A new layered zinc phosphite, H(2)tmdp center dot Zn-3(HPO3)(4) (tmdp = 4,4'-trimethylenedipiperidine), was prepared in a flux of phosphorous acid without the addition of water as a solvent. The compound could be transformed into a new three-dimensional open-framework zinc phosphite, Zn-2(H2O)(4)(HPO3)(2). H2O, with intersecting 16- and 12-ring channels at room temperature.