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

Bent uranyl complexes can be formed with chloride ligandsand 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 influenceof chloride and phenanthroline coordination enforcing the bendingon the absorption and emission spectra of this complex, spin-orbittime-dependent density functional theory calculations for the bareuranyl complexes as well as for the free UO2Cl2 subunit and the UO2Cl2(phen)(2) complexwere performed. The emission spectra have been fully simulated byab 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 excitationsof the uranyl bending mode, yielding a denser luminescence spectrum. The luminescence spectrum of a bent uranylcomplex withchloride ligands and 1,10-phenanthroline ligands has been experimentallyrecorded for the first time and also successfully computed by vibrationallyresolved ab initio calculations. Notably, we demonstrate that thebending of uranyl in UO2Cl2(phen)(2) and in the UO2Cl2 complex triggers vibronicallyinduced excitations of the uranyl bending mode, yielding denser luminescencespectra than in linear uranyl complexes.