Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr₂B₂O₅ pyroborate and crystal structures of β and α phases

Crystal structures of γ-, β- and α-Sr₂B₂O₅ polymorphs resulting from the γ ↔ (at 565 K) β ↔ (at 637 K) α′ ↔ (at 651 K) α sequence of reversible first-order phase transitions are studied by high-temperature single-crystal X-ray diffraction, high-temperature X-ray powder diffraction, differential scanning calorimetry and impedance spectroscopy. Out of these phases, the structure of γ-Sr₂B₂O₅ was already known whereas the structures of β- and α-Sr₂B₂O₅ were determined for the first time. The sequence of phase transitions is associated with an unusual change of symmetry, with triclinic intermediate β-Sr₂B₂O₅ phase and monoclinic low-temperature γ-Sr₂B₂O₅ as well as high-temperature α-Sr₂B₂O₅ phase. Taking the α-Sr₂B₂O₅ phase with space group P2₁/c as a parent structure, the γ-Sr₂B₂O₅ phase was refined as a twofold superstructure with symmetry P2₁/c, whereas the β-Sr₂B₂O₅ phase was a sixfold superstructure with symmetry P. To construct a unified structure model for all Sr₂B₂O₅ modifications, phases of γ- and β-Sr₂B₂O₅ were also refined as commensurately modulated structures using the basic unit cell of the parent α-Sr₂B₂O₅. The phase transitions are related to the orientational order–disorder arrangement of B₂O₅ pyroborate groups, where the degree of disorder grows towards the high-temperature phase. Thermal expansion is strongly anisotropic and dictated by preferable orientations of BO₃ triangles in the structure. The intermediate phase α′-Sr₂B₂O₅, stable over a narrow temperature range (637–651 K), features the largest anisotropy of expansion for the known borates: α₁₁ = 205, α₂₂ = 57, α₃₃ = −81 × 10⁻⁶ K⁻¹.

Computing details

Data collection: CrysAlis PRO 1.171.38.41 (Rigaku OD, 2015) for (Iv); CrysAlis PRO 1.171.38.41q (Rigaku OD, 2015) for v. Cell refinement: CrysAlis PRO 1.171.38.41 (Rigaku OD, 2015) for (Iv); CrysAlis PRO 1.171.38.41q (Rigaku OD, 2015) for v. Data reduction: CrysAlis PRO 1.171.38.41 (Rigaku OD, 2015) for (Iv); CrysAlis PRO 1.171.38.41q (Rigaku OD, 2015) for v.

(I)

Crystal data

B2O5Sr2	V = 491.62 (18) Å^3
Mr = 276.9	Z = 4
Monoclinic, P21/c	F(000) = 504
Hall symbol: -P 2ycb	Dx = 3.741 Mg m^−3
a = 7.763 (2) Å	Mo Kα radiation, λ = 0.71069 Å
b = 5.3386 (10) Å	µ = 21.62 mm^−1
c = 11.875 (2) Å	T = 295 K
β = 92.64 (2)°

Data collection

Radiation source: X-ray tube	θmax = 29.6°, θmin = 3.4°
3450 measured reflections	h = −10→10
1214 independent reflections	k = −6→6
1017 reflections with I > 3σ(I)	l = −15→11
Rint = 0.044

Refinement

Refinement on F	0 restraints
R[F^2 > 2σ(F^2)] = 0.031	0 constraints
wR(F^2) = 0.035	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
S = 1.17	(Δ/σ)max = 0.009
1214 reflections	Δρmax = 0.77 e Å^−3
82 parameters	Δρmin = −1.03 e Å^−3

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

	x	y	z	Uiso*/Ueq
Sr1	0.62327 (6)	0.90996 (8)	0.34035 (4)	0.00756 (15)
Sr2	0.11787 (6)	0.95066 (9)	0.36761 (4)	0.00801 (15)
O1	0.6437 (5)	0.3478 (7)	0.6483 (3)	0.0116 (11)
O2	0.0987 (5)	0.4070 (7)	0.6692 (3)	0.0125 (12)
O3	0.3928 (5)	0.2876 (7)	0.8593 (3)	0.0125 (12)
O4	0.8542 (4)	0.2998 (6)	0.9285 (3)	0.0097 (11)
O5	0.7462 (5)	0.6012 (6)	0.4932 (3)	0.0137 (12)
B1	0.6599 (8)	0.5697 (11)	0.5953 (5)	0.0081 (17)
B2	0.1611 (8)	0.5489 (11)	0.5841 (5)	0.0089 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sr1	0.0070 (3)	0.0069 (3)	0.0088 (3)	0.00038 (18)	0.00040 (18)	0.00015 (16)
Sr2	0.0072 (3)	0.0087 (3)	0.0083 (3)	0.00064 (19)	0.00160 (18)	0.00128 (17)
O1	0.012 (2)	0.0101 (19)	0.013 (2)	0.0008 (15)	0.0034 (15)	0.0022 (14)
O2	0.015 (2)	0.014 (2)	0.009 (2)	−0.0023 (16)	0.0028 (15)	0.0013 (14)
O3	0.014 (2)	0.009 (2)	0.015 (2)	0.0004 (15)	0.0054 (15)	0.0013 (14)
O4	0.0094 (19)	0.0082 (19)	0.0116 (19)	0.0017 (15)	0.0004 (14)	−0.0004 (13)
O5	0.020 (2)	0.010 (2)	0.011 (2)	0.0050 (16)	0.0075 (16)	0.0025 (14)
B1	0.007 (3)	0.011 (3)	0.006 (3)	−0.001 (2)	−0.001 (2)	0.002 (2)
B2	0.005 (3)	0.013 (3)	0.009 (3)	0.000 (2)	0.000 (2)	0.000 (2)

Bond lengths (Å)

Sr1—O1^i	2.4966 (9)	Sr2—O1^i	2.4559 (8)
Sr1—O1^ii	2.6335 (7)	Sr2—O2^iii	2.5678 (8)
Sr1—O2^i	2.7491 (10)	Sr2—O2^ii	2.4743 (8)
Sr1—O3^i	2.5926 (7)	Sr2—O3^ii	2.5569 (10)
Sr1—O3^ii	2.4284 (8)	Sr2—O4^iv	2.5509 (8)
Sr1—O4^ii	2.5574 (8)	Sr2—O4^v	2.5742 (9)
Sr1—O5	2.5999 (7)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, −y+3/2, z−1/2; (iii) −x, −y+1, −z+1; (iv) −x+1, y+1/2, −z+3/2; (v) x−1, −y+3/2, z−1/2.

(II)

Crystal data

B2O5Sr2	V = 245.81 (14) Å^3
Mr = 276.9	Z = 2
Monoclinic, P21/c(α0γ)00†	F(000) = 252
q = 0.500000a*	Dx = 3.741 Mg m^−3
a = 3.882 (2) Å	Mo Kα radiation, λ = 0.71069 Å
b = 5.3386 (10) Å	µ = 21.62 mm^−1
c = 11.875 (2) Å	T = 295 K
β = 92.64 (2)°

† Symmetry operations: (1) x₁, x₂, x₃, x₄; (2) −x₁, x₂+1/2, −x₃+1/2, −x₄; (3) −x₁, −x₂, −x₃, −x₄; (4) x₁, −x₂+1/2, x₃+1/2, x₄.

Data collection

Radiation source: X-ray tube	θmax = 29.5°, θmin = 3.4°
3450 measured reflections	h = −5→5
1214 independent reflections	k = −6→6
1017 reflections with I > 3σ(I)	l = −15→11
Rint = 0.044

Refinement

Refinement on F	0 restraints
R[F^2 > 2σ(F^2)] = 0.031	0 constraints
wR(F^2) = 0.035	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
S = 1.17	(Δ/σ)max = 0.014
1214 reflections	Δρmax = 0.79 e Å^−3
70 parameters	Δρmin = −1.12 e Å^−3

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sr	1.24116 (9)	0.93026 (6)	0.35395 (3)	0.00779 (12)
O1	1.2466 (7)	0.3746 (5)	0.6577 (2)	0.0120 (8)
O2	0.7856 (9)	0.2875 (7)	0.8593 (3)	0.0125 (12)	0.5
O2'	0.7084 (9)	0.2997 (6)	0.9285 (3)	0.0098 (11)	0.5
O3	0.4923 (10)	0.6013 (6)	0.4932 (3)	0.0137 (12)	0.5
B	1.3213 (11)	0.5581 (8)	0.5890 (4)	0.0084 (12)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sr	0.00709 (19)	0.0078 (2)	0.0085 (2)	0.00051 (13)	0.00100 (12)	0.00071 (11)
O1	0.0136 (14)	0.0117 (14)	0.0109 (14)	−0.0009 (11)	0.0031 (11)	0.0018 (10)
O2	0.014 (2)	0.009 (2)	0.015 (2)	0.0003 (15)	0.0054 (15)	0.0014 (14)
O2'	0.0094 (19)	0.0085 (19)	0.0115 (19)	0.0016 (15)	0.0004 (14)	−0.0003 (13)
O3	0.020 (2)	0.010 (2)	0.011 (2)	0.0050 (16)	0.0076 (16)	0.0024 (14)
B	0.006 (2)	0.012 (2)	0.008 (2)	−0.0005 (16)	−0.0001 (15)	0.0010 (15)

Bond lengths (Å)

	Average	Minimum	Maximum
B—O3^i	1.422 (8)	1.422 (8)	1.422 (8)
B—O3^ii	1.436 (8)	1.436 (8)	1.436 (8)

Symmetry codes: (i) x₁+1, x₂, x₃, x₄; (ii) −x₁+2, −x₂+1, −x₃+1, −x₄.

(III)

Crystal data

B2O5Sr2	γ = 91.473 (11)°
Mr = 276.9	V = 1489.9 (3) Å^3
Triclinic, P1	Z = 12
Hall symbol: -P 1	F(000) = 1512
a = 9.4662 (11) Å	Dx = 3.703 Mg m^−3
b = 13.2754 (7) Å	Mo Kα radiation, λ = 0.71073 Å
c = 11.8671 (16) Å	µ = 21.41 mm^−1
α = 88.815 (11)°	T = 583 K
β = 91.651 (11)°

Data collection

Radiation source: X-ray tube	θmax = 28.0°, θmin = 3.4°
42872 measured reflections	h = −12→12
11221 independent reflections	k = −17→17
4809 reflections with I > 3σ(I)	l = −15→15
Rint = 0.062

Refinement

Refinement on F	0 constraints
R[F^2 > 2σ(F^2)] = 0.040	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
wR(F^2) = 0.058	(Δ/σ)max = 0.043
S = 1.12	Δρmax = 1.08 e Å^−3
11221 reflections	Δρmin = −0.96 e Å^−3
486 parameters	Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
0 restraints	Extinction coefficient: 790 (30)

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sr1	0.70892 (8)	0.09510 (6)	0.34759 (6)	0.0209 (2)
Sr2	0.04720 (8)	0.92415 (5)	0.36218 (6)	0.0196 (2)
Sr3	0.37774 (8)	0.75776 (6)	0.35632 (7)	0.0267 (3)
Sr4	0.71458 (8)	0.60563 (6)	0.35623 (6)	0.0235 (2)
Sr5	0.04627 (8)	0.43538 (6)	0.36293 (6)	0.0219 (2)
Sr6	0.38104 (8)	0.27060 (6)	0.36092 (7)	0.0245 (2)
Sr7	0.38232 (8)	0.00104 (5)	0.16754 (6)	0.0209 (2)
Sr8	0.73464 (8)	0.84858 (6)	0.12191 (6)	0.0208 (2)
Sr9	0.06011 (8)	0.67659 (6)	0.12282 (6)	0.0210 (2)
Sr10	0.38921 (8)	0.50987 (5)	0.13384 (6)	0.0200 (2)
Sr11	0.71972 (8)	0.34256 (5)	0.15101 (6)	0.0197 (2)
Sr12	0.05373 (8)	0.17209 (5)	0.15907 (6)	0.0195 (2)
O1	0.5581 (6)	0.9116 (4)	0.6442 (5)	0.0310 (19)
O2	0.8883 (5)	0.7460 (4)	0.6484 (4)	0.0233 (18)
O3	0.2175 (5)	0.5739 (4)	0.6596 (4)	0.0266 (18)
O4	0.5506 (6)	0.4317 (4)	0.6725 (4)	0.0283 (19)
O5	0.8863 (6)	0.2686 (4)	0.6840 (4)	0.0273 (18)
O6	0.2079 (6)	0.1227 (5)	0.6777 (5)	0.044 (2)
O7	0.5487 (6)	0.1842 (4)	0.8312 (5)	0.039 (2)
O8	0.8972 (6)	0.0181 (4)	0.8283 (4)	0.0244 (18)
O9	0.2075 (5)	0.8379 (4)	0.8451 (4)	0.0200 (17)
O10	0.5555 (6)	0.6722 (4)	0.8354 (5)	0.038 (2)
O11	0.8780 (6)	0.5053 (4)	0.8305 (4)	0.0284 (19)
O12	0.2140 (6)	0.3378 (4)	0.8372 (4)	0.033 (2)
O13	0.3640 (6)	0.9772 (4)	0.8592 (5)	0.033 (2)
O14	0.6912 (6)	0.8194 (4)	0.8830 (6)	0.050 (3)
O15	0.6794 (6)	0.3142 (4)	0.9254 (5)	0.042 (2)
O16	0.0047 (5)	0.1471 (4)	0.9471 (4)	0.0223 (17)
O17	0.0242 (14)	0.6417 (10)	0.8702 (11)	0.027 (3)*	0.5
O18	0.3560 (13)	0.4746 (9)	0.8905 (10)	0.017 (3)*	0.5
O19	0.0179 (14)	0.6484 (10)	0.9076 (11)	0.027 (4)*	0.5
O20	0.3481 (14)	0.4793 (10)	0.9267 (10)	0.024 (3)*	0.5
O21	0.6921 (6)	0.5570 (4)	0.5724 (5)	0.039 (2)
O22	0.0258 (5)	0.3911 (3)	0.5769 (4)	0.0255 (18)
O23	0.3692 (5)	0.2274 (4)	0.5711 (4)	0.0274 (18)
O24	0.6843 (6)	0.0673 (4)	0.6140 (5)	0.034 (2)
O25	0.0218 (6)	0.9003 (4)	0.6167 (5)	0.033 (2)
O26	0.3476 (6)	0.7279 (4)	0.6336 (5)	0.037 (2)
O27	0.7022 (6)	0.9434 (4)	0.4807 (4)	0.037 (2)
O28	0.0499 (6)	0.7702 (4)	0.4961 (4)	0.040 (2)
O29	0.3570 (7)	0.6122 (4)	0.4948 (5)	0.050 (2)
O30	0.4843 (7)	0.2314 (6)	0.0032 (5)	0.088 (4)
O31	0.7923 (6)	0.0515 (4)	0.9979 (4)	0.0329 (19)
O32	0.8428 (13)	0.5561 (10)	0.0030 (11)	0.045 (4)*	0.5
O33	0.1556 (13)	0.3912 (9)	0.0057 (10)	0.036 (3)*	0.5
B1	0.6430 (9)	0.9751 (7)	0.5839 (8)	0.023 (3)
B2	0.9808 (9)	0.8046 (7)	0.5889 (7)	0.016 (3)
B3	0.3034 (9)	0.6363 (6)	0.5995 (7)	0.015 (3)
B4	0.6285 (10)	0.4676 (7)	0.5849 (7)	0.021 (3)
B5	0.9570 (9)	0.3032 (6)	0.5922 (7)	0.017 (3)
B6	0.2945 (10)	0.1412 (6)	0.5899 (7)	0.018 (3)
B7	0.2588 (9)	0.9162 (7)	0.9012 (8)	0.019 (3)
B8	0.5902 (9)	0.7493 (6)	0.9022 (7)	0.015 (3)
B9	0.9167 (9)	0.5767 (7)	0.9018 (7)	0.018 (3)
B10	0.2447 (9)	0.4102 (6)	0.9114 (7)	0.018 (3)
B11	0.5785 (10)	0.2440 (7)	0.9194 (7)	0.018 (3)
B12	0.9062 (9)	0.0735 (6)	0.9230 (7)	0.016 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sr1	0.0176 (4)	0.0190 (4)	0.0260 (4)	0.0004 (3)	0.0014 (3)	0.0043 (3)
Sr2	0.0190 (4)	0.0143 (4)	0.0255 (4)	0.0015 (3)	0.0031 (3)	0.0014 (3)
Sr3	0.0195 (4)	0.0142 (4)	0.0464 (5)	0.0021 (3)	0.0031 (4)	0.0038 (3)
Sr4	0.0196 (4)	0.0202 (4)	0.0308 (4)	0.0029 (3)	0.0034 (3)	0.0002 (3)
Sr5	0.0175 (4)	0.0173 (4)	0.0311 (4)	0.0031 (3)	0.0035 (3)	0.0003 (3)
Sr6	0.0201 (4)	0.0211 (4)	0.0324 (4)	0.0025 (3)	0.0055 (3)	0.0062 (3)
Sr7	0.0174 (4)	0.0164 (4)	0.0290 (4)	0.0001 (3)	−0.0003 (3)	−0.0042 (3)
Sr8	0.0211 (4)	0.0186 (4)	0.0232 (4)	0.0023 (3)	0.0010 (3)	−0.0046 (3)
Sr9	0.0219 (4)	0.0190 (4)	0.0222 (4)	0.0025 (3)	−0.0023 (3)	−0.0018 (3)
Sr10	0.0199 (4)	0.0169 (4)	0.0235 (4)	0.0039 (3)	−0.0005 (3)	−0.0028 (3)
Sr11	0.0210 (4)	0.0165 (4)	0.0216 (4)	0.0017 (3)	−0.0011 (3)	−0.0032 (3)
Sr12	0.0181 (4)	0.0190 (4)	0.0214 (4)	0.0020 (3)	−0.0002 (3)	−0.0018 (3)
O1	0.031 (3)	0.025 (3)	0.037 (3)	0.002 (3)	0.005 (3)	−0.001 (3)
O2	0.021 (3)	0.026 (3)	0.023 (3)	−0.001 (3)	0.004 (2)	−0.005 (2)
O3	0.026 (3)	0.025 (3)	0.029 (3)	0.001 (3)	0.005 (3)	0.007 (2)
O4	0.024 (3)	0.042 (4)	0.019 (3)	0.003 (3)	−0.001 (2)	0.000 (3)
O5	0.031 (3)	0.036 (3)	0.015 (3)	−0.002 (3)	0.006 (2)	−0.007 (2)
O6	0.031 (4)	0.072 (5)	0.029 (3)	−0.015 (3)	0.011 (3)	−0.007 (3)
O7	0.057 (4)	0.023 (3)	0.035 (4)	−0.001 (3)	−0.014 (3)	−0.012 (3)
O8	0.033 (3)	0.024 (3)	0.017 (3)	−0.003 (3)	0.007 (2)	−0.002 (2)
O9	0.023 (3)	0.014 (3)	0.023 (3)	0.001 (2)	0.001 (2)	−0.003 (2)
O10	0.050 (4)	0.027 (3)	0.036 (4)	−0.006 (3)	−0.012 (3)	−0.007 (3)
O11	0.032 (3)	0.013 (3)	0.040 (4)	−0.002 (3)	−0.011 (3)	−0.009 (3)
O12	0.041 (4)	0.027 (3)	0.032 (3)	0.005 (3)	−0.004 (3)	−0.009 (3)
O13	0.020 (3)	0.022 (3)	0.056 (4)	−0.005 (3)	0.004 (3)	−0.003 (3)
O14	0.027 (4)	0.015 (3)	0.107 (6)	−0.006 (3)	−0.002 (4)	0.006 (3)
O15	0.033 (4)	0.014 (3)	0.077 (5)	−0.005 (3)	−0.005 (3)	0.006 (3)
O16	0.020 (3)	0.019 (3)	0.028 (3)	−0.005 (2)	−0.003 (2)	−0.005 (2)
O21	0.035 (4)	0.028 (3)	0.052 (4)	−0.004 (3)	−0.001 (3)	0.005 (3)
O22	0.027 (3)	0.011 (3)	0.039 (3)	−0.003 (2)	0.009 (3)	−0.002 (2)
O23	0.023 (3)	0.025 (3)	0.034 (3)	−0.006 (3)	0.000 (2)	0.000 (2)
O24	0.030 (3)	0.011 (3)	0.061 (4)	−0.005 (3)	0.006 (3)	−0.013 (3)
O25	0.033 (4)	0.021 (3)	0.047 (4)	0.003 (3)	0.000 (3)	−0.009 (3)
O26	0.032 (4)	0.014 (3)	0.066 (4)	−0.009 (3)	0.000 (3)	−0.010 (3)
O27	0.057 (4)	0.024 (3)	0.031 (3)	−0.007 (3)	0.019 (3)	−0.005 (3)
O28	0.052 (4)	0.039 (4)	0.029 (3)	−0.009 (3)	0.020 (3)	−0.010 (3)
O29	0.080 (5)	0.037 (4)	0.034 (4)	0.004 (4)	0.018 (3)	−0.014 (3)
O30	0.073 (6)	0.146 (8)	0.048 (5)	0.026 (6)	0.037 (4)	−0.008 (5)
O31	0.035 (4)	0.038 (3)	0.025 (3)	−0.016 (3)	0.006 (3)	−0.013 (3)
B1	0.014 (5)	0.026 (5)	0.030 (5)	0.006 (4)	−0.005 (4)	−0.003 (4)
B2	0.021 (5)	0.017 (5)	0.010 (4)	0.006 (4)	0.000 (4)	0.000 (3)
B3	0.014 (5)	0.013 (4)	0.018 (4)	−0.001 (4)	−0.002 (4)	0.001 (3)
B4	0.023 (5)	0.024 (5)	0.016 (5)	0.005 (4)	−0.003 (4)	−0.002 (4)
B5	0.021 (5)	0.011 (4)	0.019 (4)	0.006 (4)	−0.004 (4)	−0.002 (4)
B6	0.027 (5)	0.012 (4)	0.016 (4)	0.007 (4)	0.000 (4)	−0.008 (4)
B7	0.012 (5)	0.017 (5)	0.028 (5)	−0.004 (4)	0.006 (4)	−0.005 (4)
B8	0.009 (4)	0.019 (5)	0.017 (4)	0.003 (4)	−0.008 (3)	−0.003 (4)
B9	0.018 (5)	0.019 (5)	0.018 (4)	−0.007 (4)	−0.001 (4)	−0.002 (4)
B10	0.020 (5)	0.013 (4)	0.022 (5)	0.005 (4)	0.007 (4)	0.000 (4)
B11	0.023 (5)	0.023 (5)	0.010 (4)	0.006 (4)	0.004 (4)	0.001 (4)
B12	0.021 (5)	0.006 (4)	0.022 (5)	0.002 (4)	−0.006 (4)	−0.002 (3)

Geometric parameters (Å, º)

O27—B1	1.437 (11)	O30—B11^iii	1.360 (11)
O27—B6^i	1.416 (10)	O31—B7^iv	1.384 (10)
O28—B2^ii	1.388 (10)	O31—B12	1.438 (10)
O28—B5^i	1.445 (10)	O32—B9^iii	1.425 (15)
O29—B3	1.401 (10)	O32—B10^i	1.415 (16)
O29—B4^i	1.446 (11)	O33—B9^i	1.390 (15)
O30—B8^i	1.375 (11)	O33—B10^iii	1.435 (15)
B1—O27—B6^i	141.1 (7)	B7^iv—O31—B12	139.7 (6)
B2^ii—O28—B5^i	144.0 (7)	B9^iii—O32—B10^i	149.2 (11)
B3—O29—B4^i	144.5 (7)	B9^i—O33—B10^iii	151.6 (11)
B8^i—O30—B11^iii	159.9 (8)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x−1, y, z; (iii) x, y, z−1; (iv) −x+1, −y+1, −z+2.

(Iv)

Crystal data

B2O5Sr2	V = 248.32 (8) Å^3
Mr = 276.9	Z = 2
Triclinic, P1(αβγ)0†	F(000) = 252
q = -0.166667a* + 0.333333b*	Dx = 3.703 Mg m^−3
a = 3.9001 (11) Å	Mo Kα radiation, λ = 0.71073 Å
b = 5.3685 (7) Å	Cell parameters from 2199 reflections
c = 11.8671 (16) Å	θ = 4.2–27.6°
α = 89.994 (11)°	µ = 21.55 mm^−1
β = 92.008 (11)°	T = 583 K
γ = 90.038 (11)°	0.27 × 0.14 × 0.11 mm

† Symmetry operations: (1) x₁, x₂, x₃, x₄; (2) −x₁, −x₂, −x₃, −x₄.

Data collection

Xcalibur, AtlasS2, Gemini ultra diffractometer	11221 independent reflections
Radiation source: X-ray tube	4809 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.062
Detector resolution: 5.1783 pixels mm^-1	θmax = 28.0°, θmin = 3.4°
ω scans	h = −5→5
Absorption correction: analytical CrysAlisPro 1.171.38.41 (Rigaku Oxford Diffraction, 2015) Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by R.C. Clark & J.S. Reid. (Clark, R. C. & Reid, J. S. (1995). Acta Cryst. A51, 887-897) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	k = −7→7
Tmin = 0.037, Tmax = 0.186	l = −15→15
42872 measured reflections

Refinement

Refinement on F	0 constraints
R[F^2 > 2σ(F^2)] = 0.041	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
wR(F^2) = 0.060	(Δ/σ)max = 0.014
S = 1.15	Δρmax = 1.15 e Å^−3
11221 reflections	Δρmin = −1.12 e Å^−3
366 parameters	Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
0 restraints	Extinction coefficient: 790 (30)

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sr1	1.22906 (9)	0.90884 (7)	0.35769 (3)	0.02280 (11)
Sr2	0.76227 (9)	0.40663 (6)	0.14340 (3)	0.02036 (11)
O1a	1.2515 (6)	0.4030 (5)	0.66439 (19)	0.0289 (8)
O1b	0.7483 (7)	0.8992 (6)	0.8355 (2)	0.0308 (9)
O2a	0.7471 (14)	0.3294 (9)	0.8807 (5)	0.050 (2)	0.3333
O2a'	0.7177 (12)	0.2994 (8)	0.9445 (4)	0.0263 (14)	0.3333
O2a''	0.766 (3)	0.306 (2)	0.8874 (8)	0.022 (2)*	0.1667
O2a'''	0.740 (3)	0.308 (2)	0.9229 (9)	0.024 (2)*	0.1667
O2b	1.2759 (9)	0.8149 (6)	0.5728 (3)	0.0293 (11)	0.5
O2b'	1.2372 (9)	0.8119 (6)	0.6238 (3)	0.0345 (12)	0.5
O3a	0.5130 (9)	0.5857 (7)	0.4911 (3)	0.0405 (13)	0.5
O3b	0.4959 (13)	−0.0735 (10)	0.0013 (4)	0.067 (2)	0.3333
O3b'	0.549 (3)	−0.0540 (16)	0.0042 (9)	0.045 (2)*	0.1667
B1	1.3265 (10)	0.5775 (8)	0.5898 (3)	0.0178 (12)
B2	0.6755 (10)	0.0717 (8)	0.9097 (3)	0.0172 (11)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sr1	0.01688 (19)	0.01957 (19)	0.03197 (19)	0.00114 (14)	0.00123 (13)	0.00408 (15)
Sr2	0.01757 (19)	0.01963 (19)	0.02392 (17)	0.00163 (14)	0.00149 (13)	−0.00292 (13)
O1a	0.0305 (15)	0.0308 (14)	0.0256 (13)	−0.0048 (12)	0.0049 (11)	0.0011 (11)
O1b	0.0358 (17)	0.0261 (15)	0.0305 (15)	0.0075 (13)	0.0002 (12)	−0.0092 (12)
O2a	0.031 (4)	0.019 (3)	0.100 (5)	0.000 (2)	−0.006 (3)	0.008 (3)
O2a'	0.028 (2)	0.016 (2)	0.035 (3)	0.0011 (16)	−0.0035 (19)	−0.0026 (18)
O2b	0.030 (2)	0.0173 (17)	0.041 (2)	0.0013 (14)	0.0022 (15)	0.0017 (15)
O2b'	0.030 (2)	0.0172 (17)	0.057 (2)	0.0056 (14)	0.0075 (17)	−0.0078 (16)
O3a	0.055 (3)	0.0363 (19)	0.0315 (19)	0.0130 (17)	0.0214 (18)	0.0036 (15)
O3b	0.067 (5)	0.095 (5)	0.039 (3)	−0.021 (4)	0.027 (3)	0.005 (3)
B1	0.014 (2)	0.021 (2)	0.0182 (18)	0.0031 (17)	−0.0006 (14)	−0.0029 (17)
B2	0.017 (2)	0.017 (2)	0.0182 (17)	0.0011 (16)	0.0017 (14)	−0.0010 (16)

Geometric parameters (Å, º)

	Average	Minimum	Maximum
B1—O1a	1.361 (14)	1.354 (14)	1.371 (14)
B1—O2b	1.337 (14)	1.318 (15)	1.362 (15)
B1—O2b'	1.340 (15)	1.318 (15)	1.363 (15)
B1—O3a^i	1.405 (15)	1.391 (16)	1.427 (16)
B1—O3a^ii	1.437 (15)	1.412 (16)	1.450 (16)
B2—O1b^iii	1.33 (7)	1.31 (8)	1.35 (8)
B2—O2a	1.35 (7)	1.33 (8)	1.38 (8)
B2—O2a'	1.34 (7)	1.34 (7)	1.35 (7)
B2—O2a''	1.38 (8)	1.35 (8)	1.40 (8)
B2—O2a'''	1.33 (8)	1.32 (8)	1.33 (8)
B2—O3b^iv	1.40 (7)	1.35 (8)	1.45 (8)
B2—O3b^v	1.38 (7)	1.37 (8)	1.39 (8)
B2—O3b'^iv	1.43 (8)	1.39 (8)	1.47 (8)
B2—O3b'^v	1.40 (8)	1.36 (8)	1.44 (8)
O1a—B1—O2b	127.5 (10)	124.8 (10)	129.7 (10)
O1a—B1—O2b'	124.5 (10)	123.9 (10)	125.3 (10)
O1a—B1—O3a^i	122.0 (10)	120.2 (10)	123.3 (10)
O1a—B1—O3a^ii	110.5 (9)	109.7 (9)	111.8 (9)
O2b—B1—O3a^ii	122.0 (10)	120.6 (10)	123.4 (10)
O2b'—B1—O3a^i	113.4 (10)	112.7 (9)	114.4 (10)
O1b^iii—B2—O2a	124 (6)	122 (6)	127 (5)
O1b^iii—B2—O2a'	126 (6)	125 (5)	128 (6)
O1b^iii—B2—O2a''	118 (6)	116 (5)	120 (6)
O1b^iii—B2—O2a'''	136 (6)	135 (6)	138 (6)
O1b^iii—B2—O3b^iv	113 (5)	111 (5)	114 (5)
O1b^iii—B2—O3b^v	123 (5)	121 (5)	126 (6)
O1b^iii—B2—O3b'^iv	106 (5)	106 (5)	107 (5)
O1b^iii—B2—O3b'^v	127 (6)	127 (6)	128 (6)
O2a—B2—O3b^v	112 (5)	112 (5)	113 (5)
O2a'—B2—O3b^iv	121 (5)	121 (5)	121 (5)
O2a''—B2—O2a'''	18.9 (14)	18.2 (14)	19.6 (14)
O2a''—B2—O3b'^iv	135 (6)	133 (6)	137 (6)
O2a''—B2—O3b'^v	113 (5)	111 (5)	114 (5)
O2a'''—B2—O3b'^iv	116 (5)	115 (5)	117 (5)
O2a'''—B2—O3b'^v	96 (5)	95 (5)	97 (5)
O3b'^iv—B2—O3b'^v	28.6 (16)	27.8 (15)	29.5 (17)

Symmetry codes: (i) x₁+1, x₂, x₃, x₄; (ii) −x₁+2, −x₂+1, −x₃+1, −x₄; (iii) x₁, x₂−1, x₃, x₄; (iv) x₁, x₂, x₃+1, x₄; (v) −x₁+1, −x₂, −x₃+1, −x₄.

(v)

Crystal data

B2O5Sr2	Z = 2
Mr = 276.9	F(000) = 252
Monoclinic, P21/c	Dx = 3.688 Mg m^−3
Hall symbol: -P 2ycb	Mo Kα radiation, λ = 0.71073 Å
a = 3.9125 Å	Cell parameters from 939 reflections
b = 5.3699 Å	θ = 4.2–27.2°
c = 11.8732 Å	µ = 21.61 mm^−1
β = 91.849°	T = 668 K
V = 249.32 Å^3	0.22 × 0.08 × 0.01 mm

Data collection

Xcalibur, AtlasS2, Gemini ultra diffractometer	572 independent reflections
Radiation source: X-ray tube	463 reflections with I > 3σ(I)
Graphite monochromator	Rint = 0.048
Detector resolution: 5.1783 pixels mm^-1	θmax = 28.2°, θmin = 3.4°
ω scans	h = −5→4
Absorption correction: analytical CrysAlisPro 1.171.38.41q (Rigaku Oxford Diffraction, 2015) Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by R.C. Clark & J.S. Reid. (Clark, R. C. & Reid, J. S. (1995). Acta Cryst. A51, 887-897) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	k = −7→7
Tmin = 0.103, Tmax = 0.773	l = −15→15
2432 measured reflections

Refinement

Refinement on F	0 constraints
R[F^2 > 2σ(F^2)] = 0.030	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
wR(F^2) = 0.036	(Δ/σ)max = 0.004
S = 1.25	Δρmax = 0.59 e Å^−3
572 reflections	Δρmin = −0.51 e Å^−3
56 parameters	Extinction correction: B-C type 1 Gaussian isotropic (Becker & Coppens, 1974)
0 restraints	Extinction coefficient: 50 (50)

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sr	1.23349 (13)	0.90193 (10)	0.35875 (5)	0.0300 (2)
O1	1.2538 (11)	0.4053 (8)	0.6668 (4)	0.0435 (16)
O2	0.763 (7)	0.325 (5)	0.8816 (15)	0.044 (6)	0.5
O2'	0.731 (6)	0.312 (5)	0.9255 (13)	0.030 (5)	0.5
O3	0.527 (5)	0.5691 (16)	0.4976 (13)	0.058 (4)	0.5
B	1.3272 (17)	0.5774 (12)	0.5902 (6)	0.024 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sr	0.0193 (4)	0.0256 (4)	0.0449 (5)	−0.0020 (2)	0.0004 (3)	0.0076 (3)
O1	0.044 (3)	0.040 (3)	0.046 (3)	−0.015 (2)	0.001 (2)	0.014 (2)
O2	0.033 (7)	0.015 (5)	0.084 (16)	0.001 (4)	0.015 (12)	0.015 (11)
O2'	0.024 (8)	0.022 (6)	0.043 (9)	0.000 (5)	−0.002 (7)	0.010 (7)
O3	0.090 (9)	0.048 (8)	0.039 (5)	−0.008 (9)	0.044 (5)	−0.003 (8)
B	0.019 (3)	0.025 (3)	0.027 (4)	0.003 (3)	0.002 (3)	0.002 (3)

Bond lengths (Å)

Sr—O1^i	2.532 (4)	Sr—O2^v	2.54 (3)
Sr—O1^ii	2.623 (4)	Sr—O2'^iv	2.605 (16)
Sr—O1^iii	2.506 (5)	Sr—O2'^iii	2.64 (2)
Sr—O2^iv	3.110 (18)	Sr—O2'^v	2.58 (2)
Sr—O2^i	3.104 (19)	Sr—O3^vi	2.666 (14)
Sr—O2^iii	2.38 (3)	Sr—O3^i	3.175 (12)

Symmetry codes: (i) −x+2, −y+1, −z+1; (ii) −x+3, −y+1, −z+1; (iii) x, −y+3/2, z−1/2; (iv) −x+2, y+1/2, −z+3/2; (v) x+1, −y+3/2, z−1/2; (vi) x+1, y, z.