Metal-abietate complexes: inorganic pigments for challenging applications

The synthesis of metal-ligand complexes is challenging in terms of structural, spectroscopic, and chemical composition behavior. The natural ligand abietate, C₂₀H₂₉O₂^-, derived from the salification of Pinus elliotti resin, has provided the synthesis of metal-abietate complexes with great ease and reproducibility. Preparing a complex requires special attention from the researcher; on the other hand, preparing a series of complexes with first-series metals (M = V, Cr, Mn, Fe, Co, Ni, Cu, Zn) has color contrast. New inorganic pigments are required for applications with biological, sensory, or catalytic properties. The colors of the complexes enable acquisition of absorption/reflectance spectra in the visible-NIR region and differentiation between warm and cool colors. And to discuss, in terms of the color parameters of the CIE L*a*b* system, an attempt to attribute spectrochemical behavior to the abietate ligand. The open challenge concerns applications such as special pigments with microbiological activity and their toxicity.