152
H.H. Kart et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 146 (2015) 151–162
basis sets [35]. Therefore, some scaling factors are used to
Introduction
Calixarenes,
eliminate the systematic errors in the force constants and frequen-
cies and provide better agreement with the observed ones. The
geometry optimization of the molecules is an important factor to
determine the NMR chemical shifts [36].
a
well-known family of macrocyclic phenol
formaldehyde oligomers, have been attracting the interest of
chemists for more than three decades. As these compounds repre-
sent readily available and precisely defined three-dimensional
structures, they found numerous applications in supramolecular
chemistry [1,2]. The unproblematic derivatization of the calix[4]
arene skeleton together with the controllable shape of the cavity
makes this molecule an ideal molecular scaffold for the construc-
tion of various receptors. Due to their excellent complexation
abilities, calix[4]arenes are frequently used for the design of novel
selective complexation agents. Depending on the substitution
pattern and the conformation, calix[4]arenes bind cations [3–5],
anions [6,7] and/or neutral compounds [8] via non covalent
The purpose of this work is to study the synthesis, experimental
and theoretical characterization of the compounds of MPcalix[4]
and MOPcalix[4]. The molecular structure, thermodynamics data,
frontier molecular orbitals, molecular electrostatic potential
(MEP), non-linear optical (NLO) properties, vibrational and NMR
spectra of ones are calculated by using the ab initio quantum
chemical method based on DFT with the basis sets of 6-31G(d)
and 6-311G(d,p). The experimental and theoretical calculations
can be very useful to make the correct assignment and understand-
ing the basic vibrational, NMR spectra and molecular structure
relations. A discussion on the experimental and theoretical studies
of these chemical compounds leads ones to a better analyzing of
the insight of them. Moreover, the results predicted from in this
work can be helpful in further studies of the compounds.
The paper is organized as follows; synthesizes and character-
ization of MPcalix[4] and MOPcalix[4] are presented in
‘Experimental Section’ as well as experimental details. The theo-
retical method used this work are introduced and the computa-
tional details are given in ‘Computational details Section’. The
quantum chemical ab initio simulation results for structural,
electronic and vibrational properties of the compounds such as
MPcalix[4] and MOPcalix[4] considered in this study are presented
and discussed in ‘Results and discussion Section’. The results pre-
dicted from theoretical methods are compared with the whenever
available experimental data in ‘Results and discussion Section’.
Finally, ‘Conclusion Section’ deals with the summary and conclu-
sions arising from this work.
interactions (cation–
bonds, electrostatic interactions, coordination bonds, van der
Waals interactions, etc.).
p interactions, p–p interactions, hydrogen
Diazo coupling reactions of chromogenic calix[4]arene which has
within the molecule an azophenol moiety as a coloration site have
been studied by Morita et al. [9] and Shinkai et al. [10] and they have
described the resulting NMR spectra. Ab initio studies of NMR
chemical shifts for calix[4]arene and its derivatives have been done
by Kara et al. [11]. Kurt et al. [12] synthesized calix[4]arene derivate
molecule and investigated the spectroscopic features with FT-IR,
FT-Raman, dispersive Raman and NMR. In our recent work, we have
synthesized a vic-dioxime derivative of calix[n]arene and have
studied its complexes [13,14], polymeric calix[n]arene derivatives
and selective extraction of transition metal cations [15,16].
The experimental studies and theoretical calculations on the
structural and vibrational properties of the azocalix[4]arenes mole-
cules such as MPcalix[4] and MOPcalix[4] are insufficient in the
literature. In order to interpret the experimental studies on the
azocalix[4]arenes, it should be done the complete theoretical stud-
ies of the molecular structure, thermodynamics properties, frontier
molecular orbitals, molecular electrostatic potential, non-linear
optical properties, vibrational and NMR spectra of them. The theo-
retical studies of the compounds provide ones to get the important
information about the physical and chemical properties of them.
Ab initio methods such as DFT and Hartree–Fock (HF) in the
computational chemistry are important theoretical tools to predict
the physical and chemical properties of molecules [17,18]. The
solution of the electronic Schrodinger equation is essential to the
applications of these methods to chemical problems in the ab initio
calculations. The development of fast digital computers has opened
the possibility of solving the electronic Schrodinger equation while
utilizing approximations for interesting systems [19]. Theoretical
calculations can allow ones to suggest frequencies that can be used
as fingerprint for the compounds. They can also make the band
assignments as well as the understanding of the relationship
between the observed spectral features and the molecular struc-
ture [20]. HF and DFT methods based on quantum mechanics are
widely used to determine the molecular structure, thermodynamic
properties, frontier molecular orbitals, molecular electrostatic
potential, non-linear optical properties, fundamental vibrational
modes and NMR spectra for small and large sized chemical mole-
cules at low computational cost [21–32]. In our previous studies
[11,33,34], we have also used these methods to investigate
structural, vibrational and NMR properties of the calix[4]arenes,
azocalix[4]arenes and dithiophosphonates.
Experimental
Materials
All of the chemical reagents and solvents used in this work are
of analytical grade purity and used without further purification. All
aqueous solutions are prepared with deionized water purified by
Human Power Plus I + UV water purification system.
Equipment
The vibrational frequencies of the title compounds by using the
FT-IR spectroscopy are measured in this work. The FT-IR spectrum
is recorded by a Perkin–Elmer 2000 FT-IR spectrophotometer in the
range of 4000–400 cmꢁ1. The 1H NMR spectrum is recorded on a
Bruker AVANCE DRX 400 NMR spectrometer in the medium of
chloroform.
Synthesis
We have synthesized p-tert-butylcalix[4]arene as a starting
material through the base catalyzed condensation reaction [37].
Di-benzoyl-tetra-p-tert-butylcalix[4]arene, di-benzoyl-di-p-tert-butyl-
calix[4]arene, 11,23-di-p-tert-butylcalix[4]arene, 25,26,27,28-tetrahy-
droxy-11,23-di-(tert-butyl)-5,17-(4-methoxyphenylazo)calix[4]arene
and 25,26,27,28-tetrahydroxy-11,23-di-(tert-butyl)-5,17-(4-methyl-
phenylazo)calix[4]arene are synthesized (Scheme 1) as described
in our previous study [38].
The harmonic vibrational frequencies calculated from the
ab initio quantum chemistry methods are usually larger than the
ones of experimental measurements. It is well known that this is
due to the neglect of anharmonic effects in the methods used in
computational chemistry. Errors are also coming from the incom-
plete incorporation of electron correlation and using the finite
Computational details
To provide complete information regarding to the structural
parameters, the fundamental vibrational modes, the chemical