SYNTHESIS AND CHARACTERIZATION OF THE NEW QUATERNARY 2-DIMENSIONAL MATERIALS KCU2NBQ4(Q = SE, S)

Reaction of K2Se5 or K2S5 with elemental Nb, Cu, and Se or S affords KCu2NbSe4 or KCu2NbS4. The structure of KCu2NbSe4 has been determined by single crystal X-ray diffraction methods. KCu2NbSe4 crystallizes with four formula units in the space group C162v-C2cm 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 CuSe4 and NbSe4 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 NbSe distances varying from 2.392(3) to 2.452(3) Å and CuSe distances from 2.427(2) to 2.440(4) Å. There are short metal-metal interactions with NbCu distances at 2.831(1) and 2.833(4) Å. From Weissenberg photography KCu2NbS4 is found to be isostructural: cell dimensions at room temperature are a = 5.76 Å, b = 18.46 Å, c = 7.45 Å. © 1991.