1. EPR of Spin Transitions in Complexes of Cu(hfac)2
with tert-ButylPyrazolylnitroxides
Irina Drozdyuk
International Tomography Center, Novosibirsk, Russia

2. Family of Cu(hfac)2LR
O
F3C CF3
N O O
N
Cu
N
N O O
R
O F3C CF3
R
L Cu(hfac)2
Cu(hfac)2LBu 0.5C7H16 Cu(hfac)2LBu 0.5C7H8
Cu(hfac)2LBu 0.5C7H16
Cu(hfac)2LEt
Cu(hfac)2LPr
Cu(hfac)2LBu 0.5C8H10
• Very sensitive to the radical structure and the organic solvents

3. Structural rearrangements and spin transitions
Strongly-coupled state (SS)
T=293 K T=203 K T=115 K
J »kT
J «kT
Weakly-coupled state (WS)
• The flip of the Jahn-Teller axes in the triads
Izv. An. 11 (2004) 2304

4. Why do we need it?
Applicable facilities Features of Cu(hfac)2LR:
 Molecular switch  Nanometer scale
 Dense storage of information (STT-RAM)  Room temperature
 Logical schemes (10-17 J, 1 ns)  Ability to control and switch transition
 Spin transistor (100% polarisation)  Combining of properties
 Accumulator of energy  Nanosecond time of relaxation
 Light-induced transition

5. EPR of Cu(hfac)2LR
S=3/2 gc=(2gR+gCu)/3
J
S=1/2 gb=gCu
2J
S=1/2 ga=(4gR-gCu)/3
low-temperature spectrum high-temperature spectrum
Cu2
Triad Cu2
Triad
1.0 1.1 1.2 1.3 1.4 1.0 1.1 1.2 1.3 1.4
Magnetic field, Т Magnetic field, Т
Inorg. Chem. 46 (2007) 11405

6. Background and motivation
590=2230
1.00 R
Cu(hfac)2L
R
Cu(hfac)2L tert
0.75
Absorbance
0.50
590=420
0.25
0.00
400 500 600 700 800 900
Wavelength, nm
• Finding new functional ligands • New radicals absorbe less light
Angew. Chem. Int. Ed. 47 (2008) 6897

7. Background and motivation
?
?
?
O
F3C CF3
O O N O
N
N
LR Cu LRtert
N
N O O N
R N
O F3C CF3
R
LR Cu(hfac)2
• Finding new functional ligands • New radicals absorbing less light
• Tuning various intercluster exchange interactions JACS 132 (2010) 13886

8. Researching compounds
( ) [Cu(hfac)2LtertPr ]n
O
N
N
N
( ) [Cu(hfac)2LtertEt ]n
eff
(B.M.) O
N
2.6
N
N
2.4
( ) [Cu(hfac)2LtertMe ]n
O
2.2
N
N
2.0 N
1.8 T (K)
0 50 100 150 200 250 300 350
Experimental dependence μeff(T), magnetic field = 1 Т

9. Installation
Bruker Elexsys E580 EPR-spectrometer X/Q band Conditions of experiment
• CW - mode
• Q-band
• T= 4-293 К
• Polycrystalline powder samples
• Averaging over axial angle
• Cryostat
• Helium cooling system
• Temperature control system

10. Experimental results Typical EPR-spectrum of Cu(hfac)2LR
T=260 K
T=140 K
T=90 K
B / мТ
250 300 350 400 450
Cu(hfac)2LtertMe Cu(hfac)2LtertEt Cu(hfac)2LtertPr
200 К 293 К
240 К 293 К
150 К
200 К 200 К
120 К
100 К 160 К 145 К
120 К 100 К
75 К
80 К
75 К
Magnetic field, Т Magnetic field, Т Magnetic field, Т
• Principal changing of EPR-spectra of Cu(hfac)2LtertR

11. Theoretical modeling
• Spin Hamiltonian of the system Cu2
   J
ˆ
H g R B S R1 S R2 g Cu1 BS Cu1 2J S R1 ˆ
S R2 S Cu1 g Cu 2 BS Cu 2 Hint er
Triad Intercluster exchange
-∑2JinterSiCu2SiR1,2
• An approach of the modified Bloch equations
2J
, where
Cu2 Triad Cu2 Triad
Jinter=0 Jinter=0
dG A 1 1
A
i A GA B
GB i 1 M 0A
dt 2
SS
WS
Jinter 0
dGB 1 1
B
i B GB A
GA i 1 M 0B Jinter 0
dt 2
Magnetic field, mТ Magnetic field, mТ

12. Results of theoretical modeling
Estimation of intercluster exchange Jinter : The set of parameters
• observed line shape ,
triad
T2 ,
Cu2
T2 ,
Compound T, K
|gA,C – gCu2|>1/ 1/ 2Jinter |Jinter|>0.1 cm-1 10
-11
s 10
-11
s 10 s
-7
• theoretical modeling Cu(hfac)2LtertMe 75 2 30 4 77
WS SS
Cu(hfac)2LtertMe 200 10 11 40 54
Compound |Jinter|, cm-1 Compound |Jinter|, cm-1 Cu(hfac)2LtertEt 80 1.1 22 40 77
Cu(hfac)2LtertMe 0.15 Cu(hfac)2LtertMe 0.8 Cu(hfac)2LtertEt 293 10 8 4 54
Cu(hfac)2LtertEt 0.15 Cu(hfac)2LtertEt 1.5 Cu(hfac)2LtertPr 75 1.1 15 40 77
Cu(hfac)2Ltert Pr - Cu(hfac)2Ltert Pr 1.5
Cu(hfac)2LtertMe Cu(hfac)2LtertEt Cu(hfac)2LtertPr
293 К 293 К
200 К
240 К
150 К 200 К
200 К
120 К
145 К
100 К 160 К
120 К 100 К
75 К
80 К
75 К
Magnetic field, Т Magnetic field, Т Magnetic field, Т

13. Conclusion
• The first EPR-study of new thermo-switchable molecular magnets [Cu(hfac)2LtertR ]n
• These compounds differ from those studied previously by the structure of a nitroxide
ligand. Replacement of the nitronyl nitroxide substituent in LR by tert-butylnitroxide one
supresses the intercluster exchange pathway between different polymer chains, and
leads also to an ehancement of intercluster exchange interaction (up to a few cm-1)
• Despite the exchange narrowing of the spectra due to the stronger intercluster
interaction in these complexes, observed line shapes are significantly different
depending on the spin state of a triad (WS or SS).
• Theoretical modeling has confirmed the assigment of the observed spectra to the
complexes with the triad in the one of these two spin states.
• This investigation explains the main trends of EPR applied for the caracterization of
phase spin transitions in new compounds and creates the basis for their future studies.

14. Thank you for your attention!