versión On-line ISSN 0717-9707
J. Chil. Chem. Soc. vol.55 no.4 Concepción dic. 2010
J. Chil. Chem. Soc., 55, N0 4 (2010)
STRUCTURAL STUDY OF A NEW 1-(2-THIENYL)-3-(3-METHYL-2-THIENYL)-PROPENONE, IN SITU RADIATION-INDUCED DIMERIZATION PRODUCTS
Y. MORENO1*, D. CONTRERAS1tA. BULJAN2, F. BROVELLP, R. BAGGIO4
1_Depto. de Quím. Analítica e Inorgánica, Fac. Cs. Químicas, Universidad de Concepción, Chile.
2_Depto. de Fisicoquímica (lab. QTC), Fac. Cs. Químicas, Universidad de Concepción, Chile.
3_Depto. de Cs. Básicas, Campus los Ángeles, Universidad de Concepción, Chile,
4_Departamento de Física, Comisión Nacional de Energía Atómica, Buenos Aires, Argentina.
The new conjugated system ("chalcone kind") reported herein, 1-(2-thienyl)-3-(3-methyl-2-thienyl)-propenone, C12H10OS2 presents a monomeric molecular structure, and it most interesting aspects are to be found in it intermolecular interactions, of varied type (CH-O, CH---7C, n-n) and strength. Some anomalies detected in the refinement process, however, provided evidence that an unexpected in-situ, radiation-induced dimerization reaction had taken place during data collection, with the starting and final products coexisting in a topotactic fashion. This effect is depended of structural packing; that is not all this kind of conjugated system presents this effect. The main factor is the distance between the double bonds of neighboring monomers (about 3 A)
The electronic and optoelectronic applications of conjugated polymers as organic wide-gap semi-conductors have attracted considerable interest in the last decade. In this field, polythiophenes derivatives are among the most studied because of their potential use in organic light-emitting diodes.1-3 These polymers (used to prepare electroluminicent devices) are obtained through monomer polymerization via electrochemical deposition on indium tin oxide.4,5
The polymeric precursors employed have been a series of heterocyclic a, ^-unsaturated ketones containing thiophene rings.2,4,5 similar to the molecule reported in this work and they have been studied and characterized by electrochemical and ab-initio methods.4,6,9
In general there is not much structural information about this class the compounds. The structural information available is related to conformational studies and crystal structure as electronic interactions between oxygen of carbonyl group and the heteroatom5,7,9 and interatomic interactions of type C-H...O, C-H...71, 71...Tt10,11
Following our interest in this kind of compounds, mainly directed to their use as potential ligands in further complex development we have synthesized and characterized a new compound in this populous family, viz: 1-(2-thienyl)-3-(3-methyl-2-thienyl)-propenone, C12H10OS2. See scheme 1.
In this work, we report the crystal structure of 1-(2-thienyl)-3-(3-methyl-2-thienyl)-propenone. The structure was solved by single crystal X-ray diffraction.EXPERIMENTAL
Compound C12H10OS2 was synthesized following methods reported in literature. 4 10,11 3-methyl-2-thiophenecarboxaldehyde (O.lmol) was mixed with 2-acetylthiophene (0.1 mol). The mixture was cooled at 0°C and KOH/ ethanol 20% solution was slowly added. The mixture was stirred during 12 h. Then the mixture was filtered and washed with cool ethanol. The product was recrystallized from an ethanol/water solution (5:1) and pale yellow crystals were obtained. The yield was 70%. The elemental analysis gives the following results: (%) (exp/theo): 61.47/61.50 (C); 4.27/4.30 (H); 6.78/6.83 (O); 27.18/27.37 (S).
Spectra of 1-(2-thienyl)-3-(3-methyl-2-thienyl)-propenone in KBr pellets were recorded on a FTIR-NICOLET MAGNA 550 spectrometer.
Diffraction spectrums were record in a Bruker SMART AXS CCD diffractometer with graphite-monochromated Mo Ka radiation (l = 0.71073 A). Semi-empirical absorption correction based on symmetry equivalent reflections was applied. A total of 8994 reflections were collected, of which 3877 reflections were unique (Rint = 0.057) .The structure was resolved by direct methods and refined by the full-matrix least-squares method based on F2. Structure solution, refinement, and generation of publication materials were performed with the use of the SHELXTL crystallographic software package1215. The final refinement includes anisotropic displacement parameters for the non-hydrogen atoms. The crystal data and structure refinement of Compound C12H10OS2 were summarized in Table 1.
Table 1-3 shows the crystal data and refinement details. The principal problems in this compound was the coexistence of symmetry related monomeric units and their cyclation dimerization products resulting from irradiation. The transformations were clearly topotactic, but resented the crystal and (accordingly) the refinement quality. The amount of dimerized material was directly related to the more or less favorable position in the original packing for such a reaction (see comment section for a detailed discussion). Hydrogen atoms were placed at calculated positions (C-H: 0.93-0.97A) and allowed to ride; methyl groups were allowed to rotate as well. Displacement factors were taken as U(H)isot = x.U(host), x: 1.2-1.5
RESULT AND DISCUSSION
Compounds C12H10O2S present two independent molecules in the asymmetric unit (Table 1-3 shows the crystal data and refinement details). We shall describe in what follows the monomeric part, drawn in shaded full thermal ellipsoids and full lines in Figures 1. The dimerization products (drawn in open ellipsoids and bonds, Fig. 1b) will be treated afterwards.
The two independent molecules present the same conformation; that is two terminal thiophene rings bridged by a propa-1-en-3-one link, with both rings almost coplanar to the whole group and with the sulfur atoms in trans conformation. The oxygen in the carbonyl group is cis to the nearest sulfur atom and trans to the other one
The planarity of the group is perturbed by a slight twist along the bridge axis, difficult to quantify due to the disordered nature of the groups. In general, the spatial arrangement is governed by a number of intermolecular interactions, of varied type and strength.
The intermolecular interactions (mainly of the C-H-O type, Table 4) do not "mix" unrelated molecules ("primed" and "unprimed" ones in Fig. 1); they generate, instead, two distinct families of non intersecting 1D structures parallel to  and  as shown in Fig 2
During the refinement of the structure, evidence of an unexpected in situ, radiation-induced dimerization reaction was apparent, with the starting and final products coexisting in a topotactic fashion. This kind of reaction have been studied by different research group in similar compound as the cinnamic acid derivates.16 In this reaction kinds, the spatial disposition (parallel) of the molecules and the distance between them, is fundamental for the dimerization phenomenon.17 The scheme 2 shows the dimerization reaction. -The X-ray radiation would undergo interactions with the matter and generate ultraviolet photons. This radiation would cause the dimerization phenomenon.
We have done the infra-red spectrum with the hope of observed any change on the structure of the compounds due to ultra-violet radiation. In general the frequencies of the bands in these conjugated compounds are smaller than simple systems. This is due to minor bond order. The infra-red spectrum before the UV radiation is similar to infra-red spectrum after radiation.
This phenomenon is a [2 + 2] photodimerization homogenous and return thermally to a pure crystal of the monomers. It is the reason why is not possible to detect the structure changes by infra-red analysis.
A new heterocyclic system was synthesized, 1-(2-thienyl)-3-(3-methyl-2-thienyl)-propenone, (C12H10OS2) and their crystal structure was established. The structure presents intermolecular interactions of varied type (CH-O, CH--Jt, jf-jt) and strength. The anomalies detected in the refinement process, however, provided evidence that an unexpected in-situ, radiation-induced dimerization reaction had taken place during data collection, with the starting and final products coexisting in a topotactic fashion.
We acknowledge funding by project DIUC 208.021.026-1.0 and 209.021.028-1.0; Chilean-French laboratoire international Associé (LIA MIF 836). Dr. Thierry Roisnel of Centre de Diffractométrie X of Université de Rennes 1 "Sciences Chimiques de Rennes" by diffraction experiences. We also acknowledge the Spanish Research Council (CSIC) for providing us with a free-of-charge license to the CSD system. 18
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Received: September 1, 2010 - Accepted: December 28, 2010)