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Elucidating the Structural Chemistry of a Hysteretic Iron(II) Spin‐Crossover Compound From its Copper(II) and Zinc(II) Congeners
Author(s) -
Pask Christopher M.,
Greatorex Sam,
Kulmaczewski Rafal,
Baldansuren Amgalanbaatar,
McInnes Eric J. L.,
Bamiduro Faith,
Yamada Mihoko,
Yoshinari Nobuto,
Konno Takumi,
Halcrow Malcolm A.
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202000101
Subject(s) - crystallography , spin crossover , chemistry , monoclinic crystal system , isostructural , tetragonal crystal system , spin transition , triclinic crystal system , crystal structure , zinc , single crystal , copper , organic chemistry
Annealing [Fe L 2 ][BF 4 ] 2 ⋅ 2 H 2 O ( L= 2,6‐ bis ‐[5‐methyl‐1 H ‐pyrazol‐3‐yl]pyridine) affords an anhydrous material, which undergoes a spin transition at T 1/2 =205 K with a 65 K thermal hysteresis loop. This occurs through a sequence of phase changes, which were monitored by powder diffraction in an earlier study. [Cu L 2 ][BF 4 ] 2 ⋅ 2 H 2 O and [Zn L 2 ][BF 4 ] 2 ⋅ 2 H 2 O are not perfectly isostructural but, unlike the iron compound, they undergo single‐crystal‐to‐single‐crystal dehydration upon annealing. All the annealed compounds initially adopt the same tetragonal phase but undergo a phase change near room temperature upon re‐cooling. The low‐temperature phase of [Cu L 2 ][BF 4 ] 2 involves ordering of its Jahn–Teller distortion, to a monoclinic lattice with three unique cation sites. The zinc compound adopts a different, triclinic low‐temperature phase with significant twisting of its coordination sphere, which unexpectedly becomes more pronounced as the crystal is cooled. Synchrotron powder diffraction data confirm that the structural changes in the anhydrous zinc complex are reproduced in the high‐spin iron compound, before the onset of spin‐crossover. This will contribute to the wide hysteresis in the spin transition of the iron complex. EPR spectra of copper‐doped [Fe 0.97 Cu 0.03 L 2 ][BF 4 ] 2 imply its low‐spin phase contains two distinct cation environments in a 2:1 ratio.