Research output: Contribution to journal › Article › peer-review
Spin Transition Resulting from the Generation of a New Polymorph in the Metastable Phase. / Tolstikov, Svyatoslav; Golomolzina, Irina; Fokin, Sergey V. et al.
In: Crystal Growth and Design, Vol. 21, No. 1, 06.01.2021, p. 260-269.Research output: Contribution to journal › Article › peer-review
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TY - JOUR
T1 - Spin Transition Resulting from the Generation of a New Polymorph in the Metastable Phase
AU - Tolstikov, Svyatoslav
AU - Golomolzina, Irina
AU - Fokin, Sergey V.
AU - Bogomyakov, Artem
AU - Morozov, Vitaly
AU - Tumanov, Sergey
AU - Minakova, Olga
AU - Veber, Sergey
AU - Fedin, Matvey V.
AU - Gromilov, Sergey A.
AU - Romanenko, Galina V.
AU - Ovcharenko, Victor
N1 - Funding Information: This study was financially supported by the Russian Science Foundation (18-13-00380). S. Tolstikov is grateful for support (Agreement between MSHE RF and IOC RAS 075-15-2020-803). M.V.F. thanks the Russian Foundation for Basic Research (grant no. 18-03-00362, EPR study). Publisher Copyright: © 2020 American Chemical Society. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2021/1/6
Y1 - 2021/1/6
N2 - The Cu(hfac)2 complex with a paramagnetic ligand 2-(1-ethyl-imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L5Et) was synthesized in the form of two polymorphs: α-[Cu(hfac)2L5Et] (bluish green crystals) and β-[Cu(hfac)2L5Et] (brown crystals). Despite the structural similarity of the two modifications, whose solid phases are formed by polymer chains with cis coordination of the hfac ligands, their magnetic properties proved quite different. For β-[Cu(hfac)2L5Et], the repeated cooling-heating cycles at temperatures of 260-180 K lead to a reversible spin transition β-[Cu(hfac)2L5Et]-HT↔β-[Cu(hfac)2L5Et]-LT, resulting from a considerable change in the Cu-ONO distances in the Cu-O•-N< heterospin exchange clusters from 2.312(6) Å (HT form) to 2.011(2) Å (LT form), which leads to a transition of ferromagnetic to antiferromagnetic exchange in them. For α-[Cu(hfac)2L5Et], the first cooling also leads to a decrease in μeff from 2.6 μB at 200 K to 0.35 μB at 100 K on the curve of the μeff(T) dependence. However, this is not a spin transition in the starting α-[Cu(hfac)2L5Et], but, rather, the consequence of the irreversible phase transformation of α-[Cu(hfac)2L5Et] into β-[Cu(hfac)2L5Et] induced by the cooling of the metastable α modification to T < 200 K. When the cooling-heating cycles are repeated further, the reversible spin transition inherent in β-[Cu(hfac)2L5Et] is reproduced. For this reason, all the μeff values recorded in the range of 200-100 K for the cooled α-[Cu(hfac)2L5Et] sample are higher than those for β-[Cu(hfac)2L5Et] up to T ∼75 K until the whole starting α modification transforms into the β form. This effect has never been observed earlier for transition metal complexes with nitroxides. The experimental μeff(T) dependence observed during the first cooling of α-[Cu(hfac)2L5Et] was called a spin transition in the nascent phase to distinguish it from the μeff(T) curve for β-[Cu(hfac)2L5Et] corresponding to the typical reversible spin transition for heterospin complexes of transition metals with organic radicals. The results of thermomagnetic measurements correlate with FTIR and EPR data.
AB - The Cu(hfac)2 complex with a paramagnetic ligand 2-(1-ethyl-imidazol-5-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L5Et) was synthesized in the form of two polymorphs: α-[Cu(hfac)2L5Et] (bluish green crystals) and β-[Cu(hfac)2L5Et] (brown crystals). Despite the structural similarity of the two modifications, whose solid phases are formed by polymer chains with cis coordination of the hfac ligands, their magnetic properties proved quite different. For β-[Cu(hfac)2L5Et], the repeated cooling-heating cycles at temperatures of 260-180 K lead to a reversible spin transition β-[Cu(hfac)2L5Et]-HT↔β-[Cu(hfac)2L5Et]-LT, resulting from a considerable change in the Cu-ONO distances in the Cu-O•-N< heterospin exchange clusters from 2.312(6) Å (HT form) to 2.011(2) Å (LT form), which leads to a transition of ferromagnetic to antiferromagnetic exchange in them. For α-[Cu(hfac)2L5Et], the first cooling also leads to a decrease in μeff from 2.6 μB at 200 K to 0.35 μB at 100 K on the curve of the μeff(T) dependence. However, this is not a spin transition in the starting α-[Cu(hfac)2L5Et], but, rather, the consequence of the irreversible phase transformation of α-[Cu(hfac)2L5Et] into β-[Cu(hfac)2L5Et] induced by the cooling of the metastable α modification to T < 200 K. When the cooling-heating cycles are repeated further, the reversible spin transition inherent in β-[Cu(hfac)2L5Et] is reproduced. For this reason, all the μeff values recorded in the range of 200-100 K for the cooled α-[Cu(hfac)2L5Et] sample are higher than those for β-[Cu(hfac)2L5Et] up to T ∼75 K until the whole starting α modification transforms into the β form. This effect has never been observed earlier for transition metal complexes with nitroxides. The experimental μeff(T) dependence observed during the first cooling of α-[Cu(hfac)2L5Et] was called a spin transition in the nascent phase to distinguish it from the μeff(T) curve for β-[Cu(hfac)2L5Et] corresponding to the typical reversible spin transition for heterospin complexes of transition metals with organic radicals. The results of thermomagnetic measurements correlate with FTIR and EPR data.
UR - http://www.scopus.com/inward/record.url?scp=85098768799&partnerID=8YFLogxK
UR - https://www.mendeley.com/catalogue/91e10023-ee6b-3b27-9c58-3446c3f2e0b2/
U2 - 10.1021/acs.cgd.0c01067
DO - 10.1021/acs.cgd.0c01067
M3 - Article
AN - SCOPUS:85098768799
VL - 21
SP - 260
EP - 269
JO - Crystal Growth and Design
JF - Crystal Growth and Design
SN - 1528-7483
IS - 1
ER -
ID: 27357622