Sr4PbPt4O11, the first platinum oxide containing Pt26+ ions

Article abstract of DOI:10.1016/j.jssc.2006.04.009

We report the synthesis and crystal structure of the new compound Sr₄PbPt₄O₁₁, containing platinum in highly unusual square pyramidal coordination. The crystals were obtained in molten lead oxide. The structure was solved by X-ray single crystal diffraction techniques on a twinned sample, the final R factors are R = 0.0260 and w R = 0.0262. The symmetry is triclinic, space group P1, with a = 5.6705 (6) A, b = 9.9852 (5) A, c = 10.0889 (5) A, α = 90.421 (3) °, β = 89.773 (8) °, γ = 90.140 (9) ° and Z = 2. The structure is built from dumbell-shaped Pt₂O₉ entities formed by a dinuclear metal-metal bonded Pt₂⁶⁺ ion with asymmetric environments of the two Pt atoms, classical PtO₄ square plane and unusual PtO₅ square pyramid. Successive Pt₂O₉ entities deduced from 90° rotations are connected through the oxygens of the PtO₄ basal squares to form [Pt₄O₁₀^8-]_∞ columns further connected through Pb²⁺ and Sr²⁺ ions. Raman spectroscopy confirmed the peculiar platinum coordination environment.

Full text of DOI:10.1016/j.jssc.2006.04.009

ARTICLE IN PRESS
Journal of Solid State Chemistry 179 (2006) 2101–2110
www.elsevier.com/locate/jssc
6
+
Sr PbPt O , the first platinum oxide containing Pt ions
4
4 11
2
Ã
Catherine Renard , Pascal Roussel, Annick Rubbens,
Sylvie Daviero-Minaud, Francis Abraham
Unit e´ de Catalyse et de Chimie du Solide, e´ quipe de Chimie du Solide (CNRS UMR 8181) ENSC Lille–UST Lille, BP 90108,
9652 Villeneuve d’Ascq cedex, France
5
Received 22 February 2006; received in revised form 30 March 2006; accepted 2 April 2006
Available online 25 April 2006
Abstract
We report the synthesis and crystal structure of the new compound Sr
pyramidal coordination. The crystals were obtained in molten lead oxide. The structure was solved by X-ray single crystal diffraction
4 4
PbPt O11, containing platinum in highly unusual square
¯
techniques on a twinned sample, the final R factors are R ¼ 0:0260 and wR ¼ 0:0262. The symmetry is triclinic, space group P1, with
˚
˚
˚
a ¼ 5:6705ð6Þ A, b ¼ 9:9852ð5Þ A, c ¼ 10:0889ð5Þ A, a ¼ 90:421ð3Þ1, b ¼ 89:773ð8Þ1, g ¼ 90:140ð9Þ1 and Z ¼ 2. The structure is built from
6
2
+
dumbell-shaped Pt O entities formed by a dinuclear metal–metal bonded Pt ion with asymmetric environments of the two Pt atoms,
2
9
classical PtO
through the oxygens of the PtO
4
square plane and unusual PtO
5
2 9
square pyramid. Successive Pt O entities deduced from 901 rotations are connected
8ꢀ
2+ 2+
and Sr
4
basal squares to form [Pt
spectroscopy confirmed the peculiar platinum coordination environment.
4
O
10
]
N
columns further connected through Pb
ions. Raman
r 2006 Elsevier Inc. All rights reserved.
6
+
Keywords: Platinum oxide; Pt
2
ion; 5-coordinated platinum; Crystal structure; X-ray diffraction
1
. Introduction
stacked and the compounds exhibit strong metal–metal
interactions leading to electronic delocalization along the
Pt–Pt chains and highly conducting materials. Similar
behaviour is observed in partially oxidized one-dimensional
tetracyano-platinates.
Many binary and ternary platinum oxides have already
been chemically and structurally studied for several reasons:
(
(
1) numerous alkaline, alkaline earth, post transition metals
Pb, Bi,y) platinum oxides were formed when platinum, a
Previous studies on compounds of the Pb/Pt/O system
allowed us to synthesize two lead platinum oxides, Pb PtO
chemically inert and stable to high temperature metal, was
used as a container for synthesis experiments using the
corresponding melted oxides, (2) they exhibit a large range
of electronic properties (3) platinum presents several
oxidation states, (4) some oxides are of technical interest
due to their catalytic and electrochemical properties and
their potential applications as, for example, H –O fuel-cell
electrocatalysts. From a structural point of view, platinum
oxides can be divided into two groups: those containing
divalent (Pt ) or partially oxidized platinum in planar
coordination and those with fully oxidized tetravalent
4
platinum (Pt ) in octahedral coordination [1]. In many
2
4
4
+
[2] and PbPt O [3]. The first one contains Pt
2
in
4
octahedral coordination, the PtO6 octahedra are edge-
shared to form rutile-type chains further connected
2
+
through Pb ions. The structure of the latter consists of
4
PtO octahedra (Pt ) and two types of PtO square planes
+
6
4
containing divalent and/or partially oxidized platinum.
3
2
2
+
2+
Partial substitution of Bi
for Pb
is achieved in
Pb1 Bi Pt O (0pxp0.3) by partial reduction of plati-
ꢀx
num in the [PtO ] chains [4]. Although Bi PtO has not
x
2
4
2
+
4 2 4
been isolated, a series Bi2 Pb PtO has been stabilized
ꢀx
x
4
+
within the range 0.33pxp0.52 [5–7] by partial oxidation
2+
of Pt in [PtO ] infinite chains to give a structure similar
partially oxidized platinum oxides, the PtO squares are
4
4
to that of Bi CuO [8] and Bi PdO [9].
2
4
2
4
Ã
In the Sr/Pt/O system, only Sr PtO with K CdCl type
4
Corresponding author. Fax: +33 3 20 43 68 14.
E-mail address: catherine.renard@ensc-lille.fr (C. Renard).
6
4
6
structure and isolated PtO octahedra has been reported
6
0022-4596/$ - see front matter r 2006 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2006.04.009

ARTICLE IN PRESS
C. Renard et al. / Journal of Solid State Chemistry 179 (2006) 2101–2110
2102
[
[
10–12]. Substitution of one Sr by divalent metals, Mg
13,14], Ni [15,16], Cu [16–18], Zn [19], leads to the largely
also applies corrections for Lorentz and polarization
effects. Due to the fineness of the needle, a semi-empirical
absorption correction was applied using the program
SADABS [21], based on redundancy. The positions of the
heavy atoms (Sr, Pb and Pt) were determined by direct
method using SIR97 [22], and then refined on jFj using
JANA2000 [23], the oxygen atoms were localized on the
Fourier difference maps. The crystallographic and experi-
mental details are summarized in Table 1.
studied Sr MPtO series. Attempts to substitute Sr by Pb
6
were unsuccessful due to the unfavorable environment of
M atom for the lone pair Pb ion. However in the course
of the investigation of the Sr/Pb/Pt/O system we have
isolated Sr PbPt O , a new compound containing di-
3
2
+
4
4
11
nuclear metal–metal bonded platinum (III) dumbell-
+
shaped Pt ions, evidenced for the first time in an oxide
6
2
compound. This paper reports the synthesis, the crystal
structure determination and Raman spectroscopy study of
this unique platinum (III) oxide.
The powder X-ray diffraction pattern was collected on
ground crystals, using a Bruker D8 diffractometer, with
˚
CuKa radiation (l ¼ 1:54056 A) and an energy dispersive
detector (sol-X). The profile fitting and the cell parameters
refinements were performed using the powder option of
JANA2000 [23].
2
. Experimental
2
.1. Synthesis
Crystals of Sr PbPt O were prepared in molten PbO as
4
4
11
a flux. Strontium carbonate, platinum and lead oxide in
proportion 2:1:5 were ground and placed in a gold crucible.
The mixture was heated at 930 1C for 3 h, and then slowly
cooled down to 850 1C at 1 1C h whereupon the furnace is
turned off and allowed to cool down to room temperature.
The crystals were extracted from the flux by dissolving PbO
in excess in hot acetic acid, isolated by filtration and rinsed
with distilled water. All the crystals are black, thin needles.
The reference compounds chosen for Raman spectroscopy
were synthesized as described in the referenced publica-
Table 1
Crystallographic data and experimental details for Sr
determination
4 4
PbPt O11 structure
ꢀ
1
Crystal data
Formula
Formula molar weight
4 4 11
Sr PbPt O
1513.98
2
Z
Unit cell dimensions
˚
a (A)
5.6705 (6)
9.9852 (5)
˚
b (A)
tions; Sr PtO [10], and PbPt O [3] were prepared via solid
6
˚
c (A)
4
2
4
10.0889 (5)
90.421 (3)
89.773 (8)
90.140 (9)
571.22 (8)
8.799 (1)
state reaction and Bi1.6Pb0.4PtO [5] crystals were obtained
4
a (1)
b (1)
g (1)
in molten PbO–Bi O .
2
3
3
˚
V (A )
Calculated density (g cm )
2
.2. EDS elemental analysis
ꢀ3
Data collection
Theta range (1)
Index range
A quantitative elemental analysis was performed by
2.02–42.35
ꢀ7php9; ꢀ18pkp18;
Energy Dispersive Spectroscopy (EDS), with a Jeol
JSM–5300 scanning microscope equipped with a IMIX
system of Princeton Gamma technology, at 15 kV.
Strontium, lead and platinum percentages were calibrated
with standards.
ꢀ
19plp18
Reflections collected
Reflections observed
Independent reflections
25363
22713
6584
Independent reflections 43s(I)
Redundancy
Criterion for observation
5852
3.852
I43s(I)
2
.3. Thermal analysis
Refinement
The thermal stability of Sr PbPt O was studied by
4
4
11
Data/restraints/parameters
Final R indices (R, wR) all
Final R indices (R wR) obs
Weighting scheme
6584/0/128
3.10, 2.67
2.60, 2.62
thermal differential analysis performed with a TG/DT 92
SETARAM instrument from room temperature to 1100 1C
under air, the decomposition compounds were identified by
X-ray powder diffraction.
2
1/s (F)
0
1
C
Twinning matrix
1
0
0
0
0
B
@
¯
1
0 A
¯
0
1
2
.4. X-ray diffraction
A black needle crystal of Sr PbPt O was mounted on a
Twin ratio
Largest diff. peak and hole [e A ]
26.74%
3
˚
˚
2.67 (0.62 A from Pt(1)), ꢀ2.31
4
4
11
˚
(0.35 A from Pb(1))
glass fibre and aligned on a Bruker X8 Apex II CCD 4 K
diffractometer. The X-rays intensity data were collected at
Extinction method
Extinction coefficient
Becker and Coppens [24]
0.00058(2)
˚
P
P
P
P
room temperature using a MoKa radiation (l ¼ 0:71073 A)
2
2
2
1=2
2
0
2
C
R¼ ðjF0j ꢀ jFCjÞ= jF0j, wR ¼ ½ wðjF j ꢀ jF jÞ = wðF Þ ꢁ , w ¼
0
selected by a graphite monochromator. The raw data
frames were integrated with SAINT program [20], which
2
2
0
2
1
=½s ðF Þ þ ðaPÞ þ bPꢁ where a and b are refinable parameters and
2
2
C
P ¼ ðF þ 2F Þ=3.
0

ARTICLE IN PRESS
C. Renard et al. / Journal of Solid State Chemistry 179 (2006) 2101–2110
2103
2
.5. Raman spectroscopy
point, it is clear that the structure is pseudo-symmetric.
Different merohedric twin possibilities (i.e. completely
overlapped ones) were then tested and the volume fraction
of the second element was refined. The structure factor for
The Raman spectra were obtained at room temperature
with the 647.1 nm excitation line from a Spectra Physics
krypton ion laser. The beam was focused onto the sample
using the microscopic configuration of the apparatus. The
scattered light was analysed with an XY Raman Dilor
spectrometer equipped with an optical multichannel charge
coupled device liquid nitrogen-cooled detector. In the
2
2
complete overlapping is calculated as F ðHÞ ¼ nF ðHT Þ þ
1
2
ð1 ꢀ nÞF ðHÞ where n is the volume fraction and T the
matrix representation of the twin operator. In our case,
¯
¯
T ¼ [100,010,001] corresponds to a pseudo-mirror perpen-
dicular to a*, i.e. the symmetry element lost during the
¯
passage from monoclinic 2/m11 to triclinic 1 symmetries.
ꢀ
1
1
40–1000 cm required range, the spectral resolution is
ꢀ
1
approximately 0.5 cm . The Raman spectra of four
platinum oxides were measured: Sr PbPt O , Sr PtO ,
Bi1.6Pb0.4PtO4 and PbPt O . The last three compounds
were chosen as references for their specific platinum
environment coordination. Sr PtO [10–12] contains only
octahedral coordinated platinum atoms, the transition
metal adopts only square plane environment in Bi1.6Pb0.4
PtO [5–7] and the PbPt O [3] crystal structure combines
Subsequently, the refinement was meaningfully improved,
R ¼ 0:026 and wR ¼ 0:0262 and twin ratio n ¼ 0:267. Note
that this twin was systematically observed on the different
crystals tested. The anisotropic displacement parameters
were allowed to vary for Sr, Pb and Pt atoms, the
displacement parameters for the oxygen atoms were kept
isotropic. The formulae deduced from the crystal structure
refinement is in good accordance with the EDS analysis
performed on single crystal which indicated Sr:Pb:Pt ratio
close to 4:1:4 and no other element.
4
4
11
4
6
2
4
4
6
4
2
4
both octahedral and square planar platinum coordinations.
3
. Results and discussion
The final atomic coordinates and displacement para-
meters are given in Tables 2 and 3, respectively. Table 4
reports the main interatomic distances and angles.
3
.1. Structure refinement
The unit cell parameters indicated a pseudo-tetragonal
3.2. Platinum polyhedra
system, the tetragonal and orthorhombic symmetry were
quickly ruled out by a simple examination of the averaging
agreement factor. The different settings in the monoclinic
symmetry were tested: Rint ¼ 0:4294, 0.4415 and 0.0894 for
There are four crystallographically independent Pt
atoms in Sr PbPt O , each is coordinated by four oxygen
atoms forming a square with Pt–O distances ranging from
4
4
11
˚
1
12/m, 12/m1, and 2/m11, respectively, with cell para-
2.005(5) to 2.046(5) A. For Pt(2) and Pt(3), the coordina-
tion polyhedra is completed by a fifth oxygen atom at a
meters given in Table 1. Then, at this level, the structure
was solved in the monoclinic system with cell parameters
˚
shorter distance, 1.993(4) and 1.984(4) A for Pt(2) and
˚
˚
˚
a ¼ 9:9852ð5Þ A, b ¼ 5:6705ð6Þ A, c ¼ 10:0889ð5Þ A and
b ¼ 90:421ð3Þ1. As the set of reflections did not evidence
any systematic extinction, space groups P2/m, Pm and P2
were tested. The atomic positions are almost related by a 21
axis, thus despite the absence of systematic extinction, the
structure refinement was undertaken in P2 and P2 /m
Pt(3), respectively, forming a square pyramid. The average
Pt–O distances are slightly larger for four-coordinated
˚
platinum Pt(1) and Pt(4), 2028(8) and 2.025(12) A,
respectively, than for five-coordinated Pt(2) and Pt(3),
˚
2.015(13) and 2.016(25) A, respectively. Planar coordina-
tion for platinum is common to many oxides. Five-
coordinated platinum atoms have been reported in
platinum complexes in trigonal bipyramid [25,26] or square
pyramid [27] environments but Sr PbPt O is the first
1
1
space groups, trying different twin possibilities. The best
results were obtained in Pm with final R ¼ 0:0742 and
wR ¼ 0:0899, but with negative isotropic displacement
parameters for some oxygen atoms and disorder for others.
The low quality of these results questioned the choice of the
crystal system. The cell parameters were then refined from
powder X-ray diffraction considering monoclinic and
4
4
11
platinum oxide, to our knowledge, containing five-coordi-
nate platinum.
3.3. Structural connectivity
triclinic systems. Refinement in the triclinic system, with
2
R ¼ 0:0877 and w ¼ 1:93, was better compared to that in
The projection of the structure of Sr PbPt O along
4
p
4
11
2
the monoclinic cell, Rp ¼ 0:1008, w ¼ 2:45. The observed
[100] is presented in Fig. 2. The structure can be described
8
ꢀ
and calculated diffraction patterns are shown in Fig. 1, the
most relevant difference between the monoclinic and
triclinic refinement is pointed out in the insert. The refined
as built from [Pt O
]
columns running down [100] and
2+
4
+
10 N
2
separated by Sr and Pb ions. The columns consist of
corner shared square planes PtO and square pyramids
4
˚
˚
cell parameters are a ¼ 5:6705ð6Þ A, b ¼ 9:9852ð5Þ A,
PtO . Each square plane is opposite to a square pyramid;
5
˚
c ¼ 10:0889ð5Þ A, a ¼ 90:421ð3Þ1, b ¼ 89:773ð8Þ1 and
this set constitutes the elemental building unit (EBU) Pt O
2
9
g ¼ 90:140ð9Þ1. The structure determination was then
and is reproduced with a rotation angle of about 901. The
successive EBU are linked by sharing the corners of the
squares (Fig. 3). Two different EBU are formed,
¯
undertaken in P1 space group. The direct methods lead
to the similar crystal structure than in Pm space group and
the refinement gave R ¼ 0:0895 and wR ¼ 0:1283. At this
Pt(1)Pt(2)O9 and Pt(3)Pt(4)O . Whatever the platinum
9

ARTICLE IN PRESS
C. Renard et al. / Journal of Solid State Chemistry 179 (2006) 2101–2110
2104
4 4
Fig. 1. Observed and calculated diffraction patterns of Sr PbPt O11 in monoclinic (a) and triclinic (b) systems. The inset points out the 30.65–31.461 2y
range.

ARTICLE IN PRESS
C. Renard et al. / Journal of Solid State Chemistry 179 (2006) 2101–2110
2105
Table 2
Final atomic coordinates and equivalent isotropic displacement parameters for Sr
4
4 11
PbPt O
Wick.
Occ
x
y
z
U
eq
Pt(1)
Pt(2)
Pt(3)
Pt(4)
Pb(1)
Sr(1)
Sr(2)
Sr(3)
Sr(4)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
O(10)
O(11)
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
2i
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0.25019(5)
0.25093(5)
0.202433(18)
0.293266(18)
0.122251(17)
0.372350(18)
ꢀ0.25565(2)
0.53435(4)
ꢀ0.03523(5)
0.12503(5)
ꢀ0.38574(5)
0.1686(4)
ꢀ0.107143(18)
ꢀ0.355274(18)
ꢀ0.277462(18)
ꢀ0.184564(18)
ꢀ0.27002(2)
ꢀ0.12683(5)
ꢀ0.39433(5)
0.04821(5)
0.00683(11)
0.00648(11)
0.00652(11)
0.00691(11)
0.01206(10)
0.0088(3)
0.0141(3)
0.0103(3)
0.0127(3)
0.0065(8)
0.0068(8)
0.0065(8)
0.0070(8)
0.0100(7)
0.0071(8)
0.0073(8)
0.0078(8)
0.0063(8)
0.0079(7)
0.0076(7)
ꢀ0.24965(5)
ꢀ0.24934(5)
ꢀ0.28261(4)
0.24977(12)
0.24879(13)
ꢀ0.24903(12)
0.24862(12)
ꢀ0.4887(8)
0.4989(8)
ꢀ0.48205(5)
ꢀ0.4156(5)
ꢀ0.3107(5)
ꢀ0.3111(4)
ꢀ0.1490(5)
ꢀ0.3643(4)
ꢀ0.0453(5)
ꢀ0.0436(5)
ꢀ0.1512(5)
ꢀ0.4164(5)
ꢀ0.2630(4)
ꢀ0.5384(4)
0.4320(4)
0.4331(4)
0.0604(4)
0.0051(8)
0.4950(8)
ꢀ0.2459(8)
0.5018(8)
ꢀ0.0566(4)
0.3321(5)
0.3329(5)
ꢀ0.0032(8)
0.0082(8)
0.0598(4)
0.1720(4)
ꢀ0.0123(8)
0.3296(7)
0.2498(8)
ꢀ0.2524(4)
0.3664(4)
P P
1
3
n
i
n
j
Ueq ¼
Uija a aiaj.
i
j
Table 3
Anisotropic displacement parameters of metal atoms for Sr
4
4 11
PbPt O
U
11
U
22
U
33
U
12
U
13
U
23
Pt(1)
Pt(2)
Pt(3)
Pt(4)
Pb(1)
Sr(1)
Sr(2)
Sr(3)
Sr(4)
0.00520(10)
0.00500(10)
0.00506(10)
0.00514(10)
0.00898(10)
0.0070(2)
0.00394(7)
0.00321(7)
0.00317(7)
0.00343(7)
0.00779(8)
0.00390(17)
0.00496(18)
0.00445(17)
0.00502(18)
0.00308(7)
0.00291(7)
0.00282(7)
0.00370(8)
0.00581(8)
0.00344(18)
0.0064(2)
0.00130(9)
0.00131(9)
0.00117(9)
0.00128(9)
0.00062(9)
0.0008(2)
0.0020(2)
0.0016(2)
0.0012(2)
ꢀ0.00009(9)
ꢀ0.00018(9)
ꢀ0.00006(9)
ꢀ0.00005(9)
ꢀ0.00006(9)
0.0000(2)
0.00096(5)
0.00085(5)
0.00012(5)
ꢀ0.00007(5)
0.00102(6)
ꢀ0.00035(13)
0.00120(15)
0.00116(14)
ꢀ0.00010(14)
0.0111(3)
0.0081(3)
0.0100(3)
ꢀ0.0008(2)
0.0000(2)
0.00434(19)
0.00552(19)
ꢀ0.0007(2)
3
+
coordination environment, the metal is slightly moved
toward the centre of the column, bending O–Pt–O angles to
units formed by two square pyramidal coordinated Pt
ions. The intermetallic distance, in the range from 2.46 to
˚
2.53 A, depending on the compounds, is imposed by the
1
72.7–174.71 and creating short Pt–Pt distance of 2.6712(3)
2
ꢀ
˚
and 2.6613(3) A for Pt(1)–Pt(2) and Pt(3)–Pt(4), respec-
tively. Such distances involve strong metal–metal interac-
tions, with a bonding between the platinum atoms, thus the
EBU can be considered as formed by dinuclear Pt ions
with asymmetric environments of the two platinum atoms.
SO or hydrogenophosphates bridges. These distances are
very short compared to those observed in Sr PbPt O ,
4
4
4
11
however in this oxide the two Pt are not bridged and the
Pt–Pt distances are comparable to the values obtained in
diplatinum (III) complexes with unsupported Pt–Pt bonds,
6
+
2
˚
Sr PbPt O is the first example of platinum oxide
11
typically 2.6964(5) and 2.694(1) A in tetrakis (-dioximato)
[36] and imino-hydroxy-dimethylpropane (-trichloro) [37]
platinum (III) complexes.
4
4
containing such a ‘lantern dimer’ Pt O . One can note
2
9
8
2
+
that dinuclear Re ions within square planes dimers have
been reported, in particular in La Re O [28] and
18
In several oxides, Pt–Pt bonding appears in columnar
stacked fourfold planes with one-dimensional interactions
like in Na Pt O [38–40], Bi1.6Pb0.4PtO [5], PbPt O [3]
6
4
La Re O [29]. In those compounds, the rhenium atoms
4
2
10
are also apart from the oxygen square plane, creating a
short metal–metal distance.
Several platinum sulphates [30,31], hydrogenopho-
x
3
4
4
2
4
with metal–metal distances homogeneous along the chains.
In PtO [41] or CaPt O [42], PtO planes are stacked in two
perpendicular directions with an unique Pt–Pt distance of
2
4
4
6
2
+
sphates [32–34] and phosphites [35] contain Pt dumbbell

ARTICLE IN PRESS
C. Renard et al. / Journal of Solid State Chemistry 179 (2006) 2101–2110
2106
Table 4
Main interatomic distances and angles in Sr
4 4 11
PbPt O
˚
Dist. (A)
˚
Dist. (A)
˚
Dist. (A)
Bond
Bond
Bond
Pt(1)–O(4)
Pt(1)–O(6)
Pt(1)–O(7)
Pt(1)–O(8)
Pt(2)–O(1)
Pt(2)–O(2)
Pt(2)–O(3)
Pt(2)–O(9)
Pt(2)–O(11)
Pt(3)–O(1)
Pt(3)O(4)
2.028(4)
2.022(5)
2.040(5)
2.023(4)
2.023(4)
2.021(4)
2.022(4)
2.016(4)
1.993(4)
2.007(5)
2.038(5)
1.984(4)
2.046(5)
2.005(5)
2.011(5)
2.019(4)
2.030(5)
2.039(5)
2.6712(3)
2.6613(3)
Pb(1)–O(5)
Pb(1)–O(10)
Pb(1)–O(11)
Sr(1)–O(2)
Sr(1)–O(3)
Sr(1)–O(6)
Sr(1)–O(6)
Sr(1)–O(7)
Sr(1)–O(7)
Sr(1)–O(10)
Sr(2)–O(1)
Sr(2)–O(1)
Sr(2)–O(4)
Sr(2)–O(5)
Sr(2)–O(5)
Sr(2)–O(5)
Sr(2)–O(8)
Sr(2)–O(9)
Sr(2)–O(9)
Sr(2)–O(10)
2.219(4)
2.200(4)
2.229(4)
2.539(5)
2.529(4)
2.617(5)
2.600(5)
2.610(5)
2.575(5)
2.581(4)
2.528(4)
2.694(5)
2.998(5)
2.828(5)
2.891(5)
2.611(4)
2.956(5)
2.559(4)
2.700(5)
2.593(4)
Sr(3)–O(4)
Sr(3)–O(4)
Sr(3)–O(6)
Sr(3)–O(7)
Sr(3)–O(8)
Sr3)O–(8)
2.547(5)
2.532(4)
2.687(5)
2.667(5)
2.563(5)
2.531(4)
2.547(4)
2.762(4)
2.898(5)
2.571(5)
2.859(4)
2.581(4)
2.731(4)
2.615(4)
2.536(4)
2.840(5)
2.859(5)
Sr(3)–O(10)
Sr(4)–O(1)
Sr(4)–O(2)
Sr(4)–O(2)
Sr(4)–O(3)
Sr(4)–O(3)
Sr(4)–O(9)
Sr(4)–O(10)
Sr(4)–O(11)
Sr(4)–O(11)
Sr(4)–O(11)
Pt(3)–O(5)
Pt(3)–O(8)
Pt(3)–O(9)
Pt(4)–O(2)
Pt(4)–O(3)
Pt(4)–O(6)
Pt(4)–O(7)
Pt(1)–Pt(2)
Pt(3)–Pt(4)
Angles
(1)
Angles
(1)
Angles
(1)
O(4)–Pt(1)–O(7)
O(6)–Pt(1)–O(8)
O(1)–Pt(2)–O(3)
O(2)–Pt(2)–O(9)
172.9(2)
173.5(2)
173.26(17)
172.68(18)
O(1)–Pt(3)–O(8)
O(4)–Pt(3)–O(9)
O(2)–Pt(4)–O(7)
O(3)–Pt(4)–O(6)
173.69(18)
174.70(18)
172.90(19)
173.13(18)
O(5)–Pb(1)–O(10)
O(5)–Pb(1)–O(11)
O(10)–Pb(1)–O(11)
95.19(16)
93.47(15)
96.68(16)
Fig. 3. The two different asymmetric dumbell-shaped Pt
2
8
O
9
elemental
ꢀ
building units (a and b) and their connection to form [Pt
connected by lead atoms (c).
4
O
10
]
N
columns
shorter Pt–Pt distance. The second Pt–Pt interaction
+
2
˚
2.99 A) appears between the columns. The Ca
(
surround the columns with helicoidally 4 related positions.
ions
2
Fig. 2. Projection of the structure of Sr
ꢀ
4
PbPt
column is pointed out with the platinum environment
4
O11 along [100]. A
2
A quasi-4 symmetry links as well Sr coordinates around
+
8
[
polyhedra.
Pt
4
O
10
]
N
2
8
ꢀ
[Pt O
4
]
columns in the triclinic Sr PbPt O structure.
10 N 4 4 11
However the coordination environments of the two alka-
line-earth ions are different since the relative columns
positions are different in the two structures. The Sr(1) and
Sr(3) atoms are seven-coordinated (Fig. 5b) and Sr(2) and
Sr(4) are ten-coordinated (Fig. 5a) with oxygen atoms. The
seven coordination environment of Sr(1) and Sr(3) can be
deduced from the ten coordination environment of Sr(2)
and Sr(4) by removing the three oxygen atoms coming
˚
.04 A in PtO and with alternating Pt–Pt distances of
3
2
˚
.79(5) and 2.99(5) A in CaPt O . This last compound has
2
4
several structural similarities with Sr PbPt O . The most
4
4
11
4
8
ꢀ
evident resemblance is the [Pt O ]N column consisting on
4
corner-shared platinum square planes (Fig. 4). The
platinum atoms are also moved toward the centre of
the column, with a O–Pt–O angle of 1711 and creating the

ARTICLE IN PRESS
C. Renard et al. / Journal of Solid State Chemistry 179 (2006) 2101–2110
2107
Table 5
4 4 11
Bond valence calculation for cations in Sr PbPt O
Atom
Supposed bond
valence
Calculated bond
valence
Pt(1)
Pt(1)
Pt(2)
Pt(2)
Pt(3)
Pt(3)
Pt(4)
Pt(4)
Pb(1)
Sr(1)
Sr(2)
Sr(3)
Sr(4)
+2
+4
+2
+4
+2
+4
+2
+4
+2
+2
+2
+2
+2
1.98
2.67
2.57
3.46
2.57
3.46
2.00
2.70
2.26
2.02
2.06
2.02
2.06
2
+
Pb
PbO E tetrahedron.
complete the environment to form a more usual
8ꢀ
3
Fig. 4. Comparison between the (a) [Pt O ] column in Sr PbPt O
4 10 N 4 4 11
4
ꢀ
and (b) the [Pt
4
O
8
]
N
2 4
columns CaPt O .
3.4. Bond valence calculation
In opposite to organic chemistry, there are various
models for chemical bonds in inorganic chemistry. The
concept of bond valence [46] provides a useful description
largely used in solid state chemistry; in this model, all
atoms are considered as cations or anions. The bond
valence sums for all cations in Sr PbPt O (Table 5) were
4
4
11
calculated using the bond valence parameters R0 from
Brese and O’Keeffe data [47] with the formula s ¼
exp½ðR0 ꢀ RÞ=bꢁ and b ¼ 0:37. These results unambigu-
ously confirm that Sr and Pb are divalent. For platinum
atoms the valence bond sums calculations using R0 ¼ 1:768
II
IV
Fig. 5. Strontium environments; (a) ten coordinated Sr(2) and Sr(4), the
light oxygen atoms are the axial oxygen of the PtO
coordinated Sr(1) and Sr(3).
for Pt and R0 ¼ 1:879 for Pt indicate that the four-
coordinated Pt(1) and Pt(4) atoms are clearly divalent,
which is an usual oxidation state for this coordination.
Actually, it can vary from +2, for example in MPt O
5
pyramid and (b) seven
3
4
(
M ¼ Mn, Co, Zn, Mg, Ni) [48], to +3 in columnar-staked
from the pyramid apex. There is a close resemblance
between the Sr(2) or Sr(4) environments and the 12
coordination observed in hexagonal-type perovskite built
PtO as in PbPt O [3] and can even take a non-integer
4
4
2
mean value like in Na Pt O [38–40]. For the five-
x
3
4
coordinated Pt atoms, Pt(2) and Pt(3), the valence bond
sums are 2.57 if these atoms are supposed to be divalent
and 3.46 if they are supposed to be tetravalent. Calculating
that the mean oxidation state of platinum is +3 in
Sr PbPt O , and the square pyramid to planar square
from the stacking of [SrO ] layers, one equilateral triangle
3
distributed oxygen atoms of the 12 coordination are
replaced by one oxygen atom in the 10 coordination.
The lead atoms link two columns via the pyramidal axial
oxygen atoms O(5) and O(11) and complete their
coordination environment with a third oxygen atom
O(10) located between the lead atoms along [100]
4
4
11
ratio is 1, one can suppose that Pt(2) and Pt(3) are
IV
Pt in better agreement with the bond valence calculations
results.
(
Pb–O distances between 2.200(4) and 2.229(4) A and
Fig. 3c). Then, the lead atoms are three coordinated with
˚
All the oxygen atoms are penta-coordinated by two Pt
and three Sr atoms (O(1) to O(4) and O(6) to O(9), one
Pt, three Sr and one Pb ((O(5) and O(11)) and four
Sr and one Pb (O(10)). The valence bond sums are in the
range from 1.71 to 2.10 v.u., it is noticeable that the
lowest values correspond to O atoms connected to only
divalent Pt.
O–Pb–O angles around 951 (Table 4). Such an asymmetric
Pb coordination environment is observed, for example,
2
+
in alkaline metal lead oxides A PbO (A ¼ K, Rb, Cs)
4
3
2
+
˚
43–45] with Pb –O distances ranging from 2.10 to 2.20 A
[
and O–Pb–O angle close to 951. Indeed, the lone pair E of

ARTICLE IN PRESS
C. Renard et al. / Journal of Solid State Chemistry 179 (2006) 2101–2110
2108
3
.5. Vibrational spectroscopy
In order to point up the unusual pyramidal environment
of the platinum, we have undertaken a Raman spectro-
scopy investigation. To identify the fingerprint of this
platinum conformation, we have synthesized the three
platinum oxide compounds: Sr PtO , Bi1.6Pb0.4PtO and
4
6
4
PbPt O . The crystallographic data of Sr PtO [10] show
2
4
4
6
regular PtO octahedral entities linked together through
6
6
3
¯
strontium cations. As the space group is R3c (D ) and the
d
¯
platinum atoms lies in 3 (S ), only the A , E and F
2g
6
1g
g
internal modes (Fig. 5) are active in Raman scattering
while F1u species are not allowed. Bi1.6Pb0.4PtO4 is
8
described in a P4/ncc ðD4 Þ space group [5] where platinum
h
and oxygen atoms form columns of square planes bonded
together through lead or bismuth ions. Active modes for
square are A , B and B . PbPt O cell [3] contains PtO
6
1
g
2g
1g
2
4
octahedra and PtO square units sharing corners or edges.
4
4 6 2 4
Fig. 7. Raman spectra of Bi1.6Pb0.4PtO4, Sr PtO , PbPt O and
4 4 11
Sr PbPt O . The specific platinum coordination environments are
The vibration motion correspondence between octahedral,
square plane and square pyramid conformations is
reported in Fig. 6. The principal differences between the
various environments lie in the axial stretching vibration
mode that is missing or forbidden in the square plane and
octahedron while it is active in the square pyramid. Fig. 7
exhibits the Raman spectra of the Sr PtO , Bi1.6Pb0.4PtO4
recalled for each compound.
assign Pt–O square plane stretching vibration modes to the
ꢀ
1
bands at 631 cm in Bi1.6Pb0.4PtO , 635, 640 in PbPt O ,
4
2
4
ꢀ
1
and 620 cm in Sr PbPt O . As the octahedron can be
4
6
4
4
11
and PbPt O references and of our Sr PbPt O com-
2
seen as a square bipyramid, common vibrational motions
can be expected in the simple square pyramid and the
4
4
4
11
pound.
In the literature [49–51], we find the stretching motion of
ꢀ
1
bipyramid. Thus, the lines at 519, 533 and 559 cm in
ꢀ
1
ꢀ1
Pt–O bond in the 450–700 cm frequency range. In this
expecting spectral domain, we observe the stretching Pt–O
Sr PtO are observed at 520, 526 and 542 cm in PbPt O
2
4
6
4
ꢀ
1
and at 506, 536 and 560 cm in Sr PbPt O . The slight
4
4
11
ꢀ
1
motion at 631 cm for Bi1.6Pb0.4PtO in which the square
frequency shifts can be explained by the various polyhedral
interactions. The specificity of Sr PbPt O spectrum lies in
4
plane is the unique platinum environment. We can note the
lower frequency values of the stretching motions in the
PtO octahedral species in Sr PtO structure. The three
4
4
11
ꢀ
1
its more intense band at 594 cm . This line, located
between the octahedral and square plane stretching
frequencies, characterizes the square pyramid, and is
attributed to the axial Pt–O stretching vibration mode.
This vibrational motion, not allowed in the octahedron and
missing in the square plane (Fig. 6), becomes active in the
square pyramidal conformation. The O–Pt–O angular
deformation corresponds to the same vibrational motion
for all the conformations. The observed frequency shifts
are due to different polyhedral interactions. They are
6
4
6
compounds Bi1.6Pb0.4PtO , PbPt O and Sr PbPt O
11
4
2
4
4
4
contain PtO square plane units. By comparison, we can
4
ꢀ
1
located at 424 and 468 cm in Bi1.6Pb0.4PtO , 356 and
4
ꢀ
1
82 cm in Sr PtO , 356 and 383 cm in PbPt O and 329
ꢀ1
3
and 360 cm in Sr PbPt O . For Bi1.6Pb0.4PtO , we have
4 6 2 4
ꢀ
1
4
4
11
4
1
ꢀ
assigned the strong intense band at 246 cm
to Bi–O
stretching motion [52]. The Raman spectroscopy has thus
evidenced the unusual square pyramidal environment of
ꢀ
1
the platinum atoms by identifying the 594 cm frequency
band as the fingerprint of this coordination. Furthermore,
in complexes containing a discrete Pt–Pt bond a Raman
active band characteristic of the Pt–Pt stretching vibration
ꢀ
1
is observed near 150 cm [53–55]. Notably, the metal–
ꢀ1
Fig. 6. Correspondence between stretching and bending vibration modes
in octahedral, square plane and square pyramidal units. Only active modes
of the octahedron have been represented except F1u species, not allowed in
Raman spectroscopy but indicated for the comparison with the axial
stretching motion of the square pyramid.
metal stretching frequency is observed at 144 cm
ꢀ
in
[55]
1
4ꢀ
[
Pt Cl (acac) ] [54] and 145 cm
2
in [Pt (CN) ]
2
2
4
10
˚
˚
for 2.70 A and 2.73 A Pt–Pt distances, respectively.
The metal–metal distances are shorter (2.6712(3) and

ARTICLE IN PRESS
C. Renard et al. / Journal of Solid State Chemistry 179 (2006) 2101–2110
2109
isolated dinuclear ions for platinum but also for other
metals such as rhodium are expected in a next future.
Acknowledgments
The ‘‘Fonds Europe
FEDER),’’ ‘‘CNRS,’’ ‘‘Re
‘Ministere de l’Education Nationale de l’Enseignement
Superieur et de la Recherche’’ are acknowledged for
´
en de De
veloppement Regional
´ ´
(
‘
´
gion Nord Pas-de-Calais’’ and
`
´
fundings of X-ray diffractometers. Dr. Vaclav Petricek,
Institute of Physics of the Academy of Sciences of the
Czech Republic, is acknowledged for fruitful discussion.
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4
4
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