A “directed” approach toward a cationic molecular square containing four isonicotinamidate ligands and (4 + 2) (en)PtII metal entities

The use of 4-cyanopyridine (4-CNpy) and 3-cyanopyridine (3-CNpy) as ditopic ligands with 180° and 120° directionalities, respectively, for the construction of molecular architectures with the 90° metal fragments (en)PtII and (en)PdII in water is hampered by the ease with which these ligands undergo hydrolysis to isonicotinamide (4-C(O)NH2py) and nicotinamide (3-C(O)NH2py). As described in this article, out of six X-ray structurally characterized complexes (1–6), only a single one (1) reveal coordination of the unchanged ligand (4-CNpy) to (en)PtII. Nevertheless also the hydrolysis products are of interest in the context of obtaining discrete metallacyclic compounds: Thus, (en)PtII and 4-C(O)NH2py form a hexanuclear complex, [PF6 ⊂ {(en)Pt}6(4-C(O)NHpy)4](NO3)7·10H2O (2), in which the anionic isonicotinamidate ligands function as tridentate, bridging ligands to produce a hybrid between a metallasquare and a 2-floor open box. The resulting cation with a +8 charge accommodates a single hexafluorophosphate anion in its interior. Adjacent cations of 2 pack in such a way as to develop Pt4 chains as typically seen in “platinum blues” and their [PtII]4 precursors.