Correlation between crystal structure, optical and chromatic properties of Diphosphate based Nickel and Magnesium

•Synthesis and characterization of new Magnesium Nickel Diphosphate solid solutions,•Structural determination/refinement of those compounds,•Relationship between structure refinement and UV analysis of Nickel in the structures. The crystal structures of Mg2-xNixP2O7 (x= 0.5; 1 and 1.5) have been investigated and refined from powder DRX using Full Prof program. All compounds crystalize in the monoclinic system with P21/c space group. Mg2-xNixP2O7 (x= 0.5; 1 and 1.5) belong to β-Mg2P2O7 structure with Mg and Ni ions are distributed with the same probability over to octahedral and square pyramid sites. The absorbance spectra in the UV-Visible range of all compounds are reported and the gap energies are extracted from Tauc plot extrapolation. The appearance of two gap energies for all compounds is due to the existence of octahedral and square pyramid coordination of Ni2+ cation, this is in good agreement with crystal structure refinement results.