The presence of two different chromophores in benzothiazole molecule namely benzothiazole and aromatic rings lead to
interesting chemical and biological properties that attract more researches on the compounds. Three new benzothiazolylbenzoythiourea
compounds namely 1-(1,3-benzothiazol-2-yl)-3-(benzoylthiourea) (BBT), 1-(1,3-benzothiazol-2-yl)-3-
(4-chlorobenzoylthiourea) (BBT-4Cl) and 1-(1,3-benzothiazol-2-yl)-3-(4-methoxybenzoylthiourea) (BBT-4OCH3
) with
different electron withdrawing substituents (R) at the para positions on the benzene ring of benzoylthiourea ring have
been synthesized from the reaction of R-benzoyl isothiocyanate (R= H, Cl, and OCH3
) and 2-aminobenzothiazole. The
compounds were characterized by spectroscopic techniques (infrared, 1
H proton NMR and UV-Vis). The IR spectra showed
the frequency signals of n (C=O), n (C=S), n (N-H) at 1664-1673, 1238-1249 and 3031-3055 cm-1, respectively. The 1
H
proton NMR spectra showed the presence of N-H amine and amide signals in the region of (12.14-12.35) and (14.17-14.43)
ppm, respectively. The proton signals of the two benzothiazole and benzoylthiourea moieties appear at 7.08-8.16 ppm.
A theoretical study based on Density Functional Theory (DFT) and Time-Dependent (TD) DFT was conducted to optimize
the geometrical structure and investigate the electronic properties of title compounds. The highest occupied molecular
orbital (HOMO) was found on the benzothiazole moiety; while, the lowest-unoccupied molecular orbital (LUMO) was
located at the benzoylthiourea fragment. The DFT optimized structures possessed an intramolecular hydrogen bonding
and the types of para substituents used influenced the properties of hydrogen bonding.
Aroylthiourea ligands, 1-aroyl-3-cyclohexyl-3-methylthiourea (HL1
), 1-(2-chloroaroyl)-3-cyclohexyl-3-methylthiourea
(HL2
), 1-(3-chloroaroyl)-3-cyclohexyl-3-methylthiourea (HL3
) and 1-(4-chloroaroyl)-3-cyclohexyl-3-methylthiourea
(HL4
) were synthesized through a condensation reaction of methylcyclohexylamine and aroylisothiocyanate with a
general formula (X-Ph)(CO)NH(CS)N(C6
H5
)(CH3
) where X = H, o-Cl, m-Cl and p-Cl, fully characterized by CHNS micro
elemental analysis, infrared spectroscopy, UV-visible, nuclear magnetic resonance (1
H, 13C) and X-ray crystallography.
1-(3-chloroaroyl)-3-cyclohexyl-3-methylthiourea (HL3
) crystallized in the monoclinic system, a=14.504(3), b=4.9599(11),
c=22.325(5) Å, β=98.461(7)°, Z= 4 and V=1588.5(6) Å with space group P21
/c. The IR spectra of the ligands exhibits
the characteristic v(CO) and v(N-H) at range 1701-1640 cm-1 and 3317-3144 cm-1, respectively. Whereas the 1
H and 13C NMR spectra shows the resonances for N-H and -CO groups at range 8.3-8.5 and 160-163 ppm, respectively. A onepot reaction involving the aroylthiourea ligand, oxovanadium(IV) ion and potassium hydrotris(3,5-dimethylpyrazolyl)
borate (KTp*) complex gave the desired [oxovanadium(IV)(tris(pyrazolyl)borate)(aroylthiourea)] complexes namely
Tp*VOL1
, Tp*VOL2
, Tp*VOL3
and Tp*VOL4
and all complexes were characterized accordingly. X-ray study showed that
Tp*VOL1
adopted a monoclinic crystal, a=3.415(2), b=19.463(3), c=14.22(3) Å, β=107.411(4)°, Z= 4 and V=3542.7(11)
Å with P21
/c space group. The VO2+ center adopted a pseudo-octahedral geometry O2N3S, with the oxovanadium(IV)
coordinated to the bidentate ligand (X-Ph)(CO)NH(CS)N(C6
H5
)(CH3
) and tridentate Tp* ligands. The results showed
that aroylthiourea ligands behave as bidentate chelate through O and S atom and the Tp* C3v symmetry adds stabilization
to the VO2+ through its protective tripodal geometry.