Crystal structure of the Anderson-type hetero­polyoxometalate; K2[H7CrIIIMo6O24]·8H2O: a redetermination revealing the position of the extra H atom in the polyanion

Joo, H.-C.; Park, K.-M.; Lee, U.

doi:10.1107/S2056989015000390

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Volume 71| Part 2| February 2015| Pages 157-160

doi:10.1107/S2056989015000390

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Crystal structure of the Anderson-type heteropolyoxometalate; K₂[H₇Cr^IIIMo₆O₂₄]·8H₂O: a redetermination revealing the position of the extra H atom in the polyanion

Hea-Chung Joo,^a Ki-Min Park ^b and Uk Lee ^a ^*

^aDepartment of Chemistry, Pukyong National University, 599-1 Daeyeon 3-dong, Nam-gu, Busan 608-737, Republic of Korea, and ^bThe Research Institute of Natural Science, Gyeongsan National University, Jinju 660-701, Republic of Korea
^*Correspondence e-mail: uklee@pknu.ac.kr

Edited by I. D. Brown, McMaster University, Canada (Received 10 October 2014; accepted 8 January 2015; online 17 January 2015)

The title compound contains a symmetric hydrogen bond in which the H atom does not lie on a crystallographic centre of symmetry. The structure of K₂[H₇Cr^IIIMo₆O₂₄]·8H₂O, namely dipotassium heptahydrogen hexamolybdochromate(III) octahydrate, previously reported by Lee [Acta Cryst. (2007), E63, i5–i7], has been redetermined in order to locate the position of the seventh H atom in the anion. Six of the H atoms are bonded to the six μ₃-O atoms and form hydrogen bonds of medium strength either to water molecules or to the terminal O atoms of other polyanions. The seventh H atom forms a very short hydrogen bond between two μ₂-O atoms on adjacent polyanions. This short bond, together with two normal hydrogen bonds, link the two crystallographically distinct centrosymmetric polyanions into chains along [011], while the length of this bond [2.461 (3) Å] suggests that the H atom lies at its centre, but unusually for such a bond, this point is not a crystallographic centre of symmetry.

Keywords: crystal structure; redetermination; B-series Anderson-type polyanion; symmetric hydrogen bond.

CCDC reference: 1042715

1. Chemical context

This redetermined structure of a typical Anderson-type heteropolyoxometalate (Anderson, 1937 ), K₂[H₇Cr^IIIMo₆O₂₄]·8H₂O reveals the position of the extra or seventh H atom in the [HCr^III(OH)₆Mo₆O₁₈]²⁻ polyanion. This has not only an extra H atom but this atom also forms a very short hydrogen bond [2.461 (3) Å]; however, the H atom that contributes to the short hydrogen bond does not lie on a crystallographic centre of symmetry.

An example of a relatively short hydrogen bond in which the H atom does lie on a crystallographic centre of symmetry in an Anderson-type polyanion was reported in the polyoxometalate, viz. K₇[H_4.5α-PtMo₆O₂₄]₂·11H₂O (Lee et al., 2010 ). In this compound, the two polyanions form a dimer, viz. [(H_4.5PtMo₆O₂₄)₂]⁷⁻ via seven hydrogen bonds, viz. four μ₃-O—H⋯μ₁–O (terminal Mo=O atom), two μ₂-O—H⋯μ₂-O and one central/symmetric μ₃-O⋯H⋯μ₃-O. The H atom of the central hydrogen bond lies on a crystallographic centre of symmetry (space group P $[\overline{1}]$ : ½, 0, ½) with a μ₃-O⋯H⋯μ₃-O ( $[\overline{1}]$ ) distance of 2.553 (3) Å. In this way, the hydrogen bond is symmetric, O⋯H⋯O, and the donor and acceptor cannot be distinguished. The dimerization of the polyanion by these hydrogen bonds is possible because the μ₃-O atoms in the polyanion are only partially protonated. The location of the H atom in the central μ₃-O⋯H⋯μ₃-O unit was determined from a centrosymmetric electron density map around the H-atom position. This centrosymmetric interpretation of the hydrogen bond is strongly supported by the bond-valence sums (BVS; Brown & Altermatt, 1985 ; Brese & O'Keeffe, 1991 ). The sum around the strongly bonded μ₃-O atom is 1.92 valence units (v.u.) in the [(H_4.5PtMo₆O₂₄)₂]⁷⁻ polyanion. The reasonable BVS values of very short or very long O—H bond distances can be obtained from the graphical correlation (Brown, 2001 ).

However, the title compound belongs to the B-series Anderson-type polyanions (Tsigdinos, 1978 ) viz. [Xⁿ⁺(OH)₆MoO₁₈]^(12−n)− (X = heteroatom), in which such dimerization is impossible because all six μ₃-O atoms are fully protonated. The polyanion structure in the title compound is shown in Fig. 1.

Figure 1
The polyanion structure in the title compound. Displacement ellipsoids are drawn at the 50% probability level for non-H atoms. H atoms are shown as small spheres of arbitrary radius. [Symmetry codes: (i) −x + 1, −y, −z + 2; (ii) −x + 1, −y + 1, −z + 1.]

2. Structural commentary

This study was carried out to clearly identify the position of the seventh or extra H atom in the [HCr^III(OH)₆Mo₆O₁₈]²⁻ polyanion. After considering the electron density maps and BVS values of the protonated OB (O-bridged μ₂-O atom) atoms in the previously reported structure (Lee, 2007 ), we came to the conclusion that the positional disorder model of the H atom was wrong. The electron density (Fig. 2) is not symmetric in the title compound, but we expect the H atoms to lie in the middle of the bond because of the short O⋯O distance of 2.461 (3) Å, which corresponds to a pseudosymmetric hydrogen bond. The description of the rest of the structure and the composition of the atoms in the polyanion are the same as in the previous report of the compound, viz. K₂[H₇Cr^IIIMo₆O₂₄]·8H₂O (Lee, 2007). The O atoms of the polyoxometalate are designated as OT (terminal Mo=O atom), OB, and OC (centre of two Mo and one Cr atom, μ₃-O atom), respectively.

Figure 2
Difference Fourier map around atom H5 where atom H5 is absent.

In the present case, the O5B⋯H5 and O16Bⁱ⋯H5 distances are both 1.23 Å (Table 1). However, since the H atom does not lie on a crystallographic centre of symmetry, the present structure is considered to be particularly significant. As a result, the H5 atom is co-shared as O5B⋯H5⋯O16Bⁱ, and the average equation of the polyanion is [Cr^III(μ₃-OH)₆{μ₂-O(0.5H)}₂Mo₆O₁₇]²⁻.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1C—H1⋯O22Tⁱ	0.70 (6)	2.11 (6)	2.789 (4)	164 (6)
O2C—H2⋯O27W	0.76 (6)	2.01 (6)	2.753 (4)	166 (6)
O3C—H3⋯O31Wⁱⁱ	0.82 (6)	1.79 (6)	2.604 (4)	176 (6)
O5B—H5⋯O16Bⁱⁱⁱ	1.23 (1)	1.23 (1)	2.461 (3)	175 (5)
O13C—H13⋯O12Tⁱⁱⁱ	0.70 (5)	2.05 (5)	2.734 (4)	167 (5)
O14C—H14⋯O32W	0.81 (5)	2.01 (5)	2.776 (4)	158 (5)
O15C—H15⋯O28W^iv	0.76 (6)	1.87 (6)	2.619 (4)	170 (6)
O25W—H25A⋯O21T	0.92 (3)	1.96 (3)	2.838 (4)	157 (5)
O25W—H25B⋯O20T	0.93 (3)	1.92 (3)	2.819 (4)	162 (5)
O26W—H26A⋯O4B^v	0.91 (3)	1.89 (3)	2.748 (4)	158 (5)
O26W—H26B⋯O24Tⁱⁱⁱ	0.91 (3)	1.91 (3)	2.798 (4)	164 (5)
O27W—H27A⋯O18B	0.90 (3)	1.95 (4)	2.775 (4)	151 (5)
O27W—H27B⋯O32W	0.91 (3)	1.92 (3)	2.825 (5)	171 (5)
O28W—H28A⋯O12T^vi	0.91 (3)	2.00 (4)	2.785 (4)	144 (5)
O28W—H28B⋯O31W^iv	0.90 (3)	1.82 (3)	2.706 (4)	170 (5)
O29W—H29A⋯O11T^v	0.95 (3)	2.11 (4)	2.949 (5)	146 (6)
O29W—H29B⋯O8T^vii	0.96 (3)	2.18 (3)	3.126 (5)	169 (6)
O31W—H31A⋯O26W^iv	0.90 (3)	1.77 (3)	2.665 (4)	170 (5)
O31W—H31B⋯O27W^iv	0.92 (3)	2.18 (4)	2.952 (4)	141 (4)
O32W—H32A⋯O30W	0.89 (3)	2.06 (3)	2.947 (6)	171 (5)
O32W—H32B⋯O6B^v	0.89 (3)	2.39 (5)	3.000 (4)	126 (5)
Symmetry codes: (i) x, y, z+1; (ii) x, y-1, z+1; (iii) -x+1, -y, -z+1; (iv) -x+1, -y+1, -z+1; (v) -x+1, -y, -z+2; (vi) x, y+1, z; (vii) -x+1, -y+1, -z+2.

The calculated BVS for the O5B and O16B atoms are 1.59 and 1.57 v.u., respectively, if the valence of the O—H bond is not included. Since the BVS value around the μ₂-O atom should be 2.0 v.u., the missing valences of O5B and O16B are 0.41 and 0.43 v.u., respectively, corresponding to the valence of the O—H bonds. The obtained graphical correlation valence of H5 from its distance, 1.232 (7) Å, is 0.41 v.u., which is sufficient to satisfy the sums around the O5B and O16B atoms. As a result, the valence sums around O5B and O16B are 2.00 and 1.98 v.u., respectively. The BVS around the unprotonated μ₂-O atoms, viz. O4B, O6B, O17B and O18B are 1.98, 1.96, 2.13 and 2.02 v.u., respectively.

The positional disordered model in the previous report (Lee, 2007) showed unreasonable BVS values. The calculated BVS for the O5B and O16B atoms are 1.62 and 1.57 v.u., respectively, if the valence of the O—H bond is not included. The obtained graphical correlation valences of H5 and H16 from its distances [O5B—H5 = 0.71 (8), H5⋯O16B = 1.79 (8) Å and O16B—H16 = 0.83 (8), H16⋯O5B = 1.65 (8) Å] are 0.24 and 0.26 v.u. Therefore, the total BVS values of O5B and O16B are 1.86 and 1.83 v.u., respectively.

As a result, we consider that the present model of the title compound is more reasonable, and the one extra H atom is located at the mid-point between the O5B and O16B atoms, and shared equally by two discrete polyanions. All H atoms and hydrogen bonds are well-defined in the title compound (Table 1).

3. Supramolecular features

Two discrete polyanions A and B are linked into chains along [011] by two normal, and one strong and pseudosymmetric hydrogen bonds (Table 1 and Fig. 3). The K⁺ ions are variously coordinated by O atoms as [K1(OT)₄(OW)₄]⁺ and [K2(OT)₄(OB)(OW)₃]⁺ in the distance range 2.722 (3)–3.075 (3) Å. Furthermore, the polyanions are three dimensionally linked via K⋯OT interactions. All water molecules form hydrogen bonds with polyanions except for the O30W and O31W water molecules.

Figure 3
Polyhedral view of the heteropolyanion in (I), with O⋯O contacts of the inter-polyanion hydrogen bonds shown as dashed lines. [Symmetry codes; (i) −x + 1, −y, −z + 1; (ii) x, y, z − 1; (iii) −x + 1, −y + 1, −z + 1; (iv) x, y + 1, z; (v) −x + 1, −y + 1, −z + 2.]

4. Synthesis and crystallization

The crude potassium salt of title compound was obtained from the reaction of an Na₃[H₆CrMo₆O₂₄]·8H₂O (Perloff, 1970 ) solution and excess KCl solution. The title compound was obtained by recrystallization of crude K₃[H₆CrMo₆O₂₄]·8H₂O at pH 1.80.

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. All the H atoms in the polyanions and all water H atoms were positioned using difference Fourier maps. All H atoms in the polyanion were refined freely, but the H5 atoms were refined with a distance restraint of O5B—H5 and O16Bⁱⁱⁱ—H5 (Table 1) using the SADI command in SHELXL97 (Sheldrick, 2008 ); σ = 0.01, the distances between the first and second named bonds were restrained to be equal with an effective standard deviation sigma in order to locate the H5 atom on the pseudocentre between the O5B and O16B atoms. The H atoms of all water molecules (OW) were refined with a distance restraint of O—H = 0.95 (3) Å using the DFIX command, and were included in the refinement with U_iso(H) = 1.5U_eq(O). The highest peak in the difference map is 1.62 Å from O9T.

Table 2
Experimental details

Crystal data
Chemical formula	K₂[H₇CrMo₆O₂₄]·8H₂O
M_r	1241.02
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	446
a, b, c (Å)	10.4588 (2), 10.8553 (2), 12.6287 (3)
α, β, γ (°)	99.296 (1), 94.469 (1), 99.283 (1)
V (Å³)	1388.44 (5)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	3.42
Crystal size (mm)	0.18 × 0.11 × 0.09

Data collection
Diffractometer	Bruker SMART APEXII CCD
Absorption correction	Multi-scan (SADABS; Sheldrick, 2008)
T_min, T_max	0.645, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	23489, 6028, 5893
R_int	0.025
(sin θ/λ)_max (Å⁻¹)	0.639

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.024, 0.064, 1.11
No. of reflections	6028
No. of parameters	450
No. of restraints	17
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	1.58, −0.67
Computer programs: APEX2 and SAINT (Bruker, 2009 ), SHELXS97 and SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 2012 ), PLATON (Spek, 2009 ) and DIAMOND (Brandenburg, 1998 ).

Supporting information

CCDC reference: 1042715

Crystal structure: contains datablock I. DOI: 10.1107/S2056989015000390/br2242sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S2056989015000390/br2242Isup2.hkl

checkCIF report

Chemical context top

This redetermined structure of a typical Anderson-type heteropolyoxometalate (Anderson, 1937), K₂[H₇Cr^IIIMo₆O₂₄]·8H₂O reveals the position of the extra or seventh H atom in the [HCr^III(OH)₆Mo₆O₁₈]^2- polyanion. This has not only an extra H atom but this atom also forms a very short hydrogen bond [2.461 (3) Å]; however, the H atom that contributes to the short hydrogen bond does not lie on a crystallographic centre of symmetry.

An example of a relatively short hydrogen bond in which the H atom does lie on a crystallographic centre of symmetry in an Anderson-type polyanion was reported in the polyoxometalate, viz. K₇[H_4.5α-PtMo₆O₂₄]₂·11H₂O (Lee et al., 2010). In this compound, the two polyanions form a dimer, viz. [(H_4.5PtMo₆O₂₄)₂]^7- via seven hydrogen bonds, viz. four µ₃-O—H···µ₁–O (terminal Mo═O atom), two µ₂-O—H···µ₂-O and one central/symmetric µ₃-O···H···µ₃-O. The H atom of the central hydrogen bond in the compound lies on a crystallographic centre of symmetry (space group P1 : 1/2, 0, 1/2) with a µ₃-O···H···µ₃-O (1) distance of 2.553 (3) Å. In this way, the hydrogen bond is symmetric, O···H···O, and the donor and acceptor cannot be distinguished. The dimerization of the polyanion by these hydrogen bonds is possible because the µ₃-O atoms in the polyanion are only partially protonated. The location of the H atom in the central µ₃-O···H···µ₃-O unit was determined from a centrosymmetric electron density map around the H-atom position. This centrosymmetric interpretation of the hydrogen bond is strongly supported by the bond-valence sums (BVS; Brown & Altermatt, 1985; Brese & O'Keeffe, 1991). The sum around the strongly bonded µ₃-O atom is 1.92 valence units (v.u.) in the [(H_4.5PtMo₆O₂₄)₂]^7- polyanion. The reasonable BVS values of very short or very long O—H bond distances can be obtained from the graphical correlation (Brown, 2001).

However, the title compound belongs to the B-series Anderson-type polyanions (Tsigdinos, 1978) viz. [Xⁿ⁺(OH)₆MoO₁₈]^(12-ⁿ^)- (X = heteroatom), in which such dimerization is impossible, because all six µ₃-O atoms are fully protonated. The polyanion structure in the title compound is shown in Fig. 1.

Structural commentary top

This study was carried out to identify the position of the seventh or extra H atom in the [HCr^III(OH)₆Mo₆O₁₈]^2- polyanion. After considering the electron density maps and BVS values of the protonated OB (O-bridged µ₂-O atom) atoms in the previously reported structure (Lee, 2007), we considered that the positional disorder model of the H atom was wrong. The electron density (Fig. 2) is not symmetric in the title compound, but we expect the H atoms to lie in the middle of the bond because of the short O···O distance of 2.461 (3) Å, which corresponds to a pseudosymmetric hydrogen bond. The description of the rest of the structure and the composition of the atoms in the polyanion are the same as in the previous report of the compound, viz. K₂[H₇Cr^IIIMo₆O₂₄]·8H₂O (Lee, 2007). The O atoms of the polyoxometalate are designated as OT (terminal Mo═O atom), OB, and OC (centre of two Mo and one Cr atom, µ₃-O atom), respectively.

In the present case, the O5B···H5 and O16Bⁱ···H5 distances are both 1.23 Å (Table 1). This hydrogen bond is considered to be a symmetric hydrogen bond because the O5B···O16Bⁱ distance, 2.461 (3) Å, is very short. However, since the H atom does not lie on a crystallographic centre of symmetry, the present structure is considered to be particularly significant. As a result, the H5 atom is co-shared as O5B···H5···O16Bⁱ, and the average equation of the polyanion is [Cr^III(µ₃-OH)₆{µ₂-O(0.5H)}₂Mo₆O₁₇]^2-.

The calculated BVS for the O5B and O16B atoms are 1.59 and 1.57 v.u., respectively, if the valence of the O—H bond is not included. Since the BVS value around the µ₂-O atom should be 2.0 v.u., the missing valences of O5B and O16B are 0.41 and 0.43 v.u., respectively, corresponding to the valence of the O—H bonds. The obtained graphical correlation valence of H5 from its distance, 1.232 (7) Å, is 0.41 v.u., which is sufficient to satisfy the sums around the O5B and O16B atoms. As a result, the valence sums around O5B and O16B are 2.00 and 1.98 v.u., respectively. The BVS around the unprotonated µ₂-O atoms, viz. O4B, O6B, O17B and O18B are 1.98, 1.96, 2.13 and 2.02 v.u., respectively.

The positional disordered model in the previous report (Lee, 2007) showed unreasonable BVS values. The calculated BVS for the O5B and O16B atoms are 1.62 and 1.57 v.u., respectively, if the valence of the O—H bond is not included. The obtained graphical correlation valences of H5 and H16 from its distances [O5B—H5 = 0.71 (8), H5···O16B = 1.79 (8) Å and O16B—H16 = 0.83 (8), H16···O5B = 1.65 (8) Å] are 0.24 and 0.26 v.u. Therefore, the total BVS values of O5B and O16B are 1.86 and 1.83 v.u., respectively.

As a result, we consider that the present model of the title compound is reasonable, and the one extra H atom is located at the mid-point between the O5B and O16B atoms, and shared equally by two discrete polyanions. All H atoms and hydrogen bonds were well-defined in the title compound (Table 1).

Supramolecular features top

Two discrete polyanions A and B are linked into chains along [011] by two normal, and one strong and pseudosymmetric hydrogen bonds (Table 1 and Fig.3). The K⁺ ions are variously coordinated by O atoms as [K1(OT)₄(OW)₄]⁺ and [K2(OT)₄(OB)(OW)₃]⁺ in the distance range 2.722 (3)–3.075 (3) Å. Furthermore, the polyanions are three dimensionally linked via clusters of K···OT, OB and OW interactions. All water molecules form hydrogen bonds with polyanions except for the O30W and O31W water molecules.

Synthesis and crystallization top

The crude potassium salt of title compound was obtained from the reaction of Na₃[H₆CrMo₆O₂₄].8H₂O (Perloff, 1970) solution and excess KCl solution. The title compound was obtained by recrystallization of crude K₃[H₆CrMo₆O₂₄].8H₂O at pH 1.80.

Refinement top

All the H atoms in the polyanions and all water H atoms were positioned using difference Fourier maps. All H atoms in the polyanion were refined freely, but the H5 atoms were refined with a distance restraint of O5B—H5 and O16Bⁱⁱⁱ—H5 (Table 1) using the SADI command in SHELXL97 (Sheldrick, 2008); σ = 0.01, the distances between the first and second named bonds were restrained to be equal with an effective standard deviation sigma in order to locate the H5 atom on the pseudocentre between the O5B and O16B atoms. The H atoms of all water molecules (OW) were refined with a distance restraint of O—H = 0.95 (3) Å using the DFIX command, and were included in the refinement with U_iso(H) = 1.5U_eq(O). The highest peak in the difference map is 1.62 Å from O9T.

Related literature top

For related literature, see: Brese & O'Keeffe (1991); Brown & Altermatt (1985); Lee (2007); Lee & Joo (2004); Perloff (1970); Sheldrick (2008); Tsigdinos (1978).

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012), PLATON (Spek, 2009) and DIAMOND (Brandenburg, 1998); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

	Fig. 1. The polyanion structure in the title compound. Displacement ellipsoids are drawn at the 50% probability level for non-H atoms. H atoms are shown as small spheres of arbitrary radius. [Symmetry codes: (i) -x + 1, -y, -z + 2; (ii) -x + 1, -y + 1, -z + 1.]
	Fig. 2. Difference Fourier map around atom H5 where atom H5 is absent.
	Fig. 3. Polyhedral view of the heteropolyanion in (I), with O···O contacts of the inter-polyanion hydrogen bonds shown as dashed lines. [Symmetry codes; (i) -x + 1, -y, -z + 1; (ii) x , y, z - 1; (iii) -x + 1, -y + 1, -z + 1; (iv) x, y + 1, z; (v) -x + 1, -y + 1, -z + 2.]

Dipotassium heptahydrogen hexamolybdochromate(III) octahydrate top

Crystal data top

K₂[H₇CrMo₆O₂₄]·8H₂O	Z = 2
M_r = 1241.02	F(000) = 1186
Triclinic, P1	D_x = 2.968 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 10.4588 (2) Å	Cell parameters from 9896 reflections
b = 10.8553 (2) Å	θ = 2.5–33.5°
c = 12.6287 (3) Å	µ = 3.42 mm⁻¹
α = 99.296 (1)°	T = 446 K
β = 94.469 (1)°	Block, purple
γ = 99.283 (1)°	0.18 × 0.11 × 0.09 mm
V = 1388.44 (5) Å³

Data collection top

Bruker SMART APEXII CCD diffractometer	6028 independent reflections
Radiation source: Rotating Anode	5893 reflections with I > 2σ(I)
Graphite multilayer monochromator	R_int = 0.025
Detector resolution: 10.0 pixels mm^-1	θ_max = 27.0°, θ_min = 1.6°
ϕ and ω scans	h = −13→13
Absorption correction: multi-scan (SADABS; Sheldrick, 2008)	k = −13→13
T_min = 0.645, T_max = 0.746	l = −16→16
23489 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.024	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.064	w = 1/[σ²(F_o²) + (0.0255P)² + 6.3059P] where P = (F_o² + 2F_c²)/3
S = 1.11	(Δ/σ)_max = 0.001
6028 reflections	Δρ_max = 1.58 e Å⁻³
450 parameters	Δρ_min = −0.67 e Å⁻³
17 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00391 (16)

Crystal data top

K₂[H₇CrMo₆O₂₄]·8H₂O	γ = 99.283 (1)°
M_r = 1241.02	V = 1388.44 (5) Å³
Triclinic, P1	Z = 2
a = 10.4588 (2) Å	Mo Kα radiation
b = 10.8553 (2) Å	µ = 3.42 mm⁻¹
c = 12.6287 (3) Å	T = 446 K
α = 99.296 (1)°	0.18 × 0.11 × 0.09 mm
β = 94.469 (1)°

Data collection top

Bruker SMART APEXII CCD diffractometer	6028 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2008)	5893 reflections with I > 2σ(I)
T_min = 0.645, T_max = 0.746	R_int = 0.025
23489 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.024	17 restraints
wR(F²) = 0.064	H atoms treated by a mixture of independent and constrained refinement
S = 1.11	Δρ_max = 1.58 e Å⁻³
6028 reflections	Δρ_min = −0.67 e Å⁻³
450 parameters

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

	x	y	z	U_iso*/U_eq
Cr1	0.5000	0.0000	1.0000	0.00813 (15)
Cr2	0.5000	0.5000	0.5000	0.00762 (15)
Mo1	0.23267 (3)	0.13627 (3)	0.99546 (2)	0.01127 (8)
Mo2	0.20792 (3)	−0.17249 (3)	0.90598 (2)	0.01086 (8)
Mo3	0.47636 (3)	−0.31129 (3)	0.92212 (2)	0.01051 (8)
Mo4	0.79232 (3)	0.42389 (3)	0.46268 (2)	0.00994 (8)
Mo5	0.52144 (3)	0.19391 (3)	0.43518 (2)	0.00938 (8)
Mo6	0.23147 (3)	0.27465 (3)	0.46825 (2)	0.00952 (8)
K1	0.06894 (8)	0.02275 (9)	0.66878 (7)	0.02014 (17)
K2	0.92835 (8)	0.58495 (9)	0.77823 (7)	0.02212 (18)
O1C	0.4157 (2)	0.1138 (2)	1.0986 (2)	0.0113 (5)
H1	0.414 (6)	0.100 (5)	1.151 (5)	0.033 (16)*
O2C	0.3526 (2)	0.0070 (2)	0.8952 (2)	0.0099 (5)
H2	0.362 (5)	0.029 (5)	0.842 (4)	0.028 (14)*
O3C	0.3916 (2)	−0.1598 (2)	1.0194 (2)	0.0109 (5)
H3	0.386 (5)	−0.166 (5)	1.083 (5)	0.034 (15)*
O4B	0.1720 (2)	−0.0378 (2)	1.0107 (2)	0.0137 (5)
O5B	0.3370 (2)	−0.2592 (2)	0.83029 (19)	0.0121 (5)
H5	0.334 (9)	−0.271 (9)	0.7314 (10)	0.12 (3)*
O6B	0.6225 (2)	−0.2660 (2)	1.0259 (2)	0.0131 (5)
O7T	0.1329 (3)	0.1463 (3)	0.8855 (2)	0.0196 (6)
O8T	0.1748 (3)	0.2124 (3)	1.1047 (2)	0.0201 (6)
O9T	0.1160 (3)	−0.1627 (3)	0.7911 (2)	0.0171 (5)
O10T	0.1270 (3)	−0.2975 (3)	0.9535 (2)	0.0192 (6)
O11T	0.3862 (3)	−0.4281 (3)	0.9735 (2)	0.0184 (5)
O12T	0.5387 (3)	−0.3860 (2)	0.8119 (2)	0.0158 (5)
O13C	0.4147 (2)	0.3516 (2)	0.3922 (2)	0.0099 (5)
H13	0.415 (5)	0.359 (5)	0.338 (4)	0.015 (12)*
O14C	0.3526 (2)	0.4487 (2)	0.5815 (2)	0.0100 (5)
H14	0.357 (5)	0.437 (5)	0.643 (4)	0.019 (12)*
O15C	0.3920 (2)	0.6197 (2)	0.4556 (2)	0.0096 (5)
H15	0.376 (5)	0.616 (5)	0.395 (5)	0.034 (15)*
O16B	0.6638 (2)	0.2882 (2)	0.36714 (19)	0.0110 (5)
O17B	0.8278 (2)	0.5773 (2)	0.56733 (19)	0.0113 (5)
O18B	0.3755 (2)	0.1934 (2)	0.5151 (2)	0.0116 (5)
O19T	0.8822 (3)	0.4581 (3)	0.3615 (2)	0.0179 (5)
O20T	0.8741 (3)	0.3335 (3)	0.5323 (2)	0.0187 (6)
O21T	0.6089 (2)	0.1094 (3)	0.5064 (2)	0.0165 (5)
O22T	0.4583 (3)	0.0957 (2)	0.3159 (2)	0.0157 (5)
O23T	0.1361 (2)	0.2368 (3)	0.5654 (2)	0.0155 (5)
O24T	0.1681 (3)	0.1718 (3)	0.3527 (2)	0.0176 (5)
O25W	0.8716 (3)	0.0732 (3)	0.5305 (2)	0.0206 (6)
H25A	0.783 (3)	0.069 (5)	0.535 (4)	0.031*
H25B	0.891 (5)	0.159 (3)	0.530 (4)	0.031*
O26W	0.8483 (3)	0.0653 (3)	0.7784 (2)	0.0235 (6)
H26A	0.863 (5)	0.051 (5)	0.847 (3)	0.035*
H26B	0.827 (5)	−0.012 (3)	0.735 (4)	0.035*
O27W	0.3568 (3)	0.1168 (3)	0.7134 (2)	0.0261 (7)
H27A	0.367 (6)	0.113 (5)	0.643 (2)	0.039*
H27B	0.337 (6)	0.194 (3)	0.739 (4)	0.039*
O28W	0.6802 (3)	0.4221 (3)	0.7521 (2)	0.0208 (6)
H28A	0.629 (4)	0.464 (5)	0.794 (4)	0.031*
H28B	0.669 (5)	0.345 (3)	0.770 (4)	0.031*
O29W	0.8747 (4)	0.5437 (4)	0.9821 (3)	0.0390 (8)
H29A	0.810 (5)	0.479 (5)	0.998 (5)	0.059*
H29B	0.851 (6)	0.611 (5)	0.948 (5)	0.059*
O30W	0.0221 (5)	0.3490 (4)	0.7849 (5)	0.0640 (14)
H30A	−0.019 (9)	0.333 (9)	0.716 (4)	0.096*
H30B	−0.022 (8)	0.268 (4)	0.786 (7)	0.096*
O31W	0.3602 (3)	0.8223 (3)	0.2192 (2)	0.0206 (6)
H31A	0.295 (4)	0.868 (5)	0.226 (4)	0.031*
H31B	0.432 (4)	0.870 (4)	0.261 (4)	0.031*
O32W	0.3044 (3)	0.3645 (3)	0.7732 (2)	0.0245 (6)
H32A	0.219 (3)	0.366 (5)	0.772 (4)	0.037*
H32B	0.346 (5)	0.392 (5)	0.839 (3)	0.037*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cr1	0.0082 (3)	0.0076 (4)	0.0084 (3)	0.0010 (3)	0.0006 (3)	0.0013 (3)
Cr2	0.0070 (3)	0.0074 (4)	0.0086 (3)	0.0013 (3)	0.0009 (3)	0.0015 (3)
Mo1	0.01095 (14)	0.01186 (15)	0.01156 (14)	0.00390 (11)	0.00131 (11)	0.00177 (11)
Mo2	0.00957 (14)	0.01067 (15)	0.01165 (14)	0.00013 (11)	0.00034 (10)	0.00198 (11)
Mo3	0.01252 (14)	0.00810 (15)	0.01083 (14)	0.00194 (11)	0.00182 (11)	0.00109 (11)
Mo4	0.00749 (13)	0.00962 (15)	0.01315 (14)	0.00208 (10)	0.00177 (10)	0.00245 (11)
Mo5	0.00942 (14)	0.00756 (14)	0.01113 (14)	0.00169 (10)	0.00103 (10)	0.00138 (10)
Mo6	0.00820 (14)	0.00838 (15)	0.01158 (14)	0.00012 (10)	0.00090 (10)	0.00201 (11)
K1	0.0189 (4)	0.0248 (4)	0.0182 (4)	0.0039 (3)	0.0019 (3)	0.0081 (3)
K2	0.0173 (4)	0.0303 (5)	0.0177 (4)	0.0012 (3)	0.0017 (3)	0.0040 (3)
O1C	0.0135 (12)	0.0115 (12)	0.0089 (12)	0.0027 (9)	0.0016 (9)	0.0011 (10)
O2C	0.0108 (11)	0.0116 (12)	0.0081 (11)	0.0022 (9)	0.0019 (9)	0.0036 (9)
O3C	0.0135 (12)	0.0103 (12)	0.0093 (11)	0.0018 (9)	0.0017 (9)	0.0024 (9)
O4B	0.0130 (12)	0.0148 (13)	0.0135 (12)	0.0022 (10)	0.0041 (9)	0.0022 (10)
O5B	0.0127 (12)	0.0128 (12)	0.0106 (11)	0.0036 (9)	0.0005 (9)	0.0004 (9)
O6B	0.0144 (12)	0.0117 (12)	0.0129 (12)	0.0024 (10)	−0.0009 (9)	0.0026 (9)
O7T	0.0159 (13)	0.0214 (15)	0.0212 (14)	0.0031 (11)	−0.0022 (10)	0.0058 (11)
O8T	0.0206 (14)	0.0200 (14)	0.0203 (13)	0.0046 (11)	0.0066 (11)	0.0019 (11)
O9T	0.0168 (13)	0.0182 (14)	0.0157 (13)	0.0024 (11)	−0.0004 (10)	0.0028 (10)
O10T	0.0184 (13)	0.0168 (14)	0.0230 (14)	0.0013 (11)	0.0040 (11)	0.0062 (11)
O11T	0.0199 (13)	0.0145 (13)	0.0219 (13)	0.0023 (11)	0.0037 (11)	0.0063 (11)
O12T	0.0198 (13)	0.0140 (13)	0.0136 (12)	0.0047 (10)	0.0029 (10)	0.0002 (10)
O13C	0.0118 (12)	0.0104 (12)	0.0073 (12)	0.0014 (9)	0.0006 (9)	0.0019 (9)
O14C	0.0086 (11)	0.0130 (12)	0.0088 (11)	0.0014 (9)	0.0007 (9)	0.0039 (9)
O15C	0.0110 (11)	0.0096 (12)	0.0082 (11)	0.0019 (9)	−0.0002 (9)	0.0021 (9)
O16B	0.0122 (11)	0.0120 (12)	0.0083 (11)	0.0014 (9)	0.0033 (9)	0.0003 (9)
O17B	0.0103 (11)	0.0106 (12)	0.0124 (11)	0.0013 (9)	−0.0005 (9)	0.0022 (9)
O18B	0.0112 (11)	0.0106 (12)	0.0140 (12)	0.0022 (9)	0.0029 (9)	0.0045 (9)
O19T	0.0144 (12)	0.0169 (14)	0.0225 (14)	0.0003 (10)	0.0089 (10)	0.0031 (11)
O20T	0.0147 (13)	0.0159 (14)	0.0263 (14)	0.0055 (10)	−0.0019 (11)	0.0055 (11)
O21T	0.0127 (12)	0.0150 (13)	0.0240 (14)	0.0046 (10)	0.0028 (10)	0.0075 (11)
O22T	0.0162 (12)	0.0136 (13)	0.0156 (12)	0.0005 (10)	0.0014 (10)	0.0001 (10)
O23T	0.0139 (12)	0.0150 (13)	0.0187 (13)	0.0008 (10)	0.0049 (10)	0.0065 (10)
O24T	0.0165 (13)	0.0187 (14)	0.0168 (13)	0.0050 (11)	−0.0018 (10)	0.0005 (10)
O25W	0.0178 (13)	0.0182 (14)	0.0278 (15)	0.0071 (11)	0.0016 (11)	0.0062 (12)
O26W	0.0302 (16)	0.0238 (16)	0.0165 (13)	0.0047 (13)	0.0058 (12)	0.0023 (12)
O27W	0.0351 (17)	0.0310 (17)	0.0174 (14)	0.0118 (14)	0.0055 (12)	0.0121 (13)
O28W	0.0271 (15)	0.0180 (14)	0.0195 (14)	0.0085 (12)	0.0042 (11)	0.0050 (11)
O29W	0.040 (2)	0.040 (2)	0.043 (2)	0.0083 (16)	0.0114 (16)	0.0201 (17)
O30W	0.046 (3)	0.038 (2)	0.117 (4)	0.015 (2)	0.013 (3)	0.030 (3)
O31W	0.0258 (15)	0.0192 (15)	0.0157 (13)	0.0010 (12)	0.0010 (11)	0.0034 (11)
O32W	0.0257 (15)	0.0305 (17)	0.0152 (13)	−0.0007 (13)	0.0019 (12)	0.0036 (12)

Geometric parameters (Å, º) top

Cr1—O1Cⁱ	1.970 (2)	Mo6—O18B	1.964 (2)
Cr1—O1C	1.970 (3)	Mo6—O14C	2.301 (2)
Cr1—O2C	1.971 (2)	Mo6—O13C	2.307 (3)
Cr1—O2Cⁱ	1.971 (2)	K1—O25Wⁱⁱⁱ	2.722 (3)
Cr1—O3Cⁱ	1.975 (2)	K1—O25W^iv	2.778 (3)
Cr1—O3C	1.975 (2)	K1—O9T	2.809 (3)
Cr2—O13Cⁱⁱ	1.970 (2)	K1—O7T	2.825 (3)
Cr2—O13C	1.970 (2)	K1—O26W^iv	2.844 (3)
Cr2—O15C	1.972 (2)	K1—O23T	2.862 (3)
Cr2—O15Cⁱⁱ	1.972 (2)	K1—O24T^v	2.950 (3)
Cr2—O14Cⁱⁱ	1.976 (2)	K1—O27W	2.997 (3)
Cr2—O14C	1.976 (2)	K2—O29W	2.767 (4)
Mo1—O8T	1.696 (3)	K2—O17B	2.769 (3)
Mo1—O7T	1.699 (3)	K2—O19T^vi	2.799 (3)
Mo1—O4B	1.939 (3)	K2—O8T^vii	2.855 (3)
Mo1—O6Bⁱ	1.962 (3)	K2—O28W	2.858 (3)
Mo1—O1C	2.299 (3)	K2—O10T^viii	2.891 (3)
Mo1—O2C	2.321 (2)	K2—O30W^ix	2.897 (4)
Mo2—O10T	1.701 (3)	K2—O9T^viii	3.074 (3)
Mo2—O9T	1.705 (3)	O1C—H1	0.70 (6)
Mo2—O4B	1.913 (3)	O2C—H2	0.76 (6)
Mo2—O5B	1.986 (2)	O3C—H3	0.82 (6)
Mo2—O3C	2.276 (2)	O5B—O16Bⁱⁱⁱ	2.461 (3)
Mo2—O2C	2.296 (3)	O5B—H5	1.232 (7)
Mo3—O11T	1.701 (3)	O13C—H13	0.70 (5)
Mo3—O12T	1.722 (3)	O14C—H14	0.81 (5)
Mo3—O6B	1.879 (2)	O15C—H15	0.76 (6)
Mo3—O5B	2.001 (2)	O16B—H5ⁱⁱⁱ	1.231 (7)
Mo3—O3C	2.233 (2)	O25W—H25A	0.92 (3)
Mo3—O1Cⁱ	2.321 (3)	O25W—H25B	0.93 (3)
Mo4—O19T	1.698 (3)	O26W—H26A	0.91 (3)
Mo4—O20T	1.702 (3)	O26W—H26B	0.91 (3)
Mo4—O17B	1.916 (2)	O27W—H27A	0.90 (3)
Mo4—O16B	1.992 (2)	O27W—H27B	0.91 (3)
Mo4—O15Cⁱⁱ	2.275 (2)	O28W—H28A	0.91 (3)
Mo4—O14Cⁱⁱ	2.306 (2)	O28W—H28B	0.90 (3)
Mo5—O21T	1.703 (3)	O29W—H29A	0.95 (3)
Mo5—O22T	1.715 (3)	O29W—H29B	0.96 (3)
Mo5—O18B	1.894 (2)	O30W—H30A	0.92 (3)
Mo5—O16B	1.998 (2)	O30W—H30B	0.93 (3)
Mo5—O15Cⁱⁱ	2.264 (2)	O31W—H31A	0.90 (3)
Mo5—O13C	2.301 (2)	O31W—H31B	0.92 (3)
Mo6—O23T	1.700 (3)	O32W—H32A	0.89 (3)
Mo6—O24T	1.703 (3)	O32W—H32B	0.89 (3)
Mo6—O17Bⁱⁱ	1.919 (2)

O1Cⁱ—Cr1—O1C	180.00 (13)	O23T—Mo6—O24T	106.46 (13)
O1Cⁱ—Cr1—O2C	96.36 (11)	O23T—Mo6—O17Bⁱⁱ	102.39 (12)
O1C—Cr1—O2C	83.64 (10)	O24T—Mo6—O17Bⁱⁱ	98.17 (12)
O1Cⁱ—Cr1—O2Cⁱ	83.64 (10)	O23T—Mo6—O18B	95.85 (11)
O1C—Cr1—O2Cⁱ	96.36 (11)	O24T—Mo6—O18B	100.31 (12)
O2C—Cr1—O2Cⁱ	180.000 (1)	O17Bⁱⁱ—Mo6—O18B	149.10 (10)
O1Cⁱ—Cr1—O3Cⁱ	96.40 (11)	O23T—Mo6—O14C	92.72 (11)
O1C—Cr1—O3Cⁱ	83.60 (11)	O24T—Mo6—O14C	160.17 (11)
O2C—Cr1—O3Cⁱ	96.11 (10)	O17Bⁱⁱ—Mo6—O14C	72.22 (9)
O2Cⁱ—Cr1—O3Cⁱ	83.89 (10)	O18B—Mo6—O14C	82.29 (10)
O1Cⁱ—Cr1—O3C	83.60 (11)	O23T—Mo6—O13C	158.88 (11)
O1C—Cr1—O3C	96.40 (11)	O24T—Mo6—O13C	92.55 (11)
O2C—Cr1—O3C	83.89 (10)	O17Bⁱⁱ—Mo6—O13C	83.47 (10)
O2Cⁱ—Cr1—O3C	96.11 (10)	O18B—Mo6—O13C	71.21 (9)
O3Cⁱ—Cr1—O3C	180.0	O14C—Mo6—O13C	69.50 (9)
O13Cⁱⁱ—Cr2—O13C	180.00 (11)	O25Wⁱⁱⁱ—K1—O25W^iv	76.62 (9)
O13Cⁱⁱ—Cr2—O15C	83.38 (10)	O25Wⁱⁱⁱ—K1—O9T	103.15 (9)
O13C—Cr2—O15C	96.62 (10)	O25W^iv—K1—O9T	139.32 (9)
O13Cⁱⁱ—Cr2—O15Cⁱⁱ	96.62 (10)	O25Wⁱⁱⁱ—K1—O7T	153.61 (9)
O13C—Cr2—O15Cⁱⁱ	83.38 (10)	O25W^iv—K1—O7T	123.85 (9)
O15C—Cr2—O15Cⁱⁱ	180.00 (14)	O9T—K1—O7T	72.86 (8)
O13Cⁱⁱ—Cr2—O14Cⁱⁱ	83.45 (11)	O25Wⁱⁱⁱ—K1—O26W^iv	140.01 (9)
O13C—Cr2—O14Cⁱⁱ	96.55 (10)	O25W^iv—K1—O26W^iv	68.70 (9)
O15C—Cr2—O14Cⁱⁱ	96.19 (10)	O9T—K1—O26W^iv	91.09 (9)
O15Cⁱⁱ—Cr2—O14Cⁱⁱ	83.81 (10)	O7T—K1—O26W^iv	66.28 (8)
O13Cⁱⁱ—Cr2—O14C	96.55 (10)	O25Wⁱⁱⁱ—K1—O23T	74.25 (8)
O13C—Cr2—O14C	83.45 (11)	O25W^iv—K1—O23T	64.14 (8)
O15C—Cr2—O14C	83.81 (10)	O9T—K1—O23T	156.00 (8)
O15Cⁱⁱ—Cr2—O14C	96.19 (10)	O7T—K1—O23T	98.65 (8)
O14Cⁱⁱ—Cr2—O14C	180.000 (1)	O26W^iv—K1—O23T	106.24 (9)
O8T—Mo1—O7T	106.84 (14)	O25Wⁱⁱⁱ—K1—O24T^v	91.73 (9)
O8T—Mo1—O4B	99.43 (12)	O25W^iv—K1—O24T^v	68.54 (8)
O7T—Mo1—O4B	100.45 (12)	O9T—K1—O24T^v	70.82 (8)
O8T—Mo1—O6Bⁱ	101.16 (12)	O7T—K1—O24T^v	110.61 (8)
O7T—Mo1—O6Bⁱ	96.54 (12)	O26W^iv—K1—O24T^v	57.72 (8)
O4B—Mo1—O6Bⁱ	148.14 (11)	O23T—K1—O24T^v	132.52 (8)
O8T—Mo1—O1C	91.58 (12)	O25Wⁱⁱⁱ—K1—O27W	83.91 (9)
O7T—Mo1—O1C	160.03 (12)	O25W^iv—K1—O27W	134.40 (9)
O4B—Mo1—O1C	83.63 (10)	O9T—K1—O27W	84.97 (8)
O6Bⁱ—Mo1—O1C	71.79 (10)	O7T—K1—O27W	69.83 (8)
O8T—Mo1—O2C	159.33 (12)	O26W^iv—K1—O27W	135.05 (9)
O7T—Mo1—O2C	93.25 (12)	O23T—K1—O27W	71.05 (8)
O4B—Mo1—O2C	71.53 (10)	O24T^v—K1—O27W	153.77 (8)
O6Bⁱ—Mo1—O2C	80.83 (10)	O29W—K2—O17B	146.30 (10)
O1C—Mo1—O2C	69.32 (9)	O29W—K2—O19T^vi	137.95 (10)
O10T—Mo2—O9T	105.54 (13)	O17B—K2—O19T^vi	70.05 (8)
O10T—Mo2—O4B	98.88 (12)	O29W—K2—O8T^vii	67.52 (10)
O9T—Mo2—O4B	104.05 (12)	O17B—K2—O8T^vii	102.90 (8)
O10T—Mo2—O5B	98.79 (12)	O19T^vi—K2—O8T^vii	140.83 (9)
O9T—Mo2—O5B	95.15 (11)	O29W—K2—O28W	73.32 (10)
O4B—Mo2—O5B	149.26 (11)	O17B—K2—O28W	74.70 (8)
O10T—Mo2—O3C	93.09 (11)	O19T^vi—K2—O28W	121.69 (9)
O9T—Mo2—O3C	157.67 (11)	O8T^vii—K2—O28W	91.06 (9)
O4B—Mo2—O3C	84.69 (10)	O29W—K2—O10T^viii	63.77 (10)
O5B—Mo2—O3C	69.42 (9)	O17B—K2—O10T^viii	147.47 (8)
O10T—Mo2—O2C	161.78 (11)	O19T^vi—K2—O10T^viii	91.15 (8)
O9T—Mo2—O2C	92.28 (11)	O8T^vii—K2—O10T^viii	74.69 (8)
O4B—Mo2—O2C	72.55 (10)	O28W—K2—O10T^viii	137.05 (8)
O5B—Mo2—O2C	83.06 (10)	O29W—K2—O30W^ix	79.00 (15)
O3C—Mo2—O2C	70.46 (9)	O17B—K2—O30W^ix	107.05 (14)
O11T—Mo3—O12T	106.13 (13)	O19T^vi—K2—O30W^ix	66.13 (12)
O11T—Mo3—O6B	100.61 (12)	O8T^vii—K2—O30W^ix	146.33 (14)
O12T—Mo3—O6B	102.43 (12)	O28W—K2—O30W^ix	82.43 (11)
O11T—Mo3—O5B	100.44 (12)	O10T^viii—K2—O30W^ix	87.75 (13)
O12T—Mo3—O5B	92.82 (11)	O29W—K2—O9T^viii	110.89 (10)
O6B—Mo3—O5B	149.33 (11)	O17B—K2—O9T^viii	94.26 (7)
O11T—Mo3—O3C	92.56 (11)	O19T^vi—K2—O9T^viii	72.19 (8)
O12T—Mo3—O3C	156.92 (11)	O8T^vii—K2—O9T^viii	69.98 (8)
O6B—Mo3—O3C	86.90 (10)	O28W—K2—O9T^viii	155.67 (8)
O5B—Mo3—O3C	70.11 (9)	O10T^viii—K2—O9T^viii	53.95 (7)
O11T—Mo3—O1Cⁱ	161.82 (11)	O30W^ix—K2—O9T^viii	121.81 (11)
O12T—Mo3—O1Cⁱ	91.92 (11)	Cr1—O1C—Mo1	103.93 (11)
O6B—Mo3—O1Cⁱ	72.66 (10)	Cr1—O1C—Mo3ⁱ	101.37 (11)
O5B—Mo3—O1Cⁱ	80.47 (10)	Mo1—O1C—Mo3ⁱ	91.53 (9)
O3C—Mo3—O1Cⁱ	70.51 (9)	Cr1—O2C—Mo2	102.54 (11)
O19T—Mo4—O20T	106.50 (14)	Cr1—O2C—Mo1	103.10 (10)
O19T—Mo4—O17B	104.09 (12)	Mo2—O2C—Mo1	92.00 (9)
O20T—Mo4—O17B	98.21 (12)	Cr1—O3C—Mo3	104.32 (11)
O19T—Mo4—O16B	94.09 (12)	Cr1—O3C—Mo2	103.08 (11)
O20T—Mo4—O16B	99.92 (12)	Mo3—O3C—Mo2	97.93 (10)
O17B—Mo4—O16B	149.41 (10)	Mo2—O4B—Mo1	119.12 (13)
O19T—Mo4—O15Cⁱⁱ	156.61 (11)	Mo2—O5B—Mo3	117.13 (12)
O20T—Mo4—O15Cⁱⁱ	93.29 (11)	Mo2—O5B—O16Bⁱⁱⁱ	121.72 (12)
O17B—Mo4—O15Cⁱⁱ	84.78 (10)	Mo3—O5B—O16Bⁱⁱⁱ	121.01 (12)
O16B—Mo4—O15Cⁱⁱ	69.81 (9)	Mo3—O6B—Mo1ⁱ	118.98 (13)
O19T—Mo4—O14Cⁱⁱ	91.56 (11)	Cr2—O13C—Mo5	102.58 (10)
O20T—Mo4—O14Cⁱⁱ	161.32 (12)	Cr2—O13C—Mo6	103.49 (11)
O17B—Mo4—O14Cⁱⁱ	72.15 (9)	Mo5—O13C—Mo6	92.48 (9)
O16B—Mo4—O14Cⁱⁱ	83.13 (9)	Cr2—O14C—Mo6	103.53 (11)
O15Cⁱⁱ—Mo4—O14Cⁱⁱ	70.30 (9)	Cr2—O14C—Mo4ⁱⁱ	102.33 (10)
O21T—Mo5—O22T	106.65 (13)	Mo6—O14C—Mo4ⁱⁱ	91.61 (8)
O21T—Mo5—O18B	99.32 (12)	Cr2—O15C—Mo5ⁱⁱ	103.82 (10)
O22T—Mo5—O18B	102.90 (12)	Cr2—O15C—Mo4ⁱⁱ	103.53 (10)
O21T—Mo5—O16B	100.17 (11)	Mo5ⁱⁱ—O15C—Mo4ⁱⁱ	97.60 (9)
O22T—Mo5—O16B	93.06 (11)	Mo4—O16B—Mo5	117.72 (11)
O18B—Mo5—O16B	150.02 (10)	Mo4—O17B—Mo6ⁱⁱ	118.91 (12)
O21T—Mo5—O15Cⁱⁱ	93.02 (11)	Mo5—O18B—Mo6	119.24 (12)
O22T—Mo5—O15Cⁱⁱ	156.22 (11)	H25A—O25W—H25B	96 (5)
O18B—Mo5—O15Cⁱⁱ	86.51 (10)	H26A—O26W—H26B	107 (5)
O16B—Mo5—O15Cⁱⁱ	69.93 (9)	H27A—O27W—H27B	108 (5)
O21T—Mo5—O13C	161.33 (11)	H28A—O28W—H28B	104 (5)
O22T—Mo5—O13C	91.69 (11)	H29A—O29W—H29B	121 (6)
O18B—Mo5—O13C	72.50 (10)	H30A—O30W—H30B	83 (7)
O16B—Mo5—O13C	81.93 (10)	H31A—O31W—H31B	107 (5)
O15Cⁱⁱ—Mo5—O13C	70.11 (9)	H32A—O32W—H32B	112 (5)

Symmetry codes: (i) −x+1, −y, −z+2; (ii) −x+1, −y+1, −z+1; (iii) −x+1, −y, −z+1; (iv) x−1, y, z; (v) −x, −y, −z+1; (vi) −x+2, −y+1, −z+1; (vii) −x+1, −y+1, −z+2; (viii) x+1, y+1, z; (ix) x+1, y, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1C—H1···O22T^x	0.70 (6)	2.11 (6)	2.789 (4)	164 (6)
O2C—H2···O27W	0.76 (6)	2.01 (6)	2.753 (4)	166 (6)
O3C—H3···O31W^xi	0.82 (6)	1.79 (6)	2.604 (4)	176 (6)
O5B—H5···O16Bⁱⁱⁱ	1.23 (1)	1.23 (1)	2.461 (3)	175 (5)
O13C—H13···O12Tⁱⁱⁱ	0.70 (5)	2.05 (5)	2.734 (4)	167 (5)
O14C—H14···O32W	0.81 (5)	2.01 (5)	2.776 (4)	158 (5)
O15C—H15···O28Wⁱⁱ	0.76 (6)	1.87 (6)	2.619 (4)	170 (6)
O25W—H25A···O21T	0.92 (3)	1.96 (3)	2.838 (4)	157 (5)
O25W—H25B···O20T	0.93 (3)	1.92 (3)	2.819 (4)	162 (5)
O26W—H26A···O4Bⁱ	0.91 (3)	1.89 (3)	2.748 (4)	158 (5)
O26W—H26B···O24Tⁱⁱⁱ	0.91 (3)	1.91 (3)	2.798 (4)	164 (5)
O27W—H27A···O18B	0.90 (3)	1.95 (4)	2.775 (4)	151 (5)
O27W—H27B···O32W	0.91 (3)	1.92 (3)	2.825 (5)	171 (5)
O28W—H28A···O12T^xii	0.91 (3)	2.00 (4)	2.785 (4)	144 (5)
O28W—H28B···O31Wⁱⁱ	0.90 (3)	1.82 (3)	2.706 (4)	170 (5)
O29W—H29A···O11Tⁱ	0.95 (3)	2.11 (4)	2.949 (5)	146 (6)
O29W—H29B···O8T^vii	0.96 (3)	2.18 (3)	3.126 (5)	169 (6)
O31W—H31A···O26Wⁱⁱ	0.90 (3)	1.77 (3)	2.665 (4)	170 (5)
O31W—H31B···O27Wⁱⁱ	0.92 (3)	2.18 (4)	2.952 (4)	141 (4)
O32W—H32A···O30W	0.89 (3)	2.06 (3)	2.947 (6)	171 (5)
O32W—H32B···O6Bⁱ	0.89 (3)	2.39 (5)	3.000 (4)	126 (5)

Symmetry codes: (i) −x+1, −y, −z+2; (ii) −x+1, −y+1, −z+1; (iii) −x+1, −y, −z+1; (vii) −x+1, −y+1, −z+2; (x) x, y, z+1; (xi) x, y−1, z+1; (xii) x, y+1, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1C—H1···O22Tⁱ	0.70 (6)	2.11 (6)	2.789 (4)	164 (6)
O2C—H2···O27W	0.76 (6)	2.01 (6)	2.753 (4)	166 (6)
O3C—H3···O31Wⁱⁱ	0.82 (6)	1.79 (6)	2.604 (4)	176 (6)
O5B—H5···O16Bⁱⁱⁱ	1.232 (7)	1.232 (7)	2.461 (3)	175 (5)
O13C—H13···O12Tⁱⁱⁱ	0.70 (5)	2.05 (5)	2.734 (4)	167 (5)
O14C—H14···O32W	0.81 (5)	2.01 (5)	2.776 (4)	158 (5)
O15C—H15···O28W^iv	0.76 (6)	1.87 (6)	2.619 (4)	170 (6)
O25W—H25A···O21T	0.92 (3)	1.96 (3)	2.838 (4)	157 (5)
O25W—H25B···O20T	0.93 (3)	1.92 (3)	2.819 (4)	162 (5)
O26W—H26A···O4B^v	0.91 (3)	1.89 (3)	2.748 (4)	158 (5)
O26W—H26B···O24Tⁱⁱⁱ	0.91 (3)	1.91 (3)	2.798 (4)	164 (5)
O27W—H27A···O18B	0.90 (3)	1.95 (4)	2.775 (4)	151 (5)
O27W—H27B···O32W	0.91 (3)	1.92 (3)	2.825 (5)	171 (5)
O28W—H28A···O12T^vi	0.91 (3)	2.00 (4)	2.785 (4)	144 (5)
O28W—H28B···O31W^iv	0.90 (3)	1.82 (3)	2.706 (4)	170 (5)
O29W—H29A···O11T^v	0.95 (3)	2.11 (4)	2.949 (5)	146 (6)
O29W—H29B···O8T^vii	0.96 (3)	2.18 (3)	3.126 (5)	169 (6)
O31W—H31A···O26W^iv	0.90 (3)	1.77 (3)	2.665 (4)	170 (5)
O31W—H31B···O27W^iv	0.92 (3)	2.18 (4)	2.952 (4)	141 (4)
O32W—H32A···O30W	0.89 (3)	2.06 (3)	2.947 (6)	171 (5)
O32W—H32B···O6B^v	0.89 (3)	2.39 (5)	3.000 (4)	126 (5)

Symmetry codes: (i) x, y, z+1; (ii) x, y−1, z+1; (iii) −x+1, −y, −z+1; (iv) −x+1, −y+1, −z+1; (v) −x+1, −y, −z+2; (vi) x, y+1, z; (vii) −x+1, −y+1, −z+2.

Experimental details

Crystal data
Chemical formula	K₂[H₇CrMo₆O₂₄]·8H₂O
M_r	1241.02
Crystal system, space group	Triclinic, P1
Temperature (K)	446
a, b, c (Å)	10.4588 (2), 10.8553 (2), 12.6287 (3)
α, β, γ (°)	99.296 (1), 94.469 (1), 99.283 (1)
V (Å³)	1388.44 (5)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	3.42
Crystal size (mm)	0.18 × 0.11 × 0.09

Data collection
Diffractometer	Bruker SMART APEXII CCD diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 2008)
T_min, T_max	0.645, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	23489, 6028, 5893
R_int	0.025
(sin θ/λ)_max (Å⁻¹)	0.639

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.024, 0.064, 1.11
No. of reflections	6028
No. of parameters	450
No. of restraints	17
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	1.58, −0.67

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 2012), PLATON (Spek, 2009) and DIAMOND (Brandenburg, 1998).

Acknowledgements

This is part of work supported by the Pukyong National University Research Fund in 2011 (C-D-2011-0829). The X-ray centre of the Gyeongsang National University is acknowledged for providing access to the single-crystal diffractometer.

References

Anderson, J. S. (1937). Nature (London), 140, 850. CrossRef Google Scholar
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Volume 71| Part 2| February 2015| Pages 157-160

doi:10.1107/S2056989015000390

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