The title compound, K5[BW12O40]·16H2O, contains a [BW12O40]5− polyanion of 222 crystallographic symmetry, with a central tetrahedrally coordinated BIII atom surrounded by four groups of three edge-sharing octahedra (W3O13 subunits), which are linked in turn to each other and to the central BO4 tetrahedron by shared O atoms at the vertices. There is a crystallographically unique B—O bond of 1.554 (10) Å, while the average W—O distances are 2.344 (17) Å for four coordinate O atoms, 1.917 (12) and 1.89 (2) Å for two coordinate O atoms within and connecting the W3O13 subunits, respectively, and 1.709 (8) Å for terminal O atoms. Not all of the K+ ions and H2O groups were located.
Supporting information
A solution of H3BO3 (1.25 g) was added to one (25 ml) of
Na2MoO4·2H2O (25.0 g) with constant stirring, followed by 6
M HCl (15 ml). The pH of the resulting solution was adjusted to 6 and
then the solution was refluxed for 24 h. The resulting precipitate of
Na10[H2W12O42].nH2O was filtered off. The pH of the filtrate was
adjusted to 2 using 6 M HCl and was again refluxed for 30 min.
Precipitation was effected by addition of KCl (5 g). The resulting product was
then isolated by filtration and redissolved in water at pH 6 using 6 M
HCl. Colourless needle-like crystals were obtained by slow evaporation of the
solvent. IR (KBr disc): 1001m, 958 s (W—O asymmetric stretch), 920 s
(B—O stretch), 906s h (W—O—W stretch), 807vs (W—O—W stretch),
507m cm-1 (W—O—W bending). Thermogravimetric analysis was used to
establish the actual water content of the bulk compound. Based on a loss of
mass of 8.75% up to 573 K, there were 16.3 water molecules per formula unit,
and so the composition was therefore close to K5[BW12O40].16H2O,
although only 8 water molecules could be established by X-ray crystallography.
The standard reflection showed a 21% loss in intensity over the data collection,
and a correction for this was applied. This may perhaps be associated with
water loss from the crystal, leading to disorder of much of the H2O
molecules (see below). The systematic absences for the compound are unique for
the space group P6222. Moreover, the compound is isomorphous and
isostructural with K5[CoIIIW12O40].16H2O (Nolan et al., 2000)
and the atomic coordinates for the heavy atoms for this structure were
therefore used for the present structure. The cations and water molecules were
subsequently found using difference-Fourier methods. Four crystallographically
unique sites containing potassium were located. One of these was fully
occupied by potassium and located along a twofold axis, while the other three
only exhibited partial occupancy by potassium together with the oxygen of a
water molecule. A similar situation has been found previously in
K5[CoIIIW12O40].16H2O. Two of these latter sites were located along
twofold axes while the third was in a general position. Based on the electron
densities at these sites, new scattering factors were constructed from those
of potassium and oxygen. These sites, OKW1, OKW2 and OKW3, had 83, 30 a nd 48%
K, with the remainder O. Upon completion of the refinement, 4.92 potassium
atoms (i.e. about the expected 5 per formula unit) and 8.08 water
molecules had been located, the latter less than the 16 water molecules per
formula unit suggested by thermogravimetric analysis. The remaining water
molecules were highly disordered and correspond, assuming a volume per water
molecule of about 40 Å3 (Peterson & Levy, 1957), to some 960 Å3 per
unit cell which are located in the interanionic voids. This assumes that the
composition of the crystal was typical of the bulk sample, with 16 water
molecules per formula unit. This remaining water is zeolitic-like in nature,
as was observed in the case of K5[CoIIIW12O40].16H2O (Nolan et
al., 2000). This study, performed on a crystal exposed to the atmosphere,
allowed the location of only 3 water molecules per formula unit. For the
related compound K6[CoIIW12O40].nH2O, a crystal was sealed in a
glass capillary to minimize efflorescence, and a subsequent X-ray study
allowed the location of 11 water molecules per formula unit, while chemical
analysis of an air-dried sample indicated only a trihydrated species
(Casañ-Pastor et al., 1991). Attempted refinement in the enantiomeric
space group P6422 gave a final R factor of 0.042 with 846 friedel
pairs not averaged, significantly higher than the 0.036 observed for P6222.
The maximum peak and minimum trough were located in the region of the W atoms,
but not in chemically significant positions.
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: local software (University of New South Wales); program(s) used to solve structure: SIR92 (Altomare, 1994); program(s) used to refine structure: RAELS (Rae, 1989); molecular graphics: ORTEPII (Johnson, 1976).
Crystal data top
K5[BW12O40](H2O)16 | Dx = 4.30 Mg m−3 |
Mr = 3340.72 | Mo Kα radiation, λ = 0.71073 Å |
Trigonal, P6222 | Cell parameters from 10 reflections |
Hall symbol: P 62 2 (0 0 -2) | θ = 9–11° |
a = 18.970 (4) Å | µ = 27.74 mm−1 |
c = 12.414 (5) Å | T = 294 K |
V = 3869 (2) Å3 | Prism, colourless |
Z = 3 | 0.34 × 0.13 × 0.10 mm |
F(000) = 4404.0 | |
Data collection top
Enraf-Nonius CAD-4 diffractometer | Rint = 0.047 |
ω–2θ scans | θmax = 25° |
Absorption correction: analytical (de Meulenaer & Tompa, 1965) | h = 0→22 |
Tmin = 0.04, Tmax = 0.11 | k = −22→0 |
5003 measured reflections | l = 0→14 |
2288 independent reflections | 1 standard reflections every 30 min |
2122 reflections with I > 3σ(I) | intensity decay: 21% |
Refinement top
Refinement on F | H-atom parameters not refined |
R[F2 > 2σ(F2)] = 0.036 | w = 1/[σ2(F) + 0.0016F2] |
wR(F2) = 0.048 | (Δ/σ)max = 0.006 |
S = 1.54 | Δρmax = 1.79 e Å−3 |
2122 reflections | Δρmin = −2.70 e Å−3 |
78 parameters | |
Crystal data top
K5[BW12O40](H2O)16 | Z = 3 |
Mr = 3340.72 | Mo Kα radiation |
Trigonal, P6222 | µ = 27.74 mm−1 |
a = 18.970 (4) Å | T = 294 K |
c = 12.414 (5) Å | 0.34 × 0.13 × 0.10 mm |
V = 3869 (2) Å3 | |
Data collection top
Enraf-Nonius CAD-4 diffractometer | 2122 reflections with I > 3σ(I) |
Absorption correction: analytical (de Meulenaer & Tompa, 1965) | Rint = 0.047 |
Tmin = 0.04, Tmax = 0.11 | 1 standard reflections every 30 min |
5003 measured reflections | intensity decay: 21% |
2288 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.036 | 78 parameters |
wR(F2) = 0.048 | H-atom parameters not refined |
S = 1.54 | Δρmax = 1.79 e Å−3 |
2122 reflections | Δρmin = −2.70 e Å−3 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
B | 0.5000 (1) | 0.0000 (1) | 0.5000 (1) | 0.0229 (2) | |
W1 | 0.37332 (4) | 0.00723 (4) | 0.30232 (5) | 0.0311 (1) | |
W2 | 0.56844 (4) | 0.14873 (4) | 0.30205 (5) | 0.0295 (2) | |
W3 | 0.44594 (4) | 0.15078 (4) | 0.49093 (5) | 0.0298 (2) | |
O123 | 0.4809 (6) | 0.0551 (6) | 0.4274 (8) | 0.0243 (2) | |
O2 | 0.6199 (7) | 0.2225 (6) | 0.2064 (8) | 0.0374 (4) | |
O1 | 0.3008 (7) | −0.0106 (7) | 0.2090 (9) | 0.0409 (2) | |
O3 | 0.4190 (7) | 0.2230 (7) | 0.5132 (11) | 0.0382 (4) | |
O12 | 0.4675 (7) | 0.0910 (7) | 0.2268 (8) | 0.0329 (2) | |
O32 | 0.5236 (7) | 0.2046 (6) | 0.3797 (8) | 0.0309 (2) | |
O21 | 0.5934 (7) | 0.0669 (6) | 0.2612 (8) | 0.0300 (2) | |
O13 | 0.3112 (6) | −0.0673 (6) | 0.4078 (8) | 0.0304 (2) | |
O23 | 0.6489 (6) | 0.1798 (6) | 0.4084 (8) | 0.0285 (2) | |
O31 | 0.3678 (7) | 0.0918 (6) | 0.3806 (9) | 0.0333 (2) | |
K1 | 0.3687 (2) | 0.7374 (3) | 0.0000 (1) | 0.040 (1) | |
OKW1 | 0.5000 (1) | 0.0000 (1) | 0.0448 (13) | 0.069 (7) | |
OKW2 | 0.4701 (11) | 0.3488 (11) | 0.3425 (14) | 0.123 (7) | |
OKW3 | 0.1305 (11) | 0.261 (2) | 0.0000 (1) | 0.205 (9) | |
OW1 | 0.1995 (16) | 0.399 (3) | 0.5000 (1) | 0.051 (9) | |
OW2 | 0.725 (3) | 0.0000 (1) | 0.0000 (1) | 0.058 (9) | |
OW3 | 0.204 (3) | 0.0000 (1) | 0.5000 (1) | 0.075 (9) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
B | 0.0263 (2) | 0.0190 (3) | 0.0209 (3) | 0.0095 (1) | 0.0000 (1) | 0.0000 (1) |
W1 | 0.0347 (2) | 0.0270 (2) | 0.0293 (2) | 0.0137 (1) | −0.0071 (2) | 0.0002 (1) |
W2 | 0.0369 (2) | 0.0225 (2) | 0.0244 (2) | 0.0114 (1) | 0.0014 (1) | 0.0035 (2) |
W3 | 0.0348 (3) | 0.0235 (2) | 0.0327 (2) | 0.0156 (2) | −0.0002 (1) | 0.0002 (1) |
O123 | 0.0284 (2) | 0.0200 (2) | 0.0225 (2) | 0.0105 (1) | −0.0007 (1) | 0.0005 (1) |
O2 | 0.0489 (4) | 0.0267 (3) | 0.0288 (4) | 0.0130 (2) | 0.0046 (2) | 0.0078 (4) |
O1 | 0.0437 (3) | 0.0366 (5) | 0.0394 (4) | 0.0179 (2) | −0.0159 (4) | −0.0004 (1) |
O3 | 0.0449 (7) | 0.0289 (4) | 0.0470 (5) | 0.0230 (5) | 0.0005 (1) | −0.0004 (1) |
O12 | 0.0428 (3) | 0.0273 (3) | 0.0252 (2) | 0.0151 (2) | −0.0045 (2) | 0.0030 (1) |
O32 | 0.0389 (3) | 0.0219 (2) | 0.0306 (3) | 0.0142 (1) | −0.0012 (1) | 0.0029 (1) |
O21 | 0.0367 (2) | 0.0251 (2) | 0.0234 (2) | 0.0117 (1) | 0.0049 (1) | 0.0019 (1) |
O13 | 0.0281 (2) | 0.0262 (2) | 0.0335 (3) | 0.0110 (1) | −0.0044 (1) | −0.0007 (1) |
O23 | 0.0308 (2) | 0.0207 (2) | 0.0277 (3) | 0.0082 (2) | 0.0025 (1) | 0.0020 (1) |
O31 | 0.0356 (2) | 0.0287 (3) | 0.0378 (3) | 0.0176 (3) | −0.0053 (1) | 0.0013 (1) |
K1 | 0.042 (2) | 0.050 (3) | 0.031 (3) | 0.025 (2) | 0.000 (2) | 0.0000 (1) |
OKW1 | 0.097 (9) | 0.039 (8) | 0.067 (9) | 0.031 (9) | 0.0000 (1) | 0.0000 (1) |
OKW2 | 0.127 (9) | 0.141 (9) | 0.106 (9) | 0.073 (9) | 0.013 (9) | 0.026 (9) |
OKW3 | 0.205 (9) | 0.205 (9) | 0.205 (9) | 0.102 (9) | 0.0000 (1) | 0.0000 (1) |
OW1 | 0.051 (9) | 0.051 (9) | 0.051 (9) | 0.026 (8) | 0.0000 (1) | 0.0000 (1) |
OW2 | 0.058 (9) | 0.058 (9) | 0.058 (9) | 0.029 (9) | 0.0000 (1) | 0.0000 (1) |
OW3 | 0.075 (9) | 0.075 (9) | 0.075 (9) | 0.038 (8) | 0.0000 (1) | 0.0000 (1) |
Geometric parameters (Å, º) top
B—O123 | 1.554 (10) | W2—O2 | 1.719 (10) |
B—O123i | 1.554 (10) | W2—O12 | 1.908 (10) |
B—O123ii | 1.554 (10) | W2—O32 | 1.917 (10) |
B—O123iii | 1.554 (10) | W2—O21 | 1.905 (10) |
W1—O123 | 2.354 (10) | W2—O23 | 1.876 (11) |
W1—O1 | 1.699 (11) | W3—O123 | 2.358 (10) |
W1—O12 | 1.938 (10) | W3—O3 | 1.708 (10) |
W1—O13 | 1.853 (10) | W3—O32 | 1.902 (10) |
W1—O31 | 1.923 (11) | W3—O31 | 1.914 (11) |
W1—O21i | 1.876 (10) | W3—O13ii | 1.923 (10) |
W2—O123 | 2.320 (9) | W3—O23iii | 1.891 (10) |
| | | |
O123—B—O123i | 109.1 (7) | O12—W2—O23 | 161.8 (4) |
O123—B—O123ii | 110.5 (7) | O32—W2—O21 | 160.8 (4) |
O123—B—O123iii | 108.8 (7) | O32—W2—O23 | 89.3 (4) |
O123i—B—O123ii | 108.8 (7) | O21—W2—O23 | 87.1 (5) |
O123i—B—O123iii | 110.5 (7) | O123—W3—O3 | 169.8 (5) |
O123ii—B—O123iii | 109.1 (7) | O123—W3—O32 | 74.3 (4) |
O123—W1—O1 | 170.4 (4) | O123—W3—O31 | 75.2 (4) |
O123—W1—O12 | 74.7 (4) | O123—W3—O13ii | 84.9 (4) |
O123—W1—O13 | 85.7 (4) | O123—W3—O23iii | 85.3 (4) |
O123—W1—O31 | 75.1 (4) | O3—W3—O32 | 98.6 (5) |
O123—W1—O21i | 85.3 (4) | O3—W3—O31 | 97.5 (5) |
O1—W1—O12 | 99.0 (5) | O3—W3—O13ii | 102.3 (5) |
O1—W1—O13 | 100.8 (5) | O3—W3—O23iii | 102.3 (5) |
O1—W1—O31 | 97.7 (5) | O32—W3—O31 | 87.7 (5) |
O1—W1—O21i | 102.0 (5) | O32—W3—O13ii | 159.1 (4) |
O12—W1—O13 | 160.2 (4) | O32—W3—O23iii | 90.3 (4) |
O12—W1—O31 | 88.4 (5) | O31—W3—O13ii | 89.1 (5) |
O12—W1—O21i | 88.0 (5) | O31—W3—O23iii | 160.2 (4) |
O13—W1—O31 | 90.0 (5) | O13ii—W3—O23iii | 85.8 (4) |
O13—W1—O21i | 86.8 (4) | B—O123—W1 | 124.9 (5) |
O31—W1—O21i | 160.3 (5) | B—O123—W2 | 125.8 (5) |
O123—W2—O2 | 169.7 (5) | B—O123—W3 | 125.0 (5) |
O123—W2—O12 | 76.1 (4) | W1—O123—W2 | 90.2 (3) |
O123—W2—O32 | 75.0 (4) | W1—O123—W3 | 89.7 (3) |
O123—W2—O21 | 85.9 (4) | W2—O123—W3 | 90.2 (3) |
O123—W2—O23 | 85.8 (4) | W1—O12—W2 | 118.9 (5) |
O2—W2—O12 | 97.3 (5) | W2—O32—W3 | 120.5 (5) |
O2—W2—O32 | 97.2 (5) | W2—O21—W1i | 148.4 (6) |
O2—W2—O21 | 102.0 (5) | W1—O13—W3ii | 150.3 (6) |
O2—W2—O23 | 100.9 (5) | W2—O23—W3iii | 149.3 (6) |
O12—W2—O32 | 88.2 (5) | W1—O31—W3 | 120.0 (6) |
O12—W2—O21 | 89.4 (5) | | |
Symmetry codes: (i) −x+1, −y, z; (ii) x−y, −y, −z+1; (iii) y−x+1, y, −z+1. |
Experimental details
Crystal data |
Chemical formula | K5[BW12O40](H2O)16 |
Mr | 3340.72 |
Crystal system, space group | Trigonal, P6222 |
Temperature (K) | 294 |
a, c (Å) | 18.970 (4), 12.414 (5) |
V (Å3) | 3869 (2) |
Z | 3 |
Radiation type | Mo Kα |
µ (mm−1) | 27.74 |
Crystal size (mm) | 0.34 × 0.13 × 0.10 |
|
Data collection |
Diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | Analytical (de Meulenaer & Tompa, 1965) |
Tmin, Tmax | 0.04, 0.11 |
No. of measured, independent and observed [I > 3σ(I)] reflections | 5003, 2288, 2122 |
Rint | 0.047 |
(sin θ/λ)max (Å−1) | 0.595 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.036, 0.048, 1.54 |
No. of reflections | 2122 |
No. of parameters | 78 |
No. of restraints | ? |
H-atom treatment | H-atom parameters not refined |
Δρmax, Δρmin (e Å−3) | 1.79, −2.70 |
Selected bond lengths (Å) topB—O123 | 1.554 (10) | W2—O32 | 1.917 (10) |
W1—O123 | 2.354 (10) | W2—O21 | 1.905 (10) |
W1—O1 | 1.699 (11) | W2—O23 | 1.876 (11) |
W1—O12 | 1.938 (10) | W3—O123 | 2.358 (10) |
W1—O13 | 1.853 (10) | W3—O3 | 1.708 (10) |
W1—O31 | 1.923 (11) | W3—O32 | 1.902 (10) |
W1—O21i | 1.876 (10) | W3—O31 | 1.914 (11) |
W2—O123 | 2.320 (9) | W3—O13ii | 1.923 (10) |
W2—O2 | 1.719 (10) | W3—O23iii | 1.891 (10) |
W2—O12 | 1.908 (10) | | |
Symmetry codes: (i) −x+1, −y, z; (ii) x−y, −y, −z+1; (iii) y−x+1, y, −z+1. |
The condensation of [WO4]2- and borate has been known to produce heteropoly species for a long time. Klein (1883) reported two tungstoboric acid isomers which crystallized with tetragonal and hexagonal lattices. These were examined by Copaux (1909) and suggested to have W/B ratios of 12 and 14, respectively. Somewhat later Souchay (1951) reported the [BW11O39]9- ion. Recently, the new tungstoborate species [BW13O46H3]8- has been identified in solution, and the hexagonal acid shown to have the composition H21[B3W39O132].69H2O by an X-ray single-crystal study (Tézé et al., 1997). The quadratic acid is known to have the α-Keggin structure. As part of our studies of the structures and range of heteroatoms found for heteropolyoxo-molybdates and -tungstates, we have examined the structure of the α-[B12O40]5- ion as the K+ salt to allow comparisons with our recent examination of the structures of α-[CoIIW12O40]6- and α-[CoIIIW12O40]5- (Nolan et al., 2000). Kraus (1936) reported unit-cell dimensions for K5[BW12O40].18H2O, which appear to be similar to the present compound (a = 19.0, c = 12.50 Å). The structure of the title compound consists of potassium cations, a [BW12O40]5- anion and water molecules of crystallization. The geometry of the anion is based on the α-Keggin structure (Pope, 1983) and confirms the previous structural determination of the anion in the related compound K5[BW12O40]·9H2O (Yamase & Ishikawa, 1996). The anion exhibits a central tetrahedrally coordinated BIII, surrounded by four groups of three edge-sharing octahedra (W3O13 subunits) which are linked in turn to each other and to the central BO4 tetrahedron by shared oxygen atoms at the vertices. A view of the anion is shown in Fig. 1. The central BIII sits at a site of 222 symmetry and is coordinated to four oxygen atoms with a B—O distance of 1.554 (10) Å. This bond distance may be compared with that of the B—O distance of 1.51 (3) or 1.52 (2) Å (this depends on the anion point symmetry) in [BW11O39CoII(H2O)]6- (Weakley, 1984), the three unique B—O distances in H21[B3W39O132].69H2O of 1.46 (5), 1.47 (3) and 1.58 (7) Å [average 1.50 (5) Å], although in the latter compound the boron sits in an environment intermediate between trigonal BO3 and tetrahedral BO4, and the B—O distances round for the two crystallographically unique [BW12O40]5- ions (with 222 and 2 symmetry) of 1.46 (3), and 1.25 (6) and 1.79 (9) Å, respectively [average 1.49 (6) Å]. For tetrahedral coordination B—O bond lengths vary from 1.43 to 1.55 Å, with an average of 1.475 Å (Wells, 1984). The B—O bond length in the present compound is therefore at the upper limit of this range, and results from the relatively rigid polyoxotungstate framework of the [W12O40]8- unit, which contains a central cavity in which the small BIII resides (Nolan et al., 2000). The O—B—O bond angles of the title compound vary from 108.8 (7) to 110.5 (7)°, and may be compared with values of 1110 (2) and 111 (2)° in the anion of 222 symmetry of K5[BW12O40]·9H2O, and 84 (6), 106 (4), 108 (4) and 134 (11)° for the lower symmetry 2 site. This latter site is obviously considerably distorted. The W—O bond lengths increase with increasing coordination, as found previously, with ranges of 2.320 (9)–2.358 (10) Å for four coordinate O atoms {K5[BW12O40]·9H2O, range for both sites, 2.33 (3)–2.47 (3) Å, 1.853 (10)–1.938 (10) Å for two coordinate O atoms {K5[BW12O40]·9H2O, 1.82 (3)–1.96 (4) Å}, and 1.699 (11)–1.719 (10) Å for the terminal O atoms {K5[BW12O40]·9H2O, 1.66 (3)–1.79 (5)Å}. For the title compound, the W—W distances within the W3O13 subunits average 3.317 (5) Å, while those connecting the W3O13 subunits average 3.641 (7) Å. these may be compared with values of 3.313 (3) and 3.645 (3), respectively, in K5[BW12O40]·9H2O. In terms of (average) bond distance comparisons, the [W12O40]8- framework appears to be most similar to the polyoxotungstate framework of the [SiW12O40]4- ion in the sequence of frameworks of the [XW12O40]n- anions, where X = PV, SiIV, CoIII and CoII, which exhibit progressively increasing size of the central heteroatom (Nolan et al., 2000). There are, however, some differences in that the W3O12 group (the W3O13 subunit minus the centrally bound oxygen atom) is slightly closer to the central boron, which is a consequence of the small size of the (formal) BIII, and necessitates that the angle at the O atoms bridging the W3O13 subunits is the smallest in the series of [XW12O40]n- anions [149.3 (8)° for the BIII-containing anion versus a range of 154.9 (20) to 151.8 (8)° in the above sequence]. All K+-anion oxygen and K+-water oxygen distances are greater than 2.65 (1) Å, with those surrounding the fully occupied K1 ranging from 2.65 (1)–3.10 (1) Å and those surrounding the partially occupied potassium sites ranging from 2.65 (1)–3.39 (1) Å. These are similar to the distances found in K6[CoIIW12O40].16H2O and K5[CoIIIW12O40].16H2O (Nolan et al., 2000).