Do the chemists Do the chemists know howknow howto align the spins to align the spins of electronsof electronsin molecules,in molecules,parallel or antiparallel ?parallel or antiparallel ?
Understanding Understanding ……
why the spins of two neighbouring electrons why the spins of two neighbouring electrons (S = 1/2) become :(S = 1/2) become :
to get magnetic compounds to get magnetic compounds ……
antiparallel ?antiparallel ?
S=OS=O
or parallel ?or parallel ?
S=1S=1
Sa Sb1 2
A B
H = - J S1S2^ ^ ^
Interaction Models between Localised Electrons
Scalar Coupling : describes, does not explain
ET
ES
EJ
0
J<0
Interactionantiferro
J>0
ESE
0
ET J
Interactionferro
Energy levels
J = 2 k + 4ßS
if S = 0Orthogonality
if S≠0;|ßS|>>kOverlap
>0 <0
H2Aufbau
ES
ET JAntiferro
O2Hund
ESET
JFerro
J. Miró« Overlap » ?
Catalogue raisonné, N°1317
J. Miró, Pomme de terre, detail
H = - J S1S2^ ^ ^
An old game …
AF
FPalace Museum, TaiPei, Neolithic period, Yang-Shao Culture
Michelangelo, Sixtin Chapel, Rome
Exchange interactions can be very weak …
order of magnitude : cm-1 or Kelvins …
≈
order of magnitude : >> 150 kJ mol-1 …
« Chemical » bondsRobust !
Exchange interactions
Energy
≈ 5 ÅNegligible Interaction !
How to create the interaction … ?
Problem :
Cu(II) Cu(II)
Orbital Interaction …≈ 5 Å
Cu(II) Cu(II)
The ligand !Solution :
Ligand
A B
Examples with the ligand
• Cyanide
Ligand
Monet Claude, Charing Cross Bridge
Non linear and linear bridges
Monet Claude, Waterloo Bridge
Cyanide Ligand
Friendly ligand : small, dissymetric, forms stable complexesWarning : dangerous, in acid medium gives HCN, lethal
C≡N-
Dinuclear µ-cyano homometallic complexes
“Models” Compounds Cu(II)-CN-Cu(II)
Compounds exp
[Cu2(tren)2CN]3+
[Cu2(tmpa)2CN]3+
-160
-100
J/cm-1
Rodríguez-Fortea et al. Inorg. Chem. 2001, 40, 5868
Overlap : antiferromatic coupling …
Cr(III) Ni(II)
Dinuclear µ-cyano heterometallic complexes
NB : A dissymetric ligand helps to get stable heterometallic complexes …« Birds of the same feathers flock together » …
Polynuclear complex, synthetic strategy
Hexacyanometalate “Heart”Lewis Base
Mononuclear ComplexLewis Acid
Polynuclear Complex
3-
+ 6
2+ 9+
Hexacyanochromate complex
x
z t2g² oct
t2g
eg
Cr(III)
[CrIII(CN)6]3-
Electrons in
M-C≡N-M'
M C N
M'C N
S = 0, JF = 2k
π σ
Example :
Cr(III) (t2g)3 JF
Ni(II),(eg)2
Polynuclear complex, ferromagnetic strategy
Cr(III)Ni(II)6S = 6x1+3/2 =S = 15/2
Orthogonality :Ferromagnetism !
M-C≡N-M’
Cr(III)Mn(II)6S = 6x5/2 + 3/2 =
S = 27/2
Overlap = antiferromagnetism
Cr(III) (t2g)3
JAF
Mn(II) (t2g)3
Example
Polynuclear complex, ferrimagnetic strategy
π
Sab ° 0, JAF ∝ Sab√(²2-δ2)
M C N
M'C N
² δ
π
Ferromagnetic …
ErosPaul KLEE
Nocturnal separation, 1922
Ferrimagnetic …
C rC u6S = 9/2
C rNi6S = 15/2
C rMn6S = 27/2
Hexagonal R -3a = b = 15,27 Å; c = 78,56 Åa = b= 90°; g = 120°; V = 4831 Å3
Hexagonal R -3a = b = 15,27 Å; c = 41,54 Åa = b= 90°; g = 120°; V = 8392 Å3
Hexagonal R -3a = b = 23,32 Å; c = 40,51 Åa = b= 90°; g = 120°; V = 19020 Å3
… High Spin Heptanuclear Complexes
Marvaud et al., Chemistry, 2003, 9, 1677 and 1692
Chemists have transformed good old Prussian blue, a blue pigment that Michael Faraday precipitated
in his time at Royal Institution, into a room temperature magnet
also useful in display devices.
Alfred Bader, « End of Mistery », Chemistry in Britain, 37, 7, July 2001, 99Greeting Card of RSC, Benevolent Fund, Thomas Graham House, Science Park, Milton Road, Registered Charity N° 207890.This painting does not depict neither W.T. Brande nor Michael Faraday making Prussian blue, Thomas Philips RA, ca 1816 (from Alfred Bader, Hon FRSC)
1704 …
Diesbach, draper in Berlin …
… prepares a blue pigment « Prussian blue »
… said to be the first coordination compound
2004 : 300th anniversary !
Anna Atkins, Cyanotypein Hart-Davis Adam Chain Reactions,pioneers of british science and technologyNational Portrait GalleryLondon, 2000
Classical coordination chemistry …
Fe2+aq+ 6CN-
aq [Fe(CN)6]4-aq
Complexes as Ligands, or « bricks »+ Lewis Acid-Base Interaction
FeH2O
H2O OH2
OH2
OH2
OH2
Fe+
[4-] [3+]
3[Fe(CN)6]4-aq + 4Fe3+aq {Fe4[Fe(CN)6]3}0•15H2O
since : 1936, modified 1972 …
an evergreen in inorganic chemistry …
a simple face-centered cubic structure …
Stoichiometry[AII]4[BII(CN)6]3or A4B3[AII]4 [BII] 3 1
= vacancy
J.F. Keggin, F.D. Miles, Nature 1936, 137, 577
A. Ludi, H.U. Güdel, Struct. Bonding (Berlin) 1973, 14, 1
Coming back to Prussian Blue
TC ∝ z |J|
z : number of magnetic neighbours|J| : coupling constant between nearest neighbours
Néel, Annales de Physique, 1948
Coming back to Prussian Blue
TC ∝ z |J|
z : number of magnetic neighbours|J| : coupling constant between nearest neighbours
Néel, Annales de Physique, 1948
TC = 5.6 K
Towards Prussian blue analogues …
TC ∝ z |J|
TC >> 5.6 K
JFerro > 0
Orthogonality
Towards Prussian blue analogues …
TC ∝ z |J|
TC >> 5.6 K
JAntiferro < 0
Overlap …
TC / K
Z
200
Ti V Cr Mn Fe Co Ni Cu Zn
300
100
• •• [Cr(CN)6]3-
(t2g)3 d3
• ••• •
6 F
9 AFMnII
d5
• ••
9 AF
(t2g)3
VIId3
• ••• 3 F
9 AF
CrII d4
• ••• •
• • •
6 F
NiIId8
V4[Cr(CN)6]8/3.nH2ORoom Temperature TCOn a rational basis !
Gadet et al., J.Am. Chem. Soc. 1992Mallah et al. Science 1993Ferlay et al. Nature, 1995
TC / K
Z
200
Ti V Cr Mn Fe Co Ni Cu Zn
300
100
• •• [Cr(CN)6]3-
(t2g)3 d3
• ••• •
6 F
9 AFMnII
d5
• ••
9 AF
(t2g)3
VIId3
• ••• 3 F
9 AF
CrII d4
• ••• •
•• ••
• ••
•• •••
•• •• •
6 F 6 F
3 F
6 AF 3 AF (eg)1
CuII
CoIIFeIId6 d7d9
• ••• •
• • •
6 F
NiIId8
V4[Cr(CN)6]8/3.nH2ORoom Temperature TCOn a rational basis !
2[CrIII(CN)6]3-+3Vaq
2+ [V3[CrIII(CN6)]2]
0
A blue, transparent, low density magnet at room temperature
MagnetMolecular
Holder (1)(2)PermanentMagnet
Light, Sun …
(2)
Image
Len
Screen(3)
Oscillating Magnet : Experiment
A thermodynamical machine transformingLight
inMechanical
Energy
QuickTime™ et un décompresseurDV - PAL sont requis pour visualiser
cette image.
Permanent Magnet
Hot
CoupleSample ( MM)
Magnetic Switch…Or thermal probe …
Other device
Up to 2004 … magnetic analogues used as …
QuickTime™ et un décompresseurDV - PAL sont requis pour visualiser
cette image.
… devices and demonstrators
Chemists have managed to transform
isolated single molecules into magnets
molecule-based magnets ? Why ?
Low densityTransparentNanosized, identical moleculesOften biocompatible and biodegradableVery flexible chemistryMild chemistry : Room T, Room P, Solution Chemistry
Fragile AgingDiluted
Specific properties
To overcome
To improve
Top down
Nanosystems• Nice Chemistry• Single molecule magnets
• Applications (far …)• Recording• Quantum computing
Fragments Threads
Dots
• New Physics• Quantum / Classical• Quantum tunneling
Bottom up
Giant Molecular Clusters
0D, Molecules
3DMetalsOxydes
Synthesis
Properties
Theory
Idea
NewMaterials
NewFunctions
NewConcepts
… Single molecule magnets Giant Molecular Clusters
Mn4and many others
High Spin + Anisotropy∆E = DSz
2 Mn12Fe8
See GatteschiHendricksonChristouWinpenny …
=
What is named Single Molecule Magnet ?
High SpinAnisotropic
High Spin Paramagnetic Molecule
H
Single Molecule Magnet
Towards information storage at the molecular level ?
Below T < TBlocking
H
Single Molecule Magnet
Towards information storage at the molecular level ?
Below T < TBlocking
Single molecule magnetsz
yx
E
- Sz
Sz+Sz
0
DSz2
0-2-4 +2 +4
Anisotropy Barrier
Tunneling
ThermalActivation
DSz2 = 400K ? |D| = 1K
S = 20(D < 0)
K. Vostrikova, P. Rey et al., JACS 2000, 122, 718
2nd generation
NCM
NC CN
CN
C
CN
N
NCM
NC CN
CN
C
CN
N
NCM
NC CN
CN
C
CN
N
Spin = 2 = Ni(II)(Rad°)2
= Ni(II)(tetren)Spin = 1
Rad°
1rst generation
Complex
Decurtins, Angewandte, 2000Hashimoto, JACS, 2000
Marvaud, Chemistry, 2003, 9, 1677 y 1692
Rey, JACS 2000, 122, 718
Some examples …
S = 27/2
S = 39/2 (AF)
S = 14/2
CoNi5
CoNi3
CoCo3
CoCu3CrNi 5/2
CrNi2
CoCo2 CoNi2CoCu2
7/2
Marvaud et al., Chemistry, 2003, 9, 1677 and 1692 Ariane Scuiller, Caroline Decroix, Martine Cantuel, Fabien Tuyèras …
CrNi2CoCo2
CoCu6
CrNi
CoNi5CrNi3
CoNi2
CoNi3CrNi3
CoCo6
CoCu2
CoCo3CrCo3
CoCu3
5/2
7/2
9/2
27/2
Anisotropy
High spin
V. Marvaud
CrMn6
CoMn6
CrNi6
15/2
CrCu6
[Mn[Mn1212OO1212(CH(CH33COO)COO)1616(H(H22O)O)44].2CH].2CH33COOH.4HCOOH.4H2200
Mn(IV)
Mn(III)
Ion Oxyde
Carbone
S=10
or Mnor Mn1212
From D.Gatteschi and R. Sessoli
S=2
S=3/2
S =8x2 -4x3/2 =
Mn12 is a hard magnet
-3 -2 -1 0 1 2 3
-20
-10
0
10
20T=2.1K
MA
GN
ETI
ZATI
ON
(µB)
MAGNETIC FIELD (T)
Bistability : in zero field the magnetisation can be positive or negative depending of the story of the sampleCoercive Field
Remnant Magnetisation
From D.Gatteschi and R. Sessoli
Ground State Energy Levels
H = 0 M=±10
M=±9
M=±8
From D.Gatteschi and R. Sessoli
At low temperature, a magnetic field populates only the M = -S state
M=-S
M=S
Energy Levels in a Magnetic Field
H≠0
S
-S
Going back to equilibrium :Thermal activation :trivial
H=0∆E=DS2
M=-SM=S
τ = τ0 exp(∆E/kBT)
Axial symmetry
E(M) = DM2
From D.Gatteschi and R. Sessoli
H=0 M=S M=-S
Tunneling effect : new !Towards equilibrium :
From D.Gatteschi and R. Sessoli
M
H
Mn12 is a Hard Magnet
+ Steps in the magnetisation curve
Msaturation
Hcoercive
Mremnant
From D.Gatteschi and R. Sessoli
Resonnant Tunneling Effect for H = nD/gµB
H = nD/gµB
M=-S
M=S
From D.Gatteschi and R. Sessoli
Conditions to observe tunnelling effect
• Degenerated wave functions must superpose• A transversal field must couple the two wave
functions • Coupling splits the two levels : “tunnel splitting”• Tunnelling Effect Probability increases with
tunnel splitting”
From D.Gatteschi and R. Sessoli
M
HTunneling Effect
From D.Gatteschi and R. Sessoli
No resonnant Tunneling Effectwith a magnetic field parallel to z
H ≠ nD/gµB
M = -S
M = S
From D.Gatteschi and R. Sessoli
M
H No tunneling effectFrom D.Gatteschi and R. Sessoli
Anisotropic precursor
[Fe(III)(bipy)(CN)4]-
R. Lescouëzec, M. Julve, Valencia, Spain D. Gatteschi, W. WernsdorferAngewandte Chem. 2003, 142, 1483-6
Feasibility of « Molecular nanowires » (or SCM) ?
[{FeIII(bpy)(CN)4}2MII(H2O)] .CH3CN . 1/2H2O [M = Mn, Co, Cu]
[{FeIII(L)(CN)4}2CoII(H2O)4] .4H2O
[{FeIII(L)(CN)4}2MII(H2O)4].4H2O [L = 2,2’-bipy and 1, 10-phen), M = Mn, Co, Cu, Zn]
Trinuclear speciesDouble
zig-zag chainsBis double
zig-zag chains
0
0.2
0.4
0.6
0.8
1
0.01 0.1 1 10 100 1000M
/Ms
t (s)
1.5 K
1.6 K
1.7 K
1.8 K
1.9 K
2.8 K
2.7 K
2.6 K2.5 K 2.3 K
2.2 K
2.1 K
2.4 K
2.0 K
M vs. t plots along the b axis.
Magnetization as a function of time
Thermally activated relaxation of the magnetization
ac: Ea= 142 K, τ0 = 6.10-11 s
Slow relaxation of the magnetisation …
W. Wernsdorfer, Grenoble
The dream …
Surface
Magnetic Tip H
≈ 10 nm
High Spin"down"
High Spin"down"
Surface
Magnetic Tip H
≈ 10 nm
High Spin"down"
High Spin"down"
… information storage at the molecular level !
Surface
Magnetic Tip H
≈ 10 nm
HSM «up»High Spin"down"
The dream …
Nanosciences …
… a challenge for chemists and friends …
Surface
H
≈ 10 nm
HSM «up»High Spin"down"