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Fe 2 and Fe 4 Clusters Encapsulated in Vacant Polyoxotungstates: Hydrothermal Synthesis, Magnetic and Electrochemical Properties, and DFT Calculations
Author(s) -
Pichon Céline,
Dolbecq Anne,
Mialane Pierre,
Marrot Jérôme,
Rivière Eric,
Goral Monika,
Zynek Monika,
McCormac Timothy,
Borshch Serguei A.,
Zueva Ekaterina,
Sécheresse Francis
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700896
Subject(s) - crystallography , chemistry , hydrothermal circulation , electrochemistry , hydrothermal synthesis , transition metal , tungsten , polyoxometalate , atomic orbital , magnetic susceptibility , metal , atom (system on chip) , antiferromagnetism , materials science , catalysis , physics , organic chemistry , electrode , quantum mechanics , seismology , electron , geology , biochemistry , condensed matter physics , computer science , embedded system
While the reaction of [PW 11 O 39 ] 7− with first row transition‐metal ions M n + under usual bench conditions only leads to monosubstituted {PW 11 O 39 M(H 2 O)} anions, we have shown that the use of this precursor under hydrothermal conditions allows the isolation of a family of novel polynuclear discrete magnetic polyoxometalates (POMs). The hybrid asymmetric [Fe II (bpy) 3 ][PW 11 O 39 Fe 2 III (OH)(bpy) 2 ] ⋅ 12 H 2 O (bpy=bipyridine) complex ( 1 ) contains the dinuclear {Fe(μ‐O(W))(μ‐OH)Fe} core in which one iron atom is coordinated to a monovacant POM, while the other is coordinated to two bipyridine ligands. Magnetic measurements indicate that the Fe III centers in complex 1 are weakly antiferromagnetically coupled ( J =−11.2 cm −1 , H =− JS 1 S 2 ) compared to other {Fe(μ‐O)(μ‐OH)Fe} systems. This is due to the long distances between the iron center embedded in the POM and the oxygen atom of the POM bridging the two magnetic centers, but also, as shown by DFT calculations, to the important mixing of bridging oxygen orbitals with orbitals of the POM tungsten atoms. The complexes [Hdmbpy] 2 [Fe II (dmbpy) 3 ] 2 [(PW 11 O 39 ) 2 Fe 4 III O 2 (dmbpy) 4 ] ⋅ 14 H 2 O ( 2 ) (dmbpy=5,5′‐dimethyl‐2,2′‐bipyridine) and H 2 [Fe II (dmbpy) 3 ] 2 [(PW 11 O 39 ) 2 Fe 4 III O 2 (dmbpy) 4 ] ⋅ 10 H 2 O ( 3 ) represent the first butterfly‐like POM complexes. In these species, a tetranuclear Fe III complex is sandwiched between two lacunary polyoxotungstates that are pentacoordinated to two Fe III cations, the remaining paramagnetic centers each being coordinated to two dmbpy ligands. The best fit of the χ M T =f( T ) curve leads to J wb =−59.6 cm −1 and J bb =−10.2 cm −1 ( H =− J wb ( S 1 S 2 + S 1 S 2* + S 1* S 2 + S 1* S 2* )− J bb ( S 2 S 2* )). While the J bb value is within the range of related exchange parameters previously reported for non‐POM butterfly systems, the J wb constant is significantly lower. As for complex 1 , this can be justified considering Fe w O distances. Finally, in the absence of a coordinating ligand, the dimeric complex [N(CH 3 ) 4 ] 10 [(PW 11 O 39 Fe III ) 2 O] ⋅ 12 H 2 O ( 4 ) has been isolated. In this complex, the two single oxo‐bridged Fe III centers are very strongly antiferromagnetically coupled ( J =−211.7 cm −1 , H =− JS 1 S 2 ). The electrochemical behavior of compound 1 both in dimethyl sulfoxide (DMSO) and in the solid state is also presented, while the electrochemical properties of complex 2 , which is insoluble in common solvents, have been studied in the solid state.