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A novel bimetallic alternating chain: synthesis, crystal structure and magnetic study
www.elsevier.nl/locate/ica Inorganica Chimica Acta 315 (2001) 249– 253
Note
A novel bimetallic alternating chain: synthesis, crystal structure and magnetic study Partha Sarathi Mukherjeee a, Tapas Kumar Maji a, Talal Mallah b, Ennio Zangrando c, Lucio Randaccio c, Nirmalendu Ray Chaudhuri a,* a
Department of Inorganic Chemistry, Indian Association for the Culti6ation of Science, Jada6pur, Calcutta 700032, India b Laboratoire de Chimie Inorganique, UMR CNRS 8613, Uni6ersite´ de Paris-Sud, 91405 Orsay, France c Dipartimento di Scienze Chimiche, Uni6ersity of Trieste, 34127 Trieste, Italy Received 11 August 2000; accepted 26 January 2001
Abstract A novel one dimensional (1D) bimetallic polymeric complex [catena-bis(m-N-(aminoethyl)-3-aminopropanolato)-di-copper(II)tetracyanonickelate(II)dihydrate] has been synthesized by the reaction of 1:1 mixture of CuCl2·2H2O and the hydoxyamine ligand, [N-(3-hydroxypropyl)ethane-1,2-diamine] with half equivalent of [Ni(CN)4] − 2 in aqueous solution. X-ray quality single crystals were obtained by slow evaporation of the ammoniacal solution of the complex. The single crystal structure reveals that it is an alkoxo bridged Cu(II) dimer linked through [Ni(CN)4]2 − in trans-fashion resulting in a 1D chain. The properties of the complex have been studied by variable temperature magnetic susceptibility measurements. The susceptibility data fit well with the Cu(lI) dimer equation to give 2J= −622 cm − 1, g=2.05. The very high coupling parameter value clearly indicates the presence of very strong antiferromagnetic interaction between the Cu(II) ions. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Crystal structure; Magnetic study; Bimetallic chain complexes; Cyano-bridged complexes; Nickel complexes
1. Introduction Since the early works of Lehn [1] and Padersen [2], construction of coordination polymers via metal coordination directed self-assembly processes has attracted the attention of scientists from different areas, ranging from chemistry to material science and also biology, because of the promising applications such as biomimic models [3] or functional materials for catalysis, absorption, nonlinear optics, and molecular magnetic materials [4–7]. The general synthetic approach for the metal assembles is to utilize metal complexes having coordination ability as a building block to react with transition metal cations. Recently, there has been an increasing interest in polynuclear or polymeric metal cyanides owing to their often remarkable structural as * Corresponding author. Tel.: +91-33-4734971; fax: + 91-334732805. E-mail address: [email protected] (N.R. Chaudhuri).
well as physicochemical properties [8–11]. The most prominent characteristic of CN− is its ability to act either as a terminal or as a bridging ligand. As it is a good super exchange pathway between the paramagnetic metal ions it is widely used in the construction of molecular based magnetic materials [12,13]. Recently, using cyanometallate as a building block a few homoand bimetallic chains were reported [14,15]. In all the previously reported bimetallic chains it is observed that two different types of metal ions are repeated alternately, but bridging through only one type of ligand. To our knowledge, there are not many reports in the literature of a bimetallic chain with two different types of metal as well as two different types of bridging ligand simultaneously repeated in a periodic fashion. In the present paper we report the synthesis, crystallization by an uncommon way, structural and magnetic study of a novel 1D bimetallic [Cu(II)Ni(II)] chain where the two different bridging moieties (alkoxide and cyanide) are repeated in a periodic fashion.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 3 5 4 - 1
P.S. Mukherjeee et al. / Inorganica Chimica Acta 315 (2001) 249–253
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2. Experimental
2.1. Reagents Copper(II) chloride dihydrate, N-(3-hydroxypropyl)ethane-1,2-diamine, potassium-tetracyanonickelate dihydrate were purchased from commercial sources and used as received.
2.2. Physical techniques The IR spectrum was taken on a Nicolet 520 FTIR spectrophotometer as KBr pellets in the range of 4000 – 400 cm − 1. Variable-temperature magnetic susceptibility measurements were carried out in the temperature range 70–380 K in applied fields of 5 kOe with a SQUID magnetometer. The diamagnetic corrections were estimated from Pascal’s constants [16].
2.3. Synthesis To a deep blue aqueous solution (10 cm3) containing CuCl2·2H2O (1 mmol) and N-(3-hydroxypropyl)ethane1,2-diamine (1 mmol) was added, slowly with continuous stirring, an aqueous solution (10 cm3) of K2[Ni(CN)4]·2H2O (0.5 mmol). A sky blue solid separated out, filtered and washed with water. It was treated with methanol (10 cm3) and stirred well to form a slurry. Dilute aqueous solution of ammonia was added
to it slowly drop by drop for dissolution. The resulting deep blue solution yields suitable single crystals for X-ray diffraction on keeping in a refrigerator for a week. The yield is about 70%. Anal. Found: C, 29.98; H, 5.26; N, 19.80. Calc. for C14H30N8Cu2NiO4: C, 30.06; H, 5.36; N, 20.09%.
2.4. X-ray structure determination A crystal suitable for X-ray analysis was mounted on an Enraf –Nonius CAD4 single-crystal diffractometer equipped with graphite monochromator and Mo Ka radiation (u= 0.7107 A, ). Diffraction measurements were carried out at room temperature (r.t.) using the – 2q scan technique. Three standard reflections, measured at regular intervals throughout the data collection, showed no decay in intensity. An absorption correction based on the -scan method was applied. The collected intensity data were corrected for Lorentz polarization effect. A total of 3523 reflections were measured and 1751 were assumed observed applying the condition I\ 2|(I). The structure was solved by Patterson and Fourier technique [17] and refined through full-matrix anisotropic least-squares method [18] using SHELXL93 [19]. The refinement converged to residual indices R1(Fo)= 0.0539; wR2(Fo 2)=0.0931 with I\2|(I). The final difference Fourier map showed maximum and minimum peak heights of 0.470, − 0.501 e A, − 3, respectively. The crystallographic data are given in Table 1.
3. Results and discussion Table 1 Crystal data and structure refinement for the complex [catenabis(m-N-(aminoethyl)-3-aminopropanolato)-di-copper(II)-tetracyanonickelate(II)dihydrate] Formula Formula weight (g) Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) h (°) i (°) g (°) V (A, 3) Z T (K) Dcalc (g cm−3) v(Mo Ka) (cm−1) u(Mo Ka) (A, ) R1 a wR2 b a b
C14H30Cu2N8NiO4 560.26 monoclinic P21/n 9.619(1) 9.723(2) 11.987(1) 90 101.10(1) 90 1100.1(3) 2 298 1.691 27.99 0.71069 0.0539 0.0931
R = Fo − Fc / Fo . Rw =[{w(Fo 2−Fc 2)2}/{w(Fo 2)2}]1/2.
3.1. Synthesis The reaction of K2[Ni(CN]4]·2H2O with CuCl2·2H2O and the tridentate hydroxyamine ligand produced a sky blue precipitate. Its crystals, suitable for structure determination, were obtained by an unusual procedure, i.e. dissolution of the precipitate in dilute solution of NH3 and slow evaporation of the ammonia. The precipitate is insoluble in common organic solvents and its solubility in ammonia is possibly due to the coordination of NH3 to the copper which breaks the bridging cyanide system. The evaporation of NH3 regenerates the tetracyanonickelate bridged polymeric complex.
3.2. IR spectra The most important aspects of the IR spectra of the title complex involve the characteristic vibration of the CN groups. The formation of a cyanide bridge in the polymeric complex was evidenced by IR spectra in the region of stretching vibration of the cyanide ligands. It shows two sharp bands at 2125 and 2150 cm − 1 in the
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251
suggests a lower symmetry about the tetracyanonickelate entity and the formation of a cyanide bridge.
3.3. Description of the structure
Fig. 1. ORTEP plot of the title compound (thermal ellipsoids at 40% probability level) with atom numbering scheme of the asymmetric unit. Table 2 Selected bond lengths (A, ) and angles (°) of the complex [catenabis(m-N-(aminoethyl)-3-aminopropanolato)-di-copper(II)-tetracyanonickelate(II)dihydrate] NiC(2) NiC(1) CuO(1) CuO(1) CuN(1)
a
C(2)NiC(1) b C(2)NiC(1) CuO(1)Cu a O(1)CuO(1) a O(1)CuN(4) O(1 a)CuN(4) O(1)CuN(3) O(1 a)CuN(3) a b
1.848(5) 1.852(4) 1.925(3) 1.927(3) 2.402(4)
CuN(3) CuN(4) N(1)C(l) N(2)C(2) Cu···Cu a Cu···Ni
1.995(3) 1.992(4) 1.147(5) 1.135(6) 2.9809(11) 5.1547(6)
90.20(18) 89.80(18) 101.40(12) 78.60(12) 94.56(14) 168.37(13) 170.55(15) 100.46(13)
O(1)CuN(1) O(1) aCuN(1) N(4)CuN(1) N(3)CuN(1) N(4)CuN(3) N(1)C(1)Ni N(2)C(2)Ni CuN(1)C(1)
97.95(14) 97.71(14) 92.51(14) 91.50(14) 84.73(15) 178.1(5) 178.2(5) 146.2(4)
Symmetry codes: −x, −y+1, −z+2. Symmetry codes: −x, −y+1, −z+1.
An ORTEP view of the NiCu2 moiety, with the atom numbering scheme of the crystallographic independent unit is shown in Fig. 1. Selected bond distances and angles are reported in Table 2. The crystal structure consists of alkoxo-bridged binuclear Cu(II) units linked by m-trans-[Ni(CN]4] − 2 anions giving a one-dimensional (1D) polymeric chain (Fig. 2). Each copper ion is in a square pyramidal coordination through two alkoxo oxygens and the nitrogen donors of the ethylenediaminopropanolato ligand. Each copper atom is displaced by about 0.1 7 A, from the N2O2 mean plane towards the cyanide nitrogen, at the apical position of the pyramid that completes the coordination sphere (CuN(1) 2.402(4) A, ). The coordination bond distances with oxygen are similar (1.925(3) and 1.927(3) A, ), as well as those with the terminal amino and imino nitrogen donors (1.995(3) and 1.992(4) A, ). These distances compare well with those found in structurally equivalent dinuclear copper(II) complexes [20]. The bond distances in the square planar Ni coordination are in the expected range, with the CuN(1)C(1) angle significantly bent (146.1(4) A, ). This angle is comparable with that found in the clathrate [Cu(en)2NCNi(CN)2CN]n (150.3(5)°) [21], but it is narrower with respect to those detected in other structures (range between 158 and 164°), both with cis- and trans-bridging Ni(CN)4-units [22,23]. The mean plane of the [Ni(CN)4]2 − anion makes a dihedral angle of 58.71(9)° with the coordination basal plane of copper. A crystallization water molecule, accommodated in the void spaces, connects three adjacent 1D chains through weak H-bonds. One of which also interacts with nitrogen N(1) of cyanide which accounts for the value of the angle at N(1) cited above. These hydrogen bonds, which stabilize the overall crystal structure ranges from 2.88 to 3.27 A, (Fig. 2 and Table 3). Table 3 Hydrogen bonds in the crystal structure of the complex [catenabis(m-N-(aminoethyl)-3-aminopropanolato)-di-copper(II)-tetracyanonickelate(II)dihydrate]
Fig. 2. Perspective view of crystal structure with hydrogen bonds involving the guest water molecules. Nitrogen atoms N(lIII) and N(4II) pertain to a third polymeric chain which is not drawn for the sake of clarity (symmetry codes in Table 3).
DH
d(DH)
d(H···A)
ÚDHA
d(D···A)
A
OwHI OwH2 N(3) aH2a N(4) bH N(3) bH1
0.894 1.101 0.900 0.910 0.900
2.018 2.093 2.293 2.609 2.481
162.73 152.83 147.99 130.66 138.67
2.883 3.113 3.093 3.275 3.212
N(2) N(1) Ow Ow N(2)
a
IR spectrum. The shift of the w(CN) to a higher wave number compared to that of K2[Ni(CN)4] (2121 cm − 1)
Symmetry codes: x+1, y, z. Symmetry codes: x+1/2, −y+1/2, z−1/2. c Symmetry codes: −x+1/2, y−1/2, −z+3/2. b
c
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Table 4 Cu−O−Cu angle (h) and magnetic data for m-alkoxo or m-hydroxo dinuclear Cu(II) complexes Complex
a
[Cu(EAEP)(OH)]2 (ClO4)2 b-[Cu(DMAEP) (OH)]2(ClO4)2 a-[Cu(DMAEP) (OH)]2(ClO4)2 Title complex (in this paper)
CuOCu angle (h) (°) 99 98.4
2J (cm−1)
Ref.
−130
[27]
−2.3
[25]
100.4
−201
[25]
101.4
−622
this study
a
EAEP, 2-(2-ethylaminoethyl)pyridine; DMAEP, 2-(2-dimethylaminoethyl)pyridine.
3.4. Magnetic study Although the title complex shows two d9 Cu(II) and one d8 Ni(II) ions in the molecular unit, the substantially flat square-planar coordination of the [Ni(CN)4]2 − diamagnetic unit permits that, from the magnetic point of view, the compound can be treated as a dimeric complex in which two d9 Cu(II) ions are linked through a bridging alkoxide anion. Again the length of the exchange pathway through the bidentate tetracyanonickelate(II) ligand is large enough to predict that the magnetic interaction takes place mainly through the alkoxide bridging moiety, which is known to be very effective in mediating antiferro- or ferromag-
netic coupling between first-row transition metal ions depending on the MOM angle [24]. The angle MOM (101.40) in our complex clearly suggests that the molecule is antiferromagnetic because complexes with CuOCu angle larger than 97° shows antiferromagnetic interaction and the extent of such interaction increases rapidly (Table 4) with increase in the CuOCu angle [24]. The thermal dependence of the molar magnetic susceptibility M of the complex (Fig. 3) is characteristic of an antiferromagnetic interaction between the copper(II) ions. Since the maximum in the M = f(T) curve is higher than T=380 K, we can safely say that the coupling constant (2J) is larger than 450 cm − 1 [25]. The molecule becomes diamagnetic below 200 K. As in all diamagnetic ground states, a small amount of paramagnetic impurities is detected which is calculated and is about 0.4%, which is reasonable. The M vs. T data of the complex fitted well using the modified Bleaney – Bowers equation for the magnetic susceptibility of isotropically coupled dinuclear S= 1/2 ions [26], adding an impurity term which is due to the presence of non-coupled monomeric species (Eq. (1)) using the Hamiltonian H= −2JSaSb. The results of the best fit, shown as a solid line in Fig. 3, were 2J= − 622 cm − 1, g = 2.05, z(residual paramagnetic impurity)=0.4% with agreement factor R=1.7×10 − 6. The very high value of 2J clearly indicates that the antiferromagnetic interaction between the Cu(II) ions is very strong, which is rare for such a type of dimeric complex and such a strong antiferromagnetic interaction results due
Fig. 3. Molar magnetic susceptibility versus temperature plot for the title complex. Solid line shows the best fit obtained by applying Eq. (1) (see text).
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to the coordination environment around the paramagnetic centers [27,28]. Each CuO2N2 environment of the dimeric part is almost planar with very low displacement (about 0.17 A, ) of the copper atom from the O2N2 mean plane. Both the copper(II) centers in the dimeric unit are square pyramidal with four short and one long bonds, indicating that the spin unpaired electron is located in basal dx 2 − y 2 orbital and dz 2 orbital contains spin paired electrons. Again the dx 2 − y 2 orbital of both the copper(II) in the dimeric unit interacts with the bridging oxygen, such an equatorial – equatorial interaction along with the large CuOCu, which determines the coupling parameter value, is comparable with the other similar type of complexes (Table 4) and is consistent with the strong magnetic interaction between the copper(II) ions in the present complex M = 2Ng 2i 2(1− z)[3 + exp( −J/kT)] − 1/kT + Ng 2i 2|/2kT +Nh
(1)
4. Conclusions We have presented the synthesis, crystal structure and magneto-structural correlation of a novel 1D polymeric chain, where an alkoxo bridged Cu(II) dimer is linked by tetracyanonickelate anion in trans-fashion. Three adjacent chains are connected to the guest water molecules through hydrogen bonding. The most striking feature of the complex is that in a same chain the two different types of metals as well as two different types of bridging ligands are repeated in periodic fashion, of which there are not many reports in the literature. The magnetic susceptibility data show that the molecule becomes diamagnetic below 200K. The best-fit using the famous Bleaney – Bowers equation for S =1/2 coupled dimeric system gives 2J = − 622 cm − 1. This high coupling parameter value clearly indicates the existence of very strong antiferromagnetic interaction between the paramagnetic Cu(II) centers.
5. Supplementary material Further data (atomic fractional coordinates, thermal parameters, complete distances and angles, etc.) can be obtained on request from the Crystallographic Data Center, University Chemical Laboratory, Lensfield Road, Cambridge CB12 1EW, UK, on quoting the number CCDC 147291.
.
253
Acknowledgements The authors wish to thank the Council of Scientific and Industrial Research, New Delhi, for financial support (granted to N.R.C.).
References [1] J.M. Lehn, Angew. Chem., Int. Ed. Engl. 27 (1988) 91. [2] C.L. Peder, Angew. Chem., Int. Ed. Engl. 27 (1988) 1021. [3] F.C.M. Van Veggel, W. Verboom, D.N. Reinhoudt, Chem. Rev. 94 (1994) 279. [4] R.K. Kumar, I. Goldberg, Angew. Chem., Int. Ed. Engl. 37 (1998) 3027. [5] S.W. Keller, S. Lopez, J. Am. Chem. Soc. 121 (1999) 6306. [6] W. Lin, O.P. Evans, R.G. Xiong, Z. Wang, J. Am. Chem. Soc. 120 (1998) 13 272. [7] R.H. Groeneman, L.R. MacGillvray, L. Atwood, Chem. Commun. (1998) 2735. [8] C.A. Bignozzi, F. Scandola, Inorg. Chem. 23 (1984) 1540. [9] C.A. Bignozzi, S. Roffia, F. Scandola, J. Am. Chem. Soc. 107 (1985) 1644. [10] S.Z. Zhan, X.Y. Chen, A. Vij, D. Guo, Q.J. Meng, Inorg. Chim. Acta 292 (1999) 157. [11] K. Kalyansundaram, M. Gratzel, M.K. Nazeeruddin, Inorg. Chem. 31 (1992) 5243. [12] O. Kahn, Nature 378 (1995) 667. [13] A. Caneschi, D. Gatteschi, J.P. Renard, P. Rey, R. Sessoli, Inorg. Chem. 30 (1991) 3937. [14] D.G. Fu, J. Chen, X.S. Tan, L.J. Jiang, S.W. Zhang, P.J. Zheng, W.X. Tang, Inorg. Chem. 36 (1997) 220. [15] G.D. Munno, M.G. Lombardi, P. Paoli, F. Lloret, M. Julve, Inorg. Chim. Acta 282 (1998) 152. [16] A. Earnshow, Introduction to Magnetochemistry, Academic Press, London, 1968. [17] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467. [18] G.M. Sheldrick, SHELXL-97, Program for crystal structure refinement, University of Go¨ttingen, Germany, 1997. [19] G.M. Sheldrick, shelxl-93, Program for solution of crystal structure, University of Go¨ttingen, Germany, 1993. [20] A.C. Villa, L. Coghi, A.G. Manfredotti, C. Guastini, Cryst. Struct. Commun. 3 (1974) 543. [21] H. Yuge, T. Iwamoto, J. Chem. Soc., Dalton Trans. (1994) 1237. [22] I. Muga, J.M. Gutierrez-Zorrilla, A. Luque, P. Roman, F. Lloret, Inorg. Chem. 36 (1997) 743. [23] M. Mikuriya, T. Harada, H. Okawa, S. Kida, Inorg. Chim. Acta. 75 (1983) 1 (and references therein). [24] M.F. Charlot, S. Jeannin, Y. Jeannin, O. Kahn, J. LucreceAbaul, J. Martin-Frere, Inorg. Chem. 18 (1979) 1675 (and references therein). [25] O. Kahn, Molecular Magnetism, VCH, Heidelberg, 1993 (chapter 8 and references therein). [26] B. Bleaney, K.D. Bowers, Proc. R. Soc. (London), Ser. A 241 (1952) 451. [27] P.J. Hay, J.C. Jilibeault, R. Hoffmann, J. Am. Chem. Soc. 97 (1975) 4884. [28] V.H. Crawford, H.W. Richardson, J.R Wasson, D.J. Hodgson, W. Hatfield, Inorg. Chem. 15 (1976) 2107.
Note
A novel bimetallic alternating chain: synthesis, crystal structure and magnetic study Partha Sarathi Mukherjeee a, Tapas Kumar Maji a, Talal Mallah b, Ennio Zangrando c, Lucio Randaccio c, Nirmalendu Ray Chaudhuri a,* a
Department of Inorganic Chemistry, Indian Association for the Culti6ation of Science, Jada6pur, Calcutta 700032, India b Laboratoire de Chimie Inorganique, UMR CNRS 8613, Uni6ersite´ de Paris-Sud, 91405 Orsay, France c Dipartimento di Scienze Chimiche, Uni6ersity of Trieste, 34127 Trieste, Italy Received 11 August 2000; accepted 26 January 2001
Abstract A novel one dimensional (1D) bimetallic polymeric complex [catena-bis(m-N-(aminoethyl)-3-aminopropanolato)-di-copper(II)tetracyanonickelate(II)dihydrate] has been synthesized by the reaction of 1:1 mixture of CuCl2·2H2O and the hydoxyamine ligand, [N-(3-hydroxypropyl)ethane-1,2-diamine] with half equivalent of [Ni(CN)4] − 2 in aqueous solution. X-ray quality single crystals were obtained by slow evaporation of the ammoniacal solution of the complex. The single crystal structure reveals that it is an alkoxo bridged Cu(II) dimer linked through [Ni(CN)4]2 − in trans-fashion resulting in a 1D chain. The properties of the complex have been studied by variable temperature magnetic susceptibility measurements. The susceptibility data fit well with the Cu(lI) dimer equation to give 2J= −622 cm − 1, g=2.05. The very high coupling parameter value clearly indicates the presence of very strong antiferromagnetic interaction between the Cu(II) ions. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Crystal structure; Magnetic study; Bimetallic chain complexes; Cyano-bridged complexes; Nickel complexes
1. Introduction Since the early works of Lehn [1] and Padersen [2], construction of coordination polymers via metal coordination directed self-assembly processes has attracted the attention of scientists from different areas, ranging from chemistry to material science and also biology, because of the promising applications such as biomimic models [3] or functional materials for catalysis, absorption, nonlinear optics, and molecular magnetic materials [4–7]. The general synthetic approach for the metal assembles is to utilize metal complexes having coordination ability as a building block to react with transition metal cations. Recently, there has been an increasing interest in polynuclear or polymeric metal cyanides owing to their often remarkable structural as * Corresponding author. Tel.: +91-33-4734971; fax: + 91-334732805. E-mail address: [email protected] (N.R. Chaudhuri).
well as physicochemical properties [8–11]. The most prominent characteristic of CN− is its ability to act either as a terminal or as a bridging ligand. As it is a good super exchange pathway between the paramagnetic metal ions it is widely used in the construction of molecular based magnetic materials [12,13]. Recently, using cyanometallate as a building block a few homoand bimetallic chains were reported [14,15]. In all the previously reported bimetallic chains it is observed that two different types of metal ions are repeated alternately, but bridging through only one type of ligand. To our knowledge, there are not many reports in the literature of a bimetallic chain with two different types of metal as well as two different types of bridging ligand simultaneously repeated in a periodic fashion. In the present paper we report the synthesis, crystallization by an uncommon way, structural and magnetic study of a novel 1D bimetallic [Cu(II)Ni(II)] chain where the two different bridging moieties (alkoxide and cyanide) are repeated in a periodic fashion.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 1 ) 0 0 3 5 4 - 1
P.S. Mukherjeee et al. / Inorganica Chimica Acta 315 (2001) 249–253
250
2. Experimental
2.1. Reagents Copper(II) chloride dihydrate, N-(3-hydroxypropyl)ethane-1,2-diamine, potassium-tetracyanonickelate dihydrate were purchased from commercial sources and used as received.
2.2. Physical techniques The IR spectrum was taken on a Nicolet 520 FTIR spectrophotometer as KBr pellets in the range of 4000 – 400 cm − 1. Variable-temperature magnetic susceptibility measurements were carried out in the temperature range 70–380 K in applied fields of 5 kOe with a SQUID magnetometer. The diamagnetic corrections were estimated from Pascal’s constants [16].
2.3. Synthesis To a deep blue aqueous solution (10 cm3) containing CuCl2·2H2O (1 mmol) and N-(3-hydroxypropyl)ethane1,2-diamine (1 mmol) was added, slowly with continuous stirring, an aqueous solution (10 cm3) of K2[Ni(CN)4]·2H2O (0.5 mmol). A sky blue solid separated out, filtered and washed with water. It was treated with methanol (10 cm3) and stirred well to form a slurry. Dilute aqueous solution of ammonia was added
to it slowly drop by drop for dissolution. The resulting deep blue solution yields suitable single crystals for X-ray diffraction on keeping in a refrigerator for a week. The yield is about 70%. Anal. Found: C, 29.98; H, 5.26; N, 19.80. Calc. for C14H30N8Cu2NiO4: C, 30.06; H, 5.36; N, 20.09%.
2.4. X-ray structure determination A crystal suitable for X-ray analysis was mounted on an Enraf –Nonius CAD4 single-crystal diffractometer equipped with graphite monochromator and Mo Ka radiation (u= 0.7107 A, ). Diffraction measurements were carried out at room temperature (r.t.) using the – 2q scan technique. Three standard reflections, measured at regular intervals throughout the data collection, showed no decay in intensity. An absorption correction based on the -scan method was applied. The collected intensity data were corrected for Lorentz polarization effect. A total of 3523 reflections were measured and 1751 were assumed observed applying the condition I\ 2|(I). The structure was solved by Patterson and Fourier technique [17] and refined through full-matrix anisotropic least-squares method [18] using SHELXL93 [19]. The refinement converged to residual indices R1(Fo)= 0.0539; wR2(Fo 2)=0.0931 with I\2|(I). The final difference Fourier map showed maximum and minimum peak heights of 0.470, − 0.501 e A, − 3, respectively. The crystallographic data are given in Table 1.
3. Results and discussion Table 1 Crystal data and structure refinement for the complex [catenabis(m-N-(aminoethyl)-3-aminopropanolato)-di-copper(II)-tetracyanonickelate(II)dihydrate] Formula Formula weight (g) Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) h (°) i (°) g (°) V (A, 3) Z T (K) Dcalc (g cm−3) v(Mo Ka) (cm−1) u(Mo Ka) (A, ) R1 a wR2 b a b
C14H30Cu2N8NiO4 560.26 monoclinic P21/n 9.619(1) 9.723(2) 11.987(1) 90 101.10(1) 90 1100.1(3) 2 298 1.691 27.99 0.71069 0.0539 0.0931
R = Fo − Fc / Fo . Rw =[{w(Fo 2−Fc 2)2}/{w(Fo 2)2}]1/2.
3.1. Synthesis The reaction of K2[Ni(CN]4]·2H2O with CuCl2·2H2O and the tridentate hydroxyamine ligand produced a sky blue precipitate. Its crystals, suitable for structure determination, were obtained by an unusual procedure, i.e. dissolution of the precipitate in dilute solution of NH3 and slow evaporation of the ammonia. The precipitate is insoluble in common organic solvents and its solubility in ammonia is possibly due to the coordination of NH3 to the copper which breaks the bridging cyanide system. The evaporation of NH3 regenerates the tetracyanonickelate bridged polymeric complex.
3.2. IR spectra The most important aspects of the IR spectra of the title complex involve the characteristic vibration of the CN groups. The formation of a cyanide bridge in the polymeric complex was evidenced by IR spectra in the region of stretching vibration of the cyanide ligands. It shows two sharp bands at 2125 and 2150 cm − 1 in the
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251
suggests a lower symmetry about the tetracyanonickelate entity and the formation of a cyanide bridge.
3.3. Description of the structure
Fig. 1. ORTEP plot of the title compound (thermal ellipsoids at 40% probability level) with atom numbering scheme of the asymmetric unit. Table 2 Selected bond lengths (A, ) and angles (°) of the complex [catenabis(m-N-(aminoethyl)-3-aminopropanolato)-di-copper(II)-tetracyanonickelate(II)dihydrate] NiC(2) NiC(1) CuO(1) CuO(1) CuN(1)
a
C(2)NiC(1) b C(2)NiC(1) CuO(1)Cu a O(1)CuO(1) a O(1)CuN(4) O(1 a)CuN(4) O(1)CuN(3) O(1 a)CuN(3) a b
1.848(5) 1.852(4) 1.925(3) 1.927(3) 2.402(4)
CuN(3) CuN(4) N(1)C(l) N(2)C(2) Cu···Cu a Cu···Ni
1.995(3) 1.992(4) 1.147(5) 1.135(6) 2.9809(11) 5.1547(6)
90.20(18) 89.80(18) 101.40(12) 78.60(12) 94.56(14) 168.37(13) 170.55(15) 100.46(13)
O(1)CuN(1) O(1) aCuN(1) N(4)CuN(1) N(3)CuN(1) N(4)CuN(3) N(1)C(1)Ni N(2)C(2)Ni CuN(1)C(1)
97.95(14) 97.71(14) 92.51(14) 91.50(14) 84.73(15) 178.1(5) 178.2(5) 146.2(4)
Symmetry codes: −x, −y+1, −z+2. Symmetry codes: −x, −y+1, −z+1.
An ORTEP view of the NiCu2 moiety, with the atom numbering scheme of the crystallographic independent unit is shown in Fig. 1. Selected bond distances and angles are reported in Table 2. The crystal structure consists of alkoxo-bridged binuclear Cu(II) units linked by m-trans-[Ni(CN]4] − 2 anions giving a one-dimensional (1D) polymeric chain (Fig. 2). Each copper ion is in a square pyramidal coordination through two alkoxo oxygens and the nitrogen donors of the ethylenediaminopropanolato ligand. Each copper atom is displaced by about 0.1 7 A, from the N2O2 mean plane towards the cyanide nitrogen, at the apical position of the pyramid that completes the coordination sphere (CuN(1) 2.402(4) A, ). The coordination bond distances with oxygen are similar (1.925(3) and 1.927(3) A, ), as well as those with the terminal amino and imino nitrogen donors (1.995(3) and 1.992(4) A, ). These distances compare well with those found in structurally equivalent dinuclear copper(II) complexes [20]. The bond distances in the square planar Ni coordination are in the expected range, with the CuN(1)C(1) angle significantly bent (146.1(4) A, ). This angle is comparable with that found in the clathrate [Cu(en)2NCNi(CN)2CN]n (150.3(5)°) [21], but it is narrower with respect to those detected in other structures (range between 158 and 164°), both with cis- and trans-bridging Ni(CN)4-units [22,23]. The mean plane of the [Ni(CN)4]2 − anion makes a dihedral angle of 58.71(9)° with the coordination basal plane of copper. A crystallization water molecule, accommodated in the void spaces, connects three adjacent 1D chains through weak H-bonds. One of which also interacts with nitrogen N(1) of cyanide which accounts for the value of the angle at N(1) cited above. These hydrogen bonds, which stabilize the overall crystal structure ranges from 2.88 to 3.27 A, (Fig. 2 and Table 3). Table 3 Hydrogen bonds in the crystal structure of the complex [catenabis(m-N-(aminoethyl)-3-aminopropanolato)-di-copper(II)-tetracyanonickelate(II)dihydrate]
Fig. 2. Perspective view of crystal structure with hydrogen bonds involving the guest water molecules. Nitrogen atoms N(lIII) and N(4II) pertain to a third polymeric chain which is not drawn for the sake of clarity (symmetry codes in Table 3).
DH
d(DH)
d(H···A)
ÚDHA
d(D···A)
A
OwHI OwH2 N(3) aH2a N(4) bH N(3) bH1
0.894 1.101 0.900 0.910 0.900
2.018 2.093 2.293 2.609 2.481
162.73 152.83 147.99 130.66 138.67
2.883 3.113 3.093 3.275 3.212
N(2) N(1) Ow Ow N(2)
a
IR spectrum. The shift of the w(CN) to a higher wave number compared to that of K2[Ni(CN)4] (2121 cm − 1)
Symmetry codes: x+1, y, z. Symmetry codes: x+1/2, −y+1/2, z−1/2. c Symmetry codes: −x+1/2, y−1/2, −z+3/2. b
c
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252
Table 4 Cu−O−Cu angle (h) and magnetic data for m-alkoxo or m-hydroxo dinuclear Cu(II) complexes Complex
a
[Cu(EAEP)(OH)]2 (ClO4)2 b-[Cu(DMAEP) (OH)]2(ClO4)2 a-[Cu(DMAEP) (OH)]2(ClO4)2 Title complex (in this paper)
CuOCu angle (h) (°) 99 98.4
2J (cm−1)
Ref.
−130
[27]
−2.3
[25]
100.4
−201
[25]
101.4
−622
this study
a
EAEP, 2-(2-ethylaminoethyl)pyridine; DMAEP, 2-(2-dimethylaminoethyl)pyridine.
3.4. Magnetic study Although the title complex shows two d9 Cu(II) and one d8 Ni(II) ions in the molecular unit, the substantially flat square-planar coordination of the [Ni(CN)4]2 − diamagnetic unit permits that, from the magnetic point of view, the compound can be treated as a dimeric complex in which two d9 Cu(II) ions are linked through a bridging alkoxide anion. Again the length of the exchange pathway through the bidentate tetracyanonickelate(II) ligand is large enough to predict that the magnetic interaction takes place mainly through the alkoxide bridging moiety, which is known to be very effective in mediating antiferro- or ferromag-
netic coupling between first-row transition metal ions depending on the MOM angle [24]. The angle MOM (101.40) in our complex clearly suggests that the molecule is antiferromagnetic because complexes with CuOCu angle larger than 97° shows antiferromagnetic interaction and the extent of such interaction increases rapidly (Table 4) with increase in the CuOCu angle [24]. The thermal dependence of the molar magnetic susceptibility M of the complex (Fig. 3) is characteristic of an antiferromagnetic interaction between the copper(II) ions. Since the maximum in the M = f(T) curve is higher than T=380 K, we can safely say that the coupling constant (2J) is larger than 450 cm − 1 [25]. The molecule becomes diamagnetic below 200 K. As in all diamagnetic ground states, a small amount of paramagnetic impurities is detected which is calculated and is about 0.4%, which is reasonable. The M vs. T data of the complex fitted well using the modified Bleaney – Bowers equation for the magnetic susceptibility of isotropically coupled dinuclear S= 1/2 ions [26], adding an impurity term which is due to the presence of non-coupled monomeric species (Eq. (1)) using the Hamiltonian H= −2JSaSb. The results of the best fit, shown as a solid line in Fig. 3, were 2J= − 622 cm − 1, g = 2.05, z(residual paramagnetic impurity)=0.4% with agreement factor R=1.7×10 − 6. The very high value of 2J clearly indicates that the antiferromagnetic interaction between the Cu(II) ions is very strong, which is rare for such a type of dimeric complex and such a strong antiferromagnetic interaction results due
Fig. 3. Molar magnetic susceptibility versus temperature plot for the title complex. Solid line shows the best fit obtained by applying Eq. (1) (see text).
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to the coordination environment around the paramagnetic centers [27,28]. Each CuO2N2 environment of the dimeric part is almost planar with very low displacement (about 0.17 A, ) of the copper atom from the O2N2 mean plane. Both the copper(II) centers in the dimeric unit are square pyramidal with four short and one long bonds, indicating that the spin unpaired electron is located in basal dx 2 − y 2 orbital and dz 2 orbital contains spin paired electrons. Again the dx 2 − y 2 orbital of both the copper(II) in the dimeric unit interacts with the bridging oxygen, such an equatorial – equatorial interaction along with the large CuOCu, which determines the coupling parameter value, is comparable with the other similar type of complexes (Table 4) and is consistent with the strong magnetic interaction between the copper(II) ions in the present complex M = 2Ng 2i 2(1− z)[3 + exp( −J/kT)] − 1/kT + Ng 2i 2|/2kT +Nh
(1)
4. Conclusions We have presented the synthesis, crystal structure and magneto-structural correlation of a novel 1D polymeric chain, where an alkoxo bridged Cu(II) dimer is linked by tetracyanonickelate anion in trans-fashion. Three adjacent chains are connected to the guest water molecules through hydrogen bonding. The most striking feature of the complex is that in a same chain the two different types of metals as well as two different types of bridging ligands are repeated in periodic fashion, of which there are not many reports in the literature. The magnetic susceptibility data show that the molecule becomes diamagnetic below 200K. The best-fit using the famous Bleaney – Bowers equation for S =1/2 coupled dimeric system gives 2J = − 622 cm − 1. This high coupling parameter value clearly indicates the existence of very strong antiferromagnetic interaction between the paramagnetic Cu(II) centers.
5. Supplementary material Further data (atomic fractional coordinates, thermal parameters, complete distances and angles, etc.) can be obtained on request from the Crystallographic Data Center, University Chemical Laboratory, Lensfield Road, Cambridge CB12 1EW, UK, on quoting the number CCDC 147291.
.
253
Acknowledgements The authors wish to thank the Council of Scientific and Industrial Research, New Delhi, for financial support (granted to N.R.C.).
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