A new family of sandwich-type polytungstophosphates containing two different types of metals in the central belt, M'M-2(2)(PW9O34)(2)(12-) (M' = Na or Li, M = Mn2+, Co2+, Ni2+, and Zn2+), have been synthesized and charactenzed by infrared spectroscopy, P-31 solution NMR spectroscopy, and elemental analysis. Compounds Na2Co2(PW9O34)(2)(12-) (Na2Co2), Na2Ni2(PW9O34)(2)(12-) (Na2Ni2), Li2Ni2(PW9O34)(2) (Li2Ni2) Na(2)M(n)2 (PW9O34)(2)(12-) (Na2Mn2) and Li2Zn2-(PW9O34)(2)(12-) (Li2Zn2) were characterized by X-ray crystallography All these compounds have similar structures, in which two transition-metal ions and two alkali metal ions (sodium or lithium) are sandwiched between two [B-alpha-PW9O34](9-) units, the transition and alkali metals reside in the internal and external (solvent exposed) positions of the central belt, respectively By adding LICI to aqueous solutions of compounds Na2M2, lithium-sodium exchanges in the external belt positions are observed by 31P solution NMR spectroscopy and X-ray crystallography. Magnetic measurements indicate ferromagnetic exchange interactions between the two Ni2+ ions in Na2Ni2 at 10-300 K and the two Co2+ ions in Na2Co2 at 6-30 K In contrast, Na2Mn2 exhibits an antiferromagnetic interaction between the Mn2+ ions at 2-50 K.