Solid‐State Interconversions: Unique 100 % Reversible Transformations between the Ground and Metastable States in Single‐Crystals of a Series of Nickel(II) Nitro Complexes

Abstract

The solid-state, low-temperature linkage isomerism in a series of five square planar group 10 phosphino nitro complexes have been investigated by a combination of photocrystallographic experiments, Raman spectroscopy and computer modelling. The factors influencing the reversible solid-state interconversion between the nitro and nitrito structural isomers have also been investigated, providing insight into the dynamics of this process. The cis-[Ni(dcpe)(NO2)2] (1) and cis-[Ni(dppe)(NO2)2] (2) complexes show reversible 100 % interconversion between the η1-NO2 nitro isomer and the η1-ONO nitrito form when single-crystals are irradiated with 400 nm light at 100 K. Variable temperature photocrystallographic studies for these complexes established that the metastable nitrito isomer reverted to the ground-state nitro isomer at temperatures above 180 K. By comparison, the related trans complex [Ni(PCy3)2(NO2)2] (3) showed 82 % conversion under the same experimental conditions at 100 K. The level of conversion to the metastable nitrito isomers is further reduced when the nickel centre is replaced by palladium or platinum. Prolonged irradiation of the trans-[Pd(PCy3)2(NO2)2] (4) and trans-[Pt(PCy3)2(NO2)2] (5) with 400 nm light gives reversible conversions of 44 and 27 %, respectively, consistent with the slower kinetics associated with the heavier members of group 10. The mechanism of the interconversion has been investigated by theoretical calculations based on the model complex [Ni(dmpe)Cl(NO2)].

Exploring possible reaction pathways for the o‐atom transfer reactions to unsaturated substrates catalyzed by a [Ni‐NO2] ↔ [Ni‐NO] redox couple using DFT methods

“…The reaction pathway is similar to that proposed by Warren et al for the [Ni(dppe)Cl(NO 2 )] → [Ni(dppe)Cl(ΟNO)] linkage isomerization process. In the linkage isomerization [Ni( ‐NO 2 )(S 2 CNHMe)(PMe 3 )] [Ni( ‐ONO)(S 2 CNHMe)(PMe 3 )] pathway the starting point is the singlet ground state ( GS ) of the [Ni( ‐NO 2 )(S 2 CNHMe)(PMe 3 )] complex, which on irradiation is transformed to the triplet excited state ( GS* ) with an energy demand of 10.1 and 7.6 kcal/mol in vacuum and solution, respectively.…”

“…Recently Warren et al reported on the synthesis and characterization of a series of square planar group 10 metal complexes that exhibit switchable metastable‐state behavior The solid‐state, low‐temperature linkage isomerism in these complexes have been investigated by a combination of photocrystallographic experiments, Raman spectroscopy and computer modeling. The mechanism of the interconversion has been investigated by theoretical calculations based on the model complex [NiCl(dppe)(NO 2 )] (dppe = 1,2‐bis(diphenylphosphino)ethane).…”

Switchable molecule-based materials for micro- and nanoscale actuating applications: Achievements and prospects

“…Examples include diarylethenes [17] and naphthalocyanine [53]. Linkage isomers are an interesting class of coordination complexes, which have one (or more) ligands with switchable connectivity to the metal ion [54]. In all of the above cases, the two states of the molecule correspond to local minima in the ground-state potential energy surface.…”

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.…”