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The crystal structures of hydro­thermally synthesized potassium scandium hydrogen arsenate(V), KSc(HAsO4)2, (I), and rubidium scandium diarsenate(V), RbScAs2O7, (II), were determined from single-crystal X-ray diffraction data collected at room temperature. Compound (I) represents a new microporous structure type, designated MCV-3, which is characterized by a three-dimensional framework of corner-sharing alternating ScO6 octahedra and HAsO4 tetrahedra. Intersecting tunnels parallel to [101] and [110] host eight-coordinate K atoms. There is one hydrogen bond of medium strength [O...O = 2.7153 (18) Å]. Compound (II) is the first reported diarsenate with a KAlP2O7-type structure and is isotypic with at least 27 AIMIII diphosphates. The average Sc—O bond lengths in (I) and (II) are 2.09 (2) and 2.09 (3) Å, respectively. The K and Sc atoms in (I) lie on an inversion centre and a twofold axis, respectively. All atoms in (II) are in general positions.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270104015938/bc1052sup1.cif
Contains datablocks global, I, II

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270104015938/bc1052Isup2.hkl
Contains datablock I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270104015938/bc1052IIsup3.hkl
Contains datablock II

Comment top

Because of interest in the crystal chemical behaviour of ScIII cations in oxysalts, and for comparison with the behaviour of trivalent cations with similar ionic radii (e.g. VIII, FeIII, CrIII and GaIII), we have recently started to investigate the crystallography and topology of metal scandium arsenates. The present contribution reports the framework crystal structures of two hydrothermally synthesized alkali scandium arsenates, KSc(HAsO4)2, (I) (new structure-type), and RbScAs2O7, (II). A second contribution (Schwendtner & Kolitsch, 2004) will be devoted to the crystal structures of the triclinic and monoclinic modifications of CsSc(HAsO4)2 and a brief overview of compounds AIMIII(HXO4)2 (AI is a monovalent cation and MIII is a trivalent cation; X = P or As).

Compound (I) is monoclinic (C2/c) and represents a new microporous framework structure type designated MCV-3 (MCV stands for Mineralogy and Crystallography Vienna). The asymmetric unit contains one K, one Sc, one As, four O and one H atoms, of which only the K and Sc atoms occupy special positions (the K atom lies on an inversion centre and the Sc atom on a twofold axis). Slightly distorted ScO6 octahedra are corner-linked to AsO4 tetrahedra and form a three-dimensional framework with slightly contorted, hexagonally shaped, tunnels parallel to [101] and narrower, more irregularly shaped, tunnels parallel to [110]; these tunnels host the eight-coordinate K atoms (Figs. 1–3). The larger tunnels have a free diameter of about 2.67 x 2.74 Å, based on the O2− ionic radius of 1.35 Å (Shannon, 1976). The H atom is bonded to the `free' corner of the AsO4 tetrahedron and is involved in a moderately strong hydrogen bond [O4—H···O2i =2.7153 (18) Å; symmetry code: (i) x, 1 − y, 1/2 + z], which extends roughly perpendicular to the (101) plane, i.e. parallel to the larger tunnels (Fig. 1a). As is typical of protonated AsO4 tetrahedra, the As—OH bond is distinctly elongated in comparison to the three remaining As—O bonds (Ferraris, 1970; Ferraris & Ivaldi, 1984). The mean As—O bond length in the protonated arsenate group (1.683 Å) nearly coincides with the grand mean length in arsenates (1.682 Å; Baur, 1981). The mean Sc—O bond length in the ScO6 octahedron (2.090 Å) is slightly smaller than the grand mean value in oxidic compounds (2.105 Å; Baur, 1981).

Bond-valence sums for all atoms were calculated using the bond-valence parameters of Brese & O'Keeffe (1991); these values are 1.01 (for K atoms), 5.04 (As), 3.13 (Sc), 2.19 (O1), 1.82 (O2), 1.97 (O3) and 1.21 valence units (v.u.) (O4), and thus are all reasonably close to ideal valences. The slightly underbonded atom O2 is an acceptor of the hydrogen bond (see above).

RbScAs2O7, (II), is monoclinic (P21/c) and isotypic with KAlP2O7 (Ng & Calvo, 1973). The asymmetric unit contains one Rb, one Sc, two As and seven O atoms, all of which occupy general positions. The atomic arrangement is based on a three-dimensional framework of corner-linked ScO6 octahedra and As2O7 groups. The charge-balancing Rb+ cations are located in distorted six-sided tunnels parallel to [001] (Figs. 4 and 5). The shortest distance between two neighbouring Rb+ cations in a single tunnel is 4.629 (1) Å. The irregular coordination environment of the Rb atoms consists of ten O ligands within 3.5 Å (an 11t h, non-bonding, O-atom neighbour is located at a distance of 3.75 Å). The ScO6 octahedron is distorted, with deviations of up to 8.7 ° from ideal geometry. The mean Sc—O bond length (2.090 Å) is, similar to the situation in (I), slightly smaller than the mean value in oxidic compounds (2.105 Å; Bauer, 1981). The mean As—O bond lengths in the two non-equivalent AsO4 tetrahedra (<As1—O> = 1.681 Å and <As2—O> = 1.684 Å) forming the As2O7 group are also close to the expected value (1.682 Å; Baur, 1981).

The As2O7 diarsenate group shows a nearly staggered conformation, with an As1—O7bridge—As2 angle of 119.62 (10) °. The bridging angle is in good agreement with reviewed data on other diarsenates (mean As—Obridge—As angle = 125.08 °; Effenberger & Pertlik, 1993). The bridging O7 atom is very weakly bonded to the Rb atom (Table 3). The conformation of the As2O7 diarsenate group in (II) appears unusual because compounds with isolated X2O7 groups (X = Si, P, S, As, Cr, Ge and V) in general show either a staggered conformation, with a bridging X—ObridgeX angle of greater than 140° (up to 180°), or an eclipsed conformation, with an X—O—X angle of less than 140°, where the Obridge atom belongs to the coordination sphere of at least one cation (Clark & Morley, 1976).

Bond-valence sums for all atoms were calculated using the bond-valence parameters of Brese & O'Keeffe (1991). For the metal atoms, these value are 0.93 (for the Rb atom), 5.09 (As1), 5.03 (As2) and 3.14 v.u. (Sc). The bond-valence sums of the O atoms are 2.07 (O1), 1.96 (O2), 2.10 (O3), 2.07 (O4), 1.95 (O5), 1.94 (O6) and 2.10 v.u·(O7). All these values are close to ideal valences.

Compound (II) is the first diarsenate reported to crystallize in a monoclinic (P21/c) structure type originally described by Ng & Calvo (1973) for KAlP2O7. Subsequent to their work, a surprisingly large number of other diphosphates, AIMIIIX2O7 (AI = H3O, Na, K, NH4, Rb, Cs, In and Tl, MIII = Al, Sc, Ti, V, Cr, Fe, Ga, Mo, In, Y and Yb, and X = P and As) have also been reported to adopt this apparently fairly flexible structure type. In fact, KAlP2O7-type compounds form the largest group among the known structure types of AIMIIIP2O7 compounds (at least seven types exist if AI = Li is included; Vītiņš et al., 2000).

The following list of 27 diphosphates isotypic with KAlP2O7 is based on a careful search in both crystallographic and literature databases and is thought to be complete (no previous such compilation exists): RbAlP2O7 (Belkouch et al., 1995), KScP2O7 and (NH4)ScP2O7 (Kaņepe et al., 1987), β-NaTiP2O7 (Leclaire et al., 1988), KTiP2O7, RbTiP2O7, and CsTiP2O7 (Wang & Wu, 1991; Huang & Ibers, 2000; Zatovs'kyi et al., 2000), (H3O)VP2O7 (El Badraoui et al., 1996), NaVP2O7 (Wang et al., 1989), KVP2O7 (Benhamada et al., 1991), RbVP2O7 (Flörke, 1990), (NH4)VP2O7 (Trommer et al., 1998), CsVP2O7 (Wang & Lii, 1989), KCrP2O7 (Gentil et al., 1997), Rb(Ni0.35Cr0.30Ti0.35)P2O7 (Yakubovich et al., 1995), CsCrP2O7 (Linde & Gorbunova, 1982), TlCrP2O7 (Bensch & Koy, 1995), NaFeP2O7—I (Gamondés et al., 1971), KFeP2O7 (Gamondés et al., 1971; Riou et al., 1988; Genkina & Timofeeva, 1989), RbFeP2O7 and CsFeP2O7 (Millet & Mentzen, 1991; Dvoncova & Lii, 1993), KGaP2O7 (Genkina & Timofeeva, 1989), KMoP2O7 (Chen et al., 1989; Leclaire et al., 1989), RbMoP2O7 (Riou et al., 1989), CsMoP2O7 (Lii & Haushalter, 1987), InIInIIIP2O7 (Thauern & Glaum, 2003), RbYP2O7 (Akrim et al., 1993), CsYP2O7 (Akrim et al., 1994), and CsYbP2O7 (Jansen et al., 1991). In addition, Rb, Cs and Tl diphosphate members with MIII = Gd, Tb, Dy, Ho, Y, Er, Tm and Yb also have KAlP2O7-type structures according to X-ray powder diffraction and spectroscopic evidence (Khay & Ennaciri, 2001; Khay et al., 2001a,2001b; Anisimova et al., 1993a,1993b). Most of the above compounds were prepared at temperatures higher than 573 K by solid-state reactions or crystallization from the melt. It was not recognized in all cases that the specific compound adopts a structure type originally described for KAlP2O7 (Ng & Calvo, 1973).

Compound (II) appears to be the first diarsenate with the structure type of KAlP2O7. A few other AIMIIIAs2O7 compounds are known at present, but they all crystallize in other structure types [e.g. monoclinic (P21/c) NaAlAs2O7 (Driss & Jouini, 1994), triclinic (P\-1) RbAlAs2O7 and KAlAs2O7 (Boughzala et al., 1993; Boughzala & Jouini, 1995), and monoclinic (C2/c) NaInAs2O7 (Belam et al., 1997)], although they show connectivities similar to those in KAlP2O7-type compounds. It appears that RbScAs2O7 crystallizes in the KAlP2O7 structure type because of a `suitable' relation between the ionic radii of the cations involved. All of the cations in (II) are slightly larger than those in KAlP2O7, and therefore the polyhedral framework in (II) is able to simply expand, without any strain. Work in progress indicates that (NH4)ScAs2O7 also has a KAlP2O7-type structure. This result is not too surprising considering that the ionic radius of the (NH4)+ cation is similar to that of the Rb+ cation (e.g. Khan & Baur, 1972).

Measured X-ray powder diffraction patterns (Cu Kα radiation) of (I) and (II) show good agreement with the respective calculated patterns.

Experimental top

Compounds (I) and (II) were prepared hydrothermally (in Teflon-lined stainless steel bombs at 493 K for 7 d, with slow furnace cooling) from a mixture of Sc2O3, arsenic acid hydrate, oxalic acid dihydrate, and KOH and Rb2CO3, respectively, with a volume ratio of approximately 1:1:1:1. The Teflon containers were then filled with distilled water to about one-third of their inner volume. The pH values of the starting and final solutions were approximately 1. Compound (I) formed small colorless tabular crystals (yield ca 98%). Compound (II) formed small colorless pseudo-disphenoidal crystals (yield ca 95%). The crystals of (I) and (II) are stable in air. Compound (I) also crystallized as small colourless pseudo-disphenoidal, often twinned (by non-merohedry), individuals from a hydrothermally reacted mixture of Sc2O3, arsenic acid hydrate and KOH (at 493 K for 7 d, with slow furnace cooling; yield 100%), the final pH of the reacted solution being about 2–3.

Refinement top

For comparison purposes, the atomic coordinates of isotypic CsVP2O7 (Wang & Lii, 1989) were used as starting parameters in the final refinement of (II). The H atom in (I) was refined freely (for O—H distance see Table 2).

Computing details top

For both compounds, data collection: COLLECT (Nonius, 2003); cell refinement: HKL SCALEPACK (Otwinowski & Minor 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997). Molecular graphics: DIAMOND (Pennington, 1999) and ORTEP-3 for Windows (Farrugia, 1997) for (I); Diamond (Pennington, 1999) and ORTEP-3 for Windows (Farrugia, 1997) for (II). For both compounds, software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. A view of the framework structure of microporous (I) along (a) [110] and (b) [101]. Protonated AsO4 tetrahedra are corner-linked to slightly distorted ScO6 octahedra. The tunnels host eight-coordinate K atoms (dark spheres). The unit cell is outlined and the hydrogen bonding is shown in (a).
[Figure 2] Fig. 2. A simplified view along [101] of the connectivity and the K-filled tunnels in the microporous framework structure of (I). The lines shown connect the centers of the tetrahedral and octahedral units (As and Sc).
[Figure 3] Fig. 3. The connectivity in (I), shown with displacement ellipsoids at the 70% probability level. The H atom is shown as a small sphere of arbitrary radius. [Symmetry codes: (iv) 1/2 − x, 1/2 − y, 1 − z; (v) x − 1/2, y − 1/2, z; (vi) −x, y, 1/2 − z; (vii) 1/2 − x, y − 1/2, 1/2 − z; (viii) x − 1/2, 1/2 − y, z − 1/2.]
[Figure 4] Fig. 4. The framework structure of (II), projected down [001]. As2O7 diarsenate groups (with a nearly staggered conformation) are corner- linked to slightly distorted ScO6 octahedra. Ten-coordinate Rb atoms are located in tunnels running parallel to [001]. The unit cell is outlined.
[Figure 5] Fig. 5. The connectivity in (II), shown with displacement ellipsoids at the 50% probability level. [Symmetry codes: (i) x, −1/2 − y, z − 1/2; (iv) 2 − x, 1/2 + y, 3/2 − z; (v) x, −3/2 − y, 1/2 + z; (vi) 1 − x, −2 − y, 1 − z.]
(I) potassium scandium hydrogen arsenate(V) top
Crystal data top
KSc(HAsO4)2F(000) = 688
Mr = 363.92Dx = 3.154 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 1459 reflections
a = 8.349 (2) Åθ = 2.0–32.6°
b = 10.590 (2) ŵ = 10.08 mm1
c = 9.189 (2) ÅT = 293 K
β = 109.37 (3)°Irregular fragment, colorless
V = 766.5 (3) Å30.16 × 0.13 × 0.10 mm
Z = 4
Data collection top
Nonius KappaCCD
diffractometer
1392 independent reflections
Radiation source: fine-focus sealed tube1352 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.009
ψ and ω scansθmax = 32.6°, θmin = 3.2°
Absorption correction: multi-scan
(HKL SCALEPACK; Otwinowski & Minor, 1997)
h = 1212
Tmin = 0.295, Tmax = 0.432k = 1616
2720 measured reflectionsl = 1313
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.014All H-atom parameters refined
wR(F2) = 0.039 w = 1/[σ2(Fo2) + (0.016P)2 + 1.3P]
where P = (Fo2 + 2Fc2)/3
S = 1.16(Δ/σ)max = 0.001
1392 reflectionsΔρmax = 1.16 e Å3
62 parametersΔρmin = 0.42 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0025 (2)
Crystal data top
KSc(HAsO4)2V = 766.5 (3) Å3
Mr = 363.92Z = 4
Monoclinic, C2/cMo Kα radiation
a = 8.349 (2) ŵ = 10.08 mm1
b = 10.590 (2) ÅT = 293 K
c = 9.189 (2) Å0.16 × 0.13 × 0.10 mm
β = 109.37 (3)°
Data collection top
Nonius KappaCCD
diffractometer
1392 independent reflections
Absorption correction: multi-scan
(HKL SCALEPACK; Otwinowski & Minor, 1997)
1352 reflections with I > 2σ(I)
Tmin = 0.295, Tmax = 0.432Rint = 0.009
2720 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0140 restraints
wR(F2) = 0.039All H-atom parameters refined
S = 1.16Δρmax = 1.16 e Å3
1392 reflectionsΔρmin = 0.42 e Å3
62 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
K0.25000.25000.00000.03447 (15)
Sc0.00000.13851 (3)0.25000.00719 (7)
As0.274921 (16)0.400932 (12)0.360826 (14)0.00846 (5)
O10.18456 (14)0.27213 (10)0.26526 (12)0.0157 (2)
O20.31637 (14)0.49688 (11)0.23319 (12)0.0159 (2)
O30.44593 (13)0.36332 (10)0.51042 (11)0.01262 (18)
O40.13381 (16)0.48085 (14)0.42883 (14)0.0228 (2)
H0.165 (4)0.478 (3)0.513 (4)0.050 (9)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
K0.0454 (3)0.0410 (3)0.0271 (3)0.0184 (3)0.0256 (3)0.0098 (2)
Sc0.00793 (14)0.00655 (14)0.00673 (13)0.0000.00195 (10)0.000
As0.00995 (8)0.00866 (7)0.00648 (7)0.00193 (4)0.00231 (5)0.00001 (4)
O10.0191 (5)0.0134 (4)0.0153 (4)0.0095 (4)0.0065 (4)0.0050 (4)
O20.0179 (5)0.0165 (5)0.0103 (4)0.0088 (4)0.0007 (3)0.0055 (4)
O30.0135 (4)0.0160 (4)0.0067 (4)0.0016 (4)0.0012 (3)0.0009 (3)
O40.0191 (5)0.0347 (7)0.0139 (5)0.0108 (5)0.0044 (4)0.0040 (5)
Geometric parameters (Å, º) top
K—O1i2.6792 (12)Sc—O3vii2.0956 (11)
K—O12.6792 (12)Sc—O3iii2.0956 (11)
K—O3ii2.8382 (12)Sc—O2viii2.1134 (11)
K—O3iii2.8382 (12)Sc—O2v2.1134 (11)
K—O4iv3.0120 (16)As—O11.6618 (11)
K—O4v3.0120 (16)As—O31.6688 (12)
K—O23.3085 (13)As—O21.6724 (10)
K—O2i3.3085 (13)As—O41.7272 (12)
Sc—O12.0623 (11)O4—H0.73 (3)
Sc—O1vi2.0623 (11)
O1—Sc—O1vi93.35 (7)O1vi—Sc—O2v178.08 (5)
O1—Sc—O3vii92.24 (5)O3vii—Sc—O2v91.05 (5)
O1vi—Sc—O3vii88.48 (5)O3iii—Sc—O2v88.20 (5)
O1—Sc—O3iii88.48 (5)O2viii—Sc—O2v89.59 (7)
O1vi—Sc—O3iii92.24 (5)O1—As—O3110.72 (6)
O3vii—Sc—O3iii178.95 (6)O1—As—O2106.94 (6)
O1—Sc—O2viii178.08 (5)O3—As—O2113.78 (5)
O1vi—Sc—O2viii88.53 (5)O1—As—O4110.42 (6)
O3vii—Sc—O2viii88.20 (5)O3—As—O4108.59 (6)
O3iii—Sc—O2viii91.05 (5)O2—As—O4106.30 (7)
O1—Sc—O2v88.53 (5)As—O4—H109 (3)
Symmetry codes: (i) x+1/2, y+1/2, z; (ii) x+1, y, z+1/2; (iii) x1/2, y+1/2, z1/2; (iv) x, y+1, z1/2; (v) x+1/2, y1/2, z+1/2; (vi) x, y, z+1/2; (vii) x+1/2, y+1/2, z+1; (viii) x1/2, y1/2, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O4—H···O2ix0.73 (3)2.01 (3)2.7153 (18)161 (3)
Symmetry code: (ix) x, y+1, z+1/2.
(II) rubidium scandium diarsenate(V) top
Crystal data top
RbSc(As2O7)F(000) = 720
Mr = 392.27Dx = 3.717 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 2668 reflections
a = 7.837 (2) Åθ = 2.0–32.6°
b = 10.625 (2) ŵ = 17.31 mm1
c = 8.778 (2) ÅT = 293 K
β = 106.45 (3)°Irregular fragment, colorless
V = 701.0 (3) Å30.08 × 0.07 × 0.05 mm
Z = 4
Data collection top
Nonius KappaCCD
diffractometer
2544 independent reflections
Radiation source: fine-focus sealed tube2152 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.019
ψ and ω scansθmax = 32.6°, θmin = 2.7°
Absorption correction: multi-scan
(HKL SCALEPACK; Otwinowski & Minor, 1997)
h = 1111
Tmin = 0.338, Tmax = 0.478k = 1616
4967 measured reflectionsl = 1313
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.023 w = 1/[σ2(Fo2) + (0.025P)2 + 0.77P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.054(Δ/σ)max = 0.001
S = 1.05Δρmax = 0.83 e Å3
2544 reflectionsΔρmin = 1.07 e Å3
101 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0018 (3)
Crystal data top
RbSc(As2O7)V = 701.0 (3) Å3
Mr = 392.27Z = 4
Monoclinic, P21/cMo Kα radiation
a = 7.837 (2) ŵ = 17.31 mm1
b = 10.625 (2) ÅT = 293 K
c = 8.778 (2) Å0.08 × 0.07 × 0.05 mm
β = 106.45 (3)°
Data collection top
Nonius KappaCCD
diffractometer
2544 independent reflections
Absorption correction: multi-scan
(HKL SCALEPACK; Otwinowski & Minor, 1997)
2152 reflections with I > 2σ(I)
Tmin = 0.338, Tmax = 0.478Rint = 0.019
4967 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.023101 parameters
wR(F2) = 0.0540 restraints
S = 1.05Δρmax = 0.83 e Å3
2544 reflectionsΔρmin = 1.07 e Å3
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
Rb1.17271 (4)0.81924 (3)0.54990 (3)0.02304 (8)
Sc0.76450 (6)0.90057 (4)0.73549 (5)0.00887 (9)
As10.86172 (3)0.59177 (2)0.66540 (3)0.00962 (6)
As20.55731 (3)0.86218 (2)0.30910 (3)0.00987 (6)
O10.8511 (3)0.9130 (2)0.9766 (2)0.0267 (5)
O20.6896 (3)0.8913 (2)0.4886 (2)0.0237 (4)
O31.0006 (2)0.98728 (17)0.7226 (2)0.0130 (3)
O40.9129 (2)0.73440 (17)0.7448 (2)0.0166 (4)
O50.6468 (2)1.08019 (18)0.7217 (3)0.0194 (4)
O60.5475 (2)0.78716 (17)0.7490 (2)0.0157 (4)
O70.6502 (2)0.94860 (18)0.1815 (2)0.0153 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Rb0.02177 (13)0.02729 (15)0.01936 (13)0.00168 (11)0.00468 (10)0.00039 (10)
Sc0.00931 (18)0.00754 (18)0.01006 (19)0.00035 (15)0.00327 (14)0.00012 (15)
As10.01055 (11)0.00993 (12)0.00902 (11)0.00214 (8)0.00382 (8)0.00056 (8)
As20.00996 (11)0.00884 (11)0.01139 (11)0.00061 (8)0.00398 (8)0.00050 (8)
O10.0288 (11)0.0441 (14)0.0080 (8)0.0154 (10)0.0067 (7)0.0026 (8)
O20.0298 (10)0.0292 (11)0.0091 (8)0.0020 (9)0.0006 (7)0.0044 (8)
O30.0131 (8)0.0123 (8)0.0144 (8)0.0047 (7)0.0051 (6)0.0041 (6)
O40.0137 (8)0.0089 (8)0.0258 (10)0.0004 (7)0.0035 (7)0.0010 (7)
O50.0130 (8)0.0123 (9)0.0355 (11)0.0033 (7)0.0113 (8)0.0004 (8)
O60.0133 (8)0.0089 (8)0.0257 (10)0.0000 (7)0.0069 (7)0.0042 (7)
O70.0114 (8)0.0166 (9)0.0199 (9)0.0033 (7)0.0080 (7)0.0070 (7)
Geometric parameters (Å, º) top
Rb—O32.9093 (19)Sc—O32.0986 (18)
Rb—O4i2.925 (2)Sc—O42.1029 (19)
Rb—O6ii2.982 (2)Sc—O52.1083 (19)
Rb—O43.140 (2)Sc—O62.1148 (18)
Rb—O3iii3.155 (2)As1—O1i1.6366 (19)
Rb—O5iii3.277 (2)As1—O3iv1.6619 (17)
Rb—O5iv3.296 (2)As1—O41.6688 (19)
Rb—O2iii3.308 (2)As1—O7v1.7564 (17)
Rb—O7iii3.423 (2)As2—O21.651 (2)
Rb—O1i3.455 (3)As2—O5vi1.6619 (19)
Sc—O12.035 (2)As2—O6i1.6670 (18)
Sc—O22.081 (2)As2—O71.7578 (18)
O1—Sc—O2176.86 (9)O5—Sc—O699.98 (7)
O1—Sc—O389.31 (8)O1i—As1—O3iv114.62 (10)
O2—Sc—O387.58 (8)O1i—As1—O4112.87 (11)
O1—Sc—O489.78 (9)O3iv—As1—O4108.70 (9)
O2—Sc—O489.45 (8)O1i—As1—O7v107.17 (10)
O3—Sc—O483.36 (7)O3iv—As1—O7v104.99 (9)
O1—Sc—O590.71 (10)O4—As1—O7v107.99 (9)
O2—Sc—O589.62 (9)O2—As2—O5vi113.68 (11)
O3—Sc—O588.72 (7)O2—As2—O6i116.12 (10)
O4—Sc—O5172.05 (7)O5vi—As2—O6i110.07 (9)
O1—Sc—O690.88 (8)O2—As2—O7104.40 (10)
O2—Sc—O692.13 (9)O5vi—As2—O7104.89 (9)
O3—Sc—O6171.30 (7)O6i—As2—O7106.61 (9)
O4—Sc—O687.94 (7)As1i—O7—As2119.62 (10)
Symmetry codes: (i) x, y3/2, z1/2; (ii) x+1, y, z; (iii) x+2, y2, z+1; (iv) x+2, y+1/2, z+3/2; (v) x, y3/2, z+1/2; (vi) x+1, y2, z+1.

Experimental details

(I)(II)
Crystal data
Chemical formulaKSc(HAsO4)2RbSc(As2O7)
Mr363.92392.27
Crystal system, space groupMonoclinic, C2/cMonoclinic, P21/c
Temperature (K)293293
a, b, c (Å)8.349 (2), 10.590 (2), 9.189 (2)7.837 (2), 10.625 (2), 8.778 (2)
β (°) 109.37 (3) 106.45 (3)
V3)766.5 (3)701.0 (3)
Z44
Radiation typeMo KαMo Kα
µ (mm1)10.0817.31
Crystal size (mm)0.16 × 0.13 × 0.100.08 × 0.07 × 0.05
Data collection
DiffractometerNonius KappaCCD
diffractometer
Nonius KappaCCD
diffractometer
Absorption correctionMulti-scan
(HKL SCALEPACK; Otwinowski & Minor, 1997)
Multi-scan
(HKL SCALEPACK; Otwinowski & Minor, 1997)
Tmin, Tmax0.295, 0.4320.338, 0.478
No. of measured, independent and
observed [I > 2σ(I)] reflections
2720, 1392, 1352 4967, 2544, 2152
Rint0.0090.019
(sin θ/λ)max1)0.7570.758
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.014, 0.039, 1.16 0.023, 0.054, 1.05
No. of reflections13922544
No. of parameters62101
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)1.16, 0.420.83, 1.07

Computer programs: COLLECT (Nonius, 2003), HKL SCALEPACK (Otwinowski & Minor 1997), HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), DIAMOND (Pennington, 1999) and ORTEP-3 for Windows (Farrugia, 1997), Diamond (Pennington, 1999) and ORTEP-3 for Windows (Farrugia, 1997), SHELXL97.

Selected bond lengths (Å) for (I) top
K—O1i2.6792 (12)Sc—O2v2.1134 (11)
K—O3ii2.8382 (12)As—O11.6618 (11)
K—O4iii3.0120 (16)As—O31.6688 (12)
K—O23.3085 (13)As—O21.6724 (10)
Sc—O12.0623 (11)As—O41.7272 (12)
Sc—O3iv2.0956 (11)
Symmetry codes: (i) x+1/2, y+1/2, z; (ii) x+1, y, z+1/2; (iii) x, y+1, z1/2; (iv) x+1/2, y+1/2, z+1; (v) x1/2, y1/2, z.
Hydrogen-bond geometry (Å, º) for (I) top
D—H···AD—HH···AD···AD—H···A
O4—H···O2vi0.73 (3)2.01 (3)2.7153 (18)161 (3)
Symmetry code: (vi) x, y+1, z+1/2.
Selected geometric parameters (Å, º) for (II) top
Rb—O32.9093 (19)Sc—O32.0986 (18)
Rb—O4i2.925 (2)Sc—O42.1029 (19)
Rb—O6ii2.982 (2)Sc—O52.1083 (19)
Rb—O43.140 (2)Sc—O62.1148 (18)
Rb—O3iii3.155 (2)As1—O1i1.6366 (19)
Rb—O5iii3.277 (2)As1—O3iv1.6619 (17)
Rb—O5iv3.296 (2)As1—O41.6688 (19)
Rb—O2iii3.308 (2)As1—O7v1.7564 (17)
Rb—O7iii3.423 (2)As2—O21.651 (2)
Rb—O1i3.455 (3)As2—O5vi1.6619 (19)
Sc—O12.035 (2)As2—O6i1.6670 (18)
Sc—O22.081 (2)As2—O71.7578 (18)
As1i—O7—As2119.62 (10)
Symmetry codes: (i) x, y3/2, z1/2; (ii) x+1, y, z; (iii) x+2, y2, z+1; (iv) x+2, y+1/2, z+3/2; (v) x, y3/2, z+1/2; (vi) x+1, y2, z+1.
 

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