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Synthesis and Structure of Benzyltriethylammonium Trichlorogermanate(II)Gerald L. Wegner, Alexander Jockisch. Hubert Schmidbaur*Anorganisch-chemisches Institut der Technischen Universität München,Lichtenbergstrasse 4, D-85747 Garching, Germany
Z. Naturforsch. 53 b, 43CM33 (1998); received January 30, 1998
Germanium Dichloride, Trichlorogermanate(II)The reaction of equimolar quantities of GeCh • dioxane with [BzEt3N]+ C P in tetrahydro-
naphthaline gives high yields of [BzEt3N]+ [GeCh]~. The asymmetric unit of the monoclinic single crystals (from CH 2CI2 , space group P2i/c, Z = 8) are comprising two pairs of crystallographically independent cations and anions, each with very similar molecular dimensions. The isolated [GeCb]- anions have a trigonal pyramidal structure with narrow Cl-Ge-Cl angles in the range from 93.41(5) to 98.27(5)° and Ge-Cl distances between 2.293(2) and 2.305(2) A. This structure is thus very similar to that of the isoelectronic AsCb molecule and of the [SeCl3 ]+ cation.
The addition of chloride anions to dichloroger- mane with formation of trichlorogermanate(II) anions is an established process [1 - 3], which has attracted considerable interest as an early example of the addition or insertion of a dichlorocarbene analogue ACI2 (A = C, Si, Ge, Sn, Pb). The resulting anions have an isoelectronic relation with neutral molecules EX3 (E = N, P, As, Sb, Bi) and are hence expected to show similar electronic and molecular structures [4 -7 ].
Salts containing the [GeCl^]- anion have also received special attention because of their structural diversity including phases with a perovskite-type anion sublattice and with piezo-/(anti)ferro-electric properties [1 - 3], For the salt Cs+ [GeCl^]- it has successfully been demonstrated that the anion can be employed as a nucleophile for the preparation of organogermanium compounds RGeCl^ [8].
In the course of a study aiming at the development of improved methods for the synthesis of compounds with Si-Ge linkages [9] we became interested in new [G eC ^]- reagents with bulky and “innocent” cations, which were expected to allow better nucleophilic properties of the anions.
Results
For the preparation of the title compound, benzyltriethylammonium chloride was reacted with equimolar quantities of the dioxane complex of
* Reprint requests to Prof. Dr. H. Schmidbaur.
germanium dichloride in tetrahydronaphthaline at 70°C. Removing dioxane in a vacuum at room temperature and cooling to -20°C gave a colourless, analytically pure product in almost 97% yield. It should be noted that preparative attempts using volatile solvents, like benzene or toluene, were not successful, since simultaneous removing of the solvent and dioxane in vacuo does not shift the equilibrium to the right completely.
GeCl2 • C4H60 2 + [BzEt3N]Cl ^[BzEt3N][GeCl2] + C4H60 2 (1)
Single crystals of the product could be grown from dichloromethane solutions. These crystals are monoclinic, space group P2]/c, with Z = 8 formula units in the unit cell. The asymmetric unit contains two crystallographically independent cations and anions. Contrary to the situation encountered in all previous studies of trichlorogermanate(II) salts, the anions of the title compound are not associated into larger aggregates.
The individual, isolated [GeCl^]- anions have no crystallographically imposed symmetry. The structures are best described as slightly distorted trigonal pyramids with Ge-Cl bond lengths and Cl-Ge-Cl angles in rather narrow ranges as given in the caption to Fig. 1.
The constitution of the [GeCl^]- anions is very similar to that documented for the isoelectronic (isosteric) species AsCb (gas and crystalline phase) and [SeCl3]+ (in its salts). All three analogues have approximate C3V symmetry with Cl-E-Cl angles
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G. L. Wegner et al. • Synthesis and Structure o f Benzyltriethylammonium Trichlorogermanate(II)______________ 431
Table I. Comparision of structural parameters of [BzEt3N][GeCF [SeCl3 ][AsF6] [12],
i] with AsCl3 (g) [10], AsCl3 (s) [11], and
Compound [BzEt3N][GeCl3] A sC13 (g) AsCl3 ( s ) [SeCl3][AsF6]
Cl-M-Cl [°1 [al M-Cl [Ä] [a1Sum of covalent radii [A] [13]
96.06(5)2.300(2)2.11
98.41(50)2.161(4)2.2
97.71(4)2.17(5)2.2
99.77(10)2.096(2)2.16
|a) average values.
Ge1
Fig. 1. Molecular structure of [GeCb]- (ORTEP drawing with 50% probability ellipsoids, only one of the two crystallographically independent anions is shown). Selected bond lengths [A] and angles [°] (second anion in brackets): G el-C ll 2.3012(13) [2.293(2)], Gel-C12 2.2980(14) [2.305(2)], Gel-C13 2.304(2) [2.2996(13)]; Cl 1 -Ge 1-C12 96.57(5) [93.41 (5)], Cl 1 -Ge 1-C13 96.36(5) [98.27(5)], C12-Gel-C13 95.29(5) [96.43(5)].
only slightly larger than 90°. The bond distances vary systematically as expected on the basis of the covalent atomic radii and the electronegativity of the elements and their electrical charge (Table I). Previous data for other trichlorogermanates(II) were not suitable for such a comparison, since extensive aggregation of the [GeC^]- anions in these lattices gives rise to a different state of bonding in the resulting (perovskite-type) framework.
The two cations are almost superimposible and show no anomalies in their dimensions and conformation (Fig. 2).
It is important to note that the germanium atoms of the anions show no tendency to approach the phenyl group of the cation in order to establish a discrete contact indicative of 7r-complex formation. By contrast, AsC13 was found to form arene complexes quite readily with a variety of aromatic hydrocarbons [14 - 15], and germanium(II) tetrachloromet- allates are also known to bind to benzene and its homologues. The germanium atom in [GeCh]- is thus the least electrophilic center of the series of
Fig. 2. Molecular structure of [BzEt3N]+ (ORTEP drawing with 50% probability ellipsoids, only one of the two crystallographically independent cations is shown, hydrogen atoms are omitted for clarity). Selected bond lengths [A] and angles [°] (second cation in brackets): N l-C l 1.516(4) [1.520(4)], N1-C3 1.524(4) [1.522(5)], N1-C5 1.521(4) [1.522(4)], N1-C7 1.535(5) [1.538(4)], C1-C2 1.512(5) [1.506(6)], C3-C4 1.504(5) [1.505(6)], C5-C6 1.510(6) [1.505(6)], C7-C8 1.508(5) [1.505(5)]; C l-N l- C3 106.7(3) [106.9(3)], C1-N1-C5 110.9(3) [110.9(3)], C1-N1-C7 111.7(3) [110.7(3)], C3-N1-C5 111.1(3) [110.7(3)], C3-N1-C7 110.7(3) [111.3(3)], C5-N1-C7 105.9(3) [106.3(3)].
isoelectronic species. By the same token, it is the strongest nucleophile as shown in a series of reactions with appropriate substrates [8],
Experimental SectionGeneral
The experiments were carried out under dry and pure nitrogen. Solvents and glassware were/was dried and saturated/filled with nitrogen. Conventional equipment was used throughout. [BzEt3N]Cl was purchased and GeCh • dioxane was prepared following a literature method [16],
Benzyltriethylammonium trichlorogermanate(II)
A slurry of GeCF dioxane (2,08 g, 9 mmol) and benzyltriethylammonium chloride (2,05 g, 9 mmol) in 10 ml of tetrahydronaphthaline was heated to 70°C and stirred for 15 min. The resulting clear solution was cooled to room temperature and volatiles were evaporated (10~2 bar). A colourless precipitate was formed and
432 G. L. Wegner et al. ■ Synthesis and Structure of Benzyltriethylammonium Trichlorogermanate(II)
Table II. Crystal data, data collection and structure refinement for [BzEt3N][GeCl3].
Crystal dataFormula C n H 22Cl3GeNMr 371.26Crystal system monoclinicSpace group P2i/c (no. 14)a (A) 25.706(3)b (A) 7.040(1)c (A) 20.037(2)a ( ° ) 90ß O 112.48(1)7 ( ° ) 90V (A3) 3350.5(6)Pcalc (gCm ) 1.472Z 8F(000)(e) 1520/u (Mo Ka ) (cm-1 ) 22.91Data collectionT (°C) -70Scan mode ijD-9hkl range 0 —> +32
-8 —► 0-25 — +23
sin(#/A)max (A-1 ) 0.64Measured refl. 7201Unique refl. 7187 (flint = 0.0092)Refl. used for refinement 7136Absorption correction ip scansTmin/Tmax 0.759/0.999RefinementRefined parameters 501Final R values [I > 2cr(I)]:
R l [a] 0.0505wR2[b] 0.0943(shift/esd)max <0.001Pfin (max/min) (eA~3) +0.395/-0.539
[aI R = EfllFnl - IFCII)/XIF0I; [bl wR2 = {[Iw (F 2 - F 2)2] /I [v K F ^ l} 1/z; w = 1 l [ o \F i) + ( ap)z + bp ] ; p = (F0 +2F2)/3; a = 0.0264; b = 4.5270.
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evaporation was continued for 12 h with stirring. The white precipitate was filtered off in the cold, washed with5 ml of pentane three times and dried in a vacuum.
(3.22 g, 96.7% yield), m.p. 85°C (decomposition), MS(FAB): m/e = 192.2 [100%, BzEt3N+],Analysis for C ^ a C h G e N (371.26)
Calcd. C 42.05 H5.97 N 3.77 Cl 28.64%,Found C 41.83 H6.15 N3.71 Cl 28.66%.Crystal structure determinations'. A specimen of
suitable quality and size of benzyltriethylammonium trichlorogermanate(II) was mounted in a glass capillary and used for measurement of precise cell constants and intensity data collection on an Enraf Nonius CAD4 diffractometer ( M o -A^q radiation, A(Mo-ArQ) = 0.71073 Ä ) . During data collection, three standard reflections were measured periodically as a general check of crystal and instrument stability. No significant changes were observed. The structures were solved by direct methods (SHELXS- 86)[ 17] and completed by full-matrix least-squares techniques against F2 (SHELXL-93)[18].The thermal motion of all non-hydrogen atoms was treated anisotropically. All hydrogen atoms of [BzEt3 N][GeCl3 ] were found and refined with isotropic contributions. Further information on crystal data, data collection, and structure refinement are summarized in Table II. Important interatomic distances and angles are given in the corresponding figure captions. Anisotropic thermal parameters, tables of distances and angles, and atomic coordinates have been deposited at Fachinformationszentrum Karlsruhe, Gesellschaft für wissenschaftlich-technische Information mbH, D-76344 Eggenstein-Leopoldshafen. The data are available on request on quoting CSD No. 408501.
Acknowledgement
Mr. J. Riede is thanked for establishing the X-ray data set. This work was supported by Deutsche Forschungsgemeinschaft and Fonds der Chemischen Industrie.
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G. L. Wegner et al. • Synthesis and Structure of Benzyltriethylammonium Trichlorogermanate(II) 433
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