A new imidazophenanthroline derivative and its Hg(II) complex: Structures, photophysical properties, and DFT calculations

Article abstract of DOI:10.1080/00958972.2012.729822

A new ligand (L) and its mercury(II) complex have been synthesized under mild conditions. X-ray single-crystal structural analyses reveal 1-D, 2-D, and 3-D supermolecular structure of L and HgLI₂. Solvent molecules and various weak interactions, including hydrogen bonds (N-H...N, O-H...O, and O-H...N) and π-π interactions play signiEcant roles in the Enal supermolecular structures. Detailed investigation on ¹H NMR spectra of L and HgLI₂ are presented. Their photophysical properties were investigated both experimentally and theoretically.

Full text of DOI:10.1080/00958972.2012.729822

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A new imidazophenanthroline
derivative and its Hg(II) complex:
structures, photophysical properties,
and DFT calculations
Zheng Zheng a , Zhi-Peng Yu a , Hong-Ping Zhou a , Jia-Xiang Yang a
, Yan Feng a , Lin Kong a , Jie-Ying Wu a & Yu-Peng Tian a b c
a Department of Chemistry, Anhui University and Key Laboratory
of Functional Inorganic Materials Chemistry of Anhui Province,
230039 Hefei, PR China
b State Key Laboratory of Crystal Materials, Shandong University,
250100 Jinan, PR China
c State Key Laboratory of Coordination Chemistry, Nanjing
University, 210093 Nanjing, PR China
Accepted author version posted online: 13 Sep 2012.Published
online: 27 Sep 2012.
To cite this article: Zheng Zheng , Zhi-Peng Yu , Hong-Ping Zhou , Jia-Xiang Yang , Yan Feng , Lin
Kong , Jie-Ying Wu & Yu-Peng Tian (2012): A new imidazophenanthroline derivative and its Hg(II)
complex: structures, photophysical properties, and DFT calculations, Journal of Coordination
Chemistry, 65:22, 3972-3982
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Journal of Coordination Chemistry
Vol. 65, No. 22, 20 November 2012, 3972–3982
A new imidazophenanthroline derivative and its Hg(II) complex:
structures, photophysical properties, and DFT calculations
ZHENG ZHENGy, ZHI-PENG YUy, HONG-PING ZHOU*y,
JIA-XIANG YANGy, YAN FENGy, LIN KONGy,
JIE-YING WUy and YU-PENG TIANyzx
yDepartment of Chemistry, Anhui University and Key Laboratory of Functional Inorganic
Materials Chemistry of Anhui Province, 230039 Hefei, PR China
zState Key Laboratory of Crystal Materials, Shandong University, 250100 Jinan, PR China
xState Key Laboratory of Coordination Chemistry, Nanjing University,
210093 Nanjing, PR China
(Received 7 May 2012; in final form 14 August 2012)
A new ligand (L) and its mercury(II) complex have been synthesized under mild conditions.
X-ray single-crystal structural analyses reveal 1-D, 2-D, and 3-D supermolecular structure of
L and HgLI2. Solvent molecules and various weak interactions, including hydrogen bonds
(N–Hꢀ ꢀ ꢀN, O–Hꢀ ꢀ ꢀO, and O–Hꢀ ꢀ ꢀN) and ꢀ–ꢀ interactions play signiEcant roles in the Enal
supermolecular structures. Detailed investigation on 1H NMR spectra of L and HgLI2 are
presented. Their photophysical properties were investigated both experimentally and
theoretically.
Keywords: Mercury(II) complex; Crystal structure; 1H NMR spectra; Optical properties;
Theoretically
1. Introduction
Recently, organic–inorganic hybrid materials have been of interest for their use in
catalysis and molecular separations and due to their fascinating structures [1–7].
Properties are derived from the natural structure and can be subtly moderated by slight
structure changes [8]. Self-assembly of molecular building blocks through molecular
recognition has led to a number of functional organic and hybrid inorganic–organic
materials [9, 10].
Organic bridging ligands play an important role in syntheses directed toward
valuating their inFuence on the formation of different networks. 1,10-Phenanthroline
can provide ꢀ–ꢀ stacking interactions in either intra- or inter-molecular mode,
contributing to the stability and formation of extended supramolecular structures [11].
The literature on imidazoles as possible donors to form coordination polymers has
expanded rapidly [12–14]. Transition-metal complexes have applications in catalysis,
*Corresponding author. Email: zhpzhp@263.net
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.729822

Imidazophenanthroline Hg
3973
adsorption, electric conducting materials, magnetic, optical materials, etc. [15–19].
In contrast to the well-documented Ru-phen complexes, only a few Hg–phen complexes
have been reported [20–25]. Therefore, investigation of structures and properties of
Hg-phen complexes may provide useful information. The aromatic ring may present a
ꢀ–ꢀ stacking to assemble into a supramolecular structure. Noncovalent interactions
(hydrogen bonds and ꢀ–ꢀ stacking interactions) are useful for supramolecular networks
from molecular building blocks.
Here we report the crystal structures of new ligand (L) and HgLI2. L was prepared
according to the literature method with some modiEcation [26], incorporating one
imidazole at the terminal (scheme 1). Investigation on the H NMR spectra of L and
1
HgLI2 are presented in this article. Theoretical and experimental studies of the
photophysical properties of L and HgLI2 are also discussed.
2. Experimental
2.1. Physical measurements
IR spectra were recorded with a Nicolet FT-IR NEXUS 870 spectrometer (KBr discs)
from 4000 to 400 cmꢁ1. 1H and 13C NMR spectra were recorded on a 400 or 500 MHz
NMR instrument using (CD3)2SO as a solvent. Chemical shifts are reported in parts per
million (ppm) relative to internal TMS (0 ppm) and coupling constants in Hz. Mass
spectra were obtained on a Bruker Autoflex III Smartbeam mass spectrometer.
2.2. Crystal structures determination and refinement
X-ray diffraction measurements were performed on a Bruker SMART CCD area
˚
detector using graphite monochromated Mo-Kꢁ radiation (ꢂ ¼ 0.71069 A) at 298 (2) K.
Intensity data were collected in the variable !-scan mode. Structures were solved by
direct methods and difference Fourier syntheses. Non-hydrogen atoms were refined
anisotropically and hydrogen atoms were introduced geometrically. Calculations were
performed with SHELXTL-97.
Scheme 1. Synthetic routes to L and HgLI2.

3974
Z. Zheng et al.
2.3. Computational details
Calculations were conducted based on the Gauss03 program and the molecular
geometry optimization used for the calculation is obtained from single crystal X-ray
diffraction crystallographic data. Calculations of L based on the density functional
theory (DFT) [27] were performed at the rb3lyp/6-311þG(d) level and calculations of
HgLI2 were carried out with rb3lyp/6-311þG(d) for C H N atoms and the Lanl2dz
basis set for Hg I without any symmetry restraints, which were downloaded from the
EMSL basis set library. For calculating absorption spectra, the 25 lowest spin-allowed
singlet–singlet transitions, up to 5 eV, were taken into account.
2.4. Syntheses
2.4.1. Synthesis of L. A mixture of 4-(1H-imidazol-1-yl)benzaldehyde (0.258 g,
1.5 mmol), 1,10-phenanthroline-5,6-dione (0.315 g, 1.5 mmol), ammonium acetate
(2.31 g, 30 mmol), and glacial acetic acid (30 mL) was reFuxed for 2 h, then cooled to
room temperature and diluted with water (ca 60 mL). Dropwise addition of concen-
trated aqueous ammonia gave a yellow precipitate, which was collected and washed
with water. The crude product was puriEed by recrystallization from a mixture of
ethanol and water to get light yellow crystals (0.49 g, yield 90%). Yellow crystalline
solid was obtained by slow evaporation at room temperature for one week.
m.p.: 4 300ꢂC. FT-IR (KBr, cm-1): 3382, 3110, 1611, 1562, 1526, 1494, 1452, 1057,
741, 695. 1H NMR (400 MHz, (CD3)2SO): ꢃ 13.87 (s, 1H), 9.05 (q, J ¼ 2.8 Hz, 2H), 8.94
(d, J ¼ 8.0 Hz, 2H), 8.43 (d, J ¼ 5.2 Hz, 2H), 8.40 (s, 1H), 7.94 (d, J ¼ 8.4 Hz, 2H), 7.91
(s, 1H), 7.85 (q, J ¼ 8.0 Hz, 2H), 7.19 (s, 1H). 13C NMR (125 MHz, (CD3)2SO): ꢃ
(ppm) ¼ 150.2, 148.5, 144.3, 138.1, 136.4, 136.1, 130.8, 130.2, 128.8, 128.2, 124.3, 124.1,
123.8, 121.1, 119.8, 118.4. MS, m/z (%): 363.25 (100).
2.4.2. Synthesis of HgLI2. L (0.018 g, 0.05 mmol) was added to 5 mL of methanol and
0.027 g (0.06 mmol) of HgI2 was added slowly with stirring over 5 min, forming a yellow
solid immediately. The solution was heated to 60ꢂC for 2 h with stirring. The solid was
collected by Eltration and washed with methanol, yield was 0.037 g (90%). Yellow
crystals were collected after slow evaporation of saturated solution of the crude
complex in DMF. m.p.: 4 300ꢂC. Anal. Calcd for C22H14HgI2N6: C, 32.35; H, 1.73; N,
1
10.29. Found: C, 32.04; H, 1.51; N, 10.53. H NMR: (400 MHz, (CD3)2SO), ꢃ (ppm):
14.088 (s, 1H), 9.153 (s, 2H), 9.118 (d, J ¼ 4.4 Hz, 2H), 8.449 (s, 1H), 8.405 (d,
J ¼ 8.4 Hz, 2H), 8.182 (s, 2H), 7.985 (d, J ¼ 8.4 Hz, 1H), 7.920 (s, 1H), 7.195 (s, 1H).
3. Results and discussion
3.1. Crystal structure of L
Single-crystal X-ray diffraction measurements reveal that
CH3CH2OH ꢀ H2O) and HgLI2 [Hg(C22H14N6)I2] conform to the space group C2/c
L
(C22H14N6 ꢀ

Imidazophenanthroline Hg
3975
Table 1. Crystallographic data for L and HgLI2.
Compound
L
HgLI2
C22H14HgI2N6
816.78
Tetragonal
I4(1)/a
Empirical formula
Formula weight
Crystal system
Space group
C48H44N12O3
836.36
Monoclinic
C2/c
ꢂ
˚
Unit cell dimensions (A, )
a
b
c
24.596(5)
13.531(5)
14.285(5)
124.776(5)
3905(2), 4
298(2)
1.451
0.097
2.07–25.00
6569
3409
28.279(5)
28.279(5)
13.589(5)
90.000(5)
10867(5), 16
298(2)
1.997
7.956
1.66–25.00
35,311
4780
ꢄ
Volume (A ), Z
Temperature (K)
3
˚
Calculated density (g cmꢁ3
)
Absorption coefficient (mmꢁ1
ꢅ range for data collection (ꢂ)
Reflections collected
Independent reflection
No. parameters refined
R1
)
287
280
0.0446
0.1284
0.899
0.0396
0.1425
1.298
wR2
Goodness-of-fit on F2
and I4(1)/a (table 1). Molecular structures showing the arrangement about L and HgLI2
are shown in figures 1 and 2, respectively.
In the crystal structure of L, there is one phen, one EtOH, and one H2O in each
independent crystallographic unit. The dihedral angle between the benzene ring and the
imidazole ring at the terminal is 48.67ꢂ and 10.56ꢂ between the benzene ring and the
phen ring. As shown in figure 3(a), L generates a 1-D chain along the b-axis through
N–Hꢀ ꢀ ꢀN interactions between two neighboring dimers, where the distance of
ꢂ
˚
N4–H4ꢀ ꢀ ꢀN7 is 2.093 A and the angle of N4–H4–N7 is 165.35 . Figure 3(b) shows
that water plays a very important role, linking two neighboring dimers generating a 2-D
layer along the c-axis with a N3–O2–N3 angle of 73.06ꢂ. Water molecule also connects
to two ethanols through O1–H52ꢀ ꢀ ꢀO2 hydrogen bonds (ethanol provided H, d(O1–
ꢂ
˚
H52ꢀ ꢀ ꢀO2) ¼ 2.110 A and ff(O1–O2–O1) ¼ 72.39 ). Finally, L forms a stable 3-D
supermolecular structure through ꢀ–ꢀ stacking interactions (the shortest distance is
˚
3.258 A) between neighboring dimers along the a-axis (figure 4).
3.2. Crystal structure of HgLI2
The asymmetric unit of HgLI2 contains one Hg(II), one phen, and two iodides, as
shown in figure 2(a). Each Hg(II) in HgLI2 is primarily coordinated by two nitrogen
˚
atoms from phen (Hg–N5 2.379(7) A; Hg–N6 2.398(7) A) and two iodides (Hg–I2
˚
˚
˚
2.681(1) A; Hg–I1 2.694(1) A) to furnish a distorted tetrahedral coordination geometry,
consistent with the literature [28]. Each bond angle around mercury is 70.0(2)–125.8(2)ꢂ.
Selected bond lengths and angles are listed in table 2. As shown in figure 5, iodide does
not participate in forming the framework, different from most coordination frame-
works of mercury [29]. However, different from L, the dihedral angle between the
benzene and the phen rings is 14.53ꢂ (larger than the same angle in L), and 27.80ꢂ

3976
Z. Zheng et al.
Figure 1. Molecular structure of L with an atom-labeling scheme.
Figure 2. (a) Molecular structure of HgLI2 with atom-labeling scheme. (b) The closed structure of HgLI2
showing the N–Hꢀ ꢀ ꢀN hydrogen bond.
Figure 3. (a) The 1-D chain of L showing the N–Hꢀ ꢀ ꢀN hydrogen bond along the b-axis. Hydrogen atoms
except H4 are omitted for clarity. (b) The 2-D layer of L showing the O1–Hꢀ ꢀ ꢀO2 and O2–Hꢀ ꢀ ꢀN hydrogen
bond along the c-axis. Hydrogen atoms except H4 and H52 are omitted for clarity.

Imidazophenanthroline Hg
3977
Figure 4. The 3-D supermolecular structure of L showing ꢀ–ꢀ stacking along the a-axis. Hydrogen atoms
except H4 and H52 are omitted for clarity.
ꢂ
˚
Table 2. Selected bond lengths (A) and angles ( ) for HgLI2.
Hg1–N5
Hg1–N6
Hg1–I2
Hg1–I1
2.379(7)
2.398(7)
2.681(1)
2.694(1)
N5–Hg1–N6
N5–Hg1–I2
N6–Hg1–I2
N5–Hg1–I1
N6–Hg1–I1
I2–Hg1–I1
70.0(2)
125.8(2)
99.9(2)
110.1(2)
107.5(2)
123.4(3)
Figure 5. The 3-D supermolecular structure of HgLI2 formed by ꢀ–ꢀ stacking interactions. Hydrogen atoms
except H4 are omitted for clarity.

3978
Z. Zheng et al.
Figure 6. The 2-D layer of HgLI2 formed by ꢀ–ꢀ stacking interactions. Hydrogen atoms except H4 are
omitted for clarity.
(smaller than the same angle in L) for the angle between the benzene and the imidazole
rings at the terminal. The shortest distance of the ꢀ–ꢀ stacking contacts (figure 6)
˚
between the benzene and the imidazole rings (3.307 A) at the terminal in HgLI2 is
˚
slightly longer than the shortest distance of the ꢀ–ꢀ stacking contacts in L (3.258 A),
perhaps due to iodides. Different from L, HgLI2 forms a closed structure through
N–Hꢀ ꢀ ꢀN bond interactions between two neighboring dimers with a N4–H4ꢀ ꢀ ꢀN1
ꢂ
˚
distance of 2.117 A and a angle of N4–H4–N7 162.40 (figure 2b). The distance of
N4–H4ꢀ ꢀ ꢀN1 is longer than L, while the angle is smaller than L. Adjacent closed
structures of HgLI2 are further connected by different ꢀ–ꢀ stacking interactions
˚
(the shortest distance is 3.307 A), generating 2-D and 3-D supermolecular structures
(figures 5 and 6).
3.3. 1H NMR Spectra studies
L and HgLI2 give well-deEned 1H NMR spectra, permitting unambiguous identiEcation
and assessment of purity. The proton on the nitrogen of imidazole resonates at ca ꢃ
13.80 for L as a weak broad singlet, characteristic of an active proton, but is observed as
a strong narrow singlet at ca ꢃ 14.088 for Hg(II) complex. In the 1H NMR spectrum of
L, signals at ꢃ 13.80, 9.15, 9.11, 8.45, 8.40, 8.18, 7.98, 7.92, and 7.19 can easily be
assigned to H(NH), Ha, Hc, Hf, Hd, He, Hg, Hb, and Hh, respectively. These chemical
shifts of protons of L allow the assignment of resonances in HgLI2, as shown in figure 7.
Signals of Ha, Hf, He, Hg, and Hh experience slight shifts compared to those of free L.
Hb and Hc show surprisingly large (0.33 and 0.22 ppm) downEeld shifts compared to
Hc (0.10 ppm). It is probable that the terminal coordinated iodide affects the signal
of Ha because of its large radius. The shift in the resonance positions of other
protons may be due to the reduced electron density of L after coordination with
Hg(II) [26, 30, 31].

Imidazophenanthroline Hg
3979
Figure 7. 1H NMR spectra of L and HgLI2 in the aromatic region between ꢃ 7.1 and 9.3 [(CD3)2SO solvent,
TMS reference].
Figure 8. (a) Experimental UV-Vis absorption spectrum. (b) Calculated UV-Vis absorption spectrum.
3.4. UV-Vis spectra and TD-DFT studies
The experimental and calculated UV-Vis absorption spectra of L and HgLI2 in DMSO
are shown in figure 8. Their absorption spectra exhibit two peaks between 280 and
330 nm. L and HgLI2 exhibit an absorption at 280 nm from ꢀ to ꢀ* transitions; the
absorption at 330 nm corresponds to the ICT transition of the main chain [32].
To investigate the geometrical, electronic, and optical properties of L and HgLI2 at a
molecular level, quantum chemical calculations based on the DFT were performed. The
experimental wavelengths (ꢂexp), calculated wavelengths (ꢂcal), and dipole moment
(Dꢆtotal) are given in table 3. Electron distribution of the HOMO and LUMO energy
levels of L and HgLI2 is shown in figure 9. In the HOMO of L and HgLI2, the electrons
are mainly spread over the molecule along the molecular axis, while in the LUMO the
electrons are mainly concentrated on phenanthroline. In the LUMO of HgLI2,
compared with L, the delocalizable electrons of phenanthroline were increased. Upon
excitation, electrons were mainly transferred from the terminal imidazoles to

3980
Z. Zheng et al.
Table 3. Experimental wavelengths (ꢂexp), calculated wavelengths (ꢂcal),
and dipole moment (Dꢆtotal) for L and HgLI2.
ꢂexp (nm)
ꢂcal (nm)
Dꢆtotal (D)
6.2
L
329
281
327
280
335
272
316
268
HgLI2
16.3
Figure 9. Energy level and electron density distribution of frontier molecular orbitals of L and HgLI2.
phenanthroline, showing a strong migration of ICT character. The calculations also
show that HgLI2 has large molecular dipole moment (Dꢆtotal ¼ 16.3 D). Obviously, it
has a strong interaction in the solid state, which results in Fuorescence quenching of
HgLI2. As shown in table 3 and figure 8, the calculated absorption spectra display a
qualitative agreement in the relative locations of the absorptions with the experimental
observations.
3.5. Solid-state luminescence emission
Solid-state luminescence of L and HgLI2 were investigated at room temperature
(figure 10). HgLI2 emits a weak blue color with a maximum at 522 nm upon excitation
at 320 nm. Comparing with L, the emission of HgLI2 is 52 nm red-shifted. This may be
caused by a change in the HOMO and LUMO energy levels of neutral ligands
coordinating to metal centers. Proved by X-ray structures, the ligand molecules became
more planar after coordination with Hg2þ. The main emission band of L is attributed to
Fuorescence emission stemming from the ligand-centered ꢀ–ꢀ* transition, while the
main emission band of HgLI2 may be tentatively attributed to metal-to-ligand charge
transfer (MLCT) and ꢀ–ꢀ* transition of phenanthroline.

Imidazophenanthroline Hg
3981
Figure 10. Solid-state luminescence spectra of L and HgLI2.
4. Conclusions
A new complex has been prepared from an asymmetric L and Hg(II). Single-crystal
X-ray diffraction measurement shows the structure of L and HgLI2. Solvent and
various weak interactions, including hydrogen bonds (N–Hꢀ ꢀ ꢀN, O–Hꢀ ꢀ ꢀO and O–
Hꢀ ꢀ ꢀN) and ꢀ–ꢀ contacts play signiEcant roles in the Enal supermolecular structures.
1H NMR spectra of L and HgLI2 were assigned. The experimental study gives
reasonable interpretation for photophysical properties based on crystallographic data,
which is supported by DFT calculations.
Supplementary material
Full crystallographic data in CIF format for L and HgLI2 have been deposited with the
Cambridge Crystallographic Data Centre (CCDC No. 848573 and CCDC No. 870552).
Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge, CB2 1EZ, U.K; Fax: þ44(0)-1223-336033; or E-mail:
deposit@ccdc.cam.ac.uk
Acknowledgments
This work was supported by Program for New Century Excellent Talents in University
(China), Doctoral Program Foundation of Ministry of Education of China
(20113401110004), National Natural Science Foundation of China (21071001,
21102001, 21101001, 21271003), Education Committee of Anhui Province
(KJ2012A024), the Team for ScientiEc Innovation Foundation of Anhui Province
(2006KJ007TD), the 211 Project of Anhui University, Ministry of Education Funded
Projects Focus on Returned Overseas Scholar.

3982
Z. Zheng et al.
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