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Examination of the Mixed‐Valence State of the Doubly Boron‐Bridged Diferrocene Cation [(FeCp) 2 {μ‐C 10 H 6 (BPh) 2 }] +
Author(s) -
Venkatasubbaiah Krishnan,
Doshi Ami,
Nowik Israel,
Herber Rolfe H.,
Rheingold Arnold L.,
Jäkle Frieder
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.200701219
Subject(s) - chemistry , valence (chemistry) , mössbauer spectroscopy , crystallography , redox , spectroscopy , boron , counterion , absorption spectroscopy , oxidation state , ion , analytical chemistry (journal) , inorganic chemistry , metal , physics , organic chemistry , quantum mechanics , chromatography
A series of mixed‐valent (MV) complexes [(FeCp) 2 (μ‐C 10 H 6 (BPh) 2 )] + X ([ 1 + ]X; X=I 5 , PF 6 , SbF 6 , B(C 6 F 5 ) 4 ) were prepared by oxidation of diboradiferrocene [(FeCp) 2 (μ‐C 10 H 6 (BPh) 2 )] ( 1 ) with I 2 , AgPF 6 , and AgSbF 6 , respectively, and through anion exchange of the I 5 − salt with [Li(Et 2 O) x ][B(C 6 F 5 ) 4 ] in the case of X=B(C 6 F 5 ) 4 . The MV state of the cation was investigated in solution by multinuclear NMR spectroscopy, CV, and UV/Vis‐NIR absorption spectroscopy, and in the solid state by IR spectroscopy, single‐crystal X‐ray crystallography, and Mössbauer spectroscopy. The cyclic voltammogram of 1 shows two distinct redox waves with a large redox splitting of Δ E =510 mV in CH 2 Cl 2 and the NIR spectrum for the mono‐oxidized species displays an intervalence charge‐transfer band at around 1500 to 1700 nm depending on the specific counterion present. The X‐ray crystal structures of [ 1 + ]X show inversion‐symmetric cations with X=I 5 and B(C 6 F 5 ) 4 and unsymmetric valence‐trapped structures composed of one ferrocene and one ferrocenium moiety with X=PF 6 and SbF 6 . Mössbauer data for X=PF 6 are consistent with valence trapping at all temperatures between 90 and 343 K. In comparison, fast electron transfer is evident on the Mössbauer timescale for X=I 5 and temperature‐dependent behavior is observed for X=B(C 6 F 5 ) 4 . The anion dependence of the X‐ray structural and Mössbauer data is discussed in the context of crystal symmetry and the possibility of static and dynamic disorder effects is considered.