A second polymorph of bis­(dimethyl­phosphino)dimethyl­phospho­nium trifluoro­methane­sulfonate

The title compound, C₆H₁₈P₃⁺·CF₃SO₃⁻, crystallizes in two polymorphic forms in the space groups P2₁/c and Pnma. In the ortho­rhom­bic form, the two crystallographically independent mol­ecular units lie across a crystallographic mirror plane. The compound lacks traditional hydrogen-bond donors and, hence, is held together by weak C—H...O and C—H...F inter­actions, forming layers. The second polymorph was obtained as a by-product from the reaction of 1,3-bis­(2,6-dimethyl­phen­yl)-2,4-ditriflato-1,3,2,4-diaza­diphosphetidine with tetra­methyl­diphosphine.

S1. Comment

P-donor ligands on P^III systems have recently become pivotal in the development of molecular main-group coordination chemistry. These donor–acceptor interactions are recognized as `homoatomic' coordination complexes in inter- and intramolecular phosphine–phosphonium complexes and are essentially unique to phosphorus (Burford et al., 2003). Facile synthetic methods for the diversification of catena-polyphosphorus cations yielded a series of new organo-substituted diphosphinophosphonium and cyclo-tetraphosphinodiphosphonium cations (Weigand et al., 2006). Recently, we reported the crystal structure of catena-hexamethyldiphosphinophosphonium trifluoromethanesulfonate, which crystallizes in the monoclinic crystal system P2₁/c (Burford et al., 2005). During our further investigation we obtained a second polymorph of the title compound, (I) [OTf^- is trifluoromethanesulfonate (trifluoromethanesulfonate)], by chance, from the reaction of 1,3-bis(2,6-dimethylphenyl)-2,4-ditriflato-1,3,2,4-diazadiphosphetidine with tetramethyldiphosphine as a reaction by-product.

The orthorhombic polymorph crystallizes with two half-formula units in the asymmetric unit. A view of the molecular structures along with the numbering scheme is depicted in Fig. 1. X-ray investigation has shown that the bond lengths in (I) do not significantly differ from that found in the monoclinic polymorph. The same unusual eclipsed/staggered conformation (local molecular symmetry C_s) of the cation is observed. The geometries of the trifluoromethanesulfonate anions in (I) are in accordance with that previously determined (You & Zhu, 2004). The interatomic distances and bond angles in the two independent molecules are almost identical, and selected molecular parameters of the cations are presented in Table 1. The cations and anions lie across a crystallographic mirror plane passing through atoms P1–P6, S1, S2, C7 and C9.

Compound (I) lacks traditional hydrogen-bond donor groups; hence, the structure is stabilized by weak C—H···O and C—H···F interactions (Table 2). These C—H···O hydrogen bonds (C2—H4···O3, C2—H6···O1ⁱⁱⁱ and C5—H14···O2; symmetry codes and geometry are given in Table 2) account for the observation of subunits consisting of two cations and two anions, and, together with the weak C—H···F interactions (C3—H8···F2 and C6—H16···F2^v; Table 2), form two-dimensional sheets (Fig. 2). The two hydrogen bonds found between these sheets (C2—H5···O4ⁱⁱ and C5—H13···O1^iv; Table 2) are the main contributors that lead to a lateral packing of the layers. The resulting layers are arranged in an antiparallel manner (ABA layer sequence), which is compatible with space group Pnma (Fig. 3). In the case of the monoclinic polymorph, a lateral packing of layers is found, similar to that of the orthorhombic polymorph. However, the layers are composed of alternating strands of cations and anions running along the c axis, stabilized by weak C—H···O and C—H···F interactions.

Related literature

For related literature, see: Burford et al. (2003, 2005); Weigand et al. (2006); You & Zhu (2004).

S2. Experimental

All manipulations were performed under an inert atmosphere of dinitrogen. A solution of tetramethyldiphosphine (126 mg, 1 mmol) in CH₂Cl₂ (2 ml) was added to a solution of 1,3-bis(2,6-dimethylphenyl)-2,4-ditriflato-1,3,2,4-diazadiphosphetidine (300 mg, 0.5 mmol) in CH₂Cl₂ (3 ml) leading to the formation of a bright-yellow solution. Addition of Et₂O resulted in the formation of a bright-yellow precipitate. Compound (I) was obtained as colorless needles from vapor diffusion of Et₂O into a CH₂Cl₂/CH₃CN solution of the yellow precipitate amidst copious amounts of a yellow oily material of unknown constitution. The analytical data are in agreement with that previously reported (Burford et al., 2005).

S3. Refinement

H atoms were located in a difference Fourier map and their coordinates were refined in the riding mode [U_iso(H) = 1.2U_eq(C)]. The data set for (I) was truncated at 2Θ = 60° as only statistically insignificant data were present above the limit.

Computing details

Data collection: PROCESS (Rigaku, 1996); cell refinement: PROCESS; data reduction: CrystalStructure (Rigaku/MSC, 2004); program(s) used to solve structure: SHELXS86 (Sheldrick, 1985); program(s) used to refine structure: CRYSTALS (Watkin et al., 1996); molecular graphics: DIAMOND (Brandenburg, 2000); software used to prepare material for publication: CrystalStructure.

Figures

	Fig. 1. A view of the molecular structure of (I), showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of an arbitrary radius. [Symmetry code: (i) x, -y + 1/2, z].
	Fig. 2. The arrangement of the ions of (I), viewed along the [010] axis. The weak C—H···O and C—H···F interactions are represented by dashed lines. H atoms not involved in these interactions have been omitted for clarity [Symmetry codes: (iii) x + 1/2, -y + 1/2, -z + 1/2; (v) x, -y + 1/2, z + 1.]
	Fig. 3. The arrangement of the ions of (I), viewed along the [001] axis. The weak C—H···O interactions between the sheets are represented by dashed lines. H atoms not involved in these interactions have been omitted for clarity [Symmetry codes: (i) x, -y + 1/2, z; (vi) -x + 1/2, -y + 1, z + 1/2; (vii) -x, y + 1/2, -z + 1].

bis(dimethylphosphino)dimethylphosphonium trifluoromethanesulfonate

Crystal data

C6H18P3^+·CF3O3S^−	F(000) = 1376.00
Mr = 332.19	Dx = 1.450 Mg m^−3
Orthorhombic, Pnma	Mo Kα radiation, λ = 0.7107 Å
Hall symbol: -P 2ac 2n	Cell parameters from 12587 reflections
a = 23.5972 (7) Å	θ = 5.0–35.7°
b = 10.7419 (4) Å	µ = 0.55 mm^−1
c = 12.0086 (4) Å	T = 123 K
V = 3043.9 (2) Å^3	Needle, colourless
Z = 8	0.40 × 0.17 × 0.12 mm

Data collection

Rigaku R-AXIS diffractometer	Rint = 0.080
Detector resolution: 10.00 pixels mm^-1	θmax = 35.7°
ω scans	h = −37→35
25123 measured reflections	k = −15→17
6230 independent reflections	l = −19→13
2682 reflections with F^2 > 2σ(F^2)

Refinement

Refinement on F	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.052	Chebychev polynomial with three parameters (Carruthers & Watkin, 1979): 22.3826, -11.8310 and 17.0026
wR(F^2) = 0.063	(Δ/σ)max < 0.001
S = 1.06	Δρmax = 1.08 e Å^−3
2682 reflections	Δρmin = −0.62 e Å^−3
193 parameters

Special details

Geometry. ENTER SPECIAL DETAILS OF THE MOLECULAR GEOMETRY

Refinement. Refinement using reflections with F² > 3.0 σ(F²). The weighted R-factor(wR), goodness of fit (S) and R-factor (gt) are based on F, with F set to zero for negative F. The threshold expression of F² > 2.0 σ(F²) is used only for calculating R-factor (gt).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
S1	−0.02148 (4)	0.2500	0.29420 (9)	0.0309 (3)
S2	0.26489 (4)	0.2500	0.59125 (9)	0.0279 (2)
P1	0.30491 (5)	0.2500	0.00516 (10)	0.0373 (3)
P2	0.27412 (4)	0.2500	0.17720 (8)	0.0234 (2)
P3	0.18032 (4)	0.2500	0.17526 (9)	0.0277 (3)
P4	−0.01508 (5)	0.2500	0.69750 (10)	0.0362 (3)
P5	0.07646 (5)	0.2500	0.65808 (10)	0.0314 (3)
P6	0.12354 (5)	0.2500	0.81492 (12)	0.0488 (4)
F1	−0.0377 (2)	0.2500	0.0796 (4)	0.143 (3)
F2	0.0360 (2)	0.1538 (7)	0.1336 (3)	0.182 (2)
F3	0.3624 (2)	0.1508 (4)	0.5432 (4)	0.1076 (13)
F4	0.3591 (2)	0.2500	0.6997 (6)	0.123 (2)
O1	−0.0544 (1)	0.3615 (3)	0.3004 (3)	0.0622 (9)
O2	0.0296 (2)	0.2500	0.3590 (3)	0.0447 (10)
O3	0.2501 (2)	0.2500	0.4765 (3)	0.067 (2)
O4	0.25075 (13)	0.1376 (3)	0.6490 (3)	0.0550 (8)
C1	0.2627 (2)	0.3816 (4)	−0.0477 (3)	0.0431 (9)
C2	0.30363 (13)	0.1159 (3)	0.2446 (3)	0.0320 (7)
C3	0.1660 (1)	0.1190 (3)	0.2687 (3)	0.0420 (9)
C4	−0.0386 (2)	0.1174 (4)	0.6123 (4)	0.0445 (9)
C5	0.0985 (1)	0.1158 (4)	0.5799 (3)	0.0395 (8)
C6	0.0880 (2)	0.3820 (4)	0.8810 (3)	0.0516 (11)
C7	0.0040 (3)	0.2500	0.1521 (6)	0.107 (3)
C9	0.3412 (2)	0.2500	0.5920 (7)	0.063 (2)
H1	0.2763	0.4569	−0.0158	0.052*
H2	0.2662	0.3857	−0.1265	0.052*
H3	0.2241	0.3701	−0.0282	0.052*
H4	0.2955	0.1193	0.3220	0.039*
H5	0.2875	0.0426	0.2136	0.038*
H6	0.3435	0.1148	0.2339	0.038*
H7	0.1814	0.1361	0.3402	0.050*
H8	0.1263	0.1071	0.2748	0.051*
H9	0.1830	0.0458	0.2394	0.051*
H10	−0.0269	0.1298	0.5374	0.053*
H11	−0.0222	0.0429	0.6402	0.053*
H12	−0.0787	0.1113	0.6153	0.053*
H13	0.0885	0.0424	0.6194	0.047*
H14	0.0802	0.1160	0.5094	0.047*
H15	0.1384	0.1181	0.5696	0.048*
H16	0.1032	0.3947	0.9533	0.062*
H17	0.0936	0.4547	0.8373	0.062*
H18	0.0485	0.3651	0.8865	0.062*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0247 (5)	0.0394 (6)	0.0285 (5)	0.0000	0.0005 (4)	0.0000
S2	0.0291 (5)	0.0286 (5)	0.0260 (5)	0.0000	0.0014 (4)	0.0000
P1	0.0313 (6)	0.0552 (8)	0.0256 (5)	0.0000	0.0052 (4)	0.0000
P2	0.0225 (4)	0.0256 (5)	0.0221 (4)	0.0000	−0.0006 (4)	0.0000
P3	0.0223 (5)	0.0340 (6)	0.0267 (5)	0.0000	−0.0010 (4)	0.0000
P4	0.0243 (5)	0.0497 (7)	0.0345 (6)	0.0000	0.0010 (5)	0.0000
P5	0.0239 (5)	0.0413 (7)	0.0290 (5)	0.0000	−0.0005 (4)	0.0000
P6	0.0299 (6)	0.0857 (11)	0.0309 (6)	0.0000	−0.0038 (5)	0.0000
F1	0.056 (3)	0.331 (10)	0.041 (2)	0.0000	−0.021 (2)	0.0000
F2	0.071 (2)	0.400 (9)	0.077 (2)	0.076 (3)	−0.002 (2)	−0.108 (4)
F3	0.060 (2)	0.098 (3)	0.165 (4)	0.030 (2)	0.040 (2)	−0.012 (3)
F4	0.065 (3)	0.174 (6)	0.129 (5)	0.0000	−0.062 (3)	0.0000
O1	0.054 (2)	0.046 (2)	0.086 (2)	0.015 (1)	−0.012 (2)	−0.005 (2)
O2	0.031 (2)	0.067 (3)	0.036 (2)	0.0000	−0.007 (1)	0.0000
O3	0.077 (3)	0.092 (4)	0.032 (2)	0.0000	−0.016 (2)	0.0000
O4	0.061 (2)	0.041 (2)	0.063 (2)	−0.005 (1)	0.014 (1)	0.014 (1)
C1	0.061 (2)	0.039 (2)	0.029 (2)	−0.005 (2)	−0.003 (2)	0.005 (1)
C2	0.032 (1)	0.030 (2)	0.034 (1)	0.0038 (12)	−0.0018 (12)	0.0026 (12)
C3	0.034 (2)	0.033 (2)	0.059 (2)	−0.0021 (13)	0.008 (2)	0.008 (2)
C4	0.032 (2)	0.043 (2)	0.059 (2)	−0.001 (1)	−0.007 (2)	0.000 (2)
C5	0.033 (2)	0.045 (2)	0.040 (2)	0.004 (1)	0.0031 (13)	−0.001 (2)
C6	0.067 (3)	0.053 (2)	0.035 (2)	−0.019 (2)	−0.003 (2)	−0.002 (2)
C7	0.035 (3)	0.26 (1)	0.029 (3)	0.0000	−0.005 (2)	0.0000
C9	0.030 (3)	0.073 (5)	0.086 (5)	0.0000	0.005 (3)	0.0000

Geometric parameters (Å, º)

S1—O1	1.429 (3)	F4—C9	1.36 (1)
S1—O2	1.435 (4)	C1—H1	0.9500
S1—C7	1.809 (7)	C1—H2	0.9500
S2—O3	1.422 (4)	C1—H3	0.9501
S2—O4	1.431 (3)	C2—H4	0.9500
S2—C9	1.801 (6)	C2—H5	0.9500
P1—P2	2.190 (2)	C2—H6	0.9499
P2—P3	2.214 (1)	C3—H7	0.9501
P1—C1	1.842 (4)	C3—H8	0.9500
P2—C2	1.793 (3)	C3—H9	0.9500
P3—C3	1.830 (4)	C4—H10	0.9500
P5—P6	2.187 (2)	C4—H11	0.9500
P4—P5	2.211 (2)	C4—H12	0.9499
P6—C6	1.828 (4)	C5—H13	0.9501
P5—C5	1.797 (4)	C5—H14	0.9500
P4—C4	1.839 (4)	C5—H15	0.9500
F1—C7	1.313 (8)	C6—H16	0.9500
F2—C7	1.299 (7)	C6—H17	0.9501
F3—C9	1.314 (6)	C6—H18	0.9501
O1^i—S1—O1	113.8 (2)	P1—C1—H3	109.4866
O2—S1—O1	115.4 (2)	P2—C2—H4	109.4204
C7—S1—O1	103.3 (2)	P2—C2—H5	109.5124
C7—S1—O2	103.4 (3)	P2—C2—H6	109.4839
S1—C7—F1	112.1 (5)	P3—C3—H7	109.5619
S1—C7—F2	110.7 (4)	P3—C3—H9	109.3910
O4—S2—O3	114.3 (2)	P3—C3—H8	109.4549
C9—S2—O3	104.5 (3)	P4—C4—H10	109.3786
O4^i—S2—O4	115.0 (2)	P4—C4—H11	109.5485
C9—S2—O4	103.3 (2)	P4—C4—H12	109.4839
S2—C9—F3	112.2 (3)	P5—C5—H15	109.5405
S2—C9—F4	108.3 (5)	P5—C5—H13	109.4586
P1—P2—P3	108.77 (6)	P5—C5—H14	109.4083
P1—P2—C2	107.3 (1)	P6—C6—H18	109.3889
P2—P3—C3	100.2 (1)	P6—C6—H17	109.4726
C1—P1—P2	98.4 (1)	P6—C6—H16	109.5483
C2—P2—P3	113.2 (1)	H2—C1—H1	109.4710
C1^i—P1—C1	100.3 (2)	H3—C1—H1	109.4783
C2^i—P2—C2	106.9 (2)	H3—C1—H2	109.4663
C3^i—P3—C3	100.4 (2)	H5—C2—H4	109.4699
P4—P5—P6	108.17 (7)	H6—C2—H4	109.4677
C5—P5—P6	107.6 (1)	H6—C2—H5	109.4729
C4—P4—P5	100.1 (1)	H9—C3—H7	109.4754
P5—P6—C6	98.1 (1)	H8—C3—H7	109.4750
P4—P5—C5	113.2 (1)	H9—C3—H8	109.4691
C6^i—P6—C6	101.6 (2)	H11—C4—H10	109.4738
C5^i—P5—C5	106.7 (2)	H12—C4—H10	109.4735
C4^i—P4—C4	101.5 (2)	H12—C4—H11	109.4690
F1—C7—F2	108.8 (4)	H15—C5—H13	109.4784
F2—C7—F2^i	105.4 (6)	H14—C5—H13	109.4729
F3—C9—F3^i	108.3 (6)	H15—C5—H14	109.4686
F3—C9—F4	107.8 (4)	H18—C6—H16	109.4776
P1—C1—H1	109.4466	H17—C6—H16	109.4685
P1—C1—H2	109.4784	H18—C6—H17	109.4713
O1—S1—C7—F1	−59.4 (4)	C1—P1—P2—P3	50.9 (3)
O1—S1—C7—F2	178.9 (4)	C1—P1—P2—C2	173.6 (2)
O2—S1—C7—F1	180.0	P1—P2—P3—C3	128.7 (2)
O2—S1—C7—F2	58.3 (5)	C2—P2—P3—C3	9.6 (2)
O3—S2—C9—F3	−61.1 (6)	C4—P4—P5—P6	−128.1 (2)
O3—S2—C9—F4	180.0	C4—P4—P5—C5	−8.9 (2)
O4—S2—C9—F3	58.8 (6)	P4—P5—P6—C6	−51.5 (3)
O4—S2—C9—F4	−60.1 (4)	C5—P5—P6—C6	−174.2 (2)

Symmetry code: (i) x, −y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H4···O3	0.95	2.56	3.380 (5)	145
C2—H5···O4^ii	0.95	2.27	3.222 (5)	177
C2—H6···O1^iii	0.95	2.46	3.402 (4)	173
C5—H13···O1^iv	0.95	2.31	3.258 (5)	173
C5—H14···O2	0.95	2.60	3.429 (5)	146
C3—H8···F2	0.95	2.77	3.491 (5)	134
C6—H16···F2^v	0.95	2.73	3.295 (5)	119

Symmetry codes: (ii) −x+1/2, −y, z−1/2; (iii) x+1/2, −y+1/2, −z+1/2; (iv) −x, y−1/2, −z+1; (v) x, −y+1/2, z+1.