Download - The „ metal-radical approach “
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The „metal-radical approach“
toward magnetic materials
N+
N
O
O
O
NMe 2
workshop synthetic strategies towards ....Kaiserslautern, 23.-25.10.2005
Eva Rentschler Universität Mainz
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The strategy is simple:
- Strong direct metal-ligand magnetic exchange interactions are achieved from the coordination of stable free radicals to paramagnetic transition-metal ions,
- and if these interactions are extended in one, two, or three spatial directions, cooperative magnetic behavior is obtainable in these molecule-based systems.
Lemaire, Pure Appl. Chem., Vol. 76, No. 2, pp. 277–293, 2004.
“Toward Molecular Magnets: The metal-radical approach“
Caneschi, D. Gatteschi, R. Sessoli, P. Rey, Acc. Chem. Res. 22, 392 (1989).
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- Since (and prior to) 1989, literally hundreds of metal-radical complexes have been reported, including a number of magnetically ordered materials.
- A wealth of knowledge about the structure and magnetic properties of coordination complexes containing stable radical ligands has been unearthed, and as a result, the metal-radical approach is recognized as one of the more fruitful efforts toward molecular magnetic materials.
Lemaire, Pure Appl. Chem., Vol. 76, No. 2, pp. 277–293, 2004.
“Toward Molecular Magnets: The metal-radical approach“
Caneschi, D. Gatteschi, R. Sessoli, P. Rey, Acc. Chem. Res. 22, 392 (1989).
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The families of radicals to be discussed
are limited to stable, isolable free-radical species
i.e., radicals that can be prepared and stored under ambient conditions.
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O
R R
R
N
O
R R
N NOO
R
S
SN
N
R
S
N
SR
R
N
N N
NRR
R'
R
N
N N
NRR
R'
O
N
NO
O
1901 Gomberg: triphenylmethyl radical
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O
R R
R
N
O
R R
N NOO
R
S
SN
N
R
S
N
SR
R
N
N N
NRR
R'
R
N
N N
NRR
R'
O
N
NO
O
1901 Gomberg: triphenylmethyl radical
COOH
Cl
Cl
ClClCl
HOOC
ClCl
Cl
ClCl
Cl
COOH
Cl
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O
R R
R
N
O
R R
N NOO
R
S
SN
N
R
S
N
SR
R
N
N N
NRR
R'
R
N
N N
NRR
R'
O
N
NO
O
phenalenyl radical
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O
R R
R
N
O
R R
N NOO
R
S
SN
N
R
S
N
SR
R
N
N N
NRR
R'
R
N
N N
NRR
R'
O
N
NO
O
phenalenyl radical
N
2-azaphenalenyl radical 2,5-di- and 2,5,8-triaza derivatives
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O
R R
R
N
O
R R
N NOO
R
S
SN
N
R
S
N
SR
R
N
N N
NRR
R'
R
N
N N
NRR
R'
O
N
NO
O
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O
R R
R
N
O
R R
N NOO
R
S
SN
N
R
S
N
SR
R
N
N N
NRR
R'
R
N
N N
NRR
R'
O
N
NO
ON
O
O
N
O
OH
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O
R R
R
N
O
R R
N NOO
R
S
SN
N
R
S
N
SR
R
N
N N
NRR
R'
R
N
N N
NRR
R'
O
N
NO
O
stable free radicals
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FeNC
NC CN
CN
FeNC
NC CN
CN
S
S
S
S
S
SS
S
TCNQ = 7,7,8,8-tetracyano-p-quinodimethane, TCNE = tetracyanoethene
[FeCp*2]+.[TCNQ] -.
[FeCp*2]+.[TCNE] -.
Bis(ethylenedithio)tetrathiafulvalene
Charge Transfer Salts
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O
R R
R
N
O
R R
N NOO
R
S
SN
N
R
S
N
SR
R
N
N N
NRR
R'
R
N
N N
NRR
R'
O
N
NO
O
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N
N
R
O
O
N
NR
O
O
N IT = 4 ,4,5 ,5-te tram ethyl-4,5-d ihydro-1 -im idazole-1-yloxyl-3-oxideH
J.H . O siecki, E .F. U llm an , , 1078-1079.J. A m . C hem . S oc. 901968
Nitronyl Nitroxide
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N – O 1.143 ÅN = O 1.316 Å
N1 – O1 1.285(1) ÅN4 – O4 1.287(1) Å
C5 – N 1.353(1) Å
C – N 1.438 Å C = N 1.260 Å
ES = ½
M = +1/2S
M = -1/2S
E = g H
1N 2N
H
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BSpinz
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purely organic: including metal ions:
NO
N O
d1d
r
R
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g = 2.0119(1), J = -143.1(1) cm-1, TIP = 2.27 * 10-4 emu mol-1.Cu(tfac)2NITMe
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Typical Values of the Magnetic Coupling Constant J for Metal-Nitroside Complexes
metal ion type of coupling J,a cm-1
copper(II)b AF 500copper(II)c F -10 to 70nickel(II) AF 500cobalt(II) AF 300manganese(II) AF 150-300
a Positive J means antiferromagnetic coupling. The energy separation between singlet and triplet is J. b The nitroxide is an equatorial site. c The nitroxide in an axial site.
Note: H = J S1.S2
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rel. weak interaction between the magnetic orbitalsthe metal-radical overlap is small, energyseparation between the two orbitals is largemolecular orbitals 1 and 2 mainly localized onmetal and on the radical fragment,respectively.Since (2-2)1/2 S
JAF (2-2)1/2S
JAF is determined by the variation of the squaredoverlap between the magnetic orbitals.
J = 2k + 4S
J 2
J S2
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For = 0°, Cu-O-N angle = 180°, * and dx2-y2 orbitals , irrespective of and . afm-contribution = 0, a moderate ferromagnetic coupling can be developed.
( the shorter the copper-oxygen distance, the larger the coupling.)
0 and angles become important. When = 0, an increase in from 0 to 90°, causes an increase of the overlap. The effect is much more pronounced at = 90° than at smaller angles.
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For = 0°, Cu-O-N angle = 180°, * and dx2-y2 orbitals , irrespective of and . afm-contribution = 0, a moderate ferromagnetic coupling can be developed.
( the shorter the copper-oxygen distance, the larger the coupling.)
0 and angles become important. When = 0, an increase in from 0 to 90°, causes an increase of the overlap. The effect is much more pronounced at = 90° than at smaller angles.
Structural and Magnetic Parameters for Diamagnetic Equatorially Coordinated Copper(I1)-Nitroxide Complexescompd R (a) Square-Planar or Square-Pyramidal ComplexesCu(hfac)2NITPh 1.955 88.4 59.0 56.5 Cu(hfac)2TEMPO 1.920 84.7 56.2 63.7CuCl2(NITPh)2 1.980 64.1 56.3 67.5(b) Trigonal-Pyramidal ComplexesCu(hfac)2NITPh 1.948 80.2 59.8 41.9Cu(tcact)2TEMPO 1.942 81.5 56.5 7.0Cu(tcact)2TEMPO 1.950 85.8 56.2 1.9Cu(tcact)2PROXYL 1.970 79.4 47.4 75.8 Cu(tcact)2PROXYL 1.961 85.2 54.0 11.7
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Geometrical, Magnetic, and Molecular Orbital Parameters for Mn(hfac)2(radical)2 Complexes
r J S Trans Adducts
M(hfac)2(TEMPO) 2.127(4) 38.6 12.8 25.5 158 4.8 Mn(hfac)2(PROXYL) 2.150 (4) 79.6 34.7 14.0 210 19.7Mn(hfac)2(NITPh)2 2.144 (5) 77.2 49.5 29.8 180 9.8
2.154 (5) 81.4 47.1 27.9 Cis AdductMn(hfac)2 (NITMe)2 2.122 (5) 86.6 52.0 80.7 187 13.2
2.127 (5) 83.0 48.9 7.2
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bridging Nitronyl Nitroxide radicals
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N N
R
OOM
N N
R
OOM
N N
R
OOM
M
M
M
MN N
R
OOM
M
non-bridging: -1,3 bridging:
-1,1 and -3,3 bridging:-1,1 bridging:
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N N
R
OOM
N N
R
OOM
N N
R
OOM
M
M
M
MN N
R
OOM
M
non-bridging: -1,3 bridging:
-1,1 and -3,3 bridging:-1,1 bridging:
180 40
3 -
Cambridge Structural Database
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non-bridging: 180
N N
R
OOM
N N
R
OO MN N
R
OO
O O
OO
CF3F3C
F3C CF3
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-1,3 bridging: 40
N N
R
OO MN N
R
OO
O O
OO
CF3F3C
F3C CF3
M
O O
OO
CF3F3C
F3C CF3
N N
R
OOMM
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[Cu(hfac)2,(NITEt) vs. T follows the Curie law with C = 0.4639S = 1/2 with g = 2.225.
nitroxide occupies an - equatorial position in the coordination environment of copper(II) strongly coupled - axial position a weak-to-moderate coupling.
Cu2------R------Cu1------R------Cu2J1 J2 J2 J1
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„head to tail“:
Spin transitions in non-classical systems
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„Change in the Jahn-Teller axis of the Cu bipyramids“:
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O
C F 3 CF 3
O
O
C F 3
O
C F 3 C F 3
O
F 3C
O
N+
NO ON+
NO O N+
NO O
O
CF 3
O
C F 3
RR R
N+
N
X
O O
N+
N
X
O O
M
N+
N
X
O O
M
M M N+
N
X
O O
MN+
N
X
O O
1 D
2D / 3D ?
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charge distribution
-0.57
-0.72 -0.68
-0.57
Ladung
-0.70 -0.70 -0.59 -0.58
-0.55 -0.55
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Cu2(NIT-PhCOO)4(DMSO)2
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C u
O
N O
N
N
O
O
C u
O
N O
N
N
O
O
N
N+
O
-
O
N
N+
O
-
O
Pyridin
0 100 200 3000.4
0.8
1.2
1.6
2.0
∙T /
emu
K m
ol-1
T / K
0 100 200 3001.0
1.2
1.4
M∙T
/ em
u K
mol
-1
T / K
H J S S = -2 Cu1 Cu2
= -0.85 KQ
gCu = 2.20JCu1-Cu2 = -150.0 cm-1
= + 0.50 K = - 0.85 K
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N+
N
X
O O
N+
N
X
O O
M
N+
N
X
O O
M
M M N+
N
X
O O
MN+
N
X
O O
hohe Spindichte2D / 3D Netzwerk
X = NX = C-CHO, C-COOH, C-P(O)Ph2
O-
N
N+
O
O-
O
N
N
O
O-
O
N
N+
O-
O-
XN
N+
O
O-
2D / 3D network high spin density
NIT phenolates as ligands
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4-hydroxo phenolates and their metal complexes
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microcrystalline film poly-vinylchloride matrix
magnetic dilution of a nitronyl nitroxide
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• syntheses of molecular building blocks
• electronic structures
• magnetic dilution
• sign of the magnetic interaction
construction of polynuclear compounds
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Ni2+: d8
dx2-y
2, dz2
dxy, dxz , dyz
dxy
dxz , dyz
dz2
dx2-y
2octahedral coord. with axial CH3OHNi ( S = 1 ) + 2 NIT (S=1/2)
Planar quadratic coord.Ni ( S = 0 ) + (S=1)
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octahedral coord. with axial CH3OHNi ( S = 1 ) + 2 NIT (S=1/2)
Planar quadratic coord.Ni ( S = 0 ) + (S=1)
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next generation of nitronyl nitroxide ligands
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N NOO
.
N
N NOO
N N
N NO.
N
N NOO
N N
R
. .
Multifunctional Radicals
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Chelating Radicals
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1 +[Cu(CH3CN)4]PF6
[Cu(1)2]+ (Td-symm.)
NIT-NIT: J = +55 cm–1.
H. Oshio et a.l. Inorg. Chem. 36, 3014 (1997).
MIICl2(2)2 (M = Mn, Co, Ni, Zn)
S. Kaizaki. J. Chem. Soc., Dalton Trans. 1566 (2001).
JM-rad = +95 (Ni) and +14.9 cm–1 (Co)JMn-rad = –23.8 cm –1. Jrad-rad = –9 cm –1.
R = Me 1 H 2
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MII(ClO4)26H2O (MII = Ni, Mn, and Zn)
[M(NITim)3](ClO4)2, [M(NITbzim)3](ClO4)2.
exhibiting strongly antiferromagnetic metal-radical interactions (-111 < J < -53 cm–1).
Metal-nitronyl nitroxide homoleptic complexes
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coordination polymers
[Mn(NITIm)(NITImH)]ClO4
Ziessel
[Mn2(NITIm)3]ClO4
Rey and Luneau
Ferromagnetic ordering temperatures
1.4 K [Mn2(NITIm)3]ClO4
40 K [Mn2(NITBzIm)3]ClO4
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Chelating Radicals
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R. Ziessel et al. Inorg. Chem., 37 (20), 5078 -5087, 1998
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R. Ziessel et al. Inorg. Chem., 37 (20), 5078 -5087, 1998
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R. Ziessel et al. Inorg. Chem., 37 (20), 5078 -5087, 1998
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For the Ln(III) with 4f1 to 4f5 electronic config. the {Ln-organic radical} interaction
Conversely, for the configurations 4f7 to 4f10
Rare earth coordination compounds
4f7-ion CuII (S=1/2): NIT (S=1/2):
J small usually not direct available from experimentdue to L.S. coupling
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Rare earth coordination compounds
For the Ln(III) with 4f1 to 4f5 electronic config. the {Ln-organic radical} interaction
Conversely, for the configurations 4f7 to 4f10
But:
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K. E. Vostrikova, D. Luneau, W. Wernsdorfer, P. Rey, and M. Verdaguer, J. Am. Chem. Soc., 122, 718-719 (2000)
A S = 7 Ground Spin-State Cluster Built from Three Shells of Different Spin Carriers Ferromagnetically Coupled, Transition-Metal Ions and Nitroxide Free Radicals
[Fe2(CN)12Ni3(IM-2Py)6]:
2 [Fe(CN) 6] + 3 CN-Ni(IM-2Py)2-NC
Ni(ClO4)2.4H2O + IM-2Py [Fe2(CN)12Ni3(IM-2Py)6]
K3[Fe(CN)6]
H2OMeOH
2 (S = ½) + 3 (S = 2)
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K. E. Vostrikova, D. Luneau, W. Wernsdorfer, P. Rey, and M. Verdaguer, J. Am. Chem. Soc., 122, 718-719 (2000)
A S = 7 Ground Spin-State Cluster Built from Three Shells of Different Spin Carriers Ferromagnetically Coupled, Transition-Metal Ions and Nitroxide Free Radicals
1.2 K
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R. J. Glauber. J. Math. Phys. 4, 294 (1963). 1D Ising ferri- or ferromagnetic materials
could exhibit slow relaxation of their magnetization.
molecular magnetic nanowires
slow relaxation in chains
favoured by spin correlation along the chains
reorientation of the magnetization becomes more difficult
The height of the barrier to magnetization reversal should scale
with the nearest-neighbor exchange coupling.
R. Sessoli, et al. Angew. Chem. Int. Ed. 40, 1760 (2001):
zig-zag / helical
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molecular magnetic nanowires
slow relaxation in chains
Co(hfac)2(NITPhOMe)
1 D- helix (trigonal crystallographic symmetry).
is highly anisotropic (gCo = 7.4) below 50 K
and slow magnetization relaxation
as well as hysteresis effects are observed.
magnetization barrier 154(2) K, (J = 220 K).
R. Sessoli, et al. Chem. Eur. J. 8, 286 (2002).
“molecular magnetic nanowires” for information storage on the molecular level
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Incorporation of an asymmetric center
into the structure of the radical ligand.
Luneau and Veciana
Inoue
Solutions exhibit optical activity, and thelow-temperature solid-state magnetic properties suggest a field-induced transitionto a ferromagnetic state (metamagnetic behavior) below 5.4 K.
chirality and magnetism in helical 1 D metal-nitroxide complexes
Quest for new magneto-chiral materials
that could exhibit novel properties that result
from the interaction of chirality and magnetism
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M. Minguet, D. Luneau, E. Lhotel, V. Villar, C. Paulsen, D. B. Amabilino, J. Veciana,Angew. Chem., Int. Ed. 41, 586 2002
An Enantiopure Molecular Ferromagnet
chiral ligand chiral molecule
Chirality induced by – atomic stereogenic centersor atropoisomeric conformations
chiral spacegroupP212121
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M. Minguet, D. Luneau, E. Lhotel, V. Villar, C. Paulsen, D. B. Amabilino, J. Veciana,Angew. Chem., Int. Ed. 41, 586 2002
An Enantiopure Molecular Ferromagnet
unusual dynamic behavior
at Tc domains with long-laminar form along easy axis
near Tc domain wall are soft and easily displaced
at higher Temp. domains become more rigid
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Verdazyl radicals
structure SOMO
Lemaire, Hicks
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The first transition-metal complex of a
Verdazyl radical 1997 by Fox et al.
J intra –271 cm-1, X = IJ intra –190 cm-1, X = ClJ intra –200 cm-1, X = Br
J inter negligable
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Robin Hicks, Martin T. Lemaire; Pure Appl. Chem. 76, 277 (2004)
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Lemaire, Hicks
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Nickel-verdazyl exchange strongly ferromagnetic ()J Ni-vd ≥ +240 cm–1
Manganes-verdazyl exchange antferromagnetic ()J Mn-vd = -45 cm –1
Robin Hicks, Martin T. Lemaire; Pure Appl. Chem. 76, 277 (2004)
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A series of 4,5-diazafluorene derivatives of Koelsch’s free radical
Reaction with CuCl2 has reportedly generated analytically pure metal-radical complexes, but which have not yet been structurally or magnetically characterized.
Plater et al. J.Chem.Soc., Perkin Trans. 1, 971 (2000)
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COOH
Cl
Cl
ClClCl
HOOC
ClCl
Cl
ClCl
Cl
COOH
Cl
Daniel Maspoch, thesis, Valencia, 2004
Triphenylmethyl-radical
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S=1/2 S=1/2S=0
Zn2+
S=1/2 S=1/2S=1/2
Cu2+
S=1/2 S=1/2S=0
Ni2+
Chemical Communications, 2002, (24), 2958 - 2959
D. Maspoch, D. Ruiz-Molina, K. Wurst, C. Rovira, J. Veciana
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D. Maspoch, J. Gómez-Segura, N. Domingo, . Ruiz-Molina, K. Wurst, C. Rovira, J. Tejada, J. Veciana ; Inorg. Chem. 44, 6936 (2005)
An Unusually Stable Trinuclear Manganese(II) Complex Bearing Bulk Carboxylic Radical Ligands:
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FeNC
NC CN
CN
FeNC
NC CN
CN
S
S
S
S
S
SS
S
TCNQ = 7,7,8,8-tetracyano-p-quinodimethane, TCNE = tetracyanoethene
[FeCp*2]+.[TCNQ] -.
[FeCp*2]+.[TCNE] -.
Bis(ethylenedithio)tetrathiafulvalene
Charge Transfer Salts
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A.H. Reis, Jr., L.D. Preston, J.M. Williams, S.W. Peterson, G.A. Candela, L.J. Swartzendruber,J.S. Miller, J. Am. Chem. Soc. 101 (1979) 2756.
Tc 4.8 K [FeIII(C5Me5)2]2[TCNE] magnet: with(i) spins residing in a p-orbital(ii) exhibiting magnetic hysteresis(iii) lacks an extended one-, two,- or three-dimensional network structure;(iv) is soluble in conventional organic solvents(v) does not require metallurgical processing.
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Variation of Tc with increasing spin number per metalin [MIII(C5Me5)2]+[TCNE]-.
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1 D- ferrimagnet
large remanent magnetizationand coercice fields27 500 Oe at 2K !!!
Tc 16 K
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V(TCNE)x · y(CH2Cl2) (x2; y 1/2) is the first example of an organic-basedmaterial with a critical temperature exceeding room temperature.
J.M. Manriquez, G.T. Yee, R.S. McLean, A.J. Epstein, J.S. Miller, Science 252 (1991) 1415.
J. Zhang, P. Zhou, W.B. Brinckerhoff, A.J. Epstein, C. Vazquez, R.S. McLean, J.S. Miller, Am.Chem. Soc. Symp. Ser. 644 (1996) 311.
V(TCNE)x · y(CH2Cl2)
by reaction of V0(CO)6 with TCNE
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spin diverse ligands,
containing two or more different kinds of spin carriers per molecule,
Nitronyl nitroxide/semiquinone hybrid biradicals very strong intraligand ferromagnetic exchange couplingJNN = > +300 and +100 cm–1
The semiquinone is stabilized by coordination to ZnTpCum,Me, where TpCum,Me = hydro-tris(3-cumenyl-5-methylpyrazolyl)-borate]:
The coupling is so strong, in fact, that these systems may be treated as singleS = 1 units.
Shultz et al.J. Am. Chem. Soc. 123, 3133 (2001)J. Am. Chem. Soc. 125, 1607 (2003)
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Y. Takano, et. al. J. Am. Chem. Soc., 124, 450 (2002)
M(II)(hfac)2(di-(4-pyridyl)phenylcarbene)
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Y. Takano, et. al. J. Am. Chem. Soc., 124, 450 (2002)
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Y. Takano, et. al. J. Am. Chem. Soc., 124, 450 (2002)
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Mn(II):
d-pd-pd-p
Cu(II):
d-pd-p
exchange pathways:
Y. Takano, et. al. J. Am. Chem. Soc., 124, 450 (2002)
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Di- and triradicals
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Di- and triradicals
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Di-radicals and Pressure effects