Two new phosphinic amides: Synthesis, crystal structure, and theoretical study of hydrogen bonding

Article abstract of DOI:10.1080/10426507.2016.1239200

Two novel phosphinic amides, (C₆H₅)₂P(O)(NH?cyclo?C₇H₁₃) (I) and (C₆H₅)₂P(O)(NH?cyclo?C₆H₁₁) (II) were synthesized and characterized by spectrosc

Full text of DOI:10.1080/10426507.2016.1239200

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Two new phosphinic amides: synthesis, crystal structure and theoretical study of hydrogen
bonding
Farahnaz Hamzeheea, Mehrdad Pourayoubia*, Abolghasem Farhadipourb*, Duane Choquesillo-
Lazartec
aDepartment of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad
9177948974, Iran
bEsfarayen University of Technology, Esfarayen, 9661998195 Esfarayen, Iran
cLaboratorio de Estudios Cristalográficos, IACT, CSIC-Universidad de Granada, Av. de las
Palmeras 4, 18100 Armilla, Granada, Spain
*To whom correspondence should be addressed. pourayoubi@um.ac.ir (Mehrdad Pourayoubi),
ab.farhadipour@hotmail.com (Abolghasem Farhadipour)
Abstract
Two novel phosphinic amides, (C6H5)2P(O)(NH-cyclo-C7H13) (I) and (C6H5)2P(O)(NH-cyclo-
C6H11) (II) were synthesized and characterized by spectroscopic methods and X-ray
crystallography. Both compounds crystallize in the orthorhombic chiral space group P212121 and
in both structures, the N—H∙∙∙O hydrogen bonds lead to one-dimensional arrangements along
the a axis. The molecular geometries and vibrational frequencies of I and II were investigated
with quantum chemical calculations at the B3LYP/6-311G** level of theory. Furthermore, the
hydrogen bonds were studied by means of the Bader theory of atoms in molecules (AIM) and
natural bond orbital (NBO) analysis.
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Keywords
Phosphinic amide; X-ray crystallography; hydrogen bond; AIM; NBO
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Introduction
The amounts of data reported on phosphorus-nitrogen compounds have increased in recent years,
due to their numerous applications in biochemistry,1 medicine,2–5 pharmacology,6–9 agriculture10–
12
and coordination chemistry.13–15 Additionally, ab initio studies have been carried out on
different aspects of these compounds, such as structural features, conformational states and
spectroscopic assignments.16–23
In continuation of our previous studies on design, synthesis, X-ray crystallography and
analysis of hydrogen bond strength24–27 as well as theoretical studies on the IR spectra and
evaluation of the strength of hydrogen bonding in phosphoramides,28,29 here we report the
synthesis, crystal structure and spectroscopic characterization of two new derivatives, belonging
to another family of phosphorus-nitrogen compounds, called phosphinic amides. The new
compounds are (C6H5)2P(O)(NH-cyclo-C7H13) (I) and (C6H5)2P(O)(NH-cyclo-C6H11) (II) as
shown in Figures 1 and 2. Furthermore, the molecular geometries, vibrational frequencies and
hydrogen bond energies were studied by quantum chemical calculations.
Results and discussion
Crystal Structure Analysis and Optimized Geometry
The crystallographic data and the details of the X-ray diffraction study of I and II are represented
in Table 1. For both structures the asymmetric unit contains one complete molecule (Figures 3
and 4). The P═O bond lengths of I and II (1.485(5) Å and 1.490(4) Å) are slightly longer than
the phosphorus-oxygen double bond length (1.45 Å).30 The P–N bond lengths (1.646(6) Å for I
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and 1.641(5) Å for II) are shorter than the standard P–N single bond length (1.77 Å).30 The
phosphorus atoms have a distorted tetrahedral configuration with bond angles at the phosphorus
atoms in the range of 104.0(3)° (N1-P1-C7) to 119.5(3)° (O1-P1-N1) for I and 102.4(3)° (N1-
P1-C13) to 119.5(3)° (O1-P1-N1) for II. In both compounds, the nitrogen atom shows a non-
planar geometry with the bond-angle sum of 342.2(4)° for I and 348(4)° for II. The hydrogen
bond patterns of both structures are very similar to each other, in which the molecules are
aggregated through N1-H1∙∙∙O1-P1 hydrogen bonds (with d(N1∙∙∙O1) = 2.905(7) Å for I and
2.842(7) Å for II) in a one-dimensional chain along the a axis for both structures, Figures 5 and
6.
In the computational study the structures of monomers and dimers of both compounds were
fully optimized without symmetry restrictions at the B3LYP/6-311G** level of theory.
Optimized selected geometry parameters and X-ray diffraction results of both compounds are
summarized in Tables 2 and 3. The agreement between the geometrical parameters calculated on
the basis of theoretical study and the experimental data is satisfactory except for dihedral angles
which are different. Comparing structures of monomer and dimer of both compounds shows that
P1-O1 bond lengths of both dimers are longer than their monomers (0.007 Å in I and 0.008 Å in
II). Also the mean values of N-H bond lengths for the dimers of both structures are predicted as
0.011 Å longer than from the corresponding monomer values. These differences in the geometry
parameters show the existence of hydrogen bonds in the dimer structures.
We quantitatively evaluated the binding energies of the dimer structures of I and II,
which are –65829.667 eV and –63691.070 eV, respectively, by subtracting the two
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monomer energies (–32914.680 eV for I and –31845.372 eV for II from the dimer
energies of –0.307 eV and –0.326 eV, respectively).
Vibrational Frequencies
Fundamental infrared band frequencies for I and II in the solid phase with the calculated
frequencies and their assignments are given in Table 4. The assignments reported in this table are
based on the calculated intensity of the bands. For the high frequencies, the assignments are
straightforward. For the low frequency motions, however, the assignments are less clear cut.
Table 4 includes an approximate description based on the normal modes in terms of the
stretching (υ) and bending (δ) of the bonds at the B3LYP method with 6-311G** basis set. The
calculated vibrational frequencies for both compounds were compared with the experimental
values, using the root mean square (RMS) error analysis. The calculated frequencies are slightly
higher than the observed values for the majority of the normal modes. Two factors may be
responsible for the discrepancies between the experimental and computed spectra of these
compounds. The first factor is caused by the environment. The second factor for these
discrepancies is the fact that the experimental value is an inharmonic frequency while the
calculated value is a harmonic frequency.
In this part just the vibrational bands of I were analyzed and the ones of II are similar to I. By
analyzing IR bands of I, the highest frequency at 3535 cm–1 is assigned to the stretching of the
N1-H1 bond. The two vibrational frequencies at 1449 and 605 cm–1 are assigned to the in plane
and out of plane bending motions of the N1-H1 bond, respectively. We have experimentally
assigned these modes to the bending of N1-H1 at 1447 and 696 cm–1 with medium broad and
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weak intensities. The IR band at 1194 cm–1 with stronger intensity, which has been assigned to
the stretching of the P1-O1 bond, is calculated at 1211 cm–1. The largest difference between
calculated frequencies and experimental data in compounds I and II are for the frequencies at
about 396 and 410 cm–1, respectively. These modes involve symmetric stretching of the N–H
bonds, having a larger effect on the dipole moment. Since in real systems N–H bonds are
engaged in interactions (e.g. hydrogen bonding) that are ignored in the ―gas-phase model‖
calculations, the vibrational frequencies seem to have increased. The other source of error may
be due to the fact that the absorption band is relatively broad. However, the intensity of the peaks
implies that they are correctly assigned.
Comparing selected vibrational modes of the monomers with those of the corresponding
dimers, in both structure I and II the frequencies for the symmetrical stretching of the N-H bands
have red shifted in the dimers from 3535 and 3536 to 3412 cm−1 and also the stretching modes of
the P=O bonds have red shifted from 1211 and 1212 to 1188 and 1186 cm−1, respectively. The
results demonstrate that the N-H and P=O bonds are weakened owing the existence the hydrogen
bond interaction in these structures.
Hydrogen Bonding
AIM Analysis
Atoms in molecules (AIM) is a very popular and useful method to analyze weak interactions.31
To better describe the nature of intermolecular interactions in the dimers of I and II, AIM
analysis was carried out for structures I and II and their dimer structures (see Table 5) and the
resultant graphs are shown in Figures 7, 8 and 9. According to AIM theory,32 presence of a
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hydrogen bond like any chemical bond must correspond to the existence of a bond path between
hydrogen atom and acceptor containing the bond critical point (BCP), in topological analysis of
electron density distribution. The most often used criteria to determine the existence of hydrogen
bonding interactions is the electron density, ρ(r), and the Laplacian of the electron density, (r),

at the BCPs. Laplacian of ρ(r) is related to bond interaction energy by a local expression of the
viral theorem.33
In structure I, it can be seen that P=O∙∙∙H–N and P=O∙∙∙H–C interactions have respective
bond critical points (BCPs) and the values for the charge densities for these paths are 0.022 and
0.010 a.u., respective. The presence of the BCP corresponding to P=O∙∙∙H–N further justifies the
existence of this hydrogen bond. It was shown by Espinosa that the relationship between
hydrogen bond energy (E) and potential energy density at the corresponding BCP (VBCP) can be
approximately described as E = VBCP/2.34 This enables us to evaluate the strength of the
P=O∙∙∙H–N and P=O∙∙∙H–C hydrogen bonds separately. The VBCP for the former and the latter
are 0.0161 and 0.006 a.u., corresponding to hydrogen bonding energy of 0.219 eV and 0.075 eV,
respectively; the sum of them is 0.294 eV (5.27 kcal.mol–1). From a comparison it is clear that
the P=O∙∙∙H–N interaction has a major contribution to the intermolecular interaction between
two molecules in I as well as in II, while the contribution from P=O∙∙∙H–C is much smaller,
though not completely negligible.
For the further investigation of the hydrogen bonding in these compounds the surfaces of the
total electron densities of the two dimers are displayed in Figure 10. On the basis of the
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monomer analysis there is a strong interaction between the two monomers in each dimer but the
interaction in the dimer of II is stronger as shown on the right side of Figure 10.
NBO Analysis
In the NBO analysis the electronic wave functions are interpreted in terms of a set of occupied
Lewis and a set of non-Lewis localized orbital’s.35 Delocalization effects can be identified from
the presence of off diagonal elements of the Fock matrix in the NBO basis. The strengths of
these delocalization interactions are estimated by second order perturbation theory. In Tables 6
and 7, the NBO occupation numbers for the σ*(N1-H1) antibonding MO, the oxygen lone pairs,
LP(O1), and their respective orbital energies, E, are reported. Furthermore, some significant
donor–acceptor interactions and their second order perturbation stabilization energies E(2), which
were calculated at the B3LYP/6-311G** level of theory, for the dimers of I and II are given in
these tables. As is common, the orbital energies E are reported in atomic unit (a.u.), while the
second order perturbation energies E(2) are reported in kcal.mol–1.
It seems that in NBO analysis of hydrogen bonded systems, the charge transfer between the
lone pairs of proton acceptor and antibonding molecular orbital of proton donor is most
significant. The occupation number of σ*(N1-H1) antibonding MO in the dimer structures of
both compounds are fairly high as compared to the monomer structures (for I the occupation
number is 0.01583 e- in monomer which increased to 0.02802 e- in its dimer and for II the
corresponding values are 0.01586 e- and 0.02844 e-, respectively). The occupation number of
antibonding MO increases from I to II and the corresponding orbital energy also increases in the
same manner. It is important to note that the oxygen lone pair’s occupation numbers differ from
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the ideal occupation significantly. These results can be rationalized in terms of the charge
transfer interaction between the orbitals. As revealed at the bottom of Tables 6 and 7, the results
of NBO analysis show that three lone pairs of the oxygen atom (O1 in I and II) participate as
donor relative to the σ*(N1–H1) antibonding MO as acceptor in the relatively strong
intermolecular charge transfer interactions, with stabilization energy values of 6.39, 0.70 and
0.27 kcal ∙ mol–1 for I and 10.52, 5.14 and 0.39 kcal ∙ mol–1 for II, respectively.
The contour diagrams of LPOs orbitals, BD*N–H orbitals and all hydrogen bond interactions
(HB1, HB2 and HB3) of compounds I and II are shown in Figures 11 and 12. As becomes
evident from these figures, the interaction between the lone pair orbitals of the oxygen atom and
the antibonding molecular orbital of the N–H bond causes the formation of the hydrogen bonds
in these structures. For the formation of HB1 the interaction between the orbitals is positive, but
for HB2 and HB3 the interactions are about zero. Therefore HB1 interactions in both structures
lead to more stabilization than HB2 and HB3 ones.
Conclusion
The synthesis and spectroscopic characterization of the two new phosphinic amides,
(C6H5)2P(O)(NH-cyclo-C7H13) (I) and (C6H5)2P(O)(NH-cyclo-C6H11) (II), are reported and the
crystal structures of them have been determined by single crystal X-ray diffraction. The
hydrogen bonds for both compounds have been theoretically investigated applying B3LYP/6-
311G** level of theory. The results obtained from the DFT optimization calculations, NBO
analysis and the topological parameters derived from the Bader theory suggest that the hydrogen
bond existing in the compound II is more stronger than compound I. There is good agreement
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between the energy of the hydrogen bond (HB) calculated from the topological parameters and
from the optimization energy.
Experimental
Instrumentation
IR spectra were obtained using KBr pellets with a Buck 500 scientific spectrometer. A Varian
Star 3400 CX mass spectrometer was used for mass spectrometry investigations. 1H, 13C and 31P
NMR spectra were obtained with a FT NMR Bruker Avance 300 spectrometer. Chemical shifts
1
are given for H and 13C relative to TMS and for 31P relative to 85 % H3PO4 as external
standards. All calculations were carried out at density functional theory (DFT) level, using
Gaussian 09 program.36 The B3LYP/6-311G** level of theory were used to optimize the
geometry of the molecules. Additionally the AIM theory of Bader33 was used to localize bond
critical points and to calculate their electron densities at bond critical points: ρBCPs. The
Laplacians of these densities were also calculated (Laplacians of electronic densities at bond
critical points: BCPs and Laplacians of electronic densities at ring critical points: RCPs).


All AIM calculations were performed using AIM2000 program.31 The NBO analysis was carried
out using version 3.1 of NBO package37 included in Gaussian 09 program at B3LYP/6-311G**
level of theory. Harmonic vibrational frequency calculations at B3LYP/6-311G** level
confirmed the structures as minima and enabled the evaluation of zero-point vibrational energies
(ZPVE). The crystal structures of both compounds were measured using a Bruker D8 Venture
diffractometer with multilayer monochromated Mo-Kα radiation. In both compounds the
hydrogen atoms attached to carbon atoms were kept in ideal positions with C–H = 0.95 – 1.00 Å
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and Uiso (H) set to 1.2Ueq (C) according to common practice. The non-hydrogen atoms were
refined using harmonic refinement. The hydrogen atom bonded to the nitrogen atom was refined
without any constrains and data were processed with the program Bruker Apex2. Both structures
were solved with direct methods and refined using SHELX software.38
Synthesis
Synthesis of (C6H5)2P(O)(NH-cyclo-C7H13) (I)
A solution of cycloheptylamine (0.589 g, 5.2 mmol) in dry chloroform (10 mL) was added to a
solution of diphenylphosphinic chloride (0.615 g, 2.6 mmol) in the same solvent at 273 K. After
stirring for 3 h the solvent was removed in vacuum and the product was washed with deionized
water. Single crystals of I were obtained from a solution of the product in methanol / heptane (4 :
1 v/v) after slow evaporation at room temperature. - IR (KBr, cm–1): 3139, 2927, 2860, 1447,
1194, 1116, 1071, 948, 885, 749, 722, 696. MS (70 eV, EI): 312 (5) [M – 1]+, 310 (95)
[C19H21NOP]+, 267 (29) [M – H2 – C3H8]+, 253 (95) [M – H2 – C4H10]+, 216 (78) [M – C7H13]+,
199 (100) [C12H8OP]+, 82 (38) [C6H10]+, 77 (93) [C6H5]+, 56 (52) [C4H8]+, 43 (44) [C3H7]+, 29
31
1
(95) [C2H5]+. P NMR (DMSO-d6, 121.78 MHz): δ = 21.9 (s). H NMR: (DMSO-d6, 300.85
MHz): δ = 1.28 – 2.12 (m, 12H, CH2 of C7H13), 2.93 (m, 1H, CH of C7H13), 3.24 (s, 1H, NH),
7.29 – 7.51 (m, 6H, Ar-H), 7.92 (m, 4H, Ar-H). 13C NMR (DMSO-d6, 75.65 MHz): δ = 23.7 (s),
28.1 (s), 38.4 (d, 3JCP = 5.3 Hz), 52.7 (d, 2JCP = 2.3 Hz), 128.5 (d, JCP = 12.1 Hz), 131.7 (d, JCP
2.3 Hz), 132.1 (d, JCP = 9.1 Hz), 133.2 (d, 1JCP = 129.4 Hz).
=
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Synthesis of (C6H5)2P(O)(NH-cyclo-C6H11) (II)
Compound II was synthesized by a similar method as described for I, however using a solution
of cyclohexylamine (0.595 g, 6.0 mmol) instead of cycloheptylamine [diphenylphosphinic
chloride (0.710 g, 3.0 mmol)]. Single crystals of II were obtained from a solution of the product
in ethanol / heptane (3 : 1 v/v) after slow evaporation at room temperature. - IR (KBr, cm–1):
3126, 2927, 2858, 1745, 1442, 1375, 1308, 1197, 1101, 995, 918, 885, 726, 692. MS (70 eV, EI):
299 (15) [M]+, 297 (81) [M – H2]+, 268 (11) [M – H – C2H6]+, 254 (81) [M – H – C3H8]+, 215
(80) [M – C6H12]+, 200 (92) [C12H9OP]+, 182 (31) [C12H7P]+, 98 (100) [C6H12N]+, 77 (80)
31
1
[C6H5]+, 56 (81) [C4H8]+, 28 (79) [C2H4]+. P NMR (DMSO-d6, 121.49 MHz): δ = 19.9 (s). H
NMR: (DMSO-d6, 300.13 MHz): δ = 0.93 – 1.87 (m, 10H, CH2 of C6H11), 2.69 (m, 1H, CH of
C6H11), 5.22 (t, J = 9.6 Hz, 1H, NH), 7.47 (m, 6H, Ar-H), 7.78 (m, 4H, Ar-H). 13C NMR
(DMSO-d6, 75.47 MHz): δ = 24.97 (s), 25.02 (s), 35.6 (d, 3JCP = 5.2 Hz), 4.99 (s), 128.3 (d, JCP
12.1 Hz), 131.2 (d, JCP = 2.3 Hz), 131.6 (d, JCP = 9.2 Hz), 134.5 (d, 1JCP = 126.3 Hz).
=
Supplementary material
Crystallographic data for the structures of compounds I and II have been deposited with the
Cambridge Crystallographic Data Centre CCDC, Nos. 1494129 for I and 1494129 for II. Copies
of the information may be obtained free of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail:deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
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E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.;
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Daniels, A. D.; Farkas; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.: Wallingford CT.,
2009.
37.
38.
Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F. NBO, Version 3.1, 2003.
Sheldrick, G. M. Acta Cryst. 2008, A64, 112–122.
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Table 1 Crystal data and structure refinement
I
II
Empirical formula
C19H24NOP
313.36
C18H22NOP
299.33
Formula weight
T (K)
100.0
100.0
Wave length (Å)
0.71073
orthorhombic
P212121
8.1412(4)
12.0198(6)
16.9183(8)
90
0.71073
orthorhombic
P212121
8.1279(2)
11.6810(4)
16.7596(5)
90
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
90
90
γ (°)
90
90
V (Å3)
1655.55(14)
4
1591.19(8)
4
Z
Calculated density (g/cm3)
Absorption coefficient (µ)
F (000)
1.257
1.250
0.168
0.172
672
640
Crystal size
0.12 × 0.12 × 0.1
2.078 to 25.160
0.12 × 0.12 × 0.11
2.430 to 25.024
θ range for data collection
(°)
Index ranges
–11 ≤ h ≤ 11
–17 ≤ k ≤ 16
–23 ≤ l ≤ 24
–9 ≤ h ≤ 9
–13 ≤ k ≤ 13
–19 ≤ l ≤ 19
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Completeness to theta
Absorption correction
25.160°, 98.6%
25.024°, 99.8%
Semi-empirical from
equivalents
Semi-empirical from
equivalents
Max and min transmission
Refinement method
0.8012 and 0.7039
0.7455 and 0.6593
Full-matrix least-squares Full-matrix least-squares
on F2
on F2
Data / restraint / parameter
Goodness of fit on F2
2932 / 0 / 202
1.114
2803 / 0 / 193
1.195
Final R indices [I > 2σ(I)]
R1 = 0.0724, wR2 =
R1 = 0.0682, wR2 = 0.1766
0.1908
R indices (all data)
R1 = 0.0784, wR2 =
0.1947
R1 = 0.0683, wR2 = 0.1766
1.141 and –0.487
Largest diff. peak and hole
(e Å–3)
1.349 and –0.520
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Table 2 Selected geometry parameters (Å, °) of compound I
Theoretical
Dimer
Parameters
Bonds
Experimental
Monomer
P1–O1
1.485(5)
1.817(6)
1.817(7)
1.646(6)
0.96(8)
1.498
1.829
1.830
1.690
1.015
1.483
1.096
---
1.505│1.504
1.830│1.830
1.825│1.833
1.683│1.677
1.014│1.026
1.481│1.482
1.095│1.096
1.971
P1–C14
P1–C8
P1–N1
N1–H1*
N1–C1
1.482(8)
1.0000
C1–H1A
H1…O1i*
N1…O1i*
Angles
1.99(8)
2.905(7)
---
2.986
O1–P1–C14
O1–P1–C8
O1–P1–N1
P1–N1–H1
C1–N1–P1
C1–N1–H1
N1–C1–H1A
N1–H1…O1i*
Torsion angles
O1–P1–N1–H1
111.5(3)
109.9(3)
119.9(3)
118(4)
111.724
110.576
120.032
112.438
120.992
112.275
106.052
---
110.842│111.119
111.094│110.035
119.935│120.391
113.063│112.394
123.495│121.481
112.780│112.241
106.347│106.517
169.94
121.2(5)
103(4)
107.5
160(6)
63.8(5)
81.907
77.608│67.303
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C14–P1–N1–H1 –60.1(5)
–41.675
–44.352│–57.206
C8–P1–N1–H1
–172.4(5)
–154.364 –157.822│–168.500
–172.672 –168.624│–177.662
H1–N1–C1–H1A –177.69
*Hydrogen bonding parameters (symmetry code (i) for I: x + 1/2, –y + 3/2, –z + 1).
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Table 3 Selected geometry parameters (Å, °) of compound II
Theoretical
Dimer
Parameters
Experimental
Monomer
Bonds
P1–O1
1.490(4)
1.821(6)
1.819(6)
1.641(5)
0.96(7)
1.487(7)
1.000
1.498
1.829
1.829
1.691
1.015
1.477
1.096
---
1.506│1.504
1.830│1.830
1.823│1.833
1.685│1.677
1.026│1.014
1.476│1.477
1.096│1.096
1.976
P1–C13
P1–C7
N1–P1
N1–H1A*
C1–N1
C1–H1
H1…O1i*
N1…O1i*
Angles
1.89(7)
2.842(7)
---
2.989
O1–P1–C13
O1–P1–C7
O1–P1–N1
P1–N1–H1A
C1–N1–P1
H1A–N1–C1
N1–C1–H1
N1–H1A…O1i*
Torsion angles
O1–P1–N1–H1
111.8(3)
110.1(3)
119.5(3)
110(4)
111.81
110.67
119.98
112.57
120.82
112.29
106.47
---
111.25│111.20
111.41│110.28
119.33│120.48
112.95│112.69
122.92│121.89
112.76│111.54
106.69│107.11
168.61
121.0(4)
117(4)
107.6
168(6)
76.23(4)
82.51
83.80│67.04
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C13–P1–N1–H1A –47.94(4)
–41.13
–38.26│–57.22
–151.22│–168.72
–173.55│179.96
C7–P1–N1–H1
–160.64(4)
–153.77
–174.40
H1–N1–C1–H1A –177.12
*Hydrogen bonding parameters (symmetry code (i) for II: x + 1/2, –y + 3/2, –z + 1).
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Table 4 Selected experimental and computed vibrational frequencies (cm–1) for compounds I
and II, using the B3LYP/6-311++G(d, p) level of the theory
Compound I
Compound II
Assignment
Experimental Theoretical (cm–1) Experimental Theoretical (cm–1)
3139
1447
1194
696
3535a (3412b)
1449 (1461)
1211 (1188)
605 (667)
3126
1442
1197
692
3536 (3412)
1450 (1471)
1207 (1186)
606 (671)
υN1-H1
δN1-H1
υP1-O1
ρN1-H1
a: Vibrational frequencies of monomer, b: Vibrational frequencies of dimer
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Table 5 AIM analysis of compounds I and II and their dimer structures
Monomer
ρ(a.u.)
Dimer
AIM analysis
Bonds
(a.u.)
ρ(a.u.)
(a.u.)


Compound I
P1-O1
0.201 –0.255 0.207│0.221 –0.194│–0.322
0.316 0.288 0.308│0.333 0.384│0.370
0.153 –0.068 0.004│0.175 –0.003│–0.094
N1-H1
P1-N1
P1-C14
0.146 0.051
0.146 0.052
0.168│0.169
0.049│0.051
P1-C8
0.013│0.171 –0.012│0.055
P1–O1∙∙∙H1–N1
P1–O1∙∙∙H1–C1
--
--
--
--
0.022
0.010
–0.022
–0.007
Compound II
P1-O1
0.224 –0.332 0.157│0.159 –0.126│–0.117
0.333 0.369 0.301│0.315 0.346│0.351
0.174 –0.088 0.136│0.140 –0.056│–0.054
N1-H1
P1-N1
P1-C13
0.169 0.050
0.169 0.051
0.140│0.139 0.045│0.042
0.141│0.139 0.050│0.043
P1-C7
P1–O1∙∙∙H1A–N1
P1–O1∙∙∙H1–C1
--
--
--
--
0.031
0.005
–0.028
–0.005
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Table 6 NBO analysis of compound I and its dimer structure
Monomer
MOs
Dimer
Occupancy E (a.u.)
Occupancy
1.96826
E (a.u.)
–0.70606
–
1.98022
LP1(O1)
LP2(O1)
LP3(O1)
0.70337
–
1.83024
1.84468
1.8128
–0.25547
0.24169
–
1.79705
–0.25461
0.24084
–
σ*(N1-H1) 0.01583
0.02802
0.47162
0.41766
Acceptor MOs in
dimer
Donor MOs in dimer
E(2) (kcal.mol–1)
LP1(O1)
LP2(O1)
LP3(O1)
σ*(N1-H1)
σ*(N1-H1)
σ*(N1-H1)
6.39
0.70
0.27
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Table 7 NBO analysis of compound II and its dimer structure
Monomer
MOs
Dimer
Occupancy E (a.u.)
Occupancy
–0.70380 1.96870
–0.24182 1.84420
E (a.u.)
–0.70875
LP1(O1)
LP2(O1)
LP3(O1)
1.98028
1.83002
1.79706
–0.25706
–0.25584
0.47006
–0.24090 1.81413
σ*(N1-H1) 0.01586
0.41689 0.02844
Acceptor MOs in
dimer
Donor MOs in dimer
E(2) (kcal.mol–1)
LP1(O1)
LP2(O1)
LP3(O1)
σ*(N1-H1)
σ*(N1-H1)
σ*(N1-H1)
10.52
5.14
0.39
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Figure 1 Chemical structure of compound I
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Figure 2 Chemical structure of compound II
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Figure 3 Displacement ellipsoid plot (50 % probability) and atom numbering scheme for I. H
atoms are drawn as spheres of arbitrary radii.
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