Photocrystallography and IR spectroscopy of light-induced linkage NO isomers in [RuBr(NO)2(PCyp3)2]BF4

Abstract

One single photo-induced linkage NO isomer (PLI) is detected and characterized in the dinitrosyl pentacoordinated compound [RuBr(NO)2(PCyp3)2]BF4 by a combination of photocrystallographic and IR analysis. In the ground state, the molecule adopts a trigonal–bipyramidal structure with the two NO ligands almost linear with angles Ru—N1—O1 = 168.92 (16), Ru—N2—O2 = 166.64 (16)°, and exactly equal distances of Ru—N = 1.7838 (17) and O—N = 1.158 (2) Å. After light irradiation of 405 nm at T = 10 K, the angle of Ru—N2—O2 changes to 114.2 (6)° by rotation of the O atom towards the Br ligand with increased distances of Ru—N2 = 1.992 (6) and N2—O2 = 1.184 (8) Å, forming a bent κN bonded configuration. Using IR spectroscopy, the optimal wavelength and maximum population of 39 (1)% of the PLI is determined. In the ground state (GS), the two symmetric νs(NO) and asymmetric νas(NO) vibrations are measured at 1820 and 1778 cm−1, respectively. Upon photo-irradiation, the detection of only one new vibrational ν(NO) stretching band at 1655 cm−1, assigned to the antisymmetric coupled vibration mode and shifted to lower wavenumbers by −123 cm−1, supports the photocrystallographic result. These experimental results are supported by additional DFT calculations, which reproduce the structural parameters and vibrational properties of both the ground state and the photo-induced linkage isomer well. Especially the experimentally characterized molecular structure of the PLI state corresponds to an energy minimum in the calculations; the stabilization of the bent κN bonded configuration of the PLI state originates from specific intramolecular orbital overlap.