Anionic N_(18)Macrocycles and a Polynitrogen Double Helix in Novel Yttrium Polynitrides YN6 and Y2N_(11)at 100 GPa

摘要

Two novel yttrium nitrides,YN6 and Y2N_(11),were synthesized by direct reaction between yttrium and nitrogen at 100 GPa and 3000 K in a laser-heated diamond anvil cell.High-pressure synchrotron single-crystal X-ray diffraction revealed that the crystal structures of YN6 and Y2N_(11)feature a unique organization of nitrogen atoms-a previously unknown anionic N_(18)macrocycle and a polynitrogen double helix,respectively.Density functional theory calculations,confirming the dynamical stability of the YN6 and Y2N_(11)compounds,show an anion-driven metallicity,explaining the unusual bond orders in the polynitrogen units.As the charge state of the polynitrogen double helix in Y2N_(11)is different from that previously found in Hf2N_(11)and because N_(18)macrocycles have never been predicted or observed,their discovery significantly extends the chemistry of polynitrides.