Anionic Polymeric Bonds in Nickel Ditelluride: Crystal Structure, and Experimental and Theoretical Band Structure

Abstract

Nickel ditelluride was prepared in different ways. Single crystal X-ray investigations reveal that the products are always nonstoichometric with respect to the Ni content. Relatively short intra- and interslab Te–Te contacts are indicative of a polymeric network with multiple Te–Te bonds explaining the very lowc/avalue of 1.37 of the hexagonal cell. Experimental valence band spectra (UPS) confirm that NiTe2is a metal. The emission at the Fermi levelEFis due to Nidand Tepstates. This assignment is supported by the results of the calculated density of states curve (DOS) which demonstrates that Tepstates contribute more than 50% to the DOS atEF. Core level spectra (XPS) give evidence that Ni is in the paramagnetic Ni(II) (d8) state. The chemical shift of the Te 3dcore level leads to the assignment of an oxidation state of −1, in good agreement with the oxidation state of about −1.2 deduced from the relation between the Te–Te distances versus oxidation states of the anion in (Te2)2−, Te2−. The three-dimensional character of NiTe2deduced from the crystal structure is further confirmed by the calculated energy dispersionE(k).