Preparation and properties of mixed-valence (.mu.-dinitrogen)bis(pentaammine) complexes of osmium and ruthenium

Photolysis of Aqueous [(NH3)5Os(μ‐N2)Os(NH3)5]5+: Cleavage of Dinitrogen by an Intramolecular Photoredox Reaction

“…The long-wavelength absorption of I at 700 nm has been assigned to an intervalence transition within the delocalized Os II /Os III system while the UV bands have been attributed to MLCT transitions to the bridging N 2 ligand. [5] These assignments are also reflected by the photoreactivity of I. Light absorption by the 700 nm band is not associated with any photoactivity.…”

“…Accordingly, we decided to examine a binuclear complex with a bridging N 2 ligand which largely preserves its integrity as a free dinitrogen molecule. For this purpose, we selected the cation [(NH 3 ) 5 Os II (m-N 2 )Os III (NH 3 ) 5 ] 5+ [5,6] (I).…”

“…The irradiation of I (absorption spectrum: [5] l max = 700 nm (e = 4000 m À1 cm À1 ) and 238 nm (e = 41 000) with a shoulder at 260 nm (e = 21 000)) results in a bleaching of the green color owing to the disappearance of the 700 nm absorption ( Figure 1). Although I is not luminescent, the photoproduct shows an orange emission at l max = 570 nm ( Figure 2) which grows with increasing irradiation time.…”

“…[4] In contrast, the reductive splitting of the NÀN triple bond in a molecular complex is certainly much more difficult to achieve (see below), and has not yet been accomplished, neither thermally nor photochemically.Accordingly, we decided to examine a binuclear complex with a bridging N 2 ligand which largely preserves its integrity as a free dinitrogen molecule. For this purpose, we selected the cation [(NH 3 ) 5 Os II (m-N 2 )Os III (NH 3 ) 5 ] 5+ [5,6] (I).This complex offers several attractive features. It is easily accessible and rather stable in aqueous solution in the absence of light.…”

“…[7][8][9] In this context, it should be stressed that the reverse reaction has been observed as photochemical [8,9] and thermal [10,11] process. It is clearly easy to couple two nitride complexes containing the Os VI N j moiety to give a binuclear N 2 complex owing to the extreme stability of the resulting NÀN triple bond.The irradiation of I (absorption spectrum: [5] l max = 700 nm (e = 4000 m À1 cm À1 ) and 238 nm (e = 41 000) with a shoulder at 260 nm (e = 21 000)) results in a bleaching of the green color owing to the disappearance of the 700 nm absorption (Figure 1). Although I is not luminescent, the photoproduct shows an orange emission at l max = 570 nm ( Figure 2) which grows with increasing irradiation time.…”