The effect of inert dopant ions on spin-crossover materials is not simply controlled by chemical pressure

Abstract

Unexpectedly, the spin-crossover midpoint temperature (T½) in [FezM1−z(bpp)2][BF4]2 is increased by doping with ruthenium(ii). This reflects that different structure:function relationships operate in these materials for different dopant ions ‘M’.

Activating a high-spin iron(ii) complex to thermal spin-crossover with an inert non-isomorphous molecular dopant

“…55,[89][90][91][92] Metric parameters from the refinements are consistent with statistical mixtures of the low-spin iron(II) and nickel(II) complexes, in those ratios (Table S6 †). 54 That is useful confirmation of the crystal metal stoichiometries in the previous paragraph.…”

“…The changes to the unit cell dimensions during SCO resemble our previous study of the [Fe x Ni 1−x (bpp) 2 ][BF 4 ] 2 system (Table S9 †). 54 The isothermal volume change during high → low-spin SCO at T1 2 (ΔV SCO ) for 1a 54 within experimental error. However ΔV SCO for 2a [−21.9(6) Å 3 ] is ca.…”

“…1. 42,47,54,57,[64][65][66][67] The energy penalty associated with the distortion, ΔE(dist), for the different complexes runs as follows (Fig. 2 and ESI; † HS = high-spin):…”

“…S10 and S11 †). 54 Neighbouring cation layers associate more loosely along c, and are separated by the ClO 4 − ions. [Fe(bpp) 2 ] 2+ derivatives with this crystal packing motif often show abrupt thermal spin-transitions with narrow thermal hysteresis; 95,96 the magnetic data from 2a and 3a imply the P2 1 phase of [Fe(bpp) 2 ][ClO 4 ] 2 behaves similarly (Fig.…”

“…26,28,[35][36][37] Solid solutions of SCO materials with isomorphous, inert dopants are an established tool for elucidating the lattice energetics of SCO processes. [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] We, and others, have also investigated doping as a way to introduce new functionality into SCO materials. 42,[55][56][57][58][59][60] Two examples are particularly relevant to this work, where doping a complex into a host lattice changes its spin state properties.…”