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M(dmit)2 salts with paramagnetic cations: synthesis and magnetic properties
ELSEVIER
SyntheticMetals103 (1999) 2296-2297
[M(dmit)J salts with paramagnetic cations : synthesis and magnetic properties C. Faulmann a* *, A. E. Pullen a,#, E. Riviere b, Y. Journaux b, L. Retailleau a and P. Cassoux a ’ Luboratoire ’ Laboratbire
de Chimie de Coordination, CNRS, 205 Route de Narbonne, 31077 Toulouse Cedex, France de Chimie Inorganique, ICMO Brit. 420, Universite Paris&d, 91405 Orsay Cedex, France
Abstract Synthesis and magnetic properties of various compounds based on the [M(dmit)z] unit (M = Ni, Fe) in combination GXth paramagnetic cations such as (Cp*~M’)’ (M’ = Mn, Ni) are presented. For instance, ferromagnetic behavior of (Cp*zMn)[Ni(dmit)zl is reported. Keykvoi;ds:organic conductors based on radical cation and anion salt, magnetic measurements,magnetic phasetransition. Introduction Since the observation of bulk ferromagnetism in (Cp*zFe)TCNE [l] , much work has been devoted to the synthesis of compounds combining metallocenium and organic acceptors such as TCNQ [Z], or metallocenium and metal dichalcogenide acceptorssuch as [M(tfd)lj [3], with the aim of producing molecular ferromagnets. More recent work has been performed by V. Da Gama and coworkers 143, using various nickel bis-dithiolenes complexes and combining them with different metallocene based cations (Cp”zM)+ (M = Fe, Mn, Cr). An even more ambitious challenge is the preparation of molecular conductors exhibiting coupled magnetic and conducting properties. Along this line, the first molecular superconductor ~-(BEDT-RF)~ IFe(ox)j(HzO)].PhCN containing magnetic anions was characterized in 1995 1.51,and more recently a magnetic-field restored conducting state has been observed in h-(BETS)zFeCld [6] implying interactions between conduction electrons of the BETS molecules and
localized magnetic moments of the anion (FeC14)‘.For a couple of years, we have been involved in the search of such compounds combining magnetic and electrical properties using the [M(dmit)t]‘ complexes as starting materials. Preliminary work has resulted in the synthesisand structural characterization of (CpzCo)[Ni(dmit)&.2CHXN [7]. We report here the synthesis and magnetic characterization of M(dmit)z derived variDus paramagnetic compounds associated with metallocenium, (Cp*zMn)* and (Cp*rNi)*.
Experimental The studied compounds have been synthesized (i) by metathesisreaction in acetoneor acetonitrile of a small excessof (Cp*zM)(PFe) (M = Mn, Ni) with the corresponding (NBud)[M’(dmit)2] salt (M’ = Ni, Fe) or (ii) by addition of the appropriate salt (Cp*2M)(PFb)to Na[M’(dmit)z] in acetone. Obtained compounds are listed in Table 1, together with the C, H and N elemental analysesand x,T values.
Table 1 Analytical data (with theoretical values for given formulation) Compound
%H (calcd)
%N (calcd)
XMT [theo] (cm” mol“ K)
40.13 (40.00)
3.46 (3.84)
0.00 (0.00)
071 IO.751
CHiCN
39.59 (40.35)
3.18 (3.91)
0.59 (0.00)
2.85 [3.05-j
CH3CN
40.03 (40.20)
3.78 (3.89)
0.00 (0.00)
1.71 II.571
Abrev.
Solvent
(Cp*INi)[Ni(dmit)l]
[NiNi]
(CH3)2CO
(Cp*2Mn)[Fe(dmit)z]
[MnFel
(Cp*zMn)[Ni(dmit)2]
[MnNi]
%C
(calcd)
The magnetic behavior of (Cp’2Ni){Ni(dmit)2] ([NiNi]), (Cp*?Mn)[Fe(dmit)z] ([MnFe]) and (Cp*?Mn)[Ni(dmit)z] (MnNi]) is shown in Figure 1. The x,T plot of [NiNi] clearly shows that the interaction between the Ni(lIl) ions is antiferromagnetic. A satisfactory fit of the experimental data was obtained with J = -19 cm.’ and g = 2.00 using the Bonner Fisher expression for the magnetic susceptibility of a S=1/2 one dimensional compound [S]. The antiferromagnetic interaction
between the Ni(Cp*)2’ and the Ni(dmit); is easily understood * considering the electronic configurations of the Ni(Cp*)* and Ni(dmit),- molecules. Single crystal EPR studies on (NBu,)[Ni(dmit),] showed that the single electron is located in an orbital of b,, (xz) symmetry [9] (a D,, symmetry is assumed for Ni(dmit),). For Ni(CpK)2t, the crystal field due to the M>Cs rings split the d orbitals in three groups with the relative energies e,,< ee2<< e,,. For Ni(Cp*)*’ cation the electronic
* Author to whom correspondenceshould be addressed.Tel (33)5 61333106; Fax (33) 5 61553003; e-mail: [email protected] # Presentaddress : Department of Chemistry, M-IT, 77 MassachusettsAve., Cambridge, MA 02139, USA 0379-6779/99/$- seefront matter0 1999 ElsevierScienceS.A. All rightsreserved. PII: SO379-6779(98)00636-5
C. Faulmann
et al. I Synthetic
configuration is (a,)*(ez)‘(e,)’ with a single electron in an e, orbital partially delocalized onto the C,Me, rings. The overlap between the spin density in the e, orbital of Ni(Cp*)2i and the b*s orbital of Ni(dmit), leads to an antiferromagnetic interaction.
0 IMnFe] (left axis) A [NiNi] (left axis) *Fit (left axis) o [MnNi] (right axis)
Metals
103 (1999)
2291
2296-2297
Several theoretical models for the ferromagnetism of metallocene-based donor acceptor compounds have been proposed [l, 11, 121. A spin polarization mechanism based on the McConnell idea [ 131 proposed by Kollmar et al. [ 121 seems to be the more convincing. The ferromagnetic coupling between Mn(Cp*),+ and Ni(dmit), arises from a local antiferromagnetic interaction betwen the negative spin density on the Cp* rings and the b,, orbital of Ni(dmit),.
6
2
0
?OOOO
40000
H (G
0
0 0 100 200 T(K) Figure 1: Temperature dependence of the magnetic susceptibility for [NiNi], [MnFe] and [MnNi]
m
0 300
For [MnFel, x~T decreases when ty teTperature is lowered and reachesa value of x,T = 1.15 cm mol K at 1.8 K. The x~,T plot is a clear evidence of an antiferromagnetic interaction between the Mn(IQ and Fe(U) ions. However, the ferrimagnetic behavior, expected for a one dimensional S=l, S=3/2 compound with an increase of the x~T value in the low temperature region is not observed. This can be due to a strong anisotropy or interstack interaction, but in the absence of crystal structure, it is difficult to draw a definitive conclusion. The magnetic behavior of [MnNi] is shown in Figure 1. xhlT at room temperature is sligthly higher than the expected val,yefor,two magnetically isolated Mn(III) and Ni(II$ ions (1.57 cm mol K, with g values equal to 2.17 and 2.06 for Mn(Cp*&+ and Ni(dmit),- respectively IS, IO]). The x~T value increasesas the temperature is lowered and reaches a value of 9.65 cm3 K mol-’ at 3 K. Below this temperature the magnetic susceptibility becomes field dependent, indicating that the compound exhibits a long range magnetic ordering. This is confirmed by the field cooled (FCM), zero field cooled (ZFCM) and remnant (REM) magnetization curves shown in Figure 2. The FCM curve presents a break around 2.5 K and the REM curve vanishes at the same temperature suggesting an ordering temperature Tc around 2SK. In the paramagnetic region, the xhlT plot clearly shows that the Mn(III)Ni(III) interaction is ferromagnetic, The magnetization versus field behavior at 2K is given in the inset in Figure 2 and bears out the ferromagnetic coupling between the Mn(III)Ni(III) ions. The magnetization increases very rapidly in low field, as expected for a magnet, and then increasessmoothly above 1 kOe. At 50 kOe the magnetization is equal to 12900 cm3 Cl mol” which is below the expected saturation value (about 18000 cm3 G mo<‘) but well higher than the expected value for a ferrimagnet (about 5800 cm3G mol.‘).
x
1.5
x
x
B 2.5
o FCM x REM A ZFCM 3s
T (K)
Figure 2: Field cooled (FCM), zero field cooled (ZFCM) and remnant (REM) magnetization curves for [MnNi]
References J.S. Miller, J.C. Calabrese, H. Rommelmann, S.R. [ll Chittipeddi, J.H. Zhang, W.M. Reiff and A.J. Epstein, J. Am. Chem. Sot. 109 (1987) 769. W.E. Broderick, J.A. Thompson, E.P. Day, B.M. [21 Hoffman, Science 28 (I 990) 401. J.S. Miller, J.C. Calabrese, A.J. Epstein, Inorg. Chem. [31 28 (1989) 4230. V. Da Gama, D. Belo, I.C. Santos, R.T. Henriques, Mol. 141 Cryst. Liq. Cryst. 306 (1997) 17 M. Kurmoo, A.W. Graham, P. Day, S.J. Coles, 1M.B. [51 Hursthouse, J.L. Caulfield, J. Singleton, F.L. Pratt, W. Hayes, L. Ducasse,P. Guionneau, J. Am. Chem. Sot., 117 (1995) 12209. 161 H. Kobayashi, H. Tomita, T. Naito, A. Kobayashi, F. Sakai, T. Watanabe, P. Cassoux, J. Am. Chem. Sot. 118 (1996) 368. C. Faulmann, F. Delpech, I. Malfant, P. Cassoux, J. [71 Chem. Sot., Dalton Trans., 2261 (1996) J.C. Bonner, M.E. Fisher, Phys. Rev. A 135 (1964) 640. PI R. Kirmse, J. Stach, W. Dietzsch, G. Steinecke, Inorg. PI Chem., 19 (1980) 2679. [lo] J.L. Robbins, N.M. Edelstein, S.R. Cooper, J.C. Smart, J. Am. Chem. Sot., 101 (1979) 3853. [ 1l] A.L. Tchougreeff, J. Chem. Phys., 96 (1992), A.L. Tchougreeff, IA. Misurkin, Phys. Rev. B, 46 (1992) 5357. [ 121 C. Kollmar, M. Couty, 0. Kahn, J. Am. Chem. Sot., 113 (1991) 1994; C. Kollmar, 0. Kahn, J. Chem. Phys., 96 (1992) 2988; C. Kollmar, 0. Kahn, Act. Chem. Res. 26 (1993) 259. [ 131 H.M. McConnell, J. Chem. Phys., 39 (1963) 1910.
SyntheticMetals103 (1999) 2296-2297
[M(dmit)J salts with paramagnetic cations : synthesis and magnetic properties C. Faulmann a* *, A. E. Pullen a,#, E. Riviere b, Y. Journaux b, L. Retailleau a and P. Cassoux a ’ Luboratoire ’ Laboratbire
de Chimie de Coordination, CNRS, 205 Route de Narbonne, 31077 Toulouse Cedex, France de Chimie Inorganique, ICMO Brit. 420, Universite Paris&d, 91405 Orsay Cedex, France
Abstract Synthesis and magnetic properties of various compounds based on the [M(dmit)z] unit (M = Ni, Fe) in combination GXth paramagnetic cations such as (Cp*~M’)’ (M’ = Mn, Ni) are presented. For instance, ferromagnetic behavior of (Cp*zMn)[Ni(dmit)zl is reported. Keykvoi;ds:organic conductors based on radical cation and anion salt, magnetic measurements,magnetic phasetransition. Introduction Since the observation of bulk ferromagnetism in (Cp*zFe)TCNE [l] , much work has been devoted to the synthesis of compounds combining metallocenium and organic acceptors such as TCNQ [Z], or metallocenium and metal dichalcogenide acceptorssuch as [M(tfd)lj [3], with the aim of producing molecular ferromagnets. More recent work has been performed by V. Da Gama and coworkers 143, using various nickel bis-dithiolenes complexes and combining them with different metallocene based cations (Cp”zM)+ (M = Fe, Mn, Cr). An even more ambitious challenge is the preparation of molecular conductors exhibiting coupled magnetic and conducting properties. Along this line, the first molecular superconductor ~-(BEDT-RF)~ IFe(ox)j(HzO)].PhCN containing magnetic anions was characterized in 1995 1.51,and more recently a magnetic-field restored conducting state has been observed in h-(BETS)zFeCld [6] implying interactions between conduction electrons of the BETS molecules and
localized magnetic moments of the anion (FeC14)‘.For a couple of years, we have been involved in the search of such compounds combining magnetic and electrical properties using the [M(dmit)t]‘ complexes as starting materials. Preliminary work has resulted in the synthesisand structural characterization of (CpzCo)[Ni(dmit)&.2CHXN [7]. We report here the synthesis and magnetic characterization of M(dmit)z derived variDus paramagnetic compounds associated with metallocenium, (Cp*zMn)* and (Cp*rNi)*.
Experimental The studied compounds have been synthesized (i) by metathesisreaction in acetoneor acetonitrile of a small excessof (Cp*zM)(PFe) (M = Mn, Ni) with the corresponding (NBud)[M’(dmit)2] salt (M’ = Ni, Fe) or (ii) by addition of the appropriate salt (Cp*2M)(PFb)to Na[M’(dmit)z] in acetone. Obtained compounds are listed in Table 1, together with the C, H and N elemental analysesand x,T values.
Table 1 Analytical data (with theoretical values for given formulation) Compound
%H (calcd)
%N (calcd)
XMT [theo] (cm” mol“ K)
40.13 (40.00)
3.46 (3.84)
0.00 (0.00)
071 IO.751
CHiCN
39.59 (40.35)
3.18 (3.91)
0.59 (0.00)
2.85 [3.05-j
CH3CN
40.03 (40.20)
3.78 (3.89)
0.00 (0.00)
1.71 II.571
Abrev.
Solvent
(Cp*INi)[Ni(dmit)l]
[NiNi]
(CH3)2CO
(Cp*2Mn)[Fe(dmit)z]
[MnFel
(Cp*zMn)[Ni(dmit)2]
[MnNi]
%C
(calcd)
The magnetic behavior of (Cp’2Ni){Ni(dmit)2] ([NiNi]), (Cp*?Mn)[Fe(dmit)z] ([MnFe]) and (Cp*?Mn)[Ni(dmit)z] (MnNi]) is shown in Figure 1. The x,T plot of [NiNi] clearly shows that the interaction between the Ni(lIl) ions is antiferromagnetic. A satisfactory fit of the experimental data was obtained with J = -19 cm.’ and g = 2.00 using the Bonner Fisher expression for the magnetic susceptibility of a S=1/2 one dimensional compound [S]. The antiferromagnetic interaction
between the Ni(Cp*)2’ and the Ni(dmit); is easily understood * considering the electronic configurations of the Ni(Cp*)* and Ni(dmit),- molecules. Single crystal EPR studies on (NBu,)[Ni(dmit),] showed that the single electron is located in an orbital of b,, (xz) symmetry [9] (a D,, symmetry is assumed for Ni(dmit),). For Ni(CpK)2t, the crystal field due to the M>Cs rings split the d orbitals in three groups with the relative energies e,,< ee2<< e,,. For Ni(Cp*)*’ cation the electronic
* Author to whom correspondenceshould be addressed.Tel (33)5 61333106; Fax (33) 5 61553003; e-mail: [email protected] # Presentaddress : Department of Chemistry, M-IT, 77 MassachusettsAve., Cambridge, MA 02139, USA 0379-6779/99/$- seefront matter0 1999 ElsevierScienceS.A. All rightsreserved. PII: SO379-6779(98)00636-5
C. Faulmann
et al. I Synthetic
configuration is (a,)*(ez)‘(e,)’ with a single electron in an e, orbital partially delocalized onto the C,Me, rings. The overlap between the spin density in the e, orbital of Ni(Cp*)2i and the b*s orbital of Ni(dmit), leads to an antiferromagnetic interaction.
0 IMnFe] (left axis) A [NiNi] (left axis) *Fit (left axis) o [MnNi] (right axis)
Metals
103 (1999)
2291
2296-2297
Several theoretical models for the ferromagnetism of metallocene-based donor acceptor compounds have been proposed [l, 11, 121. A spin polarization mechanism based on the McConnell idea [ 131 proposed by Kollmar et al. [ 121 seems to be the more convincing. The ferromagnetic coupling between Mn(Cp*),+ and Ni(dmit), arises from a local antiferromagnetic interaction betwen the negative spin density on the Cp* rings and the b,, orbital of Ni(dmit),.
6
2
0
?OOOO
40000
H (G
0
0 0 100 200 T(K) Figure 1: Temperature dependence of the magnetic susceptibility for [NiNi], [MnFe] and [MnNi]
m
0 300
For [MnFel, x~T decreases when ty teTperature is lowered and reachesa value of x,T = 1.15 cm mol K at 1.8 K. The x~,T plot is a clear evidence of an antiferromagnetic interaction between the Mn(IQ and Fe(U) ions. However, the ferrimagnetic behavior, expected for a one dimensional S=l, S=3/2 compound with an increase of the x~T value in the low temperature region is not observed. This can be due to a strong anisotropy or interstack interaction, but in the absence of crystal structure, it is difficult to draw a definitive conclusion. The magnetic behavior of [MnNi] is shown in Figure 1. xhlT at room temperature is sligthly higher than the expected val,yefor,two magnetically isolated Mn(III) and Ni(II$ ions (1.57 cm mol K, with g values equal to 2.17 and 2.06 for Mn(Cp*&+ and Ni(dmit),- respectively IS, IO]). The x~T value increasesas the temperature is lowered and reaches a value of 9.65 cm3 K mol-’ at 3 K. Below this temperature the magnetic susceptibility becomes field dependent, indicating that the compound exhibits a long range magnetic ordering. This is confirmed by the field cooled (FCM), zero field cooled (ZFCM) and remnant (REM) magnetization curves shown in Figure 2. The FCM curve presents a break around 2.5 K and the REM curve vanishes at the same temperature suggesting an ordering temperature Tc around 2SK. In the paramagnetic region, the xhlT plot clearly shows that the Mn(III)Ni(III) interaction is ferromagnetic, The magnetization versus field behavior at 2K is given in the inset in Figure 2 and bears out the ferromagnetic coupling between the Mn(III)Ni(III) ions. The magnetization increases very rapidly in low field, as expected for a magnet, and then increasessmoothly above 1 kOe. At 50 kOe the magnetization is equal to 12900 cm3 Cl mol” which is below the expected saturation value (about 18000 cm3 G mo<‘) but well higher than the expected value for a ferrimagnet (about 5800 cm3G mol.‘).
x
1.5
x
x
B 2.5
o FCM x REM A ZFCM 3s
T (K)
Figure 2: Field cooled (FCM), zero field cooled (ZFCM) and remnant (REM) magnetization curves for [MnNi]
References J.S. Miller, J.C. Calabrese, H. Rommelmann, S.R. [ll Chittipeddi, J.H. Zhang, W.M. Reiff and A.J. Epstein, J. Am. Chem. Sot. 109 (1987) 769. W.E. Broderick, J.A. Thompson, E.P. Day, B.M. [21 Hoffman, Science 28 (I 990) 401. J.S. Miller, J.C. Calabrese, A.J. Epstein, Inorg. Chem. [31 28 (1989) 4230. V. Da Gama, D. Belo, I.C. Santos, R.T. Henriques, Mol. 141 Cryst. Liq. Cryst. 306 (1997) 17 M. Kurmoo, A.W. Graham, P. Day, S.J. Coles, 1M.B. [51 Hursthouse, J.L. Caulfield, J. Singleton, F.L. Pratt, W. Hayes, L. Ducasse,P. Guionneau, J. Am. Chem. Sot., 117 (1995) 12209. 161 H. Kobayashi, H. Tomita, T. Naito, A. Kobayashi, F. Sakai, T. Watanabe, P. Cassoux, J. Am. Chem. Sot. 118 (1996) 368. C. Faulmann, F. Delpech, I. Malfant, P. Cassoux, J. [71 Chem. Sot., Dalton Trans., 2261 (1996) J.C. Bonner, M.E. Fisher, Phys. Rev. A 135 (1964) 640. PI R. Kirmse, J. Stach, W. Dietzsch, G. Steinecke, Inorg. PI Chem., 19 (1980) 2679. [lo] J.L. Robbins, N.M. Edelstein, S.R. Cooper, J.C. Smart, J. Am. Chem. Sot., 101 (1979) 3853. [ 1l] A.L. Tchougreeff, J. Chem. Phys., 96 (1992), A.L. Tchougreeff, IA. Misurkin, Phys. Rev. B, 46 (1992) 5357. [ 121 C. Kollmar, M. Couty, 0. Kahn, J. Am. Chem. Sot., 113 (1991) 1994; C. Kollmar, 0. Kahn, J. Chem. Phys., 96 (1992) 2988; C. Kollmar, 0. Kahn, Act. Chem. Res. 26 (1993) 259. [ 131 H.M. McConnell, J. Chem. Phys., 39 (1963) 1910.