Electronic and steric effects of substituents on the conformational diversity and hydrogen bonding of N-(4-X-phenyl)-N′,N″- bis(piperidinyl) phosphoric triamides (X = F, Cl, Br, H, CH3): A combined experimental and DFT study

Article abstract of DOI:10.1016/j.poly.2010.09.039

Phosphoric triamides of the general formula (4-X-C₆H ₄NH)P(O)(NC₅H₁₀)₂, X = F (1), Cl (2), Br (3), H (4) and CH₃ (5), have been synthesized and characterized. X-ray crystallography at 120 K

Full text of DOI:10.1016/j.poly.2010.09.039

Polyhedron 30 (2011) 61–69
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Electronic and steric effects of substituents on the conformational diversity
and hydrogen bonding of N-(4-X-phenyl)-N0,N00-bis(piperidinyl) phosphoric
triamides (X = F, Cl, Br, H, CH3): A combined experimental and DFT study
⇑
Khodayar Gholivand , Hamid Reza Mahzouni
Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 July 2010
Accepted 23 September 2010
Available online 4 November 2010
Phosphoric triamides of the general formula (4-X-C6H4NH)P(O)(NC5H10)2, X = F (1), Cl (2), Br (3), H (4)
and CH3 (5), have been synthesized and characterized. X-ray crystallography at 120 K reveals that the
compounds 1, 3, 4ꢀH2O and 5 are composed of one, four, two and four conformers, respectively. DFT cal-
culations were performed to investigate the electronic structures of the compounds. The X-ray data and
DFT calculations revealed that the conformational diversity in these compounds is mainly governed by
the steric effects of the substituent X rather than by electronic effects. Although substituent X does not
participate directly in hydrogen bonding, the crystal packing of the compounds is influenced by the size
of X. Atoms in molecules (AIM) and natural bond orbital (NBO) analyses confirm that the para substituent
X has no significant effect on the electronic features of the amidic proton and the phosphoryl oxygen
atom (OP). Using X-ray crystallography, AIM and NBO analyses, the structural and electronic aspects of
inter- and intramolecular hydrogen bonds of the compounds have been studied. The charge density
Keywords:
Conformer
DFT calculation
Hydrogen bond
Phosphoric triamide
X-ray crystallography
(q) at the bond critical point (bcp) of the N–H bond decreases from the fully optimized monomers to their
corresponding hydrogen bonded clusters. The N–H stretching frequency decreases from the calculated
values to the experimental results.
Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved.
1. Introduction
and four conformers [17]. In this area, a comparison of the elec-
tronic and steric effects of substituents on the structure of conform-
Phosphoric triamides have received considerable attention due
to their applications as inhibitors of urease [1–3] and acetylcholin-
esterase [4,5] and as stereoselective catalysts [6–8]. Furthermore,
we have already shown that phosphoric triamides can be consid-
ered as an efficient extracting agent for lanthanides [9]. The ring
inversion and rotation of cyclic amines around the P–N bond pro-
vide different conformers in phosphoric triamides [10,11]. Such
compounds with two [12–14], three [15,16] and four [17,18] con-
formers have been previously reported. The conformational diver-
sity in these compounds creates a wide range of hydrogen bonds
[17,18]. It is well known that hydrogen bonds play a key role in bio-
chemical processes such as enzymatic activity [19,20] and protein–
ligand interactions [21]. Moreover, physicochemical properties of
compounds (boiling and melting points, density, dipole moment,
etc.) depend on the presence of non-covalent interactions and inter-
molecular hydrogen bonds [22]. Hence, the analysis of hydrogen
bonds is helpful to rationalize the structural and physicochemical
properties of compounds. In previous works, we have performed
conformational analysis of phosphoric triamides with three [16]
ers needs to be investigated. The major aim of the present work is to
investigate which of the electronic or steric effects can influence the
formation of various conformers. In the present study, five com-
pounds with the formula (4-X-C6H4NH)P(O)(NC5H10)2, X = F (1), Cl
(2), Br (3), H (4) and CH3 (5) have been synthesized and character-
ized. The solid state structures of compounds 1 and 3–5 were deter-
mined by X-ray crystallography. The compounds 1, 3, 4ꢀH2O and 5
contain one, four, two and four conformers, respectively, in the so-
lid phase. The X-ray structures were employed as references for
quantum mechanical (QM) calculations at the B3LYP level. The elec-
tronic features of the hydrogen bonds were investigated by Natural
Bonding Orbital (NBO) and Atoms in Molecules (AIM) analyses to
rationalize the structural and physicochemical properties of the
compounds. Moreover, infrared spectroscopy was used to get a
more detailed insight into the structure of the hydrogen bonds.
2. Experimental
2.1. Instrumentation
⇑
1H, 13C and 31P spectra were recorded on a Bruker Avance DRX
500 spectrometer. 1H and 13C chemical shifts were determined
Corresponding author. Tel.: +98 21 82883443; fax: +98 21 8006544.
E-mail address: gholi_kh@modares.ac.ir (K. Gholivand).
0277-5387/$ - see front matter Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.09.039

62
K. Gholivand, H.R. Mahzouni / Polyhedron 30 (2011) 61–69
relative to internal TMS, and 31P chemical shifts relative to 85%
H3PO4 as an external standard. Infrared (IR) spectra were recorded
on a Shimadzu model IR-60 spectrometer using KBr pellets. Melt-
ing points were obtained with an Electrothermal instrument. Sin-
gle crystals of the compounds 1, 3, 4ꢀH2O and 5 were obtained
from a mixture of CH3OH/H2O at room temperature. X-ray data
were collected on a Bruker SMART area detector [23] single crystal
137.33 (s), 157.71 (d, 1J(F,C) = 239.1 Hz) ppm. 31P{1H} NMR (CDCl3,
202.46 MHz, 298 K): 12.57 (s) ppm. 31P{1H} NMR (acetone-d6,
162.01 MHz, 190 K): 10.58 (s) ppm. IR (KBr, cmꢁ1): 3180, 2930,
2820, 1602, 1501, 1437, 1379, 1332, 1280, 1208, 1185, 1066,
1024, 952, 929, 827, 716, 677, 550, 482.
2.4. N-4-chlorophenyl-N0,N00-bis(piperidinyl) phosphoric triamide (2)
diffractometer with graphite monochromated Mo K
a radiation
(k = 0.71073 Å). All the structures were refined by full-matrix
least-squares methods against F2 with SHELXL-97 [24]. Routine Lor-
entz and polarization corrections were applied and an absorption
correction was performed using the SADABS program [25] for com-
pounds 3, 4ꢀH2O and 5. The crystallographic data of compounds
1, 3, 4ꢀH2O and 5 are summarized in Table 1.
Yield: 60%, m.p. 191 °C. 1H NMR (CDCl3, 500.13 MHz, 298 K):
1.44 (m, 8H, CH2), 1.54 (m, 4H, CH2), 3.05 (m, 8H, CH2), 5.06 (d,
2J(PNH) = 7.2 Hz, 1H, NH), 7.02 (d, 3J(H,H) = 8.6 Hz, 2H, Ar-H),
7.14 (d, 3J(H,H) = 8.6 Hz, 2H, Ar-H) ppm. 13C{1H} NMR (CDCl3,
125.76 MHz, 298 K): 22.45 (s, CH2), 26.27 (d, 3J(P,C) = 5.0 Hz,
CH2), 45.71 (d, 2J(P,C) = 2.1 Hz, CH2), 119.13 (d, 3J(P,C) = 6.3 Hz,
C
ortho), 125.88 (s), 128.93 (s), 140.04 (s) ppm. 31P{1H} NMR (CDCl3,
2.2. General procedure for the synthesis of compounds 1–5
202.46 MHz, 298 K): 12.33 (s) ppm. 31P{1H} NMR (acetone-d6,
162.01 MHz, 190 K): 10.45 (s) ppm. IR (KBr, cmꢁ1): 3188, 2930,
1504, 1486, 1437, 1375, 1331, 1233, 1207, 1160, 1066, 951, 933,
718, 634, 556, 497.
The intermediates (4-X-C6H4NH)P(O)Cl2 (X = F, Cl, Br, H and
CH3) were prepared according to the literature procedures [26].
Then, a solution of 4 mmol piperidine in dry acetonitrile (30 ml)
was added dropwise to
a stirred solution of 1 mmol (4-X-
C6H4NH)P(O)Cl2 at ꢁ5 °C. After 5 h stirring, the solvent was evapo-
rated under vacuum. The resulting white product was washed with
distilled water and recrystallized from a mixture of methanol and
water.
2.5. N-4-bromophenyl-N0,N00-bis(piperidinyl) phosphoric triamide (3)
Yield: 73%, m.p. 197 °C. 1H NMR (CDCl3, 500.13 MHz, 298 K):
1.45 (m, 8H, CH2), 1.55 (m, 4H, CH2), 3.11 (m, 8H, CH2), 4.76 (d,
2J(PNH) = 5.4 Hz, 1H, NH), 6.96 (d, 3J(H,H) = 8.6 Hz, 2H, Ar-H),
7.30 (d, 3J(H,H) = 8.6 Hz, 2H, Ar-H) ppm. 1H NMR (acetone-d6,
400.22 MHz, 190 K): 1.44 (b, CH2), 1.54 (b, CH2), 3.09 (b, CH2),
6.92 (b, Ar-H), 7.20 (b, Ar-H) ppm. 13C{1H} NMR (CDCl3,
125.76 MHz, 298 K): 24.58 (s, CH2), 26.31 (d, 3J(P,C) = 5.0 Hz,
CH2), 45.78 (d, 2J(P,C) = 1.2 Hz, CH2), 113.32 (s), 119.50 (d,
3J(P,C) = 6.3 Hz, Cortho), 131.95 (s), 140.50 (s) ppm. 31P{1H} NMR
(CDCl3, 202.46 MHz, 298 K): 12.20 (s) ppm. 31P{1H} NMR (ace-
tone-d6, 162.01 MHz, 190 K): 10.48 (s) ppm. IR (KBr, cmꢁ1): 3140,
2.3. N-4-fluorophenyl-N0,N00-bis(piperidinyl) phosphoric triamide (1)
Yield: 78%, m.p. 199 °C. 1H NMR (CDCl3, 500.13 MHz, 298 K):
1.43 (m, 8H, CH2), 1.50 (m, 4H, CH2), 3.10 (m, 8H, CH2), 4.76 (d,
2J(PNH) = 7.0 Hz, 1H, NH), 6.88 (m, 2H, Ar-H), 7.02 (m, 2H, Ar-H)
ppm. 13C{1H} NMR (CDCl3, 125.76 MHz, 298 K): 26.58 (s, CH2),
26.28 (d, 3J(P,C) = 5.2 Hz, CH2), 45.73 (d, 2J(P,C) = 2.2 Hz, CH2),
115.49 (d, 2J(F,C) = 22.4 Hz), 119.30 (m, 3J[(F,C), (P,C)] = 6.9 Hz),
Table 1
Crystallographic data for compounds 1 and 3–5.
1
3
4ꢀH2O
5
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system, space group
Unit cell dimensions
a (Å)
C
16H25FN3OP
C16H25BrN3OP
386.26
120(2)
C32H54N6O3P2
632.75
120(2)
C17H28N3OP
321.39
120(2)
325.36
120(2)
0.71073
Monoclinic, P21/c
0.71073
Triclinic, P1
0.71073
Triclinic, P1
0.71073
Triclinic, P1
ꢀ
ꢀ
ꢀ
10.0001(11)
16.9181(18)
10.0303(11)
90
99.805(2)
90
1696.8(3)
4, 1.274
0.177
14.321(7)
16.291(8)
16.574(8)
73.986(10)
71.566(9)
80.593(10)
3514(3)
8, 1.460
2.422
1600
12.106(3)
12.548(3)
12.650(3)
111.627(5)
96.733(5)
106.243(5)
1700.6(7)
2, 1.236
14.2998(10)
16.2595(11)
16.6649(12)
73.878(10)
71.618(10)
81.295(10)
3523.7(5)
8, 1.212
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z, Dcalc (mg mꢁ3
)
Absorption coefficient (mmꢁ1
F(0 0 0)
)
0.169
684
0.162
1392
696
Crystal size (mm)
h Range for data collection (°)
0.35 ꢂ 0.15 ꢂ 0.10
0.10 ꢂ 0.10 ꢂ 0.05
0.22 ꢂ 0.18 ꢂ 0.17
0.35 ꢂ 0.24 ꢂ 0.20
2.04–28.07
1.63–26.02
1.77–26.00
1.31–25.00
Limiting indices
ꢁ13 ꢃ h ꢃ 13
ꢁ17 ꢃ h ꢃ 17
ꢁ14 ꢃ h ꢃ 14
ꢁ17 ꢃ h ꢃ 12
ꢁ22 ꢃ k ꢃ 12
ꢁ20 ꢃ k ꢃ 19
ꢁ12 ꢃ k ꢃ 15
ꢁ19 ꢃ k ꢃ 14
ꢁ13 ꢃ l ꢃ 12
ꢁ20 ꢃ l ꢃ 20
ꢁ14 ꢃ l ꢃ 15
ꢁ19 ꢃ l ꢃ 19
Reflections collected/unique
Completeness to h
11704/4063 [Rint = 0.0438]
98.4%
27603/12998 [Rint = 0.0584]
93.8%
10874/6621 [Rint = 0.0326]
98.8%
17884/12124 [Rint = 0.0370]
97.8%
Refinement method
Full-matrix least-squares
Full-matrix least-squares
Full-matrix least-squares
Full-matrix least-squares
on F2
on F2
on F2
on F2
Data/restraints/parameters
Goodness-of-fit on F2
4063/0/199
1.006
12998/6/793
1.064
6621/0/428
1.062
12124/0/797
1.002
Final R indices
R1 = 0.0520, wR2 = 0.1165
R1 = 0.0789, wR2 = 0.1308
0.390 and ꢁ0.297
R1 = 0.0809, wR2 = 0.1929
R1 = 0.1188, wR2 = 0.2025
4.651 and ꢁ1.186
R1 = 0.0668, wR2 = 0.1301
R1 = 0.1044, wR2 = 0.1445
0.348 and ꢁ0.364
R1 = 0.0494, wR2 = 0.0840
R1 = 0.1098, wR2 = 0.0934
0.301 and ꢁ0.357
R indices (all data)
Largest difference in peak and hole (e Åꢁ3
)

K. Gholivand, H.R. Mahzouni / Polyhedron 30 (2011) 61–69
63
Fig. 1. The model cluster of compound 1 for DFT calculations, in which the target
molecule is in the center. A similar model was also used for the other compounds.
2930, 1584, 1480, 1437, 1377, 1333, 1295, 1207, 1155, 1066, 951,
923, 720, 630, 558, 495.
2.6. N-phenyl-N0,N00-bis(piperidinyl) phosphoric triamide, (4)
Fig. 2. Thermal ellipsoids of 1 at 50% probability.
Yield: 82%, m.p. 128 °C. The spectroscopic data are represented
for the water adduct 4ꢀH2O. 1H NMR (CDCl3, 500.13 MHz, 298 K):
1.45 (m, 8H, CH2), 1.53 (m, 4H, CH2), 3.10 (m, 8H, CH2), 4.70 (d,
2J(PNH) = 6.9 Hz, 1H, NH), 6.88 (t, 3J(H,H) = 7.6 Hz, 1H, Ar-H), 7.03
(d, 3J(H,H) = 7.6 Hz, 2H, Ar-H), 7.19 (t, 3J(H,H) = 7.6 Hz, 2H, Ar-H),
7.25 (b, H2O) ppm. 13C{1H} NMR (CDCl3, 125.76 MHz, 298 K): 24.60
(s, CH2), 26.28 (d, 3J(P,C) = 5.2 Hz, CH2), 45.75 (d, 2J(P,C) = 2.3 Hz,
CH2), 117.87 (d, 3J(P,C) = 6.3 Hz, Cortho), 120.97 (s), 129.04 (s),
141.20 (s) ppm. 31P{1H} NMR (CDCl3, 202.46 MHz, 298 K): 12.51
(s) ppm. 31P{1H} NMR (acetone-d6, 162.01 MHz, 190 K): 10.46 (s)
ppm. IR (KBr, cmꢁ1): 3450, 3145, 2925, 1593, 1488, 1437, 1376,
1286, 1210, 1170, 1066, 952, 926, 743, 717, 688, 548, 481.
in which the target molecule is surrounded by two neighbors
(Fig. 1). Since X-ray crystallography cannot locate accurately the
position of the hydrogen atoms, optimization of the hydrogen
atoms positions is needed for the X-ray structures. The B3LYP/6-
31G* level of theory was used to optimize only the hydrogen atom
positions in the clusters, while other atoms were kept frozen dur-
ing the process. The electronic features of the optimized clusters
were studied by NBO [27] and AIM analyses at the B3LYP/6-
31+G* level. The AIM analysis was performed by means of the Bad-
er’s Atoms in Molecules methodology [28,29]. Moreover, the
monomers 1–5 were fully optimized in a vacuum at the B3LYP/
6-31G* level. Then, the stretching frequencies, NBO charges and
charge densities of the optimized monomers were calculated at
the B3LYP/6-31+G* level. The geometry and electronic features of
the monomers 1 and 3–5 were compared with those of clusters.
All quantum chemical calculations have been carried out using
the Gaussian 98 package [30].
2.7. N-4-methylphenyl-N0,N00-bis(piperidinyl) phosphoric triamide (5)
Yield: 77%, m.p. 177 °C. 1H NMR (CDCl3, 500.13 MHz, 298 K):
1.44 (m, 8H, CH2), 1.51 (m, 4H, CH2), 2.22 (s, 3H, CH3), 3.08 (m,
8H, CH2), 4.67 (d, 2J(PNH) = 7.1 Hz, 1H, NH), 6.92 (d,
3J(H,H) = 8.2 Hz, 2H, Ar-H), 6.98 (d, 3J(H,H) = 8.2 Hz, 2H, Ar-H)
ppm. 1H NMR (acetone-d6, 400.22 MHz, 190 K): 1.45 (b, CH2),
1.53 (b, CH2), 2.23 (s, CH3), 3.11 (b, CH2), 6.98 (b, Ar-H), 7.15 (b,
Ar-H) ppm. 13C{1H} NMR (CDCl3, 125.76 MHz, 298 K): 20.52 (s, p-
CH3), 24.63 (s, CH2), 26.30 (d, 3J(P,C) = 5.0 Hz, CH2), 45.75 (d,
2J(P,C) = 2.0 Hz, CH2), 117.98 (d, 3J(P,C) = 6.0 Hz), 129.50 (s),
130.14 (s), 138.62 (s) ppm. 31P{1H} NMR (CDCl3, 202.46 MHz,
298 K): 12.62 (s) ppm. 31P{1H} NMR (acetone-d6, 162.01 MHz,
190 K): 10.59 (s) ppm. IR (KBr, cmꢁ1): 3150, 2825, 1686, 1505,
1437, 1378, 1279, 1210, 1187, 1065, 951, 929, 808, 574, 467.
3. Results and discussion
3.1. Spectroscopic investigation
The spectroscopic data of compounds 1–5 are summarized in
Table 2. The IR spectra of compounds 1 and 2 show sharp bands
at 3180 and 3188 cmꢁ1, respectively. This indicates that the N–H
bonds are involved in one type of hydrogen bond. The IR spectra
of compounds 3, 4ꢀH2O and 5 show wide bands for the N–H
stretching frequency, because the various conformers are involved
in different, strong or weak hydrogen bonds.
2.8. Computational details
In the IR spectra, the P@O stretching frequency changes from
1155 to 1187 cmꢁ1, while the values of 1235 or 1236 cmꢁ1 were
calculated for the P@O vibration in all of the optimized monomers.
The X-ray structures were used as starting points for DFT calcu-
lations in the gas phase. The structures were modelled as clusters
Table 2
Spectroscopic data of compounds 1–5 with the formula (4-X-C6H4NH)P(O)(NC5H10)2.
Compound
d(31P) (ppm)
2JPNH (Hz)
2,3J(P,C)aliphatic (Hz)
3J(P,C)aromatic (Hz)
m
(P@O)
m
(N–H)
m(P–N)aromatic
1
2
3
12.57
12.33
12.20
12.51
12.62
7.0
7.2
5.4
6.9
7.1
2.2, 5.2
2.1, 5.0
1.2, 5.0
2.3, 5.2
2.0, 5.0
6.9
6.3
6.3
6.3
6.0
1185
1160
1155
1170
1187
3180 (s)
3188 (s)
3140 (w)
3145 (w)
3150 (w)
929
933
923
926
929
4ꢀH2Oa
5
a
The spectroscopic data are represented for the water adduct, 4ꢀH2O, that contains two conformers 4a, 4b and one water molecule.

64
K. Gholivand, H.R. Mahzouni / Polyhedron 30 (2011) 61–69
Fig. 3. Thermal ellipsoids (at the 50% probability level) of four conformers 3a (a), 3b (b), 3c (c) and 3d (d).
This difference can be attributed to hydrogen bonding in the solid
phase.
1H NMR spectra are shortened and broadened when the tempera-
ture is decreased in line with the decrease in solubility of the com-
pounds. This makes the 1H NMR experiments useless at low
temperatures.
Using IR and NMR spectroscopy and X-ray crystallography, we
have previously shown that N-benzoyl-N0,N00-bis(tert-butyl) phos-
phoric triamide, C6H4C(O)NHP(O)(NHC4H9)2, contains two con-
formers in both solution and the solid state [12]. Herein, the
NMR spectra cannot explain the conformational diversity of the
titled compounds. The 31P{1H}NMR spectra at 298 K show a single
resonance in all compounds 1–5. The phosphorus chemical shift
3.2. X-ray crystallography
The molecular structures of compounds 1 and 3–5 are shown in
Figs. 2–5. The crystalline compound 4ꢀH2O shows disorder in two
piperidine groups (Fig. 4). In this case, the H(C) atom positions
were calculated and the hydrogen atoms were refined in isotropic
approximation in the riding model with Uiso(H) parameters equal
to 1.2 Ueq(Ci), 1.2 Ueq(Ni) and 1.2 Ueq(Oi), where U(Ci), U(Ni) and
U(Oi) are the equivalent thermal parameters of the carbon, nitro-
gen and oxygen atoms, respectively, to which the corresponding
hydrogen atoms are bonded. One of the piperidine rings in each
independent molecule is disordered over two positions with
relative occupancies 0.75/0.25. The atoms N(1) and N(10) are com-
mon for both components. The occupancy of the minor component
(0.25) is too low to refine the corresponding atoms in an aniso-
tropic approximation. Hence, these atoms were refined
isotropically.
2
varies from 12.20 to 12.62 ppm and JPNH coupling constants are
in the range 5.4–7.2 Hz. Thus, it can be concluded that the para
substituent of aniline has no significant effect on the chemical
environment of the P–N–H moiety. In order to investigate the con-
formational variety of compounds 1–5 in solution, low tempera-
ture NMR experiments were performed. The 31P{1H}NMR spectra
at 190 K show also a single resonance in all compounds 1–5
indicating that these compounds present only one conformer in
solution. A slight decrease is seen in the phosphorus chemical
shifts for the low temperature experiments, probably due to the
general solvent or temperature effects. The 1H NMR data obtained
at 190 K are not able to determine whether the compounds show
more conformers at low temperatures, because the peaks in the

K. Gholivand, H.R. Mahzouni / Polyhedron 30 (2011) 61–69
65
In the following sections we describe the structural and elec-
tronic features of the hydrogen bonds of the crystalline compounds
1, 3, 4ꢀH2O and 5. The hydrogen bond data of the compounds are
given in Table 4. These hydrogen bonds display different donor–
acceptor distances. It is noteworthy that strong hydrogen bonds
are established in these compounds with donor–acceptor distances
in the range 2.724–3.000 Å. The substituent X does not participate
directly in hydrogen bonding. Also, it is not close enough to the
phosphoryl group, hence no regular correlation can be found be-
tween the electronic nature of the substituent X and the strength
of the intermolecular hydrogen bonds.
Conformers 4a and 4b are very close to each other from a
structural point of view. They are different in their P@O bond
length. The phosphoryl group of 4b produces only the (4a)N–
Hꢀ ꢀ ꢀOP(4b) hydrogen bond, while in the case of 4a it is involved
in two different hydrogen bonds (4b)N–Hꢀ ꢀ ꢀOP(4a) and OW
–
Hꢀ ꢀ ꢀOP(4a) (OW stands for the water oxygen atom) (Fig. 8). This
may lead to increase the P@O bond length from 1.471(2) Å in
4b to 1.486(2) Å in 4a. The 4aꢀ ꢀ ꢀ4b hydrogen bond in compound
4ꢀH2O is relatively weaker than those in the other compounds (Ta-
ble 4). This may explain why compound 4ꢀH2O has the lowest
melting point in comparison with the others. It should be noted
that the presence of a co-crystallized water molecule in the crys-
tal lattice is another feature that may influence the melting point
of compound 4ꢀH2O.
Fig. 4. Thermal ellipsoids (at the 50% probability level) of two conformers 4a (a)
and 4b (b).
3.3. NBO and AIM analyses
3.3.1. Fully optimized monomers in the gas phase
Selected bond lengths are given in Table 3. The mean P@O dis-
tances fall in the range 1.475–1.478 Å. This shows that the para
substituent (X) of aniline does not significantly affect the P@O
bond length. On the other hand, the mean P–Naromatic distance
decreases from 1.657 (1) to 1.646 Å (5) in line with increasing
the electron donation ability of the substituent X. It can be attrib-
uted to the charge donation of the methyl group to the phenyl
ring. As a result, the participation of the nitrogen atom in the
P–N bond is expected to be more than the nitrogen atom in the
N–Caromatic bond. In the compounds 1 and 3–5, the P@O bond
and the phenyl ring take a gauche conformation with a torsion an-
In order to investigate the effect of the para substituent of ani-
line on the electronic nature of the phosphoryl group, all com-
pounds 1–5 have been separately modelled as single molecules
in the gas phase. In all cases, a gauche configuration between the
P@O bond and the phenyl ring is stabilized by the weak intramo-
lecular CHꢀ ꢀ ꢀOP hydrogen bond between the ortho-proton of aniline
and the phosphoryl oxygen atom. This intramolecular contact cre-
ates a six-membered ring via O–P–N–C–C–H bond paths (Fig. 6).
The NBO analysis reveals a weak electronic delocalization between
the lone pair of the phosphoryl oxygen, Lp(OP), and the vacant
r
*(C–Hortho) orbital. Stabilization energies E2 of 0.97, 0.86, 0.79,
0.83 and 0.79 kcal/molꢁ1 were obtained for the Lp(OP) ?
*(C–
ortho) interaction in the compounds 1, 2, 3, 4 and 5, respectively.
gle
u
(Fig. 6 and Section 3.3.1). Rotation of the aniline and piper-
r
idine rings around the P–N bonds creates various conformers
H
(Figs. 3–5).
At the same level, AIM analysis reveals charge density (q) values
Compound 1 contains only one conformer. In the crystal lattice
of 1, one-dimensional zigzag polymeric chains are produced by the
N–Hꢀ ꢀ ꢀOP (OP stands for phosphoryl oxygen atom) hydrogen bonds.
Compound 3 contains four conformers 3a, 3b, 3c and 3d in the so-
lid state. These conformers create two types of polymeric chains
with –(3aꢀ ꢀ ꢀ3dꢀ ꢀ ꢀ3cꢀ ꢀ ꢀ3b)n– and –(3aꢀ ꢀ ꢀ3bꢀ ꢀ ꢀ3cꢀ ꢀ ꢀ3d)n– arrange-
ments in the lattice (Fig. 7). Thus, the crystalline network of com-
pound 3 includes of four types of hydrogen bond. Compound 4ꢀH2O
is composed of two conformers (4a and 4b) and one water mole-
cule in the solid state. The extended hydrogen bonds are formed
due to the presence of H2O in the unit cell. The water molecules
connect the polymeric chains to produce double strands in the
crystalline network of 4ꢀH2O, as indicated in Fig. 8. Two zigzag
chains with –(5aꢀ ꢀ ꢀ5cꢀ ꢀ ꢀ5bꢀ ꢀ ꢀ5d)n– and –(5aꢀ ꢀ ꢀ5dꢀ ꢀ ꢀ5bꢀ ꢀ ꢀ5c)n–
arrangements are also created in the crystal lattice of compound
5. This means that four types of hydrogen bond are established
among the conformers.
at the bcp of the CHꢀ ꢀ ꢀOP contacts in the range 0.0101–0.0110
a.u. for compounds 1–5. The values at the ring critical point
q
(rcp) for the aforementioned six-membered ring (Fig. 9) vary from
0.0088 to 0.0093 a.u. in compounds 1–5. Although these values are
relatively small, they confirm the formation of weak intramolecu-
lar CHꢀ ꢀ ꢀOP contacts. It is worthy to note that the
q value at the rcp
of the phenyl ring remains approximately unchanged by the
replacement of the para substituent X. These bcps and rcps are
illustrated in Fig. 9 and listed in Table 5.
The bond lengths, NBO charges, dipole moments, AIM parame-
ters and the P@O stretching frequencies are listed in Table 5 for
the fully optimized monomers 1–5 in the gas phase. The results
show that the substituent X has no significant effect on the geom-
etry and electronic features of the molecule. It has been previ-
ously described that the strength of inter-unit interactions in
phosphoryl containing compounds is governed by the quantity
of negative charge localized on OP, q(OP) [9]. Here q(OP) does
not change significantly with the para-substitution of the aniline.
Thus, no difference is expected to create hydrogen bonds for the
monomers 1–5.
It seems that the conformational diversity may change the crys-
tal system of the compounds. The symmetry of the unit cell de-
creases with increase in the multiplicity of conformers.
Accordingly, compound 1 crystallizes in the monoclinic crystal sys-
tem with space group P21/c, while the crystals of compounds 3,
The Lp(Naniline) ?
weakens the P–Naliphatic bond. The stabilization energies E2 of
the Lp(Naniline) ? *(P–Naliphatic) interaction are 9.41, 9.27, 9.11,
r
*(P–Naliphatic
)
electronic delocalization
ꢀ
4ꢀH2O and 5 belong to the triclinic system and the space group P1.
r

66
K. Gholivand, H.R. Mahzouni / Polyhedron 30 (2011) 61–69
Fig. 5. Thermal ellipsoids (at the 50% probability level) of four conformers 5a (a), 5b (b), 5c (c) and 5d (d).
Table 3
Selected bond lengths (Å) and angles (°) for compounds 1 and 3–5.
1
3
4ꢀH2O
5
P(1)–O(1)
P(1)–N(1)
P(1)–N(2)
P(1)–N(3)
N(1)–C(1)
N(2)–C(7)
N(2)–C(11)
F(1)–C(4)
O(1)–P(1)–N(1)
O(1)–P(1)–N(2)
O(1)–P(1)–N(3)
N(1)–P(1)–N(2)
N(1)–P(1)–N(3)
N(2)–P(1)–N(3)
C(1)–N(1)–P(1)
C(1)–N(1)–H(1)
P(1)–N(1)–H(1)
C(7)–N(2)–C(11)
C(7)–N(2)–P(1)
C(11)–N(2)–P(1)
1.4786(15)
1.6571(18)
1.6495(18)
1.6407(18)
1.415(3)
1.474(3)
1.473(3)
1.369(2)
113.58(9)
110.99(9)
111.13(9)
104.91(9)
106.34(9)
109.58(9)
125.81(14)
114.60(9)
116.80(9)
112.69(17)
116.61(14)
122.30(13)
P(1)–O(1)
P(1A)–O(1A)
P(1B)–O(1B)
P(1C)–O(1C)
P(1)–N(1)
P(1A)–N(1A)
P(1B)–N(1B)
P(1C)–N(1C)
O(1)–P(1)–N(1)
O(1A)–P(1A)–N(1A)
O(1B)–P(1B)–N(1B)
O(1C)–P(1C)–N(1C)
O(1)–P(1)–N(2)
O(1A)–P(1A)–N(2A)
O(1B)–P(1B)–N(2B)
O(1C)–P(1C)–N(2C)
O(1)–P(1)–N(3)
O(1A)–P(1A)–N(3A)
O(1B)–P(1B)–N(3B)
O(1C)–P(1C)–N(3C)
1.475(5)
1.469(5)
1.483(5)
1.471(5)
1.648(6)
1.654(6)
1.646(6)
1.659(6)
112.7(3)
112.7(3)
112.5(3)
112.8(3)
117.8(3)
111.8(3)
117.9(3)
111.5(3)
109.9(3)
111.0(3)
110.2(3)
111.0(3)
P(1)–O(1)
1.486(2)
1.471(2)
1.644(2)
1.651(3)
1.654(3)
1.641(3)
1.644(3)
1.654(3)
110.94(12)
111.96(14)
109.79(12)
111.06(13)
116.45(13)
113.91(14)
109.64(14)
107.49(15)
104.51(13)
105.53(13)
105.17(13)
106.47(14)
P(1)–O(1)
P(1A)–O(1A)
P(1B)–O(1B)
P(1C)–O(1C)
P(1)–N(1)
P(1A)–N(1A)
P(1B)–N(1B)
P(1C)–N(1C)
O(1)–P(1)–N(1)
O(1A)–P(1A)–N(1A)
O(1B)–P(1B)–N(1B)
O(1C)–P(1C)–N(1C)
O(1)–P(1)–N(2)
O(1A)–P(1A)–N(2A)
O(1B)–P(1B)–N(2B)
O(1C)–P(1C)–N(2C)
O(1)–P(1)–N(3)
O(1A)–P(1A)–N(3A)
O(1B)–P(1B)–N(3B)
O(1C)–P(1C)–N(3C)
1.474(2)
1.475(2)
1.479(2)
1.476(2)
1.634(3)
1.641(3)
1.638(3)
1.632(3)
111.59(14)
111.26(13)
109.67(14)
109.98(15)
110.77(14)
111.15(13)
117.75(14)
117.61(14)
113.63(14)
113.29(13)
112.64(13)
113.31(14)
P(10)–O(10)
P(1)–N(1)
P(10)–N(10)
P(1)–N(2)
P(10)–N(20)
P(1)–N(3)
P(10)–N(30)
O(1)–P(1)–N(1)
O(10)–P(10)–N(10)
O(1)–P(1)–N(2)
O(10)–P(10)–N(20)
O(1)–P(1)–N(3)
O(10)–P(10)–N(30)
N(1)–P(1)–N(2)
N(10)–P(10)–N(20)
N(1)–P(1)–N(3)
N(10)–P(10)–N(30)
N(3)–P(1)–N(2)
N(30)–P(10)–N(20)
9.68 and 9.59 kcal/mol in compounds 1, 2, 3, 4 and 5, respectively.
Thus, the amine groups can rotate similarly around the P–Naliphatic
bond in all cases. It is found that the formation of various
conformers in these compounds is independent of the electronic

K. Gholivand, H.R. Mahzouni / Polyhedron 30 (2011) 61–69
67
Fig. 6. Schematic representation of the gauche configuration for the P@O bond and
phenyl ring. The intramolecular CHorthoꢀ ꢀ ꢀOP hydrogen bond is shown by a dashed
line and the piperidine rings are reduced to their nitrogen atoms for clarity.
nature of the substituent X. Perhaps the steric effects play a dom-
inant role in the formation of various conformers. Although the
substituent X does not participate directly in hydrogen bonding,
the crystal packing of the compounds is changed by the size of
the substituents. Bulky substituents may affect the molecular
arrangements in the hydrogen bonding. As a result, various con-
formers are created during the crystal growth. It is found that
compounds 3 and 5, with the bulky substituents –CH3 and –Br,
have four conformers in the solid state. The compounds with
the small substituents –H and –F show no tendency to produce
multiple conformers. It should be noted that the conformers 4a
and 4b were converted to the equivalent structures, from energy
and structural points of view, upon full optimization in the gas
phase (Table 5). The observed conformational variety of com-
pound 4ꢀH2O can be attributed to the co-crystallization of the
water molecule in the crystal lattice.
Fig. 8. A double strand created by molecules 4a, 4b and H2O in the crystal lattice of
4ꢀH2O. The symbol O1S refers to the oxygen atom of the water molecule.
A comparison of the fully optimized monomers and the hydro-
gen bonded clusters in the gas phase reveals that the intermolec-
ular hydrogen bonding is responsible for the lengthening of the
N–H bonds in clusters. This may explain the red shift of the N–
H stretching frequencies from the calculated values to the exper-
imental spectra. NBO analysis reveals an [Lp(OP) ?
r*(N–H)]
interaction among the subunits within the clusters. This electronic
delocalization leads to the weakening of the N–H bond. This is in
good agreement with the decrease in the
q value at the bcp of the
N–H bond from the monomers to their corresponding clusters
(Tables 4 and 5). In all cases, the DHꢀ ꢀ ꢀA distances shorten from
the X-ray data to the values derived from the DFT calculations.
Moreover, the D–H–A angles in the optimized clusters are more
linear than those in the solid state structures. These indicate that
the hydrogen bonds in the optimized clusters are stronger than
those in the X-ray structures. It is observed that the charge den-
sity at the bcp of DHꢀ ꢀ ꢀA is increased when the donor–acceptor
3.3.2. Comparison of the optimized monomers and clusters
For the compound 4ꢀH2O, the modelled cluster contains 4a, 4b
and water molecules, while triplet clusters were considered for
the other compounds (Fig. 1). The donor–acceptor distances for
the hydrogen bonds in the model clusters are equal to the experi-
mental values, due to the freezing of the non-hydrogen atoms in
the calculations. The other optimized parameters of the hydrogen
bonds differ from the X-ray values (Table 4).
distance shortens. The maximum
q value is 0.0369 a.u. for the
strongest hydrogen bond, i.e. (HOH)ꢀ ꢀ ꢀOP(4b), while it is 0.0215
a.u. in the case of the 4b(NH)ꢀ ꢀ ꢀ(OP)4a hydrogen bond with the
Fig. 7. Representation of two polymeric chains with –(3a3d3c3b)n– and –(3a3b3c3d)n– arrangements in compound 3.

68
K. Gholivand, H.R. Mahzouni / Polyhedron 30 (2011) 61–69
Table 4
The dataa of the hydrogen bonds in the crystalline compounds.
D–H...A
D–A
d(D–H) Å
d(Hꢀ ꢀ ꢀA) Å
d(D–A) Å
\DHA°
SEl
qm (a.u.)
bcp1
bcp2
N(1)–H(1)ꢀ ꢀ ꢀO(1)b
1ꢀ ꢀ ꢀ1
0.958 [1.022]
0.880 [1.023]
0.880 [1.026]
0.880 [1.024]
0.880 [1.024]
0.870 [1.021]
0.820 [0.978]
0.820 [0.977]
0.871 [1.020]
0.900 [1.024]
0.976 [1.024]
0.924 [1.024]
0.938 [1.024]
1.908 [1.847]
2.068 [1.855]
2.034 [1.813]
2.041 [1.861]
2.005 [1.800]
1.979 [1.830]
1.911 [1.752]
2.023 [1.833]
2.136 [2.000]
2.045 [1.848]
1.863 [1.820]
2.007 [1.904]
1.962 [1.869]
2.859(2)
2.862(9)
2.819(8)
2.873(8)
2.807(8)
2.842(3)
2.724(3)
2.808(3)
3.000(3)
2.854(2)
2.829(2)
2.911(2)
2.880(2)
171.6 [170.1]
149.6 [167.4]
148.0 [166.1]
157.0 [169.1]
150.9 [166.7]
171.2 [170.3]
170.8 [171.6]
160.3 [176.3]
171.8 [165.9]
149.1 [166.3]
169.7 [167.4]
165.4 [166.9]
165.5 [168.7]
[18.31]
[19.85]
[22.41]
[19.36]
[22.89]
[20.19]
[18.00]
[15.19]
[10.59]
[19.90]
[21.69]
[17.01]
[19.12]
[0.0318]
[0.0316]
[0.0314]
[0.0316]
[0.0315]
[0.0319]
[0.0331]
[0.0324]
[0.0319]
[0.0315]
[0.0315]
[0.0316]
[0.0316]
[0.0299]
[0.0304]
[0.0340]
[0.0298]
[0.0347]
[0.0341]
[0.0369]
[0.0327]
[0.0215]
[0.0311]
[0.0331]
[0.0274]
[0.0295]
N(1)–H(1)ꢀ ꢀ ꢀO(1A)c
N(1A)–H(1A)ꢀ ꢀ ꢀO(1B)d
N(1B)–H(1B)ꢀ ꢀ ꢀO(1C)e
N(1C)–H(1C)ꢀ ꢀ ꢀO(1)f
N(3)–H(3)ꢀ ꢀ ꢀO(1S)g
O(1S)–H(1S)ꢀ ꢀ ꢀO(1’)g
O(1S)–H(2S)ꢀ ꢀ ꢀO(1)h
N(3’)–H(3’)ꢀ ꢀ ꢀO(1)i
3aꢀ ꢀ ꢀ3b
3bꢀ ꢀ ꢀ3c
3cꢀ ꢀ ꢀ3d
3dꢀ ꢀ ꢀ3a
4aꢀ ꢀ ꢀH2O
H2Oꢀ ꢀ ꢀ4b
H2Oꢀ ꢀ ꢀ4a
4bꢀ ꢀ ꢀ4a
5aꢀ ꢀ ꢀ5d
5bꢀ ꢀ ꢀ5c
5cꢀ ꢀ ꢀ5a
5dꢀ ꢀ ꢀ5b
N(3)–H(3N)ꢀ ꢀ ꢀO(1C)g
N(3A)–H(3NA)ꢀ ꢀ ꢀO(1B)g
N(3B)–H(3NB)ꢀ ꢀ ꢀO(1)j
N(3C)–H(3NC)ꢀ ꢀ ꢀO(1A)k
a
b
c
The values in brackets refer to the optimized clusters at the B3LYP/6-31G* level.
[x, ꢁy + 1/2, z + 1/2].
[x, y ꢁ 1, z].
d
e
f
[ꢁx + 1, ꢁy + 3, ꢁz + 1].
[ꢁx, ꢁy + 3, ꢁz + 1].
[x ꢁ 1, y + 1, z + 1].
[x, y, z].
g
h
i
[ꢁx, ꢁy + 1, ꢁz].
[x + 1, y, z].
j
[ꢁx + 1, ꢁy + 1, ꢁz + 1].
[ꢁx + 1, ꢁy + 1, ꢁz].
k
l
SE is the stabilizing energy E2 (in kcal molꢁ1) of the Lp(O) ?
r*(N–H) and Lp(O) ? r*(O–H) delocalization effects.
m
q
is the calculated charge density at the bcps of the D–H bond (bcp1) and Hꢀ ꢀ ꢀA contact (bcp2) in the cluster.
longest donor–acceptor distance (3.000 Å). Coincident with this
observation, a stabilizing energy E2 of 18.00 kcal/molꢁ1 was calcu-
lated for the Lp(OP) ?
r*(O–H) delocalization effect of the
(HOH)ꢀ ꢀ ꢀOP(4b) hydrogen bond, while it is 10.59 kcal/molꢁ1 in
the case of 4b(NH)ꢀ ꢀ ꢀ(OP)4a.
4. Conclusions
The NMR data (at 298 and 190 K) confirm that the titled com-
pounds have one conformer in solution. The crystal structures of
3, 4ꢀH2O and 5 contain four, two and four conformers, respectively,
at 120 K. Rotation of the amine groups around the P–N bonds cre-
ates various conformers and a wide range of different hydrogen
bonds. The N–H stretching frequency shows a red shift from the
calculated to the experimental values, as a result of the packing ef-
fects in the solid phase. The q(OP) and q(Hamidic) values do not
change upon para-substitution of the aniline. The conformational
diversity in these compounds is independent of the electronic ef-
fects, and it is governed by steric effects, for example compounds
3 and 5, with bulky substituents, produce four conformers in the
solid phase.
Fig. 9. Representation of the important bcp’s and rcp’s in the fully optimized
monomer 4.
Table 5
0
Selected bond lengths (AÅ), stretching frequencies (cmꢁ1), dipole moments (debye), NBO charges (eꢁ) and charge densities (a.u.) for the model monomers.
Compound
d(P@O)
d(N–H)
m
(P@O)
m(N–H)
q(OP)
q(Hamidic
)
Dipole moment
SEa
qb
(b1)
(b2)
(r1)
(r2)
1
2
3
4
1.490
1.490
1.489
1.489
1.490
1.493
1.493
1.012
1.012
1.012
1.012
1.012
1.013
1.013
1235
1235
1236
1236
1235
1229
1229
3604
3602
3602
3597
3602
3587
3587
ꢁ1.102
ꢁ1.101
ꢁ1.100
ꢁ1.101
ꢁ1.102
–
0.437
0.436
0.437
0.436
0.436
–
5.3
5.6
5.7
4.4
4.2
4.4
4.4
9.41
9.27
9.11
9.68
9.59
–
0.0107
0.0110
0.0109
0.0104
0.0101
–
0.3281
0.3282
0.3282
0.3281
0.3281
–
0.0090
0.0092
0.0093
0.0089
0.0088
–
0.0201
0.0202
0.0203
0.0201
0.0202
–
5
4ac,d
4bc,d
–
–
–
–
–
–
–
a
b
c
SE is the stabilizing energy E2 (in kcal molꢁ1) of Lp(Naniline) ?
r*(P–Naliphatic).
(b1) and (r1) are related to the bcp and rcp of the intramolecular CHꢀ ꢀ ꢀOP contact, (b2); bcp of the N–H bond, (r2); rcp of the aniline ring.
The values are related to the B3LYP/6-31+G*level.
d
The single point energy of conformer 4a (ꢁ1206.28 HF) is equal to that of 4b in the gas phase.

K. Gholivand, H.R. Mahzouni / Polyhedron 30 (2011) 61–69
69
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Acknowledgment
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Support of this work by Tarbiat Modares University is gratefully
acknowledged.
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Appendix A. Supplementary data
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CCDC 612549, 292746, 612550 and 612551 contain the supple-
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C32H54N6O3P2 and C17H28N3OP. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
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