NaIn(CrO4)2·2H2O, the first indium(III) member of the kroehnkite family

Article abstract of DOI:10.1107/S0108270106012996

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 kroehnkite [Na₂Cu^II(S ^VIO₄)₂·2H₂O]-type chains. The crystal structure is based on infinite octahedral-tetrahedral [In(CrO ₄)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 A. The CrO₄ tetrahedra are strongly distorted (mean Cr - O = 1.641 A). The Na atom shows an octahedral coordination, unprecedented among compounds with kroehnkite-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(CrO ₄)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.

Full text of DOI:10.1107/S0108270106012996

inorganic compounds
Acta Crystallographica Section C
Crystal Structure
general formula is AnM(XO4)2Á2H2O, where A = Na, K, Rb,
Cs, Ag, Tl, NH4, H or Ca and n = 1 or 2.
Communications
NaIn(CrO4)2Á2H2O belongs to the structural type F2 in the
classi®cation of Fleck et al. (2002), and is isotypic with
KAl(CrO4)2Á2H2O (Cudennec & Riou, 1977) and MFe-
(CrO4)2Á2H2O (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 ꢀ > 120ꢀ); the title
compound is described here using a standard setting.
Interestingly, NaIn(CrO4)2Á2H2O is not isotypic with the
ISSN 0108-2701
NaIn(CrO4)2Á2H2O, the first
indium(III) member of the krohnkite
È
family
È
other known sodium metal(III) chromates containing krohn-
Uwe Kolitsch
kite-type chains, viz. NaAl(CrO4)2Á2H2O (Cudennec & Riou,
1977) and NaFe(CrO4)2Á2H2O (Hardy & Gravereau, 1970),
although these two crystallize in a closely related structure
type (space group C2/c; type F1 in the classi®cation of Fleck et
al., 2002). Efforts to synthesize the K and Rb analogues of the
title compound from aqueous solutions at room temperature
have so far been unsuccessful.
Universitat Wien, Institut fur Mineralogie und Kristallographie, Geozentrum,
È
È
Althanstrasse 14, A-1090 Wien, Austria
Correspondence e-mail: uwe.kolitsch@univie.ac.at
Received 28 March 2006
Accepted 10 April 2006
Online 29 April 2006
The crystal structure of NaIn(CrO4)2Á2H2O is based on
in®nite 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
Sodium indium(III) chromate(VI) dihydrate, NaIn(CrO4)2Á-
2H2O, synthesized from an aqueous solution at room
temperature, is the ®rst indium(III) member of the large
II VI
È
family of compounds with krohnkite [Na2Cu (S O4)2Á2H2O]-
Ê
characterized by a mean InÐO distance of 2.125 A. The CrO4
tetrahedra show a very strong bond-length distortion (Table 1),
type chains. The crystal structure is based on in®nite
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
Ê
with a mean CrÐO distance of 1.641 A. The Na atom shows a
Ê
InÐO distance of 2.125 A. The CrO4 tetrahedra are strongly
Ê
distorted (mean CrÐO = 1.641 A). The Na atom shows an
octahedral coordination, unprecedented among compounds
È
with krohnkite-type chains. The NaO6 octahedra share
opposite edges with the InO4(H2O)2 octahedra to form
in®nite [001] chains. The hydrogen bonds are of medium
strength. NaIn(CrO4)2Á2H2O belongs to the structural type F2
in the classi®cation of Fleck, Kolitsch & Hertweck [Z.
Kristallogr. (2002), 217, 435±443], and is isotypic with
KAl(CrO4)2Á2H2O and MFe(CrO4)2Á2H2O (M = K, Tl or
NH4). All atoms are in special positions except one O atom.
Comment
NaIn(CrO4)2Á2H2O was synthesized from an aqueous solution
at room temperature as part of a comprehensive study of
II
È
the crystal chemistry of the large krohnkite [Na2Cu -
(SVIO4)2Á2H2O] family of oxysalts. The title compound is the
®rst InIII member of this family, which comprises both natural
and synthetic oxysalt compounds based on in®nite octahedral±
tetrahedral [M(XO4)2(H2O)2] chains, where M is either di-
valent (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 classi®cation (Fleck et al., 2002) and subsequent
contributions (Fleck & Kolitsch, 2003; Kolitsch & Fleck, 2005,
Figure 1
The crystal structure of NaIn(CrO4)2Á2H2O in views (a) along [010], in
È
the direction of the in®nite krohnkite-type octahedral±tetrahedral
[In(CrO4)2(H2O)2] chains, and (b) along [110], allowing a suitable top
È
2006). In the krohnkite-type chains, MO6 octahedra are
È
view of the krohnkite-type chains. InO4(H2O)2 octahedra are bridged by
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
CrO4 tetrahedra. The intercalated Na+ cations (shown as spheres) are
octahedrally coordinated (compare with Fig. 2). The hydrogen bonding is
indicated by dashed lines and the unit cell is outlined.
Acta Cryst. (2006). C62, i35±i37
DOI: 10.1107/S0108270106012996
# 2006 International Union of Crystallography i35

inorganic compounds
distinct octahedral coordination, with a mean NaÐO bond
Ê
length of 2.587 A (Table 1; further O-atom neighbours are at
Ê
distances greater than 3.16 A). Such an octahedral coordina-
(triclinic, type A) (Wildner & Stoilova, 2003) or Na2Cd-
(SO4)2Á2H2O (monoclinic, type D) (Wildner & Stoilova,
2003)]. Thirdly, Na may have a [6+1]-coordination [Na2Cu-
(SeO4)2Á2H2O (triclinic, type A) (Peytavin et al., 1974) or
Na2Cd(SeO4)2Á2H2O (monoclinic, type D) (Wildner & Stoi-
lova, 2003)]. In this last case, even if the seventh oxygen ligand
tion of A atoms is unprecedented among compounds based on
È
krohnkite-type chains. The distorted NaO6 octahedra share
opposite edges with the InO4(H2O)2 octahedra to form in®nite
[001] chains (Fig. 2), i.e. these octahedral±octahedral chains
extend perpendicular to the octahedral±tetrahedral chains. In
È
other krohnkite-type sodium oxysalts, the Na atoms have one
of three coordination types. Firstly, Na may have a distinct [7]-
Ê
(at about 2.7 A) 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 in®nite
octahedral±octahedral chains are formed.
È
coordination [krohnkite, Na2Cu(SO4)2Á2H2O (monoclinic,
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) 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).
type D) (Hawthorne & Ferguson, 1975) or Na2Mn(XO4)2Á-
2H2O (X = S or Se) (monoclinic, type D) (Wildner & Stoilova,
2003)]. Secondly, Na may have a poorly de®ned [7]- to [8]-
coordination [Na2M(SeO4)2Á2H2O (M = Zn, Co or Ni)
Experimental
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)3ÁH2O and CrO3 (Na:In:Cr
molar ratio unknown, but estimated to be about 2:1:4) in distilled
water. The crystals were accompanied by minor quantities of small
yellow plates of Na2Cr2O7Á2H2O (Kharitonov et al., 1969, 1970; Bulka
et al., 1973) and large colourless rounded block-shaped crystals of
NaNO3.
Crystal data
Figure 2
NaIn(CrO4)2Á2H2O
Z = 2
Dx = 3.286 Mg m
Mo Kꢁ radiation
ꢂ = 5.48 mm
T = 293 (2) K
Prism, orange±yellow
0.06 Â 0.02 Â 0.02 mm
3
Two views of the octahedral±octahedral chains in NaIn(CrO4)2Á2H2O, viz.
(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 in®nite [001] chains. Such octahedral±
octahedral chains are unprecedented among compounds containing
Mr = 405.84
Monoclinic, C2=m
1
Ê
a = 10.741 (2) A
Ê
b = 5.567 (1) A
Ê
c = 7.497 (1) A
ꢀ = 113.78 (3)ꢀ
V = 410.23 (15) A
È
krohnkite-type chains. The hydrogen bonding is indicated by dashed lines
and the unit cell is outlined.
3
Ê
Data collection
Nonius KappaCCD area-detector
diffractometer
' and ! scans
Absorption correction: multi-scan
(SCALEPACK; Otwinowski et
al., 2003)
1474 measured re¯ections
804 independent re¯ections
708 re¯ections with I > 2ꢃ(I)
Rint = 0.015
ꢄmax = 32.5ꢀ
Tmin = 0.735, Tmax = 0.898
Re®nement
Re®nement on F2
R[F2 > 2ꢃ(F2)] = 0.024
wR(F2) = 0.060
w = 1/[ꢃ2(Fo2) + (0.03P)2
+ 1.25P]
2
where P = (Fo + 2Fc2)/3
S = 1.07
804 re¯ections
49 parameters
(Á/ꢃ)max < 0.001
3
Ê
Áꢅmax = 1.12 e A
3
Ê
0.90 e A
Figure 3
Áꢅmin
=
The connectivity in NaIn(CrO4)2Á2H2O, shown with displacement
ellipsoids at the 70% probability level. [Symmetry codes: (ii) x, y, z;
(iii) x, y, z; (iv) x, y, z.]
H atoms treated by a mixture of
independent and constrained
re®nement
Extinction correction: SHELXL97
(Sheldrick, 1997)
Extinction coef®cient: 0.0040 (8)
ꢁ
i36 Uwe Kolitsch NaIn(CrO4)2Á2H2O
Acta Cryst. (2006). C62, i35±i37

inorganic compounds
Table 1
Selected bond lengths (A).
Financial support from the International Centre for
Diffraction Data (grant No. 90-03 ET) is gratefully acknowl-
edged.
Ê
InÐO4
InÐO1
CrÐO3
CrÐO2
2.102 (2)
CrÐO4
NaÐO2i
NaÐO4
1.679 (2)
2.531 (3)
2.615 (3)
2.172 (3)
1.594 (3)
1.611 (3)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: IZ3003). Services for accessing these data are
described at the back of the journal.
Symmetry code: (i) x ‡ 12; y ‡ 21; z ‡ 1.
References
Table 2
Hydrogen-bond geometry (A, ).
ꢀ
Ê
Brese, N. E. & O'Keeffe, M. (1991). Acta Cryst. B47, 192±197.
Bulka, G. R., Vinokurov, V. M., Kuz'min, E. A., Kharitonov, Yu. A. & Belov,
N. V. (1973). Kristallogra®ya, 18, 984±987. (In Russian.)
Â
Cudennec, Y. & Riou, A. (1977). C. R. Acad. Sci. Ser. C, 284, 565±568. (In
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DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
O1ÐH1Á Á ÁO3i
0.86 (4)
0.88 (5)
1.81 (4)
1.92 (6)
2.662 (4)
2.789 (5)
168 (6)
168 (13)
O1ÐH2Á Á ÁO2ii
Symmetry codes: (i) x ‡ 12; y ‡ 21; z ‡ 1; (ii) x ‡ 21; y ‡ 12; z.
Fleck, M. & Kolitsch, U. (2003). Z. Kristallogr. 218, 553±567.
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Â
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Ê
All OÐH distances were restrained to a length of 0.90 (5) A.
Isotropic displacement parameters of the H atoms were re®ned
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
Ê
electron-density peak in NaIn(CrO4)2Á2H2O is 0.42 A from the O4
Ê
site and the deepest hole in the difference map is 0.87 A from the O4
site.
Data collection: COLLECT (Nonius, 2004); cell re®nement:
SCALEPACK (Otwinowski et al., 2003); data reduction: SCALE-
PACK and DENZO (Otwinowski et al., 2003); program(s) used to
solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to
re®ne structure: SHELXL97 (Sheldrick, 1997); molecular graphics:
ATOMS (Dowty, 1999) and ORTEP-3 for Windows (Farrugia, 1997);
software used to prepare material for publication: SHELXL97.
È
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ꢁ
Acta Cryst. (2006). C62, i35±i37
Uwe Kolitsch
NaIn(CrO4)2Á2H2O i37