Solvent-free [μ-ferrocene-1,1′-diyl­bis(di­phenyl­phosphine-P)]bis­[chlorogold(I)]

The title compound, [Au₂Cl₂{Fe(C₁₇H₁₄P)₂}], (I), contains the expected linear gold centres. The ferrocene moiety acts as a P,P′-bridging ligand, wherein the Fe atom lies on an inversion centre. The P—Au—Cl angle is 177.56 (8)° and bond distances Au—P and Au—Cl are 2.2261 (18) and 2.2781 (18) Å, respectively. The structure is almost identical to that of the metal complex in (I)·2CH₂Cl₂ [Canales, Gimeno, Jones, Laguna & Sarroca (1997). Inorg. Chem. 36, 5206–5211], but differs considerably from that in 3(I)·2CHCl₃ [Hill, Girard, McCabe, Johnson, Stupik, Zhang, Reiff & Eggleston (1989). Inorg. Chem. 28, 3529–3533], in that in the latter, the two independent mol­ecules are linked by a short Au...Au contact.

S1. Comment

Much attention has been focused on the diphoshine 1,1'-bis(diphenylphosphino)ferrocene (dppf). Although it was synthesized more than two decades ago (Sollot et al., 1965; Bishop et al., 1971; Marr & Hunt, 1969; Sollot et al., 1971), its reactivity is still being widely studied due to its catalytic potential, industrial importance and chemical uniqueness. Various complexes of Co, Ni (Rudie et al., 1978), Hg (Mann et al., 1974), Mo, W (Baker et al., 1986), Pd (Hayaski et al., 1979) Pt (Clemente et al., 1986), or Rh (Cullen et al., 1985) have been described. As part of our work on the chemistry of the dppf ligand, we have recently reported some silver and gold derivatives (Gimeno et al., 1993, 1995; Canales et al., 1996, 1997). Among the latter, the title compound [Au₂Cl₂{µ-dppf)}], (I), is interesting because of the antitumour activity found in some bis(diphenyl-phosphine)gold(I) derivatives. Two structures of (I) have already been published; the first (Hill et al., 1989) was a chloroform solvate (ratio I:CHCl₃ of 3:2) with two independent molecules of (I), one with inversion symmetry, whereas the second (Canales et al., 1997) was a dichloromethane disolvate in which the molecule of (I) also displayed inversion symmetry. Here we present the structure of a solvent-free form. \sch

Compound (I) (Fig. 1) crystallizes with the Fe atom on an inversion centre. The dppf ligand coordinates both gold centres. The P—Au—Cl angle is approximately linear at 177.56 (8)°. The Au—P and Au—Cl bond distances are 2.2261 (18) and 2.2781 (18) Å, respectively, which compare well with those found in the two previously reported determinations [Au—P, 2.2262 (13), 2.222–2.239 Å; Au—Cl, 2.2815 (13), 2.273–2.300 Å; values for Canales et al. (1997) are given first]. The Fe atom lies 1.652 (3) Å out of each cyclopentadienyl (Cp) ring. The P—Au—Cl axis is rotated by 30.7 (5)° out of the Cp plane, as defined by the torsion angle C2—C1—P—Au. For the phenyl rings, corresponding angles are C12—C11—P—Au 54.5 (5) and C22—C21—P—Au −0.1 (6)°. The Au···Fe distance within the molecule is 4.1458 (7) Å. The shortest Au···Au contact is 6.3212 (13) Å (operator −x, 1 − y, 1 − z). Because of the imposed symmetry, the Cp rings are exactly parallel and ideally staggered, and the torsion angle P···Cent···Cent···P (Cent = centre of Cp ring) is exactly 180°.

The previously reported structure by Canales et al. (1997) shows little difference to that of (I). The corresponding C—C—P—Au torsion angle from the Cp ring is 30.9 (5)°; the other rings display some differences from (I), with torsion angles 51.8 (4) and 18.9 (5)°. In the absence of any unusually short intermolecular contacts (Table 2 shows some borderline non-classical interactions, but these are unlikely to have a great influence), one must conclude that the energy balance between the two forms, which both crystallize from dichloromethane/ hydrocarbon mixtures, is very delicate.

In contrast, the structure by Hill et al. (1989) displays some marked differences to that of (I), especially in the molecule without imposed symmetry. The Cp rings are slightly non-parallel (interplanar angle 3°) and non-ideally staggered (e.g. torsion angle C35···Cent···Cent···C32 20.4°), and the angle P2···Cent···Cent···P3 narrows to −125°. Additionally, there are short Au···Au contacts of 3.083 (1) Å between gold centres of the two molecules. More minor differences are also shown in the ring torsion angles (e.g. Cp C—C—P—Au −21.1 for the symmetric molecule, 38.1, 31.7° for the non-symmetric molecule). The total of these differences can well account for, or at least be consistent with, the formation of a different crystalline form of (I).

S2. Experimental

Crystals were obtained by slow diffusion of n-heptane into a dichloromethane solution of (I).

S3. Refinement

A total of 56 restraints were applied, involving local phenyl-ring symmetry (FLAT/SAME in SHELXL97; Sheldrick, 1997). Hydrogen atoms were included using a riding model, starting from idealized positions. The largest feature of residual electron density (1.06 e/ų) lies 0.98 Šfrom the gold atom.

Computing details

Data collection: XSCANS (Fait, 1991); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1994); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. Molecular structure of the title compound. Ellipsoids are drawn at the 50% probability level. H atom radii are arbitrary. Only the asymmetric unit is numbered.

(I)

Crystal data

[Au2Cl2(C34H28FeP2)]	F(000) = 960
Mr = 1019.18	Dx = 2.082 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 9.038 (2) Å	Cell parameters from 65 reflections
b = 19.130 (4) Å	θ = 10–25°
c = 9.930 (2) Å	µ = 9.73 mm^−1
β = 108.79 (2)°	T = 173 K
V = 1625.4 (6) Å^3	Tablet, brown
Z = 2	0.2 × 0.15 × 0.1 mm

Data collection

Siemens P4 diffractometer	2037 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.034
Graphite monochromator	θmax = 25.0°, θmin = 3.0°
ω–scan	h = −10→2
Absorption correction: ψ scan (XPREP; Siemens, 1994)	k = 0→22
Tmin = 0.212, Tmax = 0.378	l = −11→11
3539 measured reflections	3 standard reflections every 247 reflections
2859 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Primary atom site location: patterson
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.071	H-atom parameters constrained
S = 0.90	w = 1/[σ^2(Fo^2) + (0.0362P)^2] where P = (Fo^2 + 2Fc^2)/3
2859 reflections	(Δ/σ)max < 0.001
187 parameters	Δρmax = 1.05 e Å^−3
56 restraints	Δρmin = −1.01 e Å^−3

Special details

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.

Non-bonded distances:

8.2916 (0.0014) Au - Au_$1 4.1458 (0.0007) Au - Fe 6.6059 (0.0015) Au - Fe_$2 6.3212 (0.0013) Au - Au_$5

Operators for generating equivalent atoms:

$1 − x + 1, −y + 1, −z + 1 $2 x − 1, y, z $5 − x, −y + 1, −z + 1

============

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

6.5028 (0.0221) x + 4.7946 (0.0661) y + 3.7883 (0.0324) z = 5.8914 (0.0290)

* −0.0024 (0.0040) C1 * −0.0011 (0.0041) C2 * 0.0043 (0.0044) C3 * −0.0059 (0.0045) C4 * 0.0051 (0.0043) C5 1.6515 (0.0030) Fe

Rms deviation of fitted atoms = 0.0042

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.

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

	x	y	z	Uiso*/Ueq
Au	0.22868 (4)	0.613314 (17)	0.68878 (3)	0.03067 (11)
Fe	0.5000	0.5000	0.5000	0.0233 (3)
P	0.1956 (2)	0.61035 (11)	0.45679 (18)	0.0235 (4)
Cl	0.2716 (2)	0.61334 (14)	0.92777 (18)	0.0486 (6)
C1	0.2749 (7)	0.5315 (4)	0.4100 (7)	0.0216 (15)
C2	0.2803 (8)	0.4668 (4)	0.4830 (8)	0.0324 (17)
H2	0.2410	0.4589	0.5597	0.039*
C3	0.3526 (9)	0.4172 (4)	0.4230 (9)	0.044 (2)
H3	0.3719	0.3698	0.4523	0.053*
C4	0.3924 (9)	0.4490 (4)	0.3118 (8)	0.040 (2)
H4	0.4418	0.4263	0.2524	0.047*
C5	0.3474 (8)	0.5197 (4)	0.3023 (7)	0.0297 (17)
H5	0.3621	0.5533	0.2373	0.036*
C11	−0.0076 (7)	0.6154 (4)	0.3438 (7)	0.0260 (15)
C12	−0.0949 (8)	0.6719 (4)	0.3659 (8)	0.0348 (18)
H12	−0.0479	0.7049	0.4387	0.042*
C13	−0.2491 (8)	0.6802 (5)	0.2827 (9)	0.046 (2)
H13	−0.3082	0.7188	0.2974	0.055*
C14	−0.3163 (10)	0.6318 (4)	0.1781 (9)	0.053 (2)
H14	−0.4220	0.6376	0.1202	0.063*
C15	−0.2322 (9)	0.5746 (5)	0.1557 (8)	0.047 (2)
H15	−0.2802	0.5412	0.0841	0.056*
C16	−0.0771 (8)	0.5671 (4)	0.2393 (8)	0.0340 (18)
H16	−0.0183	0.5284	0.2245	0.041*
C21	0.2826 (7)	0.6840 (4)	0.3932 (7)	0.0253 (16)
C22	0.3606 (8)	0.7360 (4)	0.4837 (8)	0.0331 (18)
H22	0.3768	0.7322	0.5828	0.040*
C23	0.4154 (9)	0.7933 (4)	0.4313 (9)	0.046 (2)
H23	0.4694	0.8289	0.4948	0.056*
C24	0.3931 (9)	0.7998 (4)	0.2888 (8)	0.043 (2)
H24	0.4288	0.8403	0.2532	0.052*
C25	0.3183 (9)	0.7470 (4)	0.1975 (9)	0.0377 (19)
H25	0.3064	0.7499	0.0991	0.045*
C26	0.2609 (8)	0.6902 (4)	0.2499 (8)	0.0305 (17)
H26	0.2057	0.6547	0.1865	0.037*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Au	0.02985 (16)	0.04367 (19)	0.01985 (15)	0.01173 (19)	0.00990 (10)	0.00067 (17)
Fe	0.0205 (7)	0.0204 (8)	0.0269 (8)	0.0013 (6)	0.0049 (6)	−0.0028 (6)
P	0.0235 (9)	0.0278 (10)	0.0206 (9)	0.0036 (10)	0.0091 (7)	0.0006 (9)
Cl	0.0543 (13)	0.0752 (15)	0.0166 (9)	0.0197 (14)	0.0117 (9)	0.0007 (11)
C1	0.021 (4)	0.022 (3)	0.022 (4)	0.001 (3)	0.007 (3)	−0.001 (3)
C2	0.021 (4)	0.032 (4)	0.041 (4)	−0.008 (3)	0.006 (3)	0.006 (3)
C3	0.032 (5)	0.023 (4)	0.067 (6)	−0.004 (4)	0.001 (4)	−0.005 (4)
C4	0.028 (4)	0.042 (5)	0.039 (5)	0.013 (4)	−0.002 (3)	−0.018 (4)
C5	0.026 (4)	0.039 (4)	0.023 (4)	0.001 (4)	0.004 (3)	−0.007 (3)
C11	0.021 (3)	0.033 (4)	0.023 (3)	−0.001 (3)	0.006 (3)	0.009 (3)
C12	0.030 (4)	0.040 (5)	0.039 (5)	0.009 (4)	0.016 (3)	0.009 (4)
C13	0.029 (4)	0.052 (5)	0.063 (6)	0.013 (4)	0.023 (4)	0.025 (4)
C14	0.025 (4)	0.063 (6)	0.062 (6)	0.003 (4)	0.005 (4)	0.027 (4)
C15	0.039 (5)	0.064 (6)	0.033 (5)	−0.011 (4)	0.004 (3)	0.011 (4)
C16	0.035 (4)	0.036 (5)	0.031 (4)	0.001 (4)	0.010 (3)	0.003 (3)
C21	0.021 (4)	0.030 (4)	0.021 (4)	0.002 (3)	0.002 (3)	0.000 (3)
C22	0.028 (4)	0.039 (5)	0.030 (4)	−0.001 (4)	0.004 (3)	−0.008 (3)
C23	0.040 (5)	0.026 (4)	0.059 (5)	−0.010 (4)	−0.003 (4)	−0.006 (4)
C24	0.027 (4)	0.032 (5)	0.062 (5)	−0.004 (4)	0.002 (4)	0.016 (4)
C25	0.038 (5)	0.029 (4)	0.044 (5)	0.003 (4)	0.009 (4)	0.013 (3)
C26	0.029 (4)	0.032 (4)	0.029 (3)	0.001 (4)	0.007 (3)	0.001 (3)

Geometric parameters (Å, º)

Au—P	2.2261 (18)	C1—C5	1.440 (9)
Au—Cl	2.2781 (18)	C2—C3	1.391 (10)
Fe—C1	2.032 (6)	C3—C4	1.406 (12)
Fe—C1^i	2.032 (6)	C4—C5	1.408 (10)
Fe—C5	2.038 (7)	C11—C16	1.381 (9)
Fe—C5^i	2.038 (7)	C11—C12	1.397 (9)
Fe—C2	2.040 (7)	C12—C13	1.382 (9)
Fe—C2^i	2.040 (7)	C13—C14	1.378 (10)
Fe—C3^i	2.053 (7)	C14—C15	1.390 (10)
Fe—C3	2.053 (7)	C15—C16	1.388 (9)
Fe—C4^i	2.055 (7)	C21—C22	1.373 (8)
Fe—C4	2.055 (7)	C21—C26	1.377 (9)
P—C1	1.795 (7)	C22—C23	1.372 (10)
P—C11	1.820 (6)	C23—C24	1.369 (10)
P—C21	1.823 (8)	C24—C25	1.380 (9)
C1—C2	1.427 (9)	C25—C26	1.377 (9)
P—Au—Cl	177.56 (8)	C3^i—Fe—C4	140.0 (3)
C1—Fe—C1^i	180.0	C3—Fe—C4	40.0 (3)
C1—Fe—C5	41.4 (2)	C4^i—Fe—C4	180.0
C1^i—Fe—C5	138.6 (2)	C1—P—C11	107.0 (3)
C1—Fe—C5^i	138.6 (2)	C1—P—C21	107.9 (3)
C1^i—Fe—C5^i	41.4 (2)	C11—P—C21	102.0 (3)
C5—Fe—C5^i	180.0	C1—P—Au	111.0 (2)
C1—Fe—C2	41.0 (2)	C11—P—Au	114.1 (2)
C1^i—Fe—C2	139.0 (2)	C21—P—Au	114.2 (2)
C5—Fe—C2	68.8 (3)	C2—C1—C5	107.0 (6)
C5^i—Fe—C2	111.2 (3)	C2—C1—P	123.3 (5)
C1—Fe—C2^i	139.0 (2)	C5—C1—P	129.7 (5)
C1^i—Fe—C2^i	41.0 (2)	C2—C1—Fe	69.8 (4)
C5—Fe—C2^i	111.2 (3)	C5—C1—Fe	69.5 (4)
C5^i—Fe—C2^i	68.8 (3)	P—C1—Fe	124.2 (3)
C2—Fe—C2^i	180.0	C3—C2—C1	108.6 (7)
C1—Fe—C3^i	111.9 (3)	C3—C2—Fe	70.6 (4)
C1^i—Fe—C3^i	68.1 (3)	C1—C2—Fe	69.2 (4)
C5—Fe—C3^i	111.9 (3)	C2—C3—C4	108.4 (7)
C5^i—Fe—C3^i	68.1 (3)	C2—C3—Fe	69.6 (4)
C2—Fe—C3^i	140.3 (3)	C4—C3—Fe	70.1 (4)
C2^i—Fe—C3^i	39.7 (3)	C3—C4—C5	109.1 (7)
C1—Fe—C3	68.1 (3)	C3—C4—Fe	69.9 (4)
C1^i—Fe—C3	111.9 (3)	C5—C4—Fe	69.2 (4)
C5—Fe—C3	68.1 (3)	C4—C5—C1	106.9 (7)
C5^i—Fe—C3	111.9 (3)	C4—C5—Fe	70.5 (4)
C2—Fe—C3	39.7 (3)	C1—C5—Fe	69.0 (4)
C2^i—Fe—C3	140.3 (3)	C16—C11—C12	119.5 (7)
C3^i—Fe—C3	180.0	C16—C11—P	123.6 (5)
C1—Fe—C4^i	111.9 (3)	C12—C11—P	116.9 (5)
C1^i—Fe—C4^i	68.1 (3)	C13—C12—C11	120.5 (8)
C5—Fe—C4^i	139.8 (3)	C14—C13—C12	119.2 (8)
C5^i—Fe—C4^i	40.2 (3)	C13—C14—C15	121.2 (8)
C2—Fe—C4^i	112.7 (3)	C16—C15—C14	119.0 (8)
C2^i—Fe—C4^i	67.3 (3)	C11—C16—C15	120.5 (7)
C3^i—Fe—C4^i	40.0 (3)	C22—C21—C26	119.1 (7)
C3—Fe—C4^i	140.0 (3)	C22—C21—P	121.4 (6)
C1—Fe—C4	68.1 (3)	C26—C21—P	119.3 (5)
C1^i—Fe—C4	111.9 (3)	C23—C22—C21	120.1 (7)
C5—Fe—C4	40.2 (3)	C24—C23—C22	120.9 (7)
C5^i—Fe—C4	139.8 (3)	C23—C24—C25	119.3 (8)
C2—Fe—C4	67.3 (3)	C26—C25—C24	119.6 (8)
C2^i—Fe—C4	112.7 (3)	C21—C26—C25	120.8 (7)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4···Au^i	0.95	2.94	3.627 (8)	130
C26—H26···Cl^ii	0.95	2.93	3.550 (8)	124
C14—H14···Cl^iii	0.95	2.85	3.770 (8)	163
C15—H15···Cl^iv	0.95	2.96	3.681 (10)	134
C24—H24···Au^v	0.95	3.11	3.859 (8)	137

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, y, z−1; (iii) x−1, y, z−1; (iv) −x, −y+1, −z+1; (v) x+1/2, −y+3/2, z−1/2.