Crystal structure of 4-(trimethylgermyl)benzoic acid

During synthesis of the corresponding aldehyde, 4-(trimethylgermyl)benzoic acid was obtained as a side-product. It crystallizes with two independent molecules in the asymmetric unit which exhibit slightly different geometries. In the crystal structure, centrosymmetric hydrogen-bonded dimers of the molecular pairs are formed.


Chemical context
The application of 1,4-dihydropyridines (DHPs) as a pharmaceutical tool represents a novel and promising approach in the therapy of autoimmune diseases, cancer and other illnesses. The effect of drugs containing DHPs is based on the interaction with the Transforming Growth Factor (TGF). The title compound, [Ge(CH 3 ) 3 (C 7 H 5 O 2 )], (I), was obtained as a side-product in the synthesis of the corresponding aldehyde, which can be employed in the synthesis of DHPs (Lä ngle et al., 2015).
All in all, the degree of deformation in the second molecule is smaller compared to the first molecule. This difference may be the reason for the presence of two molecules in the asymmetric unit. The deformations described above may be caused by the sterically demanding substituents attached to the aromatic ring in 1-and 4-positions, or may be traced back to packing effects.

Supramolecular features
The molecules in the title compound crystallize as centrosymmetric hydrogen-bonded dimers (Fig. 2 Jeffrey (1997).

Database survey
In the isotypic structure containing silicon instead of germanium, similar distortions can be observed (Haberecht et al., 2004). In this structure, the asymmetric unit also contains two differently deformed molecules. In the first molecule, a nearly planar geometry of the aromatic ring plane is exhibited. The second molecule shows the same boat-shaped deformation of the aromatic ring as described for the Ge compound. The atoms equal to C12 and C15 deviate by À0.016 (1) Å and À0.017 (1) Å , respectively. The silicon atoms Si1 and Si2 exhibit distances to the aromatic ring plane of 0.088 (3) and À0.219 (2) Å , respectively. A comparison of these distances to those reported for the title compound reveals that the observed distortions occur in similar dimensions for both structures. This points to a comparable steric demand of the trimethylgermyl and trimethylsilyl moieties.

Synthesis and crystallization
To a solution of 1,4-dibromobenzene (1.50 g, 6.36 mmol) in Et 2 O (13 ml) was added n-BuLi (6.36 mmol, 2.5 M in hexane) at 195 K and the mixture stirred at this temperature for 4 h. Then chlorotrimethylgermane (1.10 g, 7.00 mmol) was added to the reaction mixture at 195 K, stirred at this temperature for 10 min, followed by stirring over night at room temperature. After addition of H 2 O, the organic phase was separated and the aqueous phase was extracted with Et 2 O three times. The combined organic phases were washed with brine and dried over Na 2 SO 4 . Removal of the solvent under reduced pressure afforded (4-bromophenyl)trimethylgermane (1.67 g, Acta Cryst. (2015). E71, 687-689 research communications Table 1 Deviation of atoms from the benzene ring least-squares planes (Å ). (4) Note: (*) not used in the least-squares-plane calculation.

Figure 2
6.12 mmol, 96%) as a colorless liquid. The reaction product was used in following syntheses without further purification.
To a solution of (4-bromophenyl)trimethylgermane (1.67 g, 6.12 mmol) in THF (38 ml) was added n-BuLi (6.73 mmol, 2.5 M in hexane) at 195 K and the mixture was stirred at this temperature for 15 minutes. Then dimethylformamide (1.34 g, 18.4 mmol) was added to the reaction mixture at 195 K, and it was allowed to warm to room temperature over night. After addition of a saturated aqueous NH 4 Cl solution, the organic phase was separated and the aqueous phase extracted three times with Et 2 O. The combined organic phases were washed with water and brine and dried over Na 2 SO 4 . Removal of the solvent under reduced pressure and subsequent silica gel chromatography (pentane, pentane/Et 2 O = 100:1 ! 50:1) afforded 4-(trimethylgermyl)benzaldehyde, which oxidized at ambient air conditions to give 4-(trimethylgermyl)benzoic acid, (I), (1.05 g, 4.70 mmol, 77%) as a colorless solid. A schematic representation of the synthetic procedure is shown in Fig. 3.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Hydrogen atoms were located from difference Fourier maps. They were refined with idealized positions in a riding model with U iso (H) = 1.2U eq (C) and C-H = 0.95 Å for aromatic hydrogen atoms, and with U iso (H) = 1.5U eq (C) and C-H = 0.98 Å for methyl hydrogen atoms. All CH 3 hydrogen atoms were allowed to rotate but not to tip. Hydroxyl hydrogen atoms were located from difference Fourier maps and were refined freely.