Synthesis, Characterization, and Crystal Structure of the Pd(phen)(bdt) Complex. A DFT and TDDFT Study of Its Ground Electronic and Excited States Compared to Those of Analogous Complexes

The synthesis and characterization of Pd(phen)(bdt) (1) (phen = 1,10-phenanthroline, bdt = 1,2-benzenedithiolate)
is presented. 1 crystallizes in the monoclinic space group P21/c, α = 11.281(4) Å, b = 20.498(8) Å, c = 8.374(3)
Å, β = 90.234(8), V = 1936.5(13) Å3, Z = 4, and is isostructural with its previously reported related complexes.
The ground and low lying excited electronic states in 1 and in the related complexes Pd(bpy)(bdt) (2), Pt(bpy)(bdt)
(3), Pt(bpy)(mnt) (4), and Pt(bpy)(edt) (5) [where bpy = 2,2‘-bipyridine, edt = ethylene-1,2-dithiolate, and mnt =
maleonitriledithiolate] are studied using density functional theory techniques. The electronic properties of 1−5 are
studied using the B3LYP functional. Optimized geometries are compared to experimentally observed structures.
Time dependent density functional theory (TDDFT) is employed to investigate the excited singlet and triplet states.
The calculated energies of the lowest singlet state and the lowest triplet state in all five complexes are in considerable
agreement with experimental data. It is shown that variation of both metal and dithiolate-ligand going from 1 and
2 to 3, 4, and 5 has a substantial impact on the spectroscopic and excited-state properties, indicating at the same
time the mixed metal/dithiolate character of the HOMO orbital. All the low-lying transitions are categorized as
MMLL‘CT transitions. The emissive state of all complexes is assigned as a triplet dithiolate/metal to diimine charge
transfer with differences in the structures of the emissions resulting from differences in the π* dithiolate orbital of
the mnt, bdt, and edt as well as from differences in metal.