The title compound, lithium potassium dialuminium digermanium octaoxide dihydrate, (K,Li)-(Al,Ge)-GIS (GIS is gismondine), is the result of a 50% Li
+ exchange into the K-(Al,Ge)-GIS structure. The (K,Li)-(Al,Ge)-GIS structure was determined from a 4 × 4 × 2 µm octahedral single crystal at the ESRF synchrotron X-ray source. The ion exchange results in a symmetry transformation from
I2/
a for K-(Al,Ge)-GIS to
C2/
c for (K,Li)-(Al,Ge)-GIS. The structural change is due to disordering of K
+ ions with Li
+ ions along the [001] channel and ordering of water molecules in the [101] channels. The distance between sites partially occupied by K
+ ions increases from 2.19 (3) Å in K-(Al,Ge)-GIS to 2.94 (3) Å in (K,Li)-(Al,Ge)-GIS. The Li
+ ions occupy positions along the twofold axis at the intersection of the eight-membered-ring channels in a twofold coordination with water molecules. For the four closest framework O
2- anions, the Li
O distances are 3.87 (4) Å.
Supporting information
K-(Al,Ge)-GIS crystals were synthesized according to Tripathi et al. (2000). The crystals were filtered, washed with deionized water and dried at room temperature. Their sizes ranged from approximately 4 x 4 x 2 mm to 60 x 60 x 40 mm along the octahedral edges. The synthesized crystals (10 mg) were placed in a 125 ml polypropylene bottle. LiOH (30 ml, 0.01 M) in aqueous solution was added as the exchangeable electrolyte. The crystals were agitated gently for 30 h and then removed from the bottle, filtered and washed with deionized water. A pristine 4 x 4 x 2 mm octahedral crystal was chosen for single-crystal diffraction studies at the ID-11 beamline of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Larger crystals contained cracks and stacking faults, which showed as split and streaky spots in the single-crystal diffraction patterns. 6Li MAS NMR measurements were carried out at 29.47 MHz on a CMX-200 spectrometer using a Chemagnetics probe equipped with a 4 mm rotor. The spectrum was recorded using a single pulse experiment with a spin rate of 10.17 (2) kHz and referenced to a LiCl solution (1.0 M) at 0 p.p.m.. The TGA experiment was performed on a Netzsch STA 449 C instrument. Data were collected on a 3.050 (5) mg sample between 298 and 873 K with a constant temperature ramp of 2 K min−1.
Data collection: SMART (Bruker AXS, 1996); cell refinement: SMART; data reduction: SAINT (Bruker AXS, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Endeavour (Putz et al. 1999); software used to prepare material for publication: SHELXL97.
lithium potassium dialuminum digermanium octaoxide dihydrate
top
Crystal data top
H16Al8Ge8K4Li4O40 | F(000) = 762 |
Mr = 202.64 | Dx = 2.531 Mg m−3 |
Monoclinic, C2/c | Synchrotron radiation, λ = 0.51641 Å |
a = 14.807 (1) Å | Cell parameters from 3801 reflections |
b = 9.5404 (19) Å | θ = 0.1–17.7° |
c = 10.394 (1) Å | µ = 3.30 mm−1 |
β = 134.12 (2)° | T = 293 K |
V = 1054.1 (4) Å3 | Octahedron, white |
Z = 8 | 0.00 (1) × 0.00 (1) × 0.00 (1) mm |
Data collection top
Bruker fixed kappa goniometer diffractometer | 821 reflections with I > 2σ(I) |
Radiation source: Beamline ID-11 ESRF | Rint = 0.073 |
Double crystal monochromator | θmax = 17.7°, θmin = 7.4° |
Detector resolution: 0.70 pixels mm-1 | h = −17→17 |
Bruker SMART 1500 CCD scans | k = −11→11 |
3770 measured reflections | l = −12→12 |
833 independent reflections | |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.033 | w = 1/[σ2(Fo2) + (0.0397P)2 + 6.3673P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.076 | (Δ/σ)max < 0.001 |
S = 1.07 | Δρmax = 0.68 e Å−3 |
833 reflections | Δρmin = −0.69 e Å−3 |
79 parameters | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.005 (2) |
Primary atom site location: structure-invariant direct methods | |
Crystal data top
H16Al8Ge8K4Li4O40 | V = 1054.1 (4) Å3 |
Mr = 202.64 | Z = 8 |
Monoclinic, C2/c | Synchrotron radiation, λ = 0.51641 Å |
a = 14.807 (1) Å | µ = 3.30 mm−1 |
b = 9.5404 (19) Å | T = 293 K |
c = 10.394 (1) Å | 0.00 (1) × 0.00 (1) × 0.00 (1) mm |
β = 134.12 (2)° | |
Data collection top
Bruker fixed kappa goniometer diffractometer | 821 reflections with I > 2σ(I) |
3770 measured reflections | Rint = 0.073 |
833 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.033 | 79 parameters |
wR(F2) = 0.076 | 0 restraints |
S = 1.07 | Δρmax = 0.68 e Å−3 |
833 reflections | Δρmin = −0.69 e Å−3 |
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 | x | y | z | Uiso*/Ueq | Occ. (<1) |
Ge | −0.62217 (3) | 1.16335 (4) | −1.04686 (4) | 0.0147 (3) | 1.00 (1) |
Al | −0.33300 (9) | 1.09498 (11) | −0.70816 (13) | 0.0148 (3) | 1.00 (2) |
O1 | −0.4602 (2) | 1.1979 (3) | −0.8863 (4) | 0.0258 (6) | |
O2 | −0.6636 (3) | 1.0746 (3) | −1.2269 (4) | 0.0273 (7) | |
O3 | −0.6936 (3) | 1.3260 (3) | −1.1217 (4) | 0.0272 (7) | |
O4 | −0.6679 (3) | 1.0661 (3) | −0.9591 (4) | 0.0291 (7) | |
O21 | 0.3700 (4) | 0.7525 (6) | 0.0593 (6) | 0.0648 (12) | 1.00 (4) |
K | −0.0715 (3) | 1.0011 (4) | −0.1983 (5) | 0.0731 (9) | 0.49 (1) |
Li | 0.0000 | 0.890 (4) | −0.2500 | 0.064 (7) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Ge | 0.0138 (3) | 0.0146 (4) | 0.0187 (3) | 0.00174 (12) | 0.0123 (2) | −0.00015 (12) |
Al | 0.0137 (5) | 0.0144 (6) | 0.0193 (5) | −0.0018 (4) | 0.0125 (5) | −0.0023 (4) |
O1 | 0.0167 (12) | 0.0254 (15) | 0.0316 (14) | 0.0003 (11) | 0.0154 (12) | 0.0043 (13) |
O2 | 0.0420 (16) | 0.0204 (15) | 0.0293 (14) | −0.0019 (12) | 0.0285 (13) | −0.0022 (11) |
O3 | 0.0193 (13) | 0.0155 (15) | 0.0454 (17) | 0.0038 (10) | 0.0220 (13) | 0.0019 (11) |
O4 | 0.0364 (15) | 0.0319 (17) | 0.0334 (14) | −0.0093 (13) | 0.0296 (13) | −0.0055 (12) |
O21 | 0.079 (3) | 0.067 (3) | 0.065 (3) | −0.012 (2) | 0.056 (2) | 0.007 (2) |
K | 0.0701 (18) | 0.066 (2) | 0.099 (2) | 0.0109 (15) | 0.0646 (18) | 0.0074 (17) |
Li | 0.072 (18) | 0.057 (19) | 0.09 (2) | 0.000 | 0.065 (18) | 0.000 |
Geometric parameters (Å, º) top
Ge—O3 | 1.729 (3) | O21—Liviii | 2.05 (3) |
Ge—O2 | 1.731 (3) | O21—Kix | 3.145 (6) |
Ge—O4 | 1.736 (3) | O21—Kviii | 3.291 (7) |
Ge—O1 | 1.753 (3) | K—Li | 1.81 (3) |
Ge—Ki | 3.640 (4) | K—O1ii | 2.944 (5) |
Ge—Kii | 3.847 (4) | K—O3x | 2.947 (5) |
Ge—Kiii | 3.881 (4) | K—O4i | 2.969 (5) |
Al—O2iv | 1.739 (3) | K—Kxi | 2.970 (7) |
Al—O3v | 1.747 (3) | K—Kxii | 3.054 (9) |
Al—O4i | 1.751 (3) | K—O21xiii | 3.145 (6) |
Al—O1 | 1.757 (3) | K—O21viii | 3.291 (7) |
Al—Kvi | 3.909 (4) | K—O3ii | 3.320 (5) |
Al—K | 3.912 (5) | K—Gei | 3.640 (4) |
Al—Kii | 3.985 (4) | K—Geii | 3.847 (4) |
O1—Kii | 2.944 (5) | K—Gex | 3.881 (4) |
O2—Aliv | 1.739 (3) | Li—Kxi | 1.81 (3) |
O3—Alvii | 1.747 (3) | Li—O21xiii | 2.05 (3) |
O3—Kiii | 2.947 (5) | Li—O21viii | 2.05 (3) |
O3—Kii | 3.320 (5) | Li—Kxii | 4.123 (12) |
O4—Ali | 1.751 (3) | Li—Kvi | 4.123 (12) |
O4—Ki | 2.969 (5) | | |
| | | |
O3—Ge—O2 | 107.93 (17) | O3x—K—Kxii | 67.15 (15) |
O3—Ge—O4 | 112.15 (16) | O4i—K—Kxii | 136.20 (19) |
O2—Ge—O4 | 109.29 (15) | Kxi—K—Kxii | 119.2 (3) |
O3—Ge—O1 | 105.19 (15) | Li—K—O21xiii | 38.1 (8) |
O2—Ge—O1 | 110.00 (16) | O1ii—K—O21xiii | 152.46 (19) |
O4—Ge—O1 | 112.14 (15) | O3x—K—O21xiii | 84.41 (15) |
O3—Ge—Ki | 89.59 (12) | O4i—K—O21xiii | 78.32 (16) |
O2—Ge—Ki | 71.32 (13) | Kxi—K—O21xiii | 65.04 (14) |
O4—Ge—Ki | 53.88 (13) | Kxii—K—O21xiii | 128.4 (2) |
O1—Ge—Ki | 163.43 (13) | Li—K—O21viii | 33.9 (7) |
O3—Ge—Kii | 59.41 (13) | O1ii—K—O21viii | 132.68 (17) |
O2—Ge—Kii | 131.62 (12) | O3x—K—O21viii | 90.27 (14) |
O4—Ge—Kii | 118.76 (13) | O4i—K—O21viii | 134.68 (18) |
O1—Ge—Kii | 46.96 (13) | Kxi—K—O21viii | 60.05 (11) |
Ki—Ge—Kii | 144.37 (8) | Kxii—K—O21viii | 80.68 (17) |
O3—Ge—Kiii | 45.73 (11) | O21xiii—K—O21viii | 56.35 (19) |
O2—Ge—Kiii | 89.56 (12) | Li—K—O3ii | 93.1 (7) |
O4—Ge—Kiii | 155.98 (13) | O1ii—K—O3ii | 51.99 (10) |
O1—Ge—Kiii | 72.96 (12) | O3x—K—O3ii | 122.04 (15) |
Ki—Ge—Kiii | 123.53 (6) | O4i—K—O3ii | 137.82 (16) |
Kii—Ge—Kiii | 46.55 (12) | Kxi—K—O3ii | 73.63 (14) |
O2iv—Al—O3v | 107.66 (16) | Kxii—K—O3ii | 54.88 (14) |
O2iv—Al—O4i | 102.55 (16) | O21xiii—K—O3ii | 131.11 (15) |
O3v—Al—O4i | 111.60 (18) | O21viii—K—O3ii | 81.19 (14) |
O2iv—Al—O1 | 112.98 (16) | Li—K—Gei | 135.9 (2) |
O3v—Al—O1 | 108.47 (16) | O1ii—K—Gei | 70.23 (9) |
O4i—Al—O1 | 113.40 (15) | O3x—K—Gei | 75.53 (9) |
O2iv—Al—Kvi | 63.38 (12) | O4i—K—Gei | 28.18 (7) |
O3v—Al—Kvi | 45.05 (12) | Kxi—K—Gei | 125.34 (19) |
O4i—Al—Kvi | 127.87 (14) | Kxii—K—Gei | 109.12 (16) |
O1—Al—Kvi | 118.27 (13) | O21xiii—K—Gei | 103.66 (15) |
O2iv—Al—K | 92.68 (12) | O21viii—K—Gei | 157.09 (16) |
O3v—Al—K | 72.65 (14) | O3ii—K—Gei | 121.54 (12) |
O4i—Al—K | 45.78 (12) | Li—K—Geii | 110.7 (10) |
O1—Al—K | 151.64 (13) | O1ii—K—Geii | 25.79 (7) |
Kvi—Al—K | 83.28 (8) | O3x—K—Geii | 127.38 (15) |
O2iv—Al—Kii | 153.47 (13) | O4i—K—Geii | 111.59 (13) |
O3v—Al—Kii | 78.47 (12) | Kxi—K—Geii | 81.29 (9) |
O4i—Al—Kii | 98.71 (13) | Kxii—K—Geii | 67.30 (14) |
O1—Al—Kii | 42.65 (13) | O21xiii—K—Geii | 146.32 (15) |
Kvi—Al—Kii | 114.17 (8) | O21viii—K—Geii | 106.90 (14) |
K—Al—Kii | 113.60 (7) | O3ii—K—Geii | 26.64 (6) |
Ge—O1—Al | 130.56 (19) | Gei—K—Geii | 96.01 (9) |
Ge—O1—Kii | 107.25 (15) | Li—K—Gex | 87.8 (12) |
Al—O1—Kii | 113.50 (17) | O1ii—K—Gex | 136.40 (15) |
Ge—O2—Aliv | 140.2 (2) | O3x—K—Gex | 24.85 (7) |
Ge—O3—Alvii | 138.74 (19) | O4i—K—Gex | 101.72 (12) |
Ge—O3—Kiii | 109.42 (15) | Kxi—K—Gex | 122.32 (6) |
Alvii—O3—Kiii | 110.14 (16) | Kxii—K—Gex | 66.15 (14) |
Ge—O3—Kii | 93.95 (14) | O21xiii—K—Gex | 70.34 (12) |
Alvii—O3—Kii | 116.82 (15) | O21viii—K—Gex | 65.45 (10) |
Kiii—O3—Kii | 57.96 (16) | O3ii—K—Gex | 115.68 (13) |
Ge—O4—Ali | 134.5 (2) | Gei—K—Gex | 98.85 (8) |
Ge—O4—Ki | 97.93 (15) | Geii—K—Gex | 133.45 (12) |
Ali—O4—Ki | 109.21 (16) | Kxi—Li—K | 110 (2) |
Liviii—O21—Kix | 33.1 (5) | Kxi—Li—O21xiii | 116.6 (3) |
Liviii—O21—Kviii | 29.5 (4) | K—Li—O21xiii | 108.8 (3) |
Kix—O21—Kviii | 54.91 (16) | Kxi—Li—O21viii | 108.8 (3) |
Li—K—O1ii | 130.1 (12) | K—Li—O21viii | 116.6 (3) |
Li—K—O3x | 110.5 (12) | O21xiii—Li—O21viii | 95.7 (19) |
O1ii—K—O3x | 118.17 (15) | Kxi—Li—Kxii | 116.7 (13) |
Li—K—O4i | 107.7 (2) | K—Li—Kxii | 42.84 (18) |
O1ii—K—O4i | 87.66 (13) | O21xiii—Li—Kxii | 125.9 (7) |
O3x—K—O4i | 85.02 (13) | O21viii—Li—Kxii | 75.24 (18) |
Li—K—Kxi | 35.0 (12) | Kxi—Li—Kvi | 42.84 (18) |
O1ii—K—Kxi | 95.88 (9) | K—Li—Kvi | 116.7 (13) |
O3x—K—Kxi | 145.48 (9) | O21xiii—Li—Kvi | 75.24 (18) |
O4i—K—Kxi | 103.0 (2) | O21viii—Li—Kvi | 125.9 (7) |
Li—K—Kxii | 113.4 (4) | Kxii—Li—Kvi | 151.3 (12) |
O1ii—K—Kxii | 77.65 (17) | | |
Symmetry codes: (i) −x−1, y, −z−3/2; (ii) −x−1/2, −y+5/2, −z−1; (iii) x−1/2, y+1/2, z−1; (iv) −x−1, −y+2, −z−2; (v) x+1/2, −y+5/2, z+1/2; (vi) x, −y+2, z−1/2; (vii) x−1/2, −y+5/2, z−1/2; (viii) −x+1/2, −y+3/2, −z; (ix) x+1/2, −y+3/2, z+1/2; (x) x+1/2, y−1/2, z+1; (xi) −x, y, −z−1/2; (xii) −x, −y+2, −z; (xiii) x−1/2, −y+3/2, z−1/2. |
Experimental details
Crystal data |
Chemical formula | H16Al8Ge8K4Li4O40 |
Mr | 202.64 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 293 |
a, b, c (Å) | 14.807 (1), 9.5404 (19), 10.394 (1) |
β (°) | 134.12 (2) |
V (Å3) | 1054.1 (4) |
Z | 8 |
Radiation type | Synchrotron, λ = 0.51641 Å |
µ (mm−1) | 3.30 |
Crystal size (mm) | 0.00 (1) × 0.00 (1) × 0.00 (1) |
|
Data collection |
Diffractometer | Bruker fixed kappa goniometer diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3770, 833, 821 |
Rint | 0.073 |
(sin θ/λ)max (Å−1) | 0.587 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.033, 0.076, 1.07 |
No. of reflections | 833 |
No. of parameters | 79 |
Δρmax, Δρmin (e Å−3) | 0.68, −0.69 |
Selected geometric parameters (Å, º) topGe—O3 | 1.729 (3) | Al—O1 | 1.757 (3) |
Ge—O2 | 1.731 (3) | K—O1iv | 2.944 (5) |
Ge—O4 | 1.736 (3) | K—O3v | 2.947 (5) |
Ge—O1 | 1.753 (3) | K—O4iii | 2.969 (5) |
Al—O2i | 1.739 (3) | K—O21vi | 3.145 (6) |
Al—O3ii | 1.747 (3) | Li—O21vi | 2.05 (3) |
Al—O4iii | 1.751 (3) | | |
| | | |
O3—Ge—O2 | 107.93 (17) | O3ii—Al—O4iii | 111.60 (18) |
O3—Ge—O4 | 112.15 (16) | O2i—Al—O1 | 112.98 (16) |
O2—Ge—O4 | 109.29 (15) | O3ii—Al—O1 | 108.47 (16) |
O3—Ge—O1 | 105.19 (15) | O4iii—Al—O1 | 113.40 (15) |
O2—Ge—O1 | 110.00 (16) | Ge—O1—Al | 130.56 (19) |
O4—Ge—O1 | 112.14 (15) | Ge—O2—Ali | 140.2 (2) |
O2i—Al—O3ii | 107.66 (16) | Ge—O3—Alvii | 138.74 (19) |
O2i—Al—O4iii | 102.55 (16) | Ge—O4—Aliii | 134.5 (2) |
Symmetry codes: (i) −x−1, −y+2, −z−2; (ii) x+1/2, −y+5/2, z+1/2; (iii) −x−1, y, −z−3/2; (iv) −x−1/2, −y+5/2, −z−1; (v) x+1/2, y−1/2, z+1; (vi) x−1/2, −y+3/2, z−1/2; (vii) x−1/2, −y+5/2, z−1/2. |
Zeolites and microporous materials with the gismondine (GIS) structure are characterized by perpendicular double crankshaft chains of tetrahedra. These tetrahedra are connected at all corners, thus forming pore systems that consist of two eight-membered ring (8MR) channels connected by four-membered rings (4MRs) (Baerlocher et al., 2001). The GIS topology has high framework flexibility (Bauer & Baur, 1998; Tripathi et al., 2000; Baerlocher et al., 2001), which allows the accommodation of a wide range of extra-framework cations. This flexibility offers the potential for studying the mechanisms of ion-exchange reactions within the same framework topology using an array of guest species. Previous ion-exchange studies on gismondine-type zeolites include those by Bauer & Baur (1998) and Tripathi et al. (2000). Bauer & Baur (1998) exchanged Li+ and K+ ions into crystals of Na–gismondine. The precursor material showed Na+ sites to be half-occupied and coordinated to the walls of both 8MR channels. The other half occupancy is attributed to H2O molecules. Upon Li+ exchange, Li+ ions occupied only one channel at the center of a distorted tetrahedron formed by two framework O2− anions and two H2O molecules. Upon K+ exchange, K+ ions occupied the centers of the 8MR channels where these sites were previously disordered with H2O molecules. Tripathi et al. (2000) reported the structure of 50% Na+-exchanged K-(Al,Ge)-GIS, in which Na+ and K+ ions are disordered with H2O molecules and each cation species occupies the center of separate 8MR channels. K-(Al,Ge)-GIS was chosen for ion-exchange studies because of the well characterized structure of the native material and the unique structure adopted upon ion exchange (Tripathi et al., 2000). The present study represents the first ion-exchange and structural characterization of Li+ in the (Al,Ge)-GIS structure.
Following the ex-situ ion exchange, the atomic positions were determined from the collected X-ray diffraction intensities using direct methods. The occupancies of the Al, Ge, K and extra-framework O21 sites were subsequently refined and converged to 1.00 (2) for Al, 1.00 (1) for Ge, 1.00 (4) for O21 and 0.50 (1)for K. The site occupancies of the framework O atoms were not refined, and the H atoms of the water molecule (O21) were not located. In the final difference Fourier map, the highest peak (0.68 e/Å3) was located 1.63 Å from atom O9 and the deepest hole (−0.69 e/Å3) was located 0.70 Å from the K atom. The refined atomic displacement parameters for the extra-framework species are large, which suggests that these species are highly mobile in the intracrystalline channels. Such displacement parameters are typical for extra-framework species in zeolites (Treacy et al., 1996). An attempt was made to refine the Li site occupancy, but this attempt resulted in an unacceptably large displacement parameter (Uiso > 0.14 Å2), or a low occupancy of approximately 70% (for a fixed Uiso = 0.07 Å2), which is insufficient for electroneutrality when combined with the 50% occupancy of the K site. In the final refinement cycles, the Li site occupancy was, therefore, fixed to 100% for charge balance, which led to reasonable anisotropic U parameters for the K, O21 and Li sites. The displacement ellipsoid for the Li atom was found to be elongated along the [101] direction, suggesting a high ionic conductivity for the Li+ ions, as seen in other Li+-bearing microporous structures (Park et al., 2000).
Magic angle spinning nuclear magnetic resonance (6Li MAS NMR) and thermogravimetric analysis (TGA) measurements were performed to qualitatively confirm the presence of Li and quantitatively determine the amount of H2O in the Li+-exchanged K-(Al,Ge)-GIS structure. The MAS NMR analysis showed a single peak shifted 0.9 p.p.m. from the standard [1 M LiCl (aqueous)]. Similar work by Park et al. (2002) described the Li+ ions in extra-framework positions in another Li-bearing zeolite as having small peak shifts of between 0.41 and 1.0 p.p.m., which is consistent with our results. The TGA results showed an 8.7% weight loss between 298 and 342.4 K, which agrees with the calculated H2O content (8.8 wt%) determined from the single-crystal refinement.
The sites occupied by Li+ ions correspond to crystallographic special (4 e) positions along the twofold axis, at the intersection of the [101] and [001] channels. The Li+ ions have a twofold coordination with two H2O molecules (O21) and do not coordinate with the framework O2−, anions since the shortest Li—O distances (to four framework O atoms) are 3.87 (4) Å. Similar extra-framework cation environments have been reported by Martucci et al. (2003) in modernite, in which the Ca2+ ions are only coordinated by H2O molecules. The shortest distance between K+ sites increases from 2.19 (3) Å in K-(Al,Ge)-GIS to 2.94 (3) Å in (K,Li)-(Al,Ge)-GIS. The K+ ions coordinate to two H2O molecules (O21) and to three framework O2− anions.
The gismondine structure transforms from space group I2/a to C2/c upon 50% substitution of Li+ for K+. The unit-cell transformation is a = −a'-c', b = b' and c = a', where (a, b, c) and (a', b', c') refer to the I-centered and the C-centered unit cell, respectively. The symmetry change is accompanied by a change in T—O—T angles, which range from 135.5 (2) to 136.5 (2)° in the unsubstituted K-(Al,Ge)-GIS structure (Tripathi et al., 2000) but are distorted in the (K,Li)-(Al,Ge)-GIS structure to accommodate the hydrated Li+ ions (Table 1).