Tetraphenyl­arsonium cis-bis­[1,2-bis­(tri­fluoro­meth­yl)ethene-1,2-dithiol­ato]platinate(II)

Stephanie Hosking; Alan J Lough; Ulrich Fekl

doi:10.1107/S1600536809021527

. 2009 Jun 13;65(Pt 7):m759–m760. doi: 10.1107/S1600536809021527

Tetraphenylarsonium cis-bis[1,2-bis(trifluoromethyl)ethene-1,2-dithiolato]platinate(II)

Stephanie Hosking ^a, Alan J Lough ^b, Ulrich Fekl ^a,^*

PMCID: PMC2969384 PMID: 21582694

Abstract

In the title compound, (C₂₄H₂₀As)[Pt(C₄F₆S₂)₂], the cation lies on a twofold rotation axis while the anion has crystallographic inversion symmetry. The Pt^II ion is in a slightly distorted square-planar coordination environment. The F atoms of both unique –CF₃ groups are disordered over two sets of sites, the ratios of refined occupancies being 0.677 (15):0.323 (15) and 0.640 (16):0.360 (16). The crystal structure is the first to date of a monoanionic [Pt(tfd)₂]⁻ species [tfd is 1,2-bis(trifluoromethyl)ethene-1,2-dithiolate] with a non-redox-active cation.

Related literature

For background information, see: Ray et al. (2005 ▶); Wang & Stiefel (2001 ▶); Harrison et al. (2006 ▶). For related crystal structures, see: Kogut et al. (2006 ▶); Tang et al. (2009 ▶); Kasper & Interrante (1976 ▶); Lim et al. (2001 ▶). For synthetic details, see: Davison et al. (1964 ▶). For the treatment of disordered solvent of crystallization, see: Spek (2009 ▶); Stähler et al. (2001 ▶); Cox et al. (2003 ▶); Mohamed et al. (2003 ▶); Athimoolam et al. (2005 ▶). For a detailed description of the electronic structure of metal–dithiolene complexes, see: Kirk et al. (2004 ▶).

Experimental

Crystal data

(C₂₄H₂₀As)[Pt(C₄F₆S₂)₂]
M _r = 1030.76
Monoclinic,
a = 24.9649 (10) Å
b = 7.3189 (3) Å
c = 23.6773 (6) Å
β = 117.779 (2)°
V = 3827.6 (2) Å³
Z = 4
Mo Kα radiation
μ = 4.82 mm⁻¹
T = 150 K
0.24 × 0.21 × 0.16 mm

Data collection

Nonius KappaCCD diffractometer
Absorption correction: multi-scan (SORTAV; Blessing, 1995 ▶) T _min = 0.341, T _max = 0.471
13097 measured reflections
4282 independent reflections
3269 reflections with I > 2σ(I)
R _int = 0.051

Refinement

R[F ² > 2σ(F ²)] = 0.054
wR(F ²) = 0.156
S = 1.09
4282 reflections
230 parameters
60 restraints
H-atom parameters constrained
Δρ_max = 4.18 e Å⁻³
Δρ_min = −2.83 e Å⁻³

Data collection: COLLECT (Nonius, 2002 ▶); cell refinement: DENZO–SMN (Otwinowski & Minor, 1997 ▶); data reduction: DENZO–SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809021527/su2119sup1.cif

e-65-0m759-sup1.cif^{(18.2KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809021527/su2119Isup2.hkl

e-65-0m759-Isup2.hkl^{(209.9KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

Funding by the Natural Science and Engineering Research Council (NSERC) of Canada, the Canadian Foundation for Innovation, the Ontario Research Fund, the Ontario Innovation Trust and the University of Toronto is gratefully acknowledged. We thank Mr Dan Harrison (University of Toronto) for assistance in the steps leading to the reduction of [Pt(tfd)₂].

supplementary crystallographic information

Comment

Square-planar metal bisdithiolene compounds are of fundamental importance for our understanding of metal complexes containing non-innocent ligands (Ray et al., 2005). The nickel complex [Ni(tfd)₂] (tfd = S₂C₂(CF₃)₂) has received considerable attention due to its potential applicability in ethylene separation and purification (Wang & Stiefel, 2001). The one-electron reduced form of the metal complex is involved in the mechanism of alkene binding (Harrison et al., 2006). In the course of our studies on the analogous platinum complexes we have crystallographically characterized [Pt(tfd)₂]⁰ and [Pt(tfd)₂]^2- (Kogut et al., 2006; Tang et al., 2009, respectively). These complexes contain square-planar platinum(II), and the tfd ligand is redox-active. While tfd is not fully reduced in the charge-neutral complex (and is only formally 1,2-perfluoromethylethene-1,2-dithiolate), tfd is fully reduced in the dianion. The C—C bond in the chelate ring of the neutral complex shortens upon reduction (Tang et al., 2009).

We report here on the first crystal structure of monoanionic [Pt(tfd)₂]^- with a non-redox-active cation (Fig. 1). A report on a previous structural determination (Kasper & Interrante, 1976) of the charge-transfer complex between tetrathiofulvalene and charge-neutral [Pt(tfd)₂] has proposed that [Pt(tfd)₂] is reduced by one electron and tetrathiovulvalene is oxidized to tetrathiafulvalinium; however, in order to reliably establish the structural properties of the one-electron-reduced species, use of a non-redox-active cation is preferable. [Pt(tfd)₂] in the title compound reported here is clearly monoanionic. The structure reported here completes structural characterization of the redox series [Pt(tfd)₂]^0/1-/2-. Structural features of [Pt(tfd)₂]^- (Fig. 2) are intermediate with respect to those of [Pt(tfd)₂]⁰ (Kogut et al., 2006) and [Pt(tfd)₂]^2- (Tang et al., 2009). The structural effects observed upon stepwise reduction of the neutral complex [Pt(tfd)₂]⁰ to [Pt(tfd)₂]^- and [Pt(tfd)₂]^2- are of varying statistical significance (significant within 2σ for Pt—S, borderline significant for C—C). However, they confirm observations made by Lim et al. (2001) on an analogous nickel complex containing a non-fluorinated dithiolene, the redox series [Ni(S₂C₂Me₂)₂]^0,1-,2-. The combined evidence suggests that these effects are real. A relatively straightforward rationalization, in terms of resonance structures, is shown in Fig. 2. For a detailed description of the electronic structure of metal dithiolene complexes, see Kirk et al. (2004).

Experimental

The tetraphenylarsonium salt of [Pt(tfd)₂]^- was synthesized using a slightly modified literature procedure. The literature procedure uses acetone/ethanol as the reductant, followed by precipitation with tetraphenylarsonium chloride, (Davison et al., 1964) to obtain the product in 36% yield. We repeated that literature reaction and obtained 24% yield. We then decided to use water in THF to achieve reduction of [Pt(tfd)₂], followed by addition of tetraphenylarsonium chloride. It was previously observed that water in polar solvents such as THF leads to reduction of the related nickel complex Ni[(S₂C₂(CF₃)₂]₂ (Harrison et al., 2006). In a 10 ml vial, 24.9 mg (0.0385 mmol) of [Pt(tfd)₂] were dissolved in 1.0 ml ofTHF, leading to a dark greenish-blue solution. Addition of 0.3 ml of H₂O induced a rapid colour change, to produce a brownish-yellow solution. Solid tetraphenylarsonium chloride (25.3 mg, 0.068 mmol) was added to the solution while stirring, followed by an additional 0.25 ml of THF, to produce a homogeneous solution. In order to lower the solubility of the salt again, an additional 0.4 ml of H₂O were added, and the vial was storred at 278 K for three weeks. Crystals had not formed at that time, and crystallization was induced by scratching of the inner surface of the vial with a glass rod. After three additional weeks at 378 K, [AsPh₄]⁺[Pt(tfd)₂]^- had crystallized as dark yellow blocks. The crystals were removed from the supernatant and dried under vacuum. Yield: 26.6 mg (0.0258 mmol, 67%). Inspections of the crystals with a stereomicroscope showed them to be of excellent quality. One crystal was chosen for the single-crystal X-ray structure determination.