Palladium(II) and Platinum(II) Analogues of Luminescent Diimine <i>Triangulo</i> 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 ((t)Bu(2)bpy), 4,4'-dimethylcarboxylate-2,2'-bipyridine ((CO(2)Me)(2)bpy), bis(diphenylphosphino)methane (dppm)] with Na(2)S in refluxing methanol afforded [M(3)((t)Bu(2)bpy)(3)(mu(3)-S)(2)](2+) [M = Pd (1a), Pt (2a)], [M(3)((CO(2)Me)(2)bpy)(3)(mu(3)-S)(2)](2+) [M = Pd (1b), Pt (2b)], and [Pt(3)(dppm)(3)(mu(3)-S)(2)](2+) (3) as perchlorate salts. X-ray crystal analysis revealed that 1a, 1b, 2a, and 3 have triangular M(3)S(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) A, respectively. An isosceles triangle of Pd(3) atoms is observed in the molecular structure of 1b. The (1)MLCT 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 lambda(max) 760 and 730 nm, respectively) while the 77 K solid-state emission of 1b (uncorrected lambda(max) 760 nm) is also weak. At 77 K, complexes 2a, 2b, and 3 display broad unstructured emissions at lambda(max) 616-630 nm in the solid state. Ligand-field excited states are tentatively assigned for these emissions.