Group IVA Derivatives

Brockway and Jenkins applied electron diffraction techniques as early as 1936 to determine a 7 d geometry for (CH.t)4Ge, and a Ge—C bond length of 1.98 A (31). In the light of more recent microwave data which indicate a substantially shorter Ge—C bond length in the series of methylgermanes (62, 120, 161), this structure has been redetermined (91) to yield a more reliable Ge—C bond length of 1.945 A. 

Lattice constants and space groups have been reported for two crystal modifications of (C6H5C=C)4Ge (129 ). 

Electron diffraction data for (CH t) jGeC=CCl and the analogous tri-methylsilyl and t-butyl compounds show no differences in the length of 

7r Bond formation between the acetylene groups and niobium in (tj5-C5H )Nb(CO)( 7] 2-Ph3GeC=CPh )2 (Fig. 2) produces a lengthening of both the —C=C— and Ge—C= bonds relative to H3GeC=CH (Table I) and distortions of the linear Ge—C=C—C moiety toward a cis-olefin geometry, both observations consistent with a rehybridization from sp to sp2 at carbon (110). 

The existence of two distinct types of Ge—C bond in acetyltriphenyl-germane [Ge—C(phenyl) = 1.945 Ge—C(acetyl) = 2.011 Al has been interpreted in terms of resonance structures involving ionic species, viz. 

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