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A new microporous zirconogermanate, di­ammonium zirconium trigermanate, (NH4)2ZrGe3O9 (FDZG-2), analogous to wadeite (K2ZrSi3O9), was hydro­thermally synthesized using ZrO(NO3)2·2H2O as the source of zirconium and 1,4-di­amino­butane as a structure-directing agent. Single-crystal X-ray diffraction analysis reveals that the framework structure is built up of cyclic trigermanate units crosslinked by ZrO6 octahedra. The Zr atom lies at a site with \bar3 symmetry and the unique N atom of the ammonium ion lies at a site with threefold symmetry. Large cages are observed, with two NH4+ cations in each. The structure contains intersecting six- and three-membered ring (6MR and 3MR) channels, but only the 6MR channels can accommodate the NH4+ ions.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103005353/bc1005sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270103005353/bc1005Isup2.hkl
Contains datablock I

Comment top

Ion-exchangeable materials, such as silicates and germanates, have potential applications in nuclear waste remediation (Clearfield, 1995). Recent work of our group has been directed towards the syntheses of zirconogermanates (Liu et al., 2003), of which a very limited number have been reported to date (Choisnet et al., 1973; Nosyrev et al., 1975; Ilyushin et al., 1983; Ilyushin, 1989; Pertierra et al., 1999; Li et al., 2000), although the zirconosilicate analogues have been given considerable attention during past decades (Maurice, 1949; Baussy et al., 1974; Ghose et al., 1980; Bortun et al., 1997; Lin et al., 1999; Rocha & Anderson, 2000). Wadeite (K2ZrSi3O9, P63/m, a = b = 6.893 Å, c = 10.172 Å, V = 418.6 Å3, Z = 2) is a natural zirconosilicate whose analogues, ABM3O9 (A = K, Rb; B = Ti, Sn; M = Si, Ge), have been prepared in the 1103–1273 K temperature range (Choisnet et al., 1973). We report here the synthesis and structure of its zirconogermanate analogue, (NH4)2ZrGe3O9 (denoted FDZG-2).

A single-crystal X-ray analysis reveals that the (NH4)2ZrGe3O9 structure is similar to wadeite, with Si replaced by Ge and K+ replaced by NH4+. The Ge—O bond lengths (average 1.722 Å) are close to the value expected for a Ge—O single bond (1.748 Å; Brese & O' Keeffe, 1991). The bond-valence sums (Brese & O'Keeffe, 1991) at Ge and Zr are 4.30 and 4.11, close to the expected values (4.0 and 4.0, respectively). The bond angles at the O atoms are Ge—O—Ge = 131.7 (6)° and Ge—O—Zr = 140.5 (4)°, which are smaller than the corresponding angles in wadeite.

The structure of (NH4)2ZrGe3O9 is based on an hexagonal three-dimensional framework of composition ZrGe3O9, in which Ge is tetrahedrally coordinated and Zr is octahedrally coordinated. In the structure, three GeO4 tetrahedra form cyclic trigermanate units (Ge3O9) in the ab plane, which are linked by ZrO6 octahedra (Fig. 1). The center of each cyclic trigermanate unit is located at z = 1/4, 3/4, and the Zr atoms are located on the c axis at z = 0, 1/2. This arrangement results in a cage-like topology with two kinds of cages, viz. small cages, 43, with composition Zr2Ge3O6 and large cages, 324366, with composition Zr6Ge12O15 (Fig. 2); the cage sizes are 2.38 × 2.38 × 5.29 Å3 and 4.12 × 4.12 × 10.58 Å3, respectively. In the large cages, two NH4+ ions are located near the center of a Zr triangle in the ab plane, with a slight shift of 0.58 Å above and below the Zr triangle (Fig. 2 b). The NH4+ ions not only balance the negative charges of the framework but also form weak hydrogen bonds with neighboring O atoms, which can be inferred from the three short N—O distances (2.90 Å). Because NH4+ ions were not present in the initial mixture, they may be derived from the decomposition of 1,4-diaminebutane under hydothermal conditions. The channel system of (NH4)2ZrGe3O9 is three-dimensional, with intersecting 6MR channels along the a and b axes (Fig. 3) and 3MR channels along the c axis (Fig. 1). In fact, the 6MR and 3MR channels are windows of the large cages, the free-pore diameters of which are 3.07 and 1.60 Å respectively. Because the size of the NH4+ ion is about 1.61 Å (Shannon, 1976), the movement of these ions is only free through the 6MR channels. Thus, the intersecting 6MR channels along a and b axis form two-dimensional channels for the NH4+ ions.

Experimental top

In a typical procedure, ZrO(NO3)2·2H2O (0.26 g, 0.97 mmol) was dissolved in H2O (1.07 g, 59.4 mmol), to which glycol (0.87 g, 14 mmol), GeO2 (0.24 g, 2.29 mmol) and 1,4-diaminobutane (0.50 g, 5.68 mmol) were added successively under vigorous stirring. Then a drop of 40% HF (0.05 g, 1 mmol) was added to the mixture. After stirring at room temperature for 10 h, the solution was heated at 433 K for 14 d in a Teflon-lined vessel. After the mixture was cooled to room temperature, colorless crystals were recovered. The ammonium cations in the compound are derived from the decomposition of 1,4-diaminobutane.

Refinement top

The locations of the highest peak and deepest hole in the difference Fourier map are 0.98 Å from Ge and 1.03 Å from Ge, respectively. H-atom positions were not included in the refinement.

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DS Viewerpro (Accelrys, 2002); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Ball-and-stick representation of part of the FDZG-2 structure, viewed approximately along the c axis; only one Zr position, viz. (0,0,1/2), is drawn for clarity. Dashed lines represent hydrogen bonds between NH4+ ions and the lattice O atoms.
[Figure 2] Fig. 2. Two kind of cages of FDZG-2 structure: (a) the cage of 43 topology, with composition Zr2Ge3O6; (b) the cage of 324366 topology, with composition Zr6Ge12O15. Dashed lines represent hydrogen bonds between NH4+ ions and the lattice O atoms.
[Figure 3] Fig. 3. 6MR channels in the FDZG-2 structure, viewed along the a and b axes.
diammonium zirconium getmanate top
Crystal data top
(NH4)2ZrGe3O9Dx = 3.455 Mg m3
Mr = 481.01Mo Kα radiation, λ = 0.71073 Å
Hexagonal, P63/mCell parameters from 568 reflections
a = 7.117 (5) Åθ = 5.6–23.0°
c = 10.542 (9) ŵ = 10.79 mm1
V = 462.4 (6) Å3T = 298 K
Z = 2Prism, colorless
F(000) = 4440.04 × 0.04 × 0.04 mm
Data collection top
Nonius KappaCCDr
diffractometer
367 independent reflections
Radiation source: fine-focus sealed tube280 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.085
ω scansθmax = 27.1°, θmin = 3.3°
Absorption correction: multi-scan
(SADABS; Bruker, 2001)
h = 89
Tmin = 0.672, Tmax = 0.672k = 89
2333 measured reflectionsl = 1311
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.052H-atom parameters not refined
wR(F2) = 0.110 w = 1/[σ2(Fo2) + (0.0415P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.13(Δ/σ)max < 0.001
367 reflectionsΔρmax = 1.46 e Å3
28 parametersΔρmin = 0.84 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.009 (2)
Crystal data top
(NH4)2ZrGe3O9Z = 2
Mr = 481.01Mo Kα radiation
Hexagonal, P63/mµ = 10.79 mm1
a = 7.117 (5) ÅT = 298 K
c = 10.542 (9) Å0.04 × 0.04 × 0.04 mm
V = 462.4 (6) Å3
Data collection top
Nonius KappaCCDr
diffractometer
367 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2001)
280 reflections with I > 2σ(I)
Tmin = 0.672, Tmax = 0.672Rint = 0.085
2333 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0520 restraints
wR(F2) = 0.110H-atom parameters not refined
S = 1.13Δρmax = 1.46 e Å3
367 reflectionsΔρmin = 0.84 e Å3
28 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Zr1.00001.00000.00000.0112 (6)
Ge0.8761 (2)0.6230 (2)0.25000.0135 (5)
O10.9877 (12)0.7564 (12)0.1128 (6)0.0236 (17)
O20.9235 (16)0.4027 (16)0.25000.025 (3)
N0.33330.66670.0559 (14)0.025 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Zr0.0120 (8)0.0120 (8)0.0096 (12)0.0060 (4)0.0000.000
Ge0.0118 (8)0.0101 (8)0.0182 (9)0.0052 (7)0.0000.000
O10.029 (5)0.027 (4)0.024 (4)0.020 (4)0.004 (3)0.014 (3)
O20.014 (5)0.013 (5)0.053 (7)0.011 (5)0.0000.000
N0.025 (5)0.025 (5)0.026 (9)0.012 (3)0.0000.000
Geometric parameters (Å, º) top
Zr—O1i2.068 (7)Ge—O1vi1.694 (7)
Zr—O1ii2.068 (7)Ge—O11.694 (7)
Zr—O1iii2.068 (7)Ge—O2vii1.738 (10)
Zr—O12.068 (7)Ge—O21.761 (9)
Zr—O1iv2.068 (7)O2—Geviii1.738 (10)
Zr—O1v2.068 (7)
O1i—Zr—O1ii180.0O1iii—Zr—O1v180.0
O1i—Zr—O1iii90.2 (3)O1—Zr—O1v90.2 (3)
O1ii—Zr—O1iii89.8 (3)O1iv—Zr—O1v89.8 (3)
O1i—Zr—O189.8 (3)O1vi—Ge—O1117.2 (5)
O1ii—Zr—O190.2 (3)O1vi—Ge—O2vii110.6 (3)
O1iii—Zr—O189.8 (3)O1—Ge—O2vii110.6 (3)
O1i—Zr—O1iv90.2 (3)O1vi—Ge—O2104.7 (3)
O1ii—Zr—O1iv89.8 (3)O1—Ge—O2104.7 (3)
O1iii—Zr—O1iv90.2 (3)O2vii—Ge—O2108.3 (6)
O1—Zr—O1iv180.0Ge—O1—Zr140.5 (4)
O1i—Zr—O1v89.8 (3)Geviii—O2—Ge131.7 (6)
O1ii—Zr—O1v90.2 (3)
Symmetry codes: (i) y, x+y+1, z; (ii) y+2, xy+1, z; (iii) xy+1, x, z; (iv) x+2, y+2, z; (v) x+y+1, x+2, z; (vi) x, y, z+1/2; (vii) y+1, xy, z; (viii) x+y+1, x+1, z.

Experimental details

Crystal data
Chemical formula(NH4)2ZrGe3O9
Mr481.01
Crystal system, space groupHexagonal, P63/m
Temperature (K)298
a, c (Å)7.117 (5), 10.542 (9)
V3)462.4 (6)
Z2
Radiation typeMo Kα
µ (mm1)10.79
Crystal size (mm)0.04 × 0.04 × 0.04
Data collection
DiffractometerNonius KappaCCDr
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2001)
Tmin, Tmax0.672, 0.672
No. of measured, independent and
observed [I > 2σ(I)] reflections
2333, 367, 280
Rint0.085
(sin θ/λ)max1)0.641
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.052, 0.110, 1.13
No. of reflections367
No. of parameters28
H-atom treatmentH-atom parameters not refined
Δρmax, Δρmin (e Å3)1.46, 0.84

Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2001), SAINT, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), DS Viewerpro (Accelrys, 2002), SHELXL97.

Selected geometric parameters (Å, º) top
Zr—O12.068 (7)Ge—O2i1.738 (10)
Ge—O11.694 (7)Ge—O21.761 (9)
O1—Zr—O1ii90.2 (3)O2i—Ge—O2108.3 (6)
O1iii—Ge—O1117.2 (5)Ge—O1—Zr140.5 (4)
O1—Ge—O2i110.6 (3)Geiv—O2—Ge131.7 (6)
O1—Ge—O2104.7 (3)
Symmetry codes: (i) y+1, xy, z; (ii) x+y+1, x+2, z; (iii) x, y, z+1/2; (iv) x+y+1, x+1, z.
 

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