On verdigris, part I: synthesis, crystal structure solution and characterisation of the 1–2–0 phase (Cu₃(CH₃COO)₂(OH)₄)

Abstract

Cu3(CH3COO)2(OH)4 a historic blue verdigris pigment phase was synthesised and characterised by its spectroscopic and magnetic properties.

On verdigris, part II: synthesis of the 2-1-5 phase, Cu3(CH3COO)4(OH)2·5H2O, by long-term crystallisation from aqueous solution at room temperature

“…7,8,15 In addition, carboxylate related oxygen atoms are located in the extended coordination sphere (Fig. 5a, grey, dashed bonds) with Cu-O distances ranging from 2.29 Å to 2.41 Å resulting in squared pyramidal extended coordination spheres of Cu(1) and Cu (2) and in a Jahn-Teller-like distorted octahedra extended coordination sphere of Cu(3).…”

“…Considering the unit cell volume, the site multiplicities in space group P2 1 /c (14) and the packing densities of the related copper(II)-acetate-hydroxide hydrates, 7,8,15 35 the positions of the acetate and hydroxide ions and water molecules were determined. Rigid bodies for the acetate ions were defined in z-matrix notation and translated and rotated freely through the unit cell.…”

“…Numerous synthesis attempts 1,[3][4][5][6] based on ancient recipes for verdigris revealed the existence of at least five distinct phases: 2-1-5, 1-1-5, 1-4-3, 1-2-0 and 1-3-2. Only the 1-3-2 phase 1,4,5,7-14 and very recently the 1-2-0 phase 15 were characterised in detail, as the purity of the obtained basic copper acetates could not be proved unambiguously because the phase characterisation led to contradictory results. In addition, ancient recipes, in particular the intentional corrosion of copper, were proved to lead to complex multiphase mixtures 14,16,17 comprising components which could not be identified due to a lack of reliable reference data.…”

“…25 The 1-3-2 phase can be converted into the 1-2-0 phase by ageing in concentrated Cu(CH 3 COO) 2 solution at 60°C. 4,15 Reported synthesis routes that lead to the direct formation of the 1-2-0 phase, 5,6 as well as the synthesis procedures for the 2-1-5, 1-1-5…”

“…15 In order to extend the knowledge of the formation, stability, properties, and crystal structures of verdigris phases, we performed long-term crystallisation experiments. These were carried out at room temperature since lower temperatures usually lead to phases with higher water contents although the formation, transformation and crystallisation of hydroxide salts can take years.…”