Luminescent mononuclear Pt(II) chloride complexes with C-linked 2,2′-bipyridyl tetrazole terdentate chelating ligands

Two new luminescent mononuclear Pt(II) chloride complexes possessing C-linked 2,2′-bipyridyl tetrazole terdentate chelating ligands, namely, Pt(tbpy)Cl (1) and Pt(tmbpy)Cl (2) (tbpyH = 6-(1H-tetrazol-5-yl)-2,2′-bipyridine; tmbpyH = 6-(1H-tetrazol-5-yl)-4,4′-dimethyl-2,2′-bipyridine), have been synthesized and characterized. Complex 2 adopts a distorted square-planar geometry with a mono-anionic terdentate chelate tmbpy, and it presents a zigzag head-to-tail stacking array along the a axis with alternating Pt⋯Pt separations of 3.415 and 5.469 Å. For 2, a moderately intensive broad absorption band appears at 350–425 nm in dilute DMF solution, most likely assigned as the metal-to-ligand charge transfer 1MLCT (Pt(5d) → tmbpy) transition, mixed with some halide-to-ligand charge transfer 1XLCT (Cl → tmbpy) and intraligand (IL) 1ππ* transitions inside tmbpy. It is demonstrated that the solubilities and luminescence properties of 1 and 2 are markedly influenced by the substituents in the 4 and 4′-positions of the 2,2′-bipyridyl ring. The solid-state emissions of 1 and 2 are perhaps best attributable to the 3MMLCT/3XLCT/3IL states, as supported by TD-DFT calculation of 2.