Calculation of the lattice deformation at the phase transitions of [Fe(ptz)₆](BF₄)₂from powder diffraction patterns

Abstract

The thermal and light-induced high-spin (HS: 5T2g) ----low-spin (LS: IAig ) transitions of [Fe(ptz)6](BF4)2 (ptz = 1-propyltetrazole) are investigated by X-ray powder diffractometry in the range between ambient temperature and -15 K. The anisotropic lattice deformation caused by variation of the HS fraction and by temperature change was calculated directly from the differences in peak positions of the powder diagrams measured at different temperatures. An analytical expression for the dependence of peak shifts and splittings on the deformation tensor elements was derived. The differences of the lattice deformations accompanying the thermal and lightinduced spin transitions are discussed.

Assessment of Density Functionals for the High‐Spin/Low‐Spin Energy Difference in the Low‐Spin Iron(II) Tris(2,2′‐bipyridine) Complex

“…Experimentally, this has been evidenced by a change of the crystal volume associated with the spin transition of 15-30 3 per molecular unit. [8,[12][13][14] Such a large difference of the molecular volume makes the spin-crossover phenomenon sensitive to external pressure as well as to variations in the second coordination sphere, [15] and it is responsible for the cooperative effects often observed in neat spin-crossover compounds.…”

Ground- and excited-state electronic structure of an iron-containing molecular spin photoswitch

“…1 Such spin transitions are also observed upon thermal excitation at about 135 K and are accompanied by dramatic structural rearrangements whereby a rombohedral → triclinic phase transition also occurs. 3,4 Concomitant with the magnetic transitions are significant rearrangements of orbital occupation and spin configuration of the central Fe 2+ valence shell which, in a cubic ligand field, can be described as d xy…”

“…1,2,6 Most of the optical experiments have focused on excitations of the initial S = 0 and final S = 2 states of LIESST complexes because these states can be trapped by controlling the temperature and their crystallographic structures have also been determined. [2][3][4]6 However, further theoretical understanding is needed about the detailed electronic structure of LIESST-exhibiting complexes. In particular; one wishes to elucidate their ground-and excited-state electronic structures, the origin of the optical absorption associated with the vertical singlet excited states, and how the excited-state electronic structures are related to the dramatic geometric changes observed by crystallography.…”

“…In particular; one wishes to elucidate their ground-and excited-state electronic structures, the origin of the optical absorption associated with the vertical singlet excited states, and how the excited-state electronic structures are related to the dramatic geometric changes observed by crystallography. 3,4 Such understanding will likely lead to the design and synthesis of new LIESST materials with higher critical temperatures ͑below which the high spin state is effectively trapped͒ for use in potentially novel memory storage or display technologies. 1,2,6 In this work, after a brief description of the ground-state electronic structure, we focus on the computation of singlet→ singlet excited states of the spin photoswitch ͓Fe͑ptz͒ 6 ͔͑BF 4 ͒ 2 by means of time-dependent density-functional response theory.…”

“…3,4 Due to the ability to control spin transitions and color changes in ͓Fe͑ptz͒ 6 ͔͑BF 4 ͒ 2 by means of optical excitation, this and similar complexes are seen as photoswitches for potential use in novel molecular-level memory storage or liquid-crystal display applications. 2,5 Some progress has been made in understanding the basic mechanism of LIESST, mostly based on optical and other spectroscopies.…”