The effect of counteranions on the molecular structures of phosphanegold(i) cluster cations formed by polyoxometalate (POM)-mediated clusterization

Abstract

The effect of counteranions on the molecular structures of phosphanegold(i) cluster cations formed by polyoxometalate (POM)-mediated clusterization was investigated. A novel intercluster compound, [{(AuLCl)2(μ-OH)}2]3[α-PMo12O40]2·3EtOH (1-PMo12), was obtained as orange-yellow plate crystals in 12.0% yield from a 6 : 1 molar ratio reaction of the monomeric phosphanegold(i) carboxylato complex [Au(RS-pyrrld)(LCl)] (RS-Hpyrrld = RS-2-pyrrolidone-5-carboxylic acid; LCl = tris(4-chlorophenyl)phosphane) in CH2Cl2 with the free acid-form of Keggin polyoxometalate (POM), H3[α-PMo12O40]·14H2O. An EtOH/H2O (5 : 1, v/v) solvent mixture was used. The dimeric cation [{(AuLCl)2(μ-OH)}2](2+) in 1-PMo12 was in a parallel-edge arrangement that was formed by self-assembly through the inter-cationic aurophilic interactions of the μ-OH-bridged dinuclear phosphanegold(i) cation. The POM anion in 1-PMo12 was successfully exchanged with a smaller PF6(-) anion by the use of an anion-exchange resin. POM-free, colorless block crystals of [{(AuLCl)3(μ3-O)}2](PF6)2·4CH2Cl2 (2-PF6) were obtained by vapor diffusion in 14.1% yield. During the synthesis of 2-PF6, a compound with mixed counteranions (one POM and one PF6(-) anion), i.e. [{(AuLCl)4(μ4-O)}]2[α-PMo12O40]PF6 (3-PMo12PF6), was obtained in 66.4% yield. Both products were characterized by elemental analysis, TG/DTA, FT-IR, (31)P{(1)H} NMR, (1)H NMR, and X-ray crystallography. X-ray crystallography revealed that the countercation in 2-PF6 was the dimeric cation of the μ3-O-bridged tris{phosphanegold(i)} species, whereas that in 3-PMo12PF6 consisted of an unusual μ4-O-bridged tetragonal-pyramidal tetrakis{phosphanegold(i)} cation. Therefore, we concluded that the POM anion significantly contributed to the stabilization of these countercations (parallel-edged arrangement in 1-PMo12 and μ4-O-bridged tetragonal-pyramid in 3-PMo12PF6). Moreover, the previously reported yellow crystals of [{(AuLF)2(μ-OH)}2]3[PMo12O40]2·3EtOH (4-PMo12: LF = tris(4-fluoro phenyl)phosphane) were successfully converted to the POM-free crystalline OTf(-) salt [{(AuLF)2(μ-OH)}2](OTf)2·0.5Et2O (4-OTf) by the use of an anion-exchange resin. X-ray crystallography also revealed that the parallel-edge arrangement of the dimeric cation in 4-PMo12 was converted to the crossed-edge arrangement of that in 4-OTf. These results illustrate that the AuOPOM and hydrogen-bonding (C-HOPOM and O-HOPOM) interactions between the phosphanegold(i) cluster cation and the Keggin POM anion in the solid state significantly contribute to the structure, composition, and stability of the phosphane gold(i) cluster cations in 4-PMo12.

When Gold Cations Meet Polyoxometalates

“…employed various aromatic phosphane ligands with meta ‐ or para ‐ substituents to evaluate their influence on the architecture of the SICCs. The reactions of 6, 7 or 8 equiv of tri(aryl)phosphane gold(I) ( S , R )‐2‐pyrrolidinone‐5‐carboxylate [Au(P(aryl) 3 )(( R , S )‐pyrrld)] (with aryl= m ‐FPh ( meta ‐fluorophenyl), m ‐tol ( meta ‐tolyl), p ‐tol ( para ‐tolyl), p ‐FPh ( para ‐fluorophenyl), or p ‐ClPh ( para ‐chlorophenyl)) dissolved in DCM with 1 or 2 equiv of [H] + 3 [α‐PMo 12 O 40 ] 3− , [H] + 3 [α‐PW 12 O 40 ] 3− , [H] + 4 [α‐SiMo 12 O 40 ] 4− , or [H] + 4 [α‐SiW 12 O 40 ] 4− dissolved in a layer of ethanol‐water mixture afford the SICCs [{Au(P( m ‐FPh) 3 )} 4 ( μ 4 ‐O)] 2+ 2 [{{Au(P( m ‐FPh) 3 )} 2 ( μ ‐OH)} 2 ] 2+ [α‐PMo 12 O 40 ] 3− 2 ( 25 ), [{Au(P( m ‐FPh) 3 )} 4 ( μ 4 ‐O)] 2+ 2 [α‐SiMo 12 O 40 ] 4− ( 26 ), [{Au(P( m ‐tol) 3 )} 4 ( μ 4 ‐O)] 2+ 2 [α‐SiW 12 O 40 ] 4− ( 27 ), [{Au(P( m ‐tol) 3 )} 4 ( μ 4 ‐O)] 2+ 2 [α‐SiMo 12 O 40 ] 4− ( 28 ), [{{Au(P( p ‐tol) 3 )} 2 ( μ ‐OH)} 2 ] 2+ 3 [α‐PW 12 O 40 ] 3− 2 ( 29 ), [{{Au(P( p ‐tol) 3 )} 2 ( μ ‐OH)} 2 ] 2+ 3 [α‐PMo 12 O 40 ] 3− 2 ( 30 ), [{{Au(P( p ‐FPh) 3 )} 2 ( μ ‐OH)} 2 ] 2+ 3 [α‐PMo 12 O 40 ] 3− 2 ( 31 ), [{{Au(P( p ‐ClPh) 3 )} 2 ( μ ‐OH)} 2 ] 2+ 3 [α‐PMo 12 O 40 ] 3− 2 ( 32 ), [{{Au(P( p ‐FPh) 3 )} 2 ( μ ‐OH)} 2 ] 2+ [α‐SiMo 12 O 40 {Au(P( p ‐FPh) 3 )}] 2− ( 33 ), or [{{Au(P( p ‐ClPh) 3 )} 2 ( μ ‐OH)} 2 ] 2+ [α‐SiMo 12 O 40 {Au(P( p ‐ClPh) 3 )}] 2− ( 34 ) with 35.9, 4.6, 71.4, 46.7, 78.0 %, a few %, 27.8, 73.4, 38.7, or 12.0 % yields, as crystals with the P , P , R , R , Ia d , Ia d , P , P , C 2/ c , or P space group symmetries (Figure ). A side product, not separable from 33 was detected upon crystallization, but not characterized.…”

“…The [α‐PW 12 O 40 ] 3− anions of 31 and 32 were replaced by [PF 6 ] − and [OTf] − by use of anion‐exchange resin, to evaluate the role of the POM on the geometry of the gold oxonium clusters. The compounds [{{Au(P( p ‐ClPh) 3 )} 3 ( μ 3 ‐O)} 2 ] 2+ [PF 6 ] − 2 ( 36 ) ⋅ 3 EtOH, [{{Au(P( p ‐ClPh) 3 )} 4 ( μ 4 ‐O)} 2 ] 4+ [PF 6 ] − [α‐PMo 12 O 40 ] 3− ( 37 ) and [{{Au(P( p ‐FPh) 3 )} 2 ( μ ‐OH)} 2 ] 2+ [OTf] − ( 38 ) ⋅ Et 2 O are synthesized with 14.1, 66.1 and 56.0 % yields, as crystals with the P , P 4/ n and P 4 2 / n space group symmetries . For 36 , the dimer of dinuclear gold clusters [{{Au(P( p ‐ClPh) 3 )} 2 ( μ ‐OH)} 2 ] 2+ is converted to dimer of trinuclear gold clusters, by replacing the proton of the bridging hydroxyl group by an [Au(P( p ‐ClPh) 3 )] + fragment (Figure ).…”

“…For 37 , the [{{Au(P( p ‐ClPh) 3 )} 4 ( μ 4 ‐O)} 2 ] 4+ cluster is formed by four basal gold cations capped by an oxygen atom. Compared to other tetragold‐oxonium clusters with C 3 v symmetry described previously, it has an unusual C 4 v symmetry which is characteristic of an electron deficient species with a bond order for each O−Au bond …”

“…Co-crystallized ethanoli sf ound in the crystal lattice, andt his compound is best described by (24)·EtOH. All [Au(PPh 3 )] + fragments,c hemically equivalent in (solid/liquid) 31 (28), [23] (32), [25] [ (34) [26] [24] For 25, 31, 32, 34,aparallel-edge arrangement leads to rectangular arrays of gold atoms capped by an oxygen atom (D 2h symmetry). This geometry is only encountered with thiolate-bridged tetragold clusters [{{(AuPR 3 )} 2 (m-SZ)} 2 ] 2 + (R = alkyl, aryl;Z = CMe 3 ,a niline, sugar…).…”

“…Oa re synthesized with 14.1, 66.1 and 56.0 %y ields, as crystals with the P1 , P4/n and P4 2 /n space group symmetries. [25] four basal gold cations capped by an oxygen atom. Compared to other tetragold-oxoniumc lusters with C 3v symmetry described previously,i th as an unusual C 4v symmetry which is characteristic of an electron deficient speciesw ith a 3 = 4 bond order for each OÀAu bond.…”