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A new family of hybrid materials formed by TTF layers and oxalato-bridged bimetallic magnetic clusters.
ELSEVIER
Synthetic
Metals8.5(1997)
1677-1678
A new family of hybrid materials formed by TTF layers and oxalato-bridged bimetallic magnetic clusters. E. Coronado,J. R. Galan-Mascarbs,C. Gimenez-Saiz,C. J. G6mez-Garcia Dept. Qufmica Inorganica.Univ. de Valencia.Dr. Moliner 50, E-46100Burjasot(Spain)
Abstract
An extensive family of organic/inorganicmaterialsformed b TTF and oxalato-bridgedbimetallic clustersis reported. These hybrid molecularmaterials,formulatedas(TTF)4(Mn(H20)2[M I?r(ox)s]2}.nH20(Mm = Cr andFe; M” = Mn, Fe, Co, Ni, Cu andZn), showlayers of oxalato-bridgedMm-Mu-M’= trimersalternatingwith layersof TTF+ cationspresenting,for the first time, a 1-D Klike phase.The magneticpropertiesshow ferro- and antiferromagneticexchangeinteractionsin the CrzMtt and Fe2Mn series, respectively. Keywords:
1.
Magnetic measurements, Organic conductorsbasedon radical cation salts,Magnetic phasetransitions
Introduction
Oxalato-bridged bimetallic complexeshave been shown to form a wide variety of compounds of variable dimensionality giving rise to molecule-basemagnets[I]. The two-dimensionalbimetallic phasesA[MnMU1(ox)3] are especially interestingin this respectbecausethey behaveas ferro or ferrimagnetswith critical temperaturesrangingfrom 6 to 44 K [2]. Here A is an electronically inactive counterion (NRb*, for example)which is locatedbetweenthe anion layers. The change of this innocent cation by an electroactive one, as for example the TTF organic donor or the magnetic inorganic cation decamethylferrocenium ([Cp*zFe]+) opensup a way to createnew hybrid materials having thesecations in betweenthe magneticlayers. With this idea we have synthesizedtwo new seriesof isostructural radical formulated salts (TTF)b( Mn(H20)2[M1n(C20&]~}nH~0 (M” = Mn, Fe, Go: Ni, Cu andZn; Mm = Cr andFe). Herewe presentthe structure and physical propertiesof theseseries.We report alsosome preliminary resultsfor the seriesof hybrid materialsobtained from the [Cp*2Fe]’ magneticcation,
closed neighborsin the layer by four hydrogen bonds of 2.77(1) A, formedbetweenthe axial watermoleculesof M” and onefree oxygen atomon eachterminaloxalategroup (see figure 1.a). The organic layers are formed by infinite chains of orthogonalface-to-facedimersof TTFt cationswith short S..,S distances(3.38 and 3.36 A), along the a axis. The neighboringchainsare displacedin one dimer in sucha way that the closest dimers of neighboring chains are also orthonormal(Figure 1.b). This arrangementis reminiscentof a K phase,but whereasin this phase inter and intrachain dimer-dimerdistancesare similar in both directions, in the title compoundthe intrachain dimer-dimer distances(3.54 and 3.56 A) are much shorterthan the interchain ones(6.60 and 6.61 A). Thus, this structurecan be seenasa 1-D K-like
2. Structure
The compoundsare obtained by reaction of an acetonitrile solution containing the salt (TTF)3[BF& with an aqueous solution of &hecomplex [M111(ox)a]3-and the MIT cation. All compoundsare isostructuralaccordingto their X-ray powder patterns. The structure, solved for the Cr-Mn derivative, consistsof alternating la ers of the organic donor TTF and the trimeric cluster {Mn K(Hz0)2[Cr111(ox)3]2)-4lying in the ab plane.The centrosymmetricallinear trimersM1n-M1l-M1rl are formed by two octahedralMnr(ox)3 entities connectedvia a M” atom which is coordinatedin a bidentateway by one oxalate group from each Mn1(ox)3 entity and completesits octahedralcoordinationwith two water moleculesin the axial positions.The linear trimersare connectedto the four 0379-6779/97/%17.00 0 1997 Elsevier PII SO379-6779(96)04547-X
Science S.A All rights reserved
Fig. 1. (a) Packingof the (Mn(H~O)~[M1n(ox)~]~} trimers in the inorganic layer showing the H bonds betweenthe trimers(dotted lines)and(b) Packingof the TTF dimers. Unfortunately, no electron delocalization is expected to occur in the organic layer sincethe four TTF moleculesare
1678
E. Coronado
et al. /SjwthehcMetals
completely ionized (charge +l), with one unpaired electron on each one. Furthermore, the fact that these molecules are dimerized allows us to anticipate that the dimers have no net spin, and therefore all the magnetic contribution comes from the inorganic lattice. 3.
Magnetic
properties
The magneticmeasurements are reportedin Figures2 and 3. All the compoundsexhibit at room temperaturethe Curie constant expected for magnetically diluted M1ll-M1l-Mrll trimers. When T is lowered the two seriesshow different magnetic behaviors. Thus, in the chromium series the magnetic moment increasesupon cooling (except for the Cr-Cu derivative), see fig. 2, while in the iron series a continuousdecreaseis observedfor all the members(fi ure 3). This indicates that the exchange coupling C&M H1 is seriesthis interactionis ferromagnetic,while for the Fe111-M1r antiferromagnetic.
-
18 , 16 i.
x Cr-Mn 0 Cr-Fe . Cr-Co
0 Cr-Ni l Cr-Cu 0 Cr-Zn
I ! / j
w
j 10 g 8 z6 xE A 2
0
50
100 150 200 250 T 09
300
Fig. 2. xmT vs. T plot for the Cr-M series. Solid lines representthe fits to exchange-coupled trimers Cr”‘-M”-Cr”’ with J = 0.54, 0.48, 0.12 and -0.49 cm-l for M” = Mn, Fe, Ni and Cu, respectively.
85 (1997/
1677-1678
These data have been adequately fitted from the expressions derived from the exchange hamiltonian H,, = -25 (SlS2 + SzSs). where Sr and Sa are the spin operatorsassociatedto the M1n ions, and Sz is that of the central divalent atom (solid lines,Figs. 2 and 3). No evidenceof magneticordering has beendetectedin theseseries,in agreementwith the discrete structureof the inorganic layer. However, the synthesisof hybrid materials containingbimetallic oxalate clusters,which can be viewed as the molecularprecursorsof the extended 2-D structure, opens now the way to generalize this approach to other organic or inorganic donorsof interest. With this idea we have very recently succeededin the preparation of a new family of bimetallic oxalato materialsusing the well known decamethylferroceniummagneticcation as counterion. The compounds canbe formulatedas[Cp*2Fe][MnM1n(ox)s](MIT1 = Cr andFe; MIT = Mn, Fe, Co and Cu), which suggeststhe formation of the 2-D bimetallic network. The preliminary magneticpropertiesdo supportthis extendednetwork. Thus, they exhibit magnetic features characteristic of ferro and ferrimagnets: (1) magnetic hysteresisloops at 2 K with coercive fields in the ranges20-150 G and 200-400G and remnant magnetizations Of 0.3-3.0 l.tg and 0.02-0.06 /.tg in the Cr-M and Fe-M series,respectively,and (2) the magnetic phasetransition evidenced(in the Mn-Cr derivative) by a sharppeakat T, = 4.44 K in the a-c. magneticsusceptibility and by an out-of-phasesignalbelow this temperature.Further work is now in progressin order to investigate (1) the structural and physical properties of this new family of molecule-base magnets,and (2) the insertionof a conducting network in betweentheseferromagneticlayers,the synthesis of hybrid materials having high conductivities (or even superconductivity) and ferromagnetismbeing certainly one of the main goals.
Acknowledgments
Financial support from the European Union (Grant CHRX-CT93-0271),the SpanishCICYT and the Generalitat de CataluAa(CIRIT) (Grant QFN93-4510)and the Caja de Ahorros de1Mediterrtineois acknowledged.E. C. andJ. R. G thank the Generalitat Valenciana for a travel and a predoctoral grant.
References
0
50
100
150 200 250 300 T 09
Fig. 3. xmT vs. T plot for the Fe-M series.Solid lines representthe fits to exchange-couled trimersFelll-Mn-Felll with J = -1.38, -2.35 and-3.1 cm-‘: for M” = Mn, Fe andNi.
[I] (a) Z. J. Zhong, N. Matsumoto, H. Okawa, S. Kida, Chem.Len. (1990) 87; (b) S. Decurtins,H. W. Schmalle, P. Schneuwly, J. P. Ensling, P. Gutlich, J. Am. Chetn. Sot. I16 (1994) 9521 and references therein; (c) S. Decurtins,H. W. Schmalle,R. Pellaux, P. Schneuwly,A. Hauser,Inorg. Chetn.35 (1996) 1451. [2]
(a) H. Tamaki, Z. J. Zhong, N. Matsumoto,S. Kida, M. Koikawa, N. Achiwa, Y. Hashimoto,H. Okawa, J. Am. Chem. Sot. 114 (1992) 6974; (b) C. Mathoniere, S.G. Carling, D. Yusheng, P. Day, J. Chem. Sot., Chem. Commun.(1994) 1551.
Synthetic
Metals8.5(1997)
1677-1678
A new family of hybrid materials formed by TTF layers and oxalato-bridged bimetallic magnetic clusters. E. Coronado,J. R. Galan-Mascarbs,C. Gimenez-Saiz,C. J. G6mez-Garcia Dept. Qufmica Inorganica.Univ. de Valencia.Dr. Moliner 50, E-46100Burjasot(Spain)
Abstract
An extensive family of organic/inorganicmaterialsformed b TTF and oxalato-bridgedbimetallic clustersis reported. These hybrid molecularmaterials,formulatedas(TTF)4(Mn(H20)2[M I?r(ox)s]2}.nH20(Mm = Cr andFe; M” = Mn, Fe, Co, Ni, Cu andZn), showlayers of oxalato-bridgedMm-Mu-M’= trimersalternatingwith layersof TTF+ cationspresenting,for the first time, a 1-D Klike phase.The magneticpropertiesshow ferro- and antiferromagneticexchangeinteractionsin the CrzMtt and Fe2Mn series, respectively. Keywords:
1.
Magnetic measurements, Organic conductorsbasedon radical cation salts,Magnetic phasetransitions
Introduction
Oxalato-bridged bimetallic complexeshave been shown to form a wide variety of compounds of variable dimensionality giving rise to molecule-basemagnets[I]. The two-dimensionalbimetallic phasesA[MnMU1(ox)3] are especially interestingin this respectbecausethey behaveas ferro or ferrimagnetswith critical temperaturesrangingfrom 6 to 44 K [2]. Here A is an electronically inactive counterion (NRb*, for example)which is locatedbetweenthe anion layers. The change of this innocent cation by an electroactive one, as for example the TTF organic donor or the magnetic inorganic cation decamethylferrocenium ([Cp*zFe]+) opensup a way to createnew hybrid materials having thesecations in betweenthe magneticlayers. With this idea we have synthesizedtwo new seriesof isostructural radical formulated salts (TTF)b( Mn(H20)2[M1n(C20&]~}nH~0 (M” = Mn, Fe, Go: Ni, Cu andZn; Mm = Cr andFe). Herewe presentthe structure and physical propertiesof theseseries.We report alsosome preliminary resultsfor the seriesof hybrid materialsobtained from the [Cp*2Fe]’ magneticcation,
closed neighborsin the layer by four hydrogen bonds of 2.77(1) A, formedbetweenthe axial watermoleculesof M” and onefree oxygen atomon eachterminaloxalategroup (see figure 1.a). The organic layers are formed by infinite chains of orthogonalface-to-facedimersof TTFt cationswith short S..,S distances(3.38 and 3.36 A), along the a axis. The neighboringchainsare displacedin one dimer in sucha way that the closest dimers of neighboring chains are also orthonormal(Figure 1.b). This arrangementis reminiscentof a K phase,but whereasin this phase inter and intrachain dimer-dimerdistancesare similar in both directions, in the title compoundthe intrachain dimer-dimer distances(3.54 and 3.56 A) are much shorterthan the interchain ones(6.60 and 6.61 A). Thus, this structurecan be seenasa 1-D K-like
2. Structure
The compoundsare obtained by reaction of an acetonitrile solution containing the salt (TTF)3[BF& with an aqueous solution of &hecomplex [M111(ox)a]3-and the MIT cation. All compoundsare isostructuralaccordingto their X-ray powder patterns. The structure, solved for the Cr-Mn derivative, consistsof alternating la ers of the organic donor TTF and the trimeric cluster {Mn K(Hz0)2[Cr111(ox)3]2)-4lying in the ab plane.The centrosymmetricallinear trimersM1n-M1l-M1rl are formed by two octahedralMnr(ox)3 entities connectedvia a M” atom which is coordinatedin a bidentateway by one oxalate group from each Mn1(ox)3 entity and completesits octahedralcoordinationwith two water moleculesin the axial positions.The linear trimersare connectedto the four 0379-6779/97/%17.00 0 1997 Elsevier PII SO379-6779(96)04547-X
Science S.A All rights reserved
Fig. 1. (a) Packingof the (Mn(H~O)~[M1n(ox)~]~} trimers in the inorganic layer showing the H bonds betweenthe trimers(dotted lines)and(b) Packingof the TTF dimers. Unfortunately, no electron delocalization is expected to occur in the organic layer sincethe four TTF moleculesare
1678
E. Coronado
et al. /SjwthehcMetals
completely ionized (charge +l), with one unpaired electron on each one. Furthermore, the fact that these molecules are dimerized allows us to anticipate that the dimers have no net spin, and therefore all the magnetic contribution comes from the inorganic lattice. 3.
Magnetic
properties
The magneticmeasurements are reportedin Figures2 and 3. All the compoundsexhibit at room temperaturethe Curie constant expected for magnetically diluted M1ll-M1l-Mrll trimers. When T is lowered the two seriesshow different magnetic behaviors. Thus, in the chromium series the magnetic moment increasesupon cooling (except for the Cr-Cu derivative), see fig. 2, while in the iron series a continuousdecreaseis observedfor all the members(fi ure 3). This indicates that the exchange coupling C&M H1 is seriesthis interactionis ferromagnetic,while for the Fe111-M1r antiferromagnetic.
-
18 , 16 i.
x Cr-Mn 0 Cr-Fe . Cr-Co
0 Cr-Ni l Cr-Cu 0 Cr-Zn
I ! / j
w
j 10 g 8 z6 xE A 2
0
50
100 150 200 250 T 09
300
Fig. 2. xmT vs. T plot for the Cr-M series. Solid lines representthe fits to exchange-coupled trimers Cr”‘-M”-Cr”’ with J = 0.54, 0.48, 0.12 and -0.49 cm-l for M” = Mn, Fe, Ni and Cu, respectively.
85 (1997/
1677-1678
These data have been adequately fitted from the expressions derived from the exchange hamiltonian H,, = -25 (SlS2 + SzSs). where Sr and Sa are the spin operatorsassociatedto the M1n ions, and Sz is that of the central divalent atom (solid lines,Figs. 2 and 3). No evidenceof magneticordering has beendetectedin theseseries,in agreementwith the discrete structureof the inorganic layer. However, the synthesisof hybrid materials containingbimetallic oxalate clusters,which can be viewed as the molecularprecursorsof the extended 2-D structure, opens now the way to generalize this approach to other organic or inorganic donorsof interest. With this idea we have very recently succeededin the preparation of a new family of bimetallic oxalato materialsusing the well known decamethylferroceniummagneticcation as counterion. The compounds canbe formulatedas[Cp*2Fe][MnM1n(ox)s](MIT1 = Cr andFe; MIT = Mn, Fe, Co and Cu), which suggeststhe formation of the 2-D bimetallic network. The preliminary magneticpropertiesdo supportthis extendednetwork. Thus, they exhibit magnetic features characteristic of ferro and ferrimagnets: (1) magnetic hysteresisloops at 2 K with coercive fields in the ranges20-150 G and 200-400G and remnant magnetizations Of 0.3-3.0 l.tg and 0.02-0.06 /.tg in the Cr-M and Fe-M series,respectively,and (2) the magnetic phasetransition evidenced(in the Mn-Cr derivative) by a sharppeakat T, = 4.44 K in the a-c. magneticsusceptibility and by an out-of-phasesignalbelow this temperature.Further work is now in progressin order to investigate (1) the structural and physical properties of this new family of molecule-base magnets,and (2) the insertionof a conducting network in betweentheseferromagneticlayers,the synthesis of hybrid materials having high conductivities (or even superconductivity) and ferromagnetismbeing certainly one of the main goals.
Acknowledgments
Financial support from the European Union (Grant CHRX-CT93-0271),the SpanishCICYT and the Generalitat de CataluAa(CIRIT) (Grant QFN93-4510)and the Caja de Ahorros de1Mediterrtineois acknowledged.E. C. andJ. R. G thank the Generalitat Valenciana for a travel and a predoctoral grant.
References
0
50
100
150 200 250 300 T 09
Fig. 3. xmT vs. T plot for the Fe-M series.Solid lines representthe fits to exchange-couled trimersFelll-Mn-Felll with J = -1.38, -2.35 and-3.1 cm-‘: for M” = Mn, Fe andNi.
[I] (a) Z. J. Zhong, N. Matsumoto, H. Okawa, S. Kida, Chem.Len. (1990) 87; (b) S. Decurtins,H. W. Schmalle, P. Schneuwly, J. P. Ensling, P. Gutlich, J. Am. Chetn. Sot. I16 (1994) 9521 and references therein; (c) S. Decurtins,H. W. Schmalle,R. Pellaux, P. Schneuwly,A. Hauser,Inorg. Chetn.35 (1996) 1451. [2]
(a) H. Tamaki, Z. J. Zhong, N. Matsumoto,S. Kida, M. Koikawa, N. Achiwa, Y. Hashimoto,H. Okawa, J. Am. Chem. Sot. 114 (1992) 6974; (b) C. Mathoniere, S.G. Carling, D. Yusheng, P. Day, J. Chem. Sot., Chem. Commun.(1994) 1551.