On Verdigris, Part III: Crystal Structure, Magnetic and Spectral Properties of Anhydrous Copper(II) Acetate, a Paddle Wheel Chain

Pure anhydrous Cu(CH 3 COO) 2 was obtained both, by thermal dehydration of Cu(CH 3 COO) 2 · H 2 O and by drying a commercially purchased mixture of Cu(CH 3 COO) 2 · H 2 O and Cu(CH 3 COO) 2 in a nitrogen atmosphere using P 2 O 5 as drying agent. The crystal structure was solved ab initio from synchrotron X‐ray powder diffraction (XRPD) data at 150 °C and from laboratory XRPD data at ambient conditions and found to be isotypic to anhydrous chromium(II), molybdenum(II) and rhodium(II) acetate. Cu(CH 3 COO) 2 crystallizes in space group P 1 (no. 2) with lattice parameters of a = 5.1486(3) Å, b = 7.5856(6) Å, c = 8.2832(6) Å, α = 77.984(4)°, β = 75.911(8)°, γ = 84.256(6)° at ambient conditions. Cu 2 (CH 3 COO) 4 paddle wheels with short (2.6 Å) Cu–Cu distances form chains in a direction, which is the main motif in the crystal structure. Due to their identical structural main motif Cu(CH 3 COO) 2 · H 2 O and Cu(CH 3 COO) 2 exhibit a similar bluish‐green color, almost identical UV/Vis spectra and comparable magnetic properties. The temperature dependent magnetic susceptibility also indicates only weak inter‐dimer spin exchange between neighbouring Cu 2 (CH 3 COO) 4 paddle wheels.