Buy article online - an online subscription or single-article purchase is required to access this article.
Most known compounds with five-coordinated Ti4+ are natural and synthetic titanosilicates. The crystal structure of natural fresnoite, Ba2TiSi2O8 [tetragonal, space group P4bm, a = 8.510 (1) Å, c = 5.197 (1) Å, V = 376.4 (1) Å3, Z = 2], has been refined to R = 0.011 on the basis of 807 unique single-crystal reflections with I > 2σ(I). Titanium has fivefold coordination with one short (`titanyl') bond of 1.692 (5) Å. Bonds in the TiO5 polyhedron are discussed in comparison to analogous coordination polyhedra in other minerals and compounds. A review of all known compounds with Ti4+O5 polyhedra shows that most of them are titanosilicates in which titanium forms a short Ti—O bond (∼1.61 to ∼1.77 Å). Poor Gladstone–Dale compatibility between chemical composition, optical characteristics and density of these compounds is explained by the anomalous contribution of [5]Ti4+ to the optical properties as shown by calculations based on the relationship between electronic polarizabilities and refractive indices. An improved Gladstone–Dale coefficient of 0.29 is suggested for TiO2 with [5]Ti4+. A negative correlation between `titanyl' bond lengths and wavenumbers of the bands of Ti—O stretching vibrations (in the range of 890–830 cm−1) in infrared and Raman spectra is observed.
Supporting information
CCDC reference: 2150917
Program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2018).
Crystal data top
Ba2O8Si2Ti | Dx = 4.471 Mg m−3 |
Mr = 506.76 | Mo Kα radiation, λ = 0.71073 Å |
Tetragonal, P4bm | Cell parameters from 11109 reflections |
a = 8.5104 (12) Å | θ = 3.4–33.4° |
c = 5.1975 (10) Å | µ = 11.71 mm−1 |
V = 376.44 (13) Å3 | T = 293 K |
Z = 2 | Parallelepiped, yellow |
F(000) = 452 | 0.25 × 0.14 × 0.13 mm |
Data collection top
Xcalibur, Eos diffractometer | θmax = 33.4°, θmin = 3.4° |
25512 measured reflections | h = −13→13 |
807 independent reflections | k = −13→13 |
806 reflections with I > 2σ(I) | l = −8→8 |
Rint = 0.033 | |
Refinement top
Refinement on F2 | w = 1/[σ2(Fo2) + (0.0047P)2 + 0.9597P] where P = (Fo2 + 2Fc2)/3 |
Least-squares matrix: full | (Δ/σ)max = 0.001 |
R[F2 > 2σ(F2)] = 0.012 | Δρmax = 0.87 e Å−3 |
wR(F2) = 0.027 | Δρmin = −0.65 e Å−3 |
S = 1.20 | Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
807 reflections | Extinction coefficient: 0.0165 (7) |
40 parameters | Absolute structure: Refined as an inversion twin. |
1 restraint | Absolute structure parameter: 0.01 (3) |
Special details top
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell esds is used for estimating esds involving l.s. planes. |
Refinement. Refined as a 2-component inversion twin. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Ba1 | 0.32715 (2) | 0.82715 (2) | 0.00051 (5) | 0.00865 (7) | |
Ti2 | 0.000000 | 0.000000 | 0.53608 (18) | 0.00667 (19) | |
Si1 | 0.12793 (9) | 0.62793 (9) | 0.5130 (4) | 0.00767 (17) | |
O1 | 0.000000 | 0.000000 | 0.2106 (9) | 0.0149 (9) | |
O2 | 0.000000 | 0.500000 | 0.6300 (10) | 0.0250 (13) | |
O3 | 0.1260 (3) | 0.6260 (3) | 0.2067 (6) | 0.0088 (5) | |
O4 | 0.2922 (3) | 0.5761 (4) | 0.6451 (5) | 0.0236 (7) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Ba1 | 0.00940 (8) | 0.00940 (8) | 0.00715 (9) | −0.00491 (6) | −0.00086 (9) | −0.00086 (9) |
Ti2 | 0.0071 (2) | 0.0071 (2) | 0.0057 (5) | 0.000 | 0.000 | 0.000 |
Si1 | 0.0087 (2) | 0.0087 (2) | 0.0055 (4) | 0.0013 (3) | −0.0013 (4) | −0.0013 (4) |
O1 | 0.0178 (14) | 0.0178 (14) | 0.0091 (18) | 0.000 | 0.000 | 0.000 |
O2 | 0.035 (2) | 0.035 (2) | 0.0056 (18) | −0.022 (3) | 0.000 | 0.000 |
O3 | 0.0098 (8) | 0.0098 (8) | 0.0067 (12) | −0.0013 (11) | −0.0002 (7) | −0.0002 (7) |
O4 | 0.0142 (11) | 0.0462 (19) | 0.0105 (10) | 0.0150 (12) | −0.0035 (9) | −0.0075 (11) |
Geometric parameters (Å, º) top
Ba1—O3 | 2.647 (3) | Ba1—Si1 | 3.5838 (17) |
Ba1—O3i | 2.789 (2) | Ti2—O1 | 1.692 (5) |
Ba1—O3ii | 2.789 (2) | Ti2—O4viii | 1.967 (3) |
Ba1—O4iii | 2.840 (3) | Ti2—O4ix | 1.967 (3) |
Ba1—O4iv | 2.840 (3) | Ti2—O4x | 1.967 (3) |
Ba1—O2v | 2.835 (3) | Ti2—O4xi | 1.967 (3) |
Ba1—O4vi | 2.989 (4) | Si1—O3 | 1.592 (4) |
Ba1—O4vii | 2.989 (4) | Si1—O4xii | 1.619 (3) |
Ba1—Si1iv | 3.4885 (16) | Si1—O4 | 1.619 (3) |
Ba1—Si1vii | 3.6220 (15) | Si1—O2 | 1.655 (2) |
Ba1—Si1v | 3.6220 (15) | | |
| | | |
O3—Ba1—O3i | 121.77 (10) | O4ix—Ti2—Ba1xiv | 112.91 (10) |
O3—Ba1—O3ii | 121.77 (10) | O4x—Ti2—Ba1xiv | 109.48 (9) |
O3i—Ba1—O3ii | 65.89 (12) | O4xi—Ti2—Ba1xiv | 42.28 (9) |
O3—Ba1—O4iii | 73.10 (9) | Ba1xiii—Ti2—Ba1xiv | 68.276 (14) |
O3i—Ba1—O4iii | 162.00 (10) | O1—Ti2—Ba1xv | 127.473 (13) |
O3ii—Ba1—O4iii | 116.94 (8) | O4viii—Ti2—Ba1xv | 112.91 (10) |
O3—Ba1—O4iv | 73.10 (9) | O4ix—Ti2—Ba1xv | 109.48 (9) |
O3i—Ba1—O4iv | 116.94 (8) | O4x—Ti2—Ba1xv | 42.28 (9) |
O3ii—Ba1—O4iv | 162.00 (9) | O4xi—Ti2—Ba1xv | 46.84 (11) |
O4iii—Ba1—O4iv | 54.51 (11) | Ba1xiii—Ti2—Ba1xv | 105.05 (3) |
O3—Ba1—O2v | 161.09 (10) | Ba1xiv—Ti2—Ba1xv | 68.276 (14) |
O3i—Ba1—O2v | 73.36 (8) | O1—Ti2—Ba1xvi | 127.473 (13) |
O3ii—Ba1—O2v | 73.36 (8) | O4viii—Ti2—Ba1xvi | 109.48 (9) |
O4iii—Ba1—O2v | 90.16 (10) | O4ix—Ti2—Ba1xvi | 42.28 (9) |
O4iv—Ba1—O2v | 90.16 (10) | O4x—Ti2—Ba1xvi | 46.84 (11) |
O3—Ba1—O4vi | 119.26 (6) | O4xi—Ti2—Ba1xvi | 112.91 (10) |
O3i—Ba1—O4vi | 116.50 (7) | Ba1xiii—Ti2—Ba1xvi | 68.276 (14) |
O3ii—Ba1—O4vi | 68.87 (9) | Ba1xiv—Ti2—Ba1xvi | 105.05 (3) |
O4iii—Ba1—O4vi | 54.30 (10) | Ba1xv—Ti2—Ba1xvi | 68.276 (14) |
O4iv—Ba1—O4vi | 95.49 (8) | O3—Si1—O4xii | 115.48 (13) |
O2v—Ba1—O4vi | 52.32 (6) | O3—Si1—O4 | 115.48 (13) |
O3—Ba1—O4vii | 119.26 (6) | O4xii—Si1—O4 | 106.9 (2) |
O3i—Ba1—O4vii | 68.87 (9) | O3—Si1—O2 | 110.7 (2) |
O3ii—Ba1—O4vii | 116.50 (7) | O4xii—Si1—O2 | 103.48 (17) |
O4iii—Ba1—O4vii | 95.49 (8) | O4—Si1—O2 | 103.48 (17) |
O4iv—Ba1—O4vii | 54.30 (10) | O3—Si1—Ba1xvii | 137.41 (13) |
O2v—Ba1—O4vii | 52.32 (6) | O4xii—Si1—Ba1xvii | 53.45 (12) |
O4vi—Ba1—O4vii | 95.74 (11) | O4—Si1—Ba1xvii | 53.45 (12) |
O3—Ba1—Si1iv | 70.46 (7) | O2—Si1—Ba1xvii | 111.87 (18) |
O3i—Ba1—Si1iv | 142.36 (7) | O3—Si1—Ba1xviii | 133.90 (8) |
O3ii—Ba1—Si1iv | 142.36 (7) | O4xii—Si1—Ba1xviii | 54.53 (13) |
O4iii—Ba1—Si1iv | 27.26 (6) | O4—Si1—Ba1xviii | 110.02 (13) |
O4iv—Ba1—Si1iv | 27.26 (6) | O2—Si1—Ba1xviii | 49.28 (11) |
O2v—Ba1—Si1iv | 90.63 (8) | Ba1xvii—Si1—Ba1xviii | 77.53 (4) |
O4vi—Ba1—Si1iv | 74.36 (6) | O3—Si1—Ba1xiii | 133.90 (8) |
O4vii—Ba1—Si1iv | 74.36 (6) | O4xii—Si1—Ba1xiii | 110.02 (13) |
O3—Ba1—Si1vii | 143.94 (5) | O4—Si1—Ba1xiii | 54.53 (13) |
O3i—Ba1—Si1vii | 67.00 (7) | O2—Si1—Ba1xiii | 49.28 (11) |
O3ii—Ba1—Si1vii | 94.10 (5) | Ba1xvii—Si1—Ba1xiii | 77.53 (4) |
O4iii—Ba1—Si1vii | 95.03 (8) | Ba1xviii—Si1—Ba1xiii | 70.11 (3) |
O4iv—Ba1—Si1vii | 72.44 (7) | O3—Si1—Ba1 | 42.82 (13) |
O2v—Ba1—Si1vii | 26.27 (3) | O4xii—Si1—Ba1 | 92.03 (13) |
O4vi—Ba1—Si1vii | 74.52 (6) | O4—Si1—Ba1 | 92.03 (13) |
O4vii—Ba1—Si1vii | 26.17 (5) | O2—Si1—Ba1 | 153.54 (18) |
Si1iv—Ba1—Si1vii | 83.49 (4) | Ba1xvii—Si1—Ba1 | 94.59 (3) |
O3—Ba1—Si1v | 143.94 (5) | Ba1xviii—Si1—Ba1 | 143.548 (14) |
O3i—Ba1—Si1v | 94.10 (5) | Ba1xiii—Si1—Ba1 | 143.548 (14) |
O3ii—Ba1—Si1v | 67.00 (7) | O3—Si1—Ba1xix | 43.69 (7) |
O4iii—Ba1—Si1v | 72.44 (7) | O4xii—Si1—Ba1xix | 91.58 (11) |
O4iv—Ba1—Si1v | 95.03 (8) | O4—Si1—Ba1xix | 158.05 (12) |
O2v—Ba1—Si1v | 26.27 (3) | O2—Si1—Ba1xix | 82.98 (14) |
O4vi—Ba1—Si1v | 26.17 (5) | Ba1xvii—Si1—Ba1xix | 143.696 (15) |
O4vii—Ba1—Si1v | 74.52 (6) | Ba1xviii—Si1—Ba1xix | 90.22 (2) |
Si1iv—Ba1—Si1v | 83.49 (4) | Ba1xiii—Si1—Ba1xix | 130.33 (3) |
Si1vii—Ba1—Si1v | 50.31 (4) | Ba1—Si1—Ba1xix | 75.19 (4) |
O3—Ba1—Si1 | 24.13 (7) | O3—Si1—Ba1xx | 43.69 (7) |
O3i—Ba1—Si1 | 102.32 (6) | O4xii—Si1—Ba1xx | 158.05 (12) |
O3ii—Ba1—Si1 | 102.32 (6) | O4—Si1—Ba1xx | 91.58 (11) |
O4iii—Ba1—Si1 | 94.48 (7) | O2—Si1—Ba1xx | 82.98 (14) |
O4iv—Ba1—Si1 | 94.48 (7) | Ba1xvii—Si1—Ba1xx | 143.696 (15) |
O2v—Ba1—Si1 | 174.78 (8) | Ba1xviii—Si1—Ba1xx | 130.33 (3) |
O4vi—Ba1—Si1 | 129.34 (5) | Ba1xiii—Si1—Ba1xx | 90.22 (2) |
O4vii—Ba1—Si1 | 129.34 (5) | Ba1—Si1—Ba1xx | 75.19 (4) |
Si1iv—Ba1—Si1 | 94.59 (3) | Ba1xix—Si1—Ba1xx | 68.13 (3) |
Si1vii—Ba1—Si1 | 154.718 (15) | Si1xxi—O2—Si1 | 136.9 (3) |
Si1v—Ba1—Si1 | 154.718 (15) | Si1xxi—O2—Ba1xiii | 104.45 (9) |
O1—Ti2—O4viii | 106.75 (9) | Si1—O2—Ba1xiii | 104.45 (9) |
O1—Ti2—O4ix | 106.75 (9) | Si1xxi—O2—Ba1xviii | 104.45 (9) |
O4viii—Ti2—O4ix | 85.24 (5) | Si1—O2—Ba1xviii | 104.45 (9) |
O1—Ti2—O4x | 106.75 (9) | Ba1xiii—O2—Ba1xviii | 94.41 (15) |
O4viii—Ti2—O4x | 146.51 (18) | Si1—O3—Ba1 | 113.05 (17) |
O4ix—Ti2—O4x | 85.24 (5) | Si1—O3—Ba1xix | 113.09 (11) |
O1—Ti2—O4xi | 106.75 (9) | Ba1—O3—Ba1xix | 109.98 (8) |
O4viii—Ti2—O4xi | 85.24 (5) | Si1—O3—Ba1xx | 113.09 (11) |
O4ix—Ti2—O4xi | 146.51 (18) | Ba1—O3—Ba1xx | 109.98 (8) |
O4x—Ti2—O4xi | 85.24 (5) | Ba1xix—O3—Ba1xx | 96.49 (10) |
O1—Ti2—Ba1xiii | 127.473 (13) | Si1—O4—Ti2xxii | 138.08 (18) |
O4viii—Ti2—Ba1xiii | 42.28 (9) | Si1—O4—Ba1xvii | 99.29 (14) |
O4ix—Ti2—Ba1xiii | 46.84 (11) | Ti2xxii—O4—Ba1xvii | 109.95 (13) |
O4x—Ti2—Ba1xiii | 112.91 (10) | Si1—O4—Ba1xiii | 99.30 (15) |
O4xi—Ti2—Ba1xiii | 109.48 (9) | Ti2xxii—O4—Ba1xiii | 104.49 (13) |
O1—Ti2—Ba1xiv | 127.473 (13) | Ba1xvii—O4—Ba1xiii | 99.60 (9) |
O4viii—Ti2—Ba1xiv | 46.84 (11) | | |
Symmetry codes: (i) y, −x+1, z; (ii) −y+1, x+1, z; (iii) y−1/2, x+1/2, z−1; (iv) x, y, z−1; (v) −y+1, x+1, z−1; (vi) −x+1/2, y+1/2, z−1; (vii) y, −x+1, z−1; (viii) −x+1/2, y−1/2, z; (ix) −y+1/2, −x+1/2, z; (x) x−1/2, −y+1/2, z; (xi) y−1/2, x−1/2, z; (xii) y−1/2, x+1/2, z; (xiii) −y+1, x, z+1; (xiv) x, y−1, z+1; (xv) y−1, −x, z+1; (xvi) −x, −y+1, z+1; (xvii) x, y, z+1; (xviii) y−1, −x+1, z+1; (xix) y−1, −x+1, z; (xx) −y+1, x, z; (xxi) −x, −y+1, z; (xxii) x+1/2, −y+1/2, z. |
Subscribe to Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials
The full text of this article is available to subscribers to the journal.
If you have already registered and are using a computer listed in your registration details, please email
support@iucr.org for assistance.