Isolation and Crystal Structure of (Hexamethylbenzene)gallium(I) Tetrachlorogallate(III), a Mono(arene) Complex of Gallium(I)
Ulf ThewaltT, Theodore Zafiropoulos*, and Hubert Schmidbaur* Anorganisch-chemisches Institut, Technische Universität München. Lichtenbergstraße 4. D-8046 Garching, Federal Republic of Germany Z. Naturforsch. 39b, 1642—1646 (1984); received July 31, 1984 Arene Complex, Gallium(I) Complex, Crystal Structure, Hexamethylbenzene Complex, Gallium(I) Tetrachlorogallate(III) Ga2Cl4 reacts with hexamethylbenzene in benzene to give (hexamethylbenzene)gallium(I)- tetrachlorogallate(III), (CH 3)6C6Ga+GaCl4_, in high yield. The complex crystallizes in the rhombohedral space group R3m with four formula units per cell. Cell constants are a = 12.449(3) Ä and a = 91.01(2)°. In the structure tetrameric clusters can be identified contain ing two crystallographically independent formula units, one having 3 m and the other three having m symmetry. In both types of (arene)Ga^ cations the Ga atoms are symmetrically positioned over the arene ring, 2.43(3) and 2.51(3) Ä, respectively, away from the ring plane. Four (arene)Ga+ cations and four GaCl 4 anions are aggregated in such a way that the Ga 1 atoms are surrounded by six or seven chlorine atoms, respectively, at distances in the range 3.16(1) to 3.67(1) A. The four hexamethylbenzene molecules form an efficient cover around the inorganic [Ga~GaCl 4“]4 framework. Between the tetrameric clusters there are no contacts of the Ga’ -Cl Tvpe.
Introduction if only distances below 3.5 Ä are considered, but of We have recently initiated a systematic investiga only two bromine atoms and two mesitylene rings [3] tion of arene complexes of main group metals, and in [(CH3)3C6H 3]2GaeGaBr4e . From the large varia have presented the results of synthetic and structural tion of the gallium-halogen distances and geomet studies on the first gallium(I) and indium(I) or- ries, it appears that the halogen coordination is large ganometallics with neutral aromatic hydrocarbon ly governed by steric effects, whereas the arene coor ligands [1—4], Leading references for previous work, dination is characterized by a strict preference for mainly on tin(II), lead(II), and uranium(III) analo arrangements at fixed distances perpendicular above gues, have been included in these earlier papers. the ring centers. Both the benzene and the 1,3,5-trimethylbenzene Ga(I) also forms mcwo(arene) complexes, how (mesitylene) complex of gallium(I) tetrahalogal- ever. The first example of such a complex detected is lates(III) described in parts 1 [1] and 3 [3] of this [(CH 3)6C6]Ga®GaBr4e . The metal is again exactly series were found to contain b/s(arene)gallium(I) ring-centered above the hexamethylbenzene cations with the two hydrocarbon rings at interplane molecule. A distorted tetragonal monopyramide of angles of 56 and 43.5°, respectively. The gallium(I) five bromine atoms forms a halogen cap for the re centers are located above the two ring centers, which maining part of the Ga(I) coordination sphere [2]. are either equidistant [3] or non-equally displaced The only structurally characterized indium arene from the metal [1]. These fr/s(arene)gallium(I) complex [4], bis(mesitylene)indium(I) tetrabromoin- moieties are linked up by the tetrahalogallate(III) date(III), is again a chain coordination polymer, but tetrahedra to form dimers [ 1] or infinite chains [ 3] of differs from the gallium(I) analogue [3] by the pre cations and anions. The coordination sphere of the sence of three equidistant Br atoms at the (mesityle- gallium(I) centers is composed of three chlorine ne)2In unit, instead of the two chlorine atoms at atoms and two benzene rings in (C 6H 6)2Ga~GaCl4~, (mesitylene):Ga moieties. As part 5 of the continuing program we now report on the synthesis and single crystal X-ray diffraction Visiting professor from the University of Ulm. Ulm. analysis of (hexamethylbenzene)gallium(I) tetra- West Germany; chlorogallate(III). This provides a unique chance to A. v. Humboldt Fellow 1982-1983. University of Patras. Patras. Greece; obtain further insight into the basic features of main Reprint requests to Prof. Dr. H. Schmidbaur. group metal-arene interaction, due to the complexity 0340-5087/84/1200- 1642/S 01.00/0 of the structure. U. Thewalt et al. ■ Mono(arene) Complex of Gallium(I) 1643
Experimental Section sity I = (S — B//3)cl> and a(I) = (S+B//3 2)12d> (scan General Data counts, S; total background counts, B; time ratio of total background to scan, ß). The set of 1057 reflec All experiments were carried out under an atmo tions with I>2ct(I) was used in the subsequent calcu sphere of pure and dry nitrogen. Glassware was lations. Since neither the correct chemical formula dried at 140 °C and filled with nitrogen. Hexamethyl- nor the space group was known at the beginning benzene and toluene were dried over sodium/ (there were no systematic extinctions and therefore, acetophenone, distilled under nitrogen and kept over a priori, several rhombohedral space groups were molecular sieves (4 Ä). Gallium metal was a gift of possible candidates), the solution of the structure Siemens AG, Erlangen (99.999% pure). Ga 2Cl4 was was attempted in space group R3 using direct prepared as described in ref. [ 1], methods [5], In one of the resulting E maps it was possible to identify the largest maxima to be gallium (Hexamethylbenzene)gallium (I) tetrachlorgallate(III) atoms and some weaker maxima to be chlorine atoms, and it became appearent that the arrangement had A sample of Ga 2Cl4 is transferred into a twonecked crystallographic 3 m symmetry. The usual combina flask under nitrogen (2.81 g, 1.00 mmol), covered tion of Fc and Fourier calculations yielded the re with a mixture of 50 ml of toluene and 25 ml of hexa- maining Cl atoms and the hexamethylbenzene methylbenzene (excess) and heated to 80—90 °C un groups. Since there were no point symmetry ele til the solid has dissolved completely. Slow cooling to ments in addition to 3 and m the space group is ambient temperature causes the precipitation of R3m. The Ga and Cl atoms were refined with large colourless transparent crystals. This product is anisotropic and the C atoms with isotropic tempera collected on a glass filter disk attached to the reac ture factors giving R and /?W(F) values of 0.086 and tion vessel, washed with 5 ml of cold toluene and 0.093; w = 0.87/(a2(F)+0.007F2). (An attempt to re dried by a 5 min purging with dry nitrogen (yield fine all atoms with anisotropic temperature factors 2.92 g, 65.9%), m.p. 168° (dec.). gave positive non-definite temperature ellipsoids for C 12H 18G a2Cl4 (443.52) two of the carbon atoms). Scattering factors for neu Calcd C 32.50 H 4.10, tral atoms were taken from ref. [ 6]. Correction for Found C 32.15 H 4.02. Zlf' and Zlf" were applied [7]. Final positional para The apparatus should not be evacuated in order to meters are given in Table I. Hydrogen atoms could prevent vaporization of the arene. Even under only slightly reduced pressure the crystals easily become Table I. Positional parameters for the atoms of X-ray amorphous. M e6C6G a+GaCl4“. Atom X y z X-ray crystallographic study A crystal fragment, approximately Gal 0.3584(3) -0.0338(3) -0.0338(3) C ll 0.4656(7) -0.1301(5) -0.1301(5) 0.2 x 0 .2 x 0.4 mm, was cut from a larger crystal and Cl 2 0.4470(7) 0.0755(5) 0.0755(5) mounted under argon at dry ice temperature in a Cl 3 0.2519(6) 0.0575(5) -0.1384(6) Lindemann glass capillary. All X-ray measurements Ga2 0.2830(3) 0.2830(3) 0.2830(3) were made on a Syntex P2! diffractometer using Cl 4 0.3838(4) 0.3838(4) 0.1835(6) graphite-monochromatized MoKa radiation (A = Cl 5 0.1801(6) 0.1801(6) 0.1801(6) -0.0420(3) 0.71069 Ä) at —40±5 °C. The lattice constants (de Ga3 0.2965(3) 0.2965(3) C l 0.3344(20) 0.3344(20) -0.2613(27) termined from measurements for 15 reflections) at this C2 0.2955(16) 0.4336(16) -0.2250(16) temperature for the rhombohedral crystals are: a = C3 0.3561(17) 0.4954(18) -0.1458(17) 12.449(3) Ä and a = 91.01(2)°. dcalcd= 1.527gcm_3for C4 0.4551(19) 0.4551(19) -0.1098(25) Z = 4 (referred to the formula Me 6C6Ga*GaCl4~). C l' 0.2706(24) 0.2706(24) -0.3474(32) C2' 0.1943(28) 0.4752(27) -0.2706(27) Intensity data: co scans; scan rate d> between 1.2 C3' 0.3145(27) 0.5978(27) -0.0957(24) and 29.3° min-1, depending on the intensity of a pre C4' 0.5245(22) 0.5245(22) -0.0319(31) liminary scan; scan width, 0.9°; time spent for G a4a 0.0140 0.0140 0.0140 measuring background intensities at each end of the C5 -0.1463(16) -0.1463(16) -0.0128(21) scan interval was half of scan time; a total of 1194 C 6 -0.1891(20) -0.0541(14) -0.0541(14) -0.1949(19) -0.1949(19) 0.0861(28) independent reflections was obtained ( € > l, C5' C 6' -0.2910(27) -0.0086(20) -0.0086(20) { > k > 0, h
Results and Discussion The rhombohedral unit cell contains four Me6C6Ga+GaCl4~ formula units (Z = 4). One of them (the cation containing Ga4, C5. C 6 , C 5', C 6 ' and the anion containing G a2, C14, and C15 in Fig. 1) is located on the [111] axis and has crystallo- graphic 3 m symmetry. The remaining three formula units are crystallographically equivalent. One set of these equivalent cations and anions for example are represented by Ga 3 and Ga 1 in Fig. 1. The (arene)Ga and GaCl4 moieties are situated on mirror planes and thus have crystallographic m symmetry. Only few Fig. 2. Projection of the molecular structure along the atoms adopt general positions (Cl3, C2, C3, C 2\ [111] axis (C3 axis) through Ga4 and Ga2. C15 aso lies on C3'; compare Table I). this axis. The total set of four Me 6C6Ga~ cations and four GaCl4~ anions is held together by a series of close Ga'-'-Cl contacts. The four hexamethylbenzene rings Bond distances and angles for the individual an form an efficient cover around the inorganic ions and cations as well as for the G a'—Cl contacts [Ga~GaCl4]4 framework (Fig. 2). There are no close are listed in Table II. The Ga 1 atom of the crystallo- Ga---Cl contacts between neighboring “clusters” and the contents of a unit is to be regarded as a tetra- meric species of the composition (C 6Me6)4G a8Cl16. Table II. Distances (Ä) and angles (deg) for (CH 3)6C6Ga+GaCl4 .
Distances Distances Ga 1 —Cl 1 2.170(9) Ga3---C12 3.667(5) C6 C5C6' C5' — Cl 2 2.179(8) •••C13 3.224(7) — C13 2.189(6) •••C14 3.160(8) •••C15 3.472(4) G a2 —C14 2.177(6) G a 4 -C 1 3 3.583(7) —C15 2.178(12) •••C15 3.518(13) G a3 —C l 2.83(3) —C 2 2.87(2) —C3 2.90(2) Angles“ —C4 2.91(3) G a4—C5 2.81(3) Cl 1 —Ga 1 —C12 111.7(3) —C 6 2.77(3) — C13 110.0(2) C 1 -C 2 1.41(3) C12 —Ga 1 —C13 109.8(2) C 2 -C 3 1.43(3) C13 —Ga 1 —C13u 105.3(3) C 3 -C 4 1.41(3) C14—Ga2 —C15 109.4(2) C 5 -C 6 1.38(2) —C14u 109.6(3) c i - c r 1.53(5) C 2 - C l- C 2 w 121.6(26) C 2 -C 2 ' 1.48(4) C1-C2-C3 119.6(21) C 3 -C 3 ' 1.51(4) C2-C3-C4 118.0(21) C 4 -C 4 ' 1.53(5) C 3 - C 4 - C 3 w 123.0(25) C 5 -C 5 ' 1.51(4) C 6 - C 5 - C 6 w 120.9(25) C 6 -C 6 ' 1.51(4) C5-C6-C5u 118.7(24)
Fig. 1. Projection of the tetrameric unit The letters u and w indicate symmetry operations, u: x, z, y, [C6Me6Ga*GaCl4~]4 onto the [111] axis of the crystal. w: v, .v, z. U. Thewalt et al. • Mono(arene) Complex of Gallium(I) 1645 graphically unique Me 6C6Ga+ cation, Ga4, is exactly arene. In addition, Ga3 is surrounded by five nearly centered (by space group symmetry) over the arene symmetrically displaced chlorine atoms, whereas ring and the Ga 1 atoms of the remaining three equi Ga4 has an additional set of six ligands, which form a valent cations, Ga3, are very nearly centered over regular hexagon by symmetry. their individual arene rings. The line joining Ga3 A comparable arrangement of halogens, albeit with the ring center and the normal to the ring least with four nearly symmetrically disposed Br atoms squares plane form an angle of only 1.9°. The Ga- plus a trans Br atom, has been found in the solid ring center distances of 2.51(3) Ä for Ga3 and state structure of Me 6C6Ga+GaBr4~ [2], In the two 2.43(3) Ä for Ga4 agree well with the value of analogous compounds (C 6Me6)G a+GaX4~ with X = 2.52(1) Ä in Me6C6G a*GaBr4~ [2]. Cl, Br the metal coordination sphere of the C 6Me6Ga~ The arrangement of Cl atoms around the Ga 1 units is thus completed by either a tetragonal, penta atoms is most easily demonstrated through projec gonal, or hexagonal monopyramidal cap of halogen tions onto the arene planes, as in Figs. 3 and 4. Both atoms. The existence of these three different coordi Ga atoms have one Cl ligand trans to the respective nation patterns for such closely related species indi cates that the arrangement of halogens in these com pounds around the Ga 1 centers is governed largely by m\ o packing effects originating in the relative size of the halogen atoms. The ring-centered bonding between the arene and the Ga(I) cations is the only constant and recurring feature of these novel subvalent main group element complexes. This interaction is clearly strong enough to compensate for the loss of lattice energy associ ated with the dissolution of cristalline Ga+GaBr4_ in the hydrocarbon. In fact, the tetrameric unit of the title compound may be referred to as part of the Ga+GaCl4~ crystal extracted by stoichiometric 1:1 Ga-arene complexation. In anhydrous GaTGaCl4” the Ga+ cations are sur Fig. 3. Projection of the coordination sphere of Ga4 onto the corresponding hexamethylbenzene plane. A hexagonal rounded by eight chlorine atoms in the form of a monopyramid of 7 chlorine atoms is staggered relative to distorted dodecahedron [10]. This coordination the hydrocarbon. number is at least partly retained in the hexamethyl benzene complex, where 7 or 6 halogen atoms re main in the coordination sphere of Ga4 or Ga3, re spectively.
I 0 This work was supported by Fonds der Chemi C(4 schen Industrie, Frankfurt/M. and by Siemens AG, Erlangen. The Bavarian Academy of Sciences is m thanked for access to the computing facilities, and Mr. J. Riede for the X-ray data collection. T.Z. is Fig. 4. Projection of the coordination sphere of Ga3 onto grateful for an A. v. Humboldt Fellowship and U.T. the corresponding hexamethylbenzene plane. Six chlorine thanks Prof. E. O. Fischer for having been invited to atoms form a distorted pentagonal monopyramid. Technische Universität München. 1646 U. Thewalt et al. ■ Mono(arene) Complex of Gallium(I)
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