Aurophilic interactions in μ-p-phenyl­enediethynyl-bis[(trimethyl phosphite)gold(I)] dichloro­methane hemisolvate

The title compound, [Au₂(C₁₀H₄)(C₃H₉O₃P)₂]·0.5CH₂Cl₂, is a linear monomer in which each Au atom is coordinated by one acetylene and one phosphite group. Molecules are connected through aurophilic interactions, one short and one longer, approximately perpendicular to the intramolecular di(gold acetylide) unit, with an Au...Au(x, 1 − y,  + z) distance of 3.1733 (2) Å and an Au...Au(−x, y,  − z) distance of 3.5995 (3) Å. Comparison with related compounds exhibiting aurophilic interactions shows that the packing architecture is not determined by steric factors alone.

S1. Comment

Aurophilic interactions, weakly bonding interactions between formally non-bonded gold centers, have been described and classified only in the relatively recent past (Scherbaum et al., 1988). They are of considerable current interest as both intra- and intermolecular motifs in gold compounds (Mohr et al., 2004). These interactions have strengths similar to those of hydrogen bonding (Pyykkö, 1997) and are characterized by Au···Au contacts close to the sum of two van der Waals radii (3.2 Å). Ligand bulk plays an important role in the formation of intermolecular aurophilic interactions. We report here the structure of a gold phosphite acetylide compound, (I), that exhibits two aurophilic contacts of appreciably different length.

Compound (I), shown in Fig. 1, has a typical `wheel and axle' structure with two phosphite `wheels' on the ends of the digoldacetylide `axle' (Bruce et al., 2002). The Au atom is linearly coordinated by the phosphite and acetylide, as is typical for Au^I compounds. The intramolecular bond lengths and angles, detailed in Table 1, are unexceptional in comparison to other known gold–acetylide and gold–phosphite complexes. Searches of the Cambridge Structural Database (Version 5.25; Allen, 2002) yield an average Au—P distance in seven Au—P(OMe)₃ linkages of 2.254 (7) Å and an average Au—C distance of 1.99 (4) Å from 99 Au—C distances in two-coordinate gold acetylides. The analogous Au—P distances (Å) for the title compound are 2.2459 (8) and 2.2492 (8) and, the Au—C bond lengths are both 2.000 (3) Å.

There are two aurophilic interactions present in (I), as shown in Fig. 2. Each Au1 atom bonds intermolecularly to an Au2(x, 1 − y, 1/2 + z) atom at a distance of 3.1733 (2) Å in a head-to-tail fashion. Each Au2 atom also interacts with atom Au2(−x, y, 1/2 − z) of a third molecule at a distance of 3.5995 (3) Å. The intermolecular Au···Au contacts, shown in Fig. 2, generate a herringbone lattice. The gold–gold contacts form short chains of four atoms (Au1···Au2···Au2···Au1) in which the angle at each Au2 atom is 149.55 (1)°. There is not an infinite chain of contacts through the crystal because each Au1 center is effectively a terminus for the aurophilic contacts.

A few related digold–acetylene compounds have been structurally characterized, and some of them exhibit aurophilic interactions, as summarized in Table 2. The PCy₃ analog of the title compound was recently reported (Chao et al., 2002), in which all Au···Au distances are longer than 3.6 Å. With smaller PMe₃ ligands on the ends of a digold CC—C₆H₂Me₂—CC axle, the Au atoms show aurophilic contacts of 3.1361 (9) Å (Irwin, Vittal et al., 1997). In this structure the methyl groups are in the 2- and 5-positions of the phenylene ring. A PMe₃ analog of the present compound, [(Me₃P)Au—CC—Au(PMe₃)] (Jia et al., 1993; Liau et al., 2003), with a much shorter bridge (axle) has also been reported, which has Au···Au contacts of 3.0747 (8) Å. Two gold acetylides with capping P(OMe)₃ ligands are known, both with a meta orientation of the two acetylene groups in contrast to the para orientation in the title compound. One compound has ethynyl–gold groups in the 1- and 3-positions and a methyl group in the 5-position (MacDonald et al., 2000). The Au1···Au2 contacts are 3.2196 (9) Å. When a third gold–ethynyl unit is present in approximately C₃ symmetry (Irwin, Manojlovic-Muir et al., 1997), there is an aurophilic contact between atoms Au1 and Au3 of 3.316 (1) Å, and a much longer Au1···Au2 distance of 3.973 (1) Å.

Together with data reported here, these structures show that in addition to the steric bulk of the ligand at the Au center, the geometric distribution of the gold–acetylide units around a benzene ring also affects the formation of aurophilic contacts, as summarized in Table 2. In comparing table entry D with compound (I), a shorter Au···Au interaction has been achieved with similar steric bulk of the terminal ligands, because (I) has only hydrogen substituents on the central ring. Comparison of (I) and entry E shows the reduction in distance achieved with di- versus tri-substitution. Close aurophilic contacts require both small terminal ligands on the Au atom and fewer substituents on the benzene ring to minimize steric clashes.

S2. Experimental

The title compound was synthesized by modification of a similar procedure reported by Jia et al., 1993) The P(OMe)₃ ligand was added to a slurry of the polymer {Au—CC—C₆H₄}_n, causing the polymer to dissolve as the phosphite breaks up the intermolecular gold–acetylide interactions. The solution was filtered and the new compound was recrystallized from CH₂Cl₂ layered with hexanes. ¹H NMR (300 MHz, CD₂Cl₂): δ 3.73 (d, 18 H, CH₃, ²J_HC = 12.69 Hz), 7.25 (s, 4 H, C₆H₄). ¹³C NMR (300 MHz, CD₂Cl₂): δ 52.57 (CH₃), 123.20 (Cipso), 131.61 (CH). Acetylene C atoms were not detected, consistent with previously reported work (Liau et al., 2003). UV–vis (CH₂Cl₂) [λ_max, nm (extinction coefficient, cm^-1 M⁻¹)]: 231 (136.000), 235 (133.000), 305 (269.000), 324 (410.000). Fluorescence (CH₂Cl₂) [λ_max, nm]. Excitation: 346, 357, 373. Emission: 378, 396, 412. Analysis calcualted for C₁₆H₂₂Au₂O₆P₂: C 25.08, H 2.89, Au 51.41%; found: C 24.94, H 3.06, Au 51.30%.

S3. Refinement

Compound (I) crystallizes as a dichloromethane hemisolvate. The CH₂Cl₂ molecule is disordered around a twofold axis over two positions and was refined with both C—Cl distances constrained to have the same value and isotropic dispalcement parameters for the C atom. All H atoms were placed in calculated positions and refined using a riding model [C—H = 0.93–0.97 \%A and U_iso(H) = 1.2U_iso(C)].

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART; data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2000); software used to prepare material for publication: SHELXTL.

Figures

Figure 1. A view of the structure of (I), showing the atomic numbering. The methylene chloride solvent molecule has been omitted for clarity. Displacement ellipsoids are drawn at the 50% probability level for non-H atoms. Figure 2. A packing diagram showing the aurophilic interactions. All H atoms and phosphite methyl groups have been omitted for clarity. The short and long Au···Au contacts are shown by dashed lines. Symmetry codes: (iv) 1/2 + x, 1/2 + y, z; (v) 1/2 − x, 1/2 + y, 1/2 − z; (vi) 1/2 − x, 1/2 − y, −z; (vii) 1/2 + x, 1/2 − y, −1/2 + z. ———

µ-(p-phenylenediethynyl)-bis[(trimethyl phosphite)gold(I)] dichloromethane hemisolvate

Crystal data

[Au2(C10H4)(C3H9O3P)2]·0.5CH2Cl2	F(000) = 3000
Mr = 808.69	Dx = 2.357 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 16.6892 (9) Å	Cell parameters from 5620 reflections
b = 13.8568 (8) Å	θ = 2.5–27.5°
c = 20.4250 (12) Å	µ = 13.15 mm^−1
β = 105.225 (1)°	T = 100 K
V = 4557.7 (4) Å^3	Block, yellow
Z = 8	0.22 × 0.16 × 0.12 mm

Data collection

Bruker SMART CCD area-detector diffractometer	5101 independent reflections
Radiation source: fine-focus sealed tube	4364 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.018
ϕ and ω scans	θmax = 27.5°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −21→21
Tmin = 0.160, Tmax = 0.301	k = −17→17
18988 measured reflections	l = −26→26

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.020	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.052	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0223P)^2 + 20.4573P] where P = (Fo^2 + 2Fc^2)/3
5101 reflections	(Δ/σ)max = 0.002
262 parameters	Δρmax = 0.89 e Å^−3
1 restraint	Δρmin = −0.90 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.

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	Occ. (<1)
Au1	0.268333 (8)	0.247168 (8)	0.703911 (6)	0.01723 (5)
Au2	0.078153 (8)	0.753356 (8)	0.203780 (6)	0.01685 (5)
P1	0.31078 (6)	0.15126 (6)	0.79510 (4)	0.02124 (19)
P2	0.03857 (5)	0.84523 (6)	0.11004 (4)	0.01784 (17)
O1	0.3355 (3)	0.1958 (2)	0.86847 (14)	0.0630 (12)
O2	0.39111 (16)	0.09516 (19)	0.79001 (13)	0.0293 (6)
O3	0.24760 (15)	0.07199 (17)	0.80695 (11)	0.0214 (5)
O4	0.11540 (14)	0.89541 (17)	0.09349 (12)	0.0219 (5)
O5	−0.02113 (15)	0.93378 (17)	0.11065 (12)	0.0225 (5)
O6	−0.01239 (15)	0.79279 (19)	0.04238 (12)	0.0241 (5)
C1	0.2400 (2)	0.3292 (2)	0.62044 (16)	0.0177 (6)
C2	0.2224 (2)	0.3780 (2)	0.56982 (16)	0.0170 (6)
C3	0.1986 (2)	0.4371 (2)	0.50999 (16)	0.0170 (6)
C4	0.1802 (2)	0.3972 (2)	0.44500 (16)	0.0186 (7)
H4	0.1832	0.3307	0.4398	0.022*
C5	0.1574 (2)	0.4559 (2)	0.38798 (16)	0.0177 (6)
H5	0.1451	0.4281	0.3451	0.021*
C6	0.1526 (2)	0.5562 (2)	0.39406 (16)	0.0173 (6)
C7	0.1713 (2)	0.5960 (2)	0.45958 (17)	0.0223 (7)
H7	0.1687	0.6625	0.4649	0.027*
C8	0.1937 (2)	0.5373 (2)	0.51626 (16)	0.0204 (7)
H8	0.2056	0.5649	0.5592	0.024*
C9	0.1301 (2)	0.6173 (2)	0.33532 (16)	0.0191 (7)
C10	0.1116 (2)	0.6704 (2)	0.28663 (16)	0.0186 (7)
C11	0.3268 (4)	0.2883 (4)	0.8858 (2)	0.068 (2)
H11A	0.3806	0.3174	0.9018	0.102*
H11B	0.2984	0.2903	0.9210	0.102*
H11C	0.2952	0.3230	0.8469	0.102*
C12	0.4307 (2)	0.0228 (3)	0.84000 (19)	0.0328 (9)
H12A	0.4661	0.0542	0.8788	0.039*
H12B	0.4631	−0.0201	0.8203	0.039*
H12C	0.3888	−0.0134	0.8537	0.039*
C13	0.2145 (2)	0.0059 (2)	0.75163 (18)	0.0253 (8)
H13A	0.1956	0.0415	0.7101	0.030*
H13B	0.1688	−0.0292	0.7605	0.030*
H13C	0.2571	−0.0386	0.7476	0.030*
C14	0.1076 (2)	0.9598 (3)	0.0364 (2)	0.0327 (9)
H14A	0.0812	0.9265	−0.0048	0.039*
H14B	0.1618	0.9810	0.0346	0.039*
H14C	0.0747	1.0147	0.0415	0.039*
C15	−0.0983 (2)	0.9190 (3)	0.1292 (2)	0.0355 (9)
H15A	−0.1336	0.8767	0.0969	0.043*
H15B	−0.1257	0.9799	0.1294	0.043*
H15C	−0.0868	0.8907	0.1736	0.043*
C16	0.0178 (3)	0.7021 (3)	0.0237 (2)	0.0389 (10)
H16A	0.0684	0.7128	0.0107	0.047*
H16B	−0.0230	0.6745	−0.0137	0.047*
H16C	0.0283	0.6588	0.0616	0.047*
C17	−0.0116 (7)	0.2125 (7)	0.2280 (4)	0.046 (2)*	0.50
H17A	−0.0637	0.2468	0.2220	0.056*	0.50
H17B	0.0330	0.2589	0.2429	0.056*	0.50
Cl1	−0.0036 (2)	0.1253 (3)	0.2923 (2)	0.0921 (12)	0.50
Cl2	−0.0069 (3)	0.1656 (4)	0.1506 (3)	0.1178 (17)	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Au1	0.02684 (8)	0.01502 (7)	0.00959 (7)	−0.00155 (5)	0.00433 (5)	0.00245 (4)
Au2	0.01786 (7)	0.01849 (8)	0.01276 (7)	0.00057 (5)	0.00149 (5)	0.00550 (4)
P1	0.0350 (5)	0.0170 (4)	0.0099 (4)	−0.0039 (4)	0.0026 (3)	0.0026 (3)
P2	0.0176 (4)	0.0215 (4)	0.0134 (4)	0.0011 (3)	0.0023 (3)	0.0053 (3)
O1	0.144 (4)	0.0214 (15)	0.0117 (14)	−0.0185 (19)	−0.0008 (17)	0.0012 (11)
O2	0.0222 (13)	0.0403 (15)	0.0226 (13)	−0.0019 (11)	0.0010 (10)	0.0130 (11)
O3	0.0284 (13)	0.0203 (12)	0.0175 (12)	0.0009 (10)	0.0095 (10)	0.0027 (9)
O4	0.0192 (12)	0.0275 (13)	0.0191 (12)	0.0020 (10)	0.0052 (10)	0.0103 (10)
O5	0.0224 (12)	0.0246 (12)	0.0234 (13)	0.0064 (10)	0.0113 (10)	0.0103 (10)
O6	0.0215 (13)	0.0288 (14)	0.0182 (13)	0.0044 (10)	−0.0014 (10)	0.0007 (10)
C1	0.0239 (17)	0.0159 (15)	0.0119 (15)	−0.0006 (13)	0.0025 (13)	−0.0004 (12)
C2	0.0182 (16)	0.0206 (16)	0.0129 (15)	−0.0020 (13)	0.0055 (12)	−0.0028 (12)
C3	0.0169 (15)	0.0217 (16)	0.0134 (15)	−0.0005 (13)	0.0057 (12)	0.0036 (12)
C4	0.0253 (17)	0.0168 (15)	0.0141 (15)	−0.0003 (13)	0.0059 (13)	−0.0006 (12)
C5	0.0183 (16)	0.0233 (16)	0.0116 (15)	−0.0006 (13)	0.0041 (12)	−0.0005 (12)
C6	0.0163 (15)	0.0238 (16)	0.0125 (15)	0.0024 (13)	0.0050 (12)	0.0044 (12)
C7	0.034 (2)	0.0180 (16)	0.0173 (17)	0.0037 (14)	0.0105 (14)	0.0025 (13)
C8	0.0285 (18)	0.0234 (17)	0.0106 (15)	0.0009 (14)	0.0074 (13)	−0.0008 (13)
C9	0.0195 (16)	0.0233 (17)	0.0154 (16)	0.0019 (13)	0.0063 (13)	0.0015 (13)
C10	0.0172 (15)	0.0221 (17)	0.0155 (16)	0.0019 (13)	0.0023 (12)	0.0036 (13)
C11	0.095 (4)	0.057 (3)	0.030 (2)	0.052 (3)	−0.021 (3)	−0.021 (2)
C12	0.032 (2)	0.036 (2)	0.025 (2)	0.0030 (17)	−0.0025 (16)	0.0115 (16)
C13	0.0268 (19)	0.0225 (17)	0.0243 (19)	−0.0049 (14)	0.0025 (15)	0.0021 (14)
C14	0.028 (2)	0.041 (2)	0.031 (2)	0.0031 (17)	0.0111 (16)	0.0210 (18)
C15	0.026 (2)	0.037 (2)	0.049 (3)	0.0067 (17)	0.0207 (19)	0.0128 (19)
C16	0.034 (2)	0.038 (2)	0.036 (2)	0.0067 (19)	−0.0066 (18)	−0.0138 (19)
Cl1	0.0421 (16)	0.082 (2)	0.142 (4)	0.0004 (16)	0.006 (2)	0.037 (2)
Cl2	0.115 (3)	0.120 (4)	0.136 (4)	−0.071 (3)	0.063 (3)	−0.038 (3)

Geometric parameters (Å, º)

Au1—C1	2.000 (3)	C6—C9	1.435 (4)
Au1—P1	2.2459 (8)	C7—C8	1.384 (5)
Au1—Au2^i	3.1733 (2)	C7—H7	0.9300
Au2—Au2^ii	3.5995 (3)	C8—H8	0.9300
Au2—C10	2.000 (3)	C9—C10	1.210 (5)
Au2—P2	2.2492 (8)	C11—H11A	0.9600
Au2—Au1^iii	3.1733 (2)	C11—H11B	0.9600
P1—O1	1.572 (3)	C11—H11C	0.9600
P1—O2	1.577 (3)	C12—H12A	0.9600
P1—O3	1.585 (2)	C12—H12B	0.9600
P2—O4	1.571 (2)	C12—H12C	0.9600
P2—O5	1.583 (2)	C13—H13A	0.9600
P2—O6	1.595 (2)	C13—H13B	0.9600
O1—C11	1.347 (6)	C13—H13C	0.9600
O2—C12	1.460 (4)	C14—H14A	0.9600
O3—C13	1.447 (4)	C14—H14B	0.9600
O4—C14	1.447 (4)	C14—H14C	0.9600
O5—C15	1.449 (4)	C15—H15A	0.9600
O6—C16	1.442 (5)	C15—H15B	0.9600
C1—C2	1.205 (4)	C15—H15C	0.9600
C2—C3	1.438 (4)	C16—H16A	0.9600
C3—C4	1.396 (4)	C16—H16B	0.9600
C3—C8	1.398 (5)	C16—H16C	0.9600
C4—C5	1.390 (4)	C17—Cl2	1.730 (9)
C4—H4	0.9300	C17—Cl1	1.763 (8)
C5—C6	1.400 (5)	C17—H17A	0.9700
C5—H5	0.9300	C17—H17B	0.9700
C6—C7	1.405 (5)
C1—Au1—P1	174.78 (10)	C10—C9—C6	178.7 (4)
C1—Au1—Au2^i	89.32 (10)	C9—C10—Au2	177.5 (3)
P1—Au1—Au2^i	95.56 (3)	O1—C11—H11A	109.5
C10—Au2—P2	179.03 (10)	O1—C11—H11B	109.5
C10—Au2—Au1^iii	86.65 (9)	H11A—C11—H11B	109.5
P2—Au2—Au1^iii	94.13 (2)	O1—C11—H11C	109.5
Au1^iii—Au2—Au2^ii	149.55 (1)	H11A—C11—H11C	109.5
O1—P1—O2	104.0 (2)	H11B—C11—H11C	109.5
O1—P1—O3	98.36 (17)	O2—C12—H12A	109.5
O2—P1—O3	106.25 (14)	O2—C12—H12B	109.5
O1—P1—Au1	120.33 (12)	H12A—C12—H12B	109.5
O2—P1—Au1	109.00 (10)	O2—C12—H12C	109.5
O3—P1—Au1	117.34 (10)	H12A—C12—H12C	109.5
O4—P2—O5	102.10 (13)	H12B—C12—H12C	109.5
O4—P2—O6	107.15 (14)	O3—C13—H13A	109.5
O5—P2—O6	99.58 (13)	O3—C13—H13B	109.5
O4—P2—Au2	111.09 (9)	H13A—C13—H13B	109.5
O5—P2—Au2	118.48 (9)	O3—C13—H13C	109.5
O6—P2—Au2	116.76 (10)	H13A—C13—H13C	109.5
C11—O1—P1	127.2 (3)	H13B—C13—H13C	109.5
C12—O2—P1	121.9 (2)	O4—C14—H14A	109.5
C13—O3—P1	116.9 (2)	O4—C14—H14B	109.5
C14—O4—P2	122.7 (2)	H14A—C14—H14B	109.5
C15—O5—P2	119.8 (2)	O4—C14—H14C	109.5
C16—O6—P2	118.8 (2)	H14A—C14—H14C	109.5
C2—C1—Au1	179.4 (3)	H14B—C14—H14C	109.5
C1—C2—C3	177.9 (4)	O5—C15—H15A	109.5
C4—C3—C8	118.5 (3)	O5—C15—H15B	109.5
C4—C3—C2	121.6 (3)	H15A—C15—H15B	109.5
C8—C3—C2	119.9 (3)	O5—C15—H15C	109.5
C5—C4—C3	120.5 (3)	H15A—C15—H15C	109.5
C5—C4—H4	119.7	H15B—C15—H15C	109.5
C3—C4—H4	119.7	O6—C16—H16A	109.5
C4—C5—C6	121.1 (3)	O6—C16—H16B	109.5
C4—C5—H5	119.4	H16A—C16—H16B	109.5
C6—C5—H5	119.4	O6—C16—H16C	109.5
C5—C6—C7	118.1 (3)	H16A—C16—H16C	109.5
C5—C6—C9	121.3 (3)	H16B—C16—H16C	109.5
C7—C6—C9	120.6 (3)	Cl2—C17—Cl1	114.2 (6)
C8—C7—C6	120.7 (3)	Cl2—C17—H17A	108.7
C8—C7—H7	119.7	Cl1—C17—H17A	108.7
C6—C7—H7	119.7	Cl2—C17—H17B	108.7
C7—C8—C3	121.1 (3)	Cl1—C17—H17B	108.7
C7—C8—H8	119.4	H17A—C17—H17B	107.6
C3—C8—H8	119.4

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