Self‐Association of [PtII(1,10‐Phenanthroline)(N‐pyrrolidyl‐N‐(2,2‐dimethylpropanoyl)thiourea)]+ and Non‐Covalent Outer‐Sphere Complex Formation with Fluoranthene through π–Cation Interactions: A High‐Resolution 1H and DOSY NMR Study

Competing outer-sphere self-association of [PtII(1,10-phenanthroline)(N-pyrrolidyl-N-(2,2-dimethylpropanoyl)thiourea)]+Cl– (M) and the hetero-association of M with fluoranthene (F) have been investigated by means of the significant concentration dependence of 1H NMR chemical shifts as well as by diffusion coefficients obtained from DOSY NMR spectroscopy. The NMR spectroscopic data is only consistent with the formation of a “dimer” M···M aggregate according to 2M [rlhar2] M2 in acetonitrile at several temperatures, with a calculated KD of ca. 46 ± 7 M–1 at 273.5 K. In the presence of the aromatic molecule fluoranthene, relatively strong, presumably π–cation-type interactions between M and F according to M + F [rlhar2] MF (KB ≈ 67 ± 7 M–1 at 273.5 K) occur in acetonitrile. The calculated ΔrH° and ΔrS° for M···M (–25129 ± 3112 and –61 ± 11 J mol–1) and M···F (–13560 ± 3180 and –17 ± 11 J mol–1, respectively) is indicative of π–cation interactions. Interestingly any potential F···F aggregation interactions are negligible for the fluoranthene concentration range up to 0.1 M, indicating that non-covalent π–π interactions between fluoranthene molecules 2F [rlhar2] F2 are, in contrast to π–cation interactions, negligible under these conditions in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)