Electronic structures and spectroscopic properties of nitrido-osmium(VI) complexes with acetylide ligands [OsN(C[Triple Bond]CR)4]- R=H, CH3, and Ph by density functional theory calculation

Electronic structures and spectroscopic properties of a series of nitrido-osmium (VI) complex ions with acetylide ligands, OsN(CTriple Bond]CR)(4)](-) (RDouble Bond]H, (1), CH(3) (2), and Ph (3)) were investigated theoretically. The structures of the complexes were fully optimized at the B3LYP and CIS level for the ground states and excited states, respectively. The calculated bond lengths of OsTriple Bond]N (1.639 A in 1, 1.642 A in 2, and 1.643 A in 3) and Os-C (2.040 A in 1, 2.043 A in 2, and 2.042 A in 3) in ground state agree well with the experimental results. The bond length of OsTriple Bond]N bond is lengthened by ca. 0.13 A in the A (3)B(2) excited state compared to the (1)A(1) ground state, which is consistent with the lower vibration frequency of nu(Os-N) ( approximately 780 cm(-1)) in the excited state than that ( approximately 1175 cm(-1)) in the ground state. Among the calculated dipole-allowed absorptions at lambda>250 nm, the intense absorption at 261 nm for 1, 266 nm for 2, and 300 nm for 3 were attributed to the (1)pi(CTriple Bond]C)]-->(1)pi(*)(NTriple Bond]Os)+pi(*)(CTriple Bond]C)], (1)pi(CTriple Bond]C)]-->(1)pi(*)(NTriple Bond]Os)+pi(*)(CTriple Bond]C)], and (1)pi(CTriple Bond]CPh)]-->(1)pi(*)(NTriple Bond]Os)+pi(*)(CTriple Bond]CPh)], respectively. The lowest energy absorption at lambda(max)=393 nm for 1, 400 nm for 2, and 400 nm for 3 were assigned as (1)d(xy)(Os)+pi(CTriple Bond]C)]-->(1)pi(*)(NTriple Bond]Os)+pi(*)(CTriple Bond]C)], (1)d(xy)(Os)+pi(CTriple Bond]C)]-->(1)pi(*)(NTriple Bond]Os)+pi(*)(CTriple Bond]C)], and (1)d(xy)(Os)+pi(CTriple Bond]CPh)]-->(1)pi(*)(NTriple Bond]Os)+pi(*)(CTriple Bond]CPh)], respectively. The calculated phosphorescence emission at lambda(max)=581 nm for 1, 588 nm for 2, and 609 nm for 3 were originated from (3)(pi(*)(NTriple Bond]Os)+pi(*)(CTriple Bond]C))(1)(d(xy)(Os)+pi(CTriple Bond]C))(1)], (3)(pi(*)(NTriple Bond]Os)+pi(*)(CTriple Bond]C))(1)(d(xy)(Os)+pi(CTriple Bond]C))(1)], and (3)(pi(*)(NTriple Bond]Os)+pi(*)(CTriple Bond]CPh))(1)(d(xy)(Os)+pi(CTriple Bond]CPh))(1)] excited state, respectively.