Structures of NHC Hg(II) and Ag(I) complexes and selective recognition of nitrate anion

Article abstract of DOI:10.1039/c4ce01519c

A series of bis-benzimidazolium (or bis-imidazolium) salts, and their eight N-heterocyclic carbene mercury(II) and silver(I) complexes (1-8) have been synthesized and characterized. Complexes 1-4 and 6 contain similar macrometallocycles formed via one bid

Full text of DOI:10.1039/c4ce01519c

View Article Online
View Journal
CrystEngComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Q. liu, Z. Zhao, X.
Zhao, Q. Wei, A. Chen, H. L. Li and X. Wang, CrystEngComm, 2014, DOI: 10.1039/C4CE01519C.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/crystengcomm

Page 1 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
Structures of NHC Hg(II) and Ag(I) Complexes and Selective Recognition of
Nitrate Anion
QingꢀXiang Liu*, ZhiꢀXiang Zhao, XiaoꢀJun Zhao, Qing Wei, AiꢀHui Chen,
HuiꢀLong Li, XiuꢀGuang Wang
Tianjin Key Laboratory of Structure and Performance for Functional Molecules; Key
Laboratory of InorganicꢀOrganic Hybrid Functional Material Chemistry, Ministry of
Education; College of Chemistry, Tianjin Normal University, Tianjin 300387, China.
* Corresponding author, Eꢀmail: tjnulqx@163.com
A series of bisꢀbenzimidazolium (or bisꢀimidazolium) salts, and their eight
Nꢀheterocyclic carbene mercury(II) and silver(I) complexes 1ꢀ8 have been
synthesized and characterized. Complexes 1ꢀ4 and
6
contain similar
macrometallocycles formed via one bidentate carbene ligand and one metal ion. Their
major differences are anionic units, which are related to the amount of metal sources
added. In complex 7, one 30ꢀmembered macrometallocycle is generated via two
ligands and two silver(I) atoms in dilute solution. For open structure of complexes 5
and 8, 5 contains an anionic unit [Hg3Cl8]2ꢀ, and 8 is formed as a dimer through two
monomers [L3Ag2Cl2]. The study of selective recognition of anions on the basis of
fluorescent and UV/vis spectroscopic titrations indicates that macrometallocycle 6 is
an effective chemosensor for nitrate anion.
Introduction
The design and synthesis of receptors for the selective recognition of anions are one
of the most significant areas of hostꢀguest chemistry.1 Most anion receptors have
amide, pyrrole, or urea groups as binding sites to form NꢀH···X hydrogen bonds or
the positively charged ammonium groups (or guanidinium groups) that involve
N+ꢀH···Xꢀꢀtype hydrogen bonds (X = O, N, F, Cl, Br and I).2 In recent years, the
receptors with imidazolyl groups have attracted intensive attention due to their strong
1

CrystEngComm
Page 2 of 38
View Article Online
DOI: 10.1039/C4CE01519C
binding abilities to anionic guests via nonclassical CꢀH···X hydrogen bonds.3, 4
Although a great progress has been made, the receptors with special selectivity and
high sensitivity are seldom reported. During the course of searching for receptors
bearing cavities, we became interested in cyclic Nꢀheterocyclic carbene (NHC) metal
complexes. Nꢀheterocyclic carbenes are a type of important ligand due to their strong
σꢀdonating property,5 and they can coordinate with many metals to form complexes
with various structures including tweezer,6 tripod,7 macrocycle8 and groove.9 The
special structures and multiꢀbonding sites of these complexes made them be useful
receptors.10
Nitrate salt as the environmental pollutant exists extensively in natural world
(such as water, vegetable and food). When crops are irrigated by polluted water, the
nitrate salt can be absorbed. After these crops (such as the vegetable and food) are
consumed by human, the nitrate salt can be transformed into the nitrite salt, and the
latter will make the person poisoning.11, 12 Therefore, the determination of nitrate
group in vegetable and food is of considerable importance for the environment and
human health. There are many methods to detect nitrate group, such as fluorescence13
and UV/vis spectrophotometry,14 ion chromatography15 and electrochemical
methods.16 Among these methods, the fluorescence and UV/vis spectrophotometry
have received more attention due to the high sensitivity and easyꢀoperation.17 In this
paper, we report the preparation of eight bisꢀbenzimidazolium (or bisꢀimidazolium)
salts (L1H2·Cl2ꢀL6H2·Cl2, L7H2·(PF6)2 and L8H2·(PF6)2), as well as the synthesis and
structures of eight NHC mercury(II) and silver(I) complexes (1ꢀ8). Particularly, the
selective recognition of nitrate anion using macrometallocycle 6 as a chemosensor
was studied on the basis of fluorescent and UV/vis spectroscopic titrations.
Results and discussion
Synthesis and general characterizations of bisꢀbenzimidazolium (or
bisꢀimidazolium) salts
As shown in Scheme 1, the salicylic aldehyde as starting material was etherificated
with 1,nꢀdibromoalkane (n = 1, 2, 3 or 4), followed by reduction of aldehyde groups
with sodium borohydride to form 1,nꢀbis(2ꢀhydroxymethylphenoxy)alkylene.
2

Page 3 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
Chlorination of two hydroxy groups in 1,nꢀbis(2ꢀhydroxymethylphenoxy)alkylene
using thionyl chloride gave 1,nꢀbis[2ꢀ(chloromethyl)phenoxy]alkylene, which further
reacted
with
NꢀRꢀbenzimidazole
or
NꢀRꢀimidazole
afforded
chloride
1,nꢀbis[2ꢀ(NꢀRꢀbenzimidazoliumylmethyl)phenoxy]alkylene
L1H2·Cl2ꢀL5H2·Cl2 and 1,nꢀbis[2ꢀ(NꢀRꢀimidazoliumylmethyl)phenoxy]alkylene
chloride L6H2·Cl2ꢀL8H2·Cl2. The subsequent anion exchange with ammonium
hexafluorophosphate was carried out for L7H2·Cl2 and L8H2·Cl2 in methanol to give
L7H·(PF6)2 and L8H2·(PF6)2, respectively. These bisꢀbenzimidazolium (or
bisꢀimidazolium) salts are stable to air and moisture, and soluble in DMSO, DMF,
1
CH2Cl2 or CH3CN, but insoluble in diethyl ether or hydrocarbon solvents. In the H
NMR spectra of precursors, the benzimidazole (or imidazole) proton signals (NCHN)
appear at δ = 9.15ꢀ10.19 ppm, which are consistent with the chemical shifts of the
reported benzimidazolium (or imidazolium) salts.18
HOH2C
CH2OH
OHC
CHO
O
CHO
OH
NaBH4
(CH2)n
Br
Br
2
(CH2)n
O
(CH2)n
O
O
N
O
N R
R
N
N R
N
N
2Clꢀ
Method 1
ClH2C
(CH2)n
CH2Cl
O
O
SOCl2
L1H2·Cl2: n = 2, R = nPr
L2H2·Cl2: n = 2, R = nBu
L3H2·Cl2: n = 2, R = CH2Py
L4H2·Cl2: n = 3, R = CH2Py
L5H2·Cl2: n = 4, R = nPr
(CH2)n
O
Method 1: reflux in acetone.
Method 2: (1) reflux in acetone;
(2) anionic exchange
with NH4PF6 in methanol.
N
N R
R N
N
N
N
R
2Xꢀ
Method 1
or Method 2
O
(CH2)n
O
L6H2·Cl2: n = 1, R = CH2Ph
L7H2·(PF6)2: n = 2, R = Et
L8H2·(PF6)2: n = 3, R = Et
Scheme 1 Preparation of precursors L1H2·Cl2ꢀL6H2·Cl2, L7H2·(PF6)2 and
L8H2·(PF6)2.
Synthesis and general characterization of NHC metal complexes 1ꢀ8
As shown in Scheme 2, NHC mercury(II) complexes 1ꢀ5 were prepared via the
reaction of precursors with mercury(II) salts (such as Hg(OAc)2, HgCl2 or HgI2) at
3

CrystEngComm
Page 4 of 38
View Article Online
DOI: 10.1039/C4CE01519C
different molar ratios in CH3CN or CH3CN/DMSO solution at about 80 ˚C. The
reaction of L4H2·Cl2 with 1.0 mol eq. Hg(OAc)2 afforded monomercury(II)
macrocyclic complex [L4HgCl2] (1) without the presence of bases due to the
deprotonation ability of acetate. The complex [L5Hg](HgCl4) (2) was prepared via the
reaction of L5H2·Cl2 with 2.0 mol eq. HgCl2 in the presence of KOtBu. The reaction
of L1H2·Cl2 with 2.0 mol eq. HgI2 in the presence of KOtBu in CH3CN/DMSO
solution yielded complex [L1Hg(DMSO)](HgI4) (3), in which the dimethyl sulfoxide
(DMSO) participates in coordination with Hg(II) atom. The treatment of L6H2·Cl2
with 3.0 mol eq. HgI2 afforded complex [L6Hg](Hg2I6) (4) using KOtBu as base.
Similarily, the open [L8Hg2Cl2](Hg3Cl8) (5) could be formed via the reaction of
L8H·(PF6)2 with 5.0 mol eq. HgCl2.
NHC silver(I) complexes 6ꢀ8 were prepared via the reaction of precursors with
Ag2O at different molar ratios and different concentrations of reactants in
CH3CN/CH2Cl2 solution under refluxing. The monosilver(I) macrocyclic complex
[L2Ag](Cr2O7)0.5 (6) was obtained via the reaction of L2H2·Cl2 with 0.5 mol eq. Ag2O
in a high concentration solution. In a diluted solution, the disilver(I) macrocyclic
complex [L7 Ag2](PF6)2 (7) could be generated from L7H2·(PF6)2 and 0.5 mol eq.
2
Ag2O. Treatment of L3H2·Cl2 with 1.0 mol eq. Ag2O yieled a dimer [L3Ag2Cl2]2 (8).
Complexes 1ꢀ8 are stable toward air and moisture, and soluble in acetonitrile or
DMSO, but insoluble in diethyl ether or hydrocarbon solvents. Their structures were
confirmed by 1H NMR, 13C{1H} NMR spectroscopy and Xꢀray crystallography. In the
1H NMR spectra of 1ꢀ8, the resonance signals for the benzimidazolium or
imidazolium protons (NCHN) have disappeared, which indicates the formation of the
expected metal carbene complexes. The chemical shifts of other protons are similar to
those of the corresponding precursors. In 13C{1H} NMR spectra, the signals for the
carbene carbons of 1ꢀ5 appear at 170.1ꢀ185.4 ppm, which are similar to the known
carbene metal complexes.18 The signals for the carbene carbons of silver(I) complexes
6ꢀ8 were not observed. The absence of the carbene carbon resonance is not unusual,
and this phenomenon has been previously reported for some silver(I)ꢀcarbene
complexes, which may result from the fluxional behaviour of the NHC complexes.19
4

Page 5 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
Py
Py
Cl
Cl
N
N
N
Hg
N
Hg(OAc)2
L4H2·Cl2
O
O
1
Cl
Cl
Hg
nPr
nPr
Cl
Cl
N
N
N
N
HgCl2
Hg
L5H2·Cl2
KOtBu
O
O
2
I
CH3
I
Hg
I
CH3
nPr
I
S
nPr
O
HgI2
N
N
N
L1H2·Cl2
Hg
KOtBu
N
O
O
3
I
I
Hg
I
I
I
Hg
Hg
Ph
Ph
I
N
N
N
HgI2
L6H2·Cl2
KOtBu
N
O
O
4
Cl
Hg
Cl
Hg
N Et
Cl
Cl
Cl
Cl
Hg
N
O
Cl
Et N
N
HgCl2
Hg
L8H2·(PF6)2
KOtBu
Hg
Cl
Cl
Cl
O
5
5

CrystEngComm
Page 6 of 38
View Article Online
DOI: 10.1039/C4CE01519C
nBu
nBu
N
N
N
Ag
N
Ag2O/CrO3
L2H2·Cl2
O
O
2ꢀ
0.5 Cr2O7
6
O
O
N
Et
Et
N
N
N
Et
Et
N
Ag2O
ꢀ
L7H2·(PF6)2
2PF6
Ag
Ag
N
N
N
O
O
7
N
N
Py
Cl
O
O
Ag2O
Ag
L3H2·Cl2
Ag
Py
N
N
Cl
N
Cl
N
O
N
Py
Ag
Cl
Ag
O
N
Py
8
Scheme 2 Preparation of complexes 1ꢀ8.
Crystal structure of NHC complexes 1ꢀ8
The crystals of 1ꢀ8 (Fig.1ꢀFig. 8) suitable for Xꢀray diffraction were obtained by slow
diffusion of diethyl ether into their CH3CN or CH3CN/DMSO solutions. In complexes
1ꢀ4 and 6, each mꢀmembered macrometallocycle (1: m = 16, 2: m = 17, 3 and 6: m =
15 and 4: m = 14 and) contains one bidentate carbene ligand and one metal atom
(Hg(II) for 1ꢀ4 and Ag(I) for 6). In the same ligand of complexes 1ꢀ8, the dihedral
angles between two benzene rings from phenol ether are 7.5(1)ꢀ89.2(4)˚ (Table S1 in
Supplementary Information), and the dihedral angles between benzimidazole (or
imidazole) rings and adjacent benzene rings from phenol ether are from 61.3(1)˚ to
88.4(0)˚. In NHCꢀmetalꢀNHC units of complexes 1ꢀ4, 6 and 7, the dihedral angles
between two benzimidazole (or imidazole) rings are from 8.6(5)˚ to 36.1(3)˚ (Table
6

Page 7 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
S1). In complexes 1ꢀ8, the internal ring angles (NꢀCꢀN) at the carbene centers are in
the range of 102.5(5)ꢀ108.3(4)˚, which is comparable to those of known NHCꢀmetal
complexes.20
In mercury(II) complexes 1ꢀ5, Hg(II) atoms are tetraꢀcoordinated except that Hg(1)
in 4 is triꢀcoordinated and Hg(1) and Hg(2) in 5 are diꢀcoordinated, and the bond
distances of HgꢀC are from 2.036(9) Å to 2.117(3) Å. In complexes 1ꢀ4, the angles of
CꢀHgꢀC are in the range of 154.3(1)ꢀ170.6(4)˚.
In complex 1, the bond angles of C(14)ꢀHg(1)ꢀCl(1) and Cl(1)ꢀHg(1)ꢀCl(1A) are
91.5(9)˚ and 93.6(5)˚, respectively. The distances of both HgꢀCl bonds are all 2.765(9)
Å. The dihedral angle between two pyridine rings is 26.4(4)˚, and the dihedral angle
between the benzimidazole ring and adjacent pyridine ring is 72.2(3)˚. The molecule
of 1 is situated on a 2ꢀfold axis.
n
In complex 2, two propyl chains point to the opposite directions. The distances
of Hg(1)ꢀCl(2) and Hg(1)ꢀCl(4) are 2.864(7) Å and 2.919(8) Å, respectively. In
[HgCl4]2ꢀ unit, the bond angles of ClꢀHg(2)ꢀCl are from 93.8(4)˚ to 127.8(5)˚. The
bond distances of Hg(2)ꢀCl range from 2.387(1) Å to 2.586(1) Å, and these values are
slightly shorter than those of Hg(1)ꢀCl. The Hg(1)···Hg(2) separation of 3.713(3) Å
indicates that there is no direct interaction between both metal ions (van der Waals
Radii of mercury being 1.70 Å).
In complex 3, the distance of Hg(1)ꢀO(3) is 2.671(9) Å, and similar to the reported
values.21 The bond angles of C(7)ꢀHg(1)ꢀO(3) and C(33)ꢀHg(1)ꢀO(3) are 86.2(3)˚ and
98.6(4)˚, respectively. In [HgI4]2ꢀ unit, the bond distances of Hg(2)ꢀI are from 2.743(9)
Å to 2.896(9) Å, which are similar to the reported values.6b, 22 Additionally, the
distance of Hg(1)ꢀI(2) (3.180(3) Å) is slightly longer than those of Hg(2)ꢀI, but
shorter than the sum of van der Waals Radii of mercury and iodine (3.68 Å).
In the cation of 4, the dihedral angle between two benzene rings from benzyls is
6.3(9)˚, and the dihedral angle between imidazole ring and adjacent benzene ring from
benzyl is 88.8(1)˚. In the anionic unit of 4, a building block [Hg2I6]2ꢀ is formed via two
mercury(II) atoms (Hg(2) and Hg(3)) and six iodine atoms (two bridging iodines I(3)
and I(4) and four terminal iodines I(1), I(2), I(5) and I(6)). In this building block, the
7

CrystEngComm
Page 8 of 38
View Article Online
DOI: 10.1039/C4CE01519C
bond angles of IꢀHgꢀI are in the range of 92.6(3)ꢀ123.5(3)˚, and two Hg(2)ꢀIꢀHg(3)
angles are 82.8(3)˚ and 80.9(2)˚, respectively. The distances of HgꢀIterminal
(2.661(1)ꢀ2.729(1) Å) are slightly shorter than those of HgꢀIbridge (2.805(9)ꢀ3.004(1)
Å). The distance of Hg(2)···Hg(3) (3.840(1) Å) is longer than the sum of van der
Waals Radii (3.40 Å), which shows no interaction between the metal ions.
Noteworthily, the distance of Hg(1)ꢀI(5) (3.228(8) Å) is slightly longer than those of
other HgꢀI.
In the cation of complex 5, an open structure is formed by one carbene ligand L8
and two [HgCl] units. Two CꢀHgꢀCl arrangements are approximately linear with the
angles of 174.5(3)˚ and 177.5(3)˚, and two CꢀHgꢀCl units point to the opposite
directions. The bond distances of HgꢀCl are in the range of 2.288(2)ꢀ2.288(3) Å. The
anionic unit [Hg3Cl8]2ꢀ of 5 contain five terminal chlorine atoms (Cl(3), Cl(4), Cl(8),
Cl(9) and Cl(10)) and three bridging chlorine atoms (Cl(5), Cl(6) and Cl(7)). Among
three bridging chlorine atoms, Cl(6) and Cl(7) are diꢀcoordinated, and Cl(5) is
triꢀcoordinated. The bond distances of HgꢀClbridge (2.448(3)ꢀ2.969(2) Å) are longer
than those of HgꢀClterminal (2.295(3)ꢀ2.348(3) Å). The bond angles of ClꢀHgꢀCl and
HgꢀClꢀHg are 80.0(7)ꢀ159.9(1)˚ and 83.8(7)ꢀ133.3(9)˚, respectively.
In silver(I) complexes 6ꢀ8, the bond distances of AgꢀC are in the range of
2.058(7)ꢀ2.119(4) Å. For both 6 and 7, the silver(I) atom is diꢀcoordinated with two
carbene carbon atoms. The CꢀAgꢀC arrangement is approximately linear with the
bond angles of 173.9(1)˚ for 6 and 177.4(1)˚ for 7. These values are similar to those of
2ꢀ
the reported NHCꢀsilver(I) complexes.23 In Cr2O7 unit of 6, an inversion center is
observed. Different from 6, the cation of
7
contains
a
30ꢀmembered
macrometallocycle formed by two bidentate carbene ligands L7 and two silver(I)
atoms. The Ag···Ag separation of 3.575(3) Å is longer than the sum of van der Waals
Radii (3.44 Å), which suggests no interaction between the metal ions.
In complex 8, a dimer [L3Ag2Cl2]2 is formed by two monomers [L3Ag2Cl2] via
two AgꢀCl bonds, in which an inversion center is observed. In two ends of dimer,
Ag(1) or Ag(1A) are diꢀcoordinated with one carbene carbon atom and one chlorine
atom. In the center of dimer, the quadrangular Ag2Cl2 is coplanar arrangement, where
8

Page 9 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
each silver(I) atom is triꢀcoordinated with one carbene carbon atom and two chlorine
atoms. The bond angles of the Ag(2)ꢀCl(2)ꢀAg(2A) and Cl(2)ꢀAg(2)ꢀCl(2A) are
88.3(3)˚ and 91.7(3)˚, respectively. The bond angle of C(30)ꢀAg(2)ꢀCl(2) is 136.2(1)˚,
and this value is less than that of C(13)ꢀAg(1)ꢀCl(1) (175.7(1)˚). The distance of
Ag(2)ꢀCl(2) are 2.545(1) Å, and this value is slightly longer than that of Ag(1)ꢀCl(1)
(2.339(1) Å). In each monomer, two benzimidazole rings are approximately parallel
with the dihedral angle of 1.9(3)˚, and the dihedral angle between two pyridine rings
is 69.3(2)˚. The benzimidazole ring and adjacent pyridine ring are almost
perpendicular with the dihedral angle of 87.5(2)˚. The Ag(2)···Ag(2A) separation of
of 3.567(3) Å is longer than the sum of van der Waals Radii (3.44 Å), which shows no
interaction between the metal ions.
Fig. 1 Perspective view of 1 and anisotropic displacement parameters depicting 30%
probability. All hydrogen atoms were omitted for clarity. Symm. Code: i: y, x, ꢀz.
Fig. 2 Perspective view of 2 and anisotropic displacement parameters depicting 30%
probability. All hydrogen atoms were omitted for clarity.
9

CrystEngComm
Page 10 of 38
View Article Online
DOI: 10.1039/C4CE01519C
Fig. 3 Perspective view of 3 and anisotropic displacement parameters depicting 30%
probability. All hydrogen atoms were omitted for clarity.
Fig. 4 Perspective view of 4 and anisotropic displacement parameters depicting 30%
probability. All hydrogen atoms were omitted for clarity.
Fig. 5 Perspective view of 5 and anisotropic displacement parameters depicting 30%
probability. All hydrogen atoms were omitted for clarity.
10

Page 11 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
Fig. 6 Perspective view of 6 and anisotropic displacement parameters depicting 30%
probability. All hydrogen atoms were omitted for clarity.
Fig. 7 Perspective view of 7 and anisotropic displacement parameters depicting 30%
probability. All hydrogen atoms were omitted for clarity. Symm. Code: i: 0.5 ꢀ x, 1.5 ꢀ
y, z.
Fig. 8 Perspective view of 8 and anisotropic displacement parameters depicting 30%
probability. All hydrogen atoms were omitted for clarity. Symm. Code: i: 2 ꢀ x, 1 ꢀ y, 2
ꢀ z.
11

CrystEngComm
Page 12 of 38
View Article Online
DOI: 10.1039/C4CE01519C
The crystal packings of complexes 1ꢀ8
In the crystal packing of 1, 2D supramolecular layer (Fig. S1(a) in Supplementary
Information) and 3D supramolecular architecture (Fig. S1(b)) are formed via two
types of πꢀπ stacking interactions24 (the data of π···π interactions being given in Table
S2). One is between intermolecular benzimidazole rings and benzene rings, and
another is between intermolecular benzene rings and pyridine rings.
As shown in Fig. S2(a), 2D supramolecular layer of 2 is formed through two types
of CꢀH···Cl hydrogen bonds25 (the data of hydrogen bonds being given in Table S3).
The hydrogen atoms in the hydrogen bonds are from methylene groups or
benzimidazole rings. Additionally, 2D supramolecular layers are further extended into
3D supramolecular architecture through πꢀπ stacking interactions from benzene rings
(Fig. S2(b)).
In the crystal packing of 3, the 2D supramolecular layers (Fig. S3(a)) are formed
by CꢀH···π contacts26 and π···π interactions from intermolecular benzimidazole rings.
In CꢀH···π contacts, the hydrogen atoms are from benzene rings and π systems are
from benzimidazole rings (the data of CꢀH···π contacts being given in Table S2). The
2D supramolecular layers are further extended into 3D supramolecular architecture
(Fig. S3(b)) through CꢀH···I hydrogen bonds.27 In CꢀH···I hydrogen bonds, the
hydrogen atoms are from methylene groups.
In the crystal packing of 4 (Fig. S4), 2D supramolecular layer is formed through
CꢀH···π contacts and two types of CꢀH···I hydrogen bonds. In CꢀH···π contacts, the
hydrogen atoms are from benzene rings and π systems are from benzene rings. In
CꢀH···I hydrogen bonds, the hydrogen atoms are from benzene rings.
In the crystal packing of 5 (Fig. S5), 2D supramolecular layer is formed by two
types of CꢀH···Cl hydrogen bonds. In the hydrogen bonds, the hydrogen atoms are
from different methylene groups.
In the crystal packing of 6, 2D supramolecular layer (Fig. S6(a)) is formed
through CꢀH···π contacts and two types of CꢀH···O hydrogen bonds.28 In CꢀH···π
n
contacts, the hydrogen atoms are from CH2 of butyl groups and π systems are from
benzene rings. In the hydrogen bonds, oxygen atoms are from [Cr2O7]2ꢀ units, and the
12

Page 13 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
hydrogen atoms are from CH2 of benzyl groups or ether chains. Additionally, 2D
supramolecular layers are further extended into 3D supramolecular network via new
CꢀH···O hydrogen bonds (Fig. S6(b)). In the hydrogen bonds, the oxygen atoms are
from [Cr2O7]2ꢀ units, and the hydrogen atoms are from benzimidazole rings.
In the crystal packing of 7 (Fig. S7(a) and Fig. S7(b)), 2D supramolecular layer
and 3D network are formed via the same CꢀH···π contacts. In CꢀH···π contacts, the
hydrogen atoms are from methylene groups and π systems are from the benzene rings.
In the crystal packing of 8, 2D supramolecular layer (Fig. S8(a)) is formed by
CꢀH···π contacts. In CꢀH···π contacts, the hydrogen atoms are from benzimidazole
rings and π systems are from benzene rings. 2D supramolecular layers are further
extended into 3D supramolecular architecture through new CꢀH···π contacts (Fig.
S8(b)). In new CꢀH···π contacts, the hydrogen atoms are from methylene groups of
picolyl and π systems are from benzimidazole rings.
The conformations of NHC mercury(II) and silver(I) complexes based on the
bidentate carbene ligands with different linkers
In order to further undersand the influence of different precursors and different metal
sources on the conformations of metal complexes in solid state, in the paper, eight
precursors and different metal sources (HgCl2, HgI2, Hg(OAc)2 and Ag2O) are used
for the preparation of metal complexes. In these precursors, there exist differences in
four positions as shown in Scheme 1, namely, (a) the size of linkers ((CH2)n, n = 1ꢀ4),
(b) the different R (Et, nPr, nBu, CH2Ph or CH2Py), (c) the imidazole or benzimidazole,
ꢀ
and (d) the different anions (Clꢀ and PF6 ). Complexes 1ꢀ8 contain three types of
conformations as shown in Scheme 2: the mononuclear macrocycle (e.g., complexes
1ꢀ4 and 6), the dinuclear macrocycle (e.g., complex 7), and the open structure (e.g.,
complexes 5 and 8). The differences of these conformations are mainly related to the
ratios of precursors to metal sources and the concentrations of reactants as shown in
Table 1, while the differences of precursors or metal sources have little influence on
these conformations. In NHCꢀHg(II) complexes 1ꢀ5, the different molar ratios of
precursors to mercury salts lead to diverse connectivities. For example, complexes 1ꢀ4
contain similar cationic macrometallocycles (Scheme 2(1)ꢀ(4)), but their anionic units
13

CrystEngComm
Page 14 of 38
View Article Online
DOI: 10.1039/C4CE01519C
are different. Anions are highly dependent on the amount of mercury salts added.
When mercury salts are excessive, the different anionic units [HgpYq ]2ꢀ can be formed
(Y = Cl or I; p = 1, 2 or 3; q = 4, 6 or 8), and the similar cases have been reported.19a,
29
By contrast, the formation of cyclic NHCꢀAg(I) complexes 6 and 7 are related
mainly to the concentration of reactants. Upon precursor and Ag2O at a 1:0.5 molar
ratio, a high concentration of reactants affords the mononuclear macrocycle 6 as main
product, however, a dilute solution of reactants gives dinuclear macrocycle 7 as
dominating product. This phenomenon has also been reported by Xu and Saito.30
Table 1 The molar ratios of precursors to metal sources for 1ꢀ8
Precursors:metal sources
Complexes
1:1
1
1:2
2 or 3
NHCꢀHg(II)
NHCꢀAg(I)
1:3
4
5
6
7
8
1:5
1:0.5 in high conc.
1:0.5 in dilute conc.
1:1
Based on literature reports and our results obtained here, NHC mercury(II) and
silver(I) complexes, which are formed via the reaction of the bidentate imidazolium
(or benzimidazolium) salts (A) bearing different linkers with mercury(II) compounds
or silver(I) compounds, contain mainly five types of conformations (I)ꢀ(V) as shown
in Scheme 3: (1) the mononuclear macrocycle (I) with one bidentate carbene ligand,
such as complexes 1ꢀ4, 6 and known complexes with different linkers (linkers:
phenelene6(b), 31 pyridyl, 31(i), 31(n), 32 and ether chain29(a), 29(b), 31(c), 33). Compared with
known complexes, 1ꢀ4 and 6 show similar cationic macrometallocycles, and their
ꢀ
major differences are the anionic units (such as Clꢀ, Brꢀ, Iꢀ, PF6 , OAcꢀ or [HgpYq]2ꢀ).
The high concentration of reactants is usually favorable for the preparation of this
type of macrometallocycle. (2) The dinuclear macrocycle (II) with two bidentate
carbene ligands, such as complex 7 and known complexes with different linkers
31(i), 31(r), 35
(linkers: phenelene,10(a), 10(b), 31(o), 31(r), 32(s), 34 pyridyl,19(a), 23(a), 31(e),
ether
29(c)
31(g), 31(q), 31(t),
chain8(b),
and alkyl9(b),
36). For these complexes, the diverse
distortions of macrometallocycle are the major different due to the flexibility and
14

Page 15 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
length of linkers. The dilute concentration of reactants30 and hexafluorophosphate as
31(g), 31(s), 37
counteranion10(a),
are usually helpful to the preparation of this type of
macrometallocycle. (3) The dinuclear macrocycle (III) with one bidentate carbene
ligands,9(b), 30(a), 31(g), 31(o), 31(t)ꢀ31(v) which is likely to be obtained upon precursor and
metal ion at a 1:2 molar ratio. (4) The open structure (IV) (such as complex 5 and
known complexes6(b), 19(b), 31(g), 31(s), 38). (5) The oligomer (such as complex 8 and
known complexes31(k), 31(w), 39). The conformations of complexes 5 and 8 are similar to
those of known complexes with different linkers.
On the whole, the conformations of NHC mercury(II) and silver(I) complexes
based on the bidentate carbene ligands with different linkers are mainly related to the
following factors: (a) the ratio of precursor to metal source; (b) the concentration of
reactants; (c) the flexibility and length of linkers in ligands; (d) the anionic types in
ꢀ
reaction system (involving: the anions from precursors or metal sources (such as PF6 ,
ꢀ
Clꢀ, Brꢀ, Iꢀ, OAcꢀ, CO32ꢀ or NO3 ), and new formation of anions in the reactions (such
2ꢀ
as [HgpYq]2ꢀ or Cr2O7 )). In addition, some solvents (such as CH3CN, DMSO or
DMF), which can participate in coordination with metal ions, may have also some
effects on the conformations of complexes. The other factors, such as benzimidazole
or imidazole rings, have probably little influence on the formation of diverse
conformations.
Additionally, in the preparations of NHC mercury(II) and silver(I) complexes,
whether or not the bases (such as KOtBu, K2CO3 or NaOAc) are used depends mainly
on metal sources. When the metal sources are alkaline oxide (like Ag2O) or metal
salts with OAcꢀ or CO32ꢀ anions (such as AgOAc, Ag2CO3 or Hg(OAc)2, which have
capability to snatch proton of NCHN from benzimidazolium or imidazolium salts),
the base is not required. However, when the anions of metal sources are Clꢀ, Brꢀ, Iꢀ or
ꢀ
NO3 (such as: HgCl2, HgBr2, HgI2 or AgNO3), the base must be used.
15

CrystEngComm
Page 16 of 38
View Article Online
DOI: 10.1039/C4CE01519C
linker
X = PF6, Cl, Br or I
R N
2Xꢀ
R
N
N
N
A
Agꢀcompounds (Ag2O, AgOAc, Ag2CO3 or AgNO3)
Hgꢀcompounds (HgCl2, HgBr2, HgI2 or Hg(OAc)2)
linker
linker
linker
R
N
N
N
R N
R N
N
N
N
N
N
N
N
N
N
N
M
M
M
M
M
R
R
R
R
N R
linker
I
III
II
linker
linker
M
N
N
R
N
M
N
N
R N
N
R
N
M
R
n
IV
V
Scheme 3 The conformations of NHC mercury(II) and silver(I) complexes.
Recognition of nitrate anion using 6 as a chemosensor
According to the size of cavity and structural characteristics of 6, the selective
ꢀ
ꢀ
ꢀ
recognition of some anions (Fꢀ, Clꢀ, Brꢀ, Iꢀ, H2PO4 , HSO4 , OAcꢀ and NO3 , and their
cations being tetrabutyl ammonium (TBA+)) using 6 as a chemosensor was
investigated by fluorescent and UV/vis spectroscopic methods in acetonitrile at 25 ˚C
(Fig. 9 and Fig. S9 in Supplementary Information).
As shown in Fig. 9, the chemosensor 6 exhibits double emission at ca. 296 nm and
415 nm (λex = 254 nm; the excitation and emission slits are 5 nm and 3 nm,
respectively). The peak at 296 nm is attributed to the emission of benzimidazole. The
peak at 415 nm was due to anion induced eximer formation, and the similar emission
peak is also observed in the literature of benzimidazole derivatives.40 Upon the
ꢀ
ꢀ
addition of 10.0 mol eq. Fꢀ, Clꢀ, Brꢀ, H2PO4 , HSO4 and OAcꢀ, the fluorescence
emission intensity of 6 does not obviously change. The addition of same amount of
iodide anion resulted in the slight decrease of emission intensity at 296 nm and 415
nm, which is derived from heavy atom effect of iodine.41 Whereas the addition of
16

Page 17 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
same amount of nitrate anion causes a great enhancement of emission intensity at 296
nm and 415 nm. According to the size of cavity (0.47 nm × 0.32 nm) and structural
characteristics of 6, the size of nitrate anion (0.21 nm × 0.21 nm) may match with
complex 6, and nitrate anion can be captured effectively by 6. The main force
between nitrate anion and 6 is electrostatic attraction coming from silver(I) atom and
oxygen atom of nitrate anion (Scheme S1 in Supplementary Information). Upon the
addition of nitrate anion into the solution of 6, the remarkable enhancement of
fluorescence intensity may be attributed to the electronꢀdonating effect of oxygen
atom of nitrate anion. Thus, complex 6 can be functioned as a highly selective
fluorescent chemosensor for nitrate anion. In order to further understand the
ꢀ
interactions of nitrate anion with 6, the 1H NMR spectra of 6/NO3 are compared with
those of 6. As depicted in Fig. S15, the signals of protons from the benzene rings of
phenol ether have split, and new peaks appear at δ 7.80 ppm and 8.00 ppm. This
change may result from the formation of NꢀO···H hydrogen bonds between nitrate
anion and hydrogen atoms from benzene rings of phenol ether. Thus NꢀO···H
hydrogen bonds may inhance the combination of nitrate anion and 6.
As shown in Fig. 10, upon the titration of nitrate anion into the solution of 6, the
fluorescence intensity at 296 nm and 415 nm increases gradually due to the
interactions between nitrate anion and 6.42 In the inset of Fig. 10, when the ratio of
−
C NO /C6 was below or equal to 1:1, the fluorescence intensity shows a linear
3
enhancement with the increasing concentration of nitrate anion. When the ratio was in
range of 1:1 to 4:1, the tendency of the fluorescence intensity enhancement becomes
−
slow. When the ratio exceeded 4:1, higher CNO will not lead to further emission
3
enhancement. From the changes in nitrateꢀdependent fluorescence intensity, the
detection limit is estimated to be 1.1 × 10ꢀ7 mol/L (Fig. S10).43 The association
ꢀ
constant Ks for 6/NO3 was calculated as 3.67 × 105 Mꢀ1 (R = 0.992) by using the
nonlinear leastꢀsquare analysis (Equation 1, Fig. 10),44
F/F0=1+(Fmax/2F0ꢀ1/2){1+C /C6+1/KSC6ꢀ[(1+C /C6+1/KsC6)2ꢀ4C /C6]1/2} (1)
NO3−
NO3−
NO3−
where F and F0 are the fluorescence intensity of 6 in the presence and absence of
17

CrystEngComm
Page 18 of 38
View Article Online
DOI: 10.1039/C4CE01519C
ꢀ
NO3 , respectively; Fmax is the maximum fluorescence intensity in the titration
−
experiment; CNO and C6 are the concentrations of nitrate anion and 6, respectively;
3
Ks is the association constant.
Fig. 9 Fluorescence spectra of 6 (1 × 10ꢀ5 mol/L) upon the addition of the tetrabutyl
ꢀ
ꢀ
ꢀ
ammonium salts of Fꢀ, Clꢀ, Brꢀ, Iꢀ, H2PO4 , HSO4 , OAcꢀ and NO3 (10.0 mol eq.) in
acetonitrile at 25 ˚C.
Fig. 10 Fluorescence titration spectra of 6 (1.0 × 10ꢀ5 mol/L) in the presence of
−
different concentrations of nitrate anion in acetonitrile at 25 ˚C. CNO for curves 1ꢀ16
3
(from bottom to top) are 0, 0.11, 0.25, 0.43, 0.67, 1.0, 1.25, 1.5, 2.0, 3.0, 4.0, 5.0, 7.0,
9.0, 12.0, 15.0 × 10ꢀ5 mol/L. Inset: the fluorescence at 296 nm of 6 as a function of
nitrate anion concentration.
18

Page 19 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
Fig. 11 UV/vis absorption spectra of 6 (1.0 × 10ꢀ5 mol/L) in acetonitrile at 25 ˚C. The
concentrations of nitrate anion for curves 1ꢀ15 (from bottom to top) are: 0, 0.04, 0.11,
0.17, 0.26, 0.33, 0.43, 0.67, 1.0, 1.5, 2.4, 3.0, 4.0, 6.0, 9.0 × 10ꢀ5 mol/L. Inset: The Job
ꢀ
plot for 6/NO3 complex in acetonitrile at 275 nm.
In UV/vis titration experiment of 6, the UV/vis absorption spectra increases
gradually at 204ꢀ280 nm (Fig. 11) with the increasing of nitrate anion concentration,
where a red shift at 204ꢀ225 nm is observed. The phenomenon indicates that
interactions between nitrate anion and 6 reduce π→π* transition energy of benzene
ꢀ
rings.45 It is notable that a 1:1 complexation stoichiometry for 6/NO3 complex is
established by Job’s plot analysis at 275 nm (inset of Fig. 11),9a, 46 which is in
consistent with the fluorescence titration result as displayed in inset of Figure 10. The
ꢀ
−
stability constant K for 6/NO3 calculated from the plot of A0/ꢁA versus 6/C
based
NO3
on the standard BenesiꢀHildebrand equation (Equation 2) is 2.88 × 105 Mꢀ1 (R = 0.994)
(Fig. S11),
−
A0/(A0ꢀA)=εr(1/KC +1)/(εr ꢀ εc) (2)
NO3
where A0 is the absorption of chemosensor 6 in the absence of nitrate anion, and
A0ꢀA is the discrepancy of absorption between the absence and presence of nitrate
ꢀ
anion; εr and εc are the molar extinction coefficients of 6 and 6/NO3 , respectively;
−
CNO is the concentration of nitrate anion. The stability constant K is given by the
3
ratio of intercept/slope.47
19

CrystEngComm
Page 20 of 38
View Article Online
DOI: 10.1039/C4CE01519C
In order to further study the special selective ability of 6 as a chemosensor for
nitrate anion, the competition experiments were conducted. Complex 6 (1.0 × 10ꢀ5
ꢀ
ꢀ
mol/L) was first mixed with 5.0 mol eq. various anions (Fꢀ, Clꢀ, Brꢀ, Iꢀ, H2PO4 , HSO4
and OAcꢀ), and then 1.0 mol eq. nitrate anion was added and the competition events
were monitored by fluorescent spectra. According to the fluorescent spectra, no
obvious interference in the presence of 5.0 mol eq. various anions was observed (Fig.
S12). In the case of chloride anion, the fluorescence intensity increased about 20%
than that in the presence of nitrate anion alone. The fluorescence intensities of other
anions were almost identical to that in the presence of nitrate anion alone. The results
show that chemosensor 6 can discriminate between nitrate anion and other anions,
especially dihydrogen phosphate anion and fluoride anion, which are common
interfering anions in many cases.48
Fluorescent enhancement similar to Fig. 9 was also observed after the addition of
other nitrate salts (15.0 × 10ꢀ5 mol/L) with different countercations (Li+, Na+, K+,
+
NH4 , Zn2+, Co2+ and Ni2+) to 6 (1 × 10ꢀ5 mol/L) (Fig. S13). Thus, the different
cations had no obvious influence on the binding between 6 and nitrate anion.
Reversible binding of 6 with nitrate anion was also carried out (Fig. S14). The
addition of 7.5 mol eq. mercury(II) cation to a mixture of 6 (1.0 × 10ꢀ5 mol/L) and
nitrate anion (15.0 × 10ꢀ5 mol/L) resulted in the decrease of fluorescence intensity at
296 nm and 415 nm, and the fluorescence intensity is approximately equal to 6, which
signifies the regeneration of the free 6. The fluorescence intensity increased upon
addition of nitrate anion again. This result shows that 6 is a good chemosensor for
nitrate anion with admirable ability of reversibility and regeneration.
Conclusions
In summary, a series of bisꢀbenzimidazolium (or bisꢀimidazolium) salts and their
eight Nꢀheterocyclic carbene mercury(II) and silver(I) complexes have been
synthesized and characterized. Each of complexes 1ꢀ4, 6 and 7 contains one
macrometallocycle. Complex 5 is an open structure and complex 8 is a dimer. The
different connectivities of complexes 1ꢀ8 are mainly related to the ratios of precursors
to metal sources and the concentrations of reactants, while the differences of
20

Page 21 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
precursors or metal sources have little influence on the conformations of complexes
1ꢀ8. The selective recognition of nitrate anion using macrometallocycle 6 as a
chemosensor was studied by the methods of fluorescent and UV/vis spectroscopic
titrations. Ks value of 3.67 × 105 Mꢀ1 based on the nonlinear leastꢀsquare analysis and
K value of 2.88 × 105 Mꢀ1 based on the standard BenesiꢀHildebrand equation are
similar to each other.49 Large Ks and K values show that macrometallocycle 6 has
great affinity to nitrate anion. The special selective ability of 6 for nitrate anion make
that it can discriminate nitrate anion and other anions in acetonitrile. From the
changes in nitrateꢀdependent fluorescence intensity, the detection limit was estimated
to be 1.1 × 10ꢀ7 mol/L. The high selectivity and sensitivity and the great affinity to
nitrate anion mean that the chemosensor has a potential application for quantitative
measurement of nitrate anion. Further studies on the synthesis of new organometallic
compounds from precursors L1H2·Cl2ꢀL6H2·Cl2, L7H2·(PF6)2 and L8H2·(PF6)2, and
the recognition for other guests are underway.
Experimental
General procedures
All manipulations were performed using Schlenk techniques, and solvents were
purified by standard procedures. All the reagents for synthesis and analyses were of
analytical grade and used without further purification. Melting points were determined
1
with a Boetius Block apparatus. H and 13C{1H} NMR spectra were recorded on a
Varian Mercury Vx 400 spectrometer at 400 MHz and 100 MHz, respectively.
Chemical shifts, δ, are reported in ppm relative to the internal standard TMS for both
1H and 13C NMR. J values are given in Hz. Elemental analyses were measured using a
PerkinꢀElmer 2400C Elemental Analyzer. The luminescent spectra were conducted on
a Cary Eclipse fluorescence spectrophotometer. UVꢀvis spectra were obtained using a
JASCOꢀV570 spectrometer.
Preparation of 1,2ꢀbis[2ꢀ(Nꢀnpropylbenzimidazoliumylmethyl)phenoxy]ethylene
chloride (L1H2·Cl2)
A DMF (80 mL) soulution of salicylic aldehyde (15.601 g, 127.7 mmol),
1,2ꢀdibromoethane (10.000 g, 53.2 mmol) and anhydrous K2CO3 (17.656 g, 127.7
21

CrystEngComm
Page 22 of 38
View Article Online
DOI: 10.1039/C4CE01519C
mmol) was stirred for 24 hours at 50 ˚C under nitrogen protection. The resulting
brown solution was poured into water (200 mL), and a brown precipitate was formed.
The
product
was
filtered
to
give
a
brown
powder
of
1
1,2ꢀbis[2ꢀ(formyl)phenoxy]ethylene. Yield: 12.196 g (83%). M.p.: 146ꢀ148 ˚C. H
NMR (400 MHz, DMSOꢀd6): δ 4.44 (t, J = 8.0 Hz, 4H, CH2), 7.03 (m, 4H, PhH), 7.53
(t, J = 8.8 Hz, 2H, PhH), 7.80 (d, J = 8.0 Hz, 2H, PhH), 10.53 (s, 2H, CHO).
Sodium borohydride (3.359 g, 88.8 mmol) was slowly added to a THF/C2H5OH
(150 mL, 1:1, v/v) solution of 1,2ꢀbis[2ꢀ(formyl)phenoxy]ethylene (10.000 g, 37.0
mmol) with stirring for 2 hours in the iceꢀwater bath. Then the solution was stirring
under refluxing for 10 hours. After the solvent was removed with a rotary evaporator,
H2O (150 mL) was added to the residue. Then the solution was extracted with CH2Cl2
(3 × 30 mL) and the organic phase was dried over anhydrous MgSO4. After removing
CH2Cl2, a white solid of 1,2ꢀbis[2ꢀ(hydroxymethyl)phenoxy]ethylene was obtained.
1
Yield: 9.192 g (90%). M.p.: 122ꢀ124 ˚C. H NMR (400 MHz, DMSOꢀd6): δ 2.42 (s,
2H, OH), 4.31 (s, 4H, CH2), 4.49 (s, 4H, CH2OH), 6.95ꢀ7.00 (m, 4H, PhH), 7.18 (t, J
= 10.0 Hz, 2H, PhH), 7.37 (d, J = 7.6 Hz, 2H, PhH).
To a solution of 1,2ꢀbis[2ꢀ(hydroxymethyl)phenoxy]ethylene (10.012 g, 36.5
mmol) in CHCl3 (100 mL) was added thionyl chloride (17.348 g, 145.8 mmol). The
mixture was refluxed for 12 hours and poured into water (300 mL) after cooling. The
organic phase was dried over anhydrous MgSO4. The solvent was removed and a
white solid of 1,2ꢀbis[2ꢀ(chloromethyl)phenoxy]ethylene was obtained. Yield: 8.475 g
(74%). M.p.: 96ꢀ98 ˚C. 1H NMR (400 MHz, DMSOꢀd6): δ 4.43 (s, 4H, OCH2), 4.70 (s,
4H, CH2Cl), 6.96 (d, J = 7.2 Hz, 2H, PhH), 7.14 (d, J = 8.4 Hz, 2H, PhH), 7.34ꢀ7.41
(m, 4H, PhH).
An acetone (100 mL) solution of Nꢀnpropylbenzimidazole (2.371 g, 14.8 mmol)
and 1,2ꢀbis[2ꢀ(chloromethyl)phenoxy]ethylene (2.085 g, 6.7 mmol) was stirred for 3
days under refluxing, and a white precipitate was formed. The product was filtred and
washed with small portions of acetone to give
a
white powder of
1,2ꢀbis[2ꢀ(Nꢀnbutylbenzimidazoliumylmethyl)phenoxy]ethylene chloride (L1H2·Cl2).
Yield: 3.750 g (88%). M.p.: 160ꢀ162 ˚C. Anal. Calcd for C36H40O2N4Cl2: C, 68.45; H,
22

Page 23 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
6.38; N, 8.87%. Found: C, 68.67; H, 6.54; N, 8.67%. 1H NMR (400 MHz, DMSOꢀd6):
δ 0.81 (t, J = 7.4 Hz, 6H, CH3), 1.82 (m, 4H, CH2), 4.36 (t, J = 7.6 Hz, 8H, CH2), 5.66
(s, 4H, CH2), 7.07 (t, J = 7.4 Hz, 2H, ArH), 7.16 (d, J = 8.4 Hz, 2H, ArH), 7.42 (m,
4H, ArH), 7.62 (m, 4H, ArH), 7.85 (d, J = 8.4 Hz, 2H, ArH), 8.02 (d, J = 8.4 Hz, 2H,
ArH), 10.06 (s, 2H, 2ꢀbimiH). 13C{1H} NMR (100 MHz, DMSOꢀd6): δ 10.5 (CH3),
22.0 (CH2), 47.8 (CH2), 55.9 (CH2), 66.7 (CH2), 112.5 (PhC), 113.6 (bimiC), 113.7
(bimiC), 121.0 (bimiC or PhC), 121.6 (bimiC or PhC), 126.3 (PhC), 130.7 (bimiC or
PhC), 130.8 (bimiC or PhC), 142.6 (2ꢀbimiC), 156.5 (PhC) (bimi = benzimidazole).
Bisꢀbenzimidazolium (or bisꢀimidazolium) salts L2H2·Cl2ꢀL6H2·Cl2 were
prepared in a manner analogous to that of L1H2·Cl2 (the data of analyses being given
in Supplementary Information).
Preparation
of
1,2ꢀbis[2ꢀ(Nꢀethylimidazoliumylmethyl)phenoxy]ethylene
hexafluorophosphate (L7H2·(PF6)2)
This compound was prepared through two steps of reactions, and the first step is in a
manner analogous to that of L1H2·Cl2, only Nꢀethylimidazole (1.422 g, 14.8 mmol)
was used instead of Nꢀnbutylbenzimidazole. The second step is anionic exchange with
NH4PF6. NH4PF6 (1.467 g, 9.0 mmol) was added to a methanol (60 mL) solution of
L7H2·Cl2 (2.013 g, 4.0 mmol) with stirring, and a white precipitate was formed
immediately.
A
white
powder
of
1,2ꢀbis[2ꢀ(Nꢀethylimidazoliumylmethyl)phenoxy]ethylene
hexafluorophosphate
(L7H2·(PF6)2) was obtained after filtration and washing with small portions of cold
methanol. Yield: 2.513 g (86%). M.p.: 216ꢀ218 ˚C. Anal. Calcd for C26H32O2N4P2F12:
C, 43.22; H, 4.46; N, 7.75%. Found: C, 43.51; H, 4.68; N, 7.91%. 1H NMR (400 MHz,
DMSOꢀd6): δ 1.36 (t, J = 7.2 Hz, 6H, CH3), 4.11 (t, J = 7.4 Hz, 4H, CH2), 4.44 (d, J =
7.2 Hz, 4H, OCH2), 5.29 (d, J = 7.6 Hz, 4H, CH2), 7.06 (t, J = 7.4 Hz, 2H, ArH), 7.20
(t, J = 7.8 Hz, 2H, ArH), 7.40 (d, J = 6.4 Hz, 4H, ArH), 7.43 (d, J = 7.6 Hz, 2H, ArH),
9.10 (s, 2H, ArH), 9.12 (s, 2H, 2ꢀimiH). 13C{1H} NMR (100 MHZ, DMSOꢀd6): δ 15.0
(CH3), 44.2 (CH2), 47.8 (CH2), 66.7 (CH2), 112.4 (PhC), 121.1 (PhC), 122.0 (PhC),
122.4 (PhC), 122.6 (PhC), 130.5 (imiC or PhC), 130.8 (imiC or PhC), 135.7 (2ꢀimiC),
156.2 (PhC).
23

CrystEngComm
Page 24 of 38
View Article Online
DOI: 10.1039/C4CE01519C
Bisꢀimidazolium salt L8H2·(PF6)2 was prepared in a manner analogous to that of
L7H2·(PF6)2 (the data of analyses being given in Supplementary Information).
Preparation of [L4HgCl2] (1)
A CH3CN (30 mL) suspension of L4H2·Cl2 (0.223 g, 0.3 mmol) and Hg(OAc)2 (0.095
g, 0.3 mmol) was stirred at about 80 ˚C for 12 hours, and an orange solution was
formed. The resulting solution was filtered and concentrated to 10 mL, and Et2O (5
mL) was added to precipitate a yellow powder. Isolation by filtration yields complex
1. Yield: 0.091 g (32%)，Mp: 240ꢀ242 ˚C. Anal. Calcd for C43H38Cl2HgN6O2: C,
1
54.80; H, 4.06; N, 8.91%. Found: C, 54.62; H, 4.33; N, 8.58%. H NMR (400 MHz,
DMSOꢀd6): δ 1.72 (d, J = 4.8 Hz, 2H, CH2), 3.83 (t, J = 2.8 Hz, 4H, CH2), 5.94 (s, 4H,
CH2), 6.39 (s, 4H, CH2), 6.92 (s, 2H, CH2), 7.04 (d, J = 2.4 Hz, 2H, ArH), 7.19 (d, J =
10.0 Hz, 2H, ArH), 7.35 (d, J = 10.8 Hz, 2H, ArH), 7.65 (m, 6H, ArH), 7.88 (m, 6H,
ArH), 8.14 (d, J = 8.0 Hz, 2H, ArH), 8.26 (s, 2H, ArH). 13C{1H} NMR (100 MHZ,
DMSOꢀd6): δ 28.7 (CH2), 50.3 (CH2), 51.0 (CH2), 62.7 (CH2), 111.8 (PhC), 113.1
(bimiC), 113.5 (bimiC), 120.2 (bimiC or PhC), 121.9 (bimiC or PhC), 123.1 (PhC or
PyC), 123.5 (PhC or PyC), 125.2 (PhC), 125.4 (PhC), 130.5 (bimiC or PhC), 131.9
(PyC), 132.4 (PyC), 133.7 (PyC), 137.6 (PyC), 149.5 (PyC), 153.7 (PyC), 156.3
(PhC), 185.2 (Ccarbene).
Preparation of [L5Hg](HgCl4) (2)
A CH3CN (30 mL) suspension of L5H2·Cl2 (0.197 g, 0.3 mmol), HgCl2 (0.163 g, 0.6
mmol) and KOtBu (0.078 g, 0.7 mmol) was stirred at about 80 ˚C for 12 hours, and an
orange solution was formed. The resulting solution was filtered and concentrated to
10 mL, and Et2O (5 mL) was added to precipitate a yellow powder. Isolation by
filtration yields complex 2. Yield: 0.153 g (45%), Mp: 257ꢀ259 ˚C. Anal. Calcd for
C38H42Cl4Hg2N4O2: C, 40.39; H, 3.74; N, 4.95%. Found: C, 40.52; H, 3.95; N, 4.71%.
1H NMR (400 MHz, DMSOꢀd6): δ 0.81 (t, J = 6.0 Hz, 6H, CH3), 1.37 (s, 4H, CH2),
1.90 (q, J = 8.0 Hz, 4H, CH2), 3.89 (s, 4H, CH2), 4.74 (t, J = 6.0 Hz, 4H, CH2), 5.84 (s,
4H, CH2), 6.92 (t, J = 8.0 Hz, 2H, ArH), 7.04 (d, J = 8.0 Hz, 2H, ArH), 7.31 (t, J = 4.0
Hz, 2H, ArH), 7.61 (m, 6H, ArH), 7.75 (d, J = 8.0 Hz, 2H, ArH), 8.04 (d, J = 8.0 Hz,
2H, ArH). 13C{1H} NMR (100 MHz, DMSOꢀd6): δ 10.7 (CH3), 23.2 (CH2), 25.2
24

Page 25 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
(CH2), 49.2 (CH2), 58.8 (CH2), 67.7 (CH2), 112.1 (PhC), 113.5 (bimiC), 120.4 (bimiC
or PhC), 125.5 (PhC), 130.3 (bimiC or PhC), 130.5 (bimiC or PhC), 133.0 (bimiC or
PhC), 133.2 (bimiC or PhC), 156.8 (PhC), 192.6 (Ccarbene).
Complexes [L1Hg(DMSO)](HgI4) (3), [L6Hg(Hg2I6)] (4) and [L8Hg2Cl2](Hg3Cl8)
(5) were prepared in a manner analogous to that of complex 2 (the data of analyses
being given in Supplementary Information).
Preparation of [L2Ag](Cr2O7)0.5 (6)
Silver oxide (0.034 g, 0.15 mmol) and CrO3 (0.029 g, 0.3 mmol) were added to a
CH3CN/CH2Cl2 (15 mL, 2:1, v/v) solution of precursor L2H2·Cl2 (0.197 g, 0.3 mmol),
and the suspension solution was stirred for 24 hours under refluxing. The resulting
solution was filtered and concentrated to 10 mL, and Et2O (5 mL) was added to
precipitate a yellow powder. Isolation by filtration yields complex 6. Yield: 0.173 g
(71%). M.p.: 218ꢀ220 ˚C. Anal. Calcd for C38H42AgCrN4O5.5: C, 56.86; H, 5.27; N,
1
6.98%. Found: C, 56.44; H, 5.56; N, 6.76%. H NMR (400 MHz, DMSOꢀd6): δ 0.91
(t, J = 7.2 Hz, 6H, CH3), 1.37 (q, J = 9.8 Hz, 4H, CH2), 1.89 (t, J = 9.6 Hz, 4H, CH2),
4.26 (s, 4H, OCH2), 4.53 (t, J = 6.6 Hz, 4H, NCH2), 5.76 (s, 4H, CH2Ph), 7.07 (m, 4H,
ArH), 7.44 (m, 6H, ArH), 7.62 (d, J = 9.6 Hz, 2H, ArH), 7.77 (d, J = 9.6 Hz, 2H, ArH),
7.86 (d, J = 9.6 Hz, 2H, ArH). 13C{1H} NMR (100 MHz, DMSOꢀd6): δ 15.1 (CH3),
21.2 (CH2), 33.7 (CH2), 49.8 (CH2), 50.8 (CH2), 66.7 (CH2), 112.8 (bimiC), 113.3
(bimiC), 121.2 (bimiC or PhC), 124.0 (bimiC or PhC), 124.4 (bimiC or PhC), 130.6
(bimiC or PhC), 131.8 (bimiC or PhC), 133.9 (PhC), 156.7 (PhC). The carbene carbon
was not observed.
Complexes [L7 Ag2](PF6)2 (7) and [L3Ag2Cl2]2 (8) were prepared in a manner
2
analogous to that of complex 6 (the data of analyses being given in Supplementary
Information).
UV titrations
UV titrations were performed on a JASCOꢀV570 spectrometer using a 1 cm
pathꢀlength quartz cuvette. Acetonitrile used in the titrations was freshly distilled over
calcium hydride. Titrations were carried out by placing the receptor 6 (1 × 10ꢀ5 mol/L)
into the 4 mL cuvette and adding increasing amounts of nitrate anion (0ꢀ9.0 × 10ꢀ5
25

CrystEngComm
Page 26 of 38
View Article Online
DOI: 10.1039/C4CE01519C
mol/L) using a microsyringe. The absorption spectra were recorded in the range of
200ꢀ400 nm. After each addition, an equilibration time of 8ꢀ10 min was allowed
before the absorption spectra were recorded. Statistical analysis of the data was
carried out using Origin 8.0.
Fluorescence titrations
Fluorescence titrations were performed on
a
Cary Eclipse fluorescence
spectrophotometer using a 1 cm pathꢀlength quartz fluorescence cell. Acetonitrile
used in the titrations was freshly distilled over calcium hydride. Titrations were
carried out by placing the receptor 6 (1 × 10ꢀ5 mol/L) into the 4 mL cuvette and
adding increasing amounts of nitrate anion (0ꢀ15.0 × 10ꢀ5 mol/L) using a
microsyringe. The receptor solution was excited at 254 nm, and the emission spectra
were recorded in the range of 264ꢀ500 nm. After each addition, an equilibration time
of 8ꢀ10 min was allowed before the fluorescence intensity was recorded. Statistical
analysis of the data was carried out using Origin 8.0.
Xꢀray data collection and structure determinations
For complexes 1ꢀ8, selected single crystals were mounted on a Bruker APEX II CCD
diffractometer at 173(2) K for 1 and 8, and 293(2) K for the others with MoꢀK
radiation (λ = 0.71073 Å) by ω scan mode. Data collection and reduction were
performed using the SMART and SAINT software50 with frames of 0.6˚ oscillation in
the range of 1.8˚ < θ < 25˚. An empirical absorption correction was applied using the
SADABS program.51 The structures were solved by direct methods and all
nonꢀhydrogen atoms were subjected to anisotropic refinement by fullꢀmatrix least
squares on F2 using the SHELXTL package.52 All hydrogen atoms were generated
geometrically, assigned appropriated isotropic thermal parameters and included in the
final calculations. Crystalographic data were summaried in Tables 2ꢀ4 for 1ꢀ8.
26

Page 27 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
Table 2 Summary of crystalographic data for 1ꢀ3
1·H2O
2
3
C43H38Cl2HgN6O2
·H2O
Chemical formula
C38H42Cl4Hg2N4O2 C38H44Hg2I4N4O3S
Formula weight
Cryst syst
Space group
a/Å
960.30
Tetragonal
P41212
14.5037(6)
14.5037(6)
18.1126(10)
90
1129.74
Monoclinic
P21/n
1545.61
Monoclinic
Cc
11.4527(6)
20.9738(11)
15.9974(8)
90
11.7672(9)
19.2956(9)
19.0562(11)
90
b/Å
c/Å
α/deg
β/deg
90
99.6210(10)
90
90.2920(10)
90
γ/deg
90
V/Å3
3810.1(3)
4
3788.6(3)
4
4326.8(5)
4
Z
D
calcd, Mg/m3
1.674
1.981
2.373
Abs coeff, mmꢀ1
4.230
8.417
10.030
2848
F(000)
1912
2168
Cryst size, mm
0.15 × 0.14 × 0.13 0.15 × 0.13 × 0.12 0.15 × 0.14 × 0.13
θ
min, θmax, deg
1.99, 25.00
173(2)
19292
3337
1.62 , 25.01
296(2)
19043
6678
2.03, 25.01
296(2)
10601
5605
T /K
No. of data collected
No. of unique data
No. of refined params
250
453
473
Goodnessꢀofꢀfit on F2 a
1.004
1.049
1.057
Final R indicesb [I > 2σ(I)]
R1
0.0220
0.0545
0.0259
0.0628
0.0384
0.0917
wR2
R indices (all data)
R1
0.0235
0.0311
0.0695
0.0390
0.0920
0.019(5)
wR2
0.0556
Flack params
ꢀ0.010(6)
a GOF = [Σω(Fo ꢀ Fc2)2 /(nꢀp)]1/2, where n is the number of reflection and p is the
2
number of parameters refined. R1 = Σ(||Fo| ꢀ |Fc||)/Σ|Fo|; wR2 =[Σ[w(Fo ꢀ Fc2)2 ]/
b
2
2 2 1/2
Σw(Fo ) ] .
27

CrystEngComm
Page 28 of 38
View Article Online
DOI: 10.1039/C4CE01519C
Table 3 Summary of crystalographic data for 4ꢀ6
4
5
6
Chemical formula
C35H32Hg3I6N4O2
C27H32Cl10Hg5N4O2 C38H42AgCrN4O5.5
Formula weight
Cryst syst
Space group
a/Å
1903.82
Triclinic
Pī
1802.02
Monoclinic
P21/c
802.63
Monoclinic
P21/c
11.3111(15)
13.5636(18)
16.321(2)
81.613(2)
75.368(2)
67.987(2)
2242.5(5)
2
14.4160(12)
15.8007(13)
23.0337(14)
90
10.840(4)
13.647(5)
25.631(9)
90
b/Å
c/Å
α/deg
β/deg
127.396(3)
90
102.500(13)
90
γ/deg
V/Å3
4168.3(5)
4
3702(2)
4
Z
D
calcd, Mg/m3
2.820
2.872
1.440
Abs coeff, mmꢀ1
14.408
19.025
0.871
F(000)
1688
3232
1652
Cryst size, mm
0.15 × 0.14 × 0.13
1.29, 25.01
296(2)
0.01 × 0.01 × 0.01
1.70, 25.01
296(2)
0.22 × 0.20 × 0.15
1.63, 25.01
296(2)
17003
θ
min, θmax, deg
T /K
No. of data collected
11504
20652
No. of unique data
7865
7307
6469
No. of refined params
451
435
467
Goodnessꢀofꢀfit on F2 a
1.037
1.011
1.066
Final R indicesb [I > 2σ(I)]
R1
0.0471
0.1245
0.0370
0.0788
0.0603
0.1639
wR2
R indices (all data)
R1
0.0584
0.1326
0.0539
0.0895
0.0677
0.1718
wR2
Flack params
2
a GOF = [Σω(Fo ꢀ Fc2)2 /(nꢀp)]1/2, where n is the number of reflection and p is the
b
2
number of parameters refined. R1 = Σ(||Fo| ꢀ |Fc||)/Σ|Fo|; wR2 =[Σ[w(Fo ꢀ Fc2)2 ]/
2 2 1/2
Σw(Fo ) ] .
28

Page 29 of 38
CrystEngComm
View Article Online
DOI: 10.1039/C4CE01519C
Table 4 Summary of crystalographic data for 7 and 8
7·2CH3CN
C26H30AgF6N4O2P
765.49
8·CH2Cl2
C42H36Ag2Cl2N6O2
1028.33
Monoclinic
P21/c
Chemical formula
Formula weight
Cryst syst
Space group
a/Å
Orthorhombic
Fdd2
44.800(3)
17.1348(13)
17.7314(14)
90
10.8182(5)
20.4671(10)
18.6333(9)
90
b/Å
c/Å
α/deg
β/deg
90
101.7600(10)
90
γ/deg
90
V/Å3
13611.3(17)
16
4039.1(3)
4
Z
Dcalcd, Mg/m3
Abs coeff, mmꢀ1
F(000)
1.494
1.691
0.709
1.281
6240
2064
Cryst size, mm
0.14 × 0.13 × 0.12
2.14, 25.01
296(2)
0.17 × 0.16 × 0.14
1.92 , 25.01
173(2)
θmin, θmax, deg
T /K
No. of data collected
16885
20330
No. of unique data
5992
7093
No. of refined params
419
514
Goodnessꢀofꢀfit on F2 a
1.027
1.046
Final R indicesb [I > 2σ(I)]
R1
0.0310
0.0867
0.0354
0.0877
wR2
R indices (all data)
R1
0.0356
0.0912
ꢀ0.07(3)
0.0442
0.0934
wR2
Flack params
2
a GOF = [Σω(Fo ꢀ Fc2)2 /(nꢀp)]1/2, where n is the number of reflection and p is the
b
2
number of parameters refined. R1 = Σ(||Fo| ꢀ |Fc||)/Σ|Fo|; wR2 =[Σ[w(Fo ꢀ Fc2)2 ]/
2 2 1/2
Σw(Fo ) ] .
29