Article history: Received 21 July 2010 Received in revised form 16 September 2010 Accepted 27 September 2010 Available online 8 October 2010 Keywords: Organotellurium halides Mixed oxidation state Secondary bonds
a b s t r a c t In this work we have investigated the reaction for the obtention of an uncommon complex salt of the organotellurium bromide class. The reaction was carried out without the isolation of the synthetic intermediates in one-pot procedure. The complex salt obtained presents the tellurium atoms with mixed oxidation states (TeII and TeIV). The cationic unit [5-Br-2-CH3O–C6H3Te(ETU)]+ presents the TeII atom with a ‘‘T” shape coordination geometry, and the anionic unit [4-CH3O–C6H4TeBr4] presents the TeIV atom with an octahedral coordination geometry considering the TeBr interaction of 3.600(6) Å from the dimeric arrangement presented in the solid state. Intermolecular (TeBr) secondary bonds, built up the crystalline/molecular structure. Solution NMR data are presented and discussed in the light of the X-ray structure. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction In recent years, the rich and extensive chemistry of organotellurium halides have obtained special attention due to structural features presented in the solid state, for example, the possibilities in the participation of dimeric, polymeric and supramolecular arrangements via secondary bonds of the type TeX [1–3]. Organotellurium halides are very reactive compounds which have been widely applied in several types of reactions in the field of organic synthesis such as arylation of olefins, detelluration of organotellurium halides with the formation of new C–C bonds, replacement of the tellurium halides moieties by other functionalities, etc. [4]. Reactions concerning halogenation of organotellurium species for giving compounds of tellurium in low oxidation states were reported in pioneering works by Klar and Schulz [5,6], as well as the complexation of this species with thiourea derivatives were reported by Foss and Maartmannmoe [7]. Complex salts showing aryltellurinates anions of the type [ArTeX4] (Ar = Ph, mO2NC6H4, p-NCC6H4; X = Cl, Br, I) stabilized for cations of the pyridinium type have been widely investigated and fully characterized by X-ray diffraction studies [8,9]. Moreover, telluronium cations of the type [Ar3Te]+ (Ar = Ph, Mes) stabilized for anions I3 and SbF6 were also characterized in early works [10,11]. Organochalcogen halides containing chalcogen atoms with mixed oxidation states in the same molecule are very rare and
⇑ Corresponding author. Tel.: +55 67 3410 2114; fax: +55 3410 2112. E-mail address: [email protected] (G.A. Casagrande). 0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2010.09.053
few examples were reported in the literature so far. It is very difficult to access this class of molecule due to relative instability of the synthetic intermediates as, for example, the monohalides of organotellurium. Occurrences of disproportionation reactions were reported in previous work of our research group [12]. In recent work, we have demonstrated the synthesis and structural characterization of some symmetrical examples of molecules of this nature [13]. We demonstrated that the structural organization in the solid state is more related to steric effects than electronic effects of the organic groups bonded in the chalcogen atom [14]. Recently, Beckmann and co-workers have investigated the halogenation reaction of two diarylditellurides aiming to the obtention of the new diarylditellurides with mixed oxidation states. The obtained products RX2TeTeR (R = Ph, 2,6-Mes2C6H3; X = Cl, Br) were characterized in the solid state by X-ray diffraction and structural details revealed a dimeric organization from TeX secondary bonds [15]. Secondary bonds of type TeX and XX play an important role in supramolecular self-assembling of anions of the type [RTeX4] (R = organic groups; X = Cl, Br, I), which are present in various salt complexes described in the literature [9,16]. Alcock has introduced the ‘‘secondary bond” term in the literature for classifying chemical bonds that have borderline forces between the classic covalent bonds and weak van der Waals interactions [17]. The supramolecular synthesis considers the self-assembling of the molecular entities based on the secondary bonds, and calls ‘‘tectons” the single unities which acts in the formation of the supramolecular arrays by secondary bonds [18]. In this work we present the synthesis and structural characterization of a rare unsymmetrical salt complex of the organotellurium
493
G.A. Casagrande et al. / Inorganica Chimica Acta 365 (2011) 492–495
halide family. The new salt complex presents the tellurium atoms with mixed oxidation states in the same molecule. The dimeric association via secondary bonds TeBr are present in the solid state but the NMR 125Te features suggest that such interactions are not sustained in acetone-dimethylsulfoxide solution. Multinuclear magnetic resonance has been used to demonstrate that such interactions, when present in solution, induce a considerable low-field shifting of the 125Te nucleus [19,20].
Bruker Tensor-27 spectrometer using KBr pellets. Elemental analyses were obtained in a Perkin–Elmer CHN 2400 equipment. 2.2. Preparation of the salt complex The salt complex was synthesized exploring a one-pot procedure in agreement with the outline below: ðiÞBr2
ðiiÞETU
R0 TeTeR0 ! R0 TeBr ! R0 TeðETUÞBr ðBrownÞ
ðiiiÞR00 TeBr3
2. Experimental
ðiÞ rt=5 min:
2.1. Chemicals and measurements
ðiiÞ Ethylenethiourea ðETUÞ; rt=15 min: ðiiiÞ R00 TeBr3 ; 45 C=1:5 h:
All manipulations were conducted under nitrogen by the use of standard Schlenk techniques. Br2 and ethylenethiourea are analytical grade reagents (Sigma–AldrichÒ) and were used without purification. Organotellurium derivatives were synthesized according to the literature methods [4,21] and methanol was dried with Mg/I2 and distilled prior to use [22]. The X-ray structural determinations were collected with a Bruker APEX II CCD area-detector diffractometer and graphite-monocromatized Mo Ka (0.7107 Å) radiation. The structure was solved by direct methods using SHELXS and SHELXL package implemented in the WINGX 2002 program [23]. All refinements were made by full-matrix least-squares on F2 with anisotropic displacement parameters for all non-hydrogen atoms. Hydrogen atoms were included in the refinement in calculated positions. Crystal data and more details of the data collections and refinements are shown in Table 1. All NMR spectra were recorded on a Varian Mercury plus spectrometer (7.05T) operating at 94.74 MHz for 125Te. 125Te spectra were acquired in a mixture of acetone-d6 and DMSO-d6 (9:1 by volume) and were externally referenced to Me2Te checked against Te2Ph2 in CDCl3 (d = 450 ppm) [24]. The sample temperature was maintained at 300 K during the acquisitions. The IR measurements were acquired in a
!
½R00 TeðETUÞ½R0 TeðBrÞ4
ðYellowÞ
ðYellowÞ
R0 ¼ p-CH3 O—C6 H4 ; R00 ¼ 5-Br-2-CH3 O—C6 H3 Initially, Br2 (0.032 g, 0.2 mmol) was added to a red solution of (4-CH3O–C6H4Te)2 (0.094 g, 0.2 mmol) in methanol (20 mL). After stirring for 5 min, it was produced a brown solution of 4-CH3O– C6H4TeBr. Afterwards, ethylenethiourea (0.0204 g, 0.2 mmol) was added and the solution quickly turned yellow. To this solution the organotellurium tribromide (0.088 g, 0.2 mmol) was added and maintained under stirring at 45 °C for 1.5 h. After cooling at room temperature the mixture was filtered and the slow evaporation of the solvent gave yellow needle crystals. Properties: crystalline air stable substance; C17H19Br5N2O2STe2 F.W. (970.15); Yield: 0.192 g (82%) based on the ditelluride used; Melting point: 121–123 °C; Anal. Calc. C, 21.05; H, 1.97; N, 2.89. Found: C, 21.22; H, 1.92; N, 2.92%; 1H NMR: d 8.67 (sbroad, 2H, NH), 6.8–8.4 (m, 7H, C–Harom.), 3.92–3.85 (m, 10H, CH2, OCH3); 13 C{1H} NMR: d 176.66 (C@S), 138.4, 138.00, 137.50, 115.90, 115.70, 115.30, 114.10, 113.00 (Carom), 57.00, 55.85 (OCH3), 46.17, 42.60 (CH2); IR (KBr, m/cm1) 1579, 1522, 1462 (ms-N–C@S) [25], 1252 (ms-C–O) [26], 3292 (ms-N–H) [26]. 3. Results and discussion
Table 1 Crystal data and structure refinement for the complex. Empirical formula Formula weight Temperature(K) Radiation; k (Å) Crystal system Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) Volume (Å3) Z/density calculated (g cm3) Absorption coefficient (mm1) F(0 0 0) Crystal size (mm) Range for data collection h (°) Index ranges
Reflections collected Reflections unique Completeness to theta maximum (%) Absorption correction Maximum and minimum transmission Data/restraints/parameters Goodness-of-fit F2 Final R indices [I > 2r(I)] R indices (all data) Largest difference in peak and hole (e Å3)
3.1. X-ray studies C17H19Br5N2O2STe2 970.15 295(2) Mo Ka; 0.71073 triclínic P 1 9.3936(6) 11.7872(8) 13.2069(9) 109.531(4) 96.464(4) 104.259(4) 1304.96(15) 2/2.469 9.987 892 0.32 0.32 0.26 1.67 a 32.15 14 6 h 6 14 15 6 k 6 17 19 6 l 6 16 27041 9057 99.7 semi-empirical 0.1810 and 0.1423 9057/0/262 1.062 R1 = 0.0489 wR2 = 0.1210 R1 = 0.0781, wR2 = 0.1468 1.747 e 1.112
The crystal X-ray data and the experimental conditions of the analyses for the complex are given in Table 1. Table 2 summarizes selected bond distances and angles for the title complex. Fig. 1 shows the molecular structure present in the crystallographic asymmetric unit. Fig. 2 shows the dimeric association from the secondary bond present in the solid state, the secondary interactions are identified by dashed lines. To the best of our knowledge, this complex salt is the first organotellurium halide reported in the literature containing unsymmetric organic groups bonded in the chalcogen atoms with mixed oxidation states. The structure consists of one cationic unit [5-Br-2-CH3O–C6H3Te(ETU)]+ containing the TeII atom and one anionic unit [4-CH3O–C6H4TeBr4] containing the TeIV atom. These units interact with each other through one interionic secondary bond Te(2)Br(1) of 3.2900(7) Å, this interaction is in agreement with the value of 3.1757(13) Å for a similar compound [13]. On the other hand, the anionic units interact with each other through Table 2 Bond lengths (Å) and angles (°) selected for the complex. Bond lengths S(1)–Te(2) Br(1)–Te(2) Te(1)–Br(2)#1 Br(1)–Te(1) Br(2)–Te(1)
Angles 2.4467(13) 3.2900(7) 3.6000(6) 2.7221(7) 2.6650(6)
S(1)–Te(2)–Br(1) C(11)–Te(1)–Br(2)#1 C(11)–Te(1)–Br(4) C(21)–Te(2)–S(1) Br(2)–Te(1)–Br(4)
170.09(2) 170.25(12) 89.91(12) 96.19(12) 178.97(2)
Symmetry transformations used to generate equivalent atoms: #1 x, y, z 1.
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crystallographic space group. This inversion center is located P1 in the middle point of the square formed by Te(1), Br(2), Te(1)#1, Br(2)#1 atoms. 3.2.
Fig. 1. Molecular structure of the complex with emphasis in the secondary bond Te(2)Br(1) of 3.2900(7) Å (all H-atoms have been omitted for clarity). Thermal ellipsoids are drawn at the 50% probability level.
one secondary bond Te(1)Br(2)#1 of 3.600(6) Å, this interaction is less than the sum of van der Waals radii for the same atoms (Te and Br 4.00 Å) [27]. The latter secondary bond completes the octahedral coordination sphere of the Te(1) atom, and is responsible by dimeric array organization of the structure in the solid state. The analysis of the bond angles between S(1)–Te(2)–Br(1) of 170.09(2)° and C(21)–Te(2)–S(1) of 96.19(12)° for the Te(2) atom, present in the cationic unit, shows that this atom has a ‘‘T” shape coordination geometry and this is in agreement with other compounds already mentioned in the literature [28]. Finally the dimeric array is correlated by one inversion center belonging to
125
Te NMR studies
Due to the low solubility of the title complex crystals in conventional organic solvents such as chloroform, benzene, and hexane, our investigations for the solution behavior studies were elaborated employing acetone-d6 and DMSO-d6 in a 9:1 proportion, respectively. Moreover our attention was focused on 125Te NMR once the 1H and 13C NMR spectra do not show significant structural features for the dimeric complex in solution. Two peaks were detected in the 125Te NMR spectra of the complex in solution. One sharp peak appears in d = 1210.9 ppm and one broad signal appears in d = 931.5 ppm. When the same experiment is carried out for the standard compound [Et4N][PhTeBr4] only one sharp signal is observed at d = 1199.8 ppm, this signal is assigned for the anionic unit [PhTeBr4]. For comparison purposes, we have recorded the same experiment for the neutral compound PhTeBr3, and in this case two sharp signals appeared in d = 1202.3 and d = 824.8 ppm. These results show that the PhTeBr3 ionizes in DMSO-acetone solution according to the equation: 2PhTeBr3 + DMSO ? [PhTeBr4] + [PhTe(DMSO)Br2]+ [13]. In the light of these results and supported by the performed experiments we propose that our complex ionizes in solution generating the corresponding cationic and anionic units. Accordingly, the sharp peak that appears in d = 1210.9 ppm corresponds to the anionic unit [4-CH3OC6H4TeBr4], and the broad signal that appears in d = 931.5 ppm is related to the cationic unit [5-Br-2CH3O–C6H3Te(ETU)]+. Based on this behavior, we conclude that in solution occurs the disruption of the secondary bonds (TeBr) responsible for the dimeric association represented by dashed lines in the Fig. 2. It is worth mentioning that in the complex [p-CH3O(C6H4)Te(ETU)][pCH3O(C6H4)TeI4] the 125Te NMR spectrum showed a broad signal at 933.5 ppm, attributed to the [p-CH3O(C6H4)Te(ETU)]+ cation
Fig. 2. Molecular structure and dimeric arrangement for the complex. Interionic secondary interactions are depicted in dashed lines (all H-atoms have been omitted for clarity). Thermal ellipsoids are drawn at the 50% probability level. Symmetry transformations used to generate equivalent atoms: #1 x, y, z 1.
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[14]. Thereby, the dimeric structure that we have in the solid state does not maintain its arrange in solution. 4. Conclusion The title complex presenting mixed oxidation states was synthesized in a one-pot procedure in a good yield. The data refined from the X-ray diffraction reveal the dimeric association of the molecular entities formed via secondary bonds which are present in the solid state. The comparison between 125Te NMR and X-ray data show that the structure present in the solid state is not kept in solution, moreover all secondary interactions (TeBr) are broken in solution. Acknowledgments We gratefully acknowledge the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and the FUNDECT (Fundação de Apoio ao Desenvolvimento do Ensino, Ciência e Tecnologia do Estado do Mato Grosso do Sul) for financial support. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica.2010.09.053. References [1] J.Z. Schpector, I. Haiduc, Phosphorus, Sulfur, Silicon 171 (2001) 73. [2] G.M. Oliveira, G.A. Casagrande, E.S. Lang, R.M. Muzzi, S.S. Lemos, J. Organomet. Chem. 694 (2009) 2463.
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