Spectroelectrochemical characterization of the two-step redox system {(μ-pz)[Os(CN)5]2}n- (n = 4, 5, 6; pz = pyrazine).: Similarities and differences in relation to the Creutz-Taube system

被引:37
作者
Hornung, FM
Baumann, F
Kaim, W
Olabe, JA
Slep, LD
Fiedler, J
机构
[1] Univ Stuttgart, Inst Anorgan Chem, D-70550 Stuttgart, Germany
[2] Univ Buenos Aires, Fac Ciencias Exactas & Nat, Dept Quim Inorgan Anal & Quim Fis Inquimae, RA-1428 Buenos Aires, DF, Argentina
[3] Acad Sci Czech Republic, J Heyrovsky Inst Phys Chem, CZ-18223 Prague, Czech Republic
关键词
D O I
10.1021/ic970804o
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
The pyrazine-bridged diosmium(II) complex {(mu-C4H4N2)[OS(CN)(5)](2)}(6-) has been synthesized as the hexapotassium salt and was converted to the hexakis(tetrabutylammonium) compound by ion exchange. Its stepwise oxidation to the (Os2OsII)-Os-III and (Os2OsIII)-Os-III states was monitored spectroelectrochemically in acetonitrile/0.1 M Bu4NPF6 in the UV-vis-NIR and IR regions and by EPR. The Os-2(II), species exhibits long-wavelength solvatochromic MLCT bands at 14 800 and 18 480 cm(-1). The pentaanionic mixed-valent ion has a comproportionation constant K-c of 10(5.8) and is distinguished by several electronic absorptions in the IR region. The bands at 1972, 2480, 4000, 5000, 7170, and 11 900 cm(-1) are similar but appreciably lower in energy than those reported for the analogous complex {(mu-C4H4N2)[Os(NH3)(5)](2)}(5+). In addition to CN vibrational stretching features shifted on electron transfer there is an additional sharp band only for the 5- ion at 1582 cm(-1) which is attributed to a pyrazine ring vibration. The intensity of this band suggests an unsymmetrical situation and thus valence localization on the vibrational time scale. The EPR signals at g(perpendicular to) = 2.0563 and g(parallel to) = 1.761 point toward excited states lying close to the doublet ground state and to significant metal/cyanide interaction. Compared to the Creutz-Taube ion {(mu-C4H4N2)[Ru(NH3)(5)](2)}(5+) and its osmium homologue, the 5-ion described here exhibits a lower degree of metal-metal coupling.
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页码:311 / 316
页数:6
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