Use of73Ge NMR Spectroscopy and X-ray Crystallography for the Study of electronic interactions in substituted tetrakis(phenyl)-, -(phenoxy)-, and -(thiophenoxy)germanes

Article abstract of DOI:10.1021/om900905c

NMR chemical shifts of ¹H, ¹³C, and ⁷³Ge, molecular modeling, and single-crystal X-ray diffraction results are reported for a series of substituted tris- and tetrakis(phenyl)germanes of the type (XC₆H₄)₃GeY and (XC₆H ₄)₄Ge, where X = o-, m-, and p-OCH₃, o-, m-, and p-OC₂H₅, m- and p-CF₃, H, p-C(CH ₃)₃, p-Cl; and Y = Cl and H. Chemical shifts and X-ray data are also reported for o-CH₃ and o-OCH₃ tetrakis(phenoxy)- ((XC₆H₄O)₄Ge) and thiophenoxygermanes ((XC₆H₄S)₄Ge). For tetrakis derivatives, ⁷³Ge resonances are observed for all but the o-methoxyphenoxy compound, for which the inability to detect a resonance is attributed to rapid quadrupolar relaxation caused by intramolecular interactions of the methoxy oxygen with the central atom. The observation of a relatively broad, slightly upfield ⁷³Ge resonance in the analogous phenyl and thiophenoxy derivatives suggests, as do the results of molecular modeling, that in these compounds there is some hypercoordination. The solid-state structures show bond angles at the aromatic carbon bearing the alkoxy group that suggest an interaction of the alkoxy oxygen with germanium. Oxygen-germanium bond distances are about 17% shorter than the sum of the van der Waals radii.

Full text of DOI:10.1021/om900905c

582 Organometallics 2010, 29, 582–590
DOI: 10.1021/om900905c
Use of 73Ge NMR Spectroscopy and X-ray Crystallography for the Study
of Electronic Interactions in Substituted Tetrakis(phenyl)-, -(phenoxy)-,
and -(thiophenoxy)germanes
Claude H. Yoder,*,† Tamara M. Agee,† Allison K. Griffith,† Charles D. Schaeffer, Jr.,‡
Mary J. Carroll,‡ Alaina S. DeToma,‡ Adam J. Fleisher,‡ Cameron J. Gettel,‡ and
Arnold L. Rheingold§
†Department of Chemistry, Franklin and Marshall College, Lancaster, Pennsylvania 17604-3003,
‡Department of Chemistry and Biochemistry, Elizabethtown College, Elizabethtown, Pennsylvania 17022-
2298, and Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla,
California 92093-0314
§
Received October 14, 2009
NMR chemical shifts of 1H, 13C, and 73Ge, molecular modeling, and single-crystal X-ray diffraction
results are reported for a series of substituted tris- and tetrakis(phenyl)germanes of the type (XC6H4)3GeY
and (XC6H4)4Ge, where X = o-, m-, and p-OCH3, o-, m-, and p-OC2H5, m- and p-CF3, H, p-C(CH3)3,
p-Cl; and Y = Cl and H. Chemical shifts and X-ray data are also reported for o-CH3 and o-OCH3
tetrakis(phenoxy)- ((XC6H4O)4Ge) and thiophenoxygermanes ((XC6H4S)4Ge). For tetrakis derivatives,
73Ge resonances are observed for all but the o-methoxyphenoxy compound, for which the inability to
detect a resonance is attributed to rapid quadrupolar relaxation caused by intramolecular interactions of
the methoxy oxygen with the central atom. The observation of a relatively broad, slightly upfield 73Ge
resonance in the analogous phenyl and thiophenoxy derivatives suggests, as do the results of molecular
modeling, that in these compounds there is some hypercoordination. The solid-state structures show bond
angles at the aromatic carbon bearing the alkoxy group that suggest an interaction of the alkoxy oxygen
with germanium. Oxygen-germanium bond distances are about 17% shorter than the sum of the van der
Waals radii.
Introduction
The present study is designed to explore hypercoordina-
tion in ortho-substituted tetraphenyl-, tetraphenoxy-, and
tetrathiophenoxygermanes, where coordination of a basic
ortho site would generate a four-membered ring for the
phenyl derivatives and a five-membered ring for the phenoxy
and thiophenoxy analogues.
Our recent use of 73Ge NMR spectroscopy for the study of
intra- and intermolecular coordination to germanium uti-
lized symmetrical derivatives that contained a basic, poten-
tially coordinating site at the end of an aliphatic chain.1 The
73Ge resonance in these systems was found to be easily
observable for all derivatives except the dialkylaminoethyl
derivatives. The lack of an observable resonance was attrib-
uted to the perturbation of tetrahedral symmetry caused by
hypercoordination and the consequent rapid quadrupolar
relaxation. Our recent work indicates that the low-frequency
shifts that so nicely characterize hypercoordination in silicon
and tin are also observed with the quadrupolar 73Ge, though
with greater difficulty.1-3 When the extent of hypercoordi-
nation is insufficient to cause a significant low-frequency
shift, it may nevertheless produce considerable broadening
due to its effect on the symmetry of the electric field
surrounding the 73Ge nucleus.1
Results and Discussion
Syntheses and Characterization. Tetrakis(phenyl)germanes
were prepared by Grignard reaction of the appropriate
substituted phenyl bromide with GeCl4, while the tetrakis-
(phenoxy) and tetrakis(thiophenoxy) derivatives were pre-
pared by reaction of the substituted phenol or thiophenol with
GeCl4. The attempted syntheses of the tetrakis(o-ethoxy)-,
-(o-trifluoromethyl)-, -(m-methoxy)-, and -(m-ethoxy)phenyl
derivatives using the Grignard reagent with a 5-8 h reflux in
THF produced primarily the tris derivatives (XC6H4)3GeCl.
The use of the higher boiling solvent toluene and 30-40 h
reaction times afforded the tetrakis derivatives. In one attempt
(in THF using a 20% excess of magnesium to form the
Grignard reagent in 8 M excess relative to GeBr4, followed
by a 40 h reflux period and the usual ammonium chloride
hydrolysis workup), the tris(o-ethoxyphenyl) hydride was ob-
tained.
*To whom correspondence should be addressed. E-mail: claude.
yoder@fandm.edu.
(1) Yoder, C. H.; Agee, T. M.; Schaeffer, C. D., Jr.; Carroll, M. J.;
Fleisher, A. J.; DeToma, A. S. Inorg. Chem. 2008, 47, 10765–10770.
(2) Marsmann, H. C.; Uhlig, F. In The Chemistry of Organic Germa-
nium, Tin and Lead Compounds; Rappoport, Z., Ed.; Wiley-Interscience:
New York, 2002; Vol. 2, Chapter 6.
(3) Takeuchi, Y; Takayama, T. Annu. Rep. NMR Spectrosc. 2005, 54,
155–200.
The compounds were characterized by elemental analyses
(Experimental Section) and NMR data. Carbon-13 chemical
r
pubs.acs.org/Organometallics
Published on Web 01/11/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 3, 2010 583
Table 1. Carbon-13 NMR Chemical Shift Data (δ in ppm) for
these systems. Literature values of tetraphenylgermane8-10
and tetrakis(p-tolyl)germane10-12 are in excellent agreement
with those determined here, with the exception of the 141.5
ppm carbon-13 chemical shift reported for tetraphenylger-
mane by Batchelor et al.9 for C1 (both Vaickus et al.8 and
Phenylgermanesa
X
δ C1
δ C2
δ C3
δ C4
δ C5
δ C6
A. Tetrakis(phenyl), (X-C6H4)4Ge
Drager et al.10 report 136.2 ppm). Proton shifts are reported in
€
H
136.1
127.5
127.6
127.5
138.7
127.5
133.1
132.9
138.4
138.5
133.1
135.4
163.0
136.5
162.3
119.8
136.5
135.2
136.3
131.4
135.5
135.4
128.3
110.3
113.9
109.6
159.2
114.4
125.0
128.8
131.2
125.4
129.0
129.1
129.7
160.3
129.3
116.2
159.7
151.1
136.1
127.0
132.2
138.7
128.3
120.6
113.9
120.1
129.3
114.4
125.0
128.8
129.3
125.4
129.0
135.4
136.7
136.5
137.0
127.6
136.5
135.2
136.3
134.9
135.5
135.4
Table 2.
b
o-OCH3c
p-OCH3
o-OC2H5
m-OC2H5
p-OC2H5
p-C(CH3)3
p-Cl
m-CF3
p-CF3 j
p-CH3
Hypercoordination, 73Ge Resonances. Hypercoordination
at the central germanium was explored with 73Ge NMR data,
and structures were determined by X-ray diffraction. The
73Ge NMR shifts and half-height widths are reported in
Table 2, which shows relatively sharp resonances for all of
the tetrakis(phenyl)germanes. Only four of the 12 derivatives
have half-height widths greater than 33 Hz. Ten of these
derivatives have 73Ge shifts ranging from -25 to -33 ppm,
while the two ortho-alkoxy derivatives have more negative
shifts of -41.6 and -39.6 ppm for the methoxy and ethoxy,
respectively. Thus, the germanium resonance for both the
o-alkoxy phenyl compounds is shifted upfield (to lower
frequency) by 7-8 ppm relative to the other derivatives.
The increase in the width of the 73Ge peak for these derivatives
is noteworthy, but not large. This small shielding and increase
in width could be explained by coordination of the ortho
oxygen to the germanium in solution, and there is some
evidence (see below) for this interaction in the solid-state
structures.
d
e
f
g
h
i
B. Tris(phenyl), (X-C6H4)3GeCl
k
m-OCH3l
o-OC2H5
m-OC2H5
138.6
126.1
137.2
119.4
162.1
121.4
159.2
110.6
158.6
115.6
131.2
114.8
129.4
120.5
129.2
127.7
135.4
127.5
m
C. Tris(phenyl), (X-C6H4)3GeH
125.4 162.4 110.5 130.1
D. Tris(phenoxy), (X-C6H4O)3GeH
146.5 145.6 110.7 114.5
E. Tetrakis(phenoxy), (X-C6H4O)4Ge
n
o-OC2H5
120.4
120.1
136.7
121.4
o
o-OCH3
The tetrakis(ortho-methoxyphenoxy) derivative shows
no 73Ge resonance at either -40 or 20 °C. For comparison,
the resonance for the ortho-methylphenoxy derivative had a
half-height width of 94 Hz, and the ortho-methyl- and ortho-
methoxythiophenoxy derivatives both display 73Ge reso-
nances with half-height widths of 139 and 216 Hz, respec-
tively. The lack of an observable 73Ge resonance in the ortho-
methoxyphenoxy derivative can be attributed1 to interaction
of the ortho oxygen with germanium, which changes the
electric field gradient sufficiently to increase the relaxation
time and gives rise to a very broad and unobservable
resonance.
p
o-OCH3
o-CH3
146.6
153.1
145.6
129.1
110.7
131.1
114.5
123.1
120.0
126.8
121.3
119.2
q
F. Tetrakis(thiophenoxy), (X-C6H4S)4Ge
r
o-OCH3
o-CH3
119.2
128.8
159.3
143.0
110.6
128.5
129.0
130.4
120.4
126.2
136.1
137.0
s
a Chemical shift in CDCl3 relative to external TMS. C1: germanium-
bonded ring carbon, the ipso carbon. b OCH3, 55.2. c OCH3, 55.0.
d OCH2, 62.8; CH3, 13.9. e OCH2, 63.0; CH3, 14.6. f OCH2, 63.1; CH3,
14.8. g C, 34.6; C(CH3) 3, 31.3. h CF3, 124.0. |J(13C-19F)| coupling: C-3,
32.3; C-4, 3.7; CF3, 272.7 Hz; others, not detected. i CF3, 123.9.
|J(13C-19F)| coupling: C-3,5, 3.6; C-4, 32.5; CF3, 272.4 Hz; others,
not detected. j CH3, 21.4. Lit.10,12 values. k OCH3, 54.8. l OCH2, 63.4;
CH3, 14.2. m OCH2, 63.1; CH3, 14.7. n OCH2, 63.5; CH3, 14.4. o OCH3,
55.8. p OCH3, 55.7. q CH3, 16.1. r OCH3, 55.3. s CH3, 21.9.
Interestingly, the thiophenoxy compounds do exhibit 73Ge
resonances. The smaller extent of hypercoordination in the
thio derivatives is in agreement with our previous work with
the compound Ge(SCH2CH2N(CH3)2)4 and can be attrib-
uted to the lower acidity at germanium due to the lower
electronegativity of sulfur relative to oxygen and also to the
steric hindrance provided by the larger sulfur atoms sur-
rounding the germanium. Not surprisingly, a 73Ge resonance
could not be observed for the lower-symmetry tris deriva-
tives.
shifts for all derivatives are reported in Table 1, where the ipso
ring carbon is labeled C1. Assignments of 13C resonances were
based on (1) additivity relationships; (2) off-resonance proton-
coupled spectra; (3) comparison of 13C chemical shifts with
those reported in previous studies of substituted tert-butylben-
zenes,4 phenyltrimethylsilanes,4 phenyltrimethylgermanes,4,5
and phenyltrimethylstannanes;6,7 and (4) established trends
in magnitude of J(19F-13C) coupling constants in some of
Hypercoordination, Structures. Single-crystal X-ray dif-
fraction data for six tris- and tetrakis(germanes) are sum-
marized in Table 3 and presented as ORTEP diagrams in
Figures 1-6. The considerable number of previous X-ray
(4) Schaeffer, C. D., Jr.; Zuckerman, J. J.; Yoder, C. H. J. Organomet.
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(12) Schneider-Koglin, C.; Mathiasch, B.; Drager, M. J. Organomet.
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55, 97–110.
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23, 3835–3836.
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Imanari, M.; Deguchi, K.; Fujito, T.; Sugisaka, Y. Chem. Commun.
2000, 687–688.
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Reson. Chem. 2002, 40, 241–243.
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3852.
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hedron 1995, 14, 2429–2439. (b) Charissee, M.; Zickgraf, A.; Stenger, H.;
€
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Brau, E.; Desmarquet, C.; Drager, M.; Gerstmann, S.; Dakternieks, D.; Hook,
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584 Organometallics, Vol. 29, No. 3, 2010
Yoder et al.
Table 2. 1H and 73Ge Chemical Shifts and 73Ge Line Widths for Phenyl-, Phenoxy-, and Thiophenoxygermanes
X
1H aromatic (δ in ppm)a
1H other (δ in ppm)a
δ 73Ge (δ in ppm)b
Δν1/2 (Hz)c
A. Tetrakis(phenyl), (X-C6H4)4Ge
H
7.24-7.57
6.78-7.39
6.92-7.45
6.78-7.39
6.92-7.46
6.92-7.46
7.16-7.18
7.36
-33.0
-41.6
-27.1
-39.6
-31.1
-24.6
-29.5
-36.2
-30.4
-33.3
-32.9
-31.6
30
75
29
86
81
33
26
32
28
22
11
11
o-OCH3
p-OCH3
o-OC2H5
m-OC2H5
p-OC2H5
p-C(CH3)3
p-Cl
m-CF3
p-CF3
m-CH3
p-CH3
3.31, OCH3
3.82, OCH3
0.65, CH3; 3.65, OCH2
1.23, CH3; 5.55, OCH2
1.43, CH3; 4.05, OCH2
1.21, C(CH3) 3
7.57-7.77
7.58-7.69
d
d
B. Tris(phenyl), (X-C6H4)3GeCl
m-OCH3
o-OC2H5
m-OC2H5
6.83-6.88
7.49-7.51
7.00-7.36
3.41, OCH3
1.00, CH3; 3.89, OCH2
1.42, CH3; 4.02, OCH2
n.o.
n.o.
n.o.
n.o.
n.o.
n.o.
C. Tris(phenyl), (X-C6H4)3GeH
1.03, CH3; 3.87, OCH2; H, 5.78
D. Tris(phenoxy), (X-C6H4O)3GeH
3.76, OCH3; H, 5.73
o-OC2H5
o-OCH3
6.77-7.36
6.61-6.97
n.o.
n.o.
(-300)
(>1 ꢀ 104)
E. Tetrakis(phenoxy), (X-C6H4O)4Ge
o-CH3
o-OCH3
6.89-7.30
6.88-7.33
2.33, CH3
3.88, OCH3
-98.5
n.o.
94
n.o.
F. Tetrakis(thiophenoxy), (X-C6H4S)4Ge
o-CH3
o-OCH3
6.94-7.21
6.65-7.17
2.18, CH3
3.72, OCH3
98.0
92.4
139
216
a Chemical shift in CDCl3, relative to external TMS; n.o., not observed. b Chemical shift in CDCl3, relative to external tetramethylgermanium. cHalf-
height line width for 73Ge resonances. d Lit.32 e Germanium-73 shifts for tetraphenylgermane13-15,32 and several ortho-, meta-, and para-substituted
tetrakis(phenyl)germanes16,32 in solution and solid state have been reported.
˚
structural studies on tetraphenylgermanes and tetraphenyl-
stannanes17 indicates that most have crystallographic P 421c
(S4) symmetry.18 The molecules are approximately S4 with
four smaller (ca. 108-109°) and two larger bond angles
(ca. 110-111°) around the central atom (M). The phenyl
rings are twisted out of the plane of the C-M-C
plane, giving each phenyl3M group a propeller shape.19
Tetraphenylgermane has P 421c symmetry,18,20 while
tetrakis(p-tolyl)germane has the space group Pc.11,21,22 Tris-
(o-tert-butoxybenzyl)germane has space group P 1 with
distance of about 2.8 A, except when the substituent is
methyl or phenyl (the phenyl derivative is tetrahedral,
while the methyl derivative has one germanium-oxygen
˚
distance of 3.15 A and was described as monocapped
tetrahedral24).
The structures of the ortho-substituted tetrakis(phenyl)
derivatives studied in this work show P 1, P2(1)/n, or C2/c
crystallographic symmetry (Table 3). Table 4 summarizes
bond angles around germanium and alkoxy-oxygen
to germanium distances for these compounds. Tris-
(o-ethoxyphenyl)chlorogermane has two independent
molecules in the unit cell and therefore two different sets
of bond angles. The angles around germanium are close to
tetrahedral values with variations from 105° to 112° for all
but the tris(o-ethoxyphenyl)chlorogermane. The tetrakis-
(ortho-alkoxy) compounds have one angle at germanium
that is significantly larger than the average and one angle
that is significantly smaller. For example, for the o-meth-
oxyphenyl derivative the angles are 112.0°, 110.4°, 110.4°,
109.3°, 108.5°, and 106.3°. All of the ortho derivatives have
structures with the alkyl group of the ortho substituent
pointed away from the germanium, thereby placing the lone
pairs at oxygen in a position to interact with the germa-
nium. This orientation is not necessarily adopted because of
˚
three different Ge-O distances, two of which (3.2-3.3 A)
are about 10% shorter than the sum of the van der Waals
23
radii (3.62 A). A series of tris[(o-methoxymethyl)phe-
˚
nyl]germanes containing halogens, methyl, or phenyl on ger-
manium have been described as hypercoordinated trigonal-
bipyramidal structures with at least one germanium-oxygen
(17) Wharf, I.; Simard, M. G. J. Organomet. Chem. 1997, 532, 1–9.
(18) Chieh, P. C. J. Chem. Soc. A 1972, 1207–1208.
(19) Mackay, K. M. Structural Aspect of Compounds Containing
C-E (E = Ge, Sn, Pb) Bonds. In Chemistry of Organic Germanium, Tin
and Lead Compounds; Patai, S., Ed.; Wiley: New York, 1995; Vol. 1,
p 103.
(20) Chieh, P. C. J. Chem. Soc. A 1971, 3243–3245.
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(21) Charissee, M.; Gauthey, V.; Drager, M. J. Organomet. Chem.
1993, 448, 47–53.
(22) Schneider-Koglin, C.; Mathiasch, B.; Drager, M. J. Organomet.
€
Chem. 1994, 469, 25–32.
(23) Takeuchi, Y.; Yamamoto, H.; Tanaka, K.; Ogawa, K.; Harada,
J.; Iwamoto, T.; Yuge, H. Tetrahedron 1998, 54, 9811–9822.
(24) Sugiyama, Y.; Matsumoto, T.; Yamamoto, H.; Nishikawa, M.;
Kinoshita, M.; Takei, T.; Mori, W.; Takeuchi, Y. Tetrahedron 2003, 59,
8689–8696.

Article
Organometallics, Vol. 29, No. 3, 2010 585
an intramolecular interaction, but may be a result of the
steric requirements of groups relative to the rest of the
structure.
Another structural feature suggestive of hypercoordina-
tion is the presence of a smaller bond angle at the aromatic
carbon attached to the alkoxy oxygen toward the germanium
relative to the angle at the same atom away from the
germanium. For example, Figure 7 shows that in tetrakis-
(o-methoxyphenyl)germane the average angles at each of
the four aromatic carbons bearing the methoxy substitutent
are 114.9° and 123.6°, with the smaller angle being toward
the germanium. This is particularly interesting given the
Table 3. Crystal and Structural Refinement Data
(o-CH3OC6H4)4Ge
(o-C2H5OC6H4)4Ge
C32H36GeO4
557.20
100(2)
0.71073
formula
fw
T, K
C28H28GeO4
501.09
208(2)
0.71073
triclinic
P1
˚
wavelength, A
cryst syst
space group
monoclinic
C2/c
˚
a, A
8.5326(9)
8.8304(9)
16.6832(16)
80.6290(10)
82.1780(10)
89.6300(10)
1228.5(2)
2
13.6906(12)
12.5077(11)
16.1770(14)
90
92.7420(10)
90
2766.9(4)
4
1.338
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
V, A
Z
3
˚
d(calcd), g cm-3
abs coeff, mm-1
F(000)
1.355
1.278
1.142
1168
520
0.28 ꢀ 0.28 ꢀ 0.10
cryst size, mm
θ range, deg
index ranges
no. of reflns collected
no. of indep reflns
completeness to θ = 25°
abs corr
0.28 ꢀ 0.24 ꢀ 0.20
2.34-28.67
2.21-25.35
-11 e h e 10, -10 e k e 11, -22 e l e 22
16 960
-16 e h e 16, -15 e k e 15, -19 e l e 13
9388
5651 (R(int) = 0.0439)
99.7%
multiscan
2530 (R(int) = 0.0308)
100%
multiscan
transmn, max/min
ref method
no. of data/restr/params
goodness-of-fit on F2
final R indices [I > 2θσ(I)]
R indices (all data)
0.8828/0.7161
0.8038/0.7404
full-matrix least-squares on F2
5651/0/302
0.992
full-matrix least-squares on F2
2530/0/330
1.036
R1 = 0.0361, wR2 = 0.0806
R1 = 0.0535, wR2 = 0.0890
0.357 and -0.340
R1 = 0.0266, wR2 = 0.0612
R1 = 0.0329, wR2 = 0.0640
0.481 and -0.176
-3
˚
largest diff peak and hole, e A
(o-CH3OC6H4S)4Ge
(o-CH3C6H4S)4Ge
formula
fw
T, K
wavelength, A
cryst syst
C28H28GeO4S4
629.33
100(2)
1.54178
monoclinic
P2(1)/n
18.619(2)
7.7442(9)
19.302(2)
90
101.550(7)
90
2726.8(5)
C28H28GeS4
565.33
150(2)
0.71073
monoclinic
C2/c
7.414(2)
25.203(8)
14.182(4)
90
104.424(3)
90
2566.5(13)
˚
space group
˚
a, A
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
4
1.533
4.668
1296
4
1.463
1.535
1168
d(calcd), g cm-3
abs coeff, mm-1
F(000)
cryst size, mm
θ range, deg
index ranges
no. of reflns collected
no. of indep reflns
completeness to θ = 25°
abs corr
0.24 ꢀ 0.20 ꢀ 0.14
0.38 ꢀ 0.34 ꢀ 0.30
3.69-68.27
1.62-25.54
-22 e h e 22, -7 e k e 9, -22 e l e 22
11 692
4697 (R(int) = 0.0331)
97.6%
multiscan
-8 e h e 8, -30 e k e 30, -17 e l e 17
13 651
2367 (R(int) = 0.0541)
98.9%
multiscan
transmn, max/min
ref method
no. of data/restr/params
goodness-of-fit on F2
final R indices [I > 2θσ(I)]
R indices (all data)
0.6560/0.5932
full-matrix least-squares on F2
4697/0/339
1.098
R1 = 0.0374, wR2 = 0.0882
R1 = 0.0443, wR2 = 0.0910
0.617 and -0.430
full-matrix least-squares on F2
2367/0/152
1.027
R1 = 0.0243, wR2 = 0.0627
R1 = 0.0263, wR2 = 0.0644
0.445 and -0.289
-3
˚
largest diff peak and hole, e A

586 Organometallics, Vol. 29, No. 3, 2010
Yoder et al.
Table 3. Continued
(o-C2H5OC6H4)3GeH
(o-C2H5OC6H4)3GeCl
C24H27ClGeO3
471.50
formula
fw
T, K
C24H28GeO3
437.05
100(2)
100(2)
˚
wavelength, A
cryst syst
space group
0.71073
triclinic
P1
0.71073
triclinic
P1
˚
a, A
8.8594(8)
11.4220(9)
11.5301(9)
78.028(2)
80.456(2)
69.1880(10)
1061.48(15)
2
1.367
9.2445(10)
11.2180(12)
23.106(3)
94.474(2)
98.982(2)
106.334(2)
2252.5(4)
4
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
V, A
Z
3
˚
d(calcd), g cm-3
abs coeff, mm-1
F(000)
1.390
1.500
1.464
456
976
0.22 ꢀ 0.20 ꢀ 0.08
cryst size, mm
θ range, deg
index ranges
no. of reflns collected
no. of indep reflns
completeness to θ = 25°
abs corr
transmn, max/min
ref method
no. of data/restr/params
goodness-of-fit on F2
final R indices [I > 2θσ(I)]
R indices (all data)
0.33 ꢀ 0.10 ꢀ 0.08
1.81-28.26
1.91-28.31
-11 e h e 11, -15 e k e 15, -14 e l e 15
12 833
-11 e h e 12, -14 e k e 14, -30 e l e 30
18 495
4752 (R(int) = 0.0266)
99.5%
9722 (R(int) = 0.0249)
97.4%
multiscan
semiempirical form equivalents
0.8919/0.6436
0.8894/0.7337
full-matrix least-squares on F2
4752/0/257
1.052
full-matrix least-squares on F2
9722/0/523
1.036
R1 = 0.0388, wR2 = 0.0996
R1 = 0.0452, wR2 = 0.1040
0.595 and -0.316
R1 = 0.0425, wR2 = 0.0952
R1 = 0.0571, wR2 = 0.1020
0.981 and -0.340
-3
˚
largest diff peak and hole, e A
Figure 2. Thermal ellipsoid diagram of tetrakis(o-ethoxyphe-
nyl)germane with 50% probability.
Figure 1. Thermal ellipsoid diagram of tetrakis(o-methoxyphe-
nyl)germane with 50% probability.
mean angles at the same atom reported for tetrakis-
(o-methylphenyl)germane.25 In the o-methyl case the angle
closest to the germanium is the larger one, with a mean of
123.0°, relative to the angle of 118.3° away from the germa-
nium. These two angles (along with a widening of the angle at
the ipso carbon on the side of the methyl group) were
attributed to steric repulsions between the germanium and
methyl.25 The angles at the aromatic carbon bearing the
methoxy group are therefore suggestive of movement of the
methoxy oxygen toward the germanium, presumably to
strengthen the dative interaction to that atom.
Figure 3. Thermal ellipsoid diagram of tetrakis(o-methoxythio-
phenoxy)germane with 50% probability.
(25) Belsky, V. K.; Simonenko, A. A.; Reikhsfeld, V. O. J. Organo-
met. Chem. 1984, 265, 141–143.

Article
Organometallics, Vol. 29, No. 3, 2010 587
Table 4. XRD Data for Tetrakis(phenyl)germanium Compounds
average
Ge-O
R-Ge-R bond Ge-O
anglesa (R = C distance distance
˚
(A)
˚
(A)
compound
or O, deg)
112.04(9)
tetrakis-
(o-methoxyphenyl)Ge
2.963(2) 3.001(2)
110.40(9)
110.36(9)
109.29(9)
108.45(9)
106.29(9)
111.48(14)
2.996(2)
3.011(2)
3.032(2)
tetrakis-
(o-ethoxyphenyl)Ge
2.918(7) 2.984(7)
109.65(14)
109.60(13)
109.49(15)
108.79(14)
107.77(14)
112.31(3)
2.967(7)
3.016(7)
3.034(7)
Figure 4. Thermal ellipsoid diagram of tetrakis(o-methylthio-
phenoxy)germane with 50% probability.
tetrakis-
(o-methoxythiophenoxy)Ge
3.167(4) 3.334(4)
110.41(3)
110.13(3)
109.32(3)
109.29(3)
105.29(3)
111.4(8)
3.278(4)
3.341(4)
3.551(4)
tris-
(o-ethoxyphenyl)GeH
2.978(3) 2.994(3)
111.43(10)
110.85(10)
108.94(10)
107.8(8)
2.992(3)
3.013(3)
106.2(8)
tris-
(o-ethoxyphenyl)GeCl
114.32(12),
112.81(11)
114.13(12),
112.17(12)
110.50(12),
111.76(11)
107.21(9),
110.62(8)
105.47(9),
105.24(8)
104.25(10),
103.70(9)
2.950(3), 3.002(4),
2.871(4) 2.944(4)
2.983(3),
3.013(4)
3.073(3),
2.948(4)
Figure 5. Thermal ellipsoid diagram of tris(o-ethoxyphenyl)-
germane with 50% probability.
a For the last two compounds, bond angles are R-Ge-H and
R-Ge-Cl, respectively.
Figure 7. Average angles at the aromatic carbon bearing the
methoxy group in tetrakis(o-methoxyphenyl)germane.
Figure 6. Thermal ellipsoid diagram of tris(o-ethoxyphenyl)-
chlorogermane with 50% probability.
The argument for weak hypercoordination at germanium
is also supported by the results of our DFT calculations
(Table 5), which are in good agreement with the X-ray
structural data for tetrakis(o-methoxyphenyl)germane.
The DFT results for the o-methoxyphenoxy derivative
The bond distances shown in Table 4 for the o-methoxy
and o-ethoxy derivatives are less than the sum of the van der
Waals radii26 of 3.63, but not sufficiently small (the sum of
covalent radii27 is 1.86) to suggest a strong interaction
between the oxygen and germanium.
˚
suggest the presence of two bonds of about 2.2 A in length
with angles that may indicate five- or six-coordination.
Hence, it seems reasonable to conclude that there may be
weak hypercoordination in the tetrakis- and tris(ortho-
alkoxyphenyl) derivatives that leads to slightly broader 73Ge
NMR line widths, and stronger hypercoordination for
(26) Mantina, M.; Chamberlin, A. C.; Valero, R.; Cramer, C. J.;
Truhlar, D. G. J. Phys. Chem. A 2009, 113, 5806–5812.
(27) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.;
Echeverria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans.
2008, 2832–2838.

588 Organometallics, Vol. 29, No. 3, 2010
Table 5. DFT Calculations for o-Methoxy(tetrakisphenyl)-, -(phenoxy)-, and -(thiophenoxy)germanes
Yoder et al.
R-Ge-R angle (deg)
(R = C, O, or S)
˚
compound
O-Ge distances (A)
tetrakis(o-methoxyphenyl)Ge
109.7, 109.8, 109.0,
108.9, 109.8, 109.7
88.6, 96.2, 98.4, 104.0,
115.6, 154.2
103.6, 105.4, 108.1,
111.9, 113.6, 114.1
3.00, 3.00, 3.00, 3.00
2.20, 2.22, 2.85, 4.42
2.86, 2.89, 2.94, 2.97
tetrakis(o-methoxyphenoxy)Ge
tetrakis(o-methoxythiophenoxy)Ge
Table 6. 13C and 73Ge NMR Chemical Shift Regression Analysis
Parameters for para-Substituted Tetrakis(phenyl)germanes
correlation
ra
F (ppm/σ)b
C (ppm)b
Sc
nd
δ 13C, C1 vs σ
δ 13C, C1 vs σR
δ 13C, C4 vs σ
δ 13C, C4 vs σR
δ 73Ge vs σ
0.778
0.999
0.723
0.909
0.730
0.761
10.49
20.17
132.87
136.34
143.36
133.21
-30.92
-33.49
2.789
0.201
9.839
5.947
2.976
2.822
7
7
7
7
7
7
o
o
-31.24
-58.84
-9.63
o
δ 73Ge vs σR
-15.06
a Correlation coefficient. Normal Hammett σ constants (ref 28a)
except where noted (σRo: ref 28b). b Variables of the equation δ = Fσ þ
C. c Standard deviation of residuals. d Number of compounds. e We
employ the reported10 CDCl3 13C chemical shift values for tetrakis-
(p-tolyl)germane (Table 1) and the 73Ge solution chemical shifts deter-
mined32 for tetrakis(m-tolyl)- and tetrakis(p-tolyl)germane (Table 2) in
the Hammett correlations.
tetrakis(o-methoxyphenoxy)germane that produces a 73Ge
line width sufficiently broad to preclude observation of the
resonance. The difference in degree of hypercoordination
between the phenyl and phenoxy derivatives can be attrib-
uted to the steric accommodation of dative bonding as the
“ring” size changes from four- to five-membered.
Substituent Effects. As part of our continuing interest in
electronic effects in group 14 compounds, we have also
explored the effects of substituents on the NMR chemical
shifts of the tetrakis(phenyl) compounds. The 13C chemical
shifts of the ipso carbon (C1) for the substituted tetrakis-
(phenyl)germanes are 4-6 ppm lower than the shifts for the
ipso carbons of the analogous substituted phenyltrimethyl-
germanes.5 For example, the 13C chemical shift of the ipso
carbon of (C6H5)4Ge is 136.1 ppm, whereas the analogous
shift for C6H5Ge(CH3)3 is 142.5 ppm. The same effect has
been observed in the homologous tin compounds17 and can
probably be attributed to electron release to Ge or Sn
brought about by substitution of phenyl for methyl.
Table 6 displays the results of regression analyses for the
13C and 73Ge chemical shifts of para-substituted phenyl
derivatives versus Hammett σ28a and Taft σR° constants.28b
In general, the correlation coefficients for the regression of
the carbon shifts versus normal Hammett constants were
similar to those reported previously for the substituted
phenyltrimethylgermanes but significantly lower for the
germanium shifts.5 Use of σR° gave a good correlation for
the C1 chemical shifts of the seven tetrakis(para-phenyl)
derivatives (Figure 8). The good correlations with the reso-
nance parameter σR° is consistent with the report of similar
correlations with the (tetrakis)tin homologues.17 Attempts
to improve the correlations with other parameters such as σI
were unsuccessful (r < 0.76). The presumed influence of
Figure 8. Hammett plot of 73Ge chemical shifts vs σR° for para
derivatives.
resonance effects on the C1 and 73Ge shifts may be related to
the apparent electron-releasing effect of the phenyl groups as
substituents on germanium.
Experimental Section
Materials and Methods. All syntheses were performed under
an argon atmosphere in glassware dried in an oven at 110 °C.
Commercial solvents and reagents were first dried with Drierite
˚
and subsequently stored over Linde 4 A molecular sieves.
Tetrahydrofuran (THF) was dried over molecular sieves and
then distilled from calcium hydride under an argon atmosphere
prior to use. Tetrachlorogermane and tetraphenylgermane were
purchased from Gelest and were used without further purifica-
tion. Melting points were determined on a Thomas-Hoover
capillary apparatus and are uncorrected. Schwarzkopf Micro-
analytical Laboratory, Woodside, NY, and Galbraith Labora-
tories, Knoxville, TN, performed elemental analyses. Purity of
all compounds probably exceeds 95% as indicated by the
absence of spurious resonances in the 1H and 13C NMR spectra.
Syntheses. Substituted tris- and tetrakis(phenyl)-, (phenoxy)-,
and (thiophenoxy)germane derivatives investigated in this study
were obtained by one of two standard procedures (Scheme 1):
(1) reaction of the Grignard reagent, prepared from magnesium
turnings and the appropriately substituted phenyl bromides
(Sigma Aldrich; used as received) in dry THF, with tetrachloro-
or tetrabromogermane (Gelest; used as received), followed by
5-8 h reflux, hydrolysis with saturated aqueous ammonium
chloride solution, extraction of the aqueous layer with three
small portions of THF, drying of the combined extracts over
anhydrous magnesium sulfate, removal of THF under vacuum,
and recrystallization twice from absolute ethanol or acetonitrile;
(2) reaction of the substituted phenol or thiophenol (Sigma
Aldrich) with GeCl4 in dry THF using triethylamine to scavenge
the liberated hydrogen halide, followed by a 5-8 h reflux,
(28) (a) Hansch, C.; Leo, A. Subsituent Constants for Correlation
Analysis in Chemistry and Biology; Wiley: New York, 1979. (b) Exner,
O. A. Critical Compilation of Substituent Constants. In Correlation Analysis
in Chemistry: Recent Advances; Chapman, N. B., Shorter, J., Eds.; Plenum:
New York, 1978; Chapter 10.

Article
Scheme 1. Illustrative Preparations of Substituted Tetrakis-
(phenyl)germanes
Organometallics, Vol. 29, No. 3, 2010 589
Tetrakis(o-ethoxyphenyl)germane. This tetrakis compound
was secured from a 10:1 Grignard to GeCl4 ratio with replace-
ment of THF with toluene (vide supra). Yield: 1.4 g (10%), mp
216-220 °C (lit.33 254-255 °C). Anal. Calcd for C32H36GeO4:
C, 68.98; H, 6.51. Found: C, 68.66; H, 6.64. Some attempts
to prepare the tetrakis derivative resulted in isolation of
tris(o-ethoxyphenyl)chlorogermane. Yield: 0.8 g (ca. 50%), mp
111-113 °C. Anal. Calcd for C24H27ClGeO3: C, 61.14; H, 5.77.
Found: C, 61.91; H, 6.38.
Tris(o-ethoxyphenyl)germane. In a second attempt to synthe-
size tetrakis(o-ethoxyphenyl)germane, tris(o-ethoxyphenyl)germane
was recovered. Yield: 0.4 g (25%), mp 119-122 °C. Anal. Calcd
for C24H28GeO3: C, 65.95; H, 6.46. Found: C, 66.12; H, 6.90.
Tetrakis(p-tert-butylphenyl)germane. From p-BrC6H4-t-C4H9
(12.79 g, 0.060 mol), Mg (1.61 g, 0.066 mol), GeCl4 (3.22 g,
0.015 mol). Yield: 1.5 g (17%), mp 297-301 °C (lit.31 mp 350 °C
(dec)).
filtration of triethylamine hydrochloride, removal of solvent
under vacuum, and recrystallization of solid products. Reacting
quantities for typical Grignard preparations are presented in the
following order: identity and amount of reacting substituted
phenyl bromide, amount of reacting magnesium turnings, iden-
tity and quantity of germanium tetrahalide, yield in grams and
percent. Reaction amounts for the phenoxides and thiophen-
oxides appear in the following order: identity and amount of
reacting substituted phenol or thiophenol, quantity of triethyl-
amine, identity and quantity of germanium tetrahalide, yield in
grams and percent. Pure product yields ranged from 10% to
50% and were frequently determined from multiple prepara-
tions using varying conditions. Carbon-13 and proton and
germanium-73 NMR data for the derivatives appear in Tables 1
and 2, respectively.
Tetrakis(p-trifluoromethylphenyl)germane. From p-BrC6H4-
CF3 (12.83 g, 0.057 mol), Mg (1.53 g, 0.063 mol), GeCl4 (3.06 g,
0.014 mol). Yield: 1.4 g (15%), mp 170-172 °C (lit.29 mp 173-
174 °C). Anal. Calcd for C28H16F12Ge: C, 51.50; H, 2.47.
Found: C, 50.91; H, 2.42.
Tetrakis(m-trifluoromethylphenyl)germane. From m-BrC6H4
CF3 (30.60 g, 0.136 mol), Mg (3.63 g, 0.150 mol), GeCl4 (7.30 g,
0.034 mol). Yield: 6.0 g (27%), mp 119-120 °C. Anal. Calcd for
C28H16F12Ge: C, 51.50; H, 2.47. Found: C, 50.63; H, 2.59.
Tetrakis(p-methoxyphenyl)germane. From p-BrC6H4OCH3,
(5.24 g, 0.028 mol), Mg (0.75 g, 0.031 mol), GeCl4 (1.51 g,
0.0070 mol). Yield: 0.7 g (20%), mp 175-176 °C (lit.30 mp 218-
222 °C; lit.31 mp not given; lit.32 mp 157-163 °C).
Tetrakis(m-methoxyphenyl)germane. From m-BrC6H4OCH3
(5.24 g, 0.028 mol), Mg (0.75 g, 0.031 mol), GeCl4 (1.51 g, 0.0070
mol). Yield: 0.6 g (17%), mp 158-161 °C. Anal. Calcd for
C28H28GeO4: C, 67.11; H, 5.63. Found: C, 63.71; H, 5.49.
Tetrakis(o-methoxyphenyl)germane. This tetrakis derivative
was secured from a modification30 of the standard procedure in
which THF was replaced with toluene by distillation after
formation of the Grignard reagent, followed by a 30 h reflux
period, from o-BrC6H4OCH3 (2.99 g, 0.016 mol), Mg (0.43 g,
0.018 mol), and GeCl4 (0.86 g, 0.0040 mol). Yield: 0.4 g (20%),
mp 188-190 °C (lit.30 mp 168-170 °C; lit.34 mp 213-214 °C).
Anal. Calcd for C28H28GeO4: C, 67.11; H, 5.63. Found: C,
67.71; H, 5.87.
Tetrakis(p-chlorophenyl)germane. From p-BrC6H4Cl (12.25 g,
0.064 mol), Mg (1.72 g, 0.070 mol), GeCl4 (3.43 g, 0.016 mol).
Yield: 1.0
g (12%), mp 153-157 °C. Anal. Calcd for
C24H16Cl4Ge: C, 55.56; H, 3.11. Found: C, 54.89; H, 3.41.
Tetrakis(o-methylphenoxy)germane. From o-HOC6H4CH3
(12.61 g, 0.1167 mol), (C2H5)3N (12.07 g, 0.1193 mol), GeCl4
(6.38 g, 0.029 mol). Yield: 3.1 g (20%), undistillable amber-
colored oil. Anal. Calcd for C28H28GeO4: C, 67.10; H, 5.63.
Found: C, 68.54; H, 6.91.
Tetrakis(o-methoxyphenoxy)germane. From o-HOC6H4OCH3
(5.00 g, 0.043 mol), (C2H5)3N (4.56 g, 0.0451 mol), GeCl4 (2.14 g,
0.010 mol). Yield: 2.9 g (20%), undistillable amber-colored oil.
Anal. Calcd for C28H28GeO8: C, 59.51; H, 4.99. Found: C, 61.16;
H, 5.52.
Tris(o-methoxyphenoxy)germane. Employing the synthetic
conditions for the tetrakis derivative but with diethyl ether as
reaction solvent and a 3 h reflux period produced the tris
germanium hydride. Yield: 1.5 g (15%), undistillable amber-
colored oil. Anal. Calcd for C21H22GeO6: C, 56.93; H, 5.01.
Found: C, 56.94; H, 5.52.
Tetrakis(o-methylthiophenoxy)germane. From o-HSC6H4OCH3
(4.93 g, 0.0397 mol), (C2H5)3N (4.16 g, 0.0411 mol), GeCl4 (2.16 g,
0.0101 mol). Yield: 3.5 g (50%), mp 83-85 °C. Anal. Calcd for
C28H28GeS4: C, 59.48; H, 4.99. Found: C, 59.49; H, 5.11.
Tetrakis(o-methoxythiophenoxy)germane. From o-HSC6H4OCH3
(5.12 g, 0.036 mol), (C2H5)3N (3.64 g, 0.036 mol), GeCl4 (2.00 g,
0.093 mol). Yield: 1.9 g (36%), mp 94-96 °C. Anal. Calcd for
C28H28GeO4S4: C, 53.40; H, 4.48. Found: C, 53.23; H, 4.58.
1
NMR Spectra. H and 13C NMR spectra were obtained on
Varian UNITY 300 MHz and INOVA 500 MHz spectrometers
using conditions described previously.1,5 Samples were con-
tained in 5 mm o.d. tubes. Proton chemical shifts were refer-
enced to the chloroform-d residual solvent line set to the TMS-
based chemical shift 7.24 ppm. Carbon chemical shifts were
referenced to the 13C centerline in CDCl3, taken as 77.0 ppm.
(33) Lapkin, I. I.; Dumler, V. A.; Ponosova, E. S. Zh. Obshch. Khim.
1971, 41, 133–135.
Tetrakis(p-ethoxyphenyl)germane. From p-BrC6H4OC2H5
(30.56 g, 0.152 mol), Mg (4.07 g, 0.167 mol), GeCl4 (8.14 g,
0.038 mol). Yield: 3.2 g (15%), mp 102-108 °C. Anal. Calcd for
C32H36GeO4: C, 68.98; H, 6.51. Found: C, 68.38; H, 6.46.
Tetrakis(m-ethoxyphenyl)germane. From m-BrC6H4OC2H5
(20.91 g, 0.104 mol), Mg 2.78 g, 0.114 mol), GeCl4 (5.66 g,
0.026 mol). Yield: 2.5 g (17%), mp 70-72 °C. Anal. Calcd for
C32O4H36Ge: C, 68.98; H, 6.51. Found: C, 68.40; H, 6.86.
(34) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
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Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
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Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
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Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
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Gonzalez, C.; and Pople, J. A. Gaussian 03, Version 4.1.2; Gaussian, Inc.:
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590 Organometallics, Vol. 29, No. 3, 2010
Yoder et al.
Probe temperature was 20 °C for the UNITY and 23 °C for
Molecular Modeling. Optimized geometries of selected mole-
cules were calculated using the Gaussian 03 program34 (Version
4.1.2) with density functional theory using the B3PW91 func-
tional and either the 6-31G or 3-31G basis sets. Ten to 13
starting conformations with the alkoxy in varying positions
were used to determine a global minimum.
1
the INOVA instruments. H chemical shifts are believed to be
reproducible to (0.03 ppm; 13C shifts to (0.05 ppm. Germa-
nium-73 NMR spectra were obtained on a Varian INOVA 500
MHz instrument fitted with a Low Gamma broadband probe
(
103Rh-15N, VT 500 NB) with samples contained in 10 mm o.d.
tubes. Instrumental parameters for 73Ge on the INOVA in-
cluded a transmitter frequency of 17.42 MHz, sweep width
of 100 000 Hz, pulse delay of 0 s, and acquisition time of 0.1 s.
The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence
(refocusing delay, 0.0001 s) was used to reduce baseline roll.
This pulse sequence was found to give peak widths within ca. 5%
of those obtained using the standard pulse sequence up to peak
widths of ca. 800 Hz. Germanium-73 chemical shifts were
referenced to external tetramethylgermane 20% in CDCl3 by
substitution and were constant to within (0.1 ppm based on
repeated observations of a constant sample during the course of
several days. Nevertheless, because of the greater line widths
associated with most of the 73Ge resonances, we estimate the
error as ca. (0.5 ppm. Samples for 73Ge NMR spectra were
prepared using 300-400 mg amounts dissolved in 3 mL of
CDCl3; 1H and 13C spectra were recorded using the same
solutions.
Substituent Constant Correlations. Normal Hammett σ con-
stants28a and Taft σR° values28b were taken from the literature.
Acknowledgment. The authors are indebted to the
National Science Foundation for an MRI grant support-
ing the acquisition of a Varian INOVA 500 MHz NMR
spectrometer, to Anne and Scott Moore for the Moore
Mentorship Award, to Blake Pepinsky for the Pepinsky
Research Award, to Fredrick G. Schappell for the
Shappell Research Award, and to William and Lucille
Hackman for the Hackman Endowment. The authors
also acknowledge the support of the E. Jane Valas Fund
(to A.S.D. and C.J.G.), contributions of Alexandra R.
Pagano and Professor Jeffrey A. Rood (Elizabethtown
College), and Eugene P. Mazzola (Food and Drug Ad-
ministration/Joint Institute for Food Safety & Applied
Nutrition and University of Maryland).
X-ray Crystallographic Analyses. Crystallographic data are
summarized in Table 4 and in the Supporting Information.
Where space group choices were possible, the centrosymmetric
alternative was shown to be correct by the results of refinement.
Data were collected at -173 °C with a Bruker D8 platform
diffractometer equipped with an APEX CCD detector. All non-
hydrogen atoms were refined with anisotropic thermal para-
meters, and H atoms were treated as idealized contributions. All
software was contained in the Bruker-AXS libraries (Bruker-
AXS, Madison, WI).
Supporting Information Available: X-ray crystallographic
data including CIF files for tetrakis(o-methoxyphenyl)germane,
tetrakis(o-ethoxyphenyl)germane, tetrakis(o-methoxythiophe-
noxy)germane, tetrakis(o-methylthiophenoxy)germane, tris(o-
ethoxyphenyl)germane, and tris(o-ethoxyphenyl)chloroger-
mane are available free of charge via the Internet at http://
pubs.acs.org.