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The title compound, potassium cadmium metaborate, crystallizes in a monoclinic cell, featuring infinite one-dimensional CdO5 chains and trigonal planar B atoms in hexa­gonal B3O6 metaborate ions. The trigonal bipyramidal CdO5 chains and metaborate ions are inter­linked to form a three-dimensional framework, creating channels running parallel to the [10\overline{1}] direction in which the potassium ions reside.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270109021477/fn3024sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270109021477/fn3024Isup2.hkl
Contains datablock I

Comment top

Metal borates are rich in structure owing to the flexibility of trigonal or tetrahedral borate–oxygen coordination. Therefore, crystallography of metal borates has been a focus of research for several decades (Rowsell et al., 2002), leading to new luminescent (Keszler, 1999) and nonlinear optical materials (Becker, 1998). This work originates from our ongoing interests in the optical and electrical propeties of borates consisting of highly disordered alkali–O polyhedrons and B–O groups (Wu et al., 2005, 2006, 2007). Considering the highly flexible coordination nature of boron, cadmium and potassium atoms and increasing interest in metal borates, we investigated the K2O–CdO–B2O3 system, with the title compound, (I), being the first identified compound.

The title compound crystallizes in the monoclinic space group C2/c, with 11 crystallographically independent atoms: one K, one Cd, three B and six O, all of which reside on general positions. Fig. 1 illustrates a selected unit of the compound, which highlights that the Cd atom is five-coordinated by O atoms in a distorted trigonal–bipyramidal geometry. The triangular BO3 groups form the metaborate ion with each of the three B atoms bonded to two briging O atoms, to form a planar six-membered ring, and one acyclic O atom. The cadmium centered trigonal–bipyramids are connected by sharing the O1···O1 edge and O5···O5 edge alternately, forming a one-dimensional CdO5 chain along the c axis (see Fig. 2a). The B3O6 groups are attached to each O vertex of the bipyramids, with the B—O planes almost perpendicular to the chain. Three adjacent CdO5 chains are interlinked by B3O6 units, forming a three-dimensional [CdB3O6] framework structure. The framework also affords one-dimensional open channels running parallel to the [101] direction, bounded by the edges of three CdO5 and three B3O6 units. Potassium ions are located in the channels.

The bond distances and angles of the B–O units are regular, as listed in Table 1. The mean value (m.v.) of the B—O bond lengths is 1.372 Å, with a standard deviation (s.d.) of 0.036, very close to the statistically averaged value for three-coordinate borons (1.370 Å). However, individually the B—O bonds can be divided into two groups; the three bonds connected with CdO5 chains are quite short, ranging from 1.312 (4) to 1.333 (4) Å (m.v. = 1.326 Å and s.d. = 0.012 ), while the bonds within the B3O3 rings are much longer, in the range 1.388 (4)–1.402 (4) Å (m.v. = 1.395 Å and s.d.= 0.005). This phenomenon is quite similliar to the bond-length variations when BO3 and BO4 groups are linked together (Filatov & Bubnova, 2000). The O—B—O bond angles range from 117.2 (2) to 123.0 (3)°, with a mean value of 120.0° (s.d. = 2.0). The Cd—O bond lengths are around 2.2 Å (m.v. = 2.254 Å and s.d.= 0.097), with the two smallest bond angles opposite the oxygen edges that are shared in CdO5 bipyramids. The potassium cation is weakly bonded to as many as nine neighboring O atoms in a highly irregular coordination environment. The B–O group type is the same as β-BaB2O4 (BBO) (reference?); relative angles between the B3O6 triangles are 0.0 (3), 164.8 (2), 15.2 (2) and 180.0 (3)°, respectively, in the unit cell.

KCdB3O6 is structurally very close to the triclinic LiCdBO3 (Sokolova et al., 1979). LiCdBO3 has two crystal forms – triclinic and hexagonal (Sokolova et al. 1980) – which are the only two borates made from CdO5 units. Generally, Cd atoms in borates will adopt four- or sixfold coordination. The CdO5 unit in hexagonal LiCdBO3 has a square–pyramidal geometry, and is therefore not analogus to the triclinic form. Triclinic LiCdBO3 is composed of CdO5 trigonal–bipyramidal chains that are interlinked by smaller BO3 units with lithium cations filling the cavities. Replacing BO3 with the larger B3O6 units of the title compound creates larger voids for the cation (K ion). Another similar compound is PKU-6 [Al2(OH)B3O7; Yang et al. 2007], which features infinite AlO5 chains connected by parallel B3O7 units.

Related literature top

For related literature, see: Becker (1998); Keszler (1999); Filatov & Bubnova (2000); Rowsell et al. (2002); Sokolova et al. (1979, 1980); Spek (2009); Wu et al. (2005, 2006, 2007); Yang et al. (2007).

Experimental top

Crystals of the title compound were grown by spontaneous nucleation in a platinum crucible using an electric muffle furnace. Starting materials were prepared from a mixture of K2CO3 [analytical reagent (AR) grade], CdO (AR), and H3BO3 (99.99%) in molar ratio of 1:2:6. Crystal growth was carried out at 1093 K after decomposition of the carbonate and elimination of the water. The melt was cooled at a rate of 1 K h-1 to 973 K and then to room temperature naturally. Small transparent colorless crystals appeared in the crucible and a suitable one (0.3 × 0.2 × 0.1 mm) was chosen to perform the single-crystal X-ray diffraction.

Computing details top

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: publCIF (Westrip, 2008).

Figures top
[Figure 1] Fig. 1. A fragment of the structure of KCdB3O6. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) x+1/2, y-1/2, z; (ii) x-1/2, y-1/2, z; (iii) -x+1/2, -y+1/2, -z; (iv) -x+3/2, y-1/2, -z+1/2.]
[Figure 2] Fig. 2. (a) The one-dimensional CdO5 trigonal–bipyramidal chain and the linkage to the B3O6 borate groups in KCdB3O6 (in the electronic version of the journal: CdO5, red polyhedra; BO3, dark-blue triangles; O, cyan; K, orange balls). (b) A projection of the structure along the a axis.
potassium cadmium metaborate top
Crystal data top
KCdB3O6F(000) = 1040
Mr = 279.93Dx = 3.262 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 2052 reflections
a = 7.1779 (6) Åθ = 3.1–32.6°
b = 13.2152 (12) ŵ = 4.52 mm1
c = 12.5113 (11) ÅT = 298 K
β = 106.156 (2)°Block, colourless
V = 1139.92 (17) Å30.3 × 0.2 × 0.1 mm
Z = 8
Data collection top
Bruker SMART APEX CCD
diffractometer
2082 independent reflections
Radiation source: fine-focus sealed tube2052 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.061
Detector resolution: 0 pixels mm-1θmax = 33.4°, θmin = 3.1°
ϕ scans, and ω scansh = 1011
Absorption correction: multi-scan
(SADABS; Bruker, 2001)
k = 1320
Tmin = 0.289, Tmax = 0.638l = 1915
4846 measured reflections
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.033Secondary atom site location: difference Fourier map
wR(F2) = 0.093 w = 1/[σ2(Fo2) + (0.0459P)2 + 2.9728P]
where P = (Fo2 + 2Fc2)/3
S = 1.20(Δ/σ)max = 0.036
2082 reflectionsΔρmax = 1.64 e Å3
100 parametersΔρmin = 1.92 e Å3
Crystal data top
KCdB3O6V = 1139.92 (17) Å3
Mr = 279.93Z = 8
Monoclinic, C2/cMo Kα radiation
a = 7.1779 (6) ŵ = 4.52 mm1
b = 13.2152 (12) ÅT = 298 K
c = 12.5113 (11) Å0.3 × 0.2 × 0.1 mm
β = 106.156 (2)°
Data collection top
Bruker SMART APEX CCD
diffractometer
2082 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2001)
2052 reflections with I > 2σ(I)
Tmin = 0.289, Tmax = 0.638Rint = 0.061
4846 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.033100 parameters
wR(F2) = 0.0930 restraints
S = 1.20Δρmax = 1.64 e Å3
2082 reflectionsΔρmin = 1.92 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.

The structure was first solved in the space group Cc, and then an inversion symmetry was detected using the PLATON software (Spek, 2009). Finally the centrosymmetric space group C2/c was chosen and the refinement process readily converged.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Cd10.55106 (3)0.073621 (15)0.122180 (16)0.01587 (9)
K10.07529 (10)0.24208 (6)0.13130 (5)0.02436 (14)
O60.1536 (3)0.43495 (16)0.0603 (2)0.0184 (4)
O20.7426 (3)0.38894 (16)0.1640 (2)0.0228 (4)
O30.4222 (3)0.32457 (16)0.08760 (19)0.0200 (4)
O40.7915 (4)0.56694 (15)0.1849 (2)0.0186 (4)
O50.4726 (3)0.50198 (16)0.12099 (19)0.0211 (4)
O10.6977 (3)0.21555 (16)0.1260 (2)0.0237 (4)
B10.6220 (4)0.3059 (2)0.1259 (2)0.0160 (5)
B20.6727 (5)0.4879 (2)0.1572 (3)0.0168 (5)
B30.3451 (5)0.4216 (2)0.0884 (3)0.0153 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cd10.01452 (13)0.01344 (12)0.01853 (13)0.00048 (5)0.00275 (8)0.00168 (5)
K10.0204 (3)0.0273 (3)0.0253 (3)0.0004 (2)0.0062 (2)0.0009 (2)
O60.0141 (9)0.0184 (9)0.0204 (10)0.0025 (7)0.0009 (7)0.0037 (7)
O20.0123 (8)0.0142 (9)0.0375 (12)0.0011 (7)0.0003 (8)0.0026 (8)
O30.0114 (8)0.0142 (8)0.0311 (10)0.0002 (7)0.0007 (7)0.0032 (7)
O40.0165 (10)0.0153 (9)0.0234 (10)0.0042 (6)0.0046 (8)0.0023 (7)
O50.0150 (9)0.0134 (8)0.0320 (11)0.0000 (7)0.0016 (8)0.0041 (8)
O10.0158 (9)0.0118 (9)0.0429 (13)0.0003 (7)0.0069 (9)0.0020 (8)
B10.0129 (11)0.0146 (11)0.0182 (12)0.0002 (9)0.0006 (9)0.0011 (9)
B20.0159 (12)0.0154 (11)0.0178 (12)0.0011 (9)0.0025 (10)0.0021 (10)
B30.0126 (13)0.0152 (12)0.0155 (13)0.0020 (8)0.0006 (10)0.0022 (8)
Geometric parameters (Å, º) top
Cd1—O12.145 (2)K1—O1v3.040 (3)
Cd1—O6i2.195 (2)K1—O2v3.189 (3)
Cd1—O4ii2.216 (2)K1—O2vi3.191 (2)
Cd1—O6iii2.349 (2)K1—B1iii3.197 (3)
Cd1—O4iv2.364 (2)K1—B33.200 (3)
O1—B11.312 (4)K1—O5ii3.252 (2)
O2—B11.397 (4)K1—B1v3.315 (3)
O3—B11.402 (4)O6—Cd1vii2.195 (2)
O2—B21.395 (4)O6—Cd1iii2.349 (2)
O4—B21.332 (4)O2—K1v3.189 (3)
O5—B21.393 (4)O2—K1viii3.191 (2)
O3—B31.397 (3)O3—K1iii2.882 (2)
O5—B31.388 (4)O4—Cd1ix2.216 (2)
O6—B31.332 (4)O4—Cd1x2.364 (2)
Cd1—Cd1v3.4744 (5)O4—K1ix2.763 (2)
Cd1—K1iii3.9001 (8)O5—K1ix3.252 (2)
Cd1—K14.1046 (8)O1—K1viii2.715 (2)
Cd1—K1v4.1302 (8)O1—K1v3.040 (3)
K1—O1vi2.715 (2)O1—K1iii3.318 (3)
K1—O4ii2.763 (2)B1—K1iii3.197 (3)
K1—O62.807 (2)B1—K1v3.315 (3)
K1—O3iii2.882 (2)B1—K1viii3.343 (3)
K1—O32.906 (2)B2—K1ix3.428 (3)
O1—Cd1—O6i121.83 (9)O6—K1—O5ii159.48 (7)
O1—Cd1—O4ii118.86 (8)O3iii—K1—O5ii74.06 (6)
O6i—Cd1—O4ii119.30 (8)O3—K1—O5ii123.72 (7)
O1—Cd1—O6iii103.56 (9)O1v—K1—O5ii88.83 (6)
O6i—Cd1—O6iii78.30 (9)O2v—K1—O5ii131.56 (6)
O4ii—Cd1—O6iii88.99 (9)O2vi—K1—O5ii115.42 (6)
O1—Cd1—O4iv85.27 (9)B1iii—K1—O5ii74.60 (7)
O6i—Cd1—O4iv102.53 (8)B3—K1—O5ii149.04 (7)
O4ii—Cd1—O4iv81.20 (10)O1vi—K1—B1v116.76 (8)
O6iii—Cd1—O4iv169.19 (9)O4ii—K1—B1v79.04 (7)
O1—Cd1—Cd1v101.96 (7)O6—K1—B1v85.47 (7)
O6i—Cd1—Cd1v120.14 (6)O3iii—K1—B1v140.62 (7)
O4ii—Cd1—Cd1v42.28 (6)O3—K1—B1v72.52 (7)
O6iii—Cd1—Cd1v131.27 (6)O1v—K1—B1v23.31 (6)
O4iv—Cd1—Cd1v39.09 (6)O2v—K1—B1v24.70 (6)
O1—Cd1—K1iii58.25 (7)O2vi—K1—B1v92.90 (7)
O6i—Cd1—K1iii105.04 (6)B1iii—K1—B1v165.14 (11)
O4ii—Cd1—K1iii106.55 (6)B3—K1—B1v72.07 (8)
O6iii—Cd1—K1iii45.47 (6)O5ii—K1—B1v111.60 (7)
O4iv—Cd1—K1iii142.20 (5)B3—O6—Cd1vii116.11 (18)
Cd1v—Cd1—K1iii133.442 (12)B3—O6—Cd1iii124.8 (2)
O1—Cd1—K186.11 (6)Cd1vii—O6—Cd1iii101.70 (9)
O6i—Cd1—K1145.69 (6)B3—O6—K194.50 (17)
O4ii—Cd1—K139.07 (6)Cd1vii—O6—K1122.01 (10)
O6iii—Cd1—K175.69 (6)Cd1iii—O6—K197.91 (8)
O4iv—Cd1—K199.03 (6)B2—O2—B1122.5 (2)
Cd1v—Cd1—K165.427 (10)B2—O2—K1v132.82 (18)
K1iii—Cd1—K171.147 (16)B1—O2—K1v82.71 (16)
O1—Cd1—K1v45.51 (7)B2—O2—K1viii146.30 (19)
O6i—Cd1—K1v120.11 (6)B1—O2—K1viii83.86 (16)
O4ii—Cd1—K1v101.08 (6)K1v—O2—K1viii65.09 (5)
O6iii—Cd1—K1v148.48 (6)B3—O3—B1121.9 (2)
O4iv—Cd1—K1v39.77 (5)B3—O3—K1iii113.25 (18)
Cd1v—Cd1—K1v64.662 (12)B1—O3—K1iii89.67 (16)
K1iii—Cd1—K1v103.084 (9)B3—O3—K188.92 (17)
K1—Cd1—K1v93.40 (2)B1—O3—K1135.95 (18)
O1vi—K1—O4ii112.77 (7)K1iii—O3—K1107.25 (7)
O1vi—K1—O6113.33 (7)B2—O4—Cd1ix118.67 (19)
O4ii—K1—O6133.55 (7)B2—O4—Cd1x112.61 (19)
O1vi—K1—O3iii101.99 (7)Cd1ix—O4—Cd1x98.63 (9)
O4ii—K1—O3iii79.82 (7)B2—O4—K1ix108.5 (2)
O6—K1—O3iii85.52 (7)Cd1ix—O4—K1ix110.57 (8)
O1vi—K1—O3161.01 (7)Cd1x—O4—K1ix107.05 (8)
O4ii—K1—O384.68 (7)B3—O5—B2122.0 (2)
O6—K1—O348.87 (6)B3—O5—K1ix151.95 (18)
O3iii—K1—O372.75 (7)B2—O5—K1ix85.17 (16)
O1vi—K1—O1v105.26 (6)B1—O1—Cd1126.55 (19)
O4ii—K1—O1v63.39 (7)B1—O1—K1viii107.02 (18)
O6—K1—O1v108.78 (7)Cd1—O1—K1viii126.43 (10)
O3iii—K1—O1v140.40 (7)B1—O1—K1v90.19 (18)
O3—K1—O1v88.97 (7)Cd1—O1—K1v104.28 (9)
O1vi—K1—O2v106.34 (7)K1viii—O1—K1v72.96 (6)
O4ii—K1—O2v103.75 (7)B1—O1—K1iii73.27 (17)
O6—K1—O2v68.17 (7)Cd1—O1—K1iii88.40 (8)
O3iii—K1—O2v147.09 (7)K1viii—O1—K1iii108.53 (8)
O3—K1—O2v75.02 (6)K1v—O1—K1iii163.20 (8)
O1v—K1—O2v44.13 (6)O1—B1—O2119.8 (3)
O1vi—K1—O2vi45.90 (6)O1—B1—O3123.0 (3)
O4ii—K1—O2vi150.23 (7)O2—B1—O3117.2 (2)
O6—K1—O2vi73.22 (7)O1—B1—K1iii83.59 (18)
O3iii—K1—O2vi120.72 (7)O2—B1—K1iii123.97 (19)
O3—K1—O2vi120.46 (6)O3—B1—K1iii64.32 (14)
O1v—K1—O2vi98.87 (7)O1—B1—K1v66.50 (17)
O2v—K1—O2vi71.39 (7)O2—B1—K1v72.58 (15)
O1vi—K1—B1iii77.90 (8)O3—B1—K1v134.83 (19)
O4ii—K1—B1iii98.04 (8)K1iii—B1—K1v149.95 (11)
O6—K1—B1iii86.18 (7)O1—B1—K1viii50.95 (14)
O3iii—K1—B1iii26.01 (7)O2—B1—K1viii71.60 (15)
O3—K1—B1iii92.75 (7)O3—B1—K1viii161.6 (2)
O1v—K1—B1iii161.13 (7)K1iii—B1—K1viii97.27 (8)
O2v—K1—B1iii153.71 (7)K1v—B1—K1viii62.05 (6)
O2vi—K1—B1iii96.44 (7)O4—B2—O5120.5 (3)
O1vi—K1—B3137.57 (8)O4—B2—O2121.7 (3)
O4ii—K1—B3109.65 (8)O5—B2—O2117.8 (2)
O6—K1—B324.52 (7)O4—B2—K1ix49.85 (16)
O3iii—K1—B384.44 (7)O5—B2—K1ix70.95 (15)
O3—K1—B325.88 (7)O2—B2—K1ix170.0 (2)
O1v—K1—B394.11 (7)O6—B3—O5121.6 (2)
O2v—K1—B363.35 (7)O6—B3—O3120.1 (3)
O2vi—K1—B394.59 (7)O5—B3—O3118.3 (3)
B1iii—K1—B395.61 (8)O6—B3—K160.98 (16)
O1vi—K1—O5ii70.09 (6)O5—B3—K1154.0 (2)
O4ii—K1—O5ii45.43 (6)O3—B3—K165.20 (15)
Symmetry codes: (i) x+1/2, y1/2, z; (ii) x1/2, y1/2, z; (iii) x+1/2, y+1/2, z; (iv) x+3/2, y1/2, z+1/2; (v) x+1, y, z+1/2; (vi) x1, y, z; (vii) x1/2, y+1/2, z; (viii) x+1, y, z; (ix) x+1/2, y+1/2, z; (x) x+3/2, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formulaKCdB3O6
Mr279.93
Crystal system, space groupMonoclinic, C2/c
Temperature (K)298
a, b, c (Å)7.1779 (6), 13.2152 (12), 12.5113 (11)
β (°) 106.156 (2)
V3)1139.92 (17)
Z8
Radiation typeMo Kα
µ (mm1)4.52
Crystal size (mm)0.3 × 0.2 × 0.1
Data collection
DiffractometerBruker SMART APEX CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2001)
Tmin, Tmax0.289, 0.638
No. of measured, independent and
observed [I > 2σ(I)] reflections
4846, 2082, 2052
Rint0.061
(sin θ/λ)max1)0.775
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.033, 0.093, 1.20
No. of reflections2082
No. of parameters100
Δρmax, Δρmin (e Å3)1.64, 1.92

Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009), publCIF (Westrip, 2008).

Selected geometric parameters (Å, º) top
O1—B11.312 (4)O5—B21.393 (4)
O2—B11.397 (4)O3—B31.397 (3)
O3—B11.402 (4)O5—B31.388 (4)
O2—B21.395 (4)O6—B31.332 (4)
O4—B21.332 (4)
O1—Cd1—O6i121.83 (9)O4ii—Cd1—O6iii88.99 (9)
O1—Cd1—O4ii118.86 (8)O1—Cd1—O4iv85.27 (9)
O6i—Cd1—O4ii119.30 (8)O6i—Cd1—O4iv102.53 (8)
O1—Cd1—O6iii103.56 (9)O4ii—Cd1—O4iv81.20 (10)
O6i—Cd1—O6iii78.30 (9)O6iii—Cd1—O4iv169.19 (9)
Symmetry codes: (i) x+1/2, y1/2, z; (ii) x1/2, y1/2, z; (iii) x+1/2, y+1/2, z; (iv) x+3/2, y1/2, z+1/2.
 

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