Analysis of P–O–C, P–S–C and P–O–P angles: a database survey completed with four new X-ray crystal structures

Article abstract of DOI:10.1007/s11224-016-0809-7

Four new crystal structures, P(O)(OC₆H₅)₂(NHNHC₆H₅) (I), P(S)(OCH₃)₂(NHCH(CH₃)₂) (II), P(S)(OCH₃)₂(NH-cyclo-C₅H₉

Full text of DOI:10.1007/s11224-016-0809-7

Struct Chem
DOI 10.1007/s11224-016-0809-7
ORIGINAL RESEARCH
Analysis of P–O–C, P–S–C and P–O–P angles: a database survey
completed with four new X-ray crystal structures
Fahimeh Sabbaghi1
Mehrdad Pourayoubi2 Michal Dusek Vaclav Eigner
3
3
•
•
•
•
ˇ
Monika Kucerakova
´
6,7
3
Sahar Bayat4 Krishnan Damodaran5 Marek Necas
•
•
•
ˇ
ˇ
´
´
Received: 31 March 2016 / Accepted: 18 July 2016
Ó Springer Science+Business Media New York 2016
Abstract Four new crystal structures, P(O)(OC6H5)2
(NHNHC6H5) (I), P(S)(OCH3)2(NHCH(CH3)2) (II),
P(S)(OCH3)2(NH-cyclo-C5H9) (III) and [2–Cl–C6H4CH2
NH3]2[(CH3S)P(O)(O)–O–P(O)(O)(SCH3)] (IV) were stud-
ied. The P–O–C angles were analyzed, considering phos-
phoryl compound (I) and thiophosphoryl compounds (II)
and (III) and their analogous structures deposited in the
Cambridge Structural Database (CSD), including 282
P(O)(O)2(N) structures (706 P–O–C angles) and 186
P(S)(O)2(N) structures (518 P–O–C angles) with at least one
P–O–C angle. The maximum populations of P–O–C angles
are within 120°–122° in both P(O)(O)2(N) and P(S)(O)2
(N) families of structures, confirming the hybridization state
close to sp2 for the oxygen atom of P–O–C. A survey on the
CSD resulted in 11 P(O)(O)2(S–C) structures (11 P–S–C
angles), and the structure (IV) belonging to this family of
compounds is the first diffraction study of a salt with a
(S)P(O)(O)–O–P(O)(O)(S) skeleton in the anion component.
For the P–S–C angles, the maximum population was found
in the range of 100°–104° showing the angles within those
related to unhybridized pure p orbitals (p3) and hybridized
sp3 for the sulfur atom of P–S–C. The analysis of 187 P(O)–
O–P(O) structures (with no restriction on the other two
atoms attached to phosphorus) including 538 P–O–P angles
yielded the maximum population of P–O–P angles within
132°–134°, showing the more pronounced ‘‘s’’ character of
the orbital (with respect to the sp2 and toward sp) for the
oxygen atom at the P–O–P moiety.
Keywords Cambridge Structural Database (CSD) Á
Crystal structure Á Analysis of bond angle Á Hybridization
Introduction
& Fahimeh Sabbaghi
fahimeh_sabbaghi@yahoo.com
Organophosphorus compounds, especially of the pentava-
lent type, are extremely versatile and have prevalent
environmental and industrial applications in agriculture
and medicine [1]. They comprise two main groups, namely
phosphoryl-based and thiophosphoryl-based compounds,
with typical examples of phosphoramides and thiophos-
phoramides families containing the P(O)[NR1R2] and
P(S)[NR1R2] moieties, respectively (R1 and R2 = H or a
hydrocarbon) [2–7].
1
Department of Chemistry, Zanjan Branch, Islamic Azad
University, Zanjan, Iran
2
Department of Chemistry, Faculty of Sciences, Ferdowsi
University of Mashhad, Mashhad, Iran
3
Institute of Physics AS CR, v.v.i., Na Slovance 2,
182 21 Prague 8, Czech Republic
4
Department of Chemistry, Payame Noor University, Zanjan,
Iran
In various published papers, different structural features
of phosphoramides [3–5], thiophosphoramides [6, 7] and
complexes of phosphoryl donor ligands [8–10] were stud-
ied through diffraction experiments of their derivatives and
investigation of analogous structures deposited in the
Cambridge Structural Database (CSD [11]). Such studies
help to gather the knowledge about these categories of
5
Department of Chemistry, University of Pittsburgh,
Pittsburgh, PA 15260, USA
6
Department of Chemistry, Masaryk University, Kotlarska 2,
61137 Brno, Czech Republic
7
CEITEC - Central European Institute of Technology,
Masaryk University, Kamenice 5, 62500 Brno,
Czech Republic
123

Struct Chem
compounds, such as electronic properties of atoms and
bonds [12–14], hybridization states of atoms in different
parts of molecules [7, 14, 15], preferable conformations
[7, 14], competition of different H-donor sites or H-ac-
ceptor sites in hydrogen bonding interactions [4, 12], and
designing compounds with a desirable chemical structure
[4]. The ultimate aim is prediction of crystal structures
from molecular structures [4].
almost as were accessed by the nature of bonds and
hybridization states of atoms.
TheP–O–C, P–S–CandP–O–Pbondanglesareconsidered
in these structures, and the histograms of distributions of
angles are presented. Moreover, some compounds from CSD
with interesting structural features are discussed in this paper
and the chemical structures with the CSD refcodes are gath-
ered in Table 1. This study can be used as a background for a
discussion on the preferable hybridization states of O and S
atoms attached to phosphorus. The Lewis base properties of
such oxygen and sulfur atoms are also investigated here
through a CSD analysis, in continuing the previous works
done for the N atom attached to phosphorus [4].
Among these studies, the geometries at the nitrogen
atoms were analyzed in the structures with (X)(Y)N–P(=O)
[14, 15] and (X)(Y)N–P(=S) [7] moieties (X, Y are any
atoms from CSD, typically H, C and N). For these struc-
P
tures, the sums of valence angles ( ) around nitrogen
atoms (P–N–X ? X–N–Y ? Y–N–P) showed a tendency
P
toward the sp2 hybridization state, with most of the
values near to the ideal sp2 value of 360°. For a few
structures with a distortion from a planar environment at
the nitrogen atom, the proposed direction of lone electron
pair (LEP) located on the nitrogen atom with respect to the
P=O [14] or P=S [7] groups were discussed.
Experimental
Materials and measurements
The chemicals (C6H5O)2P(O)Cl, CH3CN, C6H5NHNH2,
CHCl3, CH3OH, (CH3)2CHNH2, (CH3O)2P(S)Cl, n-C7H16,
cyclo-C5H9NH2, 2-Cl-C6H4CH2NH2 and CH3C(O)CH3
were commercially available. Acetonitrile was dried with
P2O5 and distilled prior to use. Previous articles mentioned
the syntheses of (I) [18] and (III) [19] with together the 13C
The N atom in a planar environment does not act as a
hydrogen bond acceptor in crystal structure and shows low
Lewis base character; however, the few examples of the N
atom in a pyramidal environment do not show tendency as
well. In fact, there are only a few structures with the N atom
as an H-bond acceptor [16]. Moreover, a survey of the metal
complexes on the CSD shows that the nitrogen atoms of the
(X)(N)(Y)P=O and (X)(N)(Y)P=S moieties (X, Y are any
atoms from CSD) have a very low tendency to bind the metal
cations, too; so that, for example, in metal complexstructures
including a P(S)(N)3-based ligand, it was only found a weak
SnÁÁÁN interaction which was considered as a contact (not
bond) in the corresponding paper [17].
1
NMR spectrum of (I) (DMSO-d6) [20] and the H and 31P
NMR of (III) (CDCl3) [19]. Substance (II) exists in a patent
[21] as well as in an article focusing on infrared spec-
troscopy of some P=S containing substances such as (II)
[22], with no sign of any synthesis procedure in either of
them. Other NMR experiments were not found in literature.
The procedures reported here for compounds (I) and (III) are
similar to the literature methods with a few modifications.
Moreover, we further study these compounds with single
crystal X-ray diffraction. The syntheses for the preparations
of all four compounds began with the reagents being com-
bined at ice-bath temperature, and the mixture then allowed
coming to room temperature for the rest of the procedure. IR
spectra were recorded on a Buck 500 scientific spectrometer
using a KBr disk. 1H, 13C and 31P NMR spectra were
recorded on a FT-NMR Bruker Avance 300 spectrometer for
compound (I) and on a Bruker Avance III 600 MHz NMR
Here, we focus on the geometries of the oxygen (esteratic
and anhydride) and sulfur (thioesteratic) atoms bonded to
phosphorus, considering four new crystal structures
P(O)(OC6H5)2(NHNHC6H5) (I), P(S)(OCH3)2(NHCH(CH3)2)
(II), P(S)(OCH3)2(NH-cyclo-C5H9) (III) and [2–Cl–C6H4
CH2NH3]2[(CH3S)P(O)(O)–O–P(O)(O)(SCH3)] (IV) and
analogous structures from CSD with skeletons similar to (I),
(II), (III) and (IV), i.e., with P(O)(O)2(N), P(S)(O)2(N),
P(O)(O)2(S) and P(O)–O–P(O) skeletons. The structures from
database are included in our investigation if they contain at
least one P–O–C angle for the two first skeletons and one P–
S–C angle for the third skeleton. There is no structure with a
(S)P(O)(O)–O–P(O)(O)(S) skeleton [similar skeleton of
compound (IV)] in the CSD, so the analysis of P–O–P angles
was considered in all of the families of phosphorous com-
pounds with a P(O)–O–P(O) skeleton with any restriction on
the two other atoms bonded to each phosphorus atom in the
skeleton. The structures (I) to (IV), selected for diffraction
experiments, are suitable choices as the O and S atoms are not
placed in a rigid environment allowing to have the geometries
1
spectrometer for (II) and (III). H and 13C NMR spectra
were referenced using the solvent DMSO-d6 resonances
1
(2.50 and 39.52 ppm for H and 13C, respectively), and 31P
NMR spectra were calibrated using ‘‘absolute referencing’’
1
from the H spectrum. For (I), (II) and (IV), data collection
was obtained at 120 K on a single crystal diffractometer
Gemini using mirrors-collimated Cu-Ka radiation
˚
(k = 1.5418 A). For (III), data were collected at 120 K on a
Rigaku MicroMax-007 HF rotating anode CCD diffrac-
˚
tometer using Mo-Ka radiation (k = 0.71073 A). The
structures were solved by the charge flipping algorithm of
123

Struct Chem
Table 1 Chemical structures of refcodes (arranged alphabetically) discussed in the text
But
But
Ph
ATEXAY01
HAXQOO
NH HN
O
H
N
H
C
O
P
N
Ph
C
But
P
P
But
C
C
C
O
P
O
O
O
C
Ph
Ph
Et
C
C
C
C
Ph
Ph
S
BEVGAK
HAXRAZ
Me
O
P
N
H2N
O
O
0.5 Et2O
Et
O
P
O
O
S
O
Me
Pri
O
P(S)(NEt)2
O
BOKSUP
IJUMAB
NH3
H
MeO
O
N
C(O)OEt
O
O
S
P
P
P
S
H2O
OMe
N
N
O
O
O
O
Me
O
4
C(O)Me
DANHIJ
KIVFAW
S
H3N
H2
O
P
N
N
N
H
2 H2O
O
P
OCH2But
S
O
O
OCH2But
Et
DANMAG
MAXDOG
S
O
N
Me
P
S
O
N
P
N
H
O
O
Me
N
O
Me
Me
Me
O
Me
Me
S
P
DUPCOH
PALWUU
SOYRAZ
O
Me
Me
N
Me
Me
O
O
P
P
O
S
N
Me2N
O
NMe2
P
O
O
O
P
EPGUAN10
O
O
O
Et
NH2
3 H2O
O
P
P
N
Cl
O
NH3
O
O
O
Et
H2N
O
NH2
N
H2
H2N
Me
NH2
H2
N
H
3N
GEYMUS
N
O
H2
N
3 H2O
P
H2
O
S
O
123

Struct Chem
Table 2 Crystallographic data and structure refinement details for (I) and (II)
(I)
(II)
Empirical formula
Formula weight
Temperature (K)
C18H17N2O3P
340.3
C5H14NO2PS
183.2
120.00 (10)
1.54184
120.00 (10)
1.54184
Triclinic
P–1
˚
Wavelength (A)
Crystal system
Space group
Monoclinic
P21/n
Unit cell dimension
˚
a (A)
13.5418 (10)
6.5734 (5)
8.8944 (5)
9.3128 (8)
118.121 (8)
101.560 (7)
91.243 (6)
466.20 (7)
2
˚
b (A)
5.9725 (3)
˚
c (A)
21.2750 (13)
a (°)
b (°)
c (°)
90
105.791 (6)
90
3
˚
V (A )
1655.75 (19)
Z
4
Calculated density (g cm-3
Index ranges
)
1.3648
1.3051
-15 B h B 14
-6 B k B 5
-23 B l B 25
712
-6 B h B 7
-8 B k B 10
-10 B l B 9
196
F (000)
h range for data collection (°)
Max. and min. transmission
Goodness of fit on F2
3.49–67.06
5.55–66.83
1 and 0.827
1.30
0.891 and 0.624
1.95
Reflections measured/independent/Rint
Final R factors [number of independent observed reflections]a
5564/2862/0.0475
R1 = 0.0671, wR2 = 0.1637 [2259]
1.631
2739/1599/0.0316
R1 = 0.0300, wR2 = 0.0369 [1395]
Absorption coefficient (mm-1
)
4.328
-3
)
˚
Largest difference in peak and hole (e A
0.57 and -0.41
0.21 and -0.21
a
The observability limit is I [ 3r(I) for (I) and (II)
Superflip [23] and refined by Jana 2006 [24]. MCE software
[25] was used for visualization of electron density maps. In
case of structure (I), the disordered phenyl group was refined
using rigid body refinement with occupancy constrained to
full. The resulting occupancy ratio was 0.547 (3):0.453 (3).
In case of non-centrosymmetric structure (IV), Flack
parameter [26] was refined to final value 0.32 (2). Since the
compound is not a single enantiomer, the unambiguous
value is not an issue. Further details of X-ray analysis and
data collection for structures (I) & (II) and (III) & (IV) are
given in Tables 2 and 3, and selected bond lengths and
angles are given in Tables 4 and 5.
CH3CN at ice-bath temperature. After 4 h, the solvent was
removed and the solid residue was washed with distilled
water. Single crystals were obtained from CH3CN/CHCl3/
CH3OH (1:1:2 v/v/v) by slow evaporation at room tem-
perature. IR (KBr, cm-1): 3296, 3211, 3050, 2874, 1943,
1871, 1793, 1596, 1520, 1490, 1454, 1308, 1229, 1190,
1158, 1073, 1019, 969, 888, 851, 774, 756, 688. 31P{1H}
NMR (121 MHz, DMSO-d6): d = -1.49 (s). 1H NMR
3
(300 MHz, DMSO-d6): d = 6.69 (t, JH–H = 7.2 Hz, 1H),
6.80 (d, 3JH–H = 8.3 Hz, 2H), 7.09 (t, 3JH–H = 8.1/7.5 Hz,
3
2H), 7.21 (m, 6H), 7.39 (t, JH–H = 8.1/7.5 Hz, 4H), 7.60
3
2
(d, JH–P = 3.9 Hz, 1H, NH), 7.92 (d, JH–P = 41.2 Hz,
1H, NH). 13C NMR (75 MHz, DMSO-d6): d = 112.69 (s,
C6 (ortho)), 118.70 (s, C8 (para)), 120.35 (d,
3JC–P = 4.7 Hz, C2 (ortho)), 124.92 (s, C4 (para)), 128.47
(s, C7 (meta)), 129.76 (s, C3 (meta)), 149.59 (d,
Syntheses
P(O)(OC6H5)2(NHNHC6H5) (I)
2
3JC–P = 4.8 Hz, C5 (ipso)), 150.57 (d, JC–P = 6.9 Hz, C1
Phenylhydrazine, C6H5NHNH2, was added slowly to a
stirred solution of (C6H5O)2P(O)Cl (2:1 mol ratio) in
(ipso)). The C1 to C4 and C5 to C8 correspond to the C6H5O
and C6H5NHNH groups, respectively.
123

Struct Chem
Table 3 Crystallographic data and structure refinement details for (III) and (IV)
(III)
(IV)
Empirical formula
Formula weight
Temperature (K)
C7H16NO2PS
209.24
C2H6O5P2S2, 2(C7H9ClN)
521.4
120 (2)
0.71073
Triclinic
P–1
120.01 (10)
1.54184
Monoclinic
P21
˚
Wavelength (A)
Crystal system
Space group
Unit cell dimension
˚
a (A)
12.0681 (3)
12.2552 (3)
14.8655 (4)
72.414 (2)
8.5464 (3)
˚
b (A)
11.9725 (4)
˚
c (A)
11.7919 (5)
a (°)
b (°)
c (°)
90
83.442 (2)
105.161 (3)
88.509 (2)
90
3
˚
V (A )
2082.01 (9)
8
1164.57 (8)
Z
2
Calculated density (g cm-3
Index ranges
)
1.335
1.4868
-15 B h B 15
-16 B k B 15
-20 B l B 19
896
-9 B h B 10
-14 B k B 13
-13 B l B 13
540
F (000)
h range for data collection (°)
Max. and min. transmission
Goodness of fit on F2
1.7–29.7
3.88–67.06
1.00 and 0.88
1.30
0.599 and 0.272
1.74
Reflections measured/independent/Rint
Final R factors [number of independent observed reflections]a
24,922/10,008/0.0304
R1 = 0.0361, wR2 = 0.0937 [7331]
0.429
8259/4048/0.0569
R1 = 0.0480, wR2 = 0.1085 [3843]
5.724
Absorption coefficient (mm-1
)
-3
)
˚
Largest difference in peak and hole (e A
0.33 and -0.31
0.51 and -0.31
a
The observability limit is I [ 3r(I) for (III) and (IV)
P(S)(OCH3)2(NHCH(CH3)2) (II)
P(S)(OCH3)2(NH-cyclo-C5H9) (III)
Iso-propylamine, (CH3)2CHNH2, was added slowly to a
stirred solution of (CH3O)2P(S)Cl (2:1 mol ratio) in CH3
CN at ice-bath temperature. After 4 h, the solvent was
removed and the solid formed was washed with distilled
water. Single crystals were obtained from a solution of
product in a mixture of CHCl3/n-C7H16 (4:1 v/v). IR (KBr,
cm-1): 3312, 2971, 2721, 2615, 2471, 1841, 1460, 1416,
1378, 1316, 1176, 1133, 1061, 902, 837, 781, 643. 31P{1H}
NMR (243 MHz, DMSO-d6): d = 74.83 (s). 1H NMR
(601 MHz, DMSO-d6): d = 1.06 (dd, J = 6.6, 0.7 Hz,
6H), 3.29 (ddh, J = 10.3, 9.5, 6.5 Hz, 1H), 3.54 (d,
3JH–P = 13.6 Hz, 6H), 5.45 (dd, J = 15.1, 9.5 Hz, 1H,
NH). 13C NMR (151 MHz, DMSO-d6): d = 24.68 (d,
Cyclopentylamine, cyclo-C5H9NH2, was added slowly to a
stirred solution of (CH3O)2P(S)Cl (2:1 mol ratio) in CH3CN
at ice-bath temperature. After 4 h, the solvent was removed
and the solid formed was washed with distilled water. Single
crystals were obtained from a solution of product in a
mixture of CH3OH/CH3CN (1:1 v/v) by slow evaporation at
room temperature. IR (KBr, cm-1): 3314, 2954, 2867, 1743,
1436, 1281, 1178, 1107, 1029, 936, 810, 645. 31P{1H} NMR
(243 MHz, DMSO-d6): d = 75.16 (s). 1H NMR (601 MHz,
DMSO-d6): d = 1.32–1.40 (m, 2H), 1.40–1.47 (m, 2H),
1.56–1.66 (m, 2H), 1.71–1.81 (m, 2H), 3.39–3.46 (m, 1H),
3
3.54 (d, JH–P = 13.6 Hz, 6H), 5.55 (dd, J = 15.4, 9.2 Hz,
1H, NH). 13C NMR (151 MHz, DMSO-d6): d = 22.85 (s,
CH2), 33.80 (d, JC–P = 5.7 Hz, CH2), 52.57 (d,
2
3
3JC–P = 5.7 Hz, CH(CH3)2), 43.82 (d, JC–P = 1.7 Hz,
2
CH), 52.62 (d, JC–P = 5.1 Hz, CH3O).
2
2JC–P = 4.9 Hz, CH3), 53.37 (d, JC–P = 2.3 Hz, CH).
123

Struct Chem
Table 4 Selected geometric parameters for (I) and (II)
Table 5 Selected geometric parameters for (III) and (IV)
Compound (I)
Compound (III)
S1a–P1a
P1–O1
1.471 (2)
O3–C1b
O3–C1c
N1–N2
1.403 (4)
1.410 (5)
1.406 (4)
1.431 (4)
1.9346 (6)
1.5848 (11)
1.5880 (14)
1.6152 (15)
1.476 (2)
S1c–P1c
1.9336 (6)
1.5807 (11)
1.5869 (14)
1.6141 (15)
1.479 (2)
P1–O2
1.575 (2)
P1a–O2a
P1c–O2c
P1–O3
1.573 (3)
P1a–O1a
P1c–O1c
P1–N1
1.615 (3)
N2–C1d
P1a–N1a
P1c–N1c
O2–C1a
1.406 (4)
N1a–C1a
N1c–C1c
O1–P1–O2
O1–P1–O3
O1–P1–N1
O2–P1–O3
O2–P1–N1
N1–N2–C1d
Compound (II)
P1–S1
114.38 (14)
116.30 (14)
110.15 (13)
100.44 (13)
111.67 (14)
116.3 (3)
O3–P1–N1
P1–O2–C1a
P1–O3–C1b
P1–O3–C1c
P1–N1–N2
O2–C1a–C2a
103.11 (15)
119.75 (18)
125.0 (3)
128.4 (3)
120.1 (2)
119.1 (3)
O1a–C6a
1.446 (2)
O1c–C6c
1.447 (2)
O2a–C7a
1.4499 (19)
1.9367 (6)
1.5842 (14)
1.5795 (11)
1.6145 (15)
1.469 (2)
O2c–C7c
1.454 (2)
S1b–P1b
S1d–P1d
1.9341 (6)
1.5841 (14)
1.5807 (11)
1.6142 (16)
1.471 (2)
P1b–O2b
P1d–O2d
P1b–O1b
P1d–O1d
P1b–N1b
P1d–N1d
N1b–C1b
N1d–C1d
1.9390 (7)
1.5819 (16)
1.5853 (13)
1.614 (2)
O1–C4
O2–C5
N1–C1
1.451 (4)
1.446 (3)
1.484 (3)
O1b–C6b
1.454 (2)
O1d–C6d
1.450 (2)
P1–O1
O2b–C7b
1.446 (2)
O2d–C7d
1.441 (2)
P1–O2
O2a–P1a–O1a
O2a–P1a–N1a
O1a–P1a–N1a
O2a–P1a–S1a
O1a–P1a–S1a
N1a–P1a–S1a
C1a–N1a–P1a
C6a–O1a–P1a
C7a–O2a–P1a
O2b–P1b–O1b
O2b–P1b–N1b
O1b–P1b–N1b
O2b–P1b–S1b
O1b–P1b–S1b
N1b–P1b–S1b
C1b–N1b–P1b
C6b–O1b–P1b
C7b–O2b–P1b
Compound (IV)
P1–S1
98.85 (6)
O2c–P1c–O1c
O2c–P1c–N1c
O1c–P1c–N1c
O2c–P1c–S1c
O1c–P1c–S1c
N1c–P1c–S1c
C1c–N1c–P1c
C6c–O1c–P1c
C7c–O2c–P1c
O2d–P1d–O1d
O2d–P1d–N1d
O1d–P1d–N1d
O2d–P1d–S1d
O1d–P1d–S1d
N1d–P1d–S1d
C1d–N1d–P1d
C6d–O1d–P1d
C7d–O2d–P1d
99.21 (6)
P1–N1
104.48 (7)
108.09 (8)
115.37 (5)
114.80 (5)
113.77 (5)
125.21 (11)
119.51 (10)
119.29 (10)
99.33 (6)
104.75 (7)
107.31 (8)
115.25 (5)
114.35 (5)
114.45 (5)
123.52 (11)
118.71 (10)
119.61 (10)
99.15 (6)
S1–P1–O1
S1–P1–O2
S1–P1–N1
O1–P1–O2
O1–P1–N1
114.90 (7)
115.07 (6)
112.87 (5)
99.12 (7)
O2–P1–N1
P1–O1–C4
P1–O2–C5
P1–N1–C1
N1–C1–C3
107.30 (10)
119.05 (13)
119.53 (11)
125.83 (13)
108.35 (15)
106.34 (9)
[2-Cl-C6H4CH2NH3]2[(CH3S)P(O)(O)–O–
P(O)(O)(SCH3)] (IV)
106.41 (8)
105.97 (7)
115.24 (5)
115.27 (5)
113.25 (5)
124.98 (11)
119.27 (10)
119.01 (10)
106.73 (8)
105.86 (7)
114.72 (5)
115.43 (5)
113.56 (5)
124.73 (11)
119.48 (10)
119.39 (10)
A procedure similar to the one described for (II) and (III)
was used; however, the hydrolysis happened in the synthesis
process (due to a few moisture remained in CH3CN) to yield
the pyrophosphate (IV). 2-Chlorobenzylamine, 2-Cl-C6H4
CH2NH2, was added slowly to a stirred solution of (CH3O)2
P(S)Cl (2:1 mol ratio) in CH3CN at ice-bath temperature.
After 4 h, the solvent was removed and the solid formed was
washed with distilled water. Single crystals, suitable for
X-ray crystallography, were obtained from a solution of
product in a CHCl3/CH3C(O)CH3/CH3OH mixture (1:1:1
v/v/v) by slow evaporation at room temperature. The re-
arrangement in the (CH3O)P(S)(O) fragment and transfor-
mation to (CH3S)P(O)(O) is surprising. As the product was
fortuitously obtained, good NMR data were not recorded. IR
(KBr, cm-1): 2170–3147 (b), 2975, 2938, 2747, 2672, 2612,
1730, 1478, 1394, 1243, 1175, 1036, 896, 850, 806, 754,
694.
2.0732 (13)
1.489 (3)
P2–O4
1.473 (3)
1.487 (3)
1.497 (7)
1.489 (7)
106.91 (14)
117.55 (16)
112.7 (4)
114.0 (4)
P1–O1
P2–O5
P1–O2
1.482 (3)
N1a–C7a
P2–S2
2.0832 (14)
110.88 (13)
106.59 (14)
119.51 (17)
110.35 (13)
N1b–C7b
S2–P2–O5
O4–P2–O5
N1a–C7a–C2a
N1b–C7b–C2b
S1–P1–O1
S1–P1–O2
O1–P1–O2
S2–P2–O4
123

Struct Chem
structures based on the same diffraction data and the
structures with disorder in the target angle. So, the set of
282 structures with P–O–C bond angles was finally con-
sidered in our study. The P–O–C bond angles vary in the
range of 108°–132° with the maximum population within
120°–122° (189 hits of the total hits of 706, about 27 %),
shown as histogram in Fig. 1. The maximum population of
angles is near to the angle of sp2 orbitals, similar to what
was previously found for the P–N–C angles in P(O)(N)3
[14] and P(S)(N)3 [7] structures with the N atom in a three-
coordinate (P)N(X)(Y) environment, X = C, Y is any atom
from CSD.
Analysis of P–O–C bond angles in compounds
with a P(S)(O–C)2-x(O)x(N) fragment (x = 0, 1)
The P–O–C bond angles were also analyzed for compounds
with a similar skeleton to compounds (II) and (III), i.e.,
P(S)(O)2(N)-based structures, and including at least one P–
O–C angle. After applying criteria similar to what was noted
in the previous section, the set of 186 structures was con-
sidered for analysis. The P–O–C bond angles vary in the
range of 106°–140° with the maximum population in the
similar region of P(O)(O)2(N)-based structures within 120°–
122° (119 hits of the total hits of 518, about 23 %). The
histogram is shown in Fig. 2. The data in the P(S)(O)2(-
N) structures are spread in a wider range with respect to the
data for the P(O)(O)2(N) structures, due to diverse types of
structures within this family of compounds. For example,
the minimum P–O–C angle is related to the compound with
refcode BEVGAK [27] which includes the noted angle in a
five-member heterocyclic ring, and the maximum value is
related to the structure with refcode PALWUU [28] with a
ten-member heterocyclic ring. The chemical structures of
refcodes discussed are given in Table 1.
Fig. 1 Histogram of P–O–C angles in structures with a P(O)(O–
C)2-x(O)x(N) fragment (x = 0, 1) deposited in the CSD
Analysis of P–S–C bond angles in compounds
with a P(O)(O)2(S–C) fragment
Fig. 2 Histogram of P–O–C angles in structures with a P(S)(O–
C)2-x(O)x(N) fragment (x = 0, 1) deposited in the CSD
For a comparison with P–O–C, the P–S–C bond angles
were analyzed for the compounds with the same skeleton to
the compound (IV), i.e., P(O)(O)2(S). The CSD yielded
only 11 relevant structures (11 P–S–C angles), including a
P(O)(O)2(S–C) fragment, with the P–S–C bond angles
within 97.4°–104.8°. As a few data exist in the CSD for this
skeleton, the histogram was not considered. For these data,
8 hits are within 100°–104° which are significantly (about
20°) less than the maximum population of bond angles
found for the P–O–C angles in both two previously men-
tioned families. The P–S–P and P–S–S angles were also
found in the P(O)(O)2(S) structures from the CSD (5 hits in
4 structures) ranging from 102.2° to 108.8°. The differ-
ences between P–S–P angles (the average value of 103.6°
Results and discussion
CSD analysis
Analysis of P–O–C bond angles in compounds
with a P(O)(O–C)2-x(O)x(N) fragment (x = 0, 1)
The P–O–C bond angles were analyzed for compounds
with a similar skeleton to compound (I), i.e., P(O)(O)2(N),
and including at least one P–O–C angle. The CSD in ver-
sion 5.37 (updated in February 2016) was applied, and the
search filters were used to remove metal complexes,
compounds without any P–O–C bond angle, duplicated
123

Struct Chem
Fig. 3 Histogram of P–O–P
angles in structures with a
P(O)–O–P(O) skeleton
deposited in the CSD
for 3 hits) with those of P–O–P angles (around 130°, dis-
cussed in the next section) are also significant.
(OCP) does not act as a hydrogen bond acceptor showing its
low Lewis base character. Only four exceptions were found
out of 175 structures. In one of these structures (DANHIJ
Analysis of P–O–P bond angles
[31]), the NH unit involves in N–H(ÁÁÁO=P)(ÁÁÁOCP
)
hydrogen bond. In the structure with CSD refcode DAN-
MAG [32], the spatial distances between the N atom with
The P–O–P bond angles were analyzed for the compounds
with a P(O)–O–P(O) skeleton with any restriction on the other
two atoms attached to phosphorus. A dataset of 187 relevant
structures including 538 P–O–P bond angles was used for this
discussion. The P–O–P bond angles vary in the range of
102°–144° with the maximum population at 132°–134° (121
hits, about 22 %), shown as histogram in Fig. 3. The mini-
mum value is related to a cyclic compound (refcode
ATEXAY01 [29]), and the maximum value is related to a
cation–anion structure with refcode SOYRAZ [30]. It seems
that the involvement of all of the terminal oxygen atoms of
the [(O)3P–O–P(O)3]-4 anion is responsible to such a high P–
O–P angle in SOYRAZ. The data of P–O–P angles are more
concentrated within 124°–140° (about 97 %), and also there
is not any data within 104°–118°. The bond angles at the
maximum populations are in accordance with the hybridiza-
tion with more participation of ‘‘s’’ orbital compared to the
sp2 for the oxygen atom at the P–O–P moiety.
˚
two oxygen atoms (below 3 A) also propose the N–
H(ÁÁÁO=P)(ÁÁÁOCP) hydrogen bond; however, it does not
have hydrogen atoms positions determined, and the judg-
ment is along with caveat. In one other structure
(EPGUAN10 [33]), five NH2 units are present and all of
Hydrogen bonding interactions involving
in the oxygen and sulfur atoms of the noted
structures
A CSD analysis on compounds with a P(O)(O)2(N) skele-
ton and with at least one NH or OH unit and also at least
with one P–O–C shows that the oxygen atom of P–O–C
Fig. 4 Displacement ellipsoid plot (50 % probability) is shown for
(I) with atom numbering scheme. H atoms are drawn as spheres of
arbitrary radii. Dashed lines indicate disordered C6H5 ring
123

Struct Chem
˚
the sites possible for hydrogen bond acceptor capability (N,
Cl and the oxygen atoms of P=O and P–O–C) take part in
hydrogen bonding interaction. In the remaining structure
(IJUMAB [34]), the P=O group takes part in the (C–
HÁÁÁ)(C–HÁÁÁ)O hydrogen bonding and the OCP atom takes
part in a week N–HÁÁÁO hydrogen bond interaction. This
finding is due to the better hydrogen bond acceptor capa-
bility of the oxygen atom of P=O group versus the oxygen
atom of P–O–C. This is similar to the low Lewis base
characteristic of the nitrogen atom of P(O)(N)3, which was
studied through a CSD analysis [3].
Table 6 Hydrogen bond geometry (A, °) for compound (I)
D–HÁÁÁA
D–H
HÁÁÁA
DÁÁÁA
D–HÁÁÁA
N1–H1n1ÁÁÁO1a
0.881 (15) 2.035 (15) 2.911 (4) 173 (4)
N2–H1n2ÁÁÁO1b
0.88 (3)
2.22 (3)
3.095 (4) 172 (3)
3.354 (5) 168.55
C6d–H1c6dÁÁÁO3b 0.96
2.41
a
Symmetry codes: -x ? 1, -y, -z; x, y - 1, z
b
A similar analysis for compounds with a P(S)(O)2
(N) skeleton and including at least one NH or OH unit and
at least one P–O–C was performed for a comparison
between the hydrogen bond acceptor capability of the
sulfur atom of P=S group and the oxygen atom of P–O–C
fragment. From 120 structures, 49 structures include the N–
HÁÁÁS=P hydrogen bond (and one structure includes O–
HÁÁÁS=P hydrogen bond), while 17 structures include N–
HÁÁÁOCP hydrogen bond. This analysis shows, however, the
sulfur atom makes a weak hydrogen bond, but the hydro-
gen bond acceptor capability of sulfur atom of P=S group is
larger than one for the oxygen atom of P–O–C. The dif-
ferences in the hydrogen bond acceptor capabilities of P=S
and OCP are less than the differences found in comparing
P=O group and OCP atom. Among the structures noted, 2
ones show both N–HÁÁÁS=P and N–HÁÁÁOCP hydrogen
Fig. 6 Displacement ellipsoid plot (50 % probability) is shown for
(II) with atom numbering scheme. H atoms are drawn as spheres of
arbitrary radii
bonds. In the remaining 55 structures, there are other
acceptor groups which take part in hydrogen bonding
interaction or the compound does not show the classical
hydrogen bond. These observations are important in crystal
engineering concepts for structures with P(O)(O–C)(NH)
and P(S)(O–C)(NH) moieties: While in the former, the
P=O group dominates the hydrogen bond pattern as a
prominent hydrogen bond acceptor, there is a competition
between P=S and OCP in the latter moiety with only
slightly better capability for accepting H atom by P=S
group.
X-ray crystallography experiments for new
structures
Structure (I) was studied as an example including the P
atom within a distorted tetrahedral P(O)(O)2(N) environ-
ment (Fig. 4). The P=O and P–N bond lengths [of 1.471 (2)
˚
and 1.615 (3) A, respectively] are within the standard
ranges for analogous compounds [12]. The bond angles at
the P atom vary in the range 100.44 (13)° [O2–P1–O3] to
116.30 (14)° [O1–P1–O3]. Of the two N atoms in the C6
H5NHNH group, atom N2 has more pronounced sp3-hy-
bridization relative to atom N1, which is almost perfectly
planar environment (the bond angle sums are 349 (2)° and
Fig. 5 Crystal packing for structure (I), the N–HÁÁÁO=P hydrogen
bonds are shown as dashed lines. The weakly occupied atoms and
hydrogen atoms not involved in hydrogen bonding were omitted for
the sake of clarity
123

Struct Chem
Fig. 7 Displacement ellipsoid plot (50 % probability) is shown for structure (III) with atom numbering scheme. H atoms are drawn as spheres of
arbitrary radii
˚
359 (3)°, respectively). The P1–O2–C1a bond angle is
119.75 (18)°, and the other OC6H5 group indicates disorder
over two sites. The resulting occupancy ratio of disordered
phenyl positions was refined as 0.547 (3):0.453 (3). In the
crystal structure, molecules are linked via (N–HÁÁÁ)(N–
Table 7 Hydrogen bond geometry (A, °) for compound (II)
D–HÁÁÁA
D–H
HÁÁÁA
DÁÁÁA
D–HÁÁÁA
N1–H1N1ÁÁÁS1a
Symmetry code: -x ? 2, -y ? 1, -z ? 1
0.82 (2)
2.68 (3)
3.4770 (19)
163 (3)
a
HÁÁÁ)O=P hydrogen bonds into
a
one-dimensional
arrangement parallel to the b axis (Fig. 5; Table 6). This
arrangement includes alternating R22(8) and R42(10) hydro-
gen-bonded ring motifs (for graph-set notation, see Ref.
[35]).
independent molecules (Fig. 7). The P=S bond lengths [of
˚
1.9390 (7) A for (II) and 1.9346 (6), 1.9367 (6), 1.9336 (6)
˚
and 1.9341 (6) A for (III)] are within the expected values
For a comparison with compound (I), compounds (II)
and (III) including P(S)(O)2(N) skeleton were synthesized.
The asymmetric unit of (II) is composed of one complete
molecule (Fig. 6), and for (III) it contains four symmetry
for compounds with a P(S)(O)2(N) skeleton [6]. The P–N
˚
bond lengths [of 1.614 (2) A for (II) and 1.6152 (15),
˚
1.6145 (15), 1.6141 (15) and 1.6142 (16) A, for (III)] are
within the expected range for P(S)(O)2(N)-based structures
and are shorter than the maximum population of P–N
bonds found for P(S)(N)3-based structures [6].
In structure (II), the bond angles at the P atoms vary in
the sequence S=P–O [ S=P–N [ O–P–N [ O–P–O as
follows S1–P1–O2 115.07 (6)°, S1–P1–O1 114.90 (7)°,
S1–P1–N1 112.87 (5)°, O2–P1–N1 107.30 (10)°, O1–P1–
N1 106.34 (9)°, O1–P1–O2 99.12 (7)°. In one of the
molecules of the structure (III), however, the maximum
angle is one of the S=P–O angles [O2c–P1c–S1c 115.25
(5)°], but the S=P–N is only slightly larger than the other
S=P–O angle, and the difference is within esd [O1c–P1c–
S1c angle of 114.35 (5)° and N1c–P1c–S1c angle of 114.45
(5)°]. For this molecule, the minimum angle is 99.21 (6)°
(O2c–P1c–O1c) and the two O–P–N angles follow the
sequence noted. The sequence of bond angles at the P atom
is also valid for the other three molecules in structure (III),
Fig. 8 A view of centrosymmetric dimer in structure (II) built from a
pair of N–HÁÁÁS=P hydrogen bonds
123

Struct Chem
Fig. 9 A view of symmetrically independent non-centrosymmetric
dimers in structure (III) is shown. Each dimer is built from two
different N–HÁÁÁS=P hydrogen bonds and the dimers are further
connected via non-classical hydrogen bonds C–HÁÁÁO. Different
colors introduce symmetry independent molecules (Color
figure online)
Table 8 Hydrogen bond
˚
D–HÁÁÁA
D–H
HÁÁÁA
DÁÁÁA
D–HÁÁÁA
geometry (A, °) for compound
(III)
N1a–H1n1aÁÁÁS1b
N1b–H1n1bÁÁÁS1a
N1c–H1n1cÁÁÁS1d
N1d–H1n1dÁÁÁS1c
0.880 (7)
0.880 (8)
0.880 (11)
0.880 (11)
2.720 (11)
2.590 (11)
2.665 (13)
2.563 (14)
3.5738 (14)
3.4449 (15)
3.5242 (15)
3.4169 (15)
163.8 (15)
164.3 (15)
165.6 (14)
164.0 (14)
with the maximum/minimum values of 115.37 (5)°/98.85
(6)° for P1a, 115.27 (5)°/99.33 (6)° for P1b and 115.43
(5)°/99.15 (6)° for P1d. In structures (II) and (III), the bond
angle sums at the nitrogen atoms correspond to the planar
geometry, for example, 359 (2)° in structure (II). Similar to
compound (I), in compounds (II) and (III), the P–O–C
angles are close to 120°: 119.05 (13)° and 119.53 (11)° in
compound (II) and within 118.71 (10)° to 119.61 (10)° in
four independent molecules in structure (III).
HÁÁÁS=P hydrogen bonds between two symmetry indepen-
dent molecules (Fig. 9; Table 8).
Compound (IV) is the first diffraction study of a salt
with an [S]P[O][O]–O–P[O][O][S] skeleton in the anion
component, Fig. 10. It should be mentioned that through a
search of (S)P(O)(O)(O) on the CSD, the structures of the
following salts were found: BOKSUP [36], HAXRAZ [37]
and MAXDOG [38]. Moreover, there are two zwitterionic
structures GEYMUS [39] and KIVFAW [40] in the CSD.
The asymmetric unit of (IV) is composed of two sym-
metrically independent [2-Cl-C6H4CH2NH3]? cations and
one [{[CH3S]P[O][O]}2O]-2 dianion (Fig. 10). The main
differences of the cations are reflected in the torsion angles
N1a–C7a–C2a–C1a [80.0 (5)°] and N1b–C7b–C2b–C1b
[-91.8 (6)°]. In the dianion, the P atoms are bonded in a
distorted tetrahedral P(O)(O)(O)(S) environment in which
the two (CH3S)P(O)(O) parts are bridged via an O atom.
In structure (II), the N–H unit and P=S group adopt a syn
orientation with respect to each other which is a suit-
able orientation for forming a centrosymmetric hydrogen-
bonded dimer through intermolecular N–HÁÁÁS=P hydrogen
bonds (Fig. 8; Table 7). The orientations of N–H unit and
P=S group in four symmetry independent molecules of the
structure (III) are also syn. Hence, two symmetrically
independent non-centrosymmetric dimers exist in the
structure with each dimer built through two different N–
˚
The P1–O3 [1.618 (3) A] and P2–O3 [1.614 (3) A] bond
˚
123

Struct Chem
˚
Table 9 Hydrogen bond geometry (A, °) for compound (IV)
D–HÁÁÁA
D–H
HÁÁÁA
DÁÁÁA
D–HÁÁÁA
N1a–H1n1aÁÁÁO5
N1a–H2n1aÁÁÁO2a
N1a–H3n1aÁÁÁO1b
N1b–H1n1bÁÁÁO1c
N1b–H2n1bÁÁÁO5b
N1b–H3n1bÁÁÁO4
0.88 (4)
0.88 (3)
0.88 (4)
0.88 (3)
0.88 (4)
0.88 (4)
2.00 (4)
1.91 (4)
1.90 (4)
2.03 (3)
1.91 (4)
1.81 (4)
b
2.844 (4)
2.719 (5)
2.779 (5)
2.835 (4)
2.780 (5)
2.685 (5)
160 (4)
151 (5)
173 (5)
151 (4)
170 (4)
177 (5)
a
Symmetry codes: x - 1, y, z;
-x ? 1, y - 1/2, -z ? 2;
c
-x ? 2, y - 1/2, -z ? 2
C4H9NH]2P(O)}2O HAXQOO [42]. The C–S–P angles
[99.0 (2)° and 100.9 (2)°] are in accordance with the angles
of S atoms within a di-coordinated [P]S[Y] environment
and are closer than the C–O–P angles (discussed in the
section of CSD analysis).
Fig. 10 Displacement ellipsoid plot (50 % probability) is shown for
the asymmetric unit of (IV) with atom numbering scheme. H atoms
are drawn as spheres of arbitrary radii
In the crystal, the cations and dianions are hydrogen-
bonded to each other, through N–HÁÁÁO hydrogen bonds, in
a two-dimensional network parallel to the ab plane
(Fig. 11; Table 9), so that all of the six N–H units of two
independent cations and four of the oxygen atoms of
lengths and P1–O3–P2 angle [132.6 (2)°] are standard for
the P–O–P fragment, such as reported in {[(CH3)2N][4–
CH3–C6H4–O]P(O)}2(O) DUPCOH [41] and {[tert-
Fig. 11 Crystal packing of the structure (IV), the N–HÁÁÁO=P hydrogen bonds are shown as dashed lines. Dianion is shown as green color and
two symmetry independent cations are represented as blue and red colors (Color figure online)
123

Struct Chem
Scheme 2 Chemical structure
of P(S)(OCH3)2(NHCH(CH3)2)
dianion, apart from the bridging O atom, take part in
hydrogen bond pattern. In this aggregation, each dianion is
hydrogen-bonded to six neighboring cations, whereas each
cation is hydrogen-bonded to three adjacent dianions. Due
to cooperating of smaller numbers of hydrogen bond
acceptors with respect to the number of hydrogen bond
donors, two of the oxygen atoms of each dianion act as a
double-hydrogen bond acceptor [12] to form (N–HÁÁÁ)2O
groups. The strong positive/negative charge-assisted
hydrogen bonds (for a definition of different types of
hydrogen bonds, see [43]) exist in the title salt, especially
received by O2 and O4 atoms, which have relatively short
distances of donor…acceptor. The (N–HÁÁÁ)2O hydrogen
bonds received by the O1 and O5 atoms are relatively
weaker in this structure due to the anti-cooperativity effect
[44] in the atoms which act as a double-hydrogen bond
acceptors in the crystals.
Scheme 3 Chemical structure
P(S)(OCH3)2(NH-cyclo-
of
C5H9)
Spectroscopic study (NMR, IR)
The chemical structures of compounds (I), (II), (III) and
(IV) are given in Schemes 1, 2, 3 and 4, respectively. The
31P{1H} signals of compounds (I) and (II) (in DMSO-d6)
are revealed at -1.49 and 74.83 ppm, respectively. The 31
P
1
and H NMR experiments of compound (III) were previ-
ously reported (in CDCl3), and the 31P{1H} signal in the
present work at 75.16 ppm is in accordance with the pub-
lished value (74.52 ppm) [19]. In the 1H NMR spectrum of
(I), two doublet signals at 7.60 (JH–P = 3.9 Hz) and 7.92
(JH–P = 41.2) ppm are related to the NH protons of the
P(O)NHNH moiety. The considerable difference in cou-
pling constants is similar to that was observed in com-
pounds with a PNHNH fragment, like for example in
(CH3CH2O)2P(S)(NHNHC6H5) with JH–P = 3.9 and
Scheme 4 Chemical structure of [2-Cl-C6H4CH2NH3]2[(CH3
S)P(O)(O)–O–P(O)(O)(SCH3)]
published value of 12.0 Hz for (III) [19]). The CH proton
of –CH(CH3)2 group indicates a ddh fine structure due to
the coupling with P atom, NH proton and the hydrogen
atoms of two adjacent CH3 groups. The NH protons of (II)
and (III) are revealed at 5.45 and 5.55 ppm, respectively,
both signals with a dd pattern, similar to the literature value
of 3.72 for (III) in CDCl3 with a dd pattern [19].
1
43.0 Hz [6]. In the H NMR experiments of (II) and (III),
the hydrogen atoms of –OCH3 groups show the coupling
with the P atom (3J = 13.6 Hz for both (II) and (III), the
In the 13C NMR spectrum of (I), the doublet signals at
150.57 (2JC–P = 6.9 Hz) and 120.35 (3JC–P = 4.7 Hz) ppm
are, respectively, assigned to the ipso- and ortho-carbon
atoms of the OC6H5 group and the other doublet signal at
149.59 ppm (3JC–P = 4.8 Hz) is assigned to the ipso-car-
bon atom of the NHNHC6H5 group. The chemical shifts
and coupling constants values of (I) are in accordance with
the values published [20] with a few differences due to the
amount of solute in NMR solvent.
For (II) and (III), the doublet signals at 52.62
(2J = 5.1 Hz) and 52.57 (2J = 4.9 Hz) ppm are assigned
to the carbon atoms of related OCH3 groups, respectively
[the assignment of the 13C NMR was performed by running
2D HSQC experiment]. Furthermore, for compound (II),
two doublet signals at 43.82 and 24.68 ppm are assigned to
the CH and CH3 carbon atoms of the –CH(CH3)2 group,
Scheme 1 Chemical structure of P(O)(OC6H5)2(NHNHC6H5)
123

Struct Chem
respectively, with |3JC–P| = 5.7 Hz [ |2JC–P| = 1.7 Hz.
For compound (III), the doublet signals at 53.37 and
33.80 ppm are assigned to the carbon atoms with two and
three bonds separations from the P atom, showing
|3JC–P| = 5.7 Hz [ |2JC–P| = 2.3 Hz.
The NH vibration stretching frequencies of compound
(I) centered at 3296 and 3211 cm-1 are appeared at the
lower wave numbers with respect to those of compounds II
(3312 cm-1) and (III) (3314 cm-1), due to the stronger N–
HÁÁÁO=P hydrogen bond in (I) with respect to weaker N–
HÁÁÁS=P hydrogen bonds in (II) and (III). For (IV), a broad
bond is observed within 2170–3147 cm-1 attributed to the
NH stretching frequencies involved in hydrogen bonding.
11. Groom CR, Bruno IJ, Lightfoot MP, Ward SC (2016) Acta
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CCDC numbers of (I), (II), (III) and (IV) are 1,469,940,
1,469,941, 1,469,942 and 1,469,943, respectively. 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.
ˇ´ˇ
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Acknowledgments Financial support of this work by Zanjan Branch,
Islamic Azad University is gratefully acknowledged. The X-ray part
of the work was carried out with the support of X-ray Diffraction and
Bio-SAXS Core Facility of CEITEC, and the ASTRA lab established
within the Operation program Prague Competitiveness—project
CZ.2.16/3.1.00/24510.
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