Dinuclear Platinum Complexes with Hydrogen-Bonding Functionality:  Noncovalent Assembly of Nanoscale Cyclic Arrays

The preparation and solution behavior of a series of novel, dinuclear organoplatinum(II) complexes of nicotinic acid 3 and 4, isonicotinic acid 5, and nicotinamide 6 are reported. For 3 and 4, comprehensive ¹H NMR titration studies demonstrate their spontaneous self-association to afford discrete, hydrogen-bonded aggregates in CD₂Cl₂ solution at 298 ± 0.1 K. For 3, the titration data are consistent with the formation of a nanoscale cyclic entity (3)₃ which, despite the presence of bulky PPh₃ ligands, is strongly favored in solution (K₃ = 1.99 × 10⁴ ± 7.89 × 10² mol^-2 dm⁶). Complex 4 aggregates to form a cyclic dimer (4)₂ with K₂ = 98.2 ± 1.1 mol^-1 dm³, and complexes 5 and 6 appear to afford oligomeric (or polymeric) aggregates. The X-ray crystal structure of 6 shows the dications associate to form corrugated chains connected by hydrogen bonds. This work demonstrates that the noncovalent assembly of multimeric cyclic arrays with nanoscale dimensions from simple diplatinum(II) complexes is feasible in nonaqueous solution.