6 Group 13–15 Needle-Shaped Oligomers and Nanorods: Structures. . .
241
Fig. 6.22 Distribution of valence N-Ga-N (a) and dihedral N-Ga-N-Ga (b) interring angles in
[HGaNH] 3n+1 closed (filled circles) and open H 3 [HGaNH] 3n H 3 (empty circles) oligomers of
different lengths (n = 10, 18, 38). Lines are drawn to guide the eye only
the angles vary within 0.3 ◦ along the oligomer. In the middle rings of the longest
closed oligomer, Ga-N-Ga is 115.3 ◦ , N-Ga-N is 101.7 ◦ , and N-Ga-N-Ga is 62.6 ◦ .
Corresponding values for the longest open oligomer are 115.2 ◦ , 101.6 ◦ , and 62.8 ◦ .
In the case of the open oligomers, except for rather sharp deformations near the
very edges of the rods, the Ga-N-Ga and N-Ga-N angles monotonically decrease
from the center toward the edges by about 1.5 ◦ (see Fig. 6.22a), and N-Ga-N-Ga
dihedral angles smoothly increase from the center toward the edges by about 2.5 ◦
(Fig. 6.22b). In general, open structures in the center have flatter and smaller Ga 3 N 3
rings than at the edges. The closer to the edges, the tighter the Ga 3 N 3 rings are
joined. With the exception of the very edge and with a good approximation, it can
be said that all Ga 3 N 3 rings in long closed oligomers are essentially the same and
they are evenly distributed with respect to the center of oligomer.
Systematic changes in structural parameters were also reported for the short
H 3 [BN] 3n H 3 rod-shaped oligomers (n ≤ 10) [184], where authors pointed out
monotonic changes in interring B-N bond lengths.
Comparison of inter- and intra-ring Ga-N bond lengths reveals that for all closed
oligomers, interring Ga-N bonds, except those in the outmost rings, are longer than
intra-ring bonds. The former converge to the value of 1.993 Å and the later converge
to the value of 1.981 Å. In the open oligomers, interring bonds are always shorter,
and intra-ring bonds are always longer than those in closed oligomers. In contrast to
closed oligomers, for the open oligomers, there is a qualitative change in trends
of inter- and intra-rings Ga-N bond lengths upon oligomer elongation. In open
oligomers with n < 25, all interring Ga-N bonds are shorter than intra-ring bonds.
Starting from n = 25, the Ga-N bond lengths between the central rings become
longer than the Ga-N bond lengths within the rings. For about half of [HGaNH] 3
units in the central part of the longest considered open H 3 [HGaNH] 3n H 3 oligomer
(n = 38), the interring bond lengths are longer than the intra-ring Ga-N bond lengths.
For the rest of the oligomer, the opposite situation is observed: the interring Ga-N
bonds are shorter than the intra-ring Ga-N bonds.
241
Fig. 6.22 Distribution of valence N-Ga-N (a) and dihedral N-Ga-N-Ga (b) interring angles in
[HGaNH] 3n+1 closed (filled circles) and open H 3 [HGaNH] 3n H 3 (empty circles) oligomers of
different lengths (n = 10, 18, 38). Lines are drawn to guide the eye only
the angles vary within 0.3 ◦ along the oligomer. In the middle rings of the longest
closed oligomer, Ga-N-Ga is 115.3 ◦ , N-Ga-N is 101.7 ◦ , and N-Ga-N-Ga is 62.6 ◦ .
Corresponding values for the longest open oligomer are 115.2 ◦ , 101.6 ◦ , and 62.8 ◦ .
In the case of the open oligomers, except for rather sharp deformations near the
very edges of the rods, the Ga-N-Ga and N-Ga-N angles monotonically decrease
from the center toward the edges by about 1.5 ◦ (see Fig. 6.22a), and N-Ga-N-Ga
dihedral angles smoothly increase from the center toward the edges by about 2.5 ◦
(Fig. 6.22b). In general, open structures in the center have flatter and smaller Ga 3 N 3
rings than at the edges. The closer to the edges, the tighter the Ga 3 N 3 rings are
joined. With the exception of the very edge and with a good approximation, it can
be said that all Ga 3 N 3 rings in long closed oligomers are essentially the same and
they are evenly distributed with respect to the center of oligomer.
Systematic changes in structural parameters were also reported for the short
H 3 [BN] 3n H 3 rod-shaped oligomers (n ≤ 10) [184], where authors pointed out
monotonic changes in interring B-N bond lengths.
Comparison of inter- and intra-ring Ga-N bond lengths reveals that for all closed
oligomers, interring Ga-N bonds, except those in the outmost rings, are longer than
intra-ring bonds. The former converge to the value of 1.993 Å and the later converge
to the value of 1.981 Å. In the open oligomers, interring bonds are always shorter,
and intra-ring bonds are always longer than those in closed oligomers. In contrast to
closed oligomers, for the open oligomers, there is a qualitative change in trends
of inter- and intra-rings Ga-N bond lengths upon oligomer elongation. In open
oligomers with n < 25, all interring Ga-N bonds are shorter than intra-ring bonds.
Starting from n = 25, the Ga-N bond lengths between the central rings become
longer than the Ga-N bond lengths within the rings. For about half of [HGaNH] 3
units in the central part of the longest considered open H 3 [HGaNH] 3n H 3 oligomer
(n = 38), the interring bond lengths are longer than the intra-ring Ga-N bond lengths.
For the rest of the oligomer, the opposite situation is observed: the interring Ga-N
bonds are shorter than the intra-ring Ga-N bonds.