Synthesis, characterization and magnetic properties of several copper(II)-nickel(II) heterodinuclear oxamido complexes

Polyhedron Vol. IO. No. I, pp. 103-106, Printed in Great Britain

1991 0

0277-5387/91 $3.00+.00 1991 Pergamon Press plc

SYNTHESIS, CHARACTERIZATION AND MAGNETIC PROPERTIES OF SEVERAL COPPER(wNICKEL(I1) HETERODINUCLEAR OXAMIDO COMPLEXES JUAN RIBAS,* AUXILIADORA Departament

GARCIA and MONTSERRAT

MONFORT

de Quimica InorgAnica, Universitat de Barcelona, Diagonal 647, 08028-Barcelona, Spain (Received 5 April 1990 ; accepted 29 August 1990)

Abstract-Seven

new heterodinuclear copper(IItnickel(I1) complexes, have been synthesized from the planar monomeric fragment Cu(oxpn) (oxpn = N,N’-bis(3-aminopropyl)oxamido and its 2,2’-dimethyl derivative) and characterized. Magnetic measurements between 4 K and room temperature have been carried out to study the magnetic coupling between the two paramagnetic ions. The J values thus calculated indicate a strong antiferromagnetic coupling in all cases (J = - 104 to - 115 cm- I), in accordance with the nature of the oxamido group. The average isotropic g values occur over a range of 2.092.25. The EPR spectra at room temperature confirm these values. All the complexes are soluble in most common organic solvents, but attempts to obtain single crystals suitable for X-ray structure determination have so far been unsuccessful.

The field of heteropolymetallic systems with two different paramagnetic centres is very important from both biological and physical aspects. The copper-iron site in cytochrome oxidase is a good example of the first type ;I the intramolecular ferrimagnetism which can be extended in a 3D array to achieve molecular ferromagnets, is an example of the second, corresponding to the design of new magnetic materials.* Very recently, Kahn3 has reviewed this kind of complex and clearly indicates that accurate magnetic data on heteropolymetallic systems is much less extensive than with homopolymetallic complexes. The copper(nickel(I1) complexes with the local spins Sc, = l/2 and SNi = 1, represent one of the most comprehensive examples of heterobimetallic systems.3-8 Very recently,’ starting from propylene-1,3-bis(oxamato)cuprate(II) we have synthesized the first fully characterized Ni-Cu-Ni trinuclear complex, in which both terminal nickel(H) ions were blocked with bis(3aminopropyl)amine. During the synthesis, it was possible to synthesize and characterize the corresponding Cu-Ni dinuclear complex, in which J = -94.6 cm-‘, gcu = 2.02 and gNi = 2.24. TO * Author to whom correspondence

should be addressed. 103

avoid the possibility of forming trinuclear species, we decided to start from Cu(oxpn) (I), where oxpn is N,N’-bis(3-aminopropyl)oxamido, and its 2hydroxy (II) or 2,2’-dimethyl (III) derivatives. R R’

A

R

R’

(1)

R=R’=H

(n)

R=H;

tm,

R = R’= CH,

R’=OH

With Cu(oxpn) Ojima and Nonoyama” synthesized the complex [Cu(oxpn)Ni(bipy)d(N03)2 2H20, the magnetism and EPR -spectra of which were studied by Journaux et al. ‘I In this work, four new [Cu(oxpn)Ni(ligand)](ClO,), and three new [Cu(Me20xpn)Ni(ligand)](C10& complexes, in I which’ the terminal nickel(I1) ion is blocked with

J. RIBAS et al.

104

2,2-bipyridine (bipy), 1, lo-phenanthroline (phen), 1,4,8,11-tetraazacyclotetradecane (cyclam) and 1,3-diaminopropane (tmd) have been synthesized. All attempts to start from [Cu(2-OHoxpn)] derivatives were unsuccessful, only the starting materials being obtained. EXPERIMENTAL Synthesis of starting mononuclear copper(I1) complexes

Cu(oxpn) was obtained by the literature method.‘2,‘3 Its dimethyl derivative [Cu(Me20xpn)] was obtained by the same procedure starting from 2,2’-dimethyl-1,3-diaminopropane (Fluka, without purification). The red products so formed were very soluble in water and insoluble in common organic solvents. They can be recrystallized from hot water. Synthesis of heterodinuclear copper-nickel complexes

Hereafter we abbreviate the new complexes as [Cu(oxpn)Ni(ligand)] to indicate the hydrogenderivatives and [Cu(Me,oxpn)Ni(ligand)] to indicate the dimethyl-derivatives. (a) [Cu(oxpn)Ni(cyclam)](C10d)2. An ice-cold solution of Cu(oxpn) (0.26 g, 1 mmol) in 20 cm3 of water was added with constant stirring to an icecold solution of [Ni(cyclam)](C104)2’4 (0.46 g, 1 mmol) in 30 cm3 of water. A pink precipitate was immediately formed, which was separated by filtration and recrystallized in acetonitrile. Yield : 75%. The new compound was very soluble in acetone, acetonitrile and nitromethane ; soluble in ethanol and methanol and insoluble in water. Found: C, 29.7; H, 5.3; N, 15.6; Cu, 8.8; Ni, 8.3. Calc. for C18H40Ns02CuNi(C104)2: C, 29.9; H, 5.5; N, 15.5; Cu, 8.8; Ni, 8.1%. (b) [Cu(oxpn)Ni(tmd)2](C104)2 * H20. An icecold solution of Cu(oxpn) (0.26 g, 1 mmol) in 20 cm3 of methanol was added with constant stirring to an ice-cold solution of Ni(ClO,),(aq) (0.36 g, 1 mmol) and 1,3-diaminopropane (0.15 g, 2 mmol) in 20 cm3 of methanol. No precipitate was formed. Four times volume of ether was added, whereupon a red-violet precipitate was immediately formed. This was filtered and air-dried. Yield : 60%. The compound was soluble in all common solvents, including water. Found: C, 24.7; H, 5.5; N, 16.4; Cu, 9.3; Ni, 8.7. Calc. for C14H38Ns03CuNi(C104)2: C, 24.4; H, 5.5; N, 16.3; Cu, 9.2; Ni, 8.5%. (c) [Cu(oxpn)Ni(bipy)2](C104)2. A hot solution of Cu(oxpn) (0.53 g, 2 mmol) in 25 cm3 of methanol was added with constant stirring to a hot solution of Ni(ClO,),(aq) (0.73 g, 1 mmol) and bipyridine

(0.62 g, 4 mmol) in 25 cm3 of methanol. After heating, a blue solution was formed, which was filtered to eliminate impurities. After several days, a microcrystalline powder was formed by slow evaporation, which was filtered and air-dried. Yield: 55%. The new complex was soluble in water, acetonitrile, nitromethane and acetone. Found: C, 41.0; H, 3.9; N, 13.5; Cu, 7.5; Ni, 7.1. Calc. for C28H32Ns02CuNi(C104)2: C, 40.3; H, 3.8; N, 13.4; Cu, 7.6; Ni, 7.0%. (d) [Cu(oxpn)Ni(phen)2](C104)2. The product was obtained by using the same procedure as for the bipy derivative [see (c)l. Yield: 70%. It was insoluble in water and ethanol, but soluble in acetonitrile. Found: C, 43.1; H, 5.4; N, 12.5; Cu, 7.2 ; Ni, 6.6. Calc. for C32H48N802CuNi(C104)2 : C, 42.7; H, 5.3; N, 12.5; Cu, 7.1; Ni, 6.5%. (e) [Cu(Me20xpn)Ni(cyclam)](C104)2. An icecold solution of Cu(Me,oxpn) (0.32 g, 1 mmol) in 20 cm3 of water was added, with constant stirring to an ice-cold solution of [Ni(cyclam)](C104)2’4 (0.46 g, 1 mmol) in 25 cm3 of water. A red solution was formed, without precipitation. After several days at room temperature, microcrystals of this compound were formed. Yield : 55%. The complex was filtered and air-dried. It was slightly soluble in ethanol and soluble in acetonitrile and nitromethane. Found: C, 34.1 ; H, 6.3; N, 14.6; Cu, 8.3 ; Ni, 7.5. Calc. for C22H48Ns02CuNi(C104)2 : C, 33.9; H, 6.2; N, 14.4; Cu, 8.2; Ni, 7.5%. (f) [Cu(Me20xpn)Ni(bipy)J(C104)2. The new complex was obtained by using the same procedure as for [Cu(oxpn)Ni(bipy)2](C10d)2 [see (c)l. With Cu(Me,oxpn) the precipitate obtained by mixing the starting complexes could be redissolved by boiling the solution. After concentration, the violet solution was allowed to stand at room temperature. Red microcrystals were formed after several days, which were filtered, washed and air-dried. Yield: 65%. The new complex is soluble in acetonitrile and nitromethane, slightly soluble in water and insoluble in ethanol. Found : C, 43.3 ; H, 4.5 ; N, 12.7 ; Cu, 7.3 ; Ni, 6.7. Calc. for C32H40Ns02CuNi(C104)2 : C,43.1;H,4.5;N, 12.6;&,7.1;Ni,6.6%. (g) [Cu(Me,oxpn)Ni(phen),](ClO,),. The new product was synthesized as the bipy derivative [see (f)]. Yield : 75%. It was soluble in acetonitrile and nitromethane, but insoluble in ethanol. Found : C, 45.6; H, 5.9; N, 12.0; Cu, 6.8; Ni, 6.2. Calc. for C36H56Ns02CuNi(C104)2: C, 45.3; H, 5.9; N, 11.7; Cu, 6.6; Ni, 6.1%. Physical measurements

IR spectra (4000-200 cm-‘) were recorded as KBr pellets with a Perkin-Elmer 1330 spec-

Copper(nickel(I1)

105

heterodinuclear oxamido complexes

trophotometer. Magnetic measurements were carried out with a Faraday type magnetometer equipped with a helium continuous-flow cryostat working in the 4.2-300 K temperature range. For all the compounds the independence of the magnetic susceptibility versus the applied field was checked at each temperature. Mercury tetrakis(thiocyanato) cobaltate was used as a susceptibility standard. Diamagnetic corrections were estimated from Pascal Tables. EPR measurements were recorded with a Brucker ER-200 spectrometer working at X-band frequency.

1.5 -

XT I

T (K) OO

RESULTS AND DISCUSSION

In the IR spectra all the characteristic bands attributed to the amine, oxamido and perchlorate anions are present. The most characteristic features are the very strong and wide band centred at 1600 cm-’ and the strong and sharp band centred at cu 800 cm-‘, due to the presence of the oxamido group. On the other hand, the two characteristic bands attributable to the perchlorate anion (noncoordinated) appear at 1100 cn- ’ (very strong and wide) and at 620 cm-’ (strong and sharp). Many bands (from 3500 to 400 cn- ‘) attributable to the bondings N-H, C-N (amine) are also present in all cases. Magnetic measurements Starting from the isotropic Hamiltonian H = -J&3,&, the interaction between copper(I1) and nickel(I1) leads to only two pair states (a doublet and a quartet) separated by 3J/2. The theoretical expression for the magnetic susceptibility, assuming that the isotropic interaction is much larger than the other terms of the spin Hamiltonian, is derived from the general Van Vleck

-

50

100

200

150

300

Fig. 1. XT vs T for [Cu(oxpn)Ni(bipy)d(ClO,),. (0 experimental values ; theoretical values). The XT curves for the other six complexes are very similar (see J and g values in Table 1).

equation as :3*1 5

wheregIl = (%-gcu)/3 andg3/, = Chi+gcu)P* In this formula we have neglected the possible zero-field splitting within the excited quartet state. The magnetic properties of one of the seven new complexes, which are almost equal to those of the other six, are shown in Fig. 1. When the sample is cooled, XT decreases, then reaches a plateau with XT = 0.45 cm3 mall ’ K corresponding to the temperature range where only the ground doublet state is thermally populated. Data for all complexes is given in Table 1. In all cases, R is less than lo- 4. Such a value of J (approx. - 110 cm- ‘) agrees perfectly with that reported by Joumaux et al. ’ 1for [Cu(oxpn)Ni(bipy)2](N03)2 (J = - 110.6 cm-‘). On the other hand, this value indicates that the

Table 1. Magnetic and EPR data for the dinuclear complexes (gc, and gNi are obtained from the fitting of susceptibility data. With only one average g factor, the fitting is almost equal) Compound

250

J(cm-‘)

[Cu(oxpn)Ni(cyclam)](C10,),

- 104.2

[Cu(oxpn)Ni(tmd)&ClO,), [Cu(oxpn)Ni(bipy)&C104)z [Cu(oxpn)Ni(phen)&ClO,), [Cu(Me,oxpn)Ni(cyclam)](C10,), [Cu(Me,oxpn)Ni(bipy)d(ClO,), [Cu(Me,oxpn)Ni(phen),](ClO,),

- 103.4 - 104.5 - 103.8 - 107.3 -107.1 -113.2

9CU 2.12 2.09 2.10 2.11 2.15 2.15 2.12

gNi

2.23 2.24 2.24 2.22 2.25 2.22 2.25

s(EW

2.24 2.20 2.21 2.20 2.22 2.22 2.20

106

J. RIBAS et al.

doublet-quartet gap (3J/2) is CCI165 cm- ’ >>D ; therefore the employed equation for XT is correct. Lacking structural data we only can compare these results with those reported by Journaux et al. ’ ’ for the trinuclear complex Cu-Ni-Cu with the same Cu(oxpn) as the bridging ligand (J = - 98.7 cm- ‘). The slight difference may be attributed to the structural factors. We can also compare these results with those reported by Journaux et al. ‘* for [Cu(oxpn)Cu (bipy)](ClO,), (J = -439.7 cm-‘). The magnetic orbital in the central copper(I1) ion (&_,,z) is the same in all cases. For the terminal ions, the magnetic orbitals are ~,z_~z for copper(bipy) and both d,z_,,2 and d,z for nickel(I1). Then, taking into account that the dz2 orbital is not magnetically active with this kind of geometry, the overlap between the magnetic orbitals should be very similar. But, even with the correction due to the l/n, x $,‘6 n being the number of unpaired electrons (1 x 1 for CuCu and 1 x 2 for CuNi), the results are not comparable (- 110 cm- ’ for CuNi and -220 cm-’ for CuCu). Assuming a ferromagnetic contribution in CuNi which diminishes the antiferromagnetic factor is not realistic, as has been clearly indicated by Journaux. ’ 7 Then, the only possible explanation is the less diffuse character and higher energy of the nickel(I1) d orbitals : their interaction with the orbitals of the ligands is less pronounced and, consequently, the delocalization of these d orbitals into the oxamato bridge is greater in copper(I1) than in nickel(I1). The antiferromagnetic coupling would be more efficient in a CuCu pair than in a CuNi pair.

EPR spectra

The values of g for all complexes are collected in Table 1. There is a very wide band centred at approx. g = 2.2-2.3. At room temperature the complexes exhibit a smaller band centred at approx. g = 4, as has been also reported by Journaux et al.” for [Cu(oxpn)Ni(bipy),](NO& - 2H20. The explanation would be the same as given by this author. ” Since there is lack of structural data for this kind of complex, we hope, in the future, to obtain single crystals suitable for X-ray structural determination to examine whether the inter-

molecular interactions between the dimers could be the appropriate explanation. Acknowledgement-We are very grateful for financial assistance from the CICYT (Grant no. MAT88-0545). REFERENCES 1. B. G. Malstrom, in Metal-ion Activation of Dioxygen (Edited by T. G. Spiro), p. 181. Wiley, New York (1980). 2. (a) A. Gleizes and M. Verdaguer, J. Am. Chem. Sot. 1984, 106, 3727; (b) Y. Pei, J. Sletten and 0. Khan, J. Am. Chem. Sot. 1986, 108, 3143; (c) Y. Pei, M. Verdaguer, 0. Kahn, J. Sletten and J. P. Renard, Znorg. Chem. 1987,26,138; (d) Y. Pei, M. Verdaguer, 0. Kahn, J. Sletten and J. P. Renard, J. Am. Chem. Sot. 1986,108, 7427; (e) M. Drillon, E. Coronado, D. Beltran, J. Curely, R. Georges, R. Nugteren and L. de Jongh, J. Magn. Mater. 1986,54, 1507 ; (f) D. Beltran and M. Drillon, J. Chem. Sot., Faraday Trans. 1982,78, 1773. 3. 0. Kahn, Structure and Bonding 1987, 68, 89. 4. P. Tola, 0. Kahn, C. Chauvel and H. Coudanne, Nouv. J. Chim. 1977, 1, 647. 5. J. P. Costes, J. F. Serra, F. Dahan and J. P. Laurent, Inorg. Chem. 1986,25, 2790. 0. Khan, J. Jaud and J. 6. 1. Morgenstern-Badarau, Galy, Znorg. Chem. 1982, 21, 3050. 7. E. Buluggiu, J. Phys. Chem. Solids 1980,41, 1175. 8. A. Bencini, A. Caneschi, A. Dei, D. Gatteschi, C. Zanchini and 0. Kahn, Znorg. Chem. 1986,25,1374. 9. J. Ribas, R. Costas, C. Diaz, 0. Kahn, Y. Journaux and A. Gleizes, Znorg. Chem. 1990, 29, 2042. 10. H. Ojima and K. Nonoyama, Z. Anorg. Allg. Chem. 1977,429,282. 11. Y. Journaux, J. Sletten and 0. Kahn, Znorg. Chem. 1986,25,439. 12. Y. Journaux, J. Sletten and 0. Kahn, Znorg. Chem. 1985,24,4063. 13. H. Ojima and K. Nonoyama, Z. Anorg. AZZg.Chem. 1972,389, 75. 14. B. Bosnich, M. L. Tobe and G. A. Webb, Znorg. Chem. 1965,4, 1109. 15. D. Gatteschi and S. Bencini, in Magneto-structural Correlations in Exchange Coupled Systems (Edited by R. Willet, D. Gatteschi and 0. Kahn), NATO AS1 Ser. C, Vol. 140. D. Reidel, Dordrecht (1984). 16. (a) 0. Kahn and B. Briat, J. Chem. Sot., Faraaby Trans. II 1976,72,268; (b) 0. Kahn and B. Briat, J. Chem. Sot., Faraday Trans. 1976,72,

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