Group VA Derivatives

The bonds formed between germanium and elements of Group VA can be divided into two categories those in which the element is bonded via a covalent bond and others in which a Lewis acid-Lewis base interaction between the two elements results in coordinate bond formation. The same classification of bond types is also appropriate when discussing organogermanium derivatives of Groups VIA and VII A. 

For comparison, a number of compounds incorporating coordinate N - Ge bonds have been reported, among which studies of organoger-matranes (6) by several Russian authors (12,18, 77, 87,104,105,180) predominate. 

2 Quoted as 3.8 A in Refs. (12) and (26), based upon an estimated van der Waals radius for germanium of 2.3 A. Other authors (112 see Section III,B,3) approximate the Ge — N van der Waals contact distance to the lower value of 3.5 A by analogy with As N contacts. 

The constraints of the tetradentate hemiporphyrazine ligand impose a six-coordinated frans-R2GeN4 octahedral geometry (Fig. 9) on bis(3,3-dimethyl-l-butyneyl)hemiporphyrazinogermanium, in which both covalent (1.956 A) and coordinate (2.172 A) Ge—N bonds are incorporated (92). The heterocycle is nearly planar, and this structure represents the only unequivocal example of a six-coordinated organo-germane whose structure is known thus far. 

Instances of an R Ge—P bond are confined to one example, the ada-mantane-like cage compound, [(CH3)3Ge]6P4 (51). The Ge—P distance (2.3217 A) is equal to the sum of covalent radii (2.32 A), although the strained trifurcated bonding of each phosphorus atom (Fig. 10) suggests that this may not be representative of a typical covalent Ge—P bond. Such speculation awaits further study for confirmation. 

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