Ba21Ge2O5H24 and Related Phases. A Corrected Structure Type and Composition for a Zintl Phase Stabilized by Hydrogen

Article abstract of DOI:10.1021/ic971339y

Syntheses of the so-called suboxide phases Ba₂₁T₂O₅ (T = Ge, Si, Ga, In, Tl) are achieved only in the presence of hydrogen. The heavy-atom structure of Ba₂₁Ge₂O₅H₂₄ at room temperature was redetermined by single-crystal X-ray diffraction and found to be primitive trigonal symmetry (P3₁21 (No. 152), Z = 6, a = 14,4227(5) ?, c = 35.332(3) ?) instead of the previously refined cubic (Fd3?m) result. The change greatly improves the heavy-atom parameters. Twenty-four independent deuterium atoms have also been located by time-of-flight neutron diffraction, The structure contains Ba²⁺ cations, and three different types of monatomic anions. corresponding to the oxidation states (Ba⁺²)₂₁(Ge^-4)₂(O^-2) ₅(H^-)₂₄. The deuterium atoms occupy tetrahedral, square-pyramidal, and octahedral barium interstices while the oxide anions lie in nearly regular octahedral barium polyhedra. The germanide anions are surrounded by 12 barium atoms in a distorted icosahedral configuration. Property measurements show that Ba₂₁Ge₂O₅H₂₄ is diamagnetic and is a semiconductor (or insulator). The analogues Ba₂₁Tr₂O₅H_x, Tr = Ga, In, Tl, are isotypic with the heavy-atom structure of the title phase and presumably contain 22 hydride ions.

Full text of DOI:10.1021/ic971339y

1
892
Inorg. Chem. 1998, 37, 1892-1899
Ba21Ge2O5H24 and Related Phases. A Corrected Structure Type and Composition for a
Zintl Phase Stabilized by Hydrogen
Baoquan Huang and John D. Corbett*
1
Ames LaboratorysDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011
ReceiVed October 22, 1997
Syntheses of the so-called “suboxide” phases Ba21T2O5 (T ) Ge, Si, Ga, In, Tl) are achieved only in the presence
of hydrogen. The heavy-atom structure of Ba21Ge2O5H24 at room temperature was redetermined by single-crystal
X-ray diffraction and found to be primitive trigonal symmetry (P3121 (No. 152), Z ) 6, a ) 14.4227(5) Å, c )
3
5.332(3) Å) instead of the previously refined cubic (Fd 3h m) result. The change greatly improves the heavy-atom
parameters. Twenty-four independent deuterium atoms have also been located by time-of-flight neutron diffraction.
The structure contains Ba cations, and three different types of monatomic anions, corresponding to the oxidation
2+
+
2
-4
-2
-
states (Ba )21(Ge )2(O )5(H )24. The deuterium atoms occupy tetrahedral, square-pyramidal, and octahedral
barium interstices while the oxide anions lie in nearly regular octahedral barium polyhedra. The germanide anions
are surrounded by 12 barium atoms in a distorted icosahedral configuration. Property measurements show that
Ba21Ge2O5H24 is diamagnetic and is a semiconductor (or insulator). The analogues Ba21Tr2O5Hx, Tr ) Ga, In,
Tl, are isotypic with the heavy-atom structure of the title phase and presumably contain 22 hydride ions.
Introduction
phases have been relatively ignored because contamination of
the metal by hydrogen has often gone unrecognized, largely
7
The formation, stoichiometry, and structure of barium-rich
compounds formed by the triel (Tr) (group 13) and tetrel (Tt)
because it is generally not “seen” by X-ray diffraction.
Recently, we reported on a series of Zintl phases of the alkaline-
(14) main-group elements have been controversial and incom-
8
earth metals that are stabilized by hydrogen: Ba5Ga6H2, Ae3-
plete. In 1966, Bruzzone first studied the three binary Ba-Tr
9
TtH2 (Ae ) Ca, Yb; Tt ) Sn, Pb), Ae5Pn3H (Pn ) As, Sb,
(
Tr ) Ga, In, Tl) phase diagrams and found a new family of
7,10
Bi) (“Yb5Sb3”-type), and Ae5Tt3H (Tt ) Si, Ge, Sn, Pb) and
the interesting phases that he believed to be Ba10-12Ga, Ba13In,
1
1 12
Sr5Tl3H (stuffed Cr5B3 or La5Pb3O-type ). Here we present
both the syntheses of the five compounds Ba21Tt2O5H24 (Tt )
Ge, Si) and Ba21Tr2O5Hx (Tr ) Ga, In, Tl, x ∼ 22), in which
hydrogen is an essential component, and the corrected structure
of Ba21Ge2O5H24 as determined by X-ray single-crystal and
neutron powder diffraction means.
and Ba13Tl, respectively.2 The first structure in this family was
3
determined by film methods in 1979 by Fornasini and Merlo
to be cubic Ba10Ga (Fd 3h m), which they believed to be isotypic
with Al10V. In 1995, five Ba21M2O5 compounds (M ) Ge,
4
5
Si, Zn, In, Tl ) were reported by R o¨ hr to have a cubic structure
quite similar to that of Ba10Ga. However, one cation type in
the refined structures of the first two members showed quite
large ellipsoids. This group of compounds is intriguing since
the so-called “suboxides” appear to have extraordinarily high
electron excesses.
Experimental Section
Syntheses. Sublimed barium (Aldrich-APL, 99.9%) and calcium
(
APL Engineered Materials, 99.99%), their hydrides, and the products
of the present studies are very sensitive to air and moisture, and they
were therefore handled only in He- or N -filled gloveboxes (H O < 1
On the other hand, correctly characterized compounds formed
between active alkaline-earth metals (Ae) and main-group
elements often conform to simple Zintl-Klemm valence rules
2
2
ppm vol). Binary barium and calcium hydrides were prepared from
the respective metals by reaction with hydrogen (600 Torr, Matheson,
99.999%) at 800 °C for 12 h. Their Guinier X-ray powder patterns
showed only the binary hydrides were present. Barium oxide was
prepared by decomposition of barium carbonate (Baker, 99.8%) for
6
in which the latter elements achieve octet valence states.
Therefore, it was considered possible that these “unusual”
compounds might be stabilized by additional impurities. Oxy-
gen contamination in Zintl phases is relatively easily recognized
because of its relatively high X-ray scattering power. On the
other hand, hydrogen components in many alkaline-earth metal
-
5
2
4 h in an open Ta container under a dynamic vacuum (e10 Torr)
at 1000 °C. Its Guinier X-ray pattern showed only the presence of
BaO. The other elements used were Aesar Ge (5-9’s), electronic grade
Si, Johnson-Matthey Ga and Tl, and Cerac In (5-9’s). All other
syntheses reported in this article were carried out in welded Ta
containers.
(
1) This research was supported by the Office of the Basic Energy
Sciences, Materials Sciences Division, U.S. Department of Energy.
Ames Laboratory is operated by Iowa State University under Contract
No. W-7405-Eng-82.
(7) Leon-Escamilla, E. A.; Corbett, J. D. J. Alloys Compd. 1994, 206,
L15.
(8) Henning, R. W.; Leon-Escamilla, E. A.; Zhao, J.-T.; Corbett, J. D.
Inorg. Chem. 1997, 36, 1282.
(
2) Bruzzone, G. J. Less-Common Met. 1966, 11, 249. See also: Massalski,
T. B., Ed. Binary Alloy Phase Diagrams, 2nd ed.; ASM Interna-
tional: Materials Park, OH, 1990.
(3) Fornasini, M. L.; Merlo, F. ReV. Chim. Miner. 1979, 16, 458.
(4) R o¨ hr, C. Z. Anorg. Allg. Chem. 1995, 621, 1496.
(5) R o¨ hr, C. Z. Kristallogr., Suppl. Issue No. 9, 1995, 24.
(6) Kauzlarich, S., Ed. Chemistry, Structure and Bonding in Zintl Phases
and Ions; VCH: New York, 1996.
(9) Huang, B.; Corbett, J. D. Inorg. Chem. 1997, 36, 3730.
(10) Leon-Escamilla, E. A.; Corbett, J. D. J. Alloys Compd. 1998, 265,
104.
(11) Guloy, A.; Corbett, J. D. Z. Anorg. Allg. Chem. 1992, 616, 61.
(12) Leon-Escamilla, E. A. Ph.D. Dissertation, Iowa State University, 1996.
S0020-1669(97)01339-6 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/25/1998

Ba21Ge2O5H24 and Related Phases
Inorganic Chemistry, Vol. 37, No. 8, 1998 1893
3
Ba21Ge
reactions of BaH
2
O
5
H
24. At the beginning, this compound was obtained from
Table 1. Lattice Dimensions (Å, Å ) of Isotypic Ba21
Phases, T ) Ge, Si, Ga, In, Tl
2 5 22-24
T O H
2
, BaO, and Ge in a sealed system at 1100 °C for 4 h
-
1
followed by slow cooling at 20 °C h . Excess Ge was needed for an
otherwise high-yield synthesis, perhaps because the ground Ge particles
did not completely react with BaH
prereaction of Ge with Ba and BaO solves this problem. The Ba, BaO,
and Ge in an overall proportion Ba21Ge (total amount: 250-500
mg) were welded in a Ta container under Ar that was in turn placed in
fused-silica tubing and connected to a high-vacuum source (e10
Torr). The assembly was heated at 1100 °C for 4 h to remove impurity
hydrogen and to allow Ge to react completely with Ba metal and BaO
to form Ba
container was then charged with hydrogen to 600-700 Torr, held there
for 1 h (presumably to form BaH ), then heated to 1100 °C, and held
there for 8 h (under H ) followed by cooling at 20 °C h . A parallel
reaction under high vacuum and without H gave a mixture of Ba
GeO, BaO, and Ba. The final quaternary product had a shiny black
color, was extremely sensitive to air, and gave a powder pattern that
appeared to be single phase and to be in complete agreement with that
calculated for the refined structure.
cubic cella
trigonal cellb
compd
Ba21Ge
(Fd 3h m, Z ) 8)
1
(P3 21, Z ) 6)
2
and BaO. It was later found that
O
2 5
H
24
a ) 20.3971(5)
V ) 8486.0(6)
a ) 20.398(9)
V ) 8487(7)
a ) 20.388(1)
V ) 8474(1)
a ) 20.3951(8)
V ) 8483.7(9)
a ) 20.383(10)
V ) 8469(7)
a ) 20.4659(9)
V ) 8572(1)
a ) 20.52(1)
V ) 8640(8)
a ) 20.715(1)
V ) 8888(2)
a ) 20.760
a ) 14.4227(5), c ) 35.332(3)
V ) 6364.6(5)
2 5
O
“
Ba21Ge
2
O
5
”c
-
5
Ba21Ge
O
2 5
D
24
a ) 14.415(1), c ) 35.322(6)
V ) 6356(1)
a ) 14.4207(8), c ) 35.331(4)
V ) 6363.0(7)
Ba21Si
2 5
O H
24
1
3
-1
3
GeO, and it was then cooled at 40 °C h to 600 °C. The
c
“Ba Si O ”
21
2
5
2
-
1
2
Ba21Ga
O
2 5
H
22
a ) 14.4704(8), c ) 35.456(5)
V ) 6429.6(8)
2
3
-
“
Ba10Ga”d
Ba21In
2 5
O H
22
a ) 14.649(1), c ) 35.870(8)
V ) 6665(1)
“
Ba21In
2
O
5
”e
Ba21Ge
but with D
2
O
5
D
24. The deuteride was prepared in the same manner
V ) 8947
2
instead of H and double reactions. Three Ta containers
2
Ba21Tl
2 5
O H
22
a ) 20.6510(8)
V ) 8807(1)
a ) 20.681
a ) 14.6026(9), c ) 35.767(5)
V ) 6605.0(9)
were each loaded with 4.0 g of the appropriate mixture and treated as
above. However, the deuteride product sought contained a small
amount of unreacted materials. Therefore, the samples were transferred
to new Ta containers which were welded and sealed again in fused
silica, and the assembly was preheated to 300 °C under high vacuum
to dehydrate the silica jacket somewhat. The systems were then charged
with deuterium to 600-700 Torr, heated to 1100 °C, held there for 8
e
“Ba Tl O ”
21
2
5
V ) 8845
a
Guinier data for present results (λ ) 1.540 562 Å, 22 °C). b The
equivalent trigonal cell data refined from the same Guinier pattern.
2 5 2 5 x
The tuned trigonal data for Ba21Ge O H24 and Ba21Ga O H on the
diffractometer differed by e3σ. c Reference 4. Reference 3. Refer-
d
e
-
1
h, and cooled to room temperature at a rate of 40 °C h . The main
product was Ba21Ge 24 (>90%), but BaD (Co Si-type) (<5%) and
Ba GeO (<5%) were also observed. Evolved water is possibly
responsible for the oxide impurity because of the lack of a thorough
baking of the SiO in the second step. An 8.5 g mixture of the three
ence 5.
2 5
O D
2
2
3
the germanium compound were indexed on the basis of both the cubic
and trigonal single-crystal structure solutions, and the lattice parameters
were refined for each by least-squares methods from 16 to 20 indexed
2
samples was sealed under He into a gasketed vanadium cylinder with
an inner diameter of 10 mm for the neutron diffraction experiment.
2
2 5 x
θ data. The structures of other Ba21T O H phases (above) were so
established by powder data to be isotypic with the cubic pseudocell of
the Ge compound, which generally cannot be distinguished from the
correct trigonal structure by Guinier means. Cubic and trigonal lattice
parameters similarly refined from the same Guinier film data are
summarized in Table 1 for the loaded compositions along with literature
data for the evidently equivalent ternary compositions. In no case did
A Ta container was loaded with ∼1 g of this Ba21Ge
welded under Ar, and then heated to 1100 °C under high vacuum for
h followed by cooling to room temperature. The X-ray pattern of
the product showed only Ba GeO, BaO, and Ba.
(T ) Si, Ga, In, Tl). Two Ta containers were used in
the preparation of each compound. The first was loaded with Ba metal,
BaO, and T (total ∼250 mg) at the composition Ba21 . The second
Ta tube was charged with CaH
2 5
O D24 product,
4
3
2 5 x
Ba21T O H
the trigonal lattice constants deviate significantly from the cubic
equivalents, c/a ) 61
/2
.
T O
2 5
2
(∼40 mg) and Sn (∼120 mg). The
X-ray Single-Crystal Diffraction. Crystals of the germanium phase
were sealed in thin-walled capillaries and checked for singularity by
Laue photographs. Room-temperature data were collected from one
on a Rigaku AFC6R rotating-anode diffractometer (Mo KR radiation,
graphite monochromator). Twenty-five centered reflections located and
centered by a random search starting at 2θ ∼ 12° were used for a
preliminary assessment of the symmetry. One relatively strong
reflection in this orientation set indicated a primitive trigonal unit cell,
a symmetry that was also confirmed by subsequent precession
photographs (hk0 to hk2) taken with Ni-filtered Cu KR radiation. All
other diffractometer reflections were deleted, and 49 new ones were
located starting at 2θ ∼ 20° in order to obtain a better orientation matrix.
Diffraction data were measured in an ω-2θ scan mode for 2θ < 55°.
Intensities of three standard reflections measured every 150 reflections
during the data collection did not change significantly. Analyses of
the intensity characteristics indicated a 3h m1 Laue symmetry and a
variety of trigonal space groups. The trigonal setting is responsible
two containers were each welded under Ar and sealed together in a
carefully flamed silica jacket under high vacuum. The double
containers were slowly heated to 1100 °C at the rate of 40 °C h
kept there for 4 h, and slowly cooled to room temperature. The reaction
process may perhaps be as follows: Ba reacts with Si, Ga, In, or Tl
and BaO in the first container at a low to intermediate temperature,
-
1
,
the CaH
intermediate temperature, and the H
>500 °C) to form the quaternary hydride. The amounts of CaH
5 2 5 22
loaded were to give compositions Ba21Si O H24 and Ba21Tr O H ,
2
-Sn reaction produces H
2
(plus CaSn) in the second at an
2
diffuses into the other Ta container
(
2
2
respectively. The final products had shiny black colors and were
extremely sensitive to air. Their Guinier patterns were very similar to
that of Ba21Ge O H24 and showed the yields to be about 90%. Heating
2 5
the Ga, In, and Tl hydride products under a high vacuum at 1100 °C
gave mixtures of BaO, Ba, and unknown phases.
Structural Studies. Guinier patterns were obtained from ground
samples to which NIST silicon (a ) 5.43088 Å) had been added as an
internal standard. These were mounted between pieces of cellophane
tape and measured with the aid of an Enraf-Nonius Guinier camera,
Cu KR radiation (λ ) 1.540 56 Å). The Guinier films were measured
for about 10% of the total observed reflections (at 3σ
The trigonal structure was solved by direct methods via SHELXS.
I
).
1
6
The atomic positions and thermal parameters were refined with the
TEXSAN17 package on a VAX station. Assignment of the space group
was made through comparisons of the results obtained in various
primitive trigonal space groups. Those with a centering or mirror
operation were excluded without complications by the direct methods
14
with a computer-controlled microdensitometer, and data were analyzed
by the program SCANPI to obtain the peak positions. Patterns of
1
5
(
13) Huang, B.; Corbett, J. D. To be published.
(14) Johansson, K. E.; Palm, T.; Werner, P. E. J. Phys. E: Sci. Instrum.
(16) Sheldrick, G. M. SHELXS-86. Universit a¨ t G o¨ ttingen, Germany, 1986.
(17) TEXSAN, Version 6.0; Molecular Structure Corp.: The Woodlands,
TX, 1990.
1980, 13, 1289.
(15) Malmros, G.; Werner, P.-E. Acta Chem. Scand. 1973, 27, 493.

1
894 Inorganic Chemistry, Vol. 37, No. 8, 1998
Huang and Corbett
Table 3. Powder Neutron Data Collection and Refinement
Table 2. Selected Single-Crystal X-ray Data Collection and
Refinement Parameters for Ba21Ge
a
2
O
5
H
24
2 5 24
Parameters for Ba21Ge O H
-
1
fw
space group; Z P3
temp, °C 22
3133.30
µ, cm (Mo Ka)
204.84
, % 8.5, 11.7
temp, °C
23
scattering
2), R
), R
b
for I > 3σ
lengths (10-12 cm)b
1
21; 6 R(F
R(F
o
w
I
c
o
w
for I>3σ
I
, %
7.4, 6.4
no. of data
no. of reflns
5103
11 476
; Rwp 4.66; 6.95
Ba
Ge
O
0.525
0.819
0.581
0.6674
3
dcalc, g/cm
4.894
a
residuals, %: R
p
a
b
2
2
2
Lattice dimensions in Table 1. R ) ∑||F
o
| - |F
c
| |/∑|F
o
| ; R
w
2
ø
4.74
D
2
2
2
2
2
1/2
-2
c
)
[∑w(|F
|; R
o
| - |F
c
|) /∑w(F
o
) ] ; w ) σ
F
.
R ) ∑||F
o
| - |F
c
||/
2
2
1/2
-2
a
- I
c o
)2/∑wI 2]1/2. b Reference
∑
|F
o
w
) [∑w(|F
o
| - |F
c
|) /∑w(F
o
) ] ; w ) σ
F
.
R
p
) (∑|I
o
- I
c
|)/∑I
o
; Rwp ) [∑w(I
o
2
0.
results and by preliminary refinements which gave unusually large
thermal parameters for Ba and high residuals. The remaining space
In subsequent refinements, the Ba and Ge positions in the title phase
groups were P321 (No. 150), P3
1
21 (No. 152), and P3
2
21 (No. 154).
were held fixed at the more accurate values from the single-crystal
X-ray study. The groups of Ba, Ge, and O atoms were each constrained
to have a fixed isotropic parameter, and likewise, for the two distinct
groups of deuterium, D1-D12 and D13-D24, and these refined well.
The space group P3 21 for the crystal selected was proven by the
1
successful refinements. Absorption corrections were found to be crucial
for this system because both Ba and Ge are strong absorbers of Mo
-
1
KR radiation (µ ) 204.8 cm ). The corrections were carried out
according to ψ-scan curves for 10 strong reflections at different θ values
and, after isotropic convergence, by DIFABS which gave lower R’s
2 3
Two impurity phases, BaD and Ba GeO, were also observed, and their
proportions, lattice parameters, and positional parameters were included
in the refinement; their relative amounts were found to be 4.4(3) and
5.1(2)% (by weight), respectively. The background function was a
cosine Fourier series with 12 coefficients. Refinements of the phase
fractions, background coefficients, and lattice and atomic parameters
for the three phases diverged. Therefore, we separately refined the
variables in two parts. The first included D and O positions, their
collective thermal parameters, and the lattice parameters of the main
phase, and the second, the remaining variables. These were cycled
several times and essentially converged. The variables in the final cycle
were positions of five oxygen and 24 deuterium atoms, five group
thermal parameters, and two cell dimensions. The final conventional
18
and smaller U’s. The trigonal structure, including 24 hydrogen atoms
with fixed positions obtained from subsequent neutron diffraction
2
studies, was refined on F
o
by full-matrix least-squares methods with
2
2
3
716 reflections with F
o
> 1.0σ(F
) ) 11.7, R
about 45% of the observed data fell in the region 1.0σ < F
o
) and 108 variables. The relatively
2
high residuals (R(F
o
w
) 12.6) resulted from the fact that
2
o
< 3.0σ.
Thermal motion was restricted to isotropic since we felt that there were
not enough strong primitive reflections for anisotropic refinement. The
2
2
2
conventional residual factors (%) for those with F
o
o
> 3σ(F ) are R(F )
)
8.2, R ) 11.0% and R(F) ) 7.2, R ) 6.3%. Some X-ray single-
w
w
crystal data collection and refinement parameters are listed in Table 2.
More details are given in the Supporting Information which, together
with F /F tables etc., are also available from J.D.C.
o c
p
agreement indices were R ) 4.66% and Rwp ) 6.95% with a reduced
ø of 4.74. Some neutron data collection and refinement parameters
are listed in Table 3.
2
Neutron Powder Diffraction. The atomic parameters and displace-
ment amplitudes of hydrogen and oxygen were established with the
aid of neutron powder diffraction data collected at room temperature
overnight on the Special Environment Powder Diffractometer (SEPD)
at the Intense Pulsed Neutron Source (IPNS) facility at Argonne
National Laboratory. The SEPD is a time-of-flight powder diffracto-
meter with multidetector arrays at fixed scattering angles. For this
structural refinement, the high-resolution data from the 2θ ) 144.8°
backscattering detector bank were used. The powder data were refined
The neutron diffraction pattern in Figure 1 shows the raw intensity
data and, from top to bottom, the background, the individual contribu-
tions from the refined Ba21Ge O D24 and the impurities BaD and Ba -
2 5 2 3
GeO with tick marks for the reflections included, and the difference
between calculated and observed intensity profiles.
Physical Property Measurements. The electrical resistivity of Ba -
21
Ge O H was measured by the electrodeless high-frequency “Q”
2
5
24
method.21 A fractionated ground sample with an average particle
diameter around 340 µm was isolated and mixed with chromatographic
Al O in order to reduce contact between the sample particles. The
1
9
by the Rietveld method with the PC version of the General Structure
2
3
2
0
Analysis System (GSAS) by Larson and Von Dreele. The final
refinement included data in the range 0.60 Å < d < 4.0 Å (5103 profile
points, 11 476 reflections).
mixture was loaded into a glass ampule and sealed under a vacuum.
The Q measurements were made at 35 MHz over 100-295 K with
readings every 15°. The magnetic susceptibility data were measured
at 3 T over the range 6-300 K on a Quantum Design MPMS SQUID
magnetometer. A special fused-silica container was used such that a
50-mg sample was held between the faces of two fixed silica rods.
The assembly was evacuated, backfilled with He, and sealed. Data
were corrected for container and core diamagnetism.
At the beginning, attempts were made to locate deuterium positions
in the face-centered-cubic cell (i.e., R o¨ hr’s model). Two D positions
were found: D1 (96g) atoms in square-pyramidal barium polyhedra
and D2 (96g) filling tetrahedral cavities. However, the Ba3 and D2
atoms had unusually large displacement amplitudes, i.e., Uiso) 0.12
2
2
Å for Ba3 and 0.25 Å for D2. Subsequently, we focused on a solution
of the primitive trigonal structure to resolve the thermal parameter
Results and Discussion
2 5
troubles. Since the Ba and Ge framework in Ba21Ge O was well
established from the single-crystal X-ray study, D positions were located
by successively placing a trial atom in an empty barium polyhedron,
optimizing the Ba-D distances by the program ATOM 4.0, and then
allowing either the temperature factor or the occupancy for each atom
to refine. (Several still-larger cavities near Ba21 and Ba22 were also
Syntheses. The compound Ba21Ge2O5H24 and its deuteride
are synthesized in high yields by 1100 °C reactions of Ba, BaO,
and Ge with H (D ) under a pressure of 600-700 Torr followed
2
2
by slow cooling under the same gas pressure. Substantially all
of the H2 uptake occurs at the higher temperatures. The same
reaction run at 1100 °C but under high vacuum gives only Ba
2
tested, but these all gave large ellipsoids (>0.4 Å ) or near-zero or
negative occupancies.) Twenty-four 6-fold D sites were so found: D1-
D12 atoms (D1 in the cubic model), occupying the relatively larger
square-pyramidal or octahedral holes formed by Ba, and D13-D24
atoms (D2 in the cubic model), filling the barium tetrahedra. Note
that these are direct descendants of all 2 × 96 cubic sites since the
primitive trigonal cell is 75% as large.
13
metal, BaO, and the new Ba3GeO. The analogous compounds
of Si, Ga, In, and Tl are again obtained only in the presence of
hydrogen; reactions in a vacuum produce only BaO, Ba, and
unidentified phases.
Alkaline-earth metals contaminated with oxygen are easily
recognized because their white oxides usually appear only on
the surface of metals and can be readily detected by X-ray
diffraction. Of course, the monoxides can be removed by
(18) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(19) Rietveld, H. M. Acta Crystallogr. 1967, 22, 151.
(20) Larson, A. C.; Von Dreele, R. B. General Structure Analysis System;
Report LAUR 86-748; Los Alamos National Laboratory: Los Alamos,
NM, 1995.
(21) Zhao, J.-T.; Corbett, J. D. Inorg. Chem. 1995, 34, 378.

Ba21Ge2O5H24 and Related Phases
Inorganic Chemistry, Vol. 37, No. 8, 1998 1895
Figure 1. Neutron powder pattern of Ba21Ge
pattern with fitted background; the calculated patterns for the major and impurity BaD
2
O
5
D
24 divided into two regions, d ) 0.6-1.6 and 1.6-4.0 Å. From top to bottom: the experimental
2 3
and Ba GeO phases and the locations of the reflections used
(tick marks); the difference spectrum on the same scale.
distillation without complications because of their relatively high
melting points and very low volatilities or decomposition.
However, the possibility of hydrogen contamination has been
relatively ignored. The problem arises largely because of the
ready diffusion of hydrogen (from metal-water reactions) into
the metal in the solid solution (R) region where it is not directly
discerned by X-ray techniques (except via small lattice constant
changes). (In addition, good powder pattern data of these metals
may be difficult to obtain by some methods even when hydride
has precipitated.) The commercially available distilled alkaline-
earth metals were at one time estimated to contain at least 5-20
atom % H for Ca-Ba, respectively,22 and our experiences
Information. The compound is, to our knowledge, the first
example of a Zintl phase stabilized by two types of nominal
impurity anions. It also represents a novel structure.
The structure has a surprising complexity. It can be grossly
described, to begin with, as a composite of two spherical-like
components A and B, each of which is shown in Figure 2. The
only proper symmetries are 2-fold axes normal to c and parallel
to a or b, and only two Ge and two Ba atoms lie on these. In
the A unit, a centering O4 atom (the cubic O2) is surrounded
by six Ba atoms (the cubic Ba2) in an octahedral configuration.
This Ba6O unit is tetrahedrally fused twice through shared faces,
once to four more O1,2,3,5-centered Ba octahedra and once to
four Ge-centered Ba icosahedra. These eight O and Ge atoms
form a strongly deformed cube, the larger Ge atoms lying further
from the cube center and the starting O4 atom. Each of the
four Ba octahedra in the outer tetrahedron is twice trigonally
capped by three Ge and by three D atoms (D1-D12), the last
face in each being capped by D atoms that lie in tetrahedral
interstices in unit B (below). The distorted icosahedral poly-
hedron of Ba that surrounds each Ge is connected to three outer
Ba6O octahedra by face-sharing. Unit A has approximately Td
symmetry.
7
,10,12
support these qualitatively, barium being the worst.
Further, the hydrogen in these metals is not easily removed by
the usual distillation as the evolved H2 is readily reabsorbed by
the condensate. The permeability of Ta to hydrogen above
about 500 °C is a useful property to accomplish the purification
although, alternatively, the hydrogen can also be removed in
high vacuum just below the temperature at which sublimation
starts.10
Structural Description. The structure of Ba21Ge2O5H(D)24
was refined from both X-ray single-crystal and neutron powder
diffraction data collected at room temperature. The final atomic
coordinates, the isotropic-equivalent temperature factors, and
their estimated standard deviations for the 22 Ba, 3 Ge, 5 O,
and 24 D atoms in the independent unit are listed in Table 4.
Important distances are given in Table 5, except that those within
the Ba polyhedron about each D are contained in the Supporting
In the less regular unit B (Figure 2B), the centering Ba13
(cubic Ba4) is surrounded by 12 D atoms in an irregular
configuration. This deuterium polyhedron is in turn surrounded
by 16 barium atoms in the form of an approximate tetracapped
truncated tetrahedron (Frank-Kasper 16). The entire barium
polyhedron in B, unshielded by deuterium atoms, is illustrated
in Figure 3 with the Ba5 (×2), Ba21, and Ba22 atoms that cap
(22) Peterson, D. T. J. Met. 1987, 39, 20; private communication, 1992.

1896 Inorganic Chemistry, Vol. 37, No. 8, 1998
Huang and Corbett
Table 4. Atomic Coordinates and Isotropic Thermal Parameters
2
(
×100 Å ) for Ba21Ge
2
5 24
O D
Wykoff
atoma
site
x
y
z
U
b
U
iso
c
iso
Ba1
Ba2
Ba3
Ba4
Ba5
Ba6
Ba7
Ba8
Ba9
Ba10
Ba11
Ba12
Ba13
Ba14
Ba15
Ba16
Ba17
Ba18
Ba19
Ba20
Ba21
Ba22
Ge1
Ge2
Ge3
O1
O2
O3
O4
O5
D1
D2
D3
D4
D5
D6
D7
D8
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
3b
3a
6c
3b
3a
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
6c
0.0045(9) 0.3904(8) 0.1117(3) 1.2(2) 0.58(5)
0.068(1) 0.073(1) 0.4404(4) 1.7(2)
0.067(1) 0.3288(9) 0.4441(3) 1.6(2)
0.1539(7) 0.241(1) 0.0837(3) 1.5(2)
0.1541(8) 0.4752(8) 0.3216(2) 3.5(2)
0.1558(7) 0.2445(8) 0.2625(3) 0.8(2)
0.1763(9) 0.494(1) 0.0217(2) 1.3(2)
0.191(1) 0.0416(6) 0.0196(2) 1.5(1)
0.2355(8) 0.4094(8) 0.1698(3) 1.4(2)
0.2482(8) 0.1551(7) 0.1672(3) 0.9(2)
0.2770(8) 0.6678(8) 0.2251(3) 0.6(2)
0.284(1) 0.661(1) 0.1110(4) 3.6(3)
0.3361(9) 0.337(1) 0.3750(1) 1.1(1)
0.3397(7) 0.0792(7) 0.4375(3) 1.1(2)
0.4145(8) 0.2408(8) 0.0788(2) 1.3(2)
0.423(1) 0.239(1) 0.2558(2) 2.1(2)
0.5027(7) 0.4164(8) 0.1687(3) 0.6(2)
0.508(1) 0.150(1) 0.3538(4) 2.6(3)
0.5842(8) 0.0869(7) 0.2513(3) 0.5(2)
0.5894(9) 0.0897(9) 0.0675(2) 1.7(2)
0.6337(5)
0.139(1)
0
0
5/6
1/3
2.9(2)
2.8(3)
0.500(2) 0.162(2) 0.1643(5) 0.8(2) 1.0(1)
0.156(2)
0.662(2)
0
0
5/6
1/3
1.7(6)
1.4(2)
1
0.209(5) 0.077(4) 0.0921(18)
0.215(5) 0.457(6) 0.0938(18)
0.328(4) 0.324(5) 0.2176(16)
0.329(4) 0.331(5) 0.1282(12)
0.545(5) 0.132(6) 0.4245(17)
0.005(5) 0.284(6) 0.0453(18)
0.000(6) 0.047(5) 0.0411(21)
0.073(5) 0.211(6) 0.5009(18)
0.132(5) 0.536(6) 0.1713(20)
0.129(6) 0.541(6) 0.4244(20)
0.208(6) 0.458(6) 0.4966(17)
0.207(6) 0.460(6) 0.2450(21)
0.208(7) 0.082(6) 0.2406(20)
0.374(5) 0.049(6) 0.0470(19)
0.400(6) 0.058(6) 0.2877(19)
0.611(6) 0.266(6) 0.2887(20)
0.605(6) 0.282(6) 0.0461(23)
0.012(5) 0.511(5) 0.0116(14)
0.089(6) 0.566(6) 0.0770(12)
0.109(6) 0.567(6) 0.2619(12)
0.140(6) 0.324(6) 0.3772(20)
0.134(7) 0.153(6) 0.3719(20)
0.224(5) 0.284(6) 0.4422(21)
0.269(6) 0.389(7) 0.3172(19)
0.321(6) 0.528(6) 0.3735(24)
0.334(5) 0.163(4) 0.3297(18)
0.420(7) 0.305(5) 0.4356(20)
0.476(6) 0.381(6) 0.3103(20)
0.523(6) 0.330(6) 0.3679(22)
0.5(2)
2
2.4(1)
D9
D10
D11
D12
D13
D14
D15
D16
D17
D18
D19
D20
D21
D22
D23
D24
2
3.9(1)
a
Heavy-atom positions are from X-ray data refinement of the protide;
the oxygen and deuterium parameters come from neutron data refine-
b
ment. X-ray study: refined isotropic displacements or fixed values
Figure 2. Building spheres that make up the Ba21Ge
2 5
O D24 structure.
c
used for groups of atoms. Isotropic values refined from neutron data
for the five groups of atoms (Ba, Ge, O, 5- and 6-coordinate D,
-coordinate D).
(A) the O4-centered “hard” component; (B) the “soft” Ba13-centered
deuteride component with surrounding cations. (C) The A,B composite
that makes up the structure. (Primes represent spheres rotated by
horizontal 2-fold axes.) Key: Ba, large open circles; Ge, large shaded
circles; D, small shaded circle; O, hidden.
4
the truncated tetrahedron shaded. The polyhedron defined by
the last four atoms, which are the troubled Ba3 in the cubic
model, is well centered by Ba13, but the edges of the large
tetrahedron now range from 6.73 to 7.70 Å. The symmetry of
the deuterium polyhedron within is very low (C1).
To generate the overall structure in terms of these spheres,
Figure 2C, pairs of A, A′ units are linked along bc via a shared
Ge3 atom that lies on a 2-fold axis, and these are connected to
the B units in the same string by common trigonal Ba6-Ba16-
Ba20 basal faces. Likewise, units B and B′ share the Ba21
atom on a 2-fold axis. Because this structure has a pseudocubic
symmetry, similar connection patterns can be found in three
other orientations. The more nearly horizontal connections
between A and B units are accomplished by 12 deuterium atoms
(D1-D12) in A that lie outside the surface of B and the

Ba21Ge2O5H24 and Related Phases
Inorganic Chemistry, Vol. 37, No. 8, 1998 1897
2 5 24
Table 5. Important Distances (Å) around Ba, Ge, and O Atoms in Ba21Ge O D
Ba1-D14
Ba1-D15
Ba1-D4
Ba1-D1
Ba1-D7
Ba1-D4
Ba1-O2
Ba1-Ge2
Ba2-D17
Ba2-D18
Ba2-D8
Ba2-D2
Ba2-D3
Ba2-D3
Ba2-O1
Ba2-Ge2
Ba3-D16
Ba3-D18
Ba3-D3
Ba3-D6
Ba3-D9
Ba3-D5
Ba3-O1
Ba3-Ge1
Ba4-D1
Ba4-D2
Ba4-O4
Ba4-O2
Ba4-O1
Ba4-Ge2
Ba4-Ge3
Ba5-D19
Ba5-D13
Ba5-D24
Ba5-D15
Ba5-D20
Ba5-D7
Ba5-D1
Ba5-D16
Ba5-D23
Ba6-D19
Ba6-D1
Ba6-D2
Ba6-D7
Ba6-D8
Ba6-O3
Ba6-Ge2
Ba7-D13
Ba7-D20
Ba7-D14
Ba7-D12
Ba7-D11
Ba7-D1
Ba7-D9
Ba7-O2
2.51(6)
2.69(7)
2.73(7)
2.80(7)
2.80(7)
2.89(7)
2.76(7)
3.87(2)
2.65(8)
2.74(7)
2.80(8)
2.88(7)
2.90(7)
2.93(7)
2.67(6)
3.89(2)
2.61(7)
2.65(8)
2.66(7)
2.70(7)
2.79(7)
2.81(8)
2.63(7)
3.86(2)
2.85(7)
2.97(7)
2.69(6)
2.80(7)
2.86(7)
3.506(9)
3.75(2)
2.52(7)
2.58(7)
2.70(7)
2.74(4)
2.81(8)
2.85(7)
2.86(7)
2.86(7)
2.88(7)
2.72(8)
2.75(7)
2.80(7)
2.88(7)
2.90(8)
2.67(6)
3.91(1)
2.52(6)
2.56(8)
2.79(4)
2.86(7)
2.89(8)
2.91(7)
3.01(7)
2.72(6)
Ba8-D17
Ba8-D16
Ba8-D9
2.59(9)
2.71(8)
2.76(7)
2.83(7)
2.84(7)
2.89(7)
2.60(6)
3.76(3)
2.84(7)
2.88(6)
2.60(5)
2.79(6)
2.82(6)
3.53(2)
3.73(2)
2.75(7)
2.85(6)
2.59(5)
2.76(6)
2.83(6)
3.58(2)
3.58(2)
2.48(7)
2.56(9)
2.73(7)
2.74(7)
2.76(7)
2.88(8)
2.97(7)
2.62(7)
3.81(2)
2.72(7)
2.74(7)
2.80(8)
2.81(7)
2.86(8)
2.94(7)
2.66(7)
3.72(3)
2.52(6)
2.52(6)
2.61(8)
2.63(4)
2.74(7)
2.76(7)
2.76(8)
2.78(5)
2.80(8)
2.87(7)
2.90(7)
2.97(5)
2.81(8)
2.83(7)
2.87(7)
2.86(7)
Ba14-D6
2.93(7)
2.70(5)
2.76(7)
2.76(7)
2.75(5)
2.80(5)
2.87(5)
3.530(9)
3.65(2)
2.63(7)
2.71(8)
2.79(8)
2.83(8)
2.87(6)
2.90(8)
2.62(6)
3.76(2)
2.81(7)
3.09(6)
2.60(6)
2.78(6)
2.93(6)
3.56(2)
3.65(2)
2.54(8)
2.74(6)
2.75(7)
2.80(7)
2.89(8)
2.94(8)
2.59(6)
3.86(3)
2.75(7)
2.79(7)
2.66(6)
2.69(4)
2.89(7)
3.55(2)
3.66(2)
2.61(8)
2.77(8)
2.79(7)
2.82(7)
2.95(6)
3.01(6)
3.01(7)
2.78(6)
3.97(2)
2.69(7)
2.71(6)
2.88(6)
3.16(6)
2.61(6)
2.63(7)
2.82(7)
Ba22-D8 2×
Ge1-Ba17
Ge1-Ba10
Ge1-Ba17
Ge1-Ba15
Ge1-Ba19
Ge1-Ba12
Ge1-Ba9
3.45(7)
3.56(2)
3.58(2)
3.65(2)
3.65(2)
3.66(2)
3.72(3)
3.73(2)
3.76(2)
3.81(2)
3.86(2)
3.97(2)
4.16(2)
3.506(9)
3.53(2)
3.58(2)
3.86(2)
3.87(2)
3.91(1)
3.530(9)
3.55(2)
3.75(2)
3.76(3)
3.86(3)
4.05(3)
2.60(6)
2.63(7)
2.67(6)
2.75(5)
2.83(6)
2.86(7)
2.66(7)
2.66(6)
2.72(6)
2.76(7)
2.80(7)
2.82(6)
2.62(6)
2.67(6)
2.76(6)
2.78(6)
2.78(6)
2.79(6)
2.59(5)
2.60(5)
2.60(6)
2.69(6)
2.69(4)
2.80(5)
2.59(6)
2.62(7)
2.70(5)
2.87(5)
2.89(7)
2.93(6)
Ba14-O5
Ba15-D9
Ba8-D2
Ba15-D12
Ba15-O1
Ba8-D1
Ba8-D2
Ba15-O4
Ba8-O1
Ba15-O5
Ba8-Ge3
Ba9-D7
Ba15-Ge3
Ba15-Ge1
Ba16-D23
Ba16-D10
Ba16-D11
Ba16-D8
Ge1-Ba16
Ge1-Ba11
Ge1-Ba3
Ba9-D4
Ba9-O4
Ba9-O3
Ge1-Ba20
Ge1-Ba14
Ge2-Ba4 2×
Ge2-Ba9 2×
Ge2-Ba10 2×
Ge2-Ba2 2×
Ge2-Ba1 2×
Ge2-Ba6 2×
Ge3-Ba15 2×
Ge3-Ba19 2×
Ge3-Ba4 2×
Ge3-Ba8 2×
Ge3-Ba18 2×
Ge3-Ba7 2×
O1-Ba8
Ba9-O2
Ba9-Ge2
Ba9-Ge1
Ba10-D8
Ba10-D3
Ba10-O4
Ba10-O3
Ba10-O1
Ba10-Ge1
Ba10-Ge2
Ba11-D15
Ba11-D22
Ba11-D7
Ba11-D12
Ba11-D4
Ba11-D24
Ba11-D6
Ba11-O5
Ba11-Ge1
Ba12-D14
Ba12-D5
Ba12-D20
Ba12-D11
Ba12-D6
Ba12-D4
Ba12-O2
Ba12-Ge1
Ba13-D19
Ba13-D13
Ba13-D22
Ba13-D14
Ba13-D16
Ba13-D18
Ba13-D24
Ba13-D15
Ba13-D17
Ba13-D20
Ba13-D23
Ba13-D21
Ba14-D8
Ba14-D3
Ba14-D10
Ba14-D22
Ba16-D21
Ba16-D5
Ba16-O3
Ba16-Ge1
Ba17-D5
Ba17-D6
Ba17-O4
Ba17-O3
Ba17-O5
Ba17-Ge1
Ba17-Ge1
Ba18-D24
Ba18-D21
Ba18-D10
Ba18-D11
Ba18-D10
Ba18-D12
Ba18-O5
O1-Ba3
O1-Ba2
O1-Ba15
O1-Ba10
O1-Ba4
Ba18-Ge3
Ba19-D11
Ba19-D10
Ba19-O2
Ba19-O4
Ba19-O5
O2-Ba12
O2-Ba19
O2-Ba7
O2-Ba1
O2-Ba4
O2-Ba9
Ba19-Ge3
Ba19-Ge1
Ba20-D19
Ba20-D12
Ba20-D7
O3-Ba16
O3-Ba6
O3-Ba10
O3-Ba17
O3-Ba20
O3-Ba9
Ba20-D23
Ba20-D9
O4-Ba10
O4-Ba9
O4-Ba17
O4-Ba4
O4-Ba19
O4-Ba15
O5-Ba18
O5-Ba11
O5-Ba14
O5-Ba15
O5-Ba19
O5-Ba17
Ba20-D13
Ba20-D5
Ba20-O3
Ba20-Ge1
Ba21-D22 2×
Ba21-D18 2×
Ba21-D4 2×
Ba21-D6 2×
Ba22-D21 2×
Ba22-D17 2×
Ba22-D2 2×
germanium atoms (Figure 2) that share common cations. The
more horizontal B,B′ region is that portion which was described
as “metal-like” in Ba21Ge2O5 etc.4
generally close to the expected values of 1.0 and 2.0, respec-
tively, Table 6.
Properties. An oxidation state count for the Ba21Ge2O5H24
As far as anion sites, each oxygen atom in the structure is
surrounded by six barium atoms in nearly regular octahedra with
O-Ba distances between 2.59 and 2.93 Å. Germanium anions
are surrounded by 12 barium atoms in deformed icosahedra with
a average separation of 3.72 Å. Deuterium anions exert the
least influence on their environment and so occupy interstices
defined by generally distorted tetrahedral, square-pyramidal, and
octahedral barium polyhedra with various bond distances (2.70-
structure indicates it is compositionally and structurally electron-
+
2
-4
precise and is thus a Zintl phase, i.e., 21(Ba ) + 2(Ge ) +
-2
-
5(O ) + 24(H ) in oxidation states. The electronic conduction
and magnetic properties are both consistent with this assignment.
The expected semiconducting (or insulating) behavior was
confirmed by “Q” measurements, which gave a minimum
resistivity at room temperature of 3 mΩ‚cm. As illustrated in
-
5
Figure 4, the compound is diamagnetic with ø ∼ -7.0 × 10
M
3
.15 Å in first group, 2.5-3.0 Å in second; σ ) 0.06-0.09 Å).
-1
emu‚mol over about 50-300 K after correction for core
2
3
Bond order sums about deuterium and oxygen atoms are
contributions.
Crystallographic and Other Results. The original studies
(23) Brese, N. E.; O’Keeffe, M. Acta Crystallogr. 1991, B47, 192.
by R o¨ hr reported that Ba21Ge2O5 and four other analogues

1898 Inorganic Chemistry, Vol. 37, No. 8, 1998
Huang and Corbett
the hk1 and hk2 precession films taken along the 3-fold axis
direction confirmed this assignment. None of these additional
trigonal reflections can be observed by Guinier powder diffrac-
tion, the stronger (e8.7% of Imax) because of overlap with strong
2θ-equivalent cubic data, while the strongest resolvable trigonal
datum is only 0.7% Imax.
The difficulties with the trigonal refinements stem from the
pseudocubic symmetry. The fraction of reflections observed
(3σI) in the primitive trigonal setting is quite low, about 22%,
and 90% of them belong to the cubic substructure. Anisotropic
parameters of all of the heavy atoms could not be refined
because of the quality and quantity of the X-ray data vs the
number of variables. Refinement of the neutron data on the
face-centered-cubic model was even more troublesome than
found with the X-ray data set. One of the two deuterium atoms
(D2) had a very large thermal parameter, implying that the real
position differs very much from that model. Some additional
weak reflections could also be observed in the neutron pattern
because of the relatively high neutron scattering factor of
deuterium, which atoms contribute about 50% of the total
diffracted intensity.
Figure 3. The Ba16 polyhedron and the centering Ba13 in the B sphere
inverted). This is close to a tetracapped truncated tetrahedron in which
the approximate tetrahedron of capping atoms (shaded) are equivalent
to the troubled Ba3 atoms in the cubic approximation.
(
A group-subgroup relationship exists between the ideal
cubic, the rhombohedral, and the primitive trigonal cells: Fd 3h m
f Fd 3h f F23 f R32 f P3121. X-ray refinements in space
groups from Fd 3h m to R32 showed that their atomic positions
and thermal parameters are not significantly different. However,
the symmetry change from R32 to P3121 produces about 10%
more observed X-ray reflections (from a cell with 75% of the
cubic volume) as every atom in the R-type symmetry splits into
three in primitive trigonal symmetry. The principal difference
between the two space groups is the conversion of the proper
3
-fold axis along the bc direction (hexagonal setting) into an
improper rotation axis together with the loss of some perpen-
dicular 2-fold axes (proper and improper). (The atom arrange-
ments in the trigonal structure are described in some detail in
the Supporting Information by seven sections of the structure
along bc .)
2 5 24
Figure 4. Molar magnetic susceptibility of single-phase Ba21Ge O H
as a function of temperature at a 3 T field.
Table 6. O-Ba and D-Ba Bond Order Sums in Ba21Ge
2
O
5
D
24
A simple way to contrast the solutions for the two cells is in
terms of the atom deviations from the 3-fold axes in the
rhombohedral structure, trigonal setting (along /3, /3, z; etc.).
Here the order on the axis is Ge3 f O4 f O3 f Ba13 f
Ba21 f Ba13 f O3 f O4 f Ge3, there being a perpendicular
O1-6Ba
O2-6Ba
O3-6Ba
O4-6Ba
O5-6Ba
D1-6Ba
D2-6Ba
D3-5Ba
D4-6Ba
D5-5Ba
D6-5Ba
D7-6Ba
D8-5Ba
D9-5Ba
D10-5Ba
1.92
1.82
1.84
2.24
1.77
1.15
1.06
0.99
1.13
0.93
0.81
1.21
1.00
0.94
1.06
D11-5Ba
D12-5Ba
D13-4Ba
D14-4Ba
D15-4Ba
D16-4Ba
D17-4Ba
D18-4Ba
D19-4Ba
D20-4Ba
D21-4Ba
D22-4Ba
D23-4Ba
D24-4Ba
1.03
1.02
1.40
1.26
1.24
1.04
1.22
1.06
1.50
0.98
0.90
1.21
0.86
1.09
1
2
2
-fold axis through the central Ba21. The deviations of most
atoms from this in the real structure are very small (within 3σ),
0.08 Å for Ge3, 0.05 Å for O4, 0.12 Å for O3, and 0.06 Å for
Ba13, but the Ba21 atoms, which correspond to parts of the
1
1
1
troubled Ba3 atom in the fcc structure (16d: /2, /2, /2; etc.),
have moved away from the 3-fold axis by 0.60 Å. Of course,
differences between the two entire structures include displace-
ments of other atoms surrounding this axis as well.
Deuterium atoms D13-D24, which would correspond to the
single D2 type in the cubic structure, are very much different
from the single placement. In the fcc structure, a D2 atom
polyhedron centered by a Ba4 atom (trigonal Ba13) has the form
crystallize with face-centered-cubic symmetry, space group
Fd 3h m, which can be transformed into a rhombohedral cell with
R ∼ 60°. However, the results of the structure determinations
for Ge and Si were unusual, particularly with respect to the
of a cuboctahedron with T symmetry. However, the D-Ba
d
distances therein would be much too short (<2.47 Å) in all three
1
1
1
Ba3 atoms (16d: /2, /2, /2; etc.) which showed unusually large
possible cubic groups, and such a lack of suitable cavities for
deuterium in this symmetry must in fact lead to the distortion
of this polyhedron and of the structure. This is the nature of
sphere B, Figure 2. On the other hand, oxygen and germanium
center high coordination barium polyhedra that are relatively
“rigid” or “hard” because of their higher formal charges (sphere
A, Figure 2). This dominant heavy-atom arrangement plays a
key role in the formation of the pseudo-fcc structure. In
2
thermal parameters, Uiso ) 0.183(8) Å in the germanium
example relative to e 0.018 Å for the other cations and a
maximum of 0.036(3) Å for Ba here. Precession photographs
2
2
of the cubic cell were taken, but no superstructure reflections
were mentioned. During X-ray diffractometer work, we found
some relatively strong reflections that required a primitive
trigonal cell. Subsequently, additional trigonal reflections in

Ba21Ge2O5H24 and Related Phases
Inorganic Chemistry, Vol. 37, No. 8, 1998 1899
contrast, the low-field, polarizable deuterium atoms (B) are
relatively “anomalous”24 or “soft” and end up in a variety (24)
of barium environments. These seem to be more responsible
for the adoption of the primitive trigonal symmetry.
aluminum icosahedra. The Al10V result is unusual in three
respects: a strikingly large atomic volume per atom; empty
aluminum octahedra; large, empty 16-atom aluminum polyhedra
(Figure 3) where cubic Ba4 (trigonal Ba13) is found here. The
second and third cavities are suitably sized for O and Al,
respectively. A redetermination of the structure seems necessary
to establish (at least) the correct aluminum and any oxygen
content. Likewise, a novel Ba17Al3O7 was recently reported27
that exhibits some of the same themes found in Ba21T2O5,
particularly a metal-like region with large Ba-Ba distances
(>4.43 Å) between Al-O-Ba clusters. This may again mean
hydride involvement. The compound seems especially interest-
25
The formation of pseudo-fcc structures for the three com-
pounds Ba21Tr2O5Hx, Tr ) Ga In, Tl, has also been verified by
single-crystal X-ray diffraction in parallel with the studies on
the Ge compound. The isotypic primitive trigonal cell for the
Ga example has also been confirmed on the diffractometer, but
not yet for Si, In, Tl. In cubic refinement attempts, certain
barium atoms again have troublesome thermal parameters, and
similar problems may have prevented the identification of Ba4
and thence the correct heavy-atom composition of “Ba10Ga”
from precession film data.3 According to the Zintl -phase
concepts, the trielide compounds should contain only 22
hydrogen atoms per formula and be constituted as
+
3
ing because of the implications of both oxoaluminate (Al )
-5
and aluminide (Al ) components, for which a clear hydride
count would be especially meaningful should it be electronically
closed-shell.
+
2
-5
-2
-
(
Ba )21(Tr )2(O )5(H )22. The high cation field may help
Acknowledgment. We are indebted to S. Short and J.
Jorgensen for provision of the neutron diffraction data and to
J. E. Ostenson for the magnetic measurements. This research
has benefited from the use of the Intense Pulsed Neutron Source
at Argonne National Laboratory, which is funded by the U.S.
Department of Energy, BES-Materials Sciences, under Contract
W-31-109-ENG-38.
-5
stabilize the closed-shell state Tr and therefore ensure the full
quota of 22 H , but this has not been verified for any of the
-
trielides.
The 1957 report of the structure of cubic Al10V26 shows that
3
it has a close relationship not only to that of “Ba10Ga” but
also to the present pseudocubic Ba21T2O5Hx phases. Aluminum
occupies the cubic Ba1,2,3 (but reportedly not the Ba4) type
sites, with vanadium in idealized Ga 16c positions within
Supporting Information Available: Tables giving more details
of the data collection and refinement for Ba21Ge O H24 and distances
2 5
within the polyhedra about each D atom and a figure showing seven
[001] sections of the trigonal structure (5 pages). Ordering information
is given on any current masthead page.
(
(
24) Bronger, W. Angew. Chem., Int. Ed. Engl. 1991, 30, 759.
25) Yvon, K. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.;
Wiley: New York, 1994; Vol. 3, p 1401.
(26) Brown, P. J. Acta Crystallogr. 1957, 10, 133.
(27) R o¨ hr, C.; George, R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2115.
IC971339Y