Safflorite, (Co,Ni,Fe)As(2), isomorphous with marcasite.

Safflorite, a naturally occurring cobalt-nickel-iron diarsenide (Co,Ni,Fe)As(2), possesses the marcasite-type structure, with cations (M = Co + Ni + Fe) at site symmetry 2/m and As anions at m. The MAs(6) octa-hedra share two edges, forming chains parallel to c. The chemical formula for safflorite should be expressed as (Co,Ni,Fe)As(2), rather than the end-member format CoAs(2), as its structure stabilization requires the simultaneous inter-action of the electronic states of Co, Ni, and Fe with As(2) (2-) dianions.

Related literature

For related literature, see: Anawar et al. (2003 ▶); Carlon & Bleeker (1988 ▶); Darmon & Wintenberger (1966 ▶); Ennaciri et al. (1995 ▶); Goodenough (1967 ▶); Grorud (1997 ▶); Hem et al. (2001 ▶); Holmes (1947 ▶); King (2002 ▶); Kjekshus (1971 ▶); Kjekshus et al. (1974 ▶, 1979 ▶); Lutz et al. (1987 ▶); Makovicky (2006 ▶); O’Day (2006 ▶); Ondrus et al. (2001 ▶); Palenik et al. (2004 ▶); Petruk et al. (1971 ▶); Radcliffe & Berry (1968 ▶, 1971 ▶); Reich et al. (2005 ▶); Robinson et al. (1971 ▶); Swanson et al. (1966 ▶); Tossell (1984 ▶); Tossell et al. (1981 ▶); Vaughan & Rosso (2006 ▶); Wagner & Lorenz (2002 ▶).

Experimental

Crystal data

As1.99Co0.61Fe0.17Ni0.22S0.01

M = 207.77

Orthorhombic,

a = 5.0669 (6) Å

b = 5.8739 (7) Å

c = 3.1346 (4) Å

V = 93.29 (2) Å3

Z = 2

Mo Kα radiation

μ = 43.75 mm−1

T = 293 (2) K

0.06 × 0.05 × 0.04 mm

Data collection

Bruker APEX2 CCD area-detector diffractometer

Absorption correction: multi-scan (TWINABS; Sheldrick, 2007 ▶) T min = 0.179, T max = 0.274 (expected range = 0.114–0.174)

1232 measured reflections

254 independent reflections

227 reflections with I > 2σ(I)

R int = 0.041

Refinement

R[F 2 > 2σ(F 2)] = 0.025

wR(F 2) = 0.061

S = 0.91

254 reflections

13 parameters

Δρmax = 1.44 e Å−3

Δρmin = −1.82 e Å−3

Data collection: APEX2 (Bruker, 2003 ▶); cell refinement: SAINT (Bruker, 2005 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: XtalDraw (Downs & Hall-Wallace, 2003 ▶); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 ▶).

Crystal structure: contains datablocks I, New_Global_Publ_Block. DOI: 10.1107/S1600536808026688/mg2054sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808026688/mg2054Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

As1.99Co0.61Fe0.17Ni0.22S0.01	F000 = 168
Mr = 207.77	Dx = 7.396 Mg m−3
Orthorhombic, Pnnm	Mo Kα radiation λ = 0.71073 Å
Hall symbol: -P 2 2n	Cell parameters from 153 reflections
a = 5.0669 (6) Å	θ = 5.0–31.4º
b = 5.8739 (7) Å	µ = 43.75 mm−1
c = 3.1346 (4) Å	T = 293 (2) K
V = 93.29 (2) Å3	Granular, black
Z = 2	0.06 × 0.05 × 0.04 mm

Bruker APEX2 CCD area-detector diffractometer	254 independent reflections
Radiation source: fine-focus sealed tube	227 reflections with I > 2σ(I)
Monochromator: graphite	Rint = 0.041
T = 293(2) K	θmax = 36.4º
φ and ω scan	θmin = 5.3º
Absorption correction: multi-scan(TWINABS; Sheldrick, 2007)	h = −8→7
Tmin = 0.179, Tmax = 0.274	k = −8→9
1232 measured reflections	l = −5→5

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ2(Fo2) + (0.0428P)2] where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.025	(Δ/σ)max < 0.001
wR(F2) = 0.061	Δρmax = 1.44 e Å−3
S = 0.91	Δρmin = −1.82 e Å−3
254 reflections	Extinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
13 parameters	Extinction coefficient: 0.016 (6)
Primary atom site location: structure-invariant direct methods

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.

	x	y	z	Uiso*/Ueq
M	0.0000	0.0000	0.0000	0.0130 (2)
As	0.18637 (9)	0.36589 (7)	0.0000	0.01033 (17)

	U11	U22	U33	U12	U13	U23
M	0.0090 (4)	0.0033 (4)	0.0267 (4)	0.0001 (3)	0.000	0.000
As	0.0140 (3)	0.0046 (2)	0.0124 (2)	−0.00002 (14)	0.000	0.000

M—As	2.3475 (5)	M—Asiii	2.3669 (4)
M—Asi	2.3475 (5)	M—Asiv	2.3669 (4)
M—Asii	2.3669 (4)	M—Asv	2.3669 (4)
As—M—Asii	88.016 (9)	M—As—Mvi	125.085 (13)
Asi—M—Asii	91.984 (9)	Mvi—As—Mvii	82.931 (17)
Asii—M—Asiv	82.931 (17)	M—As—Asviii	106.12 (3)
Asiii—M—Asiv	97.069 (17)	Mvi—As—Asviii	107.599 (2)