TY - JOUR

T1 - Spin transition in the Cu(hfac)2complex with (4-ethylpyridin-3-yl)-substituted nitronyl nitroxide caused by the “asymmetric” structural rearrangement of exchange clusters in the heterospin molecule

AU - Artiukhova, Natalia

AU - Romanenko, Galina

AU - Letyagin, Gleb

AU - Bogomyakov, Artem

AU - Veber, Sergey

AU - Minakova, Olga

AU - Petrova, Marina

AU - Morozov, Vitaliy

AU - Ovcharenko, Victor

PY - 2019/6/1

Y1 - 2019/6/1

N2 - Methods for the synthesis of binuclear [Cu(hfac)2LEt]2and tetranuclear [[Cu(hfac)2]4(LEt)2] heterospin compounds based on copper hexafluoroacetylacetonate [Cu(hfac)2] and 2-(4-ethylpyridin-3-yl)-4,5-bis(spirocyclopentyl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LEt), were developed. The crystals of the complexes are elastic and do not crash during repeated cooling–heating cycles. It was found that a singlet–triplet conversion occurred in all of the {Cu(II)–O•–N<} exchange clusters in the molecules of the binuclear [Cu(hfac)2LEt]2which led to spin coupling with cooling. The transition occurred in a wide temperature range with a maximum gradient ΔχT at ≈180 K. The structural transformation of the crystals takes place at T < 200 K and is accompanied by the lowering of symmetry from monoclinic to triclinic, twinning, and a considerable shortening of the Cu–ONO distance (2.19 and 1.97 Å at 295 and 50 K, respectively). For the tetranuclear [[Cu(hfac)2]4(LEt)2], two structural transitions were recorded (at ≈154 K and ≈118 K), which led to a considerable change in the spatial position of the Et substituent in the nitronyl nitroxyl fragment. The low-temperature process was accompanied by a spin transition recorded as a hysteresis loop on the χT(T) curve during the repeated cooling–heating cycles (T½↑ = 122 K, T½↓ = 115 K). This transition is unusual because it causes spin coupling in half of all of the {>N–•O–Cu2+} terminal exchange clusters, leading to spin compensation for only two paramagnetic centers of the six centers in the molecule.

AB - Methods for the synthesis of binuclear [Cu(hfac)2LEt]2and tetranuclear [[Cu(hfac)2]4(LEt)2] heterospin compounds based on copper hexafluoroacetylacetonate [Cu(hfac)2] and 2-(4-ethylpyridin-3-yl)-4,5-bis(spirocyclopentyl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (LEt), were developed. The crystals of the complexes are elastic and do not crash during repeated cooling–heating cycles. It was found that a singlet–triplet conversion occurred in all of the {Cu(II)–O•–N<} exchange clusters in the molecules of the binuclear [Cu(hfac)2LEt]2which led to spin coupling with cooling. The transition occurred in a wide temperature range with a maximum gradient ΔχT at ≈180 K. The structural transformation of the crystals takes place at T < 200 K and is accompanied by the lowering of symmetry from monoclinic to triclinic, twinning, and a considerable shortening of the Cu–ONO distance (2.19 and 1.97 Å at 295 and 50 K, respectively). For the tetranuclear [[Cu(hfac)2]4(LEt)2], two structural transitions were recorded (at ≈154 K and ≈118 K), which led to a considerable change in the spatial position of the Et substituent in the nitronyl nitroxyl fragment. The low-temperature process was accompanied by a spin transition recorded as a hysteresis loop on the χT(T) curve during the repeated cooling–heating cycles (T½↑ = 122 K, T½↓ = 115 K). This transition is unusual because it causes spin coupling in half of all of the {>N–•O–Cu2+} terminal exchange clusters, leading to spin compensation for only two paramagnetic centers of the six centers in the molecule.

KW - Cu(II) complexes

KW - Magnetostructural correlations

KW - Nitroxides

KW - Phase transitions

KW - Spin crossover

KW - DESIGN

KW - LN

KW - ANOMALIES

KW - CU-II COMPLEXES

KW - COPPER(II)

KW - phase transitions

KW - CRYSTAL

KW - spin crossover

KW - magnetostructural correlations

KW - nitroxides

KW - CHAIN

KW - LIGANDS

KW - MAGNETIC-PROPERTIES

UR - http://www.scopus.com/inward/record.url?scp=85068436381&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/7edbd0d2-8768-30f4-a3fa-2b839436dcb6/

U2 - 10.3390/cryst9060285

DO - 10.3390/cryst9060285

M3 - Article

AN - SCOPUS:85068436381

VL - 9

JO - Crystals

JF - Crystals

SN - 2073-4352

IS - 6

M1 - 285

ER -