6 Group 13–15 Needle-Shaped Oligomers and Nanorods: Structures. . .
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Fig. 6.28 Dipole moment vectors and ESP charge distribution over atoms in open
X 3 [HGaNH] 3n Y 3 oligomers with n=2 (a, b), 3 (c, d), 6 (e, f), 10 (g, h) and with terminal groups
X=CH 3 , Y=CH 3 (a,c,e,h) and X=CH 3, Y=CF 3 (b,d,f,g)
end, μ > 0 for all oligomers and dipole moment increases with the increase of
the length of the oligomer (Fig. 6.28 a, c, e, h). However, if CH 3 groups are
replaced by the electron-withdrawing CF 3 groups on N-saturated end (Fig. 6.28
b, d, f, g), it significantly reduces the dipole moment. For the smallest rod-shaped
(CH 3 ) 3 [HGaNH] 6 (CF 3 ) 3 compound, electrophilicity of the CF 3 groups overcomes
the charge separation caused by displacement of Ga 3 and N 3 planes, and the dipole
moment has small negative value, μ = −1.5 D (Fig. 6.28b).
The effect is more pronounced in case of closed XGa[HGaNH] 9 NY oligomers.
If X=H or CH 3 and Y=F or CF 3 , the electron-withdrawing power of the F and
CF 3 groups overcomes the electrostatic field provided by the spatial separation of