A Chiral Bipyrimidine-Bridged Dy2 SMM: A Comparative Experimental and Theoretical Study of the Correlation Between the Distortion of the DyO6N2 Coordination Sphere and the Anisotropy Barrier
Chiral bipyrimidine-bridged dinuclear Ln III complexes of general formula [(μ-bipym){((+)-tfacam) 3 Ln} 2 ] and [(μ-bipym){((-)-tfacam) 3 Ln} 2 ], have been prepared from the assembly of Ln(AcO) 3 ·nH 2 O (Ln III = Dy, Gd), (+)/(−)-3-(trifluoroacetyl)camphor enantiopure ligands ((+)/(-)-Htfacam) and...
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Published in | Frontiers in chemistry Vol. 6; p. 537 |
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Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Frontiers Media S.A
08.11.2018
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Subjects | |
Online Access | Get full text |
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Summary: | Chiral bipyrimidine-bridged dinuclear Ln
III
complexes of general formula [(μ-bipym){((+)-tfacam)
3
Ln}
2
] and [(μ-bipym){((-)-tfacam)
3
Ln}
2
], have been prepared from the assembly of Ln(AcO)
3
·nH
2
O (Ln
III
= Dy, Gd), (+)/(−)-3-(trifluoroacetyl)camphor enantiopure ligands ((+)/(-)-Htfacam) and bipyrimidine (bipym). The structure and chirality of these complexes have been supported by single-crystal X-Ray diffraction and circular dichroism. The study of the magnetic properties of the Gd
III
complexes revealed a very weak antiferromagnetic interaction between the Gd
III
ions through the bipyrimidine bridging ligand.
Ab initio
CASSCF calculations indicated that the ground Kramers doublet (KD) of both Dy
III
centers is almost purely axial with the anisotropy axis located close to the two tfacam
−
ligands at opposite sides of each Dy
III
atom, which create an axial crystal field. In keeping with this,
ac
dynamic measurements indicated slow relaxation of the magnetization at zero field with
U
eff
= 55.1 K, a pre-exponential factor of τ
o
= 2.17·10
−6
s and τ
QTM
= 8 μs. When an optimal dc field of 0.1 T is applied, QTM is quenched and
U
eff
increases to 75.9 K with τ
o
= 6.16 × 10
−7
s. The DyN
2
O
8
coordination spheres and SMM properties of [(μ-bipym){((+)-tfacam)
3
Ln}
2
] and their achiral [(Dy(β-diketonate)
3
)
2
(μ-bpym)]analogous have been compared and a magneto-structural correlation has been established, which has been supported by theoretical calculations. In contrast to the Gd
III
compounds, the magnetic exchange interaction between the Dy
III
ions has been calculated to be very weak and, generally, ferromagnetic in nature. Relaxation mechanisms for [(μ-bipym){((+)-tfacam)
3
Ln}
2
] and previously reported analogous have been proposed from
ab initio
calculations. As the magnetic exchange interaction found to be very weak, the observed magnetization blockade in these systems are primarily dictated by the single ion anisotropy of Dy
III
ions. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Reviewed by: Fangfang Pan, Central China Normal University, China; Julve Miguel, Universitat de València, Spain This article was submitted to Inorganic Chemistry, a section of the journal Frontiers in Chemistry Edited by: Hitoshi Ishida, Kitasato University, Japan |
ISSN: | 2296-2646 2296-2646 |
DOI: | 10.3389/fchem.2018.00537 |