Single crystals of lithium iron tungstate, LiFe(WO4)2, were obtained using a high-temperature solution growth method. The analysis was conducted using the monoclinic space group C2/c, with β = 90.597 (2)°, giving R1 = 0.0177. The Li and Fe atoms lie on twofold axes. The structure can also be refined using the orthorhombic space group Cmcm, giving slightly higher residuals. The experimental value of β and the residuals mitigate in favour of the monoclinic description of the structure. Calculated bond-valence sums for the present results are closer to expected values than those obtained using the results of a previously reported analysis of this structure.
Supporting information
Monoclinic crystals of LiFe(WO4)2 were obtained using a classical
high-temperature solution growth procedure (Elwell & Scheel, 1975), in
an
attempt to grow an iron tungstate using LiBO2 as solvent. During this
experiment, the flux reacted with the iron tungstate to form LiFe(WO4)2.
Data collection: COLLECT (Bruker, 2008); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg 1999); software used to prepare material for publication: WinGX (Farrugia, 1999).
lithium iron tungstate
top
Crystal data top
LiFe(WO4)2 | F(000) = 964 |
Mr = 558.46 | Dx = 7.136 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2yc | Cell parameters from 6452 reflections |
a = 9.2884 (3) Å | θ = 2.9–32.0° |
b = 11.4181 (3) Å | µ = 46.90 mm−1 |
c = 4.9018 (1) Å | T = 293 K |
β = 90.597 (2)° | Needle, yellow |
V = 519.84 (2) Å3 | 0.15 × 0.03 × 0.02 mm |
Z = 4 | |
Data collection top
Nonius KappaCCD diffractometer | 906 independent reflections |
Radiation source: Enraf Nonius FR590, fine-focus sealed X-ray tube | 827 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.081 |
ϕ scans, and ω scans | θmax = 32.0°, θmin = 3.6° |
Absorption correction: gaussian a grid of 8 x 8 x 52 = 3328 sampling points | h = −13→13 |
Tmin = 0.090, Tmax = 0.630 | k = −16→16 |
11306 measured reflections | l = −7→7 |
Refinement top
Refinement on F2 | 0 restraints |
Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.0165P)2 + 1.2747P] where P = (Fo2 + 2Fc2)/3 |
R[F2 > 2σ(F2)] = 0.018 | (Δ/σ)max = 0.002 |
wR(F2) = 0.041 | Δρmax = 1.67 e Å−3 |
S = 1.12 | Δρmin = −2.57 e Å−3 |
906 reflections | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
57 parameters | Extinction coefficient: 0.0091 (2) |
Crystal data top
LiFe(WO4)2 | V = 519.84 (2) Å3 |
Mr = 558.46 | Z = 4 |
Monoclinic, C2/c | Mo Kα radiation |
a = 9.2884 (3) Å | µ = 46.90 mm−1 |
b = 11.4181 (3) Å | T = 293 K |
c = 4.9018 (1) Å | 0.15 × 0.03 × 0.02 mm |
β = 90.597 (2)° | |
Data collection top
Nonius KappaCCD diffractometer | 906 independent reflections |
Absorption correction: gaussian a grid of 8 x 8 x 52 = 3328 sampling points | 827 reflections with I > 2σ(I) |
Tmin = 0.090, Tmax = 0.630 | Rint = 0.081 |
11306 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.018 | 57 parameters |
wR(F2) = 0.041 | 0 restraints |
S = 1.12 | Δρmax = 1.67 e Å−3 |
906 reflections | Δρmin = −2.57 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. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Li1 | 0.5 | 0.3428 (7) | 0.25 | 0.011 (2) | |
Fe1 | 0.5 | 0.16523 (6) | 0.75 | 0.00640 (17) | |
W1 | 0.247439 (12) | 0.091398 (11) | 0.24612 (2) | 0.00444 (8) | |
O1 | 0.3633 (3) | 0.0591 (2) | 0.9242 (5) | 0.0065 (4) | |
O2 | 0.3805 (3) | 0.1822 (3) | 0.4110 (5) | 0.0077 (5) | |
O3 | 0.1449 (3) | 0.0483 (2) | 0.5542 (5) | 0.0064 (5) | |
O4 | 0.1226 (3) | 0.1942 (2) | 0.1080 (5) | 0.0072 (5) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Li1 | 0.009 (5) | 0.020 (6) | 0.003 (4) | 0 | 0.001 (4) | 0 |
Fe1 | 0.0062 (4) | 0.0063 (4) | 0.0066 (4) | 0 | 0.0002 (3) | 0 |
W1 | 0.00575 (10) | 0.00383 (10) | 0.00374 (11) | 0.00030 (4) | −0.00002 (6) | −0.00011 (3) |
O1 | 0.0076 (11) | 0.0054 (10) | 0.0066 (11) | −0.0012 (9) | 0.0006 (9) | 0.0004 (9) |
O2 | 0.0082 (12) | 0.0077 (10) | 0.0070 (11) | −0.0002 (10) | −0.0011 (9) | −0.0003 (9) |
O3 | 0.0073 (11) | 0.0059 (11) | 0.0061 (11) | 0.0005 (9) | 0.0000 (9) | 0.0008 (8) |
O4 | 0.0075 (11) | 0.0066 (11) | 0.0075 (11) | 0.0008 (9) | −0.0006 (9) | −0.0003 (9) |
Geometric parameters (Å, º) top
Li1—O3i | 2.075 (6) | O1—O2v | 2.873 (4) |
Li1—O4ii | 2.124 (3) | O2—O2iv | 2.738 (5) |
Li1—O4iii | 2.124 (3) | O2—O4vi | 2.748 (3) |
Li1—O2 | 2.288 (7) | O2—O1viii | 2.760 (3) |
Li1—O2iv | 2.288 (7) | O2—O3 | 2.766 (4) |
Fe1—O1 | 1.958 (3) | O2—O1vii | 2.773 (4) |
Fe1—O1v | 1.958 (3) | O2—O4 | 2.808 (5) |
Fe1—O2 | 1.998 (3) | O2—O4iii | 2.817 (5) |
Fe1—O2v | 1.998 (3) | O2—O1v | 2.873 (4) |
Fe1—O4vi | 2.091 (3) | O3—Li1vi | 2.075 (6) |
Fe1—O4iii | 2.091 (3) | O3—W1x | 2.078 (3) |
W1—O4 | 1.779 (3) | O3—O1viii | 2.460 (4) |
W1—O2 | 1.799 (3) | O3—O3viii | 2.688 (2) |
W1—O3 | 1.860 (2) | O3—O3x | 2.688 (2) |
W1—O1vii | 1.954 (2) | O3—O4 | 2.756 (4) |
W1—O3viii | 2.078 (3) | O3—O4x | 2.790 (3) |
W1—O1viii | 2.203 (3) | O3—O3xi | 2.953 (5) |
O1—W1ix | 1.954 (2) | O3—O4xii | 3.089 (4) |
O1—W1x | 2.203 (3) | O4—Fe1vi | 2.091 (3) |
O1—O3x | 2.460 (4) | O4—Li1ii | 2.124 (3) |
O1—O3 | 2.710 (4) | O4—O4xii | 2.682 (5) |
O1—O2x | 2.760 (3) | O4—O2vi | 2.748 (3) |
O1—O2ix | 2.773 (4) | O4—O3viii | 2.790 (3) |
O1—O1viii | 2.798 (3) | O4—O2xiii | 2.817 (5) |
O1—O1x | 2.798 (3) | O4—O1vi | 2.824 (3) |
O1—O4vi | 2.824 (3) | O4—O1vii | 2.869 (4) |
O1—O4ix | 2.869 (4) | O4—O4ii | 2.897 (5) |
| | | |
O3vi—Li1—O3i | 106.4 (4) | O3—O2—O4iii | 145.17 (15) |
O3vi—Li1—O4ii | 99.00 (15) | O1vii—O2—O4iii | 125.97 (14) |
O3i—Li1—O4ii | 94.71 (14) | O4—O2—O4iii | 146.12 (11) |
O3vi—Li1—O4iii | 94.71 (14) | W1—O2—O1v | 114.04 (15) |
O3i—Li1—O4iii | 99.00 (15) | Li1—O2—O1v | 94.91 (14) |
O4ii—Li1—O4iii | 157.0 (5) | O2iv—O2—O1v | 59.17 (10) |
O3vi—Li1—O2 | 90.05 (11) | O4vi—O2—O1v | 91.50 (9) |
O3i—Li1—O2 | 163.5 (3) | O1viii—O2—O1v | 63.43 (12) |
O4ii—Li1—O2 | 82.4 (2) | O3—O2—O1v | 108.26 (13) |
O4iii—Li1—O2 | 79.2 (2) | O1vii—O2—O1v | 91.93 (13) |
O3vi—Li1—O2iv | 163.5 (3) | O4—O2—O1v | 150.68 (12) |
O3i—Li1—O2iv | 90.05 (11) | O4iii—O2—O1v | 59.51 (10) |
O4ii—Li1—O2iv | 79.2 (2) | W1—O2—O1 | 93.84 (12) |
O4iii—Li1—O2iv | 82.4 (2) | Li1—O2—O1 | 136.22 (13) |
O2—Li1—O2iv | 73.5 (3) | O2iv—O2—O1 | 123.69 (14) |
O1—Fe1—O1v | 103.50 (16) | O4vi—O2—O1 | 60.09 (8) |
O1—Fe1—O2 | 93.76 (11) | O1viii—O2—O1 | 59.33 (8) |
O1v—Fe1—O2 | 93.13 (11) | O3—O2—O1 | 57.23 (10) |
O1—Fe1—O2v | 93.13 (11) | O1vii—O2—O1 | 119.97 (15) |
O1v—Fe1—O2v | 93.76 (11) | O4—O2—O1 | 115.47 (13) |
O2—Fe1—O2v | 168.85 (17) | O4iii—O2—O1 | 89.80 (11) |
O1—Fe1—O4vi | 88.39 (10) | O1v—O2—O1 | 64.53 (11) |
O1v—Fe1—O4vi | 168.01 (12) | W1—O3—Li1vi | 123.9 (2) |
O2—Fe1—O4vi | 84.40 (10) | W1—O3—W1x | 109.54 (12) |
O2v—Fe1—O4vi | 87.05 (11) | Li1vi—O3—W1x | 123.16 (17) |
O1—Fe1—O4iii | 168.01 (12) | W1—O3—O1viii | 59.40 (10) |
O1v—Fe1—O4iii | 88.39 (10) | Li1vi—O3—O1viii | 163.57 (17) |
O2—Fe1—O4iii | 87.05 (11) | W1x—O3—O1viii | 50.15 (9) |
O2v—Fe1—O4iii | 84.40 (10) | W1—O3—O3viii | 50.46 (5) |
O4vi—Fe1—O4iii | 79.77 (15) | Li1vi—O3—O3viii | 132.37 (8) |
O4—W1—O2 | 103.45 (15) | W1x—O3—O3viii | 95.34 (13) |
O4—W1—O3 | 98.42 (12) | O1viii—O3—O3viii | 63.34 (11) |
O2—W1—O3 | 98.20 (11) | W1—O3—O3x | 148.62 (9) |
O4—W1—O1vii | 100.34 (11) | Li1vi—O3—O3x | 79.52 (14) |
O2—W1—O1vii | 95.18 (12) | O1viii—O3—O3x | 92.25 (13) |
O3—W1—O1vii | 153.71 (13) | O3viii—O3—O3x | 131.5 (2) |
O4—W1—O3viii | 92.33 (11) | W1—O3—O1 | 98.37 (13) |
O2—W1—O3viii | 162.85 (12) | Li1vi—O3—O1 | 98.51 (11) |
O3—W1—O3viii | 85.90 (8) | W1x—O3—O1 | 52.80 (8) |
O1vii—W1—O3viii | 75.12 (11) | O1viii—O3—O1 | 65.31 (11) |
O4—W1—O1viii | 168.33 (12) | O3viii—O3—O1 | 128.44 (9) |
O2—W1—O1viii | 86.62 (11) | O3x—O3—O1 | 54.22 (8) |
O3—W1—O1viii | 73.99 (11) | Li1vi—O3—O4 | 87.79 (17) |
O1vii—W1—O1viii | 84.36 (9) | W1x—O3—O4 | 148.62 (12) |
O3viii—W1—O1viii | 78.48 (12) | O1viii—O3—O4 | 98.69 (13) |
Fe1—O1—W1ix | 126.89 (14) | O3viii—O3—O4 | 61.65 (8) |
Fe1—O1—W1x | 128.78 (12) | O3x—O3—O4 | 166.25 (15) |
W1ix—O1—W1x | 101.33 (11) | O1—O3—O4 | 123.61 (12) |
Fe1—O1—O3x | 164.12 (17) | Li1vi—O3—O2 | 107.8 (2) |
W1ix—O1—O3x | 54.73 (9) | W1x—O3—O2 | 100.33 (11) |
W1x—O1—O3x | 46.61 (8) | O1viii—O3—O2 | 63.46 (11) |
Fe1—O1—O3 | 102.73 (11) | O3viii—O3—O2 | 89.32 (8) |
W1ix—O1—O3 | 97.71 (13) | O3x—O3—O2 | 117.77 (8) |
W1x—O1—O3 | 48.72 (7) | O1—O3—O2 | 63.65 (10) |
O3x—O1—O3 | 62.44 (10) | O4—O3—O2 | 61.15 (11) |
Fe1—O1—O2x | 124.74 (13) | W1—O3—O4x | 112.22 (11) |
W1ix—O1—O2x | 103.88 (11) | Li1vi—O3—O4x | 120.1 (2) |
O3x—O1—O2x | 63.67 (11) | O1viii—O3—O4x | 65.91 (11) |
O3—O1—O2x | 88.98 (9) | O3viii—O3—O4x | 71.28 (12) |
Fe1—O1—O2ix | 91.70 (11) | O3x—O3—O4x | 60.37 (12) |
W1x—O1—O2ix | 139.47 (12) | O1—O3—O4x | 92.15 (9) |
O3x—O1—O2ix | 94.02 (12) | O4—O3—O4x | 132.06 (12) |
O3—O1—O2ix | 129.41 (13) | O2—O3—O4x | 129.23 (11) |
O2x—O1—O2ix | 121.57 (13) | W1—O3—O3xi | 115.23 (14) |
Fe1—O1—O1viii | 84.86 (7) | Li1vi—O3—O3xi | 73.29 (17) |
W1ix—O1—O1viii | 143.46 (10) | W1x—O3—O3xi | 101.95 (13) |
O3x—O1—O1viii | 89.66 (14) | O1viii—O3—O3xi | 121.31 (17) |
O3—O1—O1viii | 53.03 (8) | O3viii—O3—O3xi | 72.00 (10) |
O2x—O1—O1viii | 59.85 (12) | O3x—O3—O3xi | 90.11 (12) |
O2ix—O1—O1viii | 176.29 (10) | O1—O3—O3xi | 144.31 (16) |
Fe1—O1—O1x | 133.36 (8) | O4—O3—O3xi | 91.27 (12) |
W1ix—O1—O1x | 51.59 (5) | O2—O3—O3xi | 152.03 (15) |
W1x—O1—O1x | 88.09 (13) | O4x—O3—O3xi | 65.00 (11) |
O3x—O1—O1x | 61.65 (11) | W1—O3—O4xii | 93.77 (10) |
O3—O1—O1x | 123.90 (9) | W1x—O3—O4xii | 153.40 (13) |
O2x—O1—O1x | 62.60 (12) | O1viii—O3—O4xii | 149.95 (14) |
O2ix—O1—O1x | 59.41 (7) | O3viii—O3—O4xii | 89.68 (7) |
O1viii—O1—O1x | 122.35 (19) | O3x—O3—O4xii | 116.65 (8) |
Fe1—O1—O4vi | 47.74 (8) | O1—O3—O4xii | 137.95 (11) |
W1ix—O1—O4vi | 83.28 (11) | O4—O3—O4xii | 54.27 (11) |
W1x—O1—O4vi | 141.11 (12) | O2—O3—O4xii | 105.85 (12) |
O3x—O1—O4vi | 123.40 (15) | O4x—O3—O4xii | 119.96 (11) |
O3—O1—O4vi | 92.43 (9) | O3xi—O3—O4xii | 54.95 (9) |
O2x—O1—O4vi | 172.46 (14) | W1—O4—Fe1vi | 137.28 (14) |
O2ix—O1—O4vi | 62.61 (9) | W1—O4—Li1ii | 121.6 (2) |
O1viii—O1—O4vi | 115.56 (11) | Fe1vi—O4—Li1ii | 98.0 (2) |
O1x—O1—O4vi | 122.02 (12) | W1—O4—O4xii | 110.85 (13) |
Fe1—O1—O4ix | 108.35 (13) | Fe1vi—O4—O4xii | 50.12 (8) |
W1x—O1—O4ix | 99.49 (11) | Li1ii—O4—O4xii | 88.74 (13) |
O3x—O1—O4ix | 62.58 (10) | W1—O4—O2vi | 91.42 (10) |
O3—O1—O4ix | 69.76 (10) | Fe1vi—O4—O2vi | 46.36 (9) |
O2x—O1—O4ix | 126.12 (11) | Li1ii—O4—O2vi | 143.19 (18) |
O2ix—O1—O4ix | 59.68 (11) | O4xii—O4—O2vi | 62.49 (10) |
O1viii—O1—O4ix | 122.78 (8) | Fe1vi—O4—O3 | 103.66 (11) |
O1x—O1—O4ix | 88.70 (7) | Li1ii—O4—O3 | 124.8 (2) |
O4vi—O1—O4ix | 61.17 (11) | O4xii—O4—O3 | 69.21 (10) |
W1ix—O1—O2v | 98.18 (11) | O2vi—O4—O3 | 68.32 (8) |
W1x—O1—O2v | 153.25 (14) | W1—O4—O3viii | 48.10 (8) |
O3x—O1—O2v | 148.67 (15) | Fe1vi—O4—O3viii | 146.55 (14) |
O3—O1—O2v | 145.33 (12) | Li1ii—O4—O3viii | 76.4 (2) |
O2x—O1—O2v | 116.57 (12) | O4xii—O4—O3viii | 96.51 (8) |
O2ix—O1—O2v | 57.99 (11) | O2vi—O4—O3viii | 126.30 (13) |
O1viii—O1—O2v | 118.34 (7) | O3—O4—O3viii | 57.98 (8) |
O1x—O1—O2v | 89.85 (7) | Fe1vi—O4—O2 | 109.01 (11) |
O4vi—O1—O2v | 59.26 (10) | Li1ii—O4—O2 | 150.94 (18) |
O4ix—O1—O2v | 107.13 (13) | O4xii—O4—O2 | 116.71 (17) |
W1—O2—Fe1 | 133.70 (15) | O2vi—O4—O2 | 65.64 (10) |
W1—O2—Li1 | 129.83 (13) | O3—O4—O2 | 59.60 (9) |
Fe1—O2—Li1 | 95.58 (11) | O3viii—O4—O2 | 86.43 (9) |
W1—O2—O2iv | 107.36 (13) | W1—O4—O2xiii | 167.37 (18) |
Fe1—O2—O2iv | 91.86 (14) | Fe1vi—O4—O2xiii | 45.10 (8) |
Li1—O2—O2iv | 53.26 (14) | Li1ii—O4—O2xiii | 52.95 (19) |
W1—O2—O4vi | 131.95 (12) | O4xii—O4—O2xiii | 59.90 (11) |
Fe1—O2—O4vi | 49.24 (7) | O2vi—O4—O2xiii | 91.23 (14) |
Li1—O2—O4vi | 83.92 (15) | O3—O4—O2xiii | 128.89 (14) |
O2iv—O2—O4vi | 120.70 (12) | O3viii—O4—O2xiii | 121.64 (14) |
W1—O2—O1viii | 52.81 (9) | O2—O4—O2xiii | 151.53 (11) |
Fe1—O2—O1viii | 85.14 (11) | W1—O4—O1vi | 130.47 (14) |
Li1—O2—O1viii | 146.74 (18) | Li1ii—O4—O1vi | 100.2 (2) |
O2iv—O2—O1viii | 93.49 (8) | O4xii—O4—O1vi | 93.96 (7) |
O4vi—O2—O1viii | 119.42 (12) | O2vi—O4—O1vi | 62.41 (11) |
Fe1—O2—O3 | 99.76 (12) | O3—O4—O1vi | 130.10 (12) |
Li1—O2—O3 | 156.70 (17) | O3viii—O4—O1vi | 168.89 (13) |
O2iv—O2—O3 | 142.64 (10) | O2—O4—O1vi | 92.21 (9) |
O4vi—O2—O3 | 92.91 (9) | O2xiii—O4—O1vi | 61.23 (10) |
O1viii—O2—O3 | 52.87 (10) | Fe1vi—O4—O1vii | 161.09 (14) |
Fe1—O2—O1vii | 133.85 (15) | Li1ii—O4—O1vii | 92.66 (16) |
Li1—O2—O1vii | 97.66 (13) | O4xii—O4—O1vii | 146.27 (9) |
O2iv—O2—O1vii | 62.84 (10) | O2vi—O4—O1vii | 124.09 (10) |
O4vi—O2—O1vii | 176.09 (11) | O3—O4—O1vii | 82.63 (11) |
O1viii—O2—O1vii | 60.74 (9) | O3viii—O4—O1vii | 51.51 (9) |
O3—O2—O1vii | 84.23 (11) | O2—O4—O1vii | 58.46 (9) |
Fe1—O2—O4 | 155.23 (16) | O2xiii—O4—O1vii | 141.61 (14) |
Li1—O2—O4 | 101.10 (11) | O1vi—O4—O1vii | 118.83 (11) |
O2iv—O2—O4 | 112.78 (16) | W1—O4—O4ii | 84.13 (13) |
O4vi—O2—O4 | 114.36 (10) | Fe1vi—O4—O4ii | 103.53 (15) |
O1viii—O2—O4 | 90.69 (9) | Li1ii—O4—O4ii | 102.63 (16) |
O3—O2—O4 | 59.25 (10) | O4xii—O4—O4ii | 152.99 (11) |
O1vii—O2—O4 | 61.87 (9) | O2vi—O4—O4ii | 95.94 (14) |
W1—O2—O4iii | 170.09 (18) | O3—O4—O4ii | 120.05 (15) |
Fe1—O2—O4iii | 47.85 (8) | O3viii—O4—O4ii | 109.89 (14) |
Li1—O2—O4iii | 47.81 (8) | O2—O4—O4ii | 61.28 (11) |
O2iv—O2—O4iii | 63.13 (11) | O2xiii—O4—O4ii | 107.87 (17) |
O4vi—O2—O4iii | 57.61 (12) | O1vi—O4—O4ii | 60.18 (11) |
O1viii—O2—O4iii | 122.54 (14) | O1vii—O4—O4ii | 58.65 (10) |
Symmetry codes: (i) x+1/2, −y+1/2, z−1/2; (ii) −x+1/2, −y+1/2, −z; (iii) x+1/2, −y+1/2, z+1/2; (iv) −x+1, y, −z+1/2; (v) −x+1, y, −z+3/2; (vi) −x+1/2, −y+1/2, −z+1; (vii) x, y, z−1; (viii) x, −y, z−1/2; (ix) x, y, z+1; (x) x, −y, z+1/2; (xi) −x, −y, −z+1; (xii) −x, y, −z+1/2; (xiii) x−1/2, −y+1/2, z−1/2. |
Experimental details
Crystal data |
Chemical formula | LiFe(WO4)2 |
Mr | 558.46 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 293 |
a, b, c (Å) | 9.2884 (3), 11.4181 (3), 4.9018 (1) |
β (°) | 90.597 (2) |
V (Å3) | 519.84 (2) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 46.90 |
Crystal size (mm) | 0.15 × 0.03 × 0.02 |
|
Data collection |
Diffractometer | Nonius KappaCCD diffractometer |
Absorption correction | Gaussian a grid of 8 x 8 x 52 = 3328 sampling points |
Tmin, Tmax | 0.090, 0.630 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 11306, 906, 827 |
Rint | 0.081 |
(sin θ/λ)max (Å−1) | 0.745 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.018, 0.041, 1.12 |
No. of reflections | 906 |
No. of parameters | 57 |
Δρmax, Δρmin (e Å−3) | 1.67, −2.57 |
Table 1. Bond-valence analysis using interatomic distances reported by
Klevtsov & Klevtsova (1970). topAtom | Li1 | Fe1 | W1 | V(O) |
O1 | | 2 × 0.83 | 0.74 | 1.88 |
| | | 0.31 | |
O2 | 2 × 0.16 | 2 × 0.68 | 1.15 | 1.99 |
O3 | 2 × 0.18 | | 1.03 | 1.88 |
| | | 0.67 | |
O4 | 2 × 0.18 | 2 × 0.44 | 1.42 | 2.04 |
V(cation) | 1.03 | 3.90 | 5.32 | |
Table 2. Bond-valence parameters derived from the present refinement. topAtom | Li1 | Fe1 | W1 | V(O) |
O1 | | 2 × 0.584 | 0.915(O1iv) | 1.966 |
| | | 0.467(O1v) | |
O2 | 2 × 0.108 | 2 × 0.524 | 1.391 | 2.023 |
O3 | 2 × 0.193 | | 1.179 | 2.026 |
| | | 0.654(O3v) | |
O4 | 2 × 0.169 | 2 × 0.408 | 1.468 | 2.045 |
V(cation) | 0.94 | 3.032 | 6.073 | |
Symmetry codes: (i) x+1/2, -y+1/2, z-1/2;
(ii) -x+1/2, -y+1/2, -z;
(iii) -x+1/2, -y+1/2, -z+1;
(iv) x, y, z-1;
(v) x, -y, z-1/2. |
Table 3. Interatomic distances (Å) from the present analysis of
LiFe(WO4)2. The shortest M···M and O···O distances are
also listed. topThe dcalc values are sums of ionic radii as given by Shannon
(1976). |
Atoms i,j | dij | Atoms i,j | dij |
Li1—O3i,O3iii | 2.075 (6) | Fe1—O1,O1viii | 1.958 (3) |
Li1—O4ii,O4vi | 2.124 (3) | Fe1—O2,O2viii | 1.998 (3) |
Li1—O2,O2vii | 2.288 (7) | Fe1—O4iii,O4vi | 2.091 (3) |
<Li—O> | 2.163 (5) | <Fe—O> | 2.016 (3) |
| | | |
dcalc(Li+—O2-) | 2.14 | dcalc(Fe3+—O2-) | 2.045 |
W1—O4 | 1.779 (3) | | |
W1—O2 | 1.799 (3) | Fe1···Li1 | 3.181 (5) |
W1—O3 | 1.860 (3) | W1···W1v | 3.219 (1) |
W1—O1iv | 1.954 (3) | Li1···W1ii | 3.405 (9) |
W1—O3v | 2.078 (3) | O1···O3ix | 2.460 (4) |
W1—O1v | 2.203 (3) | | |
<W—O> | 1.946 (3) | | |
dcalc(W6+—O2-) | 1.98 | | |
Symmetry codes: (i) x+1/2, -y+1/2, z-1/2;
(ii) -x+1/2, -y+1/2, -z;
(iii) -x+1/2, -y+1/2, -z+1;
(iv) x, y, z-1;
(v) x, -y, z-1/2;
(vi) x+1/2, -y+1/2, z+1/2;
(vii) 1-x, y, -z+1/2;
(viii) 1-x, y, -z+3/2;
(ix) x, -y, z+1/2. |
Cation distributions in the A+B3+(WO4)2 compounds of the wolframite structure [(Fe,Mn)WO4] have been studied by Le Flem et al. (1969, 1970) and Salmon et al. (1970). The analyses performed on this family of compounds, known as `double tungstates', showed that the distribution of cations in the wolframite structure depends on their relative sizes. Indeed, both homogeneous chains, encompassing a unique cation, and chains with alternating cations are encountered. Among these materials, LiFe(WO4)2 was previously obtained as single crystals and its structure was refined to R = 0.149 (Klevtsova & Belov, 1970; Klevtsov & Klevtsova, 1970; Klevtsov et al., 1971).
When the previously reported structure of LiFe(WO4)2 is analysed using the bond-valence model (Brese & O'Keeffe, 1991), some inconsistencies arise regarding the iron–tungsten network. Though values of the oxygen and lithium valences are in good agreement with the expected values, the average cationic bond-valence sums (BVS) calculated for Fe and W are considerably different from what is expected, viz. νFe = 3.90 and νW = 5.32 (Table 1). A possible explanation of these results could involve partial disorder of the iron and tungsten cations over their six-coordinate sites in the octahedral framework. Such a statistical Fe/W distribution between two distinct B sites is actually observed in perovskites with composition A3Fe2WO9 and A = Sr (Viola et al., 2003), A = Ca (Ivanov et al., 2005) and Ba (Ivanov et al., 2006). But the structural model presented by Klevtsov et al. (1971) does not indicate any disorder. So, one could speculate that the refined structure was idealized while the real sample was not perfectly ordered.
It is worth mentioning that our description of the LiFe(WO4)2 crystal structure could appear, at a first glance, compatible with higher symmetry, namely with the orthorhombic space group Cmcm (No. 63). However, the value of the cell angle β [90.597 (2)°] cannot be assigned as 90° within experimental error. Furthermore, the refinement using Cmcm yields poorer values of the reliability factors: R1 = 0.0362 and wR2 = 0.1488 for Cmcm compared to R1 = 0.017 and wR2 = 0.0413 for C2/c. The orthorhombic model requires disorder of the O atoms, which is neither required nor observed in the C2/c model. Further, refinement with Cmcm gives unreasonable displacement parameters and is not, in any event, compatible with the observed lithium iron tungstate, LiFe(WO4)2, unit-cell angle β. The Li, Fe and W atoms, as refined with the space group C2/c, do adhere quite well to Cmcm symmetry, and the O atoms are the only ones that clearly require the lower-symmetry description.
According to the bond-valence analysis of the results of our refinement (Tables 2 and 3), the structure of LiFe(WO4)2 displays full order as far as the Fe and W ions are concerned. This time the values of the BVS calculation for all ions are in very good agreement with the theoretical ones.
LiFe(WO4)2 is based on a distorted hexagonal packing of O atoms and is closely related to the wolframite structure. The structure is built of two kind of chains of edge-sharing octahedra, which are propagated along [010] (Fig. 1). The first type of chain contains Li+ and Fe3+ ions (both on twofold axes, Wyckoff sites 4e, formula [Li0.5Fe0.5O4]6-). The second chain is composed of tungstate units on general positions (formula [WO4]2-). The overall structure is the union of these two types of chains by corner sharing. All cations have octahedral coordination with bond lengths (Table 3) very close to the values expected on the basis of ionic radii (Shannon, 1976).
No structural data have been reported for LiFe(WO4)2 since 1970, although a recent work on positive electrode materials for rechargeable lithium batteries (Li & Fu, 2008) reported the electrochemical characterization of LiFe(WO4)2. Our present structural study of this double tungstate provides a more accurate description of its crystal structure than has been available up to now.