Chemical Physics Letters 381 (2003) 329–334
www.elsevier.com/locate/cplett
Vibrational spectrum and molecular structure
of [Cu(NH3)5](ClO4)2
A. Migdał-Mikuli *, E. Mikuli, M. Bara
nska, Ł. Hetma
nczyk
Department of Chemical Physics, Faculty of Chemistry, Jagiellonian University, ul. Ingardena 3, 30-060 Krak
ow, Poland
Received 26 June 2003
Published online: 24 October 2003
Abstract
[Cu(NH3 )5 ]2þ in the crystal lattice of [Cu(NH3 )5 ](ClO4 )2 form a trigonal bi-pyramid (D3h ) and/or a square-based
pyramid (C4v ), both with the rotating NH3 . Both structures were adopted for the quantum chemical calculations for
isolated [Cu(NH3 )5 ]2þ vibrations, but because the rotation of NH3 was not possible to simulate the point symmetry was
lowered to C3h and C1 . The calculated energy of equilibrium geometry and vibrational infrared and Raman spectra for
both models are practically identical. A dynamic transition is possible between both types of the cation structure. An
agreement between the experimental and calculated spectra confirmed the appropriateness of the used models.
Ó 2003 Elsevier B.V. All rights reserved.
1. Introduction
According to Tomlinson and Hathaway [1], at
room temperature the title compound has a regular structure (space group: No. 225 ¼ Fm3m ¼ O5h ),
and with four
with lattice parameter a ¼ 11:31 A
molecules in the unit cell. It is a fluorite type lattice, as was suggested for the hexaaminemetal(II)
complexes [2], but [Cu(NH3 )5 ]2þ cations with a
square-based pyramid configuration (C4v ) are
present in eight corners and six face-centers of the
unit cell [1,3]. However, a trigonal bi-pyramidal
configuration (D3h ) of the [Cu(NH3 )5 ]2þ cations is
also possible. According to Stankowski [4], orbital
*
Corresponding author. Fax: +48-12-634-0515.
E-mail address: [email protected] (A. MigdałMikuli).
level crossing occurs between C4v and D3h . The
orbital states do mix and the ground state is a
superposition of two equivalent states: jx2 y 2 i
and j3z2 r2 i. Orbital degeneracy leads to the
quantum averaging of the local field, what constitutes the dynamic Jahn–Teller effect [5] induced
by a configuration of the [Cu(NH3 )5 ]2þ cation.
Thus, orbital dynamics take place in pentaaminecooper(II) complexes [4]. The regular O5h symmetry
of the crystal lattice of [Cu(NH3 )5 ](ClO4 )2 is possible because the NH3 groups perform fast (picosecond scale of time) uniaxial reorientational
motions around the threefold axis.
The aim of the present study was to calculate
the theoretical infrared and Raman spectra for
isolated [Cu(NH3 )5 ]2þ cation in two assumed extreme cases: (1) for the bi-pyramid configuration
of the cation and (2) for the square-based pyramid
0009-2614/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.cplett.2003.07.033
330
A. Migdał-Mikuli et al. / Chemical Physics Letters 381 (2003) 329–334
configuration of the cation, and to compare the
obtained results with the experimental spectra for
solid [Cu(NH3 )5 ](ClO4 )2 .
2. Experimental and computational details
2.1. Characterization of the compound
The synthesis of the examined compound was
described exactly in paper [6]. Chemical analysis,
thermogravimetric analysis, infrared, Raman and
UV–vis spectra and also X-ray powder diffraction
analysis [6] confirmed the presence of pentaaminecopper(II) chlorate(VII). Some small excess
ÔfreeÕ ammonia was estimated as max. 3%.
basis provides the D95V basis set for proton and
nitrogen elements and a double-zeta basis set
containing ECP representations of core electrons
for cupric ion.
First of all, geometry optimisation of the model
[Cu(NH3 )5 ]2þ cation was conducted, and was followed by frequency calculations. The results in this
Letter are presented with no imaginary frequencies
at equilibrium geometry. Vibrational analysis of
frequency modes was performed using AN I M O L
[12] and MO L E K E L [13] graphical user interface.
VE D A 3.0 [14] program was used for the calculation of potential energy distribution (PED) of
normal modes.
3. Results and discussion
2.2. Spectroscopy measurements
The infrared absorption measurements (FTFIR and FT-MIR) were performed with Digilab
FTS-14 and Bruker EQUINOX 55 Fourier transform infrared spectrometers. The measurements
were made at a resolution of 2 and 1 cm1 , respectively. The FT-FIR spectra were recorded for
powder samples suspended in apiezon grease.
Polyethylene and silicon windows were used. The
FT-MIR spectra were recorded for the sample
suspended in Nujol between KBr pellets.
Fourier transform Raman scattering measurements (FT-RS) were performed at room temperature with a Bio-Rad spectrometer, resolution 4
cm1 . The incident radiation (k ¼ 1064 nm) came
from a Neodymium laser YAG Spectra-Physics.
2.3. Calculations of IR and RS spectra
Calculations were carried out at density functional theory level (DFT) using the B3LYP [7,8]
exchange-correlation functional implemented in
GA U S S I A N 98 program [9]. This method is recommended by Scott and Radom [10] and gives one
of the best agreements between experimental and
calculated frequencies. The B3LYP is a combination of B3 [7] and LYP [8] functionals. All calculations were performed with the Lanl2dz basis [11],
which includes some relativistic effects, recommended for metal complexes. Application of this
The main goal of this work is to interpret vibrational spectra of [Cu(NH3 )5 ](ClO4 )2 , and thus
quantum chemical calculations were conducted to
provide the bands assignment. As mentioned
above, [Cu(NH3 )5 ]2þ cations theoretically can
form a trigonal bi-pyramid (Fig. 1a) with rotating
NH3 groups in the corners (D3h configuration).
However, a square-based pyramidal configuration
with rotating NH3 groups (configuration C4v ) is
also possible (Fig. 1b). Both models were adopted
for quantum chemical calculations, but the rotation of NH3 groups was not possible to simulate,
so the point symmetry of both structures is lower
than described above. Calculations were conducted assuming the C3h point group symmetry for
cation in the form of trigonal bi-pyramid and C1
for square pyramid. Assuming a higher symmetry
of the square-based pyramid, Cs , three imaginary
frequencies were calculated.
Surprisingly, in spite of significant differences in
the structure of trigonal bi-pyramid and squarebased pyramid, the calculated energy of equilibrium geometry are almost identical for this both
model cations; the energy difference is DE ¼ 0:046
kcal mol1 (0.19 kJ mol1 ). One of the structure
with one imaginary frequency, obtained during the
calculations, presents a transition state and is
characterized by energy higher only by ca. 1
kcal mol1 in comparison to energy of equilibrium
geometry. Thus, we can suppose that a dynamic
A. Migdał-Mikuli et al. / Chemical Physics Letters 381 (2003) 329–334
331
* *
**
Raman Intensity [a. u.]
(a)
(b)
(c)
0
500
1000
1500
2000
2500
3000
3500
4000
Fig. 2. FT-RS spectra of [Cu(NH3 )5 ](ClO4 )2 (a) experimental
and calculated by B3LYP/Lanl2dz method assuming symmetry
of cation as: (b) trigonal bi-pyramid C3v and (c) square-based
pyramid C1 . (* denotes the ClO
4 bands.)
n
nn
*
*
(a)
Fig. 1. Assumed symmetry of the complex cation
[Cu(NH3 )5 ]2þ ; (a) trigonal bi-pyramid C3v and (b) square-based
pyramid C1 .
Absorbance [a. u.]
*
(a)
(c)
transition between these both equilibrium structures, of near equal equilibrium energies, is very
probable, too.
Experimental Raman (FT-RS) and infrared
(FT-FIR, FT-MIR) spectra of [Cu(NH3 )5 ](ClO4 )2
in solid state at room temperature are presented in
traces a in Figs. 2 and 3. Traces b and c (in Figs. 2
and 3) represent calculated spectra of the cation
[Cu(NH3 )5 ]þ2 as a trigonal bi-pyramid and a
square-based pyramid, respectively, using the
B3LYP/Lanl2dz method. In spite of the different
symmetry and structure of both model cations
[Cu(NH3 )5 ]þ2 , calculated vibrational spectra are
almost identical. Additionally, very good agreement is seen between experimental and calculated
data, confirming the appropriateness of the used
models.
0
500
1000
1500
2000
2500
3000
3500
4000
Fig. 3. Infrared (FT-FIR and FT-MIR) spectra of
[Cu(NH3 )5 ](ClO4 )2 (a) experimental and calculated by B3LYP/
Lanl2dz method assuming symmetry of cation as: (b) trigonal
bi-pyramid C3v and (c) square-based pyramid C1 . (* denotes the
ClO
4 bands and n denotes the bands from Nujol.)
Experimental vibrational bands of [Cu(NH3 )5 ]
(ClO4 )2 and theoretical frequencies calculated for
model complexes [Cu(NH3 )5 ]þ2 by B3LYP/
Lanl2dz method are listed in Table 1. The obtained frequencies were not multiplied by empirical factor because for this method of calculations it
would be almost equal to 1.0 (0.9978–1.0115 [15]).
The tetrahedral ClO
4 anion has 9 normal modes:
A1 , E and 2F2 . All of them are active in the Raman
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A. Migdał-Mikuli et al. / Chemical Physics Letters 381 (2003) 329–334
Table 1
Theoretical frequencies (in cm1 ) calculated by B3LYP/Lanl2dz method for two models of [Cu(NH3 )5 ]þ2 cation: trigonal bi-pyramid
(TBP) and square-based pyramid (SBP), and their comparison with the experimental FT-RS, FT-FIR and FT-MIR data
Frequencies in cm1
Calculated
Model TBP
(symmetry)
00
Assignments (PED
for TBP in %)
Experimental
Model SBP
RS
IR
This work
3569 (E )
3569
3569
3564 (E0 )
3564
3564
mas (NH) (91)
3564 (A0 )
3563
mas (NH) (97)
3560 (E )
3561
3561
mas (NH) (92)
3560 (E00 )
3560
3560
mas (NH) (98)
3569 (A00 )
3435 (A0 )
3568
3435
3433 (E0 )
3433
3433
3427 (A0 )
3426 (A00 )
3427
3426
1740 (E0 )
1740
1740
das (HNH) (95)
1733 (E00 )
1735
1726
das (HNH) (95)
1728 (A0 )
1719
0
00
3360 m
mas (NH) (98)
3380 st, br
3287 st
mas (NH) (98)
ms (NH) (92)
ms (NH) (95)
3205 m
3292 st, sr
3199 w
1618 w
ms (NH) (95)
ms (NH) (100)
das (HNH) (99)
1711 (E )
1713
1711
das (HNH) (96)
1709 (E0 )
1708
1707
das (HNH) (93)
1717 (A00 )
1356 (A0 )
1341 (A00 )
1717
1359
1343
0
1318 (E )
1322
1320
1314 (A0 )
–
–
–
–
1315
–
–
–
–
729 (E0 )
733
731
715 (E00 )
720
1634 st, br
1291 wv
1271 st
das (HNH) (100)
ds (HNH) (98)
ds (HNH) (100)
ds (HNH) (96)
1260 m
1074 vst
931 sh
ds (HNH) (99)
mas (ClO)F2
mas (ClO)F2
mas (ClO)F2
ms (ClO)A1
721 m
s(HNCuN) (88)
1185 sh
1121 m
1053 m
934 vst
d(HNCu) (96)
A. Migdał-Mikuli et al. / Chemical Physics Letters 381 (2003) 329–334
333
Table 1 (continued)
Frequencies in cm1
Calculated
Model TBP
(symmetry)
Assignments (PED
for TBP in %)
Experimental
Model SBP
RS
IR
This work
719
–
655 (A00 )
–
660
600 (E0 )
603
599
d(HNCu) (93)
577 (A0 )
578
d(HNCu) (99)
547
546
d(HNCu) (97)
00
544 (E )
–
–
627 st
461 vst
626 st
513 w
465 vw
430 vw
395 m
dd (OClO)F2
d(HNCu) (95)
dd (OClO)E
386 (A00 )
356 (A0 )
246 (A0 )
388
357
248
284 (E0 )
287
281
192 (E0 )
204
195
189 (A0 )
194
189 (A00 )
179 (A00 )
191
184
179 (E0 )
180
179
57 (A00 )
62
52 (E00 )
52
48
s(HNCuN) (95)
51 (E0 )
42
20
d(NCuN) (89)
430 st
312 st
287 m
m(CuN) (94)
m(CuN) (97)
m(CuN) (97)
241 m
m(CuN) (96)
194 m
d(NCuN) (95)
123 vw
s(HNCuN)
(86) + s(CuNNN)
(11)
s(HNCuN) (99)
s(CuNNN) (85)
s(CuNNN) (86)
85 m
s(HNCuN) (98)
vw – very weak, w – weak, sh – shoulder, m – medium, st – strong, vst – very strong, br – broad, sr – sharp; in bold – modes active
only in IR (A00 ) or only in Raman (A0 , E00 ) spectroscopy.
spectrum but only 2F2 are infrared active (see
Table 1 and Figs. 2 and 3).
4. Conclusions
1. The calculated energy of equilibrium geometry
of the [Cu(NH3 )5 ]þ2 cation, assuming symmetry
of trigonal bi-pyramid and square-based pyramid, is almost identical in both models
(DE ¼ 0:046 kcal mol1 (0.19 kJ mol1 )).
2. Vibrational spectra (IR and RS) of the
[Cu(NH3 )5 ]þ2 cation calculated for two above
mentioned models are practically identical and
are in good agreement with the experimental
data for solid [Cu(NH3 )5 ](ClO4 )2 .
334
A. Migdał-Mikuli et al. / Chemical Physics Letters 381 (2003) 329–334
3. Above presented facts lead us to a conclusion
that both structures of [Cu(NH3 )5 ]þ2 cation
are equally probable and a dynamic transition
between these both structures, of near equal
equilibrium energies, is very probable, too.
Acknowledgements
ciesi
Our thanks are also due to J. S
nski M.Sc.
and Dr. hab. E. Sciesi
nska from the Institute of
Nuclear Physics in Krak
ow, I. Szpyt M.Sc. from
our Faculty and Dr. A. Wesełucha-Birczy
nska
from the Regional Laboratory of Physicochemical
Analysis and Structural Research in Krak
ow for
registration of FT-FIR, FT-MIR and FT-RS
spectra, respectively.
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