Mixed azide and substituted 1,2,4-triazole co-ligand bridged 1D chain cadmium(II) motif: crystal structure, Hirshfeld surfaces and spectroscopic studies

Abstract

A novel Cd(II) coordination polymer (1) derived from azide and 3-ethyl-4-(3-methylphenyl)-5-(2-pyridyl)-1,2,4-triazole co-ligand (L), has been synthesized and structurally characterized. Complex 1, [Cd₂(μ_1,1-N₃)₂L₂(N₃)₂]·H₂O, features a primary structure with binuclear units bridged by double asymmetric μ_1,1-azido and double terminal azide. The adjacent binuclear units are linked by two syn–syn bridged ligands L into an infinite 1D structure. Water molecules, which are located on the two sides of the binuclear unit through O–H⋯N hydrogen bond interactions with the terminal azide, supported the conversion of 1D chain structures into a 3D motif. Hirshfeld surfaces analysis revealed that the main intermolecular interactions experienced by ligand L in 1 are H–H, N–H and C–H contacts. We further investigated the Raman and IR spectra of co-ligand L, complex 1 and the dehydrated form of 1, which revealed that the dehydration of 1 does not effect the crystal structure.

---

1 Introduction

In recent years, the design and synthesis of polynuclear complexes and coordination polymers with fascinating topological architectures as well as promising applications in functional materials have attracted great attention.^1–6 In this context, the azide ion (N₃⁻) has evoked considerable interest and is among the most extensively studied bridges due to its inherent flexible and versatile coordination modes.^7–10 To date, a larger number of discrete polynuclear as well as infinite polymeric metal–azido coordination complexes with a diversity of structural motifs and properties, especially magnetic properties, have been reported.^11–15

The 1,2,4-triazole derivatives, which can act as both flexible bridging ligands and spacers between transition metal ions, have attracted much attention in the field of coordination chemistry.^16,17 They have been especially used as excellent candidates for the construction of iron(II) complexes that exhibit spin-crossover phenomenon.¹⁸ Many examples of 1,2,4-triazole derivatives as well as their complexes with transition metal ions have been reported, for example: 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole,^19a 4-(4-methoxyphenyl)-3-methyl-5-(2-pyridyl)-4H-1,2,4-triazole,^19b 3-ethyl-4-(4-methylphenyl)-5-(2-pyridyl)-4H-1,2,4-triazole,^19c 4-(4-tert-butylphenyl)-3,5-di-2-pyridyl-4H-1,2,4-triazole,^19d 4-(3-methylphenyl)-3,5-di-2-pyridyl-4H-1,2,4-triazole,^19e 4-phenyl-3,5-bis(2-pyridyl)-4H-1,2,4-triazole,^19f 3-ethyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole,^19g 3-methyl-4-(3-methylphenyl)-5-(2-pyridyl)-4H-1,2,4-triazole,^19h and some of their iron(II) and copper(II) complexes with interesting magnetic properties. But the investigation of complex formation of these kinds of 1,2,4-triazoles with azide still remains rare. As part of our systematic studies on mixed azide and 1,2,4-triazole systems, we report here the synthesis, crystal structure and spectroscopic investigation of a new coordination polymer ([Cd₂(μ_1,1-N₃)₂L₂(N₃)₂]·H₂O, 1) derived from cadmium(II), azide and a new ligand L (3-ethyl-4-(3-methylphenyl)-5-(2-pyridyl)-1,2,4-triazole, Scheme 1). The primary structure of complex 1 features binuclear units bridged by double asymmetric μ_1,1-azido and double terminal azide ligands, and the different binuclear units are linked by two syn–syn bridged ligands L into an infinite 1D structure. To the best of our knowledge, this kind of connecting motif is unprecedented. We also investigated the Raman spectra of ligand L, complex 1 and the dehydrated form of 1, which revealed that the dehydration of 1 does not effect the crystal structure.

Scheme 1 The molecular structure of ligand L.

2 Results and discussion

2.1 Crystal structure

Single-crystal X-ray diffraction analysis revealed that complex 1 crystallizes in a triclinic P1̄ space group. Fig 1a shows the asymmetric unit and symmetry related fragments of 1, and selected bond distances and angles are tabulated in Table 1. In the crystal, the Cd1 atom is hexa-coordinated in a distorted octahedral geometry defined by three azide atoms (Cd1–N1 = 2.383(5), Cd1–N1A = 2.333(5) and Cd1–N4 = 2.264(6) Å) and three nitrogen atoms (Cd1–N7 = 2.366(5), Cd1–N9 = 2.424(4) and Cd1–N10 = 2.432(4) Å) from two syn–syn bridged triazole ligands L. The equatorial plane of the octahedral geometry is composed of two equivalent EO-bridged azide nitrogen atoms (N1 and N1A), a terminal azide nitrogen atom (N4), and a triazole nitrogen atom (N10) with angles of N1–Cd1–N1A = 79.73(17)°, N1–Cd1–N10 = 87.01(15)°, N4–Cd1–N1A = 99.12(18), and N4–Cd1–N10 = 90.30 (17)°. The axial positions are occupied by two nitrogen atoms from triazole ligands (N7 and N9) with angles of N7–Cd1–N9 = 169.54(14)°. The equatorial plane is distorted with a rms deviation of 0.339 Å; the largest deviation is 0.527(33) Å at N1 and −0.3233(18) Å at N1A, and the Cd atom lies at 0.3444 (44) Å out of the plane towards the axial N7 atom.

Fig. 1 (a) A di-nuclear cluster unit in complex 1 (thermal ellipsoids are drawn at 30% probability, hydrogen atoms are omitted for clarity). The symmetry code A: 1 − x, 1 − y, 1 − z; B: 2 − x, 1 − y, 1 − z; C: 1 − x, y, z. (b) The connecting motif of the adjacent di-nuclear units by substituted 1,2,4-triazole ligand. (c) The 1D chain structure formed from di-nuclear units along the a axis. (d) The backbone of the 1D chain composed of μ_1,1-azido, terminal azide and nitrogen atoms of ligand L.

Table 1 Selected bond lengths (Å) and angles (°) for 1^a

a Symmetry code: A: 1 − x, 1 − y, 1 − z.
Cd1–N1	2.384(5)	N9–Cd1–N4	90.30(17)
Cd1–N4	2.266(5)	N9–Cd1–N10	69.19(14)
Cd1–N7	2.368(4)	N11–Cd1–N1	96.08(18)
Cd1–N9	2.423(4)	N1–Cd1–N1A	79.73(17)
Cd1–N10	2.437(4)	N1–N2–N3	178.9(7)
N1–N2	1.142(6)	N7–Cd1–N1A	103.40(15)
N2–N3	1.174(7)	N7–Cd1–N10	100.43(14)
N4–N5	1.187(7)	N2–N1–Cd1	121.3(4)
N5–N6	1.189(8)	N2A–N1A–Cd1	131.0(4)
Cd1–N1A	2.332(4)	N4–N5–Cd1	117.6(4)
Cd1–N1–Cd1A	100.27(17)	N4–N5–N6	176.6(7)
N1–Cd1–N4	177.14(15)	N4–Cd1–N1A	99.12(18)
N9–Cd1–N7	169.54(14)	N4–Cd1–N7	92.16(17)
N9–Cd1–N1	87.01(15)	N4–Cd1–N10	96.08(18)
N9–Cd1–N1A	86.24(15)	N7–Cd1–N1	90.66(15)

---

The Cd1 moiety generates a Cd1A moiety through an inversion symmetry operation to give a di-nuclear [Cd₂(μ_1,1-N₃)₂L₂(N₃)₂] unit, with an angle of Cd1–N1–Cd1A = 100.27(17)°. The Cd⋯Cd distances spanned by the double μ_1,1-azido bridges are 3.621 Å. It is interesting to note that the two μ_1,1-azido groups and the two terminal azides within the di-nuclear unit are almost co-planar with a rms deviation of 0.5479 Å. Up to now, only three examples of double μ_1,1-azido and terminal azide bridged polynuclear units have been reported (Scheme 2). Hong et al.²⁰ and Wang et al.²¹ have synthesized two di-nuclear copper complexes, [Cu₂(μ_1,1-N₃)₂(aepi)₂(N₃)₂] and [Cu₂(μ_1,1-N₃)₂(Him2-py)₂(N₃)₂] (aepi = 1-(2-aminoethyl)piperidine, Him2-py = 2-(2′-pyridyl)-4,4,5,5-tetramethylimidazoline-1,3-dihydroxy), respectively, where the planes containing the terminal azide were almost vertical to the planes containing the μ_1,1-azido groups. Gao et al.²² have synthesized a 1D Mn complex, [Mn₃(L₁)₂(N₃)₆(H₂O)₂]·2H₂O (L₁ = 1,2-bis(4-carboxylatopyridinium-1-methylene)benzene), which features a tri-unclear Mn–azide unit, and the six azides (four μ_1,1-azido and two terminal azides) within the unit were located in three different planes (Scheme 2). Thus, this kind of metal–azide motif (co-plane of μ_1,1-azido and terminal azide) in this paper is unprecedented.

Scheme 2 The double asymmetric μ_1,1-azido and double terminal azide bridged metal–azido unit used to form polynuclear complexes or coordination polymers (a: ref. 20, ref. 21, b: ref. 22, c: this paper).

The ligand L serves as a bridge through the adjacent two nitrogen atoms in the triazole moiety with syn–syn bridging models (Fig. 1b), connecting the adjacent di-nuclear unit with the double ligand L through a R₆⁴ connecting motif into a 1D chain along the a axis. The torsion angle N7–Cd1–N10–Cd1A and angle N7–Cd1–N10 in the R₆⁴ ring are found to be 21.49(5)° and 100.43(14)°, respectively. The Cd⋯Cd distances spanned by the double L ligand bridges are 4.426 Å, which is much larger than the distance spanned by the double EO–azide. The Cd atoms, the azide molecules and the nitrogen atoms in ligand L comprised the skeleton of the 1D chain (Fig. 1d), then the ligand L stretches outwards from two flanks of the chain (Fig. 1c), the distance between the pyridine moiety and triazole moiety in adjacent L ligand is 4.223 Å, indicating a slight π⋯π interaction between them. In ligand L, the 2-pyridyl moiety is almost co-planar with the triazole moiety, with a dihedral angle of 34.73 (5)°, while the 3-methylphenyl moiety is almost vertical to the triazole moiety, with a dihedral angle of 62.8 (48)°, and the dihedral angle between the 2-pyridyl moiety and 3-methylphenyl moiety is 39.23 (57)°. The ethyl group, which exhibits a similar right angle motif due to the large steric hindrance of the adjacent ligand, has an angle between the two carbon bonds of 112.48(5)°.

The water molecules (O1), which are located along the two flanks of the 1D chain, bind to the terminal azide through O1–H1A⋯N4 (O⋯N distance of 3.019(15) Å) hydrogen bonding interactions (Table 2). The different 1D chain as well the water molecules on the two flanks are stacked parallel through π⋯π interactions between the 2-pyridyl moieties (distance of 3.810 (8) Å, along the b axis) into a 3D motif (Fig. 2). While the distances between the different 3-methylphenyl moieties in different 1D chains along the b and c axis are found to be 10.916 (8) and 7.177 (8) Å, respectively (Fig. 2).

Table 2 Geometrical parameters for hydrogen bonds in complex 1

D–H⋯A	D–H (Å)	H⋯A (Å)	D⋯A (Å)	∠D–H⋯A (deg)	Symmetry operation
O1–H1A⋯N4	0.9	2.32	3.019(15)	143
O1–H1B⋯N4	0.9	2.63	3.019(15)	130	1 − x, 1 − y, 1 − z
C4–H4⋯N6	0.93	2.59	3.384(15)	143	−1 + x, y, z
C31–H31B⋯N2	0.97	2.44	3.403(14)	174	1 − x, 1 − y, 1 − z

---

Fig. 2 3D stacking motif of complex 1, the distances between 2-pyridyl and 3-methylphenyl moieties are highlighted, the oxygen atoms of the water molecules are highlighted as red spheres, hydrogen atoms are omitted for clarity, hydrogen bonding interactions are shown as dashed lines.

2.2 Hirshfeld surface

The Hirshfeld surface serves as a powerful tool for identifying intermolecular interactions.^24,25 The 3D d_norm values are mapped onto the Hirshfeld surface by using a red–blue–white colour scheme: red regions represent closer contacts and negative d_norm values; blue regions represent longer contacts and positive d_norm values; and white regions represent the distance of contacts equal to vdW separation, with a d_norm value of zero. The 3D d_norm surfaces can be resolved into 2D fingerprint plots, which can analysis the intermolecular contacts at the same time and give a quantitative summary of the nature and type of intermolecular contacts experienced by the molecules in the crystal.

The 3D d_norm surface and 2D fingerprint plots of ligand L in complex 1 are shown in Fig. 3. The red points on the 3D d_norm surface correspond to the significant O–H⋯N interactions, the white points and the blue points correspond to the C–H and H–H interactions, respectively. It is clear that the blue point comprises most of the total Hirshfeld surface, followed by the white and red points. Actually, the H–H, N–H and C–H interactions comprise 47.7, 22 and 11.8% (Table 2) of the total Hirshfeld surface of ligand L, respectively. Apart from those above, the presence of O–H, N–N, C–C, N–C and C–O interactions were observed, and are summarized in Table 3.

Fig. 3 3D d_norm surfaces (a) and 2D fingerprint plots (b) of ligand L in complex 1 (1: H–H contacts, 2: N–H contacts, 3: C–H contacts).

Table 3 Summary of various contact contributions (%) to the Hirshfeld surface of ligand L in complex 1

H–H	N–H	C–H	O–H	N–N	C–C	N–C	C–O
47.7	22	11.8	3.8	3.7	3.2	1.5	0.3

---

2.3 Raman spectra

The uncoordinated water molecules in 1 sublimate at about 90 °C upon heating (confirmed by TGA measurements shown in the ESI Fig. S1,† the percentage of weight loss at about 90° C is 3.75%, which is in accordance with one molar stoichiometric ratio of water in complex 1). To investigate the peak shift of ligand L after complex formation as well as sublimation of water molecules from complex 1, we compared the Raman and IR spectra of 1 with its dehydrated form as well as ligand L. Fig. 4 shows their Raman spectra in the region 1800–200 cm⁻¹. The characteristic peaks (around 1600, 1510, 1357, and 1000 cm⁻¹) of ligand L are located in the region between 900 and 1800 cm⁻¹, while the peaks located between 200 and 900 cm⁻¹ are attributed to Cd(II) and azide. Complex formation of L with azide and Cd(II) cause almost no influence on the characteristic peaks of ligand L apart from the disappearance of a peak at 1357 cm⁻¹. Complex formation of L also leads to an increase of peaks between 900 and 1800 cm⁻¹, as have been highlighted by rectangles in Fig. 4. The peak at around 1609 cm⁻¹ for 1 and 1-water may be attributed to Cd–N bonds which does not appear in ligand L. While the increased peaks at around 1450 cm⁻¹ and 1050 cm⁻¹ may be attributed to N₃. The almost identical Raman profiles of 1 and 1-water indicate that the sublimation of water molecules does not effect the crystal structure of 1, which also was confirmed by the PXRD measurements (ESI, Fig. S2†).

Fig. 4 Raman spectra of ligand L, complex 1 and the dehydrated form of 1 (1-water), the differences between L and the metal complex are highlighted.

2.4 IR spectra

Shown in Fig. 5 are the IR spectra of ligand L, complex 1 and 1-water in the 4000–500 cm⁻¹ region. They clearly show the peak shift after complex formation. The peaks around 3000 cm⁻¹ are attributed to –CH₃ and –C₂H₅ groups, while the peaks around 2050 cm⁻¹ for complex 1 and 1-water are attributed to the presence of N₃, where peak 2036 cm⁻¹ belongs to μ_1,1-azido and peak 2058 cm⁻¹ belongs to terminal azide in complex 1. We partially zoom in to the 1800–500 cm⁻¹ region (Fig. 5, bottom) to investigate the influence of complex formation on ligand L. As have been highlighted by rectangles, the peaks at 615, 634, 1147, and 1452 cm⁻¹ for ligand L may be attributed to nitrogen atoms as they are not present in complex 1 and 1-water due to the formation of Cd–N bonds. Again, the almost identical IR profiles of 1 and 1-water indicate that the sublimation of water molecules does not effect the crystal structure of 1.

Fig. 5 IR spectra of ligand L, complex 1 and dehydrated form of 1 (1-water), the differences between L and metal complex are highlighted.

3 Conclusions

In conclusion, we have presented the synthesis, crystal structure, Hirshfeld surface, Raman and IR spectra of a novel Cd(II) coordination polymer (1) with mixed azide and a new substituent 1,2,4-triazole ligand L (3-ethyl-4-(3-methylphenyl)-5-(2-pyridyl)-1,2,4-triazole). The primary structure of 1 is the bi-nuclear unit bridged by double asymmetric μ_1,1-azide and double terminal azide, and the different bi-nuclear units are linked by ligand L into a 1D chain in R₆⁴ fashion. The water molecules bind to the terminal azide through O–H⋯N hydrogen bonds and are located on the two flanks of the 1D chain. Hirshfeld surface analysis revealed that the main intermolecular interactions experienced by ligand L in 1 are H–H, N–H and C–H contacts. Complex formation of L with Cd(II) and azide lead to the disappearance of a Raman peak at around 1357 cm⁻¹ and IR peaks at 615, 634, 1147, and 1452 cm⁻¹. Additionally, Raman, IR and PXRD measurements revealed that the sublimation of water molecules does not effect the crystal structure of complex 1.

4 Experimental

4.1 Materials and physical measurements

CdCl₂, NaN₃, 3,3′-dimethylphenylphosphazoanilide, N′-propion-yl-N-(2-pyridoyl)hydrazine and o-dichlorobenzene were all commercially available from Sigma Aldrich and used as received without further purification. Methanol was commercially available from Sinopharm Chemical Reagent Co., Ltd and used as received without further purification. Elemental analyses were performed by a Vario-EL III elemental analyzer for carbon, hydrogen, and nitrogen. Infrared spectra were recorded on a SHIMADZU IR prestige-21 FTIR-8400S spectrometer in the spectral range 4000–500 cm⁻¹, with the samples in the form of potassium bromide pellets. Raman spectra were recorded using a Raman microscope (Kaiser Optical Systems, Inc., Ann Arbor, MI, USA) with 785 nm laser excitation. The spectra were obtained for one 2 min exposure of the CCD detector in the wave-number range 50–3500 cm⁻¹.

4.2 Synthesis of ligand L (3-ethyl-4-(3-methylphenyl)-5-(2-pyridyl)-1,2,4-triazole)

The synthetic routes of the ligand L are illustrated in Scheme 3. 10 mmol 3,3′-dimethylphenylphosphazoanilide (2.42 g) and 10 mmol N′-propionyl-N-(2-pyridoyl)hydrazine (2.07 g) were dissolved in 30 mL o-dichlorobenzene, then the resulting solution was refluxed at 190–200 °C for about 3 h.²³ During which time a white solid of ligand L was formed. The white solid was collected by filtration, washed with water and air-dried at room temperature (yield 1.6 g, 60.6%). M.p. 152–155 °C. Elemental analysis anal. calcd (%): C, 72.70; N, 21.19; H, 6.10 Found: C, 72.45; N, 21.26; H, 6.04. IR (KBr, cm⁻¹): 3406, 3100, 1577, 1586, 1522, 1465, 1235, 754, 696; ¹H NMR δ: 1.26 (m, 3H), 2.35 (s, 3H), 3.23–3.26 (m, 3H), 7.31–7.50 (m, 4H), 7.64–8.20 (m, 4H); ¹³C NMR δ: 12.3, 21.4, 21.5, 124, 125.9, 126, 129, 131, 142.5, 149.8, 153.5, 155.2.

Scheme 3 The synthetic route for ligand L.

4.3 Synthesis of complex 1 ([Cd₂(μ_1,1-N₃)₂L₂(N₃)₂]·H₂O)

The synthetic route of the complex 1 is illustrated in Scheme 4. It was performed by a slow evaporation technique. A 35 mL methanol–water (2 : 1 v/v) system was used. The 2 : 2 : 1 stoichiometric mixture of NaN₃ (0.4 mmol, 0.026 g), 3-ethyl-4-(3-methylphenyl)-5-(2-pyridyl)-1,2,4-triazole (L, 0.4 mmol, 0.1056 g) and CdCl₂ (0.2 mmol, 0.037 g) was stirred at 40–50 °C for about 30 min, then the solution was kept undisturbed at room temperature. Single crystals of 1 suitable for X-ray diffraction were obtained within two weeks (yield 85%). Elemental analysis anal. calcd (%): C, 40.14; N, 29.25; H, 3.79 Found: C, 41.30; N, 28.48; H, 4.01. IR (KBr, cm⁻¹): 3455, 3082, 1608, 1560, 1520, 1465, 1230, 765, 691.

Scheme 4 The synthetic route for complex 1.

4.4 X-ray crystallographic study

The single-crystal X-ray diffraction data of the complex 1 were collected at 293 K with graphite-monochromated Mo Kα radiation (λ = 0.071073 nm) using a Rigaku SCXmini diffractometer.²⁶ The lattice parameters were integrated using vector analysis and refined from the diffraction matrix, the absorption correction was carried out by using a Bruker SADABS program with a multi-scan method. The crystallographic data, data collection, and refinement parameters for complex 1 are given in Table 4. The structures were solved by full-matrix least-squares methods on all F² data, and used the SHELXS-97 and SHELXL-97 programs²⁷ for structure solution and refinement respectively. All non-hydrogen atoms were refined anisotropically and hydrogen atoms were geometrically fixed and were inserted at their calculated positions and fixed at their positions.²⁸ The molecular graphics were prepared by using the DIAMOND program²⁹ and Mercury.³⁰

Table 4 Crystal data and structure refinements for complex 1

Complex	1
Formula	C16H18CdN10O
Formula weight	478.79
Crystal system	Triclinic
Space group	P1̄
a/Å	6.8829(14)
b/Å	10.916(2)
c/Å	13.941(3)
α/°	101.31(3)
β/°	103.97(3)
γ/°	96.41(3)
V, Å^3	982.7(3)
Z	2
D calc. (mg m^−3)	1.611
T/K	293(2)
μ (mm^−1)	1.14
No. of reflns collected	4468
No. of unique reflns	3580
No. of params	235
Goodness-of-fit on F^2	1.057
R1, wR2 ((I > 2σ(I))	0.0547, 0.1287
R1, wR2 (all data)	0.0725, 0.1394
CCDC no.	967548

---

Acknowledgements

This work has been supported by the Scientific Research Foundation of Graduate School of Southeast University (YBJJ1340), Fundamental Research Funds for the Central Universities (CXZZ12_0119), Natural Science Foundation of China (21371031) and Founds for the Ministry of Science and Technology (212401025).

Notes and references

1. J. S. Miller and M. Drillon, ed Magnetism: Molecules to Materials, Wiley-VCH, Weinheim, 2001, vol. I–IV.
2. Magnetism: Molecules to Materials, ed. J. S. Miller and M. Drillon, Willey-VCH, Weinheim, 2002–2005, vol. I–V.
3. J. L. Mendoza-Cortes, M. O'Keeffe and O. M. Yaghi, Chem. Soc. Rev., 2009, 38, 1257.
4. J. Lu, D. R. Turner, L. P. Harding, L. T. Byrne, M. V. Baker and S. R. Batten, J. Am. Chem. Soc., 2009, 131, 10372.
5. (a) Y. H. Luo, Y. T. Ma, Q. Q. Bao and B. W. Sun, J. Chem. Crystallogr., 2012, 42, 628; (b) Y. H. Luo, G. G. Wu, S. L. Mao and B. W. Sun, Inorg. Chim. Acta, 2013, 397, 1; (c) Y. H. Luo, W. T. Song, S. W. Ge and B. W. Sun, Polyhedron, 2014, 69, 160; (d) Y. H. Luo, S. W. Ge, W. T. Song and B. W. Sun, New J. Chem., 2014, 38, 723.
6. Y. H. Luo, Y. H. Lu and B. W. Sun, Inorg. Chim. Acta, 2013, 404, 188.
7. G. S. Papaefstathiou, S. P. Perlepes, A. Escuer, R. Vicente, M. Font-Barida and X. Solans, Angew. Chem., Int. Ed., 2001, 40, 884.
8. M. Monfort, I. Resino, J. Ribas and H. Stoeckli-Evans, Angew. Chem., Int. Ed., 2000, 39, 191.
9. T. C. Stamatatos, K. A. Abboud, W. Wernsdorfer and G. Christou, Angew. Chem., Int. Ed., 2008, 47, 6694.
10. J.-R. Li, Y. Tao, Q. Yu, X.-H. Bu, H. Sakamoto and S. Kitagawa, Chem.–Eur. J., 2008, 14, 2771.
11. (a) Z. G. Gu, J. L. Zuo and X. Z. You, Dalton Trans., 2007, 4067; (b) C. Adhikary and S. Koner, Coord. Chem. Rev., 2010, 254, 2933.
12. A. A. Massoud, M. A. M. Abu-Youssef, J. P. Vejpravova, V. Langer and L. Ohrstrom, CrystEngComm, 2009, 11, 223.
13. Z. Shen, J. L. Zuo, S. Gao, Y. Song, C. M. Che, H. K. Fun and X. Z. You, Angew. Chem., Int. Ed., 2000, 112, 3633.
14. W. Dong, O. Y. Yan, D. Z. Liao, S. P. Yan, P. Cheng and Z. H. Jiang, Inorg. Chim. Acta, 2006, 359, 3363.
15. T. Ueto, N. Takata, N. Muroyama, A. Nedu, A. Sasaki, S. Tanida and K. Tarada, Cryst. Growth Des., 2012, 12, 485.
16. G. S. Matouzenko, A. Bousseksou, S. A. Borshch, M. Perrin, S. Zein, L. Salmon, G. Molnar and S. Lecocq, Inorg. Chem., 2004, 43, 227.
17. K. Nakano, N. Suemura, S. Kawata, A. Fuyuhiro, T. Yagi, S. Nasu, S. Morimoto and S. Kaizaki, Dalton Trans., 2004, 982.
18. J. Krober, E. Codjovi, O. Kahn, F. Grolibre and C. Jay, J. Am. Chem. Soc., 1993, 115, 9810.
19. (a) N. Moliner, A. B. Gaspar, M. C. Munoz, V. Niel, J. Cano and J. A. Real, Inorg. Chem., 2001, 40, 3986; (b) Z.-X. Wang, Y. Lan, L.-T. Yuan and C.-Y. Liu, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2005, 61, o2033; (c) P. Wu, Z. Wang, B. Zhou and L. Huang, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2007, 63, m3060; (d) S.-P. Zhang, H.-J. Liu, S.-C. Shao, Y. Zhang, D.-G. Shun, S. Yang and H.-L. Zhu, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2004, 60, o1113; (e) S.-P. Zhang, Z.-L. You, S.-C. Shao and H.-L. Zhu, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2005, 61, o27; (f) D.-R. Zhu, Y. Xu, Y. Zhang, T.-W. Wang and X.-Z. You, Acta Crystallogr., Sect. C: Cryst. Struct. Commun., 2000, 56, 895; (g) D. Zhu, Y. Xu, Z. Yu, Z. Guo, H. Sang, T. Liu and X. You, Chem. Mater., 2002, 14, 838; (h) D.-J. Xie, W. Lu, Z.-X. Wang and D.-R. Zhu, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2009, 65, o1177.
20. Y. S. You, C. S. Hong and K. M. Kim, Polyhedron, 2005, 24, 249.
21. X. Wang, Z. Li, Y. Xu, L. Li, D. Liao and Z. Jiang, J. Coord. Chem., 2008, 61(6), 900.
22. Y.-Q. Wang, A.-L. Cheng, X. Wang and E.-Q. Gao, RSC Adv., 2012, 2, 10352.
23. E. Klingsberg, J. Org. Chem., 1958, 23, 1086.
24. (a) Y. H. Luo, C. G. Zhang, B. Xu and B. W. Sun, CrystEngComm, 2012, 14(20), 6860; (b) Y. H. Luo and B. W. Sun, Cryst. Growth Des., 2013, 13(5), 2098; (c) Y. H. Luo and B. W. Sun, CrystEngComm, 2013, 15, 7490; (d) Y. H. Luo, Q. Zhou and B. W. Sun, J. Chem. Res., 2012, 36(9), 506.
25. (a) Y.-H. Luo and B.-W. Sun, Spectrochim. Acta, Part A, 2014, 120, 228; (b) Y.-H. Luo and B.-W. Sun, Spectrochim. Acta, Part A, 2014, 120, 381; (c) Y. H. Luo, J. Xu and B. W. Sun, J. Chem. Res., 2012, 36(12), 697; (d) Y. H. Luo, B. Xu and B. W. Sun, J. Cryst. Growth, 2013, 374, 88.
26. Rigaku, CrystalClear, Version 14.0, Rigaku Corporation, Tokyo, Japan, 2005.
27. G. M. Sheldrick, SHELXS97: Programs for Crystal Structure Analysis, University of Gottingen, Germany, 1997.
28. (a) Y. H. Luo and M. L. Pan, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2012, 68, o206; (b) Y. H. Luo, J. Xu, M. L. Pan and J. F. Li, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2011, 67, o2099.
29. K. Brandenburg, DIAMOND: Crystal and Molecular Structure Visualization, Version 3.1b, Crystal Impact GbR, Bonn, Germany, 2006.
30. Mercury 2.3 Supplied with Cambridge Structural Database, CCDC, Cambridge, U.K., 2003–2004.

---

Footnote

† Electronic supplementary information (ESI) available: TGA profiles of complex 1, PXRD of 1 and its dehydrated form (1-water), CCDC number 967548 containing the crystallography information of complex 1. See DOI: 10.1039/c3ra46125d

---