3.3.2 [B 5 O 6 (OH) 6 ]
3−
The pentaborate ion, [B 5 O 6 (OH) 6 ]
3− , is given in Fig. 4. We initially started with two
C 2v structures and two C 2 structures. Neither C 2v structure is stable. Both have
imaginary A 2 , B 1 , and B 2 modes at most levels. Both C 2 structures are stable at most
levels, with the exception of B3LYP/6-311+G* (C 2 #1) and B3LYP/6-31+G* (C 2
#2), which desymmetrize to stable C 1 #1 and #2, respectively. The C 2 #3 and #4
structures, derived from C 2v #1 and #2, are unstable at all levels and desymmetrize to
the stable C 1 #3 and #4. At B3LYP/6-31G* and MP2/6-31G*, one of the central B-O
bonds in C 1 #3 breaks. Attempts to locate the C s #1 and #2 structures also result in
breaking of one of the central B-O bonds. The C s #3 and #4 structures are not stable,
D 2d #1/C 2 #2
D 2d #2/C 2 #3
C 2v #1/C s #5/
C 1 #5/6
C 2 #1
C s/1 #1
C s/1 #2
C 2/1 #1
C 2/1 #2
C 2v #1
C 2v #2
C 2 #3
C 2 #4
C s #3
C s #4
C 1 #3
C 1 #4
C 1 #5
C 1 #6
D 2d
S 4
D 2
C s
C 1 #1
C 2 #2
C 2 #3
C 1 #2
Fig. 4 Structure of pentaborate ions, [B 5 O 6 (OH) 4+2n ]
−1−2n
, n = 0 − 2
126
C. C. Pye