Theoretical Photoelectron Spectroscopy of Quadruple-Bonded Dimolybdenum(II) and Ditungsten(II) Paddlewheel Complexes: Performance of Common Density Functional Theory Methods

We have revisited the gas-phase photoelectron spectra of quadruple-bonded Mo and W paddlewheel complexes with modern DFT methods, obtaining valuable calibration of four well-known exchange-correlation functionals, namely BP86, OLYP, B3LYP*, and B3LYP. All four functionals were found to perform comparably, with discrepancies between theory and experiment ranging from < 0.1 to ~0.5 eV, with the lowest errors observed for the classic pure functional BP86. More encouragingly, all four functionals reproduce differences in IPs between analogous Mo and W complexes, as well as large, experimentally observed ligand field effects on the IPs, with near-quantitative accuracy. The calculations help us interpret a number of differences between analogous Mo and W complexes through the lens of relativistic effects. Thus, relativity results in not only significantly lower IPs for the W complexes, but also smaller HOMO-LUMO gaps and different triplet states, relative to their Mo counterparts.