Organic-soluble lacunary {M2(P2W15)2} polyoxometalate sandwiches showing a previously unseen isomerismElectronic supplementary information (ESI) available: TGA analysis, IR spectroscopy, UV/Visible Spectroscopy, Cyclic Voltammetry and X-ray diffraction data. CCDC reference numbers 872057-872061. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2dt30616f

New polyoxometalate 'sandwiches' have been formed where two [P 2 W 15 O 56 ] 12 lacunary Dawson clusters encapsulate two transition metal ions to give clusters with the general formula [M II 2 (P 2 W 15 O 56 ) 2 ] 20 (where M = Mn, Co, and Ni respectively), [Fe III 2 (P 2 W 15 O 56 ) 2 ] 18 , and [Cu II 4 (P 2 W 15 O 56 ) 2 ] 16 . The Mn, Co, and Ni clusters exhibit a hitherto unseen isomeric geometry and all five compounds are associated with tetrabutylammonium cations which allow for their dissolution in non-aqueous solvent. New polyoxometalate organic-soluble POM 'sandwiches' have the general formula [M II 2 (P 2 W 15 O 56 ) 2 ] 20 (M = Mn, Co, Ni), [Fe III 2 (P 2 W 15 O 56 ) 2 ] 18 and [Cu II 4 (P 2 W 15 O 56 ) 2 ] 16 . The Mn, Co, and Ni clusters exhibit a hitherto unseen isomeric geometry.