Selective Photoswitching of the Binuclear Spin Crossover Compound {[Fe(bt)(NCS)2]2(bpm)} into Two Distinct Macroscopic Phases

Abstract

The low-spin (LS-LS, $S=0$) diamagnetic form of the binuclear spin crossover complex $\{[\mathrm{Fe}(\mathrm{bt})(\mathrm{NCS}{)}_2{]}_2(\mathrm{bpm})\}$ was selectively photoconverted into two distinct macroscopic phases at different excitation wavelengths (1342 or 647.1 nm). These long-lived metastable phases have been identified, respectively, as the symmetry-broken paramagnetic form (HS-LS, $\mathrm{S}=2$) and the antiferromagnetically coupled (HS-HS, $S=0$) high-spin form of the compound. The selectivity may be explained by the strong coupling of the primary excited states to the paramagnetic state.