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Sodium indium(III) chromate(VI) dihydrate, NaIn(CrO4)2·2H2O, synthesized from an aqueous solution at room temperature, is the first indium(III) member of the large family of compounds with kröhnkite [Na2CuII(SVIO4)2·2H2O]-type chains. The crystal structure is based on infinite octa­hedral-tetra­hedral [In(CrO4)2(H2O)2]- chains along [010], linked via charge-balancing Na+ cations. The slightly distorted InO4(H2O)2 octa­hedra are characterized by a mean In-O distance of 2.125 Å. The CrO4 tetra­hedra are strongly distorted (mean Cr-O = 1.641 Å). The Na atom shows an octa­hedral coordination, unprecedented among compounds with kröhnkite-type chains. The NaO6 octa­hedra share opposite edges with the InO4(H2O)2 octa­hedra to form infinite [001] chains. The hydrogen bonds are of medium strength. NaIn(CrO4)2·2H2O belongs to the structural type F2 in the classification of Fleck, Kolitsch & Hertweck [Z. Kristallogr. (2002), 217, 435-443], and is isotypic with KAl(CrO4)2·2H2O and MFe(CrO4)2·2H2O (M = K, Tl or NH4). All atoms are in special positions except one O atom.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270106012996/iz3003sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106012996/iz3003Isup2.hkl
Contains datablock I

Comment top

NaIn(CrO4)2·2H2O was synthesized from an aqueous solution at room temperature as part of a comprehensive study of the crystal chemistry of the large kröhnkite [Na2CuII(SVIO4)2·2H2O] family of oxysalts. The title compound is the first InIII member of this family, which comprises both natural and synthetic oxysalt compounds based on infinite octahedral–tetrahedral [M(XO4)2(H2O)2] chains, where M is either divalent (Mg, Mn, Fe, Co, Ni, Cu, Zn or Cd) or trivalent (Al, Fe, Sc, In or Tl), and where X is either pentavalent (P or As) or hexavalent (S, Se, Cr, Mo or W), as discussed in detail in our previous classification (Fleck et al., 2002) and subsequent contributions (Fleck & Kolitsch, 2003; Kolitsch & Fleck, 2005, 2006). In the kröhnkite-type chains, MO6 octahedra are corner-linked to bridging XO4 tetrahedra. Very small to very large mono- or divalent A atoms occupy the space between adjacent chains and provide charge balance. The resulting general formula is AnM(XO4)2·2H2O, where A = Na, K, Rb, Cs, Ag, Tl, NH4, H or Ca (n = 1, 2).

NaIn(CrO4)2·2H2O belongs to the structural type F2 in the classification of Fleck et al. (2002), and is isotypic with KAl(CrO4)2·2H2O (Cudennec & Riou, 1977) and MFe(CrO4)2·2H2O (M = K, Tl or NH4) (Gravereau & Hardy, 1972). Note that the crystal structures of these previously reported chromates have been described in a non-standard setting (same space group, but with β > 120°); the title compound is described here using a standard setting.

Interestingly, NaIn(CrO4)2·2H2O is not isotypic with the other known sodium metal(III) chromates containing kröhnkite-type chains, viz. NaAl(CrO4)2·2H2O (Cudennec & Riou, 1977) and NaFe(CrO4)2·2H2O (Hardy & Gravereau, 1970), although these two crystallize in a closely related structure type (space group C2/c; type F1 in the classification of Fleck et al., 2002). Efforts to synthesize the K and Rb analogues of the title compound from aqeuous solutions at room temperature have so far been unsuccessful.

The crystal structure of NaIn(CrO4)2·2H2O is based on infinite octahedral–tetrahedral [In(CrO4)2(H2O)2] chains extending along [010], linked via charge-balancing Na+ cations (Figs. 1–3). The slightly distorted InO4(H2O)2 octahedra are characterized by a mean In—O distance of 2.125 Å. The CrO4 tetrahedra show a very strong bond-length distortion (Table 1), with a mean Cr—O distance of 1.641 Å. The Na atom shows a distinct octahedral coordination, with a mean Na—O bond length of 2.587 Å (Table 1; further O neighbours are at distances > 3.16 Å). Such an octahedral coordination of A atoms is unprecedented among compounds based on kröhnkite-type chains. The distorted NaO6 octahedra share opposite edges with the InO4(H2O)2 octahedra to form infinite [001] chains (Fig. 2), i.e. these octahedral–octahedral chains extend perpendicular to the octahedral–tetrahedral chains. In other kröhnkite-type sodium oxysalts, the Na atoms have one of three coordination types. Firstly, Na may have a distinct [7]-coordination [Kröhnkite, Na2Cu(SO4)2·2H2O (monoclinic, type D) (Hawthorne & Ferguson, 1975) or Na2Mn(XO4)2·2H2O (X = S or Se) (monoclinic, type D) (Wildner & Stoilova, 2003)]. Secondly, Na may have a poorly defined [7]- to [8]-coordination [Na2M(SeO4)2·2H2O (M = Zn, Co or Ni) (triclinic, type A) (Wildner & Stoilova, 2003) or Na2Cd(SO4)2·2H2O (monoclinic, type D) (Wildner & Stoilova, 2003)]. Thirdly, Na may have a [6 + 1]-coordination [Na2Cu(SeO4)2·2H2O (triclinic, type A) (Peytavin et al., 1974) or Na2Cd(SeO4)2·2H2O (monoclinic, type D) (Wildner & Stoilova, 2003)]. In this last case, even if the seventh O ligand (at about 2.7 Å) were to be neglected, the resulting distorted NaO6 octahedra would be connected to adjacent octahedra in a different way from that in the title compound, i.e. no infinite octahedral–octahedral chains are formed.

Bond-valence sums for all atoms were calculated using the bond-valence parameters from Brese & O'Keeffe (1991). The bond-valence sums are 0.72 (Na), 3.29 (In), 6.09 (Cr), 0.48 (O1 = H2O), 1.78 (O2), 1.72 (O3), and 2.06 (O4) v.u. (valence units), and thus are all reasonably close to ideal values. Although the relatively low bond-valence sum for the Na site might indicate that the Na+ cation is slightly too small for the void in which it is located, the equivalent displacement parameter of the Na atom does not indicate that it `rattles' within its void. The somewhat undersaturated O3 and O2 ligands are, as expected, acceptors of the two hydrogen bonds (Table 2). These bonds, which both reinforce the atomic arrangement along [001] (Figs. 1 and 2), are of medium strength (Table 2).

Experimental top

Tiny orange–yellow pointed prisms of the title compound crystallized at room temperature from an acidic aqueous solution (pH about 3) containing dissolved Na2CO3, In(NO3)3·H2O and CrO3 (Quantities or molar ratio?) in distilled water (Volume?). The crystals were accompanied by minor quantities of small yellow plates of Na2Cr2O7·2H2O (Kharitonov et al., 1969, 1970; Bulka et al., 1973) and large colourless rounded block-like crystals of NaNO3.

Refinement top

All O—H distances were restrained to a length of 0.90 (5) Å. Isotropic displacement parameters of the H atoms were refined freely; the results show that atom H2 has an anomalously high Uiso value and thus appears to be disordered to some extent (it is also involved in the weaker of the two hydrogen bonds). The highest electron-density peak in NaIn(CrO4)2·2H2O, 1.1 e Å−3, is at a distance of 0.42 Å from the O4 site. The deepest hole in the difference map, −0.9 e Å−3, is at a distance of 0.87 Å from the O4 site.

Computing details top

Data collection: COLLECT (Nonius, 2004); cell refinement: SCALEPACK (Otwinowski et al., 2003); data reduction: SCALEPACK and DENZO (Otwinowski et al., 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 1999) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The crystal structure of NaIn(CrO4)2·2H2O in views (a) along [010], in the direction of the infinite kröhnkite-type octahedral–tetrahedral [In(CrO4)2(H2O)2] chains, and (b) along [110], allowing a suitable top view of the kröhnkite-type chains. InO4(H2O)2 octahedra are bridged by CrO4 tetrahedra. The intercalated Na+ cations (shown as spheres) are octahedrally coordinated (compare Fig. 2). The hydrogen bonding is indicated as dashed lines and the unit cell is outlined.
[Figure 2] Fig. 2. Two views of the octahedral–octahedral chains in NaIn(CrO4)2·2H2O, (a) along [001], parallel to the chains, and (b) along [201], perpendicular to the chains. Distorted NaO6 octahedra share opposite edges with InO4(H2O)2 octahedra to form infinite [001] chains. Such octahedral–octahedral chains are unprecedented among compounds containing kröhnkite-type chains. The hydrogen bonding is indicated as dashed lines and the unit cell is outlined.
[Figure 3] Fig. 3. The connectivity in NaIn(CrO4)2·2H2O, shown with displacement ellipsoids at the 70% probability level. [Symmetry codes: (ii) −x,y,-z; (iii) −x,-y,-z; (iv) x,-y,z.]
sodium indium(III) chromate(VI) dihydrate top
Crystal data top
NaIn(CrO4)2·2H2OF(000) = 384
Mr = 405.84Dx = 3.286 Mg m3
Monoclinic, C2/mMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yCell parameters from 806 reflections
a = 10.741 (2) Åθ = 2.0–32.5°
b = 5.567 (1) ŵ = 5.48 mm1
c = 7.497 (1) ÅT = 293 K
β = 113.78 (3)°Prism, orange–yellow
V = 410.23 (15) Å30.06 × 0.02 × 0.02 mm
Z = 2
Data collection top
Nonius KappaCCD area-detector
diffractometer
804 independent reflections
Radiation source: fine-focus sealed tube708 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.015
ϕ and ω scansθmax = 32.5°, θmin = 4.0°
Absorption correction: multi-scan
(SCALEPACK; Otwinowski et al., 2003)
h = 1516
Tmin = 0.735, Tmax = 0.898k = 88
1474 measured reflectionsl = 1111
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.024H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.060 w = 1/[σ2(Fo2) + (0.03P)2 + 1.25P]
where P = (Fo2 + 2Fc2)/3
S = 1.07(Δ/σ)max < 0.001
804 reflectionsΔρmax = 1.12 e Å3
49 parametersΔρmin = 0.90 e Å3
2 restraintsExtinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0040 (8)
Crystal data top
NaIn(CrO4)2·2H2OV = 410.23 (15) Å3
Mr = 405.84Z = 2
Monoclinic, C2/mMo Kα radiation
a = 10.741 (2) ŵ = 5.48 mm1
b = 5.567 (1) ÅT = 293 K
c = 7.497 (1) Å0.06 × 0.02 × 0.02 mm
β = 113.78 (3)°
Data collection top
Nonius KappaCCD area-detector
diffractometer
804 independent reflections
Absorption correction: multi-scan
(SCALEPACK; Otwinowski et al., 2003)
708 reflections with I > 2σ(I)
Tmin = 0.735, Tmax = 0.898Rint = 0.015
1474 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0242 restraints
wR(F2) = 0.060H atoms treated by a mixture of independent and constrained refinement
S = 1.07Δρmax = 1.12 e Å3
804 reflectionsΔρmin = 0.90 e Å3
49 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 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
Na0.00000.00000.50000.0410 (7)
In0.00000.00000.00000.01388 (12)
Cr0.11112 (5)0.50000.31447 (7)0.01379 (13)
O10.2171 (3)0.00000.0714 (4)0.0231 (6)
O20.2492 (3)0.50000.2785 (5)0.0281 (6)
O30.1479 (3)0.50000.5428 (4)0.0373 (8)
O40.0193 (2)0.2525 (5)0.2181 (4)0.0542 (9)
H10.271 (5)0.00000.193 (6)0.039 (15)*
H20.240 (14)0.00000.028 (14)0.17 (5)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Na0.0288 (13)0.072 (2)0.0226 (13)0.0000.0111 (10)0.000
In0.01485 (17)0.01127 (17)0.01448 (18)0.0000.00484 (12)0.000
Cr0.0144 (3)0.0150 (3)0.0110 (3)0.0000.0041 (2)0.000
O10.0166 (12)0.0347 (16)0.0160 (13)0.0000.0044 (10)0.000
O20.0212 (13)0.0278 (15)0.0380 (18)0.0000.0147 (13)0.000
O30.0347 (17)0.060 (2)0.0137 (13)0.0000.0058 (12)0.000
O40.0385 (13)0.0631 (18)0.0761 (19)0.0321 (12)0.0388 (14)0.0595 (16)
Geometric parameters (Å, º) top
In—O42.102 (2)Cr—O4iv1.679 (2)
In—O4i2.102 (2)Na—O2v2.531 (3)
In—O4ii2.102 (2)Na—O2vi2.531 (3)
In—O4iii2.102 (2)Na—O4vii2.615 (3)
In—O1i2.172 (3)Na—O4ii2.615 (3)
In—O12.172 (3)Na—O4viii2.615 (3)
Cr—O31.594 (3)Na—O42.615 (3)
Cr—O21.611 (3)O1—H10.86 (4)
Cr—O41.679 (2)O1—H20.88 (5)
O2v—Na—O2vi180.00 (9)O4ii—In—O4iii180.00 (12)
O2v—Na—O4vii83.10 (9)O4—In—O1i87.19 (9)
O2vi—Na—O4vii96.90 (9)O4i—In—O1i92.81 (9)
O2v—Na—O4ii96.90 (9)O4ii—In—O1i87.19 (9)
O2vi—Na—O4ii83.10 (9)O4iii—In—O1i92.81 (9)
O4vii—Na—O4ii180.0O4—In—O192.81 (9)
O2v—Na—O4viii83.10 (9)O4i—In—O187.19 (9)
O2vi—Na—O4viii96.90 (9)O4ii—In—O192.81 (9)
O4vii—Na—O4viii65.03 (10)O4iii—In—O187.19 (9)
O4ii—Na—O4viii114.97 (10)O1i—In—O1180.00 (15)
O2v—Na—O496.90 (9)O3—Cr—O2109.49 (17)
O2vi—Na—O483.10 (9)O3—Cr—O4108.09 (13)
O4vii—Na—O4114.97 (10)O2—Cr—O4110.41 (10)
O4ii—Na—O465.03 (10)O3—Cr—O4iv108.09 (13)
O4viii—Na—O4180.0O2—Cr—O4iv110.41 (10)
O4—In—O4i180.00 (12)O4—Cr—O4iv110.3 (2)
O4—In—O4ii83.9 (2)In—O1—H1117 (4)
O4i—In—O4ii96.1 (2)In—O1—H2116 (9)
O4—In—O4iii96.1 (2)H1—O1—H2127 (10)
O4i—In—O4iii83.9 (2)
Symmetry codes: (i) x, y, z; (ii) x, y, z; (iii) x, y, z; (iv) x, y+1, z; (v) x+1/2, y+1/2, z+1; (vi) x1/2, y1/2, z; (vii) x, y, z+1; (viii) x, y, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O3v0.86 (4)1.81 (4)2.662 (4)168 (6)
O1—H2···O2ix0.88 (5)1.92 (6)2.789 (5)168 (13)
Symmetry codes: (v) x+1/2, y+1/2, z+1; (ix) x+1/2, y+1/2, z.

Experimental details

Crystal data
Chemical formulaNaIn(CrO4)2·2H2O
Mr405.84
Crystal system, space groupMonoclinic, C2/m
Temperature (K)293
a, b, c (Å)10.741 (2), 5.567 (1), 7.497 (1)
β (°) 113.78 (3)
V3)410.23 (15)
Z2
Radiation typeMo Kα
µ (mm1)5.48
Crystal size (mm)0.06 × 0.02 × 0.02
Data collection
DiffractometerNonius KappaCCD area-detector
diffractometer
Absorption correctionMulti-scan
(SCALEPACK; Otwinowski et al., 2003)
Tmin, Tmax0.735, 0.898
No. of measured, independent and
observed [I > 2σ(I)] reflections
1474, 804, 708
Rint0.015
(sin θ/λ)max1)0.756
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.024, 0.060, 1.07
No. of reflections804
No. of parameters49
No. of restraints2
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)1.12, 0.90

Computer programs: COLLECT (Nonius, 2004), SCALEPACK (Otwinowski et al., 2003), SCALEPACK and DENZO (Otwinowski et al., 2003), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ATOMS (Dowty, 1999) and ORTEP-3 for Windows (Farrugia, 1997), SHELXL97.

Selected bond lengths (Å) top
In—O42.102 (2)Cr—O41.679 (2)
In—O12.172 (3)Na—O2i2.531 (3)
Cr—O31.594 (3)Na—O42.615 (3)
Cr—O21.611 (3)
Symmetry code: (i) x+1/2, y+1/2, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O3i0.86 (4)1.81 (4)2.662 (4)168 (6)
O1—H2···O2ii0.88 (5)1.92 (6)2.789 (5)168 (13)
Symmetry codes: (i) x+1/2, y+1/2, z+1; (ii) x+1/2, y+1/2, z.
 

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