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Structure of the La12GdEuB6Ge2O34 borogermanate as probed by NMR and IR spectroscopy
The structure of fine crystalline borogermanate La 12 GdEuB 6 Ge 2 O 34 has been studied by NMR and IR spectroscopy. It has been demonstrated that this compound is isostructural to the homonuclear Ln 14 B 6 Ge 2 O 34 compounds (Ln = Pr-Gd) and crystallizes in space group P 3 1 . The rare-earth eleme...
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| Published in: | Russian journal of inorganic chemistry 2013-09, Vol.58 (9), p.1090-1096 |
|---|---|
| Main Authors: | , , , |
| Format: | Article |
| Language: | English |
| Subjects: | |
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| Summary: | The structure of fine crystalline borogermanate La
12
GdEuB
6
Ge
2
O
34
has been studied by NMR and IR spectroscopy. It has been demonstrated that this compound is isostructural to the homonuclear Ln
14
B
6
Ge
2
O
34
compounds (Ln = Pr-Gd) and crystallizes in space group
P
3
1
. The rare-earth elements have been distributed over the LnO
n
polyhedra in La
12
GdEuB
6
Ge
2
O
34
by analogy with the known structures. Lanthanum can occupy positions with CN 7–10, and the symmetry of these LnO
n
coordination polyhedra is not higher than
C
2
v
. In the La
12
GdEuB
6
Ge
2
O
34
structure, the LnO
n
coordination polyhedra are formed by oxygen atoms of oxo groups and anions, some of the oxygen atoms being shared by LnO
n
polyhedra. The BO
3
and GeO
4
groups in the structure are also bridging, i.e., are involved in bonding of LnO
n
polyhedra. One of the B-O bonds in La
12
EuGd(BO
3
)
6
(GeO
4
)
2
O
8
is elongated as compared with the B-O bond lengths in homonuclear compounds Pr
14
(BO
3
)
6
(GeO
4
)
2
O
8
and Nd
14
(BO
3
)
6
(GeO
4
)
2
O
8
. In the La
12
GdEuB
6
Ge
2
O
34
structure, germanium is located in isolated GeO
4
tetrahedra with distorted
T
d
symmetry. The local symmetry of lanthanum in fine crystalline La
12
GdEuB
6
Ge
2
O
34
have been assessed using
139
La NMR (
B
0
= 7.04 T, room temperature). For comparison, binary lanthanum compounds with a simpler structure— LaBO
3
, La(BO
2
)
3
, and La
2
GeO
5
—have been used. The spectra of all compounds are rather broad (ν
1/2
= 180–240 kHz). The
139
La NMR spectra of the LaBO
3
, La(BO
2
)
3
, and La
12
GdEu(BO
3
)
6
(GeO
4
)
2
O
8
borates show a signal at (1080 ± 40) ppm, which is absent in the spectrum of La
2
GeO
5
. The shape of the
139
La NMR spectra of La
12
GdEu(BO
3
)
6
(GeO
4
)
2
O
8
and LaBO
3
is characterized by the second-order quadrupole splitting with a downfield shoulder. The similarity of these spectra points to close
139
La NMR chemical shifts of La
12
GdEu(BO
3
)
6
(GeO
4
)
2
O
8
and LaBO
3
. No quadrupole splitting was observed in the spectra of La(BO
2
)
3
and La
2
GeO
5
. |
|---|---|
| ISSN: | 0036-0236 1531-8613 |
| DOI: | 10.1134/S0036023613090131 |