Solid State Structures of AsCl5 and SbCl5

Arsenic pentachloride has a trigonal bipyramidal structure in the solid state with As‐Cl_eq = 210.6, 211.9 pm, As‐Cl_ax= 220.7 pm, space group Pmmn, a = 706.2 (1); b = 760.3 (2), c = 623.3 (1) pm. Antimony pentachloride exists in two modifications: above ?54.1 °C it is also trigonal bipyramidal with Sb‐Cl_eq = 227.0 and Sb‐Cl_ax = 233.3 pm, space group P6₃/mmc, a = 741.4 (1), c = 799.0(2)pm. Below ?54.1 °C it changes reversibly into a double chlorine bridged dimer resulting in an edge shared double octahedral structure, space group P2₁/c, a = 952.4 (1), b = 1189.9 (1), c = 1219.7 (1) pm, β = 108, 27 (1): In presence of water the formation of AsCl₅ is hindered, two salts containing the octahedral anion AsCl₆^? have been isolated, (H₅O₂⁺)₅AsCl₆^?(Cl^?)₄], space group C2/c, a= 1416.9 (2), b = 1316.6 (3), c = 1215.3 (2) pm, β; = 94.96 (1)°, and (H₅O₂⁺)(AsCl₆^?)·AsOCl₃], space group P2₁/n, a = 771.6 (3), b = 904.5 (3), c = 2140.7(2)pm, β = 100.21(1). The AsOCl₃ moiety in this compound appears as a monomer, in contrast to pure AsOCl₃, which is a doubly oxygen bridged dimer in the solid state.