A robust 3-D porous structure of formula [ Ln(2)( PDC)(3)( DMF)(2)] has been constructed from lanthanide cations ( Ln = Er3+ or Y3+) and the non-linear anionic bridging ligand, pyridine-3,5-dicarboxylate ( PDC2-) in dimethylformamide ( DMF). The solvated framework polymers {[ M-2( PDC)(3)( DMF)(2)]center dot n( solv)}(infinity) ( M = Er, Y) undergo a solid-state, crystal-to-crystal reaction upon heating and are converted via loss of both sorbed and coordinated solvent and rearrangement of the framework core to give a desolvated and porous form with retention of structural integrity. This structural transfer is the first crystallographically characterized system with lanthanide metal ions. These porous products are shown to be effective absorbants for H-2, N-2, and benzene.