Synthesis, X-ray crystal structure, thermal behavior and spectroscopic analysis of 1-(1-naphthoyl)-3-(halo-phenyl)-thioureas complemented with quantum chemical calculations

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Highlights

  • Crystal structures and thermal properties were determined for 1-naphthoyl thioureas.

  • The Cdouble bondO and Cdouble bondS double bonds of the acyl-thiourea group are mutually oriented in opposite directions.

  • Strong Nsingle bondH⋯Odouble bondC intramolecular hydrogen bond determined the conformational properties.

  • Intermolecular Nsingle bondH⋯Sdouble bondC and Nsingle bondH⋯Odouble bondC hydrogen bonds are observed.

  • Vibrational and UV–Vis spectra are assigned.

Abstract

Two novel 1-(1-naphthoyl)-3-(halo-phenyl) substituted thioureas, namely 1-(1-naphthoyl)-3-(2,4-di-fluoro-phenyl)-thiourea (1) and 1-(1-naphthoyl)-3-(3-chloro-4-fluoro-phenyl)-thiourea (2), were synthesized and fully characterized. The X-ray crystal and molecular structures have been determined resulting in a planar acylthiourea group, with the Cdouble bondO and Cdouble bondS adopting a pseudo-antiperiplanar conformation. An intramolecular Nsingle bondH⋯Odouble bondC hydrogen bond occurs between the thioamide and carbonyl groups. The crystal packing of both compounds is characterized by extended intermolecular Nsingle bondH⋯Sdouble bondC and Nsingle bondH⋯Odouble bondC hydrogen-bonding interactions involving the acylthiourea moiety. Compound 2 is further stabilized by π-stacking between adjacent naphthalene and phenyl rings. The thermal behavior, as well as the vibrational properties, studied by infrared and Raman spectroscopy data complemented by quantum chemical calculations at the B3PW91/6-311++G(d,p) support the formation of these intra- and intermolecular hydrogen bonds. Furthermore, the UV–Vis spectrum is interpreted in terms of TD-DFT quantum chemical calculations with the shapes of the simulated absorption spectra in good accordance with the experimental data.

Introduction

Increasing attention is devoted to the structural and conformational elucidation of 1-(acyl/aroyl)-3-(mono-substituted) thiourea derivatives since these properties mostly determine the behavior of these compounds as ionophores for ion selective electrodes [1], [2], [3], [4] and chemosensors for naked-eye recognition of anions [5], [6], [7], [8]. In particular, the thiourea molecule and the acceptor anion participate in hydrogen bond interactions [9], playing also an important role in terms of biological activity displayed by these compounds [10]. It is well-documented [11] that a local planar structure of the single bondC(O)NHC(S)NHsingle bond moiety is preferred for 1-(acyl/aroyl)-3-(mono-substituted) thiourea, with opposite orientation between the Cdouble bondO and Cdouble bondS double bonds (“S-shape”) [12]. A pseudo six-membered ring is formed in this conformation, associated with the promotion of a Cdouble bondO⋯Hsingle bondN intramolecular hydrogen bond [13].

Several reports on 1-acyl-3-naphtyl substituted thiourea derivatives can be found in the literature [14], [15], [16], [17], [18], [19]. Less attention, however, has been received by the isomeric 1-(naphtoyl)-3-substituted thiourea compounds (see Scheme 1). A series of 1-(naphthoyl)-3-mono substituted and 3,3-di-substituted thioureas were synthesized by Dzurilla et al. [20] and their behavior toward the oxidation with Br2 in chloroform (Hugershoff reaction) was determined. The capabilities of (1-naphtlyl)-arylamidine compounds as ligand were investigated and their CuII-, NiII- and PdII-complexes have been prepared [21]. In these complexes, the anionic O,S bis-chelate coordination mode was found and near-square-planar geometries around the central metal with a cis arrangement was determined [21]. Di-thiourea derivatives substituted by 2-naphthoyl groups were also structurally characterized [22].

Continuing our ongoing project aimed to the synthesis of 1-(acyl/aroyl)-3-(mono-substituted) thioureas [23], [24], here we report the preparation and spectroscopic characterization of two closely related thioureas having the 1-(1-naphthoyl) group and 3-(2,4-di-fluoro-phenyl) (1) and 3-(3-chloro-4-fluoro-phenyl) (2) substitution. The crystal structures have been determined by single-crystal X-ray diffraction. Their NMR, mass spectra, infrared and Raman and UV–Vis spectroscopic properties were also discussed. The assignment of the bands was accomplished with the aid of quantum chemical calculations. The thermogravimetric studies were analyzed.

Section snippets

Instrumentation

Melting points were recorded using a digital Gallenkamp (SANYO) model MPD.BM 3.5 apparatus and are uncorrected. 1H NMR and 13C NMR spectra were determined in DMSO-d solution at 300 and 75.5 MHz respectively using a Bruker AM-300 spectrophotometer. Mass Spectra (EI, 70 eV) were taken on a GC–MS, Agilent technologies 6890 N with an inert mass selective detector 5973 mass spectrometer and elemental analyses were conducted using a LECO-183 CHNS analyzer.

Fourier transform infrared spectroscopy (FTIR),

Synthesis and characterization

The synthetic pathway is shown in the Scheme 2. 1-Naphthoyl chloride was freshly prepared from the commercial 1-naphthoic acid according to the standard procedure [37] and added to a solution of potassium thiocyanate in dry acetone to obtain the 1-naphthoyl isothiocyanate as an intermediate via stirring at room temperature followed by the reflux. The latter was separately reacted with 2,4-difluoro- and 3-chloro-4-fluoro-anilines to afford the corresponding thioureas as crude solids.

Conclusion

The conformational and structural properties have been determined for two novel 1-(1-naphthoyl)-3-(halo-phenyl) substituted thioureas. The X-ray molecular structures for both compounds here studied show that the central single bondC(O)NHC(S)NHsingle bond moiety adopts the typical six membered ring structure favored by strong Cdouble bondO⋯Hsingle bondN intramolecular hydrogen bond. Intermolecular Nsingle bondH⋯O and Nsingle bondH⋯S hydrogen bond interactions dominate the crystal packing of 1 and 2. Furthermore, a π-stacking interaction between adjacent

Acknowledgments

MFE and DBS are members of the Carrera del Investigador of CONICET (República Argentina). The Argentinean author thanks to the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), the ANPCYT and to the Facultad de Ciencias Exactas, Universidad Nacional de La Plata for financial support.

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