Formation of a new ligand by addition of 3,5-dimethylpyrazole to the cyanate group in a copper(II) complex: crystal and molecular structure of α-bis(1-carbamoyl-3,5-dimethylpyrazolato)copper(II) and the physical properties of two isomeric forms

Abstract

Two forms (α and β) of the compound [Cu(dmpz.NCO)₂](dmpz = 3,5-dimethylpyrazole) have been prepared and the structure of the α form established by single-crystal X-ray analysis. The crystals are monoclinic, space group P2₁/c, with a= 13.697(7), b= 14.759(7), c= 7.463(7)Å, β= 114.01(3)°, and Z= 8. The structure has been solved by the heavy-atom method and refined by full-matrix least squares to R= 0.052 for 1 760 independent reflections. The compound consists of nearly planar molecules, in which two 1-carbamoyl-3,5-dimethylpyrazolate anions are co-ordinated to the Cu^II atom, the Cu–N distances being 1.926(8), 1.908(1), 1.985(8), and 1.990(8)Å. This new ligand originates from a nucleophilic addition of the dmpz molecule to the NCO group in the Cu^II coordination sphere. Both forms have been studied by i.r., solid-state electronic and e.s.r. spectroscopy, and by variable-temperature magnetic susceptibility measurements. The results obtained show that substantially the same molecules are present in the β as in the α form, but an appreciable out-of-plane interaction of the Cu^II atoms with potential donor atoms of other molecules takes place.