70
4 Technetium Coordinated by Organic Ligands …
4.1 Nonaqueous Solutions
Halogen (X), diars or diphos (D) complexes of technetium ([Tc
III D 2 X 2 ]
+ ) in DMF
were analyzed by Hurst et al. (1981). These species undergo a reversible one-electron
redox reaction with participation of Tc(III)/Tc(II) couples, Eq. (4.1):
[TcD 2 X 2 ]
+
+ e
−
[TcD 2 X 2 ]
+
(4.1)
Additional redox reactions of Tc diars complexes include Tc(II)/Tc(0) although
description of these processes is less complete than for Tc(III)/Tc(II) systems. The
authors noted that the reduction potential of Tc(III) is sensitive to the nature of both
the halogen and the organic ligand. Thus, replacement of a light halogen with a
heavier one leads to an increase in the reduction potential by 0.07–0.12 V. It was
proposed that this effect is a result of π-back-bonding and stabilization of d
5 (Tc(II))
over d
4 (Tc(III)) configuration by increased acceptance of t 2g electron density. The
diphos ligand stabilizes d
5 (Tc(II)) over d
4 (Tc(III)) center more effective than the
diars ligand.
Later work of Heineman, Deutsch et al. (Libson et al. 1983; Jurisson et al. 1984;
Bandoli et al. 1984; Ichimura et al. 1984) were devoted also to technetium(III)
complexes of [TcD 2 X 2 ]
+ type where D stands for (dppb), (dppe), (dmpe) or (depe).
CV curves reveal one-electron reversible reduction reactions of Tc
III to Tc
II and Tc
II
to Tc
I and a one-electron oxidation of Tc
III to Tc
II (Jurisson et al. 1984; Ichimura
et al. 1985).
Mazzi et al. (1980) examined Tc(I) complexes with phosphine and CO
ligands by means of the voltammetric methods. [TcCl(CO) 2 (PMe 2 Ph) 3 ] and
[TcCl(CO) 3 (PMe 2 Ph) 2 ] undergo a two-electron process, which leads to the formation
of Tc(III). Electrooxidation of Tc(I) in TcCl(CO) 2 (PMe 2 Ph) 3 results in the formation of anodic waves seen on the voltammetric curves at 0.83 V (peak A) and 1.02 V
(peak B) (Fig. 4.1). The first reduction peak C at 0.74 V is linked with the anodic
peak A. E p of this redox couple equals 0.09 V and its electrochemical behavior
cannot be considered as a reversible one under diffusional control. A small peak at
−0.65 V is attributed to an irreversible reduction process. The authors noted that the
position and height of the second oxidation peak (B) vary and depend on the electrode
history as a consequence of adsorption of the technetium species. The shape of the
CV curve for the second-investigated Tc(I) complex, [TcCl(CO) 3 (PMe 2 Ph) 3 ], was
similar to that recorded for TcCl(CO) 2 (PMe 2 Ph) 3 although for the former the anodic
peaks are observed at more positive potentials (1.17 and 1.54 V). The cathodic peak of
TcCl(CO) 2 (PMe 2 Ph) 3 reduction was observed at 1.08 V indicating the same as previously peak separation (0.09 V). The conductivity of 1 mM [TcCl(CO) 2 (PMe 2 Ph) 3 ]
in ACN was determined at a level of 230
−1 cm
2 mol
−1 .
Figure 4.2 presents a complex scheme of chemical and electrochemical steps of
Tc complexes oxidation. Noteworthy is the fact that the Tc(II) species may undergo
disproportionation or chemical addition of ACN.
4 Technetium Coordinated by Organic Ligands …
4.1 Nonaqueous Solutions
Halogen (X), diars or diphos (D) complexes of technetium ([Tc
III D 2 X 2 ]
+ ) in DMF
were analyzed by Hurst et al. (1981). These species undergo a reversible one-electron
redox reaction with participation of Tc(III)/Tc(II) couples, Eq. (4.1):
[TcD 2 X 2 ]
+
+ e
−
[TcD 2 X 2 ]
+
(4.1)
Additional redox reactions of Tc diars complexes include Tc(II)/Tc(0) although
description of these processes is less complete than for Tc(III)/Tc(II) systems. The
authors noted that the reduction potential of Tc(III) is sensitive to the nature of both
the halogen and the organic ligand. Thus, replacement of a light halogen with a
heavier one leads to an increase in the reduction potential by 0.07–0.12 V. It was
proposed that this effect is a result of π-back-bonding and stabilization of d
5 (Tc(II))
over d
4 (Tc(III)) configuration by increased acceptance of t 2g electron density. The
diphos ligand stabilizes d
5 (Tc(II)) over d
4 (Tc(III)) center more effective than the
diars ligand.
Later work of Heineman, Deutsch et al. (Libson et al. 1983; Jurisson et al. 1984;
Bandoli et al. 1984; Ichimura et al. 1984) were devoted also to technetium(III)
complexes of [TcD 2 X 2 ]
+ type where D stands for (dppb), (dppe), (dmpe) or (depe).
CV curves reveal one-electron reversible reduction reactions of Tc
III to Tc
II and Tc
II
to Tc
I and a one-electron oxidation of Tc
III to Tc
II (Jurisson et al. 1984; Ichimura
et al. 1985).
Mazzi et al. (1980) examined Tc(I) complexes with phosphine and CO
ligands by means of the voltammetric methods. [TcCl(CO) 2 (PMe 2 Ph) 3 ] and
[TcCl(CO) 3 (PMe 2 Ph) 2 ] undergo a two-electron process, which leads to the formation
of Tc(III). Electrooxidation of Tc(I) in TcCl(CO) 2 (PMe 2 Ph) 3 results in the formation of anodic waves seen on the voltammetric curves at 0.83 V (peak A) and 1.02 V
(peak B) (Fig. 4.1). The first reduction peak C at 0.74 V is linked with the anodic
peak A. E p of this redox couple equals 0.09 V and its electrochemical behavior
cannot be considered as a reversible one under diffusional control. A small peak at
−0.65 V is attributed to an irreversible reduction process. The authors noted that the
position and height of the second oxidation peak (B) vary and depend on the electrode
history as a consequence of adsorption of the technetium species. The shape of the
CV curve for the second-investigated Tc(I) complex, [TcCl(CO) 3 (PMe 2 Ph) 3 ], was
similar to that recorded for TcCl(CO) 2 (PMe 2 Ph) 3 although for the former the anodic
peaks are observed at more positive potentials (1.17 and 1.54 V). The cathodic peak of
TcCl(CO) 2 (PMe 2 Ph) 3 reduction was observed at 1.08 V indicating the same as previously peak separation (0.09 V). The conductivity of 1 mM [TcCl(CO) 2 (PMe 2 Ph) 3 ]
in ACN was determined at a level of 230
−1 cm
2 mol
−1 .
Figure 4.2 presents a complex scheme of chemical and electrochemical steps of
Tc complexes oxidation. Noteworthy is the fact that the Tc(II) species may undergo
disproportionation or chemical addition of ACN.