Hydrothermal syntheses, structural characterizations and magnetic properties of cobalt(II) and manganese(II) coordination polymeric complexes containing pyrazinecarboxylate ligand

www.elsevier.com/locate/ica Inorganica Chimica Acta 328 (2002) 152– 158

Hydrothermal syntheses, structural characterizations and magnetic properties of cobalt(II) and manganese(II) coordination polymeric complexes containing pyrazinecarboxylate ligand Yu-Cang Liang, Mao-Chun Hong *, Jia-Cheng Liu, Rong Cao * State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, People’s Republic of China Received 8 June 2001; accepted 2 October 2001

Abstract Two novel coordination polymeric complexes [Co(pzca)2(H2O)]n (1) and [Mn(pzca)2]n (2) (pzca=2-pyrazinecarboxylate) have been synthesized by hydrothermal reaction of M(CH3COO)2·4H2O (M= Co, Mn) and 2-pyrazinecarboxylic acid. The complex 1 displays an infinite zigzag chain structure in which each cobalt(II) center was coordinated by three nitrogen and three oxygen atoms to generate a CoN3O3 octahedral geometry. The existence of hydrogen bond leads to the formation of the interpenetrating stacking structure. Complex 2 indicates a two-dimensional layer structure through the linkage of bridging oxygen atom of pzca ligand. Each Mn(II) center exhibits a distorted octahedral coordination environment with four oxygen atoms and two nitrogen atoms. The distances of adjacent Mn(II) atoms are 3.503 and 5.654 A, , respectively. The magnetic property analyses reveal that both complexes show weak antiferromagnetic exchange interactions between the metal centers. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Cobalt coordination polymer; Manganese coordination polymer; Hydrothermal synthesis; Crystal structures; Magnetic property

1. Introduction The research on transition metal coordination complexes has been rapidly expending because of their fascinating structural diversity and potential applications as functional materials [1 – 8]. Many coordination complexes with one-, two- and three-dimensional infinite structures have been studied, in which the choice of the organic ligand is a key step for the formation of the complexes. For instances, bridging ligands of polycarboxylate and polyamine or organic ligands containing nitrogen and oxygen hybrid atom were often used. Recently, several novel structural coordination polymers containing the derivative of pyrazinecarboxylate or pyridinecarboxylate have been obtained [9 – 11], such as [Fe{Ni(bpca)2}1.5](ClO4)2 (Hbpca =bis(2-pyridylcar* Corresponding authors. Tel.: + 86-591-379 2460; fax: + 86-591371 4946.

bonyl)amine) possessing a graphite-like structure with large cavity [11a], and [Cu9(C19H16N9O2)6](NO3)12· 9H2O having square grid structure [11b]. Our interest is to apply hydrothermal reaction to construct some coordination polymeric complexes having novel structural type using some simple ligand and to study magnetic properties of these compounds. In this paper, we wish to report the crystal structures and magnetic properties of two novel coordination polymers, [Co(pzca)2(H2O)]n (1) and [Mn(pzca)2]n (2) (pzca= 2-pyrazinecarboxylate), which were synthesized by hydrothermal reaction.

2. Experimental All reagents were commercially available and used without further purification. Elemental analyses of C, H, N were performed with a Perkin –Elmer model 240C automatic instrument at this institute.

0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 7 1 6 - 2

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2.1. Preparation of coordination polymers 2.1.1. [Co(pzca)2(H2O)]n (1) The mixture of Co(CH3COO)2·4H2O (0.125 g, 0.5 mmol), 2-pyrazinecarboxylic acid (0.124 g, 1.0 mmol), and H2O (14.0 ml) in the mole ratio of approximately 1:2:160 was sealed in a 25 ml stainless-steel reactor with Teflon liner and heated to 120 °C at speed 32 °C per hour and kept at constant temperature at 120 °C for 48 h, then slowly cooled to 30 °C at a rate of 3 °C per hour. Red polyhedral crystals of 1 were obtained in 74% yield. Anal. Calc. for C10H8CoN4O5: C, 37.17; H, 2.50; N, 17.34. Found: C, 37.18; H, 2.32; N, 17.37%. IR data (KBr pellet, w (cm − 1)): 3199 vs br, 1668 vs, 1599 s, 1410 s, 1336 vs, 1169 s, 1159 s, 1041 s, 866 s, 793 s, 735 s, 494 m, 478 m, 455 m. 2.1.2. [Mn(pzca)2]n (2) A mixture of Mn(CH3COO)2·4H2O (0.244 g, 1.0 mmol), 2-pyrazinecarboxylic acid (0.248 g, 2.0 mmol), and H2O (14.0 ml) in the mole ratio of approximately 1:2:80 in a 25 ml stainless-steel reactor with Teflon liner was heated to 120 °C at speed 10 °C per hour and kept at constant temperature for 72 h, then slowly cooled to 30 °C at a rate of 3.3 °C per hour. Bright-yellow Table 1 Crystallographic parameters of complexes 1 and 2 Compound Empirical formula Formula weight Space group a (A, ) b (A, ) c (A, ) h (°) i (°) k (°) V (A, 3) Z zcal (g cm−3) T (K) v (mm−1) u (A, ) (Mo Ka) F(000) 2q Range (°) Reflections measured Independent reflections Observed reflection Variables R a (I\2|(I)) Rw b (I\2|(I)) S Largest difference peak and hole (e A, −3)

1 C10H8CoN4O5 323.13 P212121 7.7914(2) 9.9662(4) 15.1083(6) 90 90 90 1173.17(7) 4 1.829 293(2) 1.490 0.71073 652 4.90–50.06 3243 1961 1961 183 0.0460 0.1054 1.082 1.425, −0.488

2 C10H6MnN4O4 301.13 P21/c 10.194(3) 10.917(3) 10.112(4) 90 107.97(2) 90 1070.5(6) 4 1.868 293(2) 1.251 0.71073 604 4.20–50.06 3531 1859 1855 172 0.0488 0.1033 1.054 0.464, −0.634

R =S Fo − Fc )/S Fo . Rw = [Sw(F o2−F c2)2]/S wFo 2]1/2. Weighting: 1, w=1/[| 2(F o2)+ (0.0698P)2], where P =(F o2+2F c2)/3; 2, w=1/[| 2(F o2)+(0.0465P)2+ 1.1782P]. a

b

153

crystals of 2 were obtained. Yield: 78%. Anal. Calc. for C10H6MnN4O4: C, 39.89; H, 2.01; N, 18.61. Found: C, 39.83; H, 1.96; N, 18.60%. IR data (KBr pellet, w (cm − 1)): 1664 vs, 1624 s, 1578 s, 1525 s, 1473 m, 1417 s, 1383 s, 1354 s, 1344 s, 1304 s, 1186 s, 1161 s, 1051 s, 1039 s, 889 m, 850 s, 802 s, 791 s, 731 s, 557 m, 449 s, 434 m.

2.2. Magnetic measurements and spectroscopy The magnetic susceptibility data were collected as polycrystalline samples at an external field of 10 kG for compound 1 and 2 on a Quantum Design PPMS model 6000 magnetometer in the temperature range from 5 to 300 K. The output data were corrected for experimentally determined diamagnetism of the sample holder and the diamagnetism of the samples calculated from the Pascal’s constants [12]. The IR spectra were recorded on a Magna750 FT IR spectrophotometer using the KBr pellet technique in range of 4000–400 cm − 1.

2.3. X-ray structural analyses of complexes The single crystals of complex 1 and 2 were mounted on glass fibers and coated with epoxy resin. The intensity data of 1 and 2 were collected on a SIEMENS SMART CCD diffractometer with graphite-monochromated Mo Ka (u=0.71073 A, ) radiation in the … −2q scanning mode at 293 K. The data were corrected for Lorentz and polarization effects as well as absorption. All structures were solved by direct methods. The heavy atoms were located from the E-maps, other non-hydrogen atoms were derived from the successive difference Fourier syntheses. The organic hydrogen atoms were generated geometrically (CH bond fixed at 0.96 A, ), and allowed to ride on their parent carbon atoms before the final cycle of refinement. The aqua hydrogen atoms were located from difference maps, and refined isotropic thermal parameters. All structures were refined on F 2 by full-matrix least-squares methods using the SHELXTL-97 program package on a Legend 586 computer. All non-hydrogen atoms were refined anisotropically. Crystallographic parameters of complex 1 and 2 are summarized in Table 1.

3. Results and discussion

3.1. IR spectroscopy The IR spectrum of complex 1 displays a broad band at 3199 cm − 1, corresponding to the OH stretching vibration of coordinated water molecule. The peaks at 1668 cm − 1 is attributed to the w(CO) stretching vibration of carboxylate group of pzca ligand, and 1336

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Fig. 1. The unit structure of 1, 30% probability thermal ellipsoids are shown. Table 2 Selected bond lengths (A, ) and angles (°) for complex 1 Bond lengths CoO(1) CoO(3) CoO(5)

2.040(4) 2.046(4) 2.098(4)

CoN(3) CoN(1) CoN(2)i

2.123(5) 2.144(5) 2.193(4)

Bond angles O(1)CoO(3) O(1)CoO(5) O(3)CoO(5) O(1)CoN(3) O(3)CoN(3) O(5)CoN(3) O(1)CoN(1) O(3)CoN(1) O(5)CoN(1)

176.62(16) 90.40(16) 87.88(16) 97.97(16) 79.11(16) 89.56(17) 79.40(16) 103.53(17) 91.09(17)

N(3)CoN(1) O(1)CoN(2)i O(3)CoN(2)i O(5)CoN(2)i N(3)CoN(2)i N(1)CoN(2)i C(5)O(1)Co C(10)O(3)Co

177.29(19) 93.75(16) 88.03(16) 175.74(19) 90.82(18) 88.73(16) 117.6(3) 117.6(4)

Symmetry transformations used to generate equivalent atoms: i: −x, y−1/2, −z+3/2.

cm − 1 is due to the w(CO) stretching vibration of carboxylate group. All these exhibit that carboxylate group of pzca ligand adopts a monodentate coordination mode to bond to Co(II) atom. The IR spectrum of complex 2 is similar to that of compound 1. The peak at 1664 cm − 1 is assigned to the stretching vibration of the CO bond and 1344, 1354 cm − 1 are CO vibration of carboxylate group of pzca ligand. Other bands of complexes 1 and 2 belong to characteristic peak of pzca ligand.

3.2. Crystal structure 3.2.1. Molecular structure of the complex [Co(pzca)2(H2O)]n (1) The unit structure of [Co(pzca)2(H2O)]n is shown in Fig. 1. Selected bond lengths and angles for 1 are listed in Table 2. The coordination environment of cobalt(II) center displays a distorted octahedral coordination geometry with three nitrogen atoms and two oxygen atoms from three different pzca ligands and another oxygen atom from coordination water in the apical

position. Two nitrogen (N(1) and N(3)) and oxygen (O(1) and O(3)) donors of chelating pzca ligands occupy basal plane site and another nitrogen atom (nonchelated N(2)) of pzca ligand bonds to cobalt(II) atom in apical fashion to form an infinite zigzag structure through CoN(2) bond. The dihedral angle of two chelating pzca ligand is 8.1°. The coordination environment of Co(II) in 1 is different from the coordination sphere of the Co(II) center found in the discrete coordination compound Co(C4N2COO)2(H2O)2 and [Co(C4N2COO)2(H2O)2]·2H2O, in which the Co(II) site in a pseudo-octahedral mode [8a]. The distances of CoO(O(1), O(3) and O(5)) and CoN(N(1), N(2) and N(3)) range from 2.040(4) to 2.098(4) and from 2.123(5) to 2.193(4) A, , respectively. The O(1)CoO(3) and N(1)CoN(3) bond angle is 176.62(16) and 177.29(19) A, , respectively. The N(2A)CoO(5) angle is 175.74(19) A, . In addition, the weak interaction of the hydrogen bond (O(5)H···O(3) is 2.693 A, ) between adjacent zigzag chain leads to the formation of a two-dimensional interpenetrating packing structure (Fig. 2).

3.2.2. Molecular structure of the complex [Mn(pzca)2]n (2) Single crystal X-ray diffraction analysis reveals that complex 2 is a 2D layer structure which consists of the basic unit Mn(pzca)2, as illustrated in Fig. 3. Selected bond lengths and angles of complex 2 are given in Table 3. Each manganese(II) center displays a distorted octahedral coordination environment with four oxygen atoms and two nitrogen atoms, which two oxygen (O(1), O(3)) atoms of carboxylate group and its adjacent nitrogen (N(1), N(3)) atoms from two pzca ligands coordinated to manganese(II) atom along two different direction to form two five-membered chelating rings, and other two oxygen atoms which one from the unchelated oxygen (O(2A)) atom and another from the chelated oxygen (O(3B)) atom of carboxylate group of the adjacent basic unit Mn(pzca)2. In complex 2, the carboxylate group of pzca ligand acts as two coordination roles that are shown in Scheme 1. According to the coordination mode of Scheme 1(a), the chelated oxygen (O(3)) atom adopts m3-bridging formation to link two neighboring basic Mn(pzca)2 units to fabricate binuclear unit Mn2(pzca)4 and MnMn distance is 3.503 A, . The binuclear unit were connected further together through a bridging oxygen atom of pzca ligand that adopts m2-O coordination mode (Scheme 1(b)) to entrain an extend two-dimensional layer structure (Fig. 4). Except chelated nitrogen atom (N(1), N(3)) in pzca ligand, other nitrogen atom (N(2), N(4)) is free. The 2D layer structure can also be described as: the basal unit Mn(pzca)2 was linked by a bi-bridging oxygen atom (O(2)) of carboxylate group of pzca ligand to generate an infinite chain structure and the adjacent MnMn distance is 5.654 A, . The neighboring chain was con-

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Fig. 2. The interpenetrated packing structure of complex 1 along [100] plane.

nected further together through m3-bridging oxygen atom of carboxylate group of pzca ligand to indicate a 2D layer structure. The distance between layer and layer is 9.70 A, . The distances of MnO and MnN are compatible to that of the previous reported compound [H3O]2x [Mn(pyzdc)2]x (pyzdc =2,3-pyrazinedicarboxylate) [13] and [{Na2Mn4(sal)4(pyca)4(MeOH)2}n ]·2nH2O (H2sal=salicylic acid, Hpyca=pyridine-2-carboxylic acid) [14].

seen, the MT magnitude continuously decreases upon cooling from 2.19 cm3 K mol − 1 at room temperature, to 1.33 cm3 K mol − 1 at 5 K. On the other hand, the inverse susceptibility plot is a linear as a function of temperature, data closely follow a Cure–Weiss law with C=2.207(1) cm3 K mol − 1, corresponding to about one S= 3/2 spin per formula unit with g=2.17(1) of Co(II)

4. Magnetic properties The temperature dependence of the molar magnetic susceptibility has been measured in the range of 5–300 K for complexes 1 and 2. The results are displayed in 1 the form of MT (insert  − M ) versus T, T being the absolute temperature, and M is the corrected molar magnetic susceptibility per Co (1) or per Mn (2).

4.1. [Co(pzca)2(H2O)]n (1) The magnetic data of 1 are displayed in Fig. 5 1 plotted as thermal variation of MT and  − M . As can be

Fig. 3. The unit structure of 2, 50% probability thermal ellipsoids are shown.

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Table 3 Selected bond lengths (A, ) and angles (°) for complex 2 Bond lengths MnO(2)I MnO(3)ii MnO(1)

2.100(3) 2.133(3) 2.206(3)

MnO(3) MnN(3) MnN(1)

2.217(3) 2.283(4) 2.312(4)

Bond angles O(2)iMnO(3)ii O(2)iMnO(1) O(3)iiMnO(1) O(2)iMnO(3) O(3)iiMnO(3) O(1)MnO(3) O(2)iMnN(3) O(3)iiMnN(3)

98.87(13) 158.96(13) 95.71(13) 112.98(13) 72.75(12) 85.80(12) 93.68(13) 144.85(13)

O(1)MnN(3) O(3)MnN(3) O(2)iMnN(1) O(3)iiMnN(1) O(1)MnN(1) O(3)MnN(1) N(3)MnN(1)

82.85(13) 72.12(12) 91.05(13) 96.35(13) 72.24(12) 154.59(13) 116.20(14)

Symmetry transformations used to generate equivalent atoms: i: x, −y+3/2, z+1/2; ii: −x+1, −y+2, −z.

Scheme 1. The coordination mode of pzca ligand in complex 2.

% =

Ng 2i 2S(S+ 1) (1+u) × 3kT (1−u)

where u= coth

(1)

JS(S+ 1) kT − kT JS(S+1)

M = % +TIP

(2)

The best-fit parameters are g= 2.123(2), J= − 0.669(9) cm − 1, TIP = 0.00036(3), R= 1.7×10 − 4 [R= [(MT)obs − (MT)cal]2/(MT)2obs]. The small value of J is consistent with weak antiferromagnetic coupling between paramagnetic spin sites, which suggested that m-(O,N,N)-pzca coordination provides weak exchange interaction.

4.2. [Mn(pzca)2]n (2) In Fig. 6, at room temperature, the value of the MT product (4.04 cm3 K mol − 1) is smaller than that expected for an uncoupled manganese(II) (g=2.0) ion (4.38 cm3 K mol − 1). As the temperature decreases, MT decreases and reaches 1.29 cm3 K mol − 1 at 5 K. This magnetic behavior is clearly indicative of antifer1 romagnetic interactions. In fact, as shown in the  − M versus T plot, data obey a Curie–Weiss law with C= 4.139(1), corresponding to about one S= 5/2 spin (g = 1.94) per formula unit, and [= − 8.24(5) K. We employed a simple Heisenberg models as an approximate approach based on its structure to study the magnetic properties. The first was based on a Hamiltonian type uniform chain [H= − JSAiSAi + 1 +

Fig. 4. 2D layer structure of 2 (all hydrogen atoms and uncoordinated atoms (C3, C4, C5, C8, C9, C10, N2 and N4) are omitted for clarity).

center. The Weiss temperature is [ = − 3.98 K. These results are indicative of the occurrence of antiferromagnetic coupling between metallic Co(II) centers. The magnetic data were analyzed on Fisher chain model [15], which is valid for large values of S. Taking into account Tip term, the experimental MT of complex 1 is actually fitted by Eq. (2).

Fig. 5. Top: Thermal variations of the magnetic susceptibility MT vs. T plot for [Co(pzca)2(H2O)]n (1) in the range 5 – 300 K. Bottom: 1 Thermal variations of the magnetic susceptibility  − M vs. T plot for [Co(pzca)2(H2O)]n (1) in the range 5 – 300 K. Solid line corresponds to the best fitted curves by using the parameters described in the text.

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1 Fig. 6. Thermal variations of the magnetic susceptibility MT and  − M (inset) vs. T plot for [Mn(pzca)2]n (2) in the range 5 – 300 K. Solid line corresponds to the best fitted curves by using the parameters described in the text.

D[S 2Ai(z) − SA(SA +1)/3]] formed by the OCO bridges, Eq. (1), in which J was treated as the intrachain exchange constant. Then the interactions bridged by the double m3-O bridges of pzca ligand were taken as interchain interactions using the molecular field approximation, Eq. (3) [16], in which J% is the interchain coupling constant through m3-O bridges, and Z is the number of nearest neighbors. M =

%M 1−(2zJ% ׁ%M/Ng 2i 2)

(3)

The best fit with MT (shown in Fig. 6) leads to the following parameters: g = 1.936(1), J = −0.73(1) cm − 1, zj % = −0.06(2) cm − 1 (z =1), R = 1.8 ×10 − 4 [R = [(MT)obs − (MT)cal]2/(MT)2obs]. We attempt to investigate the magnetic data in the second model, the dimmers [Mn2](II) formed by double m3-O bridges were considered, and the corresponding molar magnetic susceptibility is represented by using Heisenberg models (H= − 2JS1S2, S1 =S2 =5/2) and Eq. (4) [17], M =

2Ng 2i 2 e2x +5e6x +30e20x +55e30x × kT 1+ 3e2x +5e6x +7e12x +9e20x +11e30x (4)

where N, g, i, x are the Avogadro number, g factor, Bohr magneton and J/kT. The exchange interaction through OCO bridges may be treated as an intermolecular exchange interaction zj % by a molecular field model using Eq. (3). The least-squares fitting of the experimental MT gives g = 1.936(1), J = −0.482(8) cm − 1, zj %= − 0.154(8) cm − 1 (z =4), R = 1.8 ×10 − 4

[R= [(MT)obs − (MT)cal]2/(MT)2obs]. It can be seen that the values of g and R from the former model are equal to those obtained from the later, respectively. It is worthwhile noting that there are two pathways between bridged carboxylate manganese atoms, MnO COMn and MnOCCNMn. MnOCOMn is main magnetic exchange pathway. The comparable complex of single carboxylato bridge is very few, a dinuclear Mn(II) complex [{Mn(bipy)2(H2O)}2(g= 1.970, J= {(CH3)3NCH2CO2}](ClO4)4·2H2O −0.193 cm − 1) [18] and [Mn(MCPA)2(H2O)2]n, where MCPA = 2-methyl-4-chorophenoxyacetic acid, (g= 1.90, J = − 0.30(1) cm − 1) [19]. The 5.598 A, of Mn···Mn separation in [{Mn(bipy)2(H2O)}2{(CH3)3NCH2CO2}](ClO4)4·2H2O is slightly longer than that found in [Mn(MCPA)2(H2O)2]n (Mn···Mn = 5.4 A, ). The increased J absolute value of the antiferromagnetic interaction is probably related to the smaller separation of two paramagnetic manganese centers bridged by the carboxylato group. The Mn···Mn separation 5.654 A, in present complex is possibly corresponding to smaller J absolute value, which is − 0.04 cm − 1 of the exchange constant found in second model. On the other hand, the shorter Mn···Mn distances bridged by oxygen atom provide probably slightly stronger antiferromagnetic exchange interaction than that by carboxylato bridge [ J(m-O) \ J(m-OCO) ]. J(m-O) and J(m-OCO) are − 0.06 and −0.73 cm − 1 in first model, −0.482 and − 0.04 cm − 1 in second model, respectively. Second model can better elaborate the magnetic exchange, weak antiferromagnetic interaction are mainly from MnOMn exchange pathway.

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5. Supplementary material Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Center as supplementary publication: CCDC 163728 for 1 and CCDC 163729 for 2, respectively. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: + 44-1223-336-033; e-mail: [email protected]. ac.uk).

Acknowledgements This work was supported by grants from the National Natural Science Foundation of China, the State Key Laboratory of Structural Chemistry, and Superintendent Foundation of this Institute.

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