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 TCNQF(4) and TCNE (TCNQ = 7,7,8,8-tetracyanoquinodimethane; TCNQF(4) = 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 approximately 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 TiO(2) 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.

An explanation is presented for the unusual magnetic behavior of two Re(II) compounds, [Re(triphos) 3 ], for which magnetic susceptibility data obtained on powder samples (2-300 K) suggest unusually strong temperature-independent paramagnetism ( TIP ) (1.4-1.8) × 10 -3 cm 3 mol -1 ) and small low-temperature effective magnetic moments. A model is developed based on the jj-coupling scheme appropriate for description of the 5d shell of a Re(II) ion in a crystal field. The model accounts for a cubic crystal field, strong spin-orbit coupling, and a trigonal component of the crystal field produced by the ligand field acting on the Re(II) ions. The last two interactions act within the truncated basis containing eight lowest, strong cubic crystal field terms and result in the stabilization of two closely spaced Kramers doublets originating mainly from the 2 T 2 (t 2 5 ) term. Efficient mixing of these Kramers doublets with those arising from 6 A 1 (t 2 3 e 2 ) and 4 T 1 [t 2 4 ( 3 T 1 )e] terms is shown to result in the small low-temperature effective magnetic moments and anomalously strong temperature-independent paramagnetism, in accordance with the observed magnetic behavior. The model perfectly reproduces the T vs T dependences over a wide temperature range (2-300 K), and the energy pattern obtained with the set of the best fit parameters provides a qualitative explanation for the observed light absorption and diffuse reflectance in a wide spectral area (200-2600 nm). The theoretical consideration predicts extremely strong anisotropy of the magnetic susceptibility and g-factors for both compounds with a C 3 easy axis of magnetization.

The diimine-dithiolato ambipolar complexes Pt(dbbpy)(tdt) and Pt(dmecb)(bdt) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; tdt(2-) = 3,4-toluenedithiolate; dmecb = 4,4'-dimethoxyester-2,2'-bipyridine; bdt(2-) = benzene-1,2-dithiolate) are prepared herein. Pt(dmecb)(bdt) exhibits photoconductivity that remains constant (photocurrent density of 1.6 mA/cm(2) from a 20 nm thin film) across the entire visible region of the solar spectrum in a Schottky diode device structure. Pt(dbbpy)(tdt) acts as donor when combined with the strong nitrofluorenone acceptors 2,7-dinitro-9-fluorenone (DNF), 2,4,7-trinitro-9-fluorenone (TRNF), or 2,4,5,7-tetranitro-9-fluorenone (TENF). Supramolecular charge transfer stacks form and exhibit various donor-acceptor stacking patterns. The crystalline solids are "black absorbers" that exhibit continuous absorptions spanning the entire visible region and significant ultraviolet and near-infrared wavelengths, the latter including long wavelengths that the donor or acceptor molecules alone do not absorb. Absorption spectra reveal the persistence of donor-acceptor interactions in solution, as characterized by low-energy donor/acceptor charge transfer (DACT) bands. Crystal structures show closely packed stacks with distances that underscore intermolecular DACT. (1)H NMR provides further evidence of DACT, as manifested by upfield shifts of aromatic protons in the binary adducts versus their free components, whereas 2D nuclear Overhauser effect spectroscopy (NOESY) spectra suggest coupling between dithiolate donor protons with nitrofluorenone acceptor protons, in correlation with the solid-state stacking. The NMR spectra also show significant peak broadening, indicating some paramagnetism verified by magnetic susceptibility data. Solid-state absorption spectra reveal further red shifts and increased relative intensities of DACT bands for the solid adducts vs solution, suggesting cooperativity of the DACT phenomenon in the solid state, as further substantiated by νC-O and νN-O IR bands and solid-state tight-binding computational analysis.

Supramolecular stacked materials (dbbpy)Pt(tdt) 3 TENF and [Pt(dbbpy)(tdt)] 2 3 TENF are built from (dbbpy)Pt(tdt) donors (D) with TENF acceptors (A) (TENF=2,4,5,7-tetranitro-9-fluorenone; dbbpy= 4,4 0 -di-tert-butyl-2,2 0 -bipyridine; tdt = 3,4-toluenedithiolate). Simulations using extended H€ uckel tight binding (EHTB) and plane-wave DFT methods are performed. From EHTB analysis, the density of states (DOS) of D/A and DD/A stacks exhibit metallic behavior with a large contribution from TENF π in the valence band mixed with more significant Pt character in the D/A than in the DD/A stacks. DOS modification and charge transfer are estimated via analysis of the stacking sequences. Theoretical results from plane-wave DFT calculations give evidence of semimetallic behavior for the D/A material (gap <0.1 eV) and metallic behavior for DD/A. Fragment analysis was performed, and similarities and differences between EHTB and DFT were noted. Molecular DFT computations suggest that the close (∼3.6 A ˚) D-A distances are sufficient to allow some intermolecular donor-to-acceptor charge transfer and higher interaction energy in DD/A than in D/A units, consistent with the periodic calculations for the solid-state stacks. Calculation of metric data via modeling of a (dbbpy)Pt(tdt) 3 TENF cluster as well as neutral, cationic, and anionic TENF are used to assess the fractional charge on TENF and hence the degree of D f A charge transfer.

Light-emitting tetramers of copper(i) supported by pyrazolates with remarkable photophysical properties conducive to potential use in optoelectronic devices and/or sensors are reported.