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The previously determined structure of cadmium diborate, Cd2B2O5, has been re-investigated and a change in space-group symmetry from P1 to P\overline 1 evidenced. Cd2B2O5 crystallizes isotypically with other triclinic members of the M2B2O5 (M = Mg, Mn, Co, Fe) family and is composed of slightly distorted [CdO6] octahedra, forming ribbons built of four condensed single-chains and diborate anions, B2O52-, which are composed of corner-sharing BO3 triangles and which interconnect adjacent ribbons.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536803012157/br6105sup1.cif
Contains datablocks I, Cd2B2O5

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536803012157/br6105Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](O-B) = 0.002 Å
  • R factor = 0.022
  • wR factor = 0.056
  • Data-to-parameter ratio = 31.1

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

General Notes

ABSTM_02 The ratio of expected to reported Tmax/Tmin(RR) is > 1.10 Tmin and Tmax reported: 0.267 0.473 Tmin and Tmax expected: 0.199 0.496 RR = 1.408 Please check that your absorption correction is appropriate.

Comment top

Cd2B2O5, (I), is an interesting host material for luminescent applications when doped with tranistion metal or RE ions. Its structure has been determined by Sokolova et al. (1979) and was described in space group P1. Comparison of the symmetry and lattice parameters of other M2B2O5 members [M = Co (Berger, 1950), Mg, Fe, Mn (Block et al., 1959), Mg (Guo et al., 1995a)] and solid solutions MM'B2O5 [M = Mn, M' = Mg, Co (Utzolino & Bluhm, 1996); M = Zn, M' = Co, Ni (Busche & Bluhm, 1995)], which all crystallize with similar lattice parameters in the centrosymmetric space group P1, suggested a possible change in the space-group symmetry. Therefore the published atomic coordinates (Sokolova et al., 1979) were checked with the PLATON program (Spek, 2003) which, in fact, indicated a centre of symmetry within the default tolerances of the program. For experimental proof, single crystals of Cd2B2O5 were grown and the structure was re-determined in space group P1.

Cd2B2O5 crystallizes isotypically with the triclinic representatives of the M2B2O5 family mentioned above. For all these structures, two angles close to 90° are observed, indicating a possible phase transition to the monoclinic crystal system. At least for Mg2B2O5, a synthetic monoclinic polymorph is described (Guo et al., 1995b) which is identical to the mineral Suanite (Takeuchi, 1952).

The crystal structure is composed of two crystallographically independent and distorted [CdO6] octahedra, and B2O5 groups as the main building units. The [CdO6] octahedra have mean Cd—O distances of 2.303 Å (Cd1) and 2.334 Å (Cd2) and build chains running parallel to the [100] direction by edge-sharing (Fig. 1). Four of these chains are connected to form ribbons along the [011] direction (Fig. 2). Adjacent ribbons are held together by the interstitial B2O5 anions.

As in other diborate structures with two condensed BO3 triangles, the corresponding polyhedra are substantially distorted. The distances from B to the bridging atom O4 are considerably longer than to the terminal atoms O1, O2, O3 and O5 (see Table 1). The B—O distances for the two independent BO3 triangles are very similar, and the average B—O distances ¯d(B1—O) = 1.377 Å and ¯d(B2—O) = 1.381 Å are in good agreement with the data for many other borate structures with BO3 groups (Zobetz, 1982). The B2O5 anion (Fig. 3) deviates significantly from coplanarity; the dihedral angle between the two slanting BO3 triangles is 13.1 (1)°.

The O atoms O1, O3 and O5 exhibit coordination number 4 and are each surrounded by three Cd and one B atom. O2 has three coordination partners (2 x Cd and B) with two short Cd—O distances and a short B—O distance. O4 is the bridging atom of the diborate group and has an additional Cd atom with a long Cd—O distance in its coordination environment.

Experimental top

Stoichiometric amounts of CdCO3 (Merck, p·A.) and H3BO3 (10% excess, Merck, p·A.) were ground together finely in an agate mortar and charged in a platinum crucible which was heated to 1353 K over the course of 5 h, kept at that temperature for 1 h and cooled to 973 K over 4 d. The furnace was then shut off. After leaching with boiling demineralized water, colourless single crystals of Cd2B2O5, with mainly plate-like habit and an edge-length of up to 2 mm, were isolated.

Refinement top

The structure was refined with the atomic coordinates of the isomorphous solid solution MnMgB2O5 (Utzolino & Bluhm, 1996) as starting parameters. The refined positional parameters were afterwards standardized using the program STRUCTURE-TIDY (Gelato & Parthé, 1987). The highest difference peak is located at a distance of 0.59 Å from Cd1, and the deepest hole 0.63 Å from this atom.

Computing details top

Data collection: CAD-4 Software (Nonius, 1989); cell refinement: CAD-4 Software; data reduction: HELENA implemented in PLATON (Spek, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 2000); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Slice through the structure, approximately parallel to (011). The structure is plotted in polyhedral representation; [Cd1O6] octahedra are orange, [Cd2O6] octahedra are yellow and B2O5 groups are blue.
[Figure 2] Fig. 2. Projection of the crystal structure in polyhedral representation, viewed along [100]. [Cd1O6] octahedra are orange, [Cd2O6] octahedra are yellow and B2O5 groups are blue.
[Figure 3] Fig. 3. ORTEP plot of the diborate anion, with anisotropic displacement ellipsoids drawn at the 90% probability level.
Cadmium diborate top
Crystal data top
Cd2(B2O5)Z = 2
Mr = 326.42F(000) = 292
Triclinic, P1Dx = 5.157 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 3.4490 (2) ÅCell parameters from 25 reflections
b = 6.3603 (5) Åθ = 12.4–14.9°
c = 9.9502 (8) ŵ = 10.02 mm1
α = 105.441 (8)°T = 293 K
β = 90.807 (6)°Plate, colourless
γ = 91.933 (6)°0.22 × 0.14 × 0.07 mm
V = 210.22 (3) Å3
Data collection top
Enraf-Nonius CAD-4
diffractometer
2464 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.018
Graphite monochromatorθmax = 39.9°, θmin = 2.1°
ω/2θ scansh = 66
Absorption correction: numerical
The crystal shape was optimized by minimizing the R-value of selected ψ-scanned reflections using the program HABITUS (Herrendorf, 1993-97). The habit so derived was used for the numerical absorption correction.
k = 1111
Tmin = 0.267, Tmax = 0.473l = 1717
5166 measured reflections3 standard reflections every 500 min
2584 independent reflections intensity decay: none
Refinement top
Refinement on F2Primary atom site location: isomorphous structure methods
Least-squares matrix: full w = 1/[σ2(Fo2) + (0.0307P)2 + 0.3225P]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.022(Δ/σ)max = 0.001
wR(F2) = 0.056Δρmax = 2.33 e Å3
S = 1.13Δρmin = 2.03 e Å3
2584 reflectionsExtinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
83 parametersExtinction coefficient: 0.238 (4)
0 restraints
Crystal data top
Cd2(B2O5)γ = 91.933 (6)°
Mr = 326.42V = 210.22 (3) Å3
Triclinic, P1Z = 2
a = 3.4490 (2) ÅMo Kα radiation
b = 6.3603 (5) ŵ = 10.02 mm1
c = 9.9502 (8) ÅT = 293 K
α = 105.441 (8)°0.22 × 0.14 × 0.07 mm
β = 90.807 (6)°
Data collection top
Enraf-Nonius CAD-4
diffractometer
2464 reflections with I > 2σ(I)
Absorption correction: numerical
The crystal shape was optimized by minimizing the R-value of selected ψ-scanned reflections using the program HABITUS (Herrendorf, 1993-97). The habit so derived was used for the numerical absorption correction.
Rint = 0.018
Tmin = 0.267, Tmax = 0.4733 standard reflections every 500 min
5166 measured reflections intensity decay: none
2584 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02283 parameters
wR(F2) = 0.0560 restraints
S = 1.13Δρmax = 2.33 e Å3
2584 reflectionsΔρmin = 2.03 e Å3
Special details top

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 (Å2) top
xyzUiso*/Ueq
Cd10.22524 (3)0.34751 (2)0.593004 (13)0.00856 (4)
Cd20.24898 (4)0.77837 (2)0.125010 (13)0.00940 (5)
B10.3291 (6)0.3271 (3)0.1555 (2)0.0081 (3)
B20.6800 (6)0.1264 (3)0.3200 (2)0.0081 (3)
O10.1972 (5)0.0792 (2)0.69646 (17)0.0127 (2)
O20.2570 (5)0.2897 (3)0.01669 (16)0.0128 (2)
O30.2747 (4)0.5244 (2)0.24790 (16)0.0103 (2)
O40.4788 (5)0.1526 (2)0.20034 (16)0.0132 (2)
O50.7276 (4)0.2963 (2)0.43691 (15)0.0097 (2)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cd10.00838 (6)0.00948 (6)0.00881 (6)0.00093 (4)0.00033 (4)0.00410 (4)
Cd20.00867 (6)0.01101 (6)0.00860 (6)0.00064 (4)0.00024 (4)0.00275 (4)
B10.0082 (6)0.0091 (6)0.0072 (6)0.0008 (5)0.0005 (5)0.0027 (5)
B20.0092 (6)0.0076 (6)0.0078 (6)0.0020 (5)0.0009 (5)0.0025 (5)
O10.0181 (6)0.0097 (5)0.0122 (6)0.0055 (4)0.0028 (5)0.0055 (4)
O20.0111 (5)0.0194 (6)0.0081 (5)0.0015 (5)0.0006 (4)0.0038 (5)
O30.0118 (5)0.0092 (5)0.0095 (5)0.0027 (4)0.0002 (4)0.0015 (4)
O40.0212 (6)0.0078 (5)0.0101 (5)0.0024 (4)0.0057 (5)0.0016 (4)
O50.0107 (5)0.0098 (5)0.0080 (5)0.0010 (4)0.0005 (4)0.0013 (4)
Geometric parameters (Å, º) top
Cd1—O12.2152 (15)Cd2—O1iii2.3787 (16)
Cd1—O5i2.2544 (15)Cd2—O4vii2.4004 (15)
Cd1—O3ii2.2993 (15)Cd2—O1ii2.5603 (18)
Cd1—O52.3162 (15)Cd2—Cd2iv3.4490 (2)
Cd1—O5ii2.3631 (15)Cd2—Cd2i3.4490 (2)
Cd1—O3iii2.3722 (15)B1—O21.356 (3)
Cd1—Cd1iii3.4112 (3)B1—O31.364 (2)
Cd1—Cd1iv3.4490 (2)B1—O41.411 (3)
Cd1—Cd1i3.4490 (2)B2—O1viii1.357 (2)
Cd2—O2v2.1853 (16)B2—O51.364 (3)
Cd2—O2vi2.2071 (16)B2—O41.421 (3)
Cd2—O32.2742 (15)
O1—Cd1—O5i108.32 (6)O2vi—Cd2—O1iii167.32 (6)
O1—Cd1—O3ii82.70 (6)O3—Cd2—O1iii79.56 (5)
O5i—Cd1—O3ii167.91 (6)O2v—Cd2—O4vii116.07 (6)
O1—Cd1—O5110.00 (5)O2vi—Cd2—O4vii88.75 (6)
O5i—Cd1—O597.97 (6)O3—Cd2—O4vii127.06 (5)
O3ii—Cd1—O582.35 (5)O1iii—Cd2—O4vii79.34 (6)
O1—Cd1—O5ii160.36 (6)O2v—Cd2—O1ii170.77 (6)
O5i—Cd1—O5ii84.78 (5)O2vi—Cd2—O1ii81.11 (5)
O3ii—Cd1—O5ii83.31 (5)O3—Cd2—O1ii75.95 (5)
O5—Cd1—O5ii81.63 (5)O1iii—Cd2—O1ii88.50 (5)
O1—Cd1—O3iii80.89 (5)O4vii—Cd2—O1ii55.55 (5)
O5i—Cd1—O3iii82.07 (5)O2—B1—O3122.46 (17)
O3ii—Cd1—O3iii95.16 (5)O2—B1—O4116.53 (17)
O5—Cd1—O3iii168.29 (5)O3—B1—O4120.97 (17)
O5ii—Cd1—O3iii86.72 (5)O1viii—B2—O5126.35 (18)
O2v—Cd2—O2vi103.48 (6)O1viii—B2—O4112.94 (16)
O2v—Cd2—O3110.08 (6)O5—B2—O4120.70 (17)
O2vi—Cd2—O3104.69 (6)B1—O4—B2136.82 (16)
O2v—Cd2—O1iii85.84 (6)
Symmetry codes: (i) x1, y, z; (ii) x+1, y+1, z+1; (iii) x, y+1, z+1; (iv) x+1, y, z; (v) x, y+1, z; (vi) x+1, y+1, z; (vii) x, y+1, z; (viii) x+1, y, z+1.

Experimental details

Crystal data
Chemical formulaCd2(B2O5)
Mr326.42
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)3.4490 (2), 6.3603 (5), 9.9502 (8)
α, β, γ (°)105.441 (8), 90.807 (6), 91.933 (6)
V3)210.22 (3)
Z2
Radiation typeMo Kα
µ (mm1)10.02
Crystal size (mm)0.22 × 0.14 × 0.07
Data collection
DiffractometerEnraf-Nonius CAD-4
diffractometer
Absorption correctionNumerical
The crystal shape was optimized by minimizing the R-value of selected ψ-scanned reflections using the program HABITUS (Herrendorf, 1993-97). The habit so derived was used for the numerical absorption correction.
Tmin, Tmax0.267, 0.473
No. of measured, independent and
observed [I > 2σ(I)] reflections
5166, 2584, 2464
Rint0.018
(sin θ/λ)max1)0.903
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.022, 0.056, 1.13
No. of reflections2584
No. of parameters83
Δρmax, Δρmin (e Å3)2.33, 2.03

Computer programs: CAD-4 Software (Nonius, 1989), CAD-4 Software, HELENA implemented in PLATON (Spek, 2003), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ATOMS (Dowty, 2000), SHELXL97.

Selected geometric parameters (Å, º) top
Cd1—O12.2152 (15)Cd2—O1iii2.3787 (16)
Cd1—O5i2.2544 (15)Cd2—O4vi2.4004 (15)
Cd1—O3ii2.2993 (15)Cd2—O1ii2.5603 (18)
Cd1—O52.3162 (15)B1—O21.356 (3)
Cd1—O5ii2.3631 (15)B1—O31.364 (2)
Cd1—O3iii2.3722 (15)B1—O41.411 (3)
Cd2—O2iv2.1853 (16)B2—O1vii1.357 (2)
Cd2—O2v2.2071 (16)B2—O51.364 (3)
Cd2—O32.2742 (15)B2—O41.421 (3)
O2—B1—O3122.46 (17)O1vii—B2—O4112.94 (16)
O2—B1—O4116.53 (17)O5—B2—O4120.70 (17)
O3—B1—O4120.97 (17)B1—O4—B2136.82 (16)
O1vii—B2—O5126.35 (18)
Symmetry codes: (i) x1, y, z; (ii) x+1, y+1, z+1; (iii) x, y+1, z+1; (iv) x, y+1, z; (v) x+1, y+1, z; (vi) x, y+1, z; (vii) x+1, y, z+1.
 

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