Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270109021477/fn3024sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270109021477/fn3024Isup2.hkl |
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.
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).
KCdB3O6 | F(000) = 1040 |
Mr = 279.93 | Dx = 3.262 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2yc | Cell parameters from 2052 reflections |
a = 7.1779 (6) Å | θ = 3.1–32.6° |
b = 13.2152 (12) Å | µ = 4.52 mm−1 |
c = 12.5113 (11) Å | T = 298 K |
β = 106.156 (2)° | Block, colourless |
V = 1139.92 (17) Å3 | 0.3 × 0.2 × 0.1 mm |
Z = 8 |
Bruker SMART APEX CCD diffractometer | 2082 independent reflections |
Radiation source: fine-focus sealed tube | 2052 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.061 |
Detector resolution: 0 pixels mm-1 | θmax = 33.4°, θmin = 3.1° |
ϕ scans, and ω scans | h = −10→11 |
Absorption correction: multi-scan (SADABS; Bruker, 2001) | k = −13→20 |
Tmin = 0.289, Tmax = 0.638 | l = −19→15 |
4846 measured reflections |
Refinement on F2 | 0 restraints |
Least-squares matrix: full | Primary atom site location: structure-invariant direct methods |
R[F2 > 2σ(F2)] = 0.033 | Secondary 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 reflections | Δρmax = 1.64 e Å−3 |
100 parameters | Δρmin = −1.92 e Å−3 |
KCdB3O6 | V = 1139.92 (17) Å3 |
Mr = 279.93 | Z = 8 |
Monoclinic, C2/c | Mo Kα radiation |
a = 7.1779 (6) Å | µ = 4.52 mm−1 |
b = 13.2152 (12) Å | T = 298 K |
c = 12.5113 (11) Å | 0.3 × 0.2 × 0.1 mm |
β = 106.156 (2)° |
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 = 0.638 | Rint = 0.061 |
4846 measured reflections |
R[F2 > 2σ(F2)] = 0.033 | 100 parameters |
wR(F2) = 0.093 | 0 restraints |
S = 1.20 | Δρmax = 1.64 e Å−3 |
2082 reflections | Δρmin = −1.92 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 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. |
x | y | z | Uiso*/Ueq | ||
Cd1 | 0.55106 (3) | 0.073621 (15) | 0.122180 (16) | 0.01587 (9) | |
K1 | 0.07529 (10) | 0.24208 (6) | 0.13130 (5) | 0.02436 (14) | |
O6 | 0.1536 (3) | 0.43495 (16) | 0.0603 (2) | 0.0184 (4) | |
O2 | 0.7426 (3) | 0.38894 (16) | 0.1640 (2) | 0.0228 (4) | |
O3 | 0.4222 (3) | 0.32457 (16) | 0.08760 (19) | 0.0200 (4) | |
O4 | 0.7915 (4) | 0.56694 (15) | 0.1849 (2) | 0.0186 (4) | |
O5 | 0.4726 (3) | 0.50198 (16) | 0.12099 (19) | 0.0211 (4) | |
O1 | 0.6977 (3) | 0.21555 (16) | 0.1260 (2) | 0.0237 (4) | |
B1 | 0.6220 (4) | 0.3059 (2) | 0.1259 (2) | 0.0160 (5) | |
B2 | 0.6727 (5) | 0.4879 (2) | 0.1572 (3) | 0.0168 (5) | |
B3 | 0.3451 (5) | 0.4216 (2) | 0.0884 (3) | 0.0153 (5) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Cd1 | 0.01452 (13) | 0.01344 (12) | 0.01853 (13) | −0.00048 (5) | 0.00275 (8) | −0.00168 (5) |
K1 | 0.0204 (3) | 0.0273 (3) | 0.0253 (3) | −0.0004 (2) | 0.0062 (2) | 0.0009 (2) |
O6 | 0.0141 (9) | 0.0184 (9) | 0.0204 (10) | 0.0025 (7) | 0.0009 (7) | −0.0037 (7) |
O2 | 0.0123 (8) | 0.0142 (9) | 0.0375 (12) | −0.0011 (7) | −0.0003 (8) | −0.0026 (8) |
O3 | 0.0114 (8) | 0.0142 (8) | 0.0311 (10) | 0.0002 (7) | 0.0007 (7) | −0.0032 (7) |
O4 | 0.0165 (10) | 0.0153 (9) | 0.0234 (10) | −0.0042 (6) | 0.0046 (8) | −0.0023 (7) |
O5 | 0.0150 (9) | 0.0134 (8) | 0.0320 (11) | 0.0000 (7) | 0.0016 (8) | −0.0041 (8) |
O1 | 0.0158 (9) | 0.0118 (9) | 0.0429 (13) | 0.0003 (7) | 0.0069 (9) | 0.0020 (8) |
B1 | 0.0129 (11) | 0.0146 (11) | 0.0182 (12) | −0.0002 (9) | 0.0006 (9) | 0.0011 (9) |
B2 | 0.0159 (12) | 0.0154 (11) | 0.0178 (12) | −0.0011 (9) | 0.0025 (10) | −0.0021 (10) |
B3 | 0.0126 (13) | 0.0152 (12) | 0.0155 (13) | 0.0020 (8) | −0.0006 (10) | −0.0022 (8) |
Cd1—O1 | 2.145 (2) | K1—O1v | 3.040 (3) |
Cd1—O6i | 2.195 (2) | K1—O2v | 3.189 (3) |
Cd1—O4ii | 2.216 (2) | K1—O2vi | 3.191 (2) |
Cd1—O6iii | 2.349 (2) | K1—B1iii | 3.197 (3) |
Cd1—O4iv | 2.364 (2) | K1—B3 | 3.200 (3) |
O1—B1 | 1.312 (4) | K1—O5ii | 3.252 (2) |
O2—B1 | 1.397 (4) | K1—B1v | 3.315 (3) |
O3—B1 | 1.402 (4) | O6—Cd1vii | 2.195 (2) |
O2—B2 | 1.395 (4) | O6—Cd1iii | 2.349 (2) |
O4—B2 | 1.332 (4) | O2—K1v | 3.189 (3) |
O5—B2 | 1.393 (4) | O2—K1viii | 3.191 (2) |
O3—B3 | 1.397 (3) | O3—K1iii | 2.882 (2) |
O5—B3 | 1.388 (4) | O4—Cd1ix | 2.216 (2) |
O6—B3 | 1.332 (4) | O4—Cd1x | 2.364 (2) |
Cd1—Cd1v | 3.4744 (5) | O4—K1ix | 2.763 (2) |
Cd1—K1iii | 3.9001 (8) | O5—K1ix | 3.252 (2) |
Cd1—K1 | 4.1046 (8) | O1—K1viii | 2.715 (2) |
Cd1—K1v | 4.1302 (8) | O1—K1v | 3.040 (3) |
K1—O1vi | 2.715 (2) | O1—K1iii | 3.318 (3) |
K1—O4ii | 2.763 (2) | B1—K1iii | 3.197 (3) |
K1—O6 | 2.807 (2) | B1—K1v | 3.315 (3) |
K1—O3iii | 2.882 (2) | B1—K1viii | 3.343 (3) |
K1—O3 | 2.906 (2) | B2—K1ix | 3.428 (3) |
O1—Cd1—O6i | 121.83 (9) | O6—K1—O5ii | 159.48 (7) |
O1—Cd1—O4ii | 118.86 (8) | O3iii—K1—O5ii | 74.06 (6) |
O6i—Cd1—O4ii | 119.30 (8) | O3—K1—O5ii | 123.72 (7) |
O1—Cd1—O6iii | 103.56 (9) | O1v—K1—O5ii | 88.83 (6) |
O6i—Cd1—O6iii | 78.30 (9) | O2v—K1—O5ii | 131.56 (6) |
O4ii—Cd1—O6iii | 88.99 (9) | O2vi—K1—O5ii | 115.42 (6) |
O1—Cd1—O4iv | 85.27 (9) | B1iii—K1—O5ii | 74.60 (7) |
O6i—Cd1—O4iv | 102.53 (8) | B3—K1—O5ii | 149.04 (7) |
O4ii—Cd1—O4iv | 81.20 (10) | O1vi—K1—B1v | 116.76 (8) |
O6iii—Cd1—O4iv | 169.19 (9) | O4ii—K1—B1v | 79.04 (7) |
O1—Cd1—Cd1v | 101.96 (7) | O6—K1—B1v | 85.47 (7) |
O6i—Cd1—Cd1v | 120.14 (6) | O3iii—K1—B1v | 140.62 (7) |
O4ii—Cd1—Cd1v | 42.28 (6) | O3—K1—B1v | 72.52 (7) |
O6iii—Cd1—Cd1v | 131.27 (6) | O1v—K1—B1v | 23.31 (6) |
O4iv—Cd1—Cd1v | 39.09 (6) | O2v—K1—B1v | 24.70 (6) |
O1—Cd1—K1iii | 58.25 (7) | O2vi—K1—B1v | 92.90 (7) |
O6i—Cd1—K1iii | 105.04 (6) | B1iii—K1—B1v | 165.14 (11) |
O4ii—Cd1—K1iii | 106.55 (6) | B3—K1—B1v | 72.07 (8) |
O6iii—Cd1—K1iii | 45.47 (6) | O5ii—K1—B1v | 111.60 (7) |
O4iv—Cd1—K1iii | 142.20 (5) | B3—O6—Cd1vii | 116.11 (18) |
Cd1v—Cd1—K1iii | 133.442 (12) | B3—O6—Cd1iii | 124.8 (2) |
O1—Cd1—K1 | 86.11 (6) | Cd1vii—O6—Cd1iii | 101.70 (9) |
O6i—Cd1—K1 | 145.69 (6) | B3—O6—K1 | 94.50 (17) |
O4ii—Cd1—K1 | 39.07 (6) | Cd1vii—O6—K1 | 122.01 (10) |
O6iii—Cd1—K1 | 75.69 (6) | Cd1iii—O6—K1 | 97.91 (8) |
O4iv—Cd1—K1 | 99.03 (6) | B2—O2—B1 | 122.5 (2) |
Cd1v—Cd1—K1 | 65.427 (10) | B2—O2—K1v | 132.82 (18) |
K1iii—Cd1—K1 | 71.147 (16) | B1—O2—K1v | 82.71 (16) |
O1—Cd1—K1v | 45.51 (7) | B2—O2—K1viii | 146.30 (19) |
O6i—Cd1—K1v | 120.11 (6) | B1—O2—K1viii | 83.86 (16) |
O4ii—Cd1—K1v | 101.08 (6) | K1v—O2—K1viii | 65.09 (5) |
O6iii—Cd1—K1v | 148.48 (6) | B3—O3—B1 | 121.9 (2) |
O4iv—Cd1—K1v | 39.77 (5) | B3—O3—K1iii | 113.25 (18) |
Cd1v—Cd1—K1v | 64.662 (12) | B1—O3—K1iii | 89.67 (16) |
K1iii—Cd1—K1v | 103.084 (9) | B3—O3—K1 | 88.92 (17) |
K1—Cd1—K1v | 93.40 (2) | B1—O3—K1 | 135.95 (18) |
O1vi—K1—O4ii | 112.77 (7) | K1iii—O3—K1 | 107.25 (7) |
O1vi—K1—O6 | 113.33 (7) | B2—O4—Cd1ix | 118.67 (19) |
O4ii—K1—O6 | 133.55 (7) | B2—O4—Cd1x | 112.61 (19) |
O1vi—K1—O3iii | 101.99 (7) | Cd1ix—O4—Cd1x | 98.63 (9) |
O4ii—K1—O3iii | 79.82 (7) | B2—O4—K1ix | 108.5 (2) |
O6—K1—O3iii | 85.52 (7) | Cd1ix—O4—K1ix | 110.57 (8) |
O1vi—K1—O3 | 161.01 (7) | Cd1x—O4—K1ix | 107.05 (8) |
O4ii—K1—O3 | 84.68 (7) | B3—O5—B2 | 122.0 (2) |
O6—K1—O3 | 48.87 (6) | B3—O5—K1ix | 151.95 (18) |
O3iii—K1—O3 | 72.75 (7) | B2—O5—K1ix | 85.17 (16) |
O1vi—K1—O1v | 105.26 (6) | B1—O1—Cd1 | 126.55 (19) |
O4ii—K1—O1v | 63.39 (7) | B1—O1—K1viii | 107.02 (18) |
O6—K1—O1v | 108.78 (7) | Cd1—O1—K1viii | 126.43 (10) |
O3iii—K1—O1v | 140.40 (7) | B1—O1—K1v | 90.19 (18) |
O3—K1—O1v | 88.97 (7) | Cd1—O1—K1v | 104.28 (9) |
O1vi—K1—O2v | 106.34 (7) | K1viii—O1—K1v | 72.96 (6) |
O4ii—K1—O2v | 103.75 (7) | B1—O1—K1iii | 73.27 (17) |
O6—K1—O2v | 68.17 (7) | Cd1—O1—K1iii | 88.40 (8) |
O3iii—K1—O2v | 147.09 (7) | K1viii—O1—K1iii | 108.53 (8) |
O3—K1—O2v | 75.02 (6) | K1v—O1—K1iii | 163.20 (8) |
O1v—K1—O2v | 44.13 (6) | O1—B1—O2 | 119.8 (3) |
O1vi—K1—O2vi | 45.90 (6) | O1—B1—O3 | 123.0 (3) |
O4ii—K1—O2vi | 150.23 (7) | O2—B1—O3 | 117.2 (2) |
O6—K1—O2vi | 73.22 (7) | O1—B1—K1iii | 83.59 (18) |
O3iii—K1—O2vi | 120.72 (7) | O2—B1—K1iii | 123.97 (19) |
O3—K1—O2vi | 120.46 (6) | O3—B1—K1iii | 64.32 (14) |
O1v—K1—O2vi | 98.87 (7) | O1—B1—K1v | 66.50 (17) |
O2v—K1—O2vi | 71.39 (7) | O2—B1—K1v | 72.58 (15) |
O1vi—K1—B1iii | 77.90 (8) | O3—B1—K1v | 134.83 (19) |
O4ii—K1—B1iii | 98.04 (8) | K1iii—B1—K1v | 149.95 (11) |
O6—K1—B1iii | 86.18 (7) | O1—B1—K1viii | 50.95 (14) |
O3iii—K1—B1iii | 26.01 (7) | O2—B1—K1viii | 71.60 (15) |
O3—K1—B1iii | 92.75 (7) | O3—B1—K1viii | 161.6 (2) |
O1v—K1—B1iii | 161.13 (7) | K1iii—B1—K1viii | 97.27 (8) |
O2v—K1—B1iii | 153.71 (7) | K1v—B1—K1viii | 62.05 (6) |
O2vi—K1—B1iii | 96.44 (7) | O4—B2—O5 | 120.5 (3) |
O1vi—K1—B3 | 137.57 (8) | O4—B2—O2 | 121.7 (3) |
O4ii—K1—B3 | 109.65 (8) | O5—B2—O2 | 117.8 (2) |
O6—K1—B3 | 24.52 (7) | O4—B2—K1ix | 49.85 (16) |
O3iii—K1—B3 | 84.44 (7) | O5—B2—K1ix | 70.95 (15) |
O3—K1—B3 | 25.88 (7) | O2—B2—K1ix | 170.0 (2) |
O1v—K1—B3 | 94.11 (7) | O6—B3—O5 | 121.6 (2) |
O2v—K1—B3 | 63.35 (7) | O6—B3—O3 | 120.1 (3) |
O2vi—K1—B3 | 94.59 (7) | O5—B3—O3 | 118.3 (3) |
B1iii—K1—B3 | 95.61 (8) | O6—B3—K1 | 60.98 (16) |
O1vi—K1—O5ii | 70.09 (6) | O5—B3—K1 | 154.0 (2) |
O4ii—K1—O5ii | 45.43 (6) | O3—B3—K1 | 65.20 (15) |
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; (v) −x+1, y, −z+1/2; (vi) x−1, y, z; (vii) x−1/2, 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 formula | KCdB3O6 |
Mr | 279.93 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 298 |
a, b, c (Å) | 7.1779 (6), 13.2152 (12), 12.5113 (11) |
β (°) | 106.156 (2) |
V (Å3) | 1139.92 (17) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 4.52 |
Crystal size (mm) | 0.3 × 0.2 × 0.1 |
Data collection | |
Diffractometer | Bruker SMART APEX CCD diffractometer |
Absorption correction | Multi-scan (SADABS; Bruker, 2001) |
Tmin, Tmax | 0.289, 0.638 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 4846, 2082, 2052 |
Rint | 0.061 |
(sin θ/λ)max (Å−1) | 0.775 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.033, 0.093, 1.20 |
No. of reflections | 2082 |
No. of parameters | 100 |
Δρmax, Δρmin (e Å−3) | 1.64, −1.92 |
Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009), publCIF (Westrip, 2008).
O1—B1 | 1.312 (4) | O5—B2 | 1.393 (4) |
O2—B1 | 1.397 (4) | O3—B3 | 1.397 (3) |
O3—B1 | 1.402 (4) | O5—B3 | 1.388 (4) |
O2—B2 | 1.395 (4) | O6—B3 | 1.332 (4) |
O4—B2 | 1.332 (4) | ||
O1—Cd1—O6i | 121.83 (9) | O4ii—Cd1—O6iii | 88.99 (9) |
O1—Cd1—O4ii | 118.86 (8) | O1—Cd1—O4iv | 85.27 (9) |
O6i—Cd1—O4ii | 119.30 (8) | O6i—Cd1—O4iv | 102.53 (8) |
O1—Cd1—O6iii | 103.56 (9) | O4ii—Cd1—O4iv | 81.20 (10) |
O6i—Cd1—O6iii | 78.30 (9) | O6iii—Cd1—O4iv | 169.19 (9) |
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. |
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.