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A new μ1,5-dicyanamide bridged cyclic tetranuclear copper (II) complex with 1,5,9-triazacycledodecane ligands: structure, ESR spectroscopic and magnetic properties
Inorganic Chemistry Communications 6 (2003) 966–970 www.elsevier.com/locate/inoche
A new l1;5-dicyanamide bridged cyclic tetranuclear copper (II) complex with 1,5,9-triazacycledodecane ligands: structure, ESR spectroscopic and magnetic properties Wen Gu a, He-Dong Bian a, Jing-Yuan Xu a, Zhan-Quan Liu a, Peng Cheng a, Shi-Ping Yan a,b,*, Dai-Zheng Liao a, Zong-Hui Jiang a b
a Department of Chemistry, Nankai University, Tianjin 300071, PR China State Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, Beijing 100871, PR China
Received 26 February 2003; accepted 10 April 2003
Abstract The tetranuclear complex [Cu2 L2 (dca)2 (ClO4 )2 ]2 (1) (L ¼ 1,5,9-triazacyclododecane, dca ¼ dicyanamide [N(CN)2 ] ) has been synthesized and its crystal structure, ESR spectra and magnetic properties determined. The complex contains a tetranuclear copper (II) moiety in which two dimeric units are bridged by two dca ligands. In each dimeric moiety the two copper (II) ions are bridged by one l1;5 -dicyanamide ligand. Magnetic susceptibilities for the complex in the solid state are measured over the temperature range 4–300 K. The complex shows a weak antiferromagnetic coupling with a best fit J value )0.436 cm1 . The l1;5 -dicyanamide bridges are the principal pathway for the super-exchange interaction and the weak antiferromagnetic coupling of the complex is interpreted in term of the l1;5 -dicyanamide ligand behavior as a poor magnetic mediator. Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: Dicyanamide ligand; Tetranuclear copper (II) complex; Magnetic properties; Triazamacrocycle ligand
1. Introduction The design of high nuclearity transition metal complexes with novel magnetic properties is a major goal of current research [1]. Recent developments have afforded a variety of architecturally highly sophisticated polynuclear complexes such as molecular helicates, grids, ladders, rings and boxes [2]. Such complexes are of interest not only for their unusual structures [3] and the sample synthetic methods, but also because they allow to understand the relationship between the structure and the magnetic properties [4]. Recently relatively low nuclear coordination complexes (
Corresponding author. Tel.: +86-022-2350-9957; fax: +86-0222350-2779. E-mail address: [email protected] (S.-P. Yan).
clear Mn4 [5], Ni4 [6], Cu4 [7], Zn4 [8] complexes; hexanuclear Ni6 [9], Cu6 [10] complexes. Tetranuclear complexes are of current interest in bioinorganic modeling, multielectron transfer, catalytic and new extended materials, as well as in magnetochemical investigations [11]. Therein, owing to their ease of synthesis, and of the design of many tetranuclearing chelating ligands for use in bioinorganic model and magnetochemical studies, there are many examples of Cu4 complexes, which exhibit a large diversity of structural types and magnetic properties, for example, a planar Cu4 complex with diazine (N2 ) ligands [12], tetrahedral Cu4 complexes with tetradentate triazolate [13] and pyrazolate [14] ligands with (N2 ) bridges and tridentate Schiff-base ligands with sym-anti carboxylate bridges [7h]. The Cu4 O4 and Cu4 (O2 )4 systems exhibited ferromagnetic exchange while the Cu4 O2 (N2 )2 and Cu4 (N2 )4 systems exhibited antiferromagnetic exchange. Among them, structurally and magnetically characterized planar cyclic structures with no diagonal bridging groups are rather scarce [15].
1387-7003/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1387-7003(03)00144-8
W. Gu et al. / Inorganic Chemistry Communications 6 (2003) 966–970
In this paper, we have selected a 12-membered triazamacrocycle ligand 1,5,9-triazacyclododecane (L), based on ‘‘macrocyclic effect’’ of the aza macrocycles [16], and dicyanamide (dca), a diamagnetic bridging ligand, due to its ability to bound to multiple transition metal sites, such as monodentate [17], bidentate [18], tridentate [19] and tetradentate [20] coordination fashions. Polydentate dicyanamide has so far been utilized extensively to assemble transition metals into 1-, 2- and 3-D arrays [21]. It should be noted that, as far as we know, no fully structurally and magnetically characterized dicyanamide bridged discrete tetranuclear complexes have been reported. Taking into account the above-mentioned aspects, a new cyclic tetranuclear copper (II) complex [Cu2 L2 (dca)2 (ClO4 )2 ]2 (1) has been synthesized and magnetostructurally characterized.
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Table 1 Crystal data and details of the structure refinement for the complex 1 C22 H42 Cl2 Cu2 N12 O8 800.66 293(2) Monoclinic P 21 /c 15.165(6) 16.370(6) 14.329(5) 109.512(6) 3353(2) 4 1.586 1.490 6114/6114 R1 ¼ 0:0410; wR2 ¼ 0:0822 R1 ¼ 0:0885; wR2 ¼ 0:1053 0.516, )0.436
Formula Fw T/K Crystal system Space group a=A b=A c=A
b=° 3 V =A Z qcalcd /g cm3 l/mm1 Reflns, unique/observed Final R indices ½I > 2rðIÞ R indices (all data) 3 Largest peak, hole/e A P P R¼ P kFo j jFc k= jFP o j. Rw ¼ ½ ½wðFo2 Fc2 Þ2 = wðFo2 Þ2 1=2 .
2. Experimental 2.1. Materials and methods All the reagents were used as received from commercial suppliers without further purification. The macrocycle ligand L has been prepared as previously described [22]. Carbon, hydrogen and nitrogen analyses were performed on a Perkin–Elmer 240C analyzer. Infrared spectrum (KBr pellet) of the complex was recorded on a FT-IR NEXUS 670 (Nicolet) spectrophotometer in the range 4000–400 cm1 . The ESR spectra of the complex powder were recorded on a Berk ER 200D-SRC X-band Spectrometer at room temperature and 110 K. The magnetic susceptibility data were recorded using Quantum Design MPMS–7 SQUID Magnetometer in the temperature range from 4 to 300 K at an applied magnetic field of 5 KG. 2.2. Synthesis Cu(ClO4 )2 6H2 O (0.185 g, 0.5 mmol) was dissolved in methanol (10 ml) and added to a methanolic solution (10 ml) of the ligand L (0.084 g, 0.5 mmol) with stirring at room temperature for 2 h. NaN(CN)2 (0.089 g, 1 mmol), dissolved in water (5 ml), was then added. The mixture was stirred for 2 h. The solution was filtered and the blue precipitate was washed with methanol and recrystallized in acetonitrile by slow evaporation in air. Yield 47%. IR (KBr pellet, cm1 ): 3429b, 3275s, 2935m, 2874m, 2353m, 2323m, 2271w, 2194s, 1633w, 1452w, 1402w, 1379w, 1306w, 1259m, 1174w, 1098s, 1003m, 935w, 908w, 885w, 861w, 809w, 758w, 656w, 624s, 509m, 426w. Anal. Calcd for C22 H42 Cl2 Cu2 N12 O8 : C, 32.97%; H, 5.24%; N, 20.98%. Found: C, 32.90%; H, 5.15%; N, 20.89%.
Table 2 ) and bond angles (°) for the complex 1 Selected bond lengths (A Cu(1)–N(9) Cu(1)–N(2) Cu(1)–N(10) Cu(1)–N(3) Cu(1)–N(1) Cu(2)–N(7) Cu(2)–N(12A) Cu(2)–N(4) Cu(2)–N(6) Cu(2)–N(5)
1.959(4) 2.009(3) 2.026(4) 2.034(4) 2.133(3) 2.002(4) 2.011(4) 2.017(3) 2.057(3) 2.105(4)
N(12)–Cu(2A) N(7)–C(19) N(8)–C(19) N(8)–C(20) N(9)–C(20) N(10)–C(21) N(11)–C(22) N(11)–C(21) N(12)–C(22)
2.011(4) 1.148(5) 1.298(5) 1.311(5) 1.127(5) 1.129(6) 1.291(6) 1.305(6) 1.153(6)
N(9)–Cu(1)–N(2) N(9)–Cu(1)–N(10) N(2)–Cu(1)–N(10) N(9)–Cu(1)–N(3) N(2)–Cu(1)–N(3) N(10)–Cu(1)–N(3) N(9)–Cu(1)–N(1) N(2)–Cu(1)–N(1) N(10)–Cu(1)–N(1) N(3)–Cu(1)–N(1) N(7)–Cu(2)– N(12A) N(7)–Cu(2)–N(4) N(12A) –Cu(2)– N(4) N(7)–Cu(2)–N(6) N(12A) –Cu(2)– N(6) N(4)–Cu(2)–N(6) N(7)–Cu(2)–N(5) N(12A) –Cu(2)– N(5) N(4)–Cu(2)–N(5) N(6)–Cu(2)–N(5) C(9)–N(1)–Cu(1) C(1)–N(1)–Cu(1)
172.35(16) 88.48(17) 91.41(15) 89.29(17) 86.61(15) 146.74(18) 99.62(15) 87.56(14) 111.15(16) 101.94(16) 87.64(16)
C(4)–N(2)–Cu(1) C(3)–N(2)–Cu(1) C(7)–N(3)–Cu(1) C(6)–N(3)–Cu(1) C(18)–N(4)–Cu(2) C(10)–N(4)–Cu(2) C(13)–N(5)–Cu(2) C(12)–N(5)–Cu(2) C(15)–N(6)–Cu(2) C(16)–N(6)–Cu(2) C(19)–N(7)–Cu(2)
108.3(3) 113.3(3) 115.9(3) 109.6(4) 110.0(3) 110.8(3) 112.1(3) 113.2(3) 113.2(3) 111.2(3) 163.6(4)
91.42(15) 176.50(17)
C(19)–N(8)–C(20) C(20)–N(9)–Cu(1)
123.5(4) 172.9(4)
131.54(15) 90.27(15)
C(21)–N(10)–Cu(1) C(22)–N(12)– Cu(2A) C(19)–N(8)–C(20) C(22)–N(11)–C(21) N(7)–C(19)–N(8)
170.1(4) 156.0(4) 123.5(4) 123.0(5) 171.9(5)
N(9)–C(20)–N(8) N(10)–C(21)–N(11) N(12)–C(22)–N(11)
172.3(5) 172.0(6) 173.8(6)
87.83(14) 123.73(15) 95.63(16) 87.70(14) 104.66(13) 114.5(3) 111.6(3)
Symmetry transformations used to generate equivalent atoms: A: x þ 2; y þ 2; z þ 2.
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2.3. X-ray diffraction Single-crystal X-ray studies were performed on a Bruker SMART 1000 CCD diffractometer equipped with graphite crystal monochromator situated in the incident beam for data collection. The determination of unit cell parameters and data collections were performed ). The structure with Mo-Ka radiation (k ¼ 0:71073 A was solved by direct methods and semi-empirical absorption corrections were applied using the SHELXS-97 program [23a]. The final refinement was performed with the SHELXL-97 program [23b] by full-matrix-leastsquares methods with anisotropic thermal parameters for non-hydrogen atoms on F 2 . The hydrogen atoms were generated theoretically onto atoms to which they are attached and refined isotropically with fixed thermal factors. Crystallographic data and structure refinement details for 1 are given in Table 1. Selected key bond lengths and angles for 1 are given in Table 2. CCDC reference number 195738. See http://www.rsc.org/ for crystallographic data in CIF or other electronic format.
3. Results and discussion 3.1. Structure A perspective drawing of the complex 1 is shown in Fig. 1. It consists of a tetranuclear copper (II) complex and non-coordinated perchlorate anions. In the solid state, the complex 1 resides on an inversion center so that only half of the molecule is crystallographically unique. The tetranuclear structure can be considered as two dinuclear parts in which two copper (II) centers are
bridged by one dca ligand and then two parts are linked by another dca fragment, The Cu (II) centers are all penta-coordinated (CuN5 ) to three nitrogen atoms of the triazamacrocycle L and two nitrogen atoms of two dca bridging ligands. However, the coordination geometries around Cu(1) (Cu(1A)) and Cu(2) (Cu(2A)) are different. The Cu(1) center (or Cu(1A)) can be described as a trigonally distorted rectangular pyramid, which is reflected in the s value (0.15 here) defined by Addizon et al. [24] (s ¼ 0 for an ideal square pyramid, and 1 for an ideal trigonal bipyramid), with N(2), N(3), N(9), N(10) in the equatorial position and N(1) in the apical above the N4 position. The Cu(1) atom is 0.3542 (4) A least-squares plane toward the apical N(1) (Cu(1)–N(1) ) and for Cu(2) (or Cu(2A)) the s value is 0.75, 2.1333 A indicating a square based pyramid distorted trigonal bipyramid with N(5), N(6), N(7) in the equatorial position and N(4), N(12) in the apical position. The above the plane. In the structure, the Cu(2) is 0.0302 A four copper atom are arranged at the vertices of a nearby square-planar parallelogram with edge 8.161(4) (Cu(1)–Cu(2)) and 7.975(4) A (Cu(1)–Cu(2A)) and A diagonal 10.859(4) A (Cu(1)–Cu(1A)) and 11.937(4) A (Cu(2)–Cu(2A)). Cu(1)–Cu(2)–Cu(1A) and Cu(2)– Cu(1)–Cu(2A) angles are 84.6(15)° and 87(15)°. In the complex 1, the dca ligands are bent, with C(19)–N(8)–C(20) and C(21)–N(21)–C(22) angles around 120° and two N–C–N straight linear units with angles near 173(16)° in both case, as is typical of the [N(CN)2 ] anion [25] and coordinate to two metals via the nitrile nitrogens only. And due to the facial tridentate coordination of the macrocycle ligand, it leads to a cis-disposition of the bridging dicyanamides. The resultant topology is that of a Cu4 (dca)4 ring with a slight chair conformation, which all atoms of the dca ligands out of the Cu4 plane, which is different with the pseudo square conformation of [Mn(dca)2 (H2 O)2 ](H2 O) [26], [Mn(dca)2 (C2 H5 OH)2 ](CH3 )2 CO [26] and Cu[N(CN)2 ]2 [27] with all atoms on the mirror plane. However, the four amide N atoms (N(8), N(8A), N(11), N(11A)) of the four dca ligands are also coplanar. The dihedral angle with Cu4 plane is 22.0°. 3.2. IR and ESR spectra
Fig. 1. ORTEP drawing of the complex 1, showing the atom numbering scheme. Hydrogen atoms are omitted for clarity. Symmetry transformation used to generate equivalent atoms: A: x þ 2; y þ 2; z þ 2.
The IR spectrum of the complex 1 shows bands 2353, 2323, 2271, 2194 cm1 which can be attributed to mCN stretching absorption [21c]. The band at 3274 cm1 is assigned to mNH stretch of the 1,5,9-triazacyclododecane ligands. The bands at 2935 and 2874 cm1 are assigned to mCH stretch of the 1,5,9-triazacyclododecane ligands and at 1097 cm1 is assigned to the mClO stretch of the perchlorate anions. The X-band ESR spectrum of the complex 1 was acquired in solid state at room temperature, only an intense, almost isotropic, featureless resonance centered at
W. Gu et al. / Inorganic Chemistry Communications 6 (2003) 966–970
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molecular contacts in the structure and the tetranuclear moleculars are well isolated, the magnetic orbitals of copper (II) ions, namely dx2 y 2 , can interact through dca ligand. The weak antiferromagnetic coupling observed for the tetramer is agreed with the weak magnetic coupling (J =K ¼ 0:10–0:18 K) of the l1;5 -dca bridges [28].
4. Conclusions
Fig. 2. Thermal variations of the magnetic susceptibility vM (s) and leff (d) of the complex 1, where plots for observed result and solid lines for fitting calculations.
g ¼ 2:13. The spectrum at 110 K maintains the same shape and it g value as the ESR spectra at room temperature. 3.3. Magnetic properties The magnetic properties of a powder sample of the complex 1 are represented as vM and leff vs T are in Fig. 2. At room temperature, the leff value of the presented complex is 3.35 cm3 mol3 K, corresponding well with that expected for four isolated copper (II) ions (3.46 cm3 mol3 K). As can be seen, the leff product steadily decreases as the temperature is lowered to reach 3.35 cm3 mol3 K at 4 K, which is typical of the antiferromagnetic behavior. In keeping with the structure of the complex 1, the magnetic susceptibility data were analyzed quantitatively by Eq. (1) based on a cyclic-tetranuclear structure, where spin Hamiltonian is defined as H ¼ 2J ðS1 S2 þ S2 S3 þ S3 S4 þ S4 S1 Þ þ N a 2Ng2 b2 A vM ¼ A ¼ 2 þ 5 expð2xÞ þ expð2xÞ; B KT B ¼ 7 þ 5 expð2xÞ þ 3 expð2xÞ þ expð4xÞ x ¼ J =KT
ð1Þ
N a is the temperature independent paramagnetism, N a ¼ 240 106 cm3 mol1 . The best-fit parameters are J ¼ 0:436 cm1 , g ¼ 2:058 and R ¼ 2:252 104 (linear agreement factor). 1 Since there are no close inter1
We note that the g value derived from the magnetic susceptibility data do not agree well with those derived from ESR spectra, which are far more reliable. This is quit common and arises because a g value derived from magnetic susceptibility data acts as a sink for all of the systematic errors in the curve fitting, and therefore has little significance [7e]. In [Cu2 L2 (dca)2 (ClO4 )2 ]2 we have assumed that all four coupling pathways are equivalent, despite the fact that they are crystallographically slightly in equivalent, which would affect the derived g values.
A unique l1;5 -dca bridged cyclic tetranuclear copper (II) complex with the macrocyclic ligands has been designed and synthesized, and the coordination model of Cu (II) has been elucidated by X-ray analyse. The magnetic exchange interaction occurs via the dca bridges and the observed weak antiferromagnetic exchange within the tetranuclear compound is explained by the poor support of the l1;5 -dca bridging ligands for the magnetic exchange interaction. To date, the l1;5 -dca bridges provide weak coupling in the few examples of compounds measured [28].
Acknowledgements This work was financially supported by the NSF of China (No. 20171026) and Tianjin (No. 013605811).
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A new l1;5-dicyanamide bridged cyclic tetranuclear copper (II) complex with 1,5,9-triazacycledodecane ligands: structure, ESR spectroscopic and magnetic properties Wen Gu a, He-Dong Bian a, Jing-Yuan Xu a, Zhan-Quan Liu a, Peng Cheng a, Shi-Ping Yan a,b,*, Dai-Zheng Liao a, Zong-Hui Jiang a b
a Department of Chemistry, Nankai University, Tianjin 300071, PR China State Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, Beijing 100871, PR China
Received 26 February 2003; accepted 10 April 2003
Abstract The tetranuclear complex [Cu2 L2 (dca)2 (ClO4 )2 ]2 (1) (L ¼ 1,5,9-triazacyclododecane, dca ¼ dicyanamide [N(CN)2 ] ) has been synthesized and its crystal structure, ESR spectra and magnetic properties determined. The complex contains a tetranuclear copper (II) moiety in which two dimeric units are bridged by two dca ligands. In each dimeric moiety the two copper (II) ions are bridged by one l1;5 -dicyanamide ligand. Magnetic susceptibilities for the complex in the solid state are measured over the temperature range 4–300 K. The complex shows a weak antiferromagnetic coupling with a best fit J value )0.436 cm1 . The l1;5 -dicyanamide bridges are the principal pathway for the super-exchange interaction and the weak antiferromagnetic coupling of the complex is interpreted in term of the l1;5 -dicyanamide ligand behavior as a poor magnetic mediator. Ó 2003 Elsevier Science B.V. All rights reserved. Keywords: Dicyanamide ligand; Tetranuclear copper (II) complex; Magnetic properties; Triazamacrocycle ligand
1. Introduction The design of high nuclearity transition metal complexes with novel magnetic properties is a major goal of current research [1]. Recent developments have afforded a variety of architecturally highly sophisticated polynuclear complexes such as molecular helicates, grids, ladders, rings and boxes [2]. Such complexes are of interest not only for their unusual structures [3] and the sample synthetic methods, but also because they allow to understand the relationship between the structure and the magnetic properties [4]. Recently relatively low nuclear coordination complexes (
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clear Mn4 [5], Ni4 [6], Cu4 [7], Zn4 [8] complexes; hexanuclear Ni6 [9], Cu6 [10] complexes. Tetranuclear complexes are of current interest in bioinorganic modeling, multielectron transfer, catalytic and new extended materials, as well as in magnetochemical investigations [11]. Therein, owing to their ease of synthesis, and of the design of many tetranuclearing chelating ligands for use in bioinorganic model and magnetochemical studies, there are many examples of Cu4 complexes, which exhibit a large diversity of structural types and magnetic properties, for example, a planar Cu4 complex with diazine (N2 ) ligands [12], tetrahedral Cu4 complexes with tetradentate triazolate [13] and pyrazolate [14] ligands with (N2 ) bridges and tridentate Schiff-base ligands with sym-anti carboxylate bridges [7h]. The Cu4 O4 and Cu4 (O2 )4 systems exhibited ferromagnetic exchange while the Cu4 O2 (N2 )2 and Cu4 (N2 )4 systems exhibited antiferromagnetic exchange. Among them, structurally and magnetically characterized planar cyclic structures with no diagonal bridging groups are rather scarce [15].
1387-7003/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1387-7003(03)00144-8
W. Gu et al. / Inorganic Chemistry Communications 6 (2003) 966–970
In this paper, we have selected a 12-membered triazamacrocycle ligand 1,5,9-triazacyclododecane (L), based on ‘‘macrocyclic effect’’ of the aza macrocycles [16], and dicyanamide (dca), a diamagnetic bridging ligand, due to its ability to bound to multiple transition metal sites, such as monodentate [17], bidentate [18], tridentate [19] and tetradentate [20] coordination fashions. Polydentate dicyanamide has so far been utilized extensively to assemble transition metals into 1-, 2- and 3-D arrays [21]. It should be noted that, as far as we know, no fully structurally and magnetically characterized dicyanamide bridged discrete tetranuclear complexes have been reported. Taking into account the above-mentioned aspects, a new cyclic tetranuclear copper (II) complex [Cu2 L2 (dca)2 (ClO4 )2 ]2 (1) has been synthesized and magnetostructurally characterized.
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Table 1 Crystal data and details of the structure refinement for the complex 1 C22 H42 Cl2 Cu2 N12 O8 800.66 293(2) Monoclinic P 21 /c 15.165(6) 16.370(6) 14.329(5) 109.512(6) 3353(2) 4 1.586 1.490 6114/6114 R1 ¼ 0:0410; wR2 ¼ 0:0822 R1 ¼ 0:0885; wR2 ¼ 0:1053 0.516, )0.436
Formula Fw T/K Crystal system Space group a=A b=A c=A
b=° 3 V =A Z qcalcd /g cm3 l/mm1 Reflns, unique/observed Final R indices ½I > 2rðIÞ R indices (all data) 3 Largest peak, hole/e A P P R¼ P kFo j jFc k= jFP o j. Rw ¼ ½ ½wðFo2 Fc2 Þ2 = wðFo2 Þ2 1=2 .
2. Experimental 2.1. Materials and methods All the reagents were used as received from commercial suppliers without further purification. The macrocycle ligand L has been prepared as previously described [22]. Carbon, hydrogen and nitrogen analyses were performed on a Perkin–Elmer 240C analyzer. Infrared spectrum (KBr pellet) of the complex was recorded on a FT-IR NEXUS 670 (Nicolet) spectrophotometer in the range 4000–400 cm1 . The ESR spectra of the complex powder were recorded on a Berk ER 200D-SRC X-band Spectrometer at room temperature and 110 K. The magnetic susceptibility data were recorded using Quantum Design MPMS–7 SQUID Magnetometer in the temperature range from 4 to 300 K at an applied magnetic field of 5 KG. 2.2. Synthesis Cu(ClO4 )2 6H2 O (0.185 g, 0.5 mmol) was dissolved in methanol (10 ml) and added to a methanolic solution (10 ml) of the ligand L (0.084 g, 0.5 mmol) with stirring at room temperature for 2 h. NaN(CN)2 (0.089 g, 1 mmol), dissolved in water (5 ml), was then added. The mixture was stirred for 2 h. The solution was filtered and the blue precipitate was washed with methanol and recrystallized in acetonitrile by slow evaporation in air. Yield 47%. IR (KBr pellet, cm1 ): 3429b, 3275s, 2935m, 2874m, 2353m, 2323m, 2271w, 2194s, 1633w, 1452w, 1402w, 1379w, 1306w, 1259m, 1174w, 1098s, 1003m, 935w, 908w, 885w, 861w, 809w, 758w, 656w, 624s, 509m, 426w. Anal. Calcd for C22 H42 Cl2 Cu2 N12 O8 : C, 32.97%; H, 5.24%; N, 20.98%. Found: C, 32.90%; H, 5.15%; N, 20.89%.
Table 2 ) and bond angles (°) for the complex 1 Selected bond lengths (A Cu(1)–N(9) Cu(1)–N(2) Cu(1)–N(10) Cu(1)–N(3) Cu(1)–N(1) Cu(2)–N(7) Cu(2)–N(12A) Cu(2)–N(4) Cu(2)–N(6) Cu(2)–N(5)
1.959(4) 2.009(3) 2.026(4) 2.034(4) 2.133(3) 2.002(4) 2.011(4) 2.017(3) 2.057(3) 2.105(4)
N(12)–Cu(2A) N(7)–C(19) N(8)–C(19) N(8)–C(20) N(9)–C(20) N(10)–C(21) N(11)–C(22) N(11)–C(21) N(12)–C(22)
2.011(4) 1.148(5) 1.298(5) 1.311(5) 1.127(5) 1.129(6) 1.291(6) 1.305(6) 1.153(6)
N(9)–Cu(1)–N(2) N(9)–Cu(1)–N(10) N(2)–Cu(1)–N(10) N(9)–Cu(1)–N(3) N(2)–Cu(1)–N(3) N(10)–Cu(1)–N(3) N(9)–Cu(1)–N(1) N(2)–Cu(1)–N(1) N(10)–Cu(1)–N(1) N(3)–Cu(1)–N(1) N(7)–Cu(2)– N(12A) N(7)–Cu(2)–N(4) N(12A) –Cu(2)– N(4) N(7)–Cu(2)–N(6) N(12A) –Cu(2)– N(6) N(4)–Cu(2)–N(6) N(7)–Cu(2)–N(5) N(12A) –Cu(2)– N(5) N(4)–Cu(2)–N(5) N(6)–Cu(2)–N(5) C(9)–N(1)–Cu(1) C(1)–N(1)–Cu(1)
172.35(16) 88.48(17) 91.41(15) 89.29(17) 86.61(15) 146.74(18) 99.62(15) 87.56(14) 111.15(16) 101.94(16) 87.64(16)
C(4)–N(2)–Cu(1) C(3)–N(2)–Cu(1) C(7)–N(3)–Cu(1) C(6)–N(3)–Cu(1) C(18)–N(4)–Cu(2) C(10)–N(4)–Cu(2) C(13)–N(5)–Cu(2) C(12)–N(5)–Cu(2) C(15)–N(6)–Cu(2) C(16)–N(6)–Cu(2) C(19)–N(7)–Cu(2)
108.3(3) 113.3(3) 115.9(3) 109.6(4) 110.0(3) 110.8(3) 112.1(3) 113.2(3) 113.2(3) 111.2(3) 163.6(4)
91.42(15) 176.50(17)
C(19)–N(8)–C(20) C(20)–N(9)–Cu(1)
123.5(4) 172.9(4)
131.54(15) 90.27(15)
C(21)–N(10)–Cu(1) C(22)–N(12)– Cu(2A) C(19)–N(8)–C(20) C(22)–N(11)–C(21) N(7)–C(19)–N(8)
170.1(4) 156.0(4) 123.5(4) 123.0(5) 171.9(5)
N(9)–C(20)–N(8) N(10)–C(21)–N(11) N(12)–C(22)–N(11)
172.3(5) 172.0(6) 173.8(6)
87.83(14) 123.73(15) 95.63(16) 87.70(14) 104.66(13) 114.5(3) 111.6(3)
Symmetry transformations used to generate equivalent atoms: A: x þ 2; y þ 2; z þ 2.
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2.3. X-ray diffraction Single-crystal X-ray studies were performed on a Bruker SMART 1000 CCD diffractometer equipped with graphite crystal monochromator situated in the incident beam for data collection. The determination of unit cell parameters and data collections were performed ). The structure with Mo-Ka radiation (k ¼ 0:71073 A was solved by direct methods and semi-empirical absorption corrections were applied using the SHELXS-97 program [23a]. The final refinement was performed with the SHELXL-97 program [23b] by full-matrix-leastsquares methods with anisotropic thermal parameters for non-hydrogen atoms on F 2 . The hydrogen atoms were generated theoretically onto atoms to which they are attached and refined isotropically with fixed thermal factors. Crystallographic data and structure refinement details for 1 are given in Table 1. Selected key bond lengths and angles for 1 are given in Table 2. CCDC reference number 195738. See http://www.rsc.org/ for crystallographic data in CIF or other electronic format.
3. Results and discussion 3.1. Structure A perspective drawing of the complex 1 is shown in Fig. 1. It consists of a tetranuclear copper (II) complex and non-coordinated perchlorate anions. In the solid state, the complex 1 resides on an inversion center so that only half of the molecule is crystallographically unique. The tetranuclear structure can be considered as two dinuclear parts in which two copper (II) centers are
bridged by one dca ligand and then two parts are linked by another dca fragment, The Cu (II) centers are all penta-coordinated (CuN5 ) to three nitrogen atoms of the triazamacrocycle L and two nitrogen atoms of two dca bridging ligands. However, the coordination geometries around Cu(1) (Cu(1A)) and Cu(2) (Cu(2A)) are different. The Cu(1) center (or Cu(1A)) can be described as a trigonally distorted rectangular pyramid, which is reflected in the s value (0.15 here) defined by Addizon et al. [24] (s ¼ 0 for an ideal square pyramid, and 1 for an ideal trigonal bipyramid), with N(2), N(3), N(9), N(10) in the equatorial position and N(1) in the apical above the N4 position. The Cu(1) atom is 0.3542 (4) A least-squares plane toward the apical N(1) (Cu(1)–N(1) ) and for Cu(2) (or Cu(2A)) the s value is 0.75, 2.1333 A indicating a square based pyramid distorted trigonal bipyramid with N(5), N(6), N(7) in the equatorial position and N(4), N(12) in the apical position. The above the plane. In the structure, the Cu(2) is 0.0302 A four copper atom are arranged at the vertices of a nearby square-planar parallelogram with edge 8.161(4) (Cu(1)–Cu(2)) and 7.975(4) A (Cu(1)–Cu(2A)) and A diagonal 10.859(4) A (Cu(1)–Cu(1A)) and 11.937(4) A (Cu(2)–Cu(2A)). Cu(1)–Cu(2)–Cu(1A) and Cu(2)– Cu(1)–Cu(2A) angles are 84.6(15)° and 87(15)°. In the complex 1, the dca ligands are bent, with C(19)–N(8)–C(20) and C(21)–N(21)–C(22) angles around 120° and two N–C–N straight linear units with angles near 173(16)° in both case, as is typical of the [N(CN)2 ] anion [25] and coordinate to two metals via the nitrile nitrogens only. And due to the facial tridentate coordination of the macrocycle ligand, it leads to a cis-disposition of the bridging dicyanamides. The resultant topology is that of a Cu4 (dca)4 ring with a slight chair conformation, which all atoms of the dca ligands out of the Cu4 plane, which is different with the pseudo square conformation of [Mn(dca)2 (H2 O)2 ](H2 O) [26], [Mn(dca)2 (C2 H5 OH)2 ](CH3 )2 CO [26] and Cu[N(CN)2 ]2 [27] with all atoms on the mirror plane. However, the four amide N atoms (N(8), N(8A), N(11), N(11A)) of the four dca ligands are also coplanar. The dihedral angle with Cu4 plane is 22.0°. 3.2. IR and ESR spectra
Fig. 1. ORTEP drawing of the complex 1, showing the atom numbering scheme. Hydrogen atoms are omitted for clarity. Symmetry transformation used to generate equivalent atoms: A: x þ 2; y þ 2; z þ 2.
The IR spectrum of the complex 1 shows bands 2353, 2323, 2271, 2194 cm1 which can be attributed to mCN stretching absorption [21c]. The band at 3274 cm1 is assigned to mNH stretch of the 1,5,9-triazacyclododecane ligands. The bands at 2935 and 2874 cm1 are assigned to mCH stretch of the 1,5,9-triazacyclododecane ligands and at 1097 cm1 is assigned to the mClO stretch of the perchlorate anions. The X-band ESR spectrum of the complex 1 was acquired in solid state at room temperature, only an intense, almost isotropic, featureless resonance centered at
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molecular contacts in the structure and the tetranuclear moleculars are well isolated, the magnetic orbitals of copper (II) ions, namely dx2 y 2 , can interact through dca ligand. The weak antiferromagnetic coupling observed for the tetramer is agreed with the weak magnetic coupling (J =K ¼ 0:10–0:18 K) of the l1;5 -dca bridges [28].
4. Conclusions
Fig. 2. Thermal variations of the magnetic susceptibility vM (s) and leff (d) of the complex 1, where plots for observed result and solid lines for fitting calculations.
g ¼ 2:13. The spectrum at 110 K maintains the same shape and it g value as the ESR spectra at room temperature. 3.3. Magnetic properties The magnetic properties of a powder sample of the complex 1 are represented as vM and leff vs T are in Fig. 2. At room temperature, the leff value of the presented complex is 3.35 cm3 mol3 K, corresponding well with that expected for four isolated copper (II) ions (3.46 cm3 mol3 K). As can be seen, the leff product steadily decreases as the temperature is lowered to reach 3.35 cm3 mol3 K at 4 K, which is typical of the antiferromagnetic behavior. In keeping with the structure of the complex 1, the magnetic susceptibility data were analyzed quantitatively by Eq. (1) based on a cyclic-tetranuclear structure, where spin Hamiltonian is defined as H ¼ 2J ðS1 S2 þ S2 S3 þ S3 S4 þ S4 S1 Þ þ N a 2Ng2 b2 A vM ¼ A ¼ 2 þ 5 expð2xÞ þ expð2xÞ; B KT B ¼ 7 þ 5 expð2xÞ þ 3 expð2xÞ þ expð4xÞ x ¼ J =KT
ð1Þ
N a is the temperature independent paramagnetism, N a ¼ 240 106 cm3 mol1 . The best-fit parameters are J ¼ 0:436 cm1 , g ¼ 2:058 and R ¼ 2:252 104 (linear agreement factor). 1 Since there are no close inter1
We note that the g value derived from the magnetic susceptibility data do not agree well with those derived from ESR spectra, which are far more reliable. This is quit common and arises because a g value derived from magnetic susceptibility data acts as a sink for all of the systematic errors in the curve fitting, and therefore has little significance [7e]. In [Cu2 L2 (dca)2 (ClO4 )2 ]2 we have assumed that all four coupling pathways are equivalent, despite the fact that they are crystallographically slightly in equivalent, which would affect the derived g values.
A unique l1;5 -dca bridged cyclic tetranuclear copper (II) complex with the macrocyclic ligands has been designed and synthesized, and the coordination model of Cu (II) has been elucidated by X-ray analyse. The magnetic exchange interaction occurs via the dca bridges and the observed weak antiferromagnetic exchange within the tetranuclear compound is explained by the poor support of the l1;5 -dca bridging ligands for the magnetic exchange interaction. To date, the l1;5 -dca bridges provide weak coupling in the few examples of compounds measured [28].
Acknowledgements This work was financially supported by the NSF of China (No. 20171026) and Tianjin (No. 013605811).
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