Structural, Magnetic, and Optoelectronic Properties of (Diimine)(dithiolato)platinum(II) and -palladium(II) Complexes and Their Charge-Transfer Adducts with Nitrile Acceptors

Two new diimine dithiolato complexes, (dbbpy)Pt(dmid), 1, and (dbbpy)Pd(dmid), 2, were prepared and characterized
(dbbpy = 4,4‘-di-tert-butyl-2,2‘-bipyridine; dmid = 2-oxo-1,3-dithiole-4,5-dithiolate). Both complexes interact with
the nitrile acceptor TCNQ, and 1 also interacts with TCNQF4 and TCNE (TCNQ = 7,7,8,8-tetracyanoquinodimethane;
TCNQF4 = 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane; TCNE = tetracyanoethylene) to form supramolecular
2:1 charge-transfer solids that stack in the manner −DDADDADDA− (D = electron donor; A = electron acceptor).
All compounds have been fully characterized by magnetic, spectroscopic, electrochemical, and single-crystal X-ray
crystallographic analyses. Magnetic susceptibility studies of the charge-transfer compounds revealed that the platinum-based complexes exhibit temperature-independent paramagnetism of ∼10-3 emu/mol. The donor complexes exhibit
continuous absorption bands across the UV/visible and into the NIR region. Upon interaction with the nitrile acceptors,
the extinction coefficients of the absorption bands increase and the energies of some d−d transitions in the NIR
region change. The donor−acceptor compounds possess desired spectral features for solar cell dyes, but low
conversion efficiencies resulted when a representative compound was tested in a TiO2 solar cell. The results,
however, serve to illustrate that the donor−acceptor interactions persist in solution and the adsorption of the dye
molecules to the semiconductor surface occurs in the absence of typical anchoring groups. Evaluation of the
spectral and electrochemical data for the title compounds and the results of the preliminary solar cell study serve
as guides for future research in choosing promising candidates for efficient solar cell dyes.