| Abstract
| - A novel Pt(II) terpyridine complex that has a nicotinamide moiety linked to the terpyridyl ligandhas been synthesized in good yield and studied structurally and spectroscopically. The complex, [Pt(Nttpy)Cl](PF6)2 where Nttpy = 4‘-(p-nicotinamide-N-methylphenyl)-2,2‘:6‘,2‘ ‘-terpyridine, is observed to be brightlyluminescent in the solid state at room temperature and at 77 K. The complex exhibits reversible vapochromicbehavior and crystallographic change in the presence of several volatile organic solvents. Upon exposureto methanol vapors, the complex changes color from red to orange, and a shift to higher energy is observedin the emission maximum with an increase in excited-state lifetime and emission intensity. The crystal andmolecular structures of the orange and red forms, determined by single-crystal X-ray diffraction on thesame single crystal, were found to be equivalent in the molecular sense and only modestly different interms of packing. In both forms, the cationic Pt(II) complexes possess distorted square planar geometries.Analysis of the orange form's crystal packing reveals the presence of solvent molecules in lattice voids,Pt···Pt separations averaging 3.75 Å and a zigzag arrangement between nearest neighbor Pt atoms,whereas the red form is devoid of solvent within the crystal lattice and contains complexes stacked with anearly linear arrangement of Pt(II) ions having an average distance of 3.33 Å. On the basis of thecrystallographic data, it is evident that sorption of methanol vapor induces a change in intermolecular contactsand Pt···Pt interactions in going from red to orange. Disruption of the d8-d8 metallophilic interactionsconsequently alters the emitting state from 3[(d)σ*−π*(terpyridine)] that is formally a metal−metal-to-ligandcharge transfer (MMLCT) state in the red form to one in which the HOMO corresponds to a more localizedPt(d) orbital in the red form (3MLCT).
|
