A structural study of the N,N′-dimethylpropyleneurea solvated zinc(II) and cadmium(II) ions in solution and crystalline state

The structures of the N,N′-dimethylpropyleneurea (DMPU) solvated zinc(II) and cadmium(II) ions have been studied in solution by extended X-ray absorption fine structure (EXAFS) and large angle X-ray scattering (LAXS), and in solid state as the trifluoromethanesulfonate salts by EXAFS and crystallography. The DMPU solvated zinc(II) ion is four-coordinated in a tetrahedral fashion with a mean Zn-O bond distance of 1.925(6) Å in solid state, while the mean Zn-O bond distance is much longer in solution, 1.99(2) Å, suggesting that a five-coordinated solvate complex is dominating. As this Zn-O bond distance is somewhat shorter than expected for a five-coordinated zinc(II) complex the presence of a transient four-coordinated solvate complex in small amounts is possible. The DMPU solvated cadmium(II) ion is six-coordinated in an octahedral fashion in the solid state with a mean Cd-O bond distance of 2.260(9) Å. The crystal structure displays severe disorder of both the hexakis(N,N′-dimethylpropyleneurea)cadmium and trifluoromethanesulfonate ions. In this case, the mean Cd-O bond distance is slightly shorter in solution, 2.24(1) Å, which may indicate the existence of a transient dissociative five-coordinated species.