We have computed the structures, and select vibrational spectra, electron density and molecular orbital contour plots of plutonium(VI) complexes of environmental importance such as [PuO2(CO3)(2)](2-) and [PuO2(CO3)(3)](4-). We show that Ca2+ is efficacious in gas-phase modeling of electronic and spectroscopic properties of multiply charged plutonyl di and tricarbonate anions through complexes such as PuO2(CO3)(2)Ca and [PuO2(CO3)(3)Ca-3](2+). (C) 2007 Elsevier B.V. All rights reserved.