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A sodium calcium borate, NaCaBO3, has been synthesized by the solid-state reaction method and the structure solved from X-ray powder diffraction data. The compound crystallizes in space group Pmmn and has a desired structure type containing isolated planar BO33- anions. Mixed occupancy is found to exist in the Ca site, with partial replacement by Na. One Ca/Na mixed atom and one Na atom are at sites with mm2 symmetry, and a second Ca/Na mixed atom, an Na atom, two B and two O atoms are on mirror planes.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010401964X/iz1043sup1.cif
Contains datablocks global, I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S010827010401964X/iz1043Isup2.rtv
Contains datablock I

Comment top

Borate crystals have attracted much attention, due to their outstanding linear and nonlinear optical properties. A variety of BO atomic groups are considered to be a dominant factor for the physical properties, in particular the optical properties, of borates. Among the various anionic groups, the planar (BO3)3− group has attracted our attention, because low absorption and the anisotropy of polarizability indicate that some borates are likely to be good candidates for future deep-UV nonlinear optical and birefringent materials. The title compound was first mentioned by Stoch & Waclawska (1990), but the structure had not been established to date. In the present study, the structure is determined and refined from powder diffraction data, as shown in Fig. 1.

The fundamental building units are the isolated (BO3)3− anionic groups distributed parallel to four directions, [301], [301], [032] and [032], as shown in Figs. 2 and 3. The B—O distances vary from 1.319 (8) to 1.483 (15) Å, with an average value of 1.372 Å, and the O—B—O angles from 115.82 (8) to 128.31 (7)°, which are rather common in borates.

Both the Ca and Na cations in NaCaBO3 appear in two crystallographically different environments, as shown in Fig. 4. Mixed occupancy is found to exist in the Ca sites, with partial replacement by 20% Na (denoted M in the following text, i.e. M = 80% Ca and 20% Na). The M1 atoms (in the 8 g position) are coordinated to seven O atoms, forming seven-top decahedra. The M2 atoms (in the 2 b position) are six-coordinated to O atoms, forming M2O6 octahedra. Each M2O6 octahedron shares four edges with four adjacent M1O7 polyhedra, forming an M5O26 repeating unit, which can be seen clearly in Fig. 4. The other two special Wyckoff positions (2a and 4f) are all occupied by Na atoms. The Na3 atoms (in the 2a position) show a rather peculiar coordination, with four short distances [2.437 (6) Å] on one side and four very long distances [2.982 (6) Å] on the opposite side directed along the orthorhombic c axis. A similar phenomenon is found in some other borates, such as Na3Ln(BO3)2 (Ln is La or Nd; 2.301–2.960 Å; Mascetti et al., 1981) and Na2B8O13 (2.259–2.926 Å; Hyman et al., 1967). It is believed to be the O environment around the Na3 atoms which allows a rather large vibrational movement of this atom along one direction.

The Na and eight coordinated O atoms form a cuboid, sharing two edges with the adjacent two Na4O6 (in the 4f position, six-coordinated) trigonal prisms, forming Na3O16 repeating units. The M5O26 groups and the Na3O16 groups are distributed alternately along the [100] and [010] directions. The (BO3)3− groups are located between the two kinds of repeating units, sharing one edge with Na3O16 and two edges with M5O26 groups, forming infinite three-dimensional networks (Fig. 5).

Some known compounds, LiMBO3 (M is Mg, Ca, Sr or Ba; Norrestam, 1989; Wu et al., 2004; Cheng et al., 2001; Schlaeger & Hoppe, 1993) have the same formula type as the title compound, and contain isolated planar BO3 groups. However, their structures are all different from this new synthesized ternary borate. The fundamental building units, (BO3)3− groups, are distributed along two different directions in the four lithium borates. They are almost parallel to each other in LiMgBO3, and are perpendicular to each other in LiCaBO3. Moreover, the cations of NaCaBO3 have more complex coordination than the other four compounds, and mixed occupancy is found in the Ca sites. The Mg atoms are five-coordinated by O atoms to form roughly trigonal-bipyramidal coordination polyhedra. The Ca atoms are coordinated by seven O atoms, forming mono-caped distorted trigonal prisms, and share edges with each other, which is similar to the coordination of Sr atoms in LiSrBO3. The Ba atoms are nine-coordinated, forming a mono-capped distorted-square anti-prism. The Li atoms in the four compounds are all five-coordinated, forming different distorted trigonal bipyramids. No mixed occupancy is found in the four lithium borates. The similar radii of Na and Ca cations, and the large difference between the radii of Li and other alkali earth metal cations, might be one of the reasons why mixed occupancy is only found in NaCaBO3.

Experimental top

Appropriate amounts Quantities of Ratio? of analytically pure NaCO3, CaCO3 and H3BO3 were mixed, thoroughly ground and then fired at 923 K to decompose the carbonate and eliminate water. The sintering temperature was then raised from 973 to 1073 K in 50 K steps, each temperature being held for 24 h with intermediate grindings. No further changes were found from the diffraction patterns during the course of the reaction. The title compound was obtained as a white powder. Please check rephrased text.

Refinement top

The powder pattern was indexed based on an orthorhombic cell, with cell parameters a = 16.0933 (2), b = 10.2100 (1) and c = 3.49811 (4) Å. Systematic extinctions are consistent with space group Pmmn. The FULLPROF program (Rodriguez-Carvajal, 2003) was applied to the pattern and a total of 397 independent |Fobs| were extracted. A satisfactory preliminary structure was obtained by applying direct methods (SHELXL97; Sheldrick, 1997) to these extracted |Fobs|. The (BO3)3− atomic group and Ca and Na cations were discerned according to the interatomic distances and angles in the electron-density map. The structure was refined by the Reitveld method.

Computing details top

Data collection: Rint2400 (Rigaku, 1993); cell refinement: HIGHSCORE (Philips, 2002); data reduction: HIGHSCORE; program(s) used to solve structure: SHEXLS97 (Sheldrick, 1997); program(s) used to refine structure: FULLPROF (Rodriguez-Carvajal, 2003); molecular graphics: BALLS&STICKS (Kang & Ozawa, 2003); software used to prepare material for publication: Please provide missing information.

Figures top
[Figure 1] Fig. 1. The final Rietveld refinement plot for NaCaBO3. Small crosses (+) correspond to experimental values and the continuous line to the calculated pattern. Vertical bars indicate the positions of Bragg peaks. The lower trace depicts the difference between the experimental and calculated intensity values.
[Figure 2] Fig. 2. The structure of NaCaBO3 viewed along [001]. Large black spheres denote M atoms (M is 80% Ca and 20% Na), small black spheres B atoms, grey spheres O atoms and white spheres Na atoms.
[Figure 3] Fig. 3. The projection of NaCaBO3 viewed along (a) [010] and (b) [100]. B and O atoms have been omitted for clarity. Black triangles denote BO3 and short black lines the side faces of them. Black spheres denote M atoms (M is 80% Ca and 20% Na) and white spheres Na atoms.
[Figure 4] Fig. 4. The coordination surroundings of (a) M atoms (M is 80% Ca and 20% Na) and (b) Na atoms with O atoms. Large black spheres denote M atoms, small black spheres B atoms, grey spheres O atoms and white spheres Na atoms.
[Figure 5] Fig. 5. The networks of NaCaBO3 projected along [001]. Black triangles denote BO3, black spheres M atoms (M is 80% Ca and 20% Na), grey spheres O atoms and white spheres Na atoms.
sodium calcium orthoborate top
Crystal data top
NaCa(BO3)F(000) = 480
Mr = 487.52Dx = 2.817 Mg m3
Orthorhombic, PmmnMelting point: 945.0 K
Hall symbol: -P 2ab 2aCu Kα1, Cu Kα2 radiation, λ = 1.540562, 1.544390 Å
a = 16.0933 (2) ÅT = 295 K
b = 10.2100 (1) ÅParticle morphology: plate-like
c = 3.49811 (4) Åwhite
V = 574.78 (2) Å3flat sheet, 15 × 35 mm
Z = 2Specimen preparation: Prepared at 1073 K
Data collection top
Rigaku Rint 2400
diffractometer
Data collection mode: reflection
Radiation source: rotating-anode x-ray tubeScan method: step
None monochromator2θmin = 5°, 2θmax = 135°, 2θstep = 0.02°
Specimen mounting: packed powder pellet
Refinement top
Refinement on InetExcluded region(s): none
Least-squares matrix: full with fixed elements per cycleProfile function: pseudo-Voigt
Rp = 0.08951 parameters
Rwp = 0.1191/Yi
Rexp = 0.058(Δ/σ)max = 0.01
χ2 = 4.244Background function: square polynomial for each range
6501 data pointsPreferred orientation correction: Icorr = Iobs[G2+(1-G2)exp(G1a2)], axis (001) (March, 1932)
Crystal data top
NaCa(BO3)V = 574.78 (2) Å3
Mr = 487.52Z = 2
Orthorhombic, PmmnCu Kα1, Cu Kα2 radiation, λ = 1.540562, 1.544390 Å
a = 16.0933 (2) ÅT = 295 K
b = 10.2100 (1) Åflat sheet, 15 × 35 mm
c = 3.49811 (4) Å
Data collection top
Rigaku Rint 2400
diffractometer
Scan method: step
Specimen mounting: packed powder pellet2θmin = 5°, 2θmax = 135°, 2θstep = 0.02°
Data collection mode: reflection
Refinement top
Rp = 0.089χ2 = 4.244
Rwp = 0.1196501 data points
Rexp = 0.05851 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
M10.5990 (1)0.4662 (2)0.2387 (6)0.02 (4)*0.80 (1)
M10.5990 (1)0.4662 (2)0.2387 (6)0.02 (4)*0.20 (1)
M20.750.250.5348 (9)0.02 (1)*0.80 (1)
M20.750.250.5348 (9)0.02 (1)*0.20 (1)
Na30.750.750.3717 (17)0.03 (2)*
Na40.4169 (2)0.250.2078 (12)0.03 (1)*
O10.750.4093 (7)0.033 (2)0.04 (1)*
O20.6764 (4)0.5867 (4)0.2489 (15)0.04 (1)*
O30.4989 (3)0.6335 (6)0.2339 (16)0.05 (1)*
O40.6113 (4)0.250.4748 (18)0.05 (1)*
B10.750.5363 (13)0.172 (3)0.05 (2)*
B20.4684 (8)0.750.320 (3)0.05 (2)*
Geometric parameters (Å, º) top
M1—O32.348 (5)Na3—O22.982 (6)
M1—O42.365 (3)Na3—O2xi2.982 (6)
M1—O22.445 (5)Na3—O2xii2.982 (6)
M1—O3i2.501 (6)Na3—O2xiii2.982 (6)
M1—O2ii2.506 (5)Na3—B1viii2.702 (13)
M1—O12.599 (3)Na3—B1ii2.702 (13)
M1—O3iii2.631 (6)Na3—B12.895 (13)
M1—B2iv2.903 (8)Na3—B1xii2.895 (13)
M1—B12.913 (7)Na4—O2v2.248 (5)
M1—B2v3.142 (8)Na4—O2i2.248 (5)
M2—O42.241 (7)Na4—O3v2.374 (6)
M2—O4vi2.241 (7)Na4—O3i2.374 (6)
M2—O1ii2.385 (8)Na4—O3iii2.657 (7)
M2—O1vii2.385 (8)Na4—O3iv2.657 (7)
M2—O1vi2.392 (8)Na4—B2iv2.476 (12)
M2—O12.392 (8)Na4—B2v2.611 (12)
M2—B1ii3.098 (12)B1—O11.483 (15)
M2—B1vii3.098 (12)B1—O21.319 (8)
Na3—O2viii2.437 (6)B1—O2xiii1.319 (8)
Na3—O2ix2.437 (6)B2—O31.321 (7)
Na3—O2ii2.437 (6)B2—O3xi1.321 (7)
Na3—O2x2.437 (6)B2—O4xiv1.470 (14)
O2—B1—O2xiii127.79 (8)O3xi—B2—O3128.32 (7)
O2—B1—O1116.09 (8)O3xi—B2—O4xiv115.82 (9)
O2xiii—B1—O1116.09 (8)O3—B2—O4xiv115.82 (9)
Symmetry codes: (i) x+1, y+1, z; (ii) x, y, z+1; (iii) x+1, y+1, z+1; (iv) x+1, y1/2, z+1; (v) x+1, y1/2, z; (vi) x+3/2, y+1/2, z; (vii) x+3/2, y+1/2, z+1; (viii) x+3/2, y+3/2, z+1; (ix) x, y+3/2, z+1; (x) x+3/2, y, z+1; (xi) x, y+3/2, z; (xii) x+3/2, y+3/2, z; (xiii) x+3/2, y, z; (xiv) x+1, y+1/2, z+1.

Experimental details

Crystal data
Chemical formulaNaCa(BO3)
Mr487.52
Crystal system, space groupOrthorhombic, Pmmn
Temperature (K)295
a, b, c (Å)16.0933 (2), 10.2100 (1), 3.49811 (4)
V3)574.78 (2)
Z2
Radiation typeCu Kα1, Cu Kα2, λ = 1.540562, 1.544390 Å
Specimen shape, size (mm)Flat sheet, 15 × 35
Data collection
DiffractometerRigaku Rint 2400
diffractometer
Specimen mountingPacked powder pellet
Data collection modeReflection
Scan methodStep
2θ values (°)2θmin = 5 2θmax = 135 2θstep = 0.02
Refinement
R factors and goodness of fitRp = 0.089, Rwp = 0.119, Rexp = 0.058, χ2 = 4.244
No. of data points6501
No. of parameters51
No. of restraints?

Computer programs: Rint2400 (Rigaku, 1993), HIGHSCORE (Philips, 2002), HIGHSCORE, SHEXLS97 (Sheldrick, 1997), FULLPROF (Rodriguez-Carvajal, 2003), BALLS&STICKS (Kang & Ozawa, 2003), Please provide missing information.

Selected geometric parameters (Å, º) top
M1—O32.348 (5)Na3—O22.982 (6)
M1—O42.365 (3)Na3—O2xi2.982 (6)
M1—O22.445 (5)Na3—O2xii2.982 (6)
M1—O3i2.501 (6)Na3—O2xiii2.982 (6)
M1—O2ii2.506 (5)Na3—B1viii2.702 (13)
M1—O12.599 (3)Na3—B1ii2.702 (13)
M1—O3iii2.631 (6)Na3—B12.895 (13)
M1—B2iv2.903 (8)Na3—B1xii2.895 (13)
M1—B12.913 (7)Na4—O2v2.248 (5)
M1—B2v3.142 (8)Na4—O2i2.248 (5)
M2—O42.241 (7)Na4—O3v2.374 (6)
M2—O4vi2.241 (7)Na4—O3i2.374 (6)
M2—O1ii2.385 (8)Na4—O3iii2.657 (7)
M2—O1vii2.385 (8)Na4—O3iv2.657 (7)
M2—O1vi2.392 (8)Na4—B2iv2.476 (12)
M2—O12.392 (8)Na4—B2v2.611 (12)
M2—B1ii3.098 (12)B1—O11.483 (15)
M2—B1vii3.098 (12)B1—O21.319 (8)
Na3—O2viii2.437 (6)B1—O2xiii1.319 (8)
Na3—O2ix2.437 (6)B2—O31.321 (7)
Na3—O2ii2.437 (6)B2—O3xi1.321 (7)
Na3—O2x2.437 (6)B2—O4xiv1.470 (14)
O2—B1—O2xiii127.79 (8)O3xi—B2—O3128.32 (7)
O2—B1—O1116.09 (8)O3xi—B2—O4xiv115.82 (9)
O2xiii—B1—O1116.09 (8)O3—B2—O4xiv115.82 (9)
Symmetry codes: (i) x+1, y+1, z; (ii) x, y, z+1; (iii) x+1, y+1, z+1; (iv) x+1, y1/2, z+1; (v) x+1, y1/2, z; (vi) x+3/2, y+1/2, z; (vii) x+3/2, y+1/2, z+1; (viii) x+3/2, y+3/2, z+1; (ix) x, y+3/2, z+1; (x) x+3/2, y, z+1; (xi) x, y+3/2, z; (xii) x+3/2, y+3/2, z; (xiii) x+3/2, y, z; (xiv) x+1, y+1/2, z+1.
 

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