In situ solid state formation of copper(I) coordination polymers by thermal reduction of copper(II) precursor compounds: structure and reactivity of [Cu(NCS)2(pyrimidine)2]n

Abstract

Reaction of copper(II) thiocyanate with pyrimidine leads to the formation of the new ligand-rich 1:2 (1:2 = ratio metal salt to ligand) copper(II) compound [Cu(NCS)₂(pyrimidine)₂]_n (1). Its crystal structure was determined by X-ray single crystal investigations. It consists of linear polymeric chains, in which the Cu²⁺ cations are μ-1,3 bridged by the thiocyanato anions. The pyrimidine ligands are terminal N-bonded to the Cu²⁺ cations, which are overall octahedrally coordinated by two pyrimidine ligands and two N-bonded as well as two S-bonded thiocyanato anions. Magnetic measurements were preformed yielding weak net ferromagnetic interactions between adjacent Cu²⁺ centers mediated by the long Cu–S distances and/or interchain effects. On heating compound 1 to approx. 160 °C, two thirds of the ligands are discharged, leading to a new intermediate compound, which was identified as the ligand-deficient 2:1 copper(I) compound [(CuNCS)₂(pyrimidine)]_n by X-ray powder diffraction. Consequently, copper(II) was reduced in situ to copper(I) on heating, forming polythiocyanogen as byproduct. Elemental analysis and infrared spectroscopic investigations confirm this reaction pathway. Further investigations on other ligand-rich copper(II) thiocyanato compounds clearly show that this in situ thermal solid state reduction works in general.