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.

The Front Cover shows a vase (mono‐lacunary α‐Keggin polyoxotungstate) with one flower (N,N’‐dimethylpiperazine palladium species) or two flowers (two ethylenediamine palladium species). The mono‐lacunary α‐Keggin polyoxotungstate structure of the mono‐palladium complex undergoes a unique structural transformation to the di‐lacunary γ‐Keggin polyoxotungstate Cs7[γ‐PW10O36] upon the addition of cesium chloride. More information can be found in the Full Paper by C. N. Kato and co‐workers.