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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.

[1] A. N. Christensen, S. E. Rasmussen, Acta Chem. Scand. 19, 421 (1965).

[2] W. Depmeier, A. Möller, K.-H. Klaska, Acta Crys­tallogr. B36, 803 (1980).

[3] W. Depmeier, K. Fütterer, V. Petricek, Acta Crystal­logr. B51, 768 (1995).

[4] K. B. Dillon, A. W. G. Platt, A. Schmidpeter, F. Zwascha, W. S. Sheldrick, Z. Anorg. Allg. Chem.488,7 (1982).

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.

[5] W. Czado, U. Müller, Z. Anorg. Allg. Chem. 622, 790(1996).

[6] R. Hulme, D. Mullen, J. C. Scruton, Acta Crystal­logr. A25, 171 (1969).

[7] S. C. Nyburg, G. A. Ozin, J. T. Szymanski, Acta Crystallogr. B27, 2298 (1971).

[81 P. S. Poskozim, J. Organomet. Chem. 12, 115 (1968).

G. L. Wegner et al. • Synthesis and Structure of Benzyltriethylammonium Trichlorogermanate(II) 433

[9] G. L. Wegner, Diplomarbeit, TU München (1997).[10] P. Kisliuk, C. H. Townes, J. Chem. Phys. 18, 1109

(1950).[11] J. Galy, R. Enjalbert, J. Solid State Chem. 44, 1

(1982).[12] J. Passmore, T. S. Cameron, P. D. Boyle, G. Schatte,

T. Way, Can. J. Chem. 74, 1671 (1996).[13] R. D. Shannon, C. T. Prewitt, Acta Crystallogr. B25,

925 (1969).

[14] T. Probst, O. Steigeimann, J. Riede, H. Schmidbaur, Chem. Ber. 124, 1089(1991).

[15] H. Schmidbaur, R. Nowak, O. Steigeimann, G. Müller, Chem. Ber. 123, 1221 (1990).

[16] W. A. Herrmann, M. Denk, Deutsches Patent DE 4214281.

[17] G. M. Sheldrick, C. Krüger, R. Goddard, p. 175, Oxford Univ. Press, Oxford (1985).

[18] G. M. Sheldrick, Progr. for the refinement of struc­tures, Univ. Göttingen (1993).