title: Steady-state and pseudo-steady-state photocrystallographic studies on linkage isomers of [Ni(Et4dien)(η2-O,ON)(η1-NO2)]: identification of a new linkage isomer.
abstract: At temperatures below 150 K, the photoactivated metastable endo-nitrito linkage isomer [Ni(Et4 dien)(η(2)-O,ON)(η(1)-ONO)] (Et4 dien=N,N,N',N'-tetraethyldiethylenetriamine) can be generated with 100 % conversion from the ground state nitro-(η(1)-NO2) isomer on irradiation with 500 nm light, in the single crystal by steady-state photocrystallographic techniques. Kinetic studies show the system is no longer metastable above 150 K, decaying back to the ground state nitro-(η(1)-NO2) arrangement over several hours at 150 K. Variable-temperature kinetic measurements in the range of 150-160 K show that the rate of endo-nitrito decay is highly dependent on temperature, and an activation energy of Eact =+48.6(4) kJ mol(-1) is calculated for the decay process. Pseudo-steady-state experiments, where the crystal is continually pumped by the light source for the duration of the X-ray experiment, show the production of a previously unobserved, exo-nitrito-(η(1)-ONO) linkage isomer only at temperatures close to the metastable limit (ca. 140-190 K). This exo isomer is considered to be a transient excited-state species, as it is only observed in data collected by pseudo-steady-state methods.
authors: Department of Chemistry, University of Bath, Bath, BA2 7AY (UK).
authors: Lauren E
authors: LE
authors: Hatcher
authors: Jeppe
authors: J
authors: Christensen
authors: Michelle L
authors: ML
authors: Hamilton
authors: Jose
authors: J
authors: Trincao
authors: David R
authors: DR
authors: Allan
authors: Mark R
authors: MR
authors: Warren
authors: Ian P
authors: IP
authors: Clarke
authors: Michael
authors: M
authors: Towrie
authors: Sara
authors: S
authors: Fuertes
authors: Charles C
authors: CC
authors: Wilson
authors: Christopher H
authors: CH
authors: Woodall
authors: Paul R
authors: PR
authors: Raithby
keywords: linkage isomers; metastable states; nitro complexes; photocrystallography; solid-state kinetics