Syntheses, Molecular Structures, and Countercation‐Induced Structural Transformation of Monomeric α‐Keggin‐Type Polyoxotungstate‐Coordinated Mono‐ and Dipalladium(II) Complexes

Abstract

Monomericα-Keggin-type polyoxotungstate-coordinated mono-and di-palladium(II) complexes, i. e., Cs 5 O 39 {Pd II-(Me 2 ppz)}] • 5H 2 O (Cs-1) (Me 2 ppz = N,N'-dimethylpiperazine), [(CH 3 ) 4 N] 4 H[α-PW 11 O 39 {Pd II (Me 2 ppz)}] • 8H 2 O (TMA-1), and Cs 2.5 H 0.5 [α-PW 11 O 39 {Pd II (en)} 2 ] • 7H 2 O (en = ethylenediamine) (Cs-2), were synthesized by 1 : 1 or 1 : 2 stoichiometric reactions of mono-lacunary α-Keggin polyoxotungstate [α-PW 11 O 39 ] 7À with PdCl 2 (Me 2 ppz) and PdCl 2 (en) in aqueous solution. Subsequent purification from water afforded these compounds as analytically pure homogeneous yellow precipitates. Single-crystal Xray structural analysis of Cs-1 revealed that a palladium(II) moiety, i. e., [Pd(Me 2 ppz)] 2 + , was coordinated to two oxygen atoms in the mono-vacant site of [PW 11 O 39 ] 7À with an asymmetric configuration, resulting in an overall C 1 symmetry. With regard to the crystal structure of Cs-2, two palladium species of the [Pd(en)] 2 + type were coordinated to two oxygen atoms in the mono-vacant site with symmetric configuration, resulting in an overall C s symmetry. A unique structural transformation of the mono-lacunary α-Keggin structure of Cs-1 to the di-lacunary γ-Keggin polyoxotungstate Cs 7 [γ-PW 10 O 36 ] was observed upon the addition of cesium chloride.

Coordination of Palladium(II) and Platinum(II) Complexes to One Vacant Site in an α-Keggin-Type Polyoxotungstate

“…Therefore, the coordination of the {Pd II (bpy)} moiety to the mono-vacant site of {PW 11 O 39 } led to the splitting of 1 H NMR signals of the bpy molecule. A similar splitting was also observed for Cs 2.5 H 0.5 [α-PW 11 O 39 {Pd II (en)} 2 ]·7H 2 O . Notably, some signals due to the bpy molecule in 0.25 [Pd­(bpy)] 2+ that was present as a counter cation were also observed, as shown in Figure B.…”

“…The 10 Notably, some signals due to the bpy molecule in 0.25 [Pd(bpy)] 2+ that was present as a counter cation were also observed, as shown in Figure 6B. The signal due to the solvated acetonitrile molecules was observed at 2.10 ppm.…”

“…In contrast, even when the mixture of Pd2 and cis- Pt II (NH 3 ) 2 Cl 2 was heated at 90 °C for 2 h in water at a molar ratio of 1:1, no exchange reaction between the {Pd II (bpy)} and { cis -Pt II (NH 3 ) 2 } moieties was observed. No reaction was observed when [α-PW 11 O 39 {Pd II (Me 2 ppz)}] 5− reacted with cis- Pt II (NH 3 ) 2 Cl 2 at a molar ratio of 1:1 in water.…”

“…Some recently developed palladiumcontaining POMs include [Se )(O 2 C(CH 2 ) n CO 2 )} 2 ] 8− (n = 1, 3, and 5), 9 [α-PW 11 O 39 {Pd II (Me 2 ppz)}] 5− (Me 2 ppz = N,N′-dimethylpiperazine), 10 and [α-PW 11 O 39 {Pd II (en)} 2 ] 3− (en = ethylenediamine). 10 In the field of platinum-containing POMs, [α-PW 11 O 39 {cis-Pt II (NH 3 ) 2 } 2 ] 3− , 11,12 In this study, we obtained a palladium−platinum bimetal complex containing a mono-lacunary α-Keggin-type polyoxotungstate, Cs 2.5 {Pd II (bpy)} 0.25 [α-PW 11 O 39 {Pd II (bpy)}{cis-Pt II (NH 3 ) 2 }]•12H 2 O•2CH 3 CN (bpy = 2,2′-bipyridine) (PdPt). For comparison, the synthesis of an α-Keggin-type POM-coordinated di-palladium(II) complex, Cs 2.75 K 0.25 [α-PW 11 O 39 {Pd II (bpy)} 2 ]•12H 2 O•DMSO (Pd2), was also per-formed.…”

“…Various palladium- and platinum-containing POMs have also been reported. Some recently developed palladium-containing POMs include [Se 2 IV Pd 4 II W 14 VI O 56 H] 11– , [Se 4 IV Pd 4 II W 28 VI O 108 H 12 ] 12– , [Pd 4 II (α-P 2 W 15 O 56 ) 2 ] 16– , [Pd 3 II (TeW 9 O 33 ) 2 ] 10– , [γ-H 2 SiW 10 O 36 Pd 2 II (OAc) 2 ] 4– , [{(γ-H 2 SiW 10 O 36 Pd 2 II )­(O 2 C­(CH 2 ) n CO 2 )} 2 ] 8– ( n = 1, 3, and 5), [α-PW 11 O 39 {Pd II (Me 2 ppz)}] 5– (Me 2 ppz = N , N ′-dimethylpiperazine), and [α-PW 11 O 39 {Pd II (en)} 2 ] 3– (en = ethylenediamine) . In the field of platinum-containing POMs, [α-PW 11 O 39 { cis- Pt II (NH 3 ) 2 } 2 ] 3– , , [Pt 2 II (W 5 O 18 ) 2 ] 8– , [ anti -Pt 2 II (α-PW 11 O 39 ) 2 ] 10– , [ syn -Pt 2 II (α-PW 11 O 39 ) 2 ] 10– , and [α-PW 11 O 39 {Pt II (Me 2 ppz)}] 5− have recently been reported.…”