Structural and spectroscopic characterisation of the mixed valence platinum complex PtdabI3 (dab=o-diaminobenzene)

Article abstract of DOI:10.1016/S0020-1693(99)00004-3

The new mixed valence platinum complex PtdabI₃ (dab=o-diaminobenzene) (1) has been prepared and characterised. The crystal structure consists of separate units of planar Pt(II)dabI₂ and octahedral Pt(IV)dabI₄ molecules. The latter are arranged in linear chains with rather short intermolecular II-contacts (3.478 A) which are responsible for charge transfer interactions. In the resonance Raman spectrum strong intensity enhancements and extended overtone progressions of the symmetric I-Pt-I stretching mode have been observed.

Full text of DOI:10.1016/S0020-1693(99)00004-3

Inorganica Chimica Acta 287 (1999) 218–222
Note
Structural and spectroscopic characterisation of the mixed valence
platinum complex PtdabI3 (dab=o-diaminobenzene)ꢀ
Oliver Fritz Danzeisen a, Mirela Goanta b, Heinz Wilhelm Rotter a, Gerhard Thiele a,*
a Institut fu¨r Anorganische und Analytische Chemie und Materialforschungszentrum der Uni6ersita¨t Freiburg, Albertstraße 21,
D-79104 Freiburg, Germany
b Uni6ersitatea Al. I. Cuza, Facultatea de Chimie, B Dul Copou 11, 6600 Iasi, Romania
Received 14 May 1998; accepted 16 December 1998
Abstract
The new mixed valence platinum complex PtdabI3 (dab=o-diaminobenzene) (1) has been prepared and characterised. The
crystal structure consists of separate units of planar Pt(II)dabI2 and octahedral Pt(IV)dabI4 molecules. The latter are arranged in
˚
linear chains with rather short intermolecular I···I-contacts (3.478 A) which are responsible for charge transfer interactions. In the
resonance Raman spectrum strong intensity enhancements and extended overtone progressions of the symmetric I–Pt–I stretching
mode have been observed. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Crystals structures; Platinum complexes; Diamine complexes; Iodide complexes; Mixed-valence complexes
retical investigations [4]. This is especially true in the
case of mixed valence halogen-bridged linear chain
compounds where a large variety of possible ligands
have been found, which range from simple halides to
mono-, di-, and tertendate amino ligands and nitrates.
In this paper a case is presented whereby the ligands
influence these chains so they can no longer be formed,
however, a mixed valence compound with unusual
properties results.
1. Introduction
Mixed valence Pt(II)/Pt(IV) compounds usually con-
sist of stacks of square planar coordinated platinum
atoms. They can be obtained either by partially oxidis-
ing platinum(II) complexes or reducing platinum(IV)
compounds to the mixed valence state. In compounds
of the Wolffram’s red salt type, the PtX4 (X=ligand)
units are connected by asymmetric halogen bridges [1],
building linear chains PtL4X (L=donor ligand or
halide, X=halide) with cationic neutral or anionic
charge. In other cases the formation of metal–metal
interactions between the platinum centres caused by
partial oxidation of the metals is the driving force for
stacking [2]. In both instances, the result is a highly
unisotropic behaviour of the resulting compound with
regard to optical and electrical properties, which has
generated much theoretical and practical interest [3].
This can be seen by a large quantity of synthesised
compounds and their characterisation as well as theo-
2. Experimental
2.1. Synthesis
The starting compound used for the synthesis was
PtdabI2, which was prepared from K2PtCl4 and KI with
o-diaminobenzene (dab) in aqueous solution. The plat-
inum(II) complex PtdabI2 was oxidised with iodine in
DMF (grade 99.9%) to give PtdabI3. A typical solution
(5 ml) contains 100 mg (0.18 mmol) of PtdabI2 and is
slightly yellow in colour. On addition of iodine (20 mg,
0.09 mmol) the colour turns red. The complex can be
ꢀ Dedicated to Professor Dr W. Preetz on the occasion of his 65th
birthday.
* Corresponding author.
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00004-3

O.F. Danzeisen et al. / Inorganica Chimica Acta 287 (1999) 218–222
219
precipitated as a copper-coloured powder by adding
2.645q525° (h, k, −l), v (Mo Ka)=19.11 mm−1
,
distilled water to the solution. Anal. Found: Pt, 29.2; C,
12.2; H, 1.3; N, 4.2. Calc. Pt, 28.5; C, 10.5; H, 1.2; N,
4.1%. X-ray powder diffraction shows that the mixed
valence compound [PtdabI2] [PtdabI4] is the only
product formed regardless of the amount of iodine
added. Single crystals were obtained within a week by
slow diffusion of water into the red solution. The
copper-coloured extremely thin platelets showed metal-
lic lustre when observed in direct light and appeared
light brown when transmitted-light microscopy was
used.
N0, N0 (IB2|(I))=954, 579, n=51, R1, Rw,=6.52,
−3
8.56%, Dzmax=1.78 e A−3, Dzmin=1.97 e A
.
˚
˚
2.3. Spectroscopy
FT-Raman spectra were collected with a FRA106
Raman modul (Bruker, Nd:YAG-Laser, u=1064 nm)
in connection with an FT-IR spectrometer IFS66V,
while the resonance Raman data were obtained on a
scanning double monochromator (U1000, JOBIN
YVON). The Raman excitation energies were provided
either by a krypton ion plasma laser (u=482.5, 530.9,
568.2, 647.1 and 676.4 nm) or by a Ti-sapphire laser
pumped by an argon ion plasma laser (u=750, 800 and
830 nm, Spectra Physics). The powdered samples were
optically diluted with KClO4 (1:50) and cooled to 15 K
(closed cycle Gifford-McMahon-Kryo-Refrigerator,
LEYBOLD). High pressure FT-Raman spectra were
collected with an FT-Raman microscope, with the sam-
ple in a diamond anvil cell with a 250 micron diameter
drilled gasket and mineral oil as a pressurising fluid.
Pressure calibration was achieved by measuring the
ruby fluorescence shift on added ruby chips. Absorp-
tion spectra between 200 and 800 nm were obtained on
a CARY1e spectrometer (VARIAN).
2.2. Crystallographic data collection and refinement of
the structure
A suitable crystal was placed in a glass capillary and
tested by means of film techniques. The intensity mea-
surement was carried out on a CAD4-diffractometer.
Cell constants and the orientation matrix were based on
25 reflections in the range of 1652q540°. The posi-
tions of the Pt and I atoms were determined by Patter-
son methods [5]. Subsequent Fourier synthesis yielded
the C and N atoms. During refinement, the phenyl
rings of the ligands were treated as rigid groups (C–C
˚
bond length of 1.42 A, bond angle of 120°). The
positions of the H atoms were calculated and included
in the refinement as riding atoms. The refinement was
carried out with anisotropic thermal parameters for all
non-hydrogen atoms. The data were corrected for ab-
sorption by the C-scan method. The final circle of the
full-matrix least-squares refinement was based on N0
reflections and n variable parameters and converged
with agreement factors of R1, Rw.
3. Results
SCHAKAL drawing [6] of the structure of 1 together
with the atomic numbering scheme is shown in Fig. 1.
Selected bond distances and angles with their estimated
standard deviations are listed in Table 1. The structure
consists of isolated units of planar Pt(II)dabI2 and
octahedral Pt(IV)dabI4 molecules. The Pt(IV)–N and
Pt(II)–N bond lengths differ only slightly (2.05(5) A,
compared with 2.02(4) A). There are two different Pt–I
distances in the octahedral unit: 2.605(6) for the equa-
torial bonds and 2.672(3) A for the axial bonds, while
2.2.1. Crystal data
Pt2C12H16N4I6 (1), M=684.94, orthorhombic, space
˚
˚
group Imma, no. 74, (a=7.89(2), b=8.828(2), c=
3
˚
˚
34.897(3) A, V=2432.8(3) A , Z=8, Dcalc=3.74 g
cm−3, graphite monochromated Mo Ka radiation, u=
˚
˚
0.71 A, F(000)=2368, T=23°C. Specimen size 0.2×
again there is only a slight difference between the
corresponding equatorial Pt–I distances in the two
0.01×0.07 mm3, ꢀ–2q scan, data collection range
Fig. 1. SCHAKAL drawing of the two molecules [PtdabI4] and [PtdabI2] in the crystal structure of PtdabI3.

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O.F. Danzeisen et al. / Inorganica Chimica Acta 287 (1999) 218–222
Table 1
Table 2
a
˚
Important bond lengths (A) and angles (°)
Spectroscopic data for PtdabI3
Wavenumber (cm−1
)
Assignment
˚
Bond length (A)
Bond angle (°)
Pt(1)–N(1)
Pt(1)–I(1)
Pt(2)–N(2)
Pt(2)–I(2)
Pt(2)–I(3)
2.02(4)
2.578(5)
2.05(5)
2.672(3)
2.605(6)
N(1)–Pt(1)–N(1)
I(1)–Pt(1)–I(1)
I(1)–Pt(1)–N(1)
I(1)–Pt(1)–N(1)
N(2)–Pt(2)–N(2)
I(2)–Pt(2)–I(2)
I(3)–Pt(2)–I(3)
I(2)–Pt(2)–I(3)
I(2)–Pt(2)–N(2)
C(11)–N(1)–Pt(1)
C(21)–N(2)–Pt(2)
86(2)
142 vst (Ra)
171 w (Ra) (IR)
182 st (IR)
ws Pt(IV)–Iax (w1)
was Pt–Ieq (w2)
was Pt–Iax
93.1(3)
176.4(11)
90.5(11)
83(3)
176.0(3)
90.9(3)
91.41
88.50(11)
105(3)
115(4)
200 m (IR)
280 vst (Ra)
311 w (Ra)
423 m (Ra)
423 m (IR)
428 m (IR)
433 m (IR)
532 m (IR)
445 m (IR)
453 m (Ra)
563 m (Ra)
596 vw (Ra)
704 w (Ra)
847 w (Ra)
986 vw (Ra)
1271 vw (Ra)
1136 vw (Ra)
1407 vw (Ra)
1551 vw (Ra)
2w1
w1+w2
3w1
N(1)–C(11)
N(2)–C(21)
I(2)–I(2)
1.43(3)
1.40(3)
3.487
w Pt–N
I(1)–I(3)
5.256
2w1+w2
4w1
3w1+w2
5w1
6w1
7w1
8w1
9w1
10w1
11w1
different units. The I–Pt–I bond angles between equa-
torial iodides are 93.1(3)° for Pt(II)dabI2 and 90.9(3)°
for Pt(IV)dabI4, those between the axial bound iodides
176.0(3)°. Parallel to the (1 0 0) plane, layers of the two
different molecules with alternating orientations of the
phenyl rings are formed. The phenyl rings of the
Pt(II)dabI2 molecules lie in the plane and those of the
Pt(IV)dabI4 molecules stand perpendicular to the plane.
Within the planes along [0 1 0] direction run alternating
double rows of the constituting molecules, which lead
in the case of Pt(IV)dabI4 to short intermolecular I–I
a IR spectra were recorded as KBr pellets, Raman spectra as
KClO4 pellets. Relative intensities: vst, very strong; st, strong; m,
medium; w, weak; vw, very weak. Ra, Raman active mode; IR, IR
active mode.
˚
contacts of 3.487 A.
Table 2 shows the IR and Raman data in the region
of Pt–N and Pt–I vibrations and their tentative assign-
ment. As in other Pt–I complexes, the Pt–I stretching
vibrations are found in the region between 140 and 185
cm−1. These values correspond very well with other
Pt(II)–I and Pt(IV)–I data [7]. From intensity reasons,
it was concluded, the band at 140 cm−1 must be
attributed to the symmetric Pt–I stretching vibration ws
of the axial bound iodides in Pt(IV)dabI4. The splitting
of the was band in the IR spectrum is attributed to the
different bonding situation of equatorial and axial
bound platinum atoms in the cis-PtI4L2 unit. There was
no splitting visible between the ws Pt–Iaxial and the ws
Pt–Iequatorial as could be expected from the different
bond lengths. A strong overtone progression of the
band at 140 cm−1 was observed (11w1), by excitation in
a region of about 15000 cm−1. The electronic spectrum
of 1 shows in comparison to Pt(II)dabI2 an additional
broad band which maximises at 17800 cm−1
.
Fig. 2. SCHAKAL drawing of a molecular layer in the structure of PtdabI3.

O.F. Danzeisen et al. / Inorganica Chimica Acta 287 (1999) 218–222
221
Pt–I bonds, which shows up in shorter bond length
compared to other Pt(IV)–I compounds and which
influences the bridging ability of the halides. On the
other hand, the properties of the compound resemble
those of the mixed valence compounds of class II. The
complex PtdabI3 is bronze coloured with a metallic
lustre while the colours of the constituting molecules
are light yellow. This and the strong intensity enhance-
ment of the band at 140 cm−1 and the overtone
progression in the resonance Raman spectrum can only
be explained by considering that an electric dipole
allowed a charge transfer mechanism via the short
intermolecular II contacts between neighbouring
Pt(IV)dabI4 molecules (Fig. 3). On excitation, this must
be accompanied by a significant displacement of the
potential surface of the symmetric stretching mode in
the excited state, causing the overtone progression.
Similar effects of a lesser extent have been registered in
other Pt(IV) compounds like Pt(NH2R)2I4 (R=Me, Et,
Pr), where relatively short intermolecular I…I distances
also occur [9]. The different nature of this charge
transfer mechanism to the one found in linear chain
compounds also shows up in high pressure Raman
spectra (Fig. 4). While in linear chain compounds the
resonant mode weakens with increasing pressure to
become harder again [10] in the case of 1 the hardening
is observed from the beginning as a shift to higher
wavenumbers.
Fig. 3. Resonance Raman spectrum of PtdabI3, excitation wavelength
647.1 nm.
4. Discussion
In contrast to mixed valence compounds, where halo-
gen-bridged linear chains of alternating Pt(II) and
Pt(IV) complexes are formed, in this structure there are
no close contacts between molecules with differently
charged platinum atoms cf. Fig. 2. Therefore PtdabI3 is
one of the rare examples of a mixed valence platinum
compound of class I according to the formulations of
Robin and Day [8]. The reason why, in this case, no
linear chain halogen-bridged mixed valence compound
was formed cannot be attributed to the bulkiness of the
dab-ligand, because replacement of dab by a similar
bulky ligand such as diaminocyclohexane yields the
Wolfframs red salt type. It seems that the lower basicity
of dab is responsible for a stronger polarisation of the
5. Supplementary material
Further details of the structure determination are
available on request from Fachinformationszentrum
Karlsruhe, D-76344 Eggenstein-Leopoldshafen 2, Ger-
many on quoting the depository number CSD-410500.
Fig. 4. The pressure-dependence of the w1 Raman band of PtdabI3.

222
O.F. Danzeisen et al. / Inorganica Chimica Acta 287 (1999) 218–222
[4] (a) M.-H. Whangbo, M.J. Foshee, Inorg. Chem. 20 (1981) 113.
Acknowledgements
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[5] G.M. Sheldrick, SHELX86/SHELX97, Programs for crystal struc-
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of molecular and crystallographic models, University of
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[7] (a) D.W. James, M.J. Nolan, J. Raman Spectrosc. 1 (1973) 271.
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[8] M.P. Robin, P. Day, Adv. Inorg. Chem. Radiochem. 10 (1967)
247.
The authors thank the Deutsche Forschungsgemein-
schaft and the Fond der Chemischen Industrie. M.
Goanta thanks the Deutscher Akademischer Aus-
tauschdienst for a grant.
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