4.2 Aqueous Solutions
81
Technetium carboxylate complexes were characterized by Kennedy and Pinkerton
(e.g. 1988a, b). These authors electrochemically generated Tc-formate and Tc-acetate
complexes by applying a potential of −0.6 V versus SCE to a carbon electrode at pH
3–4 (Kennedy and Pinkerton 1988a). Considering the structure of other similar Tc
species (see: Spitsyn et al. 1985), they concluded that such types of complexes are
dioxo-bridged Tc(IV). Such types of Tc species were starting materials for chemical synthesis of Tc(III) isonitrile complexes, e.g. [Tc(CNC(CH 3 ) 3 ) 6 ]
3+ . A discussion of their electrochemical behavior can be found in a subsequent publication of
Kennedy and Pinkerton (1988b). [Tc(CNC(CH 3 ) 3 ) 6 ]
3+ species were reduced to Tc(I)
at potentials lower than ca. –0.8 V versus SCE while its oxidation took place at 0.84 V.
De Gregori and Lobos (1989) studied electrosynthesis of technetium(V) dithiolate
complexes from pertechnetates in the presence of 1,3-dimercaptopropane (DMP),
2,3-dimercaptopropanol (BAL) or 2,3-dimercaptosuccinic acid (DMSA) in alkaline
(pH = 12) aqueous media. These species were synthesized on a mercury pool electrode by applying a potential of –1.05 V versus SCE. The authors reported that Tc(V)dithiolato complexes were stable in the presence of oxygen and did not undergo a
disproportionation reaction.
Kremer et al. (1996) studied [(Tc or Re)
V O 2 (amine) 2 ]I complexes in solutions
with pH varying from 2.5 to 8.5. The selected amine was a polydentate, e.g., en or
tn. They concluded that TcO
+
2 cores are easier to oxidize at pH of 2.5 as compared
with pH of 8.5. This is explained by the fact that at low pH values, these ions
can be protonated to TcO(OH)
+ , which undergo a very fast decomposition. Anodic
branch of CV curves recorded in slightly alkaline solutions of 8.5 revealed only
the signals characteristic of the iodine oxidation. The reduction of [TcO 2 (tn) 2 ]
+ and
[TcO 2 (en) 2 ]
+ is irreversible and takes place at 0.61 and 0.54 V (vs. SHE), respectively.
As one of the main conclusions of their studies, the authors stated that the stability
of technetium(V) amine complexes in acid solutions turned out to be lower than for
their rhenium analogs (Table 4.3).
81
Technetium carboxylate complexes were characterized by Kennedy and Pinkerton
(e.g. 1988a, b). These authors electrochemically generated Tc-formate and Tc-acetate
complexes by applying a potential of −0.6 V versus SCE to a carbon electrode at pH
3–4 (Kennedy and Pinkerton 1988a). Considering the structure of other similar Tc
species (see: Spitsyn et al. 1985), they concluded that such types of complexes are
dioxo-bridged Tc(IV). Such types of Tc species were starting materials for chemical synthesis of Tc(III) isonitrile complexes, e.g. [Tc(CNC(CH 3 ) 3 ) 6 ]
3+ . A discussion of their electrochemical behavior can be found in a subsequent publication of
Kennedy and Pinkerton (1988b). [Tc(CNC(CH 3 ) 3 ) 6 ]
3+ species were reduced to Tc(I)
at potentials lower than ca. –0.8 V versus SCE while its oxidation took place at 0.84 V.
De Gregori and Lobos (1989) studied electrosynthesis of technetium(V) dithiolate
complexes from pertechnetates in the presence of 1,3-dimercaptopropane (DMP),
2,3-dimercaptopropanol (BAL) or 2,3-dimercaptosuccinic acid (DMSA) in alkaline
(pH = 12) aqueous media. These species were synthesized on a mercury pool electrode by applying a potential of –1.05 V versus SCE. The authors reported that Tc(V)dithiolato complexes were stable in the presence of oxygen and did not undergo a
disproportionation reaction.
Kremer et al. (1996) studied [(Tc or Re)
V O 2 (amine) 2 ]I complexes in solutions
with pH varying from 2.5 to 8.5. The selected amine was a polydentate, e.g., en or
tn. They concluded that TcO
+
2 cores are easier to oxidize at pH of 2.5 as compared
with pH of 8.5. This is explained by the fact that at low pH values, these ions
can be protonated to TcO(OH)
+ , which undergo a very fast decomposition. Anodic
branch of CV curves recorded in slightly alkaline solutions of 8.5 revealed only
the signals characteristic of the iodine oxidation. The reduction of [TcO 2 (tn) 2 ]
+ and
[TcO 2 (en) 2 ]
+ is irreversible and takes place at 0.61 and 0.54 V (vs. SHE), respectively.
As one of the main conclusions of their studies, the authors stated that the stability
of technetium(V) amine complexes in acid solutions turned out to be lower than for
their rhenium analogs (Table 4.3).