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]2– 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 Cd2+/Cu2+ 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.