Rim = 0.07

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118

T h e Crystal Structure o f Sodium N ick el A rse n a te, N a N iA s 0 4

Klaus-Jürgen Range* and H elm ut M eister Institut für Anorganische Chemie der Universität Regensburg, Universitätsstraße 31, D-8400 Regensburg Z. Naturforsch. 39b, 118—120 (1984); received September 19, 1983 Sodium Nickel Arsenate, Crystal Structure

and oxygen refined only isotropically. For all calcula tions the program system SHELX-76 [3] was used on a TR 440 com puter. Scattering factors and anom a lous dispersion corrections were taken from Interna tional Tables of X-ray Crystallography. Refinem ent in space group R 3 resulted in a final R = 0.045. Lattice dimensions, final atomic param eters, bond distances and angles are given in Tables I and II. Fig. 1 shows the unit cell of N aN iA s0 4. The com pound crystallizes in a pronounced layer structure

The unit cell of N aN iA s04 is rhombohedral, space group R 3, with a — 4.955(5) Ä, c = 26.47(3) Ä and Z = 6. The crystal structure com prises three-layer units consisting of one “octahe dral” layer, built up from NiO^-octahedra, and two “tetrahedral” layers, built up from A s0 4-tetrahedra. Sodium ions are situated between these layers, having a distorted (4+3) coordination.

Ladwig and Z iem er [1] investigated the compound K N iA s0 4 [2] by X-ray pow der and spectroscopic m ethods. They proposed a structural model similar to silicate micas and representing a new M M 'X 0 4 structure type: tetrahedral — octahedral — tetrahe dral three-layer units with potassium ions in the in terlayer space. H ow ever, detailed informations con cerning arrangem ent of the tetrahedra, distortion of the coordination polyhedra, kind of stacking of the three-layer units and position of the alkali ions were still lacking. The present paper gives these informa tions for the com pound N a N iA s0 4, isostructural with K N iA s0 4. Yellow-green mica-like lamellas of N aN iA s0 4 could be prepared by heating a stoichiometric mixtu re of N iC 0 3 and N aH 2A s 0 4 up to 1000 °C, followed by slow cooling to room tem perature. Single crystal X-ray data were collected for a nearly regular hexa gonal lamella (edge-length 70 /xm and thickness 1 2 //m ) on an autom atic two-circle-diffractometer (H uber R H D 402, M oK n radiation, graphite m ono chrom ator, 1847 reflections in co-26 scan mode, 26 ^ 60°, 0 < h < 3 ,|* | < 8 , |/| ^ 51, A to = ±0.6°). A fter data reduction absorption corrections were applied (transmission factors between 0.43 and 0.89). From 1015 sym m etry-independent reflexions ( Rim = 0.07) 855 with |F0| > 5 o (|F 0|) were considered as obser ved and used for calculations. The structure was solved by Patterson and Fourier methods. H ow ever, not all param eters could be re fined at the same time due to strong correlations. The tem perature factors for the light atoms sodium

* Reprint requests to Prof. D r. K.-J. Range. 0340-5087/84/0100-0118/$ 01.00/0

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119

Notizen Table I. Crystallographic data for N a N iA s0 4 (here, and in the following Table, the e .s.d.'s of the last figures are given in parentheses). Space Group: Axis: Density:

R3 a c da D*

= 4.955(3) Ä = 26.47(3)Ä = 5.34 — 3.905 g/cm3

Positional and Thermal Parameters: Atom

x/a

y/b

zlc

B (Ä 2)

N i(l) Ni(2) A s(l) A s(2) 0 ( 1) 0 (2) 0 (3 ) 0 (4 ) N a (l) Na(2)

0 0 0 0 0.0015(12) 0.6625(13) 0 0 0 0

0 0 0 0 0.3506(12) 0.9956(12) 0 0 0 0

0.1240(3) 0.4528(3) 0.7214(3) 0.8534(3) 0.4083(3) 0.4994(3) 0.6597(4) 0.9163(4) 0.0000 0.5774(4)

0.67(9) 0.41(7) 0.69(7) 0.35(6) 0.58(6) 0.66(6) 2.7(4) 1.0(3) 2.0(3) 2.5(2)

Isotropic B ’s are given for sodium and oxygen. The equi valent isotropic B ’s for nickel and arsenic were calculated from the anisotropic temperature factors U;j according to Hamilton [5].

built up from tetrahedral — octahedral — tetrahedral three-layer units. T hese three-layer units are stacked along[0 0 1 ] and shifted against each other by (2/3,1/3, 1/3), giving a layer spacing c/3 = 8.82 Ä. Each one of the three-layer units is built up from a central, twodimensional infinite N iO e-octahedral layer (mean N i(l) - 0 ( 2 ) - 0 ( 1) Ni(2) - 0 ( 1 ) - 0 (2) A s(l) —0 (1 ) -0 (3 ) As(2) —0 (2 ) -0 (4 ) N a (l) —0 (4 ) - 0 ( 1) -0 (3 ) Na(2) —0 (3 ) - 0 (2) -0 (4 )

2.003(7) 2.072(8) 2.093(7) 2.072(7) 1.694(5) 1.63(1) 1.719(5) 1.66( 1) 2.21(2) 2.56(1) 2.867(5) 2.18(2) 2.65(1) 2.684(5)

0(2)—Ni(l) —0(2) 0(1)—Ni(l) —0(1) 0(1)—Ni(l) —0(2) 0(2)—Ni(l) —0(1) 0(2)—Ni(l) —0(1) 0(2)—Ni(2) —0(2) 0(1) —Ni(2) —0(1) 0(1)—Ni(2) —0(2) 0(1) —Ni(2) —0(2) 0(1)—Ni(2) —0(2)

0 (1 ) - 0 ( 3 ) - 0 ( 1) - 0 ( 1) - 0 ( 1) - 0 (2) - 0 (2) - 0 (2) 0 (2) - 0 (2) - 0 (2) - 0 (2) -0 (4 )

92.0(3) 85.1(3) 174.5(4) 93.2(2) 89.6(2) 87.9(3) 91.7(3) 90.6(2) 89.7(2) 177.3(4)

N i- O distance 2.06 Ä ), which is enclosed by two A s 0 4-tetrahedral layers (m ean A s - O distance 1.67 Ä). In the octahedral layer each N iO e-octahedra is connected with three other N i0 6-octahedra via a common edge. In this way, a netw ork of six-membered rings built up from N i0 6-octahedra develops around unoccupied oxygen octahedra. Three oxygen atoms of an empty octahedron form the basal plane for two A s 0 4-tetrahedra pointing up and down in the c-axis direction. The Na atoms are placed in the tetrahedral layers, occupying isolated tetrahedra (distance 4.95 Ä). They are located above the three oxygen atoms of a N i0 6-octahedra at the same level as the top atoms (0 (3 ), 0 (4 )) of the A s 0 4 -tetrahedron. The N a —Odistances to the tops of the tetrahedra are the short est ones (2.2 Ä ). For Na results a (4+ 3) coordina tion. Above three triangular faces of the strongly distorted tetrahedron three additional oxygen atoms are located. The present structure determ ination for N aN iA s0 4 confirms the essential structural features proposed by Ladwig and Ziem er [1] for the hom olo gous com pound K N iA s0 4 and explains readily the capability of N aN iA s0 4 and K N iA s0 4 of forming in tercalation complexes after treatm ent with alkylammonium ions [4], The financial support of the Fonds der Chemischen In dustrie is gratefully acknowledged. All calculations were performed on the TR 440 computer of the Rechenzentrum of the University of Regensburg. Table II. Interatomic distances (A ) and angles (°).

2.70(1) 2.783(6) 2.802(9) 3.002(6) 2.87(1) 2.937(9) 2.96(1) 2.824(6) 2.878(5) 2.881(6) 2.75(1)

0 ( 3 ) —A s (l)—0 (1 ) 0 ( 1 ) —A s (l)—0 (1 ) 0 ( 4 ) —A s(2)—0 (2 ) 0 ( 2 ) —A s (2 )- 0 (2 ) 0 ( 4 ) —N a (l) —0 (1 ) 0 ( 4 ) —N a (l)—0 (3 ) 0 ( 3 ) —N a ( l) - 0 ( 3 ) 0 ( 3 ) —Na(2) —0 (2 ) 0 (3 ) —Na(2) —0 (4 ) 0 ( 4 ) —Na(2) —0 (4 )

108.5(4) 110.4(3) 108.5(4) 110.5(3) 140.8(2) 86.3(3) 119.6(1) 114.2(2) 87.1(3) 119.7(1)


N otizen

120 [1] G. Ladwig and B. Ziemer, Z. Anorg. Allg. Chem. 457, 143 (1979). [2] C. Lefevre, C. R. Acad. Sei. 110, 405 (1890). [3] G. M. Sheldrick, in: Computing in Crystallography, Delft University Press 1978, p. 34ff.

[4] K. Beneke and G. Lagaly, Clay Minerals 17, 175 (1982). [5] W. C. Hamilton, Acta Crystallogr. 12, 609 (1959).
