Synthesis and characterization of the mixed valence Cu(l)/Cu(ll) 3,5-bis(trifluoromethyl)-pyrazolate complex, [Cu(ll)2Cu(l)(F6dmpz)5]

Abstract

The reaction of molten 3,5-bis(trifluoromethyl)pyrazole (F6dmpzH) with copper metal shot under an atmosphere of dioxygen yields the green trimetallic mixed valence [Cu(II)2Cu(1)(F6dmpz)5]. Crystals of [Cu(II)2Cu(I)(F6dmpz)5] are triclinic, a = 9.0557(2), b = 9.6164(2), c = 11.8874(3) Å, α= 105.406(1)°, β = 112.317(1)°, γ = 90.662(1)°, Z= 1, space group P͞1. The crystal structure was solved by direct methods and was refined by full-matrix least-squares procedures to a final R value of 0.0538 for 2591 reflections with I≥2σ(I). Magnetic susceptibility studies over the range 2–300 K reveal strong antiferromagnetic exchange coupling between the two copper(II) centers. Fits of the magnetic data to the Bleaney-Bowers equation for two interacting S= ½ centers gives the exchange coupling constant J = –235 cm–1. Key words: trimetallic, copper, 3,5-bis(trifluoromethyl)pyrazolates, X-ray structure, antiferromagnetism.