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Exchange couplings and quantum phases in two dissimilar arrays of similar copper dinuclear units
To investigate the magnetic properties and the spin entanglement of dinuclear arrays, we prepared compounds [{Cu( p AB)(phen)H 2 O} 2 ·NO 3 · p ABH·2H 2 O], 1 , and [Cu 2 ( p AB) 2 (phen) 2 pz] n , 2 ( p ABH = p -aminobenzoic acid, phen = 1,10-phenanthroline and pz = pyrazine). The structure of 1 is...
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| Published in: | Dalton transactions : an international journal of inorganic chemistry 2020-04, Vol.49 (16), p.5228-524 |
|---|---|
| Main Authors: | , , , , , |
| Format: | Article |
| Language: | English |
| Subjects: | |
| Citations: | Items that this one cites Items that cite this one |
| Online Access: | Get full text |
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| Summary: | To investigate the magnetic properties and the spin entanglement of dinuclear arrays, we prepared compounds [{Cu(
p
AB)(phen)H
2
O}
2
·NO
3
·
p
ABH·2H
2
O],
1
, and [Cu
2
(
p
AB)
2
(phen)
2
pz]
n
,
2
(
p
ABH =
p
-aminobenzoic acid, phen = 1,10-phenanthroline and pz = pyrazine). The structure of
1
is known and we report here that of
2
. They contain similar dinuclear units of Cu
II
ions with 1/2-spins
S
1
and
S
2
bridged by pairs of
p
AB molecules, with similar intradinuclear exchange
and fine interactions
, but different 3D crystal arrays with weak interdinuclear exchange
J
′, stronger in
2
than in
1
. To investigate the magnetic properties and the spin entanglement produced by
J
′, we collected the powder spectra of
1
and
2
at 9.4 GHz and
T
between 5 and 298 K, and at 34.4 GHz and
T
= 298 K and single-crystal spectra at room
T
and 34.4 GHz as a function of magnetic field (
B
0
) orientation in three crystal planes, calculating intradinuclear magnetic parameters
J
(
1
)
0
= (−75 ± 1) cm
−1
,
J
(
2
)
0
= (−78 ± 2) cm
−1
, |
D
(
1
)
| = (0.142 ± 0.006) cm
−1
, |
D
(
2
)
| = (0.141 ± 0.006) cm
−1
and
E
(
1
)
∼
E
(
2
)
∼ 0. Single crystal data indicate a quantum entangled phase in
2
around the crossing between two fine structure EPR absorption peaks within the spin triplet. This phase also shows up in powder samples of
2
as a U-peak collecting the signals of the entangled microcrystals, a feature that allows estimating |
J
′|. Transitions between the two quantum phases are observed in single crystals of
2
changing the orientation of
B
0
. We estimate interdinuclear exchange couplings |
J
′
(
1
)
| < 0.003 cm
−1
and |
J
′
(
2
)
| = (0.013 ± 0.005) cm
−1
, in
1
and
2
, respectively. Our analysis indicates that the standard approximation of a spin Hamiltonian with
S
= 1 for the dinuclear spectra is valid only when the interdinuclear coupling is large enough, as for compound
2
(|
J
′
(
2
)
/
J
(
2
)
0
| ∼ 1.7 × 10
−4
). When
J
′ is negligible as in
1
, the real spin Hamiltonian with two spins 1/2 has to be used. Broken-symmetry DFT predicts correctly the nature and magnitude of the antiferromagnetic exchange coupling in
1
and
2
and ferromagnetic interdinuclear coupling for compound
2
.
X-ray structure and EPR spectra of two dinuclear copper compounds allow us to study spin entanglement and quantum phase transitions. Their different 3D arrays and interdinuclear exchange paths produce important effects. |
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| ISSN: | 1477-9226 1477-9234 |
| DOI: | 10.1039/d0dt00567c |