Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807037099/mg2030sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536807037099/mg2030Isup2.hkl |
A mixture of 0.3 mol SrCO_{3}, 0.6 mol MgO, 0.6 mol, H_{3}BO_{3}, 0.1 mol SrF_{2}, and 0.7 mol LiF was heated until molten. A Pt thread was dipped into the melt, and the temperature was decreased from 1173 K to 1123 K at 5 K/day, during which time crystals grew on the Pt thread. Upon cooling to room temperature at 20 K/h, block-shaped colourless crystals with dimensions up to 25×15×13 mm^{3} were obtained. The crystal used for the data collection was a fragment of the larger crystal.
Sr_{2}Mg(BO_{3})_{2} has been examined as a luminescent host material (Verstegen, 1974; Diaz & Keszler, 1997). Although Diaz & Keszler (1997) alluded to its structure determination and provided cell parameters (a = 9.035 Å, b = 5.146 Å, c = 6.099 Å, β = 118.59°), a full structure report had not appeared to date, to our knowledge. The structure determined here confirms that it is isostructural to Ba_{2}Mg(BO_{3})_{2}, which has been previously described in detail (Akella & Keszler, 1995). Briefly, MgO_{6} octahedra and BO_{3} triangles are connected to form calcite-like layers which are alternately stacked with double layers of Sr atoms (Fig. 1). Each Sr atom is nine-coordinate, in a distorted tricapped trigonal prismatic geometry.
For related literature, see: Akella & Keszler (1995); Diaz & Keszler (1997); Verstegen (1974).
Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: CrystalStructure (Rigaku/MSC, 2004).
Fig. 1. Sr_{2}Mg(BO_{3})_{2} viewed down the [010] direction. Displacement ellipsoids are drawn at the 80% probability level. |
Sr_{2}Mg(BO_{3})_{2} | F(000) = 292 |
M_{r} = 317.17 | D_{x} = 4.217 Mg m^{−}^{3} |
Monoclinic, C2/m | Mo Kα radiation, λ = 0.71070 Å |
Hall symbol: -C 2y | Cell parameters from 345 reflections |
a = 9.046 (4) Å | θ = 3.8–29.8° |
b = 5.1579 (18) Å | µ = 21.44 mm^{−}^{1} |
c = 6.103 (3) Å | T = 113 K |
β = 118.691 (12)° | Prism, colourless |
V = 249.81 (19) Å^{3} | 0.34 × 0.22 × 0.20 mm |
Z = 2 |
Rigaku Saturn diffractometer | 329 independent reflections |
Radiation source: rotating anode | 239 reflections with I > 2σ(I) |
Confocal monochromator | R_{int} = 0.124 |
Detector resolution: 7.31 pixels mm^{-1} | θ_{max} = 27.9°, θ_{min} = 3.8° |
ω scans | h = −11→11 |
Absorption correction: numerical (NUMABS; Rigaku, 2005) | k = −6→6 |
T_{min} = 0.052, T_{max} = 0.100 | l = −8→8 |
1180 measured reflections |
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})] = 0.065 | w = 1/[σ^{2}(F_{o}^{2}) + (0.0588P)^{2}] where P = (F_{o}^{2} + 2F_{c}^{2})/3 |
wR(F^{2}) = 0.153 | (Δ/σ)_{max} < 0.001 |
S = 1.14 | Δρ_{max} = 1.93 e Å^{−}^{3} |
329 reflections | Δρ_{min} = −2.76 e Å^{−}^{3} |
34 parameters | Extinction correction: SHELXL97, Fc^{*}=kFc[1+0.001xFc^{2}λ^{3}/sin(2θ)]^{-1/4} |
6 restraints | Extinction coefficient: 0.015 (3) |
Sr_{2}Mg(BO_{3})_{2} | V = 249.81 (19) Å^{3} |
M_{r} = 317.17 | Z = 2 |
Monoclinic, C2/m | Mo Kα radiation |
a = 9.046 (4) Å | µ = 21.44 mm^{−}^{1} |
b = 5.1579 (18) Å | T = 113 K |
c = 6.103 (3) Å | 0.34 × 0.22 × 0.20 mm |
β = 118.691 (12)° |
Rigaku Saturn diffractometer | 329 independent reflections |
Absorption correction: numerical (NUMABS; Rigaku, 2005) | 239 reflections with I > 2σ(I) |
T_{min} = 0.052, T_{max} = 0.100 | R_{int} = 0.124 |
1180 measured reflections |
R[F^{2} > 2σ(F^{2})] = 0.065 | 34 parameters |
wR(F^{2}) = 0.153 | 6 restraints |
S = 1.14 | Δρ_{max} = 1.93 e Å^{−}^{3} |
329 reflections | Δρ_{min} = −2.76 e Å^{−}^{3} |
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 F^{2} against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F^{2}, conventional R-factors R are based on F, with F set to zero for negative F^{2}. The threshold expression of F^{2} > σ(F^{2}) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F^{2} are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | U_{iso}*/U_{eq} | ||
Sr1 | 0.2895 (2) | 0.0000 | 0.8170 (3) | 0.0101 (9) | |
Mg1 | 0.5000 | 0.0000 | 0.5000 | 0.0100 (19) | |
O1 | −0.0227 (11) | −0.2346 (16) | 0.2319 (14) | 0.013 (2) | |
O2 | 0.2305 (15) | 0.0000 | 0.334 (2) | 0.014 (3) | |
B1 | 0.065 (3) | 0.0000 | 0.262 (4) | 0.015 (5) |
U^{11} | U^{22} | U^{33} | U^{12} | U^{13} | U^{23} | |
Sr1 | 0.0114 (11) | 0.0111 (13) | 0.0122 (11) | 0.000 | 0.0092 (8) | 0.000 |
Mg1 | 0.008 (5) | 0.013 (5) | 0.014 (4) | 0.000 | 0.009 (4) | 0.000 |
O1 | 0.017 (5) | 0.016 (5) | 0.016 (4) | 0.004 (4) | 0.015 (4) | 0.001 (4) |
O2 | 0.012 (7) | 0.009 (8) | 0.025 (7) | 0.000 | 0.012 (6) | 0.000 |
B1 | 0.015 (13) | 0.018 (14) | 0.014 (11) | 0.000 | 0.009 (10) | 0.000 |
Sr1—O1^{i} | 2.585 (8) | Mg1—Sr1^{x} | 3.302 (2) |
Sr1—O1^{ii} | 2.585 (8) | Mg1—Sr1^{viii} | 3.5196 (16) |
Sr1—O1^{iii} | 2.649 (8) | Mg1—Sr1^{xi} | 3.5197 (16) |
Sr1—O1^{iv} | 2.649 (8) | Mg1—Sr1^{vii} | 3.5197 (16) |
Sr1—O1^{v} | 2.654 (9) | Mg1—Sr1^{iv} | 3.5197 (16) |
Sr1—O1^{vi} | 2.654 (8) | O1—B1 | 1.411 (14) |
Sr1—O2^{vii} | 2.716 (4) | O1—Mg1^{xii} | 2.067 (8) |
Sr1—O2^{iv} | 2.716 (4) | O1—Sr1^{i} | 2.585 (8) |
Sr1—O2 | 2.730 (13) | O1—Sr1^{iv} | 2.649 (8) |
Sr1—B1 | 3.00 (2) | O1—Sr1^{xiii} | 2.654 (8) |
Sr1—B1^{i} | 3.01 (2) | O2—B1 | 1.34 (2) |
Sr1—B1^{vii} | 3.036 (12) | O2—Sr1^{vii} | 2.716 (4) |
Mg1—O1^{iii} | 2.067 (8) | O2—Sr1^{iv} | 2.716 (4) |
Mg1—O1^{viii} | 2.067 (8) | B1—O1^{xiv} | 1.411 (14) |
Mg1—O1^{iv} | 2.067 (8) | B1—Sr1^{i} | 3.01 (2) |
Mg1—O1^{ix} | 2.067 (8) | B1—Sr1^{vii} | 3.036 (12) |
Mg1—O2^{x} | 2.145 (12) | B1—Sr1^{iv} | 3.036 (12) |
Mg1—O2 | 2.145 (12) | ||
O1^{i}—Sr1—O1^{ii} | 55.8 (4) | O1^{iii}—Mg1—Sr1 | 53.3 (2) |
O1^{i}—Sr1—O1^{iii} | 119.65 (7) | O1^{viii}—Mg1—Sr1 | 126.7 (2) |
O1^{ii}—Sr1—O1^{iii} | 168.1 (3) | O1^{iv}—Mg1—Sr1 | 53.3 (2) |
O1^{i}—Sr1—O1^{iv} | 168.1 (3) | O1^{ix}—Mg1—Sr1 | 126.7 (2) |
O1^{ii}—Sr1—O1^{iv} | 119.65 (7) | O2^{x}—Mg1—Sr1 | 124.6 (4) |
O1^{iii}—Sr1—O1^{iv} | 62.2 (4) | O2—Mg1—Sr1 | 55.4 (4) |
O1^{i}—Sr1—O1^{v} | 90.2 (3) | Sr1^{x}—Mg1—Sr1 | 180.0 |
O1^{ii}—Sr1—O1^{v} | 119.07 (18) | O1^{iii}—Mg1—Sr1^{viii} | 46.7 (2) |
O1^{iii}—Sr1—O1^{v} | 70.2 (3) | O1^{viii}—Mg1—Sr1^{viii} | 73.4 (2) |
O1^{iv}—Sr1—O1^{v} | 101.2 (2) | O1^{iv}—Mg1—Sr1^{viii} | 106.6 (2) |
O1^{i}—Sr1—O1^{vi} | 119.07 (18) | O1^{ix}—Mg1—Sr1^{viii} | 133.3 (2) |
O1^{ii}—Sr1—O1^{vi} | 90.2 (3) | O2^{x}—Mg1—Sr1^{viii} | 50.46 (11) |
O1^{iii}—Sr1—O1^{vi} | 101.2 (2) | O2—Mg1—Sr1^{viii} | 129.54 (11) |
O1^{iv}—Sr1—O1^{vi} | 70.2 (3) | Sr1^{x}—Mg1—Sr1^{viii} | 80.56 (5) |
O1^{v}—Sr1—O1^{vi} | 62.1 (4) | Sr1—Mg1—Sr1^{viii} | 99.44 (5) |
O1^{i}—Sr1—O2^{vii} | 67.1 (3) | O1^{iii}—Mg1—Sr1^{xi} | 106.6 (2) |
O1^{ii}—Sr1—O2^{vii} | 119.9 (3) | O1^{viii}—Mg1—Sr1^{xi} | 133.3 (2) |
O1^{iii}—Sr1—O2^{vii} | 53.0 (3) | O1^{iv}—Mg1—Sr1^{xi} | 46.7 (2) |
O1^{iv}—Sr1—O2^{vii} | 112.3 (3) | O1^{ix}—Mg1—Sr1^{xi} | 73.4 (2) |
O1^{v}—Sr1—O2^{vii} | 75.1 (3) | O2^{x}—Mg1—Sr1^{xi} | 50.46 (11) |
O1^{vi}—Sr1—O2^{vii} | 136.2 (3) | O2—Mg1—Sr1^{xi} | 129.54 (11) |
O1^{i}—Sr1—O2^{iv} | 119.9 (3) | Sr1^{x}—Mg1—Sr1^{xi} | 80.56 (5) |
O1^{ii}—Sr1—O2^{iv} | 67.1 (3) | Sr1—Mg1—Sr1^{xi} | 99.44 (5) |
O1^{iii}—Sr1—O2^{iv} | 112.3 (3) | Sr1^{viii}—Mg1—Sr1^{xi} | 94.23 (5) |
O1^{iv}—Sr1—O2^{iv} | 53.0 (3) | O1^{iii}—Mg1—Sr1^{vii} | 73.4 (2) |
O1^{v}—Sr1—O2^{iv} | 136.2 (3) | O1^{viii}—Mg1—Sr1^{vii} | 46.7 (2) |
O1^{vi}—Sr1—O2^{iv} | 75.1 (3) | O1^{iv}—Mg1—Sr1^{vii} | 133.3 (2) |
O2^{vii}—Sr1—O2^{iv} | 143.5 (5) | O1^{ix}—Mg1—Sr1^{vii} | 106.6 (2) |
O1^{i}—Sr1—O2 | 100.8 (3) | O2^{x}—Mg1—Sr1^{vii} | 129.55 (11) |
O1^{ii}—Sr1—O2 | 100.8 (3) | O2—Mg1—Sr1^{vii} | 50.46 (11) |
O1^{iii}—Sr1—O2 | 68.4 (3) | Sr1^{x}—Mg1—Sr1^{vii} | 99.44 (5) |
O1^{iv}—Sr1—O2 | 68.4 (3) | Sr1—Mg1—Sr1^{vii} | 80.56 (5) |
O1^{v}—Sr1—O2 | 137.2 (3) | Sr1^{viii}—Mg1—Sr1^{vii} | 85.77 (5) |
O1^{vi}—Sr1—O2 | 137.2 (3) | Sr1^{xi}—Mg1—Sr1^{vii} | 180.0 |
O2^{vii}—Sr1—O2 | 71.7 (3) | O1^{iii}—Mg1—Sr1^{iv} | 133.3 (2) |
O2^{iv}—Sr1—O2 | 71.7 (3) | O1^{viii}—Mg1—Sr1^{iv} | 106.6 (2) |
O1^{i}—Sr1—B1 | 77.4 (4) | O1^{iv}—Mg1—Sr1^{iv} | 73.4 (2) |
O1^{ii}—Sr1—B1 | 77.4 (4) | O1^{ix}—Mg1—Sr1^{iv} | 46.7 (2) |
O1^{iii}—Sr1—B1 | 90.9 (4) | O2^{x}—Mg1—Sr1^{iv} | 129.54 (11) |
O1^{iv}—Sr1—B1 | 90.9 (4) | O2—Mg1—Sr1^{iv} | 50.46 (11) |
O1^{v}—Sr1—B1 | 148.65 (19) | Sr1^{x}—Mg1—Sr1^{iv} | 99.44 (5) |
O1^{vi}—Sr1—B1 | 148.65 (19) | Sr1—Mg1—Sr1^{iv} | 80.56 (5) |
O2^{vii}—Sr1—B1 | 73.6 (3) | Sr1^{viii}—Mg1—Sr1^{iv} | 180.0 |
O2^{iv}—Sr1—B1 | 73.6 (3) | Sr1^{xi}—Mg1—Sr1^{iv} | 85.77 (5) |
O2—Sr1—B1 | 26.5 (5) | Sr1^{vii}—Mg1—Sr1^{iv} | 94.23 (5) |
O1^{i}—Sr1—B1^{i} | 27.94 (19) | B1—O1—Mg1^{xii} | 128.9 (10) |
O1^{ii}—Sr1—B1^{i} | 27.94 (19) | B1—O1—Sr1^{i} | 92.9 (9) |
O1^{iii}—Sr1—B1^{i} | 145.9 (2) | Mg1^{xii}—O1—Sr1^{i} | 97.7 (3) |
O1^{iv}—Sr1—B1^{i} | 145.9 (2) | B1—O1—Sr1^{iv} | 91.6 (9) |
O1^{v}—Sr1—B1^{i} | 107.4 (4) | Mg1^{xii}—O1—Sr1^{iv} | 88.0 (3) |
O1^{vi}—Sr1—B1^{i} | 107.4 (4) | Sr1^{i}—O1—Sr1^{iv} | 168.1 (3) |
O2^{vii}—Sr1—B1^{i} | 93.1 (3) | B1—O1—Sr1^{xiii} | 129.1 (10) |
O2^{iv}—Sr1—B1^{i} | 93.1 (3) | Mg1^{xii}—O1—Sr1^{xiii} | 100.9 (3) |
O2—Sr1—B1^{i} | 100.7 (5) | Sr1^{i}—O1—Sr1^{xiii} | 89.8 (3) |
B1—Sr1—B1^{i} | 74.2 (7) | Sr1^{iv}—O1—Sr1^{xiii} | 78.8 (2) |
O1^{i}—Sr1—B1^{vii} | 92.0 (4) | B1—O2—Mg1 | 172.3 (13) |
O1^{ii}—Sr1—B1^{vii} | 146.1 (4) | B1—O2—Sr1^{vii} | 90.4 (4) |
O1^{iii}—Sr1—B1^{vii} | 27.7 (4) | Mg1—O2—Sr1^{vii} | 92.0 (3) |
O1^{iv}—Sr1—B1^{vii} | 89.6 (4) | B1—O2—Sr1^{iv} | 90.4 (4) |
O1^{v}—Sr1—B1^{vii} | 65.6 (4) | Mg1—O2—Sr1^{iv} | 92.0 (3) |
O1^{vi}—Sr1—B1^{vii} | 117.6 (5) | Sr1^{vii}—O2—Sr1^{iv} | 143.5 (5) |
O2^{vii}—Sr1—B1^{vii} | 26.2 (4) | B1—O2—Sr1 | 87.9 (11) |
O2^{iv}—Sr1—B1^{vii} | 135.7 (4) | Mg1—O2—Sr1 | 84.4 (4) |
O2—Sr1—B1^{vii} | 72.7 (4) | Sr1^{vii}—O2—Sr1 | 108.3 (3) |
B1—Sr1—B1^{vii} | 86.0 (5) | Sr1^{iv}—O2—Sr1 | 108.3 (3) |
B1^{i}—Sr1—B1^{vii} | 118.9 (4) | O2—B1—O1^{xiv} | 120.9 (9) |
O1^{iii}—Mg1—O1^{viii} | 97.0 (4) | O2—B1—O1 | 120.9 (9) |
O1^{iii}—Mg1—O1^{iv} | 83.0 (4) | O1^{xiv}—B1—O1 | 118.0 (17) |
O1^{viii}—Mg1—O1^{iv} | 179.998 (1) | O2—B1—Sr1 | 65.6 (10) |
O1^{iii}—Mg1—O1^{ix} | 180.0 | O1^{xiv}—B1—Sr1 | 100.5 (9) |
O1^{viii}—Mg1—O1^{ix} | 83.0 (4) | O1—B1—Sr1 | 100.5 (9) |
O1^{iv}—Mg1—O1^{ix} | 97.0 (4) | O2—B1—Sr1^{i} | 171.4 (14) |
O1^{iii}—Mg1—O2^{x} | 88.2 (4) | O1^{xiv}—B1—Sr1^{i} | 59.1 (9) |
O1^{viii}—Mg1—O2^{x} | 91.8 (4) | O1—B1—Sr1^{i} | 59.1 (9) |
O1^{iv}—Mg1—O2^{x} | 88.2 (4) | Sr1—B1—Sr1^{i} | 105.8 (7) |
O1^{ix}—Mg1—O2^{x} | 91.8 (4) | O2—B1—Sr1^{vii} | 63.4 (5) |
O1^{iii}—Mg1—O2 | 91.8 (4) | O1^{xiv}—B1—Sr1^{vii} | 60.7 (6) |
O1^{viii}—Mg1—O2 | 88.2 (4) | O1—B1—Sr1^{vii} | 165.3 (13) |
O1^{iv}—Mg1—O2 | 91.8 (4) | Sr1—B1—Sr1^{vii} | 94.0 (5) |
O1^{ix}—Mg1—O2 | 88.2 (4) | Sr1^{i}—B1—Sr1^{vii} | 118.9 (4) |
O2^{x}—Mg1—O2 | 180.0 | O2—B1—Sr1^{iv} | 63.4 (5) |
O1^{iii}—Mg1—Sr1^{x} | 126.7 (2) | O1^{xiv}—B1—Sr1^{iv} | 165.3 (13) |
O1^{viii}—Mg1—Sr1^{x} | 53.3 (2) | O1—B1—Sr1^{iv} | 60.7 (6) |
O1^{iv}—Mg1—Sr1^{x} | 126.7 (2) | Sr1—B1—Sr1^{iv} | 94.0 (5) |
O1^{ix}—Mg1—Sr1^{x} | 53.3 (2) | Sr1^{i}—B1—Sr1^{iv} | 118.9 (4) |
O2^{x}—Mg1—Sr1^{x} | 55.4 (4) | Sr1^{vii}—B1—Sr1^{iv} | 116.3 (7) |
O2—Mg1—Sr1^{x} | 124.6 (4) |
Symmetry codes: (i) −x, −y, −z+1; (ii) −x, y, −z+1; (iii) −x+1/2, y+1/2, −z+1; (iv) −x+1/2, −y−1/2, −z+1; (v) x+1/2, y+1/2, z+1; (vi) x+1/2, −y−1/2, z+1; (vii) −x+1/2, −y+1/2, −z+1; (viii) x+1/2, y+1/2, z; (ix) x+1/2, −y−1/2, z; (x) −x+1, −y, −z+1; (xi) x+1/2, y−1/2, z; (xii) x−1/2, y−1/2, z; (xiii) x−1/2, y−1/2, z−1; (xiv) x, −y, z. |
Experimental details
Crystal data | |
Chemical formula | Sr_{2}Mg(BO_{3})_{2} |
M_{r} | 317.17 |
Crystal system, space group | Monoclinic, C2/m |
Temperature (K) | 113 |
a, b, c (Å) | 9.046 (4), 5.1579 (18), 6.103 (3) |
β (°) | 118.691 (12) |
V (Å^{3}) | 249.81 (19) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm^{−}^{1}) | 21.44 |
Crystal size (mm) | 0.34 × 0.22 × 0.20 |
Data collection | |
Diffractometer | Rigaku Saturn |
Absorption correction | Numerical (NUMABS; Rigaku, 2005) |
T_{min}, T_{max} | 0.052, 0.100 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1180, 329, 239 |
R_{int} | 0.124 |
(sin θ/λ)_{max} (Å^{−}^{1}) | 0.657 |
Refinement | |
R[F^{2} > 2σ(F^{2})], wR(F^{2}), S | 0.065, 0.153, 1.14 |
No. of reflections | 329 |
No. of parameters | 34 |
No. of restraints | 6 |
Δρ_{max}, Δρ_{min} (e Å^{−}^{3}) | 1.93, −2.76 |
Computer programs: CrystalClear (Rigaku, 2005), CrystalClear, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), DIAMOND (Brandenburg, 1999), CrystalStructure (Rigaku/MSC, 2004).
Sr1—O1^{i} | 2.585 (8) | Mg1—O1^{ii} | 2.067 (8) |
Sr1—O1^{ii} | 2.649 (8) | Mg1—O2^{v} | 2.145 (12) |
Sr1—O1^{iii} | 2.654 (9) | O1—B1 | 1.411 (14) |
Sr1—O2^{iv} | 2.716 (4) | O2—B1 | 1.34 (2) |
Sr1—O2 | 2.730 (13) |
Symmetry codes: (i) −x, −y, −z+1; (ii) −x+1/2, y+1/2, −z+1; (iii) x+1/2, y+1/2, z+1; (iv) −x+1/2, −y+1/2, −z+1; (v) −x+1, −y, −z+1. |
Sr_{2}Mg(BO_{3})_{2} has been examined as a luminescent host material (Verstegen, 1974; Diaz & Keszler, 1997). Although Diaz & Keszler (1997) alluded to its structure determination and provided cell parameters (a = 9.035 Å, b = 5.146 Å, c = 6.099 Å, β = 118.59°), a full structure report had not appeared to date, to our knowledge. The structure determined here confirms that it is isostructural to Ba_{2}Mg(BO_{3})_{2}, which has been previously described in detail (Akella & Keszler, 1995). Briefly, MgO_{6} octahedra and BO_{3} triangles are connected to form calcite-like layers which are alternately stacked with double layers of Sr atoms (Fig. 1). Each Sr atom is nine-coordinate, in a distorted tricapped trigonal prismatic geometry.