Relating highly distorted Jahn–Teller MnO6 to colouration in manganese violet pigments†
Abstract
‘Manganese violet’ pigments have been known for over 150 years, but are receiving renewed interest due to their non-toxicity and earth-abundant components. For the first time we report here a detailed study into the structural aspects that define the sought-after pigment properties of these materials. This work identified two polymorphs, designated as α- and β-NH4MnP2O7 that provide the strong colouration and compared them to a commercially available sample. Rietveld analysis of (a = 8.4034(6) Å, b = 6.1498(4) Å, c = 6.1071(4) Å, α = 104.618(5)°, β = 100.748(5)° and γ = 96.802(6)°) and possessed similarly distorted MnO6 octahedra, but was found to differ from α-NH4MnP2O7 in the relative dimensions of the intersecting framework tunnels that contained the ammonium