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Tyrrellite, a naturally occurring Co–Ni–Cu selenide, has been studied by single-crystal X-ray diffraction. It possesses the normal spinel-type structure, with Cu occupying the tetrahedral site and (Co+Ni) the octahedral site. The average Cu—Se distance of 2.3688 (2) Å is close to that of 2.3703 (8) Å in CuCr2Se4, whereas the average (Co+Ni)—Se distance of 2.3840 (1) Å appears to be slightly shorter than most octahedral Co—Se or Ni—Se distances (∼2.40–2.50 Å) in other selenides. The refined structure provides a basis for a redefinition of the ideal chemical formula of tyrrellite, which should be Cu(Co,Ni)2Se4, rather than the previously suggested (Cu,Co,Ni)3Se4.
Supporting information
The tyrrellite specimen used in this study is from the type locality Eagle
Claims, Beaverlodge Lake area, Saskatchewan, Canada, and is in the collection
of the RRUFF project (deposition No. R060481; https://rruff.info). The specimen
was described by Robinson & Brooker (1952) and Harris (1970). The average
chemical composition (15 point analyses), Cu0.99(Co0.69Ni0.31)2Se4,
was determined with a CAMECA SX50 electron microprobe.
The A site was assumed to be fully occupied by Cu during the refinement. The
Co:Ni ratio in the B site was allowed to vary and yielded occupancies of
0.68 (6) for Co and 0.32 (6) for Ni.
Data collection: APEX2 (Bruker, 2003); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Please provide missing information; software used to prepare material for publication: SHELXTL (Bruker, 1997).
copper cobalt nickel tetraselenide
top
Crystal data top
Co1.36CuNi0.64Se4 | Dx = 6.627 Mg m−3 |
Mr = 497.06 | Mo Kα radiation, λ = 0.71073 Å |
Cubic, Fd3m | Cell parameters from 1008 reflections |
Hall symbol: -F 4vw 2vw | θ = 3.5–44.1° |
a = 9.9885 (1) Å | µ = 40.12 mm−1 |
V = 996.55 (2) Å3 | T = 293 K |
Z = 8 | Block, black |
F(000) = 1757 | 0.07 × 0.07 × 0.06 mm |
Data collection top
Bruker APEXII CCD area-detector diffractometer | 227 independent reflections |
Radiation source: fine-focus sealed tube | 206 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.030 |
π and ω scans | θmax = 44.8°, θmin = 3.5° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2005) | h = −18→19 |
Tmin = 0.123, Tmax = 0.142 | k = −18→12 |
2566 measured reflections | l = −17→11 |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.014 | w = 1/[σ2(Fo2) + (0.0086P)2 + 2.3104P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.028 | (Δ/σ)max = 0.001 |
S = 1.12 | Δρmax = 0.79 e Å−3 |
227 reflections | Δρmin = −1.27 e Å−3 |
9 parameters | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.00182 (6) |
Crystal data top
Co1.36CuNi0.64Se4 | Z = 8 |
Mr = 497.06 | Mo Kα radiation |
Cubic, Fd3m | µ = 40.12 mm−1 |
a = 9.9885 (1) Å | T = 293 K |
V = 996.55 (2) Å3 | 0.07 × 0.07 × 0.06 mm |
Data collection top
Bruker APEXII CCD area-detector diffractometer | 227 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2005) | 206 reflections with I > 2σ(I) |
Tmin = 0.123, Tmax = 0.142 | Rint = 0.030 |
2566 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.014 | 9 parameters |
wR(F2) = 0.028 | 0 restraints |
S = 1.12 | Δρmax = 0.79 e Å−3 |
227 reflections | Δρmin = −1.27 e Å−3 |
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 | x | y | z | Uiso*/Ueq | Occ. (<1) |
Cu1 | 0.1250 | 0.1250 | 0.1250 | 0.01020 (11) | |
Co1 | 0.5000 | 0.0000 | 0.0000 | 0.00624 (11) | 0.68 (6) |
Ni1 | 0.5000 | 0.0000 | 0.0000 | 0.00624 (11) | 0.32 (6) |
Se1 | 0.261923 (14) | −0.011923 (14) | −0.011923 (14) | 0.00705 (6) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cu1 | 0.01020 (11) | 0.01020 (11) | 0.01020 (11) | 0.000 | 0.000 | 0.000 |
Co1 | 0.00624 (11) | 0.00624 (11) | 0.00624 (11) | −0.00031 (6) | −0.00031 (6) | −0.00031 (6) |
Ni1 | 0.00624 (11) | 0.00624 (11) | 0.00624 (11) | −0.00031 (6) | −0.00031 (6) | −0.00031 (6) |
Se1 | 0.00705 (6) | 0.00705 (6) | 0.00705 (6) | 0.00027 (4) | 0.00027 (4) | −0.00027 (4) |
Geometric parameters (Å, º) top
Cu1—Se1i | 2.3688 (2) | Co1—Se1v | 2.3840 (1) |
Cu1—Se1ii | 2.3688 (2) | Co1—Se1 | 2.3840 (1) |
Cu1—Se1iii | 2.3688 (2) | Co1—Se1vi | 2.3840 (1) |
Cu1—Se1 | 2.3688 (2) | Co1—Se1vii | 2.3840 (1) |
Co1—Se1iv | 2.3840 (1) | Co1—Se1viii | 2.3840 (1) |
| | | |
Se1i—Cu1—Se1ii | 109.5 | Se1—Co1—Se1viii | 180.0 |
Se1i—Cu1—Se1iii | 109.5 | Se1vi—Co1—Se1viii | 84.137 (7) |
Se1ii—Cu1—Se1iii | 109.5 | Se1vii—Co1—Se1viii | 84.137 (7) |
Se1i—Cu1—Se1 | 109.5 | Cu1—Se1—Ni1iv | 121.213 (5) |
Se1ii—Cu1—Se1 | 109.5 | Cu1—Se1—Ni1v | 121.213 (5) |
Se1iii—Cu1—Se1 | 109.5 | Ni1iv—Se1—Ni1v | 95.576 (7) |
Se1iv—Co1—Se1v | 84.137 (7) | Cu1—Se1—Co1iv | 121.213 (5) |
Se1iv—Co1—Se1 | 84.137 (7) | Ni1iv—Se1—Co1iv | 0.0 |
Se1v—Co1—Se1 | 84.137 (7) | Ni1v—Se1—Co1iv | 95.576 (7) |
Se1iv—Co1—Se1vi | 180.0 | Cu1—Se1—Co1v | 121.213 (5) |
Se1v—Co1—Se1vi | 95.863 (7) | Ni1iv—Se1—Co1v | 95.576 (7) |
Se1—Co1—Se1vi | 95.863 (7) | Ni1v—Se1—Co1v | 0.0 |
Se1iv—Co1—Se1vii | 95.863 (7) | Co1iv—Se1—Co1v | 95.576 (7) |
Se1v—Co1—Se1vii | 180.0 | Cu1—Se1—Co1 | 121.213 (5) |
Se1—Co1—Se1vii | 95.863 (7) | Ni1iv—Se1—Co1 | 95.576 (7) |
Se1vi—Co1—Se1vii | 84.137 (7) | Ni1v—Se1—Co1 | 95.576 (7) |
Se1iv—Co1—Se1viii | 95.863 (7) | Co1iv—Se1—Co1 | 95.576 (7) |
Se1v—Co1—Se1viii | 95.863 (7) | Co1v—Se1—Co1 | 95.576 (7) |
Symmetry codes: (i) −x+1/4, y, −z+1/4; (ii) −x+1/4, −y+1/4, z; (iii) x, −y+1/4, −z+1/4; (iv) −x+3/4, y, −z−1/4; (v) −x+3/4, −y−1/4, z; (vi) x+1/4, −y, z+1/4; (vii) x+1/4, y+1/4, −z; (viii) −x+1, −y, −z. |
Experimental details
Crystal data |
Chemical formula | Co1.36CuNi0.64Se4 |
Mr | 497.06 |
Crystal system, space group | Cubic, Fd3m |
Temperature (K) | 293 |
a (Å) | 9.9885 (1) |
V (Å3) | 996.55 (2) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 40.12 |
Crystal size (mm) | 0.07 × 0.07 × 0.06 |
|
Data collection |
Diffractometer | Bruker APEXII CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2005) |
Tmin, Tmax | 0.123, 0.142 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 2566, 227, 206 |
Rint | 0.030 |
(sin θ/λ)max (Å−1) | 0.991 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.014, 0.028, 1.12 |
No. of reflections | 227 |
No. of parameters | 9 |
Δρmax, Δρmin (e Å−3) | 0.79, −1.27 |
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Selenide materials with the spinel-type structure, AB2Se4, where A and B are tetrahedrally and octahedrally coordinated sites, respectively, have been the subject of numerous studies because of their magnetic and semiconducting properties (see, for example, Juszczyk & Gogolowicz, 1991; Kim et al., 2006; Skrzypek et al., 2006; Noh et al., 2007). Of particular interest is the distribution of various cations between the A and B sites, as such structural variations could significantly alter many physical properties of these materials (see, for example, Hazen & Yang, 1999; Okonska-Kozlowska et al., 2001). Tyrrellite, a cobalt-nickel-copper selenide, was first described by Robinson & Brooker (1952) to have a face-centered cubic lattice (Fm3m) with a = 10.005–10.042 Å and a chemical formula Co3.0Ni2.0Cu3.5Se9.5. However, Machatschki & Stradner (1952) pointed out that the X-ray powder pattern of tyrrellite resembled that of spinel minerals and the calculated intensities, assuming a spinel-type structure, agree well with the probable formula of (Co,Cu,Ni)3Se4. Harris (1970) examined the original tyrrellite material separated by Robinson & Brooker (1952) using a single-crystal X-ray diffractometer and found that all the fragments gave split reflections and were unsuitable for structure determination. No further structural investigation has been reported since then. This study presents the first structure refinement of tyrrellite based on single-crystal X-ray diffraction data and provides a basis for a redefinition of its ideal chemical formula.
Tyrrellite is isostructural with spinel, with Cu and (Co+Ni), respectively, occupying the tetrahedral A and octahedral B sites in the cubic close-packed array of Se atoms (Fig. 1). The preference of Cu for the tetrahedral site has been observed for other spinel-type selenides and sulfides, such as CuCr2Se4 (Okońska-Kozlowska et al., 1993), Cu1 - xCoxCr2Se4 (Okonska-Kozlowska et al., 2001), Cu1 - xNixCr2Se4 and CuCr2 - xNixSe4 (Jendrzejewska, 2000), CuCo2S4 (Williamson & Grimes, 1974), and Cu(Ni0.25Sn0.75)2S4 (Garg et al., 2001). The Cu—Se distance of 2.3688 (2) Å in tyrrellite is comparable with the range of 2.3664–2.3740 Å in spinel-type CuCr2Se4 (Okońska-Kozlowska et al., 1993; Payer et al., 1993; Rodic et al., 1998), whereas the average (Co+Ni)—Se distance of 2.3840 (1) Å appears to be shorter than most Co—Se or Ni—Se distances (~ 2.40—2.50 Å) for six-coordinated Co or Ni in other selenides (see. for example, Furuseth et al., 1969; Kamat Dalal et al., 1971; Foecher & Jeitschko, 2001; Garcia-Garcia et al., 2004).
Unlike oxide spinels, the valence of ions in selenide spinels has been a matter of discussion. For example, three models of electronic structures have been proposed for CuCr2Se4: Cu2+Cr3+2Se2-4 (Goodenough, 1967), Cu+[Cr3+Cr4+]Se2-4 (Lotgering, 1964), and Cu+Cr3+2[Se2-3Se-] (Lotgering & Van Stapele, 1967). Although there is still some disagreement regarding the valence of Cr and Se, experimental results from X-ray photoelectron spectroscopy and neutron diffraction have demonstrated the presence of Cu+, rather than Cu2+, in CuCr2Se4 (Hollander et al., 1974; Yamashita et al., 1979; Payer et al., 1990; Rodic et al., 1998). Since the Cu—Se bond length in tyrrellite agrees very well with that in CuCr2Se4, presumably Cu in tyrrellite is also monovalent. Noteworthy, nevertheless, is the appreciably short (Co+Ni)—Se bond distance in tyrrellite compared with the Cr—Se distances (2.508–2.512 Å) in CuCr2Se4 (Okońska-Kozlowska et al., 1993; Payer et al., 1993; Rodic et al., 1998). If we assume that the chemical bond between Se and the octahedrally coordinated cation is predominately ionic (Juszczyk & Gogolowicz, 1991; Rodic et al., 1998), the calculation of the bond-valence sum using the parameters given by Brese & O'Keeffe (1991) yields a value of 3.77 v.u. for (Co+Ni), suggesting that some Co or/and Ni in tyrrellite might exist in a formal charge greater than 3+.