Comment

The title compound, (I) (Fig. 1), is isostructural with its samarium (Koskenlinna et al., 1994) and neodymium (de Pedro et al., 1994) analogues.

Compound (I) contains both (SeO₃)^2- selenite and (HSeO₃)^- hydrogen selenite anions. The unobserved lone pair of electrons of the Se^IV species gives rise to the characteristic pyramidal shape of these oxo-anions. As seen previously (Koskenlinna et al., 1994), the Se-OH vertex [1.745 (4) Å] in (I) is longer than the Se-O bonds [mean = 1.690 (15) Å] (Table 1). The Se atoms are displaced from the planes of their three attached oxygen atoms by 0.804 (2) and 0.814 (2) Å for Se1 and Se2, respectively. In terms of bond angles, the angle of the edge-sharing (to Y) O1-Se1-O2 grouping is significantly more acute [92.37 (16)°] than the other O-Se-O sets (mean = 100.4°).

The yttrium cation in (I) is surrounded by eight oxygen atoms, one of which (O7) is part of a water molecule, with a fairly narrow spread of distances [2.258 (3)-2.419 (3) Å; mean = 2.36 (5) Å]. The next nearest O atom has a distance of Y-O4ⁱ = 3.872 (3) Å [symmetry code: (i) 1 - x,  + y,  - z]. The YO₈ grouping could be described as a highly distorted square antiprism (Fig. 2) or possibly as irregular. Atoms O1, O2, O4 and O7 conform well to a square [r.m.s. deviation from the mean plane = 0.041 Å; O1O4 = 3.915 (5) Å and O2O7 = 3.988 (5) Å], whereas the nominal O1ⁱⁱⁱ, O2ⁱⁱ, O3ⁱ and O5ⁱⁱ (see Table 1 for symmetry codes) square is grossly distorted [r.m.s. deviation from the mean plane = 0.399 Å; O1ⁱⁱⁱO2ⁱⁱ = 4.440 (5) Å and O3ⁱO5ⁱⁱ = 3.339 (5) Å]. The Y atom is displaced by 1.3249 (18) Å from the first plane, and 1.1900 (18) Å from the second. The interplanar dihedral angle is 1.8 (2)°. Atoms O3, O4 and O5 are bicoordinate to Y and Se (mean Y-O-Se = 124.2°), whilst O1 and O2 are tricoordinate to one Se and two Y atoms (bond angle sums = 343.5 and 349.0°, respectively). O6 is part of a terminal Se-OH vertex and O7 and O8 are parts of water molecules.

The polyhedral connectivity in (I) (Fig. 3) involves chains of YO₈ groups sharing edges, via O1 + O2ⁱⁱ and O1ⁱⁱⁱ + O2 pairs, to result in chains propagating along [010]. The relatively acute O1-Y-O2ⁱⁱ and O1ⁱⁱⁱ-Y-O2 bond angles of 67.81 (12) and 68.02 (11)° respectively, correlate with this polyhedron-fusing role. The YYⁱⁱ separation within the chain is 3.9668 (5) Å. The Y/O chains are cross-linked in the [100] direction by the Se1O₃ groups, involving the edge-sharing motif noted above. Finally, the (HSe2O₃)^- groups decorate and reinforce the [010] Y/O chains, resulting in a structure with layered character.

The hydrogen-bonding scheme in (I) involves all the H atoms participating in O-HO links (Table 2). The Y-bonded water molecule (O7) makes a hydrogen bond to an adjacent YO₈ group in the same sheet (via H2) and to the inter-sheet water molecule (via H1). The hydrogen selenite anion makes the only direct inter-sheet hydrogen bond (Fig. 4). As well as accepting an hydrogen bond, the non-coordinated water molecule (O8) makes two hydrogen bonds to the same adjacent sheet.

The average metal-oxygen distances in these isostructural phases are Y-O = 2.36 (5) Å, Sm-O = 2.42 Å and Nd-O = 2.45 Å. This pattern is exactly consistent with the differences in the eight-coordinate atomic radii (Shannon, 1976) of Y³⁺ (1.019 Å), Sm³⁺ (1.079 Å) and Nd³⁺ (1.109 Å).

Figure 1 The asymmetric unit of (I) expanded to show the Y atom coordination (70% displacement ellipsoids; spheres of arbitrary radius for the H atoms). Symmetry codes as in Table 1.

Figure 2 Detail of (I) showing the Y atom coordination with OO contacts < 3.3 Å shown as lines (50% displacement ellipsoids). Symmetry codes as in Table 1.

Figure 3 View down [001] of a layer in (I) in polyhedral representation, showing the [010] chains of edge-sharing YO8 groups cross-linked by the Se1 atoms. Colour key: YO8 groups green, Se atoms blue, O atoms red, H atoms grey.

Figure 4 The packing in (I), viewed down [010]. Drawing convention as in Fig. 3, with the HO portions of the hydrogen bonds highlighted in yellow.

Experimental

A mixture of YCl₃·6H₂O (0.83 g, 2.74 mmol), SeO₂ (0.5 g, 4.5 mmol) and water (10 ml) was sealed in a 23 ml Teflon-lined autoclave and heated to 433 K for three days, followed by cooling to room temperature over a few hours. Product recovery by vacuum filtration and rinsing with water and acetone led to 0.173 g (16.6% based on Y) of tiny colourless bars and rods of (I).

Crystal data

[Y(HSeO3)(SeO3)(H2O)]·H2O Mr = 379.87 Orthorhombic, P 21 21 21 a = 6.5485 (3) Å b = 6.8987 (2) Å c = 16.2022 (7) Å V = 731.95 (5) Å3 Z = 4 Dx = 3.447 Mg m-3 Mo K radiation = 17.92 mm-1 T = 120 (2) K Rod, colourless 0.14 × 0.03 × 0.02 mm

Data collection

Nonius KappaCCD diffractometer and scans Absorption correction: multi-scan (SADABS; Bruker, 1999) Tmin = 0.188, Tmax = 0.716 6897 measured reflections 1667 independent reflections 1523 reflections with I > 2(I) Rint = 0.054 max = 27.5°

Refinement

Refinement on F2 R[F2 > 2(F2)] = 0.029 wR(F2) = 0.053 S = 1.05 1667 reflections 101 parameters H-atom parameters constrained w = 1/[2(Fo2) + 0.7811P] where P = (Fo2 + 2Fc2)/3 (/)max < 0.001 max = 0.63 e Å-3 min = -0.72 e Å-3 Absolute structure: Flack (1983), 664 Friedel pairs Flack parameter: 0.646 (11)

Table 1 Selected geometric parameters (Å, °) Y-O3i 2.258 (3) Y-O7 2.346 (3) Y-O5ii 2.347 (3) Y-O4 2.367 (3) Y-O2ii 2.372 (3) Y-O1iii 2.376 (4) Y-O2 2.402 (4) Y-O1 2.419 (3) Se1-O3 1.680 (3) Se1-O1 1.701 (3) Se1-O2 1.710 (3) Se2-O4 1.672 (3) Se2-O5 1.689 (3) Se2-O6 1.745 (4) Se1-O1-Yii 130.66 (18) Se1-O1-Y 101.19 (15) Yii-O1-Y 111.66 (13) Se1-O2-Yiii 135.03 (18) Se1-O2-Y 101.58 (15) Yiii-O2-Y 112.41 (13) Se1-O3-Yiv 130.39 (19) Se2-O4-Y 117.18 (17) Se2-O5-Yiii 124.96 (17) Symmetry codes: (i) x-1, y, z; (ii) ; (iii) ; (iv) x+1, y, z.

Table 2 Hydrogen-bond geometry (Å, °) D-HA D-H HA DA D-HA O6-H1O4v 0.82 1.92 2.712 (5) 164 O7-H2O5vi 0.92 1.93 2.806 (5) 159 O7-H3O8 0.86 1.82 2.644 (5) 163 O8-H4O3vii 0.94 1.93 2.874 (5) 179 O8-H5O5viii 0.93 2.03 2.964 (5) 179 Symmetry codes: (v) ; (vi) x, y+1, z; (vii) ; (viii) .

The crystal studied was an inversion twin with volume fractions of 0.354 (11):0.646 (11) for the component reported in the tables and its enantiomer, respectively. All the H atoms were located in difference maps and refined as riding in their as-found relative positions, with U_iso(H) = 1.2U_eq (carrier).

Data collection: COLLECT (Nonius, 1998); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: SCALEPACK and DENZO (Otwinowski & Minor, 1997), and SORTAV (Blessing, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and ATOMS (Shape Software, 2005); software used to prepare material for publication: SHELXL97.