Shedding light on the bonding, photophysical and magnetotropic properties of triangular Pt3 complexes and their "open-face" TlPt3 half-sandwiches

The molecular and electronic structures, stabilities, bonding features, magnetotropic and spectroscopic properties of the triangular Pt-3(mu(2)-L)(3)(L')(3) clusters and their [(mu(3)-Tl)Pt-3(mu(2)-L)(3)(L')(3)](+) (L = CO, SnR2, SnH2, SiR2, SiH2, CH3CN, PH2, C6F5, SO2 or HCN and L' = CO, PH3, CH3CN, C6F5, HCN) half-sandwiches have been studied by means of density functional theory (DFT) calculations. It is found that the optimized Pt-Pt intermetallic distances in the clusters are well below the sum of the van der Waals radii of the two Pt metal atoms (3.44 angstrom). The triangular Pt-3(mu(2)-L)(3)(L')(3) clusters trap a thallium(I) cation forming stable "open face" half-sandwiches. The distance between Tl(I) and the centroids of the Pt-3 rings in the half-sandwiches is calculated to be within the range 2.52-2.86 angstrom. Energy decomposition analysis (EDA) calculations using a dispersion corrected B3LYP-D functional reveal that the interaction of Tl(I) with the Pt-3 ring in the half-sandwiches is dominated by the interplay of electrostatic and orbital interactions with a small contribution from dispersion forces as well. In addition, charge decomposition analysis (CDA) calculations indicate strong donor-acceptor interactions between Tl(I) and the rings. The estimated proton affinities (PAs) of the triangular Pt-3(mu(2)-L)(3)(L')(3) clusters illustrate their relatively strong pi-basic character. Furthermore, an excellent linear relationship between the PAs of the Pt-3(mu(2)-L)(3)(L')(3) clusters and the bond dissociation energies (D-0) of the [(mu(3)-Tl)Pt-3(mu(2)-L)(3)(L')(3)](+) half-sandwiches was established. The magnetotropicity of these systems was studied by calculating the NICSzz-scan profiles. The spectroscopic properties of the triangular Pt-3 clusters and their TlPt3 half-sandwiches were studied by means of TDDFT calculations. The simulated absorption spectra are dominated by strong absorption bands in the UV region. The emission band maxima of the triangular Pt-3 clusters are predicted to lie within the IR region. In order to gain insight into the phosphorescence process of these systems, we have optimized their first triplet excited state, T-1. The estimated deep HOMO energy for these compounds makes them promising candidates for use as "hole" blocking materials in LED devices. Also, it is expected to exhibit small non-radiative decay rate constants due to their relatively large S-0-T-1 energy difference making them suitable PHOLED emitters or dopants in organic polymer matrices constituting the recombination layer of an OLED device.