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

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.

Multiple light-induced NO linkage isomers in the dinitrosyl complex [RuCl(NO)2(PPh3)2]BF4 unravelled by photocrystallographic and IR analysis.

Multiple light-induced reversible metastable NO linkage isomers (PLIs) have been detected in the dinitrosyl compound [RuCl(NO)2(PPh3)2]BF4 by a combination of photocrystallographic and IR analysis. The IR signature of three PLI states has been clearly identified, with estimated populations of 59% (PLI-1), 8% (PLI-2) and 5% (PLI-3) for a total population of the metastable state of 72%. The structural configuration of the major component (PLI-1) has been derived by X-ray photocrystallography. In the ground state, the structure is characterized by a bent and a linear nitrosyl, the bent one being oriented towards the linear equatorial nitrosyl with an Ru-N-O angle of 133.88 (9)°. X-ray Fourier difference maps indicate a selectivity of the photo-isomerization process in PLI-1: only the bent NO ligand changes its position, while the linear NO is unaffected. After irradiation at 405 nm, the orientation is changed by rotation towards the Cl ligand opposite the linear NO, with an Ru-N-O angle in this new position of 109 (1)°. The photocrystallographic analysis provides evidence that, in the photo-induced metastable state, the bent NO group is attached to the Ru atom through the N atom (Ru-N-O), rather than in an isonitrosyl Ru-O-N binding mode. In the IR spectra, the asymmetric NO vibrational band shifts by -33 cm(-1) to a lower value, whereas the symmetric band splits and shifts by 5 cm(-1) to a higher value and by -8 cm(-1) to a lower value. The down shift is a clear indication of the structural change, and the small upward shift in response to the new electronic configuration of the metastable structure. Variable-temperature IR kinetic measurements in the range 80-114 K show that the decay of the PLI-1 state follows an Arrhenius behaviour with an activation energy of 0.22 eV.

NO-binding in {Ru(NO)2}8-type [Ru(NO)2(PR3)2X]BF4 compounds.

Two different structure types were found for a series of mononuclear dinitrosyl complexes of the general formula [RuL2(NO)2X]BF4 (L = monodentate phosphane, X = Cl, Br, I). The {Ru(NO)2}(8)-type target compounds were prepared by the reduction of the respective {RuNO}(6) precursors and subsequent oxidative addition of (NO)BF4. About one half of the new compounds share their molecular structure with the hitherto only representative of this class of dinitrosyls, Pierpont and Eisenberg's [RuCl(NO)2(PPh3)2]PF6·C6H6 (Inorg. Chem., 1972, 11, 1088-1094). The Cs-symmetric cations exhibit both a linear and a bent Ru-N-O fragment, in line with a formal 6 + 2 split of the {Ru(NO)2}(8) electron sum in the sense of a [Ru(II)(NO(+))((1)NO(-))](2+) bonding. The coordination entity's configuration in this subgroup is described by IUPAC's polyhedral symbol SPY-5. Continuous shape measures (CShM) as defined by Alvarez et al. (Coord. Chem. Rev., 2005, 249, 1693-1708) reveal a uniform deviation from the L-M-L angles expected for SPY-5, in a narrower sense, towards a vacant octahedron (vOC-5). DFT calculations confirmed that Enemark and Feltham's analysis (Coord. Chem. Rev., 1974, 13, 339-406) of the electronic situation of the {Ru(NO)2}(8) group remains adequate. The same holds for the second subclass of new compounds the existence of which had been predicted in the same paper by Enemark and Feltham, namely C(2v)-symmetric, TBPY-5-type cations with two almost equally bonded nitrosyl ligands. In agreement with an 8 + 0 distribution of the relevant electrons, the formal [Ru(0)(NO(+))2](2+) entities are found for L/X couples that donate more electron density on the central metal. Two solid compounds (8a/b, 12a/b) were found in both structures including the special case of the P(i)Pr3/Br couple 12a/b, which led to crystals that contained both structure types in the same solid. Conversely, four compounds showed a single form in the solid but both forms in dichloromethane solution in terms of the solutions' IR spectra. The irradiation of crystalline 12 with blue laser light resulted in the photoisomerisation of, mainly, the bent (1)NO(-) ligand in terms of low-temperature IR spectroscopy.