Sn4As3 revisited: Solvothermal synthesis and crystal and electronic structure

A facile one pot method of synthesis of tin arsenide Sn4As3 starting from metallic tin and elemental arsenic under mild solvothermal conditions in ethylenediamine in the presence of ammonium chloride is offered. The dissolving of the tin metal in ethylenediamine and the role of NH4Cl are discussed. The crystal structure of Sn4As3 has been re-determined. It is shown to crystallize in the trigonal non-centrosymmetric space group R 3m , (a =4.089(1) Å, c =36.059(6) Å, Z =3), which differs from the previously reported centrosymmetric structure View the MathML source(R3¯m). The crystal structure of Sn4As3 consists of alternating layers of arsenic and tin atoms that are combined into seven-layer blocks and build up along the c-axis. The major structural feature is the short tin–tin distances (3.24 Å) between the adjacent blocks. The analysis of the density of states and band structure reveals that Sn4As3 should have metallic properties, which is in line with the previously reported experimental observations. Analysis of chemical bonding employing the electron localization function shows that only for the shortest Sn–As contacts the bonding is pairwise, while four-center bonds are formed between arsenic and tin atoms at relatively long distances (>2.85 Å). Moreover, each tin atom holds an electron lone-pair.