Reversible mechanism for spin crossover in transition-metal cyanides

Abstract

We report the mechanisms for reversible and repeatable spin transition in a Prussian blue analog crystal, KCo[Fe(CN)6], derived from first-principles calculations. The forward and reverse transitions are initiated by metal-to-metal charge transfer, followed by the d-electron rearrangement at the Co center. Further, these transitions are strongly correlated with bond lengths within the crystal lattice. Both aspects of this spin crossover are in quantitative agreement with experiments. Moreover, we find that the presence of H2O molecules within this Prussian blue analog crystal is not essential to trigger spin transitions in such materials.

High-pressure behaviour of Prussian blue analogues: interplay of hydration, Jahn-Teller distortions and vacancies

“…Prussian blue analogues (PBAs) are an interesting class of cyanide-linked coordination polymers with a diverse range of properties, including spin-crossover behaviour, photoswitchable magnetism, permanent porosity and mass transport abilities of relevance to battery applications. [1][2][3][4][5][6][7] The varied functionality can be attributed to the compositional versatility; PBAs are similar to double perovskites, with the general formula A x B y [B (CN) 6 ] z , where A (if present) is an alkali metal and B and B are transition metal ions. 8 Nearly all first-row-and many second-rowtransition metals can be incorporated on the B-sites and the stoichiometry can be varied by changing the oxidation states, rendering PBAs highly tuneable materials.…”

Effect of the shape on the spin state and exchange in quantum dots. Feynman path integral analysis

“…Since the fields w e (|r''|) and w q (|R''|) in the coordinates r'' and R'' are spherical, identity (6) and the following representation of Eq. (7) are valid in these coordinates: (9) According to this relation, the virial estimator in the case of a wall with an ellipsoidal profile, as well as in the spherical case, can be expressed in terms of sca lar products. For the numerical calculation of its near wall part W({r i (j)}, {R k }), the scaled variables r'' = A'C ⎯1 × r and R'' = A'C -1 × R should be substituted into the right hand side of Eq.…”

“…An example is spin crossover in complexes based on transition element ions with d electrons in electron shells. Such systems can exhibit transforma tions between stable states that have close energies, but significantly different spins [9][10][11][12]. In particular, two long lived stable spin states-low spin (S = 0) and high spin (S = 1)-are observed in some compounds of iron with nitrogen or sulfur in the form of octahe dral coordination sites fixed in crystal matrices of var ious types.…”

Time-dependent nonequilibrium soft x-ray response during a spin crossover

“…1. Whereas the Fe ion remains low spin, the divalent cobalt ion goes from a doublet (S = 1 2 ) to a quartet (S = 3 2 ) 13, 14,16 . The observed increase in the cobalt-ligand bond length oc-curs in less than half the oscillation period of the breathing mode 12 .…”