Photogeneration of two metastable NO linkage isomers with high populations of up to 76% in trans-[RuCl(py)₄(NO)][PF₆]₂·½H₂O

Abstract

Two light-induced metastable NO linkage isomers with oxygen-bound (SI) and side-on configuration (SII) of NO are generated in trans-[RuCl(py)(4)(NO)][PF(6)](2).(1/2)H(2)O. Irradiation by light in the blue-green spectral range (450-530 nm) leads to the population of SI. A further irradiation by near infrared light (920-1100 nm) transfers SI into SII at temperatures below 150 K. The heat release during the thermal decay of the linkage isomers shows that SI and SII are separated from the ground state (GS) by potential barriers of E(A)(SI) = 0.70(3) eV and E(A)(SII) = 0.38(3) eV, and are energetically situated at 1.42(6) eV and 1.07(7) eV above the ground state, respectively. Maximum populations of 76% for SI and of 56% for SII can be generated, as determined by the decrease of the nu(NO) stretching absorption band of the ground state. The nu(NO) stretching vibration shifts to lower energies by 143 cm(-1) in SI and by 300 cm(-1) in SII, indicating that the linkage isomers are of the same type as found in other octahedrally coordinated transition-metal nitrosyl complexes. The experimental observations are in agreement with results from calculations by the density functional theory, which predict that the metastable states correspond to a side-on bonded (SII) and an isonitrosyl (SI) configuration of the NO ligand. The calculations provide the energy minima of the ground state and the metastable states SI and SII as well as the saddle points along the reaction coordinate Q. This reaction coordinate corresponds to a rotation of the NO ligand by about 90 degrees (SII) and 180 degrees (SI), and therefore allows the comparison between observed and calculated activation energies.

Photoinduced nitrosyl linkage isomers in complexes based on the photochromic cation [RuNO(NH3)5]3+ with the paramagnetic anion [Cr(CN)6]3− and the diamagnetic anions [Co(CN)6]3− and [ZrF6]2−

“…The observed shifts of 135 cm À1 and 312 cm À1 are typical for the metastable states in [MNOL 5 ] compounds [1]. From the decrease of the area of the ground state stretching vibration m(NO) the population of SI and SII can be determined [13]. However, the area of this vibrational band is influenced, though only a little, by the arising band of SI at slightly lower wavenumbers.…”

“…Vibrational spectroscopy is a suitable method to identify the metastable linkage isomers SI and SII by the downshift of the m(NO) stretching vibration [22,23] as well as for the determination of the population numbers of the linkage isomers [13]. Fig.…”

“…Such metastable linkage isomers can also be generated in complexes containing the ligands SO, SO 2 , DMSO, and N 2 [6][7][8][9]. Up to now Fe, Ru, Os, Ni, and Pt were used as central atoms M, while the ligands L can be chosen almost arbitrary, e.g., F À , Cl À , Br À , CN À , NO 2 , NH 3 , C 2 O 2À 4 including pyridine, ethylenediamine, porphyrine, and hemoglobin [2,[10][11][12][13][14][15]. The metastable linkage isomers are stable at low temperatures and have lifetimes up to several minutes at room temperature [12].…”

cis-Chloridobis(4,4′-dimethyl-2,2′-bipyridine)nitrosylruthenium(II) bis(hexafluorophosphate)

“…Ruthenium nitrosyl complexes can either induce photochromism (Schaniel et al, 2007b) or NO photorelease (Rose & Mascharak, 2008). In the first case, photoisomerization along the rutheniumnitrosyl bond (Ru-NO/Ru-ON) is observed in the solid state when the compounds are irradiated in the blue region (Schaniel et al, 2007a;Cormary et al, 2009Cormary et al, , 2012. It offers technological applications as optical high-capacity storage devices (Imlau et al, 1999).…”

Photocrystallography reveals new metastable nitrosyl linkage isomers in the solid state

“…Until the late 2000s there were no examples of high levels of conversion between the ground and metastable states, and the factors that would favour the conversion or the stability of the metastable state were not fully understood (Schaniel et al, 2007). The understanding of the factors that are important has been pioneered by Schaniel and Woike in a series of seminal papers of which Casaretto et al (2015) is the latest.…”