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New Hybrid Semiconductor Materials Based on Viologen Salts of Bimetallic Fe–Pt and Fe–Au Carbonyl Clusters: First Structural Characterization of the Diradical π‐Dimer of the Diethylviologen Monocation and EPR Evidence of its Triplet State
Author(s) -
Femoni Cristina,
Iapalucci Maria Carmela,
Longoni Giuliano,
Tiozzo Cristina,
Wolowska Joanna,
Zacchini Stefano,
Zazzaroni Enrico
Publication year - 2007
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.200700398
Subject(s) - diradical , bimetallic strip , electron paramagnetic resonance , dimer , chemistry , crystallography , ionic bonding , ion , crystal structure , molecule , metal , nuclear magnetic resonance , excited state , singlet state , organic chemistry , physics , nuclear physics
The synthesis, structure, spectroscopic characterization and electrical resistivity of the [EtV] 2 [Fe 4 Pt(CO) 16 ], [EtV][Fe 3 Pt 3 (CO) 15 ] ⋅ THF, [EtV][Fe 4 Au(CO) 16 ] 2 ⋅ 2 THF (EtV=1,1′‐diethyl‐4,4′‐bipyridilium cation) and [NEt 4 ] 2 [Fe 4 Au(CO) 16 ] is reported. The crystal structure of [EtV] 2 [Fe 4 Pt(CO) 16 ] is based on infinite stacks of [(EtV) . + ] 2 π‐dimers rotated by 90° and isolated [Fe 4 Pt(CO) 16 ] 2− ions. Within each π‐dimer, the [EtV] . + radical ions are perfectly eclipsed and the distance between their mean planes is 3.275 Å. The EPR spectrum of the solid material at room temperature clearly indicates the presence of a significantly populated triplet state of the π‐dimer, by showing signals both at Δ m =1 and Δ m =2. The solid‐state structure of [EtV][Fe 3 Pt 3 (CO) 15 ] ⋅ THF is based on the ionic packing of [EtV] 2+ and [Fe 3 Pt 3 (CO) 15 ] 2− ions, inferred from a comparison of their molecular parameters with literature data. Significant electron transfer could have been expected to give [EtV] . + [Fe 3 Pt 3 (CO) 15 ] . − on the basis of their formal redox potentials. In spite of their different stoichiometries, the structures of [EtV][Fe 4 Au(CO) 16 ] 2 ⋅ 2 THF and [NEt 4 ] 2 [Fe 4 Au(CO) 16 ] both contain an isomer of the monoanion [Fe 4 Au(CO) 16 ] − in solution (previously characterized in the solid state as a [NMe 3 CH 2 Ph] 2 [Fe 4 Au(CO) 16 ]Cl mixed salt). Resistivity measurements on pellets of powdered samples of the above compounds indicate that their tetrasubstituted ammonium salts, and complex [EtV][Fe 4 Au(CO) 16 ] 2 ⋅ 2 THF, largely behave as insulators. However, the [EtV] 2 [Fe 4 Pt(CO) 16 ] and [EtV][Fe 3 Pt 3 (CO) 15 ] ⋅ THF samples respectively display resistivities 3 and 4 orders of magnitude less than those of their corresponding ammonium salts and could be classified as semiconductor materials.