A density functional theory study of the structure and energetics of zincate complexes

We have conducted a density functional theory (DFT) investigation of zincat e species. The accuracy of the DFT/B3LYP method and the adequacy of the ato mic basis sets employed were established through investigation of the ioniz ation potentials of Zn, the geometry and bond energy of ZnO, and the geomet ries and energies of selected Zn-OH and Zn-H2O complexes. Our investigation revealed that the [Zn(OH)](+), Zn(OH)(2), and [Zn(OH)(3)](-) zincate compl exes are stable in the gas phase. However, we found that dissociated [Zn(OH )(3)](-) + OH- is more stable than [Zn(OH)(4)](2-) in the gas phase and tha t the gas-phase geometry of [Zn(OH)(4)](2-) differs significantly from that gleaned from experimental studies of aqueous KOH/zincate solutions. We als o investigated zincate complexes involving molecular water and K+ cations i n order to better understand the influence of condensed phase effects in aq ueous KOH solutions on the stability and geometry of the zincate complexes. We found that water does not si,significantly influence complex binding en ergies or the,geometries elf the underlying [Zn(OH)(n)](2-n) complexes for n = 1, 2, and 3. In contrast, for [Zn(OH)(4)](2-) the introduction of water strongly stabilizes the complex relative to the gas phase and results in a structure close to that observed experimentally. We were unable to find a stable [Zn(OH)(4)(H2O)(2)](2-) complex with a planar Zn(OH)(4) arrangement and close Zn-H2O coordination, corresponding to a Zn-O coordination of numb er of six, as has been suggested in some interpretations of experiments. We found through investigation of the K2Zn(OH)(4) complex that K+ cations are also effective in engendering a structure that is very close to experiment and that K+ ions are even more strongly bound to the [Zn(OH)(4)](2-) compl ex than water. Finally, we determined the structure and stability of [ZnO(O H)(2)](2-)(oxodihydroxozincate), a species that has been hypothesized to be important in water-poor zincates solutions.