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During an attempt to grow crystals of the nonlinear optical material Cd3Zn3B4O12 using a KBF4 flux, crystals of a new cadmium dizinc potassium borate fluoride compound, CdZn2KB2O6F, were unexpectedly isolated. The structure consists of layers constructed of distorted corner-sharing ZnO3F tetra­hedra and BO3 triangles. Both Zn and B reside on threefold rotation axes, while the F- anion is located at a site of 3.2 symmetry. The CdII (site symmetry \overline{3}) and K+ (site symmetry 3.2) ions occupy six- and nine-coordinate inter­layer sites, respectively. The BO3 triangles and ZnO3 pyramids from the ZnO3F tetra­hedra share bridging O atoms with each other to form an extended [ZnBO3] layer parallel to (001). Although these layers are similar to the [MBO3] layers seen in other compounds, they are uniquely bridged here by the Cd centres and F- anions to form a three-dimensional framework. In so doing, a series of channels is formed along the [010] direction and the K+ cations are found in these channels.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270109050069/sq3218sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270109050069/sq3218Isup2.hkl
Contains datablock I

Comment top

Recently, numerous studies have been carried out on inorganic nonlinear optical (NLO) borate crystals, which are widely used in optical communication, laser medicine and signal processing (Becker, 1998). Some fluoride borates display good NLO properties, including KBe2BO3F2 (Wu et al., 1996), Ln3(BO3)2F3 (Ln = Sm, Eu and Gd) (Corbel et al., 1998), BaMBO3F2 (M = Ga and Al) (Park & Barbier, 2000) and ABe2BO3F2 (McMillen & Kolis, 2008). In the present work, KBF4 was added as a flux in the ternary CdO–ZnO–B2O3 system in an attempt to grow the NLO crystal Cd3Zn3B4O12 (Zhang, 2008), of interest in part due to its reported fluorescence behaviour (Harrison & Hummel, 1959). The title new fluoride borate crystal, CdZn2KB2O6F, was unexpectedly obtained and has been structurally characterized.

CdZn2KB2O6F belongs to the trigonal P31c space group and the structure consists of (001) layers formed by corner-sharing ZnO3F tetrahedra and BO3 triangles, linked by Cd atoms occupying six-coordinate interlayer sites with K atoms in interlayer channels (Fig. 1). The Zn atom is coordinated by three O atoms and an F atom to form a slightly flattened ZnO3F tetrahedron (O—Zn—O angles ~117° and O—Zn—F angles \sim 100°). The BO3 triangles are planar with ideal angles, as required by the threefold symmetry, and with B—O bonds comparable with those in other borates (Sun et al., 2003; Haberer & Huppertz, 2009).

The [BO3] triangles and [ZnO3] pyramids from the [ZnO3F] tetrahedra share bridging O atoms with each other to form an infinite [ZnBO3] layer (Fig. 2), which is related to the layers observed in crystals of Sr2Be2B2O7 (SBBO), KBe2BO3F2 (KBBF) and BaAlBO3F2 (BABF) (Becker, 1998). In the title crystal structure, the [ZnBO3] layers are distributed one upon another along the (001) direction, connected by Cd and F atoms. In SBBO, the [BO3] groups are linked through [BeO4] tetrahedra to form [Be2B2O7] layers, which are stacked in a coplanar orientation along (001) (Chen et al., 1995). In KBBF and BABF, [BO3] and [BeO3F]/[AlO3F2] sheets are very similarly stacked along (001). The layers in these crystals are essentially the same as those in CdZn2KB2O6F, with the Zn sites occupied by Be/Al atoms instead. Unlike the crystals of SBBO, KBBF and BABF, a series of CdO6 octahedra and bridging F atoms link adjacent ZnBO3 layers alternately to form a unique three-dimensional framework (Fig. 3).

Six O atoms from adjacent layers coordinate the Cd atoms to form a slightly distorted CdO6 octahedron. The F atoms are two-coordinate and bond two Zn atoms from different layers. The Zn—F bonds here make the Zn atoms deviate slightly from the BO3 layers by ~0.33 Å. The bridging Cd and F atoms together connect the [ZnBO3] layers to form a three-dimensional open framework. In this way, channels are formed along the (010) direction and the K+ cations occupy these channels. Each K+ ion is surrounded by six O atoms and three F atoms (Table 1).

The crystalline powder of CdZn2KB2O6F exhibited distinct blue photoluminescence, with emission peaks at 471 and 483 nm by excitation at 389 and 400 nm, respectively. The luminescence may be caused by the planar sandwich layers coordinated to the Cd2+ ions, which affect the charge transfer between the Cd2+ ions and the layers in a process similar to ligand-to-metal charge transfer (LMCT).

Experimental top

The precursor Cd3Zn3B4O12 was synthesized from CdO (99.8%), ZnO (99.95%) and H3BO3 (99.99%) according to the published procedure (Zhang et al., 2008). A mixture of appropriate quantities [Please give mole ratio or exact quantities] of Cd3Zn3B4O12 and KBF4 (99.0%) was ground to fine powder in a mortar and compressed into a Pt crucible. The sample was gradually heated to 1073 K and kept at this temperature for 1 d for complete melting. It was then cooled to 973 K at a rate of 1 K h-1, followed by cooling to room temperature at 20 K h-1. Colourless crystals of the title compound of millimetre dimensions could be isolated mechanically from the solidified melt for further study.

Computing details top

Data collection: XSCANS (Bruker, 1997); cell refinement: XSCANS (Bruker, 1997); data reduction: XSCANS (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The unit cell of CdZn2KB2O6F.
[Figure 2] Fig. 2. A single [ZnBO3]n layer, viewed along the c axis, showing the BO3 triangles (smaller) and ZnO3 triangles (larger) connected to each other via shared corners.
[Figure 3] Fig. 3. The extended structure of CdZn2KB2O6F, viewed along the b axis, with the CdO6 octahedra (dark, rectangular in this projection) and K atoms (large spheres) filling in the channels. The remaining polyhedra (triangular in this projection) are the [ZnO3F] tetrahedra.
cadmium dizinc potassium borate fluoride top
Crystal data top
CdZn2KB2O6FDx = 4.176 Mg m3
Mr = 418.86Mo Kα radiation, λ = 0.71073 Å
Trigonal, P31cCell parameters from 32 reflections
Hall symbol: -P 3 2cθ = 4.9–23.0°
a = 5.0381 (6) ŵ = 10.93 mm1
c = 15.1550 (19) ÅT = 295 K
V = 333.13 (7) Å3Block, colourless
Z = 20.14 × 0.1 × 0.1 mm
F(000) = 388
Data collection top
Bruker P4
diffractometer
547 reflections with I > 2σ(I)
Radiation source: sealed tubeRint = 0.053
Graphite monochromatorθmax = 37.5°, θmin = 2.7°
ω scansh = 88
Absorption correction: empirical (using intensity measurements)
(North et al., 1968)
k = 88
Tmin = 0.243, Tmax = 0.335l = 2525
2534 measured reflections3 standard reflections every 97 reflections
599 independent reflections intensity decay: none
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.037 w = 1/[σ2(Fo2) + (0.0015P)2 + 4.4689P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.083(Δ/σ)max < 0.001
S = 1.03Δρmax = 1.55 e Å3
599 reflectionsΔρmin = 2.29 e Å3
23 parametersExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0201 (17)
Crystal data top
CdZn2KB2O6FZ = 2
Mr = 418.86Mo Kα radiation
Trigonal, P31cµ = 10.93 mm1
a = 5.0381 (6) ÅT = 295 K
c = 15.1550 (19) Å0.14 × 0.1 × 0.1 mm
V = 333.13 (7) Å3
Data collection top
Bruker P4
diffractometer
547 reflections with I > 2σ(I)
Absorption correction: empirical (using intensity measurements)
(North et al., 1968)
Rint = 0.053
Tmin = 0.243, Tmax = 0.3353 standard reflections every 97 reflections
2534 measured reflections intensity decay: none
599 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.03723 parameters
wR(F2) = 0.0830 restraints
S = 1.03Δρmax = 1.55 e Å3
599 reflectionsΔρmin = 2.29 e Å3
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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
Cd10.00000.00000.50000.01415 (15)
Zn10.33330.66670.38347 (5)0.01304 (16)
K10.00001.00000.25000.0247 (4)
F10.33330.66670.25000.0320 (15)
B10.66670.33330.4055 (4)0.0145 (10)
O10.3844 (6)0.3166 (6)0.40507 (17)0.0181 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cd10.01407 (18)0.01407 (18)0.0143 (2)0.00704 (9)0.0000.000
Zn10.0119 (2)0.0119 (2)0.0153 (3)0.00596 (10)0.0000.000
K10.0266 (6)0.0266 (6)0.0209 (8)0.0133 (3)0.0000.000
F10.041 (2)0.041 (2)0.014 (2)0.0204 (12)0.0000.000
B10.0153 (15)0.0153 (15)0.013 (2)0.0077 (7)0.0000.000
O10.0146 (10)0.0176 (10)0.0234 (11)0.0090 (9)0.0023 (8)0.0037 (9)
Geometric parameters (Å, º) top
Cd1—O1i2.297 (3)K1—F12.9087 (3)
Cd1—O1ii2.297 (3)K1—O1xiii2.954 (3)
Cd1—O1iii2.297 (3)K1—O1xiv2.954 (3)
Cd1—O1iv2.297 (3)K1—O1xv2.955 (3)
Cd1—O1v2.297 (3)K1—O1xi2.955 (3)
Cd1—O12.297 (3)K1—O1xvi2.955 (3)
Cd1—K1vi3.7888 (5)K1—O1viii2.955 (3)
Cd1—K1vii3.7888 (5)K1—Zn1xi3.5430 (5)
Zn1—O1viii1.933 (3)K1—Zn1xv3.5430 (5)
Zn1—O1ix1.933 (3)F1—Zn1xvii2.0228 (7)
Zn1—O11.933 (3)F1—K1x2.9087 (3)
Zn1—F12.0228 (7)F1—K1vii2.9087 (3)
Zn1—K1vii3.5430 (5)B1—O1xviii1.382 (3)
Zn1—K13.5430 (5)B1—O11.382 (3)
Zn1—K1x3.5430 (5)B1—O1xix1.382 (3)
K1—F1xi2.9087 (3)O1—K1vii2.954 (3)
K1—F1xii2.9087 (3)
O1i—Cd1—O1ii180.000 (1)O1xiii—K1—O1xi124.25 (11)
O1i—Cd1—O1iii84.93 (10)O1xiv—K1—O1xi63.31 (8)
O1ii—Cd1—O1iii95.07 (10)O1xv—K1—O1xi168.50 (11)
O1i—Cd1—O1iv84.93 (10)F1xi—K1—O1xvi84.25 (5)
O1ii—Cd1—O1iv95.07 (10)F1xii—K1—O1xvi124.59 (5)
O1iii—Cd1—O1iv84.93 (10)F1—K1—O1xvi62.12 (5)
O1i—Cd1—O1v95.07 (10)O1xiii—K1—O1xvi63.31 (8)
O1ii—Cd1—O1v84.93 (10)O1xiv—K1—O1xvi168.51 (11)
O1iii—Cd1—O1v95.07 (10)O1xv—K1—O1xvi63.31 (8)
O1iv—Cd1—O1v180.0O1xi—K1—O1xvi110.82 (10)
O1i—Cd1—O195.08 (10)F1xi—K1—O1viii124.59 (5)
O1ii—Cd1—O184.92 (10)F1xii—K1—O1viii84.25 (5)
O1iii—Cd1—O1180.0F1—K1—O1viii62.12 (5)
O1iv—Cd1—O195.08 (10)O1xiii—K1—O1viii168.51 (11)
O1v—Cd1—O184.92 (10)O1xiv—K1—O1viii63.31 (8)
O1i—Cd1—K1vi51.22 (7)O1xv—K1—O1viii110.82 (10)
O1ii—Cd1—K1vi128.78 (7)O1xi—K1—O1viii63.31 (8)
O1iii—Cd1—K1vi51.22 (7)O1xvi—K1—O1viii124.25 (11)
O1iv—Cd1—K1vi51.22 (7)F1xi—K1—Zn1114.236 (3)
O1v—Cd1—K1vi128.78 (7)F1xii—K1—Zn1114.236 (4)
O1—Cd1—K1vi128.78 (7)F1—K1—Zn134.816 (10)
O1i—Cd1—K1vii128.78 (7)O1xiii—K1—Zn1156.96 (5)
O1ii—Cd1—K1vii51.22 (7)O1xiv—K1—Zn190.68 (5)
O1iii—Cd1—K1vii128.78 (7)O1xv—K1—Zn1111.83 (5)
O1iv—Cd1—K1vii128.78 (7)O1xi—K1—Zn157.56 (5)
O1v—Cd1—K1vii51.22 (7)O1xvi—K1—Zn194.03 (5)
O1—Cd1—K1vii51.22 (7)O1viii—K1—Zn133.07 (5)
K1vi—Cd1—K1vii180.0F1xi—K1—Zn1xi34.816 (10)
O1viii—Zn1—O1ix117.19 (5)F1xii—K1—Zn1xi114.237 (3)
O1viii—Zn1—O1117.19 (5)F1—K1—Zn1xi114.236 (3)
O1ix—Zn1—O1117.19 (5)O1xiii—K1—Zn1xi94.03 (5)
O1viii—Zn1—F199.75 (8)O1xiv—K1—Zn1xi57.56 (5)
O1ix—Zn1—F199.75 (8)O1xv—K1—Zn1xi156.96 (5)
O1—Zn1—F199.75 (8)O1xi—K1—Zn1xi33.07 (5)
O1viii—Zn1—K1vii90.12 (8)O1xvi—K1—Zn1xi111.84 (5)
O1ix—Zn1—K1vii147.13 (8)O1viii—K1—Zn1xi90.68 (5)
O1—Zn1—K1vii56.50 (8)Zn1—K1—Zn1xi90.632 (14)
F1—Zn1—K1vii55.184 (10)F1xi—K1—Zn1xv114.237 (3)
O1viii—Zn1—K156.50 (8)F1xii—K1—Zn1xv34.816 (10)
O1ix—Zn1—K190.12 (8)F1—K1—Zn1xv114.236 (3)
O1—Zn1—K1147.13 (9)O1xiii—K1—Zn1xv57.56 (5)
F1—Zn1—K155.184 (10)O1xiv—K1—Zn1xv94.03 (5)
K1vii—Zn1—K190.633 (14)O1xv—K1—Zn1xv33.07 (5)
O1viii—Zn1—K1x147.13 (8)O1xi—K1—Zn1xv156.96 (5)
O1ix—Zn1—K1x56.50 (8)O1xvi—K1—Zn1xv90.68 (5)
O1—Zn1—K1x90.12 (8)O1viii—K1—Zn1xv111.84 (5)
F1—Zn1—K1x55.184 (10)Zn1—K1—Zn1xv131.528 (6)
K1vii—Zn1—K1x90.633 (15)Zn1xi—K1—Zn1xv131.529 (6)
K1—Zn1—K1x90.633 (15)Zn1—F1—Zn1xvii180.0
F1xi—K1—F1xii120.0Zn1—F1—K190.0
F1xi—K1—F1120.0Zn1xvii—F1—K190.0
F1xii—K1—F1120.0Zn1—F1—K1x90.0
F1xi—K1—O1xiii62.13 (5)Zn1xvii—F1—K1x90.0
F1xii—K1—O1xiii84.25 (5)K1—F1—K1x120.0
F1—K1—O1xiii124.59 (5)Zn1—F1—K1vii90.0
F1xi—K1—O1xiv84.25 (5)Zn1xvii—F1—K1vii90.0
F1xii—K1—O1xiv62.13 (5)K1—F1—K1vii120.0
F1—K1—O1xiv124.59 (5)K1x—F1—K1vii120.0
O1xiii—K1—O1xiv110.82 (10)O1xviii—B1—O1119.999 (6)
F1xi—K1—O1xv124.59 (5)O1xviii—B1—O1xix119.997 (6)
F1xii—K1—O1xv62.13 (5)O1—B1—O1xix119.998 (6)
F1—K1—O1xv84.25 (5)B1—O1—Zn1123.19 (18)
O1xiii—K1—O1xv63.31 (8)B1—O1—Cd1121.6 (2)
O1xiv—K1—O1xv124.25 (11)Zn1—O1—Cd1106.79 (12)
F1xi—K1—O1xi62.13 (5)B1—O1—K1vii114.4 (3)
F1xii—K1—O1xi124.59 (5)Zn1—O1—K1vii90.43 (9)
F1—K1—O1xi84.25 (5)Cd1—O1—K1vii91.48 (9)
Symmetry codes: (i) y, x+y, z+1; (ii) y, xy, z; (iii) x, y, z+1; (iv) xy, x, z+1; (v) x+y, x, z; (vi) x, y+1, z+1; (vii) x, y1, z; (viii) x+y, x+1, z; (ix) y+1, xy+1, z; (x) x+1, y, z; (xi) x, y+1, z; (xii) x1, y, z; (xiii) x+y, y+1, z+1/2; (xiv) y, xy+1, z; (xv) y, x+1, z+1/2; (xvi) x, xy+1, z+1/2; (xvii) y+1, x+1, z+1/2; (xviii) x+y+1, x+1, z; (xix) y+1, xy, z.

Experimental details

Crystal data
Chemical formulaCdZn2KB2O6F
Mr418.86
Crystal system, space groupTrigonal, P31c
Temperature (K)295
a, c (Å)5.0381 (6), 15.1550 (19)
V3)333.13 (7)
Z2
Radiation typeMo Kα
µ (mm1)10.93
Crystal size (mm)0.14 × 0.1 × 0.1
Data collection
DiffractometerBruker P4
diffractometer
Absorption correctionEmpirical (using intensity measurements)
(North et al., 1968)
Tmin, Tmax0.243, 0.335
No. of measured, independent and
observed [I > 2σ(I)] reflections
2534, 599, 547
Rint0.053
(sin θ/λ)max1)0.856
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.037, 0.083, 1.03
No. of reflections599
No. of parameters23
Δρmax, Δρmin (e Å3)1.55, 2.29

Computer programs: XSCANS (Bruker, 1997), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Selected bond lengths (Å) top
Cd1—O12.297 (3)K1—F12.9087 (3)
Zn1—O11.933 (3)K1—O1i2.954 (3)
Zn1—F12.0228 (7)B1—O11.382 (3)
Symmetry code: (i) x+y, y+1, z+1/2.
 

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