Spin Transition Resulting from the Generation of a New Polymorph in the Metastable Phase

Spin Transition Resulting from the Generation of a New Polymorph in the Metastable Phase Научная публикация

Журнал

Crystal Growth and Design
ISSN: 1528-7483

Вых. Данные

Год: 2021, Том: 21, Номер: 1, Страницы: 260-269 Страниц : 10 DOI: 10.1021/acs.cgd.0c01067

Авторы

Tolstikov Svyatoslav ^1,2 , Golomolzina Irina ¹ , Fokin Sergey V. ¹ , Bogomyakov Artem ^1,2,3 , Morozov Vitaly ^1,3 , Tumanov Sergey ^1,3 , Minakova Olga ^1,3 , Veber Sergey ^1,3 , Fedin Matvey V. ^1,3 , Gromilov Sergey A. ⁴ , Romanenko Galina V. ¹ , Ovcharenko Victor ^1,2

Организации

1	International Tomography Center, SB RAS, 630090 Novosibirsk, Russia
2	Zelinsky Institute of Organic Chemistry, RAS, 119991 Moscow, Russia
3	Novosibirsk State University, 630090 Novosibirsk, Russia
4	Nikolaev Institute of Inorganic Chemistry, SB RAS, 63090 Novosibirsk, Russia

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.

Tolstikov S. , Golomolzina I. , Fokin S.V. , Bogomyakov A. , Morozov V. , Tumanov S. , Minakova O. , Veber S. , Fedin M.V. , Gromilov S.A. , Romanenko G.V. , Ovcharenko V.
Spin Transition Resulting from the Generation of a New Polymorph in the Metastable Phase
Crystal Growth and Design. 2021. V.21. N1. P.260-269. DOI: 10.1021/acs.cgd.0c01067 WOS Scopus

Поступила в редакцию:	3 авг. 2020 г.
Опубликована online:	17 дек. 2020 г.
Опубликована в печати:	6 янв. 2021 г.

Web of science:	WOS:000607623900029
Scopus:	2-s2.0-85098768799

БД	Цитирований
Scopus	5
Web of science	5