Silver(I) trimercury(II) antimonate(V), AgHg₃SbO₆

Single crystals of AgHg₃SbO₆ were obtained from solid-state synthesis at elevated oxygen pressures. The structure exhibits a variation of the K₄CdCl₆ structure type. Chains of face-sharing SbO₆ and elongated AgO₆ octa­hedra run along [001], and these chains are connected by linearly coordinated Hg atoms. The occurrence of AgO₆ octa­hedra instead of trigonal prisms, and of O-Hg-O dumbbells instead of irregular eight-coordinated oxygen polyhedra, distinguishes the new compound from the known analogues of this type of structure. The heavy atoms are located on special positions; Ag is at a site with 32 symmetry, Sb at a site with symmetry and Hg at a site with twofold symmetry.

S1. Comment

AgHg₃SbO₆ crystallizes rhombohedrally in space group R3c, with one independent atom of each element at the Wyckoff positions 6b, 18e, 6a and 36f of the hexagonal setting, respectively. Its crystal structure (Fig. 1) consists of isolated, almost ideal, SbO₆ octahedra, separated by Ag⁺ ions in the c direction and by Hg²⁺ ions in the ab plane. The Ag⁺ ions are found to be in an octahedral environment of oxygen and the Hg²⁺ ions in a linear coordination. All M—O distances are in very good agreement with other compounds containing these elements with similar coordination numbers. The SbO₆ octahedra are arranged in the sense of a cubic close packing. The SbO₆ and trigonally elongated AgO₆ octahedra are stacked alternately to form chains along [001] by sharing faces (Fig. 2a). These chains are surrounded by six spiral rods of Hg, and the Hg rods are in turn surrounded by three polyhedral chains.

The structure closely resembles the K₄CdCl₆ structure type (Bergerhoff & Schmitz-Dumont, 1956), where K⁺ ions at two crystallographically different sites separate isolated CdCl₆ octahedra. In detail, one K⁺ in a trigonal-prismatic oxygen coordination, together with the CdCl₆ octahedra, form chains along [001]; the octahedra in these columns are present in two alternating orientations. The remaining 3/4 of K⁺ ions are situated between these columns in irregular coordination polyhedra of eight Cl⁻ ions. Derivatives of this structure type are adopted by many oxides to form compounds of the general type A₃A'BO₆ [e.g. Sr₄PtO₆ (Randall & Katz, 1959), Sr₃LiIrO₆ (Davis et al., 2003), Sr₃NaSbO₆ (Battle et al., 2001), Sr₃CuIrO₆ (Neubacher & Müller-Buschbaum, 1992)].

Although AgHg₃SbO₆ and K₄CdCl₆ are isopointal, the structures exhibit striking differences. Firstly, the Hg²⁺ ion does not behave as a spherical alkaline or alkaline earth cation, but prefers a characteristic dumbbell-like coordination by only two O atoms in the title compound. The next four O neighbours at about 2.8–2.9 Å cannot be attributed to the first coordination sphere of Hg²⁺, and two more O atoms are found at an even more remote distance of 3.4 Å. This strongly directing feature of the packing causes significant deviations from the K₄CdCl₆ type. In particular, the SbO₆ octahedra, which share O atoms with the O—-Hg—O dumbbells, are in an eclipsed orientation along the c axis, with a dihedral angle of 6.5°. In all related compounds of this structure type with alkali or alkaline earth elements instead of mercury, this angle is found to be in the range 40–50° [e.g. 45.3° in Sr₃NaSbO₆ (Battle et al., 2001) and 42.3° in K₄CdCl₆ (Beck & Milius, 1986)]. As another consequence, the Ag⁺ ion in AgHg₃SbO₆ is coordinated by a heavily elongated but slightly twisted octahedron of O atoms, as illustrated in Fig. 2(a), while the A'O₆ polyhedra in all other compounds adopting the K₄CdCl₆ structure type must always be described as twisted trigonal prisms (Fig. 2b).

S2. Experimental

Red crystals of AgHg₃SbO₆ were obtained as a by-product from the reaction of Ag₂O, HgO and Sb₂O₃ [Quantities or mole ratio?] at elevated oxygen pressures of 100 MPa at 773 K (Linke & Jansen, 1997). The reactants were finely ground and placed in a gold crucible, which was then sealed from one side and mechanically closed from the other. Single crystals were isolated and glued onto glass capillaries.

S3. Refinement

In consideration of the tendencies of Ag and Hg to adopt similar crystal chemical environments, partial Ag occupancies of the Hg-atom positions and vice versa were used in the initial stages of refinement, but the values refined to zero immediately in both cases.

Computing details

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2000); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. A perspective view of the crystal structure of AgHg3SbO6, showing the Ag and Hg atoms and SbO6 octahedra. The octahedra are tilted outwards at an angle of 6.5°.

Fig. 2. (a) A column of SbO6 and strongly elongated AgO6 octahedra in AgHg3SbO6. The coordination of one Hg atom is indicated; dashed lines denote distances longer than 2.78 Å. Displacement ellipsoids are drawn at the 50% probability level. (b) A related column of SbO6 octahedra and twisted trigonal NaO6 prisms in Sr3NaSbO6 (K4CdCl6 type; Battle et al., 2001). One Sr^2+ ion with eight coordinating O atoms is also shown. The tilt of the octahedra is about 45.3°. All unlabelled atoms are O.

Silver(I) trimercury(II) antimonate(V)

Crystal data

AgHg3SbO6	Dx = 9.136 Mg m^−3
Mr = 927.39	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3c	Cell parameters from 3254 reflections
Hall symbol: -R 3 2"c	θ = 2.6–27.2°
a = 9.627 (3) Å	µ = 74.86 mm^−1
c = 12.601 (4) Å	T = 293 K
V = 1011.3 (5) Å^3	Block, red
Z = 6	0.2 × 0.2 × 0.2 mm
F(000) = 2316

Data collection

Stoe IPDS-2 diffractometer	254 independent reflections
Radiation source: fine-focus sealed tube	177 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.084
Detector resolution: 6.67 pixels mm^-1	θmax = 27.1°, θmin = 4.1°
ω scans	h = −12→6
Absorption correction: integration (X-SHAPE; Stoe & Cie, 2002)	k = 0→12
Tmin = 0.003, Tmax = 0.018	l = −16→15
901 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.036	w = 1/[σ^2(Fo^2) + (0.0198P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.060	(Δ/σ)max < 0.001
S = 0.85	Δρmax = 2.04 e Å^−3
254 reflections	Δρmin = −4.04 e Å^−3
20 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00039 (4)

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.

Refinement. Refinement on F² for ALL reflections except for 0 with very negative F² or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating _R_factor_obs 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 (Ų)

	x	y	z	Uiso*/Ueq
Ag	0.0000	0.0000	0.2500	0.0524 (8)
Hg	0.33954 (7)	0.0000	0.2500	0.0282 (3)
Sb	0.0000	0.0000	0.0000	0.0214 (5)
O	0.1936 (10)	0.0873 (13)	0.0930 (7)	0.028 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag	0.0648 (12)	0.0648 (12)	0.028 (2)	0.0324 (6)	0.000	0.000
Hg	0.0277 (4)	0.0236 (4)	0.0320 (5)	0.0118 (2)	−0.00090 (14)	−0.0018 (3)
Sb	0.0211 (6)	0.0211 (6)	0.0218 (12)	0.0106 (3)	0.000	0.000
O	0.025 (4)	0.027 (4)	0.027 (4)	0.009 (4)	−0.003 (3)	−0.002 (4)

Geometric parameters (Å, º)

Sb—O	1.997 (9)	Hg—Sb^xvi	3.3484 (9)
Sb—O^i	1.997 (9)	Hg—Sb^xvii	3.3484 (9)
Sb—O^ii	1.997 (9)	Hg—Hg^xviii	3.8104 (8)
Sb—O^iii	1.997 (9)	Hg—Hg^xiv	3.8104 (8)
Sb—O^iv	1.997 (9)	Hg—Hg^vii	3.8104 (8)
Sb—O^v	1.997 (9)	Ag—O	2.556 (9)
Sb—Ag^i	3.1503 (10)	Ag—O^iv	2.556 (9)
Sb—Hg^vi	3.3483 (9)	Ag—O^xi	2.556 (9)
Sb—Hg^vii	3.3483 (9)	Ag—O^xix	2.556 (9)
Sb—Hg^viii	3.3484 (9)	Ag—O^xx	2.556 (9)
Sb—Hg^ix	3.3484 (9)	Ag—O^v	2.556 (9)
Hg—O^ix	2.057 (11)	Ag—Sb	3.1503 (10)
Hg—O^x	2.057 (11)	Ag—Sb^xxi	3.1503 (10)
Hg—O	2.789 (10)	Ag—Hg^iv	3.2687 (11)
Hg—O^xi	2.789 (10)	Ag—Hg^v	3.2687 (11)
Hg—O^xii	2.899 (9)	Ag—Hg	3.2687 (11)
Hg—O^xiii	2.899 (9)	O—Hg^ix	2.057 (10)
Hg—O^xiv	3.463 (11)	O—Hg^xxii	2.899 (9)
Hg—O^xv	3.463 (11)
O^i—Sb—O	180.0	O^xiii—Hg—Sb^xvii	36.4 (2)
O^i—Sb—O^ii	89.1 (4)	Ag—Hg—Sb^xvii	117.473 (11)
O—Sb—O^ii	90.9 (4)	Sb^xvi—Hg—Sb^xvii	125.06 (2)
O^i—Sb—O^iii	89.1 (4)	O^ix—Hg—Hg^xviii	48.7 (2)
O—Sb—O^iii	90.9 (4)	O^x—Hg—Hg^xviii	134.6 (2)
O^ii—Sb—O^iii	89.1 (4)	O—Hg—Hg^xviii	85.6 (2)
O^i—Sb—O^iv	90.9 (4)	O^xi—Hg—Hg^xviii	61.0 (2)
O—Sb—O^iv	89.1 (4)	O^xii—Hg—Hg^xviii	60.3 (2)
O^ii—Sb—O^iv	90.9 (4)	O^xiii—Hg—Hg^xviii	157.7 (2)
O^iii—Sb—O^iv	180.0	Ag—Hg—Hg^xviii	64.602 (9)
O^i—Sb—O^v	90.9 (4)	Sb^xvi—Hg—Hg^xviii	55.318 (4)
O—Sb—O^v	89.1 (4)	Sb^xvii—Hg—Hg^xviii	164.739 (5)
O^ii—Sb—O^v	180.0	O^ix—Hg—Hg^xiv	86.6 (3)
O^iii—Sb—O^v	90.9 (4)	O^x—Hg—Hg^xiv	88.7 (3)
O^iv—Sb—O^v	89.1 (4)	O—Hg—Hg^xiv	99.1 (2)
O^i—Sb—Ag^i	54.1 (2)	O^xi—Hg—Hg^xiv	159.0 (2)
O—Sb—Ag^i	125.9 (2)	O^xii—Hg—Hg^xiv	90.5 (2)
O^ii—Sb—Ag^i	54.1 (2)	O^xiii—Hg—Hg^xiv	32.2 (2)
O^iii—Sb—Ag^i	54.1 (2)	Ag—Hg—Hg^xiv	146.542 (12)
O^iv—Sb—Ag^i	125.9 (2)	Sb^xvi—Hg—Hg^xiv	78.42 (2)
O^v—Sb—Ag^i	125.9 (2)	Sb^xvii—Hg—Hg^xiv	55.319 (4)
O^i—Sb—Ag	125.9 (2)	Hg^xviii—Hg—Hg^xiv	132.17 (2)
O—Sb—Ag	54.1 (2)	O^ix—Hg—Hg^vii	134.6 (2)
O^ii—Sb—Ag	125.9 (2)	O^x—Hg—Hg^vii	48.7 (2)
O^iii—Sb—Ag	125.9 (2)	O—Hg—Hg^vii	61.0 (2)
O^iv—Sb—Ag	54.1 (2)	O^xi—Hg—Hg^vii	85.6 (2)
O^v—Sb—Ag	54.1 (2)	O^xii—Hg—Hg^vii	157.7 (2)
Ag^i—Sb—Ag	180.0	O^xiii—Hg—Hg^vii	60.3 (2)
O^i—Sb—Hg^vi	76.1 (3)	Ag—Hg—Hg^vii	64.601 (8)
O—Sb—Hg^vi	103.9 (3)	Sb^xvi—Hg—Hg^vii	164.739 (5)
O^ii—Sb—Hg^vi	120.5 (3)	Sb^xvii—Hg—Hg^vii	55.320 (4)
O^iii—Sb—Hg^vi	34.9 (3)	Hg^xviii—Hg—Hg^vii	129.20 (2)
O^iv—Sb—Hg^vi	145.1 (3)	Hg^xiv—Hg—Hg^vii	92.54 (2)
O^v—Sb—Hg^vi	59.5 (3)	O^iv—Ag—O^xix	175.9 (5)
Ag^i—Sb—Hg^vi	71.722 (7)	O^iv—Ag—O^xi	116.1 (4)
Ag—Sb—Hg^vi	108.278 (7)	O^xix—Ag—O^xi	66.5 (3)
O^i—Sb—Hg^vii	103.9 (3)	O^iv—Ag—O	66.5 (3)
O—Sb—Hg^vii	76.1 (3)	O^xix—Ag—O	116.1 (4)
O^ii—Sb—Hg^vii	59.5 (3)	O^xi—Ag—O	111.2 (4)
O^iii—Sb—Hg^vii	145.1 (3)	O^iv—Ag—O^xx	111.2 (4)
O^iv—Sb—Hg^vii	34.9 (3)	O^xix—Ag—O^xx	66.5 (3)
O^v—Sb—Hg^vii	120.5 (3)	O^xi—Ag—O^xx	66.5 (3)
Ag^i—Sb—Hg^vii	108.278 (7)	O—Ag—O^xx	175.9 (5)
Ag—Sb—Hg^vii	71.722 (7)	O^iv—Ag—O^v	66.5 (3)
Hg^vi—Sb—Hg^vii	180.0	O^xix—Ag—O^v	111.2 (4)
O^i—Sb—Hg^viii	34.9 (3)	O^xi—Ag—O^v	175.9 (5)
O—Sb—Hg^viii	145.1 (3)	O—Ag—O^v	66.5 (3)
O^ii—Sb—Hg^viii	76.1 (3)	O^xx—Ag—O^v	116.1 (4)
O^iii—Sb—Hg^viii	120.5 (3)	O^iv—Ag—Sb	39.3 (2)
O^iv—Sb—Hg^viii	59.5 (3)	O^xix—Ag—Sb	140.7 (2)
O^v—Sb—Hg^viii	103.9 (3)	O^xi—Ag—Sb	140.7 (2)
Ag^i—Sb—Hg^viii	71.722 (7)	O—Ag—Sb	39.3 (2)
Ag—Sb—Hg^viii	108.278 (7)	O^xx—Ag—Sb	140.7 (2)
Hg^vi—Sb—Hg^viii	110.639 (7)	O^v—Ag—Sb	39.3 (2)
Hg^vii—Sb—Hg^viii	69.361 (7)	O^iv—Ag—Sb^xxi	140.7 (2)
O^i—Sb—Hg^ix	145.1 (3)	O^xix—Ag—Sb^xxi	39.3 (2)
O—Sb—Hg^ix	34.9 (3)	O^xi—Ag—Sb^xxi	39.3 (2)
O^ii—Sb—Hg^ix	103.9 (3)	O—Ag—Sb^xxi	140.7 (2)
O^iii—Sb—Hg^ix	59.5 (3)	O^xx—Ag—Sb^xxi	39.3 (2)
O^iv—Sb—Hg^ix	120.5 (3)	O^v—Ag—Sb^xxi	140.7 (2)
O^v—Sb—Hg^ix	76.1 (3)	Sb—Ag—Sb^xxi	180.0
Ag^i—Sb—Hg^ix	108.278 (7)	O^iv—Ag—Hg^iv	55.6 (2)
Ag—Sb—Hg^ix	71.722 (7)	O^xix—Ag—Hg^iv	122.0 (2)
Hg^vi—Sb—Hg^ix	69.361 (7)	O^xi—Ag—Hg^iv	92.0 (2)
Hg^vii—Sb—Hg^ix	110.639 (7)	O—Ag—Hg^iv	122.0 (2)
Hg^viii—Sb—Hg^ix	180.0	O^xx—Ag—Hg^iv	55.6 (2)
O^ix—Hg—O^x	174.4 (5)	O^v—Ag—Hg^iv	92.0 (2)
O^ix—Hg—O	74.3 (3)	Sb—Ag—Hg^iv	90.0
O^x—Hg—O	109.5 (3)	Sb^xxi—Ag—Hg^iv	90.0
O^ix—Hg—O^xi	109.5 (3)	O^iv—Ag—Hg^v	122.0 (2)
O^x—Hg—O^xi	74.3 (3)	O^xix—Ag—Hg^v	55.6 (2)
O—Hg—O^xi	98.2 (4)	O^xi—Ag—Hg^v	122.0 (2)
O^ix—Hg—O^xii	67.7 (4)	O—Ag—Hg^v	92.0 (2)
O^x—Hg—O^xii	109.3 (3)	O^xx—Ag—Hg^v	92.0 (2)
O—Hg—O^xii	140.08 (12)	O^v—Ag—Hg^v	55.6 (2)
O^xi—Hg—O^xii	83.6 (3)	Sb—Ag—Hg^v	90.0
O^ix—Hg—O^xiii	109.3 (3)	Sb^xxi—Ag—Hg^v	90.0
O^x—Hg—O^xiii	67.7 (4)	Hg^iv—Ag—Hg^v	120.0
O—Hg—O^xiii	83.6 (3)	O^iv—Ag—Hg	92.0 (2)
O^xi—Hg—O^xiii	140.08 (12)	O^xix—Ag—Hg	92.0 (2)
O^xii—Hg—O^xiii	119.8 (4)	O^xi—Ag—Hg	55.6 (2)
O^ix—Hg—Ag	92.8 (3)	O—Ag—Hg	55.6 (2)
O^x—Hg—Ag	92.8 (3)	O^xx—Ag—Hg	122.0 (2)
O—Hg—Ag	49.1 (2)	O^v—Ag—Hg	122.0 (2)
O^xi—Hg—Ag	49.1 (2)	Sb—Ag—Hg	90.0
O^xii—Hg—Ag	120.1 (2)	Sb^xxi—Ag—Hg	90.0
O^xiii—Hg—Ag	120.1 (2)	Hg^iv—Ag—Hg	120.0
O^ix—Hg—Sb^xvi	33.7 (2)	Hg^v—Ag—Hg	120.0
O^x—Hg—Sb^xvi	141.8 (3)	Sb—O—Hg^ix	111.4 (5)
O—Hg—Sb^xvi	107.9 (2)	Sb—O—Ag	86.7 (3)
O^xi—Hg—Sb^xvi	107.2 (2)	Hg^ix—O—Ag	110.9 (4)
O^xii—Hg—Sb^xvi	36.4 (2)	Sb—O—Hg	142.6 (5)
O^xiii—Hg—Sb^xvi	110.0 (2)	Hg^ix—O—Hg	105.7 (3)
Ag—Hg—Sb^xvi	117.472 (11)	Ag—O—Hg	75.3 (2)
O^ix—Hg—Sb^xvii	141.8 (2)	Sb—O—Hg^xxii	84.2 (3)
O^x—Hg—Sb^xvii	33.7 (2)	Hg^ix—O—Hg^xxii	99.1 (3)
O—Hg—Sb^xvii	107.2 (2)	Ag—O—Hg^xxii	149.9 (4)
O^xi—Hg—Sb^xvii	107.9 (2)	Hg—O—Hg^xxii	95.2 (3)
O^xii—Hg—Sb^xvii	110.0 (2)

Symmetry codes: (i) −x, −y, −z; (ii) y, −x+y, −z; (iii) x−y, x, −z; (iv) −x+y, −x, z; (v) −y, x−y, z; (vi) −x+y+1/3, −x+2/3, z−1/3; (vii) x−y−1/3, x−2/3, −z+1/3; (viii) x−2/3, y−1/3, z−1/3; (ix) −x+2/3, −y+1/3, −z+1/3; (x) −x+y+1/3, y−1/3, z+1/6; (xi) x−y, −y, −z+1/2; (xii) −x+y+2/3, −x+1/3, z+1/3; (xiii) y+1/3, x−1/3, −z+1/6; (xiv) y+2/3, −x+y+1/3, −z+1/3; (xv) x+1/3, x−y−1/3, z+1/6; (xvi) x+2/3, y+1/3, z+1/3; (xvii) −y+1/3, −x−1/3, z+1/6; (xviii) y+1/3, −x+y+2/3, −z+2/3; (xix) y, x, −z+1/2; (xx) −x, −x+y, −z+1/2; (xxi) −y, −x, z+1/2; (xxii) −y+1/3, x−y−1/3, z−1/3.