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Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
•
Cl
•
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
•
•
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
O
C
COO
−
Cl
Cl
Cl
Cl
+
H
3
N
+
H
3
N
+
H
3
N
H
2
N
HN
H
2
N
Cl
Cl
Cl
Cl
NH
NH
NH
NH
NH
NH
OH
OH
Si
Si
Si
Si
Si
Si
OH
OH
OH
OH
O
OH
O
OH
O
O
O
O
O
O
S
S
SiO
2
Au
SiO
2
Figure 2.25
Approaches employed to anchor PTM radical derivatives on surfaces of different nature by
chemisorptions,throughcovalentbondsorelectrostaticinteractionsbonds.(Reprintedwithpermissionfrom[93].
Copyright2009RoyalSocietyofChemistry.)
employed offer different advantages - while gold and graphite permit electroactivity and transport studies
of the functionalized surfaces, glass substrates are compatible with the use of optical techniques.
The tris(trichlorophenyl)methyl radical (
27
) was chosen as a model compound to address the magnetic
behaviour of a metal surface after physisorption. As confirmed by scanning tunneling microscopy (STM),
molecules of
27
were adsorbed on the gold surface forming aggregates of a few molecules in ordered
domains of periodic rows separated by 1
1 nm, which is consistent with the molecular size of
27
(Figure 2.26). The paramagnetic character of the surface was confirmed by EPR spectroscopy, showing a
sharp line with a weak magnetic anisotropic behavior, demonstrating unambiguously that the
27
radicals
.
5
±
0
.
H
H
Cl
Cl
Cl
Cl
(a)
H
H
Cl
Cl
Cl
Cl
H
H
(b)
Cl
3345
3350
3355
3360
3365
Magnetic field (G)
Figure2.26
Left:STMimage(60
60 nm)of
27
physisorbedongold(111).Tipsamplebias0.3Vandtunnelling
current15pA.Right:(a)EPRspectrumofagoldsurfacedecoratedwithphysisorbed
27
radicals;(b)EPRspectrum
ofthegoldsubstrate.(Reprintedwithpermissionfrom[98].Copyright2009Elsevier.)
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