Electron transfer. 144. Reductions with germanium(II)

Article abstract of DOI:10.1021/ic0004582

Solutions 0.2-0.4 M in Ge(II) and 6 M in HCl, generated by reaction of Ge(IV) with H₃PO₂, are stable for more than 3 weeks and can be diluted 200-fold with dilute HCl to give GeCl₃^- preparations to be used in redox studies. Kinetic profiles for the reduction of Fe(III) by Ge(II), as catalyzed by Cu(II), implicate the odd-electron intermediate, Ge(III), which is formed from Cu(II) and Ge(II) (k = 30 M^-1 s^-1 in 0.5 M HCl at 24 °C) and which is consumed by reaction with Fe(III) (k = 6 x 10² M^-1 s^-1). A slower direct reaction between Ge(II) and Fe(III) (k = 0.66 M^-1 s^-1) can be detected in 1.0 M HCl. The reaction of Ge(II) with I₃^- in 0.01-0.50 M iodide is zero order in oxidant and appears to proceed via a rate-determining heterolysis of a Ge(II)-OH₂ species (k = 0.045 s^-1) which is subject to H⁺-catalysis. Reductions of IrCl₆^2- and PtCl₆^2- by Ge(II) are strongly Cl^--catalyzed. The Ir(IV) reaction proceeds through a pair of 1e^- changes, of which the initial conversion to Ge(III) is rate-determining, whereas the Pt(IV) oxidant probably utilizes (at least in part) an inner-sphere Pt(IV)-Cl-Ge(II) bridge in which chlorine is transferred (as Cl⁺) from oxidant to reductant. The 2e^- reagent, Ge(II), like its 5s² counterpart, In(I), can partake in 1e^- transactions, but requires more severe constraints: the coreagent must be more powerfully oxidizing and the reaction medium more halide-rich.

Full text of DOI:10.1021/ic0004582

Inorg. Chem. 2000, 39, 4119-4122
4119
Electron Transfer. 144. Reductions with Germanium(II)1
Olga A. Babich* and Edwin S. Gould*
Department of Chemistry, Kent State University, Kent, Ohio 44242
ReceiVed April 26, 2000
Solutions 0.2-0.4 M in Ge(II) and 6 M in HCl, generated by reaction of Ge(IV) with H3PO2, are stable for more
-
than 3 weeks and can be diluted 200-fold with dilute HCl to give GeCl3 preparations to be used in redox studies.
Kinetic profiles for the reduction of Fe(III) by Ge(II), as catalyzed by Cu(II), implicate the odd-electron intermediate,
-
1 -1
Ge(III), which is formed from Cu(II) and Ge(II) (k ) 30 M
s
in 0.5 M HCl at 24 °C) and which is consumed
2
-1 -1
by reaction with Fe(III) (k ) 6 × 10 M s ). A slower direct reaction between Ge(II) and Fe(III) (k ) 0.66
-
1
-1
-
M
s ) can be detected in 1.0 M HCl. The reaction of Ge(II) with I3 in 0.01-0.50 M iodide is zero order in
-
1
oxidant and appears to proceed via a rate-determining heterolysis of a Ge(II)-OH2 species (k ) 0.045 s ) which
+
2-
2-
-
is subject to H -catalysis. Reductions of IrCl6 and PtCl6 by Ge(II) are strongly Cl -catalyzed. The Ir(IV)
-
reaction proceeds through a pair of 1e changes, of which the initial conversion to Ge(III) is rate-determining,
whereas the Pt(IV) oxidant probably utilizes (at least in part) an inner-sphere Pt -Cl-Ge bridge in which
chlorine is transferred (as Cl ) from oxidant to reductant. The 2e reagent, Ge(II), like its 5s counterpart, In(I),
IV
II
+
-
2
-
can partake in 1e transactions, but requires more severe constraints: the coreagent must be more powerfully
oxidizing and the reaction medium more halide-rich.
Only a few accounts describing the preparation and reactions
of germanium(II) species in aqueous solution have appeared,
was prepared in solution from NaHCO
(III) perchlorate, copper(II) perchlorate, germanium dioxide, hypo-
phosphorous acid, and quinoxaline (Aldrich products), KI solution and
sodium iodide (Fisher), sodium hexachloroplatinate(IV) (Na PtCl
(Alfa), and hydroxocobalamin
3 4
and concentrated HClO . Iron-
2-7
3
and systematic redox studies of this unusual donor are even
more sparse.8,9 This oxidation state (E°IV,II ) -0.227 V at pH
2
6
‚
max
4
-1
-1 13
6
H
2
O, ꢀ262 2.4 × 10 ) M cm
)
0
) is described as unstable in aqueous media in the absence of
(
B12a) hydrochloride (Sigma) were used as received. Fresh solutions
10
halide. In line with our interest in reductions by hypovalent
max
3
of sodium hexachloroiridate(IV) (Na
M
2
IrCl
6
‚6H
2
O, ꢀ489 ) 4.07 × 10
11
main group elements, we here report the preparation of
germanium(II) solutions which may be handled using conven-
tional techniques and the examination of the reactions of this
state with oxidants in aqueous halide media. The most novel
facets of this study are (a) kinetic profiles which allow estimates
of rates of reactions involving the odd-electron species, Ge-
-1
-1 14
cm
) (Aldrich) were prepared daily. Bromopentaamminecobalt-
2+
-
2
(III) perchlorate ([Br(NH ) Co] [ClO ] ) and its chloro analogue were
3 5 4
15
prepared as described. Concentrations of Fe(III) were determined
iodometrically.
Solutions of Ge(II) were prepared by a modification of the procedure
2
of Jolly and Latimer; all operations were carried out under high-purity
(
III), and (b) evidence for slow ligand substitution at a Ge(II)
2
(99.99%) argon. Just 1.0 g of GeO was dissolved in 5 mL of
concentrated NaOH, then reprecipitated, and redissolved by the addition
of 20 mL of 6 M HCl. The resulting Ge(IV) solution was reduced with
12
center. A preliminary communication deals with a portion of
these results.
7
.5 mL of 50% hypophosphorous acid at 100° for 5-6 h:
Experimental Section
IV
II
+
Ge + H O + H PO f H PO + Ge + 2H
(1)
Materials. Solutions were prepared using Millipore water that had
2
3
2
3
3
been boiled for 2 h and then sparged with N
2
for 2 h more to remove
dissolved oxygen. Sodium perchlorate (used as a supporting electrolyte)
Germanium(II) hydroxide was precipitated from the cooled solution
by addition of concentrated NH , washed twice with cold 1 M HCl,
3
(
1) Sponsorship of this work by the National Science Foundation (Grant
and then dissolved in 6 M HCl. Solutions 0.2-0.4 M in Ge(II) and 6
CHE-9714981) is gratefully acknowledged.
M in HCl were unchanged after several weeks, but diluted solutions
(
(
(
2) Jolly, W. L.; Latimer, W. M. J. Am. Chem. Soc. 1952, 74, 5751.
3) Foster, L. S. Inorg. Synth. 1950, 3, 63-4.
4) Mayer, H. P.; Rapsomanikis, S. Appl. Organomet. Chem. 1992, 6,
II
-3
-
+
(
[Ge ] ) 10 M, [Cl ] ) 0.08 M, [H ] ) 0.3 M) decomposed
gradually (t1/2 ) 60 min at 25 °C). Ge(OH) is slightly soluble in 6 M
HClO ; the reducing capacity of the resulting solution ([Ge ] ca. 0.03
M) slowly decreases, and hydrated GeO eventually precipitates.
2
II
1
73.
5) Pan, K.; Chen, J.-S.; Huang, T.-S. J. Chin. Chem. Soc. (Taipei) 1975,
2, 171.
4
(
2
2
Stoichiometric Studies. Stoichiometric determinations were carried
out under argon and monitored at or near the low-energy maximum of
each oxidant. Measured deficient quantities of Ge(II) were added to a
known excess of the oxidant. After fixed waiting periods (30 s for
(
(
(
6) Parshall, G. W. Inorg. Synth. 1974, 15, 222.
7) Poskozim, P. S.; Stone, A. L. J. Inorg. Nucl. Chem. 1970, 32, 1391.
8) Gladyshev, V. P.; Syroeshkina, T. V.; Sarieva, I. S.; Tember, G. A. J.
Anal. Chem. USSR 1978, 33, 1496; Chem. Abstr. 1979, 90, 112056n.
9) Antonov, P. G.; Zhamsueva, T. Ts. Zh. Prikl. Khim. 1993, 66, 969;
Chem. Abstr. 1994, 120, 281443e.
2-
2-
III
(
PtCl
and IrCl
, 50 min for Fe in HCl) decreases in absorbance
6
6
were compared to the initial known absorbance of the oxidant.
(
(
(
10) Bard, A. J.; Parsons, R.; Jordan, J. Standard Potentials in Aqueous
Solution; Marcel Dekker: New York, 1985; p 212.
11) (a) Chandra, S. K.; Gould, E. S. Inorg. Chem. 1997, 36, 3485. (b)
Swavey, S.; Gould, E. S. Inorg. Chem. 2000, 39, 352.
(13) Bakac, A.; Hand, T. D.; Sykes, A. G. Inorg. Chem. 1975, 14, 2540.
(14) Drury, W. D.; DeKorte, J. M. Inorg. Chem. 1983, 22, 121.
(15) Wu, M.-Y.; Paton, S. J.; Fanchiang, Y.-T.; Gelerinter, E.; Gould, E.
S. Inorg. Chem. 1978, 17, 326.
12) Babich, O. A.; Ghosh, M. C.; Gould, E. S. Chem. Commun.
(Cambridge) 2000, 907.
1
0.1021/ic0004582 CCC: $19.00 © 2000 American Chemical Society
Published on Web 08/12/2000

4
120 Inorganic Chemistry, Vol. 39, No. 18, 2000
Babich and Gould
Table 2. Representative Kinetic Data for the Oxidation of
Table 1. Stoichiometry of Reactions of Germanium(II) with
Transition Metal Oxidants
a
Germanium(II) by Iron(III) as Catalyzed by Copper(II)a
5
II
5
[H+], [Cl-], 10 [Ge ], 10 [Cu ],
4
II
6
II
10-2k
-5
b
oxidant
λ, 10 [Ge ], 10 ∆[Ox], ∆[Ox]/
k
M
6
,
7
,
10 k ,
8
5
II
-1 -1
-1 -1
(
M × 10 )
medium
1 M HCl
nm
M
M
∆[Ge ]
M
M
M
M
M
s
M
s
2
-
PtCl
6
(9.0)
262
0.49
0.47
1.45
2.16
2.8
0.96
0.98
0.89
0.83b
1.91
1.94
1.89
1.86
1.94
1.88
1.91
1.89
0.40
0.40
0.40
1.0
1.0
1.0
0.50
0.50
0.50
0.20
0.20
0.40
5.4
10.0
10.0
6.6
10.0
10.0
5.0
5.0
31
34
34
9.8
10.3
23
6.5
7.0
7.0
6.0
5.5
5.4
5.4
5.4
5.4
1.25
1.25
2.1
1
2
3
.46
.43
.4
10.0
5.0
2
-
IrCl
6
(21.1) 0.5 M HCl 489
2.0
3.8
7.7
5.0
5.0
4
6
8
.0
.0
.0
11.3
a
Reactions were carried out under argon at 23 °C and at ionic
14.8
13.2
25.6
39
-
-
III
-4
Fe(III) (65.5)c 0.4 M HCl 350
strength 1.0 M (Cl , ClO
Kinetic parameters k and k
forms of sequence 6-8 to experimental curves (see text and ref 18).
4
). [Fe ]initial ) 1.0 × 10 M throughout.
6.8
3.6
0.4
7.2
6
7
were obtained from the best fit of integrated
1
2
2
b
8
Values of k were obtained from data of Orth and Liddell (ref 19).
51
a
Reactions were carried out at 23 °C. Waiting period: 0.5 min for
2-
2-
b
2-
6
PtCl
6
II
and IrCl
6
; 50 min for Fe(III). PtCl
experiments at higher
c
-6
[
Ge ] encountered precipitation. Reactions catalyzed by 5.0 × 10
M Cu(II).
Reductions of FeIII were inconveniently slow in the absence of catalytic
-
6
quantities (5 × 10 M) of Cu(II). Results are summarized in Table 1.
Kinetic Studies. Reactions, under argon, were examined at or near
λmax of the oxidant, using either a Shimadzu-1601 instrument or a
Durrum-Gibson stopped-flow spectrophotometer interfaced with an
OLIS computer system. Temperatures were kept at 23.0 ( 0.5 °C
throughout the entire series of experiments. Ionic strength was regulated
by addition of (NaClO
A number of oxidants reacted imperceptibly slowly with Ge(II) under
the conditions used. Among these were UO
and phenylglyoxylato derivatives of (NH Co . In contrast, the corrin-
4
+ HClO
4
), (HCl + NaCl), or NaI.
2
+
2
and the chloro-, bromo-,
III
3 5
)
bound Co(III) complex, aquacobalamin (vitamin B12a), was rapidly
+
Figure 1. Kinetic profile at 240 nm for the reduction of Fe(III) (1.0
reduced to a Co(II) species, whereas the quinoxalinium cation (QH )
-
4
-4
16
•
× 10 M) by Ge(II) (6.6 × 10 M), as catalyzed by Cu(II) (5 ×
was converted, in separable steps, to the corresponding radical (QH ),
-6 - +
1
0
M) in 0.20 M Cl at 23 °C; [H ] ) 1.0 M. The solid line represents
2
and thence to its dihydro derivative (QH ).
the experimental curve whereas the circles denote absorbances calcu-
lated from numerical integration of differential equations based on
Results and Discussion
-
1
-1
2
-1
reaction sequence 6-8, taking k
6
as 9.8 M
s
, k
7
as 6 × 10 M
7
6
-1
5
-1 -1
Both Poskozim and Parshall have reported the principal
s
, and k
8
) 1.25 × 10 M
s
(ref 19). The extinction coefficient
-
used for Fe(III) is 4.7 × 10
3
M
-1 cm-1, and other species were
Ge(II) species in 3 M HCl to be the monoanion, GeCl3 , but in
17
considered to be negligibly absorbent. Optical path length ) 1.00 cm.
analogy to the behavior of Sn(II), partial further anation to
the dianion, GeCl42-, in 6 M HCl would be expected.
Stoichiometric determinations (Table 1) indicate nearly
complete conversion to Ge(IV) for oxidations by PtCl6
IrCl6 , and Fe(III) (eqs 2-4), as has been reported also for
at more nearly equal rates. The patterns strongly support
sequence 6-8.
2
-
,
2-
2
Ge(II) + Cu(II) f Ge(III) + Cu(I)
Fe(III) + Ge(III) f Ge(IV) + Fe(II)
Fe(III) + Cu(I) f Fe(II) + Cu(II)
k6
(6)
(7)
(8)
-
I3 (eq 5).
k7
Ge(II) + Pt(IV) f Ge(IV) + Pt(II)
Ge(II) + 2Ir(IV) f Ge(IV) + 2Ir(III)
(2)
(3)
(4)
k8
Expression of this sequence as a trio of differential kinetic
equations, and numerical integration using the program KIN-
Ge(II) + 2Fe(III) f Ge(IV) + 2Fe(II)
1
8
Ge(II) + I3- f Ge(IV) + 3I-
SIM, leads, after slight adjustment for the slow unimolecular
(5)
-4
-1
loss of Ge(II) (k ) 2 × 10 s ), to bimolecular rate constants
k6 and k7 listed in Table 2. Values for k8 (the Cu(I)-Fe(III)
Oxidations by Fe(III). The very slow reduction of Fe(III)
1
9
reaction) have been shown by Orth and Liddell to vary with
-
7
by Ge(II) is catalyzed markedly by Cu(II), even at the 10
M
+
-
both [H ] and [Cl ] and have been taken from the report of
these workers. A representative curve calculated in this manner
is compared with the observed profile in Figure 1. The constants
k6 and k7, pertaining to the formation and oxidation of a Ge-
level, but by none of the other usual transition metal cations.
-
II
II
With [Cl ] < 0.2 M, rates are proportional to [Ge ] and [Cu ]
III
but are independent of [Fe ], pointing to the slow formation
of one or more active intermediates, the faster reactions of which
-
II
are kinetically silent. At higher [Cl ] and [Ge ], the linear
profiles become curved, most perceptibly near the end, indicat-
ing that the initial catalytic act and the loss of Fe(III) proceed
(
18) (a) Barshop, B. A.; Wrenn, R. F.; Frieden, C. Anal. Biochem. 1983,
130, 134. (b) Chandra, S. K.; Paul, P. C.; Gould, E. S. Inorg. Chem.
1997, 36, 4688.
(19) Orth, R. J.; Liddell, K. C. Ind. Eng. Chem. Res. 1990, 29, 1178. The
data of these authors are consistent with the rate law
(
16) Chang, C.-R.; Paton, S. J.; Gelerinter, E.; Gould, E. S. Inorg. Chem.
979, 18, 1294.
1
III
I
- 2
- -1
rate ) [Fe ][Cu ](a + b[Cl ] [H ]
)
(
17) Martell, A. E.; Smith, R. M. Critical Stability Constants; Plenum:
where a ) 9.7 × 10 M s-1 and b ) 7.0 × 10 M s-1 at 23 °C.
4
-1
5
-2
New York, 1976; Vol. 4, pp 10, 109.

Reductions with Germanium(II)
Table 3. Kinetic Data for Oxidation of Germanium(II) with I -
Inorganic Chemistry, Vol. 39, No. 18, 2000 4121
-
+
3
reaction is not inhibited by added I but is accelerated by H ,
5
II
+
-
-
6
-1 b
we infer that rates are being set by Ge(II)-O bond breakage.
1
0 [Ge ], M [H ], M [Cl ], M [I ], M 10 (rate), M s
+
For the [H ]-independent component we suggest sequence 10-
2
6
1
5
2
6
6
6
6
6
6
8
8
8
8
8
8
8
.8
.9
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.10
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.120
0.020
0.020
0.020
0.020
0.020
0.020
0.40
0.030
0.030
0.030
0.030
0.030
0.010
0.150
0.48
0.030
0.030
0.030
0.10
0.10
0.10
0.10
0.10
0.10
0.10
1.6 (1.7)
4.2 (4.1)
12 (12)
19 (20)
24 (25)
4.3 (4.1)
4.2 (4.1)
4.2 (4.1)
4.2 (4.1)
4.3 (4.1)
7.2 (7.9)
5.7 (5.3)
6.9 (6.6)
7.8 (9.0)
11 (11)
1
1,
2
3
4
.9
.9
.9
.9
.9
.9
.9
.9
.9
.9
.9
.9
.9
+
0.20
and for the [H ]-proportional contribution we suggest an
analogous route (with protonation preceding scission). This
duality of paths leads to rate law 12 (algebraically equivalent
0.040
0.080
0.120
0.180
0.20
15 (15)
18 (17)
26 (23)
II
+
rate ) [Ge ](k + k [H ]/KHA)
(12)
A
HA
0.30
0.40
a
-]
to eq 9), in which rate constants kA and kHA pertain to the two
paths and KHA pertains to the protonation preequilibrium. Our
data allow calculation of the ratio kHA/KHA, but not individual
values of these parameters. We do not observe kinetic saturation
4 4 3
Reactions were run at 23.5 °C, µ ) 0.50 M (HClO /NaClO ), [I
-
6
-6
b
)
3 × 10 to 8 × 10 M. All profiles were linear. Parenthetical
II + -1
values were calculated as [Ge ](k + k′[H ]), with k ) 0.045 s and
-
1
-1
k′ ) 0.70 M
s .
+
with respect to [H ], indicating that KHA lies far above the
(
III) center, appear to be the first reported kinetic parameters
associated with this odd-electron state. Within the ranges
examined, the rate of formation of Ge(III) () 50 M
Cu ] [Cl ] at 23 °C), but not its rate of oxidation, is proportional
23
acidity range examined.
The acidic site involved in the protonation equilibrium in this
system is uncertain. Our data are consistent with a pKA below
-2
-1
II
s
[Ge ]
I
-
[
0
.0 for Ge(II)-bound H2O, i.e., more than 4 units below that
-
to [Cl ]. Neither rate is acid-dependent.
II
17
for the related Sn (aq) unit (ca. 4). This is not unreasonable,
for the acidities of aqua-substituted cations within group 14 are
unusually sensitive to cationic size. On the other hand,
-
-3
At [Cl ] ) 0.8-1.0 M and [Ge(II)] > 3 × 10 M, decay
curves become exponential, and the unimolecular loss of
Ge(II) is negligible. Combinations of parameters k7, k6, and k8
17
protonation at the unshared electron pair of Ge(II) cannot be
excluded, since nucleophilic character associated with the
-
19
(
the latter two adjusted for [Cl ]-dependence), fit the observed
-
1
-1
curves only if an additional term (0.66 M s ) pertaining to
the uncatalyzed Ge(II)-Fe(III) reaction is included in the
integrated treatment. This noncomplementary redox change very
probably passes through Ge(III) as well. As expected, the initial
step is much slower than the Fe(III)-Ge(III) reaction (k7 ) 6
10 M s ). In analogy to the In(I,III) system, the s
intermediate should be much more strongly reducing than the
parent s cation.
Oxidations by I3 . Reactions of this oxidant were carried
24
analogous halide-ligated Sn(II) has been demonstrated.
The proposed rate-determining scission at Ge(II) (eq 10) is
25
not in accord with the general view that sluggish bond-
breaking at metal complexes in aqueous solution occurs only
when activation entails a substantial loss in ligand field
stabilization. There are, however, an array of reports of
2
-1 -1
20
1
×
26
measurably slow substitutions at centers such as Ti(III),
2
27
28
Zn(II), and Al(III), which are conventionally considered to
be substitution-labile. In addition, heterolysis (eq 10) may be
considered unusual since it involves loss of a ligand from a
tricoordinate species without compensation by attendant bond-
-
-
-
out in 0.01-0.50 M iodide to minimize dissociation of I3 (I3
-
-3
21
a I2 + I ; K ) 1.4 × 10 at 25°). In analogy with reported
-
22
speciations in Sn(II)-I systems, we would expect partial
making.
-
2-
conversion to GeI3 and GeI4 in the solutions taken.
Reactions of IrCl62- and PtCl62-. Reactions of both
With Ge(II) in excess, all profiles are linear (i.e., rates do
not vary with [I3 ]). Slopes are proportional to [Ge(II)], are
independent of [I ], and rise with [H ].
hexachloro-substituted oxidants were first-order each in the
participating redox species. Conversions of the Ir(IV) center
were run with Ge(II) in excess whereas transformations of
Pt(IV) were carried out with excess oxidant to minimize
complications resulting from formation of a Pt(II)-Ge(II)
-
-
+
Kinetic data are listed in Table 3. Within the ranges studied,
rates conform to binomial expression 9. Refinement yields k )
-1
-1 -1
(
4.5 ( 0.2) × 10-2
s
and k′ ) 0.70 ( 0.02 M s .
29
adduct. Results are summarized in Table 4.
Both reactions are seen to be accelerated by chloride, pointing
to the involvement of this anion in the activation processes.
II
- 0
+
rate ) [Ge ][I ] (k + k′[H ])
(9)
3
The most unusual feature of this system, the zero-order
(23) At even higher acidities, for which satisfactory data could not be
obtained by our methods, more marked (and, as yet, inexplicable)
acceleration was perceived.
-
dependence on I3 , requires that the oxidant enter the picture
only after a pair of competing slow steps, both involving just
the reductant. We are then almost certainly dealing with rate-
determining heterolyses of Ge(II) centers at different protonation
levels (the more protonated form the more reactive), yielding
one or more coordinatively unsaturated intermediates. Since this
(
24) See, for example: (a) Holt, M. S.; MacDougall, J. J.; Mathey, F.;
Nelson, J. H. Inorg. Chem. 1984, 23, 449. (b) Herbert, I. R.; Pregosin,
P. S.; Ruegger, H. Inorg. Chim. Acta 1986, 112, 29.
(
25) See, for example: Basolo, F.; Pearson, R. G. Mechanisms of Inorganic
Reactions, 2nd ed.; Wiley: New York, 1968, Chapter 3. These authors
summarize this view and offer specific warnings against its mis-
application.
(
(
20) Al-Ajlouni, A. M.; Gould, E. S. Res. Chem. Intermed. 1998, 24, 653.
21) Swift, E. H. A System of Chemical Analysis; Prentice-Hall: Englewood
Cliffs, NJ, 1940; p 69.
(26) (a) Thompson, G. A. K.; Sykes, A. G. Inorg. Chem. 1976, 15, 638.
(b) Birk, J. P. Inorg. Chem. 1975, 14, 1724.
(27) Paquette, G.; Zador, M. Inorg. Chim. Acta, 1978, 26, I.23.
(28) Dash, A. C.; Nanda, Inorg. Chem. 1973, 12, 2024.
(22) Haight, G. P., Jr.; Johansson, L. Acta Chem. Scand. 1968, 22, 961.

4122 Inorganic Chemistry, Vol. 39, No. 18, 2000
Babich and Gould
Table 4. Representative Kinetic Data for Oxidation of Germanium(II) with IrCl 2
-
2- a
and PtCl
6
6
II
2-
II
2-
6
A. Ge + IrCl
6
B. Ge + PtCl
4
II
[H+],
M
[Cl-],
M
-5
6
II
10-5[PtIV],
M
[H+],
M
[Cl-],
M
-2
2
10 k ,
M s
b
1
0 [Ge ],
M
10
M
k
2
-1
,
10 [Ge ],
M
-
1
-1 -1
s
2
7
5
5
.5
.5
.0
.0
1.00
1.00
0.50
0.50
0.50
0.80
0.50
0.50
0.50
0.40
0.40
0.40
0.50
0.50
0.40
0.20
0.60
0.80
1.96
2.04
2.06
2.6
16.0
7.5
4.0
8.0
8.0
8.0
8.0
8.0
9.9
6.8
2.7
5.4
5.4
5.4
5.4
5.4
1.00
1.00
1.00
0.75
0.50
1.00
1.00
1.00
1.00
1.00
1.00
1.99
1.00
0.75
0.50
0.25
9.5 (9.1)
8.7 (9.1)
9.3 (8.1)
9.3 (9.1)
8.3 (9.1)
7.9 (7.7)
6.3 (6.2)
4.6 (4.8)
1
5.0
2.4
5
5
4
4
.0
.0
.3
.3
2.02
0.92
2.9
3.8
a
). b Parenthetical values were calculated as (3.3 × 10 + 5.8 × 10 [Cl ]) M
2
2
-
-1
4 4
Reactions were carried out at 23.5 °C, µ ) 1.0 M (HClO /NaClO
1
s- (see text).
For the Ir(IV) reaction, which is very nearly first-order in halide,
-
2-
the Cl -related step is preponderant, whereas the PtCl6 data
conform to the binomial rate law (eq 13),
Alternatively, and perhaps additionally, reaction may occur
-
IV
II
by a series of 1e transfers, in which the initial Pt -Ge step
II
IV
-
rate ) [Ge ][Pt ](k + k [Cl ])
(13)
2-
1
2
(eq 16) is rate-determining. If, as in the IrCl6 reduction, the
Cl-
IV
II
III
III
where k1 ) (3.3 ( 0.4) × 10 M s-1 and k2 ) (5.8 ( 0.5) ×
2
-1
Pt + Ge
8 Pt + Ge
(16)
(17)
(18)
2
-2 -1
1
0 M s . The coordinatively saturated oxidants cannot
III
II
II
III
-
Pt + Ge f Pt + Ge
(rapid)
(rapid)
accommodate an additional Cl , nor is it reasonable that a
reaction between negatively charged redox partners be favored
electrostatically by a third anion. The “extra” chloride then is
almost certainly attached to the Ge(II) center where, in analogy
IV
III
III
IV
Pt + Ge f Pt + Ge
-
conversion to Ge(III) is favored at high [Cl ], it is reasonable
to associate the chloride-independent term in rate law 13 with
with our observations of the Ge(II)-Fe(III) system, it would
-
be expected to ease the formation of Ge(III).3
possibly reflects an increased conversion of GeCl3 to GeCl4
0,31
the indicated bridged path and the [Cl ]-proportional term to
This effect
the stepwise route 16-18 involving a Pt(III) intermediate.33
-
2-
,
In sum, this survey of the redox chemistry of Ge(II) tells us
which more closely resembles the probable Ge(III) intermediate
-
2
-
that this 2e donor, like its 5s counterpart, In(I), can partake
in single electron transactions, but only under more stringent
constraints. The coreagent should be a more powerful oxidant
and/or the reaction medium must be halide-rich to facilitate
initial conversion to Ge(III). The contrast is most vividly
illustrated in reactions with an array of Co(III) oxidants which
are reduced by In(I) (albeit sometimes slowly) but are inert to
Ge(II). A possible exception is the Co(III)-bound corrin, B12a;
(
GeCl4 ) and therefore may lower the Franck-Condon barrier
to the initial electron transfer act.
The reaction with IrCl62- (a 1e oxidant) must pass through
-
this odd-electron transient, but our exponential decay curves
exhibit no irregularities attributable to its formation or destruc-
1
tion, indicating that initial conversion to the s transient
III
-
(
designated noncommitally as Ge (Cl ), is rate-determining and
its further oxidation is kinetically silent, as is the case with an
-
array of reported reductions by In(I).11
2e reduction by Ge(II) may conceivably convert this to its
Co(I) analogue, B12s (cob(I)alamin), which is known to undergo
rapid comproportionation with B12a (Co + Co f 2Co ).
I
III
II 34
Cl-
IrIV
IrIV
II
II
-
III
-
IV
-
Ge y z Ge (Cl ) 8 Ge (Cl )
8 Ge (Cl ) (14)
rapid
Acknowledgment. We are grateful to Dr. Manik Ghosh, Dr.
Shawn Swavey, and Dr. Ksenija Namjesnik-Dejanovic for help
in experimental procedures and to Mrs. Arla McPherson for
technical assistance.
Two sequences come to mind for the reduction of PtCl62-.
-
The more direct is an inner-sphere 2e path proceeding via a
+
chlorine bridge and involving net transfer of chloronium (Cl )
IV
II
from Pt to Ge , in a manner similar to that demonstrated for
IC0004582
a number of Pt(II)-Pt(IV) systems.3
2
(
32) (a) Mason, W. R.; Johnson, R. C. Inorg. Chem. 1965, 4, 1258. (b)
(
(
(
29) For related behavior in Pt(II)-Sn(II) systems, see: Cramer, R. D.;
Basolo, F.; Morris, M. L.; Pearson, R. G. Discuss. Faraday Soc. 1960,
Jenner, E. L.; Lindsey, R. V., Jr.; Stolberg, U. G. J. Am. Chem. Soc.
29, 80.
III
1963, 85, 1691.
(33) Opinion is divided as to the likelihood of intervention of Pt species
in platinum redox chemistry. For differing views, see: (a) Glennon,
C. S.; Hand, T. D.; Sykes, A. G. J. Chem. Soc., Dalton Trans. 1980,
19. (b) Hindmarsh, K.; House, D. A.; van Eldik, R. Inorg. Chim. Acta
1998, 278, 32.
(34) Ryan, D. A.; Espenson, J. H.; Meyerstein, D.; Mulac, W. A. Inorg.
Chem. 1978, 17, 3725.
30) Evidence for analogous stabilization of a Sn(III) center in reactions
-
of Sn(II) with 1e oxidants has been presented. See, for example:
Wetton, E. A. M.; Higginson, W. C. E. J. Chem. Soc. 1965, 5890.
31) For a report of stabilization of Sn(III) and Ge(III) in S-ligated systems,
see: Glaser, T.; Bill, E.; Weyhermuller, T.; Meyer-Klauke, W.;
Wieghardt, K. Inorg. Chem. 1999, 38, 2632.