Palladium(II) and platinum(II) analogues of luminescent diimine triangulo complexes supported by triply bridging sulfide ligands: Structural and spectroscopic comparisons

Abstract

Reaction of [M(L-L)Cl 2] [M = Pd, Pt; L-L = 4,4′-di-tert-butyl-2,2′-bipyridine ( tBu 2bpy), 4,4′-dimethylcarboxylate-2,2′-bipyridine ((CO 2Me) 2bpy), bis(diphenylphosphino)methane (dppm)] with Na 2S in refluxing methanol afforded [M 3( tBu 2bpy)3 (μ 3-S)2] 2+ [M = Pd (1a), Pt (2a)], [M 3((CO 2Me) 2bpy) 3 (μ 3-S) 2] 2+ [M = Pd (1b), Pt (2b)], and [Pt 3(dppm) 3 (μ 3-S) 2] 2+ (3) as perchlorate salts. X-ray crystal analysis revealed that 1a, 1b, 2a, and 3 have triangular M 3S 2 core structures. The three metal atoms in 1a, 2a, and 3 form virtual equilateral triangles with intramolecular Pd-Pd and Pt-Pt separations of 3.027(1)-3.065(1) and 3.104(1)-3.154(1) Å, respectively. An isosceles triangle of Pd 3 atoms is observed in the molecular structure of 1b. The 1MLCT absorption of 2a and 2b appears at 415 and 448 nm, respectively, in dichloromethane and is significantly red-shifted from the lowest energy absorption band of the Pd 3 analogues. Complex 1a exhibits weak photoluminescence in the solid state at 77 and 298 K (uncorrected λ max 760 and 730 nm, respectively) while the 77 K solid-state emission of 1b (uncorrected λ max 760 nm) is also weak. At 77 K, complexes 2a, 2b, and 3 display broad unstructured emissions at λ max 616-630 nm in the solid state. Ligand-field excited states are tentatively assigned for these emissions.