Structures and syntheses of layered and framework amine-bearing uranyl phosphate and uranyl arsenates

Article abstract of DOI:10.1016/j.jssc.2004.03.045

Two hydrated uranyl arsenates and a uranyl phosphate were synthesized by hydrothermal methods in the presence of amine structure-directing agents and their structures determined: (N₂C₆H₁₄)[(UO ₂)(AsO₄)]₂(H₂O)₃, DabcoUAs, {NH(C₂H₅)₃}[(UO₂) ₂(AsO₄)(AsO₃OH)], TriethUAs, and (N ₂C₄H₁₂)(UO₂)[(UO₂) (PO₄)]₄(H₂O)₂, PiperUP. Intensity data were collected at room temperature using MoKα X-radiation and a CCD-based area detector. The crystal structures were refined by full-matrix least-squares techniques on the basis of F² to agreement indices (DabcoUAs, TriethUAs, PiperUP) wR₂=5.6%, 8.3%, 7.2% for all data, and R₁=2.9%, 3.3%, 4.0%, calculated for 1777, 5822, 9119 unique observed reflections (|F_o|≥4σ_F), respectively. DabcoUAs is monoclinic, space group C2/m, Z=2, a=18.581(1), b=7.1897(4), c=7.1909(4)A, β=102.886(1)°, V=936.43(9)A³, D_calc=3.50g/cm³. TriethUAs is monoclinic, space group P2₁/n, Z=4, a=9.6359(4), b=18.4678(7), c=10.0708(4)A, β=92.282(1)°, V=1790.7(1)A³, D_calc=3.41g/ cm³. PiperUP is monoclinic, space group Pn, Z=2, a=9.3278(4), b=15.5529(7), c=9.6474(5)A, β=93.266(1)°, V=1397.3(1) A³, D_calc=4.41g/cm³. The structure of DabcoUAs contains the autunite-type sheet formed by the sharing of vertices between uranyl square bipyramids and arsenate tetrahedra. The triethylenediammonium cations are located in the interlayer along with two H₂O groups and are disordered. Both TriethUAs and PiperUP contain sheets formed of uranyl pentagonal bipyramids and tetrahedra (arsenate and phosphate, respectively) with the uranophane sheet-anion topology. In TriethUAs, triethlyammonium cations are located in the interlayer. In PiperUP, the sheets are connected by a uranyl pentagonal bipyramid that shares corners with phosphate tetrahedra of adjacent sheets, resulting in a framework with piperazinium cations and H₂O groups in the cavities of the structure.

Full text of DOI:10.1016/j.jssc.2004.03.045

ARTICLE IN PRESS
Journal of Solid State Chemistry 177 (2004) 2675–2684
Structures and syntheses of layered and frameworkamine-bearing
uranyl phosphate and uranyl arsenates
Andrew J. Locock* and Peter C. Burns
Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556-0767, USA
Received 27 February 2004; received in revised form 22 March 2004; accepted 28 March 2004
Abstract
Two hydrated uranyl arsenates and a uranyl phosphate were synthesized by hydrothermal methods in the presence of
amine structure-directing agents and their structures determined: (N2C6H14)[(UO2)(AsO4)]2(H2O)3, DabcoUAs,
fNHðC2H5Þ3g½ðUO2Þ2ðAsO4ÞðAsO3OHފ; TriethUAs, and (N2C4H12)(UO2)[(UO2)(PO4)]4(H2O)2, PiperUP. Intensity data were
collected at room temperature using MoKa X-radiation and a CCD-based area detector. The crystal structures were refined by full-
matrix least-squares techniques on the basis of F2 to agreement indices (DabcoUAs, TriethUAs, PiperUP) wR2 ¼ 5:6%; 8.3%, 7.2%
for all data, and R1 ¼ 2:9%; 3.3%, 4.0%, calculated for 1777, 5822, 9119 unique observed reflections (jFojX4sF), respectively.
DabcoUAs is monoclinic, space group C2=m; Z ¼ 2; a ¼ 18:581ð1Þ; b ¼ 7:1897ð4Þ; c ¼ 7:1909ð4Þ A, b ¼ 102:886ð1Þꢀ;
V ¼ 936:43ð9Þ A3, Dcalc ¼ 3:50 g/cm3. TriethUAs is monoclinic, space group P21=n; Z ¼ 4; a ¼ 9:6359ð4Þ; b ¼ 18:4678ð7Þ;
c ¼ 10:0708ð4Þ A, b ¼ 92:282ð1Þꢀ; V ¼ 1790:7ð1Þ A3, Dcalc ¼ 3:41 g/cm3. PiperUP is monoclinic, space group Pn, Z ¼ 2; a ¼
9:3278ð4Þ; b ¼ 15:5529ð7Þ; c ¼ 9:6474ð5Þ A, b ¼ 93:266ð1Þꢀ; V ¼ 1397:3ð1Þ A3, Dcalc ¼ 4:41 g/cm3. The structure of DabcoUAs
contains the autunite-type sheet formed by the sharing of vertices between uranyl square bipyramids and arsenate tetrahedra. The
triethylenediammonium cations are located in the interlayer along with two H2O groups and are disordered. Both TriethUAs and
PiperUP contain sheets formed of uranyl pentagonal bipyramids and tetrahedra (arsenate and phosphate, respectively) with the
uranophane sheet-anion topology. In TriethUAs, triethlyammonium cations are located in the interlayer. In PiperUP, the sheets are
connected by a uranyl pentagonal bipyramid that shares corners with phosphate tetrahedra of adjacent sheets, resulting in a
frameworkwith piperazinium cations and H O groups in the cavities of the structure.
2
r 2004 Elsevier Inc. All rights reserved.
Keywords: Uranyl arsenate; Uranyl phosphate; Intercalation; Framework; Mixed organic–inorganic; Crystal structure refinement; Hydrothermal
synthesis
1. Introduction
The addition of organic components to form mixed
organic–inorganic uranyl compounds considerably in-
creases the potential structural variability, and such
structures have been the focus of considerable research
in recent years [10–28]. In the organic–uranyl–phos-
phate system, the use of simple amines as structure-
directing agents has produced layered and framework
structures [8,16] that contain uranyl phosphate sheets
based on the uranophane sheet-anion topology [1].
Uranyl phosphate crown ether compounds [17] contain
one-dimensional chains of uranyl pentagonal bipyra-
mids and phosphate tetrahedra that are identical
topologically to those found in simple inorganic uranyl
phosphate and uranyl arsenate structures [29,30].
Extension of the system to phosphonate and its
derivatives adds to the structural diversity, producing
The crystal chemistry of hexavalent uranium is rich in
diversity because of the high coordination numbers (six,
seven, or eight) accessible to U6+ and the polarized
distribution of bond strengths within uranyl polyhedra [1].
Polymerization of uranyl bipyramidal polyhedra generally
occurs only through the equatorial ligands, usually
yielding infinite chains or sheets, with three-dimensional
frameworkstructures occasionally being facilitated by
linkages through non-uranyl polyhedra such as silicate
[2–4], molybdate [5,6], vanadate [7], or phosphate [8,9].
*Corresponding author. Fax: 219-247-1206.
E-mail addresses: alocock@nd.edu (A.J. Locock), pburns@nd.edu
(P.C. Burns).
0022-4596/$ - see front matter r 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2004.03.045

ARTICLE IN PRESS
A.J. Locock, P.C. Burns / Journal of Solid State Chemistry 177 (2004) 2675–2684
2676
chains, sheets, frameworks and even uranyl phospho-
nate tubes. The uranyl phosphonate chains are based
either on uranyl square bipyramids [18,19] and are
similar to the uranyl arsenate chains of the walpurgite
group minerals [31,32], or are based on uranyl
pentagonal bipyramids [20] and are similar to those
chains found in the crown ether compounds and simple
uranyl phosphate and uranyl arsenate compounds
[17,26,27]. Sheet structures based on the uranophane
sheet-anion topology [1] are known from uranyl
phosphonates [18,21], as are tube structures [22–25],
but new sheet and frameworktopologies as yet
undiscovered in inorganic uranyl phosphate or uranyl
arsenate systems have also been crystallized in uranyl
phosphonates [26]. In addition to the framework
structures formed in the phosphate- and phosphonate-
based systems, novel microporous solids have been
synthesized in the organic–uranyl–phosphite and or-
ganic–uranyl–phosphate–fluoride systems [27,28].
We are interested in extending our understanding of
the rich solid-state chemistry of uranium, and to this
end, have undertaken the hydrothermal synthesis of
uranyl arsenates and uranyl phosphates in the presence
of amine structure-directing agents, and report their
crystal structures herein.
autoclave was then removed to air and allowed to cool
to room temperature.
2.1.2. {NH(C2H5)3}[(UO2)2(AsO4)(AsO3OH)]
TriethUAs was synthesized by hydrothermal reaction
of UO2(CH3COO)2(H2O)2 (111.1 mg, 0.262 mmol),
N(C2H5)3
(144.8 mg,
1.431 mmol),
H5As3O10
(116.0 mg, 0.298 mmol), concentrated HCl (0.1445 g,
1.474 mmol) and ultrapure H2O (4132 mg). The mixture
was heated at 6ꢀ per hour from 60ꢀC to 220(1)ꢀC, held at
220(1)ꢀC for 24 h and cooled to 90(1)ꢀC at 6ꢀ per hour.
The autoclave was then removed to air and allowed to
cool to room temperature.
2.1.3. (N2C4H12)(UO2)[(UO2)(PO4)]4(H2O)2
PiperUP, was synthesized by hydrothermal reaction
of UO2(CH3COO)2(H2O)2 (99.9 mg, 0.236 mmol),
N2C6H12
(11.8 mg,
0.105 mmol),
Ca5(PO4)3F
(105.7 mg, 0.210 mmol), concentrated HCl (0.1858 g,
1.896 mmol) and ultrapure H2O (4074 mg). The mixture
was heated at 190(1)ꢀC in a Fisher Isotemp oven for 3
days. The autoclave was then removed to air and allowed
to cool to room temperature. Interestingly, the product of
this reaction contains the piperazinium cation
(N2C4H12)2+, rather than the triethylenediammonium
cation (N2C6H14)2+. The breakdown of triethylenedia-
mine under these reaction conditions is not entirely
unexpected. In aqueous solution at room temperature,
chlorine dioxide can produce piperazine from triethylene-
diamine by oxidative fragmentation [34]. The decomposi-
tion of triethylenediamine under hydrothermal conditions
to produce the ammonium cation has also been observed
in the DABCO–U–F system [14].
2. Experiment
2.1. Crystal synthesis
Single crystals of (N2C6H14)[(UO2)(AsO4)]2(H2O)3,
DabcoUAs,
{NH(C2H5)3}[(UO2)2(AsO4)(AsO3OH)],
TriethUAs, and (N2C4H12)(UO2)[(UO2)(PO4)]4(H2O)2,
PiperUP, were obtained by hydrothermal reaction.
Uranyl acetate, UO2(CH3COO)2(H2O)2 (98%, Alfa
Aesar), triethylenediamine, N2C6H12 (1,4-diazabicy-
clo[2.2.2]octane, DABCO, 98%, Aldrich), triethylamine,
N(C2H5)3 (99%, Aldrich), concentrated HCl (37.2%,
Fisher), and natural fluorapatite, Ca5(PO4)3F (Liscombe
Deposit, near Wilberforce, Ontario, Canada) were used
as received. Hydrogen arsenate, H5As3O10, was prepared
from As2O3 (99%, Aldrich) and concentrated HNO3
(69.2%, Fisher) by the method of Walton [33]. Millepore-
filtered ultrapure water (18 MO resistance) was used in all
reactions. Reactions were carried out in 23mL polytetra-
fluoroethylene-lined Parr acid-reaction vessels. Reaction
yields were not quantitatively determined.
2.2. Single-crystal X-ray diffraction data collection
For each of the three samples, a suitable crystal was
mounted on a Bruker PLATFORM three-circle X-ray
diffractometer operated at 50 keV and 40 mA, and
equipped with a 4 K APEX CCD detector and a crystal
to detector distance of B4.7 cm. Data were collected at
room temperature using graphite-monochromatized
MoKa X-radiation and frame widths of 0.3ꢀ in o:
Comparison of the intensities of equivalent reflections
measured at different times during data collection
showed no significant decay for any of the three
compounds. Selected data collection parameters and
crystallographic data are provided in Table 1. SMART
software [35] was used for data collection, SAINT [36]
for data integration, and corrections for absorption
were made with the program XPREP [37].
2.1.1. (N2C6H14)[(UO2)(AsO4)]2(H2O)3
DabcoUAs, was synthesized by hydrothermal reaction
of UO2(CH3COO)2(H2O)2 (124.0 mg, 0.294 mmol),
N2C6H12 (109.6 mg, 0.972 mmol), H5As3O10 (153.7 mg,
0.394 mmol), concentrated HCl (0.334 g, 3.406 mmol)
and ultrapure H2O (6107 mg). The mixture was heated
at 190(1)ꢀC in a Fisher Isotemp oven for 3 days. The
Systematic absences of reflections for DabcoUAs were
consistent with space groups C2=m; C2 and Cm; the best
solution was obtained in C2=m: In the case of
TriethUAs, systematic absences of reflections were
consistent with space group P21=n: Systematic absences

ARTICLE IN PRESS
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2677
Table 1
Crystallographic data and details of the structure refinements
Compound
DabcoUAs
TriethUAs
PiperUP
a (A)
b (A)
c (A)
18.581(1)
7.1897(4)
7.1909(4)
102.886(1)
936.43(9)
C2=m
9.6359(4)
18.4678(7)
10.0708(4)
92.282(1)
1790.7(1)
P21=n
9.3278(4)
15.5529(7)
9.6474(5)
93.266(1)
1397.3(1)
Pn
b (deg)
V (A3)
Space group
Z
2
4
2
Formula
(N2C6H14)[(UO2)
(AsO4)]2(H2O)3
986.128
{NH(C2H5)3}[(UO2)2
(AsO4)(AsO3OH)]
921.099
(N2C4H12)(UO2)
[(UO2)(PO4)]4(H2O)2
1854.206
1596
Formula weight
F(000)
m (mmÀ1
Dcalc (g/mL)
880
20.86
3.497
1620
21.79
3.413
)
29.22
4.407
Crystal size (mm)
Color and habit
Temperature (K)
Width (deg), time(s)
Collection (h)
y range
Data collected
Absorptiona
Total refl.
0.20 Â 0.10 Â 0.02
Yellow plate
293(2)
0.50 Â 0.08 Â 0.08
Yellow needle
293(2)
0.20 Â 0.20 Â 0.02
yellow plate
293(20)
0.3, 20
0.3, 10
0.3, 7
Sphere, 16
2.9–34.5ꢀ
h729, k711, l711
plate (100) 0.5ꢀ
9541
Sphere, 8
2.0–34.5ꢀ
h715, k729, l715
Ellipsoid
36364
sphere, 6
2.5–34.5ꢀ
h714, k724, l715
plate (010) 3ꢀ
25986
Unique refl., Rint
Unique jFoj44sF
Parameters
2087, 0.088
1777
85
7446, 0.088
5822
194
11271, 0.061
9119
358
R1 for jFoj44sF
R1 all data, wR2
Weighting a
2.9
3.6, 5.6
3.3
4.2, 8.3
4.0
4.9, 7.2
0.0
0.873
0.0427
0.970
0.0145
0.878
Goodness of fit
Mean shift/esd
Peaks (e/A3)
0.000
3.2, À1.0
0.000
5.0, À2.7
0.000
2.6, À3.2
P
P
P
P
2
2
0:5
2
R1 ¼ ½ jjFoj À jFcjjŠ= jFoj  100: wR2 ¼ ½ ½wðFo2 À Fc2Þ Š= ½wðFo2Þ ŠŠ  100; w ¼ 1=ðs2ðFo2Þ þ ðaPÞ ; and P ¼ 1=3 maxð0; Fo2Þ þ 2=3Fc2:
a Corrections for absorption are semi-empirical (crystal modeled either as an ellipsoid, or as a plate rejecting data within Xꢀ of the primary X-ray beam).
of reflections for PiperUP were consistent with space
groups P21=n; P21; P2=n; and Pn; trial solutions were
obtained in all four space groups, but the best solution
was obtained in Pn: The unit cells of TriethUAs and
PiperUP can be transformed to the conventional setting
with space groups P21=c and Pc, respectively, by the
matrix [100/010/À101]; however, the resultant cells are
quite oblique (b 134.93ꢀ and 135.72ꢀ, respectively) and
therefore these structures were refined in the setting with
b closer to 90ꢀ. Scattering curves for neutral atoms,
together with anomalous dispersion corrections, were
taken from International Tables for X-ray Crystal-
lography, Vol. C [38]. The SHELXTL Version 5 series
of programs [39] was used for the solution and
refinement of the crystal structures.
The structure of DabcoUAs was solved in space group
C2=m using direct methods. A structure model including
anisotropic displacement parameters for all non-H
atoms converged, and gave an agreement index (R1) of
2.9%, calculated for the 1771 observed unique reflec-
tions (jFojX4sF). The locations of the H atoms in the
unit cell were not determined.
The structure of TriethUAs was solved in space group
P21=n using Patterson methods. A structure model
including anisotropic displacement parameters for U,
As, N and O atoms converged, and gave an agreement
index (R1) of 3.3%, calculated for the 5822 observed
unique reflections (jFojX4sF). Possible H atom posi-
tions around N(1) and O(12) were located in difference-
Fourier maps, calculated following refinement of the
model. Their positions were refined with the restraint
that O–H bond-lengths be B0.96 A and with fixed
isotropic displacement parameters.
3. Structure solution and refinement
The structure of PiperUP was solved in space group
Pn using direct methods. A structure model including
the racemic twin law [À100/0À10/00À1] and anisotropic
displacement parameters for U, P and fully occupied O
atoms converged, and gave an agreement index (R1) of
All three structures were refined on the basis of F2 for
all unique data. In the final cycle of each refinement, the
mean parameter shift/esd was 0.000.

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2678
Table 3
Atomic coordinates ( Â 104) and displacement parameters (A2 Â 103)
4.0%, calculated for the 9119 observed unique reflec-
tions (jFojX4sF). The racemic twin-component scale
factor refined to 0.491(7), consistent with an even
distribution of the enantiomorphic components. The
locations of the H atoms in the unit cell were not
determined. The refined solution obtained for PiperUP
was checked with the ADDSYM algorithm in the
program PLATON [40,41] but no higher symmetry
was found. The arrangement of the U atoms in PiperUP
is consistent with a non-centrosymmetric structure;
upon testing the Pn model with only isotropic U atoms
present, the ADDSYM algorithm does not reveal any
higher symmetry, and solutions by direct or Patterson
methods of PiperUP in space groups P21=n; P21 and
P2=n yield U positions with displacement parameters
and interatomic distances that are physically unrealistic.
The atomic positional parameters and displacement
parameters of the three compounds are given in Table
2—DabcoUAs, Table 3—TriethUAs, and Table 4—
PiperUP. Selected interatomic distances are listed in
Table 5—DabcoUAs, Table 6—TriethUAs and Table
7—PiperUP.
for TriethUAs, {NH(C2H5)3}[(UO2)2(AsO4)(AsO3OH)]
x
y
z
Ueq
U(1)
U(2)
As(1)
As(2)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
O(10)
O(11)
O(12)
N(1)
C(1)
801(1)
2325(1)
2340(1)
2850(1)
2172(1)
2741(2)
2530(2)
2895(2)
2148(2)
2301(2)
2550(2)
1376(2)
1364(2)
1401(2)
3267(2)
3273(2)
3700(2)
À8(3)
810(1)
14(1)
13(1)
15(1)
13(1)
20(1)
20(1)
23(1)
20(1)
26(1)
21(1)
23(1)
24(1)
24(1)
27(1)
26(1)
31(1)
49(2)
59(2)
65(2)
69(2)
94(3)
82(6)
50(4)
88(6)
66(4)
50a
À228(1)
À1681(1)
À2774(1)
À3552(3)
À2714(3)
À3405(3)
À1025(3)
À851(3)
À1692(3)
1000(3)
4679(1)
À1939(1)
2437(1)
1361(3)
4007(3)
À1763(3)
2261(3)
À891(4)
À3522(3)
654(3)
À3510(3)
À511(4)
618(4)
2426(3)
4841(3)
1003(4)
4474(4)
À1863(4)
2521(6)
2375(8)
7751(8)
3611(9)
4873(12)
3918(13)
3681(13)
4600(20)
4977(19)
À1850(70)
2410(60)
47(4)
À1035(4)
À2354(6)
À831(9)
À49(9)
145(5)
C(2)
C(3)
538(6)
À1953(9)
À1982(12)
À2290(20)
À2885(17)
À3580(20)
À2550(20)
À40(20)
À2780(60)
4582(5)
5005(7)
À318(12)
À433(8)
À11(12)
À6(10)
3710(40)
476(19)
C(4)
C(5A)
C(5B)
C(6A)
C(6B)
H(1)
H(2)
4. Results
50a
4.1. Structure description
Note: Ueq is defined as one-third of the trace of the orthogonalized Uij
tensor.
DabcoUAs contains the well-known corrugated autu-
nite-type sheet formed by the sharing of vertices between
uranyl square bipyramids and arsenate tetrahedra (Fig.
1), with composition [(UO2)(AsO4)]À, which was origin-
ally described by Beintema [42]. The triethylenediam-
monium cations are located in the interlayer region
between the uranyl arsenate sheets (Fig. 2), along with
C(5A), C(5B), C(6A) and C(6B) are half occupied. C(5A) is separated
from C(5B) by 0.65(2) A. C(6A) is separated from C(6B) by 1.05(3) A.
a Value constrained during refinement.
two symmetrically independent H2O groups that are
held in the structure only by hydrogen bonding. Most of
the interlayer contents in DabcoUAs are disordered,
with the pseudo-trigonal triethylenediammonium cation
occupying either of two orientations in competition with
an H2O group (Fig. 3). Thus, N(1A), C(2A), and
OW(2A) are half occupied, and N(1A) is separated from
its symmetry equivalent by 1.39(2) A, whereas OW(2A)
is separated from C(2A) by 1.27(1) A. The local
environment is displayed in Fig. 4: the triethylenediam-
monium cation is separated locally from OW(2A) by
3.4–3.5 A. The disorder present in the C2=m model for
DabcoUAs prompted a search for a larger unit cell in
accord with the cautions of Marsh [43]. The intensity
data were examined carefully, but no significant indica-
tions of a larger cell were found, despite the high
sensitivity of the CCD detector [44].
Table 2
Atomic coordinates ( Â 104) and displacement parameters (A2 Â 103)
for DabcoUAs, (N2C6H14)[(UO2)(AsO4)]2(H2O)3
x
y
z
Ueq
U(1)
3042(1)
2510(1)
3099(3)
4041(3)
3055(3)
2063(3)
1953(2)
409(4)
5000
5000
À2158(1)
2514(1)
1049(6)
12(1)
15(1)
22(1)
23(1)
26(1)
30(1)
26(1)
65(2)
61(4)
29(2)
31(1)
35(3)
As(1)
O(1)
O(2)
5000
5000
À1571(7)
4706(6)
O(3)
O(4)
5000
5000
À2655(7)
2129(5)
7111(9)
O(5)
3144(4)
0
5000
OW(1)
OW(2A)
N(1A)
C(1)
699(8)
157(5)
À601(19)
5975(12)
À5416(8)
7967(15)
3252(12)
3944(7)
3935(16)
612(3)
530(7)
C(2A)
TriethUAs is isostructural with its phosphate analo-
gue, {NH(C2H5)3}[(UO2)2(PO4)(PO3OH)], [16], CSD
collection code NECPEQ, space group P21=n: These
compounds contain uranyl arsenate and uranyl phos-
phate sheets, respectively, that are topologically
Note: Ueq is defined as one-third of the trace of the orthogonalized Uij
tensor.
OW(2A), N(1A) and C(2A) are half occupied. N(1A) is separated from
its symmetry equivalent by 1.39(2) A. OW(2A) is separated from C(2A)
by 1.27(1) A.

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2679
Table 4
Atomic coordinates ( Â 104) and displacement parameters (A2 Â 103)
Table 5
Selected interatomic distances (A) and angles (deg) for DabcoUAs
for PiperUP, (N2C4H12)(UO2)[(UO2)(PO4)]4(H2O)2
U(1)–O(4)
U(1)–O(2)
U(1)–O(5)
U(1)–O(5)a
U(1)–O(3)
U(1)–O(1)
/U(1)–Oap
1.774(5)
1.809(5)
2.260(3)
2.260(3)
2.261(4)
2.285(4)
1.79
As(1)–O(3)
As(1)–O(5)
As(1)–O(5)b
As(1)–O(1)
/As(1)–OS
1.672(5)
1.674(3)
1.673(3)
1.680(4)
1.675
x
y
z
Ueq
U(1)
U(2)
U(3)
U(4)
U(5)
P(1)
1420(1)
2385(1)
1337(1)
2285(1)
2166(1)
4800(3)
À1214(3)
4888(3)
À1136(3)
3242(8)
497(8)
170(1)
228(1)
290(1)
À3651(1)
13(1)
15(1)
14(1)
15(1)
14(1)
16(1)
13(1)
13(1)
12(1)
13(1)
14(2)
20(2)
23(2)
15(2)
22(2)
21(2)
20(2)
18(2)
17(2)
19(2)
23(2)
27(2)
31(2)
23(2)
21(2)
26(2)
25(2)
26(2)
22(2)
26(2)
20(2)
28(2)
18(2)
21(2)
32(2)
27(2)
73(4)
89(5)
64(4)
47(4)
80(6)
52(4)
73(5)
145(14)
112(10)
4892(1)
4707(1)
7488(1)
4369(2)
4739(2)
638(2)
À3945(1)
3112(1)
S
N(1A)–C(1)
N(1A)–C(2A)
N(1A)–C(1)c
C(1)–C(1)b
1.48(1)
1.53(1)
1.53(1)
1.52(1)
1.53(2)
/U(1)–Oeq
S
2.27
178.2(2)
À1617(2)
À2250(3)
À1378(3)
À2008(2)
À1220(8)
À2165(8)
À2448(9)
À1463(8)
À417(8)
À125(9)
À3185(8)
À720(8)
À3350(8)
À798(7)
À3014(9)
À3603(9)
À3302(9)
349(8)
O(4)–U(1)–O(2)
P(2)
P(3)
OW(1)–N(1A)
OW(1)–N(1A)d
OW(1)–O(1)
2.486(9)
2.486(9)
2.793(8)
2.89(1)
C(2A)–C(2A)b
P(4)
O(1)
300(2)
563(6)
425(6)
OW(2A)–N(1A)
OW(2A)–N(1A)e
2.748(15)
2.748(15)
O(2)
O(3)
OW(1)–C(2A)
401(9)
4606(6)
4445(6)
5948(6)
À896(5)
4606(5)
5047(5)
5393(5)
5175(5)
À397(6)
5806(6)
À880(6)
3828(6)
8(6)
O(4)
O(5)
3140(8)
1799(8)
1823(8)
4886(8)
5579(8)
À1849(8)
À1190(7)
À1760(9)
2372(8)
2452(9)
817(7)
Symmetry transformations used to generate equivalent atoms: a: x þ
1=2; Ày þ 1=2; Àz; b: x; Ày þ 1; z; c: x; y; z þ 1; d: x; Ày; z; e: x;
Ày þ 1; z À 1:
O(6)
O(7)
O(8)
O(9)
Table 6
Selected interatomic distances (A) and angles (deg) for TriethUAs
O(10)
O(11)
O(12)
O(13)
O(14)
O(15)
O(16)
O(17)
O(18)
O(19)
O(20)
O(21)
O(22)
O(23)
O(24)
O(25)
O(26)
O(27)
N(1)
N(2)
C(1)
U(1)–O(10)
U(1)–O(7)
U(1)–O(5)
U(1)–O(4)
U(1)–O(2)
U(1)–O(6)
U(1)–O(3)
1.760(4)
1.771(3)
2.292(4)
2.354(3)
2.372(3)
2.493(3)
2.564(3)
1.765
As(1)–O(5)
As(1)–O(3)
As(1)–O(6)
As(1)–O(12)
/As(1)–OS
1.647(4)
1.680(3)
1.687(3)
1.691(4)
1.68
5673(8)
2160(8)
974(8)
À431(8)
À4240(8)
663(8)
3600(5)
1237(6)
3914(6)
À70(6)
1126(5)
327(5)
À2030(8)
À1110(8)
À1934(8)
4985(8)
2329(9)
5293(7)
5374(7)
2850(8)
1475(8)
4728(11)
417(18)
2527(15)
À705(16)
3531(18)
2884(16)
5041(17)
4280(40)
À180(30)
À2311(8)
À507(7)
À2171(8)
À2895(7)
À3961(8)
À1319(7)
À1165(7)
4854(9)
As(2)–O(8)
As(2)–O(1)
As(2)–O(4)
As(2)–O(2)
/As(2)–OS
1.651(3)
1.666(3)
1.702(3)
1.712(3)
1.68
/U(1)–Oap
S
/U(1)–Oeq
S
2.42
178.7(2)
O(10)–U(1)–O(7)
1328(5)
3474(5)
1538(5)
7455(6)
7518(6)
7484(7)
7718(12)
2718(9)
7591(11)
2572(14)
2150(11)
2750(14)
7310(30)
1920(20)
U(2)–O(11)
U(2)–O(9)
U(2)–O(1)
U(2)–O(3)
U(2)–O(6)
U(2)–O(2)
U(2)–O(4)
1.756(4)
1.764(3)
2.298(3)
2.363(3)
2.372(3)
2.488(3)
2.549(3)
1.76
N(1)–C(3)
N(1)–C(1)
N(1)–C(5B)
N(1)–C(5A)
1.50(1)
1.51(1)
1.514(8)
1.517(9)
1388(8)
2317(14)
À1950(17)
2191(14)
À958(15)
1100(20)
À6592(15)
1801(18)
7750(40)
À5450(30)
N(1)–H(2)
H(2)?O(8)
N(1)–H(2)?O(8)
0.99(2)
1.79(2)
173
/U(2)–Oap
/U(2)–Oeq
O(11)–U(2)–O(9)
S
C(2)
C(3)
S
2.41
178.6(2)
C(4)
OW(1)
OW(2)
C(1)–C(2)
C(3)–C(4)
1.53(1)
1.49(1)
1.55(3)
1.55(3)
O(12)–H(1)
H(1)?O(8)
O(12)–H(1)?O(8)
0.95(2)
1.68(2)
153
C(5A)–C(6A)
C(5B)–C(6B)
Note: Ueq is defined as one-third of the trace of the orthogonalized Uij
tensor.
D–H?A angles rounded to the nearest degree.
OW(1) and OW(2) are half occupied and separated from each other by
2.15(5) A.
rise to a chain of alternating U(1) and U(2) bipyramids
that is one polyhedron wide, and that extends along
[10À1]. The arsenate tetrahedra are attached to either
side of the chains by sharing edges with uranyl
polyhedra (Fig. 5), and equatorial vertices with uranyl
polyhedra from adjacent chains, resulting in sheets that
are parallel to (010). The orientations of the tetrahedra
alternate along the length of any chain such that the
apical (non-sheet) tetrahedral ligand occurs alternately
above and below the sheet. This arrangement is the
identical to the uranyl silicate sheets in uranophane-
beta, Ca[(UO2)SiO3OH)]2(H2O)5 [45]. There are two
symmetrically independent U atoms in TriethUAs, each
of which is part of an approximately linear (UO2)2+
cation. The uranyl ions are coordinated by five
additional ligands arranged at the equatorial positions
of pentagonal bipyramids, with the uranyl O atoms at
the apices of the bipyramids. The U(1) and U(2)
pentagonal bipyramids share an equatorial edge, giving

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Table 7
Selected interatomic distances (A) and angles (deg) for PiperUP
U(1)–O(6)
U(1)–O(17)
U(1)–O(11)
U(1)–O(1)
U(1)–O(21)
U(1)–O(19)
U(1)–O(2)
1.751(9)
1.754(9)
2.317(9)
2.381(7)
2.392(7)
2.469(7)
2.505(8)
1.75
U(4)–O(12)
U(4)–O(16)
U(4)–O(8)
U(4)–O(3)
U(4)–O(10)
U(4)–O(7)
U(4)–O(4)
1.74(1)
1.748(9)
2.302(8)
2.342(9)
2.355(7)
2.499(7)
2.513(8)
1.74
P(3)–O(24)
P(3)–O(15)
P(3)–O(21)
P(3)–O(1)
/P(3)–OS
1.483(8)
1.501(8)
1.549(7)
1.555(8)
1.52
P(4)–O(20)
P(4)–O(11)
P(4)–O(2)
P(4)–O(19)
/P(4)–OS
1.489(8)
1.546(9)
1.552(8)
1.556(8)
1.54
/U(1)–Oap
S
/U(4)–OapS
/U(1)–Oeq
S
2.41
178.2(4)
/U(4)–Oeq
S
2.40
178.1(4)
O(6)–U(1)–O(17)
O(12)–U(4)–O(16)
U(2)–O(22)
U(2)–O(13)
U(2)–O(15)
U(2)–O(19)
U(2)–O(2)
U(2)–O(1)
U(2)–O(21)
1.736(9)
1.76(1)
2.307(8)
2.351(7)
2.353(8)
2.489(7)
2.497(7)
1.75
U(5)–O(26)
U(5)–O(25)
U(5)–O(20)
U(5)–O(18)
U(5)–O(23)
U(5)–O(24)
U(5)–O(27)
1.750(7)
1.764(8)
2.335(8)
2.349(8)
2.388(7)
2.389(7)
2.551(9)
1.76
N(1)–C(4)
N(1)–C(1)
1.43(2)
1.47(2)
N(2)–C(2)
N(2)–C(3)
1.47(2)
1.49(2)
/U(2)–Oap
/U(2)–Oeq
O(22)–U(2)–O(13)
S
/U(5)–Oap
/U(5)–Oeq
O(26)–U(5)–O(25)
S
C(1)–C(3)
C(2)–C(4)
1.48(2)
1.55(1)
S
2.40
178.8(4)
S
2.40
179.6(4)
OW(1)–N(2)
OW(1)–O(12)
3.11(4)
3.17(4)
U(3)–O(5)
U(3)–O(14)
U(3)–O(9)
U(3)–O(4)
U(3)–O(7)
U(3)–O(10)
U(3)–O(3)
1.753(9)
1.760(9)
2.291(7)
2.369(8)
2.394(7)
2.480(7)
2.522(8)
1.76
P(1)–O(23)
P(1)–O(8)
P(1)–O(7)
P(1)–O(4)
/P(1)–OS
1.488(8)
1.523(9)
1.563(8)
1.568(8)
1.54
OW(2)–O(27)
OW(2)–O(15)
2.83(3)
3.10(4)
P(2)–O(18)
P(2)–O(3)
P(2)–O(10)
P(2)–O(9)
/P(2)–OS
1.490(9)
1.543(9)
1.556(7)
1.562(8)
1.54
/U(3)–Oap
/U(3)–Oeq
O(5)–U(3)–O(14)
S
S
2.41
176.6(3)
aa|aa geometrical isomer of the uranophane sheet-anion
topology [46].
There are two symmetrically independent As atoms in
TriethUAs, both of which are in distorted tetrahedral
coordination (Table 6). As(1) is the center of an
AsO3OH group; the apical (non-sheet) ligand of the
tetrahedron, O(12), has the longest distance to As(1),
and with H(1), comprises a hydroxyl group (Table 6).
As(2) is the center of an AsO4 group; the apical ligand,
O(8), has the shortest distance to As(2), and accepts
hydrogen bonds from H(1) and H(2).
The triethylammonium cation in TriethUAs is located
in the interlayer between the uranyl arsenate sheets
(Fig. 6). The C(5)–C(6) ethyl group of this cation is
disordered. During least-squares refinement, the
C(5)–C(6) bond length refined to an unreasonably
short distance, B1.37 A, and the displacement para-
meters of both atoms were larger than expected. The
disorder was modeled with split positions (Table 3),
yielding two half-occupied ethyl groups, C(5A)–C(6A)
and C(5B)–C(6B) whose orientation is reminiscent of a
pair of crossed arms (Fig. 7). It is likely that similar
disorder is present in the phosphate isostructure,
fNHðC2H5Þ3g½ðUO2Þ2ðPO4ÞðPO3OHފ; despite data
collection having been undertaken at 150 K. The
Fig. 1. The autunite-type uranyl arsenate sheet found in DabcoUAs,
projected onto (010). The uranyl polyhedra are shown in shades of
gray and the arsenate tetrahedra are stippled.

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2681
Fig. 4. The local environment of the triethylenediammonium cation.
The separation distance from OW(2A) is 3.4–3.5 A.
Fig. 2. The structure of DabcoUAs projected along [001]. The
triethylenediammonium cations are represented as rods, and OW(1)
as small spheres. OW(2A) is omitted for clarity.
Fig. 5. The uranophane-beta type uranyl arsenate sheet in the
structure of TriethUAs, projected along [010]. Tetrahedra on both
sides of the uranyl chains alternate orientations along the chain length,
giving rise to the geometrical isomer designation aa|aa. The uranyl
polyhedra are shown in shades of gray and the arsenate tetrahedra are
stippled.
The structure of PiperUP is also based on the aa|aa
geometrical isomer of the uranophane sheet-anion
topology. The uranyl phosphate sheet in PiperUP is
topologically identical to the uranyl arsenate sheet in
TriethUAs, and is oriented similarly with the sheet
parallel to (010) and the direction of chain propagation
along [10À1], but contains four symmetrically indepen-
dent U atoms and four P atoms. The U(5) pentagonal
bipyramid is located in the interlayer, between the
uranyl phosphate sheets. Four equatorial oxygen atoms
of the U(5) pentagonal bipyramid are shared with
phosphate tetrahedra, providing linkage of the sheets,
and resulting in an open uranyl phosphate framework
structure (Fig. 8). The coordination polyhedron about
U(5) is completed by an H2O group—O(27). The
Fig. 3. Part of the structure of DabcoUAs projected along [010],
showing the orientation and disorder of the triethylenediammonium
cations and H2O groups. N(1A) is shown as striped spheres, and is
half-occupied, separated from its symmetry equivalent by 1.39(2) A.
C(2A) is shown as cross-hatched spheres and OW(2A) is shown as
darkgray spheres; these positions are half-occupied and separated
from each other by 1.27(1) A. C(1) is fully occupied and shown as light
gray spheres. OW(1) is omitted for clarity.
reported C(5)–C(6) bond length in this compound [16]
is 1.24 A, inconsistent with the presence of a single
bond [47].

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2682
Fig. 8. The structure of PiperUP projected along [001]. The
piperazinium cations occupy the large cavities of the structure. Carbon
atoms are shown as light gray spheres and nitrogen atoms as medium
gray spheres. The interstitial H2O groups, OW(1) and OW(2), are half-
occupied and separated from each other by 2.15(5) A, and are shown
as darkgray spheres. The uranyl polyhedra are shown in shades of
gray and the arsenate tetrahedra are stippled.
Fig. 6. The structure of TriethUAs projected along [001]. The
triethylammonium cations are represented as isolated irregular
polyhedra between the uranyl arsenate sheets.
4.2. Bond valence analysis
Bond valence analysis was performed using the
coordination-specific parameters of Burns et al. [48]
for U6+, and the parameters of Brown and Altermatt
[49] for As and P. For DabcoUAs, the bond valence sum
at the U(1) site is 6.16 valence units (vu) and the sum at
the As(1) site is 5.13 vu, consistent with formal valences
of U6+ and As5+. The bond valence sums for O(1) to
O(5) range from 1.61 to 2.01 vu, consistent with their
assignment as O atoms.
For TriethUAs, the bond valence sums at the U sites
are 5.93 and 5.96 vu for U(1) and U(2), respectively,
whereas the sums at the As sites are 5.12 and 5.03 vu for
As(1) and As(2), respectively, consistent with formal
valences of U6+ and As5+. The bond valence sum for
O(12) is 1.23 vu, consistent with its assignment as an
hydroxyl group, whereas the bond valence sum for O(8)
is rather low at 1.37 vu. If the hydrogen bonds from
H(1) and H(2) to O(8) are included into the calculation
[50], then the bond valence sum for O(8) increases to
1.83 vu, an acceptable value for an O atom. The bond
valence sums for the remaining O atoms range from 1.71
to 2.18 vu.
Fig. 7. Ball and stickrepresentation of the triethylammonium cation
in TriethUAs, showing the ‘‘crossed arm’’ disorder of the half-occupied
C(5A)–C(6A) and C(5B)–C(6B) ethyl groups.
For PiperUP, the bond valence sums at the U sites are
6.00, 6.11, 5.99, 6.13, and 6.03 vu for U(1)–U(5),
respectively, and the sums at the P sites are 5.01, 4.97,
5.19 and 5.00 vu for P(1) to P(4), respectively, consistent
with formal valences of U6+ and P5+. The bond valence
sum for O(27) is 0.37 vu, consistent with its assignment
as an H2O group. The bond valence sums for the
O(1)–O(26) atoms range from 1.73 to 2.17 vu.
piperazinium cation occupies the large cavities in the
framework( Fig. 8) along with two half-occupied H2O
groups—OW(1) and OW(2)—that are held in the
structure only by hydrogen bonding.

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2683
5. Discussion
in the third dimension [9,46,74–76]. The cavities in these
frameworks are occupied by H2O groups and low-
valence cations.
5.1. Autunite-type sheets
The use of amines as structure-directing agents in the
synthesis of uranyl phosphates and uranyl arsenates can
lead both to uranophane-type sheet structures (triethyl-
amine, tetrapropylamine [16, this work]) and framework
structures (diethylamine, piperazine [8, this work])
analogous to those of inorganic uranyl phosphates and
uranyl arsenates. The exact role of the organic cations in
the formation of extended structures has remained
elusive [77], beyond their charge-balancing and space-
filling roles. Careful control of hydrothermal reaction
conditions in the piperazine–uranyl–phosphonate sys-
tem has demonstrated that structural diversity is a
function of reactant concentrations [26], consistent with
the concept of a structure-directing agent, rather than a
template sensu stricto [78].
Layered compounds containing the autunite-type
sheet have long been known for their ion exchange
properties [51]. A wide variety of inorganic cations can
be intercalated between the negatively charged uranyl
phosphate or uranyl arsenate sheets, including
alkali metals, alkaline earths, transition metals,
aluminum, and lanthanides, as well as complex ions
such as oxonium, ammonium and metal-amine com-
plexes [51–63].
Organic cations, generally protonated amines, have
also been intercalated between autunite-type sheets
[64,65], with recent attention focused on the intercala-
tion and post-intercalative polymerization of aniline
[66–70], and the intercalation of polyamine metal
complexes [71]. Until now, no crystal structures of
amine-bearing autunite-type compounds have been
reported, possibly because the intercalation process
does not yield single crystals; the expansion or contrac-
tion of interlayer space during the exchange process
induces disorder and the resultant mosaic spread is more
consistent with a powder sample [72,73]. DabcoUAs is
apparently the first organic-bearing autunite-type struc-
ture to be refined. It is probable that synthesis using
mild hydrothermal conditions would yield further well-
crystallized examples of this structure type, and permit a
more detailed understanding of the configurations of the
organic guest molecules between the sheets.
Acknowledgments
This research was supported by the Environmental
Management Science Program of the Office of Science,
US Department of Energy, grants DE-FGO7-
97ER14820 and DE-FGO7-02ER63489. We thank
Sergey Krivovichev for encouraging this work. AJL
thanks the Environmental Molecular Sciences Institute,
University of Notre Dame, for a 2003 EMSI Fellowship,
and the International Centre for Diffraction Data for a
2004 Ludo Frevel Crystallography Scholarship.
5.2. Uranophane topology
References
The uranophane sheet-anion topology is adapted by a
wide variety of minerals and inorganic uranyl com-
pounds, including silicates, phosphates, arsenates and
vanadates (reviewed in Ref. [46]). Geometrical varia-
bility within the uranophane type-sheet is generally
limited to changes in the orientation of the tetrahedra,
for which six geometrical isomers have been recognized
[46], but the sheet does not have to remain planar, and
puckered [16] or even highly corrugated examples have
been described [46]. Extension of the chemical system to
phosphonates reveals similar themes in structures based
on the uranophane-type sheet: a uranyl methylpho-
sphonate has the aa|aa geometrical isomer [18], whereas
a uranyl chloromethylphosphonate shows the du|du
isomer [21]. One of the uranyl phenylphosphonate
compounds is unique in that the uu|uu isomer of the
uranophane sheet has been curved to form tubes of finite
width and infinite length, rather than infinite sheets [22].
In addition to sheet structures, inorganic framework
structures are observed, in which interlayer uranyl
polyhedra share equatorial vertices with the tetrahedra
of the uranophane-type sheet, thereby providing linkage
[1] P.C. Burns, M.L. Miller, R.C. Ewing, Can. Mineral. 34 (1996)
845–880.
[2] F. Demartin, C.M. Gramaccioli, T. Pilati, Acta Crystallogr. C 48
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