Supramolecular aggregates of complex cations via unusual purine - Purine base pairing in a new organorhodium(III) compound containing the antileukemic drug purine-6-thione

The reaction of [RhCl2(Ph)(PPh3)2] with purine-6-thione (H2tp) in alcohol produced the title compound which consists of aggregates of [Rh(C6H5)(H1,H9 -H2-tp)2(PPh3)]2+ and [Rh(C6H5)(H1, H9-H2tp)(H9-Htp)- (PPh3)]+ cations held together by a N(1) - H···N-hydrogen bond assisted by weak C - H···S interactions from an unusual {H2tp···Htp}- base pair. The formation energy for the metal free base pair as computed through DFT methods is -27.912 kcal, larger than previously reported GC - Watson - Crick base-pairing energy.