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Slow magnetic relaxation in a complex of photochromic spiropyran in a merocyanine form and cobalt() hexafluoroacetylacetonate
The interaction between photochromic 8-methoxy-1′,3′,3′-trimethyl-6-nitro-spiro[chromene-2,2′-indole] (MNSP) and cobalt( ii ) hexafluoroacetylacetonate yields a deep red-violet solution due to the coordination-induced transition of MNSP from a colorless closed state to a colored open merocyanine (MC...
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| Published in: | Dalton transactions : an international journal of inorganic chemistry 2024-02, Vol.53 (7), p.3159-3166 |
|---|---|
| Main Authors: | , , , , , , |
| Format: | Article |
| Language: | English |
| Subjects: | |
| Citations: | Items that this one cites |
| Online Access: | Get full text |
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| Summary: | The interaction between photochromic 8-methoxy-1′,3′,3′-trimethyl-6-nitro-spiro[chromene-2,2′-indole] (MNSP) and cobalt(
ii
) hexafluoroacetylacetonate yields a deep red-violet solution due to the coordination-induced transition of MNSP from a colorless closed state to a colored open merocyanine (MC) form. The resulting complex {Co
II
(hfac)
2
·MNSP} (
1
) is obtained as crystals, and its structure at 250 K shows the coordination of two oxygen atoms from MNSP with Co
II
, forming a distorted octahedral surrounding around Co
II
. The unit cell of
1
contracts below 170 K by 5.5%, which is accompanied by shortening O-Co bonds and altering O-Co-O angles in the structure solved at 150 K. The
χ
M
T
value of 3.06 emu K mol
−1
at 300 K indicates the formation of high-spin Co
II
(
S
= 3/2) with a large orbital contribution characteristic of the octahedral surrounding. The contraction of the unit cell of
1
below 170 K provides a reversible 2.2% change of
χ
M
T
in the 170-160 K range during heating and cooling regimes without hysteresis. The electron paramagnetic resonance signal of
1
was simulated with
g
-values of
g
x
= 2.342,
g
y
= 2.364, and
g
z
= 2.084, and an isotropic
g
-factor of 2.267. The temperature-dependent
χ
M
T
and field-dependent magnetization of
1
allow us to determine a positive zero-field splitting parameter of +20.1 cm
−1
. A study of the dynamic properties of
1
shows slow magnetic relaxation for Co
II
in a static field of 1000 Oe. Magnetic hysteresis loops were observed for
1
at 0.5 and 2 K; these loops are closed in the zero field region but opened at fields higher than ±100 and 700 Oe, respectively. The collapse of the loop is observed at 5 K. Excitation of the solution of
1
with green light decreases partially the intensity of the bands of the complex, whereas subsequent exposure of this solution to UV light partially restores these intensities.
A merocyanine isomer of photochromic 8-methoxy-1′,3′,3′-trimethyl-6-nitro-spiro[chromene-2,2′-indole] spiropyran forms a complex with cobalt(
ii
) hexafluoroacetylacetonate. Co
II
has a high-spin state in a distorted octahedral environment. SQUID and shows slow magnetic relaxation. |
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| ISSN: | 1477-9226 1477-9234 |
| DOI: | 10.1039/d3dt04253g |