Photochemistry of tricarbonylnitrosylcobalt in frozen gas matrices at 20 K. Infrared spectroscopic evidence for dicarbonylnitrosylcobalt and dicarbonyl(dinitrogen)nitrosylcobalt

Abstract

Infrared evidence is presented for the formation of a three-co-ordinate species, [Co(CO),(NO)], on the U.V. photolysis of [Co(CO),(NO)] in argonand methane matrices,andfortheforniation of four-co-ordinate species, [Co(CO),-(N,)(N@)] and probably [Co(CQ)(N,),(NO)],in nitrogen matrices a t 20 K. The primary photolysis steps are readily reversed by irradiation withvisible light and by annealing the matrix in the case of the reaction of [Co(CO),-(N@)] with CO. The results are discussed in reletion to the postulate of co-ordinatively unsaturated and expandedco-ordination-shell species as intermediates in the thermal substitution reactions of [Co(CO), (NOj]. THE thermal substitution reactionsof the pseudo-first stage in the decomposition of [Ni(CO)J both [Ni(CO),] series of complexes [M(CO),-,(NO),] have been thermally and photochemically also involves CO loss, extensively studied.l Tetracarbonylnickel undergoes slow fast substitution and exchanges CO by a dissociative "i(CO)d ---t [~i(CO),] -"i(CO)&I mechanism, (l), with a first-order rate law (2).2 The Southampton SO9 5NH.

Direct Observation of Photoinduced Bent Nitrosyl Excited-State Complexes

“…The spectra in Figure 4 show peaks that are not attributable to either of the CO-or NO-loss pathways that have been observed in past studies, 25,29 The peak labeled D NO partially decays with a time constant of τ = 11 ± 1 ps (Table 1) Species B, C, and D have lower energy stretching frequencies than species A by 92, 113, and 52 cm -1 , respectively. Thus, any of these species could correspond to either a complex with an ON or a bent-NO ligand.…”

“…The UV-visible absorption spectrum in Figure 2 indicates that the formation of the bent-NO complexes is a minor photochemical pathway, 25,27 which is further verified by the low intensity of the B NO and C NO peaks in Figure 4. We expect that the triplet bent-NO complexes were not observed in past studies of Co(CO) 3 (NO) because the quantum yield for this pathway is so low.…”

“…We expect that the triplet bent-NO complexes were not observed in past studies of Co(CO) 3 (NO) because the quantum yield for this pathway is so low. 25 It is possible that this pathway is more significant in other systems, but since the bent-NO complexes are excited state structures, they may be too short-lived to be observed by conventional methods. 80 Further experimental and theoretical investigations are suggested to determine the generality of this mechanism and to determine the effect that this pathway has on the photophysical properties of other transition-metal-NO compounds.…”

“…24 However, the only photochemical reaction observed via IR studies of Co(CO) 3 (NO) in frozen matrices and in the gas phase is the dissociation of a CO or NO ligand. 25,26,29 The goal of this study is to determine whether a bent-NO complex is formed from visible photolysis of Co(CO) 3 (NO), and, if it is formed, to determine the mechanism for its formation.…”

One- and two-dimensional infrared spectroscopic studies of solution-phase homogeneous catalysis and spin-forbidden reactions

“…[56] The agreement between the calculated NO stretching frequency for Co(CO) 3 (NO) (1842 cm −1 ) is in reasonable agreement with the known experimental values (1808 cm −1 ) and is typical of the observed accuracy for this functional. or NO-loss pathways that have been observed in past studies, [112,116] Table 4.1: Peak assignments and dynamics for the features shown in Figure 4 electronic transition; DFT predicts that these orbitals are 76 kcal/mol apart (ca. 375 nm).…”