Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010200687X/br1367sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S010827010200687X/br1367Isup2.hkl |
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.
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).
K2SrNb6Cl18 | Dx = 3.488 Mg m−3 |
Mr = 1361.4 | Mo Kα radiation, λ = 0.71073 Å |
Trigonal, R3 | Cell parameters from 34 reflections |
Hall symbol: -R 3 | θ = 2.7–12.5° |
a = 9.3025 (8) Å | µ = 6.77 mm−1 |
c = 25.9412 (18) Å | T = 273 K |
V = 1944.1 (3) Å3 | Truncated cuboctahedron, black |
Z = 3 | 0.25 × 0.22 × 0.20 mm |
F(000) = 1884 |
Bruker P4 diffractometer | 1072 reflections with I > 2σ(I) |
Radiation source: normal-focus sealed tube | Rint = 0.035 |
Graphite monochromator | θmax = 30.2°, θmin = 2.4° |
ω scans | h = −12→12 |
Absorption correction: empirical (using intensity measurements) via ψ scan (North et al., 1968) | k = −13→13 |
Tmin = 0.554, Tmax = 0.923 | l = −36→36 |
2837 measured reflections | 3 standard reflections every 297 reflections |
1288 independent reflections | intensity decay: none |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary 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 = 0.90 | Δρmax = 0.76 e Å−3 |
1288 reflections | Δρmin = −0.75 e Å−3 |
43 parameters | Extinction correction: SHELXL (Sheldrick, 1997a), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.00170 (11) |
K2SrNb6Cl18 | Z = 3 |
Mr = 1361.4 | Mo Kα radiation |
Trigonal, R3 | µ = 6.77 mm−1 |
a = 9.3025 (8) Å | T = 273 K |
c = 25.9412 (18) Å | 0.25 × 0.22 × 0.20 mm |
V = 1944.1 (3) Å3 |
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 = 0.923 | 3 standard reflections every 297 reflections |
2837 measured reflections | intensity decay: none |
1288 independent reflections |
R[F2 > 2σ(F2)] = 0.031 | 43 parameters |
wR(F2) = 0.073 | 0 restraints |
S = 0.90 | Δρmax = 0.76 e Å−3 |
1288 reflections | Δρmin = −0.75 e Å−3 |
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. |
x | y | z | Uiso*/Ueq | ||
Nb | 0.16564 (4) | 0.19468 (4) | 0.045953 (14) | 0.00999 (12) | |
Sr | 0.3333 | 0.6667 | 0.1667 | 0.0152 (2) | |
Cl1 | 0.42185 (12) | 0.26214 (13) | −0.00009 (4) | 0.0164 (2) | |
Cl2 | 0.22717 (13) | 0.03393 (13) | 0.10867 (4) | 0.0164 (2) | |
Cl3 | 0.37873 (13) | 0.43532 (13) | 0.10374 (4) | 0.0194 (2) | |
K | 0.6667 | 0.3333 | 0.11171 (10) | 0.0403 (5) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Nb | 0.01050 (18) | 0.01012 (19) | 0.00911 (18) | 0.00498 (14) | −0.00058 (12) | −0.00084 (12) |
Sr | 0.0153 (3) | 0.0153 (3) | 0.0148 (5) | 0.00766 (15) | 0.000 | 0.000 |
Cl1 | 0.0106 (4) | 0.0170 (5) | 0.0174 (5) | 0.0038 (4) | 0.0009 (4) | −0.0026 (4) |
Cl2 | 0.0190 (5) | 0.0154 (5) | 0.0142 (4) | 0.0082 (4) | −0.0061 (4) | −0.0007 (4) |
Cl3 | 0.0192 (5) | 0.0172 (5) | 0.0193 (5) | 0.0074 (4) | −0.0042 (4) | −0.0070 (4) |
K | 0.0377 (8) | 0.0377 (8) | 0.0454 (14) | 0.0189 (4) | 0.000 | 0.000 |
Nb—Cl1i | 2.4497 (11) | Cl1—Nbiii | 2.4497 (11) |
Nb—Cl1 | 2.4505 (11) | Cl1—K | 3.539 (2) |
Nb—Cl2 | 2.4631 (11) | Cl2—Nbiv | 2.4635 (11) |
Nb—Cl2ii | 2.4635 (11) | Cl2—Kx | 3.533 (2) |
Nb—Cl3 | 2.5982 (11) | Cl2—K | 3.6182 (11) |
Nb—Nbi | 2.9237 (6) | Cl3—K | 3.2648 (12) |
Nb—Nbiii | 2.9237 (6) | K—Cl3xi | 3.2648 (12) |
Nb—Nbii | 2.9309 (7) | K—Cl3xii | 3.2648 (12) |
Nb—Nbiv | 2.9309 (7) | K—Cl2xiii | 3.533 (2) |
Sr—Cl3v | 2.8954 (11) | K—Cl2vii | 3.533 (2) |
Sr—Cl3vi | 2.8954 (11) | K—Cl2x | 3.533 (2) |
Sr—Cl3vii | 2.8954 (11) | K—Cl1xii | 3.539 (2) |
Sr—Cl3 | 2.8954 (11) | K—Cl1xi | 3.539 (2) |
Sr—Cl3viii | 2.8954 (11) | K—Cl2xii | 3.6182 (11) |
Sr—Cl3ix | 2.8954 (11) | K—Cl2xi | 3.6182 (11) |
Cl1i—Nb—Cl1 | 88.905 (13) | Cl3—K—Cl2xiii | 119.69 (6) |
Cl1i—Nb—Cl2 | 163.11 (4) | Cl3xi—K—Cl2vii | 62.45 (3) |
Cl1—Nb—Cl2 | 89.19 (4) | Cl3xii—K—Cl2vii | 119.69 (6) |
Cl1i—Nb—Cl2ii | 89.05 (4) | Cl3—K—Cl2vii | 97.16 (5) |
Cl1—Nb—Cl2ii | 163.15 (4) | Cl2xiii—K—Cl2vii | 57.89 (5) |
Cl2—Nb—Cl2ii | 87.92 (5) | Cl3xi—K—Cl2x | 119.69 (6) |
Cl1i—Nb—Cl3 | 82.74 (4) | Cl3xii—K—Cl2x | 97.16 (5) |
Cl1—Nb—Cl3 | 80.51 (4) | Cl3—K—Cl2x | 62.45 (3) |
Cl2—Nb—Cl3 | 80.40 (4) | Cl2xiii—K—Cl2x | 57.89 (5) |
Cl2ii—Nb—Cl3 | 82.64 (4) | Cl2vii—K—Cl2x | 57.89 (5) |
Cl1i—Nb—Nbi | 53.38 (3) | Cl3xi—K—Cl1xii | 86.44 (5) |
Cl1—Nb—Nbi | 95.99 (3) | Cl3xii—K—Cl1xii | 57.17 (3) |
Cl2—Nb—Nbi | 143.50 (3) | Cl3—K—Cl1xii | 116.65 (7) |
Cl2ii—Nb—Nbi | 96.19 (3) | Cl2xiii—K—Cl1xii | 111.26 (2) |
Cl3—Nb—Nbi | 136.11 (3) | Cl2vii—K—Cl1xii | 142.86 (2) |
Cl1i—Nb—Nbiii | 96.11 (3) | Cl2x—K—Cl1xii | 151.49 (2) |
Cl1—Nb—Nbiii | 53.36 (3) | Cl3xi—K—Cl1 | 116.65 (7) |
Cl2—Nb—Nbiii | 96.20 (3) | Cl3xii—K—Cl1 | 86.44 (5) |
Cl2ii—Nb—Nbiii | 143.48 (3) | Cl3—K—Cl1 | 57.17 (3) |
Cl3—Nb—Nbiii | 133.86 (3) | Cl2xiii—K—Cl1 | 142.85 (2) |
Nbi—Nb—Nbiii | 60.165 (17) | Cl2vii—K—Cl1 | 151.49 (2) |
Cl1i—Nb—Nbii | 95.82 (3) | Cl2x—K—Cl1 | 111.26 (2) |
Cl1—Nb—Nbii | 143.36 (3) | Cl1xii—K—Cl1 | 59.53 (5) |
Cl2—Nb—Nbii | 95.70 (3) | Cl3xi—K—Cl1xi | 57.17 (3) |
Cl2ii—Nb—Nbii | 53.49 (3) | Cl3xii—K—Cl1xi | 116.65 (7) |
Cl3—Nb—Nbii | 136.12 (3) | Cl3—K—Cl1xi | 86.44 (5) |
Cl1i—Nb—Nbiv | 143.38 (3) | Cl2xiii—K—Cl1xi | 151.49 (2) |
Cl1—Nb—Nbiv | 95.91 (3) | Cl2vii—K—Cl1xi | 111.26 (2) |
Cl2—Nb—Nbiv | 53.50 (3) | Cl2x—K—Cl1xi | 142.85 (2) |
Cl2ii—Nb—Nbiv | 95.69 (3) | Cl1xii—K—Cl1xi | 59.53 (5) |
Cl3—Nb—Nbiv | 133.88 (3) | Cl1—K—Cl1xi | 59.53 (5) |
Nbi—Nb—Nbiv | 90.0 | Cl3xi—K—Cl2xii | 63.55 (3) |
Nbiii—Nb—Nbiv | 59.918 (8) | Cl3xii—K—Cl2xii | 56.42 (3) |
Nbii—Nb—Nbiv | 60.0 | Cl3—K—Cl2xii | 173.95 (8) |
Cl3v—Sr—Cl3 | 91.33 (3) | Cl2xiii—K—Cl2xii | 63.52 (3) |
Cl3vi—Sr—Cl3 | 91.33 (3) | Cl2vii—K—Cl2xii | 88.88 (4) |
Cl3vii—Sr—Cl3 | 88.67 (3) | Cl2x—K—Cl2xii | 121.31 (6) |
Cl3v—Sr—Cl3viii | 88.67 (3) | Cl1xii—K—Cl2xii | 57.62 (3) |
Cl3vi—Sr—Cl3viii | 180.0 | Cl1—K—Cl2xii | 117.00 (6) |
Cl3vii—Sr—Cl3viii | 91.33 (3) | Cl1xi—K—Cl2xii | 91.61 (4) |
Cl3—Sr—Cl3viii | 88.67 (3) | Cl3xi—K—Cl2 | 173.95 (8) |
Cl3v—Sr—Cl3ix | 88.67 (3) | Cl3xii—K—Cl2 | 63.55 (3) |
Cl3vi—Sr—Cl3ix | 88.67 (3) | Cl3—K—Cl2 | 56.42 (3) |
Cl3vii—Sr—Cl3ix | 91.33 (3) | Cl2xiii—K—Cl2 | 88.88 (4) |
Cl3—Sr—Cl3ix | 180.0 | Cl2vii—K—Cl2 | 121.31 (6) |
Cl3viii—Sr—Cl3ix | 91.33 (3) | Cl2x—K—Cl2 | 63.52 (3) |
Nbiii—Cl1—Nb | 73.26 (3) | Cl1xii—K—Cl2 | 91.61 (4) |
Nbiii—Cl1—K | 138.87 (4) | Cl1—K—Cl2 | 57.62 (3) |
Nb—Cl1—K | 95.80 (4) | Cl1xi—K—Cl2 | 117.00 (6) |
Nb—Cl2—Kx | 106.97 (4) | Cl2xii—K—Cl2 | 119.953 (4) |
Nbiv—Cl2—Kx | 106.96 (4) | Cl3xi—K—Cl2xi | 56.42 (3) |
Nb—Cl2—K | 93.62 (4) | Cl3xii—K—Cl2xi | 173.95 (8) |
Nbiv—Cl2—K | 136.56 (6) | Cl3—K—Cl2xi | 63.55 (3) |
Kx—Cl2—K | 116.48 (3) | Cl2xiii—K—Cl2xi | 121.31 (6) |
Nb—Cl3—Sr | 129.32 (4) | Cl2vii—K—Cl2xi | 63.52 (3) |
Nb—Cl3—K | 99.76 (4) | Cl2x—K—Cl2xi | 88.88 (4) |
Sr—Cl3—K | 128.76 (5) | Cl1xii—K—Cl2xi | 117.00 (6) |
Cl3xi—K—Cl3xii | 119.603 (11) | Cl1—K—Cl2xi | 91.61 (4) |
Cl3xi—K—Cl3 | 119.603 (11) | Cl1xi—K—Cl2xi | 57.62 (3) |
Cl3xii—K—Cl3 | 119.603 (11) | Cl2xii—K—Cl2xi | 119.953 (4) |
Cl3xi—K—Cl2xiii | 97.16 (5) | Cl2—K—Cl2xi | 119.953 (4) |
Cl3xii—K—Cl2xiii | 62.45 (3) |
Symmetry codes: (i) x−y, x, −z; (ii) −y, x−y, z; (iii) y, −x+y, −z; (iv) −x+y, −x, z; (v) −x+y, −x+1, z; (vi) −y+1, x−y+1, z; (vii) x−y+2/3, x+1/3, −z+1/3; (viii) y−1/3, −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, x−y, z; (xiii) y+2/3, −x+y+1/3, −z+1/3. |
Experimental details
Crystal data | |
Chemical formula | K2SrNb6Cl18 |
Mr | 1361.4 |
Crystal system, space group | Trigonal, R3 |
Temperature (K) | 273 |
a, c (Å) | 9.3025 (8), 25.9412 (18) |
V (Å3) | 1944.1 (3) |
Z | 3 |
Radiation type | Mo Kα |
µ (mm−1) | 6.77 |
Crystal size (mm) | 0.25 × 0.22 × 0.20 |
Data collection | |
Diffractometer | Bruker P4 diffractometer |
Absorption correction | Empirical (using intensity measurements) via ψ scan (North et al., 1968) |
Tmin, Tmax | 0.554, 0.923 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 2837, 1288, 1072 |
Rint | 0.035 |
(sin θ/λ)max (Å−1) | 0.708 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.031, 0.073, 0.90 |
No. of reflections | 1288 |
No. of parameters | 43 |
Δρmax, Δρmin (e Å−3) | 0.76, −0.75 |
Computer programs: XSCANS (Bruker, 1996), XSCANS, SHELXTL (Sheldrick, 1997a), SHELXS97 (Sheldrick, 1997b), SHELXL97 (Sheldrick, 1997b).
Nb—Cl1i | 2.4497 (11) | Nb—Nbii | 2.9309 (7) |
Nb—Cl1 | 2.4505 (11) | Sr—Cl3iii | 2.8954 (11) |
Nb—Cl2 | 2.4631 (11) | K—Cl3iv | 3.2648 (12) |
Nb—Cl2ii | 2.4635 (11) | K—Cl2v | 3.533 (2) |
Nb—Cl3 | 2.5982 (11) | K—Cl1vi | 3.539 (2) |
Nb—Nbi | 2.9237 (6) | K—Cl2vi | 3.6182 (11) |
Symmetry codes: (i) x−y, x, −z; (ii) −y, x−y, 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, x−y, z. |
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.