Distrontium lithium beryllium triborate, Sr₂LiBeB₃O₈

Single crystals of distrontium lithium beryllium triborate, Sr₂LiBeB₃O₈, were obtained by spontaneous nucleation from a high-temperature melt. In the Sr₂Li[BeB₃O₈] structure, [BeB₂O₇]⁶⁻ rings, made up from one BeO₄ tetra­hedron and two BO₃ triangles, are connected to each other by [BO₃] triangles to form the smallest repeat unit {[BeB₃O₈]⁸⁻} and then form chains along the b axis. The Sr²⁺ cations are seven- or eight-­coordinated and Li⁺ cations are tetra-­coordinated and lie between the chains.

Related literature

Non-linear optical (NLO) applications of borate crystals with trigonal BO₃ anions have been discussed by Chen et al. (1999). Among this group of compounds, beryllium borates are reported to exhibit the shortest transmission cut-off wavelength (Li, 1989). A review of the geometry of the BO₃ group is given by Zobetz (1982), and a similar configuration of the [BeB₂O₇]⁶⁻ unit is found in LiB₃O₅ (LBO; Chen et al., 2005) in which [B₃O₇]⁵⁻ rings are present. The structure of the beryllium borate group [BeB₂O₇]⁶⁻ is given by Li & Ye (2007).

Experimental

Crystal data

• Sr₂LiBeB₃O₈

• M_r = 351.62

• Monoclinic, P 2₁ /c

• a = 8.609 (5) Å

• b = 6.486 (4) Å

• c = 12.868 (8) Å

• β = 106.91 (1)°

• V = 687.4 (7) ų

• Z = 4

• Mo Kα radiation

• μ = 15.53 mm⁻¹

• T = 293 K

• 0.20 × 0.12 × 0.10 mm

Data collection

• Rigaku Mercury2 diffractometer

• Absorption correction: multi-scan (CrystalClear; Rigaku, 2007) T_min = 0.123, T_max = 0.212

• 5147 measured reflections

• 1574 independent reflections

• 1429 reflections with I > 2σ(I)

• R_int = 0.038

Refinement

• R[F² > 2σ(F²)] = 0.026

• wR(F²) = 0.060

• S = 1.05

• 1574 reflections

• 137 parameters

• Δρ_max = 0.97 e Å⁻³

• Δρ_min = −0.81 e Å⁻³

Data collection: CrystalClear (Rigaku, 2007); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2004); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Supporting information

S1. Comment

Based on a theoretical study, beryllium borates possess the largest energy gap among all alkaline and alkaline earth borates, and hence the shortest transmission cut-off wavelength (Li, 1989). In addition, borate crystals containing parallelly aligned BO₃ anionic groups are considered to be good candidates for NLO applications (Chen et al., 1999). Therefore, beryllium borates are studied intensively with the purpose of searching for novel compounds with potential applications in the UV region. The title compound, Sr₂LiBeB₃O₈, was found from the investigation of the beryllium borate system containing strontium and lithium.

A perspective view of the Sr₂LiBeB₃O₈ structure in the a-c plane is shown in Fig.1. It contains a similar beryllium borate group [BeB₂O₇]^6- which was found in the structure Na₂BeB₂O₅(Li & Ye, 2007) as the basic group in the Sr₂LiBeB₃O₈ structure. In the structure of non-planar six-ring [BeB₂O₇]^6-, the Be atoms are bonded to four O atoms to form distorted BeO₄ tetrahedral. The B atoms are coordinated to three O atoms to form planar BO₃ triangles and two planar BO₃ groups share one common O1 atom, and each of them also shares a different O atom with a BeO₄ tetrahedral.(Fig.3) This structure of the basic structural unit, [BeB₂O₇]^6-, is similar to that of [B₃O₇]^5- in LiB₃O₅ (LBO) (Chen et al., 2005), with a BO₄ replaced by BeO₄. In the Sr₂LiBeB₃O₈ structure, the [BeB₂O₇]^6- rings are linked each other by a bridging BO₃ group(B3 atom) to form the smallest repeat unit {[BeB₃O₈]^8-} (n→∞) one dimensional chains along the b Axis (Fig.2). From the study of LBO, it is known that the [B₃O₇]^5- group can yield large NLO effects and short UV transmission cut-offs, but spatial arrangement of the endless helices of [B₃O₇](n→∞) chains along the z axis is unfavorable for producing a large birefringence. Therefore, the resulting layer structure of [BeB₂O₇](n→∞) along the b axis may be a good candidate for DUV NLO applications. Unfortunately, in the case of Sr₂LiBeB₃O₈, the direction of [BeB₂O₇]^6- group along the b axis are completely opposite and, therefore, their contributions to the NLO effect cancel out.

Related literature

Non-linear optical (NLO) applications of borate crystals with trigonal BO₃ anions have been discussed by Chen et al. (1999). Among this group of compounds, beryllium borates are reported to exhibit the shortest transmission cut-off wavelength (Li, 1989). A review of the geometry of the BO₃ group is given by Zobetz (1982), and a similar configuration of the [BeB₂O₇]^6- unit is found in LiB₃O₅ (LBO; Chen et al., 2005) in which [B₃O₇]^5- rings are present. The structure of the beryllium borate group [BeB₂O₇]^6- is given by Li & Ye (2007).

S2. Experimental

Single crystals of Sr₂LiBeB₃O₈ were grown from a high-temperature solution using SrO-B₂O₃—Li₂CO₃ as a flux. This solution was prepared in a platinum crucible after melting of a mixture of SrCO₃, BeO, B₂O₃ and Li₂CO₃ at the ratio of SrO/BeO/B₂O₃/Li₂CO₃=4:2:3:2. The mixture (10 g) was heated in a temperature-programmable electric furnace at 1273 K until the melt became transparent and clear. The homogenized melt solution was then cooled rapidly (323 K/h) to the initial crystallization temperature (1073 K). It was further cooled slowly (276 K/h) to the final crystallization temperature (973 K) and then allowed to cool to room temperature after the furnace was turned off. The flux attached to the crystal was readily dissolved in water.

Computing details

Data collection: CrystalClear (Rigaku, 2007); cell refinement: CrystalClear (Rigaku, 2007); data reduction: CrystalClear (Rigaku, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2004); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The crystal structure of Sr2Li[BeB3O8], viewed along the b axis, and drawn with anisotropic displacement paremeters at the 50% probability level. Sr—O bonds and Li—O bonds were omitted for clarity.
	Fig. 2. The parallel arrangement of the smallest repeat unit {[BeB3O8]^8-} (n→∞) along b axis which forms a one-dimensional infinite chain.
	Fig. 3. [BeB2O7]^6- building unit in the title compound.

Distrontium lithium beryllium triborate

Crystal data

Sr2LiBeB3O8	F(000) = 648
Mr = 351.62	Dx = 3.397 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 764 reflections
a = 8.609 (5) Å	θ = 4.1–27.5°
b = 6.486 (4) Å	µ = 15.53 mm^−1
c = 12.868 (8) Å	T = 293 K
β = 106.91 (1)°	Prism, colorless
V = 687.4 (7) Å^3	0.20 × 0.12 × 0.10 mm
Z = 4

Data collection

Rigaku Mercury2 diffractometer	1574 independent reflections
Radiation source: fine-focus sealed tube	1429 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.038
Detector resolution: 13.6612 pixels mm^-1	θmax = 27.5°, θmin = 2.5°
CCD_Profile_fitting scans	h = −11→9
Absorption correction: multi-scan (CrystalClear; Rigaku, 2007)	k = −7→8
Tmin = 0.123, Tmax = 0.212	l = −16→16
5147 measured reflections

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)] = 0.026	w = 1/[σ^2(Fo^2) + (0.0325P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.060	(Δ/σ)max < 0.001
S = 1.05	Δρmax = 0.97 e Å^−3
1574 reflections	Δρmin = −0.81 e Å^−3
137 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0525 (14)

Special details

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.

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
Sr1	0.35975 (4)	0.24425 (5)	0.42862 (2)	0.00870 (12)
Sr2	0.96530 (4)	0.89027 (5)	0.34184 (2)	0.01077 (12)
B1	0.7378 (5)	0.2697 (6)	0.4861 (3)	0.0081 (7)
B2	0.9374 (5)	0.3471 (6)	0.3805 (3)	0.0086 (7)
B3	0.4005 (5)	0.4529 (6)	0.2060 (3)	0.0089 (7)
Be1	0.6756 (5)	0.5709 (7)	0.3439 (3)	0.0087 (9)
Li1	0.3681 (9)	0.7734 (10)	0.3261 (5)	0.0212 (15)
O1	0.8842 (3)	0.2319 (4)	0.4584 (2)	0.0115 (5)
O2	0.6391 (3)	0.4284 (4)	0.43886 (18)	0.0108 (5)
O3	0.7074 (3)	0.1423 (4)	0.56005 (19)	0.0135 (5)
O4	0.8589 (3)	0.5215 (4)	0.3371 (2)	0.0143 (5)
O5	1.0594 (3)	0.2620 (4)	0.3497 (2)	0.0118 (5)
O6	0.5555 (3)	0.5273 (4)	0.22195 (18)	0.0105 (5)
O7	0.6566 (3)	0.8100 (4)	0.37736 (19)	0.0132 (5)
O8	0.3055 (3)	0.5106 (4)	0.26900 (19)	0.0114 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sr1	0.01050 (19)	0.0059 (2)	0.01079 (19)	0.00014 (11)	0.00487 (13)	0.00049 (11)
Sr2	0.01267 (19)	0.00595 (19)	0.01254 (19)	−0.00039 (12)	0.00184 (13)	0.00046 (12)
B1	0.0104 (19)	0.0045 (19)	0.0099 (18)	−0.0021 (14)	0.0039 (14)	−0.0027 (14)
B2	0.0091 (18)	0.008 (2)	0.0102 (17)	−0.0036 (14)	0.0042 (14)	−0.0019 (15)
B3	0.0151 (19)	0.0043 (19)	0.0073 (17)	0.0016 (15)	0.0032 (14)	0.0022 (14)
Be1	0.012 (2)	0.005 (2)	0.010 (2)	−0.0002 (16)	0.0055 (16)	0.0020 (16)
Li1	0.039 (4)	0.010 (4)	0.021 (3)	−0.007 (3)	0.019 (3)	−0.005 (3)
O1	0.0113 (13)	0.0102 (14)	0.0147 (12)	0.0034 (9)	0.0063 (9)	0.0045 (10)
O2	0.0117 (12)	0.0087 (13)	0.0136 (12)	0.0004 (9)	0.0062 (9)	0.0027 (10)
O3	0.0227 (14)	0.0057 (13)	0.0154 (12)	0.0011 (10)	0.0109 (10)	0.0022 (10)
O4	0.0122 (13)	0.0085 (13)	0.0248 (13)	0.0011 (10)	0.0093 (10)	0.0070 (11)
O5	0.0127 (13)	0.0097 (14)	0.0148 (12)	0.0001 (9)	0.0069 (10)	−0.0013 (10)
O6	0.0123 (12)	0.0091 (13)	0.0112 (12)	−0.0013 (9)	0.0050 (9)	−0.0012 (10)
O7	0.0253 (14)	0.0039 (13)	0.0091 (11)	0.0031 (10)	0.0029 (10)	0.0009 (10)
O8	0.0126 (12)	0.0103 (14)	0.0125 (12)	−0.0018 (10)	0.0054 (9)	−0.0019 (10)

Geometric parameters (Å, º)

Sr1—O5^i	2.491 (3)	B1—O3	1.342 (4)
Sr1—O7^ii	2.565 (3)	B1—O2	1.360 (5)
Sr1—O3^iii	2.586 (3)	B1—O1	1.428 (5)
Sr1—O8	2.620 (3)	B2—O5	1.344 (4)
Sr1—O2	2.654 (3)	B2—O4	1.352 (5)
Sr1—O6^iv	2.663 (3)	B2—O1	1.428 (4)
Sr1—O2^ii	2.722 (3)	B3—O8	1.361 (5)
Sr1—O3	3.051 (3)	B3—O6	1.377 (5)
Sr2—O8^v	2.478 (3)	B3—O7^iv	1.395 (5)
Sr2—O5^vi	2.536 (3)	Be1—O7	1.630 (5)
Sr2—O5^vii	2.551 (3)	Be1—O6	1.634 (5)
Sr2—O4	2.556 (3)	Be1—O2	1.634 (5)
Sr2—O1^viii	2.642 (3)	Be1—O4	1.638 (5)
Sr2—O3^viii	2.740 (3)	Li1—O3^ii	1.849 (7)
Sr2—O7	2.872 (3)	Li1—O8	1.872 (7)
Sr2—O1^vi	2.873 (3)	Li1—O6^v	1.940 (7)
Sr2—O4^vii	3.217 (3)	Li1—O7	2.389 (8)
O5^i—Sr1—O7^ii	93.38 (9)	O8^v—Sr2—O7	52.40 (8)
O5^i—Sr1—O3^iii	81.09 (8)	O5^vi—Sr2—O7	117.75 (8)
O7^ii—Sr1—O3^iii	74.69 (8)	O5^vii—Sr2—O7	105.89 (8)
O5^i—Sr1—O8	73.89 (8)	O4—Sr2—O7	59.49 (8)
O7^ii—Sr1—O8	143.67 (8)	O1^viii—Sr2—O7	90.30 (8)
O3^iii—Sr1—O8	133.75 (8)	O3^viii—Sr2—O7	141.98 (7)
O5^i—Sr1—O2	144.86 (8)	O8^v—Sr2—O1^vi	74.15 (8)
O7^ii—Sr1—O2	108.59 (8)	O5^vi—Sr2—O1^vi	50.90 (8)
O3^iii—Sr1—O2	130.36 (8)	O5^vii—Sr2—O1^vi	142.30 (8)
O8—Sr1—O2	72.22 (8)	O4—Sr2—O1^vi	126.47 (8)
O5^i—Sr1—O6^iv	101.50 (8)	O1^viii—Sr2—O1^vi	81.27 (9)
O7^ii—Sr1—O6^iv	137.73 (9)	O3^viii—Sr2—O1^vi	101.09 (8)
O3^iii—Sr1—O6^iv	69.01 (8)	O7—Sr2—O1^vi	71.36 (8)
O8—Sr1—O6^iv	78.59 (9)	O8^v—Sr2—O4^vii	93.68 (8)
O2—Sr1—O6^iv	80.66 (8)	O5^vi—Sr2—O4^vii	64.26 (7)
O5^i—Sr1—O2^ii	91.93 (8)	O5^vii—Sr2—O4^vii	47.06 (8)
O7^ii—Sr1—O2^ii	59.23 (8)	O4—Sr2—O4^vii	118.07 (7)
O3^iii—Sr1—O2^ii	132.93 (8)	O1^viii—Sr2—O4^vii	125.21 (8)
O8—Sr1—O2^ii	86.79 (9)	O3^viii—Sr2—O4^vii	73.47 (8)
O2—Sr1—O2^ii	77.27 (8)	O7—Sr2—O4^vii	144.26 (7)
O6^iv—Sr1—O2^ii	156.42 (7)	O1^vi—Sr2—O4^vii	113.95 (7)
O5^i—Sr1—O3	166.09 (8)	O3—B1—O2	123.9 (3)
O7^ii—Sr1—O3	75.73 (8)	O3—B1—O1	116.1 (3)
O3^iii—Sr1—O3	87.60 (8)	O2—B1—O1	120.0 (3)
O8—Sr1—O3	120.00 (7)	O5—B2—O4	124.2 (3)
O2—Sr1—O3	48.81 (8)	O5—B2—O1	115.4 (3)
O6^iv—Sr1—O3	81.75 (7)	O4—B2—O1	120.2 (3)
O2^ii—Sr1—O3	89.86 (7)	O8—B3—O6	122.7 (3)
O8^v—Sr2—O5^vi	87.68 (9)	O8—B3—O7^iv	120.2 (3)
O8^v—Sr2—O5^vii	75.33 (8)	O6—B3—O7^iv	117.2 (3)
O5^vi—Sr2—O5^vii	106.52 (6)	O7—Be1—O6	109.5 (3)
O8^v—Sr2—O4	90.61 (9)	O7—Be1—O2	106.6 (3)
O5^vi—Sr2—O4	177.22 (8)	O6—Be1—O2	114.5 (3)
O5^vii—Sr2—O4	75.13 (8)	O7—Be1—O4	111.9 (3)
O8^v—Sr2—O1^viii	140.12 (7)	O6—Be1—O4	105.4 (3)
O5^vi—Sr2—O1^viii	100.72 (8)	O2—Be1—O4	109.1 (3)
O5^vii—Sr2—O1^viii	136.21 (8)	O3^ii—Li1—O8	116.9 (3)
O4—Sr2—O1^viii	79.23 (8)	O3^ii—Li1—O6^v	103.4 (3)
O8^v—Sr2—O3^viii	163.40 (8)	O8—Li1—O6^v	137.1 (4)
O5^vi—Sr2—O3^viii	77.37 (8)	O3^ii—Li1—O7	109.2 (3)
O5^vii—Sr2—O3^viii	101.86 (8)	O8—Li1—O7	110.9 (3)
O4—Sr2—O3^viii	104.60 (8)	O6^v—Li1—O7	65.3 (2)
O1^viii—Sr2—O3^viii	51.76 (7)

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