Assembly of positively charged porphyrins driven by metal ions: A novel polymeric arrangement of cationic metalloporphyrin

Crystallization and crystal structure analysis of chlorohydrates of either tri- or tetracationic copper porphyrins, namely copper(5,-10,15-tris(N-methyl- pyridinium-4-yl)-20-pyridine-porphyrinato) (1) and copper(5,10,15,20-tetrakis(N- methyl-pyridinium-4-yl)-porphyrinato), respectively, have been performed. Two crystalline forms, 2 and 3, of the latter have been obtained under different preparation conditions. A novel kind of slipped stack chains of these cationic porphyrins has been detected. The pronounced saddle conformation of the porphyrin reveals π-like interactions between the peripheral pyrrole C _b-C_b "double bond" and the metal center. DFT calculations on the isolated porphyrins clearly show the HOMO orbitals with the correct topology to yield a bonding interaction among the stacked porphyrin units. To our knowledge, a slipped stack chain of positively charged porphyrins has never been previously reported, if the arrangement of faced units of monocationic metalloporphyrins or phthalocyanins is excluded.