A new family of cuprates, Li2Cu3(SiO3)(4) (1) and Na2CU3(GeO3)(4) (2), was isolated in molten salt media. The extended lattices contain ladderlike periodic arrays Of (CU3O8](10-) magnetic nanostructures. Magnetic properties of the Na2Cu3Ge4-xSixO12 series, where x = 0, 0.86, and 1.72, were systematically studied. The geometrically induced magnetic couplings are tunable upon cation substitution.