Pnicogen, halogen and hydrogen bonds in (E)-1-(2,2-dichloro-1-(2-nitrophenyl)vinyl)-2-(para-substituted phenyl)-diazenes

Article abstract of DOI:10.1016/j.dyepig.2018.06.022

Schiff base condensation of 2-nitrobenzaldehyde with (para-substituted phenyl)hydrazine in the presence of CH₃COONa in EtOH at 80 °C produces (E)-1-(para-substituted phenyl)-2-(2-nitrobenzylidene)hydrazines [?OCH₃ (1), ?CH₃

Full text of DOI:10.1016/j.dyepig.2018.06.022

DyesandPigments159(2018)135–141
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Pnicogen, halogen and hydrogen bonds in (E)-1-(2,2-dichloro-1-(2-
nitrophenyl)vinyl)-2-(para-substituted phenyl)-diazenes
Abel M. Maharramova, Namiq Q. Shikhaliyeva, Gulnar T. Suleymanovaa, Atash V. Gurbanova,b
Gulnara V. Babayevaa, Gunay Z. Mammadovaa, Fedor I. Zubkovc, Valentine G. Nenajdenkod,
Kamran T. Mahmudovb,e,∗, Armando J.L. Pombeirob,∗∗
,
a
Organic Chemistry Department, Baku State University, Z. Xalilov Str. 23, Az 1148, Baku, Azerbaijan
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049–001, Lisbon, Portugal
Organic Chemistry Department, Faculty of Science, Peoples' Friendship University of Russia (RUDN University), 6 Miklukho-Maklaya St., Moscow, 117198, Russian
Federation
Department of Chemistry, M. V. Lomonosov Moscow State University, 1 Leninskie Gory, 119992, Moscow, Russian Federation
b
c
d
e
Department of Ecology and Soil Sciences, Baku State University, Z. Xalilov Str. 23, Az 1148, Baku, Azerbaijan
A R T I C L E I N F O
A B S T R A C T
Keywords:
Schiff base condensation of 2-nitrobenzaldehyde with (para-substituted phenyl)hydrazine in the presence of
CH3COONa in EtOH at 80 °C produces (E)-1-(para-substituted phenyl)-2-(2-nitrobenzylidene)hydrazines
[−OCH3 (1), −CH3 (2), −H (3), −Br (4), −Cl (5), −F (6)]. CuCl catalyzed olefination of 1−6 with CCl4 in the
presence of tetramethylethylenediamine (TMEDA) in DMSO leads to (E)-1-(2,2-dichloro-1-(2-nitrophenyl)vinyl)-
2-(para-substituted phenyl)-diazenes [−OCH3 (7), −CH3 (8), −H (9), −Br (10), −Cl (11), −F (12)], re-
spectively. 1–12 were characterized by 1H and 13C NMR spectroscopies, ESI-MS, elemental and X-ray diffraction
(for 8, 9 and 12) analysis. The single crystal X-ray analysis of 8, 9 and 12 evidence the intramolecular N⋯Cl
pnicogen bonds which is significantly strengthened in view of the planarity of the four atoms involved in the 1,4-
membered synthon. The intermolecular halogen and hydrogen bonds also contribute to stabilize the crystal
structures of 8, 9 and 12. In DMSO solution 1–12 exist in the E-isomeric form, which stabilized by inter- and
intramolecular noncovalent interactions. Solvatochromic behavior on UV–vis absorption spectra of azo dyes
7–12 were studied in CH2Cl2, DMF and MeOH, which λmax is dependent on the attached substituents at para-
position of aromatic moiety.
Pnicogen bonding
Halogen bonding
Hydrogen bonding
Noncovalent interactions
Azo dyes
1. Introduction
intermolecular version, the examples on intramolecular noncovalent
interactions are limited, which they can also play a crucial role in
Noncovalent interactions are known to be responsible for the con-
formation of organic and inorganic molecules [1,2]. Due to the fun-
damental importance of “σ-hole” interactions, such as halogen bonding,
chalcogen bonding, pnicogen bonding, and tetrel bonding, in crystal
packing and supramolecular assembly, these specific noncovalent in-
teractions have become a hot topic in synthesis, catalysis and design of
materials [3–8]. Similarly, to the hydrogen bonds [9–11], the “σ-hole”
bonds can also be classified into several fundamental types: negative
charged assisted, positive charged assisted, conventional (or “neutral”)
and resonance assisted halogen, chalcogen, pnicogen or tetrel bonds.
The strength of these directional interactions, and then their ability to
organize/control the formation of supramolecular assemblies, de-
pending on their intra- and intermolecular versions. In comparison to
synthesis, catalysis, crystal engineering, drug design and delivery, etc.
[7,8,11–21]. In the present work, we report the role of intramolecular
N⋯Cl pnicogen bond as well as intermolecular halogen and hydrogen
bonds in the synthesis and design of diazene dyes.
In recent years, copper-catalyzed transformation of hydrazones into
halogenated diazenes (catalytic olefination) have received increasing
research interest [22,23], due to the cooperative actions of conjugated
N=N and C=C bonds leading to chromophoric properties [24]
(Scheme 1). Intramolecular N⋯Cl pnicogen bond can also contribute to
N=N and C=C conjugation in diazene dyes and absorb some wave-
length visible light photon energy. We therefore decided to system-
atically investigate the structure-property relationship of a series of (E)-
1-(2,2-dichloro-1-(2-nitrophenyl)vinyl)-2-(para-substituted
phenyl)-
∗
Corresponding author. Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049–001, Lisbon, Portugal.
Corresponding author.
∗∗
E-mail addresses: kamran_chem@mail.ru, kamran_chem@yahoo.com (K.T. Mahmudov), pombeiro@tecnico.ulisboa.pt (A.J.L. Pombeiro).
https://doi.org/10.1016/j.dyepig.2018.06.022
Received 17 May 2018; Received in revised form 13 June 2018; Accepted 15 June 2018
Availableonline19June2018
0143-7208/©2018ElsevierLtd.Allrightsreserved.

A.M. Maharramov et al.
DyesandPigments159(2018)135–141
Scheme 1. Synthesis of 1–12.
diazenes in terms of their intramolecular pnicogen bond as well as in-
termolecular halogen bond strength (Scheme 1). The para-substituents
on the aromatic moiety range from typical electron donating groups
(−OCH3 and −CH3) to typical electron withdrawing ones (−Br, −Cl
and −F).
MS: m/z: 256.26 [M+H]+
3: red solid (92%); mp 150 °C. Anal. Calcd for
.
C
13H11N3O2
(M = 241.25): C, 64.72; H, 6.81; N, 17.03; found: C, 64.66; H, 6.77; N,
17.00%. 1H NMR (300 MHz, DMSO‑d6): δ 10.89 (s, 1H, NH), 8.26 (s,
1H, CH), 8.16 (d, J = 8.10 Hz, 1H, arom), 7.96 (d, J = 8.29 Hz, 1H,
arom), 7.70 (t, J = 7.54 Hz, 1H, arom), 7.48 (t, J = 7.54 Hz, 1H, arom),
7.26 (t, J = 7.35 Hz, 2H, arom), 7.12 (d, J = 7.91 Hz, 2H, arom), 6.82
(t, J = 6.97 Hz, 1H, arom).13C NMR (75 MHz, DMSO‑d6): δ 147.19,
145.00, 133.54, 131.10, 129.68, 128.57, 127.42, 124.96, 120.25,
2. Experimental
2.1. Materials and instrumentation
112.89. ESI-MS: m/z: 242.18 [M+H]+
.
4: red solid (95%); mp 170–174 °C. Anal. Calcd for C13H10BrN3O2
(M = 320.15): C, 48.77; H, 3.15; N, 13.13; found: C, 48.71; H, 3.07; N,
13.08%. 1H NMR (300 MHz, DMSO‑d6): δ 11.01 (s, 1H, NH), 8.26 (s,
1H, CH), 8.16 (d, J = 7.91 Hz, 1H, arom), 7.98 (d, J = 8.10 Hz, 1H,
arom), 7.72 (t, J = 7.54 Hz, 1H, arom), 7.52 (t, J = 8.10 Hz, 1H, arom),
7.41 (d, J = 8.85 Hz, 2H, arom), 7.06 (d, J = 8.85 Hz, 2H, arom). 13C
NMR (75 MHz, DMSO‑d6): δ 147.32, 144.33, 133.66, 132.35, 130.09,
128.95, 127.56, 125.04, 123.52, 114.78, 111.17. ESI-MS: m/z: 321.12
All the chemicals were obtained from commercial sources (Aldrich)
and used as received. Infrared spectra (4000–400 cm−1) were recorded
on a Vertex 70 (Bruker) instrument in KBr pellets. Carbon, hydrogen,
and nitrogen elemental analyses were done using a “2400 CHN
Elemental Analyzer” (Perkin Elmer). The 1H and 13C NMR spectra were
recorded on Bruker Advance II+ 300.13 (75.468 carbon-13) MHz
(UltraShield™ Magnet) spectrometer at ambient temperature. The che-
mical shifts are reported in ppm using tetramethylsilane as the internal
reference. Electrospray mass spectra (ESI-MS) were run with an ion-trap
instrument (Varian 500-MS LC Ion Trap Mass Spectrometer) equipped
with an electrospray ion source. For electrospray ionization, the drying
gas and flow rate were optimized according to the particular sample
with 35 p.s.i. nebulizer pressure. Scanning was performed from m/z 0 to
1100 in methanol solution. The compounds were observed in the po-
sitive mode (capillary voltage = 80–105 V). The UV–vis absorption
spectra in the 200–700 nm regions were recorded with a scan rate of
[M+H]+
.
5: pink solid (80%); mp 183 °C. Anal. Calcd for C13H10ClN3O2
(M = 275.69): C, 56.64; H, 3.66; N, 15.24; found: C, 56.59; H, 3.58; N,
15.20%. 1H NMR (300 MHz, DMSO‑d6): δ 11.01 (s, 1H, NH), 8.26 (s,
1H, CH), 8.16 (d, J = 7.72 Hz, 1H, arom), 7.98 (d, J = 8.29 Hz, 1H,
arom), 7.72 (t, J = 7.35 Hz, 1H, arom), 7.52 (t, J = 7.35 Hz, 1H, arom),
7.29 (d, J = 8.67 Hz, 2H, arom), 7.10 (d, J = 8.67 Hz, 2H, arom). 13C
NMR (75 MHz, DMSO‑d6): δ 147.32, 143.95, 133.65, 132.12, 130.10,
128.92, 127.56, 125.02, 114.29. ESI-MS: m/z: 276.56 [M+H]+
.
240 nm∙min−1 by using
a Lambda 35 UV–vis spectrophotometer
6: red solid (93%); mp 150 °C. Anal. Calcd for C13H10FN3O2
(M = 259.24): C, 60.23; H, 3.89; N, 16.21; found: C, 60.19; H, 3.81; N,
16.15%. 1H NMR (300 MHz, DMSO‑d6): δ 10.90 (s, 1H, NH), 8.23 (s,
1H, CH), 8.15 (d, J = 7.91 Hz, 1H, arom), 7.97 (d, J = 8.10 Hz, 1H,
arom), 7.71 (t, J = 7.54 Hz, 1H, arom), 7.49 (t, J = 7.91 Hz, 3H, arom),
7.10 (d, J = 6.59 Hz, 4H, arom). 13C NMR (75 MHz, DMSO‑d6): δ
158.46, 155.34, 147.17, 141.65, 133.57, 131.15, 128.62, 127.44,
(Perkin-Elmer) in 1.00 cm quartz cells at room temperature, with a
concentration of 7−12 of 1.00∙10−6 mol L−1 in CH2Cl2, DMF or MeOH.
2.2. Synthesis of 1–6
Schiff bases 1–6 were synthesized according to the reported method
[23,24]. A mixture of 2-nitrobenzaldehyde (10 mmol), CH3COONa
(0.82 g), ethanol (50 mL) and corresponding (para-substituted phenyl)
hydrazine (10.2 mmol) was refluxed at 80 °C with stirring for 2 h. The
reaction mixture was cooled to room temperature and water (50 mL)
was added to give a precipitate of crude product, which filtered off,
washed with diluted ethanol (1:1 with water) and dried in vacuo of
rotary evaporator.
124.99, 116.40, 116.10, 113.93. ESI-MS: m/z: 260.20 [M+H]+
.
2.3. Synthesis of 7–12
Diazene dyes 7–12 were synthesized according to the reported
method [23,24]. A 20 mL screw neck vial was charged with DMSO
(10 mL), 1, 2, 3, 4, 5 or 6 (1 mmol), tetramethylethylenediamine
(TMEDA) (295 mg, 2.5 mmol), CuCl (2 mg, 0.02 mmol) and CCl4
(20 mmol, 10 equiv). After 1–3 h (until TLC analysis showed complete
consumption of corresponding Schiff base) reaction mixture was poured
into ∼0.01 M solution of HCl (100 mL, ∼pH = 2–3), and extracted
with dichloromethane (3 × 20 mL). The combined organic phase was
washed with water (3 × 50 mL), brine (30 mL), dried over anhydrous
Na2SO4 and concentrated in vacuo of the rotary evaporator. The residue
was purified by column chromatography on silica gel using appropriate
mixtures of hexane and dichloromethane (3/1-1/1), and corresponding
diazene dyes 7–12 were obtained.
7: yellow solid (50%); mp 93–95 °C. Anal. Calcd for C15H11Cl2N3O3
(M = 352.17): C, 51.16; H, 3.15; N, 11.93; found: C, 51.09; H, 3.11; N,
11.90%. 1H NMR (300 MHz, CDCl3): δ 8.23 (d, J = 9.04 Hz, 1H, arom),
7.71 (t, J = 7.72 Hz 1H, arom), 7.69 (d, J = 8.85 Hz, 2H, arom), 7.63
(t, J = 9.04 Hz, 1H, arom), 7.34 (d, J = 7.72 Hz, 1H, arom), 6.92 (d,
J = 8.85 Hz, 2H, arom), 3.86 (s, 3H, OCH3). 13C NMR (75 MHz, CDCl3):
1: pink solid (91%); mp 180–184 °C. Anal. Calcd for C14H13N3O3
(M = 271.28): C, 61.99; H, 4.83; N, 15.49; found: C, 61.93; H, 4.81; N,
15.43%. 1H NMR (300 MHz, DMSO‑d6): δ 10.76 (s, 1H, NH), 8.19 (s,
1H, CH), 8.15 (d, J = 7.72 Hz, 1H, arom), 7.95 (d, J = 8.10 Hz, 1H,
arom), 7.69 (t, J = 7.36 Hz, 1H, arom), 7.46 (t, J = 7.54 Hz, 1H, arom),
7.04 (d, J = 9.04 Hz, 2H, arom). 6.88 (d, J = 8.85 Hz, 2H, arom), 3.70
(s, 3H, OCH3). 13C NMR (75 MHz, DMSO‑d6): δ 149.26, 146.89, 138.86,
133.52, 129.64, 128.14, 127.18, 125.00, 115.17, 113.93, 55.73. ESI-
MS: m/z: 272.22 [M+H]+
.
2: red solid (90%); mp 140–142 °C. Anal. Calcd for C14H13N3O2
(M = 255.28): C, 65.87; H, 5.13; N, 16.46; found: C, 65.83; H, 5.08; N,
16.40%. 1H NMR (300 MHz, DMSO‑d6): δ 10.82 (s, 1H, NH), 8.22 (s,
1H, CH), 8.16 (d, J = 7.91 Hz, 1H, arom), 7.96 (d, J = 8.10 Hz, 1H,
arom), 7.70 (t, J = 7.54 Hz, 1H, arom), 7.47 (t, J = 7.35 Hz, 1H, arom),
7.07 (d, J = 8.48 Hz, 2H, arom), 7.01 (d, J = 8.29 Hz, 2H, arom), 2.50
(s, 3H, CH3). 13C NMR (75 MHz, DMSO‑d6): δ 162.23, 147.03, 142.69,
133.57, 130.28, 130.12, 128.37, 127.28, 125.01, 112.88, 20.74. ESI-
136

A.M. Maharramov et al.
DyesandPigments159(2018)135–141
Table 1
δ 162.83, 146.84, 135.74, 133.56, 132.27, 130.53, 129.95, 129.28,
125.46, 124.40, 114.21, 55.61. ESI-MS: m/z: 353.08 [M+H]+
.
Crystallographic data and structure refinement details for 8, 9 and 12.
8: orange solid (74%); mp 92 °C. Anal. Calcd for C15H11Cl2N3O2
(M = 336.17): C, 53.59; H, 3.30; N, 12.50; found: C, 53.55; H, 3.29; N,
12.46%. 1H NMR (300 MHz, CDCl3): δ 8.21 (d, J = 7.35 Hz, 1H, arom),
7.68 (t, J = 7.16 Hz, 1H, arom), 7.68 (d, J = 7.72 Hz, 2H), 7.60 (t,
J = 7.35 Hz, 1H, arom), 7.34 (d, J = 7.16 Hz, 1H, arom), 7.23 (d,
J = 7.72 Hz, 2H, arom), 2.38 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3): δ
150.59, 150.46, 148.19, 142.95, 134.40, 133.85, 132.32, 130.25,
8
9
12
Empirical formula
fw
Temperature (K)
Cryst. Syst.
Space group
a (Å)
b (Å)
C15H11Cl2N3O2
336.17
296(2)
Triclinic
P-1
8.3927(14)
14.112(3)
14.251(3)
72.648(5)
89.988(6)
80.342(6)
1586.0(5)
4
1.408
0.418
688
0.0720
0.1559
1.015
C14H9Cl2N3O2
322.14
296(2)
Orthorhombic
Pbcn
15.0020 (6)
15.0993 (6)
13.0629 (5)
90
C14H8Cl2FN3O2
340.13
296(2)
Orthorhombic
Pbcn
14.9218(6)
15.3776(6)
13.0918(5)
90
90
90
3004.1(2)
8
1.504
129.85, 128.56, 124.47, 123.47, 21.65. ESI-MS: m/z: 337.10 [M+H]+
.
c (Å)
9: red solid (75%); mp 130 °C. Anal. Calcd for C14H9Cl2N3O2
(M = 322.15): C, 52.20; H, 2.82; N, 13.04; found: C, 52.15; H, 2.78; N,
13.00%. 1H NMR (300 MHz, CDCl3): δ 8.23 (d, J = 8.10 Hz, 1H),
7.73–7.69 (m, 3H, arom), 7.61 (t, J = 8.10 Hz, 1H), 7.44–7.40 (m, 3H,
arom), 7.34 (d, J = 7.54 Hz, 1H, arom). 13C NMR (75 MHz, CDCl3): δ
152.36, 150.40, 148.12, 135.34, 133.77, 132.26, 131.98, 130.22,
α, °
β, °
90
90
γ, °
V (Å3)
Z
2959.0 (2)
8
1.446
0.445
1312
0.0377
0.0934
1.048
ρcalc (g cm−3
)
μ(Mo Kα) (mm−1
F (000)
)
0.452
1376
0.0540
0.1361
1.012
129.09, 128.45, 124.51, 123.38. ESI-MS: m/z: 323.12 [M+H]+
.
R1a (I ≥ 2σ)
wR2b (I ≥ 2σ)
GOOF
10: orange-red solid (63%); mp 75–80 °C. Anal. Calcd for
14H8BrCl2N3O2 (M = 401.04): C, 41.93; H, 2.01; N, 10.48; found: C,
C
41.89; H, 2.00; N, 10.36%. 1H NMR (300 MHz, CDCl3): δ 8.21 (d,
J = 8.10 Hz, 1H, arom), 7.70 (t, J = 7.35 Hz, 1H, arom), 7.62–7.51 (m,
5H, arom), 7.33 (d, J = 7.35 Hz, 1H, arom). 13C NMR (75 MHz, CDCl3):
δ 151.05, 150.46, 148.04, 136.10, 133.87, 132.36, 132.25, 130.36,
a
R1 = Σ||Fo| – |Fc||/Σ|Fo|.
wR2 = [Σ[w(Fo – Fc2)2]/Σ[w(Fo2)2]]1/2
.
b
2
128.17, 126.57, 124.79, 124.56. ESI-MS: m/z: 402.00 [M+H]+
.
Fig. 1. Crystal structures of 8, 9 and 12 with partial atom numbering scheme. Intramolecular pnicogen bonds are shown as dashed pink lines. (For interpretation of
the references to colour in this figure legend, the reader is referred to the Web version of this article.)
137

A.M. Maharramov et al.
DyesandPigments159(2018)135–141
Fig. 2. Intermolecular halogen bonds in 9 and 12 [shown as dashed light blue (Cl⋯O) and red (F···π) lines]. (For interpretation of the references to colour in this
figure legend, the reader is referred to the Web version of this article.)
11: orange-red solid (55%); mp 70–73 °C. Anal. Calcd for
14H8Cl3N3O2 (M = 356.59): C, 47.16; H, 2.26; N, 11.78; found: C,
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.ccdc.cam.ac.uk/data_request/cif).
C
47.11; H, 2.13; N, 11.70%. 1H NMR (300 MHz, CDCl3): δ 8.23 (d,
J = 8.10 Hz, 1H, arom), 7.75–7.59 (m, 4H, arom), 7.40–7.33 (m, 3H,
arom). 13C NMR (75 MHz, CDCl3): δ 150.73, 150.41, 148.07, 137.96,
135.99, 133.82, 132.24, 130.32, 129.37, 128.25, 124.62, 124.56. ESI-
Table 2
MS: m/z: 357.46 [M+H]+
.
Absorption maxima (λmax) of 7−12 in CH2Cl2, DMF and MeOH.
12: orange solid (70%); mp 100 °C. Anal. Calcd for C14H8Cl2FN3O2
(M = 340.14): C, 49.44; H, 2.37; N, 12.35; found: C, 49.40; H, 2.29; N,
12.33%. 1H NMR (300 MHz, CDCl3): δ 8.23 (d, J = 8.10 Hz, 1H, arom),
7.76–7.70 (m, 3H, arom), 7.63 (t, J = 8.10 Hz, 1H, arom), 7.35 (d,
J = 7.35 Hz, 1H, arom), 7.10 (t, J = 8.29 Hz, 2H, arom). 13C NMR
(75 MHz, CDCl3): δ 166.57, 163.21, 150.25, 148.95, 148.10, 133.79,
132.25, 130.26, 128.34, 125.58, 125.45, 124.42, 116.28, 115.98. ESI-
CH2Cl2
DMF
MeOH
σp [28]
−0.27
7
265
372
410
300
361
431
304
365
434
308
375
440
276
373
437
269
358
424
41
231
349
395
245
326
375
263
319
364
269
322
375
265
318
375
258
302
352
44
256
326
390
232
302
402
278
313
398
257
288
394
249
264
395
242
262
365
55
8
−0.17
0.00
MS: m/z: 341.06 [M+H]+
.
9
2.4. X-ray structure determinations
10
11
12
0.23
X-ray diffraction patterns of 8, 9 and 12 were collected using a
Bruker SMART APEX-II CCD area detector equipped with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å) at 296(2) K, re-
spectively. Absorption correction was applied by SADABS [25,26]. The
structures were solved by direct methods and refined on F2 by full-
matrix least-squares using Bruker's SHELXTL-97 [27]. All non-hydrogen
atoms were refined anisotropically. The hydrogen atoms were inserted
at calculated positions. The details of the crystallographic data for 8, 9
and 12 are summarized in Table 1. Crystallographic data for the
structural analysis have been deposited to the Cambridge Crystal-
lographic Data Center (CCDC 1841658 for 8, 1841659 for 9 and
1841657 for 12). Copy of this information can be obtained free of
0.23
0.06
εa
αb [35]
0.13
0.10
0.00
0.69
0.98
0.66
βc [35]
a
Electric permittivity of solvent.
H-bond donating ability of solvent.
H-bonding acceptor ability of solvent.
b
c
138

A.M. Maharramov et al.
DyesandPigments159(2018)135–141
Fig. 3. Absorption spectra of 7−12 in CH2Cl2 (a), DMF (b) and MeOH (c).
139

A.M. Maharramov et al.
DyesandPigments159(2018)135–141
3. Results and discussion
dyes showed three absorption maxima in all solvents in the UV–vis
spectra (Table 2, Fig. 3). The first bands in the range 265–308 (in
CH2Cl2), 231–269 (in DMF) and 232–278 (in MeOH) nm can be as-
signed to the excitation of the π-electrons within the C=C bonds in
olefin moiety [31–34]. The second UV absorption bands around
358–375 (in CH2Cl2), 302–349 (in DMF) and 262–326 (in MeOH) nm
can be assigned to the π→π* transition in the aromatic rings [31–34].
The third maximums in UV spectra of 7−12 in the range 410–447 (in
CH2Cl2), 352–395 (in DMF) and 365–402 (in MeOH) nm can be as-
signed to the n→π* transition in N=N bonds as well as π→π* transition
in 1,4-membered pnicogen bond closed rings and intermolecular non-
covalent interactions [31–34]. As can be seen in Table 2 and Fig. 3, the
absorption maxima and intensity of these dyes are strongly solvent
dependent and vary with solvent polarity. Generally, negative solva-
tochromism (hypsochromic shift) was observed upon increasing the
solvent polarity [35] (Table 2). Thus, dyes 7–12 in the ground state and
in the excitation state to have different polarities. Under excitation,
7–12 can differently shift between the E- and Z-isomeric forms, de-
pending on the H-bond donor or H-bond acceptor ability (α or β) of the
solvent [35] and intermolecular noncovalent interactions [11], as well
as on the electron-donating or electron-withdrawing character of the
substituents. The data from Table 2 indicate that the maximum ab-
sorption wavelength strongly depend on the nature of para-substituents,
but there is no clear trend/correlation between λmax and σp. As it can be
seen in Fig. 3, the absorption intensity of the dyes is increase with a
decrease of the solvent polarity, indicating relatively strong non-
covalent interactions between the dye molecules and CH2Cl2.
3.1. Synthesis and characterization of 1–12
Six new Schiff bases, (E)-1-(para-substitutedbenzylidene)-2-(2-ni-
trophenyl)hydrazines [−OCH3 (1), −CH3 (2), −H (3), −Br (4), −Cl
(5), −F (6)], have been synthesized from the condensation of 2-ni-
trobenzaldehyde with (para-substituted phenyl)hydrazines in the pre-
sence of CH3COONa in EtOH at 80 °C. In the 300 MHz 1H NMR spectra
of the compounds in DMSO‑d6 solution, the N−H and −CH=N−
protons resonated as a singlet at 10.76–11.01 and 8.19–8.26 ppm, re-
spectively (Figs. S1–S6). All the aromatic and aliphatic, as well as
−OCH3 (for 1) and −CH3 (for 2), protons were observed at expected
regions. ESI-MS showed that found [M+H]+ peak accorded with cal-
culated value. Elemental analysis was also consistent with the mole-
cular composition of the compounds.
CuCl-catalyzed olefination of 1−6 with CCl4 in the presence of
tetramethylethylenediamine (TMEDA) in DMSO yields to (E)-1-(2,2-
dichloro-1-(2-nitrophenyl)vinyl)-2-(para-substituted phenyl)-diazenes
[−OCH3 (7), −CH3 (8), −H (9), −Br (10), −Cl (11), −F (12)], re-
spectively. In the 1H NMR spectra of 7−12 in CDCl3 solution at room
temperature show a resonance at δ 6.93–8.24, which can be assigned to
the protons of the aromatic moiety (Figs. S7–S12). All the aromatic,
aliphatic [−OCH3 (for 1) and −CH3 (for 2)] protons were observed at
expected regions. In the 13C NMR spectra of 7−12 all carbon atoms
were also found at expected regions (Figs. S7–S12). Their ESI-MS
spectra in methanol solution (Experimental section) display the parent
peaks at 353.08 [M+H]+ (7), 337.10 [M+H]+ (8), 323.12 [M+H]+
(9), 402.00 [M+H]+ (10), 357.46 [M+H]+ (11) and 341.06 [M+H]+
(12), which support the formulations. Elemental analysis is also clearly
support the predicted chemical structures of 7−12.
4. Conclusion
A series of (E)-1-(2,2-dichloro-1-(2-nitrophenyl)vinyl)-2-(para-sub-
stituted phenyl)-diazenes [−OCH3 (7), −CH3 (8), −H (9), −Br (10),
−Cl (11), −F (12)] dyes were synthesized by catalytic olefination of
(E)-1-(para-substituted phenyl)-2-(2-nitrobenzylidene)hydrazines with
CCl4 in the presence of tetramethylethylenediamine (TMEDA) in
DMSO. 7–12 are stabilized in the E-isomeric form in CDCl3 solution and
in the solid state by an intramolecular pnicogen and the intermolecular
π···π interactions, hydrogen and halogen bonds. The UV spectra of the
7–12 showed three absorption maxima in all solvents (CH2Cl2, DMF,
MeOH), which can be assigned the excitation of the π-electrons within
the C=C bonds, the π→π* transition in the aromatic rings and the n→
π* transition in N=N bonds as well as π→π* transition in 1,4-mem-
bered pnicogen bond closed rings, respectively, and intermolecular
noncovalent interactions. The visible absorption spectra of the dyes
were found to exhibit a strong solvent dependence, i.e., negative sol-
vatochromism (hypsochromic shift) was observed upon increasing the
solvent polarity. λmax is strongly depending on the nature of para-sub-
stituents, whereas there is no clear trend with σp. Thus, in this work, we
have shown the cooperative actions of noncovalent interactions (in-
tramolecular pnicogen bonding and intermolecular hydrogen and ha-
logen bonds, as well as π···π interactions) in the design of diazene dyes.
The obtained results may be useful for the decoration of new dyes and
functional materials with improved physical-chemical properties.
Single crystal X-ray analyses of 8, 9 and 12 show that these mole-
cules having strong intramolecular pnicogen bonds in 1,4-membered
quasi-rings, the N=N⋯Cl angles and the N⋯Cl distances are 175.7(3)°
and 2.885(4) and 176.9(2)° and 2.904(3) Å (for 8), 174.5(1)° and
2.940(1) Å (for 9) and 174.3(2)° and 2.935(2) (for 12) (Fig. 1), and all
distances are significantly less than the sum of the van der Waals radius
of interacting atoms (N + Cl = 1.55 + 1.75 = 3.30 Å) [28]. The
crystal structure of 8 comprises two independent molecules with dif-
ferent intramolecular pnicogen bond parameters (Fig. 1). The Ham-
mett's σp para-substituent constants [−0.17 −CH3 (8), 0.00 −H (9),
0.06 −F (12)] [29] versus the N=N⋯Cl pnicogen bond angles show
that this angle appears to tend to decrease with an increase of the
electron-withdrawing character of the substituent, whereas there is no a
clear correlation between σp and N⋯Cl pnicogen bond distance.
Moreover, 9 and 12 contain an intermolecular Cl⋯O type of halogen
bonds with the distance of 3.019(2) and 3.079 Å, what both are shorter
than the sum of van der Waals radius of interacting atoms
(Cl + O = 1.75 + 1.52 = 3.27 Å) [25] (Fig. 2), and the C−Cl⋯O
angles of 164.3(7) and 163.03°, respectively. In 12 a F(1) atom spon-
taneously behaves as a halogen bond donor [30] and a H-bond acceptor
towards neighboring aromatic π system and CH of aromatic moiety
leading to a weak intermolecular F···π halogen and CH⋯F types of hy-
drogen bonds with distances of 3.754 and 2.699 Å, respectively (Fig. 2).
Besides the pnicogen and halogen bonds, all structures are stabilized by
multiple weak intermolecular hydrogen bonds as well as π···π interac-
tions (Table S1 and Fig. S13).
Acknowledgements
This work has been partially supported by the Foundation for
Science and Technology (FCT) (Project UID/QUI/00100/2013),
Portugalas well as by the Organic Chemistry Department of Baku State
University, Azerbaijan. The publication was prepared with the support
of the “RUDN University Program 5–100”. This work was also sup-
ported by the Science Development Foundation of Azerbaijan (RFBR
18-53-06006 az_a). Authors are thankful to the Portuguese NMR
Network (IST-UL Centre) for access to the NMR facility and the IST
Node of the Portuguese Network of mass-spectrometry for the ESI-MS
measurements.
3.2. UV–vis spectra of 7−12
In order to study the solvatochromism of (E)-1-(2,2-dichloro-1-(2-
nitrophenyl)vinyl)-2-(para-substituted phenyl)-diazenes (7–12), sol-
vents of various polarities, namely dichloromethane (CH2Cl2), di-
methylformamide (DMF) and methanol (MeOH) were selected, and the
absorption spectra were recorded in the wavelength rang
200–700 nm at a concentration 10−6 mol L−1 (Table 2, Fig. 3). The
140

A.M. Maharramov et al.
DyesandPigments159(2018)135–141
Appendix A. Supplementary data
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