KNi₃(AsO₄)(As₂O₇)

The structure of the title compound, potassium trinickel arsenate diarsenate, is built up from corner- and edge-sharing NiO₆ octahedra, AsO₄ tetrahedra and As₂O₇ groups, giving rise to a polyhedral connectivity which produces large tunnels running along the crystallographic [010] direction. The K⁺ cations are located within these tunnels.

S1. Comment

Until now, in the system K₂O-NiO-As₂O₅ only the structure of K₄Ni₇(AsO₄)₆ (Ben Smail et al., 1999) has been refined from single-crystal data. For KNiAsO₄ (Buckley et al., 1988), the crystal structure has been determined by high-resolution powder neutron diffraction. In this paper we present the synthesis and structural determination of the new potassium nickel arsenate KNi₃(AsO₄)(As₂O₇) refined from single-crystal data. The structure of this compound, viewed along the b axis, is shown in Fig. 1. It contains parallel tunnels running along the [010] direction, wherein the K⁺ cations are located. The three-dimensional open anionic framework is made up of corner- and edge-sharing NiO₆ octahedra, AsO₄ tetrathedra and As₂O₇ groups. It can be described in terms of layers lying parallel to the (100) plane. These layers are connected to each other by corner sharing with the As3O₄ tetrahedron of the As2As3O₇ group and with the Ni3O₆ octahedron. In each layer centrosymmetric pairs of Ni1O₆, Ni2O₆ and Ni3O₆ octahedra share six edges to constitute an Ni₆O₂₄ unit. Each unit is connected to its four adjacent neighbours by eight corners (Fig. 2). The cohesion between these units is reinforced by As1O₄ tetrahedra and As2As3O₇ groups. Each As1O₄ tetrahedron shares two edges, O8—O11 and O10—O11, with two adjacent NiO₆ octahedra of one Ni₆O₂₄ unit and two corners, O3 and O10, with two NiO₆ octahedra of another unit. The diarsenate group shares five corners, O1, O2, O4, O6 and O7, with three units of one layer and the sixth, O5, with one unit of another layer. The As₂O₇ group has no internal symmetry and a nearly eclipsed conformation, with O9 as the bridging oxygen. The As2—O9—As3 bridging angle is 120.4 (2)°. The average As—O bond distance is 1.649 (3) Å. Both values agree with those generally observed for As₂O₇ groups (Effenberger & Pertlik, 1993).

The As—O bond lengths range from 1.640?(3) to 1.788 (3) Å. These values compare well with those obtained in the two arsenate diarsenates previously reported: Ag₅Cu(AsO₄)(As₂O₇) (Effenberger & Pertlik, 1993) and Na₅Bi₂(AsO₄)(As₂O₇)₂ (Boughzala & Jouini, 1998).

The three Ni atoms in the asymmetric unit exhibit a normal octahedral coordination, with average Ni—O distances of 2.083 (3), 2.079 (3) and 2.086?(3) Å for Ni1, Ni2 and Ni3, respectively. These values are in the same range as those found in K₄Ni₇(AsO₄)₆ and KNiAsO₄.

The K⁺ ion is eleven-coordinated. The K···O distances range between 2.809 (4) and 3.105 (4) Å, with a mean distance of 2.960?(9) Å. We note here that the structure of the rubidium cadmium vanadate, NaCd₃(VO₄)(V₂O₇) (Mertens & Müller-Buschbaum, 1997), although analogous in composition, is fundamentally different in structure from the arsenate studied in the present work.

S2. Experimental

The title compound was prepared by the reaction of NiO, As₂O₅ and K₂CO₃ in the molar ratio 0.5:1:1. The mixture was ground in an agate mortar and heated at 673 K for 12 h. After grinding, the mixture was heated at 968 K for 6 h, following by slow cooling at a rate of 10 K h^-1 to 773 K and from 773 K to room temperature at 100 K h^-1.

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL93 (Sheldrick, 1993); molecular graphics: DIAMOND (Brandenburg, 1997); software used to prepare material for publication: SHELXL93.

Figures

	Fig. 1. A projection of the KNi3(AsO4)(As2O7) structure along the b axis.
	Fig. 2. A perspective view of a portion of the structure of KNi3(AsO4)(As2O7), showing the connections between the NiO6 octahedra, AsO4 tetrahedra and As2O7 groups.

potassium trinickel arsenate diarsenate

Crystal data

KNi3(AsO4)(As2O7)	F(000) = 1160
Mr = 615.99	Dx = 4.727 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2ybc	Cell parameters from 25 reflections
a = 10.066 (1) Å	θ = 11.5–17.0°
b = 9.681 (2) Å	µ = 18.38 mm^−1
c = 10.234 (1) Å	T = 293 K
β = 119.780 (1)°	Parallelepiped, green
V = 865.6 (2) Å^3	0.14 × 0.07 × 0.05 mm
Z = 4

Data collection

Enraf-Nonius CAD4 diffractometer	1851 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.023
Graphite monochromator	θmax = 30.0°, θmin = 2.3°
ω/2θ scans	h = 0→14
Absorption correction: ψ-scan (North et al., 1968)	k = −13→0
Tmin = 0.217, Tmax = 0.371	l = −14→12
2653 measured reflections	2 standard reflections every 120 min
2526 independent reflections	intensity decay: 0.6%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.032	Calculated w = 1/[σ^2(Fo^2) + (0.0225P)^2 + 1.2839P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.059	(Δ/σ)max = −0.001
S = 1.10	Δρmax = 1.08 e Å^−3
2526 reflections	Δρmin = −1.21 e Å^−3
164 parameters	Extinction correction: SHELXL93 (Sheldrick, 1993), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00219 (14)

Special details

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 on F² for ALL reflections except for 0 with very negative F² or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating _R_factor_obs 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 (Ų)

	x	y	z	Uiso*/Ueq
Ni1	0.91265 (7)	0.13238 (6)	0.73634 (7)	0.0059 (1)
Ni2	0.09243 (7)	0.12885 (6)	0.10055 (7)	0.0056 (1)
Ni3	0.73818 (7)	0.13548 (6)	0.38145 (7)	0.0060 (1)
K	0.4101 (1)	0.2333 (1)	0.9109 (1)	0.0154 (2)
As1	0.09995 (6)	0.15740 (5)	0.43237 (5)	0.0048 (1)
As2	0.77020 (6)	0.07247 (5)	0.08381 (5)	0.0048 (1)
As3	0.59179 (6)	0.05737 (5)	0.73943 (5)	0.0053 (1)
O1	0.7641 (4)	0.2450 (3)	0.0640 (4)	0.0068 (6)
O2	0.5818 (4)	0.2279 (4)	0.7291 (4)	0.0090 (7)
O3	0.8965 (4)	0.0149 (3)	0.5653 (4)	0.0070 (6)
O4	0.7446 (4)	0.0151 (4)	0.2205 (4)	0.0101 (7)
O5	0.5576 (4)	0.0315 (4)	0.3831 (4)	0.0087 (7)
O6	0.7562 (4)	0.0031 (4)	0.7487 (4)	0.0069 (6)
O7	0.0753 (4)	0.0027 (3)	0.9153 (4)	0.0065 (6)
O8	0.2371 (4)	0.2360 (4)	0.5841 (4)	0.0081 (7)
O9	0.6135 (4)	0.0128 (4)	0.9186 (4)	0.0086 (7)
O10	0.0871 (4)	0.2268 (3)	0.2731 (4)	0.0080 (7)
O11	0.9383 (4)	0.2388 (3)	0.4152 (4)	0.0070 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni1	0.0062 (3)	0.0050 (3)	0.0054 (3)	0.0000 (2)	0.0021 (2)	0.0002 (2)
Ni2	0.0056 (3)	0.0054 (3)	0.0055 (3)	0.0000 (2)	0.0025 (2)	0.0005 (2)
Ni3	0.0055 (3)	0.0059 (3)	0.0056 (3)	0.0002 (2)	0.0020 (2)	−0.0002 (2)
K	0.0115 (5)	0.0140 (5)	0.0188 (6)	0.0000 (4)	0.0061 (5)	0.0002 (4)
As1	0.0046 (2)	0.0044 (2)	0.0047 (2)	0.0002 (2)	0.0017 (2)	−0.0002 (2)
As2	0.0040 (2)	0.0050 (2)	0.0046 (2)	0.0000 (2)	0.0016 (2)	−0.0002 (2)
As3	0.0035 (2)	0.0060 (2)	0.0051 (2)	−0.0001 (2)	0.0011 (2)	−0.0005 (2)
O1	0.010 (2)	0.005 (2)	0.007 (2)	−0.000 (1)	0.005 (1)	0.000 (1)
O2	0.005 (2)	0.006 (2)	0.012 (2)	0.001 (1)	0.002 (1)	0.000 (1)
O3	0.010 (2)	0.003 (1)	0.008 (2)	0.002 (1)	0.005 (1)	0.000 (1)
O4	0.015 (2)	0.008 (2)	0.010 (2)	−0.002 (1)	0.009 (2)	0.000 (1)
O5	0.006 (2)	0.014 (2)	0.006 (2)	−0.006 (1)	0.003 (1)	−0.004 (1)
O6	0.004 (2)	0.008 (2)	0.007 (2)	0.002 (1)	0.002 (1)	0.001 (1)
O7	0.005 (2)	0.006 (2)	0.008 (2)	−0.001 (1)	0.003 (1)	0.001 (1)
O8	0.004 (2)	0.009 (2)	0.008 (2)	−0.001 (1)	0.000 (1)	−0.004 (1)
O9	0.009 (2)	0.011 (2)	0.004 (2)	−0.004 (1)	0.001 (1)	0.001 (1)
O10	0.010 (2)	0.008 (2)	0.008 (2)	0.002 (1)	0.006 (1)	0.001 (1)
O11	0.005 (2)	0.008 (2)	0.008 (2)	−0.000 (1)	0.004 (1)	−0.001 (1)

Geometric parameters (Å, º)

Ni1—O3	2.025 (3)	K—O9	2.931 (4)
Ni1—O1^i	2.033 (3)	K—O9^ix	3.032 (4)
Ni1—O6	2.064 (3)	K—O8^i	3.055 (4)
Ni1—O10^ii	2.104 (3)	K—O6^x	3.095 (4)
Ni1—O11^i	2.122 (3)	K—O1^xi	3.102 (4)
Ni1—O7^iii	2.152 (3)	K—O2	3.105 (4)
Ni1—As1^ii	2.8220 (8)	K—As1^i	3.4056 (13)
Ni2—O6^iv	2.000 (3)	As1—O8	1.663 (3)
Ni2—O8^v	2.026 (3)	As1—O3^iv	1.669 (3)
Ni2—O10	2.028 (3)	As1—O10	1.707 (3)
Ni2—O7^vi	2.056 (3)	As1—O11^xii	1.737 (3)
Ni2—O11^vii	2.173 (3)	As1—Ni2^i	2.7165 (9)
Ni2—O7^viii	2.188 (3)	As1—Ni1^vii	2.8220 (8)
Ni2—As1^v	2.7165 (9)	As1—K^v	3.4055 (13)
Ni2—K^v	3.4649 (13)	As2—O4	1.640 (3)
Ni3—O4	2.045 (4)	As2—O1	1.680 (3)
Ni3—O2^v	2.054 (3)	As2—O7^iv	1.713 (3)
Ni3—O5	2.085 (3)	As2—O9^viii	1.741 (3)
Ni3—O1^i	2.101 (3)	As2—K^iv	3.4867 (14)
Ni3—O3	2.112 (3)	As2—K^viii	3.5102 (13)
Ni3—O11	2.118 (3)	As3—O5^iv	1.643 (3)
Ni3—K^v	3.6875 (14)	As3—O2	1.654 (3)
K—O5^i	2.809 (4)	As3—O6	1.694 (3)
K—O4^iv	2.817 (4)	As3—O9	1.788 (3)
K—O2^i	2.854 (4)	As3—K^xiii	3.4900 (14)
K—O10^i	2.856 (4)	As3—K^v	3.5565 (13)
K—O8	2.904 (4)
O3—Ni1—O1^i	82.48 (13)	O2^v—Ni3—O5	88.54 (14)
O3—Ni1—O6	88.63 (14)	O4—Ni3—O1^i	172.16 (14)
O1^i—Ni1—O6	98.75 (14)	O2^v—Ni3—O1^i	91.74 (14)
O3—Ni1—O10^ii	102.71 (13)	O5—Ni3—O1^i	89.00 (13)
O1^i—Ni1—O10^ii	88.03 (14)	O4—Ni3—O3	95.23 (14)
O6—Ni1—O10^ii	167.51 (13)	O2^v—Ni3—O3	170.49 (14)
O3—Ni1—O11^i	177.16 (14)	O5—Ni3—O3	90.04 (14)
O1^i—Ni1—O11^i	97.30 (13)	O1^i—Ni3—O3	78.83 (13)
O6—Ni1—O11^i	94.19 (13)	O4—Ni3—O11	89.58 (13)
O10^ii—Ni1—O11^i	74.45 (13)	O2^v—Ni3—O11	97.36 (13)
O3—Ni1—O7^iii	96.25 (13)	O5—Ni3—O11	171.45 (13)
O1^i—Ni1—O7^iii	177.92 (13)	O1^i—Ni3—O11	84.65 (13)
O6—Ni1—O7^iii	82.84 (13)	O3—Ni3—O11	83.12 (13)
O10^ii—Ni1—O7^iii	90.64 (13)	O8—As1—O3^iv	116.2 (2)
O11^i—Ni1—O7^iii	83.88 (13)	O8—As1—O10	110.2 (2)
O6^iv—Ni2—O8^v	99.97 (14)	O3^iv—As1—O10	113.4 (2)
O6^iv—Ni2—O10	88.06 (14)	O8—As1—O11^xii	100.9 (2)
O8^v—Ni2—O10	95.83 (14)	O3^iv—As1—O11^xii	117.9 (2)
O6^iv—Ni2—O7^vi	86.91 (14)	O10—As1—O11^xii	95.9 (2)
O8^v—Ni2—O7^vi	171.69 (14)	O4—As2—O1	115.3 (2)
O10—Ni2—O7^vi	89.00 (14)	O4—As2—O7^iv	112.2 (2)
O6^iv—Ni2—O11^vii	171.94 (13)	O1—As2—O7^iv	113.7 (2)
O8^v—Ni2—O11^vii	77.17 (13)	O4—As2—O9^viii	105.4 (2)
O10—Ni2—O11^vii	99.68 (13)	O1—As2—O9^viii	104.6 (2)
O7^vi—Ni2—O11^vii	95.39 (13)	O7^iv—As2—O9^viii	104.3 (2)
O6^iv—Ni2—O7^viii	90.81 (14)	O5^iv—As3—O2	118.0 (2)
O8^v—Ni2—O7^viii	92.22 (13)	O5^iv—As3—O6	112.3 (2)
O10—Ni2—O7^viii	171.94 (13)	O2—As3—O6	109.9 (2)
O7^vi—Ni2—O7^viii	82.97 (14)	O5^iv—As3—O9	104.8 (2)
O11^vii—Ni2—O7^viii	81.84 (13)	O2—As3—O9	106.2 (2)
O4—Ni3—O2^v	94.27 (14)	O6—As3—O9	104.4 (2)
O4—Ni3—O5	96.18 (14)

Symmetry codes: (i) x, −y+1/2, z+1/2; (ii) x+1, −y+1/2, z+1/2; (iii) x+1, y, z; (iv) −x+1, −y, −z+1; (v) x, −y+1/2, z−1/2; (vi) −x, −y, −z+1; (vii) x−1, −y+1/2, z−1/2; (viii) x, y, z−1; (ix) −x+1, −y, −z+2; (x) −x+1, y+1/2, −z+3/2; (xi) x, y, z+1; (xii) x−1, y, z; (xiii) −x+1, y−1/2, −z+3/2.