Cobalt(ii), copper(ii), zinc(ii) and cadmium(ii) complexes based on dibenzimidazolyl bidentate ligands with alkanyl linkers: Crystal structure, weak interactions and conformations

Article abstract of DOI:10.1039/c3dt33013c

Eight metal complexes, {[Co(bibim-4)₂(H₂O) ₂](NO₃)₂}_n (1), {[Cu(bibim-4) ₂(NO₃)](NO₃)}_n (2), [Co(bibim-3)(TP)]_n (3), [Zn₂(bibim-3)]₂(OAc) ₄] (4), [Co(bibim-2)(NO₃)₂]_n (5), [Zn(bibim-4)(NO₃)₂]_n (6), [Zn(bibim-4)(OAc) ₂]_n (7) and [Cd(bibim-4)(NO₃) ₂(DMF)]_n (8) (bibim-2 = 1,2-bis(benzimidazol-l-yl)ethane, bibim-3 = 1,3-bis(benzimidazol-l-yl)propane, bibim-4 = 1,4-bis(benzimidazol-l- yl)butane and TP = terephthalate) have been prepared by means of the self-assembly of Co(ii), Cu(ii), Zn(ii) or Cd(ii) salts, dibenzimidazolyl bidentate ligands bearing alkanyl linkers and terephthalic acid. These complexes are structurally characterized by X-ray diffraction analyses. In complexes 1 and 2, 2D network layers with macrometallocycles are formed via metal centers and the ligand bibim-4. A 2D network layer with macrometallocycles in 3 is formed via Co(ii) centers, the ligand bibim-3 and terephthalate molecules. In complex 4, a 20-membered macrometallocycle is formed by two bibim-3 ligands and two Zn(ii) atoms. In complexes 5-8, 1D polymeric chains are formed via metal centers and the bibim-2 or bibim-4 ligands. In the crystal packings of complexes 1-8, 2D supramolecular layers and 3D supramolecular frameworks are formed via intermolecular weak interactions, including π-π interactions and hydrogen bonds. The different types of π-π interactions from the benzimidazole ring as well as the conformations of the ligands and metal complexes are described. Additionally, the fluorescence emission spectra of the ligands and metal complexes are reported.

Full text of DOI:10.1039/c3dt33013c

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Cobalt(II), copper(II), zinc(II) and cadmium(II) complexes
based on dibenzimidazolyl bidentate ligands with
alkanyl linkers: crystal structure, weak interactions and
conformations†
Cite this: Dalton Trans., 2013, 42, 5902
Qing-Xiang Liu,*a,b Qing Wei,a,b Xiao-Jun Zhao,a,b Hong Wang,a,b Shu-Juan Lia,b and
Xiu-Guang Wanga,b
Eight metal complexes, {[Co(bibim-4)2(H2O)2](NO3)2}n (1), {[Cu(bibim-4)2(NO3)](NO3)}n (2), [Co(bibim-3)-
(TP)]n (3), [Zn2(bibim-3)]2(OAc)4] (4), [Co(bibim-2)(NO3)2]n (5), [Zn(bibim-4)(NO3)2]n (6), [Zn(bibim-4)-
(OAc)2]n (7) and [Cd(bibim-4)(NO3)2(DMF)]n (8) (bibim-2 = 1,2-bis(benzimidazol-l-yl)ethane, bibim-3 = 1,3-
bis(benzimidazol-l-yl)propane, bibim-4 = 1,4-bis(benzimidazol-l-yl)butane and TP = terephthalate) have
been prepared by means of the self-assembly of Co(II), Cu(II), Zn(II) or Cd(II) salts, dibenzimidazolyl bidentate
ligands bearing alkanyl linkers and terephthalic acid. These complexes are structurally characterized by
X-ray diffraction analyses. In complexes 1 and 2, 2D network layers with macrometallocycles are formed via
metal centers and the ligand bibim-4. A 2D network layer with macrometallocycles in 3 is formed via Co(II)
centers, the ligand bibim-3 and terephthalate molecules. In complex 4, a 20-membered macrometallocycle
is formed by two bibim-3 ligands and two Zn(II) atoms. In complexes 5–8, 1D polymeric chains are formed
via metal centers and the bibim-2 or bibim-4 ligands. In the crystal packings of complexes 1–8, 2D supra-
molecular layers and 3D supramolecular frameworks are formed via intermolecular weak interactions,
including π–π interactions and hydrogen bonds. The different types of π–π interactions from the benzimida-
zole ring as well as the conformations of the ligands and metal complexes are described. Additionally, the
fluorescence emission spectra of the ligands and metal complexes are reported.
Received 30th October 2012,
Accepted 30th January 2013
DOI: 10.1039/c3dt33013c
www.rsc.org/dalton
important building blocks to construct coordination frame-
works of diverse sizes and shapes. Furthermore, organic
Introduction
Metal–organic frameworks (MOFs) from organic ligands and diacids (like terephthalic acid) are often used together with
transition metals have become a field of rapid growth in supra- other organic ligands in order to form some porous coordi-
molecular and material chemistry due to their intriguing struc- nation architectures. Among the family of organic ligands,
tural diversity1 and potential applications in the fields of ligands bearing N-donors are a type of important ligating
fluorescence,2 magnetism,3 catalysis4 and host–guest chem- moiety connecting the metal atoms and their N-donor units
istry.5 For researchers, the construction of coordination com- contain mainly pyridine,6 benzimidazole,7 imidazole,8 tria-
pounds is still a big challenge because the self-assembly of zole,9 pyrrole10 and imino groups.11
metal ions and ligands into coordination architectures is not
Bidentate ligands with different linkers are usually the
easily controlled. In crystal engineering, the metal centers are typical building elements in multidimensional networks in
important connecting nodes in multidimensional arrays due which non-rigid linkers, such as polyether chains,12 polyimino
to their varied coordinating models. Organic ligands are chains13 and alkyl chains14 may provide a greater possibility
for the construction of unusual coordination frameworks due
to the conformationally flexible nature of the bidentate
aTianjin Key Laboratory of Structure and Performance for Functional Molecules, Key
Laboratory of Inorganic-Organic Hybrid Functional Material Chemistry, Ministry of
Education, College of Chemistry, Tianjin Normal University, Tianjin 300387, China
ligands. Therefore, the design and synthesis of new bidentate
ligands are important for crystal engineering. Additionally,
among the ligands containing nitrogen atoms, imidazolyl (or
benzimidazolyl) ligands have prominent importance because
the imidazole ring is a structural component of many com-
pounds occurring in living organisms.15 In the mechanisms of
bState Key Laboratory of Elemento-organic Chemistry, Nankai University, Tianjin
300071, China. E-mail: tjnulqx@163.com
†CCDC 888544–888551 for 1–8. For crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c3dt33013c
5902 | Dalton Trans., 2013, 42, 5902–5915
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the majority of enzymatic reactions, metal complexes based on slightly poorer. During the course of the preparation of metal
imidazole play important roles in physiology.16 Therefore, the complexes using dibenzimidazole with alkanyl linkers as a
preparation and investigating the structure of metal complexes ligand, using only water as the solvent is not suitable. Using
from imidazolyl (or benzimidazolyl) has great significance water and an organic solvent as a mixed solvent or only using
toward knowing the coordinating process between the imida- organic solvents is necessary. Thus, the crystallization of com-
zole (or benzimidazolyl) ring and metal ions in life science.
So far, a lot of metal complexes based on diimidazolyl metal salts occurs readily in the appropriate solvent.
bidentate ligands with different alkanyl linkers have been Complexes {[Co(bibim-4)2(H2O)2](NO3)2}n (1), {[Cu(bibim-4)2-
plexes from dibenzimidazolyl bidentate ligands and inorganic
reported,17–26 but only a few examples of metal complexes (NO3)](NO3)}n (2), [Zn2(bibim-3)]2(OAc)4] (4), [Co(bibim-2)-
based on dibenzimidazolyl bidentate ligands with a 1,4-butene (NO3)2]n (5), [Zn(bibim-4)(NO3)2]n (6), [Zn(bibim-4)(OAc)2]n (7)
linker have been described.27–29 The main difference of diben- and [Cd(bibim-4)(NO3)2(DMF)]n (8) were prepared via the reac-
zimidazolyl bidentate ligands in contrast to diimidazolyl tion of bibim-m with the metal salts (Co(NO3)2·6H2O for 1 and
bidentate ligands is that the conjugated system of the benzimi- 5, Cu(NO3)2·3H2O for 2, Zn(OAc)2·2H2O for 4 and 7, Zn-
dazole ring is bigger than that of the imidazole ring and the (NO3)2·6H2O for 6 and Cd(NO3)2·4H2O for 8) in DMF–CH3OH,
benzimidazole ring participates in π–π interactions between while complex [Co(bibim-3)(TP)]n (3) was prepared via the reac-
molecules more easily. π–π interactions, along with other weak tion of bibim-3 and terephthalic acid with Co(NO3)2·6H2O in
interactions (like hydrogen bonds), can provide more opportu- the presence of Et3N in DMF–CH3OH. Crystals of 1–8 suitable
nities for constructing supramolecular architectures. Addition- for X-ray diffraction were grown by slowly evaporating the
ally, π–π stacking interactions also play an important role in DMF–CH3OH solution at room temperature. Complexes 1–8
stabilizing supramolecular architectures.28,30 In order to are stable and can retain their structural integrity at room
further understand the structure of metal complexes based on temperature for a considerable length of time.
dibenzimidazolyl bidentate ligands with different alkanyl
Structure of complexes 1–8
linkers, we here report the preparation of three dibenzimidazo-
lyl bidentate ligands, 1,2-bis(benzimidazol-l-yl)ethane (bibim- Complexes 1 and 2 have similar 2D network layers with quad-
2), 1,3-bis(benzimidazol-l-yl)propane (bibim-3) and 1,4-bis- rangle cavities, as shown in Fig. 1(a) and 2(a). The adjacent
(benzimidazol-l-yl)butane (bibim-4), as well as the preparation, quadrangle cavities are connected via metal atoms (Co(II) for 1
structures and fluorescence emission spectra of eight metal and Cu(II) for 2). Each quadrangle cavity of central symmetry is
complexes, {[Co(bibim-4)2(H2O)2](NO3)2}n (1), {[Cu(bibim-4)2- formed by four bis-benzimidazole bibim-4 ligands and two
(NO3)](NO3)}n (2), [Co(bibim-3)(TP)]n (3), [Zn2(bibim-3)]2(OAc)4] metal atoms. In the quadrangle cavities of 1 and 2, the adja-
(4), [Co(bibim-2)(NO3)2]n (5), [Zn(bibim-4)(NO3)2]n (6), [Zn- cent distances of M⋯M are 13.757(1) Å for the Co⋯Co of 1
(bibim-4)(OAc)2]n (7) and [Cd(bibim-4)(NO3)2(DMF)]n (8) (TP = and 11.757(2) Å for the Cu⋯Cu of 2 and the distances of oppo-
terephthalate). Additionally, the conformations of the ligands site M⋯M are 16.916(2) Å for the Co⋯Co of 1 and 23.178(3) Å
and metal complexes are described.
for the Cu⋯Cu of 2. In complexes 1 and 2, the dihedral angles
of two benzimidazole rings within the same ligand are 0.6(1)°
for 1 and 11.0(1)° for 2. The benzimidazole ring and other
three benzimidazole rings linked to the same metal center
form dihedral angles of 68.5(1)°, 51.6(1)° and 80.3(1)° for 1
and 90.2(1)°, 88.8(1)° and 90.6(1)° for 2.
In complex 1, each Co(II) atom is surrounded by four nitro-
gen atoms from four bis-benzimidazole bibim-4 ligands and
two oxygen donors from two water molecules to adopt an octa-
hedral geometry. The axial positions of the octahedron are occu-
pied by O(1) and O(2) with an O(1)–Co(1)–O(2) angle of 180°.
The bond distances of Co(1)–O(1) and Co(1)–O(2) are 2.191(5) Å
and 2.066(4) Å, respectively. Four N(1), N(1A), N(3) and N(3A)
atoms lie in the equatorial plane. The distances of the Co–N
bond are from 2.132(4) Å to 2.161(3) Å. The bond angle of
N–Co–O is in the ranges of 87.2(2)° to 92.7(8)°. The bond angles
Results and discussion
Synthesis and characterization of the ligands (bibim-m) and
metal complexes 1–8
The bis-benzimidazole ligands 1,2-bis(benzimidazol-l-yl)ethane of N(1)–Co(1)–N(1A) and N(3)–Co(1)–N(3A) are 177.1(2)° and
(bibim-2), 1,3-bis(benzimidazol-l-yl)propane (bibim-3) and 1,4- 174.4(5)°, respectively. These values are favorably comparable
bis(benzimidazol-l-yl)butane (bibim-4) were prepared through with other analogous imidazole derivatives of Co(II).31
the reaction of benzimidazole with 1,m-dibromoalkane (m = 2,
In complex 2, each Cu(II) atom is surrounded by four nitro-
3 and 4). The ligands (bibim-m) are white powders and they are gen donors from four bis-benzimidazole bibim-4 ligands and
soluble in common organic solvents (such as CH3OH, CH3CN one oxygen donor from a nitrate group to adopt a pentagonal
and DMF). In contrast to the diimidazolyl bidentate ligands, pyramidal geometry. The bond angles of N–Cu–N are in the
the solubility of dibenzimidazolyl bidentate ligands in water is ranges of 88.6(5)° to 170.3(9)° and the bond angles of N–Cu–O
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Fig. 2 (a) 2D layer of 2. All hydrogen atoms were omitted for clarity. Selected
bond lengths (Å) and angles (°): Cu(1)–N(1) 2.019(4), Cu(1)–N(8)i 2.001(4), Cu(1)–
N(4)ii 1.992(4), Cu(1)–N(5) 2.014(4), Cu(1)–O(1) 2.352(4); N(1)–Cu(1)–N(5)
88.7(6), N(1)–Cu(1)–N(4) 169.9(5), N(5)–Cu(1)–N(8) 170.3(9), N(1)–Cu(1)–O(1)
93.6(5), N(4)–Cu(1)–O(1) 96.1(8). N(5)–Cu(1)–O(1) 92.8(9). Symmetry code: i:
3/2 − x, −1/2 + y, −1/2 + z; ii: 3/2 − x, 1/2 + y, −1/2 + z. (b) 3D supramolecular
frameworks of 2 formed by interlayer C–H⋯O hydrogen bonds. All hydrogen
atoms except those participating in the C–H⋯O hydrogen bonds were omitted
for clarity. Symmetry code: iii: 1 − x, −y, 1/2 + z.
Fig. 1 (a) 2D layer of 1. All hydrogen atoms were omitted for clarity. Selected
bond lengths (Å) and angles (°): Co(1)–O(1) 2.191(5), Co(1)–O(2) 2.066(4), Co(1)–
N(1) 2.161(3), Co(1)–N(3) 2.132(4); O(2)–Co(1)–N(3) 92.7(8), O(2)–Co(1)–N(1)
91.4(4), N(1)–Co(1)–N(3) 89.1(8), O(1)–Co(1)–O(2) 180.0(0), N(3)–Co(1)–O(1)
87.2(2), N(1)–Co(1)–O(1) 88.5(6), N(1)–Co(1)–N(1A)i 177.1(2), N(3)–Co(1)–N(3A)i
174.4(5). Symmetry code: i: 2 − x, 2 − y, 1 − z. (b) 3D supramolecular frame-
works of 1 formed by interlayer O–H⋯O hydrogen bonds. All hydrogen atoms
except those participating in the O–H⋯O hydrogen bonds were omitted for
clarity. Symmetry code: ii: 1/2 + x, 1 − y, 1/2 + z; iii: 1 − x, 1 − y, 2 − z; iv: 3 − x,
1 − y, 2 − z.
Each relatively small 20-membered ring in 3 is formed by
are in the ranges of 92.8(9)° to 96.7(1)°. These values are two bis-benzimidazole bibim-3 ligands and two Co(II) atoms,
within the normal ranges.32
in which the dihedral angle between two benzimidazole rings
In complex 3, a 2D network layer with 56-membered within the same ligand is nearly perpendicular with a dihedral
hexagon cavities of central symmetry is formed by two rela- angle of 87.7(1)° and the dihedral angle of two benzimidazole
tively little 20-membered rings, four terephthalates (TP) and rings connected to the same Co(II) atom is 88.7(1)°. The
six Co(II) atoms, as shown in Fig. 3(a). The size of the 56-mem- Co⋯Co distance in the 20-membered rings is 9.748(1) Å.
bered hexagon cavity is ca. 18.691(2) Å × 7.413(9) Å. In the The size of the 20-membered ring of central symmetry is ca.
hexagon cavity, the two pairs of opposite benzene rings from 9.748(1) Å × 5.806(6) Å.
the terephthalate molecules are parallel to each other, respect-
Interestingly, each acetone molecule in 3 is connected to an
ively, with separations of 14.292(1) Å and 20.328(1) Å. The uncoordinated oxygen atom of the carboxyl group via C–H⋯O
Co⋯Co distance at two ends of the terephthalate molecule is hydrogen bonds (the data of the hydrogen bonds is given in
11.013(1) Å. The dihedral angle between two benzene rings of Table 1). In the hydrogen bonds, the hydrogen atoms are from
terephthalate connected to the same Co(II) center is 80.2(1)°. the CH3 of acetone and the oxygen atoms are from the carboxyl
The dihedral angles between one benzimidazole ring and two group. As a result, each 56-membered hexagon cavity includes
benzene rings of the terephthalate molecule connected to the two acetone molecules. Analysis of the crystal structure of 3
same Co(II) atom are 110.6(1)° and 128.7(9)°, respectively.
reveals that each Co(II) center adopts a distorted tetrahedral
5904 | Dalton Trans., 2013, 42, 5902–5915
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respectively. The bond angle of O–Co–N is in the range of
102.4(3)° to 128.5(3)°. These values are comparable with those
of complex 1 and the reported Co(II) complexes.33
In complex 4 (Fig. 4(a)), one 20-membered macrometallo-
cycle is formed by two didentate bibim-3 ligands and two
Zn(II) atoms, in which the dihedral angle of two benzimidazole
rings connected to the same Zn(II) atom is 84.8(1)° and the
dihedral angle of two benzimidazole rings within the same
ligand is 84.6(1)°. Each Zn(II) atom is surrounded by two nitro-
gen donors from two benzimidazole rings and two oxygen
donors from two acetate groups to adopt a distorted tetrahe-
dral geometry. The bond distances of Zn(1)–O(1) and Zn(1)–
N(1) bond are 1.949(4) Å and 2.007(2) Å, respectively. The bond
angles of O(1)–Zn(1)–O(3) and N(1)–Zn(1)–N(4A) are 109.7(4)°
and 101.9(4)°, respectively. The bond angles of O–Zn–N range
from 102.3(7)° to 120.9(8)°. These values are consistent with
those from published Zn(II) complexes.32
1D zigzag polymeric chains of complexes 5–8 are formed
via didentate ligands and metal atoms (bibim-2 and Co(II) for
5, bibim-4 and Zn(II) for 6 and 7, bibim-4 and Cd(II) for 8)
(Fig. 5(a)–8(a)). The two benzimidazole rings connected to the
same metal center form dihedral angles of 83.9(3)° for 5, 64.8°
for 6, 55.7° for 7 and 81.1(4)° for 8. Two benzimidazole rings
within the same ligand are parallel for 5–8. In 5, the neighbor-
ing Co⋯Co separation is 11.613(4) Å and the angle of the
neighboring Co⋯Co⋯Co is 84.6(4)°. In 6 and 7, the neighbor-
ing Zn⋯Zn separation is 11.940(6) Å for 6 and 11.915(1) Å for
7 and the angles of the neighboring Zn⋯Zn⋯Zn are 103.6(1)°
for 6 and 81.2(5)° for 7. In 8, the neighboring Cd⋯Cd sepa-
ration is 12.338(1) Å and the angle of the neighboring
Cd⋯Cd⋯Cd is 112.3(1)°.
In complex 5, the hexa-coordinated Co(II) atom is sur-
rounded by two nitrogen donors from two benzimidazole rings
and four oxygen donors from two nitrate groups to adopt a dis-
torted octahedral geometry. The axial positions of the octa-
hedron are occupied by N(1) and O(2) with axial distances of
4.044(1) Å and a N(1)–Co(1)–O(2) angle of 140.3(3). Four N(3),
O(1), O(4) and O(5) atoms lie in the equatorial plane. The
bond distances of Co–O range from 2.155(9) Å to 2.390(1) Å,
and Co–N distances are 2.005(6) Å and 2.018(6) Å, respectively.
The N(1)–Co(1)–N(3) bond angle is 105.6(2)° and the value of
the bond angles around the Co(II) center varied from 52.1(3)°
to 140.3(3)°. These values are favorably comparable with those
of complexes 1 and 3 and the reported Co(II) complexes.31
In complexes 6 and 7, each Zn(II) atom is surrounded by
two nitrogen donors from two benzimidazole rings and two
oxygen donors (from two nitrite groups for 6 and from two
acetate groups for 7) to form a distorted tetrahedral geometry.
The distances of Zn–O are from 1.926(5) Å to 1.963(5) Å and
the distances of Zn–N are from 2.005(7) Å to 2.040(3) Å. The
bond angles of O–Zn–O are from 110.0(9)° to 113.4(9)°, the
bond angles of N–Zn–N are from 103.1(1)° to 111.6(8)° and the
bond angles of O–Zn–N range from 96.2(0)° to 119.1(7)°. These
values fall in the normal ranges of Zn(II) complexes.31,34
There is a solvent accessible void in the unit cell of com-
plexes 6 or 7. Each unit cell of 6 contains one disordered water
Fig. 3 (a) 2D layer of 3. All hydrogen atoms except those participating in the
C–H⋯O hydrogen bonds were omitted for clarity. Selected bond lengths (Å)
and angles (°): Co(1)–O(1) 1.963(5), Co(1)–O(3) 1.950(8), Co(1)–N(1) 2.012(7),
Co(1)–N(1A) 2.012(7); O(1)–Co(1)–O(3) 105.3(3), O(3)–Co(1)–N(1) 128.5(3),
O(1)–Co(1)–N(1) 110.6(3), N(1)–Co(1)–N(1A)i 102.5(2). Symmetry code: i: 1 − x,
2 − y, 1 − z; ii: x, 1 + y, 1 + z. (b) 3D supramolecular frameworks of 3 via weak
π–π interactions. All hydrogen atoms were omitted for clarity.
Table 1 H-bonding geometry (Å, °) for complexes 1–8
Compounds D–H⋯A
D–H
H⋯A
D⋯A
D–H⋯A
1
O(1)–H(1A)⋯O(6)ii
0.85(1) 1.977(2) 2.814(3) 168.0(1)
O(2)iv–H(2A)⋯O(7)iii 0.85(1) 1.877(2) 2.711(3) 166.7(1)
O(7)–H(7B)⋯O(6)ii
0.85(2) 1.944(2) 2.794(3) 177.0(1)
2
3
4
5
6
7
8
C(25)–H(25)⋯O(2)iii 0.93(4) 2.440(4) 3.329(6) 159.7(2)
C(31)–H(31A)⋯O(4)ii 0.96(1) 1.898(2) 2.805(3) 156.6(1)
C(8)–H(8A)⋯O(4)ii
C(9)–H(9)⋯O(3)i
C(1)–H(1)⋯O(5)i
C(8)–H(8B)⋯O(4)i
C (7)–H(7)⋯O(3)ii
0.97(1) 2.437(1) 3.308(2) 149.2(4)
0.93(4) 2.463(9) 3.376(1) 167.2(4)
0.93(1) 2.375(1) 3.158(2) 141.7(2)
0.97(1) 2.592(3) 3.420(4) 143.5(1)
0.93(1) 2.555(3) 3.413(4) 153.4(1)
Symmetry code: ii: 1/2 + x, 1 − y, 1/2 + z. iii: 1 − x, 1 − y, 2 − z. iv: 3 −
x, 1 − y, 2 − z for 1. iii: 1 − x, −y, 1/2 + z for 2. ii: x, 1 + y, 1 + z for 3. ii:
x, 2 − y, −1/2 + z for 4. i: x, 1/2 − y, 1/2 + z for 5. i: 1 − x, 2 − y, 2 − z for
6. i: 2 − x, 1 − y, 1 − z for 7. ii: 1/2 − x, 1/2 − y, 1 − z for 8.
geometry formed by two oxygen donors from two different car-
boxyls (the Co–O distances vary from 1.950(8) Å to 1.963(5) Å)
and two nitrogen donors from two benzimidazole rings (the
Co–N distance is 2.012(7) Å). The bond angles of O(1)–Co(1)–
O(3) and N(1)–Co(1)–N(4A) are 105.3(3)° and 102.6(3)°,
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Fig. 5 (a) 1D polymeric chain of 5. All hydrogen atoms were omitted for
clarity. Selected bond lengths (Å) and angles (°): Co(1)–N(1) 2.018(6), Co(1)–N(3)
2.005(6), Co(1)–O(1) 2.155(9), Co(1)–O(2) 2.306(8); N(1)–Co(1)–N(3) 105.6(2),
N(1)–Co(1)–O(1) 88.7(3), N(1)–Co(1)–O(2) 140.3(3), N(1)–Co(1)–O(4) 90.8(3),
N(1)–Co(1)–O(5) 117.2(3), N(3)–Co(1)–O(5) 86.4(3), O(1)–Co(1)–O(2) 53.3(3),
O(1)–Co(1)–O(4) 87.0(4). (b) 2D supramolecular layer of 5 constructed via inter-
chain π–π interactions. All hydrogen atoms were omitted for clarity. (c) 3D supra-
molecular frameworks of 5 formed by π–π interactions and C–H⋯O hydrogen
bonds. All hydrogen atoms except those participating in the C–H⋯O hydrogen
bonds were omitted for clarity. Symmetry code: i: x, 1/2 − y, 1/2 + z.
Fig. 4 (a) Perspective view of 4 and the anisotropic displacement parameters
depicting 50% probability. All hydrogen atoms were omitted for clarity. Selected
bond lengths (Å) and angles (°): Zn(1)–O(1) 1.949(4), Zn(1)–O(3) 1.958(5), Zn(1)–
N(1) 2.007(2), Zn(1)–N(4A)i 2.054(2); O(1)–Zn(1)–O(3) 109.7(4), O(1)–Zn(1)–N(1)
121.9(8), O(1)–Zn(1)–N(4A) 106.3(5), O(3)–Zn(1)–N(1) 113.1(6), O(3)–Zn(1)–
N(4A) 102.3(7), N(1)–Zn(1)–N(4A) 101.9(4). Symmetry code: i: 1/2 − x, 3/2 − y,
−z. (b) 2D supramolecular layer of 4 formed via C–H⋯O interactions. All hydro-
gen atoms except those participating in the C–H⋯O hydrogen bonds were
omitted for clarity. Symmetry code: ii: x, 2 − y, −1/2 + z. (c) 3D supramolecular
frameworks of 4 formed by π–π interactions and C–H⋯O hydrogen bonds. All
hydrogen atoms except those participating in the C–H⋯O hydrogen bonds
were omitted for clarity.
disordered molecules have been treated as a diffuse contri-
bution to the overall scattering without specific atom positions
by squeeze.
In complex 8, the coordination polyhedron of the hepta-
coordinated Cd(II) center can be regarded as a distorted penta-
gonal bipyramid, where the Cd(II) atom is coordinated by two
molecule and each unit cell of 7 contains two disordered water
molecules and two disordered methanol molecules. These
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Fig. 7 (a) 1D polymeric chain of 7. All hydrogen atoms were omitted for
clarity. Selected bond lengths (Å) and angles (°): Zn(1)–O(1) 1.963(5), Zn(1)–O(3)
1.926(5), Zn(1)–N(1) 2.005(7), Zn(1)–N(3) 2.017(6); N(1)–Zn(1)–N(3) 111.6(8),
O(1)–Zn(1)–O(3) 110.0(9), O(1)–Zn(1)–N(1) 108.9(4), O(1)–Zn(1)–N(3) 96.2(0),
O(3)–Zn(1)–N(1) 116.3(9). (b) 2D supramolecular layer of 7 constructed via inter-
chain π–π interactions and C–H⋯O hydrogen bonds. All hydrogen atoms except
those participating in the C–H⋯O hydrogen bonds were omitted for clarity.
Symmetry code: i: 2 − x, 1 − y, 1 − z.
Fig. 6 (a) 1D polymeric chain of 6. All hydrogen atoms were omitted for
clarity. Selected bond lengths (Å) and angles (°): Zn(1)–O(1) 1.944(3), Zn(1)–O(4)
1.959(3), Zn(1)–N(1) 2.040(3), Zn(1)–N(3) 2.021(3); N(1)–Zn(1)–N(3) 103.1(1),
O(1)–Zn(1)–O(4) 113.4(9), O(1)–Zn(1)–N(1) 106.1(5), O(1)–Zn(1)–N(3) 119.1(7),
O(4)–Zn(1)–N(1) 102.5(4), O(4)–Zn(1)–N(3) 110.3(2). (b) 2D supramolecular layer
of 6 formed via π–π interactions. All hydrogen atoms were omitted for clarity. (c)
3D supramolecular frameworks of 6 formed by π–π interactions and C–H⋯O
hydrogen bonds. All hydrogen atoms except those participating in the C–H⋯O
hydrogen bonds were omitted for clarity. Symmetry code: i: 1 − x, 2 − y, 2 − z.
The crystal packings of complexes 1–8
nitrogen donors from the benzimidazole rings and five oxygen
donors (four oxygen donors are from two nitrate groups and
the fifth is from DMF). In the hepta-coordinated CdO5N2 skele-
ton, the pentagonal plane for Cd(II) is composed of O(1), O(2),
O(4), O(1A) and O(2A) and the axial positions are occupied by
N(1) and N(1A) with axial distances of 4.552(8) Å. The axial
position is slightly distorted with a N(1)–Cd(1)–N(1A) angle of
174.5(7)°. The degree of pentagonal bipyramid distortion is
also reflected in the angles around the Cd(II) atom in the equa-
torial plane (a regular pentagon value being 72°). In the hepta-
coordinated Cd(II) environment, the distances of Cd–O vary
from 2.322(4) Å to 2.459(2) Å. The Cd(1)–N(1) distance is
2.279(2) Å. The bond angles of N–Cd–O range from 82.0(9)° to
92.5(1)° and the O–Cd–O bond angles range from 51.9(2)° to
172.4(0)°. These values are favorably comparable with analo-
gous values from Cd(II) complexes.35
In the crystal packing of 1 (Fig. 1(b)), 2D network layers are
further extended into 3D supramolecular frameworks by
O–H⋯O hydrogen bonds36 with the help of two free H2O mole-
cules as bridges (the data of the hydrogen bonds is given in
Table 1). In the hydrogen bonds, the hydrogen atoms and
oxygen atoms are from coordinated H2O molecules and free
H2O molecules.
In the crystal packing of 2 (Fig. 2(b)), 2D network layers are
further extended into 3D supramolecular frameworks by
C–H⋯O hydrogen bonds37 (Table 1). In the hydrogen bonds,
the hydrogen atoms are from imidazole rings and the oxygen
atoms are from nitrate groups.
In the crystal packing of 3 (Fig. 3(b)), 2D network layers can
be extended into a 3D supramolecular framework via π–π stack-
ing interactions38 from the benzene rings of terephthalates
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Table 2 Distances (Å) of the π–π interactions for 3–8
π–π
Compounds
Face-to-face
Center-to-center
3
4
5
6
7
8
3.455(5)
3.597(1)
3.403(2)
3.454(2)
3.453(4)
3.496(4)
3.867(5)
3.630(2)
3.605(1)
3.856(2)
3.633(1)
3.704(4)
through π–π stacking interactions from the benzimidazole
rings (Table 2). The 2D supramolecular layers are further
extended into 3D supramolecular architectures via C–H⋯O
hydrogen bonds, as shown in Fig. 5(c) and 6(c) (Table 1). In
the hydrogen bonds, the hydrogen atoms are from the imida-
zole rings and the oxygen atoms are from the nitrate groups.
In the crystal packing of 7 (Fig. 7(b)), 2D supramolecular
layer is formed through π–π stacking interactions from benz-
imidazole rings (Table 2) and C–H⋯O hydrogen bonds
(Table 1). In the hydrogen bonds, the hydrogen atoms are
from the CH2 of alkyl chains, and oxygen atoms are from
acetate groups.
In the crystal packing of 8 (Fig. 8(b)), 1D polymeric chains
are extended into 2D supramolecular layers via π–π stacking
interactions (Table 2). The 2D supramolecular layers are
further extended into 3D supramolecular architectures via
C–H⋯O hydrogen bonds, as shown in Fig. 8(c) (Table 1). In the
hydrogen bonds, the hydrogen atoms are from the imidazole
rings and the oxygen atoms are from nitrate groups.
Compared with the diimidazolyl bidentate ligands, the
main feature of dibenzimidazolyl bidentate ligands is that the
benzimidazole ring is easer to participate in π–π interactions
between molecules due to a large conjugated system. The π–π
interactions between the benzimidazole rings generally
include three types (Scheme 1), namely, a head-to-tail type
(such as complexes 5–7 and the Co(II) complexes reported28), a
tail-to-tail type (like complex 4) and a shoulder-to-shoulder
type (like complex 8). These different overlaps may be related
to the metal atoms connected to the benzimidazole rings and
the steric hindrance around the benzimidazole rings. Further-
more, the benzimidazole ring and other π systems (like
benzene rings) can also form π–π interactions (such as
complex 3 and the Ni(II) complexes reported29). These π–π
interactions along with other weak interactions (like hydrogen
bonds) can provide more opportunities for constructing supra-
molecular architectures. Additionally, the π–π stacking
Fig. 8 (a) 1D polymeric chain of 8. All hydrogen atoms were omitted for
clarity. Selected bond lengths (Å) and angles (°): Cd(1)–N(1) 2.279(2), Cd(1)–
O(1) 2.414(2), Cd(1)–O(2) 2.459(2), Cd(1)–O(4) 2.322(4); N(1)–Cd(1)–N(1A)i
174.5(7), N(1)–Cd(1)–O(1) 84.0(3), N(1)–Cd(1)–O(2) 86.6(4), O(1)–Cd(1)–O(2)
51.9(2), O(1)–Cd(1)–O(4) 141.8(2). Symmetry code: i: −x, y, 1/2 − z. (b) 2D supra-
molecular layer of 8 formed via π–π interactions. All hydrogen atoms were
omitted for clarity. (c) 3D supramolecular frameworks of 6 formed via π–π inter-
actions and C–H⋯O hydrogen bonds. All hydrogen atoms except those partici-
pating in the C–H⋯O hydrogen bonds were omitted for clarity. Symmetry code:
ii: 1/2 − x, 1/2 − y, 1 − z.
and benzimidazole rings (the data of the π–π interactions is
given in Table 2).
As shown in Fig. 4(b), 2D supramolecular layers of 4 are
formed by 20-membered macrometallocycles via intermolecu-
lar C–H⋯O hydrogen bonds (Table 1). In the hydrogen bonds,
the hydrogen atoms are from CH2 groups of alkyl chains and
the oxygen atoms are from acetate groups. The 2D supramole-
cular layers are further extended into 3D supramolecular archi-
tectures via π–π stacking interactions from the benzimidazole
rings, as shown in Fig. 4(c) (Table 2).
In the crystal packings of 5 and 6 (Fig. 5(b) and 6(b)), 1D
polymeric chains are extended into 2D supramolecular layers Scheme 1 The π–π interactions from the benzimidazole ring.
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interactions are also helpful in stabilizing the supramolecular chains (I) formed by the bidentate ligands and metal atoms
architectures.
(such as complexes 5–8, {[Ag(biim-1)](ClO4)}n,17 [Zn(bibim-1)-
(hba)]n (hba = p-hydroxybenzoate)18 and [Zn(biim-6)Cl2]n19), in
which the 1D polymeric chain adopts a zig-zag coordination
geometry. (2) 1D double-stranded polymeric chains (II) formed
by bidentate ligands and metal atoms (such as {[Cu(biim-1)2-
(H2O)2](Cl)2}n,17 {[(Cu(biim-1)2(OH)](Cl)}n and [Cu(biim-1)2-
The conformations of the bidentate ligands (bibim-m or
biim-m) and their metal complexes
According to literature reports and our results obtained here,
the dibenzimidazolyl (or diimidazolyl) bidentate ligands with
alkanyl linkers (bibim-m or biim-m, bibim = 1,m-bis(benzimi-
dazol-l-yl)alkane, biim = 1,m-bis(imidazol-l-yl)alkane, m = 1–6)
can rotate and bend freely around the –(CH2)m– linkers when
coordinating to the central metal atoms. These bidentate
ligands contain mainly three types of conformations, namely,
cis-, trans- and gauche-conformations, as shown in Scheme 2.
In the different conformations, the dihedral angles between
two benzimidazole (or imidazole) rings are different.
20
(NO3)2]n and [Co(biim-5)2(H2O)2]n21), in which the monomer
of the polymeric chain is a macrometallocycle and each macro-
metallocycle is formed by two bidentate ligands and two metal
atoms. Among the coordinating atoms of each metal center,
four of them are nitrogen donors from four different dibenz-
imidazolyl (or diimidazolyl) bidentate ligands and the other
coordinating atoms are from counter-ions or solvent mole-
cules. (3) The metallomacrocycle (III) formed by two bidentate
ligands and two metal atoms (such as complex 4 and
[Cd2(biim-1)2(HL)4)] (H2L = 3-methylsalicylic acid)22), in which
the metallomacrocycle is similar to the above-mentioned
macrometallocycle monomer of II. However, among the co-
ordinating atoms of each metal center in III, two of them are
nitrogen donors from two different dibenzimidazolyl (or di-
imidazolyl) bidentate ligands and the other coordinating
atoms are from counter-ions, solvent molecules or single func-
tional group ligands (such as acetate, p-methylbenzoate and
p-bromobenzoate). Therefore, this case can form only single
metallomacrocycles. (4) 2D layers with the metallomacrocycles
The metal complexes formed via bidentate ligands (bibim-
m or biim-m) and metal salts contain mainly five types of con-
formations (Scheme 3): (1) 1D single-stranded polymeric
17
(IV) (such as complexes 1 and 2, {[Cu(biim-1)2](BF4)2}n and
Scheme 2 The conformations of the dibenzimidazolyl (or diimidazolyl) biden-
[Fe(biim-2)2(N3)2]n23), in which each metallomacrocycle
tate ligands with alkanyl linkers.
Scheme 3 The conformations formed by the dibenzimidazolyl (or diimidazolyl) bidentate ligands and metal salts.
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monomer is constructed via four dibenzimidazolyl (or diimida-
zolyl) bidentate ligands and four metal atoms. (5) 3D frame-
works (V) formed by dibenzimidazolyl (or diimidazolyl)
bidentate ligands and metal atoms (such as {[Ni(biim-4)3]-
24
(NO3)2}n and {[Zn(biim-1)3](ClO4)2}n17), in which each metal
atom is coordinated to six nitrogen donors from six different
bidentate ligands. When the dibenzimidazolyl (or diimidazo-
lyl) bidentate ligands with alkanyl linkers and other com-
pounds (like organic diacids) as mixed ligands are coordinated
to metal atoms, distinct dimensionality and connectivity of the
complexes can also be afforded (such as complex 3 and other
complexes reported25–27).
Additionally, the influence of metal ions on the confor-
mations of metal complexes can also not be ignored. Different
transition metal ions have different electronic structure charac-
teristics. In the course of preparing metal complexes, when the
metal ion is different and ligand is the same, the structure of
the complexes obtained may be different or similar. For
example, the Co(II) complex 1 and Zn(II) complex 6 contain
different metal ions and the same bibim-4 ligand and they
have different conformations (the former is a 2D network layer
and the latter is a 1D polymeric chain (Fig. 1(a) and 6(a))). In
contrast, the Co(II) complex 1 and Cu(II) complex 2 also
contain different metal ions and the same bibim-4 ligand, but
they have similar 2D network layers (Fig. 1(a) and 2(a)). Like-
wise, the Zn(II) complex 6 and Cd(II) complex 8 contain
different metal ions and the same bibim-4 ligand and they
have similar 1D polymeric chains (Fig. 6(a) and 8(a)). It is
notable that the same metal ion in the complexes may possess
a different coordination number, such as the coordination
number of Co(II) is 4 for complex 3, 5 for [Co(bibim-4)(gluta-
rate)]n29 and 6 for complex 1.
In complexes 6 and 7, the metal ion and ligand are all the
same, only the counter-ions are different, and the two com-
plexes possess similar 1D polymeric chains. This indicates that
counter-ions have a relatively small influence on the confor-
mation of complexes. On the whole, the conformations of
metal complexes based on the dibenzimidazolyl (or diimidazo-
lyl) bidentate ligands are related mainly to the length of the
alkanyl chains, metal ions and counter-ions as well as the
steric hindrance around the metal centers.
Fig. 9 Emission spectra of the ligands (bibim-m, m = 2–4) and complexes 1–8
at room temperature in a CH3CN (5.0 × 10−6 M) solution.
terephthalate or DMF. The middle absorption bands at
1378–1395 cm−1 for 2, 5, 6 and 8 correspond to ν(N–O) of the
nitrate groups.
Fluorescence emission spectra of the ligands (bibim-m) and
complexes 1–8
As indicated in Fig. 9, the fluorescence emission spectra of the
ligands (bibim-m, m = 2–4), and complexes 1–8 in acetonitrile
at room temperature are obtained upon excitation at 240 nm.
These ligands (bibim-m) have similar fluorescence emission
spectra and they show weak double emission bands centered
at 305 nm and 335 nm, corresponding to intraligand tran-
sitions.39 The fluorescence emission of complexes 1–8 are
similar to those of the ligands (bibim-m) but they are stronger
than those of the ligands (bibim-m), which should originate
from metal perturbed intraligand processes.40 In complexes
1–8, a new peak at about 280–285 nm is observed and it may
be ascribed to the incorporation of metal–ligand coordination
interactions.41
Conclusions
IR spectra analysis of 1–8
In complexes 1–8, the absorption bands around Among eight Co(II), Zn(II), Cu(II) and Cd(II) complexes based on
3000–2800 cm−1 can be assigned to aromatic ν(C–H) modes. dibenzimidazolyl bidentate ligands with alkyl linkers, seven
The bands in the region of 1653–1515 cm−1 may be ascribed to complexes, 1, 2 and 4–8, were prepared by an analogous
the C–H bending vibrations. The bands around method via the reaction of the corresponding ligands with the
1619–1609 cm−1 may result from ν(CvN) of the benzimidazole metal salts in CH3OH–DMF (the molar ratio between the
rings. The bands in the 1265–1200 cm−1 region may result ligand and metal salt being 1 : 2). But the method of prep-
from νs(C–C) or νs(C–N) of the benzene rings or imidazole aration of complex 3 was somewhat different from the above-
rings. These values are similar to those of the ligands (bibim- mentioned method. In the preparation of complex 3, although
m, m = 2–4). The strong absorption bands about 1395 cm−1 bibim-3 and Co(NO3)2·6H2O (1 : 2) were added, 1 equivalent of
originate from ν(C–O) of the acetate groups for 4 and 7. The terephthalic acid was also used in the presence of Et3N. As a
strong bands at 3448 cm−1 for 1 should be ascribed to ν(O–H) result, the terephthalate group together with bibim-3 partici-
of coordinated water molecules. The strong bands at pate in the coordination with the Co(II) atoms to afford 2D
1594–1652 cm−1 for 3, 4, 7 and 8 correspond to ν(CvO) of network layers with macrometallocycles.
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In complexes 1 and 2, 2D network layers with macrometal- at ambient temperature. Then KOH (0.925 g, 16.5 mmol) and
locycles are formed via the bibim-4 ligand and Co(II) or Cu(II) tetrabutylammonium bromide (0.106 g, 33.3 mmol) were
atoms. In complex 4, a 20-membered macrometallocycle is added. After the mixture was stirred for 2 h under refluxing,
formed by two bibim-3 ligands and two Zn(II) atoms. In com- 1,2-dibromoethane (0.939 g, 5.0 mmol) was slowly added
plexes 5–8, 1D polymeric chains are formed via the bibim-2 or through a syringe and stirred continually for 24 h at 80 °C. The
bibim-4 ligands and Co(II), Zn(II) or Cd(II) centers. The dibenz- reaction was stopped and the solvent was removed under
imidazolyl (or diimidazolyl) bidentate ligands (bibim-m or vacuum to afford a yellow oil. The yellow oil was dissolved in
biim-m) with alkanyl linkers contain mainly three types of con- CH2Cl2 (100 mL) and washed with water (100 mL × 3) and the
formations (i.e. cis-, trans- and gauche-conformations) and organic layer was dried over anhydrous MgSO4. After filtering,
their complexes contain mainly five types of conformations the filtrate was evaporated to give the crude product and the
(i.e. 1D single-stranded polymeric chains, 1D double-stranded product was further purified by recrystallization from metha-
polymeric chains, the metallomacrocycle, 2D layers with the nol–diethyl ether to give 1,2-bis(benzimidazol-l-yl)ethane as a
metallomacrocycles and 3D frameworks). In the crystal pack- white powder (bibim-2). Yield: 0.590
g
(45%). M.p.:
ings of complexes 1–8, 2D supramolecular layers or 3D supra- 240–242 °C. 1H NMR (400 MHz, DMSO-d6): δ 4.72 (s, 4H, CH2),
molecular frameworks are formed via intermolecular weak 7.16 (m, 4H, PhH), 7.38 (d, J = 4.8, 2H, PhH), 7.58 (d, J = 4.8,
interactions, including π–π interactions and hydrogen bonds. 2H, PhH), 7.89 (s, 2H, 2-imiH). Anal. Calc. for C16H14N4: C,
The coordination of dibenzimidazolyl bidentate ligands 73.26; H, 5.37; N, 21.36%. Found: C, 73.53; H, 5.44; N, 21.51%.
bearing alkanyl linkers with metal atoms is similar to the case IR (KBr, cm−1): 2963w, 1606w, 1490s, 1461s, 1410w, 1370m,
of diimidazolyl bidentate ligands. The main difference of the 1334m, 1289w, 1266s, 1204m, 1167s, 1001w, 941w, 881m,
dibenzimidazolyl bidentate ligands and diimidazolyl bidentate 770m, 756vs, 628m, 583w.
ligands is that the conjugated system of the benzimidazole
The ligands 1,3-bis(benzimidazol-l-yl)propane (bibim-3)
ring is bigger than that of the imidazole ring and the benzimi- and 1,4-bis(benzimidazol-l-yl)butane (bibim-4) were prepared
dazole ring participates more easily in π–π interactions in a manner analogous to that of bibim-2, only with 1,3-
between molecules. Therefore, the complexes based on diben- dibromopropane or 1,4-dibromobutane instead of 1,2-
zimidazolyl bidentate ligands can form more varied architec- dibromoethane.
tures via π–π interactions and other weak interactions (like
hydrogen bonds). The resultant structures of the complexes
Preparation of 1,3-bis(benzimidazol-l-yl)propane (bibim-3)
will provide valuable experimental data for crystal engineering Yield: 1.075 g (79%). M.p.: 152–154 °C. 1H NMR (400 MHz,
and supramolecular chemistry. Additionally, the macrocyclic DMSO-d6): δ 2.49 (m, 2H, CH2), 4.30 (s, 4H, NCH2), 7.22 (m,
structures of these metal complexes suggest that they may 4H, PhH), 7.55–7.65 (m, 4H, PhH), 8.25 (s, 2H, 2-imiH). Anal.
have potential applications in host–guest chemistry. Further Calc. for C17H16N4: C, 73.89; H, 5.84; N, 20.27%. Found: C,
studies on new organometallic compounds from the precur- 73.63; H, 5.96; N, 20.57%. IR (KBr, cm−1): 2925w, 1731w,
sors and analogous ligands are underway.
1611m, 1478s, 1449s, 1387m, 1370m, 1334w, 1283s, 1225s,
1200w, 1143w, 1055m, 1001m, 925w, 889w, 871m, 740vs, 631w,
416m.
Experimental
Preparation of 1,4-bis(benzimidazol-l-yl)butane (bibim-4)
General procedures
Yield: 0.975 g (73%). M.p.: 174–175 °C. 1H NMR (400 MHz,
DMSO-d6): δ 1.78 (m, 4H, CH2), 4.27 (s, 4H, NCH2), 7.23 (m,
4H, PhH), 7.57–7.66 (m, 4H, PhH), 8.22 (s, 2H, 2-imiH). Anal.
Calc. for C18H18N4: C, 74.46; H, 6.25; N, 19.30%. Found: C,
74.54; H, 6.65; N, 19.43%. IR (KBr, cm−1): 2929m, 2855m,
1752w, 1606m, 1499vs, 1459s, 1436s, 1378s, 1281s, 1250s,
1154m, 1160m, 1009m, 925w, 889w, 876m, 740vs, 640m.
The bibim-m ligands (m = 2, 3 and 4) were prepared with ana-
logous methods to the literature.42 All the reagents for the syn-
thesis and analyses were of analytical grade and used without
further purification. Melting points were determined with a
Boetius Block apparatus. H NMR spectra were recorded on a
Varian Mercury Vx 400 spectrometer at 400 MHz and 100 MHz,
1
respectively. Chemical shifts, δ, are reported in ppm relative to
the internal standard TMS for both H NMR and J values are
1
Preparation of {[Co(bibim-4)2(H2O)2](NO3)2}n (1)
given in Hz. The elemental analyses of all compounds were
obtained from the recrystallised powder compounds and
measured using a Perkin-Elmer 2400C Elemental Analyzer. IR
spectra (KBr) were taken on an Bruker Equinox 55 spec-
trometer. The luminescent spectra were conducted on a Cary
eclipse fluorescence spectrophotometer.
A DMF solution (5 mL) containing bibim-4 (0.100 g, 0.3 mmol)
was added to a methanol solution (15 mL) of Co(NO3)2·6H2O
(0.175 g, 0.6 mmol). The reaction mixture was stirred for
30 min at about 40 °C. Then the reaction mixture was filtered
and the filtrate was left to stand at room temperature. Purple
block crystals suitable for X-ray analysis were obtained by slow
evaporation of the solvents within seven days. Yield: 99.1 mg
(59%) (based on bibim-4). M.p.: 318–319 °C. Anal. Calc. for
Preparation of 1,2-bis(benzimidazol-l-yl)ethane (bibim-2)
Benzimidazole (1.300 g, 11.0 mmol) and CH3CN (100 mL) were C36H40CoN10O8: C, 46.96; H, 6.22; N, 14.41%. Found: C, 47.14;
added to a flask fitted with a condenser and stirred for 15 min H, 6.56; N, 14.64%. IR (KBr, cm−1): 3440s, 2934w, 2884w,
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2361w, 2025w, 2017w, 1652m, 1615m, 1515s, 1461s, 1387vs, analysis were obtained within two weeks. Yield: 0.102 g (62%)
1333vs, 1257s, 1204m, 1009w, 926w, 893w, 827w, 760s, 740s, (based on bibim-4). M.p.: 258–260 °C. Anal. Calc. for
449w, 429w.
C18H18ZnN6O6: C, 45.06; H, 3.78; N, 17.52%. Found: C, 45.33;
H, 3.86; N, 17.83%. IR (KBr, cm−1): 2946w, 2871w, 2370w,
2029w, 1619m, 1582s, 1548s, 1520s, 1461s, 1378vs, 1329s,
Preparation of {[Cu(bibim-4)2(NO3)](NO3)}n (2)
This complex was prepared in a manner analogous to that of 1 1295s, 1258m, 1201w, 1009w, 939w, 925w, 756s, 738s, 672m,
only using Cu(NO3)2·6H2O (0.145 g, 0.6 mmol) instead of Co 618m, 498m, 422m.
(NO3)2·6H2O and blue block single crystals of 2 suitable for
Preparation of [Zn(bibim-4)(OAc)2]n (7)
X-ray analysis were obtained within two weeks. Yield: 77.8 mg
(57%) (based on bibim-4). M.p.: 294–296 °C. Anal. Calc. for
C36H36CuN10O6: C, 56.28; H, 4.72; N, 18.23%. Found: C, 56.54;
H, 4.53; N, 18.43%. IR (KBr, cm−1): 2950w, 2353w, 2025m,
1615m, 1515s, 1467m, 1395s, 1316s, 1287s, 1262m, 1196m,
1045w, 1009w, 929w, 867w, 772m, 748s, 653w, 618m.
This complex was prepared in a manner analogous to that of 1
only Zn(OAc)2·2H2O (0.176 g, 0.8 mmol) was used instead of
Co(NO3)2·6H2O. Colorless single crystals of 7 suitable for X-ray
analysis were obtained within two weeks. Yield: 0.110 g (59%)
(based on bibim-4). M.p.: 274–276 °C. Anal. Calc. for
C22H24ZnN4O4: C, 55.76; H, 5.11; N, 11.82%. Found: C, 55.73;
H, 5.36; N, 11.65%. IR (KBr, cm−1): 2950w, 2926w, 2356w,
2328w, 2025w, 1594vs, 1523s, 1470m, 1391vs, 1333m, 1299m,
1258m, 1225m, 1196m, 1171m, 1005m, 925m, 751s, 678m,
621w, 431m.
Preparation of [Co(bibim-3)(TP)]n (3)
A DMF solution (5 mL) containing terephthalic acid (0.066 g,
0.4 mmol) and bibim-3 (0.100 g, 0.4 mmol) was added to a
methanol solution (15 mL) of Co(NO3)2·6H2O (0.233 g,
0.8 mmol) and the pH value of the solution was adjusted to
approximately 7 by triethylamine. The reaction mixture was
stirred for 30 min at about 40 °C. Then the reaction mixture
was filtered and the filtrate was left to stand at room tempera-
ture. Purple crystals suitable for X-ray analysis were obtained
by slow evaporation of the solvents within seven days. Yield:
0.120 g (53%) (based on bibim-3). M.p.: >320 °C. Anal. Calc.
for C50H40Co2N8O8: C, 60.13; H, 4.04; N, 11.22%. Found: C,
60.43; H, 4.32; N, 11.46%. IR (KBr, cm−1): 2952w, 2357w,
2025w, 1602m, 1582s, 1503m, 1391s, 1291w, 1258w, 1196w,
1013w, 916w, 824w, 740s, 520w, 425w.
Preparation of [Cd(bibim-4)(NO3)2(DMF)]n (8)
This complex was prepared in a manner analogous to that of
1, and only Cd(NO3)2·4H2O (0.185 g, 0.6 mmol) was used
instead of Co(NO3)2·6H2O and colorless needle-like single crys-
tals of 8 suitable for X-ray analysis were obtained within two
weeks. Yield: 0.126
g (61%) (based on bibim-4), M.p.:
340–342 °C. Anal. Calc. for C21H25CdN7O7: C, 42.05; H, 4.20;
N, 16.34%. Found: C, 42.42; H, 4.41; N, 16.53%. IR (KBr,
cm−1): 2963m, 2938m, 2880w, 2365w, 2029w, 1652m, 1615m,
1523s, 1465s, 1382vs, 1333vs, 1295s, 1225s, 1014w, 918m,
876m, 823m, 752s, 618m, 511m, 422m.
Preparation of [Zn2(bibim-3)]2(OAc)4] (4)
X-ray data collection and structure determinations
This complex was prepared in a manner analogous to that of 1
only bibim-3 (0.100 g, 0.4 mmol) and Zn(OAc)2·2H2O (0.176 g,
0.8 mmol) was used instead of bibim-4 and Co(NO3)2·6H2O.
Colorless single crystals of 4 suitable for X-ray analysis were
obtained within two weeks. Yield: 0.105 g (57%) (based on
bibim-3). M.p.: 120–122 °C. Anal. Calc. for C21H22N4ZnO4: C,
54.85; H, 4.82; N, 12.18%. Found: C, 54.84; H, 4.63; N, 12.42%.
IR (KBr, cm−1): 2971w, 2921w, 1615vs, 1586s, 1515m, 1395s,
1337m, 1200m, 922m, 744s, 675m, 618w, 498w, 428w.
X-ray single-crystal diffraction data for complexes 1–8 were col-
lected using a Bruker Apex II CCD diffractometer at 296(2) K
with Mo–Kα radiation (λ = 0.71073 M) using the ω scan mode.
There was no evidence of crystal decay during the data collec-
tion in all cases. Semiempirical absorption corrections were
applied using SADABS and the program SAINT was used for
the integration of the diffraction profiles.43 All the structures
were solved by direct methods using the SHELXS program of
the SHELXTL package and refined with SHELXL44 by the full-
matrix least-squares method, with anisotropic thermal para-
meters for all non-hydrogen atoms on F2. Hydrogen atoms
bonded to C atoms were placed geometrically and presumably
solvent H atoms were first located in difference Fourier maps
and then fixed in the calculated sites. Further details for the
crystallographic data and structural analysis are listed in
Tables 3–5, generated using Crystal-Maker.45
Preparation of [Co(bibim-2)(NO3)2]n (5)
This complex was prepared in a manner analogous to that of
1, and only bibim-2 (0.105 g, 0.4 mmol) was used instead of
bibim-4. Pink single crystals of 5 suitable for X-ray analysis
were obtained within two weeks. Yield: 0.105 g (62%) (based
on bibim-2). M.p.: 358–360 °C. Anal. Calc. for C16H14CoN6O6:
C, 43.16; H, 3.17; N, 18.87%. Found: C, 43.44; H, 3.51; N,
18.64%. IR (KBr, cm−1): 2961w, 2021w, 1615w, 1490vs, 1461s,
1382s, 1287vs, 1204m, 1009m, 922m, 810m, 744s, 628w, 420m.
Acknowledgements
Preparation of [Zn(bibim-4)(NO3)2]n (6)
This complex was prepared in a manner analogous to that of 1 This work was financially supported by the National Natural
only using Zn(OAc)2·2H2O (0.176 g, 0.8 mmol) instead of Co Science Foundation of China (No. 21172172), Tianjin Natural
(NO3)2·6H2O. Colorless single crystals of 6 suitable for X-ray Science Foundation (No. 11JCZDJC22000) and the Open
5912 | Dalton Trans., 2013, 42, 5902–5915
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Paper
Table 3 Crystal data and structure refinements for 1–3
1
2
3
Chemical formula
fw
Cryst syst
Space group
C
36H42CoN10O10·3H2O·MeOH
C72H72Cu2N20O14·H2O
C50H40Co2N8O8·2DMF·2CH3COCH3
919.82
Monoclinic
P2/n
1586.59
Orthorhombic
Pna21
1261.11
Triclinic
ˉ
P1
a/Å
b/Å
C/Å
α/°
15.226(3)
9.601(5)
16.916(3)
90
97.8(6)
90
2449.7(7)
2
1.247
14.090(0)
16.386(2)
16.393(2)
90
90
90
3784.8(8)
2
1.392
0.640
1648
9.968(3)
11.420(2)
14.055(2)
74.5(9)
82.3(7)
83.5(6)
1524.0(4)
1
β/°
γ/°
V/Å3
Z
Dcalcd/Mg m−3
Abs coeff/mm−1
F(000)
1.374
0.614
658
0.418
966
Cryst size/mm
θmin, θmax/°
T/K
No. of data collected
No. of unique data
No. of refined params
Goodness-of-fit on F2 a
Final R indicesb [I > 2σ(I)]
R1
0.28 × 0.22 × 0.20
2.43, 24.74
296(2)
12 138
4329
295
1.095
0.23 × 0.20 × 0.18
1.76, 25.01
296(2)
18 511
5458
500
1.060
0.23 × 0.22 × 0.12
2.07, 25.03
296(2)
6398
5243
392
1.074
0.0734
0.2412
0.0533
0.1451
0.1002
0.2311
wR2
R indices (all data)
R1
wR2
0.0878
0.2558
0.0587
0.1507
0.1708
0.2640
a Goof = [Σω(Fo − Fc2)2/(n − p)]1/2, where n is the number of reflections and p is the number of parameters refined. b R1 = Σ(||Fo| − |Fc||)/Σ|Fo|;
2
wR2 = 1/[σ2(Fo2) + (0.0691P) + 1.4100P] where P = (Fo2 + 2Fc2)/3.
Table 4 Crystal data and structure refinements for 4–6
4
5
6
Chemical formula
fw
Cryst syst
Space group
C42H44N8Zn2O8·2EtOH
1011.73
Monoclinic
C2/c
C16H14CoN6O6
445.26
Monoclinic
P21/c
C18H18NZn6O6·0.25H2O
484.26
Monoclinic
P21/c
a/Å
b/Å
c/Å
α/°
23.392(8)
9.347(2)
22.029(9)
90
15.631(1)
7.591(5)
14.592(9)
90
9.409(3)
16.653(5)
14.836(1)
90
β/°
94.4(0)
90
4802.8(5)
4
1.399
1.063
93.0(4)
90
1729.0(1)
4
1.710
1.045
101.1(3)
90
2281.0(3)
4
1.410
1.122
γ/°
V/Å3
Z
Dcalcd/Mg m−3
Abs coeff/mm−1
F(000)
2112
908
994
Cryst size/mm
θmin, θmax/°
T/K
No. of data collected
No. of unique data
No. of refined params
Goodness-of-fit on F2a
Final R indicesb [I >2σ(I)]
R1
0.22 × 0.20 × 0.16
1.75, 25.03
296(2)
11 996
4239
327
1.020
0.38 × 0.36 × 0.20
1.30, 25.03
296(2)
8250
3047
262
1.019
0.36 × 0.32 × 0.26
1.86, 25.03
296(2)
11 513
4025
280
1.014
0.0332
0.0804
0.0754
0.1981
0.0539
0.1766
wR2
R indices (all data)
R1
wR2
0.0522
0.0888
0.1122
0.2363
0.0604
0.1821
a Goof = [Σω(Fo − Fc2)2/(n − p)]1/2, where n is the number of reflections and p is the number of parameters refined. b R1 = Σ(||Fo| − |Fc||)/Σ|Fo|;
2
wR2 = 1/[σ2(Fo2) + (0.0691P) + 1.4100P] where P = (Fo2 + 2Fc2)/3.
This journal is © The Royal Society of Chemistry 2013
Dalton Trans., 2013, 42, 5902–5915 | 5913

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Paper
Dalton Transactions
46, 3278–3283; (k) O. Shekhah, K. Hirai, H. Wang,
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Table 5 Crystal data and structure refinements for 7 and 8
7
8
Chemical formula
fw
Cryst syst
Space group
C
26H37N5O7Zn
C21H25CdN7O7
599.88
Monoclinic
C2/c
596.98
Triclinic
P1
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Q. Xu, Chem. Commun., 2007, 2467–2469; (b) S. Hu,
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a/Å
b/Å
c/Å
α/°
8.951(8)
10.837(4)
14.050(5)
76.6(4)
76.3(0)
79.0(9)
1275.4(3)
2
1.554
1.020
628
0.28 × 0.26 × 0.22
1.95, 25.02
296(2)
6537
4459
282
17.857(4)
9.759(3)
14.519(2)
90
102.2(1)
90
2473.0(8)
4
1.611
0.938
1216
0.25 × 0.23 × 0.20
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2176
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a Goof = [Σω(Fo2 − Fc2)2/(n − p)]1/2, where n is the number of reflections
and p is the number of parameters refined. b R1 = Σ(||Fo| − |Fc||)/Σ|Fo|;
wR2 = 1/[σ2(Fo2) + (0.0691P) + 1.4100P] where P = (Fo2 + 2Fc2)/3.
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