Abrupt two-step and symmetry breaking spin crossover in an iron(iii) complex: an exceptionally wide [LS–HS] plateau

Abstract

[Fe(qsal-Br)2]NO3·2MeOH is reported which undergoes abrupt two step symmetry breaking spin crossover, T½(1st step) = 136 K and T½(2nd step) = 232 K with a hysteresis of 16 K and 5 K, respectively, and an unprecedented [HS-LS] plateau of 96 K.

Solvent modified spin crossover in an iron(iii) complex: phase changes and an exceptionally wide hysteresis

“…Moreover, the length of the 1D π–π chain, which is coincident with the b axis in 1 , 2 and 5 (the a axis for 3 and 4 ), shortens most in 1 and 2 following SCO to the LS state. This confirms earlier studies that the 1D π–π chains are vital for SCO 34,38,51 and further that large differences between the two spin states will lead to abrupt SCO. 58,59 …”

“…The packing in 1–6 is similar consisting of 1D chains held together by two sets of π–π interactions involving pairs of qsal-I ligands and is common for [Fe(qsal-X) 2 ] + complexes; 35,38,43,51,52 (Tables 3 and S8–S13†). The first set of π–π interactions (type A) contains triflate embraces (Fig.…”

“…Cooling of the sample reveals a full LS state at 220 K. The difference between the Mössbauer spectroscopic and magnetic data of the fresh sample is probably due to partial solvent loss during the measurement, something previously observed in [Fe(qsal-Br) 2 ]NO 3 ·2MeOH. 51 …”

Heteroleptic Iron(III) Spin Crossover Complexes; Ligand Substitution Effects

“…Since this is a magnetic spectrum, the quadrupole shift, ε, is listed, which is half the common quadrupole splitting, ∆, normally listed for doublets. The parameters are similar to those of other related Fe(III) complexes [10][11][12], with the outer doublet clearly attributable to a LS Fe(III) site and the inner doublet to a HS Fe(III) site. In Table 1, we see that the sign of the quadrupole shifts is opposite for the two sites, however the absolute value of the signs is undetermined and has been given relative to the positive value ascribed to the hyperfine magnetic field.…”

Competing Phases Involving Spin-State and Ligand Structural Orderings in a Multistable Two-Dimensional Spin Crossover Coordination Polymer

“…Although, crystallographic symmetry breaking giving intermediate steps was previously observed for the mononuclear SCO complexes [Fe 27-29 So far, a relatively small number of complete two-step or incomplete (only one step of two expected) SCO events with symmetry breaking have been observed in mononuclear, [30][31][32][33][34][35][36][37][38][39] polynuclear, [40][41][42][43] and polymeric [44][45][46][47][48][49][50][51][52][53] Fe II SCO complexes, and reviewed recently. 54,55 This phenomenology has also been described for a reduced number of Fe III , [56][57][58][59][60] Co II 61 and Mn III 62 complexes. Most of these examples exhibit spontaneous generation of a stable state characterized by a plateau at HS molar fraction HS ≈ 1/2 and an ordered distribution of the HS and LS centers directly observed from single crystal X-ray analysis.…”