Synthesis, characterization and crystal structure of four new asymmetric triazene ligands: An example of linear HgII complex with Hg. π secondary bonding interactions

Article abstract of DOI:10.1007/s12039-015-0979-7

In this work, the asymmetric ligands [1-(phenyl)-3-(2-nitro-4-methylphenyl)]triazene (1), [1-(4- methylphenyl)-3-(2-nitro-4-methylphenyl)]triazene (2), [1-(4-ethylphenyl)-3-(2-nitro-4-methylphenyl)]triazene (3) and [1-(4-ethoxyphenyl)-3-(2-nitro-4-methylp

Full text of DOI:10.1007/s12039-015-0979-7

c
J. Chem. Sci. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-0979-7
Synthesis, characterization and crystal structure of four new asymmetric
triazene ligands: An example of linear HgII complex with Hg...π
secondary bonding interactions
MOHAMMAD REZA MELARDIa, FATEMEH BABER SHAMSI MOGOIIa,
AYOOB BABAII SAJIRANIa, JAFAR ATTAR GHARAMALEKIb, BEHROUZ NOTASHc and
MOHAMMAD KAZEM ROFOUEIb,∗
aDepartment of Chemistry, Islamic Azad University, Karaj Branch, Karaj, Iran
bFaculty of Chemistry, Kharazmi University, Tehran, Iran
cDepartment of Chemistry, Shahid Beheshti University, G. C., Evin, Tehran 1983963113, Iran
e-mail: rofouei_k@yahoo.com
MS received 29 May 2015; revised 31 August 2015; accepted 7 September 2015
Abstract. In this work, the asymmetric ligands [1-(phenyl)-3-(2-nitro-4-methylphenyl)]triazene (1), [1-(4-
methylphenyl)-3-(2-nitro-4-methylphenyl)]triazene (2), [1-(4-ethylphenyl)-3-(2-nitro-4-methylphenyl)]tria-
zene (3) and [1-(4-ethoxyphenyl)-3-(2-nitro-4-methylphenyl)]triazene (4), were synthesized. The reaction of
the ligand (3) with HgCl2 in methanol resulted in the formation of the [HgL2] complex, (5). All compounds
were characterized by means of CHN analysis, FT-IR, 1H NMR, 13C NMR spectroscopy. In addition, the crys-
tal structures of the ligands (2) to (4) were investigated by single crystal X-ray analysis. In the solid state,
all ligands exhibited trans conformation about the –N=N– double bond. The HgII complex (5) crystallized in
monoclinic system with C2/c space group. The triazene ligand was found to be deprotonated prior to coordina-
tion and acts as monodentate ligand. The HgII which lies on inversion center (site symmetry ¯ı), is surrounded
by two N atoms from L ligands forming a linear geometry. The other two Hg–N bonds are relatively longer
and can only be regarded as weak secondary bonds. Also, Hg-η3-arene π-interactions are present in this com-
pound. Hydrogen bonds, π · · · π and C–H· · · π stacking interactions help in the stabilization of the resulted
frameworks. These C–H· · · π edge-to-face interactions are present with H· · · π distance of 3.00 Å.
Keywords. Mercury(II) complex; Hg· · · π interaction; asymmetric triazene; crystal structure.
asymmetric-substituted triazenide complexes of HgII
which have a remarkable ability to self-assemble in dif-
ferent manners through metal-η-arene π-interactions
have been reported.11 In recent years, our group
has been involved in the complexation of transition
metal ions with several triazene compounds, starting
from different bis(diaryl) symmetric and asymmetric-
substituted triazenides. In this regard, the synthesis
of 1,3-bis(2-methoxyphenyl)]triaz-1-ene19 [1,3-bis(2-
ethoxyphenyl)]triaz-1-ene20 [1,3-bis(2-cyanophenyl)]
triaz-1-ene21 1-(3,5-dichlorophenyl)-3-(2-methoxyphe-
nyl)triaz-1-ene22 and 3-(2-ethoxyphenyl)-1-(3-nitrophe-
nyl)triaz-1-ene23 molecules have been reported to act
as ligands. Additionally, we have published the HgII
complexes with [1,3-bis(2-methoxyphenyl)]triazene by
1. Introduction
Aryl triazenes have been studied over several years
for their interesting structural and anticancer reac-
tivity properties.1–5 The study of transition-metal
complexes containing 1,3-diaryltriazene ligands has
greatly increased in the past few years due to the
potential reactivity of these ligands.6,7 As ligands,
the (–NH–N=N–) moieties can show different types
of coordination in metal complexes. The coordina-
tion modes can be monodentate, (N1, N3)-chelating
towards one metal atom or (N1, N3)-bridging over two
metal atoms over a wide variety of transition metal
complexes.8–10 In these compounds secondary bonds or
interactions such as hydrogen bonds and metal π-aryl
interactions can play important roles in the struc-
tural stability.11–18 Several bis(diaryl) symmetric and
24
25
using HgCl2 HgBr2 Hg(CH3COO)2 and Hg(SCN)2
salts as starting materials.26 Just recently, a HgII com-
plex with [1,3-bis(2-ethoxyphenyl)]triazene as ligand
has been reported, in which HgCl2 has been used as
starting salt.27 From recent structural studies, it was
∗For correspondence

Mohammad Reza Melardi et al.
argued that counter-anions play an important role in 2. Experimental
determining the solid state lattices of these compounds.
More recently, HgII complexes with several asym-
metric triazenes have been prepared and their crystal
structures reported.28–30
2.1 Materials and physical techniques
All chemicals were of analytical grade and were used
without further purification. FT-IR spectra in the fre-
quency range of 4000–400 cm−1 were recorded using
Perkin–Elmer RXI spectrometer using KBr disks. Ele-
mental analysis was carried out using a Perkin–Elmer
2400(II) CHNS/O analyzer. Melting points were mea-
sured on a Barnstead Electrothermal 9200 apparatus. 1H
NMR and 13C NMR spectra were recorded using Bruker
Avance 300 instrument.
To investigate the effect of the substituted deriva-
tives on coordination behavior of the triazene ligands,
we have introduced ortho-, meta- and para- bis(phe-
nyltriazene) benzenes (and substituted derivatives), as
ligands in order to investigate the stoichiometry of the
resulting mercury(II) complexes. In continuation with
previous work, we herein report the synthesis, charac-
terization, and molecular structure of new asymmetric
[[1-(phenyl)-3-(2-nitro-4-methylphenyl)]triazene (1), [1-
(4-methylphenyl)-3-(2-nitro-4-methylphenyl)]triazene
(2), [1-(4-ethylphenyl)-3-(2-nitro-4-methylphenyl)]tri-
azene (3) and [1-(4-ethoxyphenyl)-3-(2-nitro-4-methyl-
phenyl)]triazene (4), and a linear HgII complex [HgL2],
(5) in methanol as solvent. Scheme 1 presents the
starting materials and the reaction procedure.
2.2 Crystal structure determination and refinement
The X-ray diffraction measurements were made on a
STOE IPDS-II diffractometer with graphite monochro-
mated Mo-Kα radiation (λ = 0.71073 Å). Cell con-
stants and orientation matrices for data collection were
Scheme 1. General procedure for the preparation of the triazenes (1) to (4) and a linear HgII complex, (5).

A linear HgII complex with asymmetric triazenes
Table 1. Crystallographic and structure refinement data for (2) to (5).
Compound reference
(2)
(3)
(4).MeOH
(5)
Chemical formula
Formula Mass
C14H14N4O2
270.29
C15H16N4O2
284.32
C15H16N4O3.CH3OH
332.36
C30H30HgN8O4
767.21
Crystal system
Space group
Monoclinic
P21/n
Triclinic
P¯ı
Monoclinic
P21/c
Monoclinic
C2/c
a/Å
b/Å
12.994(3)
5.7068(11)
18.004(4)
–
91.66(3)
–
7.7526(16)
9.3955(19)
11.264(2)
67.73(3)
75.55(3)
88.64(3)
6.7762(14)
18.031(4)
13.732(3)
–
104.22(3)
–
14.527(3)
17.691(4)
12.011(2)
–
110.95(3)
–
c/Å
α/◦◦
γ/
β/◦
Crystal size (mm)
0.45 × 0.15 × 0.02 0.5 × 0.5 × 0.3
0.5 × 0.3 × 0.2
1626.4 (6)
1.357
0.35 × 0.25 × 0.2
2882.7(12)
1.768
Unit cell volume/Å3
1334.5(5)
1.345
732.9(2)
1.288
Density (Mg m−3
Temperature/K
)
120(2)
298(2)
120(2)
120(2)
No. of formula units per unit cell, Z
Absorption coefficient, mm−1
Data collected
Unique data, (Rint)
parameters / restraints
Final R indices [I>2σ(I)]
4
2
4
0.10
11054
4353, (0.0967)
227 / 0
R1 = 0.0698
wR2 =0.1511
R1 = 0.1114
wR2 = 0.1700
1.071
4
0.094
9605
2348, (0.1782)
187 / 0
R1 = 0.0736
wR2 = 0.1691
R1 = 0.1032
wR2 = 0.1825
1.1091
0.089
7923
3912, (0.0672)
196 / 0
R1 = 0.0596
wR2 = 0.1513
R1 = 0.1223
wR2 = 0.1768
0.878
5.391
11319
3865, (0.0491)
198 / 0
R1 = 0.0310
wR2 = 0.0633
R1 = 0.0594
wR2 = 0.0699
1.010
R indices (all data)
Goodness-of-fit on F2(S)
Largest diff. peak and hole, (e. Å−3
)
0.255, −0.264
0.224, −0.260
0.275, −0.307
1.719,−1.205
obtained by least-squares refinement of diffraction data phenyl)]triazene, was prepared as follows: 10 g of ice
from 2348 unique reflections for (2), 3912 for (3), 4353 and 150 mL of water were poured into a 250 mL flask.
for (4) and 3865 for compound (5). Data were col- Then 0.304 g (2 mmol) of 4-methyl-2-nitroaniline and
lected to a maximum 2θ value of 50◦ for (2), 58.4◦ 15 mL of hydrochloric acid (37%) were added to this
for (3), 58.3◦ for (4) and 58.3◦ for (5), in a series of flask. After that, a solution containing NaNO2 (0.13 g)
ω scans in 1◦ oscillations and integrated using Stoe X- in 5 mL of water was then added slowly to the resultant
AREA31 software package. A numerical absorption cor- solution during a 15 min period. The pH of the solu-
rection was applied using X-RED32 and X-SHAPE33 tion was then adjusted to 6 by adding a solution con-
software. The data were corrected for Lorentz and taining 4 g of sodium acetate in 15 mL of water. After
Polarizing effects. The structures were solved by direct mixing for 15 min, the obtained solution was added to
methods34 and subsequent difference Fourier maps and a solution of 0.25 mL (2 mmol) of aniline, 10 mL of
then refined on F2 by a full-matrix least-squares pro- methanol and 5 mL of water. After mixing for 24 h,
cedure using anisotropic displacement parameters.35 the orange precipitate was filtered off and dried. Prop-
The atomic factors were taken from the International erties: IR (KBr): υ(cm−1): 3320(s), 3050 (w), 2966(w),
Tables for X-ray Crystallography.36 All refinements 1660(w), 1602(s), 1569(s), 1523(s), 1459(s), 1407(s),
were performed using the X-STEP32 crystallographic 1339(s), 1303(s), 1286(w), 1144(s), 1077(s), 934(w),
1
software package.37 A summary of crystal data, exper- 847(s), 819(s), 761(s), 614(s). H NMR (300 MHz,
imental details and refinement results are given in d6-DMSO): δ 1.16 (3H, CH3), 2.36 (3H, CH3), 2.58
table 1.
(2H, CH2), 7.2–7.85 (7H, aromatic), 12.91 (1H, NH)
ppm.13C NMR (d6-DMSO): δ 15.7, 20.1, 27.7, 117.8-
145.5 ppm. Elemental Anal. calc. for C15H16N4O2: C,
63.37; H, 5.67; N, 19.7%. Found: C, 63.49; H, 5.26; N,
19.56%.
2.3 Syntheses
2.3a Synthesis of C14H14N4O2, (1): All materials
and solvents were obtained from commercial source
and used without further purification The asym- 2.3b 2.Synthesis of C14H14N4O2, (2): The [1-(4-
metric ligand (1), [1-(phenyl)-3-(2-nitro-4-methyl- methylphenyl)-3-(2-nitro-4-methylphenyl)]triazene (2)

Mohammad Reza Melardi et al.
ligand was prepared according to the method described crystals suitable for X-ray analysis of the complex (5)
above with the difference that 4-methylaniline was used were obtained by slow evaporation of the solvent in two
instead of aniline. Suitable crystals of this compound weeks. Properties: air stable, yellow crystalline mate-
were obtained by slow evaporation of the solvent dur- rial. M.p.: 201–203◦C. IR (KBr): υ(cm−1): 3650(w),
ing three days. Properties: M.p.: 98–100◦C. IR (KBr): 3435(br), 2966(w), 1601(s), 1568(s), 1520(s), 1504(s),
υ(cm−1): 3432(br), 3305(s), 2913(w), 1626(s), 1568(s), 1392(s), 1320(s), 1273(s), 1197(s), 1148(s), 1080(w),
1
1520(s), 1457(s), 1405(s), 1305(s), 1208(w), 1142(s), 835(s), 817(s), 791(s), 765(s), 676(w), 534(w). H
1
1071(br), 818(s). H NMR (300 MHz, d6-DMSO): NMR (300 MHz, d6-DMSO): δ = 1.19 (6H, CH3), 2.30
δ 2.28 (3H, CH3), 2.36 (3H, CH3), 7.19–7.66 (7H, (6H, CH3), 2.35 (3H, O-CH3), 2.62(4H, -CH2), 7.20–
aromatic), 12.82 (1H, NH).13C NMR, (d6-DMSO): δ 7.65 (14H, aromatic).13C NMR (300 MHz, d6-DMSO):
20.2, 20.7 and 114-145 ppm. Elemental Anal. calc. for δ 20.0, 20.5, 118.5-124.3 and 174.6 ppm. Elemental
C14H14N4O2: C, 62.21; H, 5.22; N, 20.73%. Found: C, Anal. calc. for C30H30HgN8O4: C, 46.97; H, 3.94; N,
62.3; H, 5.66; N, 20.8%.
14.61%. Found: C, 47.09; H, 3.41; N, 14.1%.
2.3c Synthesis of C15H16N4O2, (3): The ligand (3)
was prepared with the same procedure with this
difference that 4-ethylaniline was used instead of
aniline as starting material. Suitable crystals of this
compound were obtained by slow evaporation of the
solvent during three days. Properties: M.p.: 92–94◦C.
IR (KBr): υ(cm−1): 3435(br), 3320(s), 2966(w),
1625(s), 1569(s), 1523(s), 1459(s), 1407(s), 1339(s),
1303(s), 1286(s), 1202(w), 1144(s), 1077(s), 819(s).
1H NMR (300 MHz, d6-DMSO): δ 1.17 (3H, CH3),
2.36 (3H, CH3), 2.58 (2H, CH2), 7.22–7.85 (6H, aro-
matic), 12.82 (1H, NH).13C NMR, (d6-DMSO): δ 15.7,
20.1, 27.7 and 128-145 ppm. Elemental Anal. calc. for
C15H16N4O2: C, 63.37; H, 5.67; N, 19.71%. Found: C,
63.49; H, 5.26; N, 19.56%.
3. Results and Discussion
In the FT-IR spectrum of the ligand (2), the band at
3305 cm−1 is responsible for N–H bond stretching. The
N–N and N=N bond stretching modes appear at 1142
and 1457 cm−1, respectively. The peak at 1520 cm−1 is
assigned to the stretching of N–O bond of NO2 frag-
ment and the stretching frequency of the formal C–N
single band appears at 1305 cm−1. In H NMR spec-
1
trum, the peak at δ = 12.82 ppm can be assigned
to the presence of N–H group. Hydrogen atoms of
methyl groups exhibit signals at 2.28 and 2.36 ppm,
respectively. The seven hydrogen atoms of the two aro-
matic rings appear from 7.19 to 7.66 ppm. In the 13C
NMR spectrum, the carbon atoms of methyl groups
on the aromatic ring show signals at 20.2 and 20.7
ppm, respectively. The carbon atoms belong to two
aromatic rings show signals ranging from 114 to 145
ppm, indicating the presence of twelve different car-
bon atoms. The molecular structure of compound (2)
is shown in figure 1 with thermal ellipsoids drawn
at 50% probability level. Compound (2) crystallized
in monoclinic system with P 21/n space group and
four molecules per unit cell. Crystallographic data and
parameters for complex are summarized in table 1.
Also, selected bond lengths and angles are listed in
table 2. As it can be seen, the molecule adopts trans
configuration with respect to the (–N=N–) bond. The
N1=N2 and N2–N3 bond lengths are 1.261(4) Å and
1.352 (4) Å, respectively, which proves the presence
2.3d Synthesis of C15H16N4O3, (4): In the synthesis
of the ligand (4), 4-ethoxylaniline was used as start-
ing material and the preparation method was the same
as above. Properties: M.p.: 100–102◦C. IR (KBr):
υ(cm−1): 3449(s), 3336(s), 2976(w), 1629(s), 1586(s),
1521(s), 1493(s), 1471(w), 1426(s), 1389(s), 1334(s),
1257(br), 1158(w), 1120(s), 1065(s), 1044(s), 926(s),
1
918(s), 836(s), 745(s), 715(s). H NMR (300 MHz,
d6-DMSO): δ = 1.36 (3H, CH3), 2.35 (3H, CH3),
4.08 (2H, CH2), 6.93–7.76 (6H, aromatic), 11.93 (1H,
NH).13C NMR, (d6-DMSO): δ = 14.6, 20.0, 20.5,
63.9 and 102-145 ppm. Elemental Anal. calc. for
C15H16N4O3: C, 59.99; H, 5.37; N, 18.66%. Found: C,
63.49; H, 5.26; N, 19.56%.
2.3e Synthesis of C30H30HgN8O4, (5): The com- of distinct single and double bonds between nitrogen
plex was prepared by mixing 0.6 g (2 mmol) of atoms and hence the (–NH–N=N–) moiety. These val-
[1-(4-ethylphenyl)-3-(2-nitro-4-methylphenyl)]triazene ues are in good agreement with the reported data for
(3), in 25 mL of anhydrous methanol with 0.27 g (1 N–N and N=N bond distances.25 For example, in 1,3-
mmol) of mercury(II) chloride in 15 mL of anhydrous bis(2-cyanophenyl)triazene, the N–N and N=N bond
methanol. After mixing for an hour, a precipitate was distances are 1.335(5) and 1.289(5) Å.21 Also, the N1–
obtained. The resultant precipitate after filtration and N2–N3 bond angle is 109.2 (3)◦. The angle between
washing was dissolved in THF. Yellow needle-like two planes of the aromatic rings of triazene molecule is

A linear HgII complex with asymmetric triazenes
Figure 1. Molecular structure of compound (2) with thermal ellipsoids drawn at 50%
probability level. The intramolecular N3–H3A· · · O1 hydrogen bond is shown as dashed line.
Table 2. Selected bond distances (Å) and angles (◦ ) for compounds (2) to (5).
Compound (2)
N1—N2
N2—N3
N1—N2—N3
1.264(4)
1.353(4)
109.3(3)
N4—O1
N4—O2
O1—N4—O2
1.235(3)
1.226(3)
121.7(3)
Compound (3)
N1—N2
N2—N3
1.254(2)
1.350(2)
N4—O1
N4—O2
1.2256(19)
1.211(2)
N1—N2—N3
111.01(15)
O1—N4—O2
121.40(17)
Compound (4)
N1—N2
N2—N3
O1—C2
O1—C3
1.266(3)
1.353(3)
1.445(3)
1.365(3)
111.33(18)
N4—O2
N4—O3
O4—C16
1.237(2)
1.228(2)
1.411(3)
N1—N2—N3
O2—N4—O3
122.2(2)
Compound (5)
Hg1—N1
N1—N2
2.067(3)
1.316(5)
180.000(1)
N2—N3
O1—N4—O2
N1—N2—N3
1.276(5)
123.5(4)
113.8(3)
N1—Hg1—N1
15.49(3)◦ which indicates that this molecule is deviated
from planar geometry.
stretching modes appear at 1144 and 1459 cm−1,
respectively. The peak at 1523 cm−1 is assigned to
the stretching of N–O bond of NO2 fragment and the
stretching frequency of the formal C–N single band
In the lattice structure of the ligand (2), intramolec-
ular N3–H3A· · · O1 hydrogen bond with N3· · · O1 =
2.610 (3) Å, as well as non-classic hydrogen bonds, C3–
H3· · · O1 #1 (#1: −x+1/2, y+3/2, −z+1/2) and C10–
H10· · · O2 #2 (#2: −x, −y−1, −z) with C3· · · O1 =
3.508(4) Å and C10· · · O2 = 3.352(4) Å are present
(table 3).
1
appears at 1303 cm−1. In H NMR spectrum, the peak
at δ = 12.82 ppm can be assigned to the presence of N–
H group. Hydrogen atoms of methyl groups of (CH3-
CH2-) exhibit signals at 1.17 ppm. Two hydrogen atoms
of -CH2- group appear at 2.58 ppm and methyl group
attached to the aromatic ring shows signal at 2.36 ppm.
The seven hydrogen atoms of the two aromatic rings
Compound (3) was also characterized by using
1
FT-IR, H NMR and 13C NMR spectroscopy. In the
FT-IR spectrum of the ligand (3) was very similar to appear from 7.22 to 7.85 ppm. In the 13C NMR spec-
that of ligand (2). The band at 3320 cm−1 is responsi- trum, the carbon atoms of methyl groups show signals
ble for N–H bond stretching. The N–N and N=N bond at 15.7 and 20.1 ppm, respectively. The carbon atom

Mohammad Reza Melardi et al.
Table 3. Hydrogen bonding parameters (Å , ◦) for compounds (2) to (5).
D–H· · · ·A
d(D–H)
d(H· · · ·A)
d(D· · · ·A)
<(D–H· · · ·A)
Compound (2)
N3—H3A· · · O1
C3—H3· · · O1#1
C10—H10· · · O2
C10—H10· · · O2#2
0.90(4)
0.95
0.95
1.91(4)
2.58
2.34
2.610(3)
3.509 (4)
2.671(4)
3.353(4)
133(3)
165.8
100.1
155.4
0.95
2.47
Compound (3)
N3—H3· · · O1
C4—H4· · · O1#3
C11—H11· · · O2#4
0.89
0.93
0.93
1.99
2.54
2.59
2.612(3)
3.446 (3)
3.392 (2)
127
165
145
Compound (4)
N3—H3A· · · O2
N3—H3A· · · O4#5
O4—H4A· · · N1#6
C2—H2A· · · O4#7
C13—H13C· · · O3#8
0.84
0.84
0.84
0.99
0.98
2.09
2.24
2.17
2.53
2.57
2.638 (3)
2.979 (3)
2.810 (3)
3.366 (3)
3.412 (3)
123
147
133
142
144
Compound (5)
C6—H6· · · O1#9
0.95
0.95
2.55
2.43
3.351 (6)
3.245 (6)
142
144
C15—H15· · · O2#10
Symmetry codes: (#1) −x+1/2, y+3/2, −z+1/2; (#2) −x, −y−1, −z; (#3) −x+1, −y, −z+1; (#4) −x+1, −y−1, −z; (#5)
x−1, y, z; (#6) x+1, y, z; (#7) x−2, y, z; (#8) −x+2, −y+1, −z+1; (#9) −x+2, y, −z+3/2; (#10) x−1/2, −y+1/2, z−1/2.
Figure 2. Molecular structure of compound (3) with thermal ellipsoids drawn at 50%
probability level. The intramolecular N3–H3· · · O1 hydrogen bond is shown as dashed line.
of methylene group appears at 27.7 ppm. The carbon
atoms belong to two aromatic rings show signals rang-
ing from 128 to 145 ppm, indicating the presence of
twelve different carbon atoms. The molecular structure
of compound (3) is shown in figure 2 with thermal ellip-
soids drawn at 50% probability level. Compound (3)
crystallized in monoclinic system with P 21/n space
group and four molecules per unit cell. Selected bond
lengths and angles for (3) are listed in table 2. The
molecule again adopts trans conformation with respect
lengths are 1.254(2) Å and 1.350 (2) Å, respectively
Also, the N1–N2–N3 bond angle is 111.01 (15)◦. The
angle between two planes passing from aromatic rings
of triazene molecule is 16.20(3)◦ and indicates that this
molecule is deviated from planar geometry.
In the lattice structure of the ligand (3), intramolec-
ular N3–H3· · · O1 hydrogen bond with N3· · · O1 =
2.612(3) Å is present. Also, oxygen atoms of NO2
group are involved in the hydrogen bonding. The non-
classic C4–H4· · · O1 #3 (#3: −x+1, −y, −z+1) and
to the (–N=N–) bond. The N1=N2 and N2–N3 bond C11–H11· · · O2 #4 (#4: −x+1, −y−1, −z) hydrogen

A linear HgII complex with asymmetric triazenes
3336 cm−1 is responsible for N–H bond stretching. The
bonds with C4· · · O1 = 3.446(3) Å and C11· · · O2 =
3.392(2) Å connect the triazene molecules into chains
in [110] direction (figure 3).
The ligand (4) is also an asymmetric substituted
triazene bearing ethoxy group on the aromatic ring.
In the FT-IR spectrum of compound (4), the band at
N–N and N=N bond stretching modes appear at 1120
and 1426 cm−1, respectively. The peak at 1521 cm−1 is
assigned to the stretching of N–O bond of NO2 frag-
ment. and the stretching frequency of the formal C–
1
N single band appears at 1334 cm−1. In H NMR
Figure 3. Non-classic C4–H4· · · O1 and C11–H11· · · O2 hydrogen bonds connect
the triazene molecules (3) into chains along [110] direction.
Figure 4. Molecular structure of compound (4) with thermal ellipsoids drawn at 50%
probability level. The intramolecular N3–H3A· · · O2 hydrogen bond is shown as dashed line.

Mohammad Reza Melardi et al.
spectrum, the peak at δ = 11.93 ppm can be assigned to hydrogen atoms of -CH2- group appear at 4.08 ppm
the presence of N–H group. Hydrogen atoms of methyl and methyl group attached to the aromatic ring shows
groups of (CH3-CH2-O) exhibit signal at 1.36 ppm. Two signal at 2.35 ppm. The seven hydrogen atoms of the
Figure 5. π · · · π stacking interactions between Cg1· · · Cg2 with centroid-centroid distances of 3.632 (15) Å in compound
(4). All hydrogen bonds are also shown as dashed lines. Methanol molecule makes two distinct hydrogen bonds with
triazene (4).
Figure 6. Molecular structure of compound (5) with thermal ellipsoids drawn at 30% probability level.

A linear HgII complex with asymmetric triazenes
two aromatic rings appear from 6.93 to 7.76 ppm. In
and C13· · · O3 = 3.412(3) Å are present. In addi-
tion, π · · · π stacking interactions help in the stabiliza-
tion of the resulted framework. These π · · · π stacking
interactions are present between Cg1· · · Cg2 (−1+x, y,
z) with centroid-centroid distance of 3.632 (15) Å. Cg1
and Cg2 are centroids for C3-C8 and C9-C12, C14,C15
rings, respectively (figure 5).
the 13C NMR spectrum, the carbon atoms of methyl
groups show signals at 14.6 and 20.5 ppm, respec-
tively. The carbon atom of methylene group (-CH2-O)
appears at 63.9 ppm. The carbon atoms belong to two
aromatic rings show signals ranging from 102 to 145
ppm, indicating the presence of twelve different car-
bon atoms. The molecular structure of compound (4) is
shown at figure 4 with thermal ellipsoids drawn at 50%
probability level.
The ligand (4) crystallized in monoclinic system with
P 21/c space group and four molecules per unit cell.
The N1=N2 and N2–N3 bond lengths are 1.266(3)
Å and 1.353 (3) Å, respectively Also, the N1–N2–
N3 bond angle is 111.33 (18)◦. The angle between the
two planes of the aromatic rings of triazene molecule
is 9.53(3)◦. In addition, a methanol molecule is
present in the crystal structure of this compound. In the
lattice structure of the ligand (4), intramolecular N3–
H3A· · · O2 hydrogen bond with N3· · · O2 = 2.638(3)
Å is present. Also, oxygen atom of CH3OH group plays
as donor and acceptor atom in the hydrogen bonding
and makes N3–H3A· · · O4 #5 (#5: x−1, y, z) hydro-
gen bond with N3· · · O4 = 2.979(3) Å and O4–H4A· · ·
Compound (5), [Hg(C16H16N3O3)2] or [HgL2], was
prepared by reacting the corresponding ligand L (3)
with HgCl2 salt in methanol as solvent. By comparison
of 1H NMR spectrum of the complex (5) with that of the
free ligand, it is found that the signal for N–H (at 12.82
ppm) has disappeared which indicates deprotonation of
the N–H group prior to complexation. The molecular
structure of the compound (5) is shown in figure 6.
The molecule crystallized in C2/c space group with
four molecules per unit cell. The N1–N2 and N2–N3
bond distances are 1.316(5) Å and 1.276(5) Å, respec-
tively which indicates the formation of resonance struc-
ture. The N1–N2–N3 bond angle is 113.8 (3)◦. The
HgII which lies on inversion center (site symmetry ¯ı),
is coordinated by two triazenide ions. Each triazenide
ion is coordinated to central atom through two nitrogen
atoms [Hg1–N1 = 2.067(3) Å and Hg1–N3 = 2.670
N1 #6 (#6: x+1, y, z) hydrogen bond with O4· · · N1 = (3) Å] of which the latter one is relatively weaker inter-
2.810(3) Å. Also, non-classic C2–H2A· · · O4 #7 (#7: action. Hence, HgII is coordinated in a linear form, the
x−2, y, z) and C13–H13C· · · O3 #8 (#8: −x+2, −y+1, other two Hg–N bonds are much longer and can only be
regarded as weak secondary bonds. The linear geometry
−z+1) hydrogen bonds with C2· · · O4 = 3.366(3) Å
Figure 7. Secondary weak metal-η3 interactions in compound (5) involve the Hg1
atom and C3 [3.632(2) Å], C4 [3.241(1) Å] and C6 [3.328(2) Å] atoms with related
symmetry code (2−x, y, 3/2−z).

Mohammad Reza Melardi et al.
is well known for cations with d10 electronic configura-
tion. The N1–Hg1–N1A (symmetry code (A): −x+1,
y, −z+3/2) bond angle is 180◦ .
conts/retrieving.html, or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
In addition, the presence of non-classic C6–H6· · · O1
#9 (#9: −x+2, y, −z+3/2) and C15–H15· · · O2 #10
(#10: x−1/2, −y+1/2, z−1/2) hydrogen bonds with
D· · · A distance of 3.351(6) Å and 3.245(6) Å con-
nect the monomeric fragments into infinite chains in a
wave-like shape along the crystallographic [010] and
[101] directions. Within the chains, each HgII is addi-
tionally coordinated by two peripheral phenyl rings of
two neighboring complexes by secondary weak metal-
η3 interactions. These metal-π interactions involve the
Hg1 atom and C3 [3.632(2) Å], C4 [3.241(1) Å]
and C6 [3.328(2) Å] atoms with related symmetry
code (2−x, y, 3/2−z) (see figure 7). As mentioned
weaker π · · · π and C–H· · · π stacking interactions
help to stabilize the resulted structure (details are
provided in table 3). These π· · · π interactions exist
and the mean centroid–centroid distance is 3.537(2)
Å for Cg2· · · Cg2, in which Cg2 is center of C9/C15
ring (2−x, y, 3/2−z). Also, there are interesting weak
C—H· · · π edge-to-face interactions between the C−H
groups and the aromatic phenyl rings with H· · · π dis-
tance of 2.71 Å for C1–H1A· · · Cg2 (3/2−x, -1/2+y,
3/2−z). The sum of these weak non-covalent interac-
tions seems to play an important role in the crystal
packing and the formation of a desired framework.
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4. Conclusions
In this article, the synthesis of four new asymmetric tri-
azene ligands are described and characterized by FT-
IR, NMR, elemental analysis and single crystal X-ray
technique. In the solid state, all ligands exhibited trans
conformation about the –N=N– double bond. Hydro-
gen bonding (O–H· · · N, N–H· · · O and C–H· · · O) and
slipped π· · · π stacking interactions played an essen-
tial role in the creation and stabilization of their 3D
networks. A linear HgII complex was also synthesized
in which central atom is coordinated by two triazenide
ions by their nitrogen atoms (HgL2). Each HgII is addi-
tionally coordinated by two peripheral phenyl rings
of two neighboring complexes by secondary weak
metal-η3 interactions.
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Gharamaleki J 2009 Inorg. Chim. Acta 362 3777
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M K 2009 Acta Crystallogr. Sect. E 65 m302
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A linear HgII complex with asymmetric triazenes
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