6 Group 13–15 Needle-Shaped Oligomers and Nanorods: Structures. . .
253
Fig. 6.30 Dipole moments of closed XGa[HGaNH] 114 NY (a) and open X 3 [HGaNH] 114 Y 3
(b) oligomers. Reproduction of material from PCCP (Physical Chemistry Chemical Physics).
(Reproduced from Ref. [59] with permission from the PCCP Owner Societies)
can see that μ = −2.4D for n = 6 (Fig. 6.29f), μ = −3.3D for n = 3 (Fig. 6.29d),
and μ = −3.9 for n = 2 (Fig. 6.29b).
In general, the dipole moments of the oligomers increase linearly with the
increase of the oligomer lengths, although some small nonlinearity is noticeable
for open types of oligomers of shorter lengths. The dipole moment values of the
longest (3n = 114) oligomers are given in Fig. 6.30.
Capping of the H 3 [HGaNH] 3n H 3 oligomer by terminal XGa and NY groups
significantly (by 317–330 D) reduces the dipole moment (Fig. 6.30a) not only
because the Ga-terminated end has only one XGa group instead of three in open
oligomers but also due to the different chemical environment around the Ga atom.
In closed oligomers terminal Ga atom is bonded with one X group and three N
atoms, but in open oligomers each terminal Ga atom is bonded to one X group,
one H, and two N atoms. It leads to an overall decrease of the charge at the Gaterminated end in closed oligomers. For example, the ESP charge in the outermost
Ga atom of CH 3 Ga[HGaNH] 6 NCH 3 is about 0.478, while the charge of each Ga
atom in the outermost plane in (CH 3 ) 3 [HGaNH] 6 (CH 3 ) 3 is 0.515. Values of the
sum of partial charges in the vicinity of Ga- and N-terminated ends for several open
and closed oligomers are presented in Table 6.6. Partial charge accumulated on the
Ga-terminated end in open oligomers is more than three times larger than the one
on XGa groups in closed oligomers.
For the longest considered oligomers with n = 38, the dipole moment calculated
per monomeric HGaNH unit varies from 3.24 (X=CH 3 ,Y=CF 3 ) to 3.44 D (X=CF 3 ,
Y=CH 3 ) for open and from 0.44 (X=CH 3 , Y=CF 3 ) to 0.54 D (X=CF 3 , Y=CH 3 )
for closed oligomers.
253
Fig. 6.30 Dipole moments of closed XGa[HGaNH] 114 NY (a) and open X 3 [HGaNH] 114 Y 3
(b) oligomers. Reproduction of material from PCCP (Physical Chemistry Chemical Physics).
(Reproduced from Ref. [59] with permission from the PCCP Owner Societies)
can see that μ = −2.4D for n = 6 (Fig. 6.29f), μ = −3.3D for n = 3 (Fig. 6.29d),
and μ = −3.9 for n = 2 (Fig. 6.29b).
In general, the dipole moments of the oligomers increase linearly with the
increase of the oligomer lengths, although some small nonlinearity is noticeable
for open types of oligomers of shorter lengths. The dipole moment values of the
longest (3n = 114) oligomers are given in Fig. 6.30.
Capping of the H 3 [HGaNH] 3n H 3 oligomer by terminal XGa and NY groups
significantly (by 317–330 D) reduces the dipole moment (Fig. 6.30a) not only
because the Ga-terminated end has only one XGa group instead of three in open
oligomers but also due to the different chemical environment around the Ga atom.
In closed oligomers terminal Ga atom is bonded with one X group and three N
atoms, but in open oligomers each terminal Ga atom is bonded to one X group,
one H, and two N atoms. It leads to an overall decrease of the charge at the Gaterminated end in closed oligomers. For example, the ESP charge in the outermost
Ga atom of CH 3 Ga[HGaNH] 6 NCH 3 is about 0.478, while the charge of each Ga
atom in the outermost plane in (CH 3 ) 3 [HGaNH] 6 (CH 3 ) 3 is 0.515. Values of the
sum of partial charges in the vicinity of Ga- and N-terminated ends for several open
and closed oligomers are presented in Table 6.6. Partial charge accumulated on the
Ga-terminated end in open oligomers is more than three times larger than the one
on XGa groups in closed oligomers.
For the longest considered oligomers with n = 38, the dipole moment calculated
per monomeric HGaNH unit varies from 3.24 (X=CH 3 ,Y=CF 3 ) to 3.44 D (X=CF 3 ,
Y=CH 3 ) for open and from 0.44 (X=CH 3 , Y=CF 3 ) to 0.54 D (X=CF 3 , Y=CH 3 )
for closed oligomers.