The serendipitous discovery of a 3D [Cu(CO3)(2-)](n) network with the topology of the 4(2)6(4) socialite net in [Cu-6(CO3)(12)(CH6N3)(8)].K-4.8H(2)O paved the way for the deliberate engineering of an extensive series of structurally related guanidinium-templated metal carbonates of composition [M-6(CO3)(12)(CH6N3)(8)]Na-3-[N(CH3)(4)].xH(2)O, where the divalent metal M in the framework may be Mg, Mn, Fe, Co, Ni, Cu, Zn, or Cd. A closely related crystalline material with a [Ca(CO3)(2)(2-)], sodalite-like framework, but containing K+ rather than Na+, of composition [Ca-6(CO3)(12)(CH6N3)(8)]K-3[N(CH3)(4)].3H(2)O was also isolated. All of these compounds were obtained under the simplest possible conditions from aqueous solution at room temperature, and their structures were determined by single-crystal X-ray diffraction. Pairs of guanidinium cations are associated with the hexagonal windows of the sodalite cages, alkali-metal cations are associated with their square windows, and N(CH3)(4)(+) ions are located at their centers. Structures fall into two classes depending on the metal, M-11, in the framework. One type, the BC type (lm (3) over barm), comprising the compounds for which M2+ = Ca2+, Mn2+, Cu2+, and Cd2+, has a body-centered cubic unit cell, while the second type, the FC type (Fd (3) over barc), for which M2+ = Mg2+, Fe2+, Co2+, Ni2+, and Zn2+, has a face-centered cubic unit cell with edges on the order of twice those of the BC structural type. The metal M in the BC structures has four close carbonate oxygen donors and four other more distant ones, while M in the FC structures has an octahedral environment consisting of two bidentate chelating carbonate ligands and two cis monodentate carbonate ligands.