A new pillared lithium bis­muth phosphate, LiBi_7.37P₃O₁₉, with elliptical channels

The structure of a new lithium bis­muth phosphate, LiBi_7.37P₃O₁₉, consists of infinite OBi₄ edge-sharing tetra­hedral chains in the ac plane, which form Bi₂O₂ layers parallel to the b axis. They are sandwiched between PO₄ tetra­hedral and Bi polyhedral layers. The PO₄-Bi-PO₄ layers are bridged by columns formed by one Bi polyhedron flanked on each side by LiO₄ tetra­hedra. This bridging Bi atom lies on a twofold axis, special position 4e of the C2/c space group. This arrangement creates pillared open elliptical channels parallel to [010].

S1. Comment

The discovery of the oxygen ion conductor Bi₄V₂O₁₁ (Abraham et al., 1988) initiated an intensive sequence of research on compounds in complex phase space formed by Bi–Pb–transition metal phosphates, arsenates and vanadates (Steinfink et al., 2005; Steinfink & Lynch, 2004; Giraud et al., 2003; Cousin et al., 2002; Roussel et al., 2002). The structural motif of many of these compounds is related to the δ-Bi₂O₃ and CaF₂ structures, where the metals occupy the Bi or Ca sites and O atoms form irregular polyhedra around them. The structures usually consist of edge-sharing OBi₄ tetrahedra that articulate into chains and planes, which are linked by PO₄ tetrahedra and transition metal octahedra into a three-dimensional network (Abraham et al., 2002). The polyhedra are distorted by the presence of nonbonding 6s² electrons on Bi. Aliovalent metal substitutions give rise to oxygen vacancies, thus opening pathways for the transport of ions (Giraud et al., 2003). Many structures are pseudo-centrosymmetric because the metal ions are in nearly centrosymmetric sites, but oxygen ions frequently destroy this arrangement. The compositions are nonstoichiometric, subject to extensive formations of solid solutions, twinning, and the formation of commensurate and incommensurate superstructures. Only two lithium bismuth phosphates, LiBi₄O₅(PO₄) and Li₃Bi₂(PO₄)₃, have been reported, characterized only by X-ray powder diffraction (Berul, 1971). Recently, the crystal structure of Bi_4.25(PO₄)₂O_3.375 was reported, which also displays a CaF₂-related structure (Muktha & Guru Row, 2006). It appeared to us that this structure might be able to intercalate lithium ions and we prepared a mixture of Li₂CO₃, Bi₂O₃ and NH₄H₂PO₄. Green–yellow single crystals were found in the annealed reaction mixture formed from these precursors and were used for the crystal structure determination. We report here the crystal structure of a new lithium bismuth phosphate.

The structure, viewed parallel to [010], is shown in Fig. 1. It displays the formation of infinite Bi₂O₂ chains perpendicular to [010], formed by the edge-sharing OBi₄ tetrahedra that are observed in so many of these structures (Abraham et al., 2002). The Bi₂O₂ chains in the ac plane form layers parallel to the b axis and are sandwiched between PO₄ tetrahedral and Bi6 and Bi7 polyhedral layers. The PO₄–Bi–PO₄ layers are bridged by columns formed by Bi8 polyhedra flanked on each side by LiO₄ tetrahedra. This arrangement creates pillared, open, elliptical channels parallel to [010] (Fig. 2). Atoms Bi6 and Bi7 are in rectangular-pyramidal coordination to O atoms at distances ranging from 2.04 (1) to 2.75 (3) Å. The coordination polyhedron formed by eight O atoms around atom Bi8 at distances ranging from 2.34 (3) to 2.78 (3) Å can best be described as a distorted bicapped trigonal prism. The bases of the tetrahedra and pyramids form the walls of the channels and the Bi8–Li–O columns form the pillars. The Li ions are part of the columnar pillars and would not be expected to be mobile. However, it is reasonable to expect that ion transport might occur through these channels. Such experiments are in progress. The irregular coordination polyhedra around Bi have been described in related structures and are attributed to the non-bonding 6s² electrons (Giraud et al., 2000).

The displacement parameter for atom Bi8 was anomalously large. Refinement of the site occupation factor showed that atom Bi8 is present 92% of the time. The anisotropic displacement parameters for Bi are disk-shaped, with the disk nearly perpendicular to [001]. The displacement parameters for atoms O15–O19, all in PO₄ tetrahedra, are larger than those for the other oxygen ions. Similarly, atom P3 has a larger displacement value than the other two P atoms. Atom P3 can be modeled as disordered over closely adjacent sites, but in the final refinement, averaged positional parameters were used. This explains the large displacements of atoms O18 and O19. Atoms O15–O17 are part of the P1 and P2 tetrahedra, and it is likely that these may have a large value of libration (Giraud et al., 2003). The P—O bond lengths range from 1.487 (17)–1.598 (18) Å and the Li—O bonds range from 1.86 (5)–2.12 (5) Å, while selected Bi—O bond lengths are shown in Table 1.

S2. Experimental

Lithium bismuth phosphate, Li₄Bi₁₇P₈O₁₅₂, was synthesized by the ceramic method by reacting a mixture of analytical grade Bi₂O₃, NH₄H₂PO₄ and Li₂CO₃ [quantities of reagents?]. The precursors were mixed to yield a putative lithium-containing phase with a ratio of 17 Bi:8 P:4 Li. Prior to use, Bi₂O₃ was dried in air at 873 K for 24 h in order to remove any moisture or carbonates associated with it. The mixture was initially heated in air at 468 K for 2 h to decompose NH₄H₂PO₄ and finally at 873 K for 12 h in alumina crucibles. The intermediate product was then ground, reheated in air at 1103 K for 1 h in a gold boat, and further heated to 1163 K and annealed at that temperature for about 12 h. Green–yellow single crystals of a new phase were obtained by cooling the reaction mixture from 1163 to 1073 K at a rate of 5 k h⁻¹ and then furnace cooling to room temperature. The product was analyzed by inductively coupled plasma optical emission spectroscopy yielding a Bi:Li ratio of 6.73:1.2 on the basis of three stoichiometric P atoms.

S3. Refinement

Bi8, which is in the special position 4e, showed anomalously large displacement parameters and the occupancy factor refinement converged to 0.368 (3). With anisotropic displacement parameters only for Bi, the final R1 value was 0.049. The stoichiometry based on the structure determination is LiBi_7.3P₃O₁₉.

Computing details

Data collection: KappaCCD Server Software (Nonius, 1997); cell refinement: DENZO–SMN (Otwinowski & Minor, 1997); data reduction: DENZO–SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2005); software used to prepare material for publication: program (reference)?.

Figures

	Fig. 1. (a) A view of the asymmetric unit of LiBi7.3P3O19, parallel to the b axis. (b) The complete unit cell.
	Fig. 2. An in-depth view of the structure of LiBi7.3P3O19, parallel to the b axis, emphasizing the elliptical channels and Bi2O2 layers.

lithium haptabismuth triphosphorus nonadecaoxide

Crystal data

LiBi7.37P3O19	Z = 1
Mr = 15548.92	F(000) = 6492
Monoclinic, C2/c	Dx = 7.682 Mg m^−3
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71073 Å
a = 30.796 (6) Å	µ = 77.25 mm^−1
b = 5.2836 (11) Å	T = 293 K
c = 24.594 (5) Å	Plate, green–yellow
β = 122.87 (3)°	0.10 × 0.05 × 0.03 mm
V = 3361.1 (16) Å^3

Data collection

Nonius KappaCCD diffractometer	3337 independent reflections
Radiation source: fine-focus sealed tube	3337 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.065
ϕ scans, and ω scans with κ offsets	θmax = 27.5°, θmin = 1.7°
Absorption correction: numerical (SADABS; Sheldrick, 2007)	h = 0→39
Tmin = 0.022, Tmax = 0.145	k = 0→6
3845 measured reflections	l = −31→26

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.049	w = 1/[σ^2(Fo^2) + (0.0729P)^2 + 434.2758P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.134	(Δ/σ)max = 0.005
S = 1.17	Δρmax = 8.81 e Å^−3
3337 reflections	Δρmin = −4.55 e Å^−3
164 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
19 restraints	Extinction coefficient: 0.000113 (10)

Special details

Experimental. Several crystals were examined on a Nonius κ automated CCD diffractometer equipped with a graphite monochromator with Mo Kα radiation, λ = 0.71079 Å. The best crystal displaying the lowest mosaicity was used for the data collection. The diffracted intensities generated by a scan of 1.7° ω and 219 s exposure time per frame were recorded on 131 frames at ϕ = 222.7°, 70 frames over a range of 119.0° ω and 67 frames over a range of 113.9° ω. The intensities were collected on the basis of a C-centered monoclinic cell, a = 30.7962 (5), b = 5.2836 (1), c = 24.5945 (4) Å, β = 122.8732 (6)°·Data reduction and scaling were performed using DENZO-SMN (Otwinowski & Minor, 1997). Details of crystal data, data collection and structure refinement are listed in Table 1. The structure was solved with the direct methods program SHELXS (Sheldrick, 1997) in space group C2/c that yielded the heavy atom positions. Difference electron density maps revealed the phosphorus and oxygen atoms. The refinement proceeded by least squares using SHELXL (Sheldrick, 1997).

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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Bi1	0.06705 (2)	0.97528 (12)	0.01639 (3)	0.00510 (19)
Bi2	0.23997 (2)	0.47138 (12)	0.29705 (3)	0.00537 (18)
Bi3	0.02906 (3)	0.48930 (11)	0.08829 (3)	0.00657 (19)
Bi4	0.13587 (2)	0.00884 (11)	0.19803 (3)	0.00562 (19)
Bi5	0.16158 (2)	0.50367 (11)	0.11745 (3)	0.00493 (19)
Bi6	0.28079 (3)	0.52892 (12)	0.09630 (3)	0.0104 (2)
Bi7	0.11038 (3)	0.54344 (13)	−0.07078 (4)	0.0138 (2)
Bi8	0.0000	0.4882 (3)	0.2500	0.0185 (5)	0.736 (6)
P1	0.18840 (18)	1.0349 (9)	0.0315 (2)	0.0105 (9)*
P2	0.0089 (2)	−0.0025 (9)	0.3431 (3)	0.0176 (11)*
P3	0.1304 (2)	0.5032 (10)	0.3010 (3)	0.026 (2)*
Li1	−0.0878 (16)	0.004 (7)	0.189 (2)	0.028 (9)*
O1	0.0006 (4)	0.748 (2)	−0.0002 (5)	0.004 (2)*
O2	0.0972 (4)	0.752 (2)	0.1074 (5)	0.005 (2)*
O3	0.0972 (4)	0.253 (2)	0.1104 (5)	0.006 (2)*
O4	0.1975 (4)	0.254 (2)	0.2057 (5)	0.004 (2)*
O5	0.1970 (4)	0.761 (2)	0.2021 (5)	0.002 (2)*
O6	0.1735 (5)	0.987 (2)	0.0822 (7)	0.013 (3)*
O7	0.0803 (5)	0.565 (3)	−0.0140 (7)	0.021 (3)*
O8	0.1446 (5)	0.247 (2)	0.3393 (6)	0.019 (3)*
O9	0.2631 (5)	0.572 (3)	0.1647 (7)	0.019 (3)*
O10	0.0505 (6)	0.190 (3)	0.3515 (7)	0.027 (3)*
O11	0.1922 (5)	1.321 (3)	0.0250 (7)	0.021 (3)*
O12	−0.0057 (6)	0.028 (3)	0.3933 (8)	0.023 (3)*
O13	0.1465 (9)	0.937 (4)	−0.0332 (11)	0.054 (5)*
O14	0.1279 (8)	0.464 (3)	0.2395 (8)	0.057 (6)*
O15	−0.0407 (11)	0.070 (5)	0.2764 (14)	0.078 (8)*
O16	0.0255 (10)	−0.264 (5)	0.3413 (12)	0.080 (8)*
O17	0.2384 (9)	0.906 (5)	0.0503 (11)	0.066 (6)*
O18	0.0852 (7)	0.621 (4)	0.2966 (10)	0.077 (7)*
O19	0.1794 (8)	0.680 (4)	0.3452 (10)	0.098 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Bi1	0.0040 (3)	0.0075 (3)	0.0056 (3)	−0.00024 (19)	0.0038 (3)	0.0013 (2)
Bi2	0.0071 (3)	0.0071 (3)	0.0050 (3)	0.0002 (2)	0.0053 (3)	−0.0008 (2)
Bi3	0.0111 (3)	0.0056 (3)	0.0073 (4)	0.0002 (2)	0.0077 (3)	−0.0001 (2)
Bi4	0.0079 (3)	0.0068 (3)	0.0063 (3)	−0.0003 (2)	0.0065 (3)	0.0002 (2)
Bi5	0.0071 (3)	0.0054 (3)	0.0043 (3)	0.00082 (19)	0.0045 (3)	−0.00021 (19)
Bi6	0.0128 (3)	0.0142 (4)	0.0111 (4)	0.0012 (2)	0.0110 (3)	0.0009 (2)
Bi7	0.0208 (4)	0.0158 (4)	0.0169 (4)	−0.0022 (3)	0.0181 (3)	−0.0022 (3)
Bi8	0.0292 (9)	0.0228 (8)	0.0110 (8)	0.000	0.0159 (7)	0.000

Geometric parameters (Å, º)

Bi1—O1	2.211 (11)	Bi6—O19^iv	2.249 (19)
Bi1—O2	2.239 (11)	Bi6—O8^v	2.273 (12)
Bi1—O1^i	2.393 (11)	Bi6—O17	2.31 (2)
Bi1—O7	2.402 (15)	Bi6—O11^viii	2.556 (13)
Bi1—O3^ii	2.455 (11)	Bi7—O7	2.055 (16)
Bi1—O12^iii	2.611 (15)	Bi7—O10^iii	2.283 (15)
Bi1—O6	2.760 (13)	Bi7—O13	2.30 (2)
Bi2—O4	2.212 (11)	Bi7—O11^viii	2.616 (13)
Bi2—O5^iv	2.227 (11)	Bi7—O16^ix	2.75 (3)
Bi2—O9^iv	2.334 (14)	Bi7—O18^iii	3.04 (2)
Bi2—O4^v	2.464 (11)	Bi8—O16^ii	2.34 (2)
Bi2—O5	2.489 (11)	Bi8—O16^x	2.34 (2)
Bi2—O6^iv	2.708 (13)	Bi8—O18	2.33 (3)
Bi2—O14	2.91 (2)	Bi8—O18^vii	2.33 (3)
Bi2—O19	2.93 (2)	Bi8—O10^vii	2.630 (15)
Bi3—O1^vi	2.226 (11)	Bi8—O10	2.630 (15)
Bi3—O3	2.241 (11)	Bi8—O15	2.79 (3)
Bi3—O1	2.305 (11)	Bi8—O15^vii	2.79 (3)
Bi3—O2	2.340 (11)	P1—O13	1.50 (2)
Bi3—O12^vii	2.647 (15)	P1—O17	1.51 (2)
Bi3—O7^vi	2.843 (14)	P1—O11	1.529 (15)
Bi4—O4	2.219 (11)	P1—O6	1.564 (16)
Bi4—O3	2.221 (11)	P2—O16	1.48 (3)
Bi4—O5^viii	2.251 (11)	P2—O12	1.534 (18)
Bi4—O2^viii	2.314 (11)	P2—O10	1.559 (16)
Bi4—O14	2.676 (17)	P2—O15	1.57 (3)
Bi5—O5	2.215 (11)	P3—O14	1.487 (17)
Bi5—O4	2.253 (11)	P3—O18	1.475 (17)
Bi5—O2	2.275 (11)	P3—O8	1.571 (13)
Bi5—O3	2.314 (11)	P3—O19	1.598 (18)
Bi5—O9	2.702 (14)	Li1—O15	1.86 (5)
Bi5—O6	2.785 (12)	Li1—O8^vii	1.97 (4)
Bi5—O7	2.836 (14)	Li1—O18^xi	2.05 (4)
Bi5—O6^viii	2.947 (12)	Li1—O10^vii	2.12 (5)
Bi6—O9	2.044 (15)
O13—P1—O17	108.5 (13)	O18—P3—O14	117.3 (9)
O13—P1—O11	107.4 (10)	O18—P3—O8	110.6 (9)
O17—P1—O11	110.8 (11)	O14—P3—O8	109.6 (8)
O13—P1—O6	109.6 (10)	O18—P3—O19	108.0 (9)
O17—P1—O6	112.0 (11)	O14—P3—O19	106.2 (9)
O11—P1—O6	108.4 (8)	O8—P3—O19	104.1 (8)
O16—P2—O12	112.3 (12)	O15—Li1—O8^vii	106 (2)
O16—P2—O10	109.9 (12)	O15—Li1—O18^xi	93 (2)
O12—P2—O10	113.7 (9)	O8^vii—Li1—O18^xi	130 (2)
O16—P2—O15	110.6 (15)	O15—Li1—O10^vii	100 (2)
O12—P2—O15	105.8 (13)	O8^vii—Li1—O10^vii	97.9 (17)
O10—P2—O15	104.1 (12)	O18^xi—Li1—O10^vii	124 (2)

Symmetry codes: (i) −x, −y+2, −z; (ii) x, y+1, z; (iii) x, −y+1, z−1/2; (iv) −x+1/2, y−1/2, −z+1/2; (v) −x+1/2, y+1/2, −z+1/2; (vi) −x, −y+1, −z; (vii) −x, y, −z+1/2; (viii) x, y−1, z; (ix) x, −y, z−1/2; (x) −x, y+1, −z+1/2; (xi) −x, y−1, −z+1/2.