Synthesis, conformational and NQR analysis of phosphoric triamides containing the P(O)[N]3 skeleton

Article abstract of DOI:10.1016/j.molstruc.2012.03.045

New phosphoric triamides with general formula P(O)X₃ where X = N-4-methylpiperazinyl (1), N-4-phenylpiperazinyl (2), N-4-ethoxycarbonyl piperazinyl (3), N-2-tetrahydrofurfuryl (4) were synthesized and characterized by ¹H, ¹³C, ³¹P NMR, IR, Mass spectroscopy and elemental analysis. The molecular structure for compounds 1-4 were obtained by using quantum chemical calculations (HF and B3LYP methods with the 6-31+G ^** basis set). Moreover, optimized structures for previously reported 4-FC₆H₄C(O)NHP(O)X₂ phosphoric triamides, X = pyrrolidin-1-yl (5), piperidin-1-yl (6) and hexamethyleneimin-1-yl (7) were obtained using the solid state structure (CIF files) as a starting point for the gas phase computation in which all independent molecules in structures 6 (seven structures) and 7 (two structures) were included. The computed results were in good agreement with the data obtained from the X-ray crystal structures reported earlier. The nuclear quadrupole coupling constants (NQCCs or χs) were calculated about 5.0 and 10.0 MHz for the ¹⁷O atoms of PO and CO bonds. For nitrogen atoms bonded to the phosphorus the NQCCs were found in the range between 4.0 and 5.5 MHz, whereas for compounds 4-7, the expected values for amidic hydrogen atoms are near 300 kHz.

Full text of DOI:10.1016/j.molstruc.2012.03.045

Journal of Molecular Structure 1023 (2012) 18–24
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, conformational and NQR analysis of phosphoric triamides containing
the P(O)[N]3 skeleton
b,c,
b
a
Zahra Shariatinia a, , Carlos O. Della Védova
, Mauricio F. Erben , Vahid Tavasolinasab ,
⇑
⇑
Khodayar Gholivand d
a Department of Chemistry, Amirkabir University of Technology, P.O. Box 159163-4311, Tehran, Iran
b CEQUINOR (UNLP-CONICET, CCT La Plata), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CC 962, 47 esq. 115, 1900 La Plata, Argentina
c Laboratorio de Servicios a la Industria y al Sistema Científico (UNLP-CIC-CONICET), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata,
La Plata, Argentina
d 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:
Available online 29 March 2012
New phosphoric triamides with general formula P(O)X3 where X = N-4-methylpiperazinyl (1), N-4-phe-
nylpiperazinyl (2), N-4-ethoxycarbonyl piperazinyl (3), N-2-tetrahydrofurfuryl (4) were synthesized and
characterized by 1H, 13C, 31P NMR, IR, Mass spectroscopy and elemental analysis. The molecular structure
for compounds 1–4 were obtained by using quantum chemical calculations (HF and B3LYP methods with
the 6-31+G⁄⁄ basis set). Moreover, optimized structures for previously reported 4-FC6H4C(O)NHP(O)X2
phosphoric triamides, X = pyrrolidin-1-yl (5), piperidin-1-yl (6) and hexamethyleneimin-1-yl (7) were
obtained using the solid state structure (CIF files) as a starting point for the gas phase computation in
which all independent molecules in structures 6 (seven structures) and 7 (two structures) were included.
The computed results were in good agreement with the data obtained from the X-ray crystal structures
Dedicated to Prof. Dr. Jaan Laane on
occasion of his 70th anniversary
Keywords:
Phosphoric triamide
NMR
Ab initio computations
NQR
reported earlier. The nuclear quadrupole coupling constants (NQCCs or vs) were calculated about 5.0 and
10.0 MHz for the 17O atoms of P@O and C@O bonds. For nitrogen atoms bonded to the phosphorus the
NQCCs were found in the range between 4.0 and 5.5 MHz, whereas for compounds 4–7, the expected val-
ues for amidic hydrogen atoms are near 300 kHz.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
on phosphoric triamides may be a result of non-rigidity of some
parts of molecules resulting in different torsion angles [11–14].
Phosphoric triamides have attracted renewed attention since
their feasibility for acting as ligands in coordination chemistry –
especially with lanthanide metals – has been recently demon-
strated [1,2]. Moreover, lithiated anions derived from phosphoric
triamides have been early reported [3], which are recognized as
homoenolate equivalent in the reaction with halogenated acetal
Furthermore, several crystal structures with disordered atoms in
the solid state owing to rapid inversions or rotations exist
[11,14]. Ab initio quantum chemical computations were applied
on them both to predict the structural parameters and for the sake
of comparison with experimental results [15–17]. It is noteworthy
that, as far as we know, the nuclear quadrupole coupling constants
of these molecules have not been reported so far. Calculation of nu-
and ketal giving regioselectively the c-alkylation adducts [4]. Inter-
esting features associated with distinctive crystal motif and con-
formational properties in the crystalline state have been also
determined [5–7]. Thus, many efforts have been made for the syn-
thesis, characterization and structural investigations on phospho-
ric triamides [8–10]. The presence of more than one conformer
clear quadrupole coupling constants (
a powerful tool to estimate the structural properties of the mole-
vs) of nuclei with spin P1 is
cules [18–22]. Previous studies have reported
v values of about
5.0, 10.0 MHz, and 300.0 kHz, respectively, for the 14N, 17O and
2H atoms [19].
In this work, four new phosphoric triamides (1–4) were synthe-
sized and characterized by multinuclear (1H, 13C and 31P) NMR, IR,
Mass spectroscopy and elemental analysis. Also, their molecular
structures were computed and compared with previously reported
phosphoric triamides for which X-ray crystallographic data are
⇑
Corresponding authors. Address: CEQUINOR (UNLP-CONICET, CCT La Plata),
Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La
Plata, CC 962, 47 esq. 115, 1900 La Plata, Argentina (C.O. Della Védova). Tel./fax: +54
221 4714527.
available [11]. Nuclear quadrupole coupling constants (
v) were
E-mail addresses: shariati@aut.ac.ir (Z. Shariatinia), carlosdv@quimica.unlp.
edu.ar (C.O. Della Védova).
calculated for the quadrupole 14N, 2H and 17O atoms.
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.03.045

Z. Shariatinia et al. / Journal of Molecular Structure 1023 (2012) 18–24
19
(7), 247 [P(O)((NHN(CH2)2N(CH2)2)2]+ (27), 99 [N(CH2)2N(CH2)2]+
(13), 56 [N(CH2)2N] (8).
2. Experimental
2.1. Spectroscopic measurements
2.2.2. N,N0,N00-tris(4-phenylpiperazinyl) phosphoric triamide (2)
To a solution of phosphoryl chloride (10 mmol, 1.54 g) in dry
acetonitrile, N-4-phenylpiperazine (60 mmol, 3.18 g) was added
dropwise at 0 °C and the mixture stirred for 20 h. Then the precip-
itate (by-product) was filtered and the solution was evaporated.
The resulting solid was washed with n-hexane and diethyl ether.
Yield: 62%; Anal. Calc. For C30H39N6OP: C, 67.90; H, 7.41; N,
15.84%. Found: C, 67.88; H, 7.40; N, 15.85%. 31P{1H} NMR (CDCl3):
d = 17.99 (s). 1H NMR (CDCl3): d = 3.17 (m, 4 H, CH2-ring), 3.38 (m,
4 H, CH2-ring), 6.91 (t, 3J(H,H) = 7.3 Hz, 2 H, Ar-H), 6.94 (d,
3J(H,H) = 7.3 Hz, 2 H, Ar-H), 7.29 (t, 3J(H,H) = 7.3 Hz, 1 H, Ar-H).
13C NMR (CDCl3): d = 45.06 (s, CH2-ring), 50.16 (d, 3J(P,C) = 5.9 Hz,
CH2-ring), 116.51 (s), 120.36 (s), 129.16 (s), 151.34 (s). IR (KBr,
1H, 13C and 31P NMR spectra were recorded on a Bruker Avance
DRX 500 spectrometer. 1H and 13C chemical shifts were deter-
mined relative to internal TMS, 31P chemical shifts relative to
85% H3PO4 as external standard. Infrared (IR) spectra were re-
corded on a Shimadzu model IR-60 spectrometer. Elemental anal-
ysis was performed using a Heraeus CHNAO-RAPID apparatus.
Melting points were obtained with an Electrothermal instrument.
The mass spectra were recorded on a 5973 Network Mass Selective
Detector (Agilent Technology, HP) with 70 eV electron impact (EI).
2.2. Synthesis
cmꢀ1): 2832 (
mCH), 1596, 1497, 1235 (mP@O), 1127, 966 (mPAN),
2.2.1. N,N0,N00-tris(4-methylpiperazinyl) phosphoric triamide (1)
To a solution of phosphoryl chloride (10 mmol, 1.54 g) in dry
acetonitrile, 1-amino-4-methylpiperazine (60 mmol, 2.33 g) was
added dropwise at 0 °C. This mixture was stirred for 24 h and
was filtered to remove the alkylamine hydrochloride by-products.
Then the yellow solution was evaporated and the residue was
washed with ethyl acetate and dissolved in diethyl ether. The
resulting solution was evaporated again and the yellow precipitate
was washed with CCl4. Yield: 49%; Anal. Calc. For C15H33N6OP: C,
52.31; H, 9.66; N, 24.40%. Found: C, 52.29; H, 9.65; N, 24.38%.
31P{1H} NMR (CDCl3): d = 18.50 (s). 1H NMR (CDCl3): d = 2.30 (s, 3
H, 4-CH3), 2.34 (s, 4H, CH2-ring), 3.11 (s, 4H, CH2-ring). 13C NMR
(CDCl3): d = 44.71 (s, 4-CH3), 46.20 (s, CH2-ring), 55.42 (d,
745, 684. MS (70 eV, EI): m/z (%): 530 [M]+ (3), 513 [P(N(CH2)2
N(CH2)2APh)3)]+ (3), 453 [P(O)(N(CH2)2N(CH2)2APh)2)(N(CH2)2
N(CH2)2)]+ (4), 369 [P(O)(N(CH2)2N(CH2)2APh)2)]+ (5), 344 [P(N
(CH2)2N(CH2)2APh) (N(CH2)2N(CH2)2)(N(CH2)2N)]+ (11), 287 [P(O)
(N(CH2)2N(CH2)2APh)(N(CH2)2N(CH2)2)]+ (12), 274 [P(N(CH2)2
N(CH2)2APh)(N(CH2)2N(CH2)2)]+ (76), 245 [P(N(CH2)2N(CH2)2A
Ph)(N(CH2)2N)]+ (100), 174 [P(O)(N(CH2)2N(CH2)2)(N(CH2)2)]+
(24), 162 [(N(CH2)2N(CH2)2APh]+ (10), 147 [(CH2)2N(CH2)2APh]+
(13), 120 [N(CH2)2APh]+ (4), 99 [P@N(CH2)2NCH2]+ (63), 71
[N(CH2)2NCH2]+ (14), 56 [(N(CH2)2N]+ (16), 42 [(N(CH2)2]+ (17).
2.2.3. N,N0,N00-tris(4-ethoxy carbonylpiperazinyl) phosphoric triamide
(3)
3J(P,C) = 5.6 Hz, CH2-ring). IR (KBr, cmꢀ1): 2938
(m
CH), 2851
(m
CH), 2800 (
m
CH), 1453, 1287, 1189 (
mP@O), 1000 (
mPAN), 782,
To a solution of phosphoryl chloride (10 mmol, 1.54 g) in dry
acetonitrile, N-4-ethoxy carbonylpiperazine (60 mmol, 3.11 g)
was added dropwise at 0 °C and the mixture stirred for 48 h. Then
727. MS (70 eV, EI): m/z (%): 389 [M]+ (2), 345 [P(O)((NHN(CH2)2
N(CH2)2ACH3)3]+ (100), 274 [P(O)((NHN(CH2)2N(CH2)2ACH3)2]+
O
P
N
N
N
N
N
H3C
CH3
N
CH3
O
(1)
O
P
O
P
N
N
HN
N
H
N
N
N
Ph
Ph
NH
O
P(O)Cl3 + 6 NR
N
O
Ph
O
P
(2)
(4)
N
N
N
N
N
C2H5O(O)C
C(O)OC2H5
N
C(O)OC2H5
(3)
Scheme 1. The preparation pathway of compounds 1–4.

20
Z. Shariatinia et al. / Journal of Molecular Structure 1023 (2012) 18–24
Table 1
the precipitate (by-product) was filtered and the solution was
evaporated. The resulting yellow solid was washed with CCl4 and
diethyl ether. Yield: 62%; Anal. Calc. For C21H39N6O7P: C, 48.64;
H, 7.58; N, 16.21%. Found: C, 48.62; H, 7.57; N, 16.20%. 31P{1H}
NMR (CDCl3): d = 18.27 (s). 1H NMR (CDCl3): d = 1.18 (t, 3J(H,H)=
7.0 Hz, CH3), 3.00 (m, 4H, CH2-ring), 3.36 (m, 4H, CH2-ring), 4.06
(q, 3J(H,H)= 7.0 Hz, OCH2). 13C NMR (CDCl3): d = 14.49 (s, CH3),
44.28 (s, CH2-ring), 48.26 (s, CH2-ring), 61.48 (s, OCH2), 150.15 (s,
Selected spectroscopic NMR and IR data of compounds 1–4.
Compound d(31P)
2J(P,C)
(Hz)
3J(P,C)
(Hz)
m
(P@O)
m(PAN)
(ppm)
(cmꢀ1
)
(cmꢀ1
)
1
2
3
4
18.50
17.99
18.27
19.19
–
–
–
5.1
5.6
5.9
–
1189
1235
1241
1188
1000
966
986
944
7.7
C@O). IR (KBr, cmꢀ1): 2982 (
C@O), 1426, 1241 ( P@O), 1130, 986 (m
mCH), 2906 (mCH), 2849 (mCH), 1687
(m
m
PAN), 961, 766, 724. MS
(70 eV, EI): m/z (%): 518 [M]+ (2), 344 [P(O)(N(CH2)2N(CH2)2 AC(O)
(OC2H5))(N(CH2)2N(CH2)2AC(O)(OCH2))]+ (9), 287 [P(O) (N(CH2)2
N(CH2)2AC(O)(OC2H5))(N(CH2)2N(CH2)2)]+ (8), 274 [P(O) (N(CH2)2
N(CH2)2AC(O)(OC2H5)) (N(CH2)2NCH2)]+ (55), 246 [P(O) (N(CH2)2N
(CH2)2AC(O)(OC2H5))(N(CH2)2)]+ (71), 174 [P(N(CH2)2 N(CH2)2A
C(O)(OCH3))]+ (22), 158 [N(CH2)2N(CH2)2AC(O)(OC2H5)]+ (30), 101
[NCH2AC(O)(OC2H5)]+ (24), 85 [N(CH2)2N(CH2)2]+ (16), 72 [OC(O)
NCH2]+ (17), 56 [CH3CH2C]+ (88), 44 [OC(O)]+ (100).
Table 2
The P@O stretching wavenumber and its square correlated with the sum of the
Pauling electronegativities of the atoms and groups attached to the P@O group in
OPXYZ compounds and with the vertical ionization potential.
Compound
m
(P@O)
(
m
(P@O))2 ꢁ 10ꢀ6 Sum of
Vertical
(cmꢀ1
)
(cmꢀ2
)
electronegativities ionization
of X, Y and Z
potential
(eV)
OPF3
1415
2.002
11.94
13.52 [28]
12.62**
2.2.4. N,N0,N00-tris(2-tetrahydrofurfuryl) phosphoric triamide (4)
To a solution of phosphorylchloride (10 mmol, 1.54 g) in dry
acetonitrile, 2-tetrahydrofurfurylamine (60 mmol, 2.08 g) was
added dropwise at 0 °C and the mixture stirred for 24 h. Then the
crude mixture was filtered and the yellow solution evaporated.
The resulting solid was re-crystallized in acetone and the yellow
solid was further washed with n-heptane and CCl4. Yield: 62%;
Anal. Calc. For C15H30N3O4P: C, 51.86; H, 8.70; N, 12.10%. Found:
C, 51.84; H, 8.71; N, 12.09%. 31P{1H} NMR (CDCl3): d = 19.19 (s).
1H NMR (CDCl3): d = 1.49 (m, 6 H, CH2), 2.76 (m, 1 H, CH), 2.96
(m, 1 H, CH), 3.29 (m, 1 H, CH-ring), 3.76 (m, 1 H, NH). 13C NMR
(CDCl3): d = 35.55 (s), 35.59 (s), 42.83 (d, 3J(P,C) = 2.9 Hz, CH2),
43.91 (s), 64.00 (d, 3J(P,C) = 7.7 Hz, CH), 106.82 (s, CH2O). IR (KBr,
OPClF2
OPBrF2
OPCl2F
OPBr2F
OPCl3
1384
1380
1358
1337
1290
1.915
1.904
1.844
1.788
1.664
11.12
10.92
10.30
9.90
11.53**
11.47**
11.04**
11.91 [28]
11.16**
10.68**
10.72**
11.07 [28]
10.76**
10.44 [28]
7.49**
9.48
OPBrCl2
OPBr2Cl
OPBr3
1285
1275
1261
1.651
1.625
1.590
9.28
9.08
8.88
OP[N(CH3)2]3 1160
1.346
8.52*
Compound 3 1241
Compound 2 1235
Compound 1 1189
Compound 4 1188
1.540
1.525
1.414
1.411
8.52*
8.52*
8.52*
8.28*
7.42**
6.37**
6.60**
cmꢀ1): 3367 (
1224, 1188 ( P@O), 1147, 1042, 944 (
mNH), 2955 (
m
CH), 2927 (mCH), 2890 (mCH), 1331,
7.52**
m
m
PAN), 894, 725, 660. MS
Group electronegativity, Eg ¼ ½VꢂcEc þ Sum of Ni ꢂ Eiꢃ=N where, Vc and Ec are the
*
(70 eV, EI): m/z (%): 347 [M]+ (2), [P(NHCH2AC4H7O)3]+ (19), 142
[P(CH2)(NCH2AC4H7O)]+ (100), 99 [NCHAC4H7O)]+ (24), 87
[CH2AC4H7O)]+ (24), 71 [C4H7O)]+ (4), 56 [NHCH2CHCH2]+ (15),
42 [CH2CH2CH2]+ (18).
valence of the central atom and its atomic electronegativity value respectively. Ni
and Ei are the number of the bond of atomic or group i connecting to the central
atom and the atomic electronegativity of i atom.
Calculated at B3LYP/6-31+G⁄⁄ level of theory.
**
3. Computational details
The structures of compounds 1–4 and also those of phosphoric
triamides with formula 4-F-C6H4C(O)NHP(O)X2, X = NC4H8 (5),
NC5H10 ( 6, 6A-1, 6A-2, 6B-1, 6B-2, 6C-1, 6C-2) and NC6H12 (7,
7A) were optimized using the Gaussian 98 program [23]. The
optimizations were followed by computations of the harmonic
vibrational frequencies at HF/6-31G⁄ method. No imaginary
frequencies were obtained at these computations. Nuclear quadru-
pole coupling constants (v) were calculated from the equation
v
= e2qzzQ/h [24], supposing that the electric quadrupole moments
(Q) of 2H, 17O and 14N nuclei are 2.860, ꢀ25.58, and 20.44 mb,
respectively [25]. The principal components of the electron field
gradient tensor (EFG), qii, are computed in atomic unit (1 au =
2
1
9.717365 ꢁ 1021 V mꢀ2), with |qzz| P |qyy| P |qxx| and qxx + qyy
+
qzz = 0. These diagonal elements relate to each other by the asym-
metry parameter:
the EFG tensor deviation from axial symmetry. The computed qzz
g
Q = |qyy ꢀ qxx|/|qzz|, 0 6 gQ 6 1, which measures
component of EFG tensor is used to obtain the nuclear quadrupole
coupling constants (v).
4. Results and discussion
4.1. Spectroscopic study
4
3
Fig. 1. Optimized structures obtained for compounds 1–4 at HF, B3LYP/6-31+G⁄⁄
In this study, new phosphoric triamides 1–4 were synthesized
from the reaction of POCl3 with different amines (Scheme 1) and
levels of theory.

Z. Shariatinia et al. / Journal of Molecular Structure 1023 (2012) 18–24
21
(189.5)
(191.9)
H6
(180.8)
H5
(5.28)
(179.6)
N
H5
O1
(5.26)
O1
P
H6
P
(5.46)
N2
N
(4.87)
(5.36)
N2
4
N
(4.89)
4
N
N
N
N3
H3C
CH3
N3
Ph
Ph
(5.41)
(5.29)
N
N
CH3
(1)
(2)
Ph
(191.6)
H6
O
(179.9)
H5
(5.29)
N4
O1
P
(5.19)
O1
(253.8)
H5
H
N2 (5.41)
(4.84)
P
N
N2
H6
N
N
(4.58)
4
(4.93)
N3
C2H5O(O)C
C(O)OC2H5
N3
(4.83)
(5.17)
(260.8)
O
N
O
C(O)OC2H5
(3)
(4)
(10.56)
O8
O2 (4.96)
(10.52)
(5.00)
O8
O2
P1
(302.3)
H4
(302.3)
H4
P
N6
N
(4.17)
(6.06)
N6
(5.84)
3
N
(4.25)
3
N5
(5.89)
N5
(5.76)
F
F
(5)
(6C-2)
(10.44)
O8
O2
P
(5.13)
N6
(302.0)
H4
(6.23)
(4.17) N3
N5
(5.76)
F
(7)
Scheme 2. The structural formula along with the NQCCs in parentheses for compounds 1–4 (at B3LYP/6-31+G⁄⁄ level) and 5, 6C-2, 7 (at HF/6-311++G⁄⁄ level).
fully characterized by NMR and IR spectroscopy. A summary of the
spectroscopic data of these compounds are given in Table 1. The
comparative analysis of the NMR spectra reveals interesting fea-
tures. The 31P{1H} NMR spectra of compounds 1–4 indicate the
phosphorus chemical shift, d(31P), in the range of 17.99–
19.19 ppm displaying nearly the same electron donation of amino
substituents to the phosphorus atoms.
The 1H NMR spectra of molecules 1–3 exhibit two signals for
the methylene protons of the six membered piperazinyl rings.
The 13C NMR spectrum of this molecule indicates six separated
peaks for the five carbon atoms that are due to the different orien-
tations of the aliphatic five membered rings. The methylene carbon
atom presents a 2J(P,C) = 2.9 Hz and the CH group shows the
3J(P,C) = 7.7 Hz. The signal related to the carbon atom of CH2AO
Fig. 2. Optimized structures obtained for compound 5 at HF/6-311++G⁄⁄ level of
theory.
moiety appears at the most down field (106.82 ppm). The 13C

22
Z. Shariatinia et al. / Journal of Molecular Structure 1023 (2012) 18–24
Fig. 3. Optimized structures obtained for compounds 6, 6A-1, 6A-2, 6B-1, 6B-2, 6C-1 and 6C-2 at HF/6-311++G⁄⁄ level of theory.
NMR spectra of compounds 1 and 2 also demonstrate 3J(P,C) equal
to 5.6 and 5.9 Hz, respectively. In addition, the mass spectra con-
firm the formation of structures 1–4 by analyzing the fragmenta-
tion patterns and the corresponding base peaks.
cluded for OPF3 (13.52 eV), OPCl3 (11.91 eV), OPBr3 (11.07 eV)
and OP[N(CH3)2]3 (10.44 eV). As indicated in Table 2, the correla-
tions between m
(P@O)2 and sum of substituents electronegativities
attached to P atom, and vertical ionization potential for phosphoric
triamides 1–4 are in qualitative agreement with the trend ob-
served for simple phosphoryl halides. As expected for phosphoric
triamide molecules, however, it is plausible that not only the elec-
tronegativity of the substituent, but also other phenomena – such
as electron withdrawing/releasing nature, hyperconjugative effect
– play a major role in determining the electronic properties of
phosphoric triamide compounds.
The analysis of the IR spectra indicate that the fundamental
m(P@O) stretching modes for compounds 1 and 4 appear at lower
frequencies than that of compounds 2–3, while the (PAN) of 1
m
shows the greatest value among those of 1–4. The trend of the
P@O normal mode of vibration bears a resemblance to the behavior
of the C@O stretching mode as earlier reported by the foundational
work of Kagarise [26]. In the present case, the square of the P@O
wavenumber correlates fairly well with the sum of the Pauling
electronegativities of the atoms or groups attached to the P@O
moiety. Table 2 serves to exemplify this behavior and lists data
for relevant and simple selected exponents found in the literature
[27]. Moreover, this correlation can be extended to the vertical ion-
ization potentials. Thus, selected values [28] have been also in-
4.2. Computational study
4.2.1. Compounds 1–4
Herein, to more investigate on the above prepared phosphoric
triamides (1–4), their molecular structures have been optimized

Z. Shariatinia et al. / Journal of Molecular Structure 1023 (2012) 18–24
23
using Gaussian 98 software at HF and B3LYP method with
6-31+G⁄⁄ standard basis set. Fig.
indicates the optimized
respectively. Similar results were obtained for the nitrogen atoms
of other structures here presented.
1
structures of the compounds 1–4. In the optimized structures of
compounds 1 and 2, the 4-Me and 4-Ph substituents place in pseu-
do-axial positions, but the 4-C(O)OEt moieties in 3 are in pseudo-
equatorial positions (likely due to the planar carbon atom of C@O
group). Also, the CH2 groups in compound 4 connected to aliphatic
five-membered rings are in pseudo-equatorial positions (Fig. 1).
Quantum chemical calculations also show that among seven
plausible forms of compound 6, compound 6C-2 is the most stable
and between compounds 7 and 7A, compound 7 is more stable
than 7A. The 4-fluorobenzoyl moieties in 7 and 7A indicate cis
and trans conformations relative to the P@O groups with
O@Pꢄ ꢄ ꢄFAC torsion angles equal to 176.26° and 147.84°,
respectively.
The selected calculated NQCCs (v
s) for the quadrupole 14N, 2H
and 17O nuclei of compounds 1–4 at HF and B3LYP methods with
The selected calculated NQCC (v
) for the quadrupole 14N, 2H
6-31+G⁄⁄ basis set are represented in Table S3 and Scheme 2. The
and 17O nuclei of compounds 5–7 at HF/6-311++G⁄⁄ are repre-
v
values for the oxygen and nitrogen atoms are about 5.0 MHz,
sented in Scheme 2 and Table S4 (Supplementary material). The
while for the 2H atoms of CH and NH groups they are near 200
and 300 kHz, respectively.
oxygen atoms of P@O and C@O bonds have
v
values about 5.0
values
and 10.0 MHz, respectively. The reason for the almost half
v
of oxygen atoms in phosphoryl moieties with respect to carbonyl
groups could be the more negative carbonyl oxygen atoms owing
to the resonance interactions. For the amidic and endocyclic amino
4.2.2. Compounds 5–7
The structural properties of phosphoric triamides (5–7) that are
similar to compounds (1–4) have also been optimized at HF/6-
31G⁄ and HF/6-311++G⁄⁄ levels of theory. In the Scheme 2, a draw-
ing of the studied compounds is given and Figs. 2–4 show the opti-
mized structures. The species 5–7 have been previously
synthesized and the geometries of N-4-fluorobenzoyl phosphoric
triamides including their conformers and disorders structures
were studied by X-ray diffraction [11]. The aliphatic five- and se-
ven-membered rings in compounds 5, 7 and 7A have puckered
shapes while the six-membered rings of seven forms of 6 show
chair conformation. For compounds 5–7, the P@O bond presents
an anti conformation with respect to the C@O double bonds. The
pseudo-torsion angles O@Pꢄ ꢄ ꢄC@O in compounds 5, 6C-2 and 7
are 170.46°, 172.79° and 166.17°, respectively. This result confirms
the earlier X-ray structures reported elsewhere [11]. In these mol-
ecules, the bond angles around the P atom indicate a distorted con-
formation varying from 103.95° to 119.67° in 5 at HF/6-31G⁄
method. Similar results were observed for other compounds at
both HF/6-31G⁄ and HF/6-311++G⁄⁄ levels of theory.
nitrogen atoms, the
respectively, and for the H atoms they were near 300 kHz. The
smaller values for the amidic N atoms may be due to the electron
v values compute about 4.0 and 5.5 MHz,
v
withdrawing of 4-fluorobenzoyl moiety that leads to deshielding of
amidic N compared with amino N atom.
Acknowledgements
The financial support of this work by the Research Councils of
Amirkabir University of Technology and Tarbiat Modares Univer-
sity is gratefully acknowledged. CODV and MFE are indebted to
the Agencia Nacional de Promoción Científica y Tecnológica (AN-
PCyT), Consejo Nacional de Investigaciones Científicas y Técnicas
(CONICET), and the Comisión de Investigaciones Científicas de la
Provincia de Buenos Aires (CIC), República Argentina, for financial
support. He also thanks the Facultad de Ciencias Exactas, Univers-
idad Nacional de La Plata, República Argentina for financial
support.
The computed bond lengths, angles and torsion angles at HF/6-
31G⁄ and HF/6-311++G⁄⁄ are compared with their related data ob-
tained from the X-ray crystal structures of these molecules [11]
that are in good agreement with each other, however it is seen that
HF/6-31G⁄ has a better correspondence with the experimental val-
ues than HF/6-311++G⁄⁄. In compounds 5–7, the PAN(amide)
bonds are longer than the PAN(amine) bonds, because of the reso-
Appendix A. Supplementary material
The molecular formula of compounds 1–7 with atom number-
ing are shown in Scheme S1. The computed bond lengths, angles
and torsion angles of compounds 1–4 (at B3LYP/6-31+G⁄⁄ level)
and 5–7 (at HF/6-311++G⁄⁄ level) are presented in Tables S1 and
S2, respectively. Selected calculated NQCCs (vs) for compounds
nance interaction of the N(amide) with the C@O
p system. In fact,
1–4 and 5–7 are given in Tables S3 and S4, respectively. Supple-
mentary data associated with this article can be found, in the on-
line version, at http://dx.doi.org/10.1016/j.molstruc.2012.03.045.
all PAN bonds in compounds 1–7 are shorter than the typical PAN
single bond (1.77 Å [29]) whereas the P@O bond lengths are larger
than the reported P@O bond length (1.45 Å) [29]. In molecules 1–7,
the nitrogen environment is practically planar. For example, in
compound 5 the angles P(1)AN(3)AC(7), P(1)AN(3)AH(4) and
C(7)AN(3)AH(4) are 130.00°, 111.07° and 118.09°, respectively
with average 119.72°. The sum of surrounding angles around
N(3), N(5) and N(6) atoms are 359.16°, 358.34° and 352.18°,
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