Proof of the Existence of a Linear, Centrosymmetric Polyiodide Ion I: the crystal structure of Cu(NH3)4 I4

Tetrammine‐copper(II)‐tetraiodide Cu(NH3)4I4 crystallizes in the monoclinic space group C 2/m. The crystal structure has been determined from X‐ray diffractometer data and refined to Rw = 2.2%. Four coplanar nitrogen atoms and two axial iodine atoms form an octahedral coordination around Cu(II) with a pronounced 4 + 2 tetragonal distortion. A connection of the Cu(II) atoms by linear, centrosymmetric I polyiodide ions results in infinite chains of [Cu(NH3) I ]‐units. The central I‐I‐bond distance in I is 2.802(1) Å; a considerable amount of I‐I bonding is indicated by the distance of 3.342(1) Å found for the terminal bonds. These intramolecular bond distances correspond to calculated I‐I‐bond orders of 0.80 and 0.43.