Tetragonal Diiodotetrapyridinedicopper(I): Structure, Luminescence, and Computational Modeling

We report on a new crystal modification of (CuIPy2)n (Py = pyridine), a compound first reported by White et al. In contrast to White’s orthorhombic structure, which is comprised of rhomboid iodide-bridged dimers, Cu2I2Py4, our new tetragonal crystal structure in space group P41212 is disordered and can be interpreted as either iodide-bridged dimers or helical chains. To determine the structure type, variable temperature X-ray diffraction and luminescence measurements were carried out. The photoluminescence spectrum shows a distinct cluster-centered transition at high excitation energies which is consistent with the dimer structure. DFT and TD-DFT calculations were performed to explain the difference between the emission spectrum at high energies compared to low energies. Furthermore, correlation of the luminescence spectrum with the X-ray results as temperature is varied demonstrates that the cluster-centered luminescence band in Cu2I2Py4 arises from close Cu⋯Cu distances which vary with temperature. A low temperature X-ray crystallographic redetermination of the cubane tetrameric Cu4I4Py4 is also presented. Both Cu2I2Py4 and Cu4I4Py4 structures show distortion of the CunIn core cluster at low temperature resulting in reduced Cu⋯Cu distances, but with I⋯I distances roughly unchanged.