Rb2BaNb2Se11: A new quaternary niobium polyselenide with infinite anionic chains composed of Nb2Se11 building block

The quaternary compound Rb2BaNb2Se11 has been synthesized by reacting Nb metal with an in situ formed flux of Rb2Se3, BaSe and Se at 773 K. Rb2BaNb2Se11 crystallizes in the monoclinic space group P21/c with four formula units and lattice parameters a=7.8438(5) Å, b=13.6959(6) Å, c=17.0677(13) Å, β=97.917(9)°. The structure consists of one-dimensional anionic chains formed by interconnection of dimeric [Nb2Se11] units. The chains are directed along the crystallographic c-axis with Rb+ and Ba2+ ions being located between the chains. The [Nb2Se11] units are formed by face sharing of two NbSe7 bipyramids and are joined by Se22− dianions to form infinite 1∞[Nb2Se114−] chains. The compound was characterized with infrared spectroscopy in the FIR region, Raman and UV/Vis diffuse reflectance spectroscopy.