Synthesis and characterization of the new quaternary two-dimensional materials KCu 2Nb Q4( Q = Se, S)

Abstract

Reaction of K 2Se 5 or K 2S 5 with elemental Nb, Cu, and Se or S affords KCu 2NbSe 4 or KCu 2NbS 4. The structure of KCu 2NbSe 4 has been determined by single crystal X-ray diffraction methods. KCu 2NbSe 4 crystallizes with four formula units in the space group C 16 2 v - C2 cm of the orthorhombic system in a cell of dimensions a = 5.663(2) Å, b = 18.791(5) Å, c = 7.645(3) Å at −167°C. The structure consists of two-dimensional metal-chalcogen layers separated by K + cations. The Nb atom and two independent Cu atoms are in tetrahedral sites, and there appears to be some substitutional disorder among these sites, as judged from the isotropic thermal parameters. The CuSe 4 and NbSe 4 tetrahedra share edges and corners to make up the two-dimensional layers. If we arbitrarily choose a cutoff of 4.00 Å then the K atom is coordinated by nine Se atoms. The metal tetrahedra have their expected dimensions with NbSe distances varying from 2.392(3) to 2.452(3) Å and CuSe distances from 2.427(2) to 2.440(4) Å. There are short metal-metal interactions with NbCu distances at 2.831(1) and 2.833(4) Å. From Weissenberg photography KCu 2NbS 4 is found to be isostructural: cell dimensions at room temperature are a = 5.76 Å, b = 18.46 Å, c = 7.45 Å.