Synthesis, crystal structure and properties of K4Ba2(Nb2S11)2

The reaction of K2S3, BaS, Nb and S in a molar ratio of 2:1:2:8 at 773 K yields dark red crystals of the new quaternary niobium sulfide K4Ba2(Nb2S11)2. The compound crystallizes in the monoclinic space group P21/c with a=14.5408(11), b=12.6577(6), c=17.5700(13)Å, β=94.791(9)°, V=3222.5(4)Å3 and Z=4. The structure is composed of two different dimeric [Nb2S11] units which are separated by Ba2+ and K+ cations. The Nb atoms are coordinated by S22− and S2− ligands according to [Nb2(μ2-S)(μ2-η2,η1-S2)2(η2-S2)2(S)2]. Each Nb atom is surrounded by seven sulfur ions forming a strongly distorted pentagonal bipyramid. The two NbS7 polyhedra share a common face thus yielding the [Nb2S11] units. The potassium and barium cations are statistically distributed over the crystallographic sites.The compound was characterized with IR, Raman spectroscopy and solid state UV/Vis diffuse reflectance spectroscopy.