Stepwise transformation of the molecular building blocks in a porphyrin-encapsulating metal-organic material.

When immersed in solutions containing Cu(II) cations, the microporous metal-organic material P11 ([Cd4(BPT)4]·[Cd(C44H36N8)(S)]·[S], BPT = biphenyl-3,4',5-tricarboxylate) undergoes a transformation of its Cd2(COO)6 molecular building blocks (MBBs) into novel tetranuclear [Cu4X2(COO)6(S)2] MBBs to form P11-Cu. The transformation occurs in single-crystal to single-crystal fashion, and its stepwise mechanism was studied by varying the Cd(2+)/Cu(2+) ratio of the solution in which crystals of P11 were immersed. P11-16/1 (Cd in framework retained, Cd in encapsulated porphyrins exchanged) and other intermediate phases were thereby isolated and structurally characterized. P11-16/1 and P11-Cu retain the microporosity of P11, and the relatively larger MBBs in P11-Cu permit a 20% unit cell expansion and afford a higher surface area and a larger pore size.