Growing crystalline selenidostannates in deep eutectic solvent

By using deep eutectic solvent mixture of ChCl (ChCl = choline chloride) and 1,8-diaminooctane as reaction medium, three new selenidostannates were synthesized, namely [Cr(en)₃]_2.5[SnSe₄]·Cl_3.5·(pip)_0.5·1.5H₂O (1) (en = ethylenediamine, pip = piperazine), [Ni(en)₃][Sn₃Se_6.5(Se₂)_0.5] (2), and [Ni(en)₃][Sn₃Se₇] (3). Compound 1 features a primary unit of SnSe₄ tetrahedron, in which the [Cr(en)₃]³⁺ complex acts as charge balance agent. In compound 2, there are two kinds of one dimensional chains, including [Sn₃Se₇]_n^2n– and [Sn₃Se₆(Se)₂]_n^2n– anionic chains. The [Sn₃Se₇]_n^2n– chain is constructed by connecting [Sn₃Se₉] units via edge-sharing Se^2- ion, while the [Sn₃Se₆(Se)₂]_n^2n– chain is constructed by linking [Sn₃Se₁₀] units via sharing one Se^2- ion and one Se₂^2- ion. Compound 3 features a lamellar anionic [Sn₃Se₇]_n^2n– structure, where the [Ni(en)₃]²⁺ ions are located in inter-lamellar space. The optical absorption spectra indicate band gaps of 2.23 eV for 1, 1.95 eV for 2, and 2.01 eV for 3.