A second polymorph of chlorido(hydroxydiphenylphosphane)gold(I)

The title complex, [AuCl{(C6H5)2P(OH)-κP}] or [AuCl(C12H11OP)], contains two independent molecules in the asymmetric unit and is a polymorph of a previously reported structure [Hollatz et al. (1999 ▶) J. Chem. Soc. Dalton Trans. pp. 111–114]. The crystal structure exhibits intermolecular Au⋯Au interactions with alternate distances of 3.0112 (3) Å and 3.0375 (2) Å. The Cl—Au—P bond angle varies between different molecular units, depending on the degree of influence of the intramolecular the O—H⋯Cl hydrogen bond; the angle thus varies between negligible distortion from linearity at 179.23 (3)° and more significant distortion at 170.39 (4)°, which differs from the previously reported polymorph in which both these angles are approximately 170°. The Au—Cl [2.3366 (9) and 2.3131 (10)Å] and Au—P [2.2304 (10) and 2.2254 (10) Å] bond lengths vary slightly between the two independent molecules but overall, the bond lengths are in good agreement with those in the previously reported polymorph.


Related literature
For background to polymorphism, see: Braga & Grepioni (2007). Polymorphs of chlorogold(I) phosphine complexes are relatively common (Healy, 2003) and often display interesting photochemical properties (Hoshino et al., 2010). For the previously reported polymorph of the title compound, see: Hollatz et al. (1999). For our studies on gold and P-based ligand complexes, see: Van Zyl (2010).
WEvZ gratefully acknowledges financial support through a UKZN Competitive Grant, and also thanks Rand Refineries (South Africa) for a gift of the gold salt. SVS thanks the National Research Foundation (NRF) for an Innovative Grant.
P1 with four formula units per unit cell and a final R value of 0.036. Due to the nearness of the respective data collection temperatures, we disregard an interpretation of this result as indicating that the structure had undergone a significant phase transition between 173 and 195 K, and thus conclude that the structure of complex (I) presented here is a genuine polymorph and not the consequence of a phase transition. Indeed, polymorphs of chlorogold(I) phosphine complexes are relatively common (Healy, 2003) and often display interesting photochemical properties (Hoshino et al., 2010).
In our continued studies on gold and P-based ligand complexes (Van Zyl, 2010), the title complex [AuCl{(C 6 H 5 ) 2 P(OH)}], (I), was readily synthesized from the reaction between Ph 2 PCl in wet dichloromethane (i.e. containing traces of water) followed by addition of [AuCl(tht)] (tht = tetrahydrothiophene). In the previously reported study of the polymorph, [AuCl(Me 2 S)] was reacted with Ph 2 P(OH) in CH 2 Cl 2 solvent with the elimination of Me 2 S, forming [AuCl{(C 6 H 5 ) 2 P(OH)}]. A solution 31 P NMR study showed a sharp singlet at δ = 89.5 for (I) which corresponds well with the value of δ = 90.4 for the polymorph (Hollatz et al., 1999). Since polymorphs must have the same resonance in solution, and since the same solvent (CDCl 3 ) was used in both cases, the small difference (0.9 p.p.m.) is ascribed to possible difference in temperature (293 versus 298 K) during data acquisition. A single-crystal X-ray analysis of the compound subsequently provided unambiguous proof of the authenticity of the complex, and for it to be a polymorph.
The crystal structure of (I) presented here includes four molecular units along a virtual chain (described as two "inner" and two "outer" units) all linked through intermolecular Au···Au interactions with alternate distances of 3.0112 (3) Å (between the two inner units) and 3.0375 (2) Å between an inner and outer unit which are both shorter than the corresponding distance for the reported polymorph, at 3.1112 (7) Å. The Cl-Au-P bond angles between the two inner complexes have in one case negligible distortion away from linearity at 179.23 (3)° while in the other case it has significant distortion at 170.39 (4)°, which differs from the previously reported polymorph where both these angles are approximately 170°. This difference originates through the varying influence of O-H···Cl type hydrogen bonding within the respective molecular units: the stronger the H-bonding, the more the distortion. In the case of (I), the one Cl-Au-P unit is positioned too far from a P-O-H unit for any O-H···Cl hydrogen bonding [d(H···Cl) = 2.23 Å] to occur whilst the other Cl-Au-P unit is much closer to a P-O-H unit at d(H···Cl) = 2.16 Å, and this causes the observed distortion. In the triclinic polymorph, hydrogen bonding is present on both monomeric units at d(H···Cl) = 2.03 and 2.11 Å, respectively, which leads to significant distortion from linearity for both Cl-Au-P units.The Au-Cl bond length of the inner unit is 2.3366 (9) and for the outer unit 2.3131 (10) Å, respectively, whilst the Au-P bond lengths are slightly shorter at 2.2304 (10) (inner) and 2.2254 (10) Å (outer), respectively; these bond length results are in good agreement with the previously reported structure. The P-O bond length in (I) is 1.592 (3) Å versus 1.597 (5) Å in the triclinic polymorph. Based on the current studies, it cannot supplementary materials sup-2 readily be inferred whether the polymorph with the shorter Au···Au interactions is the thermodynamically more stable of the two. Note that structure (I) has a slightly lower calculated density at 2.289 g/cm 3 compared to the other polymorph at 2.309 g/cm 3 , suggesting the molecular packing in the latter is more efficient, presumably resulting from a larger extent of hydrogen bonding.

Experimental
Preparation and characterization of complex (I): A Schlenk flask equipped with a magnetic stirrer bar was charged with wet dichloromethane (5 ml) and this was followed by addition of ClPPh 2 (0.210 ml, 1.11 mmol). The mixture was stirred for 20 minutes at room temperature. A dichloromethane solution of [AuCl(tht)] (354 mg, 1.11 mmol) was added in one portion and the resulting mixture stirred for a further 15 minutes. All of the solvent and tht were removed and the product isolated as a free-flowing white powder. 31 P NMR (101 MHz, CDCl 3 , 298 K) δ P = 89.2 (s, 1P). Single crystals were obtained by slow diffusion of hexane vapor into a saturated dichloromethane solution.