2 dioxane and [{Li2(dioxane)3Cl}n][TaCl6]n

www.elsevier.nl/locate/ica Inorganica Chimica Acta 298 (2000) 9 – 15

Polymeric structures containing self-assembled Lidioxane networks; syntheses and crystal structures of [{Li(dioxane)2.5TaCl4S}n ]·n/2 dioxane and [{Li2(dioxane)3Cl}n ][TaCl6]n Sven Hasche a, Christian Mock a, Jens Otto a, Florian Schweppe a, Kristin Kirschbaum b, Bernt Krebs a, A. Alan Pinkerton b,* a

Anorganisch-Chemisches Institut der Westfa¨lischen Wilhelms Uni6ersita¨t, Wilhelm-Klemm-Straße 8, 48149 Mu¨nster, Germany b Department of Chemistry, The Uni6ersity of Toledo, Toledo, OH 43606 -3390, USA Received 23 April 1999; accepted 14 July 1999 Dedicated to Professor Peter Bo¨ttcher on the occasion of his 60th birthday

Abstract The preparation and X-ray structure analyses of the compounds [{Li(dioxane)2.5TaCl4S}n ]·n/2 dioxane (1) and [{Li2(dioxane)3Cl}n ][TaCl6]n (2) are described. The title compounds were isolated from a refluxed solution of TaCl5 and Li2S in dioxane/CH3CN. The compounds both crystallize in the monoclinic space group C2/c and contain a network of dioxane bridged Li+ cations. In 1, the polymeric network is further extended by TaCl4S units. The sixth coordination site of the central metal in these TaCl4S units is occupied by an O-atom of one of the Li coordinating dioxane molecules. In contrast, the [TaCl6]− complex anion in 2 is isolated within a three-dimensional LiCldioxane network. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Crystal structures; Dioxane bridged Li+ cations; TaCl4S units; [TeCl6]− complex anion

1. Introduction In 1962 Fairbrother and Nixon [1] published the first paper on sulfur containing complexes of niobium and tantalum. Even though the interest in thiolate chemistry of the neighbouring elements in the periodic table increased, only a few compounds containing niobium or tantalum were reported before 1980 [2]. Since this time it has been shown that there is a rich sulfur chemistry of niobium and tantalum [3]. While the earlier studies in this field mainly concentrated on lower oxidation states, during the last 10 years the interest in the oxidation state + 5 has increased and now dominates the literature [4].

* Corresponding author. Tel.: + 1-419-530 2109; fax: + 1-419-530 4033. E-mail address: [email protected] (A.A. Pinkerton)

For synthetic purposes, a convenient starting point in niobium chemistry is the [NbCl4S]− anion with a fivecoordinate central Nb atom [5]. So far, no analogous tantalum complex has been structurally characterized. While attempting to prepare such a derivative using Li2S as the source of sulfide, we have isolated two new tantalum containing compounds which are characterized by novel frameworks based on 1,4-dioxane bridged Li+ cations. Their preparation and structural characterization are described herein.

2. Experimental All reactions were carried out under argon in an inert-atmosphere glove box. All solvents were dried and distilled by standard procedures and stored over molecular sieves. The tantalum chloride was sublimed before use.

0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 9 9 ) 0 0 3 8 0 - 1

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TaCl5 (360 mg, 1 mmol) was dissolved in 5 ml 1,4-dioxane. Li2S (46 mg, 1 mmol) was dissolved in 2 ml CH3CN. Both solutions were combined and refluxed for 2 h. The resulting mixture was dark brown. A small amount of an unidentified black precipitate (B 5 mg) was removed and the reddish brown solution slowly evaporated. After several days, pale yellow plates of 1 and colorless prisms of 2 were isolated.

3. Crystal data Preliminary examination and data collection were carried out with a Siemens SMART platform diffractometer. Intensity data were collected using 0.30° omega scans at three different phi settings corresponding to a nominal hemisphere of data. The intensities were corrected for absorption and decay (SADABS [6]). The structures were solved by Patterson syntheses (SHELXS-86 [7]). One molecule of uncoordinated solvent in 1, disordered over two sites, was included in the refinement with isotropic thermal parameters. All other non hydrogen atoms were refined with anisotropic thermal parameters by full-matrix least-squares on F 2 using all unique data (SHELXL-93 [8]). The hydrogen atoms Table 1 Summary of crystal data, structure solution and refinement

Empirical formula Formula weight (g mol−1) Crystal system a (A, ) b (A, ) c (A, ) b (°) V (A, 3) Space group Z Dcalc (g cm−3) m(Mo Ka) (mm−1) Radiation l (A, ) Temperature (K) u (max) (°) Total reflections Unique reflections R(int) Observed reflections (I\2s(I)) Solution Refinement [8] No. variables R1(F), observed data wR2(F 2), all data Goodness of fit Shift/e.s.d.max DFmax (e A, −3) DFmin (e A, −3)

1

2

C12H24LiCl4SO6Ta 626.06 monoclinic 20.6761(4) 9.5850(1) 21.8099(4) 95.553(1) 4302.01(12) C2/c 8 1.933 5.726 Mo Ka, 0.71073 170(1) 28.27 16016 5236 0.0485 4329

C12H24Li2Cl7O6Ta 707.29 monoclinic 15.9453(4) 17.4202(4) 11.0792(3) 123.926(1) 2553.56(11) C2/c 4 1.840 5.059 Mo Ka, 0.71073 150(1) 28.29 8887 3163 0.0404 2820

Patterson [7] F2 223 0.0425 0.1131 1.068 B0.001 1.75 −2.49

Patterson [7] F2 146 0.0286 0.0664 1.019 B0.001 1.17 −1.46

were included with idealized geometry. No hydrogen atoms were added to the non-bonded disordered dioxane ring. Crystal data, structure solution and refinement are summarized in Table 1.

4. Results and discussion The synthesis of these two products from a reaction of TaCl5 and S2 − includes a chloride transfer from one tantalum center to another. The lack of a chloride transfer in pure tantalum pentachloride [9], as well as previous observations of chloride transfer in the presence of sulfur containing ligands [10], allows us to suggest a mechanism for the ligand exchange in the tantalum pentachloride –dioxane adduct: TaCl5 + 1,4-dioxane“ TaCl5·dioxane [11]

(1)

TaCl5·dioxane+ S2 − “ [TaCl4S(dioxane)]− + Cl −

(2)

TaCl5·dioxane+ Cl “ [TaCl6] + 1,4-dioxane

(3)

−

−

The two anionic complexes [TaCl4S·dioxane]− and [TaCl6]− were isolated either bound via a dioxane link to, or intercalated within, a self-assembled polymeric Li–dioxane network. The crystals of both compounds are air sensitive and show immediate decomposition with traces of water. Compound 1 (Fig. 1) crystallizes as pale yellow plates in space group C2/c. Dioxane molecules link the Li+ cations into layers extending parallel to the ab plane, each lithium ion being tetrahedrally coordinated. The lithium cations form a puckered hexagonal net where each edge is a dioxane bridge (Fig. 2). The Li–O distances vary from 1.888(12) to 1.960(10) A, and the OLiO angles lie between 101.3(5) and 115.0(6)°. The average bond lengths and bond angles are in the expected range for dioxane molecules in the chair conformation. Perpendicular to these cation layers are [TaCl4S]− anions bonded to the layers via the fourth dioxane ring, the ether oxygen trans to sulfur completing the pseudo-octahedral coordination sphere of tantalum. Van der Waals intermolecular forces between S atoms (3.561 A, ) in alternate layers connect them in the third dimension thus producing two interpenetrating lattices (Fig. 3). There is enough space between the tantalum moieties of adjacent layers to incorporate an additional non-bonded dioxane molecule. In the pseudo-octahedral tantalum moiety, the distance between the tantalum and the sulfur atom (2.1640(15) A, ) is short in agreement with the multiple bond character. This short bond causes the four chlorine atoms to be repelled resulting in an enlargement of the ClTaS angles to an average of 99.43°, while the ClTaO angles average to 80.58°. Crystallographically determined structures containing a tantalum sulfur double bond are rare [12–17] and the only comparable

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Fig. 1. The structure of 1 showing the atom labeling and displacement ellipsoids drawn at 50% probability level.

complex with one central six-coordinated tantalum atom, [TaCl3S(PhSC2H4SPh)], reveals a slightly longer tantalum sulfur bond of 2.204(5) A, [18]. Although several structures containing a terminal sulfide have been published in the related niobium chemistry [5,12,16,17,19– 29], only three contain an octahedrally coordinated central atom with unambiguously determined niobium sulfur bond lengths. In comparison to 1, the dinuclear [{Nb(Cl)3S(PPh)3}2] [30] contains slightly stronger metal sulfur bonds as indicated by an averaged niobium sulfur distance of 2.121 A, , while the mononuclear [NbS(SC2H4S)(SC2H4SC2H4S)]− [31] shows a weaker niobium sulfur double bond of 2.192(3) A, in trans position to the weaker thioether niobium bond. Of particular interest are the isometric cage compounds [M6S17]4 − (M =Nb, Ta) [17] with MS bond lengths for the five octahedrally coordinated metal atoms of 2.177 A, (av.), which again are trans to a very long MS bond of 2.94 A, (av.). Surprisingly few structural studies of the coordination of ether oxygen to tantalum(V) have been carried out, single crystal studies of complexes containing an octahedrally coordinated central atom being limited to diethyl ether and THF coordination [32 – 36] and one

example of a more complex ether, tetraethyleneglycolate, coordinating the central tantalum(V) cation [37]. While these complexes contain tantalum oxygen distances between 2.151(5) [34] and 2.379(4) A, [32], the tantalumdioxane oxygen bond in 1 is 2.479(4) A, , the longest reported so far. In agreement with the above discussed complexes [TaCl3S(PhSC2H4SPh)] [18], [NbS(SC2H4S)(SC2H4SC2H4S)]− [31] and [M6S17]4 − (M=Nb, Ta) [17], this long bond is located trans to the metal sulfur double bond. The average TaCl bond length in the six-coordinate Ta(Cl)4S(dioxane) unit in 1 (2.383 A, ) lies within the broad range of tantalum chlorine distances in related compounds, e.g. 2.241(6) [18] and 2.553(2) A, [38]. Bond distances and angles for 1 are summarized in Table 2. Compound 2 crystallizes in space group C2/c with four of the monomeric formula units in the unit cell. The solid state structure of 2 consists of discrete [TaCl6]− octahedra and a three-dimensional cationic LiCldioxane network (Fig. 4). Similar to 1, Li–dioxane layers extend parallel to the bc plane but, in contrast to 1, they are connected into a three-dimensional network through LiClLi bonds perpendicular to

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S. Hasche et al. / Inorganica Chimica Acta 298 (2000) 9–15

Fig. 2. Part of a Lidioxane layer in 1 parallel to the ab plane.

Fig. 3. Plot of 1 showing the two interpenetrating lattices. The dioxane molecules have been replaced by solid lines to simplify the drawing and to accentuate the chair conformation of the Li6 rings in the puckered layers.

S. Hasche et al. / Inorganica Chimica Acta 298 (2000) 9–15 Table 2 Selected geometric parameters for 1 (A, , °) Ta(1)S(1) Ta(1)Cl(1) Ta(1)Cl(2) Ta(1)Cl(3) Ta(1)Cl(4) Ta(1)O(1)

2.1640(15) 2.3739(16) 2.3842(13) 2.3903(15) 2.3850(15) 2.479(4)

Li(1)O(2) Li(1)O(3) Li(1)O(4) Li(1)O(5)

1.916(12) 1.888(12) 1.934(10) 1.960(10)

S(1)Ta(1)O(1) Cl(1)Ta(1)S(1) Cl(1)Ta(1)O(1) Cl(1)Ta(1)Cl(2) Cl(1)Ta(1)Cl(3) Cl(1)Ta(1)Cl(4) Cl(2)Ta(1)S(1) Cl(2)Ta(1)O(1) Cl(2)Ta(1)Cl(3) Cl(2)Ta(1)Cl(4) Cl(3)Ta(1)S(1) Cl(3)Ta(1)O(1) Cl(3)Ta(1)Cl(4) Cl(4)Ta(1)S(1) Cl(4)Ta(1)O(1)

178.58(10) 99.95(6) 79.80(11) 88.90(6) 160.47(7) 90.62(6) 99.76(6) 81.64(10) 86.32(5) 161.55(5) 99.52(6) 80.77(11) 88.00(5) 98.48(6) 80.13(10)

Ta(1)O(1)C(1) Ta(1)O(1)C(4) C(2)O(2)Li(1) C(3)O(2)Li(1) C(5)O(3)Li(1) C(6)O(3)Li(1) C(7)O(4)Li(1) C(8)O(4)Li(1) C(9)O(5)Li(1) C(10)O(5)Li(1) O(2)Li(1)O(3) O(2)Li(1)O(4) O(2)Li(1)O(5) O(3)Li(1)O(4) O(3)Li(1)O(5) O(4)Li(1)O(5)

124.2(4) 125.4(3) 123.2(5) 126.2(5) 125.9(4) 123.6(5) 124.4(5) 124.2(5) 124.8(5) 124.5(5) 107.6(5) 111.3(5) 109.7(6) 115.0(6) 111.9(5) 101.3(5)

that plane. These links form two channels parallel to c, one being significantly larger than the other. Each of the larger channels contains a zigzag chain of [TaCl6]− anions (Fig. 5) which are disordered over crystallographic two-fold axes in order to avoid exact alignment of the TaClClTa vector. The average TaCl distance

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in the anion is 2.341 A, with ClTaCl angles of 86.33(18) to 94.1(2)° and 174.3(2) to 179.31(4)° — similar to other examples of structures containing the [TaCl6]− anion in the literature [37,39–53]. Three oxygen atoms of 1,4-dioxane molecules and one chlorine atom surround each lithium ion in a distorted tetrahedral environment with enlarged angles at the chlorine atoms. The average ClLiO angle is 113.6°, while the OLiO angles are about 105.0°. The distance between Li and Cl is 2.274(6) A, and the LiO bonds have a length between 1.930(6) and 1.947(7) A, . The LiClLi angle at 172.3(3)° is close to linear. The bond lengths and angles of the dioxane molecules are in the expected range. A summary of important bond lengths and angles is given in Table 3. A Cambridge Structural Data Base search [2] for crystal structures containing 1,4-dioxane coordinated Li+ cations revealed several different structural elements. Solely monodentate coordination of 1,4-dioxane to Li+ can be found in neutral [54,55] and ionic [56] species. Evans et al. [57] and Mu¨ller and Krausse [58] synthesized structures in which the cations contain a single dioxane ring connecting two lithium centers, respectively. Neutral dimers containing Li+ cations coordinated by monodentate and bridging dioxane molecules have been reported by Cramer et al. [59] and Uhl et al. [60]. In contrast to this, formation of a neutral polymeric network has sometimes been observed [61–65]. These networks include lithium–dioxane chains connecting anionic centers.

Fig. 4. The structure of 2 showing the atom labeling, the bridging of lithium cations by dioxane molecules, linking of layers by LiClLi bonds and the lack of interaction with the [TaCl6]− moiety. Displacement ellipsoids are drawn at the 50% probability level.

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Fig. 5. View showing the channels containing [TaCl6]− ions. The dioxane molecules have been replaced with solid lines for clarity and to accentuate the puckering of the Li6 rings in the cationic planes.

Table 3 Selected geometric parameters for 2 (A, , °) a Ta(1)Cl(1) (2x) Ta(1)Cl(2) Ta(1)Cl(3) Ta(1)Cl(2A) Ta(1)Cl(3A)

2.3442(8) 2.292(7) 2.303(4) 2.355(6) 2.407(4)

Cl(2)Ta(1)Cl(1) 89.9(2) Cl(3)Ta(1)Cl(1) 90.65(9) Cl(1) c1Ta(1)Cl(1) 179.31(4) Cl(1)Ta(1)Cl(2A)c1 87.80(18) Cl(1)Ta(1)Cl(3A)c1 92.44(11) Cl(2)Ta(1)Cl(3) 94.1(2) Cl(2)Ta(1)Cl(1)c 1 89.7(2) Cl(2)Ta(1)Cl(2A)c1 91.42(17) Cl(2)Ta(1)Cl(3A)c1 176.7(2) Cl(3)Ta(1)Cl(1)c1 89.92(10) Cl(3)Ta(1)Cl(2A)c 1 174.3(2) Cl(3)Ta(1)Cl(3A)c1 88.25(19) Cl(1)c(1)Ta(1)Cl(2A)c1 91.67(18) Cl(1)c(1)Ta(1)Cl(3A)c1 87.96(11) Cl(2A)c1Ta(1)Cl(3A)c1 86.33(18) a

Li(1)Cl(4) Li(1)O(1)c 2 Li(1)O(2) Li(1)O(3)

2.274(6) 1.930(6) 1.943(6) 1.947(7)

O(1)c2Li(1)O(2) O(1)c2Li(1)O(3) O(2)Li(1)O(3) O(1)c2Li(1)Cl(4) O(2)Li(1)Cl(4) O(3)Li(1)Cl(4) Li(1)c2Cl(4)Li(1)

101.9(3) 107.0(3) 106.1(3) 119.0(3) 111.0(3) 110.9(3) 172.3(3)

Symmetry operations: c1: 1−x, y, 1.5−z; c 2: x, −y, z+0.5.

However, so far only one structure is known, in which a polymeric cation is built up by lithium–dioxane layers that intercalate discrete anions: Taube et al. [66] describe a structure in which tetra(allyl) lanthanum anions are located in a polymeric Li–dioxane cationic matrix. The Li containing layers have the same puckered ring structure as observed for 2 with the lithium coordination completed by interactions with a carbon atom from the allyl residue of the complex anion. The structures reported here thus have no close analogs in the literature, however, they suggest that it should be possible to rationally construct framework structures based on lithium–dioxane bridges in much the same way as hydrogen bonding schemes are currently employed. Acknowledgements The authors thank the College of Arts and Science for generous support of the X-ray facility, the Office of Naval Research (grant number N00014-95-1-1252)

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and the Ohio Board of Regents for funding for the diffractometer and NATO for partial funding of this project.

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