Reinvestigation of Hg₂GeSe₄ based on single-crystal data

Dimercury(II) germanium(IV) tetraselenide, Hg₂GeSe₄, adopts a cation-deficient diamond-like structure. It crystallizes in space group I of the tetragonal system. The structure consists of tetrahedral [HgSe₄] and [GeSe₄] groups. These groups are interconnected by sharing common corners. The previous structure report on Hg₂GeSe₄ based on powder diffraction data [Parasyuk et al., (2003). J. Alloys Compd, 351, 135-144] is comparable with our results except for the absolute configuration determination. In the asymmetric unit, the site symmetries of the Hg and Ge atoms are .

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](Se-Ge) = 0.003 Å
• R factor = 0.056
• wR factor = 0.145
• Data-to-parameter ratio = 15.5

checkCIF/PLATON results

No syntax errors found



Alert level G
REFLT03_ALERT_4_G  WARNING: Large fraction of Friedel related reflns may
                     be needed to determine absolute structure
           From the CIF: _diffrn_reflns_theta_max           27.42
           From the CIF: _reflns_number_total                263
           Count of symmetry unique reflns          222
           Completeness (_total/calc)            118.47%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured        41
           Fraction of Friedel pairs measured     0.185
           Are heavy atom types Z>Si present          yes

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   0 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion

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Computing details

Data collection: MXC3 (MacScience, 1994); cell refinement: MXC3; data reduction: MXC3; program(s) used to solve structure: SHELXS86 (Sheldrick, 1985); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

(I)

Crystal data

Hg2GeSe4	Dx = 7.241 Mg m^−3
Mr = 789.63	Mo Kα radiation, λ = 0.7107 Å
Tetragonal, I4	Cell parameters from 22 reflections
Hall symbol: I -4	θ = 12.0–14.5°
a = 5.6741 (17) Å	µ = 66.39 mm^−1
c = 11.249 (5) Å	T = 150 K
V = 362.2 (2) Å^3	Needle, black
Z = 2	0.40 × 0.02 × 0.01 mm
F(000) = 656

Data collection

MacScience MXC3 diffractometer	Rint = 0.066
ω/2θ scans	θmax = 27.4°, θmin = 3.6°
Absorption correction: analytical (de Meulenaer & Tompa, 1965)	h = 0→7
Tmin = 0.220, Tmax = 0.520	k = 0→7
288 measured reflections	l = 0→14
263 independent reflections	2 standard reflections every 100 reflections
260 reflections with I > 2σ(I)	intensity decay: 0.5%

Refinement

Refinement on F^2	w = 1/[σ^2(Fo^2) + (0.12P)^2 + 19.6039P] where P = (Fo^2 + 2Fc^2)/3
Least-squares matrix: full	(Δ/σ)max < 0.001
R[F^2 > 2σ(F^2)] = 0.056	Δρmax = 3.24 e Å^−3
wR(F^2) = 0.145	Δρmin = −5.17 e Å^−3
S = 1.08	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
263 reflections	Extinction coefficient: 0.027 (4)
17 parameters	Absolute structure: Flack (1983), 38 Friedel pairs
0 restraints	Absolute structure parameter: −0.01 (6)

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Hg1	0	0.5	0.25	0.0109 (8)
Hg2	0	0	0.5	0.0126 (8)
Ge	0	0.5	0.75	0.0085 (16)
Se	0.8068 (6)	0.2374 (4)	0.8823 (2)	0.0072 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg1	0.0109 (9)	0.0109 (9)	0.0109 (11)	0	0	0
Hg2	0.0134 (9)	0.0134 (9)	0.0109 (11)	0	0	0
Ge	0.009 (2)	0.009 (2)	0.008 (3)	0	0	0
Se	0.0099 (14)	0.0062 (15)	0.0053 (12)	−0.0015 (12)	−0.0018 (11)	−0.0002 (11)

Geometric parameters (Å, º)

Hg1—Se^i	2.658 (3)	Ge—Se^viii	2.374 (2)
Hg1—Se^ii	2.658 (3)	Ge—Se^ix	2.374 (2)
Hg1—Se^iii	2.658 (3)	Ge—Se^x	2.374 (2)
Hg1—Se^iv	2.658 (3)	Ge—Se^v	2.374 (2)
Hg2—Se^v	2.646 (3)	Se—Ge^xi	2.374 (2)
Hg2—Se^vi	2.646 (3)	Se—Hg2^xii	2.646 (3)
Hg2—Se^iii	2.646 (3)	Se—Hg1^xiii	2.658 (3)
Hg2—Se^vii	2.646 (3)
Se^i—Hg1—Se^ii	108.29 (5)	Se^iii—Hg2—Se^vii	119.97 (12)
Se^i—Hg1—Se^iii	111.86 (11)	Se^viii—Ge—Se^ix	102.34 (13)
Se^ii—Hg1—Se^iii	108.29 (5)	Se^viii—Ge—Se^x	113.15 (7)
Se^i—Hg1—Se^iv	108.29 (5)	Se^ix—Ge—Se^x	113.15 (7)
Se^ii—Hg1—Se^iv	111.86 (11)	Se^viii—Ge—Se^v	113.15 (7)
Se^iii—Hg1—Se^iv	108.29 (5)	Se^ix—Ge—Se^v	113.15 (7)
Se^v—Hg2—Se^vi	119.97 (12)	Se^x—Ge—Se^v	102.34 (13)
Se^v—Hg2—Se^iii	104.49 (5)	Ge^xi—Se—Hg2^xii	105.31 (9)
Se^vi—Hg2—Se^iii	104.49 (5)	Ge^xi—Se—Hg1^xiii	105.62 (9)
Se^v—Hg2—Se^vii	104.49 (5)	Hg2^xii—Se—Hg1^xiii	97.74 (12)
Se^vi—Hg2—Se^vii	104.49 (5)

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