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The structure of dipotassium strontium hexaniobium octadeca­chloride is based on [Nb6Cli12Cla6]4- units (i and a denote `inner' and `outer' ligands, respectively), which have crystallographically imposed \bar3 symmetry, linked together by K+ and Sr2+ cations. The K+ cation occupies a tetrahedral site in the face-centered cubic lattice of cluster units, and is bonded to 12 Cl ligands. The Sr atom is located in an octahedral site and is bonded to six outer Cl ligands.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010200687X/br1367sup1.cif
Contains datablocks K2SrNb6Cl18, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010200687X/br1367Isup2.hkl
Contains datablock I

Comment top

A large number of metal-rich niobium halides with [Nb6Cl18]n--type cluster units have been previously crystallized using a variety of metal cations, for instance, ARENb6Cl18 (where A is an alkali and RE is a rare earth element; Ihmaine et al., 1989) and ATiNb6Cl18 (A is an alkali or group 13 element; Nagele et al., 2000). Recently, Pb was used to prepare the cluster compound Cs2PbNb6Cl18 (Gulo et al., 2001).

In this paper, we describe the structure of the new cluster compound dipotassium strontium hexaniobium octadecachloride, K2SrNb6Cl18, crystallized using Sr2+. The new compound crystallizes in the trigonal space group R3. The structure is based on discrete anionic cluster units, [(Nb6Cli12)Cla6]4- (where i and a denote `inner' and `outer' ligands, respectively). The cluster unit consists of an Nb6 octahedron in which all edges are bridged by chlorines, and six other ligands are in apical positions (Fig.1). The Nb—Cl bond lengths [Nb—Cli = 2.4497 (11)–2.4636 (11) Å and Nb—Cla = 2.5982 (11) Å] are typical for Nb6Cl18 clusters. The Nb—Nb bond lengths [2.9237 (6)–2.9309 (7) Å] indicate that the VEC of the cluster core is 16. The three-dimensional structure of the title compound is based on the cluster units interlinked together by K+ and Sr2+ cations to form cluster layers. The cluster layers are arranged according to face-centred cubic stacking along the c axis (Fig. 2). The K+ ions occupy tetrahedral sites between the units and are bonded to 12 Cl ligands, with K—Cl distances in the range 3.2648 (12)–3.6182 (11) Å. The Sr2+ ions are located in octahedral sites between the units, and are bonded to six Cl ligands in a perfect octahedral geometry, with Sr—Cl distances of 2.8954 (11) Å.

The quaternary chloride compound K2SrNb6Cl18 is isostructural with Cs2PbNb6Cl18 (Gulo et al., 2001), Cs2PbTa6Cl18 (Cordier et al., 1999) and KGdNb6Cl18 (Ihmaine et al., 1987). The alkali site, only half occupied in KGdNb6Cl18, is in contrast to the fully occupied site in the title compound. In order to obtain 16 VEC per cluster the substitution of the trivalent gadolinium by the divalent strontium is compensated by the presence of two K atoms, as is the case in Cs2PbNb6Cl18.

Experimental top

The title compound, K2SrNb6Cl18, was initially obtained as black shiny gem-like crystals from a reaction proposed to yield an oxychloride compound of composition KSr3Nb6Cl10O6. Then, the compound was prepared quantitatively from a stoichiometric mixture containing NbCl5 (Alfa, 99.8%), Nb powder (Alfa 99.8%), SrCl2 (Alfa 99.8%) and KCl (Alfa, 99.99%). The mixture was handled under an argon atmosphere and the reaction was performed in a sealed quartz tube at 1023 K over a period of 7 d. The heating and cooling ramps were 20 and 10 K h-1, respectively. The crystals obtained were between 0.1 and 0.4 mm in size, stable in air, and dark green in color when ground.

Computing details top

Data collection: XSCANS (Bruker, 1996); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 1997a); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997b); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997b).

Figures top
[Figure 1] Fig. 1. The chloride cluster anion [Nb6Cli12Cla6]4- present in K2SrNb6Cl18 (i and a denote `inner' and `outer' ligands, respectively).
[Figure 2] Fig. 2. Projection of the crystal structure of K2SrNb6Cl18 in the [110] direction.
Dipotassium strontium hexaniobium octadecachloride top
Crystal data top
K2SrNb6Cl18Dx = 3.488 Mg m3
Mr = 1361.4Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3Cell parameters from 34 reflections
Hall symbol: -R 3θ = 2.7–12.5°
a = 9.3025 (8) ŵ = 6.77 mm1
c = 25.9412 (18) ÅT = 273 K
V = 1944.1 (3) Å3Truncated cuboctahedron, black
Z = 30.25 × 0.22 × 0.20 mm
F(000) = 1884
Data collection top
Bruker P4
diffractometer
1072 reflections with I > 2σ(I)
Radiation source: normal-focus sealed tubeRint = 0.035
Graphite monochromatorθmax = 30.2°, θmin = 2.4°
ω scansh = 1212
Absorption correction: empirical (using intensity measurements)
via ψ scan (North et al., 1968)
k = 1313
Tmin = 0.554, Tmax = 0.923l = 3636
2837 measured reflections3 standard reflections every 297 reflections
1288 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)] = 0.031 w = 1/[σ2(Fo2) + (0.0431P)2]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.073(Δ/σ)max < 0.001
S = 0.90Δρmax = 0.76 e Å3
1288 reflectionsΔρmin = 0.75 e Å3
43 parametersExtinction correction: SHELXL (Sheldrick, 1997a), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.00170 (11)
Crystal data top
K2SrNb6Cl18Z = 3
Mr = 1361.4Mo Kα radiation
Trigonal, R3µ = 6.77 mm1
a = 9.3025 (8) ÅT = 273 K
c = 25.9412 (18) Å0.25 × 0.22 × 0.20 mm
V = 1944.1 (3) Å3
Data collection top
Bruker P4
diffractometer
1072 reflections with I > 2σ(I)
Absorption correction: empirical (using intensity measurements)
via ψ scan (North et al., 1968)
Rint = 0.035
Tmin = 0.554, Tmax = 0.9233 standard reflections every 297 reflections
2837 measured reflections intensity decay: none
1288 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.03143 parameters
wR(F2) = 0.0730 restraints
S = 0.90Δρmax = 0.76 e Å3
1288 reflectionsΔρmin = 0.75 e Å3
Special details top

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
Nb0.16564 (4)0.19468 (4)0.045953 (14)0.00999 (12)
Sr0.33330.66670.16670.0152 (2)
Cl10.42185 (12)0.26214 (13)0.00009 (4)0.0164 (2)
Cl20.22717 (13)0.03393 (13)0.10867 (4)0.0164 (2)
Cl30.37873 (13)0.43532 (13)0.10374 (4)0.0194 (2)
K0.66670.33330.11171 (10)0.0403 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Nb0.01050 (18)0.01012 (19)0.00911 (18)0.00498 (14)0.00058 (12)0.00084 (12)
Sr0.0153 (3)0.0153 (3)0.0148 (5)0.00766 (15)0.0000.000
Cl10.0106 (4)0.0170 (5)0.0174 (5)0.0038 (4)0.0009 (4)0.0026 (4)
Cl20.0190 (5)0.0154 (5)0.0142 (4)0.0082 (4)0.0061 (4)0.0007 (4)
Cl30.0192 (5)0.0172 (5)0.0193 (5)0.0074 (4)0.0042 (4)0.0070 (4)
K0.0377 (8)0.0377 (8)0.0454 (14)0.0189 (4)0.0000.000
Geometric parameters (Å, º) top
Nb—Cl1i2.4497 (11)Cl1—Nbiii2.4497 (11)
Nb—Cl12.4505 (11)Cl1—K3.539 (2)
Nb—Cl22.4631 (11)Cl2—Nbiv2.4635 (11)
Nb—Cl2ii2.4635 (11)Cl2—Kx3.533 (2)
Nb—Cl32.5982 (11)Cl2—K3.6182 (11)
Nb—Nbi2.9237 (6)Cl3—K3.2648 (12)
Nb—Nbiii2.9237 (6)K—Cl3xi3.2648 (12)
Nb—Nbii2.9309 (7)K—Cl3xii3.2648 (12)
Nb—Nbiv2.9309 (7)K—Cl2xiii3.533 (2)
Sr—Cl3v2.8954 (11)K—Cl2vii3.533 (2)
Sr—Cl3vi2.8954 (11)K—Cl2x3.533 (2)
Sr—Cl3vii2.8954 (11)K—Cl1xii3.539 (2)
Sr—Cl32.8954 (11)K—Cl1xi3.539 (2)
Sr—Cl3viii2.8954 (11)K—Cl2xii3.6182 (11)
Sr—Cl3ix2.8954 (11)K—Cl2xi3.6182 (11)
Cl1i—Nb—Cl188.905 (13)Cl3—K—Cl2xiii119.69 (6)
Cl1i—Nb—Cl2163.11 (4)Cl3xi—K—Cl2vii62.45 (3)
Cl1—Nb—Cl289.19 (4)Cl3xii—K—Cl2vii119.69 (6)
Cl1i—Nb—Cl2ii89.05 (4)Cl3—K—Cl2vii97.16 (5)
Cl1—Nb—Cl2ii163.15 (4)Cl2xiii—K—Cl2vii57.89 (5)
Cl2—Nb—Cl2ii87.92 (5)Cl3xi—K—Cl2x119.69 (6)
Cl1i—Nb—Cl382.74 (4)Cl3xii—K—Cl2x97.16 (5)
Cl1—Nb—Cl380.51 (4)Cl3—K—Cl2x62.45 (3)
Cl2—Nb—Cl380.40 (4)Cl2xiii—K—Cl2x57.89 (5)
Cl2ii—Nb—Cl382.64 (4)Cl2vii—K—Cl2x57.89 (5)
Cl1i—Nb—Nbi53.38 (3)Cl3xi—K—Cl1xii86.44 (5)
Cl1—Nb—Nbi95.99 (3)Cl3xii—K—Cl1xii57.17 (3)
Cl2—Nb—Nbi143.50 (3)Cl3—K—Cl1xii116.65 (7)
Cl2ii—Nb—Nbi96.19 (3)Cl2xiii—K—Cl1xii111.26 (2)
Cl3—Nb—Nbi136.11 (3)Cl2vii—K—Cl1xii142.86 (2)
Cl1i—Nb—Nbiii96.11 (3)Cl2x—K—Cl1xii151.49 (2)
Cl1—Nb—Nbiii53.36 (3)Cl3xi—K—Cl1116.65 (7)
Cl2—Nb—Nbiii96.20 (3)Cl3xii—K—Cl186.44 (5)
Cl2ii—Nb—Nbiii143.48 (3)Cl3—K—Cl157.17 (3)
Cl3—Nb—Nbiii133.86 (3)Cl2xiii—K—Cl1142.85 (2)
Nbi—Nb—Nbiii60.165 (17)Cl2vii—K—Cl1151.49 (2)
Cl1i—Nb—Nbii95.82 (3)Cl2x—K—Cl1111.26 (2)
Cl1—Nb—Nbii143.36 (3)Cl1xii—K—Cl159.53 (5)
Cl2—Nb—Nbii95.70 (3)Cl3xi—K—Cl1xi57.17 (3)
Cl2ii—Nb—Nbii53.49 (3)Cl3xii—K—Cl1xi116.65 (7)
Cl3—Nb—Nbii136.12 (3)Cl3—K—Cl1xi86.44 (5)
Cl1i—Nb—Nbiv143.38 (3)Cl2xiii—K—Cl1xi151.49 (2)
Cl1—Nb—Nbiv95.91 (3)Cl2vii—K—Cl1xi111.26 (2)
Cl2—Nb—Nbiv53.50 (3)Cl2x—K—Cl1xi142.85 (2)
Cl2ii—Nb—Nbiv95.69 (3)Cl1xii—K—Cl1xi59.53 (5)
Cl3—Nb—Nbiv133.88 (3)Cl1—K—Cl1xi59.53 (5)
Nbi—Nb—Nbiv90.0Cl3xi—K—Cl2xii63.55 (3)
Nbiii—Nb—Nbiv59.918 (8)Cl3xii—K—Cl2xii56.42 (3)
Nbii—Nb—Nbiv60.0Cl3—K—Cl2xii173.95 (8)
Cl3v—Sr—Cl391.33 (3)Cl2xiii—K—Cl2xii63.52 (3)
Cl3vi—Sr—Cl391.33 (3)Cl2vii—K—Cl2xii88.88 (4)
Cl3vii—Sr—Cl388.67 (3)Cl2x—K—Cl2xii121.31 (6)
Cl3v—Sr—Cl3viii88.67 (3)Cl1xii—K—Cl2xii57.62 (3)
Cl3vi—Sr—Cl3viii180.0Cl1—K—Cl2xii117.00 (6)
Cl3vii—Sr—Cl3viii91.33 (3)Cl1xi—K—Cl2xii91.61 (4)
Cl3—Sr—Cl3viii88.67 (3)Cl3xi—K—Cl2173.95 (8)
Cl3v—Sr—Cl3ix88.67 (3)Cl3xii—K—Cl263.55 (3)
Cl3vi—Sr—Cl3ix88.67 (3)Cl3—K—Cl256.42 (3)
Cl3vii—Sr—Cl3ix91.33 (3)Cl2xiii—K—Cl288.88 (4)
Cl3—Sr—Cl3ix180.0Cl2vii—K—Cl2121.31 (6)
Cl3viii—Sr—Cl3ix91.33 (3)Cl2x—K—Cl263.52 (3)
Nbiii—Cl1—Nb73.26 (3)Cl1xii—K—Cl291.61 (4)
Nbiii—Cl1—K138.87 (4)Cl1—K—Cl257.62 (3)
Nb—Cl1—K95.80 (4)Cl1xi—K—Cl2117.00 (6)
Nb—Cl2—Kx106.97 (4)Cl2xii—K—Cl2119.953 (4)
Nbiv—Cl2—Kx106.96 (4)Cl3xi—K—Cl2xi56.42 (3)
Nb—Cl2—K93.62 (4)Cl3xii—K—Cl2xi173.95 (8)
Nbiv—Cl2—K136.56 (6)Cl3—K—Cl2xi63.55 (3)
Kx—Cl2—K116.48 (3)Cl2xiii—K—Cl2xi121.31 (6)
Nb—Cl3—Sr129.32 (4)Cl2vii—K—Cl2xi63.52 (3)
Nb—Cl3—K99.76 (4)Cl2x—K—Cl2xi88.88 (4)
Sr—Cl3—K128.76 (5)Cl1xii—K—Cl2xi117.00 (6)
Cl3xi—K—Cl3xii119.603 (11)Cl1—K—Cl2xi91.61 (4)
Cl3xi—K—Cl3119.603 (11)Cl1xi—K—Cl2xi57.62 (3)
Cl3xii—K—Cl3119.603 (11)Cl2xii—K—Cl2xi119.953 (4)
Cl3xi—K—Cl2xiii97.16 (5)Cl2—K—Cl2xi119.953 (4)
Cl3xii—K—Cl2xiii62.45 (3)
Symmetry codes: (i) xy, x, z; (ii) y, xy, z; (iii) y, x+y, z; (iv) x+y, x, z; (v) x+y, x+1, z; (vi) y+1, xy+1, z; (vii) xy+2/3, x+1/3, z+1/3; (viii) y1/3, x+y+1/3, z+1/3; (ix) x+2/3, y+4/3, z+1/3; (x) x+2/3, y+1/3, z+1/3; (xi) x+y+1, x+1, z; (xii) y+1, xy, z; (xiii) y+2/3, x+y+1/3, z+1/3.

Experimental details

Crystal data
Chemical formulaK2SrNb6Cl18
Mr1361.4
Crystal system, space groupTrigonal, R3
Temperature (K)273
a, c (Å)9.3025 (8), 25.9412 (18)
V3)1944.1 (3)
Z3
Radiation typeMo Kα
µ (mm1)6.77
Crystal size (mm)0.25 × 0.22 × 0.20
Data collection
DiffractometerBruker P4
diffractometer
Absorption correctionEmpirical (using intensity measurements)
via ψ scan (North et al., 1968)
Tmin, Tmax0.554, 0.923
No. of measured, independent and
observed [I > 2σ(I)] reflections
2837, 1288, 1072
Rint0.035
(sin θ/λ)max1)0.708
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.031, 0.073, 0.90
No. of reflections1288
No. of parameters43
Δρmax, Δρmin (e Å3)0.76, 0.75

Computer programs: XSCANS (Bruker, 1996), XSCANS, SHELXTL (Sheldrick, 1997a), SHELXS97 (Sheldrick, 1997b), SHELXL97 (Sheldrick, 1997b).

Selected bond lengths (Å) top
Nb—Cl1i2.4497 (11)Nb—Nbii2.9309 (7)
Nb—Cl12.4505 (11)Sr—Cl3iii2.8954 (11)
Nb—Cl22.4631 (11)K—Cl3iv3.2648 (12)
Nb—Cl2ii2.4635 (11)K—Cl2v3.533 (2)
Nb—Cl32.5982 (11)K—Cl1vi3.539 (2)
Nb—Nbi2.9237 (6)K—Cl2vi3.6182 (11)
Symmetry codes: (i) xy, x, z; (ii) y, xy, z; (iii) x+y, x+1, z; (iv) x+y+1, x+1, z; (v) y+2/3, x+y+1/3, z+1/3; (vi) y+1, xy, z.
 

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