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Synthesis, crystal structure and magnetic properties of novel copper(II)–nickel(II) complexes of macrocyclic oxamides
Polyhedron 20 (2001) 923– 927 www.elsevier.nl/locate/poly
Synthesis, crystal structure and magnetic properties of novel copper(II) –nickel(II) complexes of macrocyclic oxamides En-Qing Gao* a,1, Dai-Zheng Liao* b,2, Zong-Hui Jiang b, Shi-Ping Yan b a
Department of Chemistry, Qufu Normal Uni6ersity, Qufu, 273165 Shandong, People’s Republic of China b Department of Chemistry, Nankai Uni6ersity, Tianjin 300071, People’s Republic of China Received 23 October 2000; accepted 11 January 2001
Abstract Three novel oxamido-bridged heterobinuclear copper(II)– nickel(II) complexes derived from macrocyclic oxamido compounds have been synthesized and characterized by IR, ESR and electronic spectra. They are of the formula [(CuL1)Ni(pmtn)(NCS)]ClO4 (1), [Cu(L2)Ni(pmtn)(NCS)]ClO4 (2) and [(CuL3)Ni(pmtn)(NCS)]ClO4 (3), where H2L1 = 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclopentadeca-7,12-diene, H2L2 = 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)3 1,4,8,11-tetraazacyclotetradeca-7,11-diene and H2L = 2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12- bis(ethoxycarbonyl)-1,4,8,11tetraazacyclotetradeca-7,11-diene, respectively. The crystal structure of 2 has been determined by X-ray crystallography. The nickel(II) ion is pseudo-octahedrally coordinated and the copper(II) ion is in a distorted square-pyramidal environment. The temperature dependence of the magnetic susceptibility for 1 and 2 has been analyzed using the Hamiltonian H. = −2JS. 1·S. 2, leading to J= −47.5 and −47.2 cm − 1, for 1 and 2, respectively. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Macrocyclic compound; Copper(II)–nickel(II) complexes; Crystal structures; Magnetism
1. Introduction Polynuclear complexes are of interest for designing new magnetic materials and for investigating the structure and the role of the polymetallic active sites in biological systems [1 – 3]. A very useful strategy to design polynuclear species is the ‘complex as ligand’ approach, i.e. using mononuclear complexes that contain potential donor groups to coordinate to another metal ion [4–7]. By using mononuclear Cu(II) complexes of some N,N%-bis(coordinating group substituted) oxamides such as [Cu(oxpn)] and [Cu(obze)]2 − (Scheme 1) as ligands, many oxamido-bridged polynuclear complexes have been prepared and studied magnetically in recent years [6 – 13]. Recently, this approach has been extended by using the macrocyclic analogues of the above oxamides [14 – 17]. Non-cyclic oxamides
1
*Corresponding author. Tel.: + 86-537-4455961; [email protected] 2 *Corresponding author.
may adopt a cis or trans conformation on coordination, and this flexibility allows less control over the type of complex formed [6,7]. The macrocyclic oxamides allow us to synthesize polynuclear systems in a more controlled fashion. We have reported a series of heterotetranuclear [(CuLi)3M] species (M= transition metal ions) derived from mononuclear copper(II) complexes of [15]N4 and [14]N4 macrocyclic oxamides (Scheme 1, [CuLi], i =1–3) [14 –16]. Robertson et al. have also reported the synthesis and magnetic properties of [CuII 3] trinuclear complexes derived from [CuL4] (Scheme 1) [17]. In addition, these macrocyclic complexes are potentially of bioinorganic relevance. In continuation of our work on polynuclear complexes of macrocyclic oxamides, here we report the synthesis and characterization of three heterobinuclear CuIINiII complexes: [(CuL1)Ni(pmtn)(NCS)]ClO4 (1), [Cu(L2)Ni(pmtn)(NCS)]ClO4 (2) and [(CuL3)Ni(pmtn)(NCS)]ClO4 (3), where pmtn= N,N,N%,N%,N¦pentamethyldiethylenetriamine. The crystal structure of 2 and the magnetic properties of 1 and 2 were investigated.
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 1 ) 0 0 7 5 5 - 0
E.-Q. Gao et al. / Polyhedron 20 (2001) 923–927
924
Scheme 1. Some oxamido–Cu(II) complexes that have been used as ligands
2. Experimental
2.1. Materials and syntheses All chemicals were of A. R. grade and used as received, The mononuclear precursors, [CuL1], [CuL2], [CuL3] were prepared as described elsewhere [15]. The binuclear complexes 1 3 were prepared as follows: a solution of pmtn (0.3 mmol) in ethanol (10 ml) and the solid samples of [(CuLi)] (i= 1, 2 or 3, 0.3 mmol) and NH4SCN (0.3 mmol) were successively added to the solution of Ni(ClO4)2·6H2O (0.3 mmol) in ethanol (10 ml). The mixture was stirred at 60– 70°C for 1.5 h and then left to cool down. The resulting dark green (for 1) or dark red (for 2 and 3) polycrystalline product was filtered off and recrystallized from ethanol –acetone (1:1). Yield, 75– 86%. Good prism crystals of 2 were obtained by slow evaporation of its solution in acetonitrile–n-butanol. All efforts to grow single crystals of the other two compounds failed. Anal. Found: C, 44.87; H, 5.51; N, 11.80. Calc. for C35H47N8O10SClCuNi (1): C, 45.22; H, 5.10; N, 12.05%. Anal. Found: C, 44.50; H, 5.28; N, 12.63. Calc. for C34H45N8O10SClCuNi (2): C, 44.60; H, 4.95; N, 12.24%. Anal. Found: C, 45.15; H, 5.33; N, 12.01. Calc. for C35H47N8O10SClCuNi (3): C, 45.22; H, 5.10; N, 12.05%. Main IR bands (KBr pellet, cm − 1): 1, 2050s, 1728s, 1620sh, 1580s (br), 1545s, 1470m, 1435m, 1340s, 1190m, 1075s; 2, 2075s, 1730s, 1620sh, 1595s, 1574s, 1545s, 1475m, 1435m, 1340m, 1195s, 1070s; 3, 2050s, 1730s, 1620sh, 1595s, 1573s, 1545m, 1465m, 1432m, 1338s, 1195m, 1080s. Molar conductance (10 − 3 mol l − 1 acetonitrile solution, V − 1 cm2 mol − 1): 1, 125; 2, 136; 3, 139.
2.2. Physical measurements Elemental analyses (C, H, N) were performed on a Perkin –Elmer 240 analyzer. Conductivities of the complexes in acetonitrile were measured using a DDS-11A conductometer. IR spectra were recorded on a Shimadzu IR-408 spectrometer as KBr pellets, electronic
spectra on a Shimadzu UV-365 UV– Vis – NIR recording spectrophotometer in acetonitrile, and X-band ESR spectra on a Bruker ER 200 D-SRC ESR spectrometer. Variable-temperature magnetic susceptibilities were measured on a Quantum Design MPMS-7 SQUID magnetometer. Diamagnetic corrections were made with Pascal’s constants for all the constituent atoms [18].
2.3. X-ray crystallography A single crystal of 2 of dimensions 0.20× 0.20×0.15 mm was mounted on a Bruker Smart 1000 area detector diffractometer with graphite-monochromated Mo Ka radiation (u= 0.71073 A, ). A total of 8220 unique reflections (Rint = 0.1369) were measured at 298(2) K within 3.36° 5 2q552.92°. The structure was solved by the direct method and successive Fourier difference synthesis, and refined by the full-matrix least-squares method on F 2 with anisotropic thermal parameters for all non-hydrogen atoms [19]. Hydrogen atoms were generated geometrically and refined isotropically. A total of 505 parameters were refined. The final refinement converged at R1 = 0.0615, wR2 = 0.0896 for 3600 observed reflections with I] 2|(I), and R1 =0.1700, wR2 = 0.1138 for all data with S= 0.922. The largest difference peak and hole were 0.544 and − 0.637 e A, 3, respectively. Crystal data: C34H45ClCuN8NiO10S, M=915.54, monoclinic, P21/c, a =19.632(2), b= 15.3969(17), c= 13.2888(13) A, , i=94.658(2)°, V= 4003.6(7) A, 3, Z=4. 3. Results and discussion
3.1. General characterization The molar conductance values of complexes 1 –3 fall within the range expected for 1:1 electrolytes [20], indicating that the perchlorate ion is non-coordinated in acetonitrile solutions. The IR spectra of the three complexes are very similar. The very sharp band at approximately 2050 cm − 1 is characteristic of thiocyanate ions coordinating
E.-Q. Gao et al. / Polyhedron 20 (2001) 923–927
Fig. 1.
ORTEP
925
view of the binuclear complex cation in 2.
to metal ions through nitrogen [21]. The broad strong band at approximately 1080 cm − 1 is due to perchlorate ions. The bands at approximately 1730 and 1630 cm − 1, which show no significant shift relative to the corresponding bands of the mononuclear [CuLi] complexes (i= 1 –3), are attributed to w(CO) (ester) and w(CN), respectively [15]. The strong w(CO) (oxamido) band observed at approximately 1650 cm − 1 for the mononuclear precursors [15] is replaced by a strong band at approximately 1580 cm − 1 in the spectra of the binuclear complexes. The significant bathochromic shift is consistent with the decrease in the CO bond strengths on coordination, as is confirmed by X-ray crystallographic studies (6ide infra). The electronic absorption spectra of the three binuclear complexes in acetonitrile below 500 nm are dominated by intense bands due to intra-ligand and charge-transfer transitions in the Cu(II) chromophore. In the 500–1200 nm region, they exhibit two broad bands: (i) a weak near-infrared absorption (m = 37–45 M − 1 cm − 1) centered at 1028, 1032 and 1030 nm for 1, 2 and 3, respectively, assignable to the 3A2g(Ni) 3 T2g(Ni) transition, assuming a Oh site symmetry for Ni(II); (ii) for 1, a stronger band centered at 625 nm (m= 285 M − 1 cm − 1), mainly attributed to the envelope of the d –d transitions of Cu(II) in an approximate square-planar environment [22]. The corresponding band for 2 and 3 appears at approximately 520 nm as a shoulder of the charge-transfer band. Such a significant red shift in the maximum of the d– d (Cu) band for 1 relative to those for 2 and 3 has also been observed for the corresponding [CuLi] species, where the red shift has been attributed to the more significant distortion of the CuN4 chromophore in [CuL1] relative to those in [CuL2] and [CuL3] [22]. The other two spin-allowed transitions for the Ni(II) chromophore may be obscured by the d–d and charge-transfer bands in the Cu(II) chromophore.
3.2. Structure of [Cu(L 2)Ni(pmtn)(NCS)]ClO4 (2) The structure of complex 2 consists of heterobinuclear cations [Cu(L2)Ni(pmtn)(NCS)]+ and weakly coordinated perchlorate ions. A perspective view of the complex cation is depicted in Fig. 1. Selected bond lengths and angles are listed in Table 1. In the binuclear unit, the copper and nickel atoms are bridged by an oxamido group. The copper atom resides in the coordination cavity of the deprotonated [14] N4 macrocyclic oxamido ligand. The deviations of the four donor atoms from the mean plane are 9 0.112(2)–0.114(3) A, , and the copper atom is only 0.003(2) A, out of the plane. A perchlorate ion is weakly Table 1 Selected bond lengths (A, ) and angles (°) for 2 Bond distances Ni(1)N(8) Ni(1)N(7) Ni(1)O(1) Cu(1)N(3) Cu(1)N(2) Cu(1)O(7) O(1)C(1) N(1)C(1) N(1)C(7) N(4)C(6) N(4)C(4) S(1)C(34)
2.014(5) 2.160(4) 2.118(3) 1.919(4) 1.936(4) 2.749(5) 1.245(5) 1.339(6) 1.418(6) 1.279(6) 1.480(6) 1.630(7)
Bond angles N(8)Ni(1)O(2) 93.25(17) N(8)Ni(1)N(5) 92.9(2) N(6)Ni(1)N(7) 83.60(18) O(2)Ni(1)O(1) 76.42(12) O(2)Ni(1)N(7) 166.32(16) N(3)Cu(1)N(1) 87.07(16) N(1)Cu(1)N(2) 94.76(17) N(1)Cu(1)N(4) 173.47(17)
Ni(1)N(6) Ni(1)N(5) Ni(1)O(2) Cu(1)N(1) Cu(1)N(4) C(1)C(2) O(2)C(2) N(3)C(2) N(3)C(13) N(2)C(5) N(2)C(3) N(8)C(34)
2.119(5) 2.193(5) 2.103(3) 1.920(4) 1.941(4) 1.527(6) 1.245(5) 1.328(5) 1.418(6) 1.294(6) 1.470(6) 1.154(7)
N(8)Ni(1)O(1) 90.64(18) N(8)Ni(1)N(7) 91.7(2) N(6)Ni(1)N(5) 83.5(2) O(1)Ni(1)N(5) 163.55(17) N(8)Ni(1)N(6) 173.18(19) N(3)Cu(1)N(2) 172.96(17) N(3)Cu(1)N(4) 93.13(17) N(2)Cu(1)N(4) 85.82(17)
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E.-Q. Gao et al. / Polyhedron 20 (2001) 923–927
and 1.334 A, , respectively, while the corresponding distances for the mononuclear [CuL2] precursor are 1.211 and 1.355 A, , respectively [22]. The increase in the CO distances and the decrease in the CN ones in the binuclear complex reflect the delocalization of the electron density from the nitrogen atoms towards the oxygen atoms upon the coordination of the oxygen atoms to Ni(II).
3.3. ESR spectra
Fig. 2. Polycrystalline X-band ESR spectra of complexes 1 and 2 at room temperature.
The polycrystalline X-band ESR spectra for complexes 1 and 2 were measured at room temperature and are shown in Fig. 2. The two complexes present very similar behavior, exhibiting a broad band centered at approximately g=2.26 and another broad signal with the maximum at g=5.41 for 1 and g= 4.85 for 2. The antiferromagnetic interaction in CuIINiII pairs gives rise to an S=1/2 ground state and an S= 3/2 excited state. According to Escuer et al. [9], the allowed 1/2, −1/ 2 1/2, 1/2 transition within the doublet state will exhibit a resonance at a field close to g= 2. On the other hand, assuming that the zero-field splitting of the quartet state is axial, the allowed transition within the 3/2, 91/2 Kramer’s doublet will produce two resonant signals: one near g= 2 and the other at approximately half-field with g\ 4 [9]. According to magnetic studies (6ide infra), the doublet–quartet gap 3J (B 150 cm − 1) is smaller than the kT value at room temperature (approximately 205 cm − 1), suggesting that the excited quartet state is significantly populated. The signals of the quartet state are superimposed on that of the doublet state to produce the observed spectra.
3.4. Magnetic properties Fig. 3. M vs T and MT vs T plots for complexes 1 and 2.
coordinated to the copper(II) ion [Cu1O7 = 2.749(5) A, ]. The copper(II) ion may be said to assume a distorted square-pyramidal coordination geometry (4+ 1) with the perchlorate ion at the apical position. The nickel atom is in a distorted octahedral environment. The tridentate pmtn ligand coordinates to the nickel(II) ions in a meridional fashion, with the two terminal nitrogen atoms (N5 and N7) being trans to the two oxamido oxygens (O1 and O2) from the macrocyclic ligand. The coordination polyhedron around nickel is completed by the nitrogen atom of a thiocyanato ion. The C2O2N2 bridging group is approximately planar, and the copper and nickel atoms are displaced towards the opposite sides of the bridge plane by −0.396(5) and 0.175(5) A, , respectively. The Cu···Ni separation within the binuclear cation is 5.34 A, . The average CO and CN bond lengths in the bridging group are 1.245
The temperature dependence of the molar magnetic susceptibility (M) and its product with temperature (MT) for 1 and 2 are shown in Fig. 3, respectively. The MT products at room temperature are 1.26 and 1.21 cm3 mol − 1 K for 1 and 2, respectively, below the spinonly value (1.38 cm3 mol − 1 K) expected for an uncoupled Cu(II)Ni(II) pair. The product for each compound decreases as the temperature is lowered, and finally reaches a plateau below approximately 30 K, with MT= 0.42 0.41 cm3 mol − 1 K, respectively. These features are quite typical of isolated Cu(II)Ni(II) pairs with antiferromagnetic intramolecular interaction. The plateaus indicate that only the doublet ground state is thermally populated at low temperature. The magnetic data were fitted on the basis of the isotropic model H. = − 2JS. 1·S. 2, where J is the interaction parameter between two paramagnetic centers. For copper(II)–nickel(II) complexes, the theoretical expression of the magnetic susceptibility is
M =
Ni g 4kT
2 1/2
2 3/2
+10g exp(3J/kT) 1+ 2 exp(3J/kT)
n
E.-Q. Gao et al. / Polyhedron 20 (2001) 923–927
where the gS (S= 1/2, 3/2) factors are related to local g factors by g1/2 =(4gNi −gCu)/3, and g3/2 =(2gNi + gCu)/ 3. The simulations of the experimental data using the above expression are quite satisfactory, as shown in Fig. 3. The best-fitted parameters are J = −47.5 cm − 1, gNi =2.12, gCu =2.15 with R = 3.7 ×10 − 4 for 1 and J= − 47.2 cm − 1, gNi =2.08, gCu =2.02 with R = 4.2× 10 − 5 for 2, where R is defined as R = (obsd −calcd2)/ 2obsd. 4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 151036. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk). Acknowledgements This work was supported by the Natural Science Foundation of China (No. 20071019).
References [1] O. Kahn, Struct. Bond. (Berlin) 68 (1987) 89. [2] D. Gatteschi, O. Kahn, J.S. Miller, F. Palacio (Eds.), Molecular Magnetic Materials, NATO ASI Series, Kluwer, Dordrecht, 1991.
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[3] E.I. Solomon, T.C. Brunold, M.Z. Davis, J.N. Kemsley, S.-K. Lee, N. Lehnert, A.J. Skulan, Y.S. Yang, J. Zhou, Chem. Rev. 100 (2000) 235. [4] S.J. Gruber, C.M. Harris, E. Sinn, J. Inorg. Nucl. Chem. 30 (1968) 1805. [5] N.B. O’Brien, T.O. Maier, I.C. Paul, R.S. Drago, J. Am. Chem. Soc. 95 (1973) 6640. [6] H. Ojima, K. Nonoyama, Coord. Chem. Rev. 92 (1988) 85. [7] R. Ruiz, J. Faus, F. Lloret, M. Julve, Y. Journaux, Coord. Chem. Rev. 193 – 195 (1999) 1069. [8] J.L. Sanz, R. Ruiz, A. Gleizes, F. Lloret, J. Faus, M. Julve, J.J. Borra´ s-Almenar, Y. Journaux, Inorg. Chem. 35 (1996) 7384. [9] A. Escuer, R. Vicente, J. Ribas, R. Costa, X. Solans, Inorg. Chem. 31 (1992) 2627. [10] Z.-Y. Zhang, D.-Z. Liao, Z.-H. Jiang, S.-Q. Hao, X.-K. Yao, H.-G. Wang, G.-L. Wang, Inorg. Chim. Acta 173 (1990) 201. [11] J. Larionova, S.A. Chavan, J.V. Yakhmi, A.G. Frøystein, J. Sletten, C. Sourisseau, O. Kahn, Inorg. Chem. 36 (1997) 6374. [12] F. Lloret, Y. Journaux, M. Julve, Inorg. Chem. 29 (1990) 3967. [13] F. Lloret, M. Julve, R. Ruiz, Y. Journaux, K. Nakatani, O. Kahn, J. Sletten, Inorg. Chem. 32 (1993) 27. [14] E.-Q. Gao, G.-M. Yang, J.-K. Tang, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, Polyhedron 18 (1999) 3643. [15] E.-Q. Gao, G.-M. Yang, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, G.-L. Wang, H.-Z. Kou, Trans. Met. Chem. 24 (1999) 244. [16] E.-Q. Gao, G.-M. Yang, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, G.-L. Wang, J. Chem. Res. (S) (1999) 278. [17] L. Cronin, A.R. Mount, S. Parsons, N. Robertson, J. Chem. Soc., Dalton Trans. (1999) 1925. [18] P.W. Selwood, Magnetochemistry, Interscience, New York, 1956 (p. 78). [19] G.M. Sheldrick, SHELXS-97 and SHELXL-97, Software for Crystal Structure Analysis; Siemens Analytical X-ray Instruments Inc., Wisconsin, Madison, USA, 1997. [20] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81. [21] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed., Wiley, New York, 1997. [22] E.-Q. Gao, W.-M. Bu, G.-M. Yang, D.-Z. Liao, Z.-H. Jiang, S.-P. Yan, G.-L. Wang, J. Chem. Soc., Dalton Trans. (2000) 1431.
Synthesis, crystal structure and magnetic properties of novel copper(II) –nickel(II) complexes of macrocyclic oxamides En-Qing Gao* a,1, Dai-Zheng Liao* b,2, Zong-Hui Jiang b, Shi-Ping Yan b a
Department of Chemistry, Qufu Normal Uni6ersity, Qufu, 273165 Shandong, People’s Republic of China b Department of Chemistry, Nankai Uni6ersity, Tianjin 300071, People’s Republic of China Received 23 October 2000; accepted 11 January 2001
Abstract Three novel oxamido-bridged heterobinuclear copper(II)– nickel(II) complexes derived from macrocyclic oxamido compounds have been synthesized and characterized by IR, ESR and electronic spectra. They are of the formula [(CuL1)Ni(pmtn)(NCS)]ClO4 (1), [Cu(L2)Ni(pmtn)(NCS)]ClO4 (2) and [(CuL3)Ni(pmtn)(NCS)]ClO4 (3), where H2L1 = 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclopentadeca-7,12-diene, H2L2 = 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)3 1,4,8,11-tetraazacyclotetradeca-7,11-diene and H2L = 2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12- bis(ethoxycarbonyl)-1,4,8,11tetraazacyclotetradeca-7,11-diene, respectively. The crystal structure of 2 has been determined by X-ray crystallography. The nickel(II) ion is pseudo-octahedrally coordinated and the copper(II) ion is in a distorted square-pyramidal environment. The temperature dependence of the magnetic susceptibility for 1 and 2 has been analyzed using the Hamiltonian H. = −2JS. 1·S. 2, leading to J= −47.5 and −47.2 cm − 1, for 1 and 2, respectively. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Macrocyclic compound; Copper(II)–nickel(II) complexes; Crystal structures; Magnetism
1. Introduction Polynuclear complexes are of interest for designing new magnetic materials and for investigating the structure and the role of the polymetallic active sites in biological systems [1 – 3]. A very useful strategy to design polynuclear species is the ‘complex as ligand’ approach, i.e. using mononuclear complexes that contain potential donor groups to coordinate to another metal ion [4–7]. By using mononuclear Cu(II) complexes of some N,N%-bis(coordinating group substituted) oxamides such as [Cu(oxpn)] and [Cu(obze)]2 − (Scheme 1) as ligands, many oxamido-bridged polynuclear complexes have been prepared and studied magnetically in recent years [6 – 13]. Recently, this approach has been extended by using the macrocyclic analogues of the above oxamides [14 – 17]. Non-cyclic oxamides
1
*Corresponding author. Tel.: + 86-537-4455961; [email protected] 2 *Corresponding author.
may adopt a cis or trans conformation on coordination, and this flexibility allows less control over the type of complex formed [6,7]. The macrocyclic oxamides allow us to synthesize polynuclear systems in a more controlled fashion. We have reported a series of heterotetranuclear [(CuLi)3M] species (M= transition metal ions) derived from mononuclear copper(II) complexes of [15]N4 and [14]N4 macrocyclic oxamides (Scheme 1, [CuLi], i =1–3) [14 –16]. Robertson et al. have also reported the synthesis and magnetic properties of [CuII 3] trinuclear complexes derived from [CuL4] (Scheme 1) [17]. In addition, these macrocyclic complexes are potentially of bioinorganic relevance. In continuation of our work on polynuclear complexes of macrocyclic oxamides, here we report the synthesis and characterization of three heterobinuclear CuIINiII complexes: [(CuL1)Ni(pmtn)(NCS)]ClO4 (1), [Cu(L2)Ni(pmtn)(NCS)]ClO4 (2) and [(CuL3)Ni(pmtn)(NCS)]ClO4 (3), where pmtn= N,N,N%,N%,N¦pentamethyldiethylenetriamine. The crystal structure of 2 and the magnetic properties of 1 and 2 were investigated.
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 1 ) 0 0 7 5 5 - 0
E.-Q. Gao et al. / Polyhedron 20 (2001) 923–927
924
Scheme 1. Some oxamido–Cu(II) complexes that have been used as ligands
2. Experimental
2.1. Materials and syntheses All chemicals were of A. R. grade and used as received, The mononuclear precursors, [CuL1], [CuL2], [CuL3] were prepared as described elsewhere [15]. The binuclear complexes 1 3 were prepared as follows: a solution of pmtn (0.3 mmol) in ethanol (10 ml) and the solid samples of [(CuLi)] (i= 1, 2 or 3, 0.3 mmol) and NH4SCN (0.3 mmol) were successively added to the solution of Ni(ClO4)2·6H2O (0.3 mmol) in ethanol (10 ml). The mixture was stirred at 60– 70°C for 1.5 h and then left to cool down. The resulting dark green (for 1) or dark red (for 2 and 3) polycrystalline product was filtered off and recrystallized from ethanol –acetone (1:1). Yield, 75– 86%. Good prism crystals of 2 were obtained by slow evaporation of its solution in acetonitrile–n-butanol. All efforts to grow single crystals of the other two compounds failed. Anal. Found: C, 44.87; H, 5.51; N, 11.80. Calc. for C35H47N8O10SClCuNi (1): C, 45.22; H, 5.10; N, 12.05%. Anal. Found: C, 44.50; H, 5.28; N, 12.63. Calc. for C34H45N8O10SClCuNi (2): C, 44.60; H, 4.95; N, 12.24%. Anal. Found: C, 45.15; H, 5.33; N, 12.01. Calc. for C35H47N8O10SClCuNi (3): C, 45.22; H, 5.10; N, 12.05%. Main IR bands (KBr pellet, cm − 1): 1, 2050s, 1728s, 1620sh, 1580s (br), 1545s, 1470m, 1435m, 1340s, 1190m, 1075s; 2, 2075s, 1730s, 1620sh, 1595s, 1574s, 1545s, 1475m, 1435m, 1340m, 1195s, 1070s; 3, 2050s, 1730s, 1620sh, 1595s, 1573s, 1545m, 1465m, 1432m, 1338s, 1195m, 1080s. Molar conductance (10 − 3 mol l − 1 acetonitrile solution, V − 1 cm2 mol − 1): 1, 125; 2, 136; 3, 139.
2.2. Physical measurements Elemental analyses (C, H, N) were performed on a Perkin –Elmer 240 analyzer. Conductivities of the complexes in acetonitrile were measured using a DDS-11A conductometer. IR spectra were recorded on a Shimadzu IR-408 spectrometer as KBr pellets, electronic
spectra on a Shimadzu UV-365 UV– Vis – NIR recording spectrophotometer in acetonitrile, and X-band ESR spectra on a Bruker ER 200 D-SRC ESR spectrometer. Variable-temperature magnetic susceptibilities were measured on a Quantum Design MPMS-7 SQUID magnetometer. Diamagnetic corrections were made with Pascal’s constants for all the constituent atoms [18].
2.3. X-ray crystallography A single crystal of 2 of dimensions 0.20× 0.20×0.15 mm was mounted on a Bruker Smart 1000 area detector diffractometer with graphite-monochromated Mo Ka radiation (u= 0.71073 A, ). A total of 8220 unique reflections (Rint = 0.1369) were measured at 298(2) K within 3.36° 5 2q552.92°. The structure was solved by the direct method and successive Fourier difference synthesis, and refined by the full-matrix least-squares method on F 2 with anisotropic thermal parameters for all non-hydrogen atoms [19]. Hydrogen atoms were generated geometrically and refined isotropically. A total of 505 parameters were refined. The final refinement converged at R1 = 0.0615, wR2 = 0.0896 for 3600 observed reflections with I] 2|(I), and R1 =0.1700, wR2 = 0.1138 for all data with S= 0.922. The largest difference peak and hole were 0.544 and − 0.637 e A, 3, respectively. Crystal data: C34H45ClCuN8NiO10S, M=915.54, monoclinic, P21/c, a =19.632(2), b= 15.3969(17), c= 13.2888(13) A, , i=94.658(2)°, V= 4003.6(7) A, 3, Z=4. 3. Results and discussion
3.1. General characterization The molar conductance values of complexes 1 –3 fall within the range expected for 1:1 electrolytes [20], indicating that the perchlorate ion is non-coordinated in acetonitrile solutions. The IR spectra of the three complexes are very similar. The very sharp band at approximately 2050 cm − 1 is characteristic of thiocyanate ions coordinating
E.-Q. Gao et al. / Polyhedron 20 (2001) 923–927
Fig. 1.
ORTEP
925
view of the binuclear complex cation in 2.
to metal ions through nitrogen [21]. The broad strong band at approximately 1080 cm − 1 is due to perchlorate ions. The bands at approximately 1730 and 1630 cm − 1, which show no significant shift relative to the corresponding bands of the mononuclear [CuLi] complexes (i= 1 –3), are attributed to w(CO) (ester) and w(CN), respectively [15]. The strong w(CO) (oxamido) band observed at approximately 1650 cm − 1 for the mononuclear precursors [15] is replaced by a strong band at approximately 1580 cm − 1 in the spectra of the binuclear complexes. The significant bathochromic shift is consistent with the decrease in the CO bond strengths on coordination, as is confirmed by X-ray crystallographic studies (6ide infra). The electronic absorption spectra of the three binuclear complexes in acetonitrile below 500 nm are dominated by intense bands due to intra-ligand and charge-transfer transitions in the Cu(II) chromophore. In the 500–1200 nm region, they exhibit two broad bands: (i) a weak near-infrared absorption (m = 37–45 M − 1 cm − 1) centered at 1028, 1032 and 1030 nm for 1, 2 and 3, respectively, assignable to the 3A2g(Ni) 3 T2g(Ni) transition, assuming a Oh site symmetry for Ni(II); (ii) for 1, a stronger band centered at 625 nm (m= 285 M − 1 cm − 1), mainly attributed to the envelope of the d –d transitions of Cu(II) in an approximate square-planar environment [22]. The corresponding band for 2 and 3 appears at approximately 520 nm as a shoulder of the charge-transfer band. Such a significant red shift in the maximum of the d– d (Cu) band for 1 relative to those for 2 and 3 has also been observed for the corresponding [CuLi] species, where the red shift has been attributed to the more significant distortion of the CuN4 chromophore in [CuL1] relative to those in [CuL2] and [CuL3] [22]. The other two spin-allowed transitions for the Ni(II) chromophore may be obscured by the d–d and charge-transfer bands in the Cu(II) chromophore.
3.2. Structure of [Cu(L 2)Ni(pmtn)(NCS)]ClO4 (2) The structure of complex 2 consists of heterobinuclear cations [Cu(L2)Ni(pmtn)(NCS)]+ and weakly coordinated perchlorate ions. A perspective view of the complex cation is depicted in Fig. 1. Selected bond lengths and angles are listed in Table 1. In the binuclear unit, the copper and nickel atoms are bridged by an oxamido group. The copper atom resides in the coordination cavity of the deprotonated [14] N4 macrocyclic oxamido ligand. The deviations of the four donor atoms from the mean plane are 9 0.112(2)–0.114(3) A, , and the copper atom is only 0.003(2) A, out of the plane. A perchlorate ion is weakly Table 1 Selected bond lengths (A, ) and angles (°) for 2 Bond distances Ni(1)N(8) Ni(1)N(7) Ni(1)O(1) Cu(1)N(3) Cu(1)N(2) Cu(1)O(7) O(1)C(1) N(1)C(1) N(1)C(7) N(4)C(6) N(4)C(4) S(1)C(34)
2.014(5) 2.160(4) 2.118(3) 1.919(4) 1.936(4) 2.749(5) 1.245(5) 1.339(6) 1.418(6) 1.279(6) 1.480(6) 1.630(7)
Bond angles N(8)Ni(1)O(2) 93.25(17) N(8)Ni(1)N(5) 92.9(2) N(6)Ni(1)N(7) 83.60(18) O(2)Ni(1)O(1) 76.42(12) O(2)Ni(1)N(7) 166.32(16) N(3)Cu(1)N(1) 87.07(16) N(1)Cu(1)N(2) 94.76(17) N(1)Cu(1)N(4) 173.47(17)
Ni(1)N(6) Ni(1)N(5) Ni(1)O(2) Cu(1)N(1) Cu(1)N(4) C(1)C(2) O(2)C(2) N(3)C(2) N(3)C(13) N(2)C(5) N(2)C(3) N(8)C(34)
2.119(5) 2.193(5) 2.103(3) 1.920(4) 1.941(4) 1.527(6) 1.245(5) 1.328(5) 1.418(6) 1.294(6) 1.470(6) 1.154(7)
N(8)Ni(1)O(1) 90.64(18) N(8)Ni(1)N(7) 91.7(2) N(6)Ni(1)N(5) 83.5(2) O(1)Ni(1)N(5) 163.55(17) N(8)Ni(1)N(6) 173.18(19) N(3)Cu(1)N(2) 172.96(17) N(3)Cu(1)N(4) 93.13(17) N(2)Cu(1)N(4) 85.82(17)
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and 1.334 A, , respectively, while the corresponding distances for the mononuclear [CuL2] precursor are 1.211 and 1.355 A, , respectively [22]. The increase in the CO distances and the decrease in the CN ones in the binuclear complex reflect the delocalization of the electron density from the nitrogen atoms towards the oxygen atoms upon the coordination of the oxygen atoms to Ni(II).
3.3. ESR spectra
Fig. 2. Polycrystalline X-band ESR spectra of complexes 1 and 2 at room temperature.
The polycrystalline X-band ESR spectra for complexes 1 and 2 were measured at room temperature and are shown in Fig. 2. The two complexes present very similar behavior, exhibiting a broad band centered at approximately g=2.26 and another broad signal with the maximum at g=5.41 for 1 and g= 4.85 for 2. The antiferromagnetic interaction in CuIINiII pairs gives rise to an S=1/2 ground state and an S= 3/2 excited state. According to Escuer et al. [9], the allowed 1/2, −1/ 2 1/2, 1/2 transition within the doublet state will exhibit a resonance at a field close to g= 2. On the other hand, assuming that the zero-field splitting of the quartet state is axial, the allowed transition within the 3/2, 91/2 Kramer’s doublet will produce two resonant signals: one near g= 2 and the other at approximately half-field with g\ 4 [9]. According to magnetic studies (6ide infra), the doublet–quartet gap 3J (B 150 cm − 1) is smaller than the kT value at room temperature (approximately 205 cm − 1), suggesting that the excited quartet state is significantly populated. The signals of the quartet state are superimposed on that of the doublet state to produce the observed spectra.
3.4. Magnetic properties Fig. 3. M vs T and MT vs T plots for complexes 1 and 2.
coordinated to the copper(II) ion [Cu1O7 = 2.749(5) A, ]. The copper(II) ion may be said to assume a distorted square-pyramidal coordination geometry (4+ 1) with the perchlorate ion at the apical position. The nickel atom is in a distorted octahedral environment. The tridentate pmtn ligand coordinates to the nickel(II) ions in a meridional fashion, with the two terminal nitrogen atoms (N5 and N7) being trans to the two oxamido oxygens (O1 and O2) from the macrocyclic ligand. The coordination polyhedron around nickel is completed by the nitrogen atom of a thiocyanato ion. The C2O2N2 bridging group is approximately planar, and the copper and nickel atoms are displaced towards the opposite sides of the bridge plane by −0.396(5) and 0.175(5) A, , respectively. The Cu···Ni separation within the binuclear cation is 5.34 A, . The average CO and CN bond lengths in the bridging group are 1.245
The temperature dependence of the molar magnetic susceptibility (M) and its product with temperature (MT) for 1 and 2 are shown in Fig. 3, respectively. The MT products at room temperature are 1.26 and 1.21 cm3 mol − 1 K for 1 and 2, respectively, below the spinonly value (1.38 cm3 mol − 1 K) expected for an uncoupled Cu(II)Ni(II) pair. The product for each compound decreases as the temperature is lowered, and finally reaches a plateau below approximately 30 K, with MT= 0.42 0.41 cm3 mol − 1 K, respectively. These features are quite typical of isolated Cu(II)Ni(II) pairs with antiferromagnetic intramolecular interaction. The plateaus indicate that only the doublet ground state is thermally populated at low temperature. The magnetic data were fitted on the basis of the isotropic model H. = − 2JS. 1·S. 2, where J is the interaction parameter between two paramagnetic centers. For copper(II)–nickel(II) complexes, the theoretical expression of the magnetic susceptibility is
M =
Ni g 4kT
2 1/2
2 3/2
+10g exp(3J/kT) 1+ 2 exp(3J/kT)
n
E.-Q. Gao et al. / Polyhedron 20 (2001) 923–927
where the gS (S= 1/2, 3/2) factors are related to local g factors by g1/2 =(4gNi −gCu)/3, and g3/2 =(2gNi + gCu)/ 3. The simulations of the experimental data using the above expression are quite satisfactory, as shown in Fig. 3. The best-fitted parameters are J = −47.5 cm − 1, gNi =2.12, gCu =2.15 with R = 3.7 ×10 − 4 for 1 and J= − 47.2 cm − 1, gNi =2.08, gCu =2.02 with R = 4.2× 10 − 5 for 2, where R is defined as R = (obsd −calcd2)/ 2obsd. 4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 151036. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk). Acknowledgements This work was supported by the Natural Science Foundation of China (No. 20071019).
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