THE PH-DEPENDENT SYNTHESIS AND STRUCTURAL STUDY OF DIMER AND CYCLIC TRIMER COMPLEXES OF 9-METHYLHYPOXANTHINE OR 9-ETHYLHYPOXANTHINE NUCLEOBASES WITH (ETA(5)-PENTAMETHYLCYCLOPENTADIENYL)RHODIUM AQUA COMPLEXES

η 1(N1)‐ and η2(N7,O6)‐coordination of the Rh atoms by 9‐ethylhypoxanthin (9‐EH) is evident in the cyclic trimer 1 (see picture). This is formed from [(C5Me5RhCl2)2], AgOSO2CF3, and 9‐EH in water at pH 6.1. An entirely different coordination arises at pH 10.2 for the complex with the ligand 9‐methyl‐hypoxanthin (9‐MH): in the dimer 2 the metal atoms are η1(N1)‐coordinated. The formation of dramatically different structures at various pH values could be explained by the changes in the nucleophilicity of the N7, O6, and N1 binding sites. (Formula Presented.) (Figure Presented.) Copyright © 1995 by VCH Verlagsgesellschaft mbH, Germany