Chapter 2
Comprehensive Electrochemistry of Tc
and Its Periodic Table Neighbors
Technetium is located in group 7 of the periodic table together with manganese
and rhenium. When elements of the periods of the periodic table are analyzed, one
finds technetium in the period 5 surrounded with molybdenum and ruthenium as its
neighbors (Fig. 2.1). Being transition metal technetium has seven valence electrons
and these electrons reside in the 5s and 4d subshells. These seven electrons located
outside of the krypton’s noble gas core can participate in the formation of chemical
bonds. As a result, the technetium forms compounds with oxidation states varying
from −1 to +7.
Although many aspects of technetium chemistry are similar to what is observed
for all its neighbors from the periodic table, its chemical properties most resemble
those exhibited by rhenium. This phenomenon is attributed to the equal values of
atomic radii of technetium and rhenium, which is a result of lanthanides contraction
effects (see Table 2.1). Further on, the electronegativity of both elements is also
very similar. Both elements have extensive and often similar oxohalides chemistry
(Rard 1985; Rouschias 1974). Therefore, rhenium is most common considered as a
technetium analog that can be used for deduction of properties of the latter.
Among chemical properties of Tc that are similar to those exhibited by Mo and
Ru, the most notable is tendency to form polymeric species containing several Tc
atoms. The polymeric species of ruthenium and molybdenium with +3 or +4 oxidation states (e.g., [Ru 4 (OH) 12 ]
4+ or [Mo 3 O 4 ]
3+ ) are well known (Ardon and Pernick
1974; Paffett and Anson 1983; Isherwood 1985) and their examples are listed in
Table 2.1. The tendency to polymerization (or dimerization) is also characteristic for
reduced technetium(III/IV). Well known are -Tc-O-Tc- species, e.g., [Tc 2 O 2 ]
3/4+ or
[Tc 3 O 5 ]
2+ , whose structures are similar to the respective Mo or Ru polymers (see
e.g. Mausolf et al. 2011; Baumann et al. 2018).
According to Encyclopedia Britannica, the metals that are located in the VIIB,
VIII, and IB groups (old CAS notation) of the second and third transition series
(Tikkanen 2008) are considered as the noble ones. Although this classification is
not recommended by IUPAC, but it is still common. Consequently, technetium and
rhenium, which are located in group VIIB, are sometimes considered as noble metals
© Springer Nature Switzerland AG 2021
M. Chotkowski and A. Czerwi´ nski, Electrochemistry of Technetium,
Monographs in Electrochemistry, https://doi.org/10.1007/978-3-030-62863-5_2
11
Comprehensive Electrochemistry of Tc
and Its Periodic Table Neighbors
Technetium is located in group 7 of the periodic table together with manganese
and rhenium. When elements of the periods of the periodic table are analyzed, one
finds technetium in the period 5 surrounded with molybdenum and ruthenium as its
neighbors (Fig. 2.1). Being transition metal technetium has seven valence electrons
and these electrons reside in the 5s and 4d subshells. These seven electrons located
outside of the krypton’s noble gas core can participate in the formation of chemical
bonds. As a result, the technetium forms compounds with oxidation states varying
from −1 to +7.
Although many aspects of technetium chemistry are similar to what is observed
for all its neighbors from the periodic table, its chemical properties most resemble
those exhibited by rhenium. This phenomenon is attributed to the equal values of
atomic radii of technetium and rhenium, which is a result of lanthanides contraction
effects (see Table 2.1). Further on, the electronegativity of both elements is also
very similar. Both elements have extensive and often similar oxohalides chemistry
(Rard 1985; Rouschias 1974). Therefore, rhenium is most common considered as a
technetium analog that can be used for deduction of properties of the latter.
Among chemical properties of Tc that are similar to those exhibited by Mo and
Ru, the most notable is tendency to form polymeric species containing several Tc
atoms. The polymeric species of ruthenium and molybdenium with +3 or +4 oxidation states (e.g., [Ru 4 (OH) 12 ]
4+ or [Mo 3 O 4 ]
3+ ) are well known (Ardon and Pernick
1974; Paffett and Anson 1983; Isherwood 1985) and their examples are listed in
Table 2.1. The tendency to polymerization (or dimerization) is also characteristic for
reduced technetium(III/IV). Well known are -Tc-O-Tc- species, e.g., [Tc 2 O 2 ]
3/4+ or
[Tc 3 O 5 ]
2+ , whose structures are similar to the respective Mo or Ru polymers (see
e.g. Mausolf et al. 2011; Baumann et al. 2018).
According to Encyclopedia Britannica, the metals that are located in the VIIB,
VIII, and IB groups (old CAS notation) of the second and third transition series
(Tikkanen 2008) are considered as the noble ones. Although this classification is
not recommended by IUPAC, but it is still common. Consequently, technetium and
rhenium, which are located in group VIIB, are sometimes considered as noble metals
© Springer Nature Switzerland AG 2021
M. Chotkowski and A. Czerwi´ nski, Electrochemistry of Technetium,
Monographs in Electrochemistry, https://doi.org/10.1007/978-3-030-62863-5_2
11