Bismuth octaborate, Bi₂B₈O₁₅

In the title compound, Bi₂B₈O₁₅, the Bi atom is coordinated to five or six O atoms. The B atoms exhibit two kinds of hybridization, sp² and sp³, seen in the BO₃ triangles and BO₄ tetrahedra, respectively. Three BO₃ triangles are connected to form a B₃O₆ planar ring. All atoms in the structure are connected together to form an infinite three-dimensional network.

S1. Comment

The growing field of nonlinear optical (NLO) research and applications still requires new materials for developing new laser sources and extending applications. Much effort has been spent on developing the borate series. Among them, β-BaB₂O₄ (BBO), LiB₃O₅ (LBO), YCa₄(BO₃)₃O (YCOB) and BiB₃O₆ (BIBO), have been studied as promising NLO crystals (Becker, 1998). The B atom usually coordinates with either three or four O atoms forming BO₃ or BO₄ groups, where the electronic orbitals are hybridized to a planar sp² or a three-dimensional sp³ configuration. The structural unit can comprise several different B_mO_n groups through different combinations, such as the B₃O₆ group in BBO, the B₃O₇ group in LBO, and a combination of BO₃ and BO₄ groups as in BIBO (Xue & Zhang, 1997). Levin & McDaniel (1962) investigated the binary system Bi₂O₃—B₂O₃, and described Bi₂B₈O₁₅ for the first time. Based on their study, the authors have grown a low-temperature form of Bi₂B₈O₁₅ single crystals. To our best knowledge, Bi₂B₈O₁₅ has not been grown as a single-crystal in the past.

The crystal structure of Bi₂B₈O₁₅ is shown in Fig. 1. The three-dimensional framework of the structure is composed of two principal components; (a) Bi atoms of fivefold and sixfold coordination, (b) BO₃ triangles, (c) B₃O₆ planar rings, and (d) BO₄ tetrahedra. The BiO₅ and BiO₆ polyhedra are linked to B₃O₆ rings via BO₃ triangles or BO₄ tetrahedra. The ratio of BO₃ triangles and BO₄ tetrahedra is 3:1. The lone-pair electrons are supposedly located near the Bi cation (Hellwig et al., 1999).

The crystal consists of nearly planar B₃O₆ rings bonded through Bi cations as shown in Fig. 2. The average B—O distances in B₃O₆ six-membered rings is 1.39 Å. The B2—O3 bond length [1.44 (3) Å] is significantly longer than others, including B3—O3 [1.36 (3) Å] and B1—O2 [1.34 (3) Å]. The average B—O—B angle is 120.8(X)° with the angles B1—O2—B3 [119.3 (16)°] and B3—O3—B2 [121.0 (17)°] showing the the largest deviation. The Bi atom has a distorted octahedral coordination, with the average Bi—O distance of 2.396(X)Å.

The anionic group theory (Chen & Wu, 1989) revealed that the B₃O₆ groups in BBO play an important role contributing to its excellent NLO responses. Accordingly, the NLO-active clusters in Bi₂B₈O₁₅ should be B₃O₆ rings. The additional presence of distorted BiO₆ and BiO₅ polyhedra and lone-pair electrons of Bi may enhance the NLO effect (Zhang & Wang, 1996). The structural features indicated above show that the Bi₂B₈O₁₅ is a potential NLO crystal, and in fact, the authors observed a strong second harmonic generation (SHG) effect by the irradiation of infrared light.

S2. Experimental

Since the crystal melts congruently the top-seeded solution method was used. Bi₂B₈O₁₅ contains two modifications. The low-temperature form was obtained by annealing the as-grown crystal.

S3. Refinement

The structure was refined as a racemic twin with components 0.81 (6) and 0.19 (6). 856 Friedel pairs were used. Because the anisotropic atomic displacement parameter (ADP) of the light atoms are very large in this kind of structure, the SHELXTL commands DELU, ISOR and SIMU (Bruker, 1997) were used for all atoms in the refinement to restrain their ADP parameters in the direction of the bond to be equal within a standard deviation 0.01; atoms closer than 1.7 Å were restrained with standard deviation 0.04 to have the same ADP components and to approximate isotropic behavior with standard deviation 0.1. The high R factor and large residual electron density is probably due to the poor crystal quality (R_int=0.072). Δρ_max was located at the position x = 0.2966, y =0.2605, z = 0.115, 0.66 Å from Bi1 atom.

Computing details

Data collection: XSCANS (Siemens,1996); cell refinement: XSCANS (Siemens,1996); data reduction: Bruker SHELXTL (Bruker,1997); program(s) used to solve structure: Bruker SHELXTL (Bruker,1997); program(s) used to refine structure: Bruker SHELXTL (Bruker,1997); molecular graphics: Bruker SHELXTL (Bruker,1997).

Figures

	Fig. 1. : Packing diagram showing the layers parallel (010) of sixfold coordinated Bi atoms alternate with borate layers and [B3O6] rings.
	Fig. 2. : The molecular structure of Bi2B8O15 showing 50% probability displacement ellipsoids.

(I)

Crystal data

B8Bi2O15	F(000) = 652
Mr = 744.44	Dx = 4.152 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 4.3142 (7) Å	Cell parameters from 40 reflections
b = 22.141 (4) Å	θ = 5.5–15.9°
c = 6.4675 (10) Å	µ = 29.60 mm^−1
β = 105.441 (11)°	T = 293 K
V = 595.49 (16) Å^3	Prism, colourless
Z = 2	0.10 × 0.10 × 0.09 mm

Data collection

Bruker P4 diffractometer	2655 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.072
Graphite monochromator	θmax = 35.0°, θmin = 3.3°
θ/2θ scans	h = −6→1
Absorption correction: ψ scan SCANS (Siemens,1996)	k = −35→1
Tmin = 0.05, Tmax = 0.07	l = −10→10
3607 measured reflections	3 standard reflections every 97 reflections
2751 independent reflections	intensity decay: none

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)] = 0.070	w = 1/[σ^2(Fo^2) + (0.1457P)^2 + 1.4317P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.171	(Δ/σ)max < 0.001
S = 1.07	Δρmax = 11.45 e Å^−3
2751 reflections	Δρmin = −6.20 e Å^−3
227 parameters	Absolute structure: Flack H D (1983), Acta Cryst. A39, 876-881
341 restraints	Absolute structure parameter: 0.19 (6)

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Bi2	0.82447 (12)	0.64754 (3)	0.66890 (8)	0.01683 (14)
Bi1	0.61092 (13)	0.78383 (3)	0.89404 (8)	0.01693 (14)
B1	0.442 (7)	0.9889 (12)	0.571 (3)	0.031 (3)
B2	0.462 (8)	0.9644 (13)	0.208 (4)	0.036 (3)
B3	0.693 (6)	0.8982 (11)	0.511 (3)	0.027 (2)
B4	0.867 (4)	0.7863 (10)	0.480 (2)	0.0159 (18)
B5	1.280 (4)	0.7847 (12)	0.265 (3)	0.019 (2)
B6	0.573 (4)	0.6447 (12)	1.086 (3)	0.0182 (19)
B7	0.147 (3)	0.6475 (13)	1.304 (3)	0.018 (2)
B8	0.609 (7)	0.5321 (12)	1.089 (3)	0.030 (3)
O1	0.357 (6)	1.0016 (9)	0.349 (2)	0.038 (3)
O2	0.602 (5)	0.9387 (9)	0.650 (2)	0.033 (3)
O3	0.632 (5)	0.9103 (9)	0.299 (2)	0.035 (3)
O4	0.821 (4)	0.8454 (7)	0.5930 (19)	0.0205 (17)
O5	1.180 (3)	0.7842 (7)	0.4473 (18)	0.0177 (16)
O6	0.836 (3)	0.7429 (7)	0.649 (2)	0.0175 (16)
O7	1.098 (3)	0.7911 (9)	1.057 (2)	0.025 (2)
O8	0.610 (3)	0.7813 (9)	1.284 (2)	0.0204 (19)
O9	0.829 (3)	0.6540 (7)	0.2850 (19)	0.019 (2)
O10	0.339 (3)	0.6410 (10)	0.506 (2)	0.024 (2)
O11	0.595 (3)	0.6872 (8)	0.9208 (19)	0.0202 (17)
O12	0.251 (3)	0.6488 (9)	1.1206 (19)	0.0195 (18)
O13	0.597 (4)	0.5844 (7)	0.987 (2)	0.0233 (19)
O14	0.647 (5)	0.5302 (9)	1.307 (2)	0.033 (3)
O15	0.580 (6)	0.4758 (8)	0.986 (2)	0.036 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Bi2	0.0128 (2)	0.0220 (2)	0.0158 (2)	0.00064 (19)	0.00411 (15)	0.00035 (17)
Bi1	0.0127 (2)	0.0226 (2)	0.0155 (2)	0.00083 (17)	0.00382 (14)	0.00052 (16)
B1	0.051 (7)	0.028 (6)	0.016 (4)	0.012 (6)	0.013 (5)	−0.001 (5)
B2	0.056 (8)	0.036 (6)	0.019 (5)	0.012 (6)	0.017 (5)	0.000 (5)
B3	0.038 (6)	0.026 (4)	0.018 (4)	0.009 (5)	0.011 (4)	0.001 (4)
B4	0.016 (4)	0.016 (4)	0.016 (4)	−0.003 (4)	0.003 (3)	0.000 (4)
B5	0.016 (5)	0.025 (6)	0.016 (5)	−0.003 (6)	0.003 (4)	−0.004 (6)
B6	0.020 (4)	0.022 (4)	0.014 (4)	0.000 (5)	0.006 (3)	0.002 (4)
B7	0.005 (4)	0.029 (6)	0.018 (5)	−0.001 (5)	0.001 (3)	−0.007 (6)
B8	0.049 (7)	0.026 (4)	0.015 (4)	−0.008 (5)	0.008 (5)	0.001 (4)
O1	0.062 (7)	0.034 (6)	0.018 (4)	0.013 (5)	0.010 (5)	−0.001 (4)
O2	0.047 (6)	0.031 (5)	0.019 (4)	0.011 (5)	0.007 (4)	−0.002 (4)
O3	0.058 (7)	0.035 (5)	0.017 (4)	0.011 (5)	0.017 (4)	0.004 (4)
O4	0.026 (4)	0.021 (3)	0.015 (3)	0.000 (4)	0.007 (3)	−0.002 (3)
O5	0.013 (3)	0.022 (4)	0.019 (4)	0.003 (4)	0.006 (3)	0.000 (4)
O6	0.016 (4)	0.020 (3)	0.019 (4)	0.003 (3)	0.007 (3)	0.001 (3)
O7	0.013 (4)	0.045 (8)	0.017 (4)	−0.002 (5)	0.005 (3)	−0.001 (4)
O8	0.015 (4)	0.028 (6)	0.018 (4)	0.004 (5)	0.004 (3)	0.001 (4)
O9	0.014 (4)	0.029 (6)	0.012 (4)	0.005 (4)	0.001 (3)	−0.002 (4)
O10	0.011 (4)	0.043 (8)	0.015 (4)	−0.004 (5)	−0.001 (3)	−0.002 (5)
O11	0.023 (4)	0.025 (4)	0.014 (3)	−0.001 (4)	0.009 (3)	0.001 (3)
O12	0.009 (3)	0.030 (5)	0.020 (4)	−0.002 (4)	0.004 (3)	−0.001 (4)
O13	0.028 (5)	0.026 (4)	0.018 (4)	−0.001 (4)	0.010 (4)	0.000 (3)
O14	0.054 (8)	0.034 (6)	0.012 (4)	−0.012 (6)	0.011 (5)	−0.003 (4)
O15	0.066 (9)	0.028 (5)	0.014 (4)	−0.009 (6)	0.012 (5)	−0.004 (4)

Geometric parameters (Å, º)

Bi2—O10	2.084 (12)	B4—O4	1.54 (2)
Bi2—O6	2.117 (15)	B5—O5	1.36 (2)
Bi2—O11	2.294 (13)	B5—O7^v	1.37 (2)
Bi2—O9	2.493 (12)	B5—O8^vi	1.40 (2)
Bi2—O10^i	2.700 (13)	B6—O11	1.45 (2)
Bi2—Bi1	3.5763 (9)	B6—O12	1.47 (2)
Bi1—O7	2.090 (13)	B6—O9^vii	1.47 (2)
Bi1—O11	2.149 (17)	B6—O13	1.50 (3)
Bi1—O6	2.259 (13)	B7—O9^viii	1.350 (19)
Bi1—O8	2.522 (13)	B7—O10^vii	1.36 (2)
Bi1—O7^ii	2.697 (13)	B7—O12	1.37 (2)
Bi1—O4	2.722 (13)	B8—O13	1.32 (3)
B1—O14^iii	1.33 (3)	B8—O14	1.38 (2)
B1—O2	1.34 (3)	B8—O15	1.40 (3)
B1—O1	1.41 (3)	O7—B5^vii	1.37 (2)
B2—O15^iv	1.24 (3)	O7—Bi1^i	2.697 (13)
B2—O1	1.39 (3)	O8—B5^viii	1.40 (2)
B2—O3	1.44 (3)	O8—B4^vii	1.45 (2)
B3—O4	1.34 (3)	O9—B7^vi	1.350 (19)
B3—O3	1.36 (3)	O9—B6^v	1.47 (2)
B3—O2	1.40 (3)	O10—B7^v	1.36 (2)
B4—O5	1.42 (2)	O10—Bi2^ii	2.700 (13)
B4—O8^v	1.45 (2)	O14—B1^ix	1.33 (3)
B4—O6	1.49 (2)	O15—B2^x	1.24 (3)
O10—Bi2—O6	94.3 (7)	O5—B4—O4	110.3 (15)
O10—Bi2—O11	79.6 (5)	O8^v—B4—O4	108.4 (14)
O6—Bi2—O11	71.6 (5)	O6—B4—O4	98.9 (12)
O10—Bi2—O9	77.0 (5)	O5—B5—O7^v	128.5 (15)
O6—Bi2—O9	82.8 (5)	O5—B5—O8^vi	118.2 (13)
O11—Bi2—O9	143.6 (5)	O7^v—B5—O8^vi	113.2 (14)
O10—Bi2—O10^i	128.3 (6)	O11—B6—O12	109.0 (17)
O6—Bi2—O10^i	89.7 (6)	O11—B6—O9^vii	111.9 (17)
O11—Bi2—O10^i	148.3 (5)	O12—B6—O9^vii	112.4 (14)
O9—Bi2—O10^i	52.4 (4)	O11—B6—O13	103.9 (13)
O10—Bi2—Bi1	86.0 (5)	O12—B6—O13	107.2 (18)
O6—Bi2—Bi1	36.5 (3)	O9^vii—B6—O13	112.1 (16)
O11—Bi2—Bi1	35.0 (4)	O9^viii—B7—O10^vii	116.1 (14)
O9—Bi2—Bi1	115.4 (4)	O9^viii—B7—O12	118.5 (14)
O10^i—Bi2—Bi1	122.1 (4)	O10^vii—B7—O12	125.3 (13)
O7—Bi1—O11	94.9 (7)	O13—B8—O14	121 (2)
O7—Bi1—O6	79.8 (5)	O13—B8—O15	123.8 (17)
O11—Bi1—O6	71.7 (5)	O14—B8—O15	115.4 (19)
O7—Bi1—O8	76.5 (5)	B2—O1—B1	120 (2)
O11—Bi1—O8	83.6 (5)	B1—O2—B3	119.3 (16)
O6—Bi1—O8	143.9 (5)	B3—O3—B2	121.0 (17)
O7—Bi1—O7^ii	128.2 (6)	B3—O4—B4	130.4 (14)
O11—Bi1—O7^ii	88.9 (6)	B3—O4—Bi1	122.6 (12)
O6—Bi1—O7^ii	148.1 (5)	B4—O4—Bi1	91.3 (9)
O8—Bi1—O7^ii	52.5 (4)	B5—O5—B4	131.4 (13)
O7—Bi1—O4	80.8 (5)	B4—O6—Bi2	134.4 (11)
O11—Bi1—O4	125.4 (4)	B4—O6—Bi1	113.2 (11)
O6—Bi1—O4	54.0 (5)	Bi2—O6—Bi1	109.6 (6)
O8—Bi1—O4	144.6 (5)	B5^vii—O7—Bi1	136.1 (12)
O7^ii—Bi1—O4	135.5 (5)	B5^vii—O7—Bi1^i	93.6 (10)
O7—Bi1—Bi2	86.4 (5)	Bi1—O7—Bi1^i	128.2 (6)
O11—Bi1—Bi2	37.8 (3)	B5^viii—O8—B4^vii	126.5 (13)
O6—Bi1—Bi2	33.9 (4)	B5^viii—O8—Bi1	100.6 (9)
O8—Bi1—Bi2	117.2 (4)	B4^vii—O8—Bi1	132.0 (10)
O7^ii—Bi1—Bi2	122.5 (4)	B7^vi—O9—B6^v	125.0 (13)
O4—Bi1—Bi2	87.8 (3)	B7^vi—O9—Bi2	100.5 (9)
O14^iii—B1—O2	122.9 (19)	B6^v—O9—Bi2	131.2 (10)
O14^iii—B1—O1	115 (2)	B7^v—O10—Bi2	138.7 (11)
O2—B1—O1	121.7 (18)	B7^v—O10—Bi2^ii	91.0 (9)
O15^iv—B2—O1	124 (2)	Bi2—O10—Bi2^ii	128.3 (6)
O15^iv—B2—O3	120 (2)	B6—O11—Bi1	135.8 (12)
O1—B2—O3	116.4 (19)	B6—O11—Bi2	113.7 (12)
O4—B3—O3	121.4 (18)	Bi1—O11—Bi2	107.2 (6)
O4—B3—O2	117.6 (16)	B7—O12—B6	132.1 (14)
O3—B3—O2	120.8 (19)	B8—O13—B6	124.6 (15)
O5—B4—O8^v	113.6 (13)	B1^ix—O14—B8	131 (2)
O5—B4—O6	111.3 (14)	B2^x—O15—B8	129 (2)
O8^v—B4—O6	113.3 (14)

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