PGSE and NOE NMR evidence for higher order aggregation in some cationic ruthenium complexes in both protic and aprotic solvents

PGSE and NOE NMR measurements were carried out for complexes Ru(eta(6)-cymene)((2-R-C(6)H(4))N=C(Me)-C(Me)=N(2-R-C(6)H(4)))Cl]X (X = BF(4) or BPh(4)) in both protic and aprotic solvents with a relative permettivity (epsilon(r)) ranging from 2.27 (benzene-d(6)) to 46.45 (dimethyl sulfoxide-d(6)). PGSE and NOE results indicate that complexes have a tendency to aggregate even in medium-polarity solvents such as ethanol (epsilon(r) = 24.55) and methanol (epsilon(r) = 32.66). In addition, the aggregation process is favored by a decrease of epsilon(r) and, unexpectedly, by protic solvents. NOE measurement investigations, interpreted with the help of theoretical calculations and confirmed by X-ray single crystal studies, suggest different aggregation processes for the two counteranions: two cationic moieties approach each other when X = BF(4) while the anion bridges two cationic moieties when X = BPh(4).