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Three CdII complexes based on 2-(1H-imidazol-1-methyl)-1H-benzimidazole and homologous aliphatic dicarboxylates
Accepted Manuscript Three CdII complexes based on 2-(1H-imidazol-1-methyl)- 1H-benzimidazole and homologous aliphatic dicarboxylates Guiyang Zhang, Xiaoli Zhou, Ting Li, Xiangru Meng PII: DOI: Reference:
S0020-1693(14)00294-1 http://dx.doi.org/10.1016/j.ica.2014.05.016 ICA 15998
To appear in:
Inorganica Chimica Acta
Received Date: Revised Date: Accepted Date:
21 March 2014 15 May 2014 19 May 2014
Please cite this article as: G. Zhang, X. Zhou, T. Li, X. Meng, Three CdII complexes based on 2-(1H-imidazol-1methyl)- 1H-benzimidazole and homologous aliphatic dicarboxylates, Inorganica Chimica Acta (2014), doi: http:// dx.doi.org/10.1016/j.ica.2014.05.016
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Three CdII complexes based on 2-(1H-imidazol-1-methyl)1H-benzimidazole and homologous aliphatic dicarboxylates Guiyang Zhanga, Xiaoli Zhoub, Ting Lia, Xiangru Menga,* a
College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, P. R. China
b
State-owned Assets Manegement, Zhongzhou University, Zhengzhou 450044, P. R. China
ABSTRACT Three cadmium complexes incorporating both aliphatic α,ω-dicarboxylate and 2-(1H-imidazol-1methyl)-1H-benzimidazole
(imb)
have
been
prepared
and
structurally
characterized.
[Cd2 Cl2(suc)(imb)2(H2 O)]n (1) manifests 2D layered structure built from the linkage of tetranuclear [Cd4 Cl4(suc)2(H2O)2] units through two kinds of imb ligands. {[Cd(glu)(imb)]·H2O}n (2) contains ladderlike [Cd(glu)]n chains which are bridged by imb ligands to form the 2D layers. {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) also displays 2D network in which dinuclear units [Cd2Cl2] were linked by imb ligands to form double-stranded chains and these chains were further linked by adi2- ligands. Results indicate that aliphatic dicarboxylate ligands play an important role in governing the formation of final frameworks. Additionally, IR spectra, PXRD patterns, TG analyses and fluorescent properties of certain complexes have been determined.
Keywords: Cadmium complex; Crystal structure; Aliphatic dicarboxylate; Fluorescence; Thermogravimetric analysis
1. Introduction Researches on the synthesis, characterization and properties of metal-organic * Corresponding author. Tel. +86-371-67783126 E-mail address: [email protected] (X. R, Meng)
coordination frameworks are getting more and more productive [1-5]. Thus elaborative selection of decent reactant materials has become particularly important in order to obtain complexes with intriguing structures and desired properties [6-8]. Among all the potential organic linker choices, multicarboxylate compounds have turned out to be nice building blocks due to the commendable traits of carboxylate. Carboxylate is a common O-donor which is apt to bond to one, two, three or up to four metal ions via various kinds of coordination modes [9-15]. For a compound which owns two or more carboxylates, its great richness and variation of coordination modes can generate unforeseen structure patterns and packing frameworks, which lead to the outstanding performances of multicarboxylate compounds in coordination chemistry [16-17]. With regard to the aliphatic α,ω-dicarboxylate ligands, their two carboxylates are separated by –(CH2)n– spacers which can bend and rotate freely, generating conformational changes to accommodate the coordination environments. This flexibility accesses diverse structures and topologies in complexes containing N,N-type tethering ligands [18-19]. Our group has been committed to the exploitation of complexes based on N-heterocyclic ligand 2-(1H-imidazol-1-methyl)-1H-benzimidazole (imb). We’ve synthesized a series of imb-contained complexes and made a systematic investigation about how the external or internal conditions such as temperature, counter ions, solvent system, etc. influence the structures and properties eventually [20-23]. As an extension of previous works, we selected a series of aliphatic α,ω-diacid, namely, succinic acid (H2suc), glutaric acid (H2glu) and adipic acid (H2adi) as coligands (Scheme 1) to investigate their effect on the structures of imb-contained Cd II complexes. Three new complexes, namely, [Cd2Cl2(suc)(imb)2(H2O)]n (1),
{[Cd(glu)(imb)]·H2O}n (2) and {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) were obtained and their IR spectra, PXRD patterns, TG analyses and fluorescent properties have been investigated.
2. Experimental Section 2.1. General information and materials 2-(1H-imidazole-1-methyl)-1H-benzimidazole was synthesized
according to
the
literature method [24]. All other chemicals were purchased of AR grade from commercial sources and used without further purification. IR data were recorded on a BRUKER TENSOR 27 spectrophotometer with KBr pellets in 4000–400 cm-1 region. Elemental analyses for C, H and N were carried out on a FLASH EA 1112 element analyzer. PXRD patterns were recorded using CuKα radiation on a PANalytical X’Pert PRO diffractometer. Thermographic analysis was performed on a NETZSCH STA 409 PC/PG differential thermal analyzer from 30°C to 800°C with a heating rate of 10°C·min-1 under air flow. Steady state fluorescence measurements were performed using a Fluoro Max-P spectrofluorimeter at room temperature in solid state.
2.2. Synthesis of [Cd2Cl2(suc)(imb)2(H2O)]n (1) A mixture of CdCl2·2.5H2O (0.1 mmol), imb (0.1 mmol), H2suc (0.1 mmol) and water (6 mL) was placed in a 25 mL Teflon-lined stainless steel vessel and heated at 120 °C for 72 hours. After the mixture had been cooled down to room temperature at a rate of 10°C·h-1, crystals of 1 suitable for X-ray diffraction were obtained and then collected by hand, washed with distilled water, and dried in air (yield: 56% based on Cd). Anal. Calcd. for
C26H26Cd 2Cl2N8O5 (826.25): C, 37.80; H, 3.15; N, 13.56 (%). Found: C, 37.59; H, 3.33; N, 13.81 (%). IR (KBr, cm-1): 3481(m), 3137(m), 2902(m), 1553(s), 1487(s), 1450(s), 1391(m), 1236(m), 1206(m), 1029(m), 749(m), 656(w).
2.3. Synthesis of {[Cd(glu)(imb)]·H2O}n (2) The preparation of 2 was similar with that of 1 except that H2suc was replaced by H2 glu. Colorless crystals of 2 were collected (yield: 62% based on Cd). Anal. Calcd. for C16H18CdN4O5 (458.74): C, 41.89; H, 3.92; N, 12.21 (%). Found: C, 41.29; H, 4.01; N, 12.55 (%). IR (KBr, cm-1): 3483(m), 3133(m), 2949(m), 1553(s), 1528(m), 1449(s), 1403(m), 1279(m), 1234(m), 1023(m), 750(s), 656(w).
2.4. Synthesis of {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) The preparation of 3 was similar with that of 2 except that H2glu was replaced by H2adi. Colorless crystals of 3 were collected (yield: 51% based on Cd). Anal. Calcd. for C14H16CdClN4O3 (436.16): C, 38.55; H, 3.67; N, 12.85 (%). Found: C, 38.12; H, 3.81; N, 13.02 (%). IR (KBr, cm-1): 3441(m), 3130(m), 2872(m), 1542(s), 1455(m), 1281(m), 1233(m), 1088(m), 743(m), 656(w).
2.5. X-ray crystallography A suitable single crystal of each complex was carefully selected and glued to a thin glass fiber. Crystal structure determination by X-ray diffraction was performed on a Rigaku Saturn 724 CCD area detector with graphite monochromator for the X-ray source (MoKα radiation, λ
= 0.71073 Å) operating at 50 kV and 40 mA. The data were collected by ω scan mode at 293(2) K; the crystal-to-detector distance was 45 mm. An empirical absorption correction was applied. The data were corrected for Lorentz-polarization effects. The structures were solved by direct methods and refined by full-matrix least-squares and difference Fourier techniques based on F2 using SHELXS-97 program [25]. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms of the ligands were positioned geometrically and refined using a riding model. Hydrogen atoms of water molecules were found at reasonable positions in the differential Fourier map and located there. All hydrogen atoms were included in the final refinement. Crystallographic parameters and structural refinement for the complexes are summarized in Table 1. Selected bond lengths and bond angles are listed in Table 2. Hydrogen bonds are listed in Table 3.
3. Results and Discussion 3.1. IR spectra IR spectra show broad bands at 3481 cm-1 for 1, 3483 cm-1 for 2 and 3441 cm-1 for 3 attributed to O–H stretch. Absorptions at 3137 cm-1 for 1, 3133 cm-1 for 2 and 3130 cm-1 for 3 can be ascribed to Ar–H stretch. Absorptions at 2902 cm-1 for 1, 2949 cm-1 for 2 and 2872 cm-1 for 3 can be ascribed to C–H stretches on the aliphatic –(CH2)n– chains. Free carboxylic acid presents strong C=O absorption band at the range of 1740-1650 cm-1; upon complexation to a metal center, this band disappears and two new bands relating to the asymmetric ν(O–C–O)a and symmetric ν(O–C–O)s stretches appear in the regions 1620-1480 and
1450-1340 cm-1 [26, 27]. The absorption bands at 749 cm-1 for 1, 750 cm-1 for 2 and 743 cm-1 for 3 can be assigned to characteristic stretching vibrations of 1,2-substituted benzene rings. The above assignments are in consistent with the results of X-ray diffraction.
3.2. Crystal structure of [Cd2Cl2(suc)(imb)2(H2O)]n (1) Self-assembly of H2suc, imb and CdCl2·2.5H2O gives complex 1. Single-crystal X-ray diffraction reveals that 1 crystallizes in triclinic space group P-1. Each asymmetric unit contains two crystallographically distinct CdII cations, two crystallographically distinct imb ligands, two crystallographically distinct Cl- anions, one suc2- anion and one coordinated water molecule. As shown in Fig. 1a, Cd1 situates in a distorted octahedral coordination geometry completed by two nitrogen atoms from two imb ligands, two bridging chlorine anions, one oxygen atom from suc2- group and one oxygen atom from coordinated water molecule. The vertices are occupied by Cl1 and O5 with the Cl1–Cd1–O5 bond angle of 172.98(6)° while N1, Cl2, N4#2 and O4#1 constitute the equatorial plane for which the mean deviation is 0.0011(4) Å. The environment of Cd2 is similar with Cd1 except that the two ligating oxygen atoms belong to a chelating carboxylate instead of one monodentate carboxylate and one water molecule. Ligating atoms around Cd2 present a disordered octahedral geometry in which the apical positions are occupied by N5#3 and Cl1 with the N5#3–Cd2–Cl1 bond angle of 170.71(7)°. O1, O2, N7, Cl2 and Cd2 are almost coplanar (mean deviation: 0.0762 Å). The bond lengths around Cd1 and Cd2 are similar to the reported complexes
such
as
{[Cd(imb)Cl2]·CH3OH}n,
{[Cd(imb)Cl2]·DMF}n
and
[Cd(OH)2(imb)2(4,4’-bipyridine)2] [21, 22]. Cd1 and Cd2 are linked together via two µ2-bridging chlorine anions, leading to the [Cd2Cl2] binuclear unit with a Cd···Cd separation of 3.7580(11) Å. H2suc was entirely deprotonated in the construction process of 1. As shown in Fig. 1b, µ2-suc2- exist in an anti conformation with a torsion angle of 125.29°. One carboxylate of each suc2- chelates to Cd2 while the other coordinates to Cd1 monodentately. Two suc2- connect two binuclear [Cd 2Cl2] units together, forming a eighteen-membered [Cd 4Cl4(suc)2(H2O)2] ring in which the four Cd II ions are coplanar. Cd1···Cd2 distance separated by one suc2- is 8.0082(32) Å. Fig. 1c depicts how the [Cd4Cl4(suc)2(H2O)2] rings outspread bidimensionally. Bridging imb ligands could be divided into two kinds due to their different conformations. One kind of imb ligands (turquoise) bridge two Cd1 ions by imidazole N1 and benzimidazole N4 leading to
the
ladderlike
polymeric
chain
···[Cd4Cl4(suc)2(H2O)2]–(imb)2–
[Cd 4Cl4(suc)2(H2O)2]–(imb)2··· along a axis. The Cd1···Cd1 distance separated by one imb ligand is 9.1790(18) Å. The other kind of imb ligands (green) bridge two Cd2 ions by imidazole
N5
and
benzimidazole
N7
forming
the
linear
polymeric
chain ···[Cd4Cl4(suc)2(H2O)2]–(imb)2–[Cd 4Cl4(suc)2(H2O)2]–(imb)2··· along b axis. The Cd2···Cd2 distance separated by one imb ligand is 6.548(2) Å. The two kinds of polymeric chains in different directions intersect together to accomplish a 2D layered structure. As illustrated in Fig. S1, there are two kinds of intralaminar N–H···O hydrogen bonds between the benzimidazole rings and carboxylates and one kind of intralaminar O–H···O hydrogen bonds between the carboxylates and coordinated water molecules. These hydrogen bonding intereactions further stabilize the layered structure. There is also one kind of
interlaminar O–H···O hydrogen bonds between the carboxylates and coordinated water molecules from adjacent layers. In addition, the benzimidazole rings from adjacent layers are parallel to each other with a centroid-centroid distance of 3.496(4) Å, which drops into the range for common π-π intereactions [28]. The adjacent layers are piled up by the interlaminar hydrogen bonds and π-π intereactions to give a 3D supramolecular framework as depicted in Fig. S2.
3.3. Crystal structure of {[Cd(glu)(imb)]·H2O}n (2) When succinic acid was replaced by glutaric acid while other experimental conditions remain unchanged, new complex 2 with different architecture from 1 was obtained. Water molecules were not coordinated to any metal center but cocrystallize with the complex and chlorine anions don’t participate in coordination in 2. Single-crystal X-ray diffraction reveals that 2 crystallizes in triclinic space group P-1. Each asymmetric unit contains one CdII cation, one imb ligand, one glu2- anion and one uncoordinated water molecule. As shown in Fig. 2a, each CdII ion is six-coordinated with two nitrogen atoms from two symmetry-related imb ligands and four oxygen atoms from three carboxylates, featuring an irregular CdN2O4 coordination geometry. As shown in Table 2, most of the bond angles around the central CdII ion deviate dramatically from the ideal angles of 90° or 180° expected for an octahedral geometry, as exemplified by the angles of O1–Cd1–O2, O3#1–Cd1–N1, and O3#1–Cd1–O1 (53.60(7)°, 135.43(7)° and 141.90(7)°, respectively). The Cd–N and Cd–O bond lengths are similar to those in 1 and other reported complexes [20-22]. H2suc was entirely deprotonated in the construction process of 2. Each glu2- bridges three
Cd II ions, two through tridentate bridging mode, with an additional CdII ion bound to one oxygen atom of the other carboxylate. These µ3-glu2-, taken together with the gauche-anti conformation of the aliphatic tether (four-atom torsion angles: 69.76° and 178.44°), lead to the propagation of infinite double-stranded chain ···Cd 2–(glu)2–Cd 2–(glu)2··· along b axis as shown in Fig. 2b. Cd···Cd distance separated by a glu2- is 9.715(1) Å. These 1D chains are further connected by bidentate bridging imb ligands with the Cd···Cd distance of 8.9736(18) Å, and thus giving rise to the formation of 2D layered structure (Fig. 2c). Additionally, there are two kinds of interlaminar O–H···O hydrogen bonds between the carboxylates and uncoordinated water molecules, and one kind of interlaminar N–H···O hydrogen bonds between the benzimidazole rings and uncoordinated water molecules. Adjacent layers are linked by these hydrogen bonds and the π-π intereactions between benzene rings from neighbouring layers with a centroid-centroid distance of 3.8438(14) Å to give a 3D supramolecular framework in solid state with small solvent-accessible void space (2.9 %) occupied by uncoordinated water molecules (Fig. S3).
3.4. Crystal structure of {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) Complex 3 other from 1 and 2 were obtained when glutaric acid was replaced by adipic acid while other experimental conditions stay the same. X-ray crystallographic analysis reveals that 3 crystallizes in triclinic space group P-1. Each asymmetric unit contains one CdII cation, one imb ligand, one Cl- anion, a half adi2- anion and one uncoordinated water molecule. Water molecules are not coordinated to any metal center but cocrystallize with the complex. As shown in Fig. 3a, CdII ion is six-coordinated with a octahedral geometry completed by two
nitrogen atoms from two symmetry-related imb ligands, two symmetry-related chlorine anions and two oxygen atoms from one adi2- group. The apical positions are occupied by N1 and Cl1#2 with the N1–Cd–Cl1#2 bond angle of 173.10(6)°. The equatorial plane is completed by Cl1, O1, O2 and N4#1 with a mean deviation of 0.1091(4) Å. The Cd–N, Cd–O and Cd–Cl bond lengths are similar to those in 1, 2 and other reported complexes [20-22]. Two CdII ions are bridged by two µ2-bridging chlorine anions forming a binuclear [Cd 2Cl2] grid with a Cd···Cd distance of 3.9194(15) Å. The [Cd2Cl2] grids are connected by bidentate
bridging
imb
ligands
leading
to
a
double-stranded
linear
chain ···[Cd 2Cl2]–(imb)2–[Cd 2Cl2]–(imb)2··· along a axis (Fig. 3b). The Cd···Cd distance separated by one imb ligand is 8.6158(17) Å. Fully deprotonated µ2-adi2- group feature an anti–anti–anti conformation (four-atom torsion angles: 171.99°, 180.00° and 171.99°) and its two carboxylates chelate two Cd II ions respectively, connecting the 1D chains to form a 2D layered structure (Fig. 3c). The Cd···Cd distance separated by an adi2- group along b axis is 11.5216(33) Å. Additionally, there are one kind of interlaminar N–H···O hydrogen bond between the benzimidazole rings and uncoordinated water molecules, and two kinds of interlaminar O–H···O hydrogen bonds between the carboxylates and uncoordinated water molecules. The benzimidazole rings from adjacent layers are parallel to each other with a centroid-centroid distance of 3.8312(14) Å, generating weak π-π interactions. The adjacent layers are piled up through the above three kinds of hydrogen bonds and π-π interactions resulting in a 3D supramolecular framework in solid state with small solvent-accessible void space (7.4%) occupied by uncoordinated water molecules (Fig. S4).
Topology analyses are investigated to make an explicit description of complexes 1–3. For 1, Cd1 and Cd2 could be viewed as 4- and 3-connected nodes respectively. Both imb and suc2- ligands act as linear linkers. The overall motif of 1 is a 2D (4,3)-connected (4·64·8)(4·8 2) network (Fig. 1d). For 2, CdII ions and glu2- ligands can be viewed as 5- and 3-connected nodes respectively while the imb ligands act as linear linker. The 2D layer of 2 is a (5,3)-connected network with (4 2·67·8)(42·6) topology (Fig. 2d). CdII ions in 3 can be topologically counted as 4-connected nodes and all the ligands in 3 act as linear linkers. The 2D layer of 3 is a 4-connected network with 4 4·62 topology (Fig. 3d). The above analyses imply that aliphatic dicarboxylate ligands of different lengths can take different coordination modes to generate complexes with completely different structures and topologies in some cases.
By
contrast,
in
complexes
{[Cd(suc)(dpa)]·H2O}n,
[Cd(glu)(dpa)]n,
and
{[Cd(adi)(dpa)]}n (dpa = 4,4’-dipyridylamine), aliphatic dicarboxylate ligand connect the CdII ions along orthometric directions to form a (4,4) [Cd(L)]n (L = suc2-, glu2- or adi2-) layer and parallel layers are then pillared by the tethering dpa ligands to form a doubly interpenetrated 6-connected 3D [Cd(L)(dpa)]n network with 412·63 topology [29–31]. Aliphatic dicarboxylate ligands of different lenths perform similarly in the crystallization process of these three complexes, indicating that the flexibility of the aliphatic dicarboxylates can permit generation of similar polymeric networks in nature under proper conditions.
3.5. PXRD patterns and TG analyses PXRD patterns for 1–3 were recorded to confirm the phase purity of the samples and they were comparable to the corresponding simulated ones calculated from the single-crystal
diffraction data (Fig. S5), indicating a pure phase of each bulk sample. Thermogravimetric (TG) analysis of 2 was performed by heating the sample from 30°C to 800°C in air (Fig. S6). Complex 2 is stable up to 196°C and the first mass loss of 3.90% occurs from 196°C to 223°C, corresponding to the release of uncoordinated water molecules (Calcd. 3.92%). Then a plateau region is observed from 223°C to 324°C. Continuous mass loss from 324°C to 610°C corresponds to the gradually decomposition of the glu2- groups and imb ligands. Finally a plateau occurs from 610°C to 800°C. A brown residue which is attributed to be CdO (observed: 27.46%, Calcd. 27.99%) is remained. The results are in agreement with the crystal structure. TG analyses of halogen-containing compounds are not supported by the NETZSCH STA 409 PC/PG differential thermal analyzer, so TG analyses of 1 and 3 have not been carried out.
3.6. Fluorescence A number of complexes with d10 metal centers have been investigated regarding to their fluorescence properties which result in potential applications in chemical sensors, photochemistry, and light-emitting diodes [32-34]. According to our previous work, free imb ligand gives a relatively sharp emission band at 300 nm upon excitation at 270 nm [22]. In this study, we have investigated the fluorescence of the three complexes in solid state at room temperature. As shown in Fig. 4, intense emissions are observed at 306 nm for 1, 313 nm for 2 and 334 nm for 3 under the excitation at 287 nm. The resemblance between the emissions of 1–3 and that of free imb indicates that the emissions of 1–3 originate from π*→π transition of
imb. To the best of our knowledge, the emissions of aliphatic dicarboxylates belongs to π*→n transition which is very weak compared to π*→π transition, so the dicarboxylates have little contribution to the fluorescent emissions of the complexes [35]. All the fluorescence curves of the complexes present more or less bathochromic shift in contrast to that of imb, which should be attributed to the metal-ligand coordination interactions [35]. The difference of the peak positions are considered to be the result of unequable coordination environments of the metal centers under the intervention of different dicarboxylates.
4. Conclusion In summary, we have introduced a series of dicarboxylic acids (H2suc, H2glu and H2adi) into a CdII-imb system and obtained three new complexes. All complexes present 2D layered structure but showing structural diversity because of influence of the homologous aliphatic coligands. For 1, binuclear units are bridged by suc2- anions to form a tetranuclear 18-ring and then outspreads bidimensionally via the connection of two kinds of imb ligands to accomplish the 2D layer. For 2, ladderlike linear chains formed by glu2- anions and CdII ions are linked by bridging imb ligands to form the 2D layer. For 3, ladderlike linear chains are composed of [CdCl2] binuclear units and imb ligands and adi2- anions further connect the chains together to generate the 2D layer. These results suggest that the change of aliphatic dicarboxylate coligands can influence the detailed structures and then influence the properties of the complexes.
Supporting Information Crystallographic data reported in this paper have been deposited with the Cambridge Crystallographic Data Center as supplementary publication. CCDC numbers are 971029-971031.
These
data
can
be
obtained
free
of
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033).
Acknowledgement We gratefully acknowledge the financial support by the National Natural Science Foundation of China (No. J1210060).
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O.S. Wolfbeis, Fluorescence Methods and Applications: Spectroscopy, Imaging, and Probes, New Jersey: Wiley-Blackwell.
Captions Schem 1. Schematic description of the ligands in this study and their coordination modes. Fig. 1. (a) Coordination environment of the CdII centers in 1, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms are omitted for clarity. (b) 18-Ring unit [Cd4Cl4(suc)2(H2O)2] in 1. (c) 2D network structure in 1. (d) Topological net for 1 where the ligands were represented by corresponding pillar sticks: purple for suc2-, yellow for Cl-, turquoise and green for two kinds of imb.
Fig. 2. (a) Coordination environment of the CdII centers in 2, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms and uncoordinated water molecule are omitted for clarity. (b) Double-stranded chain along b axis. (c) 2D network structure in 2. Benzene rings are omitted for clarity. (d) Topological net for 2 where the ligands were represented by corresponding pillar sticks: purple for glu2- and turquoise for imb.
Fig. 3. (a) Coordination environment of the CdII centers in 3, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms and uncoordinated water molecules are omitted for clarity. (b) Double-stranded chain along a axis. (c) 2D network structure in 3. Benzene rings are omitted for clarity. (d) Topological net for 3 where the ligands were represented by corresponding pillar sticks: yellow for Cl-, purple for adi2and turquoise for imb. Fig. 4. Fluorescent spectra of complexes 1–3 in solid state at room temperature.
Schem 1. Schematic description of the ligands in this study and their coordination modes.
a
b
c
d
Fig. 1. (a) Coordination environment of the CdII centers in 1, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms are omitted for clarity. (b) 18-Ring unit [Cd4Cl4(suc)2(H2O)2] in 1. (c) 2D network structure in 1. (d) Topological net for 1 where the ligands were represented by corresponding pillar sticks: purple for suc2-, yellow for Cl-, turquoise and green for two kinds of imb.
a
b
c
d
Fig. 2. (a) Coordination environment of the CdII centers in 2, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms and uncoordinated water molecule are omitted for clarity. (b) Double-stranded chain along b axis. (c) 2D network structure in 2. Benzene rings are omitted for clarity. (d) Topological net for 2 where the ligands were represented by corresponding pillar sticks: purple for glu2- and turquoise for imb.
a
b
c
d
Fig. 3. (a) Coordination environment of the CdII centers in 3, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms and uncoordinated water molecules are omitted for clarity. (b) Double-stranded chain along a axis. (c) 2D network structure in 3. Benzene rings are omitted for clarity. (d) Topological net for 3 where the ligands were represented by corresponding pillar sticks: yellow for Cl-, purple for adi2and turquoise for imb.
Fig. 4. Fluorescent spectra of complexes 1–3 in solid state at room temperature.
Table 1 Crystal data and structural refinement for complexes 1–3. Complex Empirical formula
1 C26H26Cd2Cl2N8O5
2 C16H18CdN4O5
3 C14H16CdClN4O3
Formula weight Temperature (K) Crystal system Space group Unit cell dimensions (Å, °) a b c α β γ Volume (Å3)
826.25 293(2) Triclinic P-1
458.74 293(2) Triclinic P-1
436.16 293(2) Triclinic P-1
9.1790(18) 11.445(2) 13.977(3) 100.86(3) 90.23(3) 98.37(3) 1425.9(5)
8.9736(18) 9.7152(19) 11.339(2) 69.15(3) 67.52(3) 78.80(3) 851.7(3)
8.6158(17) 8.7031(17) 11.442(2) 106.36(3) 99.64(3) 98.35(3) 794.6(3)
Z Absorption coefficient (mm-1)
2 1.732
2 1.319
2 1.562
F(000) Crystal size (mm3)
816 0.18 × 0.14 × 0.10
460 0.19 × 0.18 × 0.15
434 0.19 × 0.16 × 0.12
θ range for data collection (°) Limiting indices R(int) Data / Restraints / Parameters Goodness-of-fit on F2
1.83–27.86 -12 ≤ h ≤ 11, -15 ≤ k ≤ 14, -18 ≤ l ≤ 18 0.0288 6736 / 0 / 388 1.025
2.25–27.83 -11 ≤ h ≤ 11, -12 ≤ k ≤ 12, -14 ≤ l ≤ 14 0.0234 3994 / 0 / 235 1.040
1.90–25.50 -10 ≤ h ≤ 10, -10 ≤ k ≤ 10, -13 ≤ l ≤ 13 0.0195 2946 / 0 / 208 1.083
R indices [I > 2σ(I)]
R1 = 0.0330, wR2 = 0.0764
R1 = 0.0301, wR2 = 0.0667
R1 = 0.0258, wR2 = 0.0639
R1 = 0.0399, wR2 = 0.0809
R1 = 0.0325, wR2 = 0.0681
R1 = 0.0275, wR2 = 0.0650
0.545 and -0.725
0.413 and -0.549
1.004 and -0.549
R indices (all data) 3
Largest difference peak and hole (eA )
Table 2 Selected bond lengths and bond angles of complexes 1–3. a Complex 1 Cd(1)–O(4)#1 Cd(1)–N(1) Cd(1)–Cl(1) Cd(2)–O(1) Cd(2)–N(5)#3 Cd(2)–Cl(1) O(4)#1–Cd(1)–N(4)#2 O(4)#1–Cd(1)–N(1) N(4)#2–Cd(1)–N(1) O(4)#1–Cd(1)–Cl(2) N(1)–Cd(1)–Cl(2) O(4)#1–Cd(1)–Cl(1) N(1)–Cd(1)–Cl(1) Cl(2)–Cd(1)–Cl(1) N(5)#3–Cd(2)–O(1) N(5)#3–Cd(2)–O(2) O(1)–Cd(2)–O(2) N(7)–Cd(2)–Cl(2) O(2)–Cd(2)–Cl(2) N(7)–Cd(2)–Cl(1) O(2)–Cd(2)–Cl(1) Cd(1)–Cl(1)–Cd(2)
2.317(2) 2.326(3) 2.6365(10) 2.370(2) 2.291(3) 2.6879(10) 84.77(9) 79.03(9) 163.42(9) 170.41(6) 92.01(8) 95.83(7) 90.33(7) 87.54(4) 86.86(9) 83.91(10) 54.64(8) 97.73(7) 107.18(6) 96.18(7) 87.26(7) 89.78(4)
Cd(1)–O(5) Cd(1)–N(4)#2 Cd(1)–Cl(2) Cd(2)–O(2) Cd(2)–N(7) Cd(2)–Cl(2) O(4)#1–Cd(1)–O(5) N(4)#2–Cd(1)–O(5) N(1)–Cd(1)–O(5) N(4)#2–Cd(1)–Cl(2) O(5)–Cd(1)–Cl(2) N(4)#2–Cd(1)–Cl(1) O(5)–Cd(1)–Cl(1) N(5)#3–Cd(2)–N(7) N(7)–Cd(2)–O(1) N(7)–Cd(2)–O(2) N(5)#3–Cd(2)–Cl(2) O(1)–Cd(2)–Cl(2) N(5)#3–Cd(2)–Cl(1) O(1)–Cd(2)–Cl(1) Cl(2)–Cd(2)–Cl(1) Cd(2)–Cl(2)–Cd(1)
2.390(2) 2.322(3) 2.6076(11) 2.412(2) 2.351(2) 2.5746(9) 86.36(9) 92.05(9) 83.52(9) 103.94(7) 89.28(7) 94.79(7) 172.98(6) 90.65(10) 100.82(8) 155.01(8) 98.22(8) 160.71(6) 170.71(7) 85.67(6) 87.13(4) 92.96(4)
Complex 2 Cd(1)–O(3)#1 Cd(1)–O(2) Cd(1)–O(1) O(3)#1–Cd(1)–N(1) N(1)–Cd(1)–N(4)#2 N(1)–Cd(1)–O(2) O(3)#1–Cd(1)–O(1) N(4)#2–Cd(1)–O(1) O(3)#1–Cd(1)–O(2)#3 N(4)#2–Cd(1)–O(2)#3 O(1)–Cd(1)–O(2)#3
2.212(2) 2.365(2) 2.498(2) 135.43(7) 105.96(9) 125.67(8) 141.90(7) 81.36(8) 79.63(7) 163.80(8) 102.95(7)
Cd(1)–O(2)#3 Cd(1)–N(1) Cd(1)–N(4)#2 O(3)#1–Cd(1)–N(4)#2 O(3)#1–Cd(1)–O(2) N(4)#2–Cd(1)–O(2) N(1)–Cd(1)–O(1) O(2)–Cd(1)–O(1) N(1)–Cd(1)–O(2)#3 O(2)–Cd(1)–O(2)#3
2.644(2) 2.236(2) 2.325(2) 87.40(8) 92.74(7) 98.15(9) 82.64(7) 53.60(7) 90.13(8) 73.04(8)
Complex 3 Cd(1)–N(4)#1 Cd(1)–N(1) Cd(1)–Cl(1)
2.301(2) 2.337(3) 2.5591(10)
Cd(1)–O(1) Cd(1)–O(2) Cd(1)–Cl(1)#2
2.312(2) 2.463(2) 2.6785(14)
N(4)#1–Cd(1)–O(1) O(1)–Cd(1)–N(1) O(1)–Cd(1)–O(2) N(4)#1–Cd(1)–Cl(1) N(1)–Cd(1)–Cl(1) N(4)#1–Cd(1)–Cl(1)#2 N(1)–Cd(1)–Cl(1)#2 Cl(1)–Cd(1)–Cl(1)#2 a
149.35(8) 84.71(9) 54.58(7) 111.37(6) 94.55(7) 96.30(7) 173.10(6) 83.14(4)
N(4)#1–Cd(1)–N(1) N(4)#1–Cd(1)–O(2) N(1)–Cd(1)–O(2) O(1)–Cd(1)–Cl(1) O(2)–Cd(1)–Cl(1) O(1)–Cd(1)–Cl(1)#2 O(2)–Cd(1)–Cl(1)#2 Cd(1)–Cl(1)–Cd(1)#2
90.60(9) 95.40(8) 91.32(9) 99.20(6) 152.48(6) 89.23(7) 87.84(6) 96.86(4)
Symmetry transformations used to generate equivalent atoms: For 1, #1 –x, –y, –z; #2 x+1, y, z; #3 –x+1, –y+1, –z; #4 x-1, y, z. For 2, #1 x, y–1, z; #2 x–1, y, z; #3 –x+1, –y+1, –z; #4 x+1, y, z; #5 x, y+1, z. For 3, #1 x–1, y, z; #2 –x+1, –y+3, –z+1; #3 x+1, y, z; #4 -x+2, -y+2, -z+1.
Table 3 Hydrogen bonds in complexes 1–3. D–H…A
d(D–H) (Å)
d(H…A) (Å)
d(D…A) (Å)
(D–H…A) (°)
1 N(3)–H(3B)…O(3)#1 O(5)–H(1W)…O(3)#1 N(8)–H(8B)…O(2)#2 O(5)–H(2W)…O(3)#5
0.86 0.85 0.86 0.85
1.9 1.9 1.9 2.31
2.733(3) 2.733(3) 2.736(3) 2.931(3)
161.8 165.0 162.7 130.1
2 N(2)–H(2C)…O(5) O(5)–H(1W)…O(1)#6 O(5)–H(2W)…O(4)#6
0.86 0.85 0.85
1.93 1.98 2.11
2.736(3) 2.828(3) 2.955(3)
155.7 172.6 175.3
3 O(3)–H(1W)…O(2)#3 O(3)–H(2W)…O(2)#3 N(3)–H(3B)…O(3)#5
0.85 0.85 0.86
2.31 2.29 1.96
2.734(3) 2.734(3) 2.763(3)
111.3 113.1 154.1
Graphical abstract: picture Three CdII complexes based on 2-(1H-imidazol-1-methyl)-1Hbenzimidazole and homologous aliphatic dicarboxylates Guiyang Zhang, Xiaoli Zhou, Ting Li, Xiangru Meng
Graphical abstract: Synopsis Three CdII complexes based on 2-(1H-imidazol-1-methyl)-1Hbenzimidazole and homologous aliphatic dicarboxylates Guiyang Zhang, Xiaoli Zhou, Ting Li, Xiangru Meng
Three new CdII complexes with the formulas [Cd2Cl2(suc)(imb)2(H2O)]n (1), {[Cd(glu)(imb)]·H2O}n (2) and {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) were synthesized and structurally characterized by single-crystal X-ray diffraction. Dicarboxylate coligands play an important role in tuning the detailed structure and characters of the complexes. IR spectra, PXRD patterns, TG analyses and fluorescent properties of certain complexes have also been investigated.
Highlights ►CdII complexes based on 2-(1H-imidazol-1-methyl)-1H-benzimidazole and aliphatic dicarboxylate ligands. ►Diverse architectures and topological networks of the complexes. ►Aliphatic dicarboxylate ligands exert regulating effects on the structural features. ►The complexes are characterized by IR, luminescence and TGA techniques.
S0020-1693(14)00294-1 http://dx.doi.org/10.1016/j.ica.2014.05.016 ICA 15998
To appear in:
Inorganica Chimica Acta
Received Date: Revised Date: Accepted Date:
21 March 2014 15 May 2014 19 May 2014
Please cite this article as: G. Zhang, X. Zhou, T. Li, X. Meng, Three CdII complexes based on 2-(1H-imidazol-1methyl)- 1H-benzimidazole and homologous aliphatic dicarboxylates, Inorganica Chimica Acta (2014), doi: http:// dx.doi.org/10.1016/j.ica.2014.05.016
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Three CdII complexes based on 2-(1H-imidazol-1-methyl)1H-benzimidazole and homologous aliphatic dicarboxylates Guiyang Zhanga, Xiaoli Zhoub, Ting Lia, Xiangru Menga,* a
College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, P. R. China
b
State-owned Assets Manegement, Zhongzhou University, Zhengzhou 450044, P. R. China
ABSTRACT Three cadmium complexes incorporating both aliphatic α,ω-dicarboxylate and 2-(1H-imidazol-1methyl)-1H-benzimidazole
(imb)
have
been
prepared
and
structurally
characterized.
[Cd2 Cl2(suc)(imb)2(H2 O)]n (1) manifests 2D layered structure built from the linkage of tetranuclear [Cd4 Cl4(suc)2(H2O)2] units through two kinds of imb ligands. {[Cd(glu)(imb)]·H2O}n (2) contains ladderlike [Cd(glu)]n chains which are bridged by imb ligands to form the 2D layers. {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) also displays 2D network in which dinuclear units [Cd2Cl2] were linked by imb ligands to form double-stranded chains and these chains were further linked by adi2- ligands. Results indicate that aliphatic dicarboxylate ligands play an important role in governing the formation of final frameworks. Additionally, IR spectra, PXRD patterns, TG analyses and fluorescent properties of certain complexes have been determined.
Keywords: Cadmium complex; Crystal structure; Aliphatic dicarboxylate; Fluorescence; Thermogravimetric analysis
1. Introduction Researches on the synthesis, characterization and properties of metal-organic * Corresponding author. Tel. +86-371-67783126 E-mail address: [email protected] (X. R, Meng)
coordination frameworks are getting more and more productive [1-5]. Thus elaborative selection of decent reactant materials has become particularly important in order to obtain complexes with intriguing structures and desired properties [6-8]. Among all the potential organic linker choices, multicarboxylate compounds have turned out to be nice building blocks due to the commendable traits of carboxylate. Carboxylate is a common O-donor which is apt to bond to one, two, three or up to four metal ions via various kinds of coordination modes [9-15]. For a compound which owns two or more carboxylates, its great richness and variation of coordination modes can generate unforeseen structure patterns and packing frameworks, which lead to the outstanding performances of multicarboxylate compounds in coordination chemistry [16-17]. With regard to the aliphatic α,ω-dicarboxylate ligands, their two carboxylates are separated by –(CH2)n– spacers which can bend and rotate freely, generating conformational changes to accommodate the coordination environments. This flexibility accesses diverse structures and topologies in complexes containing N,N-type tethering ligands [18-19]. Our group has been committed to the exploitation of complexes based on N-heterocyclic ligand 2-(1H-imidazol-1-methyl)-1H-benzimidazole (imb). We’ve synthesized a series of imb-contained complexes and made a systematic investigation about how the external or internal conditions such as temperature, counter ions, solvent system, etc. influence the structures and properties eventually [20-23]. As an extension of previous works, we selected a series of aliphatic α,ω-diacid, namely, succinic acid (H2suc), glutaric acid (H2glu) and adipic acid (H2adi) as coligands (Scheme 1) to investigate their effect on the structures of imb-contained Cd II complexes. Three new complexes, namely, [Cd2Cl2(suc)(imb)2(H2O)]n (1),
{[Cd(glu)(imb)]·H2O}n (2) and {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) were obtained and their IR spectra, PXRD patterns, TG analyses and fluorescent properties have been investigated.
2. Experimental Section 2.1. General information and materials 2-(1H-imidazole-1-methyl)-1H-benzimidazole was synthesized
according to
the
literature method [24]. All other chemicals were purchased of AR grade from commercial sources and used without further purification. IR data were recorded on a BRUKER TENSOR 27 spectrophotometer with KBr pellets in 4000–400 cm-1 region. Elemental analyses for C, H and N were carried out on a FLASH EA 1112 element analyzer. PXRD patterns were recorded using CuKα radiation on a PANalytical X’Pert PRO diffractometer. Thermographic analysis was performed on a NETZSCH STA 409 PC/PG differential thermal analyzer from 30°C to 800°C with a heating rate of 10°C·min-1 under air flow. Steady state fluorescence measurements were performed using a Fluoro Max-P spectrofluorimeter at room temperature in solid state.
2.2. Synthesis of [Cd2Cl2(suc)(imb)2(H2O)]n (1) A mixture of CdCl2·2.5H2O (0.1 mmol), imb (0.1 mmol), H2suc (0.1 mmol) and water (6 mL) was placed in a 25 mL Teflon-lined stainless steel vessel and heated at 120 °C for 72 hours. After the mixture had been cooled down to room temperature at a rate of 10°C·h-1, crystals of 1 suitable for X-ray diffraction were obtained and then collected by hand, washed with distilled water, and dried in air (yield: 56% based on Cd). Anal. Calcd. for
C26H26Cd 2Cl2N8O5 (826.25): C, 37.80; H, 3.15; N, 13.56 (%). Found: C, 37.59; H, 3.33; N, 13.81 (%). IR (KBr, cm-1): 3481(m), 3137(m), 2902(m), 1553(s), 1487(s), 1450(s), 1391(m), 1236(m), 1206(m), 1029(m), 749(m), 656(w).
2.3. Synthesis of {[Cd(glu)(imb)]·H2O}n (2) The preparation of 2 was similar with that of 1 except that H2suc was replaced by H2 glu. Colorless crystals of 2 were collected (yield: 62% based on Cd). Anal. Calcd. for C16H18CdN4O5 (458.74): C, 41.89; H, 3.92; N, 12.21 (%). Found: C, 41.29; H, 4.01; N, 12.55 (%). IR (KBr, cm-1): 3483(m), 3133(m), 2949(m), 1553(s), 1528(m), 1449(s), 1403(m), 1279(m), 1234(m), 1023(m), 750(s), 656(w).
2.4. Synthesis of {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) The preparation of 3 was similar with that of 2 except that H2glu was replaced by H2adi. Colorless crystals of 3 were collected (yield: 51% based on Cd). Anal. Calcd. for C14H16CdClN4O3 (436.16): C, 38.55; H, 3.67; N, 12.85 (%). Found: C, 38.12; H, 3.81; N, 13.02 (%). IR (KBr, cm-1): 3441(m), 3130(m), 2872(m), 1542(s), 1455(m), 1281(m), 1233(m), 1088(m), 743(m), 656(w).
2.5. X-ray crystallography A suitable single crystal of each complex was carefully selected and glued to a thin glass fiber. Crystal structure determination by X-ray diffraction was performed on a Rigaku Saturn 724 CCD area detector with graphite monochromator for the X-ray source (MoKα radiation, λ
= 0.71073 Å) operating at 50 kV and 40 mA. The data were collected by ω scan mode at 293(2) K; the crystal-to-detector distance was 45 mm. An empirical absorption correction was applied. The data were corrected for Lorentz-polarization effects. The structures were solved by direct methods and refined by full-matrix least-squares and difference Fourier techniques based on F2 using SHELXS-97 program [25]. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms of the ligands were positioned geometrically and refined using a riding model. Hydrogen atoms of water molecules were found at reasonable positions in the differential Fourier map and located there. All hydrogen atoms were included in the final refinement. Crystallographic parameters and structural refinement for the complexes are summarized in Table 1. Selected bond lengths and bond angles are listed in Table 2. Hydrogen bonds are listed in Table 3.
3. Results and Discussion 3.1. IR spectra IR spectra show broad bands at 3481 cm-1 for 1, 3483 cm-1 for 2 and 3441 cm-1 for 3 attributed to O–H stretch. Absorptions at 3137 cm-1 for 1, 3133 cm-1 for 2 and 3130 cm-1 for 3 can be ascribed to Ar–H stretch. Absorptions at 2902 cm-1 for 1, 2949 cm-1 for 2 and 2872 cm-1 for 3 can be ascribed to C–H stretches on the aliphatic –(CH2)n– chains. Free carboxylic acid presents strong C=O absorption band at the range of 1740-1650 cm-1; upon complexation to a metal center, this band disappears and two new bands relating to the asymmetric ν(O–C–O)a and symmetric ν(O–C–O)s stretches appear in the regions 1620-1480 and
1450-1340 cm-1 [26, 27]. The absorption bands at 749 cm-1 for 1, 750 cm-1 for 2 and 743 cm-1 for 3 can be assigned to characteristic stretching vibrations of 1,2-substituted benzene rings. The above assignments are in consistent with the results of X-ray diffraction.
3.2. Crystal structure of [Cd2Cl2(suc)(imb)2(H2O)]n (1) Self-assembly of H2suc, imb and CdCl2·2.5H2O gives complex 1. Single-crystal X-ray diffraction reveals that 1 crystallizes in triclinic space group P-1. Each asymmetric unit contains two crystallographically distinct CdII cations, two crystallographically distinct imb ligands, two crystallographically distinct Cl- anions, one suc2- anion and one coordinated water molecule. As shown in Fig. 1a, Cd1 situates in a distorted octahedral coordination geometry completed by two nitrogen atoms from two imb ligands, two bridging chlorine anions, one oxygen atom from suc2- group and one oxygen atom from coordinated water molecule. The vertices are occupied by Cl1 and O5 with the Cl1–Cd1–O5 bond angle of 172.98(6)° while N1, Cl2, N4#2 and O4#1 constitute the equatorial plane for which the mean deviation is 0.0011(4) Å. The environment of Cd2 is similar with Cd1 except that the two ligating oxygen atoms belong to a chelating carboxylate instead of one monodentate carboxylate and one water molecule. Ligating atoms around Cd2 present a disordered octahedral geometry in which the apical positions are occupied by N5#3 and Cl1 with the N5#3–Cd2–Cl1 bond angle of 170.71(7)°. O1, O2, N7, Cl2 and Cd2 are almost coplanar (mean deviation: 0.0762 Å). The bond lengths around Cd1 and Cd2 are similar to the reported complexes
such
as
{[Cd(imb)Cl2]·CH3OH}n,
{[Cd(imb)Cl2]·DMF}n
and
[Cd(OH)2(imb)2(4,4’-bipyridine)2] [21, 22]. Cd1 and Cd2 are linked together via two µ2-bridging chlorine anions, leading to the [Cd2Cl2] binuclear unit with a Cd···Cd separation of 3.7580(11) Å. H2suc was entirely deprotonated in the construction process of 1. As shown in Fig. 1b, µ2-suc2- exist in an anti conformation with a torsion angle of 125.29°. One carboxylate of each suc2- chelates to Cd2 while the other coordinates to Cd1 monodentately. Two suc2- connect two binuclear [Cd 2Cl2] units together, forming a eighteen-membered [Cd 4Cl4(suc)2(H2O)2] ring in which the four Cd II ions are coplanar. Cd1···Cd2 distance separated by one suc2- is 8.0082(32) Å. Fig. 1c depicts how the [Cd4Cl4(suc)2(H2O)2] rings outspread bidimensionally. Bridging imb ligands could be divided into two kinds due to their different conformations. One kind of imb ligands (turquoise) bridge two Cd1 ions by imidazole N1 and benzimidazole N4 leading to
the
ladderlike
polymeric
chain
···[Cd4Cl4(suc)2(H2O)2]–(imb)2–
[Cd 4Cl4(suc)2(H2O)2]–(imb)2··· along a axis. The Cd1···Cd1 distance separated by one imb ligand is 9.1790(18) Å. The other kind of imb ligands (green) bridge two Cd2 ions by imidazole
N5
and
benzimidazole
N7
forming
the
linear
polymeric
chain ···[Cd4Cl4(suc)2(H2O)2]–(imb)2–[Cd 4Cl4(suc)2(H2O)2]–(imb)2··· along b axis. The Cd2···Cd2 distance separated by one imb ligand is 6.548(2) Å. The two kinds of polymeric chains in different directions intersect together to accomplish a 2D layered structure. As illustrated in Fig. S1, there are two kinds of intralaminar N–H···O hydrogen bonds between the benzimidazole rings and carboxylates and one kind of intralaminar O–H···O hydrogen bonds between the carboxylates and coordinated water molecules. These hydrogen bonding intereactions further stabilize the layered structure. There is also one kind of
interlaminar O–H···O hydrogen bonds between the carboxylates and coordinated water molecules from adjacent layers. In addition, the benzimidazole rings from adjacent layers are parallel to each other with a centroid-centroid distance of 3.496(4) Å, which drops into the range for common π-π intereactions [28]. The adjacent layers are piled up by the interlaminar hydrogen bonds and π-π intereactions to give a 3D supramolecular framework as depicted in Fig. S2.
3.3. Crystal structure of {[Cd(glu)(imb)]·H2O}n (2) When succinic acid was replaced by glutaric acid while other experimental conditions remain unchanged, new complex 2 with different architecture from 1 was obtained. Water molecules were not coordinated to any metal center but cocrystallize with the complex and chlorine anions don’t participate in coordination in 2. Single-crystal X-ray diffraction reveals that 2 crystallizes in triclinic space group P-1. Each asymmetric unit contains one CdII cation, one imb ligand, one glu2- anion and one uncoordinated water molecule. As shown in Fig. 2a, each CdII ion is six-coordinated with two nitrogen atoms from two symmetry-related imb ligands and four oxygen atoms from three carboxylates, featuring an irregular CdN2O4 coordination geometry. As shown in Table 2, most of the bond angles around the central CdII ion deviate dramatically from the ideal angles of 90° or 180° expected for an octahedral geometry, as exemplified by the angles of O1–Cd1–O2, O3#1–Cd1–N1, and O3#1–Cd1–O1 (53.60(7)°, 135.43(7)° and 141.90(7)°, respectively). The Cd–N and Cd–O bond lengths are similar to those in 1 and other reported complexes [20-22]. H2suc was entirely deprotonated in the construction process of 2. Each glu2- bridges three
Cd II ions, two through tridentate bridging mode, with an additional CdII ion bound to one oxygen atom of the other carboxylate. These µ3-glu2-, taken together with the gauche-anti conformation of the aliphatic tether (four-atom torsion angles: 69.76° and 178.44°), lead to the propagation of infinite double-stranded chain ···Cd 2–(glu)2–Cd 2–(glu)2··· along b axis as shown in Fig. 2b. Cd···Cd distance separated by a glu2- is 9.715(1) Å. These 1D chains are further connected by bidentate bridging imb ligands with the Cd···Cd distance of 8.9736(18) Å, and thus giving rise to the formation of 2D layered structure (Fig. 2c). Additionally, there are two kinds of interlaminar O–H···O hydrogen bonds between the carboxylates and uncoordinated water molecules, and one kind of interlaminar N–H···O hydrogen bonds between the benzimidazole rings and uncoordinated water molecules. Adjacent layers are linked by these hydrogen bonds and the π-π intereactions between benzene rings from neighbouring layers with a centroid-centroid distance of 3.8438(14) Å to give a 3D supramolecular framework in solid state with small solvent-accessible void space (2.9 %) occupied by uncoordinated water molecules (Fig. S3).
3.4. Crystal structure of {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) Complex 3 other from 1 and 2 were obtained when glutaric acid was replaced by adipic acid while other experimental conditions stay the same. X-ray crystallographic analysis reveals that 3 crystallizes in triclinic space group P-1. Each asymmetric unit contains one CdII cation, one imb ligand, one Cl- anion, a half adi2- anion and one uncoordinated water molecule. Water molecules are not coordinated to any metal center but cocrystallize with the complex. As shown in Fig. 3a, CdII ion is six-coordinated with a octahedral geometry completed by two
nitrogen atoms from two symmetry-related imb ligands, two symmetry-related chlorine anions and two oxygen atoms from one adi2- group. The apical positions are occupied by N1 and Cl1#2 with the N1–Cd–Cl1#2 bond angle of 173.10(6)°. The equatorial plane is completed by Cl1, O1, O2 and N4#1 with a mean deviation of 0.1091(4) Å. The Cd–N, Cd–O and Cd–Cl bond lengths are similar to those in 1, 2 and other reported complexes [20-22]. Two CdII ions are bridged by two µ2-bridging chlorine anions forming a binuclear [Cd 2Cl2] grid with a Cd···Cd distance of 3.9194(15) Å. The [Cd2Cl2] grids are connected by bidentate
bridging
imb
ligands
leading
to
a
double-stranded
linear
chain ···[Cd 2Cl2]–(imb)2–[Cd 2Cl2]–(imb)2··· along a axis (Fig. 3b). The Cd···Cd distance separated by one imb ligand is 8.6158(17) Å. Fully deprotonated µ2-adi2- group feature an anti–anti–anti conformation (four-atom torsion angles: 171.99°, 180.00° and 171.99°) and its two carboxylates chelate two Cd II ions respectively, connecting the 1D chains to form a 2D layered structure (Fig. 3c). The Cd···Cd distance separated by an adi2- group along b axis is 11.5216(33) Å. Additionally, there are one kind of interlaminar N–H···O hydrogen bond between the benzimidazole rings and uncoordinated water molecules, and two kinds of interlaminar O–H···O hydrogen bonds between the carboxylates and uncoordinated water molecules. The benzimidazole rings from adjacent layers are parallel to each other with a centroid-centroid distance of 3.8312(14) Å, generating weak π-π interactions. The adjacent layers are piled up through the above three kinds of hydrogen bonds and π-π interactions resulting in a 3D supramolecular framework in solid state with small solvent-accessible void space (7.4%) occupied by uncoordinated water molecules (Fig. S4).
Topology analyses are investigated to make an explicit description of complexes 1–3. For 1, Cd1 and Cd2 could be viewed as 4- and 3-connected nodes respectively. Both imb and suc2- ligands act as linear linkers. The overall motif of 1 is a 2D (4,3)-connected (4·64·8)(4·8 2) network (Fig. 1d). For 2, CdII ions and glu2- ligands can be viewed as 5- and 3-connected nodes respectively while the imb ligands act as linear linker. The 2D layer of 2 is a (5,3)-connected network with (4 2·67·8)(42·6) topology (Fig. 2d). CdII ions in 3 can be topologically counted as 4-connected nodes and all the ligands in 3 act as linear linkers. The 2D layer of 3 is a 4-connected network with 4 4·62 topology (Fig. 3d). The above analyses imply that aliphatic dicarboxylate ligands of different lengths can take different coordination modes to generate complexes with completely different structures and topologies in some cases.
By
contrast,
in
complexes
{[Cd(suc)(dpa)]·H2O}n,
[Cd(glu)(dpa)]n,
and
{[Cd(adi)(dpa)]}n (dpa = 4,4’-dipyridylamine), aliphatic dicarboxylate ligand connect the CdII ions along orthometric directions to form a (4,4) [Cd(L)]n (L = suc2-, glu2- or adi2-) layer and parallel layers are then pillared by the tethering dpa ligands to form a doubly interpenetrated 6-connected 3D [Cd(L)(dpa)]n network with 412·63 topology [29–31]. Aliphatic dicarboxylate ligands of different lenths perform similarly in the crystallization process of these three complexes, indicating that the flexibility of the aliphatic dicarboxylates can permit generation of similar polymeric networks in nature under proper conditions.
3.5. PXRD patterns and TG analyses PXRD patterns for 1–3 were recorded to confirm the phase purity of the samples and they were comparable to the corresponding simulated ones calculated from the single-crystal
diffraction data (Fig. S5), indicating a pure phase of each bulk sample. Thermogravimetric (TG) analysis of 2 was performed by heating the sample from 30°C to 800°C in air (Fig. S6). Complex 2 is stable up to 196°C and the first mass loss of 3.90% occurs from 196°C to 223°C, corresponding to the release of uncoordinated water molecules (Calcd. 3.92%). Then a plateau region is observed from 223°C to 324°C. Continuous mass loss from 324°C to 610°C corresponds to the gradually decomposition of the glu2- groups and imb ligands. Finally a plateau occurs from 610°C to 800°C. A brown residue which is attributed to be CdO (observed: 27.46%, Calcd. 27.99%) is remained. The results are in agreement with the crystal structure. TG analyses of halogen-containing compounds are not supported by the NETZSCH STA 409 PC/PG differential thermal analyzer, so TG analyses of 1 and 3 have not been carried out.
3.6. Fluorescence A number of complexes with d10 metal centers have been investigated regarding to their fluorescence properties which result in potential applications in chemical sensors, photochemistry, and light-emitting diodes [32-34]. According to our previous work, free imb ligand gives a relatively sharp emission band at 300 nm upon excitation at 270 nm [22]. In this study, we have investigated the fluorescence of the three complexes in solid state at room temperature. As shown in Fig. 4, intense emissions are observed at 306 nm for 1, 313 nm for 2 and 334 nm for 3 under the excitation at 287 nm. The resemblance between the emissions of 1–3 and that of free imb indicates that the emissions of 1–3 originate from π*→π transition of
imb. To the best of our knowledge, the emissions of aliphatic dicarboxylates belongs to π*→n transition which is very weak compared to π*→π transition, so the dicarboxylates have little contribution to the fluorescent emissions of the complexes [35]. All the fluorescence curves of the complexes present more or less bathochromic shift in contrast to that of imb, which should be attributed to the metal-ligand coordination interactions [35]. The difference of the peak positions are considered to be the result of unequable coordination environments of the metal centers under the intervention of different dicarboxylates.
4. Conclusion In summary, we have introduced a series of dicarboxylic acids (H2suc, H2glu and H2adi) into a CdII-imb system and obtained three new complexes. All complexes present 2D layered structure but showing structural diversity because of influence of the homologous aliphatic coligands. For 1, binuclear units are bridged by suc2- anions to form a tetranuclear 18-ring and then outspreads bidimensionally via the connection of two kinds of imb ligands to accomplish the 2D layer. For 2, ladderlike linear chains formed by glu2- anions and CdII ions are linked by bridging imb ligands to form the 2D layer. For 3, ladderlike linear chains are composed of [CdCl2] binuclear units and imb ligands and adi2- anions further connect the chains together to generate the 2D layer. These results suggest that the change of aliphatic dicarboxylate coligands can influence the detailed structures and then influence the properties of the complexes.
Supporting Information Crystallographic data reported in this paper have been deposited with the Cambridge Crystallographic Data Center as supplementary publication. CCDC numbers are 971029-971031.
These
data
can
be
obtained
free
of
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033).
Acknowledgement We gratefully acknowledge the financial support by the National Natural Science Foundation of China (No. J1210060).
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Captions Schem 1. Schematic description of the ligands in this study and their coordination modes. Fig. 1. (a) Coordination environment of the CdII centers in 1, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms are omitted for clarity. (b) 18-Ring unit [Cd4Cl4(suc)2(H2O)2] in 1. (c) 2D network structure in 1. (d) Topological net for 1 where the ligands were represented by corresponding pillar sticks: purple for suc2-, yellow for Cl-, turquoise and green for two kinds of imb.
Fig. 2. (a) Coordination environment of the CdII centers in 2, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms and uncoordinated water molecule are omitted for clarity. (b) Double-stranded chain along b axis. (c) 2D network structure in 2. Benzene rings are omitted for clarity. (d) Topological net for 2 where the ligands were represented by corresponding pillar sticks: purple for glu2- and turquoise for imb.
Fig. 3. (a) Coordination environment of the CdII centers in 3, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms and uncoordinated water molecules are omitted for clarity. (b) Double-stranded chain along a axis. (c) 2D network structure in 3. Benzene rings are omitted for clarity. (d) Topological net for 3 where the ligands were represented by corresponding pillar sticks: yellow for Cl-, purple for adi2and turquoise for imb. Fig. 4. Fluorescent spectra of complexes 1–3 in solid state at room temperature.
Schem 1. Schematic description of the ligands in this study and their coordination modes.
a
b
c
d
Fig. 1. (a) Coordination environment of the CdII centers in 1, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms are omitted for clarity. (b) 18-Ring unit [Cd4Cl4(suc)2(H2O)2] in 1. (c) 2D network structure in 1. (d) Topological net for 1 where the ligands were represented by corresponding pillar sticks: purple for suc2-, yellow for Cl-, turquoise and green for two kinds of imb.
a
b
c
d
Fig. 2. (a) Coordination environment of the CdII centers in 2, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms and uncoordinated water molecule are omitted for clarity. (b) Double-stranded chain along b axis. (c) 2D network structure in 2. Benzene rings are omitted for clarity. (d) Topological net for 2 where the ligands were represented by corresponding pillar sticks: purple for glu2- and turquoise for imb.
a
b
c
d
Fig. 3. (a) Coordination environment of the CdII centers in 3, showing 35% probability ellipsoids. The symmetry codes are listed in Table 2. Hydrogen atoms and uncoordinated water molecules are omitted for clarity. (b) Double-stranded chain along a axis. (c) 2D network structure in 3. Benzene rings are omitted for clarity. (d) Topological net for 3 where the ligands were represented by corresponding pillar sticks: yellow for Cl-, purple for adi2and turquoise for imb.
Fig. 4. Fluorescent spectra of complexes 1–3 in solid state at room temperature.
Table 1 Crystal data and structural refinement for complexes 1–3. Complex Empirical formula
1 C26H26Cd2Cl2N8O5
2 C16H18CdN4O5
3 C14H16CdClN4O3
Formula weight Temperature (K) Crystal system Space group Unit cell dimensions (Å, °) a b c α β γ Volume (Å3)
826.25 293(2) Triclinic P-1
458.74 293(2) Triclinic P-1
436.16 293(2) Triclinic P-1
9.1790(18) 11.445(2) 13.977(3) 100.86(3) 90.23(3) 98.37(3) 1425.9(5)
8.9736(18) 9.7152(19) 11.339(2) 69.15(3) 67.52(3) 78.80(3) 851.7(3)
8.6158(17) 8.7031(17) 11.442(2) 106.36(3) 99.64(3) 98.35(3) 794.6(3)
Z Absorption coefficient (mm-1)
2 1.732
2 1.319
2 1.562
F(000) Crystal size (mm3)
816 0.18 × 0.14 × 0.10
460 0.19 × 0.18 × 0.15
434 0.19 × 0.16 × 0.12
θ range for data collection (°) Limiting indices R(int) Data / Restraints / Parameters Goodness-of-fit on F2
1.83–27.86 -12 ≤ h ≤ 11, -15 ≤ k ≤ 14, -18 ≤ l ≤ 18 0.0288 6736 / 0 / 388 1.025
2.25–27.83 -11 ≤ h ≤ 11, -12 ≤ k ≤ 12, -14 ≤ l ≤ 14 0.0234 3994 / 0 / 235 1.040
1.90–25.50 -10 ≤ h ≤ 10, -10 ≤ k ≤ 10, -13 ≤ l ≤ 13 0.0195 2946 / 0 / 208 1.083
R indices [I > 2σ(I)]
R1 = 0.0330, wR2 = 0.0764
R1 = 0.0301, wR2 = 0.0667
R1 = 0.0258, wR2 = 0.0639
R1 = 0.0399, wR2 = 0.0809
R1 = 0.0325, wR2 = 0.0681
R1 = 0.0275, wR2 = 0.0650
0.545 and -0.725
0.413 and -0.549
1.004 and -0.549
R indices (all data) 3
Largest difference peak and hole (eA )
Table 2 Selected bond lengths and bond angles of complexes 1–3. a Complex 1 Cd(1)–O(4)#1 Cd(1)–N(1) Cd(1)–Cl(1) Cd(2)–O(1) Cd(2)–N(5)#3 Cd(2)–Cl(1) O(4)#1–Cd(1)–N(4)#2 O(4)#1–Cd(1)–N(1) N(4)#2–Cd(1)–N(1) O(4)#1–Cd(1)–Cl(2) N(1)–Cd(1)–Cl(2) O(4)#1–Cd(1)–Cl(1) N(1)–Cd(1)–Cl(1) Cl(2)–Cd(1)–Cl(1) N(5)#3–Cd(2)–O(1) N(5)#3–Cd(2)–O(2) O(1)–Cd(2)–O(2) N(7)–Cd(2)–Cl(2) O(2)–Cd(2)–Cl(2) N(7)–Cd(2)–Cl(1) O(2)–Cd(2)–Cl(1) Cd(1)–Cl(1)–Cd(2)
2.317(2) 2.326(3) 2.6365(10) 2.370(2) 2.291(3) 2.6879(10) 84.77(9) 79.03(9) 163.42(9) 170.41(6) 92.01(8) 95.83(7) 90.33(7) 87.54(4) 86.86(9) 83.91(10) 54.64(8) 97.73(7) 107.18(6) 96.18(7) 87.26(7) 89.78(4)
Cd(1)–O(5) Cd(1)–N(4)#2 Cd(1)–Cl(2) Cd(2)–O(2) Cd(2)–N(7) Cd(2)–Cl(2) O(4)#1–Cd(1)–O(5) N(4)#2–Cd(1)–O(5) N(1)–Cd(1)–O(5) N(4)#2–Cd(1)–Cl(2) O(5)–Cd(1)–Cl(2) N(4)#2–Cd(1)–Cl(1) O(5)–Cd(1)–Cl(1) N(5)#3–Cd(2)–N(7) N(7)–Cd(2)–O(1) N(7)–Cd(2)–O(2) N(5)#3–Cd(2)–Cl(2) O(1)–Cd(2)–Cl(2) N(5)#3–Cd(2)–Cl(1) O(1)–Cd(2)–Cl(1) Cl(2)–Cd(2)–Cl(1) Cd(2)–Cl(2)–Cd(1)
2.390(2) 2.322(3) 2.6076(11) 2.412(2) 2.351(2) 2.5746(9) 86.36(9) 92.05(9) 83.52(9) 103.94(7) 89.28(7) 94.79(7) 172.98(6) 90.65(10) 100.82(8) 155.01(8) 98.22(8) 160.71(6) 170.71(7) 85.67(6) 87.13(4) 92.96(4)
Complex 2 Cd(1)–O(3)#1 Cd(1)–O(2) Cd(1)–O(1) O(3)#1–Cd(1)–N(1) N(1)–Cd(1)–N(4)#2 N(1)–Cd(1)–O(2) O(3)#1–Cd(1)–O(1) N(4)#2–Cd(1)–O(1) O(3)#1–Cd(1)–O(2)#3 N(4)#2–Cd(1)–O(2)#3 O(1)–Cd(1)–O(2)#3
2.212(2) 2.365(2) 2.498(2) 135.43(7) 105.96(9) 125.67(8) 141.90(7) 81.36(8) 79.63(7) 163.80(8) 102.95(7)
Cd(1)–O(2)#3 Cd(1)–N(1) Cd(1)–N(4)#2 O(3)#1–Cd(1)–N(4)#2 O(3)#1–Cd(1)–O(2) N(4)#2–Cd(1)–O(2) N(1)–Cd(1)–O(1) O(2)–Cd(1)–O(1) N(1)–Cd(1)–O(2)#3 O(2)–Cd(1)–O(2)#3
2.644(2) 2.236(2) 2.325(2) 87.40(8) 92.74(7) 98.15(9) 82.64(7) 53.60(7) 90.13(8) 73.04(8)
Complex 3 Cd(1)–N(4)#1 Cd(1)–N(1) Cd(1)–Cl(1)
2.301(2) 2.337(3) 2.5591(10)
Cd(1)–O(1) Cd(1)–O(2) Cd(1)–Cl(1)#2
2.312(2) 2.463(2) 2.6785(14)
N(4)#1–Cd(1)–O(1) O(1)–Cd(1)–N(1) O(1)–Cd(1)–O(2) N(4)#1–Cd(1)–Cl(1) N(1)–Cd(1)–Cl(1) N(4)#1–Cd(1)–Cl(1)#2 N(1)–Cd(1)–Cl(1)#2 Cl(1)–Cd(1)–Cl(1)#2 a
149.35(8) 84.71(9) 54.58(7) 111.37(6) 94.55(7) 96.30(7) 173.10(6) 83.14(4)
N(4)#1–Cd(1)–N(1) N(4)#1–Cd(1)–O(2) N(1)–Cd(1)–O(2) O(1)–Cd(1)–Cl(1) O(2)–Cd(1)–Cl(1) O(1)–Cd(1)–Cl(1)#2 O(2)–Cd(1)–Cl(1)#2 Cd(1)–Cl(1)–Cd(1)#2
90.60(9) 95.40(8) 91.32(9) 99.20(6) 152.48(6) 89.23(7) 87.84(6) 96.86(4)
Symmetry transformations used to generate equivalent atoms: For 1, #1 –x, –y, –z; #2 x+1, y, z; #3 –x+1, –y+1, –z; #4 x-1, y, z. For 2, #1 x, y–1, z; #2 x–1, y, z; #3 –x+1, –y+1, –z; #4 x+1, y, z; #5 x, y+1, z. For 3, #1 x–1, y, z; #2 –x+1, –y+3, –z+1; #3 x+1, y, z; #4 -x+2, -y+2, -z+1.
Table 3 Hydrogen bonds in complexes 1–3. D–H…A
d(D–H) (Å)
d(H…A) (Å)
d(D…A) (Å)
(D–H…A) (°)
1 N(3)–H(3B)…O(3)#1 O(5)–H(1W)…O(3)#1 N(8)–H(8B)…O(2)#2 O(5)–H(2W)…O(3)#5
0.86 0.85 0.86 0.85
1.9 1.9 1.9 2.31
2.733(3) 2.733(3) 2.736(3) 2.931(3)
161.8 165.0 162.7 130.1
2 N(2)–H(2C)…O(5) O(5)–H(1W)…O(1)#6 O(5)–H(2W)…O(4)#6
0.86 0.85 0.85
1.93 1.98 2.11
2.736(3) 2.828(3) 2.955(3)
155.7 172.6 175.3
3 O(3)–H(1W)…O(2)#3 O(3)–H(2W)…O(2)#3 N(3)–H(3B)…O(3)#5
0.85 0.85 0.86
2.31 2.29 1.96
2.734(3) 2.734(3) 2.763(3)
111.3 113.1 154.1
Graphical abstract: picture Three CdII complexes based on 2-(1H-imidazol-1-methyl)-1Hbenzimidazole and homologous aliphatic dicarboxylates Guiyang Zhang, Xiaoli Zhou, Ting Li, Xiangru Meng
Graphical abstract: Synopsis Three CdII complexes based on 2-(1H-imidazol-1-methyl)-1Hbenzimidazole and homologous aliphatic dicarboxylates Guiyang Zhang, Xiaoli Zhou, Ting Li, Xiangru Meng
Three new CdII complexes with the formulas [Cd2Cl2(suc)(imb)2(H2O)]n (1), {[Cd(glu)(imb)]·H2O}n (2) and {[Cd2Cl2(adi)(imb)2]·2H2O}n (3) were synthesized and structurally characterized by single-crystal X-ray diffraction. Dicarboxylate coligands play an important role in tuning the detailed structure and characters of the complexes. IR spectra, PXRD patterns, TG analyses and fluorescent properties of certain complexes have also been investigated.
Highlights ►CdII complexes based on 2-(1H-imidazol-1-methyl)-1H-benzimidazole and aliphatic dicarboxylate ligands. ►Diverse architectures and topological networks of the complexes. ►Aliphatic dicarboxylate ligands exert regulating effects on the structural features. ►The complexes are characterized by IR, luminescence and TGA techniques.