Synthesis, crystal structure and magnetic properties of a chain coordination polymer {[Cu4L2(H2O)] · H2O}n

Inorganica Chimica Acta 359 (2006) 2053–2058 www.elsevier.com/locate/ica

Synthesis, crystal structure and magnetic properties of a chain coordination polymer {[Cu4L2(H2O)] Æ H2O}n Ruo-Jie Tao a,*, Fu-An Li a, Yan-Xiang Cheng b,*, Shuang-Quan Zang a, Qing-Lun Wang c, Jing-Yang Niu a, Dai-Zheng Liao c b

a College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475001, China Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China c Department of Chemistry, Nankai University, Tianjin 300071, China

Received 21 September 2005; received in revised form 16 January 2006; accepted 17 January 2006 Available online 6 March 2006

Abstract A chain coordination polymer with the chemical formula {[Cu4L2(H2O)] Æ H2O}n, has been synthesized by the assembly reaction of K2CuL Æ 1.5H2O and Cu(OAC)2 Æ H2O with a 1:1 mole ratio in methanol, where H4L = 2-hydroxy-3-[(E)-({2-[(2-hydroxybenzoyl)imino]ethyl}imino)methyl] benzoic acid, OAC = CH3COO. The crystal structure was determined by single-crystal X-ray diffraction analysis, the compound has chain molecular structure formed by dissymmetrical tetranuclear units. The magnetic measurements showed that Cu–Cu of the complex exhibit antiferromagnetic interactions, and satisfactory fittings to the observed magnetic susceptibility data were obtained by assuming a binuclear system, and further using molecular field approximation to deal with magnetic exchange interactions between binuclear systems.  2006 Published by Elsevier B.V. Keywords: Copper; Coordination polymer; Crystal structure; Magnetic properties

1. Introduction The rational design and synthesis of novel coordination polymers are of current interest in the field of supramolecular chemistry and crystal engineering, not only because of their intriguing structural motifs but also because of their potential application in catalysis, magnetism, and molecular sensing [1–3]. Consequently, a variety of coordination polymers with interesting compositions and topologies have been prepared through taking certain factors into account, such as the coordination nature of the metal ion and the shape, functionality, flexibility, and symmetry of organic ligand [4], of which many examples are derived from multicarboxylate ligands [5], not from multifunction ligands. *

Corresponding authors. E-mail addresses: [email protected] (R.-J. Tao), [email protected] (Y.-X. Cheng). 0020-1693/$ - see front matter  2006 Published by Elsevier B.V. doi:10.1016/j.ica.2006.01.004

The ligands containing amido and phenoxo groups are known to be versatile organic ligands, which can chelate as well as bridge metal ions to construct discrete and extended structures. This kind of mononuclear complexes and their polynuclear complexes have been designed and obtained in the literature [6–11]. These complexes are all discrete polynuclear molecules, while coordination polymers related to these groups are very limited so far. Carboxylate group is a very good bridging group [12–18]. When Carboxylate group linked to these molecules, these discrete polynuclear molecules may be further united together to form supermolecular complexes or coordination polymers. With this idea, we have successfully synthesized Schiff-base ligand H4L with phenol–oxygen, amido and carboxylate groups, and obtained the copper precursors complex K2CuL Æ 1.5H2O. Through ‘‘complex as ligand’’, we have successfully synthesized copper coordination polymer {[Cu4L2(H2O)] Æ H2O}n with 1D chain, and investigated its magnetic properties.

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2. Experimental O

2.1. Syntheses

C OEt OH + NH2

3-Carboxylsalicylidene was prepared by the literature method [19], 1-(2-hydroxybenzamido)-2-(amino)ethane was prepared by the literature method [7]. Other chemicals were of reagent grade and obtained commercially without further purification.

O O

C NH OH

+ NH2

2.2. Physical measurements Elemental analyses for carbon, hydrogen and nitrogen were carried out on a Perkin–Elmer 2400II analyzer. The metal contents were determined by EDTA titration. The infrared spectra were recorded on an Avatar-360 spectrometer using KBr pellets in a range of 400–4000 cm1. The temperature-dependent Magnetic susceptibilities in temperature range of 5–300 K under a constant external magnetic field of 10 KG were measured with a MPMS-7 SQUID magnetometer.

N

O Cu(OAC)2·H2O

H4L

O Cu

N C H

C O

H 2-

C N

OH OH

C

O

H

NH2

CH3OH

2.1.2. Synthesis of the title complex A methanol solution (100 mL) of the K2CuL Æ 1.5H2O (0.25 g, 0.5 mmol) was gently poured into a methanol solution (100 mL) of copper acetate monohydrate (0.12 g, 0.5 mmol) at ambient temperature. The resulting solution was allowed to stand for several days. The light red crystals that formed were collected by filtration and dried in air. The yield based on (Cu2L Æ Cu2(H2O)L) Æ H2O: 93.37%. The crystals were not soluble in common organic and inorganic solvents, only soluble in dimethyl sulphoxide (DMSO). Therefore, the single crystals suitable for X-ray analysis were grown by a slow diffusion method using a test-tube. 5 mL of 5 mmol L1 Cu(OAC)2 Æ H2O aqueous solution, 10 mL 3:1 (v:v) ethanol–water solution and 5 mL of 5 mmol L1K2CuL Æ 1.5H2O methanol solution were carefully added orderly to a 30 mL test-tube from the bottom to the top, and then the top of the tube was sealed. The light red single crystals of the title complex were formed at the upper interface in a month. Anal. Calc. for C34H28Cu4N4O12: Cu, 27.08; C, 43.50; H, 3.01; N, 5.97. Found: Cu, 27.12; C, 43.61; H, 3.10; N, 6.01%. IR (KBr pellet, cm1): mC@O(amido moiety) at 1647 cm1. The synthesis route is shown in Scheme 1.

OH C

C

{[Cu4L2(H2O)]·H2O}n

2.1.1. Syntheses of the ligand H4L and the copper precursor (K2CuL Æ 1.5H2O) [20] The ligand H4L was synthesized by the reaction of 1-(2hydroxybenzamido)-2-(amino)ethane (0.55 g, 3 mmol) and 3-carboxyl salicylidene (0.50 g, 3 mmol) with a 1:1 mole ratio at 60 C for 2 h in 50 mL ethanol. The copper precursor (K2CuL Æ 1.5H2O) was prepared by the reaction of H4L (0.66 g, 2 mmol), KOH (0.45 g, 8 mmol) and copper(II) acetate monohydrate (0.40 g, 2 mmol) with a 1:4:1 mole ratio at 60 C for 2 h.

OH

O

C NH OH

KOH O

O

Cu(OAC)2·H2O

C O

K2CuL1.5H2O

Scheme 1. Synthetic route.

2.3. Crystallographic studies The single crystals used for data collection of the title complex (0.375 · 0.222 · 0.114 mm3) were selected and mounted on a Bruker Smart APEX diffractometer with CCD detector using graphite monochromated Mo Ka ˚ ). Data were collected by the x radiation (k = 0.71073 A scan mode at 293(2) K to a hmax of 26.40 with a total 9455 reflection collected including 6567 independent reflections (Rint = 0.0545). A summary of the crystallographic data is given in Table 1. Lorentz and polarization factors were made for the intensity data and absorption corrections were performed using SADABS program [21]. The crystal structures were solved using the SHELXTL program and refined using full-matrix least-squares [22]. The positions of hydrogen atoms were calculated theoretically and included in the final cycles of refinement in a riding model along with attached carbons. Selected bond distances and bond angles are given in Table 2. Table 1 Crystal data and structure refinement for the title complex Parameters Empirical formula Formula weight Crystal system Space group ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z h, k, l h DCalc (g cm3) ˚) k(Mo Ka) (A l(Mo Ka) (mm1) T (K) R1[(I > 2r)]a wR2 a

C34H28Cu4N4O12 938.804 triclinic P 1 10.479(2) 10.889(2) 15.191(3) 90.935(3) 106.893(3) 93.564(3) 1654.2(5) 2 13 < h < 11,  13 < k < 11,  19 < l < 18 1.40 6 h 6 26.40 1.885 0.71073 2.611 293(2) 0.0414 0.1040

w1 ¼ ½r2 ðF 2o Þ þ ð0:0600P Þ2 þ 0:0000P ; p ¼ ½ðF 2o Þ þ 2F 2c =3.

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Table 2 ˚ ) and bond angles () for the title complex Selected bond length (A

3.2. Description of crystal structure

Bond length Cu1–O2 Cu1–N2 Cu1  Cu2 Cu2–O2 Cu2–O9#1 Cu3–N4 Cu3–O6 Cu3  Cu4 Cu4–O5 Cu4–O7

Crystallographic data of the title complex are summarized in Table 1. Selected bond distances and bond angles are shown in Table 2. Each unit of the title complex consists of a dissymmetrical tetranuclear unit and a solvent water molecule (Fig. 1). The tetranuclear unit comprises two different neutral binuclear moieties Cu1Cu2(H2O)L (Cu1Cu2(H2O)L = A) and Cu3Cu4L (Cu3Cu4L = B), which are united together by the carboxylic group (O3C17O4) of A moiety. The dihedral of A and B moieties is 83.3. In A moiety, the Cu1 has square planar coordination geometry with the N2O2 (N1, N2, O1 and O2) donor ˚ ) distance are shorter atoms. The Cu1–O2(amido) (1.898(2) A ˚ ), but Cu1–N disthan that of Cu1–O1Schiff (1.933(2) A tances (Cu1–N1 = 1.900(3), Cu1–N2 = 1.905(3)) have only small difference in the moiety. The Cu2 ion are coordinated by two bridged phenoxo atoms (O1 and O2), one carboxylic oxygen atom (O3) from A, one oxygen atom (Ow1) from water molecule and one amido oxygen atom (O9#1) from A moiety (A#1) of the adjacent unit to form a pentacoordinated geometry with O5 oxygen atoms, as shown in Figs. 1 and 2a. Both Cu–N and Cu–O distances are similar to the literature [6,7,16]; the Cu1  Cu2 distance ˚ ) is considerably shorter than that of (3.0005(7) A ˚ ) in the literature [6]. From Cu(1)  Cu(2) (3.132(2) A Fig. 2a, we can also find that the A moiety and the A#1 moiety of the adjacent unit are bridged together through two coordination bonds Cu2–O9#1 and Cu2#1–O9 ˚ ) to form a novel cyclic cylindrical tetranuclear (2.114(6) A structure (AA). From bond angles, the pentacoordinated Cu2 (or Cu2#1) has three almost coplanar bonds Cu2– O9#1, Cu2–Ow1, Cu2–O1 with the bond angles of O1– Cu2–O9#1 = 142.61(11), O9#1–Cu2–Ow1 = 102.73(11), Ow1–Cu2–O1 = 114.43(11) and two axial bonds Cu2– O2, Cu2–O3 with the bond angle of O2–Cu2– O3 = 166.79(9). Therefore, the pentacoordinated Cu2 (or Cu2#1) are located at distorted trigonal bipyramidal geometry. The structure of B moiety is similar to that of A moiety except as follows: (1) Cu3–N4(adiom) distance (1.889(3)) are shorter than that of Cu3–N3(Schiff) (1.903(3)); (2) Although

Bond angles O2–Cu1–N1 N1–Cu1–N2 N1–Cu1–O1 O3–Cu2–O2 O2–Cu2–O1 O2–Cu2–O9#1 O3–Cu2–Ow1 O1–Cu2–Ow1 N4–Cu3–O6 N4–Cu3–O5 O6–Cu3–O5 O7–Cu4–O5 O7–Cu4–O6 O5–Cu4–O6 O4–Cu4–O10#2 O6–Cu4–O10#2

1.898(2) 1.905(3) 3.0005(7) 1.976(2) 1.990(2) 1.889(3) 1.900(2) 2.9851(7) 1.969(2) 1.909(3) 174.78(10) 86.15(12) 94.71(10) 166.79(9) 76.91(9) 95.62(9) 89.26(11) 114.43(11) 97.66(12) 173.78(11) 81.98(10) 90.20(11) 167.13(11) 78.13(10) 119.77(10) 91.56(10)

Cu1–N1 Cu1–O1 Cu2–O1 Cu2–Ow1 Cu2–O3 Cu3–O5 Cu3–N3 Cu4–O10#2 Cu4–O4 Cu4–O6 O2–Cu1–N2 O2–Cu1–O1 N2–Cu1–O1 O3–Cu2–O1 O3–Cu2–O9#1 O1–Cu2–O9#1 O2–Cu2–Ow1 O9#1–Cu2–Ow1 N4–Cu3–N3 N3–Cu3–O6 N3–Cu3–O5 O7–Cu4–O4 O4–Cu4–O5 O4–Cu4–O6 O7–Cu4–O10#2 O5–Cu4–O10#2

1.900(3) 1.933(2) 1.989(2) 2.152(3) 1.926(2) 1.924(2) 1.903(3) 2.205(3) 1.933(2) 2.011(2) 98.75(11) 80.12(9) 168.55(12) 89.88(9) 94.73(10) 142.61(11) 96.42(10) 102.73(11) 87.42(14) 174.74(12) 93.12(12) 88.13(12) 144.56(10) 99.16(11) 93.36(12) 95.66(10)

(#1) x + 1, y + 1, z + 1; (#2) x + 1, y + 2, z.

3. Results and discussion 3.1. Syntheses ‘‘Bridging ligand complex’’ K2CuL Æ 1.5H2O plays a very important role during the construction of the coordination polymers. Through self-assembly method, 1D chain coordination polymers with carboxylate and amido bridges have been obtained. The single crystals suitable for X-ray analysis are obtained by the slow diffusion method in test-tube. Because the K2CuL Æ 1.5H2O were not soluble in ethanol and slowly hydrolyze in water, the ethanol– water solution with higher ethanol contents was used as separating layer to decrease the diffusion and the hydrolysis of the K2CuL Æ 1.5H2O in water.

Fig. 1. The tetranuclear dissymmetrical unit of the title complex. The hydrogen atoms are omitted for clarity.

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Fig. 2. (a) The tetranuclear cycle is constructed by Cu3Cu4L moieties of two adjacent units and selected atoms are labeled. (b) The tetranuclear cycle is constructed by Cu1Cu2(H2O)L moieties of two adjacent units and selected atoms are labeled.

Cu4 is still a distorted trigonal bipyramidal configuration, the coordination atoms are very different from Cu2. Cu4 ion is coordinated by two bridged phenoxo atoms (O5, O6), one carboxylic oxygen atom (O7), one carboxylic oxygen atom (O4) from A moiety and an amido oxygen atom (O10#2) from the B moiety (B#2) of the another adjacent unit, as shown in Figs. 1 and 2b; (3) The carboxylic group (O7C34O8) in B moiety are not a bridge group, as shown in Figs. 1 and 2b. Similar to A, a cyclic cylindrical tetranuclear structure (BB) is also formed by the coordination bonds Cu4#2–O10 and Cu4–O10#2 (Fig. 2b). From above discussion, the dissymmetrical unit forms two different tetranuclear cycles (AA and BB) through Cu2–O9#1, Cu2#1–O9, Cu4#2–O10 and Cu4–O10#2. A number of dissymmetrical tetranuclear units are united together by these coordination bonds between amido oxygen atoms and CuII ions to form a novel . . .(AA)(BB)(AA)(BB)(AA)(BB). . .1D chain, as shown in Fig. 3. No hydrogen bonds are shown in the interchains (Fig. 3).

3.3. IR spectra The ligand H4L exhibits an intense absorption band assignable to the mC@O vibration of the amido moiety at 1638 cm1, the band shifted to higher frequency by 6 and 15 cm1 in IR spectra of the K2CuL Æ 1.5H2O and the title complex [6,7], respectively. Owing to the conjugation of C@N group on the aromatic ring, mC@N band of the H4L occurs at 1590 cm1; The bands shifted to higher frequency by 5 and 6 cm1 in IR spectra of the K2CuL Æ 1.5H2O and the title complex, respectively. The COO asymmetrical vibration bands of the title complex mas(coo) exhibits two intense absorption at 1567 and 1524 cm1, which may be attributed to mas(coo) bands of the monodentate and the bidentate coordination carboxyl groups, while two intense absorption at 1396 and 1437 cm1 may be assigned to ms(coo) the symmetrical vibration bands of monodentate and bidentate coordination carboxyl groups.

Fig. 3. Showing two adjacent chains for the title compound.

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3.4. Magnetic properties The variable temperature magnetic susceptibility data for a crystalline sample of the title complex were measured on a MPMS-7 SQUID magnetometer over the temperature range of 5–300 K. The plots of leff (where leff is the effective magnetic moment) and vM versus T are shown in Fig. 4, at 300 K, leff is equal to 2.52 BM, a value slightly larger than that expected for two non-interacting S = 1/2 CuII centers 2.49 BM. With decreasing the temperature, the leff value decreases steadily approaching a minimum at around 5 K with leff = 0.59 BM. The temperature behavior of the magnetic susceptibility of the title complex indicates that the S = 1/2 state of these Cu(II) ions are antiferromagnetically coupled interactions. There are at least three kinds of magnetic interactions for the present systems, namely: (i) CuII–CuII through phenoxo bridge; (ii) CuII1CuII2–CuII4CuII3 through carboxylate oxygen bridge; (iii) CuII1CuII2–CuII1#1Cu2#2 through amido bridge, as shown in Fig. 2. These magnetic interactions compete to produce the magnetic property of the title complex. We take the system as an isolated binuclear moiety with only (i) CuII–CuII through phenoxo bridges and take (ii) and (iii) into account in the interactions of these binuclear moieties. The magnetic analysis was then carried out by using the theoretical expression of the magnetic susceptibility deduced from the spin Hamiltonian ^ ¼ 2J S^Cu1 S^Cu2 . The expression of the magnetic susceptiH bility for a CuII1–CuII2 system is   2Ng2 b2 1 vM ¼ þ N a; 3 þ expð2J =KT Þ KT N a ¼ 120  10

6

3

cm mol ;

3 0.010

0.008

μeff / B.M.

3

χ M /cm mol

-1

2 0.006

0.004

1

0.002

0.000

0 50

netic interactions between binuclear systems, Na is the temperature- independent paramagnetism. The agreement with the observed magnetic susceptibility is good except at low temperature where the calculated values are lower than the experimental ones. The discrepancy is probably due to paramagnetic impurities, whose contribution becomes relevant when the compound is practically diamagnetic. In order to overcome it, we introduce q to take into account the presence of such impurities. Thus, the expression of the magnetic susceptibility for this system becomes v0M ¼ vM ð1  qÞ þ

Ng2 b2 X S I ðS i þ 1Þ  q. 3KT

The best fit to the experimental data gives J = 2 1 0 130.5 cm1, g = 2.26, q = 4.51 P · 10 , zj =21.18 P 2cm . The agreement factor R ¼ ðvobsd  vcalcd Þ = vobsd is 6.65 · 103, which corresponds to a good agreement as seen in Fig. 4. The negative J and zj 0 values suggest that the interactions between CuII1 and CuII2 ions, and between binuclear systems are all antiferromagnetic. 4. Supplementary material Crystallographic data (excluding structure factors) for the structural analysis has been deposited with the Cambridge Crystallographic Data Centre as Supplementary Publication No. 281761 for the title complex. Copies of the data can be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44 1223 336 033; e-mail: [email protected]). Acknowledgments

1

and further using molecular field approximation to deal with magnetic exchange interactions between binuclear systems. vM v0M ¼ ; 0 1  ð2zj =Ng2 b2 ÞvM where J is the exchange integral between two copper ions inner the binuclear moiety (Cu1 and Cu2), zj 0 is the mag-

0

2057

100

150

200

250

300

T/K Fig. 4. The plots of leff and vM of the title complex vs. T.

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