B. Gierczyk et al. / Journal of Molecular Structure 513 (1999) 149–153
151
Table 1
1H NMR chemical shifts (ppm) of tris(oxaalkyl) borates. ((s)-singlet, (t)-triplet, (m)-multiplet)
Borate
C2H
C3H
C5H
C6H
C8H
C9H
C11H
B2
B3
B4
3.64(t)
3.64(m)
3.64(m)
3.45(t)
3.61(m)
3.62(m)
3.35(s)
3.52(m)
3.62(m)
3.52(m)
3.62(m)
3.35(s)
3.53(m)
3.51(m)
3.34(s)
given in Table 1. The signals of the C1H protons are
shifted slightly towards lower fields due to the
deshielding effect of the boron atom. The signals of
the CH3 protons are always observed at 3.35 ppm, i.e.
they are independent of the length of the oxaalkyl
chains.
After the addition of the corresponding metal salts
to tris(oxaalkyl) borates, all C–H signals broaden
strongly indicating strong interactions between the
three oxaalkyl ligands and the cations.
Table 3
11B NMR chemical shifts (ppm) of tris(oxaalkyl) borates and their
complexes with some metal cations
Borates
Chemical shifts of complexes (ppm)
Free
CoCl2
NiCl2
CuCl2
B2
B3
B4
19.274
19.274
19.274
39.371
41.654
41.527
27.262
27.642
27.528
24.599
24.853
24.346
The 13C NMR chemical shifts of tris(oxaalkyl)
borates and their 1:1 complexes with various cations
are given in Table 2. A comparison of the chemical
shifts of the corresponding 13C NMR signals of free
borates with those of their complexes indicate a strong
interaction between the oxaalkyl ligands and the
respective cations.
In the case of 1:1 complexes of CoCl2, NiCl2 or
CuCl2 with tris(oxaalkyl) borates, the corresponding
13C NMR signals are strongly shifted towards higher
fields, indicating the formation of stable complexes.
From our previous paper, it is known that in
complexes these cations are always bonded with one
chlorine atom [11]. It is interesting to note that parti-
cularly strong complexes are formed between B4 and
Co2ϩ cations.
The 11B NMR chemical shifts of the 1:1 complexes
of CoCl2, NiCl2 or CuCl2 with tris(oxaalkyl) borates
are shown in Table 3. A comparison of the respective
signals of free borates with those of their complexes
show that for complexes the 11B NMR signals are
strongly shifted downfield. The greatest shift is
observed for the complexes with Co2ϩ cations,
much smaller for Ni2ϩ and the smallest for Cu2ϩ
cations. This result is consistent with the 13C NMR
observations.
The 17O NMR chemical shifts of free tris(oxaalkyl)
borates and their complexes with CoCl2 are given in
Table 4. The 17O NMR spectra directly reflect the
coordination sites of the cation and the O-atoms in
Table 2
13C NMR chemical shifts (ppm) of tris(oxaalkyl) borates and their
complexes with metal cations
Compound Chemical shifts (ppm)
C2
C3
C5
C6
C8
C9
C11
Table 4
17O chemical shifts (ppm) of tris(oxaalkyl) borates and its
complexes with cobalt salts
B2
62.03 75.11 59.08
B2 ϩ CoCl2 69.65 84.24 64.70
B2 ϩ NiCl2 69.67 80.40 64.79
B2 ϩ CuCl2 67.0 82.30 62.10
Borates Metal cation Oxygen-17 chemical shifts (ppm)
O1
O4
O7
O10
B3
62.16 71.15 72.95 73.67 59.11
B3 ϩ CoCl2 70.75 80.92 83.98 86.25 62.73
B3 ϩ NiCl2 66.74 70.64 78.45 81.37 59.90
B3 ϩ CuCl2 68.30 78.30 81.00 82.70 66.70
B2
B3
B4
Free
CoCl2
Free
CoCl2
Free
CoCl2
35.4
Ϫ11.2
36.0
Ϫ8.9
37.2
39.8
Ϫ29.4
Ϫ59.5
Ϫ8.4
Ϫ8.9
Ϫ6.0
B4
62.15 71.31 71.33 71.53 72.87 73.65 59.09
Ϫ27.6
Ϫ8.9
B4 ϩ CoCl2 76.64 86.80 97.70 88.38 89.50 91.32 68.22
B4 ϩ NiCl2 67.35 71.20 78.97 80.07 80.64 81.19 60.85
B4 ϩ CuCl2 67.50 78.00 78.40 80.00 82.30 65.70 58.10
Ϫ6.0
Ϫ15.9
Ϫ26.4
Ϫ15.9
Ϫ15.9