Two chains of [K(As11)]2− clusters, one helical and one linear, have been synthesized and characterized by X-ray crystallography. The stoichiometries of the two conformations differ only in the number of solvent: 3 ethylenediamine per cluster for the helix and 2 for the straight chain. The solvent molecules interact with the potassium cations which link the Arsenic clusters. Theoretical investigations reveal that without solvent, the linear chain is most stable, because the K–As11 distances are minimized while the helix has increased spacing between the K cation and As11 which enhances binding between ethylenediamine and the potassium cations, stabilizing the helical assembly.