Mixed‐Metal Dawson Sandwich Complexes: Synthesis, Spectroscopic Characterization and Electrochemical Behaviour of Na 16 [M II Co 3 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ] (M = Mn, Co, Ni, Zn and Cd)

Mixed‐metal Dawson sandwich complexes [MCo 3 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 16– (represented as {MCo 3 P 4 W 30 }) have been synthesized by the reaction of M 2+ (where M = Mn, Co, Ni, Zn and Cd) with the “lacunary” sandwich complex αβ‐[NaCo 3 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 17– (represented as {NaCo 3 P 4 W 30 }): [NaCo 3 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 17– + M 2+  → [MCo 3 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 16– + Na + . The {MCo 3 P 4 W 30 } species were characterized by IR spectroscopy, elemental analysis and 31 P solution NMR spectroscopy. The electrochemical behaviour of these mixed‐metal sandwich complexes was investigated in aqueous solution and compared with that of ββ‐[Co 4 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 16– (represented as ββ‐{Co 4 P 4 W 30 }) and {NaCo 3 P 4 W 30 }. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)