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 H-1 NMR titration studies demonstrate their spontaneous self-association to afford discrete, hydrogen-bonded aggregates in CD2Cl2 solution at 298 +/- 0.1 It. 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 (K-3 = 1.99 x 10(4) +/- 7.89 x 10(2) mol(-2) dm(6)). Complex 4 aggregates to form a cyclic dimer (4)(2) with K-2 = 98.2 +/- 1.1 mol(-1) dm(3), 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.