The structure of acetyltriphenylgermane
Crystals of acetyltriphenylgermane, Ph3Ge·CO·CH3, are monoclinic, a= 15·30, b= 14·53, c= 7·68 Å, β= 94·8°, Z= 4, space group P21/c. The structure was determined with Cu-Kα scintillation counter data from Patterson and electron-density maps and refined by least-squares methods, the final R being 0·068 for 1834 observed reflexions.
The acetyl and three phenyl groups are arranged tetrahedrally around the germanium atom. The phenyl rings are oriented in a propeller fashion; the angles between the ring planes and the C(acetyl)–Ge–C(phenyl) planes are about 60° for two of the rings, and about 40° for the third ring, this deviation from a symmetrical propeller orientation being probably a result of intra- and inter-molecular steric interactions. The mean aromatic C–C distance is 1·383Å, and the mean C–H length is 1·09 Å.
Two distinct Ge–C bond lengths are found: Ge–C(phenyl)= 1·945 Å(σ= 0·008 Å), and Ge–C(acetyl)= 2·011 Å(σ= 0·015 Å). The longer Ge–C bond can be explained by a contribution from a resonance structure in which there is no formal bond between germanium and the carbonyl carbon atom, and which is in accord with the electronegativity difference between carbon and germanium. There is no evidence for π-bonding involving germanium 4d orbitals.