A dynamic disorderlinked reversible phase transition in a new chloroform solvate of cisdichloridobis(triethylphosphane)platinum(II)

Article abstract of DOI:10.1107/S0108270111008353

The title compound, cisdichloridobis(triethylphosphane)platinum(II) chloroform monosolvate, [PtCl₂(C₆H₁₅P) ₂]·CHCl₃, has been obtained from ligand scrambling in the cis-[PtCl₂(Cyp2PCl)(PEt₃)] (Cyp = cyclopentyl) system in CHCl₃ solvent. Unlike the two previously reported unsolvated polymorphs, which are both monoclinic, the compound crystallizes in an orthorhombic setting. Furthermore, the system exhibits a reversible temperaturedependent structural phase transition, coupling a reduction in anisotropic displacement parameters and a reduction in crystallographic symmetry on cooling. The hightemperature phase adopts space group Pnma with the complex and solvent molecules sitting across a crystallographic mirror plane (Z′ = 0.5). The low-temperature phase adopts the space group P₂₁₂₁₂₁ with Z′ = 1.

Full text of DOI:10.1107/S0108270111008353

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
were sampled for each data point, with the temperature of the
data point being assigned to that at the mid-point of the scan.
Each point on the graph therefore represents data recorded
over 1 K. Full data collections and structural determinations
were then carried out above and below the phase-transition
temperature at 220 K, (1a), and 120 K, (1b), respectively.
ISSN 0108-2701
A dynamic disorder-linked reversible
phase transition in a new chloroform
solvate of cis-dichloridobis(triethyl-
phosphane)platinum(II)
Keith B. Dillon,a Judith A. K. Howard,a Philippa K.
Monks,a Michael R. Proberta* and Helena J. Shepherdb
aChemistry Department, Durham University, Science Site, South Road, Durham
DH1 3LE, England, and bLaboratoire de Chimie de Coordination, CNRS UPR8241,
F-31077 Toulouse, France
At 220 K, the space group of the solvated complex, (1a), is
Pnma, with a mirror plane bisecting both the Pt complex and
the solvent molecule, resulting in a structure with Z0 = 0.5. The
CHCl3 molecule shows dynamic disorder, rotating about the
C—H bond axis in a symmetrical fashion with respect to the
mirror plane.
Correspondence e-mail: m.r.probert@durham.ac.uk
Received 18 January 2011
Accepted 4 March 2011
Online 10 March 2011
The title compound, cis-dichloridobis(triethylphosphane)-
platinum(II) chloroform monosolvate, [PtCl2(C6H15P)2]ꢀ-
CHCl3, has been obtained from ligand scrambling in the cis-
[PtCl2(Cyp2PCl)(PEt3)] (Cyp = cyclopentyl) system in CHCl3
solvent. Unlike the two previously reported unsolvated
polymorphs, which are both monoclinic, the compound
crystallizes in an orthorhombic setting. Furthermore, the
system exhibits a reversible temperature-dependent structural
phase transition, coupling a reduction in anisotropic displace-
ment parameters and
a reduction in crystallographic
symmetry on cooling. The high-temperature phase adopts
space group Pnma with the complex and solvent molecules
sitting across a crystallographic mirror plane (Z0 = 0.5). The
low-temperature phase adopts the space group P212121 with
Z0 = 1.
Figure 1
Graph showing the evolution of the c-axis length of (1) with temperature.
Comment
As part of our studies on hydrolysis/hydroxylation of chloro-
phosphane ligands in situ on platinum(II) centres (Cornet et
al., 2011), we have prepared in solution the complex cis-
[PtCl2(Cyp2PCl)(PEt3)] (Cyp = cyclopentyl) and allowed it to
hydrolyse slowly by exposure to air. During the hydrolysis
process, however, the 31P NMR solution-state spectra of the
reaction mixture demonstrated that ligand scrambling was
occurring. Crystals suitable for single-crystal X-ray diffraction
were isolated from the reaction mixture which proved to be a
new 1:1 solvate of cis-[PtCl2(PEt3)2] with CHCl3, (1).
Analysis of the variation of the length of the crystal-
lographic c axis of (1) with temperature (Fig. 1) clearly
demonstrates the onset of a phase transition at 149 K. Data for
the calculation of these unit-cell parameters were collected
during continuous very slow cooling (2 K hꢁ1); the data
collections were such that equal amounts of reciprocal space
Figure 2
The molecular structure of (1a) at 220 K (left, the mirror plane runs
through atoms Pt1, Cl1S and C1S) and (1b) at 120 K (right). Atomic
displacement parameters are shown at 50% probability in all crystal-
lographic figures. [Symmetry code: (0) x, ꢁy + 21, z.]
Acta Cryst. (2011). C67, m111–m114
doi:10.1107/S0108270111008353
# 2011 International Union of Crystallography m111

metal-organic compounds
Upon cooling below the phase transition, the rotation of the
solvent molecule ceases, with respect to the time scale of the
diffraction experiment, and appears to ‘lock’ into place. The
CHCl3 molecule is subsequently no longer symmetrical about
a mirror plane, causing a reduction in the symmetry of the
system. The structure of (1b) thus adopts the space group
P212121 with Z0 = 1 at 120 K. This transition is illustrated in
Figs. 2 and 3. A whole-molecule twist, of both the complex and
solvent molecules, with respect to the unit cell appears to be
driven by a decrease in intermolecular distances, causing
stronger Clꢀ ꢀ ꢀH interactions. This results in movements of the
ethyl ‘arms’, further breaking the higher-temperature
symmetry, as seen from the positions of atoms C32A/B in
Fig. 2. The system reverts to the Pnma setting on returning to
higher temperatures, demonstrating that the transition is fully
reversible within the constraint that the temperature ramping
one substituent on each P atom in (1) that lies very near the
PtP2Cl2 plane. However, unlike in the previously reported
structures, these in-plane substituents point towards one
another, as shown in the Scheme. It may be expected that this
arrangement of the ethyl groups will be somewhat sterically
unfavourable, although it does give rise to an increased
number of C—Hꢀ ꢀ ꢀCl interactions, made possible by the
presence of the CHCl3 solvent.
The packing motifs of the solvated and unsolvated struc-
tures are dominated by C—Hꢀ ꢀ ꢀCl interactions. In the case of
(2), the only short intermolecular interaction is C121—
i
1
2
˚
H12Bꢀ ꢀ ꢀCl1 [Hꢀ ꢀ ꢀCl = 2.905 A; symmetry code: (i) x + ,
1
2
1
2
ꢁy + , z + ], which forms one-dimensional chains along the
[101] direction. In contrast, (1a) and (1b) form extended
hydrogen-bonding networks (Tables 2 and 3); (1a) forms two-
dimensional sheets which, upon cooling, interlink to give rise
to the three-dimensional hydrogen-bonding network found in
(1b), shown in Fig. 5.
rates are ꢂ 120 K hꢁ1
.
Electron-density maps (Fobs) through the mean plane
defined by the Cl atoms of the chloroform molecule at the two
temperatures are shown in Fig. 4, highlighting the decrease in
dynamic disorder across the phase transition.
The Pt—Cl distances (Table 1) are almost identical in (1a),
(1b) and (2), although the Pt—P bond lengths show some
variation and are shorter in both forms of (1). The most
instructive differences between (1) and (2) lie in the bond
Selected bond distances and angles for (1a) and (1b) are
listed in Table 1, together with data for one of the previously
identified unsolvated monoclinic polymorphs, (2), at 293 K
(space group Cc; Otto & Muller, 2001) for which atomic
coordinates are available. The second reported unsolvated
polymorph (Caldwell et al., 1977) is not included in Table 1 as
no three-dimensional coordinates are available, although Otto
& Muller describe it as being isostructural with their cis-
[PtCl2(AsEt3)2] complex. The known unsolvated polymorphs
differ from the title compound (1) not only by the absence of
the solvent molecule but also in the relative configuration of
the PEt3 groups (see Scheme).
The difference in orientation of the PEt3 ligands around the
Pt—P bonds may be better understood by considering the
ethyl moiety that lies close to the PtP2Cl2 plane of the Pt atom.
As in the case of the previously reported structures, there is
Figure 4
Electron-density maps (Fobs) through the mean plane defined by the Cl
atoms of the chloroform solvent molecule in the structures atꢁ2320 K (left)
˚
and 120 K (right). Contour lines are displayed at 0.5 e A intervals
(higher contour levels have been omitted for clarity for the 120 K data).
Figure 5
Hydrogen-bonding networks of (1a) at 220 K (left) and (1b) at 120 K
(right). The displayed intermolecular interactions were identified using
the same threshold delta function in OLEX2 (Dolomanov et al., 2009) of
1.68 A to highlight the difference between the structures either side of the
phase transition. H atoms not involved in intermolecular contacts have
been omitted for clarity.
Figure 3
Projection of the crystal packing along the [100] direction of (1a) and (1b)
(left and right, respectively), showing the shift in relative molecular
orientations as well as the layered motif exhibited in both structures. H
atoms have been omitted for clarity.
˚
ꢃ
m112 Dillon et al. [PtCl2(C6H15P)2]ꢀCHCl3
Acta Cryst. (2011). C67, m111–m114

metal-organic compounds
Table 1
Selected geometric parameters (A, ) for (1a), (1b) and (2).
angles in the approximately square-planar coordination
geometry. While the Cl—Pt—Cl angles are very similar, the
P—Pt—P angle is over 5ꢄ larger in the new polymorphs,
reflecting the increased steric repulsion between the PEt3
groups. There is far less variation in the Cl—Pt—P angles
found in the polymorphs of (1) (all within 1ꢄ) compared with
the monoclinic form, where they differ by greater than 6ꢄ, a
result explained by the differing steric demands on the posi-
tions of the two Cl atoms in these structures. These effects may
arise from the difference in alignment of the ethyl substituents
on the PEt3 ligands, compared with that in (2) described by
Otto & Muller (2001). The geometric parameters for (1a) and
(1b) are similar to the literature data for other cis-
[PtCl2(PR3)2] complexes (Table 4).
ꢄ
˚
(1a)
(1b)
(2)
Pt1—Cl1A
Pt1—Cl1B
Pt1—P1A
Pt1—P1B
P1A—Pt1—P1B*
P1A—Pt1—Cl1A
P1A—Pt1—Cl1B
Cl1A—Pt1—Cl1B*
2.3627 (17)
2.2540 (16)
2.3696 (10)
2.3665 (11)
2.2524 (11)
2.2550 (11)
103.89 (4)
85.18 (4)
2.364 (2)
2.374 (2)
2.264 (2)
2.2616 (18)
98.39 (7)
84.63 (9)
91.33 (7)
85.66 (9)
104.77 (9)
84.71 (6)
85.06 (4)
85.94 (4)
85.80 (10)
Note: (*) symmetry equivalent for (1a) using symmetry operation (x, ꢁy + 12, z).
Table 2
Hydrogen-bond geometry (A, ) for (1a).
ꢄ
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
C21A—H21Bꢀ ꢀ ꢀCl1Ai
C31A—H31Aꢀ ꢀ ꢀCl2Sii
C1S—H1Sꢀ ꢀ ꢀCl1Aiii
C1S—H1Sꢀ ꢀ ꢀCl1Aiv
0.98
0.98
0.99
0.99
2.97
2.93
2.70
2.70
3.717 (7)
3.802 (9)
3.505 (10)
3.505 (10)
134
149
139
138
Experimental
During the synthesis of cis-[PtCl2(PCyp2Cl)(PEt3)], all manipula-
tions, including NMR sample preparation, were carried out either
under an inert atmosphere of dry nitrogen or in vacuo, using standard
Schlenk line or glove-box techniques. Chemicals of the best available
commercial grade were used, in general without further purification.
The 31P NMR spectra of all phosphorus-containing starting materials
were recorded, to verify that no major impurities were present. The
synthesis of trans-[PtCl(ꢀ-Cl)(PEt3)]2 was carried out according to
the literature procedure of Dillon et al. (2010). 31P NMR spectra were
obtained on a Varian Mercury 400 Fourier-transform spectrometer at
161.91 MHz; chemical shifts are referenced to 85% H3PO4, with the
high-frequency direction taken as positive.
1
2
1
2
3
2
Symmetry codes: (i) x; y; z þ 1; (ii) ꢁx þ 1; ꢁy; ꢁz þ 2; (iii) x ꢁ ; ꢁy þ ; ꢁz þ ; (iv)
1
2
3
2
x ꢁ ; y; ꢁz þ .
Data collection
Bruker SMART CCD 1K
area-detector diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
Tmin = 0.759, Tmax = 1.0
15061 measured reflections
2928 independent reflections
2317 reflections with I > 2ꢃ(I)
Rint = 0.053
Cyp2PCl (0.042 ml, 0.22 mmol) was added via syringe to a solution
of trans-[PtCl(ꢀ-Cl)(PEt3)]2 (0.0840 g, 0.11 mmol) in CDCl3 (1 ml).
Refinement
R[F2 > 2ꢃ(F2)] = 0.039
wR(F2) = 0.105
S = 1.02
103 parameters
H-atom parameteꢁrs3 constrained
Formation of cis-[PtCl2(PBCyp2Cl)(PAEt3)] was confirmed using 31P
1
˚
Áꢄmax = 2.19 e A
NMR spectroscopy: ꢁPA 13.6 p.p.m. (singlet + satellites, JPt—P
=
=
ꢁ3
˚
3506 Hz, 2JP—P = 13 Hz), ꢁPB 113.0 p.p.m. (singlet + satellites, 1JPt—P
2928 reflections
Áꢄmin = ꢁ1.98 e A
2
4024 Hz, JP—P = 13 Hz). Attempted hydrolysis of this complex
resulted in ligand scrambling to afford compound (1), cis-
Compound (1b)
1
[PtCl2(PEt3)2] [31P NMR: ꢁ10.2 p.p.m. (singlet + satellites, JPt—P
=
3514 Hz)], and also cis-[PtCl2(PCyp2Cl)2] [31P NMR: ꢁ108.1 p.p.m.
(singlet + satellites, 1JPt—P = 4037 Hz)]. Colourless crystals of (1) were
obtained by slow evaporation of solvent from the reaction mixture.
Crystals of (1) were also isolated from hydrolysis reactions of cis-
[PtCl2(PCy2Cl)(PEt3)] and cis-[PtCl2(PCyCl2)(PEt3)] (Cy = cyclo-
hexyl).
Crystal data
3
˚
V = 2233.5 (2) A
Z = 4
[PtCl2(C6H15P)2]ꢀCHCl3
Mr = 621.66
Orthorhombic, P212121
Mo Kꢂ radiation
ꢀ = 7.02 mmꢁ1
T = 120 K
0.21 ꢅ 0.20 ꢅ 0.18 mm
˚
a = 18.9529 (9) A
˚
b = 15.7268 (8) A
˚
c = 7.4934 (4) A
A crystal of (1) was mounted in inert oil and placed in the cold gas
stream of an N2 cryostream device (Cosier & Glazer, 1986) at 220 K.
Data were collected at this temperature before ramping at a rate of
120 K hꢁ1 to 120 K, where the diffraction experiment was repeated.
The temperature was again ramped at 120 K hꢁ1 to 220 K where a
short data collection was performed to assess the reversibility of the
transition.
Data collection
Bruker SMART CCD 1K
area-detector diffractometer
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
Tmin = 0.757, Tmax = 1.000
25676 measured reflections
5546 independent reflections
5240 reflections with I > 2ꢃ(I)
Rint = 0.045
Refinement
R[F2 > 2ꢃ(F2)] = 0.023
wR(F2) = 0.045
S = 1.04
196 parameters
H-atom parameteꢁrs3 constrained
Compound (1a)
˚
Crystal data
Áꢄmax = 0.91 e A
ꢁ3
˚
3
5546 reflections
Áꢄmin = ꢁ1.02 e A
˚
[PtCl2(C6H15P)2]ꢀCHCl3
V = 2285.56 (19) A
Z = 4
Mo Kꢂ radiation
ꢀ = 6.86 mmꢁ1
T = 220 K
Mr = 621.66
Orthorhombic, Pnma
H atoms were constrained to idealized geometries, riding on their
˚
a = 19.0103 (9) A
˚
associated C atoms, with fixed C—H distances (0.97–1.00 A) and with
Uiso(H) = 1.2Ueq(C) [or 1.5Ueq(C) for methyl H atoms]. On trans-
˚
b = 15.7378 (7) A
˚
c = 7.6394 (4) A
0.21 ꢅ 0.20 ꢅ 0.18 mm
ꢃ
Acta Cryst. (2011). C67, m111–m114
Dillon et al.
[PtCl2(C6H15P)2]ꢀCHCl3 m113

metal-organic compounds
Table 3
Hydrogen-bond geometry (A, ) for (1b).
For both compounds, data collection: SMART (Bruker, 1999); cell
refinement: SAINT (Bruker, 2003); data reduction: SAINT;
program(s) used to solve structure: SHELXS97 (Sheldrick, 2008);
program(s) used to refine structure: SHELXL97 (Sheldrick, 2008);
molecular graphics: OLEX2 (Dolomanov et al., 2009); software used
to prepare material for publication: OLEX2.
ꢄ
˚
D—Hꢀ ꢀ ꢀA
D—H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D—Hꢀ ꢀ ꢀA
C1S—H1Sꢀ ꢀ ꢀCl1A
1.00
1.00
0.99
0.99
0.98
0.98
0.99
2.67
2.63
2.72
2.85
2.97
2.93
2.97
3.482 (4)
3.466 (4)
3.606 (5)
3.601 (5)
3.727 (5)
3.797 (5)
3.817 (4)
138
141
149
133
135
148
145
C1S—H1Sꢀ ꢀ ꢀCl1B
C21A—H21Bꢀ ꢀ ꢀCl1Ai
C21A—H21Aꢀ ꢀ ꢀCl2Sii
C12A—H12Aꢀ ꢀ ꢀCl1S
C32B—H32Fꢀ ꢀ ꢀCl1Sii
C31B—H31Dꢀ ꢀ ꢀCl2Siii
We thank the EPSRC (UK) for research grant No. EP/
C536436/1 (MRP) and for a research studentship (HJS), the
Maria da Grac¸a Memorial Fund/Chemistry Department,
Durham University (PKM), for financial support, and Johnson
Matthey plc for the loan of precious metal compounds.
1
2
1
2
1
2
1
2
Symmetry codes: (i) x; y; z þ 1; (ii) x ꢁ ; ꢁy þ ; ꢁz þ 1; (iii) ꢁx þ ; ꢁy; z þ .
Table 4
Selected geometric parameters (A, ) for cis-[PtCl2(PR3)2] complexes.
ꢄ
˚
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: LN3146). Services for accessing these data are
described at the back of the journal.
Compound
PMe3
Pt—P
Pt—Cl
P—Pt—P
96.2 (4)
Cl—P—Cl
87.47 (3)
84.2 (3)
86.55 (5)
82.1
Reference
2.256 (8)
2.239 (6)
2.321 (5)
2.344 (5)
2.242 (1)
2.245 (1)
2.299 (4)
2.289 (3)
2.2633 (9)
2.2517 (9)
2.2515 (12)
2.2544 (13)
2.364 (8)
2.388 (8)
2.367 (6)
2.349 (6)
2.359 (1)
2.355 (1)
*
a
b
c
d
e
f
PtBu3
107.3 (4)
94.80 (4)
107.6
References
PMe2Ph
PCy3
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´
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ꢃ
m114 Dillon et al. [PtCl2(C6H15P)2]ꢀCHCl3
Acta Cryst. (2011). C67, m111–m114