An Unusual Geometry of Five-Coordinate Copper(II): The Structure of Cu(terpy)I2 and Spectroscopic Investigations of Complexes Cu(terpy)X2 (X: I, NCS)

The structure of the compound Cu(terpy)I₂ (terpy 2,2′: 6′, 2″ terpyridine) was determined at room temperature. It is monoclinic, space group I2/c with a = 13.689(3), b = 9.510(2), c = 11.605(3) A, β = 97.59(4)° and Ζ = 4. The copper(II) ions are five-coordinated by the three nitrogen atoms from the terpy ligand and the two iodine atoms. The CuN₃I₂ polyhedron exhibits the same unusual “reverse” geometry as is observed for Cu(terpy)(NCS)₂. Single crystal EPR measurements of the iodide and the isothio-cyanate complexes confirmed the structural results, excluding the possibility of a dynamically averaged geometry.