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Aliovalent KTP isomorphic compounds potassium chromium niobium oxide phosphate, KCr0.5Nb0.5OPO4, and potassium iron niobium oxide phosphate, KFe0.5Nb0.5OPO4, exhibit structures that differ from that of the non-centrosymmetric KTiOPO4. There are two crystallographically independent octa­hedral sites, M1 and M2, statistically occupied by Nb and Cr (or Fe) atoms. The M1O6 and M2O6 octa­hedra are connected alternately to form a chain with a cis-trans arrangement. The Nb atoms prefer the M2 sites arranged in a cis-like configuration. Each PO4 tetra­hedon has the P atom on a twofold axis. Site-splitting at the K-atom position is observed in both compounds. In the isomorphous structures, one Nb atom lies on an inversion centre and the other on a twofold axis. Similarly with the pairs of Fe/Cr sites, one is on an inversion centre and the other on a twofold axis.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270106028678/iz3009sup1.cif
Contains datablocks global, I, II

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106028678/iz3009Isup2.hkl
Contains datablock I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106028678/iz3009IIsup3.hkl
Contains datablock II

Comment top

Compounds with KTiOPO4 (KTP) structure have possible nonlinear optical properties (Zumsteg et al., 1976). The Nb5+-doped KTP crystal shows considerably improved secondary harmonic generation (SHG) (Thomas & Watts, 1990; Zhang et al., 2004). There are aliovalent isomorphs constructed on the principle xM5+ + yM2+ = zM4+, where M denotes a cation at an octahedral site. Such modeling for the replacement of Ti4+ ions is observed in KMg0.33Nb0.67OPO4 (McCarron & Calabrese, 1993). The Nb(Mg)—O bond lengths peculiar to the undistorted octahedron explain the small value of the SHG intensity. The Rietveld analysis of kV0.5Nb0.5OPO4 (Rangan et al., 1998) indicated a selective occupation of Nb at Ti1 and that of V at Ti2 sites. The Nb1(V1)O6 octahedron is more distorted than Nb2(V2)O6. Compounds with general formula KM0.5M'0.5OPO4 (M = NbV and TaV; M' = TiIII, VIII, CrIII and FeIII) and their derivatives, such as K0.5M0.5M'0.5OPO4 (M = NbV and TaV; M ' = TiIV and VIV) were also investigated by powder diffraction (Gopalakrishnan et al., 1994).

The present research is devoted to studying new isomorphic KTP compounds, viz. KCr0.5Nb0.5OPO4, (I), and KFe0.5Nb0.5OPO4, (II). In these compounds, M1O6 and M2O6 octahedra are linked to each other via a common O2 atom and form an infinite chain along the [011] direction. The polyhedral linkage is based on the cistrans arrangement as observed in KTP (Tordjman et al., 1974). In both structures, disorder of Nb and Cr (or Fe) atoms is observed at octahedral sites. Nb atoms preferentially occupy M2 sites, while Cr or Fe atoms occupy M1 sites. The M2O6 octahedra arranged in the cis-like principle along the chain are considerably distorted; the M2—O bond lengths are in the range 1.826 (4)–2.107 (4) Å for (I) and 1.833 (5)–2.114 (5) Å for (II) (Tables 1 and 2). The M2—O2 bond length along the chain is much shorter than the others. The M1O6 octahedron is more regular than M2O6, with M1—O bond lengths of 1.930 (4)–2.044 (5) Å.

The three-dimensional structure arises from the [MO6] chains interlinked by PO4 tetrahedra. Each PO4 tetrahedron has a symmetry of mm2. The anionic framework contains cavities in which K+ ions are placed. The K-site splitting into K1 and K2 is observed for both (I) and (II). The split K1 and K2 sites have site occupancies of 0.5 and are distant from one another by 1.426 (7) Å for (I) and 1.481 (7) Å for (II). The K atoms are coordinated by eight O atoms with K—O distances less than 3.2 Å. Four O atoms, namely, O1, O2, O3 and O4, lie practically on a plane parallel to (010) (Fig. 2), and are common for both the K1 and K2 environments with short K—O distances [2.666 (6)–2.792 (6) for (I) and 2.693?(6)–2.773?(7) Å for (II)]. The other O atoms around K are distant up to 3.188 (7) Å in (I) and 3.163 (7) Å in (II). A similar splitting has been reported for the K atom in KTP structures (Thomas & Watts, 1990; Norberg & Ishizawa, 2005).

Experimental top

Crystals of (I) were obtained by the self-flux method from KPO3 (5.17 g), K4P2O7 (7.14 g), CrPO4 (1.16 g) and Nb2O5 (1.85 g). An initial mixture was powdered in an agate mortar, placed in a 25 ml platinum crucible, and then exposed at 1323 K for 2 h under constant stirring every 0.5 h [`every 0.5 h' implies that stirring is not `constant'; please clarify] with a platinum mixer. The solution was cooled at a rate of 40 K h−1 to 1093 K. The rest of the glass was washed away with plenty of hot deionized water, adding 5% solutions of the bisubstituted salt of ethylenediaminetetraacetic acid. Among a significant number of druses there were well formed green crystals with a typical KTP morphology (Bolt & Bennema, 1990). Similarly, red crystals of (II) were grown from KPO3 (5.17 g), K4P2O7 (7.14 g), Fe2O3 (1.16 g) and Nb2O5 (1.85 g) in the same conditions as described for (I) above. The presence of iron, chromium, and niobium were determined using X-ray fluorescence analysis. The composition of the single crystals was verified using scanning electron microscopy.

Refinement top

The centrosymmetric group Pnna was chosen, with Rint = 0.053 for (I) and Rint = 0.039 for (II). No indication of twinning was revealed during data processing. Linear combination restraints were applied in the process of the Cr/Nb and Fe/Nb ratio refinement (Sheldrick, 1997).

Computing details top

For both compounds, data collection: CrysAlis CCD (Oxford Diffraction, 2005); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997). Molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Bradenburg, 2006) for (I); ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND Bradenburg, 2006) for (II). For both compounds, software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. The common structure for KCr0.5Nb0.5OPO4 and KFe0.5Nb0.5OPO4 shown in the best view projection (50% probability displacement ellipsoids)·[Symmetry codes: (i) −x + 1/2, −y, z; (ii) −x + 1/2, y + 1/2, −z + 1/2; (iii) x, y + 1/2, z + 1/2; (iv) −x, −y, −z; (v) x + 1/2, y, −z; (vi) x + 1/2, −y + 1/2,/z + 1/2.] Please check symmetry codes in figure; two different atoms are labelled O5ii and code iii is not used.
[Figure 2] Fig. 2. The planar arrangement of atoms O1, O2, O3 and O4, common for the K1 and K2 environment in KCr0.5Nb0.5OPO4 and KFe0.5Nb0.5OPO4. The symmetry codes are given in Tables 1 and 2 (50% probability displacement ellipsoids).
(I) potassium chromium niobium oxide phosphate top
Crystal data top
KCr0.5Nb0.5OPO4F(000) = 852
Mr = 222.53Dx = 3.335 Mg m3
Orthorhombic, PnnaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2a 2bcCell parameters from 320 reflections
a = 12.849 (3) Åθ = 15–25°
b = 10.672 (2) ŵ = 3.86 mm1
c = 6.4635 (13) ÅT = 293 K
V = 886.3 (3) Å3Prism, dark green
Z = 80.4 × 0.15 × 0.06 mm
Data collection top
Oxford Diffraction XCalibur-3
diffractometer
1075 independent reflections
Radiation source: sealed tube1066 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.036
ϕ and ω scansθmax = 28°, θmin = 3.2°
Absorption correction: multi-scan
(Blessing, 1995)
h = 1616
Tmin = 0.510, Tmax = 0.770k = 1214
13131 measured reflectionsl = 88
Refinement top
Refinement on F288 parameters
Least-squares matrix: full1 restraint
R[F2 > 2σ(F2)] = 0.050 w = 1/[σ2(Fo2) + (0.0308P)2 + 16.1755P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.114(Δ/σ)max < 0.001
S = 1.24Δρmax = 3.20 e Å3
1075 reflectionsΔρmin = 1.50 e Å3
Crystal data top
KCr0.5Nb0.5OPO4V = 886.3 (3) Å3
Mr = 222.53Z = 8
Orthorhombic, PnnaMo Kα radiation
a = 12.849 (3) ŵ = 3.86 mm1
b = 10.672 (2) ÅT = 293 K
c = 6.4635 (13) Å0.4 × 0.15 × 0.06 mm
Data collection top
Oxford Diffraction XCalibur-3
diffractometer
1075 independent reflections
Absorption correction: multi-scan
(Blessing, 1995)
1066 reflections with I > 2σ(I)
Tmin = 0.510, Tmax = 0.770Rint = 0.036
13131 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0501 restraint
wR(F2) = 0.114 w = 1/[σ2(Fo2) + (0.0308P)2 + 16.1755P]
where P = (Fo2 + 2Fc2)/3
S = 1.24Δρmax = 3.20 e Å3
1075 reflectionsΔρmin = 1.50 e Å3
88 parameters
Special details top

Experimental. X-ray fluorescence analysis: Philips PW1400 spectrometer.

Scanning electron microscopy: REMMA 202M Link Systems microscope with a resolution of 150 eV for the 5.9 keV line.

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Nb20.3811 (8)0.2500 (1)0.2500 (1)0.00760.796
Nb10.5000 (1)0.0000 (1)0.0000 (1)0.00780.204
Cr10.5000 (1)0.0000 (1)0.0000 (1)0.00780.796
P10.4331 (7)0.2500 (1)0.7500 (1)0.0095
P20.2500 (1)0.0000 (1)0.0867 (2)0.0089
Cr20.3811 (8)0.2500 (1)0.2500 (1)0.00760.204
O10.3457 (5)0.0174 (2)0.0512 (6)0.0112
O20.4760 (4)0.1248 (5)0.2107 (2)0.0101
O30.2613 (1)0.1160 (1)0.2276 (2)0.0146
O40.5024 (4)0.1359 (9)0.7887 (4)0.0130
O50.3625 (8)0.2245 (1)0.5622 (3)0.0140
K10.1311 (2)0.0554 (3)0.5328 (8)0.04370.500
K20.1471 (5)0.1865 (2)0.5618 (9)0.04690.500
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Nb20.010 (1)0.006 (1)0.006 (7)0.000 (1)0.000 (1)0.000 (5)
Nb10.004 (9)0.007 (2)0.011 (2)0.000 (5)0.000 (5)0.003 (1)
Cr10.004 (9)0.007 (2)0.011 (2)0.000 (5)0.000 (5)0.003 (1)
P10.014 (9)0.007 (4)0.006 (1)0.000 (1)0.000 (1)0.001 (2)
P20.007 (6)0.008 (4)0.010 (7)0.000 (6)0.000 (1)0.000 (1)
Cr20.010 (1)0.006 (1)0.006 (7)0.000 (1)0.000 (1)0.000 (5)
O10.008 (5)0.010 (4)0.014 (7)0.002 (6)0.001 (5)0.002 (6)
O20.010 (6)0.012 (1)0.007 (6)0.003 (6)0.000 (9)0.002 (8)
O30.012 (1)0.013 (8)0.017 (9)0.003 (5)0.004 (6)0.005 (8)
O40.014 (8)0.010 (9)0.013 (4)0.006 (1)0.001 (5)0.004 (1)
O50.013 (6)0.018 (1)0.010 (5)0.003 (3)0.001 (4)0.000 (3)
K10.052 (9)0.051 (5)0.026 (5)0.018 (7)0.014 (7)0.007 (3)
K20.023 (5)0.075 (4)0.041 (8)0.001 (1)0.010 (6)0.003 (1)
Geometric parameters (Å, º) top
K1—K21.426 (4)Nb2—O21.825 (9)
K1—O32.667 (6)Nb2—O32.106 (7)
K1—O2i2.696 (6)Nb2—O52.050 (3)
K1—O1ii2.734 (6)Nb2—O2vi1.825 (9)
K1—O4i2.792 (6)Nb2—O3vi2.106 (7)
K1—O5iii2.994 (6)Cr1—O12.018 (1)
K1—O3iii3.025 (6)Cr1—O21.930 (1)
K1—O4iii3.138 (6)Cr1—O4viii1.992 (9)
K1—O2iii3.152 (6)Cr1—O1ix2.018 (1)
K2—O32.717 (6)Cr1—O2ix1.930 (1)
K2—O2i2.726 (6)Cr1—O4x1.992 (9)
K2—O52.797 (6)Cr2—O52.050 (3)
K2—O4i2.981 (6)Cr2—O21.825 (9)
K2—O1ii3.085 (7)Cr2—O32.106 (7)
K2—O2iv3.133 (6)Cr2—O5vi2.050 (3)
K2—O1v3.162 (7)Cr2—O2vi1.825 (9)
K2—O3vi3.177 (6)Cr2—O3vi2.106 (7)
K2—O4vii3.189 (6)P1—O41.529 (10)
Nb1—O21.930 (1)P1—O51.540 (8)
Nb1—O4viii1.992 (9)P1—O4xi1.529 (10)
Nb1—O1ix2.018 (1)P1—O5xi1.540 (8)
Nb1—O2ix1.930 (1)P2—O11.530 (6)
Nb1—O4x1.992 (9)P2—O31.5437 (14)
Nb1—O12.018 (1)P2—O1iii1.530 (6)
Nb2—O5vi2.050 (3)P2—O3iii1.5437 (14)
O1—Nb1—O291.3 (1)O1ix—Cr1—O288.6 (9)
O1—Nb1—O4viii88.2 (8)O2—Cr1—O2ix180.0 (1)
O1—Nb1—O1ix180.0 (1)O2—Cr1—O4x90.9 (6)
O1—Nb1—O2ix88.6 (9)O1ix—Cr1—O4viii91.7 (2)
O1—Nb1—O4x91.7 (2)O2ix—Cr1—O4viii90.9 (6)
O2—Nb1—O4viii89.0 (4)O4viii—Cr1—O4x180.0 (1)
O1ix—Nb1—O288.6 (9)O1ix—Cr1—O2ix91.3 (1)
O2—Nb1—O2ix180.0 (1)O1ix—Cr1—O4x88.2 (8)
O2—Nb1—O4x90.9 (6)O2ix—Cr1—O4x89.0 (4)
O1ix—Nb1—O4viii91.7 (2)O2—Cr2—O3vi173.7 (8)
O2ix—Nb1—O4viii90.9 (6)O2—Cr2—O5vi92.1 (8)
O4viii—Nb1—O4x180.0 (1)O3—Cr2—O583.8 (2)
O1ix—Nb1—O2ix91.3 (1)O2vi—Cr2—O3173.7 (8)
O1ix—Nb1—O4x88.2 (8)O3—Cr2—O3vi86.0 (4)
O2ix—Nb1—O4x89.0 (4)O3—Cr2—O5vi86.4 (1)
O2—Nb2—O388.9 (7)O2vi—Cr2—O592.1 (8)
O2—Nb2—O596.7 (5)O3vi—Cr2—O586.4 (1)
O2—Nb2—O2vi96.2 (4)O5—Cr2—O5vi166.6 (1)
O2—Nb2—O3vi173.7 (8)O2vi—Cr2—O3vi88.9 (7)
O2—Nb2—O5vi92.1 (8)O2vi—Cr2—O5vi96.7 (5)
O3—Nb2—O583.8 (2)O3vi—Cr2—O5vi83.8 (2)
O2vi—Nb2—O3173.7 (8)O2—Cr2—O388.9 (7)
O3—Nb2—O3vi86.0 (4)O2—Cr2—O596.7 (5)
O3—Nb2—O5vi86.4 (1)O2—Cr2—O2vi96.2 (4)
O2vi—Nb2—O592.1 (8)O4—P1—O5109.4 (3)
O3vi—Nb2—O586.4 (1)O4—P1—O4xi108.7 (5)
O5—Nb2—O5vi166.6 (1)O4—P1—O5xi110.7 (8)
O2vi—Nb2—O3vi88.9 (7)O4xi—P1—O5110.7 (8)
O2vi—Nb2—O5vi96.7 (5)O5—P1—O5xi107.8 (1)
O3vi—Nb2—O5vi83.8 (2)O4xi—P1—O5xi109.4 (3)
O1—Cr1—O291.3 (1)O1—P2—O3111.43 (14)
O1—Cr1—O4viii88.2 (8)O1—P2—O1iii108.7 (4)
O1—Cr1—O1ix180.0 (1)O1—P2—O3iii108.7 (8)
O1—Cr1—O2ix88.6 (9)O1iii—P2—O3108.7 (8)
O1—Cr1—O4x91.7 (2)O3—P2—O3iii107.6 (9)
O2—Cr1—O4viii89.0 (4)O1iii—P2—O3iii111.4 (3)
Symmetry codes: (i) x3/2, y, z+1; (ii) x+1/2, y, z+1; (iii) x+1/2, y, z; (iv) x1, y1/2, z1/2; (v) x, y+1/2, z+1/2; (vi) x+1/2, y+1/2, z+1/2; (vii) x1, y1/2, z3/2; (viii) x, y, z1; (ix) x+1, y, z; (x) x+1, y, z+1; (xi) x+1/2, y+1/2, z+3/2.
(II) potassium iron niobium oxide phosphate top
Crystal data top
KFe0.5Nb0.5OPO4F(000) = 860
Mr = 224.45Dx = 3.323 Mg m3
Orthorhombic, PnnaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2a 2bcCell parameters from 450 reflections
a = 12.9675 (13) Åθ = 15–26°
b = 10.705 (3) ŵ = 4.22 mm1
c = 6.4638 (7) ÅT = 293 K
V = 897.3 (3) Å3Prism, dark red
Z = 80.2 × 0.15 × 0.1 mm
Data collection top
Oxford Diffraction XCalibur-3
diffractometer
1087 independent reflections
Radiation source: sealed tube1021 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.027
ϕ and ω scansθmax = 28.0°, θmin = 3.1°
Absorption correction: multi-scan
(Blessing, 1995)
h = 1517
Tmin = 0.387, Tmax = 0.496k = 1414
18570 measured reflectionsl = 88
Refinement top
Refinement on F21 restraint
Least-squares matrix: full w = 1/[σ2(Fo2) + (0.P)2 + 22.555P]
where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.048(Δ/σ)max < 0.001
wR(F2) = 0.113Δρmax = 1.47 e Å3
S = 1.33Δρmin = 1.32 e Å3
1087 reflectionsExtinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
88 parametersExtinction coefficient: 0.0048 (5)
Crystal data top
KFe0.5Nb0.5OPO4V = 897.3 (3) Å3
Mr = 224.45Z = 8
Orthorhombic, PnnaMo Kα radiation
a = 12.9675 (13) ŵ = 4.22 mm1
b = 10.705 (3) ÅT = 293 K
c = 6.4638 (7) Å0.2 × 0.15 × 0.1 mm
Data collection top
Oxford Diffraction XCalibur-3
diffractometer
1087 independent reflections
Absorption correction: multi-scan
(Blessing, 1995)
1021 reflections with I > 2σ(I)
Tmin = 0.387, Tmax = 0.496Rint = 0.027
18570 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0481 restraint
wR(F2) = 0.113 w = 1/[σ2(Fo2) + (0.P)2 + 22.555P]
where P = (Fo2 + 2Fc2)/3
S = 1.33Δρmax = 1.47 e Å3
1087 reflectionsΔρmin = 1.32 e Å3
88 parameters
Special details top

Experimental. X-ray fluorescence analysis: Philips PW1400 spectrometer.

Scanning electron microscopy: REMMA 202M Link Systems microscope with a resolution of 150 eV for the 5.9 keV line.

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Nb20.3810 (1)0.2500 (1)0.2500 (1)0.00940.869
Nb10.5000 (1)0.0000 (1)0.0000 (1)0.01120.131
Fe10.5000 (1)0.0000 (1)0.0000 (1)0.01120.869
P10.4329 (2)0.2500 (1)0.7500 (1)0.0097
P20.2500 (1)0.0000 (1)0.0840 (1)0.0098
Fe20.3810 (1)0.2500 (1)0.2500 (1)0.00940.131
O10.3451 (7)0.0178 (6)0.0514 (1)0.0139
O20.4758 (1)0.1248 (5)0.2143 (8)0.0127
O30.2625 (6)0.1151 (2)0.2267 (4)0.0153
O40.5016 (8)0.3639 (3)0.7145 (1)0.0146
O50.3624 (6)0.2270 (3)0.5627 (6)0.0152
K10.1292 (1)0.0536 (4)0.5307 (6)0.03330.500
K20.1454 (1)0.1897 (8)0.5557 (9)0.03740.500
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Nb20.010 (3)0.008 (4)0.009 (5)0.000 (1)0.000 (1)0.000 (1)
Nb10.009 (6)0.010 (8)0.013 (2)0.000 (5)0.000 (6)0.002 (5)
Fe10.009 (6)0.010 (8)0.013 (2)0.000 (5)0.000 (6)0.002 (5)
P10.011 (7)0.009 (6)0.007 (9)0.000 (1)0.000 (1)0.001 (2)
P20.008 (9)0.007 (7)0.012 (6)0.000 (8)0.000 (1)0.000 (1)
Fe20.010 (3)0.008 (4)0.009 (5)0.000 (1)0.000 (1)0.000 (1)
O10.012 (2)0.013 (7)0.015 (8)0.001 (2)0.003 (1)0.000 (7)
O20.013 (6)0.012 (8)0.011 (6)0.003 (8)0.001 (4)0.004 (1)
O30.013 (6)0.015 (4)0.017 (1)0.003 (9)0.003 (2)0.006 (8)
O40.016 (7)0.013 (1)0.014 (1)0.004 (6)0.004 (8)0.004 (9)
O50.014 (1)0.017 (4)0.014 (1)0.000 (5)0.000 (5)0.000 (1)
K10.040 (3)0.039 (1)0.020 (3)0.011 (3)0.009 (9)0.003 (7)
K20.024 (6)0.057 (7)0.030 (1)0.002 (1)0.008 (1)0.003 (4)
Geometric parameters (Å, º) top
K1—K21.481 (3)Nb2—O32.113 (5)
K1—O2i2.693 (7)Nb2—O52.050 (7)
K1—O32.700 (7)Nb2—O2viii1.832 (6)
K1—O1ii2.748 (7)Nb2—O3viii2.113 (5)
K1—O4iii2.774 (7)Fe1—O12.044 (1)
K1—O5iv3.013 (7)Fe1—O21.950 (6)
K1—O3iv3.016 (7)Fe1—O4viii2.011 (2)
K1—O2iv3.113 (7)Fe1—O1ix2.044 (1)
K1—O4v3.117 (7)Fe1—O2ix1.950 (6)
K2—O32.734 (7)Fe1—O4x2.011 (2)
K2—O2i2.743 (7)Fe2—O52.050 (7)
K2—O52.844 (7)Fe2—O21.832 (6)
K2—O4iii2.944 (7)Fe2—O32.113 (5)
K2—O1vi3.132 (8)Fe2—O5viii2.050 (7)
K2—O2vii3.134 (7)Fe2—O2viii1.832 (6)
K2—O4i3.162 (7)Fe2—O3viii2.113 (5)
K2—O3viii3.163 (7)P1—O41.527 (7)
Nb1—O21.950 (6)P1—O51.537 (6)
Nb1—O4viii2.011 (2)P1—O4xi1.527 (7)
Nb1—O1ix2.044 (1)P1—O5xi1.537 (6)
Nb1—O2ix1.950 (6)P2—O11.524 (7)
Nb1—O4x2.011 (2)P2—O31.548 (3)
Nb1—O12.044 (1)P2—O1iv1.524 (7)
Nb2—O5viii2.050 (7)P2—O3iv1.548 (3)
Nb2—O21.832 (6)
O1—Nb1—O291.2 (3)O1ix—Fe1—O288.7 (7)
O1—Nb1—O4viii88.0 (7)O2—Fe1—O2ix180.0 (1)
O1—Nb1—O1ix180.0 (1)O2—Fe1—O4x90.2 (7)
O1—Nb1—O2ix88.7 (7)O1ix—Fe1—O4viii91.9 (3)
O1—Nb1—O4x91.9 (3)O2ix—Fe1—O4viii90.2 (7)
O2—Nb1—O4viii89.7 (3)O4viii—Fe1—O4x180.0 (1)
O1ix—Nb1—O288.7 (7)O1ix—Fe1—O2ix91.2 (3)
O2—Nb1—O2ix180.0 (1)O1ix—Fe1—O4x88.0 (7)
O2—Nb1—O4x90.2 (7)O2ix—Fe1—O4x89.7 (3)
O1ix—Nb1—O4viii91.9 (3)O2—Fe2—O3viii174.7 (4)
O2ix—Nb1—O4viii90.2 (7)O2—Fe2—O5viii92.4 (3)
O4viii—Nb1—O4x180.0 (1)O3—Fe2—O584.4 (3)
O1ix—Nb1—O2ix91.2 (3)O2viii—Fe2—O3174.7 (4)
O1ix—Nb1—O4x88.0 (7)O3—Fe2—O3viii86.7 (7)
O2ix—Nb1—O4x89.7 (3)O3—Fe2—O5viii85.7 (9)
O2—Nb2—O388.8 (1)O2viii—Fe2—O592.4 (3)
O2—Nb2—O596.6 (1)O3viii—Fe2—O585.7 (9)
O2—Nb2—O2viii95.7 (6)O5—Fe2—O5viii166.5 (3)
O2—Nb2—O3viii174.7 (4)O2viii—Fe2—O3viii88.8 (1)
O2—Nb2—O5viii92.4 (3)O2viii—Fe2—O5viii96.6 (1)
O3—Nb2—O584.4 (3)O3viii—Fe2—O5viii84.4 (3)
O2viii—Nb2—O3174.7 (4)O2—Fe2—O388.8 (1)
O3—Nb2—O3viii86.7 (7)O2—Fe2—O596.6 (1)
O3—Nb2—O5viii85.7 (9)O2—Fe2—O2viii95.7 (6)
O2viii—Nb2—O592.4 (3)O4—P1—O5110.9 (2)
O3viii—Nb2—O585.7 (9)O4—P1—O4xi108.6 (1)
O5—Nb2—O5viii166.5 (3)O4—P1—O5xi109.7 (3)
O2viii—Nb2—O3viii88.8 (1)O4xi—P1—O5109.7 (3)
O2viii—Nb2—O5viii96.6 (1)O5—P1—O5xi107.0 (1)
O3viii—Nb2—O5viii84.4 (3)O4xi—P1—O5xi110.9 (2)
O1—Fe1—O291.2 (3)O1—P2—O3110.9 (4)
O1—Fe1—O4viii88.0 (7)O1—P2—O1iv109.9 (4)
O1—Fe1—O1ix180.0 (1)O1—P2—O3iv109.1 (1)
O1—Fe1—O2ix88.7 (7)O1iv—P2—O3109.1 (1)
O1—Fe1—O4x91.9 (3)O3—P2—O3iv106.8 (4)
O2—Fe1—O4viii89.7 (3)O1iv—P2—O3iv110.9 (1)
Symmetry codes: (i) x3/2, y, z+1; (ii) x+1/2, y, z+1; (iii) x3/2, y1/2, z3/2; (iv) x+1/2, y, z; (v) x+1/2, y1/2, z+3/2; (vi) x+1/2, y+1/2, z+1/2; (vii) x3/2, y1/2, z1/2; (viii) x, y+1/2, z+1/2; (ix) x+1, y, z; (x) x+1, y3/2, z3/2; (xi) x, y+1/2, z+3/2.

Experimental details

(I)(II)
Crystal data
Chemical formulaKCr0.5Nb0.5OPO4KFe0.5Nb0.5OPO4
Mr222.53224.45
Crystal system, space groupOrthorhombic, PnnaOrthorhombic, Pnna
Temperature (K)293293
a, b, c (Å)12.849 (3), 10.672 (2), 6.4635 (13)12.9675 (13), 10.705 (3), 6.4638 (7)
V3)886.3 (3)897.3 (3)
Z88
Radiation typeMo KαMo Kα
µ (mm1)3.864.22
Crystal size (mm)0.4 × 0.15 × 0.060.2 × 0.15 × 0.1
Data collection
DiffractometerOxford Diffraction XCalibur-3
diffractometer
Oxford Diffraction XCalibur-3
diffractometer
Absorption correctionMulti-scan
(Blessing, 1995)
Multi-scan
(Blessing, 1995)
Tmin, Tmax0.510, 0.7700.387, 0.496
No. of measured, independent and
observed [I > 2σ(I)] reflections
13131, 1075, 1066 18570, 1087, 1021
Rint0.0360.027
(sin θ/λ)max1)0.6610.660
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.050, 0.114, 1.24 0.048, 0.113, 1.33
No. of reflections10751087
No. of parameters8888
No. of restraints11
w = 1/[σ2(Fo2) + (0.0308P)2 + 16.1755P]
where P = (Fo2 + 2Fc2)/3
w = 1/[σ2(Fo2) + (0.P)2 + 22.555P]
where P = (Fo2 + 2Fc2)/3
Δρmax, Δρmin (e Å3)3.20, 1.501.47, 1.32

Computer programs: CrysAlis CCD (Oxford Diffraction, 2005), CrysAlis CCD, CrysAlis RED (Oxford Diffraction, 2005), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND (Bradenburg, 2006), ORTEP-3 for Windows (Farrugia, 1997) and DIAMOND Bradenburg, 2006), WinGX (Farrugia, 1999).

Selected bond lengths (Å) for (I) top
K1—K21.426 (4)K2—O2iv3.133 (6)
K1—O32.667 (6)K2—O1v3.162 (7)
K1—O2i2.696 (6)K2—O3vi3.177 (6)
K1—O1ii2.734 (6)K2—O4vii3.189 (6)
K1—O4i2.792 (6)Cr1—O12.018 (1)
K1—O5iii2.994 (6)Cr1—O21.930 (1)
K1—O3iii3.025 (6)Cr1—O4viii1.992 (9)
K1—O4iii3.138 (6)Cr2—O52.050 (3)
K1—O2iii3.152 (6)Cr2—O21.825 (9)
K2—O32.717 (6)Cr2—O32.106 (7)
K2—O2i2.726 (6)P1—O41.529 (10)
K2—O52.797 (6)P1—O51.540 (8)
K2—O4i2.981 (6)P2—O11.530 (6)
K2—O1ii3.085 (7)P2—O31.5437 (14)
Symmetry codes: (i) x3/2, y, z+1; (ii) x+1/2, y, z+1; (iii) x+1/2, y, z; (iv) x1, y1/2, z1/2; (v) x, y+1/2, z+1/2; (vi) x+1/2, y+1/2, z+1/2; (vii) x1, y1/2, z3/2; (viii) x+1, y, z+1.
Selected bond lengths (Å) for (II) top
K1—K21.481 (3)K2—O2vii3.134 (7)
K1—O2i2.693 (7)K2—O4i3.162 (7)
K1—O32.700 (7)K2—O3viii3.163 (7)
K1—O1ii2.748 (7)Fe1—O12.044 (1)
K1—O4iii2.774 (7)Fe1—O21.950 (6)
K1—O5iv3.013 (7)Fe1—O4viii2.011 (2)
K1—O3iv3.016 (7)Fe2—O52.050 (7)
K1—O2iv3.113 (7)Fe2—O21.832 (6)
K1—O4v3.117 (7)Fe2—O32.113 (5)
K2—O32.734 (7)P1—O41.527 (7)
K2—O2i2.743 (7)P1—O51.537 (6)
K2—O52.844 (7)P2—O11.524 (7)
K2—O4iii2.944 (7)P2—O31.548 (3)
K2—O1vi3.132 (8)
Symmetry codes: (i) x3/2, y, z+1; (ii) x+1/2, y, z+1; (iii) x3/2, y1/2, z3/2; (iv) x+1/2, y, z; (v) x+1/2, y1/2, z+3/2; (vi) x+1/2, y+1/2, z+1/2; (vii) x3/2, y1/2, z1/2; (viii) x, y+1/2, z+1/2.
 

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