The Chevrel phase HgMo₆S₈

Abstract

The crystal structure of HgMo₆S₈, mercury(II) hexa­molybdenum octa­sulfide, is based on (Mo₆S₈)S₆ cluster units ( symmetry) inter­connected through inter­unit Mo—S bonds. The Hg²⁺ cations occupy large voids between the different cluster units and are covalently bonded to two S atoms. The Hg atoms and one S atom lie on sites with crystallographic and 3 symmetry, respectively. Refinement of the occupancy factor of the Hg atom led to the composition Hg_0.973 (3)Mo₆S₈.

Related literature

For isotypic structures, see: Chevrel & Sergent (1982 ▶). For a previous report on the title compound as a polycrystalline material, see: Tarascon et al. (1983 ▶). For crystallographic background, see: Becker & Coppens (1974 ▶); Johnson & Levy (1974 ▶).

Experimental

Crystal data

• Hg_0.973Mo₆S₈

• M _r = 1027.3

• Trigonal,

• a = 9.4319 (3) Å

• c = 10.7028 (3) Å

• V = 824.57 (4) ų

• Z = 3

• Mo Kα radiation

• μ = 21.62 mm⁻¹

• T = 293 K

• 0.08 × 0.07 × 0.06 mm

Data collection

• Nonius KappaCCD diffractometer

• Absorption correction: analytical (de Meulenaer & Tompa, 1965 ▶) T _min = 0.298, T _max = 0.384

• 5784 measured reflections

• 1121 independent reflections

• 1069 reflections with I > 2σ(I)

• R _int = 0.044

Refinement

• R[F ² > 2σ(F ²)] = 0.025

• wR(F ²) = 0.026

• S = 1.74

• 1121 reflections

• 31 parameters

• Δρ_max = 2.64 e Å⁻³

• Δρ_min = −1.57 e Å⁻³

Data collection: COLLECT (Nonius, 1998 ▶); cell refinement: COLLECT; data reduction: EVALCCD (Duisenberg et al., 2003 ▶); program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: JANA2000 (Petříček & Dušek, 2000 ▶); molecular graphics: DIAMOND (Bergerhoff, 1996 ▶); software used to prepare material for publication: JANA2000.

Supplementary Material

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

Table 1. Selected bond lengths (Å).

Hg1—S1	2.3914 (8)
Mo1—Mo1i	2.7184 (3)
Mo1—Mo1ii	2.7515 (3)
Mo1—S1	2.4108 (7)
Mo1—S2	2.4236 (6)
Mo1—S2iii	2.4896 (8)
Mo1—S2ii	2.4933 (6)
Mo1—S2iv	2.4340 (8)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) .

supplementary crystallographic information

Comment

The superconducting compound HgMo₆S₈ was first synthesized as a powder sample by Tarascon et al. (1983), but no details were given on its crystal structure. In the present study, we present the crystal structure refinement of HgMo₆S₈ that has been determined from single-crystal X-ray diffraction data. The title compound is isostructural with the hexagonal Chevrel phases MMo₆X₈ where M is a large cation (M = alkali metal, alkaline earth, lanthanide, actinide etc.; X = S, Se, Te) [see, for instance, Chevrel & Sergent (1982)]. As a consequence its crystal structure consists of octahedral Mo₆ clusters surrounded by fourteen sulfur atoms with eight of them forming a distorted cube (i-type ligands) and the remaining six capping the faces of the S₈ cube (a-type ligands). In the structure of HgMo₆S₈, a part of the chalcogen atoms of the Mo₆Sⁱ₈S^a₆ unit are shared according to the formula Mo₆Sⁱ₂S^i-a_6/2S^a-i_6/2 to form the three-dimensional Mo—S network. The Mo₆S₈ cluster unit is centered at Wyckoff position 6b (3 symmetry). The Mo—Mo distances within the Mo₆ clusters are 2.7184 (3) Å for the intra-triangle distances (distances within the Mo₃ triangles formed by the Mo atoms related through the threefold axis) and 2.7515 (3) Å for the inter-triangle distances. Each Mo atom is surrounded by five S atoms (4 S1 and 1 S2) forming a distorted square-based pyramid. The apex of the pyramid is shared with an adjacent unit and thus ensures the three-dimensional cohesion. Consequently, each Mo₆S₈ unit is interconnected to 6 Mo₆S₈ units to form the Mo—S framework. It results from this arrangement that the shortest intercluster Mo1—Mo1 distances between the Mo₆ clusters is 3.2934 (3) Å, indicating only weak metal-metal interaction. The Hg²⁺ cations reside in the large eight-coordinate voids formed by the chalcogen atoms from eight different Mo₆S₈ units. They are covalently bonded to two S2 atoms at a distance of 2.3914 (8) Å.

HgMo₆S₈ was found to be superconducting at 8 K from DC-susceptibility measurements on a batch of single crystals.

Experimental

HgMo₆S₈ was obtained in three steps involving, first, the syntheses of single-crystal of InMo₆S₈ by solid state reaction, then the preparation of the binary compound Mo₆S₈ by 'chimie douce' methods and, finally, the synthesis of the title compound by inserting mercury into the Mo₆S₈ host structure at low temperatures. Single crystals of InMo₆S₈ were obtained from a stoichiometric mixture of In₂S₃, MoS₂ and Mo. All handlings of materials were done in an argon-filled glove box. The initial mixture (ca 5 g) was cold pressed and loaded into a molybdenum crucible, which was sealed under a low argon pressure using an arc-welding system. The charge was heated at the rate of 300 K/h up to 1773 K, the temperature which was held for six hours, then cooled at 100 K/h down to 1273 K and finally furnace cooled. Mo₆S₈ was obtained by oxidation of single-crystals of InMo₆S₈ by iodine in a glass tube sealed under vacuum. The end of the tube containing the crystals of the In compound and an excess of iodine was placed in a furnace with about 3 cm of the other end sticking out of the furnace, at about room temperature. The furnace was then heated at 523 K for 96 h. At the end of the reaction, crystals of InI₃ and I₂ were obtained at the cooler end of the tube. Finally, HgMo₆S₈ was prepared by diffusion of mercury into crystals of Mo₆S₈ in a silica glass tube sealed under vacuum at 673 K during 96 h.

Refinement

The structure was refined using an anisotropic approximation and converged at an reliability factor R(F) = 0.034. Analyses of the difference Fourier maps revealed positive and negative residual peaks around the Hg atom. Fourth-order tensors in the Gram-Charlier expansion (Johnson & Levy, 1974) of the mercury displacement factor were used to describe the electron density around this site. The resulting R value dropped to 0.025 for only five additional parameters. Refinement of the occupancy factor of the Hg atom led to the final composition Hg_0.973 (3)Mo₆S₈.

Figures

Fig. 1.

: View of HgMo6S8 along [110].

Fig. 2.

: Plot showing the atom-numbering scheme and the interunit linkage of the (Mo6S8)S6 cluster units. Displacement ellipsoids are drawn at the 97% probability level.

Crystal data

Hg0.973Mo6S8	Dx = 6.204 (1) Mg m−3
Mr = 1027.3	Mo Kα radiation, λ = 0.71069 Å
Trigonal, R3	Cell parameters from 7043 reflections
Hall symbol: -R 3	θ = 2.0–42.1°
a = 9.4319 (3) Å	µ = 21.62 mm−1
c = 10.7028 (3) Å	T = 293 K
V = 824.57 (4) Å3	Truncated cube, black
Z = 3	0.08 × 0.07 × 0.06 mm
F(000) = 1374

Data collection

Nonius KappaCCD diffractometer	1121 independent reflections
Radiation source: fine-focus sealed tube	1069 reflections with I > 2σ(I)
horizontally mounted graphite crystal	Rint = 0.044
Detector resolution: 9 pixels mm-1	θmax = 39.8°, θmin = 3.1°
ω– and φ–scans	h = −16→16
Absorption correction: analytical (de Meulenaer & Tompa, 1965)	k = −16→16
Tmin = 0.298, Tmax = 0.384	l = −13→19
5784 measured reflections

Refinement

Refinement on F	Weighting scheme based on measured s.u.'s w = 1/σ2(F)
R[F2 > 2σ(F2)] = 0.025	(Δ/σ)max = 0.001
wR(F2) = 0.026	Δρmax = 2.64 e Å−3
S = 1.74	Δρmin = −1.57 e Å−3
1121 reflections	Extinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974)
31 parameters	Extinction coefficient: 0.020681

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Hg1	0	0	0	0.0339 (4)	0.973 (3)
Mo1	−0.01555 (2)	−0.17363 (2)	−0.394419 (15)	0.00748 (7)
S1	0	0	−0.22344 (8)	0.0113 (2)
S2	−0.03460 (6)	−0.31591 (7)	−0.58775 (4)	0.00933 (17)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Hg1	0.0384 (4)	0.0384 (4)	0.0249 (6)	0.0192 (2)	0	0
Mo1	0.00780 (9)	0.00831 (9)	0.00617 (10)	0.00391 (6)	0.00003 (5)	−0.00036 (5)
S1	0.0126 (2)	0.0126 (2)	0.0088 (3)	0.00628 (12)	0	0
S2	0.0097 (2)	0.0096 (2)	0.0087 (2)	0.00476 (17)	0.00067 (15)	−0.00032 (15)

Geometric parameters (Å, °)

Hg1—S1	2.3914 (8)	Mo1—Mo1ix	2.7184 (3)
Hg1—S1i	2.3914 (8)	Mo1—Mo1x	2.7515 (3)
Hg1—S2ii	3.2056 (4)	Mo1—Mo1xi	2.7184 (4)
Hg1—S2iii	3.2056 (4)	Mo1—Mo1xii	2.7515 (2)
Hg1—S2iv	3.2056 (7)	Mo1—S1	2.4108 (7)
Hg1—S2v	3.2056 (7)	Mo1—S2	2.4236 (6)
Hg1—S2vi	3.2056 (8)	Mo1—S2xiii	2.4896 (8)
Hg1—S2vii	3.2056 (8)	Mo1—S2x	2.4933 (6)
Mo1—Mo1viii	3.8679 (3)	Mo1—S2xii	2.4340 (8)
Mo1—Mo1iii	3.2131 (2)
S1—Hg1—S1i	180	Mo1x—Mo1—Mo1iii	97.693 (7)
S1—Hg1—S2ii	105.278 (8)	Mo1x—Mo1—Mo1ix	90
S1—Hg1—S2iii	74.722 (8)	Mo1x—Mo1—Mo1xi	60.398 (8)
S1—Hg1—S2iv	105.278 (9)	Mo1x—Mo1—Mo1xii	59.205 (7)
S1—Hg1—S2v	74.722 (9)	Mo1x—Mo1—S1	115.964 (15)
S1—Hg1—S2vi	105.278 (9)	Mo1x—Mo1—S2	55.677 (18)
S1—Hg1—S2vii	74.722 (9)	Mo1x—Mo1—S2xiii	138.626 (14)
S1i—Hg1—S1	180	Mo1x—Mo1—S2x	54.776 (13)
S1i—Hg1—S2ii	74.722 (8)	Mo1x—Mo1—S2xii	114.515 (14)
S1i—Hg1—S2iii	105.278 (8)	Mo1xi—Mo1—Mo1iii	96.739 (8)
S1i—Hg1—S2iv	74.722 (9)	Mo1xi—Mo1—Mo1ix	60.000 (8)
S1i—Hg1—S2v	105.278 (9)	Mo1xi—Mo1—Mo1x	60.398 (8)
S1i—Hg1—S2vi	74.722 (9)	Mo1xi—Mo1—Mo1xii	90
S1i—Hg1—S2vii	105.278 (9)	Mo1xi—Mo1—S1	55.682 (12)
S2ii—Hg1—S2iii	180	Mo1xi—Mo1—S2	116.065 (18)
S2ii—Hg1—S2iv	113.319 (18)	Mo1xi—Mo1—S2xiii	135.971 (18)
S2ii—Hg1—S2v	66.681 (18)	Mo1xi—Mo1—S2x	55.48 (2)
S2ii—Hg1—S2vi	113.319 (17)	Mo1xi—Mo1—S2xii	117.362 (19)
S2ii—Hg1—S2vii	66.681 (17)	Mo1xii—Mo1—Mo1iii	148.317 (7)
S2iii—Hg1—S2ii	180	Mo1xii—Mo1—Mo1ix	60.398 (6)
S2iii—Hg1—S2iv	66.681 (18)	Mo1xii—Mo1—Mo1x	59.205 (7)
S2iii—Hg1—S2v	113.319 (18)	Mo1xii—Mo1—Mo1xi	90
S2iii—Hg1—S2vi	66.681 (17)	Mo1xii—Mo1—S1	115.964 (13)
S2iii—Hg1—S2vii	113.319 (17)	Mo1xii—Mo1—S2	57.184 (12)
S2iv—Hg1—S2ii	113.319 (18)	Mo1xii—Mo1—S2xiii	133.837 (19)
S2iv—Hg1—S2iii	66.681 (18)	Mo1xii—Mo1—S2x	113.894 (15)
S2iv—Hg1—S2v	180	Mo1xii—Mo1—S2xii	55.318 (14)
S2iv—Hg1—S2vi	113.319 (19)	S1—Mo1—S2	170.65 (2)
S2iv—Hg1—S2vii	66.681 (19)	S1—Mo1—S2xiii	93.53 (2)
S2v—Hg1—S2ii	66.681 (18)	S1—Mo1—S2x	90.323 (17)
S2v—Hg1—S2iii	113.319 (18)	S1—Mo1—S2xii	91.758 (14)
S2v—Hg1—S2iv	180	S2—Mo1—S2xiii	95.79 (2)
S2v—Hg1—S2vi	66.681 (19)	S2—Mo1—S2x	87.39 (2)
S2v—Hg1—S2vii	113.319 (19)	S2—Mo1—S2xii	88.750 (19)
S2vi—Hg1—S2ii	113.319 (17)	S2xiii—Mo1—S2	95.79 (2)
S2vi—Hg1—S2iii	66.681 (17)	S2xiii—Mo1—S2x	99.70 (2)
S2vi—Hg1—S2iv	113.319 (19)	S2xiii—Mo1—S2xii	91.39 (2)
S2vi—Hg1—S2v	66.681 (19)	S2x—Mo1—S2	87.39 (2)
S2vi—Hg1—S2vii	180	S2x—Mo1—S2xiii	99.70 (2)
S2vii—Hg1—S2ii	66.681 (17)	S2x—Mo1—S2xii	168.58 (2)
S2vii—Hg1—S2iii	113.319 (17)	S2xii—Mo1—S2	88.750 (19)
S2vii—Hg1—S2iv	66.681 (19)	S2xii—Mo1—S2xiii	91.39 (2)
S2vii—Hg1—S2v	113.319 (19)	S2xii—Mo1—S2x	168.58 (2)
S2vii—Hg1—S2vi	180	Hg1—S1—Mo1	139.382 (14)
Mo1viii—Mo1—Mo1iii	133.459 (8)	Hg1—S1—Mo1ix	139.382 (13)
Mo1viii—Mo1—S1	85.136 (14)	Hg1—S1—Mo1xi	139.382 (14)
Mo1viii—Mo1—S2	85.600 (16)	Mo1—S1—Mo1ix	68.64 (2)
Mo1viii—Mo1—S2xiii	176.394 (13)	Mo1—S1—Mo1xi	68.64 (2)
Mo1viii—Mo1—S2x	83.677 (18)	Mo1ix—S1—Mo1	68.64 (2)
Mo1viii—Mo1—S2xii	85.310 (16)	Mo1ix—S1—Mo1xi	68.64 (2)
Mo1iii—Mo1—Mo1viii	133.459 (8)	Mo1xi—S1—Mo1	68.64 (2)
Mo1iii—Mo1—Mo1ix	147.479 (10)	Mo1xi—S1—Mo1ix	68.64 (2)
Mo1iii—Mo1—Mo1x	97.693 (7)	Hg1xiv—S2—Mo1	125.450 (18)
Mo1iii—Mo1—Mo1xi	96.739 (8)	Hg1xiv—S2—Mo1x	98.407 (18)
Mo1iii—Mo1—Mo1xii	148.317 (7)	Hg1xiv—S2—Mo1xv	97.225 (18)
Mo1iii—Mo1—S1	92.988 (11)	Hg1xiv—S2—Mo1xii	156.59 (2)
Mo1iii—Mo1—S2	92.457 (12)	Mo1—S2—Mo1x	69.005 (19)
Mo1iii—Mo1—S2xiii	49.898 (13)	Mo1—S2—Mo1xv	132.74 (2)
Mo1iii—Mo1—S2x	49.797 (18)	Mo1—S2—Mo1xii	68.041 (15)
Mo1iii—Mo1—S2xii	141.203 (18)	Mo1x—S2—Mo1	69.005 (19)
Mo1ix—Mo1—Mo1iii	147.479 (10)	Mo1x—S2—Mo1xv	129.09 (2)
Mo1ix—Mo1—Mo1x	90	Mo1x—S2—Mo1xii	66.955 (19)
Mo1ix—Mo1—Mo1xi	60.000 (8)	Mo1xv—S2—Mo1	132.74 (2)
Mo1ix—Mo1—Mo1xii	60.398 (6)	Mo1xv—S2—Mo1x	129.09 (2)
Mo1ix—Mo1—S1	55.682 (11)	Mo1xv—S2—Mo1xii	80.305 (15)
Mo1ix—Mo1—S2	117.489 (13)	Mo1xii—S2—Mo1	68.041 (15)
Mo1ix—Mo1—S2xiii	131.337 (14)	Mo1xii—S2—Mo1x	66.955 (19)
Mo1ix—Mo1—S2x	115.28 (2)	Mo1xii—S2—Mo1xv	80.305 (15)
Mo1ix—Mo1—S2xii	57.566 (18)

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