Quantum chemical, spectroscopic, and X-ray diffraction studies of N-diphenylphosphino-4-methylpiperidine selenide (1)

Article abstract of DOI:10.1080/15421406.2013.822302

The title molecule, N-diphenylphosphino-4-methylpiperidine selenide(1), was prepared and characterized by elemental analysis, ¹H-NMR, ³¹P-{¹H} NMR, IR, and X-ray single-crystal determination. The compound crystallizes in t

Full text of DOI:10.1080/15421406.2013.822302

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Quantum Chemical, Spectroscopic,
and X-Ray Diffraction Studies of N-
diphenylphosphino-4-methylpiperidine
Selenide (1)
H. SaraÇoĞlua, Ö. SariÖzb & S. Öznergİzb
a Department of Middle Education, Educational Faculty, Ondokuz
Mayis University, Kurupelit, Samsun, Turkey
b Department of Chemistry, Faculty of Science and Arts, Nigde
University, Nigde, Turkey
Published online: 08 Apr 2014.
To cite this article: H. SaraÇoĞlu, Ö. SariÖz & S. Öznergİz (2014) Quantum Chemical, Spectroscopic,
and X-Ray Diffraction Studies of N-diphenylphosphino-4-methylpiperidine Selenide (1), Molecular
Crystals and Liquid Crystals, 591:1, 47-63, DOI: 10.1080/15421406.2013.822302
To link to this article: http://dx.doi.org/10.1080/15421406.2013.822302
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Mol. Cryst. Liq. Cryst., Vol. 591: pp. 47–63, 2014
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2013.822302
Quantum Chemical, Spectroscopic,
and X-Ray Diffraction Studies of
N-diphenylphosphino-4-methylpiperidine
Selenide (1)
1,∗
2
2
˘
¨
¨
¨
˙
H. SARAC¸ OGLU, O. SARIOZ, AND S. OZNERGIZ
1Department of Middle Education, Educational Faculty, Ondokuz Mayis
University, Kurupelit, Samsun, Turkey
2Department of Chemistry, Faculty of Science and Arts, Nigde University,
Nigde, Turkey
The title molecule, N-diphenylphosphino-4-methylpiperidine selenide(1), was prepared
1
and characterized by elemental analysis, 1H-NMR, 31P-{ H} NMR, IR, and X-ray single-
crystal determination. The compound crystallizes in the monoclinic space group P 21/c.
In addition to the molecular geometry from X-ray determination, vibrational frequencies
1
and gauge, including atomic orbital (GIAO) 1H- and 31P-{ H} NMR chemical shift val-
ues of the title compound (1) in the ground state, were calculated using the Hartree–Fock
and density functional methods with the 6-31G(d, p) basis set. The calculated results
show that the optimized geometries can well reproduce the crystal structures. Besides,
the theoretical vibrational frequencies and chemical shift values show good agreement
with experimental values. The predicted nonlinear optical (NLO) properties of the title
compound are greater than those of urea. In addition, density functional theory (DFT)
calculations of the molecular electrostatic potentials (MEPs), frontier molecular or-
bitals (FMOs) of the title compound were carried out at the B3LYP/6-31G(d) level of
theory.
[Supplementary materials are available for this article. Go to the publisher’s online
edition of Molecular Crystals and Liquid Crystals for the following free supplemental:
Crystallographic data for the structural analysis have been deposited with the Cam-
bridge Crystallographic Data Centre, CCDC No 844574. Copy of this information
may be obtained free of charge from the Director, CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk).]
Keywords Aminophosphines; chalcogenides; computational chemistry; NMR spec-
troscopy; X-ray structure determination
Introduction
Aminophosphines are tricoordinate phosphorus compounds containing one to three po-
lar and labile P(III)–N, bonds and they are considered as one of the most intriguing in
chemistry [1]. Aminophosphines and their derivatives play an important role in the fight
∗Address correspondence to H. Sarac¸og˘lu, Department of Middle Education, Educational Fac-
ulty, Ondokuz Mayis University, 55139 Kurupelit, Samsun, Turkey. Tel.: +90 362 457 60 77; Fax:
+90 362 4576078. E-mail: hanifesa@omu.edu.tr
47

˘
H. Sarac¸oglu et al.
48
against cancer, as part of catalytic systems in industrially important reactions, as well as
herbicidal, neuroactive, and antimicrobial agents [2]. In addition, they have shown promis-
ing application potential in some electronic devices. More importantly, aminophosphines
have also started serving as effective ligands in synthesizing a variety of metal complexes
which in turn have found applications as catalysts in a real huge variety of organic reac-
tions and conversions [3]. The design of highly active and selective catalysts is becoming
more and more important in the study of catalytic processes, such as hydroformylation of
alkenes. An extensive study has been carried out on the steric and electronic properties
of the ligands [4] Aminophosphines are one of the most important ligands in catalysis
because they allow the tuning of catalysts in terms of steric and electronic effects. The
fact that the donor and acceptor properties of P(III) compounds are easily tuned by chang-
ing the nature of the substituents on the phosphorus atom or nitrogen atom makes them
good examples for developing their coordination behavior with transition metal substrates
[3, 5]. Therefore, varying substituents on the nitrogen offers scope for maneuvering the
aminophosphine ligands to best suit for a specific catalytic application. Aminophosphines
undergo oxidative addition reactions with chalcogens/chalcogen sources to give the corre-
sponding aminophosphine chalcogenide, which themselves possess ligating behavior, and
hence they find applications in catalysis, besides being used as carriers of Group 16 ele-
ments in electronic industries, and they are more stable compared with the corresponding
free aminophosphines [1, 6–8]. Characterization of phosphine selenides also provides an
1
insight into electronic properties of phosphine ligands. The value of the JPSe coupling
constant in phosphine selenides can be correlated with the electron donating or electron
withdrawing properties of the phosphines [9].
This has prompted us to extend our studies on the synthesis and solid-state structure
of new aminophosphine selenide derivative, which might be useful for transition metal
chemistry and catalytic applications. As a part of our research program on this subject, we
present results of a detailed investigation of the synthesis and structural characterization
of N-diphenylphosphino-4-methylpiperidine selenide (1) by using single crystal X-ray,
1
1
IR, H-NMR, and 31P-{ H} NMR. The vibrational assignments of the title compounds
(1) in the ground state have been calculated by using the Hartree-Fock (HF)/6-31G(d,
p) and DFT(B3LYP)/6-31G(d, p) method. The structural geometry, molecular electrostatic
potential (MEP), frontier molecular orbitals (FMO), and nonlinear optical (NLO) properties
of the title compound were studied at the B3LYP/6-31G(d) level. A comparison of the
experimental and theoretical spectra can be very useful in making correct assignments
and understanding the basic chemical shift molecular structure relationship. And so, these
calculations allow a precise description of the properties of phosphine ligands and a priori
modeling of new phosphines with desired properties.
Experimental
General
Reactions were routinely carried out using Schlenk-line techniques under pure dry nitrogen
gas. Solvents were dried and distilled prior to use. All other chemicals were reagent
grade, available commercially and used without further purification. Melting points were
1
determined on an Electrothermal A 9100 and are uncorrected. 31P-{ H} and 1H NMR spectra
were taken on Bruker UltraShield-400 spectrophotometer. Infrared spectra were recorded
on a Perkin Elmer FT-IR System Spectrum BX. Elemental analysis was performed in a
TruSpec Micro.

Quantum Chemical, Spectroscopic, and X-Ray Studies
Synthesis of Aminophosphine Chalcogenide
49
Preparation of PPh2NC5H9CH3. Triethylamine (3.8 mL, 27.41 mmol) and Ph2PCl
(5.0 mL, 27.19 mmol) were sequentially added with stirring to a solution of 4-
methylpiperidine (3.2 mL, 27.10 mmol) in tetrahyrofuran (THF) (20 mL). The reaction
mixture was stirred for 6 h and then filtered to remove Et3N.HCl. The resulting solution
was evaporated under reduced pressure and the product dissolved with diethyl ether in
an acetone–dry ice bath. The mixture was allowed to warm slowly at room temperature.
The solvent was removed under vacuum to give a white solid of the crude product, which
was crystallized from CH2Cl2/diethyl ether mixture (2:1) at 0◦C. Yield 6.30 g (82%).
m.p.: 158◦C. Elemental Analysis: C18H22PN (283.35 g mol−1) Found (Required): C, 76.18
(76.30); H, 7.62 (7.83); N, 4.66 (4.94).
Preparation of Ph2P(Se)NC5H9CH3 (1). A mixture of PPh2NC5H9CH3 (0.526 g,
1.85 mmol) and grey Se (0.15 g, 1.90 mmol) in toluene (20 mL) was heated under re-
flux for 3 h to give a clear solution. Ligand 1 (0.526 g, 1.85 mmol) and grey Se (0.15 g,
1.90 mmol) were refluxed in toluene (20 mL) for 3 h. The reaction mixture was concen-
trated to ca. 1–2 mL in vacuo and diethylether (20 mL) was added. The precipitate was
filtered and dried in air to yield 1. Yield 0.42 g (63%). m.p.: 133◦C. Elemental Analysis:
C18H22PNSe (362.31 g mol−1) Found (Required): C, 59.55 (59.67); H, 6.04 (6.12); N, 3.68
(3.87).
Crystallography
The data collection was performed at 296 K on a Stoe-IPDS-2 diffractometer equipped with
a graphite monochromated Mo-Kα radiation (λ = 0.71073 Å). The structure was solved
by direct methods using SHELXS-97 and refined by a full-matrix least-squares procedure
using the program SHELXL-97 [10]. All nonhydrogen atoms were easily found from the
different Fourier maps and refined anisotropically. All hydrogen atoms were included using
a riding model and refined isotropically with CH = 0.93 (for phenyl groups), CH2 = 0.97,
CH3 = 0.96, CH = 0.98 Å. Uiso(H) = 1.2 Ueq (1.5 Ueq for methyl group). Details of the data
collection conditions and the parameters of the refinement process are given in Table 1.
Theoretical Calculations
The molecular structure of the title compound (1) in the ground state (in vacuo) was
optimized by HF/6-31G(d, p) method and B3LYP method with 6-31G(d), 6-31G(d, p)
basis sets. For the modeling, the initial guess of the title compound (1) was first obtained
from the X-ray coordinates. Then, vibrational frequencies for optimized molecular structure
with HF/6-31G(d, p) and B3LYP/6-31G(d, p) methods were calculated and scaled by 0.9181
and 0.9806 [11], respectively. The geometry of the title compound (1), together with those
1
of tetramethylsilane (TMS) and phosphoric acid (H3PO4), was fully optimized. H- and
1
31P-{ H} NMR chemical shifts were calculated within GIAO approach [12, 13] applying
B3LYP and HF methods [14] with 6–31G(d, p) basis set.
To investigate the reactive sites of the title compound, the MEP was evaluated using
the B3LYP/6-31G(d) method. MEP, V(r), at a given point r (x, y, z) in the vicinity of
the molecule is defined in terms of the interaction energy between the electrical charge
generated by the molecule’s electrons and nuclei and a positive test charge (a proton)
located at r. For the system studied, the V(r) values were calculated as described previously

˘
50
H. Sarac¸oglu et al.
Table 1. Crystallographic data for the title compound (1)
Empirical formula
Molecular weight
Temperature, T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C18 H22 N P Se
362.30
296
0.71073
monoclinic
P 21/c
10.6014 (3)
13.7441 (4)
12.2003 (4)
93.307 (3)
1774.71 (9)
4
b (Å)
c (Å)
β (◦)
Volume, V (Å3)
Z
Calculated density (g cm–3)
1.356
2.200
744
μ (mm−1
F(000)
)
Crystal size(mm)
0.800 × 0.457 × 0.250
ꢀ range(◦)
1.9/27.6
Index range (h, k, l)
Reflections collected
−13/13, −17/17, −15/15
29075
Independent reflections (Rint)
Observed reflections[I > 2σ(I)]
Data/parameters
4087 (0.115)
3383
4087/190
1.09
0.054
0.140
0.86 and −0.48
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
wR indices [I > 2σ(I)]
Largest diff. Peak and hole (e. Å−3
)
using the equation [15]
ꢂ ꢃ
ꢁ
ρ rꢀ
ꢀ
ZA
V (r) =
−
d3rꢀ
(1)
|RA − r|
|rꢀ − r|
ꢂ ꢃ
where ZA is the charge of nucleus A, located at RA, ρ rꢀ is the electronic density function
of the molecule, and rꢀ is the dummy integration variable. The mean linear polarizability and
mean first hyperpolarizability properties of the title compound were obtained from molecu-
lar polarizabilities based on theoretical calculations. All the calculations were performed by
using Gauss–View molecular visualization program [16] and Gaussian 03 program package
[17] on personal computer without specifying any symmetry for the title molecule (1).
Results and Discussion
Although many synthetic methods like condensation, scrambling, and transamination re-
actions are reported in the literature, the condensation route is the most widely used and
the best one for synthesizing a wide variety of P(III)–N compounds [1]. The reaction of

Quantum Chemical, Spectroscopic, and X-Ray Studies
51
4-methylpiperidine with diphenylchlorophosphine affords the corresponding aminophos-
pine. Oxidation of PPh2NC5H9CH3 by grey selenium gave the corresponding selenide (1).
The synthesis of aminophosphine chalcogenide is shown in Scheme 1.
Scheme 1. Synthesis of N-diphenylphosphino-4-methylpiperidine selenide (I).
It is interesting to note that if a ligand is strongly electron-rich, it also has a high
tendency to be oxidized, thus making it highly air sensitive. Therefore, we could not
obtained P O derivative of the aminophosphine.
Crystal Structure
The compound (1) crystallizes in the monoclinic space group P21/c. Details of crystal
parameters, data collection, structure solution, and refinement are given in Table 1. The
structure of the title compound (1) is shown in Fig. 1 [18].
The title compound (1) contains two phenyl rings and a methylpiperidine ring. The
two phenyl rings are planar with maximum deviations of 0.0064(25) and 0.0075(30) Å,
respectively. The dihedral angles among the 4-methylpiperidine plane A (N1/C13-C17),
the phenyl plane B (C1–C6), and the other phenyl plane C (C7–C12) are 51.28 (12)◦ (A/B),
60.13 (12)◦ (A/C), and 80.32 (10)◦ (B/C).
The P−N bond length of 1.66 Å is shorter than the normally accepted value for a
single bond (1.77 Å) [19]. The P Se bond length, 2.1071(7) Å, agree with well literature
values [20–22]. In fact, variations in P Se bond length values elucidated from X-ray
crystallography in such selenide compounds are generally attributed to the various extent
of contribution of dipolar and π-bond structures [1]. Studies led to the conclusion that the
dipolar form is important for E = S and Se. This was supported by dipole moment studies
carried out for P E and was found that the polarity of the molecule increases with the
increase in the atomic size: O < S < Se [1]. P Se bond distances are observed in the range
2.04–2.11 Å. There is a correlation between the electronic nature of the substituents and the
P–Se distance, with electron donating groups leading to larger bond lengths than electron
withdrawing groups. The P Se bond length is longer than average P Se bond length. This
can be understood on the basis of the two resonance forms R3P Se and R3P+–Se−. The
P–Se bond length (2.1071 Å) is a consequence of the greater contribution of the R3P+–Se−
resonance form. The ionic resonance form is stabilized by electron donating substituents
[9]. The P Se bond distance shows that Ph2PNC5H9CH3 is strong σ-donor.
The 4-methylpiperidine ring is in a chair conformation, as indicated by the Cremer
and Pople puckering parameters (Q = 0.590(3) Å, φ = 348(5)◦, and θ = 3.1(3)◦) [23].
The phosphorus centre, coordinated by two phenyl rings and the 4-methylpiperidine ring
(P C C C), adopts an antiperiplanar conformation. The PNC2Se coordination forms a
slightly distorted tetrahedral geometry, the angles around the P atom ranging form 103.1(12)
to 117.23(9)◦. The bond lengths and angles in (1) are shown in Table 2.
Within the title compound (1), there are two intra-molecular C H · Se hydrogen bonds
(Table 3), with the Se atom acting as an acceptor in the formation of two S(5) motif [24].
In crystal packing, no classical hydrogen bond is found. The C5 atom of phenyl ring (B)

˘
H. Sarac¸oglu et al.
52
Figure 1. Ortep III diagram of the title compound (1). Displacement ellipsoids are drawn at the 30%
probability level and H atoms are shown as small spheres of arbitrary radii.
in the molecule (1) at (x, y, z) acts as a hydrogen-bond donor, via atom H5, to the phenyl
ring (C) at (x, 1/2 – y, –1/2 + z), linking the chain along the c axis, as shown in Fig. 2. In
addition, there is intermolecular π · π interaction between the phenyl rings. Dipole–dipole
and van der Waals interactions are also effective in the molecular packing in the crystal
structure (1).
Optimized Structure (1)
Theoretically calculations were performed on the title compound (Ph2P(Se)NC5H9CH3)
at HF/6-31G(d, p), B3LYP/6-31G(d), and B3LYP/6-31G(d, p) levels. Some optimized
geometric parameters are also listed in Table 2. Using the root mean square error (RMSE)
for evaluation, HF/6-31G(d, p) is the ab initio calculation that the best predicts the bond
distances. DFT/6-31G(d) calculation provides the lowest RMSE for bond angles (0.921◦).
The dihedral angles between optimized counterparts of the title compound (1) are
calculated at 61.42◦ (A/B), 61.42◦ (A/C), and 73.52◦ (B/C) for HF/6-31G(d, p), at 63.88◦
(A/B), 63.92◦ (A/C), and 72.72◦ (B/C) for B3LYP/6-31G(d), at 63.95◦ (A/B), 63.98◦ (A/C),
and 72.67◦ (B/C) for B3LYP/6-31G(d, p).

Quantum Chemical, Spectroscopic, and X-Ray Studies
53
Table 2. Selected theoretical and experimental geometric parameters in the title compound
(1) (bond lengths in Å, bond angles in degrees)
HF 6-31
B3LYP 6-31
B3LYP 6-31
Experimental
(d, p)
(d)
(d, p)
Bond lengths (Å)
P–Se
P N
P–C7
N–C13
2.1071(7)
1.663(2)
1.816(3)
1.476(4)
1.529(5)
2.109
1.690
1.828
1.473
1.528
0.013
0.027
2.114
1.721
1.840
1.483
1.532
0.028
0.058
2.113
1.720
1.839
1.483
1.531
0.028
0.057
C15–C18
RMSEa
Max. differencea
Bond Angles (◦)
Se–P N
117.23(9)
113.88(9)
113.23(9)
103.65(12)
103.01(12)
104.33(11)
111.5(3)
115.77
113.00
113.00
105.49
104.27
104.28
112.03
1.083
117.48
113.09
113.08
105.50
103.19
103.19
112.19
0.921
117.42
113.07
113.07
105.55
103.21
103.21
112.20
0.934
Se–P–C1
Se–P–C7
C1–P–C7
N1–P–C7
N1–P–C1
C16–C15–C18
RMSEa
Max. differencea
Dihedral angles (◦)
C2–C1–P–Se
C6–C1–P–Se
C13–N–P–Se
C17–N–P–Se
C8–C7–P N
1.840
1.850
1.900
−23.0(3)
161.9(2)
65.0(2)
−14.81
167.27
65.45
−13.62
168.43
64.16
−13.67
168.36
64.11
−70.7(2)
−65.48
−64.12
−64.07
142.6(2)
141.37
141.48
141.50
aRMSE and maximum differences between the bond lengths and the bond angles computed by the
theoretical method and those obtained from X-ray diffraction.
Analyses of Vibrational Spectra of (1)
FT-IR spectrum was recorded on a Perkin Emler FT-IR System Spectrum BX as KBr pellets.
Harmonic vibrational frequencies of the title compound (1) were calculated by using HF
Table 3. Hydrogen bond geometries in crystal structure 1 (Å, ◦)
D–H · A
D–H (Å)
H · A (Å)
D · A (Å)
D–H · A(◦)
C2–H2 · Se1
C8–H8 · Se1
C5–H5 · Cg3i
0.93
0.93
0.93
2.97
2.94
2.98
3.482(3)
3.457(3)
3.619(4)
116
117
127
Cg3 is the centroid of the C ring.
Symmetry code: (i): x, 1/2 – y, –1/2 + z.

˘
H. Sarac¸oglu et al.
54
Figure 2. A partial packing diagram for the compound (1), showing the C−H · π interactions as
broken lines. Hydrogen atoms not involved in hydrogen bonding have been omitted. [Symmetry
code: x, 1/2 – y, –1/2 + z].
and DFT methods with 6-31G(d, p) basis set, and the obtained frequencies were scaled by
0.9181 and 0.9806 [11]. In order to facilitate assignment of the observed peaks, we have
analyzed vibrational frequencies and compared our calculation of the title compound (1)
with their experimental results and shown in Table 4.
The aromatic structure shows the presence of C H stretching vibrations in the region
2900–3150 cm−1 which is the characteristic region for the ready identification of the C H
stretching vibrations [25,26]. In this molecule, experimentally C H stretching vibration of
the title compound (1) is observed at 2946 cm−1, while it has been calculated at 3092 cm−1
for HF and 3142 cm−1 for B3LYP. The vibrations in this region (2900–3150 cm−1) are in
agreement with experimental assignment. The experimental P N and P Se stretch modes
were observed at 933 and 516 cm−1, which have been calculated with HF and DFT methods
at 925–550 cm−1 and 903–545 cm−1, respectively. The P Se stretch mode agrees with well
literature value [27]. The other calculated vibrational frequencies can be seen in Table 4.
In general, when the calculated IR frequencies are compared with the experimental data of
the title compound, all these data agree with calculated vibrations.
1
1H and 31P-{ H} NMR Spectra of the Title Compound (1)
DFT and HF methods differ in that no electron correlation effects are taken into account
in HF. DFT methods treat the electronic energy as a function of the electron density of
1
all electrons simultaneously and thus include electron correlation effect [28]. GIAO H
1
and 31P-{ H} chemical shift values (with respect to TMS and H3PO4, respectively) were

Quantum Chemical, Spectroscopic, and X-Ray Studies
55
Table 4. Comparison of the observed and calculated vibrational spectra of the title com-
pound (1)
HF 6-31G
B3LYP 6-31G
Assignments
Experimental
2946
(d, p)
(d, p)
νs C H (aromatic)
νs C H (aromatic)
νs C H (aromatic)
νs C H (aromatic)
νas C H (aromatic)
νas C H (aromatic)
νs C H2 (aromatic)
νas C H2(aromatic)
νas C H3
3111
3110
3093
3092
3081
—
3018
3016
2977
2975
—
3155
3149
3144
3142
3133
3126
3056
3055
3048
3042
3017
3014
2977
νas C H3
2844
νas C—H2 (aromatic)
νas C H2 (aromatic)
νs C H3 + νs C H2
(aromatic)
—
2958
νs C H2 (aromatic)
νs C H2 (aromatic) + νs
C H3
2954
2921
2968
—
νs C H2 (aromatic)
νs C H2 (aromatic)
ν C H (aromatic) + νs C H2
(aromatic)
2917
2915
—
—
—
2945
ν C H (aromatic) + νs C H2
—
2937
(aromatic)
νs C H3
2912
2911
1517
1466
1433
1351
1273
—
1198
1195
1178
1171
—
1123
1115
1108
1106
1097
1055
956
—
2935
—
1451
1391
—
1249
1188
1182
—
νs C H2 (aromatic)
γ CH (aromatic)
γ CH (aromatic)
γ CH2 (aromatic)
γ CH (aromatic)
α CH2 (aromatic)
α CH (aromatic)
α CH2 (aromatic)
α CH (aromatic)
γ CH2 (aromatic)
β CH2 (aromatic)
γ CH (aromatic)
ν C C (aromatic)
α CH (aromatic)
ν P C
1476
1438
1371
1311
1242
1178
—
—
1094
1093
—
1091
1083
—
1097
1052
α CH (aromatic)
ω CH2 (aromatic)
α CH2 (aromatic)
β CH (aromatic)+ ω CH2
(aromatic)
1036
—
(Continued on next page)

˘
H. Sarac¸oglu et al.
56
Table 4. Comparison of the observed and calculated vibrational spectra of the title com-
pound (1) (Continued)
HF 6-31G
B3LYP 6-31G
Assignments
Experimental
(d, p)
(d, p)
ν P N
933
788
925
785
781
774
727
715
713
703
569
550
522
505
444
903
758
—
ω CH (aromatic)
ω CH2 (aromatic)
ω CH (aromatic)
ω CH2 (aromatic)
θ (aromatic)
ω CH (aromatic)
θ (aromatic)
ω CH2 (aromatic)
ν P Se
758
743
720
710
694
748
713
705
701
696
567
545
514
—
516
504
498
480
δ CH (aromatic)
δ CH (aromatic)
δ CH (aromatic)
—
Vibrational modes: ν, stretching; β, bending; α, scissoring; γ , rocking; ω, wagging; δ, twisting;
θ, ring breathing; s, symmetric; as, asymmetric.
calculated using the HF and B3LYP methods with 6-31G(d, p) basis set and compared with
1
experimental 1H and 31P-{ H} chemical shift values. The results of these calculations are
shown in Table 5.
The signals in the range 1.29–2.96 ppm were assigned to C(13)H2, C(14)H2, C(16)H2,
and C(17)H2 protons, and were calculated at 1.13–2.41 ppm for HF/6-31G(d, p) and
1.34–2.79 ppm for B3LYP/6-31G(d, p). The C H signal of the 4-methylpiperidine ring
was observed at 1.54 ppm. The phenyl protons were observed at 7.47 ppm and 8.09 ppm.
1
31P-{ H} NMR spectrum of the compound (1) shows the signal at 68.1 ppm. The signal
has been calculated as 98.46 ppm for HF level, 109.32 ppm for B3LYP level. Table 5
shows the other calculated chemical shift values. As can be seen from Table 5, calculated
1
1H and 31P-{ H} chemical shift values of the title compound (1) are agreement with the
1
experimental 1H and 31P-{ H} shift data.
The 31 P-{1H} NMR spectrum of compound (1) consists of singlet with 77Se satellites
and the coupling constant value (1JPSe) is 750.58 Hz. The coupling constant value (1JPSe),
which varies over a wide range depending upon the nature of substituents on phosphorus,
1
is so useful that the basicity of phosphines was determined based on 31P-{ H} NMR. There
is a good established correlation between 1JPSe and the electronic properties of the parent
phosphorus ligands, which takes the form of an inverse relationship with the σ-basicity [9].
The value of the 1JPSe coupling constant for 1 (1JPSe = 750.58 Hz) is significantly smaller
than for the aminophosphine selenides derived from piperazine which we reported earlier [7]
(Ph2P(Se)NC4H8NC6H5, 1JPSe = 773.80 Hz; Ph2P(Se)NC4H8NC6H5, 1JPSe = 765.60 Hz),
suggesting that Ph2PNC5H9CH3 is a strong σ-donor and the electron withdrawing of 4-
methypiperidine group attached to phosphorus is low. The value of the coupling constant
(1JPSe = 750.58 Hz) of Ph2P(Se)NC5H9CH3 shows that Ph2PNC5H9CH3 is a strong σ-
donor and the electron withdrawing of 4-methypiperidine group attached to phosphorus is

Quantum Chemical, Spectroscopic, and X-Ray Studies
57
Table 5. Theorical and experimental 31P and 1H isotropic chemical shifts (with respect to
H3PO4 and TMS all values in ppm) for the title compound (1)
Calculated chemical shift (ppm)
Experimental
Atom
(ppm) CDCl3
HF
B3LYP
P
H2
H3
H4
H5
H6
H8
H9
H10
H11
H12
H13a
H13b
H14a
H14b
H15
H16a
H16b
H17a
H17b
H18∗
68.1
8.09
7.47
7.47
7.47
8.09
8.09
7.47
7.47
7.47
8.09
2.59
2.96
1.29
1.67
1.54
1.67
1.29
2.96
2.59
0.97
98.46
8.96
7.64
7.72
7.56
8.46
8.96
7.64
7.72
7.56
8.46
2.32
2.41
1.13
1.27
1.27
1.27
1.13
2.41
2.32
0.95
109.32
8.65
7.45
7.40
7.38
8.31
8.65
7.45
7.40
7.38
8.31
2.65
2.79
1.34
1.49
1.57
1.49
1.35
2.79
2.65
0.91
∗Average.
low. The new very electron-rich ligand prepared here should, given its ease of preparation,
be a useful tool in organometallic chemistry and catalysis.
Two resonance forms for aminophosphine chalcogenides are known and the dipolar
form is important for selenide derivatives. 31P chemical shift value of the title compound (1)
supports the fact that for aminophosphine selenide 1, the dipolar form P+–E− predominates
[3]. The dipolar form is stabilized by electron donating substituents [9]. Also, the value of
the coupling constant of 1 shows that Ph2PNC5H9CH3 is a strong σ-donor. Therefore, the
P Se bond length is longer than average P Se bond length.
Molecular Electrostatic Potential (MEP)
The MEP is related to the electronic density and is a very useful descriptor in understanding
sites of electrophilic attack and nucleophilic reactions as well as hydrogen bonding inter-
actions [29–31]. The electrostatic potential V(r) is also well suited for analyzing processes
based on the “recognition” of one molecule by another, such as in drug–receptor, and
enzyme–substrate interactions, because it is through their potentials that the two species
first “see” each other [32, 33]. Being a real physical property, V(r) can be determined
experimentally by diffraction or by computational methods [34].

˘
58
H. Sarac¸oglu et al.
Figure 3. Molecular electrostatic potential map calculated at B3LYP/6-31G(d) level.
MEP was calculated by using B3LYP/6-31G(d) method. The red regions and blue
regions of MEP represent negative and positive potentials, respectively. As can be seen in
Fig. 3, this molecule has one possible site of electrophilic attack. The negative region is
localized on selenium atom with minimum value of –0.036 a.u. Also, positive electrostatic
potential regions are over the carbon atoms of the phenyl rings and the 4-methylpiperidine
ring. The positive V(r) values are about +0.019 a.u. for C15 atom, which is the most positive
region, about +0.016 a.u. for C5 atom. According to these calculated results, the MEP map
shows that the negative potential site is on electronegative atom as well as the positive
potential sites are around the hydrogen atoms. These sites give information concerning the
region from where the compound can undergo noncovalent interactions.
Frontier Molecular Orbitals
The FMOs play an important role in the electric and optical properties, as well as in UV–Vis
spectra and chemical reactions [35]. Figure 4 shows the distributions and energy levels of
the HOMO–1, HOMO, LUMO, and LUMO+1 orbitals computed at the B3LYP/6-31G(d)
level for the title compound.
As can be seen from Fig. 4, the HOMO-1 is mainly localized on P Se bond and N atom
of the 4-methylpiperidine ring. For the HOMO, the electrons are delocalized on P Se bond
and partly delocalized over the diphenyl ring. While the electrons are delocalized over the
diphenyl ring in the LUMO+1, they are delocalized over the diphenyl ring, the P Se bond
and partly delocalized over the 4-methylpiperidine ring on the LUMO. Both the HOMOs
and LUMOs are mostly the π antibonding type orbitals. The energy separation between
the HOMO and LUMO is 4.207 eV. This large HOMO–LUMO gap automatically means
high excitation energies for many of the excited states, good stability and a large chemical
hardness for the title compound.
Nonlinear Optical Effects (NLO)
NLO effects arise from the interactions of electromagnetic fields in various media to produce
new fields altered in phase, frequency, amplitude, or other propagation characteristics

Quantum Chemical, Spectroscopic, and X-Ray Studies
59
Figure 4. Molecular orbital surfaces and energy levels given in parentheses for the HOMO-1,
HOMO, LUMO, and LUMO+1 of the title compound (1) computed at B3LYP/6-31G(d) level.
from the incident fields [36]. NLO is at the forefront of current research because of its
importance in providing the key functions of frequency shifting, optical modulation, optical
switching, optical logic, and optical memory for the emerging technologies in areas such
as telecommunications, signal processing, and optical interconnections [37–40].
The NLO response of an isolated molecule in an electric field Ei(ω) can be presented
as a Taylor series expansion of the total dipole moment, μtot, induced by the field:
μtot = μo + αij Ej + βijk Ej Ek + . . . ,
(2)
where αij is the linear polarizability, μo is the permanent dipole moment, and βijk are the
first hyperpolarizability tensor components. The isotropic (or average) linear polarizability
is defined as [41]:
αxx + αyy + αzz
αtot
=
(3)
3
First hyperpolarizability is a third rank tensor that can be described by 3 × 3 × 3 matrix.
The 27 components of 3D matrix can be reduced be to 10 components due to the Kleinman
symmetry [42] (βxyy = βyxy = βyyx, βyyz = βyzy = βzyy ; · likewise other permutations also
take same value). The output from Gaussian 03 provides 10 components of this matrix as
βxxx, βxxy, βxyy, βyyy, βxxz, βxyz, βyyz, βxzz, βyzz, βzzz, respectively. The components of the

˘
H. Sarac¸oglu et al.
60
first hyperpolarizability can be calculated using the following equation [41]:
ꢀ
1
βi = βiii
+
(βijj + βjij + βjji
)
(4)
3
i=j
Using the x, y, and z components of β, the magnitude of the first hyperpolarizability tensor
can be calculated by:
ꢄ
βtot
=
(βx2 + βy2 + βz2)
(5)
The complete equation for calculating the magnitude of β from Gaussian 03W output is
given as follows:
ꢄ
2
βtot
=
(βxxx + βxyy + βxzz)2 + (βyyy + βyzz + βyxx)2 + (βzzz + βzxx + βzyy
)
(6)
The calculations of the total molecular dipole moment (μ), linear polarizability (α), and
first-order hyperpolarizability (β) from the Gaussian output have been explained in detail
previously [43], and DFT has been extensively used as an effective method to investigate the
organic NLO materials [44]. The electronic dipole moment μi (i = x, y, z), polarizability
αij and the first hyperpolarizability βijk of the title compound were calculated at the
B3LYP/6-31G(d) level using Gaussian 03W program package and listed in Table 6.
The calculated values of μtot, αtot, and βtot for the title compound are 1.708 D, 34.651
Å3, and 1.399×10−30 cm5 esu–1, which are greater than those of urea (the μtot, αtot, and
βtot of urea are 1.373 D, 3.831 Å3, and 0.37289 × 10−30 cm5 esu–1 obtained by B3LYP/6-
31G(d) method) [36]. The title molecule shows a deviation from the planarity due to the
steric interactions of protons of methyl and phenyl rings. The lack of planarity of the title
molecule may be due to the free rotation of 4-methylpiperidine ring. Two phenyl rings of
the molecule (I) are connected with selenium atom through two intramolecular hydrogen
bonds, which will eventually stop the free rotation. When it is compared with the similar
double bond compounds in literature, the calculated value of βtot of (I) is smaller than that
of 4-(2,3,4-trihydroxybenzylideneamino) antipyrine (βtot = 10.0125 × 10−30 cm5 esu–1)
[36] and 4-(2,3-dichlorobenzylideneamino) antipyrine (βtot = 25.191 × 10−30 cm5 esu–1)
[45] calculated with B3LYP/6-31G(d) method. Therefore, the title compound is a good
candidate as a second-order NLO material.
Table 6. The calculated dipole moments (Debye), static polarizability components (a.u.)
and first hyperpolarizability components (a.u.) for the title compound (1)
μx
μy
μz
0.3620
0.0001
−1.6693
βxxx
βxxy
βxyy
βyyy
βxxz
βxyz
βyyz
βxzz
βyzz
βzzz
22.7297
0.0471
11.1246
−0.1746
69.8768
0.0220
−2.7970
−11.7573
0.0438
−227.5240
αxx
αxy
αyy
αxz
αyz
αzz
223.2985
0.0089
244.6856
−12.4008
−0.0288
233.4562

Quantum Chemical, Spectroscopic, and X-Ray Studies
61
Many research works have indicated that the FMOs have significant effect on material
NLO properties [43,46–49]. In quest of the NLO characteristics, the surfaces of FMOs of
the studied molecules were investigated and shown in Fig. 4. We can see that the FMOs
are mainly composed of atomic p-electron orbitals. It is evident that the NLO properties
of the compounds are caused by the charge-transferring characteristics of FMOs of the
molecules. However, the correlation between the first hyperpolarizabilities and energy gaps
of HOMO–LUMO of the studied molecules are not following with the empirically inverse
relationship reported previously [43, 48, 49].
Conclusions
In this work, the title compound (1) has been characterized by elemental analysis, 1H NMR,
31P NMR, X-ray analysis, and FT-IR techniques. Crystal packing of the title compound
(1) is mainly dominated by intermolecular C−H · π hydrogen bonds formed during prepa-
ration or crystallization. Although it is well known that DFT-optimized bond lengths are
usually longer and more accurate than HF because of the inclusion of electron correlation,
the HF method correlates better for the bond length than the DFT method according to our
calculations. However, the DFT method seems to be more appropriate than the HF method
for obtaining the bond angles. The calculated results show that the optimized geometries
can well reproduce the crystal structure, and the theoretical vibrational frequencies and
chemical shift values. The MEP map shows that the negative potential site is on elec-
tronegative atom while the positive potential sites are around the hydrogen atoms. These
sites give information about the region from where the compound can undergo intra- and
intermolecular interactions. The predicted NLO properties of the title compound (1) are
greater than those of urea. The title compound is a good candidate as a second-order NLO
material.
As a result, all of these calculations will be provide helpful information to further
studies on the title compound. Also, such response data will allow us to test different model
approaches and explore the reliability of predictions.
A truly rational design and evaluation of novel catalysts remain out of reach, but
we are optimistic that improving the description of ligand properties will prove vital for
the interpretation and prediction of ligand effects on a broad range of catalytic reactions
and that such insights can contribute to the development of novel catalysts. In addition,
structure-activity relationship of the aminophosphine and derivatives can be investigated to
make accurate and reliable predictions of the biological activity of new compounds and to
facilitate the design and development of more effective drugs.
Acknowledgments
This study was financially supported by the Research Centre of Ondokuz Mayıs University
(Project No: F-425) and TUBITAK (Project no: 110T572).
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