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Journal of the Chilean Chemical Society

versión On-line ISSN 0717-9707

J. Chil. Chem. Soc. v.54 n.4 Concepción dic. 2009

http://dx.doi.org/10.4067/S0717-97072009000400032 

J. Chil. Chem. Soc., 54, Nº 4 (2009), págs. 470-472.

 

SYNTHESIS AND STRUCTURAL DETERMINATION OF A NEW CHALCONE 1,5-BIS(3-METHYL-2-THIENYL)PENTA-1,4-DIEN-3-ONE, C15H14OS2

 

D. CONTRERAS1, Y. MORENO1*, C. SOTO1, M. SAAVEDRA2, F. BROVELLI3, R. BAGGIO4

1Depto. de Química Analítica e Inorgánica, Facultad de Ciencias Químicas, Universidad de Concepción, Chile. e-mail: ymoreno@udec.cl

2Depto. de Fisicoquímica, Facultad de Ciencias Químicas, Universidad de Concepción, Chile.

3Depto. de Ciencias Básicas, Lab. Biotecnología y estudios ambientales, Campus Los Ángeles, Universidad de Concepción, Chile.

4Depto. de Física, Comisión Nacional de Energía Atómica, Buenos Aires, Argentina.


ABSTRACT

This is a structure in a family concerning new polythiophene derivatives. This kind of compounds, a chalcones, has interesting aspects about its intermolecular interactions, of varied type (C15H14OS2) and strength. In the case of the title compound, C15H14OS2, interactions of all three types generate a rather compact, evenly connected 3D structure.


 

INTRODUCTION

The electronic and optoelectronic applications of conjugated polymers as organic wide-gap semi-conductors have attracted considerable interest in the last decade. In this feld, 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 flms obtained show photoluminiscent emission between 660 and 720 nm and exhibit a turn-on voltage at about 2-4 V. The I-V curves of device have been interpreted by mean tunneling process described by the Fowler-ordheim theory.5,6 The polymeric precursors employed have been a series of heterocyclic α, β'-unsaturated ketones containing thiophene rings 4,5,7,8 similar to the molecule reported in this work and it has been studied and characterized by electrochemical and ab-initio methods.9,10

Computational studies proved that the conformation of these molecules are the result of the interaction between the electronic pair of the oxygen in the carbonyl group and the heteroatom in the neighboring ring, indicating a favored conformation.11-13 Electrochemical studies showed the existence of irreversible and asymmetrical peaks. This behavior was explained by the simultaneous oxidation of the heterocyclic rings and the functional groups acting as bridges.14-16 The reduction of the species involves only the carbonyl groups through a free radical.17 This process is very close to the reduction mechanism of chalcones proposed in Cassidy & Whitcher18 and in Tiroufet & Corvaisier.19


Following our interest in this kind of compounds, mainly directed to their use as potential ligand in further complex development we have synthesized and structurally characterized a new compound in this populous family: 1,5-bis(3-Methyl-2-thienyl)penta-1,4-dien-3-one, C15H14OS2 (see scheme 1).

EXPERIMENTAL

SYNTHESIS

The compound was synthesized according to Miller & Nord.20 3-methyl-2-thiophenecarboxaldehyde (0.0219 mol) was mixed with acetone (0.0267 mol). The mixture was cooled to 0ºC and KOH/Ethanol 20% was slowly added.

The mixture was further stirred by 7 h, it was fltered and washed with ethanol. Pale yellow crystals were obtained from an ethanol/water solution (5:1). The yield was 70%. Elemental Analysis (%) (exp/theo): 65.65/65.66 (C); 5.08/5.14 (H); 5.73/5.83 (O); 23.12/23.37 (S).

The IR spectrum shows the characteristic bands of the functional groups of the compound, but slightly displaced. The molecule is nearly planar and the

conjugation of C=O with a C=C bond result in delocalization of the π electrons in both unsaturated groups, causing absorption at lower wave-numbers; then C=O, 1651cm-1; C=C, 1600cm-1.

STRUCTURE DETERMINATION

The present structure posed no problems for data collection. Hydrogen atoms were placed at calculated positions (C-H: 0.93-0.97 Å) 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

COMPUTING DETAILS

Data collection: SMART-NT;21 cell refnement: SAINT-NT;21 data reduction: SAINT-NT; program(s) used to solve structure: SHELXS97;22 program(s) used to refne structure: SHELXL97;22 molecular graphics: SHELXTL-NT;23 software used to prepare material for publication: SHELXTL-NT, PLATON.24

RESULT AND DISCUSSION

Figure 1 shows an ellipsoid plot of C15H14OS2; the molecule consists of two terminals thiophene rings bridged by a penta-1,4-diene-3-one link, in such a way as to have both sulfur atoms in the rings at the same side of the bridge, the carbonyl oxygen being trans to both. The Table 1 shows some crystal data.



The overall group is almost planar, with a slight twist along the bridge axis, leading to a small rotation (16.1(1)%) between the terminal rings. G. Liang et al. has found a similar rotation (5.16(9)º) in a similar but more rigid compound.8

Bonds along the bridge are almost theoretical, with differences between equivalent ones being smaller that their respective s.u.'s; slightly larger, though still non signifcant, differences appear in the thiophene rings.

In fact, in several of similar studied compounds the molecules can be considered featureless and their most appealing details should be looked at their intermolecular interactions, of varied type and strength, leading to different packing schemes. In the present case, oxygen O1 lies in a rather unscreened position (Fig 1), favoring its role as a triple H-bond acceptor (Fig 2) of three non-conventional C-H···O bonds (Table 2, three uppermost entries). These interactions are completed by a C-H···π H-bond (Table 2, last entry) as well as π-π contacts (Table 3) which connect evenly neighboring molecules to generate a rather compact 3D structure. Other important distances are in Table 4.





ACKNOWLEDGEMENTS

We acknowledge funding by project DIUC 208.021.026-1.0 and 209.021.028-1.0. 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 (Allen, 200227).

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(Received: July 14, 2009 - Accepted: September 24, 2009).