OsIII(N2)OsIIComplexes at the Localized-to-Delocalized, Mixed-Valence Transition

Demadis, Konstantinos D.; El-Samanody, El-Sayed A.; Coia, and George M.; Meyer, Thomas J.

doi:10.1021/ja982802o

Cited by 98 publications

(108 citation statements)

References 82 publications

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“…Adding N to NO to give N 2 O is exothermic by 114.9 kcal mol -1 . 21 Coupling these values in a thermochemical cycle gives D(Ost N) < 135 kcal mol -1 (Scheme 2).The ability of 1 to add NO is consistent with the general reactivity of this class of osmium(VI) nitrido complexes: reactions typically involve both reduction of the osmium and bond formation to the nitrido ligand. For instance, Cp 2 Co induces N-N coupling, forming [TpCl 2 Os III (N 2 )Os II Cl 2 Tp] -, and amines and carbanions add to the nitrido ligand to form reduced hydrazido and amido complexes.…”

supporting

confidence: 57%

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Nitric Oxide Abstracts a Nitrogen Atom from an Osmium Nitrido Complex To Give Nitrous Oxide

et al. 2000

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The chemistry of nitric oxide, NO, is attracting widespread interest, from environmental to biological chemistry. 1,2 As a free radical, NO reacts rapidly with other odd-electron species, such as superoxide and alkyl radicals, and reversibly dimerizes to N 2 O 2 . NO can be oxidized to NO + or to NO 2 -(by formal addition of O •-). Reduction of NO to N 2 O commonly occurs via deoxygenation of N 2 O 2 , often in a metal-mediated process. 3 Reported here is the first example of reduction of NO to N 2 O that occurs by one-step nitrogen-atom transfer.Stirring a benzene solution of the osmium nitrido complex TpOs(N)Cl 2 (1) 4 under ∼0.75 atm of NO for 24 h results in stoichiometric conversion to N 2 O and the osmium nitrosyl complex TpOs(NO)Cl 2 (2) 5 (eq 1; Tp ) HBpz 3 , hydrotris-(pyrazolyl)borate). 6 The osmium stoichiometry was determined by 1 H NMR and the N 2 O was detected by gas-phase IR. The IR spectrum of N 2 O at moderate pressures (∼0.10 Torr), using a low-resolution PE1600 FT-IR, shows broad R and P branches, with maxima at 2214 and 2238 cm -1 and a minimum at 2224 cm -1 (the unobserved Q-branch position; Figure 1). The yield of N 2 O was 90 ( 10%, based on a Beer's law calibration at 2224 cm -1 and subtraction of the residual N 2 O present in the NO reactant (Figure 1, inset). 7 Kinetic data obtained by 1 H NMR in CD 2 Cl 2 under 3 atm of NO (pseudo-first-order conditions) are consistent with first-order decay of 1. Reducing the pressure by a factor of 3 increases the half-life by roughly the same factor. Reaction 1 thus appears to be first order in both 1 and NO, with rate constant k ≈ 3 × 10 -4 M -1 s -1 at 21°C. 8 There are two reasonable types of mechanisms for reaction 1. The nitrosyl complex 2 could be formed by oxygen atom transfer to the nitrido ligand in 1, analogous to the conversion of 1 to 2 by Me 3 NO (eq 2). 9 In reaction 1, the source of oxygen could be from an NO-derived species such as bound or free N 2 O 2 . Alternatively, addition of NO to the nitrido ligand would form the osmium-N 2 O complex, [TpOs(NNO)Cl 2 ] (Scheme 1). Loss of N 2 O would give [TpOsCl 2 ], which would be converted to 2 by the excess NO present. An 15 N-labeling experiment can distinguish the two pathways because the first incorporates the nitrido ligand into the nitrosyl group, while the second converts the nitrido ligand into the terminal nitrogen of the N 2 O. The reaction of TpOs( 15 N)Cl 2 4 with 14 NO supports the second pathway (Scheme 1), as only TpOs( 14 NO)Cl 2 is formed by IR and mass spectroscopies [<10% Os( 15 NO)]. Gas-phase IR spectra of the volatiles from the reaction show both the residual 14 N 14 NO impurity in the NO (unobserved Q branch at 2224 cm -1 ) and a new feature at lower frequency whose R branch overlaps with the P branch of 14 N 14 NO (Figure 1, bottom). The Q branch minimum of the new feature at 2201 cm -1 agrees at this level of resolution with the 2202.5 cm -1 reported for 15 N 14 NO. 10 Direct, rate-limiting attack of NO on the nitrido ligand of 1 is consistent with the apparent...

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supporting

confidence: 57%

“…Adding N to NO to give N 2 O is exothermic by 114.9 kcal mol -1 . 21 Coupling these values in a thermochemical cycle gives D(Ost N) < 135 kcal mol -1 (Scheme 2).…”

Section: ) [Tposclmentioning

confidence: 99%

Nitric Oxide Abstracts a Nitrogen Atom from an Osmium Nitrido Complex To Give Nitrous Oxide

et al. 2000

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“…The predicted spectral pattern of five low-energy bands has been observed in the near-IR/IR regions for mixedvalence Os dimers [5,9] in Class II-III.…”

mentioning

confidence: 82%

Observation of Three Intervalence‐Transfer Bands for a Class II–III Mixed‐Valence Complex of Ruthenium

et al. 2007

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Mixed valency in metal complexes such as the Creutz-Taube ion [1,2] [(NH 3 ) 5 Ru II (m-pz)Ru III (NH 3 ) 5 ] 5+ (1; pz = pyrazine) has been investigated for over forty years, [2][3][4][5][6][7] although a major remaining challenge is to develop a detailed understanding of the localized-to-delocalized transition (that is, Class II to Class III in the Robin-Day classification scheme). [4][5][6]8] A useful probe for assessing the extent of electronic delocalization has come from analysis of the intervalence-transfer (IT) absorption bands that typically appear in the near-IR spectra. [2,3,5,6] In the valence-localized limit, these IT bands arise from photoinduced intramolecular electron transfer across the ligand bridging the mixed-valence centers, that is, MA semi-classical theoretical treatment of electronic coupling and localization versus delocalization was provided by Hush.[3] This treatment was based on the average-mode approximation and assumed a single orbital interaction. However, the multiple ligand-mediated orbital interactions in transition-metal complexes, such as 1, can result in multiple IT transitions split by low symmetry and spin-orbit coupling.[5]For dp 6 -dp 5 systems, in particular, this is predicted to give rise to five low-energy transitions, three of IT origin and two of interconfigurational (IC) origin, as depicted in Figure 1.Neglecting the reorganization energy for the IC transitions, the IT band energies are related by E IT(1) = l, E IT(2) % E IT(1) + E IC(1) , and E IT(3) % E IT(1) + E IC(2) , where l is the reorganization energy for the bridge-mediated electron transfer. The IC band energies E IC(1) and E IC(2) depend on the local symmetry at M III and the magnitude of the spin-orbit coupling constant z.[5] Only the lowest-energy IT(1) absorption arises from electron transfer in the ground state-the higher-energy IT(2) and IT(3) absorptions lead to IC excited states at the donor site and are of mixed IT/IC character.The predicted spectral pattern of five low-energy bands has been observed in the near-IR/IR regions for mixedvalence Os dimers [5,9] in Class II-III.[5] Although valences (oxidation states) are localized in this intermediate class, electron transfer between the metal sites is sufficiently rapid that solvent is averaged and no longer contributes to l. As a consequence, the decreased band energies and widths result in well separated IT absorptions for Os systems, where the large spin-orbit coupling constant of Os III (z % 3000 cm À1 ) increases the energy spacings for both IT and IC transitions.Although the model is generally applicable to d 6 -d 5 systems, there is limited evidence for analogous behavior in complexes of Ru or Fe, for which the decreased magnitudes of the spin-orbit coupling (z(Ru III ) % 1000 cm À1 ; z(Fe III ) % 400-500 cm À1 ) lead to closely spaced IT bands with overlapping absorptions as well as IC bands that are shifted into the IR and have greatly reduced absorptivities (which vary as the square of the spin-orbit coupling constant [5] (2 À ; tppz = 2,3...

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“…[11,54,55] Alternatively, the asymmetry of the IVCT bands may be attributed to a manifold of discrete, underlying transitions which are identified as spinorbit components. [10,[56][57][58] Spectral deconvolution of the reduced (AEe(n)/n dn) NIR bands reveals three underlying gaussian-shaped components ( Table 2). The differences observed between the energies, intensities and bandwidths for the diastereoisomers lie well outside the limits of experimental error.…”

Section: Complexmentioning

confidence: 99%

Intervalence Charge Transfer (IVCT) in Ruthenium Dinuclear and Trinuclear Assemblies Containing the Bridging Ligand HAT {1,4,5,8,9,12‐hexaazatriphenylene}

D’Alessandro

Keene

2005

Chemistry A European J

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The IVCT characteristics of the mixed-valence forms of the dinuclear [{Ru(bpy)(2)}(2)(mu-hat)](n+) and the trinuclear [{Ru(bpy)(2)}(3)(mu-hat)](n+) species {HAT = 1,4,5,8,9,12-hexaazatriphenylene; bpy = 2,2'-bipyridine} show a marked dependence on the nuclearity, and in the trinuclear case on the extent of oxidation. Small differences are also found between the diastereoisomers of the dinuclear complex {meso (DeltaLambda) and rac (DeltaDelta/LambdaLambda)}, and between the homochiral (Delta(3)/Lambda(3)) and heterochiral (Delta(2)Lambda/Lambda(2)Delta) diastereoisomers of the trinuclear case. The strong metal-metal interactions result in unusual spectroscopic and electrochemical properties of the singly-oxidised (+7) and doubly-oxidised (+8) trinuclear mixed-valence species. A qualitative localised bonding description based on the geometrical properties of the dpi(Ru(II/III)) orbitals is invoked to explain the IVCT behaviour in the di- and trinuclear systems.

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Os^III(N₂)Os^IIComplexes at the Localized-to-Delocalized, Mixed-Valence Transition

Abstract: On the basis of the appearance of ν(NtN) from 2007 to 2029 cm -1 in CD 3 CN, oxidation states at Os in cis,cis-[(

Cited by 98 publications

References 82 publications

Nitric Oxide Abstracts a Nitrogen Atom from an Osmium Nitrido Complex To Give Nitrous Oxide

Nitric Oxide Abstracts a Nitrogen Atom from an Osmium Nitrido Complex To Give Nitrous Oxide

Observation of Three Intervalence‐Transfer Bands for a Class II–III Mixed‐Valence Complex of Ruthenium

Intervalence Charge Transfer (IVCT) in Ruthenium Dinuclear and Trinuclear Assemblies Containing the Bridging Ligand HAT {1,4,5,8,9,12‐hexaazatriphenylene}

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