Barium dierbium(III) tetra­sulfide

Mesbah, A.; Stojko, W.; Ibers, J.A.

doi:10.1107/S1600536813003541

inorganic compounds

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Volume 69| Part 3| March 2013| Page i17

doi:10.1107/S1600536813003541

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Barium dierbium(III) tetrasulfide

Adel Mesbah,^a Wojciech Stojko ^a and James. A Ibers ^a ^*

^aDepartment of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA
^*Correspondence e-mail: ibers@chem.northwestern.edu

(Received 31 January 2013; accepted 4 February 2013; online 13 February 2013)

Barium dierbium(III) tetrasulfide, BaEr₂S₄, crystallizes with four formula units in the orthorhombic space group Pnma in the CaFe₂O₄ structure type. The asymmetric unit contains two Er, one Ba, and four S atoms, each with .m. site symmetry. The structure consists of channels formed by corner- and edge-sharing ErS₆ octahedra in which Ba atoms reside. The resultant coordination of Ba is that of a bicapped trigonal prism.

Related literature

The unit-cell parameters of BaEr₂S₄, which crystallizes in the CaFe₂O₄ structure type (Decker & Kasper, 1957 ), were previously determined from X-ray powder diffraction data (Patrie et al., 1964 ). For related structures, see: Bugaris & Ibers (2009 ); Narducci et al. (2000 ); Carpenter & Hwu (1992 ); Flahaut et al. (1965 ); Schurz & Schleid (2011 ). For synthetic details, see: Bugaris & Ibers (2008 ); Haneveld & Jellinek (1969 ). For standardization of structural data, see: Gelato & Parthé (1987 ).

Experimental

Crystal data

BaEr₂S₄
M_r = 600.10
Orthorhombic, P n m a
a = 12.1455 (3) Å
b = 3.9884 (1) Å
c = 14.3837 (4) Å
V = 696.76 (3) Å³
Z = 4
Mo Kα radiation
μ = 30.53 mm⁻¹
T = 100 K
0.16 × 0.03 × 0.02 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: numerical face indexed (Sheldrick, 2008a ) T_min = 0.084, T_max = 0.528
9866 measured reflections
1207 independent reflections
1196 reflections with I > 2σ(I)
R_int = 0.030

Refinement

R[F² > 2σ(F²)] = 0.017
wR(F²) = 0.050
S = 1.87
1207 reflections
44 parameters
Δρ_max = 2.46 e Å⁻³
Δρ_min = −2.58 e Å⁻³

Data collection: APEX2 (Bruker, 2009 ); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008b ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008b); molecular graphics: CrystalMaker (Palmer, 2012 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536813003541/br2222sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536813003541/br2222Isup2.hkl

checkCIF report

Comment top

Orange needles of BaEr₂S₄ were obtained in a solid-state reaction. The compound was synthesized previously (Patrie et al., 1964), and its unit cell parameters were determined from X-powder diffraction data. In the BaLn₂S₄ family (Ln = rare earth element) no structures have been determined from single-crystal data but that of the closely related compound BaLu₂S₄ has (Schurz & Schleid, 2011). Here, from X-ray diffraction single-crystal data we find that BaEr₂S₄ crystallizes in the CaFe₂O₄ structure type (Decker & Kasper, 1957) with four formula units in space group Pnma of the orthorhombic system. In the asymmetric unit there are two Er, one Ba, and four S atoms, each with site symmetry .m.. A projection of the structure down [010] is shown in Figure 1. The structure consists of ErS₆ octahedra that form dimers by edge-sharing. Four such dimers form an infinite channel by corner-sharing in the (010) plane. Each channel is filled by one Ba atom. Each Er1 atom is octahedrally coordinated to one S2, three S3, and two S4 atoms; each Er2 atom is coordinated to three S1, two S2, and one S4 atom. The interatomic Er - S distances at 2.6706 (10) to 2.7376 (7) Å compare favorably to those of 2.672 (4) to 2.720 (4) Å in the structure of BaLu₂S₄ (Schurz & Schleid, 2011). As there are no S - S bonds in the structure, formal oxidation states may be assigned as Ba²⁺, Er³⁺, and S^2-.

Related literature top

The unit-cell parameters of BaEr₂S₄, which crystallizes in the CaFe₂O₄ structure type (Decker & Kasper, 1957), were previously determined from X-ray powder diffraction data (Patrie et al., 1964). For related structures, see: Bugaris & Ibers (2009); Narducci et al. (2000); Carpenter & Hwu (1992); Flahaut et al. (1965); Schurz & Schleid (2011). For synthetic details, see: Bugaris & Ibers (2008); Haneveld & Jellinek (1969). For standardization of structural data, see: Gelato & Parthé (1987).

Experimental top

In an exploration of the quaternary solid-state Ba/Er/U/S system, orange needles of BaEr₂S₄ were obtained instead in a two-step reaction. Uranium powder was obtained by hydridization and decomposition of ²³⁸U turnings (Oak Ridge National Laboratory) (Bugaris & Ibers, 2008; Haneveld & Jellinek, 1969). The other reactants were used as obtained. In the first step, a mixture consisting of powdered ²³⁸U (20.9 mg, 0.088 mmol), Er (14.0 mg, 0.084 mmol), BaS (42.7 mg, 0.252 mmol), and S (8.0 mg, 0.25 mmol) was loaded into a carbon-coated fused-silica tube under an Ar atmosphere in a glove box. The tube was evacuated to 10 ^-4 Torr, and flame sealed. It was placed in computer-contolled furnace, heated to 1273 K in 48 h, held there for 8 d, then cooled to 293 K at 3 K/h. In the second step, the resultant black powder was ground and mixed thoroughly with 50 mg of Sb₂S₃. This mixture was re-loaded into a carbon-coated fused-silica tube, evacuated, sealed, and then placed in a computer-controlled furnace The tube was heated to 1273 K in 24 h, held there for 4 d, then cooled to 293 K at 2 K/h. Orange needles were obtained in about 50 wt% yield. Analysis of these orange crystals on an EDX– equipped Hitachi S-3400 SEM showed the presence of Ba, Er, and S in the approximate ratio 1:2:4 but no U. The other products were black crystals of Sb₂S₃ and US₂.

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008b); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008b); molecular graphics: CrystalMaker (Palmer, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008b).

Figures top

Fig. 1. Structure of BaEr₂S₄ viewed approximatly down [010]. Displacement ellipsoids are drawn at 95% probability level.

Barium dierbium(III) tetrasulfide top

Crystal data top

BaEr₂S₄	F(000) = 1024
M_r = 600.10	D_x = 5.721 Mg m⁻³
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2n	Cell parameters from 8150 reflections
a = 12.1455 (3) Å	θ = 2.3–30.5°
b = 3.9884 (1) Å	µ = 30.53 mm⁻¹
c = 14.3837 (4) Å	T = 100 K
V = 696.76 (3) Å³	Needle, orange
Z = 4	0.16 × 0.03 × 0.02 mm

Data collection top

Bruker APEXII CCD diffractometer	1207 independent reflections
Radiation source: fine-focus sealed tube	1196 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.030
ϕ and ω scans	θ_max = 30.5°, θ_min = 2.2°
Absorption correction: numerical face indexed (Sheldrick, 2008a)	h = −17→17
T_min = 0.084, T_max = 0.528	k = −5→5
9866 measured reflections	l = −20→20

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)] = 0.017	1/[s²(F_o²) + (0.0192F_o²)²]
wR(F²) = 0.050	(Δ/σ)_max = 0.002
S = 1.87	Δρ_max = 2.46 e Å⁻³
1207 reflections	Δρ_min = −2.58 e Å⁻³
44 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008a), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00257 (16)

Crystal data top

BaEr₂S₄	V = 696.76 (3) Å³
M_r = 600.10	Z = 4
Orthorhombic, Pnma	Mo Kα radiation
a = 12.1455 (3) Å	µ = 30.53 mm⁻¹
b = 3.9884 (1) Å	T = 100 K
c = 14.3837 (4) Å	0.16 × 0.03 × 0.02 mm

Data collection top

Bruker APEXII CCD diffractometer	1207 independent reflections
Absorption correction: numerical face indexed (Sheldrick, 2008a)	1196 reflections with I > 2σ(I)
T_min = 0.084, T_max = 0.528	R_int = 0.030
9866 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.017	44 parameters
wR(F²) = 0.050	0 restraints
S = 1.87	Δρ_max = 2.46 e Å⁻³
1207 reflections	Δρ_min = −2.58 e Å⁻³

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Er1	0.079448 (16)	0.2500	0.398817 (12)	0.00349 (8)
Er2	0.566211 (16)	0.2500	0.608465 (12)	0.00444 (8)
Ba1	0.24191 (2)	0.2500	0.662667 (18)	0.00705 (9)
S1	0.08229 (8)	0.2500	0.07671 (7)	0.00485 (18)
S2	0.29294 (9)	0.2500	0.33808 (7)	0.00537 (18)
S3	0.37564 (8)	0.2500	0.02341 (7)	0.00449 (18)
S4	0.47727 (8)	0.2500	0.78311 (7)	0.00490 (18)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Er1	0.00359 (11)	0.00300 (12)	0.00388 (11)	0.000	0.00010 (5)	0.000
Er2	0.00495 (12)	0.00349 (12)	0.00487 (11)	0.000	−0.00020 (5)	0.000
Ba1	0.00595 (14)	0.00835 (14)	0.00683 (13)	0.000	0.00015 (8)	0.000
S1	0.0057 (4)	0.0040 (4)	0.0049 (4)	0.000	−0.0004 (3)	0.000
S2	0.0037 (4)	0.0044 (4)	0.0080 (4)	0.000	−0.0006 (3)	0.000
S3	0.0046 (4)	0.0037 (4)	0.0052 (4)	0.000	0.0009 (3)	0.000
S4	0.0061 (4)	0.0039 (4)	0.0047 (4)	0.000	0.0015 (3)	0.000

Geometric parameters (Å, º) top

Er1—S4ⁱ	2.6872 (6)	Ba1—S4	3.3426 (11)
Er1—S4ⁱⁱ	2.6872 (6)	Ba1—Er2^x	3.9231 (3)
Er1—S3ⁱⁱⁱ	2.7164 (10)	Ba1—Ba1^xi	3.9884 (1)
Er1—S3^iv	2.7360 (7)	Ba1—Ba1^xii	3.9884
Er1—S3^v	2.7360 (7)	S1—Er2ⁱⁱⁱ	2.6706 (10)
Er1—S2	2.7362 (11)	S1—Er2ⁱ	2.7273 (7)
Er1—Ba1	4.2774 (3)	S1—Er2ⁱⁱ	2.7273 (7)
Er2—S1^vi	2.6706 (10)	S1—Ba1ⁱⁱ	3.1725 (8)
Er2—S1^v	2.7274 (7)	S1—Ba1ⁱ	3.1725 (8)
Er2—S1^iv	2.7274 (7)	S2—Er2^vii	2.7376 (7)
Er2—S4	2.7345 (9)	S2—Er2^viii	2.7376 (7)
Er2—S2^vii	2.7376 (7)	S2—Ba1ⁱ	3.2437 (9)
Er2—S2^viii	2.7376 (7)	S2—Ba1ⁱⁱ	3.2437 (9)
Er2—Ba1^ix	3.9231 (3)	S3—Er1^vi	2.7163 (10)
Er2—Ba1	4.0153 (3)	S3—Er1ⁱ	2.7360 (7)
Ba1—S3^v	3.1666 (8)	S3—Er1ⁱⁱ	2.7360 (7)
Ba1—S3^iv	3.1666 (8)	S3—Ba1ⁱⁱ	3.1666 (8)
Ba1—S1^iv	3.1725 (8)	S3—Ba1ⁱ	3.1666 (8)
Ba1—S1^v	3.1725 (8)	S4—Er1^iv	2.6873 (6)
Ba1—S2^iv	3.2438 (9)	S4—Er1^v	2.6873 (6)
Ba1—S2^v	3.2438 (9)	S4—Ba1^ix	3.3074 (11)
Ba1—S4^x	3.3074 (11)

S4ⁱ—Er1—S4ⁱⁱ	95.82 (3)	S3^iv—Ba1—Er2^x	106.592 (19)
S4ⁱ—Er1—S3ⁱⁱⁱ	91.23 (3)	S1^iv—Ba1—Er2^x	133.879 (16)
S4ⁱⁱ—Er1—S3ⁱⁱⁱ	91.23 (3)	S1^v—Ba1—Er2^x	133.879 (16)
S4ⁱ—Er1—S3^iv	176.07 (3)	S2^iv—Ba1—Er2^x	43.642 (15)
S4ⁱⁱ—Er1—S3^iv	85.17 (2)	S2^v—Ba1—Er2^x	43.642 (15)
S3ⁱⁱⁱ—Er1—S3^iv	84.95 (3)	S4^x—Ba1—Er2^x	43.408 (16)
S4ⁱ—Er1—S3^v	85.17 (2)	S4—Ba1—Er2^x	91.735 (18)
S4ⁱⁱ—Er1—S3^v	176.07 (3)	S3^v—Ba1—Ba1^xi	129.032 (11)
S3ⁱⁱⁱ—Er1—S3^v	84.95 (3)	S3^iv—Ba1—Ba1^xi	50.967 (11)
S3^iv—Er1—S3^v	93.58 (3)	S1^iv—Ba1—Ba1^xi	51.054 (12)
S4ⁱ—Er1—S2	92.59 (3)	S1^v—Ba1—Ba1^xi	128.946 (12)
S4ⁱⁱ—Er1—S2	92.59 (3)	S2^iv—Ba1—Ba1^xi	52.064 (12)
S3ⁱⁱⁱ—Er1—S2	174.30 (3)	S2^v—Ba1—Ba1^xi	127.936 (12)
S3^iv—Er1—S2	91.16 (3)	S4^x—Ba1—Ba1^xi	90.0
S3^v—Er1—S2	91.16 (3)	S4—Ba1—Ba1^xi	90.0
S4ⁱ—Er1—Ba1	131.894 (15)	Er2^x—Ba1—Ba1^xi	90.0
S4ⁱⁱ—Er1—Ba1	131.894 (15)	S3^v—Ba1—Ba1^xii	50.967 (11)
S3ⁱⁱⁱ—Er1—Ba1	93.15 (2)	S3^iv—Ba1—Ba1^xii	129.032 (11)
S3^iv—Er1—Ba1	47.693 (15)	S1^iv—Ba1—Ba1^xii	128.946 (12)
S3^v—Er1—Ba1	47.693 (15)	S1^v—Ba1—Ba1^xii	51.054 (12)
S2—Er1—Ba1	81.15 (2)	S2^iv—Ba1—Ba1^xii	127.936 (12)
S1^vi—Er2—S1^v	83.18 (3)	S2^v—Ba1—Ba1^xii	52.064 (12)
S1^vi—Er2—S1^iv	83.18 (3)	S4^x—Ba1—Ba1^xii	90.0
S1^v—Er2—S1^iv	93.97 (3)	S4—Ba1—Ba1^xii	90.0
S1^vi—Er2—S4	160.92 (3)	Er2^x—Ba1—Ba1^xii	90.0
S1^v—Er2—S4	83.84 (3)	Ba1^xi—Ba1—Ba1^xii	180.0
S1^iv—Er2—S4	83.84 (3)	S3^v—Ba1—Er2	108.630 (19)
S1^vi—Er2—S2^vii	103.56 (3)	S3^iv—Ba1—Er2	108.630 (19)
S1^v—Er2—S2^vii	173.17 (3)	S1^iv—Ba1—Er2	42.616 (14)
S1^iv—Er2—S2^vii	85.85 (2)	S1^v—Ba1—Er2	42.616 (14)
S4—Er2—S2^vii	89.36 (3)	S2^iv—Ba1—Er2	106.201 (19)
S1^vi—Er2—S2^viii	103.56 (3)	S2^v—Ba1—Er2	106.201 (19)
S1^v—Er2—S2^viii	85.85 (2)	S4^x—Ba1—Er2	177.557 (18)
S1^iv—Er2—S2^viii	173.17 (3)	S4—Ba1—Er2	42.413 (17)
S4—Er2—S2^viii	89.36 (3)	Er2^x—Ba1—Er2	134.149 (8)
S2^vii—Er2—S2^viii	93.51 (3)	Ba1^xi—Ba1—Er2	90.0
S1^vi—Er2—Ba1^ix	142.85 (2)	Ba1^xii—Ba1—Er2	90.0
S1^v—Er2—Ba1^ix	120.02 (2)	Er2ⁱⁱⁱ—S1—Er2ⁱ	96.82 (3)
S1^iv—Er2—Ba1^ix	120.02 (2)	Er2ⁱⁱⁱ—S1—Er2ⁱⁱ	96.82 (3)
S4—Er2—Ba1^ix	56.22 (2)	Er2ⁱ—S1—Er2ⁱⁱ	93.97 (3)
S2^vii—Er2—Ba1^ix	54.861 (19)	Er2ⁱⁱⁱ—S1—Ba1ⁱⁱ	115.97 (3)
S2^viii—Er2—Ba1^ix	54.861 (19)	Er2ⁱ—S1—Ba1ⁱⁱ	147.08 (4)
S1^vi—Er2—Ba1	105.39 (2)	Er2ⁱⁱ—S1—Ba1ⁱⁱ	85.422 (12)
S1^v—Er2—Ba1	51.961 (18)	Er2ⁱⁱⁱ—S1—Ba1ⁱ	115.97 (3)
S1^iv—Er2—Ba1	51.961 (18)	Er2ⁱ—S1—Ba1ⁱ	85.422 (12)
S4—Er2—Ba1	55.53 (2)	Er2ⁱⁱ—S1—Ba1ⁱ	147.08 (4)
S2^vii—Er2—Ba1	123.95 (2)	Ba1ⁱⁱ—S1—Ba1ⁱ	77.89 (2)
S2^viii—Er2—Ba1	123.95 (2)	Er1—S2—Er2^vii	120.17 (3)
Ba1^ix—Er2—Ba1	111.755 (5)	Er1—S2—Er2^viii	120.17 (3)
S3^v—Ba1—S3^iv	78.06 (2)	Er2^vii—S2—Er2^viii	93.51 (3)
S3^v—Ba1—S1^iv	116.92 (2)	Er1—S2—Ba1ⁱ	97.16 (3)
S3^iv—Ba1—S1^iv	70.19 (2)	Er2^vii—S2—Ba1ⁱ	138.40 (4)
S3^v—Ba1—S1^v	70.19 (2)	Er2^viii—S2—Ba1ⁱ	81.498 (14)
S3^iv—Ba1—S1^v	116.92 (2)	Er1—S2—Ba1ⁱⁱ	97.16 (3)
S1^iv—Ba1—S1^v	77.89 (2)	Er2^vii—S2—Ba1ⁱⁱ	81.498 (14)
S3^v—Ba1—S2^iv	145.12 (3)	Er2^viii—S2—Ba1ⁱⁱ	138.40 (4)
S3^iv—Ba1—S2^iv	92.639 (19)	Ba1ⁱ—S2—Ba1ⁱⁱ	75.87 (2)
S1^iv—Ba1—S2^iv	90.26 (2)	Er1^vi—S3—Er1ⁱ	95.05 (3)
S1^v—Ba1—S2^iv	141.02 (3)	Er1^vi—S3—Er1ⁱⁱ	95.05 (3)
S3^v—Ba1—S2^v	92.639 (19)	Er1ⁱ—S3—Er1ⁱⁱ	93.58 (3)
S3^iv—Ba1—S2^v	145.12 (3)	Er1^vi—S3—Ba1ⁱⁱ	98.65 (3)
S1^iv—Ba1—S2^v	141.02 (3)	Er1ⁱ—S3—Ba1ⁱⁱ	164.41 (4)
S1^v—Ba1—S2^v	90.26 (2)	Er1ⁱⁱ—S3—Ba1ⁱⁱ	92.590 (8)
S2^iv—Ba1—S2^v	75.87 (2)	Er1^vi—S3—Ba1ⁱ	98.65 (3)
S3^v—Ba1—S4^x	73.20 (2)	Er1ⁱ—S3—Ba1ⁱ	92.590 (8)
S3^iv—Ba1—S4^x	73.20 (2)	Er1ⁱⁱ—S3—Ba1ⁱ	164.41 (4)
S1^iv—Ba1—S4^x	138.242 (15)	Ba1ⁱⁱ—S3—Ba1ⁱ	78.07 (2)
S1^v—Ba1—S4^x	138.242 (15)	Er1^iv—S4—Er1^v	95.82 (3)
S2^iv—Ba1—S4^x	71.93 (2)	Er1^iv—S4—Er2	132.085 (15)
S2^v—Ba1—S4^x	71.93 (2)	Er1^v—S4—Er2	132.085 (15)
S3^v—Ba1—S4	135.514 (16)	Er1^iv—S4—Ba1^ix	95.91 (3)
S3^iv—Ba1—S4	135.514 (16)	Er1^v—S4—Ba1^ix	95.91 (3)
S1^iv—Ba1—S4	68.06 (2)	Er2—S4—Ba1^ix	80.37 (3)
S1^v—Ba1—S4	68.06 (2)	Er1^iv—S4—Ba1	95.84 (3)
S2^iv—Ba1—S4	73.05 (2)	Er1^v—S4—Ba1	95.84 (3)
S2^v—Ba1—S4	73.05 (2)	Er2—S4—Ba1	82.05 (3)
S4^x—Ba1—S4	135.144 (10)	Ba1^ix—S4—Ba1	162.42 (3)
S3^v—Ba1—Er2^x	106.592 (19)

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

Experimental details

Crystal data
Chemical formula	BaEr₂S₄
M_r	600.10
Crystal system, space group	Orthorhombic, Pnma
Temperature (K)	100
a, b, c (Å)	12.1455 (3), 3.9884 (1), 14.3837 (4)
V (Å³)	696.76 (3)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	30.53
Crystal size (mm)	0.16 × 0.03 × 0.02

Data collection
Diffractometer	Bruker APEXII CCD diffractometer
Absorption correction	Numerical face indexed (Sheldrick, 2008a)
T_min, T_max	0.084, 0.528
No. of measured, independent and observed [I > 2σ(I)] reflections	9866, 1207, 1196
R_int	0.030
(sin θ/λ)_max (Å⁻¹)	0.714

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.017, 0.050, 1.87
No. of reflections	1207
No. of parameters	44
Δρ_max, Δρ_min (e Å⁻³)	2.46, −2.58

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008b), SHELXL97 (Sheldrick, 2008b), CrystalMaker (Palmer, 2012).

Acknowledgements

The research was kindly supported at Northwestern University by the US Department of Energy, Basic Energy Sciences, Chemical Sciences, Biosciences, and Geosciences Division and Division of Materials Science and Engineering Grant ER-15522. Use was made of the IMSERC X-ray Facility at Northwestern University, supported by the International Institute of Nanotechnology (IIN).

References

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