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Synthesis and structural characterisation of a cyano-bridged trinuclear complex [(CuL)2Fe(CN)6][ClO4]·2CH3OH·H2O
Polyhedron 20 (2001) 2473– 2476 www.elsevier.com/locate/poly
Synthesis and structural characterisation of a cyano-bridged trinuclear complex [(CuL)2Fe(CN)6][ClO4]·2CH3OH·H2O Nijhuma Mondal a, Samiran Mitra a,*, Georgina Rosair b b
a Department of Chemistry, Jada6pur Uni6ersity, Calcutta 700 032, India Department of Chemistry, Heriot-Watt Uni6ersity, Edinburgh, EH14 4AS, UK
Received 15 January 2001; accepted 10 May 2001
Abstract The trinuclear complex [(CuL)2Fe(CN)6][ClO4]·2CH3OH·H2O [L = N,N%-bis(2-pyridyl imine)propane-1,3-diamine] has been prepared and characterised by spectroscopic, elemental analysis, room temperature magnetic moment and single crystal X-ray analysis. Both copper(II) ions have a distorted square pyramidal geometry and are trans to each other, linked via cyanide bridges to the iron(III) centre. At the Cu(1) copper centre there is disorder between flattened chair and boat conformations in the saturated chelate ring. Of the six CN− groups around the octahedral iron(III) centre, four are terminal and the remaining two are coordinated to the [Cu(L)]2 + moieties, giving nonlinear Fe– CN– Cu linkages. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Cyano-bridge; Trinuclear complexes; Crystal structures; Spectroscopic studies
1. Introduction The field of molecular magnetism has advanced considerably in the last decade [1 – 3]. One approach in the design of molecular based magnets uses the hexacyanometallate ion as a building block which reacts with simple metal ions to produce Prussian Blue and its analogues [4–8] and with metal complexes to generate mixed valence multidimensional networks [9–12]. When coordinately unsaturated complexes are used instead of simple metal ions, hexacyanometallate ions can adopt many different bridging modes to form bimetallic assemblies of either discrete molecules or extended network structures. Recently, we reported a 2-D polymeric polynuclear compound with an exceptional 1,1 end-on cyanide bridge [13], and a pentanuclear complex [(CuL)4Fe(CN)6]·16H2O [L =N,N-dimethyl-N%-(amethylsalicylidene)ethane-1,2-diamine] [14]. Combining Schiff base cationic complexes with the hexacyanometallate ions generates large variations in magnetic properties and structure [15]. Previous investi-
gations [15 –19] varied (i) Schiff base ligands (ii) the nature of the counter anion and (iii) the transition metal couple. The range of such mixed-valence and mixed-metal complexes is still limited, so by investigating the structure and magnetic properties of these species, we hope to improve the design of multinuclear magnetic complexes. Focusing our interest in this area, we have synthesised a cationic Cu(II) complex with the neutral tetradentate Schiff base ligand L, where L= N,N%-bis(2-pyridyl imine)propane-1,3-diamine. These types of Schiff base ligand have been used for designing Cu2Zn2SOD (SOD = superoxide dismutase) model complexes [19,20]. In this article, we have extended this study by assembling the [CuL]2 + cation with the low spin iron(III) (S= 1/2) [Fe(CN)6]3 − via the reaction of [CuL][ClO4]2 with [NEt4]3[Fe(CN)6].
2. Experimental
2.1. Physical measurements * Corresponding author. Tel.: + 91-33-668-4193; fax: +91-33-4734266. E-mail address: smitra – [email protected] (S. Mitra).
Elemental analyses were carried out using a Perkin – Elmer 2400 II elemental analyser. Infrared spectra were
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recorded on a Perkin– Elmer 883-Instrument using KBr pellets and electronic spectra in the solid state were recorded with a Hitachi U-3400 (UV– vis-NIR) spectrophotometer. Magnetic susceptibility measurements at 293 K were carried out using vibrating sample magnetometer.
2.2. Materials Reagent grade pyridine-2-carboxaldehyde (Fluka), 1,3-diaminopropane (Merck) and Cu(ClO4)2·6H2O (Aldrich) were obtained commercially and used as received.
2.3. Synthesis of the ligand and metal complexes The ligand [N,N%-bis(2-pyridylimine)propane-1,3-diamine] was prepared by the condensation of a methanolic solution of 1,3-diaminopropane (0.37 g, 5 mmol) with pyridine-2-carboxaldehyde (1.07 g, 10 mmol) for half an hour. The resulting brown solution was used for complex preparation without further purification. [CuL][ClO4]2 was prepared by mixing Cu[ClO4]2· 6H2O (3.70 g, 10 mmol) in 50 ml methanol to the above ligand solution with stirring. [NEt4]3[Fe(CN)6] was also prepared according to the reported procedure [21].
Table 1 Crystal data for 1 Empirical formula Temperature (K) Wavelength (A, ) Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) h (°) i (°) k (°) V (A, 3) Z Dcalc (Mg m−3) Absorption coefficient (mm−1) Crystal size (mm) q Range for data collection (°) Reflections collected Data/restraints/parameters Goodness-of-fit on F 2 Final R indices [I\2|(I)] R indices (all data) Largest difference peak and hole (e A, −3)
2.4. Synthesis of the title complex Since the hexacyanometallate ion has a tendency to decompose during heating and irradiation, the complex was synthesised at room temperature (r.t.) and crystallised in the dark. [NEt4]3[Fe(CN)6] (0.60 g, 1 mmol), dissolved in 20 ml of methanol, was added to a solution of [CuL][ClO4]2 (1.02 g, 2 mmol) in methanol (50ml). Dark green crystals appeared after 5 days from this solution, and were collected by suction filtration, washed with a minimum volume of ethanol and dried in air.
2.5. X-ray crystallography of complex 1 A green air stable plate-shaped crystal of 1 was mounted on a glass fibre, and the crystallographic data were measured on a Bruker AXS P4 four-circle diffractometer at 160 K. Semi-empirical absorption corrections were applied using scans. Structure solution and refinement were performed using the SHELXL 5.1 suite of programs. The structure was refined by a full-matrix least-squares based on F 2 [22]. All hydrogen atoms were included in the idealised positions and refined using a riding model with riding isotropic U which was 1.2× Ueq of the bound C atom. No hydrogen atoms were included in the model for the water and methanol solvent atoms. The disordered methanol molecule was modelled as one C atom at 100% occupancy, O at 75% and another C atom at 25% occupancy. The crystallographic data are presented in Table 1.
3. Results and discussion C38H42ClCu2FeN14O7 160(2) 0.71073 monoclinic P21/c 17.606(3) 14.153(4) 17.636(2) 90 102.84(2) 90 4284.6(15) 4 1.589 1.446 0.42×0.38×0.06 1.86–25.00 9034 7530/0/562 1.023 R1 = 0.0792, wR2 = 0.1835 R1 = 0.1523, wR2 = 0.2246 0.866 and −0.739
3.1. Infrared spectrum The IR spectrum shows a broad peak in the range 3550–3300 cm − 1, indicating the presence of water in the lattice. The band at 2118 cm − 1 is assigned as w(CN) and the band at 1603 cm − 1 as an imine stretching frequency, slightly lower than in other Schiff base complexes where it was reported between 1610 and 1630 cm − 1 [23]. The broad band near 1150–1090 cm − 1 and three sharp bands in the range 625–540 cm − 1 indicated the presence of uncoordinated perchlorate anion. All the other bands appeared at their usual positions.
3.2. Electronic spectrum The electronic spectrum in the solid state of the title complex shows bands with maxima at 608 and 377 nm. In the solution state these bands were at 620 and 380 nm. The broad band with maxima at 608 nm shows a sensible bathochromic shift with respect to the parent
N. Mondal et al. / Polyhedron 20 (2001) 2473–2476
Fig. 1. A perspective view of 1 with atom numbering scheme. Solvent atoms have been omitted.
Cu(II) complex. The sharp band at 377 nm cannot be easily assigned, as several transitions with different origins can be expected: iron(III) d– d transition, charge transfer from ligand to iron and charge transfer between copper and iron in either direction.
3.3. Magnetic susceptibility The room temperature magnetic moment value (3.76vB) is very slightly lower than the expected value for the total of three (two from the copper centres and one from iron centre) unpaired electrons.
3.4. Crystal structure of the complex The molecular structure of complex consists of discrete trinuclear mixed metal species with two copper centres linked to an iron centre through bent cyanobridges [C(150–N(5) – Cu(1), 146.5(6); C(120)– N(12)– Cu(2), 150.4(7)°] along with the two (one disordered and one ordered) molecules of methanol and one water molecule. The arrangement of the trinuclear unit is shown in Fig. 1 and selected bond distances and angles are given in Table 2. The closely related polymeric Fe(II)– CN –Cu(II) species [24], has two types of copper centre, one identical to that in 1 (i.e. with the same tetradentate ligand) and a second type which is bound by a smaller tridentate ligand (2-pyridylmethylene-1,3propanediamine). This second type of copper centre is bound to two bridging cyanides, thereby propagating the M –CN –M chain. Both the copper centres in 1 have distorted square pyramidal geometry with the geometrical factor ~, 0.15 for Cu(1) and 0.07 for Cu(2), emphasising that the metal centre geometry is much closer to square pyramidal than trigonal bipyramidal. The environment around both copper atoms is very similar, with slight differ-
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ences in bond lengths and angles. The four Schiff base nitrogen atoms occupy the basal plane and the cyanide nitrogen atom occupies the axial position. The tetraimine ligand is twisted slightly at the copper centres. Cu(1) and Cu(2) are both displaced out of the basal plane by 0.29 A, toward the iron centre. The basal planes [N(1), N(2), N(3), N(4) and N(6), N(7), N(8), N(9)] are almost parallel (normals of the two planes are inclined at 3.1° to each other). There is disorder between flattened chair and boat conformations (72 and 28%, respectively) in the saturated chelate ring at Cu(1), whereas at Cu(2) the same chelate ring exists as a flattened chair with no obvious sign of disorder. In the chemically-identical copper centre to 1 in the polymeric iron–cyano–copper species [24], the chelate ring also possesses a flattened chair conformation and the equatorial Cu–N bond lengths are in the range 1.981(6) to 2.110(6) A, . The equivalent Cu –N lengths in 1 are very similar, with the shortest set associated with the alkyl N atoms. [1.998(7), 2.019(7) 2.087(7), 2.035(6), A, for Cu(1)– N(1), Cu(1)– N(4) Cu(1)–N(2), Cu(1)–N(3), and 1.962(9), 2.002(9), 2.041(8), 2.011(9) A, for Cu(2)–N(7), Cu(2)–N(8), Cu(2)–N(6) and Cu(2)–N(9), respectively]. As expected, the axial Cu–NC distances [2.143(7) A, for Cu(1)–N(5) and 2.146(7) A, for Cu(2)– N(12)] are substantially longer than equatorial distances. When the Table 2 Selected bond lengths (A, ) and bond angles (°) for 1 Bond lengths Cu(1)–N(1) Cu(1)–N(2) Cu(1)–N(3) Cu(1)–N(4) Cu(1)–N(5) Fe(1)–C(100) Fe(1)–C(120) Fe(1)–C(130)
1.998(7) 2.087(7) 2.035(6) 2.019(7) 2.143(7) 1.932(9) 1.916(8) 1.959(11)
Cu(2)–N(6) Cu(2)–N(7) Cu(2)–N(8) Cu(2)–N(9) Cu(2)–N(12) Fe(1)–C(110) Fe(1)–C(140) Fe(1)–C(150)
2.041(8) 1.962(9) 2.002(9) 2.011(9) 2.146(7) 1.951(10) 1.946(10) 1.936(8)
Bond angles C(150)–N(5)–Cu(1) N(5)–C(150)–Fe(1) N(1)–Cu(1)–N(4) N(1)–Cu(1)–N(3) N(4)–Cu(1)–N(3) N(1)–Cu(1)–N(2) N(4)–Cu(1)–N(2) N(3)–Cu(1)–N(2) N(1)–Cu(1)–N(5) N(4)–Cu(1)–N(5) N(3)–Cu(1)–N(5) N(2)–Cu(1)–N(5) C(120)–Fe(1)–C(100) C(120)–Fe(1)–C(150) C(100)–Fe(1)–C(150) C(120)–Fe(1)–C(140) C(100)–Fe(1)–C(140) C(150)–Fe(1)–C(140) C(120)–Fe(1)–C(110) C(100)–Fe(1)–C(110)
146.5(6) 176.3(7) 91.7(3) 167.7(3) 80.3(3) 81.0(3) 157.8(3) 102.9(3) 93.1(3) 100.8(3) 97.6(2) 100.6(3) 87.1(3) 175.9(4) 90.3(3) 92.1(3) 89.4(4) 90.9(3) 88.2(3) 90.9(4)
C(120)–N(12)–Cu(2) N(12)–C(120)–Fe(1) N(7)–Cu(2)–N(8) N(7)–Cu(2)–N(9) N(8)–Cu(2)–N(9) N(7)–Cu(2)–N(6) N(8)–Cu(2)–N(6) N(9)–Cu(2)–N(6) N(7)–Cu(2)–N(12) N(8)–Cu(2)–N(12) N(9)–Cu(2)–N(12) N(6)–Cu(2)–N(12) C(150)–Fe(1)–C(110) C(140)–Fe(1)–C(110) C(120)–Fe(1)–C(130) C(100)–Fe(1)–C(130) C(150)–Fe(1)–C(130) C(140)–Fe(1)–C(130) C(110)–Fe(1)–C(130)
150.4(7) 175.5(8) 90.1(5) 164.5(4) 81.7(4) 81.4(4) 159.9(4) 102.0(4) 105.0(4) 104.3(3) 89.8(4) 95.6(3) 88.8(3) 179.6(4) 92.8(4) 177.2(4) 90.0(3) 87.8(4) 91.9(4)
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two alkyl bound nitrogen atoms are protonated in the tetradentate ligand L, as in the mononuclear copper species [25] a twist conformation is observed in the saturated chelate ring. The Cu– N lengths are in the range 2.008–2.028 A, , a smaller range than found for 1, however the structure determination was at room temperature and there was no axial ligand. The trans bond angles around the Cu centres are N(3) –Cu(1)–N(1), N(4)– Cu(1) – N(2), N(6)– Cu(2)– N(8) and N(7)–Cu(2) – N(9) are 167.7(3), 157.8(3), 159.9(4) and 164.5(4)°, respectively. The two trans angles around Cu(1) are significantly different, despite the C2 symmetry of the tetradentate ligand. This is also found at the same copper centre in Ref. [24], [167.3(2), 156.3(2)°]. The iron centre has almost ideal octahedral geometry and is bound to the two copper(II) centres via trans bridging cyanide groups. The average Fe– C and CN distances are 1.94(9)1 and 1.157(10) A, whilst the Fe···Cu distances are 4.987(2) and 5.053(2) A, for Cu(1) and Cu(2), respectively. The bridging cyanides are bent significantly at both nitrogen atoms [C(150)– N(5)– Cu(1) and C(120)– N(12) – Cu(2) are 146.5(6) and 150.4(7)°, respectively] whilst the angles at carbon are much closer to 180°. The zig – zag polymeric structure [24] has more pronounced bending of the CN bridges at nitrogen [136.4(6), 140.8(6)°] and the equivalent Fe···Cu distance is shorter, 4.811(4) A, . The closest contacts made to the cyanide complex by the perchlorate ion are between O1 and Cu1 [2.941(3) A, ]. O4 (methanol) atom and O11 (perchlorate) are 2.60(2) A, apart, probably involved in a hydrogen bond involving the unlocated H atom from MeOH. The water does not make any contacts closer than 2.6 A, with other non-H atoms.
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 155691. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1233-336-033; e-mail: deposit@ ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk). 1
Standard deviation of the population.
Acknowledgements This work is supported by grants from CSIR, UGC, AICTE and DST (New Delhi, India).
References [1] O. Kahn, Advances in Inorganic Chemistry, vol. 43, Academic Press, San Diego, 1995, p. 179. [2] O. Kahn, Molecular Magnetism, VCH, Weinheim, 1993. [3] D. Gatteschi, O. Kahn, J.S. Miller, F. Palacio (Eds.), Magnetic Molecular Materials, NATO ASI Series E, Kluwer Academic, Dordrecht, The Netherlands, 1991, p. 198. [4] V. Gadet, T. Mallah, I. Castro, P. Veillet, M. Verdaguer, J. Am. Chem. Soc. 114 (1992) 9213. [5] F. Herren, P. Fischer, A. Ludi, W. Halg, Inorg. Chem. 19 (1980) 956. [6] T. Mallah, S. Thiebaut, M. Verdaguer, P. Veillet, Science 262 (1993) 1554. [7] W.R. Entley, G.S. Girolami, Science 268 (1995) 397. [8] M. Verdaguer, Science 272 (1996) 698. [9] H.-Z. Kou, S. Gao, W.-M. Bu, D.-Z. Liao, B.-Q. Ma, Z.-H. Jiang, S.-P. Yan, Y.-G. Fan, G.-L. Wang, J. Chem. Soc., Dalton Trans. (1999) 2477. [10] M. Ohba, N. Usuki, N. Fukita, H. O( kawa, Inorg. Chem. 37 (1998) 3349. [11] H.-Z. Kou, W.-M. Bu, D.-Z Liao, Z.-H. Jiang, S.-P. Yan, Y.-G. Fan, G.-L. Wang, J. Chem. Soc., Dalton. Trans. (1998) 4161. [12] M. Ferbinteanu, S. Tanase, M. Andruh, Y. Journaux, F. Cimpoesu, I. Strenger, E. Rivie`re, Polyhedron 18 (1999) 3019. [13] N. Mondal, M.K. Saha, B. Bag, S. Mitra, V. Gramlich, J. Ribas, M.S. El Fallah, J. Chem. Soc., Dalton Trans. (2000) 1601. [14] N. Mondal, M.K. Saha, B. Bag, S. Mitra, G. Rosair, M.S. El Fallah, Polyhedron (communicated). [15] H. Miyasaka, N. Matsumoto, H. O( kawa, N. Re, E. Gallo, C. Floriani, J. Am. Chem. Soc. 118 (1996) 981. [16] H. Miyasaka, N. Matsumoto, N. Re, E. Gallo, C. Floriani, Inorg. Chem. 36 (1997) 670. [17] N. Re, R. Crescenzi, C. Floriani, H. Miyasaka, N. Matsumoto, Inorg. Chem. 37 (1998) 2717 and references therein. [18] M.J. Scott, S.C. Lee, R.H. Holm, Inorg. Chem. 33 (1994) 4651. [19] C.-M. Liu, R.-G. Xiong, X.-Z. You, Y.-J. Liu, K.-K. Cheung, Polyhedron 15 (1996) 4565. [20] C.-M. Liu, R.-G. Xiong, X.-Z. You, H.-K. Fun, K. Sivakumar, Polyhedron 16 (1997) 119. [21] P.K. Mascharak, Inorg. Chem. 25 (1986) 245. [22] G.M. Sheldrick, Structure Determination and Refinement Programs, version 5.1. Bruker AXS Inc., Madison, WI, 1997. [23] (a) S. Mandal, P.K. Bharadwaj, Polyhedron 12 (1993) 543; (b) R. Shukla, P.K. Bharadwaj, J. van Hall, K.H. Whitmire, Polyhedron 13 (1994) 2387. [24] E. Colacio, J.-M. Dominguez-Vera, M. Ghazi, R. Kivekas, J.M. Moreno, A. Pajunen J. Chem. Soc., Dalton Trans. (2000) 505. [25] A. Jantti, K. Rissanen, J. Valkonen, Acta Chem. Scand. 52 (1998) 1010.
Synthesis and structural characterisation of a cyano-bridged trinuclear complex [(CuL)2Fe(CN)6][ClO4]·2CH3OH·H2O Nijhuma Mondal a, Samiran Mitra a,*, Georgina Rosair b b
a Department of Chemistry, Jada6pur Uni6ersity, Calcutta 700 032, India Department of Chemistry, Heriot-Watt Uni6ersity, Edinburgh, EH14 4AS, UK
Received 15 January 2001; accepted 10 May 2001
Abstract The trinuclear complex [(CuL)2Fe(CN)6][ClO4]·2CH3OH·H2O [L = N,N%-bis(2-pyridyl imine)propane-1,3-diamine] has been prepared and characterised by spectroscopic, elemental analysis, room temperature magnetic moment and single crystal X-ray analysis. Both copper(II) ions have a distorted square pyramidal geometry and are trans to each other, linked via cyanide bridges to the iron(III) centre. At the Cu(1) copper centre there is disorder between flattened chair and boat conformations in the saturated chelate ring. Of the six CN− groups around the octahedral iron(III) centre, four are terminal and the remaining two are coordinated to the [Cu(L)]2 + moieties, giving nonlinear Fe– CN– Cu linkages. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Cyano-bridge; Trinuclear complexes; Crystal structures; Spectroscopic studies
1. Introduction The field of molecular magnetism has advanced considerably in the last decade [1 – 3]. One approach in the design of molecular based magnets uses the hexacyanometallate ion as a building block which reacts with simple metal ions to produce Prussian Blue and its analogues [4–8] and with metal complexes to generate mixed valence multidimensional networks [9–12]. When coordinately unsaturated complexes are used instead of simple metal ions, hexacyanometallate ions can adopt many different bridging modes to form bimetallic assemblies of either discrete molecules or extended network structures. Recently, we reported a 2-D polymeric polynuclear compound with an exceptional 1,1 end-on cyanide bridge [13], and a pentanuclear complex [(CuL)4Fe(CN)6]·16H2O [L =N,N-dimethyl-N%-(amethylsalicylidene)ethane-1,2-diamine] [14]. Combining Schiff base cationic complexes with the hexacyanometallate ions generates large variations in magnetic properties and structure [15]. Previous investi-
gations [15 –19] varied (i) Schiff base ligands (ii) the nature of the counter anion and (iii) the transition metal couple. The range of such mixed-valence and mixed-metal complexes is still limited, so by investigating the structure and magnetic properties of these species, we hope to improve the design of multinuclear magnetic complexes. Focusing our interest in this area, we have synthesised a cationic Cu(II) complex with the neutral tetradentate Schiff base ligand L, where L= N,N%-bis(2-pyridyl imine)propane-1,3-diamine. These types of Schiff base ligand have been used for designing Cu2Zn2SOD (SOD = superoxide dismutase) model complexes [19,20]. In this article, we have extended this study by assembling the [CuL]2 + cation with the low spin iron(III) (S= 1/2) [Fe(CN)6]3 − via the reaction of [CuL][ClO4]2 with [NEt4]3[Fe(CN)6].
2. Experimental
2.1. Physical measurements * Corresponding author. Tel.: + 91-33-668-4193; fax: +91-33-4734266. E-mail address: smitra – [email protected] (S. Mitra).
Elemental analyses were carried out using a Perkin – Elmer 2400 II elemental analyser. Infrared spectra were
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 8 3 5 - X
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recorded on a Perkin– Elmer 883-Instrument using KBr pellets and electronic spectra in the solid state were recorded with a Hitachi U-3400 (UV– vis-NIR) spectrophotometer. Magnetic susceptibility measurements at 293 K were carried out using vibrating sample magnetometer.
2.2. Materials Reagent grade pyridine-2-carboxaldehyde (Fluka), 1,3-diaminopropane (Merck) and Cu(ClO4)2·6H2O (Aldrich) were obtained commercially and used as received.
2.3. Synthesis of the ligand and metal complexes The ligand [N,N%-bis(2-pyridylimine)propane-1,3-diamine] was prepared by the condensation of a methanolic solution of 1,3-diaminopropane (0.37 g, 5 mmol) with pyridine-2-carboxaldehyde (1.07 g, 10 mmol) for half an hour. The resulting brown solution was used for complex preparation without further purification. [CuL][ClO4]2 was prepared by mixing Cu[ClO4]2· 6H2O (3.70 g, 10 mmol) in 50 ml methanol to the above ligand solution with stirring. [NEt4]3[Fe(CN)6] was also prepared according to the reported procedure [21].
Table 1 Crystal data for 1 Empirical formula Temperature (K) Wavelength (A, ) Crystal system Space group Unit cell dimensions a (A, ) b (A, ) c (A, ) h (°) i (°) k (°) V (A, 3) Z Dcalc (Mg m−3) Absorption coefficient (mm−1) Crystal size (mm) q Range for data collection (°) Reflections collected Data/restraints/parameters Goodness-of-fit on F 2 Final R indices [I\2|(I)] R indices (all data) Largest difference peak and hole (e A, −3)
2.4. Synthesis of the title complex Since the hexacyanometallate ion has a tendency to decompose during heating and irradiation, the complex was synthesised at room temperature (r.t.) and crystallised in the dark. [NEt4]3[Fe(CN)6] (0.60 g, 1 mmol), dissolved in 20 ml of methanol, was added to a solution of [CuL][ClO4]2 (1.02 g, 2 mmol) in methanol (50ml). Dark green crystals appeared after 5 days from this solution, and were collected by suction filtration, washed with a minimum volume of ethanol and dried in air.
2.5. X-ray crystallography of complex 1 A green air stable plate-shaped crystal of 1 was mounted on a glass fibre, and the crystallographic data were measured on a Bruker AXS P4 four-circle diffractometer at 160 K. Semi-empirical absorption corrections were applied using scans. Structure solution and refinement were performed using the SHELXL 5.1 suite of programs. The structure was refined by a full-matrix least-squares based on F 2 [22]. All hydrogen atoms were included in the idealised positions and refined using a riding model with riding isotropic U which was 1.2× Ueq of the bound C atom. No hydrogen atoms were included in the model for the water and methanol solvent atoms. The disordered methanol molecule was modelled as one C atom at 100% occupancy, O at 75% and another C atom at 25% occupancy. The crystallographic data are presented in Table 1.
3. Results and discussion C38H42ClCu2FeN14O7 160(2) 0.71073 monoclinic P21/c 17.606(3) 14.153(4) 17.636(2) 90 102.84(2) 90 4284.6(15) 4 1.589 1.446 0.42×0.38×0.06 1.86–25.00 9034 7530/0/562 1.023 R1 = 0.0792, wR2 = 0.1835 R1 = 0.1523, wR2 = 0.2246 0.866 and −0.739
3.1. Infrared spectrum The IR spectrum shows a broad peak in the range 3550–3300 cm − 1, indicating the presence of water in the lattice. The band at 2118 cm − 1 is assigned as w(CN) and the band at 1603 cm − 1 as an imine stretching frequency, slightly lower than in other Schiff base complexes where it was reported between 1610 and 1630 cm − 1 [23]. The broad band near 1150–1090 cm − 1 and three sharp bands in the range 625–540 cm − 1 indicated the presence of uncoordinated perchlorate anion. All the other bands appeared at their usual positions.
3.2. Electronic spectrum The electronic spectrum in the solid state of the title complex shows bands with maxima at 608 and 377 nm. In the solution state these bands were at 620 and 380 nm. The broad band with maxima at 608 nm shows a sensible bathochromic shift with respect to the parent
N. Mondal et al. / Polyhedron 20 (2001) 2473–2476
Fig. 1. A perspective view of 1 with atom numbering scheme. Solvent atoms have been omitted.
Cu(II) complex. The sharp band at 377 nm cannot be easily assigned, as several transitions with different origins can be expected: iron(III) d– d transition, charge transfer from ligand to iron and charge transfer between copper and iron in either direction.
3.3. Magnetic susceptibility The room temperature magnetic moment value (3.76vB) is very slightly lower than the expected value for the total of three (two from the copper centres and one from iron centre) unpaired electrons.
3.4. Crystal structure of the complex The molecular structure of complex consists of discrete trinuclear mixed metal species with two copper centres linked to an iron centre through bent cyanobridges [C(150–N(5) – Cu(1), 146.5(6); C(120)– N(12)– Cu(2), 150.4(7)°] along with the two (one disordered and one ordered) molecules of methanol and one water molecule. The arrangement of the trinuclear unit is shown in Fig. 1 and selected bond distances and angles are given in Table 2. The closely related polymeric Fe(II)– CN –Cu(II) species [24], has two types of copper centre, one identical to that in 1 (i.e. with the same tetradentate ligand) and a second type which is bound by a smaller tridentate ligand (2-pyridylmethylene-1,3propanediamine). This second type of copper centre is bound to two bridging cyanides, thereby propagating the M –CN –M chain. Both the copper centres in 1 have distorted square pyramidal geometry with the geometrical factor ~, 0.15 for Cu(1) and 0.07 for Cu(2), emphasising that the metal centre geometry is much closer to square pyramidal than trigonal bipyramidal. The environment around both copper atoms is very similar, with slight differ-
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ences in bond lengths and angles. The four Schiff base nitrogen atoms occupy the basal plane and the cyanide nitrogen atom occupies the axial position. The tetraimine ligand is twisted slightly at the copper centres. Cu(1) and Cu(2) are both displaced out of the basal plane by 0.29 A, toward the iron centre. The basal planes [N(1), N(2), N(3), N(4) and N(6), N(7), N(8), N(9)] are almost parallel (normals of the two planes are inclined at 3.1° to each other). There is disorder between flattened chair and boat conformations (72 and 28%, respectively) in the saturated chelate ring at Cu(1), whereas at Cu(2) the same chelate ring exists as a flattened chair with no obvious sign of disorder. In the chemically-identical copper centre to 1 in the polymeric iron–cyano–copper species [24], the chelate ring also possesses a flattened chair conformation and the equatorial Cu–N bond lengths are in the range 1.981(6) to 2.110(6) A, . The equivalent Cu –N lengths in 1 are very similar, with the shortest set associated with the alkyl N atoms. [1.998(7), 2.019(7) 2.087(7), 2.035(6), A, for Cu(1)– N(1), Cu(1)– N(4) Cu(1)–N(2), Cu(1)–N(3), and 1.962(9), 2.002(9), 2.041(8), 2.011(9) A, for Cu(2)–N(7), Cu(2)–N(8), Cu(2)–N(6) and Cu(2)–N(9), respectively]. As expected, the axial Cu–NC distances [2.143(7) A, for Cu(1)–N(5) and 2.146(7) A, for Cu(2)– N(12)] are substantially longer than equatorial distances. When the Table 2 Selected bond lengths (A, ) and bond angles (°) for 1 Bond lengths Cu(1)–N(1) Cu(1)–N(2) Cu(1)–N(3) Cu(1)–N(4) Cu(1)–N(5) Fe(1)–C(100) Fe(1)–C(120) Fe(1)–C(130)
1.998(7) 2.087(7) 2.035(6) 2.019(7) 2.143(7) 1.932(9) 1.916(8) 1.959(11)
Cu(2)–N(6) Cu(2)–N(7) Cu(2)–N(8) Cu(2)–N(9) Cu(2)–N(12) Fe(1)–C(110) Fe(1)–C(140) Fe(1)–C(150)
2.041(8) 1.962(9) 2.002(9) 2.011(9) 2.146(7) 1.951(10) 1.946(10) 1.936(8)
Bond angles C(150)–N(5)–Cu(1) N(5)–C(150)–Fe(1) N(1)–Cu(1)–N(4) N(1)–Cu(1)–N(3) N(4)–Cu(1)–N(3) N(1)–Cu(1)–N(2) N(4)–Cu(1)–N(2) N(3)–Cu(1)–N(2) N(1)–Cu(1)–N(5) N(4)–Cu(1)–N(5) N(3)–Cu(1)–N(5) N(2)–Cu(1)–N(5) C(120)–Fe(1)–C(100) C(120)–Fe(1)–C(150) C(100)–Fe(1)–C(150) C(120)–Fe(1)–C(140) C(100)–Fe(1)–C(140) C(150)–Fe(1)–C(140) C(120)–Fe(1)–C(110) C(100)–Fe(1)–C(110)
146.5(6) 176.3(7) 91.7(3) 167.7(3) 80.3(3) 81.0(3) 157.8(3) 102.9(3) 93.1(3) 100.8(3) 97.6(2) 100.6(3) 87.1(3) 175.9(4) 90.3(3) 92.1(3) 89.4(4) 90.9(3) 88.2(3) 90.9(4)
C(120)–N(12)–Cu(2) N(12)–C(120)–Fe(1) N(7)–Cu(2)–N(8) N(7)–Cu(2)–N(9) N(8)–Cu(2)–N(9) N(7)–Cu(2)–N(6) N(8)–Cu(2)–N(6) N(9)–Cu(2)–N(6) N(7)–Cu(2)–N(12) N(8)–Cu(2)–N(12) N(9)–Cu(2)–N(12) N(6)–Cu(2)–N(12) C(150)–Fe(1)–C(110) C(140)–Fe(1)–C(110) C(120)–Fe(1)–C(130) C(100)–Fe(1)–C(130) C(150)–Fe(1)–C(130) C(140)–Fe(1)–C(130) C(110)–Fe(1)–C(130)
150.4(7) 175.5(8) 90.1(5) 164.5(4) 81.7(4) 81.4(4) 159.9(4) 102.0(4) 105.0(4) 104.3(3) 89.8(4) 95.6(3) 88.8(3) 179.6(4) 92.8(4) 177.2(4) 90.0(3) 87.8(4) 91.9(4)
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two alkyl bound nitrogen atoms are protonated in the tetradentate ligand L, as in the mononuclear copper species [25] a twist conformation is observed in the saturated chelate ring. The Cu– N lengths are in the range 2.008–2.028 A, , a smaller range than found for 1, however the structure determination was at room temperature and there was no axial ligand. The trans bond angles around the Cu centres are N(3) –Cu(1)–N(1), N(4)– Cu(1) – N(2), N(6)– Cu(2)– N(8) and N(7)–Cu(2) – N(9) are 167.7(3), 157.8(3), 159.9(4) and 164.5(4)°, respectively. The two trans angles around Cu(1) are significantly different, despite the C2 symmetry of the tetradentate ligand. This is also found at the same copper centre in Ref. [24], [167.3(2), 156.3(2)°]. The iron centre has almost ideal octahedral geometry and is bound to the two copper(II) centres via trans bridging cyanide groups. The average Fe– C and CN distances are 1.94(9)1 and 1.157(10) A, whilst the Fe···Cu distances are 4.987(2) and 5.053(2) A, for Cu(1) and Cu(2), respectively. The bridging cyanides are bent significantly at both nitrogen atoms [C(150)– N(5)– Cu(1) and C(120)– N(12) – Cu(2) are 146.5(6) and 150.4(7)°, respectively] whilst the angles at carbon are much closer to 180°. The zig – zag polymeric structure [24] has more pronounced bending of the CN bridges at nitrogen [136.4(6), 140.8(6)°] and the equivalent Fe···Cu distance is shorter, 4.811(4) A, . The closest contacts made to the cyanide complex by the perchlorate ion are between O1 and Cu1 [2.941(3) A, ]. O4 (methanol) atom and O11 (perchlorate) are 2.60(2) A, apart, probably involved in a hydrogen bond involving the unlocated H atom from MeOH. The water does not make any contacts closer than 2.6 A, with other non-H atoms.
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 155691. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1233-336-033; e-mail: deposit@ ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk). 1
Standard deviation of the population.
Acknowledgements This work is supported by grants from CSIR, UGC, AICTE and DST (New Delhi, India).
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