metal-organic compounds
trans-Di-μ-bromo-bis[bromo(triethylphosphine-κP)platinum(II)]
aDepartment of Chemistry, University of Durham, South Road, Durham DH1 3LE, England
*Correspondence e-mail: a.l.thompson@durham.ac.uk
The title compound, [Pt2Br4(C6H15P)2], is a centrosymmetric dinuclear platinum(II) complex consisting of two square-planar platinum centres connected by two bridging Br atoms.
Comment
Bridged chloride complexes of the form [PtCl2(PR3)]2 have been used extensively as starting materials in the synthesis of mononuclear platinum–phosphine complexes, which are formed through cleavage of the bridging Pt—Cl bond (Chatt & Venanzi, 1955; Meidine & Nixon, 1988; Dillon & Goodwin, 1992, 1994). Similar synthetic methodology can also be applied to bromide analogues (Cornet, 2002). However, while the crystal structures of the chloro-bridged complexes [PtCl2(PMe3)]2, [PtCl2(PEt3)]2 and [PtCl2(PPr3)]2 are known (Boag & Ravetz, 1996; Blake et al., 1989; Black et al., 1969), structures of complexes exhibiting the central heavy-atom skeleton [PtCl2P]2 are surprisingly rare, with only a handful known (Simms et al., 1987; Cobley et al., 2000).
The title complex, (I), was prepared by the CHCl2-mediated reaction of equimolar quantities of PtBr2 and [PtBr2(PEt3)2]. Given the rarity of crystal structures containing the [PtCl2P]2 fragment, it is unsurprising that (I) is the first structure to be reported containing the [PtBr2P]2 motif.
The chloride complexes [PtCl2(PR3)]2 (where R = CH3, C2H5 and C3H7) and the title compound are closely related, and all four complexes possess an inversion centre in the middle of the dimer, with the PR3 ligands in a trans geometry (Fig. 1). In addition, all four structures are asymmetric around the bridging halide ligands, but this asymmetry is reduced in (I) with respect to the chloride complexes (Table 1). This degree of asymmetry in (I) is presumably due to the relative positions of the Cl, Br and P atoms in the trans influence series and the increased ionic radius of the bromide ligand. These factors also appear to reduce the effect bridging has on the bond lengths, since the bonds to the bridging Br atoms are only 0.023 and 0.122 Å longer than those to the terminal Br atoms, compared with averages of 0.033 and 0.146 Å in [PtCl2(PR3)]2 (where R = CH3, C2H5 and C3H7; Boag & Ravetz, 1996; Blake et al., 1989; Black et al., 1969, respectively).
Experimental
PtBr2 (1.48 g, 4.2 mmol) in PhCN (10 ml) was heated to 373 K to give a bright-orange solution and a yellow precipitate on cooling {cis-[PtBr2(PhCN)2], yield 81%}. PEt3 (1.75 g, 2.18 ml, 14.8 mmol) was then added to a solution of [PtBr2(PhCN)2] (1.77 g, 3.15 mmol) in CH2Cl2 (15 ml) and the mixture stirred for 3 h. Evaporation of the solvent produced a white solid {cis-[PtBr2(PEt3)2], yield 83%}, some of which (1.45 g, 2.45 mmol) was added to a solution of PtBr2 (1.03 g, 2.9 mmol) in (CHCl2)2 and heated to 423 K for 4 h. The yellow crystals of (I) obtained on cooling were recrystallized from CH2Cl2 (yield 79%). Analysis calculated for C12H30Br4P2Pt2: C 15.23, H 3.20%; found: C 15.27, H 3.23%. 31P NMR (CDCl3): δ 10.9 (singlet with Pt satellites, 1JP—Pt = 3701 Hz, 3JP—Pt = 24.4 Hz, 4JP—P = 1.6 Hz). The AA`XX' part of the spectrum was insufficiently resolved for 2JPt—Pt to be evaluated (Kiffen et al., 1975).
Crystal data
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Refinement
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All H atoms were placed geometrically and refined using a riding model (C—H = 0.98 and 0.99 Å), with their Uiso(H) values fixed at 1.2 or 1.5 times Ueq of the parent C atom. Although there are difference density holes larger than 1 e Å−3, they are within 1 Å of the Pt atom.
Data collection: SMART-NT (Bruker, 1998); cell SMART-NT; data reduction: SAINT-NT (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXS97 (Sheldrick, 1997a); molecular graphics: SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL.
Supporting information
10.1107/S0108270104032731/hj1034sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S0108270104032731/hj1034Isup2.hkl
PtBr2 (1.48 g, 4.2 mmol) in PhCN (10 ml) was heated to 373 K to give a bright-orange solution and a yellow precipitate on cooling {cis-[PtBr2(PhCN)]2, yield 81%}. PEt3 (1.75 g, 2.18 ml, 14.8 mmol) was then added to a solution of [PtBr2(PhCN)2] (1.77 g, 3.15 mmol) in CH2Cl2 (15 ml) and stirred for 3 h. Evaporation of the solvent produced a white solid {cis-[PtBr2(PEt3)2], yield 83%}, some of which (1.45 g, 2.45 mmol) was added to a solution of PtBr2 (1.03 g, 2.9 mmol) in (CHCl2)2 and heated to 423 K for four hours. The yellow crystals of (I) obtained on cooling were recrystallized from CH2Cl2 (yield 79%). Analysis calculated for C12H30Pt2Br4P2 (946.09): C 15.23, H 3.20%; found: C 15.27, H 3.23%. 31P NMR (CDCl3): δ 10.9 (singlet with Pt satellites, 1JP—Pt = 3701 Hz, 3JP—Pt = 24.4 Hz, 4JP—P 1.6 Hz). The AA'XX' part of the spectrum was insufficiently resolved for 2JPt—Pt to be evaluated (Kiffen et al., 1975).
All H atoms were placed geometrically and refined using a riding model (C—H = 0.98 and 0.99 Å), with their Uiso(H) values fixed at 1.2 or 1.5 times Ueq of the parent C atom. Although there are difference density holes larger than 1 e Å−3, they are within 1 Å of the Pt atom.
Data collection: SMART-NT (Bruker, 1998); cell
SMART-NT; data reduction: SMART-NT and/or SAINT? (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997a); program(s) used to refine structure: SHELXS97 (Sheldrick, 1997a); molecular graphics: SHELXTL (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL.[Pt2Br4(C6H15P)2] | F(000) = 1712 |
Mr = 946.12 | Dx = 2.910 Mg m−3 |
Monoclinic, C2/c | Melting point: not measured K |
Hall symbol: -C 2yc | Mo Kα radiation, λ = 0.71073 Å |
a = 26.522 (6) Å | Cell parameters from 7378 reflections |
b = 6.8720 (13) Å | θ = 1.9–30.6° |
c = 13.811 (4) Å | µ = 20.48 mm−1 |
β = 120.930 (7)° | T = 120 K |
V = 2159.3 (9) Å3 | Block, clear intense orange |
Z = 4 | 0.20 × 0.10 × 0.10 mm |
Bruker SMART CCD 1K area-detector diffractometer | 2355 independent reflections |
Radiation source: fine-focus sealed tube | 2158 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.036 |
Detector resolution: 8 pixels mm-1 | θmax = 27.0°, θmin = 3.1° |
ω scans | h = −32→33 |
Absorption correction: multi-scan SADABS (G.M.Sheldrick, 1998) | k = −8→8 |
Tmin = 0.450, Tmax = 1.000 | l = −17→17 |
10540 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.020 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.046 | H-atom parameters constrained |
S = 1.11 | w = 1/[σ2(Fo2) + (0.0168P)2 + 10.3265P] where P = (Fo2 + 2Fc2)/3 |
2355 reflections | (Δ/σ)max = 0.001 |
94 parameters | Δρmax = 0.85 e Å−3 |
0 restraints | Δρmin = −1.75 e Å−3 |
[Pt2Br4(C6H15P)2] | V = 2159.3 (9) Å3 |
Mr = 946.12 | Z = 4 |
Monoclinic, C2/c | Mo Kα radiation |
a = 26.522 (6) Å | µ = 20.48 mm−1 |
b = 6.8720 (13) Å | T = 120 K |
c = 13.811 (4) Å | 0.20 × 0.10 × 0.10 mm |
β = 120.930 (7)° |
Bruker SMART CCD 1K area-detector diffractometer | 2355 independent reflections |
Absorption correction: multi-scan SADABS (G.M.Sheldrick, 1998) | 2158 reflections with I > 2σ(I) |
Tmin = 0.450, Tmax = 1.000 | Rint = 0.036 |
10540 measured reflections |
R[F2 > 2σ(F2)] = 0.020 | 0 restraints |
wR(F2) = 0.046 | H-atom parameters constrained |
S = 1.11 | w = 1/[σ2(Fo2) + (0.0168P)2 + 10.3265P] where P = (Fo2 + 2Fc2)/3 |
2355 reflections | Δρmax = 0.85 e Å−3 |
94 parameters | Δρmin = −1.75 e Å−3 |
Experimental. The data collection nominally covered full sphere of reciprocal Space, by a combination of 5 sets of ω scans each set at different ϕ and/or 2θ angles and each scan (15 s exposure) covering 0.3° in ω. Crystal to detector distance 4.51 cm. |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
Pt1 | 0.173674 (6) | 0.33758 (2) | 0.405282 (12) | 0.00514 (6) | |
Br1 | 0.082264 (18) | 0.24997 (7) | 0.39380 (4) | 0.01277 (10) | |
Br2 | 0.270073 (17) | 0.38814 (6) | 0.42624 (3) | 0.00937 (10) | |
P1 | 0.12538 (4) | 0.53020 (16) | 0.25526 (8) | 0.0068 (2) | |
C1 | 0.0734 (2) | 0.6930 (7) | 0.2632 (4) | 0.0175 (10) | |
H1A | 0.0440 | 0.6133 | 0.2693 | 0.021* | |
H1B | 0.0949 | 0.7713 | 0.3330 | 0.021* | |
C2 | 0.0406 (2) | 0.8323 (7) | 0.1624 (4) | 0.0194 (10) | |
H2A | 0.0114 | 0.9064 | 0.1704 | 0.029* | |
H2B | 0.0208 | 0.7571 | 0.0921 | 0.029* | |
H2C | 0.0687 | 0.9223 | 0.1604 | 0.029* | |
C3 | 0.08351 (19) | 0.3885 (6) | 0.1265 (4) | 0.0133 (9) | |
H3A | 0.0563 | 0.3012 | 0.1348 | 0.016* | |
H3B | 0.0596 | 0.4779 | 0.0628 | 0.016* | |
C4 | 0.1230 (2) | 0.2655 (7) | 0.0988 (4) | 0.0202 (10) | |
H4A | 0.0986 | 0.1759 | 0.0369 | 0.030* | |
H4B | 0.1509 | 0.1909 | 0.1656 | 0.030* | |
H4C | 0.1447 | 0.3515 | 0.0762 | 0.030* | |
C5 | 0.17176 (19) | 0.6889 (6) | 0.2284 (3) | 0.0092 (8) | |
H5A | 0.2018 | 0.6092 | 0.2248 | 0.011* | |
H5B | 0.1473 | 0.7524 | 0.1541 | 0.011* | |
C6 | 0.2027 (2) | 0.8466 (7) | 0.3192 (4) | 0.0155 (9) | |
H6A | 0.2280 | 0.9247 | 0.3019 | 0.023* | |
H6B | 0.2266 | 0.7848 | 0.3932 | 0.023* | |
H6C | 0.1732 | 0.9308 | 0.3204 | 0.023* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Pt1 | 0.00558 (9) | 0.00576 (9) | 0.00475 (9) | 0.00104 (5) | 0.00313 (6) | 0.00095 (5) |
Br1 | 0.0081 (2) | 0.0174 (2) | 0.0128 (2) | −0.00237 (16) | 0.00532 (17) | 0.00299 (17) |
Br2 | 0.00831 (19) | 0.0121 (2) | 0.0096 (2) | 0.00340 (15) | 0.00597 (16) | 0.00552 (16) |
P1 | 0.0062 (5) | 0.0083 (5) | 0.0058 (5) | 0.0020 (4) | 0.0031 (4) | 0.0019 (4) |
C1 | 0.017 (2) | 0.020 (3) | 0.022 (2) | 0.0115 (19) | 0.015 (2) | 0.005 (2) |
C2 | 0.020 (2) | 0.015 (2) | 0.020 (2) | 0.0095 (19) | 0.008 (2) | 0.0029 (19) |
C3 | 0.011 (2) | 0.011 (2) | 0.011 (2) | −0.0053 (17) | 0.0009 (17) | −0.0018 (17) |
C4 | 0.026 (3) | 0.014 (2) | 0.015 (2) | −0.001 (2) | 0.006 (2) | −0.0034 (19) |
C5 | 0.010 (2) | 0.008 (2) | 0.009 (2) | 0.0011 (16) | 0.0049 (17) | 0.0008 (16) |
C6 | 0.020 (2) | 0.011 (2) | 0.014 (2) | −0.0041 (18) | 0.0077 (19) | −0.0034 (18) |
Pt1—P1 | 2.2266 (11) | C2—H2C | 0.98 |
Pt1—Br1 | 2.4229 (7) | C3—C4 | 1.540 (7) |
Pt1—Br2 | 2.4455 (7) | C3—H3A | 0.99 |
Pt1—Br2i | 2.5451 (6) | C3—H3B | 0.99 |
Br2—Pt1i | 2.5451 (6) | C4—H4A | 0.98 |
P1—C5 | 1.819 (4) | C4—H4B | 0.98 |
P1—C3 | 1.820 (4) | C4—H4C | 0.98 |
P1—C1 | 1.822 (4) | C5—C6 | 1.537 (6) |
C1—C2 | 1.539 (6) | C5—H5A | 0.99 |
C1—H1A | 0.99 | C5—H5B | 0.99 |
C1—H1B | 0.99 | C6—H6A | 0.98 |
C2—H2A | 0.98 | C6—H6B | 0.98 |
C2—H2B | 0.98 | C6—H6C | 0.98 |
P1—Pt1—Br1 | 90.53 (3) | C4—C3—P1 | 112.6 (3) |
P1—Pt1—Br2 | 95.28 (3) | C4—C3—H3A | 109.1 |
Br1—Pt1—Br2 | 173.291 (15) | P1—C3—H3A | 109.1 |
P1—Pt1—Br2i | 178.38 (3) | C4—C3—H3B | 109.1 |
Br1—Pt1—Br2i | 90.288 (19) | P1—C3—H3B | 109.1 |
Br2—Pt1—Br2i | 83.826 (18) | H3A—C3—H3B | 107.8 |
Pt1—Br2—Pt1i | 96.174 (18) | C3—C4—H4A | 109.5 |
C5—P1—C3 | 105.0 (2) | C3—C4—H4B | 109.5 |
C5—P1—C1 | 104.8 (2) | H4A—C4—H4B | 109.5 |
C3—P1—C1 | 106.6 (2) | C3—C4—H4C | 109.5 |
C5—P1—Pt1 | 114.85 (14) | H4A—C4—H4C | 109.5 |
C3—P1—Pt1 | 111.18 (15) | H4B—C4—H4C | 109.5 |
C1—P1—Pt1 | 113.59 (16) | C6—C5—P1 | 113.0 (3) |
C2—C1—P1 | 114.9 (3) | C6—C5—H5A | 109.0 |
C2—C1—H1A | 108.5 | P1—C5—H5A | 109.0 |
P1—C1—H1A | 108.5 | C6—C5—H5B | 109.0 |
C2—C1—H1B | 108.5 | P1—C5—H5B | 109.0 |
P1—C1—H1B | 108.5 | H5A—C5—H5B | 107.8 |
H1A—C1—H1B | 107.5 | C5—C6—H6A | 109.5 |
C1—C2—H2A | 109.5 | C5—C6—H6B | 109.5 |
C1—C2—H2B | 109.5 | H6A—C6—H6B | 109.5 |
H2A—C2—H2B | 109.5 | C5—C6—H6C | 109.5 |
C1—C2—H2C | 109.5 | H6A—C6—H6C | 109.5 |
H2A—C2—H2C | 109.5 | H6B—C6—H6C | 109.5 |
H2B—C2—H2C | 109.5 | ||
P1—Pt1—Br2—Pt1i | −178.65 (3) | C3—P1—C1—C2 | −58.9 (4) |
Br2i—Pt1—Br2—Pt1i | 0.0 | Pt1—P1—C1—C2 | 178.3 (3) |
Br1—Pt1—P1—C5 | 168.94 (16) | C5—P1—C3—C4 | 60.5 (4) |
Br2—Pt1—P1—C5 | −14.43 (16) | C1—P1—C3—C4 | 171.4 (3) |
Br1—Pt1—P1—C3 | −72.02 (16) | Pt1—P1—C3—C4 | −64.3 (3) |
Br2—Pt1—P1—C3 | 104.62 (16) | C3—P1—C5—C6 | 169.7 (3) |
Br1—Pt1—P1—C1 | 48.27 (19) | C1—P1—C5—C6 | 57.5 (4) |
Br2—Pt1—P1—C1 | −135.09 (19) | Pt1—P1—C5—C6 | −67.9 (3) |
C5—P1—C1—C2 | 52.1 (4) |
Symmetry code: (i) −x+1/2, −y+1/2, −z+1. |
Experimental details
Crystal data | |
Chemical formula | [Pt2Br4(C6H15P)2] |
Mr | 946.12 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 120 |
a, b, c (Å) | 26.522 (6), 6.8720 (13), 13.811 (4) |
β (°) | 120.930 (7) |
V (Å3) | 2159.3 (9) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 20.48 |
Crystal size (mm) | 0.20 × 0.10 × 0.10 |
Data collection | |
Diffractometer | Bruker SMART CCD 1K area-detector diffractometer |
Absorption correction | Multi-scan SADABS (G.M.Sheldrick, 1998) |
Tmin, Tmax | 0.450, 1.000 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 10540, 2355, 2158 |
Rint | 0.036 |
(sin θ/λ)max (Å−1) | 0.639 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.020, 0.046, 1.11 |
No. of reflections | 2355 |
No. of parameters | 94 |
H-atom treatment | H-atom parameters constrained |
w = 1/[σ2(Fo2) + (0.0168P)2 + 10.3265P] where P = (Fo2 + 2Fc2)/3 | |
Δρmax, Δρmin (e Å−3) | 0.85, −1.75 |
Computer programs: SMART-NT (Bruker, 1998), SMART-NT and/or SAINT? (Bruker, 1998), SHELXS97 (Sheldrick, 1997a), SHELXTL (Sheldrick, 1997b), SHELXTL.
[PtCl2(PMe3)]2 | [PtCl2(PEt3)]2 | [PtCl2(PPr3)]2 | I | |
Pt—P | 2.205 (3) Å | 2.212 (3) Å | 2.230 (9) Å | 2.2266 (11) Å |
Pt—HalTerminal | 2.281 (3) Å | 2.282 (3) Å | 2.279 (9) Å | 2.4229 (7) Å |
Pt—HalBridging | 2.309 (3) Å | 2.318 (3) Å | 2.315 (8) Å | 2.4455 (7) Å |
2.423 (3) Å | 2.431 (3) Å | 2.425 (8) Å | 2.5451 (6) Å | |
Pt—Hal—Pt | 96.19 (10)° | 96.48 (10)° | 96.4 (3)° | 96.17 (2)° |
Hal—Pt—Hal | 83.81 (10)° | 83.52 (9)° | 83.6 (2)° | 83.83 (2)° |
Acknowledgements
The authors thank the EPSRC for postgraduate studentships (SMMC and ALT) and Johnson–Matthey plc for the loan of platinum compounds.
References
Black, M., Mais, R. H. B. & Owston, P. G. (1969). Acta Cryst. B25, 1760–1766. CSD CrossRef CAS IUCr Journals Web of Science Google Scholar
Blake, A. J., Gould, R. O., Marr, A. M., Rankin, D. W. H. & Schröder, M. (1989). Acta Cryst. C45, 1218–1219. CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
Boag, N. M. & Ravetz, M. S. (1996). Acta Cryst. C52, 1942–1943. CSD CrossRef CAS Web of Science IUCr Journals Google Scholar
Bruker (1998). SMART-NT, SAINT-NT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Chatt, J. & Venanzi, L. M. (1955). J. Chem. Soc. pp. 2787–2793. CrossRef Web of Science Google Scholar
Cobley, C. J., Ellis, D. D., Orpen, A. G. & Pringle, P. G. (2000). J. Chem. Soc. Dalton Trans. pp. 1101–1107. Web of Science CSD CrossRef Google Scholar
Cornet, S. M. M. (2002). PhD thesis, University of Durham, England. Google Scholar
Dillon, K. B. & Goodwin, H. P. (1992). J. Organomet. Chem. 428, 169–171. CrossRef Web of Science Google Scholar
Dillon, K. B. & Goodwin, H. P. (1994). J. Organomet. Chem. 469, 125–128. CrossRef CAS Web of Science Google Scholar
Kiffen, A. A., Masters, C. & Visser, J. P. (1975). J. Chem. Soc. Dalton Trans. pp. 1311–1315. CrossRef Web of Science Google Scholar
Meidine, M. F. & Nixon, J. F. (1988). Private communication to K. B. Dillon. Google Scholar
Sheldrick, G. M. (1997a). SHELXL97 and SHELXS97. University of Göttingen, Germany. Google Scholar
Sheldrick, G. M. (1997b). SHELXTL. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Simms, B. L., Shang, M., Lu, J., Youngs, W. J. & Ibers, J. A. (1987). Organometallics, 6, 1118–1126. CSD CrossRef CAS Web of Science Google Scholar
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Bridging chloride complexes of the form [PtCl2(PR3)]2 have been used extensively as starting materials in the synthesis of mononuclear platinum–phosphine complexes, which are formed through cleavage of the bridging Pt—Cl bond (Chatt & Venanzi, 1955; Meidine & Nixon, 1988; Dillon & Goodwin, 1992, 1994). Similar synthetic methodology can also be applied to bromo analogues (Cornet 2002). However, while the crystal structures of the chloro-bridged complexes [PtCl2(PMe3)]2, [PtCl2(PEt3)]2 and [PtCl2(PPr3)]2 are known (Boag & Ravetz, 1996; Blake et al., 1989; Black et al., 1969), structures of complexes exhibiting the central heavy-atom skeleton [PtCl2P]2 are suprisingly rare, with only a handful known (Simms et al., 1987; Cobley et al., 2000).
The title complex, (I), was prepared by the (CHCl2)2-mediated reaction of equimolar quantities of PtBr2 and [PtBr2(PEt3)2]. Given the rarity of crystal structures containing the [PtCl2P]2 fragment, it is unsurprizing that (I) is the first structure to be reported containing the [PtBr2P]2 motif.
The chloride complexes [PtCl2(PR3)]2 (where R = CH3, C2H5 and C3H7) and the title compound are closely related and all four complexes sit with an inversion centre in the middle of the dimer, with the PR3 ligands in a trans geometry (Fig. 1). In addition, all four structures are asymmetric around the bridging halide ligands, but this is reduced in (I) with respect to the chloride complexes (Table 1); this behaviour is presumably due the relative positions of the Cl, Br and P atoms in the trans influence series and the increased ionic radius of the bromide ligand. This? also appears to reduce the effect bridging has on the bond lengths, since the bonds to the bridging bromides are only 0.023 and 0.122 Å longer than those to the terminal bromide, compared with averages of 0.033 and 0.146 Å in [PtCl2(PR3)]2 (where R = CH3, C2H5 and C3H7; Boag & Ravetz, 1996; Blake et al., 1989; Black at al., 1969, respectively).