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Structure factors for rubidium oxotitanium arsenate, RbTiOAsO4, were measured at 293 K with focused synchrotron X-radiation [λ = 0.7500 (9) Å] using a fast avalanche photodiode counter. The accurate synchrotron single-crystal data are of sufficient quality and resolution to detect the splitting positions of the Rb cations at room temperature. Strong accumulation of the Δρ difference charge density near the Rb atoms at a distance of ∼0.5 Å in the −c direction can be attributed to the partial occupancy of additional sites related by pseudosymmetry. This type of static and/or dynamic disorder is temperature-dependent and seems to be universal for the KTiOPO4 family of compounds. The best modelling of the experimental data was obtained with the Rb atom in split positions described within the harmonic approximation and the multipole functions for the other atoms. The Δρ density features in the Ti—O and As—O covalent bonds can be related to the linear and non-linear susceptibility using bond-polarization theory. The charge-density maps reflect the anisotropy of non-linear susceptibility, which is larger for directions where locally antisymmetric components of Δρ are strong.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768100006285/os0048sup1.cif
Contains datablocks RoomT, publ

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108768100006285/os00481sup2.hkl
Contains datablock 1

Computing details top

Data collection: bl14a; cell refinement: bl14a; data reduction: Xtal DIFDAT ADDREF SORTRF ABSORB; program(s) used to solve structure: Xtal; program(s) used to refine structure: Xtal CRYLSQ xd; molecular graphics: Xtal; software used to prepare material for publication: Xtal BONDLA CIFIO xd.

Figures top
[Figure 1]
[Figure 2]
(RoomT) top
Crystal data top
RbTiOAsO4F(000) = 1056
Mr = 288.27Dx = 4.038 Mg m3
Orthorhombic, Pna21Synchrotron xray vertical wiggler radiation, λ = 0.75 Å
Hall symbol: P 2c -2nCell parameters from 12 reflections
a = 13.2352 (11) Åθ = 42.5–50.8°
b = 6.6666 (7) ŵ = 21.09 mm1
c = 10.7483 (9) ÅT = 293 K
V = 948.36 (15) Å3Rectangular, colourless
Z = 80.06 × 0.06 × 0.04 mm
Data collection top
Bl14a 4-circle
diffractometer
5982 reflections with F2 > 0
Radiation source: photon factory bl14aRint = 0.054
Si(111) monochromatorθmax = 60°, θmin = 3.3°
ω–2θ scansh = 3030
Absorption correction: analytical
Alcock (1974)
k = 1515
Tmin = 0.344, Tmax = 0.494l = 2424
46432 measured reflections6 standard reflections every 94 reflections
6310 independent reflections intensity decay: 8.8%
Refinement top
Refinement on Fw = 1/σ2(F)
Least-squares matrix: full(Δ/σ)max = 0.01
R[F2 > 2σ(F2)] = 0.018Extinction correction: Becker-Coppens Gaussian
wR(F2) = 0.015Extinction coefficient: 28925 (1184)
S = 1.22Absolute structure: Flack XABS refined
5982 reflectionsAbsolute structure parameter: 0.424 (3)
533 parameters
Crystal data top
RbTiOAsO4V = 948.36 (15) Å3
Mr = 288.27Z = 8
Orthorhombic, Pna21Synchrotron xray vertical wiggler radiation, λ = 0.75 Å
a = 13.2352 (11) ŵ = 21.09 mm1
b = 6.6666 (7) ÅT = 293 K
c = 10.7483 (9) Å0.06 × 0.06 × 0.04 mm
Data collection top
Bl14a 4-circle
diffractometer
5982 reflections with F2 > 0
Absorption correction: analytical
Alcock (1974)
Rint = 0.054
Tmin = 0.344, Tmax = 0.4946 standard reflections every 94 reflections
46432 measured reflections intensity decay: 8.8%
6310 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.018533 parameters
wR(F2) = 0.015Absolute structure: Flack XABS refined
S = 1.22Absolute structure parameter: 0.424 (3)
5982 reflections
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Rb10.38246 (4)0.78159 (6)0.70236 (3)0.017
Rb20.10885 (6)0.69335 (10)0.95521 (4)0.014
Rb30.3871 (2)0.7878 (4)0.6741 (2)0.014
Rb40.1110 (4)0.6983 (5)0.9340 (3)0.011
Ti10.373747 (13)0.50505 (3)1.027988 (17)0.005
Ti20.248776 (15)0.26999 (3)0.777903 (18)0.005
As10.499652 (9)0.328210 (14)0.770681 (13)0.004
As20.179890 (7)0.505071 (17)0.516443 (11)0.005
O10.48731 (8)0.48947 (16)0.88714 (9)0.011
O20.51039 (7)0.46126 (15)0.63784 (8)0.010
O30.39509 (6)0.18744 (14)0.74880 (9)0.009
O40.60025 (6)0.17655 (14)0.79062 (9)0.009
O110.28160 (7)0.45211 (14)0.88764 (8)0.008
O120.21791 (7)0.05542 (14)0.63748 (8)0.009
O50.10983 (8)0.30341 (13)0.48072 (9)0.009
O60.10713 (8)0.70414 (13)0.54832 (10)0.010
O70.25824 (8)0.54470 (15)0.39454 (9)0.010
O80.25779 (8)0.45857 (15)0.63651 (8)0.010
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Rb10.02131 (9)0.00722 (6)0.02104 (12)0.00289 (5)0.00609 (11)0.00211 (9)
Rb20.01048 (8)0.01382 (10)0.01740 (17)0.00368 (6)0.00058 (12)0.00088 (10)
Rb30.0159 (5)0.0073 (5)0.0181 (8)0.0028 (3)0.0055 (7)0.0020 (6)
Rb40.0107 (5)0.0065 (4)0.0147 (9)0.0019 (3)0.0010 (7)0.0006 (6)
Ti10.00519 (5)0.00489 (5)0.00490 (5)0.00005 (5)0.00018 (4)0.00091 (5)
Ti20.00502 (4)0.00500 (5)0.00473 (5)0.00028 (5)0.00064 (5)0.00014 (5)
As10.00378 (3)0.00446 (3)0.00510 (3)0.00004 (3)0.00065 (2)0.00029 (3)
As20.00624 (3)0.00344 (3)0.00513 (3)0.00027 (3)0.00029 (3)0.00061 (2)
O10.0100 (3)0.0117 (3)0.0105 (3)0.0033 (2)0.0038 (2)0.0062 (2)
O20.0087 (3)0.0117 (3)0.0091 (2)0.0020 (2)0.0031 (2)0.0047 (2)
O30.0058 (2)0.0073 (2)0.0127 (3)0.0015 (2)0.0005 (2)0.0019 (2)
O40.0048 (2)0.0088 (2)0.0138 (3)0.0011 (2)0.0005 (2)0.0024 (2)
O110.0082 (2)0.0090 (2)0.0078 (2)0.0005 (2)0.0027 (2)0.0031 (2)
O120.0092 (3)0.0092 (3)0.0085 (2)0.0005 (2)0.0031 (2)0.0022 (2)
O50.0116 (3)0.0048 (2)0.0119 (3)0.0018 (2)0.0039 (2)0.0007 (2)
O60.0123 (3)0.0053 (2)0.0139 (3)0.0009 (2)0.0038 (2)0.0003 (2)
O70.0106 (3)0.0103 (3)0.0090 (2)0.0032 (2)0.0031 (2)0.0045 (2)
O80.0117 (3)0.0110 (3)0.0081 (2)0.0039 (2)0.0043 (2)0.0044 (2)
Bond lengths (Å) top
Rb1—Rb30.312 (3)Ti2—O111.7476 (8)
Rb2—Rb3i3.585 (3)Ti2—O122.1192 (9)
Rb2—Rb40.233 (4)Ti2—O7i1.9586 (9)
Rb3—Rb4ii3.762 (4)Ti2—O81.9760 (9)
Ti1—O12.1358 (9)As1—O11.6581 (8)
Ti1—O2iii1.9484 (9)As1—O21.6869 (8)
Ti1—O111.9716 (8)As1—O31.6885 (9)
Ti1—O12iv1.7232 (8)As1—O41.6855 (8)
Ti1—O5iv2.0644 (9)As2—O51.6777 (9)
Ti1—O6i2.0337 (8)As2—O61.6751 (9)
Ti2—O32.0374 (9)As2—O71.6917 (9)
Ti2—O4v2.0025 (8)As2—O81.6806 (9)
Symmetry codes: (i) x+1/2, y1/2, z+1/2; (ii) x+1/2, y+1/2, z1/2; (iii) x+1, y+1, z+1/2; (iv) x+1/2, y+1/2, z+1/2; (v) x1/2, y+1/2, z.

Experimental details

Crystal data
Chemical formulaRbTiOAsO4
Mr288.27
Crystal system, space groupOrthorhombic, Pna21
Temperature (K)293
a, b, c (Å)13.2352 (11), 6.6666 (7), 10.7483 (9)
V3)948.36 (15)
Z8
Radiation typeSynchrotron xray vertical wiggler, λ = 0.75 Å
µ (mm1)21.09
Crystal size (mm)0.06 × 0.06 × 0.04
Data collection
DiffractometerBl14a 4-circle
diffractometer
Absorption correctionAnalytical
Alcock (1974)
Tmin, Tmax0.344, 0.494
No. of measured, independent and
observed (F2 > 0) reflections
46432, 6310, 5982
Rint0.054
(sin θ/λ)max1)1.155
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.018, 0.015, 1.22
No. of reflections5982
No. of parameters533
No. of restraints?
Δρmax, Δρmin (e Å3)?, ?
Absolute structureFlack XABS refined
Absolute structure parameter0.424 (3)

Computer programs: bl14a, Xtal DIFDAT ADDREF SORTRF ABSORB, Xtal CRYLSQ xd, Xtal BONDLA CIFIO xd.

Selected bond lengths (Å) top
Rb1—Rb30.312 (3)Ti2—O111.7476 (8)
Rb2—Rb3i3.585 (3)Ti2—O122.1192 (9)
Rb2—Rb40.233 (4)Ti2—O7i1.9586 (9)
Rb3—Rb4ii3.762 (4)Ti2—O81.9760 (9)
Ti1—O12.1358 (9)As1—O11.6581 (8)
Ti1—O2iii1.9484 (9)As1—O21.6869 (8)
Ti1—O111.9716 (8)As1—O31.6885 (9)
Ti1—O12iv1.7232 (8)As1—O41.6855 (8)
Ti1—O5iv2.0644 (9)As2—O51.6777 (9)
Ti1—O6i2.0337 (8)As2—O61.6751 (9)
Ti2—O32.0374 (9)As2—O71.6917 (9)
Ti2—O4v2.0025 (8)As2—O81.6806 (9)
Symmetry codes: (i) x+1/2, y1/2, z+1/2; (ii) x+1/2, y+1/2, z1/2; (iii) x+1, y+1, z+1/2; (iv) x+1/2, y+1/2, z+1/2; (v) x1/2, y+1/2, z.
 

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