How Does Bending the Uranyl Unit Influence Its Spectroscopy and Luminescence?

Bent uranyl complexes can be formed with chloride ligands and 1,10-phenanthroline (phen) ligands bound to the equatorial and axial planes of the uranyl(VI) moiety, as revealed by the crystal structures, IR and Raman spectroscopy, and quantum-chemical calculations. With the goal of probing the influence of chloride and phenanthroline coordination enforcing the bending on the absorption and emission spectra of this complex, spin-orbit time-dependent density functional theory calculations for the bare uranyl complexes as well as for the free UO2Cl2 subunit and the UO2Cl2(phen)2 complex were performed. The emission spectra have been fully simulated by ab initio methods and compared to experimental photoluminescence spectra, recorded for the first time for UO2Cl2(phen)2. Notably, the bending of uranyl in UO2Cl2 and UO2Cl2(phen)2 triggers excitations of the uranyl bending mode, yielding a denser luminescence spectrum.