[Te₈][NbOCl₄]₂ containing an infinite chain-like {[Te-Te-Te-(Te₅)]²⁺}_n polycation

The title compound, [Te₈][NbOCl₄]₂, was obtained as trans­lucent black crystals by reaction of elemental tellurium, niobium(V) chloride and niobium(V) oxychloride in the ionic liquid BMImCl (BMImCl is 1-butyl-3-methyl­imidazolium chloride). The synthesis was performed in argon-filled glass ampoules. According to X-ray structure analysis based on single crystals, the title compound crystallizes with triclinic lattice symmetry and consists of infinite {[Te₈]²⁺}_n cations associated with pyramidal [NbOCl₄]^- anions. The novel catena-octa­tellurium(2+) cation is composed of Te₅ rings that are linked via Te₃ units [Te-Te = 2.6455 (18)-2.8164 (19) Å]. The composition and purity of [Te₈][NbOCl₄]₂ were further confirmed by energy-dispersive X-ray diffraction (EDX) analysis.

S1. Comment

Tellurium is well known for its chain-like structural arrangement. Such infinite chains are characteristic to the structure of the element (Straumanis, 1940) and are also found in compounds containing polycationic tellurium species such as Te₈[Bi₄Cl₁₄] (Beck & Stankowski, 2001), Te₈[U₂Br₁₀] (Beck & Fischer, 2002) and [Te₈]₂[Ta₄O₄Cl₁₆] (Freudenmann & Feldmann, 2011a,b). Similar to these compounds, we could [were able to?] now obtain [Te₈][NbOCl₄]₂ which also exhibits an infinite chain-like {[Te₈]²⁺}_n cation. While the other known catena-octatellurium(2+) cations in Te₈[Bi₄Cl₁₄], Te₈[U₂Br₁₀] and [Te₈]₂[Ta₄O₄Cl₁₆] are composed of Te₆ rings linked via Te₂ units, the title compound [Te₈][NbOCl₄]₂ shows an arrangement of Te₅ rings that are linked via Te₃ units. Te₅ rings have been described for [Te₆][HfCl₆] which, however, exhibits a [Te₅–Te–Te₅] connectivity (Beck & Baumann, 2004). [Te₈][NbOCl₄]₂ has been obtained as part of our studies concerning the use of ionic liquids in inorganic chemistry while aiming at novel polycationic (Freudenmann & Feldmann, 2011a,b) or polyanionic species (Wolff et al., 2011; Freudenmann et al., 2011).

The title compound, [Te₈][NbOCl₄]₂, was prepared by reaction of tellurium, niobium(V) chloride and niobium(V) oxychloride in the ionic liquid BMImCl (BMImCl is 1-butyl-3-methylimidazolium chloride). The synthesis resulted in translucent, black, moisture-sensitive crystals. X-ray structure analysis based on single crystals revealed that the compound crystallizes with the triclinic space group P1. The title compound is constituted of infinite {[Te–Te–Te–(Te₅)]²⁺}_n chains and a chain-like arrangement of [NbOCl₄]^- counter-anions which are both directed along the crystallographic a axis (Fig. 1). The chemical composition of [Te₈][NbOCl₄]₂ has been validated based on EDX [energy-dispersive X-ray diffraction?] analysis with values of 61.2 wt% Te, 12.2 wt% Nb and 17.0 wt% Cl resulting in a Te:Nb:Cl ratio of 3.6:1:4 (calculated data: 67.0 wt% Te, 12.2 wt% Nb and 18.6 wt% Cl; Te:Nb:Cl ratio: 4:1:4).

The most interesting aspect of [Te₈][NbOCl₄]₂ is related to the infinite polycationic {[Te₈]²⁺}_n building unit. This cation is composed of Te₅ rings that are interlinked by Te₃ units via its 1,3-positions. As a result of this linkage, an infinite chain-like tellurium polycation according to the description [Te–Te–Te–(Te₅)]_n²⁺ is obtained. Although infinite Te chains are well known in principle, this concrete arrangement has not been found for tellurium yet. Five-membered chalcogen rings which are interconnected via Te atoms into chains are known for compounds such as [Te₆][HfCl₆], exhibiting a [Te₅–Te–Te₅] arrangement (Beck & Baumann, 2004). Moreover, triatomic chalcogen bridges are known for the mixed Te/Se compound [Se_4.85Te_3.15][WOCl₄]₂. Herein, the folding of the chalcogen chain is however different, and the precise position of Se and Te in [Se_4.85Te_3.15][WOCl₄]₂ remains partially unsolved (Beck & Schlörb, 1997).

For [Te₈][NbOCl₄]₂, the Te—Te distances range from 2.645 (1) to 2.816 (1) Å (Fig. 2). These distances are in agreement with literature values, indicating a Te—Te single bond (i.e. 2.74 Å on average) (Brownridge et al., 2000; Beck & Bock, 1995; Lange et al., 2007). Thus, the bonding situation is very comparable to known polycationic tellurium species (Straumanis, 1940; Beck & Stankowski, 2001; Beck & Fischer, 2002; Freudenmann & Feldmann, 2011a,b). Discrete tellurium polycations containing [Te₈]²⁺ species with different conformation have already been characterized in compounds such as [(Te₆)(Te₈)][WCl₆]₄ (Beck, 1997) and Te₈[MCl₆] (M = Hf, Re; Beck & Müller-Buschbaum, 1997). Bicyclic polycations such as in Te₈[WCl₆]₂ have also been reported (Beck, 1990). Moreover, structural isomers of {[Te₈]²⁺}_n have been discovered in Te₈[U₂Br₁₀] (Beck & Fischer, 2002), [Te₈]₂[Ta₄O₄Cl₁₆] (Freudenmann & Feldmann, 2011a,b) and Te₈[Bi₄Cl₁₄] (Beck & Schlörb, 1997). These compounds also contain infinite {[Te₈]²⁺}_n chains, but with six-membered tellurium rings connected via Te₂ bridges (Fig. 3; from top to bottom: Freudenmann & Feldmann, 2011a,b; Beck & Stankowski, 2001; Beck & Schlörb, 1997). A connectivity of Te₅ rings with Te₃ bridges such as in [Te₈][NbOCl₄]₂ is however firstly observed for the {[Te₈]²⁺}_n species.

The {[Te₈]²⁺}_n polycation is coordinated by two to four Cl atoms of [NbOCl₄]^- anions with Te—Cl distances ranging from 3.380 (2) to 4.291 (1) Å. This indicates only a weak Te—Cl interaction when compared to bulk Te₃Cl₂ (Te—Cl = 2.50–2.86 Å; Kniep et al., 1976). The pyramidal [NbOCl₄]^- anion is associated with infinite {[NbOCl₄]^-}_n chains. Herein, the O atom of each [NbOCl₄]^- unit is in contact with a second [NbOCl₄]^- anion. The Nb—O distances are in the range 1.703 (1)–1.717 (1) Å within the anion and 2.221 (1)–2.241 (1) Å between different [NbOCl₄]^- anions. These data are in agreement with similar compounds, such as [Te₇][NbOCl₄]Cl, and can be attributed to an Nb—O double bond (1.70 Å on average) and an Nb—O coordinative bonding (around 2.25 Å; Beck & Bock, 1994). The Nb—O—Nb angles range from 172.7 to 173.3° and indicate a certain tilting of the anionic chain. Finally, the Nb—Cl bond lengths in [NbOCl₄]^- [2.339 (1)–2.414 (1) Å] also match literature values (2.32–2.40 Å; Collins et al., 1987).

Altogether, it is well known that the type of synthesis (e.g., liquid-phase synthesis, high-temperature gas-phase synthesis or chemical-transport reaction) and the concrete experimental conditions (e.g., type of solvent, type of starting material, temperature, concentration) have a strong impact on the composition and structure of polycationic tellurium–selenium compounds (Ahmed & Ruck, 2011). Thus, it is not a surprise that the mild conditions of the reaction (423 K) and the weakly coordinating properties of the ionic liquid result in a new polycationic species with a connectivity of the tellurium atoms different from that in already known compounds.

Related literature

For related literature, see: Ahmed & Ruck (2011); Beck (1990, 1997); Beck & Baumann (2004); Beck & Bock (1994, 1995); Beck & Fischer (2002); Beck & Müller-Buschbaum (1997); Beck & Schlörb (1997); Beck & Stankowski (2001); Brauer (1981); Brownridge et al. (2000); Collins et al. (1987); Freudenmann & Feldmann (2011a, 2011b); Freudenmann et al. (2011); Kniep et al. (1976); Lange et al. (2007); Straumanis (1940); Wolff et al. (2011).

S2. Experimental

All compound and sample handling was carried out under standard Schlenk and argon glove-box techniques. Reaction took place in argon-filled and sealed glass ampoules that were dried at 573 K before use. The commercially available starting materials niobium(V) chloride (99.99%, ABCR) and tellurium powder (99.99%, ABCR) were dried in a vacuum for 24 h and used without further purification. Niobium(V) oxychloride was prepared according to a literature procedure (Brauer, 1981). The commercially available ionic liquid BMImCl (IoLiTec) was recrystallized and dried for 2 d in a vacuum prior to use.

In a typical reaction, tellurium (150 mg, 1.1 mmol), niobium(V) chloride (79.4 mg, 0.29 mmol) and niobium(V) oxychloride (62.4 mg, 0.29 mmol) were reacted in the ionic liquid BMImCl at 423 K for 14 d. Black crystals were obtained after cooling to room temperature at a rate of 1 K h^-1. These crystals were separated from the ionic liquid by filtration through a glass filter, followed by washing (four times) with dried tetrahydrofuran (THF, 2ml). Finally, the product was dried in a vacuum overnight and obtained in a yield of about 30%.

EDX measurements were carried out using an AMETEC EDAX mounted on a Zeiss SEM Supra 35 VP scanning electron microscope. Powdered samples were pressed into pellets, which were then fixed with conductive carbon pads on aluminium sample holders.

Computing details

Data collection: EXPOSE (Stoe & Cie, 2001); cell refinement: CELL and SELECT (Stoe & Cie, 2001); data reduction: INTEGRATE (Stoe & Cie, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2012); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. The unit cell of [Te8][NbOCl4]2, showing infinite {[Te8]^2+}n chains and the chain-like arrangement of pyramidal [NbOCl4]^- anions. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. The {[Te–Te–Te–(Te5)]^2+}n polycation in [Te8][NbOCl4]2. Displacement ellipsoids are drawn at the 50% probability level. Distances are in Å.
	Fig. 3. The infinite {[Te–Te–Te–(Te5)]^2+}n chain in [Te8][NbOCl4]2 compared with [Te8]2[Ta4O4Cl16], [Te8][U2Br10], [Te8][Bi4Cl14] and [Se4.85Te3.15][WOCl4]2.

(I)

Crystal data

[Te8][NbOCl4]2	Z = 2
Mr = 1522.22	F(000) = 1300
Triclinic, P1	Dx = 4.438 Mg m^−3
a = 7.8670 (16) Å	Mo Kα radiation, λ = 0.71073 Å
b = 12.049 (2) Å	Cell parameters from 1058 reflections
c = 12.481 (3) Å	θ = 3.0–60.0°
α = 80.85 (3)°	µ = 11.98 mm^−1
β = 82.17 (3)°	T = 200 K
γ = 78.84 (3)°	Needle, black
V = 1139.1 (4) Å^3	0.25 × 0.23 × 0.21 mm

Data collection

Stoe IPDS II diffractometer	4371 independent reflections
Radiation source: fine-focus sealed tube	2699 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.070
image–plate diffraction system scans	θmax = 26.4°, θmin = 1.7°
Absorption correction: numerical (X-SHAPE; Stoe & Cie, 2001)	h = −9→9
Tmin = 0.39, Tmax = 0.54	k = −15→15
8557 measured reflections	l = −15→15

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)] = 0.047	w = 1/[σ^2(Fo^2) + (0.0414P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.115	(Δ/σ)max < 0.001
S = 0.91	Δρmax = 1.87 e Å^−3
4371 reflections	Δρmin = −1.53 e Å^−3
182 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.00159 (14)

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. For single-crystal structure analysis, suitable single crystals were chosen and adhered into glass capillaries with inert oil (KEL-F). Data collection was performed at 200 K on an IPDS II image-plate diffractometer (Stoe) using graphite-monochromated Mo Kα (0.71073 Å) radiation and a low-temperature device. Data reduction was performed using the program package X-AREA (Stoe & Cie, 2001); space-group determination was carried out via XPREP (Stoe & Cie, 2001). The structure was solved by direct methods using SHELXS97 (Sheldrick, 2008). Anisotropic refinement on 4σF was carried out for all atoms by full-matrix least-squares methods using SHELXL97 (Sheldrick, 2008). A numerical absorption correction was applied and H atoms were geometrically constructed. All crystallographic illustrations were created with DIAMOND (Brandenburg, 2012). publCIF (Westrip, 2010) has been used to prepare material for publication. More details concerning the crystallographic data can be requested from the Inorganic Crystal Structure Database (ICSD) at the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen (www.fiz-karlsruhe.de) with the deposition number CSD-424139.

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
Te3	0.43168 (16)	0.42340 (10)	0.28111 (10)	0.0290 (3)
Te7	0.24771 (17)	0.12246 (10)	0.24102 (11)	0.0327 (3)
Te4	0.75713 (17)	0.34177 (11)	0.35879 (11)	0.0356 (3)
Te6	0.21770 (16)	0.26864 (11)	0.38746 (10)	0.0313 (3)
Te1	0.76503 (17)	0.15379 (10)	0.12227 (10)	0.0326 (3)
Te2	0.51624 (17)	0.35157 (11)	0.08236 (10)	0.0341 (3)
Te5	0.72432 (18)	0.12996 (10)	0.34614 (11)	0.0353 (3)
Te8	0.07161 (18)	0.24869 (11)	0.08088 (10)	0.0344 (3)
Nb1	0.4428 (2)	0.24104 (13)	0.73156 (13)	0.0230 (4)
Nb2	0.9443 (2)	0.24170 (13)	0.72627 (12)	0.0218 (4)
Cl1	0.8496 (6)	0.3614 (4)	0.8686 (4)	0.0317 (10)
Cl2	0.4310 (6)	0.0993 (4)	0.8827 (4)	0.0382 (12)
Cl3	0.9092 (6)	0.4073 (3)	0.5978 (4)	0.0289 (10)
Cl4	0.4908 (6)	0.1030 (4)	0.6088 (4)	0.0332 (10)
Cl5	0.3830 (6)	0.3893 (4)	0.5838 (4)	0.0318 (10)
Cl6	0.9606 (6)	0.1270 (4)	0.5871 (3)	0.0300 (10)
Cl7	0.3216 (6)	0.3822 (4)	0.8482 (4)	0.0313 (10)
Cl8	0.9176 (6)	0.0814 (4)	0.8615 (4)	0.0311 (10)
O1	1.1645 (16)	0.2310 (9)	0.7293 (9)	0.027 (3)
O2	0.6563 (15)	0.2508 (10)	0.7300 (9)	0.028 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Te3	0.0276 (7)	0.0274 (6)	0.0315 (7)	−0.0031 (5)	−0.0024 (6)	−0.0056 (5)
Te7	0.0333 (7)	0.0315 (6)	0.0353 (7)	−0.0066 (5)	−0.0091 (6)	−0.0052 (5)
Te4	0.0349 (8)	0.0406 (7)	0.0341 (7)	−0.0005 (6)	−0.0115 (6)	−0.0139 (6)
Te6	0.0294 (7)	0.0405 (7)	0.0262 (6)	−0.0094 (6)	−0.0030 (6)	−0.0068 (5)
Te1	0.0332 (7)	0.0370 (7)	0.0293 (7)	−0.0041 (6)	−0.0035 (6)	−0.0121 (5)
Te2	0.0367 (8)	0.0410 (7)	0.0232 (6)	−0.0059 (6)	−0.0048 (6)	−0.0001 (5)
Te5	0.0383 (8)	0.0319 (7)	0.0317 (7)	−0.0003 (6)	−0.0036 (6)	0.0005 (5)
Te8	0.0349 (7)	0.0414 (7)	0.0263 (6)	−0.0087 (6)	−0.0022 (6)	−0.0020 (5)
Nb1	0.0185 (8)	0.0279 (8)	0.0232 (8)	−0.0059 (6)	−0.0026 (7)	−0.0029 (6)
Nb2	0.0180 (8)	0.0270 (8)	0.0208 (8)	−0.0048 (6)	−0.0024 (7)	−0.0032 (6)
Cl1	0.034 (3)	0.036 (2)	0.026 (2)	−0.003 (2)	−0.004 (2)	−0.0102 (18)
Cl2	0.034 (3)	0.044 (3)	0.033 (3)	−0.007 (2)	−0.004 (2)	0.004 (2)
Cl3	0.033 (3)	0.026 (2)	0.026 (2)	−0.0040 (18)	−0.002 (2)	0.0000 (17)
Cl4	0.032 (3)	0.036 (2)	0.033 (2)	−0.004 (2)	−0.004 (2)	−0.0093 (19)
Cl5	0.036 (3)	0.034 (2)	0.025 (2)	−0.009 (2)	−0.003 (2)	−0.0016 (18)
Cl6	0.032 (3)	0.035 (2)	0.024 (2)	−0.0042 (19)	−0.003 (2)	−0.0093 (18)
Cl7	0.031 (2)	0.040 (2)	0.026 (2)	−0.010 (2)	−0.001 (2)	−0.0099 (19)
Cl8	0.036 (3)	0.032 (2)	0.026 (2)	−0.008 (2)	−0.007 (2)	−0.0008 (18)
O1	0.039 (7)	0.023 (6)	0.027 (6)	−0.022 (5)	−0.015 (6)	0.002 (5)
O2	0.020 (7)	0.043 (7)	0.021 (6)	−0.003 (6)	−0.002 (6)	−0.005 (5)

Geometric parameters (Å, º)

Te3—Te2	2.7121 (19)	Nb1—Cl2	2.339 (5)
Te3—Te4	2.8037 (18)	Nb1—Cl4	2.381 (5)
Te3—Te6	2.809 (2)	Nb1—Cl5	2.382 (4)
Te7—Te8	2.6832 (19)	Nb1—Cl7	2.388 (5)
Te7—Te6	2.6915 (19)	Nb2—O1	1.718 (12)
Te4—Te5	2.6455 (18)	Nb2—O2	2.241 (11)
Te1—Te5	2.7439 (19)	Nb2—Cl3	2.349 (4)
Te1—Te2	2.800 (2)	Nb2—Cl6	2.361 (4)
Te1—Te8^i	2.8164 (19)	Nb2—Cl8	2.376 (4)
Te8—Te1^ii	2.8164 (19)	Nb2—Cl1	2.415 (5)
Nb1—O2	1.704 (11)	O1—Nb1^i	2.221 (11)
Nb1—O1^ii	2.221 (11)
Te2—Te3—Te4	97.02 (6)	O2—Nb1—Cl7	97.6 (4)
Te2—Te3—Te6	101.47 (6)	O1^ii—Nb1—Cl7	82.7 (3)
Te4—Te3—Te6	105.06 (6)	Cl2—Nb1—Cl7	89.31 (18)
Te8—Te7—Te6	102.70 (6)	Cl4—Nb1—Cl7	165.90 (16)
Te5—Te4—Te3	90.18 (6)	Cl5—Nb1—Cl7	86.18 (16)
Te7—Te6—Te3	102.08 (6)	O1—Nb2—O2	177.3 (5)
Te5—Te1—Te2	98.46 (6)	O1—Nb2—Cl3	96.5 (4)
Te5—Te1—Te8^i	99.51 (6)	O2—Nb2—Cl3	86.0 (3)
Te2—Te1—Te8^i	100.02 (6)	O1—Nb2—Cl6	97.3 (4)
Te3—Te2—Te1	103.32 (6)	O2—Nb2—Cl6	83.7 (3)
Te4—Te5—Te1	95.31 (6)	Cl3—Nb2—Cl6	90.48 (16)
Te7—Te8—Te1^ii	99.24 (6)	O1—Nb2—Cl8	94.8 (4)
O2—Nb1—O1^ii	178.5 (5)	O2—Nb2—Cl8	82.7 (3)
O2—Nb1—Cl2	96.9 (4)	Cl3—Nb2—Cl8	168.48 (17)
O1^ii—Nb1—Cl2	84.6 (3)	Cl6—Nb2—Cl8	90.41 (16)
O2—Nb1—Cl4	96.2 (4)	O1—Nb2—Cl1	97.2 (4)
O1^ii—Nb1—Cl4	83.4 (3)	O2—Nb2—Cl1	81.8 (3)
Cl2—Nb1—Cl4	91.51 (18)	Cl3—Nb2—Cl1	88.36 (16)
O2—Nb1—Cl5	96.2 (4)	Cl6—Nb2—Cl1	165.53 (17)
O1^ii—Nb1—Cl5	82.4 (3)	Cl8—Nb2—Cl1	87.91 (16)
Cl2—Nb1—Cl5	166.65 (18)	Nb2—O1—Nb1^i	172.7 (6)
Cl4—Nb1—Cl5	89.86 (16)	Nb1—O2—Nb2	173.2 (7)

Symmetry codes: (i) x+1, y, z; (ii) x−1, y, z.