Octa­hedral distortion caused by hydrogen bonding in tris­(diethyl­ammonium) hexa­chloridoanti­mon­ate(III)

The factors influencing the distortion of inorganic anions in the structures of chlorido­anti­monates(III) with organic cations, in spite of numerous structural studies on those compounds, have not been clearly described and separated. The title compound, [(C₂H₅)₂NH₂]₃[SbCl₆], consisting of isolated distorted [SbCl₆]³⁻ octa­hedra that have C₃ symmetry and [(C₂H₅)₂NH₂]⁺ cations, unequivocally shows the role played by hydrogen bonding in the geometry variations of inorganic anions. The organic cations, which are linked to the inorganic substructure through N—H...Cl hydrogen bonds, are clearly responsible for the distortion of the octa­hedral coordination of Sb^III in terms of differences (Δ) in both Sb—Cl bond lengths [Δ = 0.4667 (6) Å] and Cl—Sb—Cl angles [Δ = 9.651 (17)°].

S1. Comment

Chloroantimonates(III) with organic cations are considered as organic–inorganic perovskite-like hybrid materials. They consist of organic cations within anionic inorganic substructures. The interest in this group of compounds is focused on two areas: (a) the structural phase transitions, some of them to polar phases, which mainly arise from the large polarizability of the complex anions, changes in the dynamic disorder of the organic cations and consequent changes in the hydrogen-bonding scheme; (b) the complex crystal chemistry – the inorganic chloroantimonate(III) anions may assume several structural geometries with varying degrees of distortion depending on the size, shape and ability to form hydrogen bonds to the organic cations (Fischer & Norman, 1994; Sobczyk et al., 1997; Mitzi, 2001; Bujak & Angel, 2005, 2006). The distortion of chloroantimonate(III) inorganic units is associated with the presence of the lone pair of electrons on the Sb^III central atom (Wang & Liebau, 1996). This distortion has been correlated to a 'primary deformation', connected with the tendency of [SbCl₆]^3- octahedra and [SbCl₅]^2- square pyramids to share Cl atoms with each other in forming more complicted arrangements, and a 'secondary deformation', resulting from the presence of interactions between oppositely charged organic and inorganic components of the structures (Bujak & Zaleski, 2001, 2002).

Tris(diethylammonium) hexachoridooantimonate(III), [(C₂H₅)₂NH₂]₃[SbCl₆], (I), is a perfect model structure for understanding and separating the factors influencing distortion of inorganic polyhedra in chloroantimonates(III) because the inorganic substructure consists of single isolated units (the 'primary deformation' factor is thus eliminated), the organic cations are fully ordered, the postions of the H atoms are well defined and only one crystallographically independent Cl atom is involved in relatively strong well defined hydrogen-bonding interactions (Fig. 1). [(C₂H₅)₂NH₂]₃[SbCl₆], in the rhombohedral R3c space group, is isomorphous with its bismuth analogue – tris(diethylammonium) hexachloridobismuthate(III) (Lazarini, 1987; Jarraya et al., 1993). The structure of (I) consists of inorganic [SbCl₆]^3- octahedra and organic diethylammonium [(C₂H₅)₂)NH₂]⁺ cations that adopt an extended relative conformation of the ethyl groups with expected dimensions (Wahlberg, 1978). The [SbCl₆]^3- octahedra show C₃ symmetry with three short [2.4715 (4) Å] and three longer [2.9382 (4) Å] Sb—Cl bonds, distributed mutually in a trans fashion, with a difference of 0.4667 (6) Å. The Cl—Sb—Cl angles are also significantly distorted. They range from 83.450 (12)°, the angle between the short and longer bonds, to 93.101 (12)°, the angle between the longer Sb–Cl bonds (Table 1), giving a difference of 9.651 (17)°. Although the distortion found in (I) is relatively large and somewhat unusual, it is not the first example of such large differences in Sb—Cl bond distances. A similar situation, with even larger Sb—Cl deviations was found in the structures of pentakis(benzidinediium) bis[hexachlordioantimony(III)] tetrachloride sesquihydrate (Dobrzycki & Woźniak, 2009), 2-ammonioguanidinium 2-aminoguanidinium hexachloridoantimonate(III) (Bujak et al., 2001) and diethylenetriammonium hexachloridoantimonate(III) (Vezzosi et al., 1984).

The observed differences in Sb—Cl bond lengths and Cl—Sb—Cl angles correlate well with the presence of N—H···Cl hydrogen bonds between the anionic substructure and the organic cations (Table 2 and Fig. 2). All N—H···Cl interactions are associated with the longer Sb1—Cl2 distances, causing the distortion of inorganic units from the ideal octahedral symmetry. The distortion is realised by a shift of the central Sb^III atoms from the centre of the octahedra, by ca 0.1 Å, along the crystallographic c axis towards the three Cl1 atoms. Taking into account the geometrical parameters of the hydrogen bonds and their influence on the geometry of the inorganic substructure, they can be considered as a relatively strong among Sb–Cl···H–N interactions (Bruno et al., 2002; Steiner, 2002).

As expected, the distortion from ideal octahedral symmetry in (I) is more pronounced than that found in its bismuth(III) analogue, where the differences in Bi—Cl bond lengths and Cl—Bi—Cl angles are 0.288 (2) Å and 8.89 (6)°, respectively (Jarraya et al., 1993). This behaviour can be best rationalized on the basis of the valence shell electron pair repulsion model (Gillespie & Nyholm, 1957; Gillespie & Robinson, 2005), together with the electronic-distortion approach (Brown, 2002), in terms of a stereochemical activity (localization) of the lone pair of electrons along with the difference in polarizability of the central Sb^III and Bi^III atoms. Intermediate Sb—Cl bond lengths of 2.652 (6) and 2.6552 (3) Å are observed in the slightly distorted, isolated [SbCl₆]^3- octahedra in which all six Cl atoms are involved in hydrogen bonding rather than just three (Schroeder & Jacobson, 1973; Podesta & Orpen, 2005). Thus in (I), the asymmetric hydrogen-bond pattern is clearly responsible for the much longer Sb1—Cl2 distances and the pronounced angular distortion.

Related literature

For related literature, see: Bruno et al. (2002); Bujak & Angel (2005, 2006); Bujak & Zaleski (2001, 2002); Bujak, Osadczuk & Zaleski (2001); Dobrzycki & Woźniak (2009); Fischer & Norman (1994); Jarraya et al. (1993); Lazarini (1987); Mitzi (2001); Podesta & Orpen (2005); Schroeder & Jacobson (1973); Sobczyk et al. (1997); Steiner (2002); Vezzosi et al. (1984); Wahlberg (1978); Wang & Liebau (1996).

S2. Experimental

SbCl₃ (2.28 g, 1 mmol) dissolved in 6 M HCl (6 ml) was treated with (C₂H₅)₂NH (5.2 ml, 5 mmol) added slowly, dropwise, with stirring, to 6 M HCl (10 ml). Slow evaporation of the acid solution at room temperature yielded transparent, colourless crystals of [(C₂H₅)₂NH₂]₃[SbCl₆].

S3. Refinement

All H atoms were located in Fourier difference maps, refined with C—H distances constrained (methyl groups allowed rotational freedom) and U_eq values for –CH₃ and >CH₂, equal to 1.5 and 1.2 times the U_eq value of their carriers, respectively. The >NH₂⁺ group H-atom parameters were refined freely. The absolute structure is determined reliably.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2009); cell refinement: CrysAlis PRO (Oxford Diffraction, 2009); data reduction: CrysAlis PRO (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. The packing diagram of [(C2H5)2NH2]3[SbCl6]. Displacement ellipsoids are plotted at the 50% probability level.
	Fig. 2. The octahedral [SbCl6]^3- anion in [(C2H5)2NH2]3[SbCl6] with geometrical distortion caused by N—H···Cl hydrogen-bonded (red lines in the electronic version of the paper) organic cations. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) -y, x - y, z; (ii) -x + y, -x, z; (iii) x, x - y, z - 1/2; (iv) -x + y + 1/3, -x + 2/3, z - 1/3.] [DON'T MATCH TABLES]

Tris(diethylammonium) hexachloridoantimonate(III)

Crystal data

(C4H12N)3[SbCl6]	Dx = 1.559 Mg m^−3
Mr = 556.90	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3c	Cell parameters from 8381 reflections
Hall symbol: R 3 -2"c	θ = 2.8–29.7°
a = 14.71917 (18) Å	µ = 1.84 mm^−1
c = 18.9694 (3) Å	T = 85 K
V = 3559.19 (8) Å^3	Tabular, colourless
Z = 6	0.19 × 0.19 × 0.15 mm
F(000) = 1692

Data collection

Oxford Diffraction Xcalibur diffractometer	2056 independent reflections
Radiation source: fine-focus sealed tube	2018 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.012
ω–scan	θmax = 29.5°, θmin = 2.7°
Absorption correction: analytical CrysAlis RED (Oxford Diffraction, 2009); analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by Clark & Reid (1995)	h = −20→18
Tmin = 0.713, Tmax = 0.760	k = −14→20
9101 measured reflections	l = −26→25

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.008	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.030	w = 1/[σ^2(Fo^2) + (0.0038P)^2 + 4.6787P] where P = (Fo^2 + 2Fc^2)/3
S = 1.48	(Δ/σ)max < 0.001
2056 reflections	Δρmax = 0.53 e Å^−3
78 parameters	Δρmin = −0.54 e Å^−3
1 restraint	Absolute structure: Flack (1983), 973 Friedel pairs
Primary atom site location: heavy-atom method	Absolute structure parameter: 0.001 (16)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 (Ų)

	x	y	z	Uiso*/Ueq
Sb1	0.0000	0.0000	−0.000139 (14)	0.00777 (4)
Cl1	0.01743 (3)	0.14641 (3)	0.07349 (2)	0.01389 (8)
Cl2	0.16498 (3)	0.16960 (3)	−0.08459 (2)	0.01228 (8)
N1	0.29887 (12)	0.22044 (12)	0.35085 (8)	0.0114 (3)
H1	0.2657 (17)	0.1554 (17)	0.3647 (10)	0.010 (5)*
H2	0.360 (2)	0.241 (2)	0.3335 (13)	0.028 (7)*
C1	0.31842 (15)	0.28205 (13)	0.41751 (11)	0.0151 (3)
H11	0.3513	0.2576	0.4526	0.018*
H12	0.2505	0.2689	0.4370	0.018*
C2	0.38888 (14)	0.39873 (14)	0.40580 (10)	0.0176 (4)
H21	0.4579	0.4126	0.3896	0.026*
H22	0.3967	0.4362	0.4501	0.026*
H23	0.3576	0.4229	0.3701	0.026*
C3	0.22999 (14)	0.23397 (14)	0.29888 (9)	0.0146 (3)
H31	0.2693	0.3043	0.2770	0.018*
H32	0.1684	0.2290	0.3236	0.018*
C4	0.19323 (15)	0.15046 (15)	0.24191 (10)	0.0191 (4)
H41	0.2542	0.1562	0.2170	0.029*
H42	0.1482	0.1604	0.2085	0.029*
H43	0.1536	0.0809	0.2635	0.029*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sb1	0.00776 (5)	0.00776 (5)	0.00778 (6)	0.00388 (2)	0.000	0.000
Cl1	0.01554 (19)	0.01321 (19)	0.01340 (18)	0.00755 (16)	0.00087 (16)	−0.00293 (15)
Cl2	0.01352 (18)	0.01190 (18)	0.01190 (17)	0.00670 (16)	0.00194 (15)	−0.00073 (15)
N1	0.0091 (7)	0.0099 (7)	0.0145 (7)	0.0042 (6)	0.0015 (5)	0.0017 (5)
C1	0.0160 (9)	0.0183 (8)	0.0121 (7)	0.0094 (8)	0.0011 (7)	−0.0010 (8)
C2	0.0180 (9)	0.0170 (9)	0.0183 (9)	0.0090 (7)	−0.0006 (7)	−0.0046 (7)
C3	0.0148 (8)	0.0157 (8)	0.0144 (8)	0.0084 (7)	0.0004 (7)	0.0027 (7)
C4	0.0213 (9)	0.0173 (9)	0.0161 (8)	0.0077 (8)	−0.0023 (7)	0.0002 (7)

Geometric parameters (Å, º)

Sb1—Cl1	2.4715 (4)	C1—H12	0.9900
Sb1—Cl2	2.9382 (4)	C2—H21	0.9800
N1—C1	1.498 (2)	C2—H22	0.9800
N1—C3	1.497 (2)	C2—H23	0.9800
C1—C2	1.514 (2)	C3—H31	0.9900
C3—C4	1.519 (3)	C3—H32	0.9900
N1—H1	0.87 (2)	C4—H41	0.9800
N1—H2	0.85 (3)	C4—H42	0.9800
C1—H11	0.9900	C4—H43	0.9800
Cl1—Sb1—Cl1^i	91.200 (16)	C1—C2—H21	109.5
Cl1—Sb1—Cl2	83.450 (12)	C1—C2—H22	109.5
Cl1—Sb1—Cl2^i	173.514 (13)	H21—C2—H22	109.5
Cl1^i—Sb1—Cl2	92.570 (13)	C1—C2—H23	109.5
Cl2^i—Sb1—Cl2	93.101 (12)	H21—C2—H23	109.5
N1—C1—C2	112.22 (16)	H22—C2—H23	109.5
N1—C3—C4	110.60 (14)	N1—C3—H31	109.5
C1—N1—C3	114.41 (14)	C4—C3—H31	109.5
C3—N1—H1	107.4 (14)	N1—C3—H32	109.5
C1—N1—H1	104.1 (13)	C4—C3—H32	109.5
C3—N1—H2	111.1 (16)	H31—C3—H32	108.1
C1—N1—H2	105.3 (17)	C3—C4—H41	109.5
H1—N1—H2	115 (2)	C3—C4—H42	109.5
N1—C1—H11	109.2	H41—C4—H42	109.5
C2—C1—H11	109.2	C3—C4—H43	109.5
N1—C1—H12	109.2	H41—C4—H43	109.5
C2—C1—H12	109.2	H42—C4—H43	109.5
H11—C1—H12	107.9
C3—N1—C1—C2	−70.72 (19)	C1—N1—C3—C4	−166.34 (15)

Symmetry code: (i) −x+y, −x, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···Cl2^ii	0.87 (2)	2.28 (2)	3.135 (2)	170 (2)
N1—H2···Cl2^iii	0.85 (3)	2.39 (3)	3.186 (2)	154 (2)

Symmetry codes: (ii) x, x−y, z+1/2; (iii) −y+2/3, x−y+1/3, z+1/3.