The Metal-NO Interaction in the Redox Systems [Cl5Os(NO)]n-, n = 1-3, and cis-[(bpy)2ClOs(NO)]2+/+
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- 作者：Priti Singh ; Biprajit Sarkar ; Monika Sieger ; Mark Niemeyer ; Jan Fiedler ; Stanislav Zá ; li
rc="http ; //pubs.acs.org/images/entities/scaron.gif" border="0"> ; and Wolfgang Kaim
- 刊名：Inorganic Chemistry
- 出版年：2006
- 出版时间：June 12, 2006
- 年：2006
- 卷：45
- 期：12
- 页码：4602 - 4609
- 全文大小：121K
- 年卷期：v.45,no.12(June 12, 2006)
- ISSN：1520-510X
文摘
Experimental and computational results for the two-step redox system [Cl5Os(NO)]n- (n = 1-3) are reported anddiscussed in comparison to the related one-step redox systems [Cl5Ru(NO)]n- and [Cl5Ir(NO)]n- (n = 1, 2). Theosmium system exhibits remarkably low oxidation and reduction potentials. The structure of the precursor (PPh4)2[Cl5Os(NO)] is established as an {MNO}6 species with almost linear OsNO arrangement at 178.1
. Density-functionaltheory (DFT) calculations confirm this result, and a comparison of structures calculated for several oxidation statesreveals an increased labilization of the trans-positioned M-Cl bond on reduction in the order M = Ir < Os < Ru.Accordingly, the intact reduced form [Cl5Os(NO)]3- could not be observed in fluid solution even on electrolysis at-70 C in n-butyronitrile solution, as confirmed both by DFT calculations and by comparison with the electronparamagnetic resonance and infrared spectroelectrochemically characterized redox pairs cis-[(bpy)2ClOs(NO)]2+/+and [(CN)5Os(NO)]2-/3-. The DFT calculations indicate that the oxidation of [Cl5Os(NO)]2- occurs largely on themetal, the highest occupied molecular orbital (HOMO) of the precursor being composed of Os 5d (58%) and Cleq3p orbitals (41%). As for the related [(CN)5Os(NO)]2-, the reduction is largely NO centered, the lowest unoccupiedmolecular orbital (LUMO) of [Cl5Os(NO)]2- has 61% 
rs/pi.gif" BORDER=0 >*(NO) character with significant 5d Os contributions (34%).A rather large degree of metal-NO back-donation is estimated to occur in the {OsNO}7 configuration of [Cl5Os(NO)]3-which leads to an unusual low value of 1513 cm-1 calculated for rs/nu.gif" BORDER=0 >(NO), signifying contributions from an OsIII(NO-)formulation. Detailed analyses of the conformational dependence of the g anisotropy suggest that the differentreduced species reported previously for [Cl5Os(NO)]3- in AgCl host lattices may be distinct in terms of eclipsed orstaggered conformations of the bent NO
axial ligand relative to the OsIICl4 equatorial plane. The staggered formis calculated to be more stable by 105 cm-1. The weak absorptions of [Cl5Os(NO)]2- at 573, 495, and 437 nm areassigned as MLCT/LLCT transitions to the doubly degenerate rs/pi.gif" BORDER=0 >*(NO) LUMO. The oxidized form [Cl5Os(NO)]-contains OsIII in an {OsNO}5 configuration with a spin density of 0.711 on Os. In all three states of [Cl5Os(NO)]n-,the N bonded form is vastly preferred over the NO-side-on bonded alternative.
. Density-functionaltheory (DFT) calculations confirm this result, and a comparison of structures calculated for several oxidation statesreveals an increased labilization of the trans-positioned M-Cl bond on reduction in the order M = Ir < Os < Ru.Accordingly, the intact reduced form [Cl5Os(NO)]3- could not be observed in fluid solution even on electrolysis at-70 C in n-butyronitrile solution, as confirmed both by DFT calculations and by comparison with the electronparamagnetic resonance and infrared spectroelectrochemically characterized redox pairs cis-[(bpy)2ClOs(NO)]2+/+and [(CN)5Os(NO)]2-/3-. The DFT calculations indicate that the oxidation of [Cl5Os(NO)]2- occurs largely on themetal, the highest occupied molecular orbital (HOMO) of the precursor being composed of Os 5d (58%) and Cleq3p orbitals (41%). As for the related [(CN)5Os(NO)]2-, the reduction is largely NO centered, the lowest unoccupiedmolecular orbital (LUMO) of [Cl5Os(NO)]2- has 61% rs/pi.gif" BORDER=0 >*(NO) character with significant 5d Os contributions (34%).A rather large degree of metal-NO back-donation is estimated to occur in the {OsNO}7 configuration of [Cl5Os(NO)]3-which leads to an unusual low value of 1513 cm-1 calculated for rs/nu.gif" BORDER=0 >(NO), signifying contributions from an OsIII(NO-)formulation. Detailed analyses of the conformational dependence of the g anisotropy suggest that the differentreduced species reported previously for [Cl5Os(NO)]3- in AgCl host lattices may be distinct in terms of eclipsed orstaggered conformations of the bent NO axial ligand relative to the OsIICl4 equatorial plane. The staggered formis calculated to be more stable by 105 cm-1. The weak absorptions of [Cl5Os(NO)]2- at 573, 495, and 437 nm areassigned as MLCT/LLCT transitions to the doubly degenerate rs/pi.gif" BORDER=0 >*(NO) LUMO. The oxidized form [Cl5Os(NO)]-contains OsIII in an {OsNO}5 configuration with a spin density of 0.711 on Os. In all three states of [Cl5Os(NO)]n-,the N bonded form is vastly preferred over the NO-side-on bonded alternative.