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Three interesting coordination compounds based on metalloligand and alkaline-earth ions: Syntheses, structures, thermal behaviors and magnetic property
Journal of Molecular Structure 1119 (2016) 340e345
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Three interesting coordination compounds based on metalloligand and alkaline-earth ions: Syntheses, structures, thermal behaviors and magnetic property Qiang Zhou a, 1, Jun Qian a, 1, Chi Zhang a, b, * a
China-Australia Joint Research Center for Functional Molecular Materials, Scientific Research Academy, Jiangsu University, Zhenjiang 212013, PR China China-Australia Joint Research Center for Functional Molecular Materials, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 February 2016 Received in revised form 6 April 2016 Accepted 11 April 2016 Available online 30 April 2016
Based on metalloligand LCu ([Cu(2,4-pydca)2]2, 2,4-pydca2 ¼ pyridine-2,4-dicarboxylate) and alkalineearth ions (Ca2þ, Sr2þ, and Ba2þ), three interesting coordination compounds, [Ca(H2O)7][LCu$H2O]$H2O (1), {Sr[LCu$H2O]$4H2O}n (2), and {Ba[LCu$H2O]$8H2O}n (3), have been synthesized and wellcharacterized by elemental analysis, infrared spectroscopy, thermogravimetric and single-crystal X-ray diffraction analysis. X-ray crystallographic studies reveal that 1 features a discrete 0D coordination compound, while 2 and 3 exhibit the 2D network and 1D chain structures, respectively. Compound 2 is constructed from {LCu}2 dimers connected with {Sr2} units, which is fabricated by two Sr2þ ions bridged via two m2-O bridges, while compound 3 is formed by 1D {Ba}n chain linked with metalloligands LCu and exhibits an interesting sandwich like chain structure. It is noted that the coordination numbers of alkaline-earth ions are in positive correlation with their radiuses. Moreover, the magnetic property of compound 2 has been studied. © 2016 Elsevier B.V. All rights reserved.
Keywords: Coordination compounds Metalloligand Crystal structure Alkaline-earth ions Magnetic property
1. Introduction During the past decade, coordination compounds have attracted a great deal of attention not only for their interesting molecular structures [1e3] but also for the potential applications as functional materials [4e6]. It has been found that the judicious choices of synthetic approach are of significance to the architectures and physical properties of coordination compounds [7e11]. In recent years, the application of metalloligands has been developed to an important strategy for the construction of coordination compounds [12e20]. For example, building blocks [M(CN)8]3/4 (M ¼ W, Mo, Nb) and [MS4]2 (M ¼ W, Mo) have been regarded as ideal metalloligands for the construction of coordination compounds with magnetic and non-linear optical properties, respectively [21]. Recently, a new metalloligand [Cu(2,4-pydca)2]2 built from the
* Corresponding author. China-Australia Joint Research Center for Functional Molecular Materials, Scientific Research Academy, Jiangsu University, Zhenjiang 212013, PR China. E-mail addresses: [email protected], [email protected] (C. Zhang). 1 Q. Zhou and J. Qian contributed equally to this work. http://dx.doi.org/10.1016/j.molstruc.2016.04.034 0022-2860/© 2016 Elsevier B.V. All rights reserved.
ligand 2,4-pydca (pyridine-2,4-dicarboxylate) has been developed. Shin-ichiro Noro and his co-workers have reported several heterometallic coordination compounds with novel structures based on the metalloligand [Cu(2,4-pydca)2]2 [22]. To the best our knowledge, the investigation on such kind of metalloligand is still rare [23e27]. From the synthetic point of view, the construction of coordination compounds can also be affected by several factors, such as pH values, solvent polarities, auxiliary ligands, and the metal centers. Among these factors, the metal center plays an important role to the structures and physical properties of coordination compounds due to the various coordination modes and diverse chemical valences. It is well known that a large number of 3d and 4f transition metals have been employed as the metal centers in the fabrication of coordination compounds [28,29]. Compared with transition metal ions, alkaline-earth ions are rare used as metal centers in the construction of coordination compounds due to the fact of that the alkaline-earth ions are hard to be coordinated [30e34]. To extend the alkaline-earth-based coordination compounds, three alkaline-earth ions Ca2þ, Sr2þ, and Ba2þ will be invited as the metal centers. In the present work, three new coordination compounds,
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[Ca(H2O)7][LCu$H2O]$H2O (1), {Sr[LCu$H2O]$4H2O}n (2), and {Ba [LCu$H2O]$8H2O}n (3), have been prepared from metalloligand LCu and alkaline-earth ions. Single-crystal X-ray diffraction analysis reveals that compound 1 contains metalloligand LCu with [Ca(H2O)7]2þ as a counterion, while compounds 2 and 3 consist of polymeric 2D network and 1D chain, respectively. The network of compound 2 is constructed from {LCu}2 dimers connected with {Sr2} units, which is built by two Sr2þ ions bridged through two m2O bridges, while the sandwich like chain structure of compound 3 is formed by metalloligands LCu linked with 1D {Ba}n chain, which is fabricated by Ba2þ ions connected with each other via m2-O bridges. Interestingly, the coordination numbers of alkaline-earth ions in these compounds are in positive correlation with their radiuses. Thermal behaviors of all three compounds have been investigated in the temperature range of 25e800 C. Moreover, the magnetic property of compound 2 has also been studied. 2. Experimental section 2.1. Materials and methods All the chemicals were commercially available and used without further purification. Pyridine-2,4-dicarboxylate acid and metalloligand LCu were synthesized according to the literature [22]. Element analyses for C, H and N were performed with a PerkineElmer 240C system. Infrared spectra were recorded in the region 400e4000 cm1 with a Nicolet Nexus 470 spectrometer (Germany) with samples as KBr disks. Thermogravimetric analysis (TGA) measurements were carried out with a PerkineElmer Pyis 1 system in a nitrogen purge with a heating rate of 10 C min1. 2.2. Preparation of [Ca(H2O)7][LCu·H2O]·H2O (1) A methanol solution (1 mL) of Ca(NO3)2$4H2O (24 mg, 0.1 mmol) and 1 mL blank aqueous solution were carefully put onto an aqueous solution (1 mL) of LCu (62 mg, 0.1 mmol) in a little straight glass tube. Blue crystals of 1 were obtained in dark after several days. Yield: 21 mg (36% based on Cu). Anal. Calcd for C14H24CaCuN2O17 (595.98): C, 28.19; H, 4.03; N, 4.70. Found: C, 28.13; H, 4.02; N, 4.68. IR (KBr, cm1): 3765(w), 3661(m), 3396(s), 2931(m), 2366(m), 1648(s), 1611(s), 1550(m), 1464(w), 1384(m), 1335(m), 1262(w), 1188(w), 1089(w), 1035(w), 783(m), 734(m), 697(m), 630(m), 562(m), 519(m), 470(m), 427(m). 2.3. Preparation of {Sr[LCu·H2O]·4H2O}n (2) 2 was obtained as blue block crystals by the same way as that of 1 except that Ca(NO3)2$4H2O was replaced by Sr(NO3)2 (21 mg, 0.1 mmol). Yield: 30 mg (52% based on Cu). Anal. Calcd for C14H16SrCuN2O13 (571.45): C, 29.42; H, 2.80; N, 4.90. Found: C, 29.31; H, 2.81; N, 4.86. IR (KBr, cm1): 3759(w), 3439(s), 2359(m), 1659(s), 1591(m), 1542(m), 1475(w), 1389(m), 1334(m), 1254(w), 1095(w), 1033(w), 916(w), 843(w), 788(w), 738(m), 689(m), 560(m), 469(m). 2.4. Preparation of {Ba[LCu·H2O]·8H2O}n (3) A mixed solution (methanol/water ¼ 2:1, 1 mL) of Ba(NO3)2 (26 mg, 0.1 mmol) and 1 mL blank aqueous solution were successively added on the aqueous solution (1 mL) of LCu (62 mg, 0.1 mmol) in a little straight glass tube. The resulting solution was placed in the dark and allowed to diffuse slowly at room temperature. Blue crystals of 3 were obtained after several days. Yield: 15 mg (17% based on Cu). Anal. Calcd for C14H24BaCuN2O17 (693.23): C, 24.24; H, 3.46; N, 4.04. Found: C, 24.37; H, 3.45; N, 4.05. IR (KBr,
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cm1): 3764(w), 3457(s), 3384(s), 2365(m), 1665(s), 1597(m), 1543(m), 1475(w), 1389(m), 1334(m), 1254(w), 1095(w), 1027(w), 904(w), 836(w), 782(w), 738(m), 695(m), 572(m), 475(m). 2.5. Crystal structure determination Single crystals with high qualities of all three compounds were chosen directly from glass tubes and mounted on glass fibes. All measurements were made on a Rigaku Saturn 724þ CCD diffratometer with graphite-monochromated Mo-Ka radiation (l ¼ 0.71073 Å) at 293K. Structures were solved by direct methods, and non-hydrogen atoms were subjected to anisotropic refinement by full-matrix least squares on F2 using the SHELX-97 package [35e37]. All the non-hydrogen atoms were refined with anisotropic thermal displacement coefficients. All the hydrogen atoms were placed at the calculated positions and refined following the riding model. Details of the crystal parameters, data collection and refinement of coordination compounds 1e3 are summarized in Table 1, while the selected bond lengths of coordination compounds 1e3 are listed in Table 2.
3. Results and discussion 3.1. Synthetic method All three compounds 1e3 were synthesized under similar reaction conditions with the inter-diffusion method. The reaction of metalloligand LCu and alkaline-earth salts Ca(NO3)2$4H2O/ Sr(NO3)2/Ba(NO3)2 in a 1:1 M ratio in methanol/aqueous solution at room temperature gave rise to the crystals of coordination compounds 1, 2, and 3. Compared to the direct synthetic approach, the inter-diffusion method here plays an important role in the crystallization of compound 1e3. It has been found that the blank solution used in the reaction process can provide a stable environment for the reaction of two different kinds of reactive components [21]. The structure difference in compounds 1e3 may be attributed to different coordination modes of alkaline-earth ions. 3.2. Crystal structure of 1 Compound 1 was synthesized from the reaction of metalloligand LCu and Ca(NO3)2$4H2O in the molar ratio of 1:1. Singlecrystal X-ray diffraction analysis reveals that 1 consists of sevencoordinated cation [Ca(H2O)7]2þ and metalloligand LCu (Fig. 1). As displayed in Fig. 1, Cu atom is coordinated with two N atoms and three O atoms from one water molecule and two pyridine-2,4dicarboxylate, which form a distorted tetragonal pyramid geometry. Bond lengths of CueN range from 1.981(3) to 1.984(3) Å, while the distances of CueO bond are in the range of 1.971(3) to 2.238(4) Å. The bond lengths of CueO between Cu atoms and O atoms from water molecules are larger than the values between Cu atoms and O atoms from carboxylates. Bond lengths of CaeO are in the range of 2.348(3) to 2.451(3) Å. As shown in Fig. 2, the cations [Ca(H2O)7]2þ connect with each other to form a supramolecular double chain along a axis through the OeH$$$O hydrogen bonds (Table S1). These chains are further extended to a 3D supramolecular structure via the multiple hydrogen bonds (Fig. S1). Hydrogen bonds between water molecules and carboxilates and p-p interactions (3.38e3.50 Å) between pyridine-carboxylates enhance the stability of such 3D supramolecular structure. The shortest distance between Ca2þ ions is 5.070(1) Å, while the shortest distance between Ca2þ and Cu2þ is 6.103(1) Å.
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Table 1 Crystal data for 1, 2 and 3. Compound
1
2
3
Empirical formula Formula weight Crystal system Space group a/Å b/Å c/Å a/ b/ g/ Volume/Å3 Z Absorption coefficient F(000) Rint Completeness GooF R(I > 2s(I))
C14H24CaCuN2O17 595.98 Monoclinic P2(1)/c 6.9345(14) 15.088(3) 22.985(5) 90 105.16(3) 90 2321.2(8) 4 1.247 1228 0.0297 98.30% 1.177 R1 ¼ 0.0550 wR2 ¼ 0.1199 R1 ¼ 0.0708 wR2 ¼ 0.1278 0.839, 0.634
C14H16SrCuN2O13 571.45 Triclinic P-1 6.8520(14) 8.1466(16) 17.482(3) 93.60(3) 99.38(3) 112.22(3) 883.0(3) 2 4.306 570 0.0240 96.00% 1.053 R1 ¼ 0.0224 wR2 ¼ 0.0600 R1 ¼ 0.0245 wR2 ¼ 0.0608 0.308, 0.477
C14H24BaCuN2O17 693.23 Triclinic P-1 7.1132(14) 10.908(2) 14.581(3) 77.66(3) 87.18(3) 87.40(3) 1103.2(4) 2 2.828 686 0.0260 98.10% 1.038 R1 ¼ 0.0185 wR2 ¼ 0.0447 R1 ¼ 0.0214 wR2 ¼ 0.0454 0.417, 0.495
R(all data) Largest diff peak and hole
3.3. Crystal structure of 2
Table 2 Selected bond lengths (Å) for 1, 2 and 3. 1 Cu(1)eO(7) Cu(1)eO(4) Cu(1)eN(2) Cu(1)eN(1) Cu(1)eO(5) Ca(1)eO(22) Ca(1)eO(20) Ca(1)eO(21) 2 Sr(1)eO(1) Sr(1)eO(5) Sr(1)eO(2)#1 Sr(1)eO(6) 3 Ba(1)eO(11) Ba(1)eO(7) Ba(1)eO(8) Ba(1)eO(22)#1 Ba(1)eO(5)#1 Ba(1)eO(22) Cu(1)eN(2)
1.971(3) 1.973(3) 1.981(3) 1.984(3) 2.238(4) 2.348(3) 2.375(3) 2.403(3)
Cu(1)eO(9) Cu(1)eO(12) Cu(1)eN(1) Cu(1)eN(2) Cu(1)eO(13) Ca(1)eO(23) Ca(1)eO(19) Ca(1)eO(24)#1
1.967(2) 1.981(2) 1.983(2) 1.984(2) 2.277(2) 2.361(3) 2.392(3) 2.448(3)
2.570(2) 2.582(2) 2.605(2) 2.621(2)
Sr(1)eO(3) Sr(1)eO(20A)#2 Sr(1)/Sr(1)#1 Sr(1/Sr(1)#2
2.670(2) 2.694(2) 4.427(1) 4.600(2)
2.704(2) 2.724(2) 2.860(2) 2.866(2) 2.879(2) 2.887(2) 1.981(2)
Ba(1)eO(10) Ba(1)eO(10)#2 Ba(1)eO(5) Cu(1)eN(1) Cu(1)eO(1) Cu(1)eO(2) Ba(1)/Ba(1)#1
2.900(3) 2.945(2) 3.005(2) 1.962(2) 1.972(2) 1.980(2) 4.232(1)
Symmetry transformations used to generate equivalent atoms for 1: #1 xþ1, y, z; for 2: #1 xþ1, yþ1, zþ1; #2 xþ2, yþ1, zþ1; for 3: #1 xþ1, yþ1, zþ1; #2 x, yþ1, zþ1.
Compound 2 exhibits a 2D network structure, which is constructed from {LCu}2 dimers connected with {Sr2} units, which is fabricated by two Sr2þ ions bridged via two m2-O bridges (Fig. 3c). As in Fig. 3a, the oxygen-bridged {Sr2} units are connected with each other to form a zigzag chain through the m3-O bridges, which are from carboxylates. The {LCu}2 dimer is fabricated by a pair of metalloligand LCu connected by two CueO bridges (Fig. 3b). With the connection between {LCu}2 dimers and {Sr2} units, aforementioned zigzag chains are pillared by {LCu}2 dimers to the 2D sheet. These sheets are further extended to a 3D supramolecular structure via the OeH/O hydrogen bonds (Fig. S2, Table S2). Compared to the coordination mode of Ca atom in compound 1, each Sr atom here is coordinated with eight O atoms in which five O atoms are from water molecules with the remainder three ones are from carboxylates. Bond lengths of SreO are in the range of 2.562(4) to 2.762(3) Å. The coordination mode of Cu atom in compound 2 is also different with that of compound 1. In compound 2, the Cu atom is coordinated with two N atoms and four O atoms from two pyridine-2,4-dicarboxylate ligand and one H2O molecule, forming a distorted octahedral configuration. Bond lengths of CueO and CueN range from 1.963(3) to 2.784(1) Å and 1.985(5) to 1.991(5) Å. The shortest distance of Sr/Sr and Cu/Cu are 4.427(1) Å and 3.540(1) Å, while the shortest distance of Sr/Sr between neighbouring sheets is 5.020(1) Å. 3.4. Crystal structure of 3
Fig. 1. View of LCu in 1. All hydrogen atoms are omitted for clarity.
Compound 3 features a 1D sandwich like chain structure, which is built from 1D {Ba}n chain connected with metalloligands LCu. As shown in Fig. 4a, the Ba atoms are bridged by two m2-O bridges to form a zigzag chain. Such {Ba}n chain then connects with metalloligands LCu to form a sandwich like chain via the BaeO bonds, in which the O atoms are from carboxylates (Fig. 4b). Interestingly, this sandwich like chain have two kinds of bridging modes, double bridge (two m2-O bridges) and quadruple bridge (two m2-O bridges and two m3-O bridges), which appear alternately in the chain. These chains are also further extended to a 3D supramolecular structure via the OeH/O hydrogen bonds (Fig. S3, Table S3). In compound 3, each Ba atom is coordinated with nine O atoms. Among these O
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Fig. 2. Hydrogen-bonded Ca chain along a axis.
Fig. 3. (a) {Sr} chain in compound 2. (b) LCu dimmer in compound 2. View of 2D network in compound 2. (c) All hydrogen atoms are omitted for clarity.
atoms, two of them are from carboxylates, while residual seven ones are from water molecules. The lengths of BaeO bond fall in the range of 2.7035(2) to 3.0054(2) Å. The coordination mode of Cu atom is the same as that of compound 1. The distance of Ba$$$Ba in the double bridge form is 4.814 Å, while the value in quadruple bridge is 4.232(2) Å. The shortest distances of Cu/Ba and Cu/Cu are 5.173 Å and 7.113 Å, respectively. 3.5. Coordination modes of alkaline-earth ions Although the alkaline-earth ions in all three coordination compounds 1e3 have the same chemical valence, the coordination numbers of them are quite different. As in compound 1, each Ca2þ ion is coordinated with seven O atoms with the radius as 0.99 Å. The Sr2þ and Ba2þ ions are eight- and nine-coordinated in compounds 2e3, in which the alkaline-earth radiuses are 1.13 Å and 1.35 Å respectively. It seems that the coordination numbers of alkaline-earth ions are in positive correlation with their radiuses. Due to the different coordination modes of alkaline-earth ions, the molecular structures of compounds 1e3 vary from 0D discrete
compound, 1D chain to 2D network framework. In particular, the metalloligands LCu in compound 2 have been changed into {LCu}2 dimers. 3.6. Thermogravimetric analysis Thermal properties of all three compounds were evaluated by thermogravimetric from 25 C to 800 C in a nitrogen atmosphere with a heating rate of 10 C$min1. TGA measurements revealed that compounds 1e3 are unstable in N2 atmosphere with the increase in temperature. As shown in the Fig. 5, the first weight loss of compound 1 (8.34%) occurs from 67 C to 115 C, corresponding to the loss of three water molecules per unit of [Ca(H2O)7][LCu$H2O]$ H2O (calcd: 9.34%). Further weight loss of 6.24% appears from 146 C to 201 C, corresponding to the loss of two water molecules (calcd: 6.23%). After 331 C, the organic groups start to lose and the structure of compound 1 begins to decompose. As for compound 2, the first weight loss of 9.08% (calcd: 9.56%) is observed from 72 C to 151 C, which is in accordance with the loss of three water molecules. The second weight loss of 6.52% occurs from 153 C to
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Fig. 4. (a) View of {Ba} chain in compound 3. (b) Chain structure of compound 3. All hydrogen atoms are omitted for clarity.
3.7. Magnetic property of compound 2 To gain further insight into the structure of LCu dimmer in compound 2, the magnetic property of compound 2 was studied. Variable-temperature magnetic susceptibility measurement was performed on powder sample in the temperature range of 2e300 K with a field of 1000 Oe. As shown in Fig. 6a, cmT value of compound 2 at room temperature per Cu2 unit is 0.971 cm3 K mol1, which is close to the expected value of 1.0 cm3 K mol1 for two spin-only CuⅡ ion with S ¼ 1/2, g ¼ 2.00. Upon sample cooling, the cmT value decreases continuously. The variation tendency of cmT value from room temperature to 2 K reveals a intradimer antiferromagnetic behavior. As in Fig. 6b, the magnetic data in the range of 30e300 K followed the CurieeWeiss law with a Curie constant of C ¼ 1.014 cm3 K mol1 and a negative Weiss constant of q ¼ 15.680 K, which confirm the weak antiferromagnetic interactions between two Cu2þ centers at 30e300 K.
4. Conclusion Fig. 5. TGA curves of compounds 1, 2 and 3.
C,
232 which is corresponding to the loss of two water molecules (calcd: 6.31%). As the temperature increases, the 2D network structure of compound 2 begins to collapse after 339 C. The first weight loss of 14.95% for compound 3 is observed from 82 C to 169 C, which is corresponding to six water molecules (calcd: 15.58%). After that, the structure keeps stable until 330 C. With the increase in temperature, the 1D chain structure of compound 3 begins to collapse.
In summary, three interesting coordination compounds have been synthesized from metalloligand LCu and alkaline-earth ions (Ca2þ 1, Sr2þ 2, and Ba2þ 3). All three compounds were wellcharacterized by elemental analysis, infrared spectroscopy, thermogravimetric and single-crystal X-ray diffraction analysis. X-ray crystallographic analysis shows that compound 1 is a 0D discrete structure, while compounds 2 and 3 exhibit 2D network and 1D chain structure, respectively. Compound 2 is constructed from {LCu}2 dimers connected with {Sr2} units, which is fabricated by two Sr2þ ions bridged with two m2-O bridges, while of compound 3 is formed by metalloligands LCu linked with 1D oxygen bridged {Ba}n chain and exhibits a sandwich like chain structure. Interestingly, the coordination numbers of alkaline-earth ions in these
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References
Fig. 6. (a) cmT versus T curve of compound 2. (b) c1 m versus T curve of compound 2.
compounds are in positive correlation with their radiuses. Additionally, the magnetic property of compound 2 has been investigated. Acknowledgments Financial support from the National Natural Science Foundation of China (Grants 50925207, 51172100, and 51432006), the Ministry of Science and Technology of China for the International Science Linkages Program (Grant 2011DFG52970), the Ministry of Education of China for the Changjiang Innovation Research Team (Grant IRT13R24), and the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (Grant B13025) are gratefully acknowledged. Appendix A. Supplementary data Supplementary data related to this article can be found at http://
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Three interesting coordination compounds based on metalloligand and alkaline-earth ions: Syntheses, structures, thermal behaviors and magnetic property Qiang Zhou a, 1, Jun Qian a, 1, Chi Zhang a, b, * a
China-Australia Joint Research Center for Functional Molecular Materials, Scientific Research Academy, Jiangsu University, Zhenjiang 212013, PR China China-Australia Joint Research Center for Functional Molecular Materials, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 February 2016 Received in revised form 6 April 2016 Accepted 11 April 2016 Available online 30 April 2016
Based on metalloligand LCu ([Cu(2,4-pydca)2]2, 2,4-pydca2 ¼ pyridine-2,4-dicarboxylate) and alkalineearth ions (Ca2þ, Sr2þ, and Ba2þ), three interesting coordination compounds, [Ca(H2O)7][LCu$H2O]$H2O (1), {Sr[LCu$H2O]$4H2O}n (2), and {Ba[LCu$H2O]$8H2O}n (3), have been synthesized and wellcharacterized by elemental analysis, infrared spectroscopy, thermogravimetric and single-crystal X-ray diffraction analysis. X-ray crystallographic studies reveal that 1 features a discrete 0D coordination compound, while 2 and 3 exhibit the 2D network and 1D chain structures, respectively. Compound 2 is constructed from {LCu}2 dimers connected with {Sr2} units, which is fabricated by two Sr2þ ions bridged via two m2-O bridges, while compound 3 is formed by 1D {Ba}n chain linked with metalloligands LCu and exhibits an interesting sandwich like chain structure. It is noted that the coordination numbers of alkaline-earth ions are in positive correlation with their radiuses. Moreover, the magnetic property of compound 2 has been studied. © 2016 Elsevier B.V. All rights reserved.
Keywords: Coordination compounds Metalloligand Crystal structure Alkaline-earth ions Magnetic property
1. Introduction During the past decade, coordination compounds have attracted a great deal of attention not only for their interesting molecular structures [1e3] but also for the potential applications as functional materials [4e6]. It has been found that the judicious choices of synthetic approach are of significance to the architectures and physical properties of coordination compounds [7e11]. In recent years, the application of metalloligands has been developed to an important strategy for the construction of coordination compounds [12e20]. For example, building blocks [M(CN)8]3/4 (M ¼ W, Mo, Nb) and [MS4]2 (M ¼ W, Mo) have been regarded as ideal metalloligands for the construction of coordination compounds with magnetic and non-linear optical properties, respectively [21]. Recently, a new metalloligand [Cu(2,4-pydca)2]2 built from the
* Corresponding author. China-Australia Joint Research Center for Functional Molecular Materials, Scientific Research Academy, Jiangsu University, Zhenjiang 212013, PR China. E-mail addresses: [email protected], [email protected] (C. Zhang). 1 Q. Zhou and J. Qian contributed equally to this work. http://dx.doi.org/10.1016/j.molstruc.2016.04.034 0022-2860/© 2016 Elsevier B.V. All rights reserved.
ligand 2,4-pydca (pyridine-2,4-dicarboxylate) has been developed. Shin-ichiro Noro and his co-workers have reported several heterometallic coordination compounds with novel structures based on the metalloligand [Cu(2,4-pydca)2]2 [22]. To the best our knowledge, the investigation on such kind of metalloligand is still rare [23e27]. From the synthetic point of view, the construction of coordination compounds can also be affected by several factors, such as pH values, solvent polarities, auxiliary ligands, and the metal centers. Among these factors, the metal center plays an important role to the structures and physical properties of coordination compounds due to the various coordination modes and diverse chemical valences. It is well known that a large number of 3d and 4f transition metals have been employed as the metal centers in the fabrication of coordination compounds [28,29]. Compared with transition metal ions, alkaline-earth ions are rare used as metal centers in the construction of coordination compounds due to the fact of that the alkaline-earth ions are hard to be coordinated [30e34]. To extend the alkaline-earth-based coordination compounds, three alkaline-earth ions Ca2þ, Sr2þ, and Ba2þ will be invited as the metal centers. In the present work, three new coordination compounds,
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[Ca(H2O)7][LCu$H2O]$H2O (1), {Sr[LCu$H2O]$4H2O}n (2), and {Ba [LCu$H2O]$8H2O}n (3), have been prepared from metalloligand LCu and alkaline-earth ions. Single-crystal X-ray diffraction analysis reveals that compound 1 contains metalloligand LCu with [Ca(H2O)7]2þ as a counterion, while compounds 2 and 3 consist of polymeric 2D network and 1D chain, respectively. The network of compound 2 is constructed from {LCu}2 dimers connected with {Sr2} units, which is built by two Sr2þ ions bridged through two m2O bridges, while the sandwich like chain structure of compound 3 is formed by metalloligands LCu linked with 1D {Ba}n chain, which is fabricated by Ba2þ ions connected with each other via m2-O bridges. Interestingly, the coordination numbers of alkaline-earth ions in these compounds are in positive correlation with their radiuses. Thermal behaviors of all three compounds have been investigated in the temperature range of 25e800 C. Moreover, the magnetic property of compound 2 has also been studied. 2. Experimental section 2.1. Materials and methods All the chemicals were commercially available and used without further purification. Pyridine-2,4-dicarboxylate acid and metalloligand LCu were synthesized according to the literature [22]. Element analyses for C, H and N were performed with a PerkineElmer 240C system. Infrared spectra were recorded in the region 400e4000 cm1 with a Nicolet Nexus 470 spectrometer (Germany) with samples as KBr disks. Thermogravimetric analysis (TGA) measurements were carried out with a PerkineElmer Pyis 1 system in a nitrogen purge with a heating rate of 10 C min1. 2.2. Preparation of [Ca(H2O)7][LCu·H2O]·H2O (1) A methanol solution (1 mL) of Ca(NO3)2$4H2O (24 mg, 0.1 mmol) and 1 mL blank aqueous solution were carefully put onto an aqueous solution (1 mL) of LCu (62 mg, 0.1 mmol) in a little straight glass tube. Blue crystals of 1 were obtained in dark after several days. Yield: 21 mg (36% based on Cu). Anal. Calcd for C14H24CaCuN2O17 (595.98): C, 28.19; H, 4.03; N, 4.70. Found: C, 28.13; H, 4.02; N, 4.68. IR (KBr, cm1): 3765(w), 3661(m), 3396(s), 2931(m), 2366(m), 1648(s), 1611(s), 1550(m), 1464(w), 1384(m), 1335(m), 1262(w), 1188(w), 1089(w), 1035(w), 783(m), 734(m), 697(m), 630(m), 562(m), 519(m), 470(m), 427(m). 2.3. Preparation of {Sr[LCu·H2O]·4H2O}n (2) 2 was obtained as blue block crystals by the same way as that of 1 except that Ca(NO3)2$4H2O was replaced by Sr(NO3)2 (21 mg, 0.1 mmol). Yield: 30 mg (52% based on Cu). Anal. Calcd for C14H16SrCuN2O13 (571.45): C, 29.42; H, 2.80; N, 4.90. Found: C, 29.31; H, 2.81; N, 4.86. IR (KBr, cm1): 3759(w), 3439(s), 2359(m), 1659(s), 1591(m), 1542(m), 1475(w), 1389(m), 1334(m), 1254(w), 1095(w), 1033(w), 916(w), 843(w), 788(w), 738(m), 689(m), 560(m), 469(m). 2.4. Preparation of {Ba[LCu·H2O]·8H2O}n (3) A mixed solution (methanol/water ¼ 2:1, 1 mL) of Ba(NO3)2 (26 mg, 0.1 mmol) and 1 mL blank aqueous solution were successively added on the aqueous solution (1 mL) of LCu (62 mg, 0.1 mmol) in a little straight glass tube. The resulting solution was placed in the dark and allowed to diffuse slowly at room temperature. Blue crystals of 3 were obtained after several days. Yield: 15 mg (17% based on Cu). Anal. Calcd for C14H24BaCuN2O17 (693.23): C, 24.24; H, 3.46; N, 4.04. Found: C, 24.37; H, 3.45; N, 4.05. IR (KBr,
341
cm1): 3764(w), 3457(s), 3384(s), 2365(m), 1665(s), 1597(m), 1543(m), 1475(w), 1389(m), 1334(m), 1254(w), 1095(w), 1027(w), 904(w), 836(w), 782(w), 738(m), 695(m), 572(m), 475(m). 2.5. Crystal structure determination Single crystals with high qualities of all three compounds were chosen directly from glass tubes and mounted on glass fibes. All measurements were made on a Rigaku Saturn 724þ CCD diffratometer with graphite-monochromated Mo-Ka radiation (l ¼ 0.71073 Å) at 293K. Structures were solved by direct methods, and non-hydrogen atoms were subjected to anisotropic refinement by full-matrix least squares on F2 using the SHELX-97 package [35e37]. All the non-hydrogen atoms were refined with anisotropic thermal displacement coefficients. All the hydrogen atoms were placed at the calculated positions and refined following the riding model. Details of the crystal parameters, data collection and refinement of coordination compounds 1e3 are summarized in Table 1, while the selected bond lengths of coordination compounds 1e3 are listed in Table 2.
3. Results and discussion 3.1. Synthetic method All three compounds 1e3 were synthesized under similar reaction conditions with the inter-diffusion method. The reaction of metalloligand LCu and alkaline-earth salts Ca(NO3)2$4H2O/ Sr(NO3)2/Ba(NO3)2 in a 1:1 M ratio in methanol/aqueous solution at room temperature gave rise to the crystals of coordination compounds 1, 2, and 3. Compared to the direct synthetic approach, the inter-diffusion method here plays an important role in the crystallization of compound 1e3. It has been found that the blank solution used in the reaction process can provide a stable environment for the reaction of two different kinds of reactive components [21]. The structure difference in compounds 1e3 may be attributed to different coordination modes of alkaline-earth ions. 3.2. Crystal structure of 1 Compound 1 was synthesized from the reaction of metalloligand LCu and Ca(NO3)2$4H2O in the molar ratio of 1:1. Singlecrystal X-ray diffraction analysis reveals that 1 consists of sevencoordinated cation [Ca(H2O)7]2þ and metalloligand LCu (Fig. 1). As displayed in Fig. 1, Cu atom is coordinated with two N atoms and three O atoms from one water molecule and two pyridine-2,4dicarboxylate, which form a distorted tetragonal pyramid geometry. Bond lengths of CueN range from 1.981(3) to 1.984(3) Å, while the distances of CueO bond are in the range of 1.971(3) to 2.238(4) Å. The bond lengths of CueO between Cu atoms and O atoms from water molecules are larger than the values between Cu atoms and O atoms from carboxylates. Bond lengths of CaeO are in the range of 2.348(3) to 2.451(3) Å. As shown in Fig. 2, the cations [Ca(H2O)7]2þ connect with each other to form a supramolecular double chain along a axis through the OeH$$$O hydrogen bonds (Table S1). These chains are further extended to a 3D supramolecular structure via the multiple hydrogen bonds (Fig. S1). Hydrogen bonds between water molecules and carboxilates and p-p interactions (3.38e3.50 Å) between pyridine-carboxylates enhance the stability of such 3D supramolecular structure. The shortest distance between Ca2þ ions is 5.070(1) Å, while the shortest distance between Ca2þ and Cu2þ is 6.103(1) Å.
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Table 1 Crystal data for 1, 2 and 3. Compound
1
2
3
Empirical formula Formula weight Crystal system Space group a/Å b/Å c/Å a/ b/ g/ Volume/Å3 Z Absorption coefficient F(000) Rint Completeness GooF R(I > 2s(I))
C14H24CaCuN2O17 595.98 Monoclinic P2(1)/c 6.9345(14) 15.088(3) 22.985(5) 90 105.16(3) 90 2321.2(8) 4 1.247 1228 0.0297 98.30% 1.177 R1 ¼ 0.0550 wR2 ¼ 0.1199 R1 ¼ 0.0708 wR2 ¼ 0.1278 0.839, 0.634
C14H16SrCuN2O13 571.45 Triclinic P-1 6.8520(14) 8.1466(16) 17.482(3) 93.60(3) 99.38(3) 112.22(3) 883.0(3) 2 4.306 570 0.0240 96.00% 1.053 R1 ¼ 0.0224 wR2 ¼ 0.0600 R1 ¼ 0.0245 wR2 ¼ 0.0608 0.308, 0.477
C14H24BaCuN2O17 693.23 Triclinic P-1 7.1132(14) 10.908(2) 14.581(3) 77.66(3) 87.18(3) 87.40(3) 1103.2(4) 2 2.828 686 0.0260 98.10% 1.038 R1 ¼ 0.0185 wR2 ¼ 0.0447 R1 ¼ 0.0214 wR2 ¼ 0.0454 0.417, 0.495
R(all data) Largest diff peak and hole
3.3. Crystal structure of 2
Table 2 Selected bond lengths (Å) for 1, 2 and 3. 1 Cu(1)eO(7) Cu(1)eO(4) Cu(1)eN(2) Cu(1)eN(1) Cu(1)eO(5) Ca(1)eO(22) Ca(1)eO(20) Ca(1)eO(21) 2 Sr(1)eO(1) Sr(1)eO(5) Sr(1)eO(2)#1 Sr(1)eO(6) 3 Ba(1)eO(11) Ba(1)eO(7) Ba(1)eO(8) Ba(1)eO(22)#1 Ba(1)eO(5)#1 Ba(1)eO(22) Cu(1)eN(2)
1.971(3) 1.973(3) 1.981(3) 1.984(3) 2.238(4) 2.348(3) 2.375(3) 2.403(3)
Cu(1)eO(9) Cu(1)eO(12) Cu(1)eN(1) Cu(1)eN(2) Cu(1)eO(13) Ca(1)eO(23) Ca(1)eO(19) Ca(1)eO(24)#1
1.967(2) 1.981(2) 1.983(2) 1.984(2) 2.277(2) 2.361(3) 2.392(3) 2.448(3)
2.570(2) 2.582(2) 2.605(2) 2.621(2)
Sr(1)eO(3) Sr(1)eO(20A)#2 Sr(1)/Sr(1)#1 Sr(1/Sr(1)#2
2.670(2) 2.694(2) 4.427(1) 4.600(2)
2.704(2) 2.724(2) 2.860(2) 2.866(2) 2.879(2) 2.887(2) 1.981(2)
Ba(1)eO(10) Ba(1)eO(10)#2 Ba(1)eO(5) Cu(1)eN(1) Cu(1)eO(1) Cu(1)eO(2) Ba(1)/Ba(1)#1
2.900(3) 2.945(2) 3.005(2) 1.962(2) 1.972(2) 1.980(2) 4.232(1)
Symmetry transformations used to generate equivalent atoms for 1: #1 xþ1, y, z; for 2: #1 xþ1, yþ1, zþ1; #2 xþ2, yþ1, zþ1; for 3: #1 xþ1, yþ1, zþ1; #2 x, yþ1, zþ1.
Compound 2 exhibits a 2D network structure, which is constructed from {LCu}2 dimers connected with {Sr2} units, which is fabricated by two Sr2þ ions bridged via two m2-O bridges (Fig. 3c). As in Fig. 3a, the oxygen-bridged {Sr2} units are connected with each other to form a zigzag chain through the m3-O bridges, which are from carboxylates. The {LCu}2 dimer is fabricated by a pair of metalloligand LCu connected by two CueO bridges (Fig. 3b). With the connection between {LCu}2 dimers and {Sr2} units, aforementioned zigzag chains are pillared by {LCu}2 dimers to the 2D sheet. These sheets are further extended to a 3D supramolecular structure via the OeH/O hydrogen bonds (Fig. S2, Table S2). Compared to the coordination mode of Ca atom in compound 1, each Sr atom here is coordinated with eight O atoms in which five O atoms are from water molecules with the remainder three ones are from carboxylates. Bond lengths of SreO are in the range of 2.562(4) to 2.762(3) Å. The coordination mode of Cu atom in compound 2 is also different with that of compound 1. In compound 2, the Cu atom is coordinated with two N atoms and four O atoms from two pyridine-2,4-dicarboxylate ligand and one H2O molecule, forming a distorted octahedral configuration. Bond lengths of CueO and CueN range from 1.963(3) to 2.784(1) Å and 1.985(5) to 1.991(5) Å. The shortest distance of Sr/Sr and Cu/Cu are 4.427(1) Å and 3.540(1) Å, while the shortest distance of Sr/Sr between neighbouring sheets is 5.020(1) Å. 3.4. Crystal structure of 3
Fig. 1. View of LCu in 1. All hydrogen atoms are omitted for clarity.
Compound 3 features a 1D sandwich like chain structure, which is built from 1D {Ba}n chain connected with metalloligands LCu. As shown in Fig. 4a, the Ba atoms are bridged by two m2-O bridges to form a zigzag chain. Such {Ba}n chain then connects with metalloligands LCu to form a sandwich like chain via the BaeO bonds, in which the O atoms are from carboxylates (Fig. 4b). Interestingly, this sandwich like chain have two kinds of bridging modes, double bridge (two m2-O bridges) and quadruple bridge (two m2-O bridges and two m3-O bridges), which appear alternately in the chain. These chains are also further extended to a 3D supramolecular structure via the OeH/O hydrogen bonds (Fig. S3, Table S3). In compound 3, each Ba atom is coordinated with nine O atoms. Among these O
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Fig. 2. Hydrogen-bonded Ca chain along a axis.
Fig. 3. (a) {Sr} chain in compound 2. (b) LCu dimmer in compound 2. View of 2D network in compound 2. (c) All hydrogen atoms are omitted for clarity.
atoms, two of them are from carboxylates, while residual seven ones are from water molecules. The lengths of BaeO bond fall in the range of 2.7035(2) to 3.0054(2) Å. The coordination mode of Cu atom is the same as that of compound 1. The distance of Ba$$$Ba in the double bridge form is 4.814 Å, while the value in quadruple bridge is 4.232(2) Å. The shortest distances of Cu/Ba and Cu/Cu are 5.173 Å and 7.113 Å, respectively. 3.5. Coordination modes of alkaline-earth ions Although the alkaline-earth ions in all three coordination compounds 1e3 have the same chemical valence, the coordination numbers of them are quite different. As in compound 1, each Ca2þ ion is coordinated with seven O atoms with the radius as 0.99 Å. The Sr2þ and Ba2þ ions are eight- and nine-coordinated in compounds 2e3, in which the alkaline-earth radiuses are 1.13 Å and 1.35 Å respectively. It seems that the coordination numbers of alkaline-earth ions are in positive correlation with their radiuses. Due to the different coordination modes of alkaline-earth ions, the molecular structures of compounds 1e3 vary from 0D discrete
compound, 1D chain to 2D network framework. In particular, the metalloligands LCu in compound 2 have been changed into {LCu}2 dimers. 3.6. Thermogravimetric analysis Thermal properties of all three compounds were evaluated by thermogravimetric from 25 C to 800 C in a nitrogen atmosphere with a heating rate of 10 C$min1. TGA measurements revealed that compounds 1e3 are unstable in N2 atmosphere with the increase in temperature. As shown in the Fig. 5, the first weight loss of compound 1 (8.34%) occurs from 67 C to 115 C, corresponding to the loss of three water molecules per unit of [Ca(H2O)7][LCu$H2O]$ H2O (calcd: 9.34%). Further weight loss of 6.24% appears from 146 C to 201 C, corresponding to the loss of two water molecules (calcd: 6.23%). After 331 C, the organic groups start to lose and the structure of compound 1 begins to decompose. As for compound 2, the first weight loss of 9.08% (calcd: 9.56%) is observed from 72 C to 151 C, which is in accordance with the loss of three water molecules. The second weight loss of 6.52% occurs from 153 C to
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Fig. 4. (a) View of {Ba} chain in compound 3. (b) Chain structure of compound 3. All hydrogen atoms are omitted for clarity.
3.7. Magnetic property of compound 2 To gain further insight into the structure of LCu dimmer in compound 2, the magnetic property of compound 2 was studied. Variable-temperature magnetic susceptibility measurement was performed on powder sample in the temperature range of 2e300 K with a field of 1000 Oe. As shown in Fig. 6a, cmT value of compound 2 at room temperature per Cu2 unit is 0.971 cm3 K mol1, which is close to the expected value of 1.0 cm3 K mol1 for two spin-only CuⅡ ion with S ¼ 1/2, g ¼ 2.00. Upon sample cooling, the cmT value decreases continuously. The variation tendency of cmT value from room temperature to 2 K reveals a intradimer antiferromagnetic behavior. As in Fig. 6b, the magnetic data in the range of 30e300 K followed the CurieeWeiss law with a Curie constant of C ¼ 1.014 cm3 K mol1 and a negative Weiss constant of q ¼ 15.680 K, which confirm the weak antiferromagnetic interactions between two Cu2þ centers at 30e300 K.
4. Conclusion Fig. 5. TGA curves of compounds 1, 2 and 3.
C,
232 which is corresponding to the loss of two water molecules (calcd: 6.31%). As the temperature increases, the 2D network structure of compound 2 begins to collapse after 339 C. The first weight loss of 14.95% for compound 3 is observed from 82 C to 169 C, which is corresponding to six water molecules (calcd: 15.58%). After that, the structure keeps stable until 330 C. With the increase in temperature, the 1D chain structure of compound 3 begins to collapse.
In summary, three interesting coordination compounds have been synthesized from metalloligand LCu and alkaline-earth ions (Ca2þ 1, Sr2þ 2, and Ba2þ 3). All three compounds were wellcharacterized by elemental analysis, infrared spectroscopy, thermogravimetric and single-crystal X-ray diffraction analysis. X-ray crystallographic analysis shows that compound 1 is a 0D discrete structure, while compounds 2 and 3 exhibit 2D network and 1D chain structure, respectively. Compound 2 is constructed from {LCu}2 dimers connected with {Sr2} units, which is fabricated by two Sr2þ ions bridged with two m2-O bridges, while of compound 3 is formed by metalloligands LCu linked with 1D oxygen bridged {Ba}n chain and exhibits a sandwich like chain structure. Interestingly, the coordination numbers of alkaline-earth ions in these
Q. Zhou et al. / Journal of Molecular Structure 1119 (2016) 340e345
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dx.doi.org/10.1016/j.molstruc.2016.04.034.
References
Fig. 6. (a) cmT versus T curve of compound 2. (b) c1 m versus T curve of compound 2.
compounds are in positive correlation with their radiuses. Additionally, the magnetic property of compound 2 has been investigated. Acknowledgments Financial support from the National Natural Science Foundation of China (Grants 50925207, 51172100, and 51432006), the Ministry of Science and Technology of China for the International Science Linkages Program (Grant 2011DFG52970), the Ministry of Education of China for the Changjiang Innovation Research Team (Grant IRT13R24), and the Ministry of Education and the State Administration of Foreign Experts Affairs for the 111 Project (Grant B13025) are gratefully acknowledged. Appendix A. Supplementary data Supplementary data related to this article can be found at http://
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