Examination of the mixed-valence state of the doubly boron-bridged diferrocene cation [(FeCp)2{mu-C10H6(BPh)2}]+.
A series of mixed-valent (MV) complexes [(FeCp)2(mu-C10H6(BPh)2)]+X ([1+]X; X=I 5, PF6, SbF6, B(C6F5)4) were prepared by oxidation of diboradiferrocene [(FeCp)2(mu-C10H6(BPh)2)] (1) with I 2, AgPF6, and AgSbF6, respectively, and through anion exchange of the I 5(-) salt with [Li(Et2O)x][B(C6F5)4] in the case of X=B(C6F5)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 Delta E=510 mV in CH2Cl2 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(C6F5)4 and unsymmetric valence-trapped structures composed of one ferrocene and one ferrocenium moiety with X=PF6 and SbF6. Mössbauer data for X=PF6 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(C6F5)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.
Venkatasubbaiah
Krishnan
K
Department of Chemistry, Rutgers University Newark, 73 Warren Street, Newark, NJ 07102, USA.
Doshi
Ami
A
Nowik
Israel
I
Herber
Rolfe H
RH
Rheingold
Arnold L
AL
Jäkle
Frieder
F
D001895:Boron / Q000737:chemistry*; D002412:Cations / Q000138:chemical synthesis / Q000737:chemistry; D018360:Crystallography, X-Ray; D005296:Ferrous Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods; D015204:Spectroscopy, Mossbauer / Q000379:methods; D013237:Stereoisomerism
D002412:Cations; D005296:Ferrous Compounds; D009942:Organometallic Compounds; C064804:ferrocenium; D007501:Iron; D001895:Boron