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(Et 4 dien)(h 2 -O,ON)(h 1 -ONO)] (Et 4 dien = N,N,N',N'-tetraethyldiethylenetriamine) can be generated with 100 % conversion from the ground state nitro-(h 1 -NO 2 ) 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-(h 1 -NO 2 ) 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 E act = +48.6(4) kJ mol À1 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-(h 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 pseudosteady-state methods.

Solid‐State Reactions of Eicosaborate [B20H18]2− Salts and Complexes

“…[3,4] But in both cases it can affect the reactionp ath, andl imits the number of intermediates so that only selective reactions may occur in solids. [7][8][9][10][11] and medium sized [6,[12][13][14][15] ligands, or even solid-state trans-cis (diag-lat)i somerization of some Re, W, and Mo complexes [16][17][18] and the E/Z photoisomerization of aZ nc omplex. [5] Typically,a tomic movement in the course of a solid-state chemical reaction is accompanied with degradation of am aterial, and inspection of such reactions in situ by means of diffraction techniques is challenging.…”

“…[5] Typically,a tomic movement in the course of a solid-state chemical reaction is accompanied with degradation of am aterial, and inspection of such reactions in situ by means of diffraction techniques is challenging. [9,13,15,18,19,21] The number of atoms involvedi nt he above isomerization reactionsd oes not exceed seven,s ot he question arises about the maximal limit of atoms that can be simultaneously involved in rearrangement, as well as about any crystal packing effectso ns uch multiatomic solid-stater eactions. [7][8][9][10][11] and medium sized [6,[12][13][14][15] ligands, or even solid-state trans-cis (diag-lat)i somerization of some Re, W, and Mo complexes [16][17][18] and the E/Z photoisomerization of aZ nc omplex.…”

“…The fact that isomerization reactions require moderate atomicshifts, allowed the investigation with XRD techniques of an umber of photo-, thermal-, and pressure-induced linkage isomerizationr eactions of metal complexes with small (NO 2 ,S O 2 ,e tc.) [7][8][9][10][11] and medium sized [6,[12][13][14][15] ligands, or even solid-state trans-cis (diag-lat)i somerization of some Re, W, and Mo complexes [16][17][18] and the E/Z photoisomerization of aZ nc omplex. [19] Note, that in some cases unprecedented stability of solids even allowed the characterization of reaction intermediates [20] or the investigation of reactionmechanismsand kinetics of processes.…”

Redoxaktive NOx‐Liganden in palladiumvermittelten Prozessen

“…[40] Die Bindungsisomerisierung kann entweder thermisch oder photochemisch erfolgen und führt zur endo-Konfiguration der "ON = O"-Gruppe am Pd-Zentrum (siehe 32'). [42] Die mçgliche photochemische Reaktion zur Bindungsisomerisierung "Pd-NO 2 " 32 ! "Pd-ONO" 32' bestätigt, dass das chemische Verhalten von NO 2 -Liganden am Pd II durch Licht beeinflusst werden kann.…”

Perspective: On the relevance of slower-than-femtosecond time scales in chemical structural-dynamics studies

“…They report photo-activated reorientation of one of the nitro groups in [Ni(Et 4 dien)(η 2 -O,ON)(η 1 -NO 2 )] (Et 4 dien = N,N,N′,N′ tetraethyldiethylenetriamine). The group rearranges from N-bound η 1 -NO 2 to O-bound η 1 -ONO (nitrito) (Figure 5), on exposure to 500 nm light (Hatcher et al , 2014; Hatcher et al , 2011). Variable temperature studies in the 150–165 K range show the activation energy of decay to be 48.6 kJ/mol.…”