Pt(bph)(bpy) and Pt(bph)(phen), where bph is the 2,2'-biphenyl dianion, bpy is 2,2'-bipyridine, and phen is 1,10-phenanthroline, crystallize in the space groups I4(1)/a and P2(1)/c, respectively, in two different configurations as X-shaped and bowed (B). The distance between Pt centers is 3.5 Å indicative of π-π stacking. The complexes are optically active, absorb light at 440 nm, and emit in the solid state at room temperature and in the solid glass phase at 77 K. The emission maxima for both in the glass occur near 581 nm but are red-shifted to ∼700 nm in the solid state. Both complexes exhibit solvatochromism in nitrile-based solvents with the Pt(bph)(phen) complex showing greater excited state dipole character compared to the Pt(bph)(bpy) derivative. Frontier orbitals for the HOMO determined by DFT calculations contain electronic contributions from the biphenyl ligand and the platinum center. The LUMO orbitals primarily reside on the diimine ligands. TDDFT calculations indicate the low-energy transitions occur from the metal/bph combination to the diimine ligand.
A series of platinum(ii) biphenyl 2,2'-bipyridine complexes containing electron-donating and electron-withdrawing moieties on the 4 and 4' positions of the bipyridine ligand exhibit emission from excited states in the 600 nm region of the spectrum upon excitation in the metal-to-ligand charge transfer transition located near 450 nm. These complexes are distorted from planarity based on both single crystal structure determinations and density functional theory (DFT) calculations of isolated molecules in acetonitrile. The DFT also reveals the geometry of the lowest-lying triplet state (LLTS) of each complex that is important for emission behavior. The LLTS are assigned based on the electron spin density distributions and correlated with the singlet excited states to understand the mechanism of electronic excitation and relaxation. Time-dependent DFT calculations are performed to compute the singlet excited state energies of these complexes so as to help interpret their UV-Vis absorption spectra. Computational and experimental results, including absorption and emission energy maxima, electrochemical reduction potentials, LLTS, singlet excited states, and LUMO and HOMO energies, exhibit linear correlations with the Hammett constants for para-substituents σp. These correlations are employed to screen complexes that have not yet been synthesized. The correlation analysis indicates that the electronic structure and the HOMO-LUMO energy gap in Pt(ii) complexes can be effectively controlled using electron-donating and electron-withdrawing moieties covalently bonded to the ligands. The information presented in this paper provides a better understanding of the fundamental electronic and thermodynamic behavior of these complexes and could be used to design systems with specific applications.
The C4S2donor set in the title compound, [Pt(C12H8){(C2H5)2S}]2, defines a distorted square-planar geometry about the two PtIIatoms, with very small deviations from planarity. The bidentate nature of the biphenyl dianionic ligand results in C—Pt—C bond angles of 80.9 (2) and 81.2 (2)°; the S—Pt—S bond angles are 78.08 (5) and 78.09 (5)°. The average Pt—C bond length is 2.023 Å [range 2.016 (5)–2.028 (6) Å] and the average of Pt—S bond length is 2.3790 Å [range 2.3742 (14)–2.3837 (14) Å].
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